- Email: [email protected]
Laser surface structuring of ceramics, metals and polymers for biomedical applications
Laser surface structuring of ceramics, metals and polymers for biomedical applications: a review
10
P. Shukla1, D.G. Waugh1, J. Lawrence1, R. Vilar2 1Thornton Science Park, University of Chester, Chester, United Kingdom; 2Instituto Superior Tecnico and CeFEMA - Centre of Physics and Engineering of Advanced Materials, Lisbon University, Lisbon, Portugal
10.1 Introduction 10.1.1 Research background Laser-induced periodic surface structures (LIPSSs) have been observed since 1965 [1]. They are known as random or self-organised, micrometre-sized surface textures (waves, cones and ripples) which have been observed in surfaces treated with continuous wave and pulsed laser irradiation. Their formation mechanism has been the object of intense controversy from before 1975 to 2015. Many of them are of hydrodynamic origin with frozen-in waves and crests usually explained by fluid flow driven by the Marangoni effect and recoil pressure, but periodic wavelets are also found which can be explained by Rayleigh–Taylor instabilities [1–4]. The formation of micro-sized cones and columns is explained by shadowing of radiation by impurities [1], differential ablation [2] or hydrodynamic effects [3]. Moreover, when ultrashort pulse duration lasers are used at fluences near the ablation threshold, periodic self-organised wavelets with wavelengths in the range 200–700 nm and amplitude 10–100 nm can be observed in a wide range of materials, in particular semiconductors, metals and polymers [4]. Their mechanism of formation is essentially unknown, despite a number of recent studies [1–4]. Laser micro- and nanotexturing may lead to considerable modification of properties relevant to osseointegration, namely biocompatibility, protein adsorption and cell/surface interactions [5], and the process has the potential to become a powerful tool in biomedical surface engineering. It is essential for the efficiency and service lifetime of endosseous implants that a solid bone/material interface is established, with no fibrous tissue formation [6]. However, most materials currently used for bone replacement show negligible bioactivity and originate some form of encapsulation. It is generally recognized that further progress can only be achieved by endowing biomaterials with a higher degree of surface functionality, obtained through structured surfaces with a high degree of complexity. This would mimic the surface relief of natural hard tissues (biomimetic materials) [6–10]. Recent work has shown that Laser Surface Modification of Biomaterials. http://dx.doi.org/10.1016/B978-0-08-100883-6.00010-1 Copyright © 2016 Elsevier Ltd. All rights reserved.
282
Laser Surface Modification of Biomaterials
osteoblast activity is considerably enhanced by nanosized surface features [11,12] and that properly designed nanostructured surfaces may represent a large step forward in biomedical device functionality [6]. Surprisingly, measurements of bone/implant, bond disruption forces showed that achieving high bond strength depends more on the surface nanotexture than on the nature of the material underneath, justifying the hope that inert biomaterials may be rendered more bioactive by providing them with a suitable nanoscale surface texture [13]. Various researchers have demonstrated that biomimetic surfaces consisting of LIPSSs can be obtained by using specific laser treatment methods [14–16]. Under some processing conditions LIPSSs overlap as a random micrometre-sized columnar topography, leading to a bimodal surface relief. The features on these surfaces can be controlled by changing the radiation wavelength, fluence, and polarisation and laser treatment techniques. One of the main potential applications of femtosecond laser texturing is the creation of implants with improved biocompatibility. Ultrafast lasers also have the potential to drastically change surface properties that are difficult to improve by other methods, such as wetting (superwetting, superhydrophobicity [17]) and spectral selectivity [18].
10.1.2 Research scope and rationale LIPSSs are important for modification of biomedical materials so that enhancement in their performance can be achieved with respect to properties such as coefficient of friction, wear, wettability adhesion, fracture and impact strengths just to name a few. Since its first introduction in 1965, much work has been conducted in this area [1,5,19–50]. Thus, there is a need for not just a review but also a focus on the gaps in knowledge, particularly for applications of LIPSSs in the biomedical sector. Thus, this chapter reviews research works focused on LIPSSs, applicable to biomedical materials, namely polymers, ceramics and metals/alloys. The work entails various types of laser-induced surface structures, their applications to biomedical sectors, new prospective and future trends and the state-of-the-art literature that has been published to date in this area. Presented herein are gaps in knowledge and new ideas and the chapter allows one to quickly grasp the process parameters used in previous research for generating various types of LIPSSs. A map showing the scope of the chapter is presented in Fig. 10.1.
10.1.3 Fundamentals and theory of laser-induced periodic surface structures LIPSSs are formed when the material is exposed to certain laser energy densities for a given time period [19]. To date, the physical processes in the time scale from nanoseconds and longer pulsed durations to the use of continuous wave (CW) lasers are well understood [19,25,31]. However, there is still a gap in knowledge when it comes to the effects exhibited from femtosecond and picosecond pulse interactions. The accepted principle of LIPSSs is that they are generated by interaction of the incident laser beam with a surface electromagnetic wave. Since the 1980s several authors
Laser surface structuring of ceramics, metals and polymers
Laser-induced periodic surface structures
Applications
Bioceramic
Types of structures and adaptive parameters
New prospectives and future trends
State-of-the-art research in relation to biomedical sectors Other biosuitable materials
283
Biometals/ alloys Biopolymers
Figure 10.1 A map showing the scope of the chapter.
have explored in detail the generation of LIPSSs [19–22]. During the generation of LIPSSs, there will be a melt zone with a certain depth of ablation by the pulsed laser, the electron photon relaxation time and the thermal diffusivity. Within the melt zone, there is evaporation which travels to the edge of the irradiated area forming a range of droplets [27]. The shape of a LIPSS is dependent on the driving force of the melt recoil pressure and the time that heating and solidification takes place [27]. This in turn leads to rapid cooling, creating sharp peaks and small droplets in the case of short pulses such as nanosecond, picosecond and more distinctively with femtosecond laser interactions. Sipe and colleagues introduced a theory of LIPSSs in the early 1980s [19–22]. This work used a Fourier component of induced structure with the corresponding Fourier component of inhomogeneous energy deposition just beneath the surface. The theory assumed that surface roughness was confined to a region of height that was smaller than the wavelength of the laser light, resulting in symmetry breaking and leading to inhomogeneous deposition. Thus, strong peaks were produced in this deposition in Fourier space that eventually led to the predictions of induced fringe patterns with spacing and orientation dependent on the angle of incidence and polarization of the laser beam [19–22]. Li et al.’s [49] explanation of the LIPSSs theory was that the driving force for the rippling effect starts from the interference of the incident and reflected or refracted laser beam with the scattered/diffracted light near the material interaction. Such diffraction/scattering of the incident light could create microscopic roughness of the surface, by defects or by spatial variations in the dielectric constant. An interference between different waves could consequently lead to an inhomogeneous energy input to the electron system. Combining this with a positive feedback mechanism consequently causes the ripple effect. Laser beams can be polarized to produce an orientated ripple formation [49]. This tends to control the material excitation. Linear polarization of the laser could orient
284
Laser Surface Modification of Biomaterials
the ripples perpendicular to the polarization direction. Also, fine ripples with an orientation parallel with the polarization direction can be found. If the laser light is circularly polarized then ripples without a specific orientation can be found. The periodicity of the rippling effect is subject to laser energy, pulse duration, number of pulses, wavelength, laser beam polarization and the angle of incidence. Various types of surface features that are usually in the range of 1 μm and above using the conventional laser sources ranging from ultraviolet to infrared could be created. However, to create nanostructures, deep ultraviolet lasers can be implemented that in turn could generate 130 nm lines and lower, which is ideal [49]. It is necessary that the desired LIPSSs should be half the size of the wavelength of the laser and also smaller than the smallest allowable spot size of the laser beam. This is why deep ultraviolet sources are better suited for surface structuring. Eq. [10.1] governs this factor, where d is the minimum beam spot diameter, λ is the laser wavelength, n is the refractive index of the beam delivery to the material and α is the beam divergence angle [49].
d =
λ 2n sin α
[10.1]
10.2 State of the art in laser-induced periodic surface structures on various materials 10.2.1 Biopolymers Polymeric materials have been extensively used in biomedical applications since 1995 to 2015 [51–55]. Polymers such as nylon, teflon, polypropylene, polyethylene, polytetrafluoroethylene and many others are noncarcinogenic and nonmigrating and have minimal foreign body reactions [51]. Since then, CO2 lasers have also been used to improve the surface properties of polymers so that cell adhesion, proliferation and bonding on such laser-modified surfaces could be improved [52–54]. Using an excimer laser, Duncan et al. [55] developed microgrooves that were 30 by 10 μm at 1 J/cm2 with a 248 nm wavelength, and 20 ns pulse length, to find that osteoprogenitor cells adhere on the surface of polyethylene terephthalate (PET) with minimal groove width and depth. However, cell adhesion was restrained at the bottom of the grooves due to the given surface chemistry effect. Using a femtosecond laser, Aguilar et al. [56] created micropatterning of polycaprolactone and polyglycolic acid in ambient atmosphere. Micrometre-sized channels and holes were created in both biodegradable microdevices. Microfeatures were etched in the aforementioned polymers of 30 μm. Pfleging et al. [57] also modified a polystyrene with respect to applications in microfluidics and cell culture. Their results showed that helium or oxygen allowed control of the wetting angle, between 2 and 150 degrees. In addition, the modified surfaces were deemed hydrophilic and hydrophobic, respectively, due to the changes in the surface topography and chemistry [57]. Periodic lines and micropatterns were created on polycarbonate using a q-switched Nd:YAG laser by Fayou et al. [58]. This was carried out rather using a laser interference lithography
Laser surface structuring of ceramics, metals and polymers
285
within a short time. Moreover, cell interactions were studied to show that HPFs (high pressure freezings) grew parallel to the line structure and showed bipolar morphology on point micropatterns. Laser machining is another technique that can bring about surface structures such as convex domes and dimple cavities on a low-density polyethylene, high-density polyethylene, and acrylonitrile butadiene styrene [59]. Thus, a nonsmooth surface can be created to imitate the body/surface morphology of a polymer-based biological system. Surface structures such as grooves and domes created on polymer PET surfaces have also shown fibroblast cell adhesion and spreading due to changes in the surface morphology and wettability of the PET using both a CO2 and a KrF excimer laser [60]. Péres et al. [61]. reported on the formation of LIPSSs on self-standing films of biopolymers, namely chitosan starch and the blend of chitosan with a synthetic polymer polyvinyl pyrrolidone. This was using linear polarized laser beams of 193, 213 and 26 nm wavelength with a pulse duration ranging between 6 and 17 ns. Their result showed that formation of LIPSSs occurred parallel to the laser polarization direction, with periods that were close to the laser wavelength. However, the formation of LIPSSs was not seen in the crystalline starch biopolymer. Although the work was a systematic investigation, the result did not report on the potential applicability to biomedical applications. Comparatively, Castillejoa [62] reported that the end application in the biomedical area usually dictates the applicability of LIPSSs to a particular biopolymer surface. Their investigation also used chitosan starch, PET, PTT and PC polymeric materials by applying several thousand pulses between 15 and 120 ns, at wavelengths ranging from 193 to 795 nm [62]. Zhen et al. [43] generated laser-induced long periodic surface structures on polyimide to improve its crystallinity. This may have several benefits directly. The improvement in crystallinity may not only affect the mechanical and optical properties of the polyimide but also affects the surface wettability so that the polyimide surface can be deemed to improve the biocompatibility. Generating LIPSSs on polymers has proven to be common with the use of variety of lasers, wavelengths and processing parameters. With that said, Lu et al. [33] suggested that using 266 nm wavelengths generated regular periodic structures when compared to 355 nm especially when laser processing a polyimide. Thus, future studies could elucidate the possibility of laser-treating a variety of polymers using various different wavelengths at short and ultrashort pulses to explore the occurrence of LIPSSs on such biomedical materials.
