Influence of the intramedullary nail preparation method on nail's mechanical properties and degradation rate

Materials Science and Engineering C 51 (2015) 99–106

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Materials Science and Engineering C journal homepage: www.elsevier.com/locate/msec

Influence of the intramedullary nail preparation method on nail