10.2.2 Biometals/alloys Titanium/alloys have been employed for biomedical applications for number of years [63–72]. Titanium/alloys have the tendency to be less corrosive and are easier to shape and machine. They also have good fatigue strength and are biocompatible in particular. However, such biometals/alloys do not always comply with clinical requirements; thus, surface treatments, particularly using ultrashort pulse lasers may be needed [64]. Surface features, namely nanopores, nanoprotrusions and sphere-like nanostructures ranging in size from 10 to 20 nm were reported on titanium implants by Vorobyev and Guo [64]. Through the work of Vorobyev and Guo, it has been suggested that short pulse lasers in comparison to long pulse lasers are more ideal for the treatment of not just
286
Laser Surface Modification of Biomaterials
titanium dental applications but also for other biomedical applications [64]. This confirms the previous statements regarding the use of deep ultraviolet wavelengths for generating LIPSSs. No further details were given in terms of implementing their work in the biomedical area. Ultrafast laser pulses were introduced to Ti, Al, Cu and stainless steel. In particular, Ti surfaces were textured to around 100–500 μm as reported by Nayak and Gupta [65]. They also showed that the thermo-physical and optical properties of the material tends to dictate the experimental parameters. Gaseous assistance is a must for generating such micro- and nanostructures also. Nonetheless, the authors noted that implementing such structures not only for biomedical but also for microelectronics and photovoltaics applications would be highly beneficial [65]. Chunha et al. [66] published a parametric study of ultrafast laser texturing (500 fs) of TI-6AL-4V for biomedical applications. Different types of surface structures were produced, namely ripples, nanopillars and microcolumns. Their results showed an increase in wettability and the surface became hydrophilic. Chunha et al. further stated that this type of surface treatment could also control the behaviour of human mesenchymal stem cells. Further, it was also reported that a reduction in cell spreading and no cell proliferation were observed on the femtosecond laser-textured surfaces. But cytoskeleton stretching and stress fibres were evident [66]. Gaggl et al. [67] surface-treated four different titanium-based implants with various techniques which included laser, spray coating, machining and aluminium oxide coating. The optimal surface structure with the least contamination was found for the laser-treated surfaces of the titanium [67]. Titanium alloys (Ti-6Al-4V) were laser-structured using an excimer laser (193 nm wavelength) by Pfleging et al. [68]. The wavelength used was 193 nm at 5 ns pulse duration. The characterisation of the textured surfaces (both the top surface and the cross-section) was carried out to find various microstructural changes, namely: rutile, anatase and a few Ti2O3 phases. In addition, an increase in wettability was found that yielded a total surface energy increase of 67.6 mN/m compared to the as-received Ti-6Al-4V (37 mN/m). The effect of the polar component influences the surface energy of textured surfaces causing such structures to be biocompatible [68]. Generating microporous surfaces can help in creating mechanical interlocking (crucial for osseointegration). Titanium implants were first modelled in 3-D and then treated using a 20 W fibre laser. The surface was then deemed to be a good bone stabilizer as reported by Çelena et al. [69]. Based on their findings, it can be postulated that the fibre laser was modulated to deliver short pulses. Thus, the generated LIPSS would be in the range of 1 μm and above due to its wavelength and pulse duration. Kumari et al. [70] reported a detailed study on wear, corrosion and bioactivity behaviours of laser surface textured titanium alloy (Ti-6Al-4V) by an ArF excimer laser at a wavelength of 193 nm with a pulse length of 5 ns. In addition, the authors studied the effects of bioactivity and cell attachment and found a significant increase in wear resistance and a marginal change in corrosion resistance. More importantly, the textured surfaces manifested significant improvement in bioactivity in terms of calcium phosphate deposition rate. Improvement in cell viability of the laser-textured Ti-6Al-4V was comparable to that of the as-received Ti-alloy. Cell attachment studies show a reduced cell density in the textured surface with a maximum reduction in the dimple textured
Laser surface structuring of ceramics, metals and polymers
287
surface. Lastly, the cells aligned themselves along the direction of texturing in the linear textured surface [70].
10.2.3 Bioceramics Research in the area of laser surface structuring of ceramics is generally scare. There is a need to develop such structures on materials such as ceramics because in doing so could manifest a change in the range of functional and physical, chemical, and mechanical properties to name a few. In terms of biomedical properties, laser microand nanotexturing may lead to considerable modification of properties relevant to osseointegration such as biocompatibility, protein adsorption and cell/surface interactions, wetting (superwetting, superhydrophobicity) and spectral selectivity [7,12,73]. Moreover, ceramics are ideal for bone implants and thus, surface texturing would be highly beneficial for rendering them bioactive, although ceramics such as alumina and zirconia are known to be bio-inert materials [14]. Surprisingly, measurements of bone/implant bond disruption forces showed that achieving high bond strength depends more on the surface nanotexture than on the nature of the material underneath, justifying the hope that inert biomaterials (for example alumina and zirconia) may be rendered more bioactive by providing them with a suitable nanoscale surface texture [14]. The applicants demonstrated that biomimetic surfaces consisting of LIPSSs can be obtained by using proper laser treatment methods [14–16]. Other investigations were performed to explore the optimised conditions for the growth of LIPSSs by varying pulse durations and pulse energies during ultrashort pulsed laser ablation of zirconium [74]. This also led to some success as the micrographs showed nanoscale ripples for all pulse durations. It was further reported that LIPSSs are more distinct and well organized for the shortest pulse duration of 25 fs with such ceramics, whereas, LIPSSs become diffused and indistinct with the increase in the pulse duration. This indicated that a shortest pulse duration of 25 fs was the most suitable for the growth of nanoscale ripples [74]. Other investigators have also worked with zirconia using an excimer laser KrF with 248 nm wavelength, 18 ns pulse duration and a repetition rate of 30 Hz using a laser fluence of 3.8–5.1 J/cm2. Their results revealed a growth of grains on the laser surface-treated zirconium. They reported that with increasing fluence, the crystal grain became larger [75]. Grojo et al. [76] also conducted a laser ablation and plasma diagnostics study of zirconium [76]. Samant et al. [77] laser surface structured an alumina ceramic and observed the effects of the laser pulse width, repetition rate and the scanning speed. Their results showed that the pulse repetition played an important role in minimising the interdendritic porosity while the scanning speed contributed significantly to increase of the grain size [77]. However very little work, if any, has been conducted on surface structuring of ceramics in general, especially in relation to its applicability in the biomedical sector. This is a strong indicator that laser surface structuring of bioceramics would require further studies ranging from basic parametric investigations addressing the effects of nanosecond, picosecond and femtosecond lasers to an in-depth study demonstrating the biocompatibility after successfully achieving laser-structured ceramics.
288
Laser Surface Modification of Biomaterials
10.3 Variety of laser-induced periodic surface structures and required parameters LIPSS formation comprises the growth of wavy surfaces that can occur on a wide variety of materials and entails surface features that are periodicity equal or smaller than the wavelength of the laser irradiation. The ripple period may depend on the laser energy applied. Regular surface structures are possible to form by laser irradiating the material at an energy level lower than the ablation threshold of the materials. Such structures can be found of uniform sizes at the nanometre scale. Grooves of the size of nanometres in a synthetic single-crystal CVD diamond were made using femtosecond laser pulses [49]. The grooves were perpendicular to the direction of the laser polarization and were 40 nm wide, 500 nm deep, and had an average spacing of 146 ± 7 nm [49]. In cases where energy level increases, the periodic surface structures became chaotic structures [39]. The heights of ripple-type structures tend to range from around 10 to 100 nm [78] as shown in Table 10.1. LIPSSs, particularly the ripple effect, have been exhibited on variety of materials; metals, semiconductors, dielectrics (glass and diamond), ceramics and polymers show periodic structures. In the 1970s and 1980s nanosecond pulses were used and in the 1990s and the first decade of this century picosecond and femtosecond pulses became available for micro/nanoripple or periodic structure formation. Fig. 10.2 shows the variety of LIPSSs that can be formed followed by Fig. 10.3 demonstrating high-resolution images of LIPSS from various published literature [82–86].
10.4 Applications of laser-induced periodic surface structures LIPSSs were first considered as laser-induced damage to the surface of optical components [42]. With that said, it was then realized that such surfaces (rippled in particular) comprise of useful properties. In addition, it is also easy to surface-treat large areas continuously with overlapping shots of short and ultrashort laser pulses, which in turn became useful for several known industrial applications [87–93]. Liao et al. [87] reported that 3D structures can be built on glass substrates using femtosecond lasers by direct writing. The structures are 3D so applications such as microfluidic devices requiring a wide array of lab-on-a-chip can be desirable with high efficiency, flexibility and cost-effectiveness [87]. Transparent substrates can now be fabricated using femtosecond lasers (maskless) to construct 3D functional structures. Also, nanoripples as such could be produced on the sidewalls of a microcell substrate. Such ablated surfaces with submicrometre wavelength structures are then integrated with liquid crystal electrooptic phase modulators and optical waveguides [88]. Nanostructure generation using femtosecond lasers was also reported by Chang et al. [89]. Periodic surface structures on Ag that had spacing of 500–600 μm were produced. For practical use laser-structured surfaces showed that surface-enhanced Raman scattering intensity was improved by 15-fold [89].
Table 10.1 Adaptable
parameters from previous research for the negation of laser-induced periodic surface
structures Parameters Type of structure
Structure size/depth
Pulse duration
PRR
Laser energy
Scan speed
Wavelength
No. pulses
Laser type
References
Ripples Ripples Ripples Ripples
4–15 nm 150 nm 50 nm 100 nm
25 ns 5 ns 20–40 ns 67 ps
100 Hz 10 Hz – 400 KHz
58–800 mJ/cm2 2.8–5 mJ/cm2 2.5–8 mJ/cm2 12.5 μJ
– 5 mm/s – –
248 nm 266–355 nm 193–248 nm 1030 nm
30 – 1000 –
Excimer Nd:YAG ArF excimer Yb:YAG
[43] [33] [28] [79]
Ripples
1 μm
20 ns
10 Hz
10.5–12.5 mJ/ cm2
–
248 nm
6000
KrF excimer
[80]
Ripples and 500 nm 5 ps to nanopores 500 fs Ripples 1.4–3 μm 10 ns Grooves, 150–670 nm 30–230 fs ripples, cones
–
0.6–1.2 J/cm2
–
248 nm
–
KrF excimer
[27]
10 Hz 290–700 mJ 1–200 KHz 6.5–130 nJ
– 1 μm/s
532 nm 0–200 790–1026 nm 50
Nd:YAG fs
[26] [47,81]
Alumina
Ripples
100–200 nm 0.5–8 ms
8–25
1064 nm
–
Nd:YAG
[77]
Zirconium
Ripples, flakes
80–120 nm
1 KHz
2.87–7.62 cm/ min –
800 nm
–
Ti: Sapphire laser
[74]
Materials
Polymers Polyimide Polyimide PET Wafer chucks Polystyrene
Metals Copper Iron Titanium/ alloys
Ceramics 25–100 fs
200–600 μJ
290
Laser Surface Modification of Biomaterials
Micro/nano grooves & striations (particles) Micro/nano riples
Flakes
Gratings
Types of laserinduced surface structures
Spheres/bubbles/ domes/dimples
Cones micro/nano protrutions
Nano-pores
Figure 10.2 The different types of LIPSSs that can be exhibited on variety of biomaterials.
Many periodic nanostructures can also be used for unique applications such as “smart marking”, whereby, the effects of colour by diffraction on metallic surfaces can be shown [90]. The method is very simple; an image is obtained using a scanner and the information is transferred on the workpiece. Moreover, especially the rippled structure was reported to influence surface modification for improving processes such as adhesion, friction, lubrication and coating de-icing [90]. Furthermore, hydrophilic materials were made hydrophobic by no chemical coating. This is when laser structuring, namely: microgrooves, is made useful for manipulating metals such as titanium and Ti alloys bioactive so that they can be useful for dental orthopaedic implants. New methods such as multiscale texturing have also shown promise for the development of structured topography that may help osteogenesis and improve osseointegration of metal implants [90]. Structuring the surfaces to improve friction properties was also reported by Eichstädt et al. [79]. They found that the friction coefficient was improved by 1.6 times after applying LIPSSs in comparison to the surface that was untreated [79]. Such improvement could influence the materials’ tribological properties so that issues such as stiction on computer hard drives could be minimised and in turn eliminated [91]. Nanopatterning of synthetic polymer structures can be transformed into gold nanowires using UV nanosecond laser ablation at a certain angle. This has the potential to be applicable for
Laser surface structuring of ceramics, metals and polymers
D
E
G
H
291
F
I
J
Figure 10.3 SEM images showing the formed rippled structure (a) [82]; nanopore induced into copper at 500 fs (b) [27]; nanoparticles at 150 fs (c) [83]; nanocones (d) [84]; microcolumns (e) [85]; nanobubbles (f) [45]; and microcones (g) [86].
biosensors. Tissue engineering the biosensors, in particular, could further be imbedded directly into devices used in biotechnology [80]. Applications of submicrometre structures in various technological areas are shown in Fig. 10.4. A particular requirement for this is where surface properties need improvement but at the same time do not affect the appearance of the material. The reporting showed surface that roughness can be improved, which in turn leads to low friction and wear rate [1]. Graphene is currently a material in demand [92]. LIPSSs were reported to be induced into the material for the first time by Beltaos et al. [92]. Their results showed inducement of LIPSSs that were 0.5–1.5 μm in length and 35 ± 5 nm on 10–15 layered graphene in an ambient environment. Their breakthrough findings also demonstrated that high-end materials such as graphene can be treated by LIPSSs that could be induced quickly and cheaply. They also reported that such material surface modifications could consequently open new avenues for future applications where
292
Laser Surface Modification of Biomaterials
Microfluidic devices
Stiction reduction
Electro-optic phase
Optical waveguide
Biotechnology devices
Applications of LIPSSs
Photonics & Plasmonics
Graphene surface property enhancement
Optoelectronics
Thermal Radiation
Coating de-icing
Bio-medical
Smart marking and imaging Lubrication
Wetting & Adhesion
Friction
Metals implants
Dental orthopaedic
Figure 10.4 A spider diagram of current and future applications of LIPSSs.
graphene might be more desirable than other materials. Vorobyev et al. [93] reported that femtosecond laser induced periodic surface structuring techniques in general have a great potential to be applicable for photonics, plasmonics, optoelectronics, thermal radiation sources and biooptical devices [93].
10.5 New prospective and future trends It is now better understood by the scientific world and the industry that surface properties are significantly important because they tend to be the limiting factor for a number of various applications. Thus, there has recently been a large increase in the amount of scientific publications on surface treatments and potential applications. As an example, a recent (28 May 2015) Web of Science literature search has shown that publications relating to LIPSS have significantly increased over the last year with approximately 80 publications in 2014–2015 compared to 2005–2015. This had approximately 25 publications per year relating to LIPSSs. With this increase in surface treatment research activity, nanostructuring both topographically and chemically will likely provide a number of fields with a method for enhancing surface properties. From 2010 to 2015 this research has shown how laser induced periodic nanostructures can control frictional properties of materials [79], how these nanostructures can manipulate plasmonic and hydrodynamic properties [94], and how the optical properties of materials can be modulated using LIPSS [93]. Moreover, further studies have been carried out
Laser surface structuring of ceramics, metals and polymers
293
relating to the mechanisms and modelling of LIPSS [50,95,96]. The modelling and understanding of the LIPSS mechanisms for polymers, metals and ceramics are of great importance as a full in-depth understanding of the LIPSSs will ensure that further surface property enhancements can be investigated and realized. With the increase in research with regards to LIPSS for nanostructuring, it has recently been seen over the latter two years that applications of LIPSS have been advanced and evidenced. For example, Beltaos et al. [92] investigated and showed how periodic surface structures can be induced into multilayer graphene using the same laser processing parameters as seen with previous experimental findings with other materials. This particular research has highlighted that, through further research and development, LIPSSs can likely be applied to numerous other material types to modify the surface properties, producing similar material processing results compared to those materials which have already been studied. Other recent research has concentrated on the formation of both ablative and thermochemical LIPSSs [81] and showed that LIPSSs can be implemented as a process for high selectivity etching of titanium oxides. Future work will likely show that ablative and thermochemical LIPSSs can impact materials in different ways, augmenting and undermining the surface properties depending on the material and LIPSS processing parameters. With the realisation of the importance of surface properties with regards to biomedical applications many researchers are now turning to surface treatments for the modification of surface topography and surface chemistry to further enhance the biomimetic nature of materials. As a result, considerable work has been conducted applying many surface treatments to applications which involve the attachment of biological cells [97,98]. This research has led the bioengineering community to understand the significance of surface treatments, giving rise to micromachining and even the significant importance of surface treatments which give rise to nanomachining. With this in mind, it is likely that future research involving LIPSSs will consider the effects of the precise nanoscale surface modification on the biocompatibility properties and cell–substrate adhesion. Furthermore, the effects of the nanoscale features on cell viability and proliferation will also be an important aspect for investigating to ascertain the feasibility of using LIPSSs on a larger scale for biomaterial processing. Such work has already commenced with Barb et al. [80], who showed that a ns-pulsed UV laser can be implemented to generate LIPSSs in PET for the manipulation of human myoblast cells. More research in to the application of LIPSSs to process biomaterials will lead to further enhancements in surface properties of many materials to promote cell adhesion and cell growth. As a result, this offers a significant opportunity to further develop and drive forward the growing biomedical industry by providing researchers and clinicians with a highly controllable material processing technique. This consequently can be used to control and manipulate biological cell lines.
10.6 Conclusions A comprehensive review was undertaken in relation to LIPSSs applied to metals, polymers and ceramic materials as used for biomedical applications. The review included the state of the art behind LIPSSs applied to the aforementioned biomaterials and also addressed
294
Laser Surface Modification of Biomaterials
the future trends, adaptive parameters that one can apply to metals, polymers and ceramics for further research. Moreover, a brief overview on the fundamentals and theory of LIPSSs, type of structures and their applications was discussed. The benefits of LIPSSs on the surface properties are becoming more obvious not only within the science sector but also by biotechnologists. This verifies that short pulse and ultrashort pulse lasers, although well known with certain materials (range of polymers), are useful for implementation. Moreover, further work in relation to a wide range of metals/alloys and bioceramics will fill the gap in knowledge and bring about industrial progress in surface engineering and biotechnology sectors where surface treatment using LIPSSs is beneficial.
References [1] Birnbaum M. Semiconductor surface damage produced by ruby lasers. J Appl Phys 1965;36:3688–9. [2] Dyer PE, Jenkins SD, Sidhu J. Development and origin of conical structures on XeCl laser ablated polyimide. Appl Phys Lett 1986;49(8):453–5. [3] Oliveira V, Simões F, Vilar R. Column growth mechanics during KrF laser micromachining of Al2O3-TiC ceramics. Appl Phys A - Mater Sci Process 2005;81:1157–62. [4] Sanchez F, Morenza JL, Aguiar R, Delgado JC, Varela M. Dynamics of the hydrodynamical growth of columns on silicon exposed to excimer-laser irradiation. Appl Phys A 1998;66:83–6. [5] Van Driel HM, Sipe JE, Young JF. Laser-induced periodic surface structure on solids: a universal phenomenon. Phys Rev Lett 1982;49:1955–8. [6] Liang C, et al. Surface modification of cp-Ti using femtosecond laser micromachining and the deposition of Ca/P layer. Mater Lett 2008;62:3783–6. [7] Anselme K. Osteoblast adhesion on biomaterials. Biomaterials 2000;21(7):667–81. [8] Mendonca G, et al. Advancing dental implant surface technology - from micron- to nanotopography. Biomaterials 2008;29(28):3822–35. [9] Roach P, et al. Modern biomaterials: a review-bulk properties and implications of surface modifications. J Mater Sci-Mater Med 2007;18(7):1263–77. [10] Zhang L, Webster T. Nanotechnology and nanomaterials: promises for improved tissue generation. Nano Today 2008;4(1):66–80. http://dx.doi.org/10.1016/j.nantod.2008.10.014. [11] Albrektsson T, et al. The interface zone of inorganic implants invivo - titanium implants in bone. Ann Biomed Eng 1983;11(1):1–27. [12] Zorba V, et al. Biomimetic artificial surfaces quantitatively reproduce the water repellency of a Lotus leaf. Adv Mater 2008;20(21):4049. [13] Hansson S, Norton M. The relation between surface roughness and interfacial shear strength for bone-anchored implants. A mathematical model. J Biomech 1999;32(8):829–36. [14] Mendes V, Moineddin R, Davies J. The effect of discrete calcium phosphate nanocrystals on bone-bonding to titanium surfaces. Biomaterials 2007;28:4748–55. [15] Oliveira V, Ausset S, Vilar R. Surface micro/nanostructuring of titanium under stationary and non-stationary femtosecond laser irradiation. Appl Surf Sci 2009;255(17):7556–60. [16] Oliveira V, Cunha A, Vilar R. Multi-scaled femtosecond laser structuring of stationary titanium surfaces. J Optoelectron Adv Mater 2010;12(3):654–8. [17] Oliveira V, Nunes B, Vilar R. Wetting response of KrF laser ablated polyimide surfaces. Nucl Instrum Methods Phys Res Sect B-Beam Interact Mater Atoms 2010;268(10): 1626–30.
Laser surface structuring of ceramics, metals and polymers
295
[18] Matthias B, Lazare S. Submicron periodic structures produced on polymer surfaces with polarized excimer laser ultraviolet radiation. Appl Surf Sci 1992;65/66:349–54. [19] Sipe JE, Young JF, Preston JS, Van Driel HM. Laser-induced periodic surface structure. I. Theory. Phys Rev 1983;B27:1141. [20] Young JF, Preston JS, Van Driel HM, Sipe JE. Laser-induced periodic surface structure. II. Experiments on Ge, Si, Al, and brass. Phys Rev B 1983;27:1155. [21] Young JF, Preston JS, Sipe JE, Van Driel HM. Time-resolved evolution of laser-induced periodic surface structure on germanium. Phys Rev B 1983;27:1424(R). [22] Young JF, Sipe JE, Van Driel HM. Laser-induced periodic surface structure. III. Fluence regimes, the role of feedback, and details of the induced topography in germanium. Phys Rev B 1984;30:2001. [23] Allmen MV. Laser-beam interactions with materials. Series in materials science, vol. 2. Berlin: Springer; 1987. [24] Clark SE, Emmony DC. Ultraviolet-laser-induced periodic surface structures. Phys Rev B 1989;40:2031. [25] Bolle M, Lazare S. Large scale excimer laser production of submicron periodic structures on polymer surfaces. Appl Surf Sci 1993;69:31B. [26] Dauscher A, Feregotto V, Cordier P, Thorny A. Laser induced periodic surface structures on iron. Appl Surf Sci 1996;96–98:410–4. [27] Simon P, Ihlemann PJ. Ablation of submicron structures on metals and semiconductors by femtosecond UV-laser pulses. Appl Surf Sci 1997;109/110:25–9. [28] Csete M, Bor Z. Laser-induced periodic surface structure formation on polyethylene-terephthalate. Appl Surf Sci 1998;133:5–16. [29] Ozkan AM, Malshe AP, Railkar TA, Brown WD, Shirk MD, Molian PA. Femtosecond laser-induced periodic structure writing on diamond crystals and microclusters. Appl Phys Lett 1999;75:3716. [30] Csete M, Marti O, Bor Z. Laser-induced periodic surface structures on different poly-carbonate films. Appl Phys A 2001;73(4):521–6. [31] Bozhevolnyi SI, Erland J, Leosson K, Skovgaard PMW, Hvam JM. Waveguiding in surface plasmon polariton band gap structures. Phys Rev Lett 2001;86:3008. [32] Li M, Lu QH, Yin J, Sui Y, Li G, Qian Y, et al. Periodic microstructure induced by 532 nm polarized laser illumination on poly(urethane-imide) film: orientation of the azobenzene chromophore. Appl Surf Sci 2002;193:46–51. [33] Lu XM, Lu QH, Zhu ZK, Yin J, Wang ZG. Laser-induced periodic surface structure on polyimide doped with lecithin. Mater Lett 2003;57:3636–40. [34] Csete M, Hild S, Plettl A, Ziemann P, Bor Z, Marti O. The role of original surface roughness in laser-induced periodic surface structure formation process on poly-carbonate films. Thin Solid Films 2004;453–454:114–20. http://dx.doi.org/10.1016/j.tsf.2003.11.086. [35] Wang J, Guo C. Ultrafast dynamics of femtosecond laser-induced periodic surface pattern formation on metals. Appl Phys Lett 2005;87(25):251914. [36] Tran DV, Zheng HY, Lam YC, Murukeshan VM, Chai JC, Hardt DE. Femtosecond laser-induced damage morphologies of crystalline silicon by sub-threshold pulses. Opt Lasers Eng 2005;43:977–86. http://dx.doi.org/10.1016/j.optlaseng.2004.10.006. [37] Bleiner D, Bogaerts A. Multiplicity and contiguity of ablation mechanism in laser-assisted analytical micro-sampling. Spectrochim Acta B 2006;61:421–32. [38] Vorobyev AY, Makin VS, Guo C. Periodic ordering of random surface nanostructures induced by femtosecond laser pulses on metals. J Appl Phys 2007;101:034903. [39] Groenendijk MNW, Meijer J. Surface microstructures obtained by femtosecond laser pulses. Ann CIRP 2006;55(1):183–6. http://dx.doi.org/10.1016/S0007-8506(07)60394-1.
296
Laser Surface Modification of Biomaterials
[40] Reif J, Costache F, Bestehorn M. Self-organised surface nano-structuring by femtosecond laser processing. In: Perriere J, Millon E, Fogarassy E, editors. Recent advances in laser processing of materials. Elsevier; 2007. p. 275–90. [Chapter 9]. [41] Vorobyev AY, Guo C. Femtosecond laser-induced periodic surface structure formation on tungsten. J Appl Phys 2008;104:063523. [42] Papernov S, Schmidt AW. Laser-induced surface damage of optical materials: absorption sources, initiation, growth, and mitigation. Proc SPIE 2008;7132: 71321J:27. [43] Zheng HY, Tan TT, Zhou W. Studies of KrF laser-induced long periodic structures on polyimide. Opt Lasers Eng 2009;47:180–5. http://dx.doi.org/10.1016/j.optlaseng.2008.06.015. [44] Shinoda M, Gattass RR, Mazur E. Femtosecond laser-induced formation of nanometer-width grooves on synthetic single-crystal diamond surfaces. J Appl Phys 2009;105:053102. [45] Skolski JZP, Römer GRBE, Huis in’t Veld AJ, Mitko VS, Obona JV, Ocelik V, et al. Modeling of laser induced periodic surface structures. J Laser Micro/Nanoeng 2010;5(3): 263–8. http://dx.doi.org/10.2961/jlmn.2010.03.001. [46] Zhihua L, Li P, Fan J, Fang R, Zhang D. Energy accumulation effect and parameter optimization for fabricating of high-uniform and large-area period surface structures induced by femtosecond pulsed laser. Opt Lasers Eng 2010;48:64–8. http://dx.doi.org/ 10.1016/j.optlaseng.2009.07.017. [47] Bonse J, Rosenfeld A, Krüger J. Implications of transient changes of optical and surface properties of solids during femtosecond laser pulse irradiation to the formation of laser-induced periodic surface structures. Appl Surf Sci 2011;257:5420–3. http://dx.doi.org/10.1016/j.apsusc.2010.11.059. [48] Varlamovaa O, Reif J, Varlamovb S, Bestehornb M. The laser polarization as control parameter in the formation of laser-induced periodic surface structures: comparison of numerical and experimental results. Appl Surf Sci 2011;257:5465–9. http://dx.doi.org/ 10.1016/j.apsusc.2010.11.157. [49] Lin Li, Hong M, Schmidt M, Zhong M, Malshe A, Huis in’tVeld B, et al. Laser nano-manufacturing – state of the art and challenges. CIRP Ann – Manuf Technol 2011;60:735–55. [50] Bonse J, Krüger J, Höhm S, Rosenfeld A. Femtosecond laser-induced periodic surface structures. J Laser Appl 2012;24:042006. [51] Makropoulou M, Serafetinides AA, Skordoulis CD. Ultra-violet and infra-red laser ablation studies of biocompatible polymers. Lasers Med Sci 1995;10:201–6. [52] Mirzadeh H, Katabab AA, Burfford RP. CO2-laser graft copolymerization of HEMA and NVP onto ethylene-propylene rubber (EPR) as biomaterial-(III). Radiat Phys Chem 1995;46(4–6):859–62. [53] Mirzadeh H, Katabab AA, Khorasani MT, Burfford RP, Gorgin E, Golestani A. Cell attachment to laser-induced AAm-and HEMA-grafted ethylene-propylene rubber as biomaterials: in vivo study. Biomaterials 1995;16:641–8. [54] Wu PK, Ringeisen BR, Callaham J, Brooks M, Bubb DM, Wu HD, et al. The deposition, structure, patterns deposition, and activity of biomaterial thin-film by matrix-assisted pulsed-laser evaporation (MAPLE) and MAPLE direct write. Thin Solid Films 2001;398–399: 607–14. [55] Duncan AC, Weisbuch F, Rouais F, Lazare S, Baquey C. Laser microfabricated model surfaces for controlled cell growth. Biosens Bioelectron 2002;17:423–6. [56] Anguilar CA, Lu Yi, Samuel M, Shaxhen C. Direct micro-patterning of biodegradable polymers using ultraviolet and femtosecond lasers. Biomaterials 2005;26:7642–9. [57] Pfleging W, Burns M, Welle A, Wilson S. Laser-assisted modification of polystyrene surfaces for cell culture applications. Appl Surf Sci 2007;253:9177–84.
Laser surface structuring of ceramics, metals and polymers
297
[58] Fayou K, Mücklich F, Li P, Shen H, Mathur S, Lehr C-M, et al. In vitro cell response to a polymer surface micropatterned by laser interference lithography. Biomacromolecules 2005;6:1160–7. [59] Hongyu S, Zhou H, Sun N, Luquan R, Li C, Xianzhou L. Study on adhesion resistance behaviour of sample with striated non-smooth surface by laser processing technique. J Mater Process Technol 2008;199(1–3):221–9. [60] Mirzadeh H, Dadsetan M. Influence of laser surface modifying of polyethylene terephthalate on fibroblast cell adhesion. Radiat Phys Chem 2003;67:381–5. [61] Pérez S, Rebollar E, Mohamed O, Martín M, Castillejo M. Laser-induced periodic surface structuring of biopolymers. Appl Phys A 2013;110:683–90. [62] Castillejoa M, Ezquerrab TA, Martína M, Oujjaa M, Péreza S, Rebollar E. Laser nanostructuring of polymers: ripples and applications. In: International symposium on high power laser ablation, May 3, 2012, Santa Fe, USA, vol. 1464. 2012. p. 372–80. [63] Mills D, Kreouzis T, Sapelkin A, Unal B, Zyuzikov N, Kolasinski KW. Surface texturing of Si, porous Si and TiO2 by laser ablation. Appl Surf Sci 2007;253:6575–9. [64] Vorobyev AY, Guo C. Femtosecond laser structuring of titanium implants. Appl Surf Sci 2007;253:7272–80. [65] Nayak BK, Gupta M,C. Self-organized micro/nano structures in metal surfaces by ultrafast laser irradiation. Opt Lasers Eng 2010;48:940–9. [66] Chunha A, Oliveira V, Serro AP, Zouani OF, Almeida A, Durrieu MC, et al. Ultrafast laser texturing of Ti-6Al-4V, surfaces for biomedical applications, (N405). In: The 32nd International Congress on Applications of Lasers & Electro-Optics (ICALEO®) 2013, October 6–10 in Miami, FL. 2013. p. 910–8. [67] Gaggl A, Schultes G, Müller WD, Kärcher H. Scanning electron microscopical analysis of laser-treated titanium implant surfaces—a comparative study. Biomaterials 2000;21:1067–73. [68] Pfleging W, Kumaria R, Besserb H, Scharnweberc T, Majumdar JD. Laser surface textured titanium alloy (Ti-6Al-4V): part 1 – surface characterization. Appl Surf Sci 2015;355:104–11. [69] Çelena S, Efeoğlub C, Özdena H. Pulsed laser-induced micro-pits: as bone stabilizers. In: Lasers in manufacturing 2011-proceedings of the sixth international WLT conference on lasers in manufacturing, vol. 12 (B). 2011. p. 245–51. [70] Kumari R, Scharnweber T, Pfleging W, Besser H, Majumdar JD. Laser surface textured titanium Alloy (Ti-6Al-4V)-part II-studies on bio-compatibility. Appl Surf Sci 2015;357A:750–8 (Published online on September 1, 2015). [71] Buividasa R, Mikutis M, Juodkazis S. Surface and bulks structuring of materials by ripples with long and short laser pulses: recent advances. Prog Quantum Electron 2014;38:119–56. [72] Hu T, Hu L, Ding Q. Effective solution for the tribological problems of Ti-6Al-4V: combination of laser surface texturing and solid lubricant film. Surf Coat Technol 2012;206:5060–6. [73] Serpengüzel A, Kurt A, Inanç I, Cary JE, Mazur E. Luminescence of black silicon. J Nanophot February 21, 2008;2:021770. [74] Shazia B, Rafique S, Husinsky W. Liquid assisted ablation of zirconium for the growth of LIPSS at varying pulse durations and pulse energies by femtosecond laser irradiation. Nucl Instrum Methods Phys Res B 2015;349:230–8. [75] Jelani M, Shazia B, Akram M, Yousaf D, Afzal N, Ahmad S. Mechanical behaviour of excimer laser irradiated polycrystalline zirconium. Phys Scr 2014;89(2):025703 (7 pp.). [76] Grojo D, Hermann J, Perrone A. Plasma analyses during femtosecond laser ablation of Ti, Zr, and Hf. J Appl Phys 2005;97:063306.
298
Laser Surface Modification of Biomaterials
[77] Samant AN, Paital SR, Dahotre NB. Process optimization in laser surface structuring of alumina. J Mater Process Technol 2008;203:498–504. [78] Huis in’t Veld B, Groenendijk M, Fischer H. Initiation of femtosecond laser machining ripples in steel observed by scanning helium ion microscopy. J Laser Micro/Nanoeng 2010;5(1):28–34. [79] Eichstadt J, Romer GRBE, Veld AJHI. Towards friction control using laser-induced periodic surface structures. Phys Procedia 2011;12:7–15. [80] Barb R-A, Hrelescu C, Dong L, Heitz J, Siegel J, Slepicka P, et al. Laser-induced periodic surface structures on polymers for formation of gold nanowires and activation of human cells. Appl Phys A 2014;117:295–300. [81] Dostovalov AV, Korolkov VP, Babin SA. Simultaneous formation of ablative and thermochemical laser-induced periodic surface structures on Ti film at femtosecond irradiation. Laser Phys Lett 2015;12:036101. http://dx.doi.org/10.1088/1612-2011/12/3/036101. [82] Tan B, Venkatakrishnan K. A femtosecond laser-induced periodical surface structure on crystalline silicon. J Micromech Microeng 2006;16:1080–5. http://dx.doi.org/ 10.1088/0960-1317/16/5/029. [83] Guo XD, Li Xr, Hang Y, Xu ZZ, Yu BK, Ma HL, et al. Femtosecond laser-induced periodic surface structure on ZnO. Mater Lett 2008;62:1769–71. http://dx.doi.org/ 10.1016/j.matlet.2007.09.082. [84] Savas TA, Farhoud M, Smith HI, Hwang M, Ross CA. Properties of large area nanomagnetic arrays with 100 nm period made by interferometric lithography. J Appl Phys 1999;85:6160. [85] Lowndes DH, Fowlkes JD, Pedraza AJ. Early stages of pulsed-laser growth of silicon microcolumns and microcones in air and SF6. Appl Surf Sci 2000;154–155. [86] Carey JE. Femtosecond-laser microstructuring of silicon for novel optoelectronic devices [A Doctoral thesis]. Cambridge, Massachusetts: Harvard University; 2004. [87] Liao Y, Song J, Cheng Y, Zhizhan X. Rapid prototyping of three-dimensional microfluidic mixers in glass by femtosecond laser direct writing. In: Progress in electromagnetics research symposium abstracts, Malaysia, March 27–30. 2012. [88] Cheng Y, Liao Y, Huang M, Zhizhan X. Harnessing ultrafast laser-induced subwavelength structures for liquid crystal photonics application. In: Progress in electromagnetics research symposium abstracts, Malaysia, March 27–30. 2012. [89] Chang HW, Lin CY, Cheng CW, Lin YW, Wu TM, Tsai YC. Preparation of nanostructured Ag substrate with femtosecond laser as surface-enhanced Raman scattering substrates. In: Progress in electromagnetics research symposium abstracts, Malaysia, March 27–30. 2012. [90] Audouard E. Ripples formation under femtosecond laser irradiation: actual and potential applications. In: Progress in electromagnetics research symposium abstracts, Malaysia, March 27–30. 2012. [91] Yu JJ, Lu YF. Laser induced ripple structure on Ni-P substrate. Appl Surf Sci 1999;148(3–4):248–52. [92] Beltaos B, Kivačević AG, Matković A, Ralević U, Savić-Sević S, Jovanovič D, et al. Femtosecond laser induced periodic surface structures on multi-layered graphene. J Appl Phys 2014;116:204306. http://dx.doi.org/10.1063/1.4902950 (1–6). [93] Vorobyev AY, Makin VS, Guo C. Optical properties of femtosecond laser-induced periodic surface structures on metals. In: Circuits and systems, 2009. MWSCAS ‘09. 52nd IEEE international midwest symposium, 909–912, 2–5 August, Cancun, Mexico. 2009. [94] Colombier JP, Garrelie F, Brunet P, Bruyère A, Pigeon F, Stoian R, et al. Plasmonic and hydrodynamic effects in ultrafast laser-induced periodic surface structures on metals. J Laser Micro/Nanoeng 2012;7:362–8.
Laser surface structuring of ceramics, metals and polymers
299
[95] Gräf S, Müller FA. Polarisation-dependent generation of fs-laser induced periodic surface structures. Appl Surf Sci 2015;331:150–5. [96] Hwang TY, Guo C. Angular effects of nanostructure-covered femtosecond laser induced periodic surface structures on metals. J Appl Phys 2010;108:073523. [97] Razavi M, Fathi M, Savabi O, Vashaee D, Tayebi L. In vivo study of nanostructured akermanite/PEO coating on biodegradable magnesium alloy for biomedical applications. J Biomed Mater Res Part A 2014;103:1798–808. http://dx.doi.org/10.1002/jbm.a.35324. [98] Sgura R, Reis MC, Hernandes AC, Fantini MCA, Andreeta MRB. Surface treatment of dental porcelain: CO2 laser as an alternative to oven glaze. Lasers Med Sci 2015;30:661–7.
10
P. Shukla1, D.G. Waugh1, J. Lawrence1, R. Vilar2 1Thornton Science Park, University of Chester, Chester, United Kingdom; 2Instituto Superior Tecnico and CeFEMA - Centre of Physics and Engineering of Advanced Materials, Lisbon University, Lisbon, Portugal
10.1 Introduction 10.1.1 Research background Laser-induced periodic surface structures (LIPSSs) have been observed since 1965 [1]. They are known as random or self-organised, micrometre-sized surface textures (waves, cones and ripples) which have been observed in surfaces treated with continuous wave and pulsed laser irradiation. Their formation mechanism has been the object of intense controversy from before 1975 to 2015. Many of them are of hydrodynamic origin with frozen-in waves and crests usually explained by fluid flow driven by the Marangoni effect and recoil pressure, but periodic wavelets are also found which can be explained by Rayleigh–Taylor instabilities [1–4]. The formation of micro-sized cones and columns is explained by shadowing of radiation by impurities [1], differential ablation [2] or hydrodynamic effects [3]. Moreover, when ultrashort pulse duration lasers are used at fluences near the ablation threshold, periodic self-organised wavelets with wavelengths in the range 200–700 nm and amplitude 10–100 nm can be observed in a wide range of materials, in particular semiconductors, metals and polymers [4]. Their mechanism of formation is essentially unknown, despite a number of recent studies [1–4]. Laser micro- and nanotexturing may lead to considerable modification of properties relevant to osseointegration, namely biocompatibility, protein adsorption and cell/surface interactions [5], and the process has the potential to become a powerful tool in biomedical surface engineering. It is essential for the efficiency and service lifetime of endosseous implants that a solid bone/material interface is established, with no fibrous tissue formation [6]. However, most materials currently used for bone replacement show negligible bioactivity and originate some form of encapsulation. It is generally recognized that further progress can only be achieved by endowing biomaterials with a higher degree of surface functionality, obtained through structured surfaces with a high degree of complexity. This would mimic the surface relief of natural hard tissues (biomimetic materials) [6–10]. Recent work has shown that Laser Surface Modification of Biomaterials. http://dx.doi.org/10.1016/B978-0-08-100883-6.00010-1 Copyright © 2016 Elsevier Ltd. All rights reserved.
282
Laser Surface Modification of Biomaterials
osteoblast activity is considerably enhanced by nanosized surface features [11,12] and that properly designed nanostructured surfaces may represent a large step forward in biomedical device functionality [6]. Surprisingly, measurements of bone/implant, bond disruption forces showed that achieving high bond strength depends more on the surface nanotexture than on the nature of the material underneath, justifying the hope that inert biomaterials may be rendered more bioactive by providing them with a suitable nanoscale surface texture [13]. Various researchers have demonstrated that biomimetic surfaces consisting of LIPSSs can be obtained by using specific laser treatment methods [14–16]. Under some processing conditions LIPSSs overlap as a random micrometre-sized columnar topography, leading to a bimodal surface relief. The features on these surfaces can be controlled by changing the radiation wavelength, fluence, and polarisation and laser treatment techniques. One of the main potential applications of femtosecond laser texturing is the creation of implants with improved biocompatibility. Ultrafast lasers also have the potential to drastically change surface properties that are difficult to improve by other methods, such as wetting (superwetting, superhydrophobicity [17]) and spectral selectivity [18].
10.1.2 Research scope and rationale LIPSSs are important for modification of biomedical materials so that enhancement in their performance can be achieved with respect to properties such as coefficient of friction, wear, wettability adhesion, fracture and impact strengths just to name a few. Since its first introduction in 1965, much work has been conducted in this area [1,5,19–50]. Thus, there is a need for not just a review but also a focus on the gaps in knowledge, particularly for applications of LIPSSs in the biomedical sector. Thus, this chapter reviews research works focused on LIPSSs, applicable to biomedical materials, namely polymers, ceramics and metals/alloys. The work entails various types of laser-induced surface structures, their applications to biomedical sectors, new prospective and future trends and the state-of-the-art literature that has been published to date in this area. Presented herein are gaps in knowledge and new ideas and the chapter allows one to quickly grasp the process parameters used in previous research for generating various types of LIPSSs. A map showing the scope of the chapter is presented in Fig. 10.1.
10.1.3 Fundamentals and theory of laser-induced periodic surface structures LIPSSs are formed when the material is exposed to certain laser energy densities for a given time period [19]. To date, the physical processes in the time scale from nanoseconds and longer pulsed durations to the use of continuous wave (CW) lasers are well understood [19,25,31]. However, there is still a gap in knowledge when it comes to the effects exhibited from femtosecond and picosecond pulse interactions. The accepted principle of LIPSSs is that they are generated by interaction of the incident laser beam with a surface electromagnetic wave. Since the 1980s several authors
Laser surface structuring of ceramics, metals and polymers
Laser-induced periodic surface structures
Applications
Bioceramic
Types of structures and adaptive parameters
New prospectives and future trends
State-of-the-art research in relation to biomedical sectors Other biosuitable materials
283
Biometals/ alloys Biopolymers
Figure 10.1 A map showing the scope of the chapter.
have explored in detail the generation of LIPSSs [19–22]. During the generation of LIPSSs, there will be a melt zone with a certain depth of ablation by the pulsed laser, the electron photon relaxation time and the thermal diffusivity. Within the melt zone, there is evaporation which travels to the edge of the irradiated area forming a range of droplets [27]. The shape of a LIPSS is dependent on the driving force of the melt recoil pressure and the time that heating and solidification takes place [27]. This in turn leads to rapid cooling, creating sharp peaks and small droplets in the case of short pulses such as nanosecond, picosecond and more distinctively with femtosecond laser interactions. Sipe and colleagues introduced a theory of LIPSSs in the early 1980s [19–22]. This work used a Fourier component of induced structure with the corresponding Fourier component of inhomogeneous energy deposition just beneath the surface. The theory assumed that surface roughness was confined to a region of height that was smaller than the wavelength of the laser light, resulting in symmetry breaking and leading to inhomogeneous deposition. Thus, strong peaks were produced in this deposition in Fourier space that eventually led to the predictions of induced fringe patterns with spacing and orientation dependent on the angle of incidence and polarization of the laser beam [19–22]. Li et al.’s [49] explanation of the LIPSSs theory was that the driving force for the rippling effect starts from the interference of the incident and reflected or refracted laser beam with the scattered/diffracted light near the material interaction. Such diffraction/scattering of the incident light could create microscopic roughness of the surface, by defects or by spatial variations in the dielectric constant. An interference between different waves could consequently lead to an inhomogeneous energy input to the electron system. Combining this with a positive feedback mechanism consequently causes the ripple effect. Laser beams can be polarized to produce an orientated ripple formation [49]. This tends to control the material excitation. Linear polarization of the laser could orient
284
Laser Surface Modification of Biomaterials
the ripples perpendicular to the polarization direction. Also, fine ripples with an orientation parallel with the polarization direction can be found. If the laser light is circularly polarized then ripples without a specific orientation can be found. The periodicity of the rippling effect is subject to laser energy, pulse duration, number of pulses, wavelength, laser beam polarization and the angle of incidence. Various types of surface features that are usually in the range of 1 μm and above using the conventional laser sources ranging from ultraviolet to infrared could be created. However, to create nanostructures, deep ultraviolet lasers can be implemented that in turn could generate 130 nm lines and lower, which is ideal [49]. It is necessary that the desired LIPSSs should be half the size of the wavelength of the laser and also smaller than the smallest allowable spot size of the laser beam. This is why deep ultraviolet sources are better suited for surface structuring. Eq. [10.1] governs this factor, where d is the minimum beam spot diameter, λ is the laser wavelength, n is the refractive index of the beam delivery to the material and α is the beam divergence angle [49].
d =
λ 2n sin α
[10.1]
10.2 State of the art in laser-induced periodic surface structures on various materials 10.2.1 Biopolymers Polymeric materials have been extensively used in biomedical applications since 1995 to 2015 [51–55]. Polymers such as nylon, teflon, polypropylene, polyethylene, polytetrafluoroethylene and many others are noncarcinogenic and nonmigrating and have minimal foreign body reactions [51]. Since then, CO2 lasers have also been used to improve the surface properties of polymers so that cell adhesion, proliferation and bonding on such laser-modified surfaces could be improved [52–54]. Using an excimer laser, Duncan et al. [55] developed microgrooves that were 30 by 10 μm at 1 J/cm2 with a 248 nm wavelength, and 20 ns pulse length, to find that osteoprogenitor cells adhere on the surface of polyethylene terephthalate (PET) with minimal groove width and depth. However, cell adhesion was restrained at the bottom of the grooves due to the given surface chemistry effect. Using a femtosecond laser, Aguilar et al. [56] created micropatterning of polycaprolactone and polyglycolic acid in ambient atmosphere. Micrometre-sized channels and holes were created in both biodegradable microdevices. Microfeatures were etched in the aforementioned polymers of 30 μm. Pfleging et al. [57] also modified a polystyrene with respect to applications in microfluidics and cell culture. Their results showed that helium or oxygen allowed control of the wetting angle, between 2 and 150 degrees. In addition, the modified surfaces were deemed hydrophilic and hydrophobic, respectively, due to the changes in the surface topography and chemistry [57]. Periodic lines and micropatterns were created on polycarbonate using a q-switched Nd:YAG laser by Fayou et al. [58]. This was carried out rather using a laser interference lithography
Laser surface structuring of ceramics, metals and polymers
285
within a short time. Moreover, cell interactions were studied to show that HPFs (high pressure freezings) grew parallel to the line structure and showed bipolar morphology on point micropatterns. Laser machining is another technique that can bring about surface structures such as convex domes and dimple cavities on a low-density polyethylene, high-density polyethylene, and acrylonitrile butadiene styrene [59]. Thus, a nonsmooth surface can be created to imitate the body/surface morphology of a polymer-based biological system. Surface structures such as grooves and domes created on polymer PET surfaces have also shown fibroblast cell adhesion and spreading due to changes in the surface morphology and wettability of the PET using both a CO2 and a KrF excimer laser [60]. Péres et al. [61]. reported on the formation of LIPSSs on self-standing films of biopolymers, namely chitosan starch and the blend of chitosan with a synthetic polymer polyvinyl pyrrolidone. This was using linear polarized laser beams of 193, 213 and 26 nm wavelength with a pulse duration ranging between 6 and 17 ns. Their result showed that formation of LIPSSs occurred parallel to the laser polarization direction, with periods that were close to the laser wavelength. However, the formation of LIPSSs was not seen in the crystalline starch biopolymer. Although the work was a systematic investigation, the result did not report on the potential applicability to biomedical applications. Comparatively, Castillejoa [62] reported that the end application in the biomedical area usually dictates the applicability of LIPSSs to a particular biopolymer surface. Their investigation also used chitosan starch, PET, PTT and PC polymeric materials by applying several thousand pulses between 15 and 120 ns, at wavelengths ranging from 193 to 795 nm [62]. Zhen et al. [43] generated laser-induced long periodic surface structures on polyimide to improve its crystallinity. This may have several benefits directly. The improvement in crystallinity may not only affect the mechanical and optical properties of the polyimide but also affects the surface wettability so that the polyimide surface can be deemed to improve the biocompatibility. Generating LIPSSs on polymers has proven to be common with the use of variety of lasers, wavelengths and processing parameters. With that said, Lu et al. [33] suggested that using 266 nm wavelengths generated regular periodic structures when compared to 355 nm especially when laser processing a polyimide. Thus, future studies could elucidate the possibility of laser-treating a variety of polymers using various different wavelengths at short and ultrashort pulses to explore the occurrence of LIPSSs on such biomedical materials.
10.2.2 Biometals/alloys Titanium/alloys have been employed for biomedical applications for number of years [63–72]. Titanium/alloys have the tendency to be less corrosive and are easier to shape and machine. They also have good fatigue strength and are biocompatible in particular. However, such biometals/alloys do not always comply with clinical requirements; thus, surface treatments, particularly using ultrashort pulse lasers may be needed [64]. Surface features, namely nanopores, nanoprotrusions and sphere-like nanostructures ranging in size from 10 to 20 nm were reported on titanium implants by Vorobyev and Guo [64]. Through the work of Vorobyev and Guo, it has been suggested that short pulse lasers in comparison to long pulse lasers are more ideal for the treatment of not just
286
Laser Surface Modification of Biomaterials
titanium dental applications but also for other biomedical applications [64]. This confirms the previous statements regarding the use of deep ultraviolet wavelengths for generating LIPSSs. No further details were given in terms of implementing their work in the biomedical area. Ultrafast laser pulses were introduced to Ti, Al, Cu and stainless steel. In particular, Ti surfaces were textured to around 100–500 μm as reported by Nayak and Gupta [65]. They also showed that the thermo-physical and optical properties of the material tends to dictate the experimental parameters. Gaseous assistance is a must for generating such micro- and nanostructures also. Nonetheless, the authors noted that implementing such structures not only for biomedical but also for microelectronics and photovoltaics applications would be highly beneficial [65]. Chunha et al. [66] published a parametric study of ultrafast laser texturing (500 fs) of TI-6AL-4V for biomedical applications. Different types of surface structures were produced, namely ripples, nanopillars and microcolumns. Their results showed an increase in wettability and the surface became hydrophilic. Chunha et al. further stated that this type of surface treatment could also control the behaviour of human mesenchymal stem cells. Further, it was also reported that a reduction in cell spreading and no cell proliferation were observed on the femtosecond laser-textured surfaces. But cytoskeleton stretching and stress fibres were evident [66]. Gaggl et al. [67] surface-treated four different titanium-based implants with various techniques which included laser, spray coating, machining and aluminium oxide coating. The optimal surface structure with the least contamination was found for the laser-treated surfaces of the titanium [67]. Titanium alloys (Ti-6Al-4V) were laser-structured using an excimer laser (193 nm wavelength) by Pfleging et al. [68]. The wavelength used was 193 nm at 5 ns pulse duration. The characterisation of the textured surfaces (both the top surface and the cross-section) was carried out to find various microstructural changes, namely: rutile, anatase and a few Ti2O3 phases. In addition, an increase in wettability was found that yielded a total surface energy increase of 67.6 mN/m compared to the as-received Ti-6Al-4V (37 mN/m). The effect of the polar component influences the surface energy of textured surfaces causing such structures to be biocompatible [68]. Generating microporous surfaces can help in creating mechanical interlocking (crucial for osseointegration). Titanium implants were first modelled in 3-D and then treated using a 20 W fibre laser. The surface was then deemed to be a good bone stabilizer as reported by Çelena et al. [69]. Based on their findings, it can be postulated that the fibre laser was modulated to deliver short pulses. Thus, the generated LIPSS would be in the range of 1 μm and above due to its wavelength and pulse duration. Kumari et al. [70] reported a detailed study on wear, corrosion and bioactivity behaviours of laser surface textured titanium alloy (Ti-6Al-4V) by an ArF excimer laser at a wavelength of 193 nm with a pulse length of 5 ns. In addition, the authors studied the effects of bioactivity and cell attachment and found a significant increase in wear resistance and a marginal change in corrosion resistance. More importantly, the textured surfaces manifested significant improvement in bioactivity in terms of calcium phosphate deposition rate. Improvement in cell viability of the laser-textured Ti-6Al-4V was comparable to that of the as-received Ti-alloy. Cell attachment studies show a reduced cell density in the textured surface with a maximum reduction in the dimple textured
Laser surface structuring of ceramics, metals and polymers
287
surface. Lastly, the cells aligned themselves along the direction of texturing in the linear textured surface [70].
10.2.3 Bioceramics Research in the area of laser surface structuring of ceramics is generally scare. There is a need to develop such structures on materials such as ceramics because in doing so could manifest a change in the range of functional and physical, chemical, and mechanical properties to name a few. In terms of biomedical properties, laser microand nanotexturing may lead to considerable modification of properties relevant to osseointegration such as biocompatibility, protein adsorption and cell/surface interactions, wetting (superwetting, superhydrophobicity) and spectral selectivity [7,12,73]. Moreover, ceramics are ideal for bone implants and thus, surface texturing would be highly beneficial for rendering them bioactive, although ceramics such as alumina and zirconia are known to be bio-inert materials [14]. Surprisingly, measurements of bone/implant bond disruption forces showed that achieving high bond strength depends more on the surface nanotexture than on the nature of the material underneath, justifying the hope that inert biomaterials (for example alumina and zirconia) may be rendered more bioactive by providing them with a suitable nanoscale surface texture [14]. The applicants demonstrated that biomimetic surfaces consisting of LIPSSs can be obtained by using proper laser treatment methods [14–16]. Other investigations were performed to explore the optimised conditions for the growth of LIPSSs by varying pulse durations and pulse energies during ultrashort pulsed laser ablation of zirconium [74]. This also led to some success as the micrographs showed nanoscale ripples for all pulse durations. It was further reported that LIPSSs are more distinct and well organized for the shortest pulse duration of 25 fs with such ceramics, whereas, LIPSSs become diffused and indistinct with the increase in the pulse duration. This indicated that a shortest pulse duration of 25 fs was the most suitable for the growth of nanoscale ripples [74]. Other investigators have also worked with zirconia using an excimer laser KrF with 248 nm wavelength, 18 ns pulse duration and a repetition rate of 30 Hz using a laser fluence of 3.8–5.1 J/cm2. Their results revealed a growth of grains on the laser surface-treated zirconium. They reported that with increasing fluence, the crystal grain became larger [75]. Grojo et al. [76] also conducted a laser ablation and plasma diagnostics study of zirconium [76]. Samant et al. [77] laser surface structured an alumina ceramic and observed the effects of the laser pulse width, repetition rate and the scanning speed. Their results showed that the pulse repetition played an important role in minimising the interdendritic porosity while the scanning speed contributed significantly to increase of the grain size [77]. However very little work, if any, has been conducted on surface structuring of ceramics in general, especially in relation to its applicability in the biomedical sector. This is a strong indicator that laser surface structuring of bioceramics would require further studies ranging from basic parametric investigations addressing the effects of nanosecond, picosecond and femtosecond lasers to an in-depth study demonstrating the biocompatibility after successfully achieving laser-structured ceramics.
288
Laser Surface Modification of Biomaterials
10.3 Variety of laser-induced periodic surface structures and required parameters LIPSS formation comprises the growth of wavy surfaces that can occur on a wide variety of materials and entails surface features that are periodicity equal or smaller than the wavelength of the laser irradiation. The ripple period may depend on the laser energy applied. Regular surface structures are possible to form by laser irradiating the material at an energy level lower than the ablation threshold of the materials. Such structures can be found of uniform sizes at the nanometre scale. Grooves of the size of nanometres in a synthetic single-crystal CVD diamond were made using femtosecond laser pulses [49]. The grooves were perpendicular to the direction of the laser polarization and were 40 nm wide, 500 nm deep, and had an average spacing of 146 ± 7 nm [49]. In cases where energy level increases, the periodic surface structures became chaotic structures [39]. The heights of ripple-type structures tend to range from around 10 to 100 nm [78] as shown in Table 10.1. LIPSSs, particularly the ripple effect, have been exhibited on variety of materials; metals, semiconductors, dielectrics (glass and diamond), ceramics and polymers show periodic structures. In the 1970s and 1980s nanosecond pulses were used and in the 1990s and the first decade of this century picosecond and femtosecond pulses became available for micro/nanoripple or periodic structure formation. Fig. 10.2 shows the variety of LIPSSs that can be formed followed by Fig. 10.3 demonstrating high-resolution images of LIPSS from various published literature [82–86].
10.4 Applications of laser-induced periodic surface structures LIPSSs were first considered as laser-induced damage to the surface of optical components [42]. With that said, it was then realized that such surfaces (rippled in particular) comprise of useful properties. In addition, it is also easy to surface-treat large areas continuously with overlapping shots of short and ultrashort laser pulses, which in turn became useful for several known industrial applications [87–93]. Liao et al. [87] reported that 3D structures can be built on glass substrates using femtosecond lasers by direct writing. The structures are 3D so applications such as microfluidic devices requiring a wide array of lab-on-a-chip can be desirable with high efficiency, flexibility and cost-effectiveness [87]. Transparent substrates can now be fabricated using femtosecond lasers (maskless) to construct 3D functional structures. Also, nanoripples as such could be produced on the sidewalls of a microcell substrate. Such ablated surfaces with submicrometre wavelength structures are then integrated with liquid crystal electrooptic phase modulators and optical waveguides [88]. Nanostructure generation using femtosecond lasers was also reported by Chang et al. [89]. Periodic surface structures on Ag that had spacing of 500–600 μm were produced. For practical use laser-structured surfaces showed that surface-enhanced Raman scattering intensity was improved by 15-fold [89].
Table 10.1 Adaptable
parameters from previous research for the negation of laser-induced periodic surface
structures Parameters Type of structure
Structure size/depth
Pulse duration
PRR
Laser energy
Scan speed
Wavelength
No. pulses
Laser type
References
Ripples Ripples Ripples Ripples
4–15 nm 150 nm 50 nm 100 nm
25 ns 5 ns 20–40 ns 67 ps
100 Hz 10 Hz – 400 KHz
58–800 mJ/cm2 2.8–5 mJ/cm2 2.5–8 mJ/cm2 12.5 μJ
– 5 mm/s – –
248 nm 266–355 nm 193–248 nm 1030 nm
30 – 1000 –
Excimer Nd:YAG ArF excimer Yb:YAG
[43] [33] [28] [79]
Ripples
1 μm
20 ns
10 Hz
10.5–12.5 mJ/ cm2
–
248 nm
6000
KrF excimer
[80]
Ripples and 500 nm 5 ps to nanopores 500 fs Ripples 1.4–3 μm 10 ns Grooves, 150–670 nm 30–230 fs ripples, cones
–
0.6–1.2 J/cm2
–
248 nm
–
KrF excimer
[27]
10 Hz 290–700 mJ 1–200 KHz 6.5–130 nJ
– 1 μm/s
532 nm 0–200 790–1026 nm 50
Nd:YAG fs
[26] [47,81]
Alumina
Ripples
100–200 nm 0.5–8 ms
8–25
1064 nm
–
Nd:YAG
[77]
Zirconium
Ripples, flakes
80–120 nm
1 KHz
2.87–7.62 cm/ min –
800 nm
–
Ti: Sapphire laser
[74]
Materials
Polymers Polyimide Polyimide PET Wafer chucks Polystyrene
Metals Copper Iron Titanium/ alloys
Ceramics 25–100 fs
200–600 μJ
290
Laser Surface Modification of Biomaterials
Micro/nano grooves & striations (particles) Micro/nano riples
Flakes
Gratings
Types of laserinduced surface structures
Spheres/bubbles/ domes/dimples
Cones micro/nano protrutions
Nano-pores
Figure 10.2 The different types of LIPSSs that can be exhibited on variety of biomaterials.
Many periodic nanostructures can also be used for unique applications such as “smart marking”, whereby, the effects of colour by diffraction on metallic surfaces can be shown [90]. The method is very simple; an image is obtained using a scanner and the information is transferred on the workpiece. Moreover, especially the rippled structure was reported to influence surface modification for improving processes such as adhesion, friction, lubrication and coating de-icing [90]. Furthermore, hydrophilic materials were made hydrophobic by no chemical coating. This is when laser structuring, namely: microgrooves, is made useful for manipulating metals such as titanium and Ti alloys bioactive so that they can be useful for dental orthopaedic implants. New methods such as multiscale texturing have also shown promise for the development of structured topography that may help osteogenesis and improve osseointegration of metal implants [90]. Structuring the surfaces to improve friction properties was also reported by Eichstädt et al. [79]. They found that the friction coefficient was improved by 1.6 times after applying LIPSSs in comparison to the surface that was untreated [79]. Such improvement could influence the materials’ tribological properties so that issues such as stiction on computer hard drives could be minimised and in turn eliminated [91]. Nanopatterning of synthetic polymer structures can be transformed into gold nanowires using UV nanosecond laser ablation at a certain angle. This has the potential to be applicable for
Laser surface structuring of ceramics, metals and polymers
D
E
G
H
291
F
I
J
Figure 10.3 SEM images showing the formed rippled structure (a) [82]; nanopore induced into copper at 500 fs (b) [27]; nanoparticles at 150 fs (c) [83]; nanocones (d) [84]; microcolumns (e) [85]; nanobubbles (f) [45]; and microcones (g) [86].
biosensors. Tissue engineering the biosensors, in particular, could further be imbedded directly into devices used in biotechnology [80]. Applications of submicrometre structures in various technological areas are shown in Fig. 10.4. A particular requirement for this is where surface properties need improvement but at the same time do not affect the appearance of the material. The reporting showed surface that roughness can be improved, which in turn leads to low friction and wear rate [1]. Graphene is currently a material in demand [92]. LIPSSs were reported to be induced into the material for the first time by Beltaos et al. [92]. Their results showed inducement of LIPSSs that were 0.5–1.5 μm in length and 35 ± 5 nm on 10–15 layered graphene in an ambient environment. Their breakthrough findings also demonstrated that high-end materials such as graphene can be treated by LIPSSs that could be induced quickly and cheaply. They also reported that such material surface modifications could consequently open new avenues for future applications where
292
Laser Surface Modification of Biomaterials
Microfluidic devices
Stiction reduction
Electro-optic phase
Optical waveguide
Biotechnology devices
Applications of LIPSSs
Photonics & Plasmonics
Graphene surface property enhancement
Optoelectronics
Thermal Radiation
Coating de-icing
Bio-medical
Smart marking and imaging Lubrication
Wetting & Adhesion
Friction
Metals implants
Dental orthopaedic
Figure 10.4 A spider diagram of current and future applications of LIPSSs.
graphene might be more desirable than other materials. Vorobyev et al. [93] reported that femtosecond laser induced periodic surface structuring techniques in general have a great potential to be applicable for photonics, plasmonics, optoelectronics, thermal radiation sources and biooptical devices [93].
10.5 New prospective and future trends It is now better understood by the scientific world and the industry that surface properties are significantly important because they tend to be the limiting factor for a number of various applications. Thus, there has recently been a large increase in the amount of scientific publications on surface treatments and potential applications. As an example, a recent (28 May 2015) Web of Science literature search has shown that publications relating to LIPSS have significantly increased over the last year with approximately 80 publications in 2014–2015 compared to 2005–2015. This had approximately 25 publications per year relating to LIPSSs. With this increase in surface treatment research activity, nanostructuring both topographically and chemically will likely provide a number of fields with a method for enhancing surface properties. From 2010 to 2015 this research has shown how laser induced periodic nanostructures can control frictional properties of materials [79], how these nanostructures can manipulate plasmonic and hydrodynamic properties [94], and how the optical properties of materials can be modulated using LIPSS [93]. Moreover, further studies have been carried out
Laser surface structuring of ceramics, metals and polymers
293
relating to the mechanisms and modelling of LIPSS [50,95,96]. The modelling and understanding of the LIPSS mechanisms for polymers, metals and ceramics are of great importance as a full in-depth understanding of the LIPSSs will ensure that further surface property enhancements can be investigated and realized. With the increase in research with regards to LIPSS for nanostructuring, it has recently been seen over the latter two years that applications of LIPSS have been advanced and evidenced. For example, Beltaos et al. [92] investigated and showed how periodic surface structures can be induced into multilayer graphene using the same laser processing parameters as seen with previous experimental findings with other materials. This particular research has highlighted that, through further research and development, LIPSSs can likely be applied to numerous other material types to modify the surface properties, producing similar material processing results compared to those materials which have already been studied. Other recent research has concentrated on the formation of both ablative and thermochemical LIPSSs [81] and showed that LIPSSs can be implemented as a process for high selectivity etching of titanium oxides. Future work will likely show that ablative and thermochemical LIPSSs can impact materials in different ways, augmenting and undermining the surface properties depending on the material and LIPSS processing parameters. With the realisation of the importance of surface properties with regards to biomedical applications many researchers are now turning to surface treatments for the modification of surface topography and surface chemistry to further enhance the biomimetic nature of materials. As a result, considerable work has been conducted applying many surface treatments to applications which involve the attachment of biological cells [97,98]. This research has led the bioengineering community to understand the significance of surface treatments, giving rise to micromachining and even the significant importance of surface treatments which give rise to nanomachining. With this in mind, it is likely that future research involving LIPSSs will consider the effects of the precise nanoscale surface modification on the biocompatibility properties and cell–substrate adhesion. Furthermore, the effects of the nanoscale features on cell viability and proliferation will also be an important aspect for investigating to ascertain the feasibility of using LIPSSs on a larger scale for biomaterial processing. Such work has already commenced with Barb et al. [80], who showed that a ns-pulsed UV laser can be implemented to generate LIPSSs in PET for the manipulation of human myoblast cells. More research in to the application of LIPSSs to process biomaterials will lead to further enhancements in surface properties of many materials to promote cell adhesion and cell growth. As a result, this offers a significant opportunity to further develop and drive forward the growing biomedical industry by providing researchers and clinicians with a highly controllable material processing technique. This consequently can be used to control and manipulate biological cell lines.
10.6 Conclusions A comprehensive review was undertaken in relation to LIPSSs applied to metals, polymers and ceramic materials as used for biomedical applications. The review included the state of the art behind LIPSSs applied to the aforementioned biomaterials and also addressed
294
Laser Surface Modification of Biomaterials
the future trends, adaptive parameters that one can apply to metals, polymers and ceramics for further research. Moreover, a brief overview on the fundamentals and theory of LIPSSs, type of structures and their applications was discussed. The benefits of LIPSSs on the surface properties are becoming more obvious not only within the science sector but also by biotechnologists. This verifies that short pulse and ultrashort pulse lasers, although well known with certain materials (range of polymers), are useful for implementation. Moreover, further work in relation to a wide range of metals/alloys and bioceramics will fill the gap in knowledge and bring about industrial progress in surface engineering and biotechnology sectors where surface treatment using LIPSSs is beneficial.
References [1] Birnbaum M. Semiconductor surface damage produced by ruby lasers. J Appl Phys 1965;36:3688–9. [2] Dyer PE, Jenkins SD, Sidhu J. Development and origin of conical structures on XeCl laser ablated polyimide. Appl Phys Lett 1986;49(8):453–5. [3] Oliveira V, Simões F, Vilar R. Column growth mechanics during KrF laser micromachining of Al2O3-TiC ceramics. Appl Phys A - Mater Sci Process 2005;81:1157–62. [4] Sanchez F, Morenza JL, Aguiar R, Delgado JC, Varela M. Dynamics of the hydrodynamical growth of columns on silicon exposed to excimer-laser irradiation. Appl Phys A 1998;66:83–6. [5] Van Driel HM, Sipe JE, Young JF. Laser-induced periodic surface structure on solids: a universal phenomenon. Phys Rev Lett 1982;49:1955–8. [6] Liang C, et al. Surface modification of cp-Ti using femtosecond laser micromachining and the deposition of Ca/P layer. Mater Lett 2008;62:3783–6. [7] Anselme K. Osteoblast adhesion on biomaterials. Biomaterials 2000;21(7):667–81. [8] Mendonca G, et al. Advancing dental implant surface technology - from micron- to nanotopography. Biomaterials 2008;29(28):3822–35. [9] Roach P, et al. Modern biomaterials: a review-bulk properties and implications of surface modifications. J Mater Sci-Mater Med 2007;18(7):1263–77. [10] Zhang L, Webster T. Nanotechnology and nanomaterials: promises for improved tissue generation. Nano Today 2008;4(1):66–80. http://dx.doi.org/10.1016/j.nantod.2008.10.014. [11] Albrektsson T, et al. The interface zone of inorganic implants invivo - titanium implants in bone. Ann Biomed Eng 1983;11(1):1–27. [12] Zorba V, et al. Biomimetic artificial surfaces quantitatively reproduce the water repellency of a Lotus leaf. Adv Mater 2008;20(21):4049. [13] Hansson S, Norton M. The relation between surface roughness and interfacial shear strength for bone-anchored implants. A mathematical model. J Biomech 1999;32(8):829–36. [14] Mendes V, Moineddin R, Davies J. The effect of discrete calcium phosphate nanocrystals on bone-bonding to titanium surfaces. Biomaterials 2007;28:4748–55. [15] Oliveira V, Ausset S, Vilar R. Surface micro/nanostructuring of titanium under stationary and non-stationary femtosecond laser irradiation. Appl Surf Sci 2009;255(17):7556–60. [16] Oliveira V, Cunha A, Vilar R. Multi-scaled femtosecond laser structuring of stationary titanium surfaces. J Optoelectron Adv Mater 2010;12(3):654–8. [17] Oliveira V, Nunes B, Vilar R. Wetting response of KrF laser ablated polyimide surfaces. Nucl Instrum Methods Phys Res Sect B-Beam Interact Mater Atoms 2010;268(10): 1626–30.
Laser surface structuring of ceramics, metals and polymers
295
[18] Matthias B, Lazare S. Submicron periodic structures produced on polymer surfaces with polarized excimer laser ultraviolet radiation. Appl Surf Sci 1992;65/66:349–54. [19] Sipe JE, Young JF, Preston JS, Van Driel HM. Laser-induced periodic surface structure. I. Theory. Phys Rev 1983;B27:1141. [20] Young JF, Preston JS, Van Driel HM, Sipe JE. Laser-induced periodic surface structure. II. Experiments on Ge, Si, Al, and brass. Phys Rev B 1983;27:1155. [21] Young JF, Preston JS, Sipe JE, Van Driel HM. Time-resolved evolution of laser-induced periodic surface structure on germanium. Phys Rev B 1983;27:1424(R). [22] Young JF, Sipe JE, Van Driel HM. Laser-induced periodic surface structure. III. Fluence regimes, the role of feedback, and details of the induced topography in germanium. Phys Rev B 1984;30:2001. [23] Allmen MV. Laser-beam interactions with materials. Series in materials science, vol. 2. Berlin: Springer; 1987. [24] Clark SE, Emmony DC. Ultraviolet-laser-induced periodic surface structures. Phys Rev B 1989;40:2031. [25] Bolle M, Lazare S. Large scale excimer laser production of submicron periodic structures on polymer surfaces. Appl Surf Sci 1993;69:31B. [26] Dauscher A, Feregotto V, Cordier P, Thorny A. Laser induced periodic surface structures on iron. Appl Surf Sci 1996;96–98:410–4. [27] Simon P, Ihlemann PJ. Ablation of submicron structures on metals and semiconductors by femtosecond UV-laser pulses. Appl Surf Sci 1997;109/110:25–9. [28] Csete M, Bor Z. Laser-induced periodic surface structure formation on polyethylene-terephthalate. Appl Surf Sci 1998;133:5–16. [29] Ozkan AM, Malshe AP, Railkar TA, Brown WD, Shirk MD, Molian PA. Femtosecond laser-induced periodic structure writing on diamond crystals and microclusters. Appl Phys Lett 1999;75:3716. [30] Csete M, Marti O, Bor Z. Laser-induced periodic surface structures on different poly-carbonate films. Appl Phys A 2001;73(4):521–6. [31] Bozhevolnyi SI, Erland J, Leosson K, Skovgaard PMW, Hvam JM. Waveguiding in surface plasmon polariton band gap structures. Phys Rev Lett 2001;86:3008. [32] Li M, Lu QH, Yin J, Sui Y, Li G, Qian Y, et al. Periodic microstructure induced by 532 nm polarized laser illumination on poly(urethane-imide) film: orientation of the azobenzene chromophore. Appl Surf Sci 2002;193:46–51. [33] Lu XM, Lu QH, Zhu ZK, Yin J, Wang ZG. Laser-induced periodic surface structure on polyimide doped with lecithin. Mater Lett 2003;57:3636–40. [34] Csete M, Hild S, Plettl A, Ziemann P, Bor Z, Marti O. The role of original surface roughness in laser-induced periodic surface structure formation process on poly-carbonate films. Thin Solid Films 2004;453–454:114–20. http://dx.doi.org/10.1016/j.tsf.2003.11.086. [35] Wang J, Guo C. Ultrafast dynamics of femtosecond laser-induced periodic surface pattern formation on metals. Appl Phys Lett 2005;87(25):251914. [36] Tran DV, Zheng HY, Lam YC, Murukeshan VM, Chai JC, Hardt DE. Femtosecond laser-induced damage morphologies of crystalline silicon by sub-threshold pulses. Opt Lasers Eng 2005;43:977–86. http://dx.doi.org/10.1016/j.optlaseng.2004.10.006. [37] Bleiner D, Bogaerts A. Multiplicity and contiguity of ablation mechanism in laser-assisted analytical micro-sampling. Spectrochim Acta B 2006;61:421–32. [38] Vorobyev AY, Makin VS, Guo C. Periodic ordering of random surface nanostructures induced by femtosecond laser pulses on metals. J Appl Phys 2007;101:034903. [39] Groenendijk MNW, Meijer J. Surface microstructures obtained by femtosecond laser pulses. Ann CIRP 2006;55(1):183–6. http://dx.doi.org/10.1016/S0007-8506(07)60394-1.
296
Laser Surface Modification of Biomaterials
[40] Reif J, Costache F, Bestehorn M. Self-organised surface nano-structuring by femtosecond laser processing. In: Perriere J, Millon E, Fogarassy E, editors. Recent advances in laser processing of materials. Elsevier; 2007. p. 275–90. [Chapter 9]. [41] Vorobyev AY, Guo C. Femtosecond laser-induced periodic surface structure formation on tungsten. J Appl Phys 2008;104:063523. [42] Papernov S, Schmidt AW. Laser-induced surface damage of optical materials: absorption sources, initiation, growth, and mitigation. Proc SPIE 2008;7132: 71321J:27. [43] Zheng HY, Tan TT, Zhou W. Studies of KrF laser-induced long periodic structures on polyimide. Opt Lasers Eng 2009;47:180–5. http://dx.doi.org/10.1016/j.optlaseng.2008.06.015. [44] Shinoda M, Gattass RR, Mazur E. Femtosecond laser-induced formation of nanometer-width grooves on synthetic single-crystal diamond surfaces. J Appl Phys 2009;105:053102. [45] Skolski JZP, Römer GRBE, Huis in’t Veld AJ, Mitko VS, Obona JV, Ocelik V, et al. Modeling of laser induced periodic surface structures. J Laser Micro/Nanoeng 2010;5(3): 263–8. http://dx.doi.org/10.2961/jlmn.2010.03.001. [46] Zhihua L, Li P, Fan J, Fang R, Zhang D. Energy accumulation effect and parameter optimization for fabricating of high-uniform and large-area period surface structures induced by femtosecond pulsed laser. Opt Lasers Eng 2010;48:64–8. http://dx.doi.org/ 10.1016/j.optlaseng.2009.07.017. [47] Bonse J, Rosenfeld A, Krüger J. Implications of transient changes of optical and surface properties of solids during femtosecond laser pulse irradiation to the formation of laser-induced periodic surface structures. Appl Surf Sci 2011;257:5420–3. http://dx.doi.org/10.1016/j.apsusc.2010.11.059. [48] Varlamovaa O, Reif J, Varlamovb S, Bestehornb M. The laser polarization as control parameter in the formation of laser-induced periodic surface structures: comparison of numerical and experimental results. Appl Surf Sci 2011;257:5465–9. http://dx.doi.org/ 10.1016/j.apsusc.2010.11.157. [49] Lin Li, Hong M, Schmidt M, Zhong M, Malshe A, Huis in’tVeld B, et al. Laser nano-manufacturing – state of the art and challenges. CIRP Ann – Manuf Technol 2011;60:735–55. [50] Bonse J, Krüger J, Höhm S, Rosenfeld A. Femtosecond laser-induced periodic surface structures. J Laser Appl 2012;24:042006. [51] Makropoulou M, Serafetinides AA, Skordoulis CD. Ultra-violet and infra-red laser ablation studies of biocompatible polymers. Lasers Med Sci 1995;10:201–6. [52] Mirzadeh H, Katabab AA, Burfford RP. CO2-laser graft copolymerization of HEMA and NVP onto ethylene-propylene rubber (EPR) as biomaterial-(III). Radiat Phys Chem 1995;46(4–6):859–62. [53] Mirzadeh H, Katabab AA, Khorasani MT, Burfford RP, Gorgin E, Golestani A. Cell attachment to laser-induced AAm-and HEMA-grafted ethylene-propylene rubber as biomaterials: in vivo study. Biomaterials 1995;16:641–8. [54] Wu PK, Ringeisen BR, Callaham J, Brooks M, Bubb DM, Wu HD, et al. The deposition, structure, patterns deposition, and activity of biomaterial thin-film by matrix-assisted pulsed-laser evaporation (MAPLE) and MAPLE direct write. Thin Solid Films 2001;398–399: 607–14. [55] Duncan AC, Weisbuch F, Rouais F, Lazare S, Baquey C. Laser microfabricated model surfaces for controlled cell growth. Biosens Bioelectron 2002;17:423–6. [56] Anguilar CA, Lu Yi, Samuel M, Shaxhen C. Direct micro-patterning of biodegradable polymers using ultraviolet and femtosecond lasers. Biomaterials 2005;26:7642–9. [57] Pfleging W, Burns M, Welle A, Wilson S. Laser-assisted modification of polystyrene surfaces for cell culture applications. Appl Surf Sci 2007;253:9177–84.
Laser surface structuring of ceramics, metals and polymers
297
[58] Fayou K, Mücklich F, Li P, Shen H, Mathur S, Lehr C-M, et al. In vitro cell response to a polymer surface micropatterned by laser interference lithography. Biomacromolecules 2005;6:1160–7. [59] Hongyu S, Zhou H, Sun N, Luquan R, Li C, Xianzhou L. Study on adhesion resistance behaviour of sample with striated non-smooth surface by laser processing technique. J Mater Process Technol 2008;199(1–3):221–9. [60] Mirzadeh H, Dadsetan M. Influence of laser surface modifying of polyethylene terephthalate on fibroblast cell adhesion. Radiat Phys Chem 2003;67:381–5. [61] Pérez S, Rebollar E, Mohamed O, Martín M, Castillejo M. Laser-induced periodic surface structuring of biopolymers. Appl Phys A 2013;110:683–90. [62] Castillejoa M, Ezquerrab TA, Martína M, Oujjaa M, Péreza S, Rebollar E. Laser nanostructuring of polymers: ripples and applications. In: International symposium on high power laser ablation, May 3, 2012, Santa Fe, USA, vol. 1464. 2012. p. 372–80. [63] Mills D, Kreouzis T, Sapelkin A, Unal B, Zyuzikov N, Kolasinski KW. Surface texturing of Si, porous Si and TiO2 by laser ablation. Appl Surf Sci 2007;253:6575–9. [64] Vorobyev AY, Guo C. Femtosecond laser structuring of titanium implants. Appl Surf Sci 2007;253:7272–80. [65] Nayak BK, Gupta M,C. Self-organized micro/nano structures in metal surfaces by ultrafast laser irradiation. Opt Lasers Eng 2010;48:940–9. [66] Chunha A, Oliveira V, Serro AP, Zouani OF, Almeida A, Durrieu MC, et al. Ultrafast laser texturing of Ti-6Al-4V, surfaces for biomedical applications, (N405). In: The 32nd International Congress on Applications of Lasers & Electro-Optics (ICALEO®) 2013, October 6–10 in Miami, FL. 2013. p. 910–8. [67] Gaggl A, Schultes G, Müller WD, Kärcher H. Scanning electron microscopical analysis of laser-treated titanium implant surfaces—a comparative study. Biomaterials 2000;21:1067–73. [68] Pfleging W, Kumaria R, Besserb H, Scharnweberc T, Majumdar JD. Laser surface textured titanium alloy (Ti-6Al-4V): part 1 – surface characterization. Appl Surf Sci 2015;355:104–11. [69] Çelena S, Efeoğlub C, Özdena H. Pulsed laser-induced micro-pits: as bone stabilizers. In: Lasers in manufacturing 2011-proceedings of the sixth international WLT conference on lasers in manufacturing, vol. 12 (B). 2011. p. 245–51. [70] Kumari R, Scharnweber T, Pfleging W, Besser H, Majumdar JD. Laser surface textured titanium Alloy (Ti-6Al-4V)-part II-studies on bio-compatibility. Appl Surf Sci 2015;357A:750–8 (Published online on September 1, 2015). [71] Buividasa R, Mikutis M, Juodkazis S. Surface and bulks structuring of materials by ripples with long and short laser pulses: recent advances. Prog Quantum Electron 2014;38:119–56. [72] Hu T, Hu L, Ding Q. Effective solution for the tribological problems of Ti-6Al-4V: combination of laser surface texturing and solid lubricant film. Surf Coat Technol 2012;206:5060–6. [73] Serpengüzel A, Kurt A, Inanç I, Cary JE, Mazur E. Luminescence of black silicon. J Nanophot February 21, 2008;2:021770. [74] Shazia B, Rafique S, Husinsky W. Liquid assisted ablation of zirconium for the growth of LIPSS at varying pulse durations and pulse energies by femtosecond laser irradiation. Nucl Instrum Methods Phys Res B 2015;349:230–8. [75] Jelani M, Shazia B, Akram M, Yousaf D, Afzal N, Ahmad S. Mechanical behaviour of excimer laser irradiated polycrystalline zirconium. Phys Scr 2014;89(2):025703 (7 pp.). [76] Grojo D, Hermann J, Perrone A. Plasma analyses during femtosecond laser ablation of Ti, Zr, and Hf. J Appl Phys 2005;97:063306.
298
Laser Surface Modification of Biomaterials
[77] Samant AN, Paital SR, Dahotre NB. Process optimization in laser surface structuring of alumina. J Mater Process Technol 2008;203:498–504. [78] Huis in’t Veld B, Groenendijk M, Fischer H. Initiation of femtosecond laser machining ripples in steel observed by scanning helium ion microscopy. J Laser Micro/Nanoeng 2010;5(1):28–34. [79] Eichstadt J, Romer GRBE, Veld AJHI. Towards friction control using laser-induced periodic surface structures. Phys Procedia 2011;12:7–15. [80] Barb R-A, Hrelescu C, Dong L, Heitz J, Siegel J, Slepicka P, et al. Laser-induced periodic surface structures on polymers for formation of gold nanowires and activation of human cells. Appl Phys A 2014;117:295–300. [81] Dostovalov AV, Korolkov VP, Babin SA. Simultaneous formation of ablative and thermochemical laser-induced periodic surface structures on Ti film at femtosecond irradiation. Laser Phys Lett 2015;12:036101. http://dx.doi.org/10.1088/1612-2011/12/3/036101. [82] Tan B, Venkatakrishnan K. A femtosecond laser-induced periodical surface structure on crystalline silicon. J Micromech Microeng 2006;16:1080–5. http://dx.doi.org/ 10.1088/0960-1317/16/5/029. [83] Guo XD, Li Xr, Hang Y, Xu ZZ, Yu BK, Ma HL, et al. Femtosecond laser-induced periodic surface structure on ZnO. Mater Lett 2008;62:1769–71. http://dx.doi.org/ 10.1016/j.matlet.2007.09.082. [84] Savas TA, Farhoud M, Smith HI, Hwang M, Ross CA. Properties of large area nanomagnetic arrays with 100 nm period made by interferometric lithography. J Appl Phys 1999;85:6160. [85] Lowndes DH, Fowlkes JD, Pedraza AJ. Early stages of pulsed-laser growth of silicon microcolumns and microcones in air and SF6. Appl Surf Sci 2000;154–155. [86] Carey JE. Femtosecond-laser microstructuring of silicon for novel optoelectronic devices [A Doctoral thesis]. Cambridge, Massachusetts: Harvard University; 2004. [87] Liao Y, Song J, Cheng Y, Zhizhan X. Rapid prototyping of three-dimensional microfluidic mixers in glass by femtosecond laser direct writing. In: Progress in electromagnetics research symposium abstracts, Malaysia, March 27–30. 2012. [88] Cheng Y, Liao Y, Huang M, Zhizhan X. Harnessing ultrafast laser-induced subwavelength structures for liquid crystal photonics application. In: Progress in electromagnetics research symposium abstracts, Malaysia, March 27–30. 2012. [89] Chang HW, Lin CY, Cheng CW, Lin YW, Wu TM, Tsai YC. Preparation of nanostructured Ag substrate with femtosecond laser as surface-enhanced Raman scattering substrates. In: Progress in electromagnetics research symposium abstracts, Malaysia, March 27–30. 2012. [90] Audouard E. Ripples formation under femtosecond laser irradiation: actual and potential applications. In: Progress in electromagnetics research symposium abstracts, Malaysia, March 27–30. 2012. [91] Yu JJ, Lu YF. Laser induced ripple structure on Ni-P substrate. Appl Surf Sci 1999;148(3–4):248–52. [92] Beltaos B, Kivačević AG, Matković A, Ralević U, Savić-Sević S, Jovanovič D, et al. Femtosecond laser induced periodic surface structures on multi-layered graphene. J Appl Phys 2014;116:204306. http://dx.doi.org/10.1063/1.4902950 (1–6). [93] Vorobyev AY, Makin VS, Guo C. Optical properties of femtosecond laser-induced periodic surface structures on metals. In: Circuits and systems, 2009. MWSCAS ‘09. 52nd IEEE international midwest symposium, 909–912, 2–5 August, Cancun, Mexico. 2009. [94] Colombier JP, Garrelie F, Brunet P, Bruyère A, Pigeon F, Stoian R, et al. Plasmonic and hydrodynamic effects in ultrafast laser-induced periodic surface structures on metals. J Laser Micro/Nanoeng 2012;7:362–8.
Laser surface structuring of ceramics, metals and polymers
299
[95] Gräf S, Müller FA. Polarisation-dependent generation of fs-laser induced periodic surface structures. Appl Surf Sci 2015;331:150–5. [96] Hwang TY, Guo C. Angular effects of nanostructure-covered femtosecond laser induced periodic surface structures on metals. J Appl Phys 2010;108:073523. [97] Razavi M, Fathi M, Savabi O, Vashaee D, Tayebi L. In vivo study of nanostructured akermanite/PEO coating on biodegradable magnesium alloy for biomedical applications. J Biomed Mater Res Part A 2014;103:1798–808. http://dx.doi.org/10.1002/jbm.a.35324. [98] Sgura R, Reis MC, Hernandes AC, Fantini MCA, Andreeta MRB. Surface treatment of dental porcelain: CO2 laser as an alternative to oven glaze. Lasers Med Sci 2015;30:661–7.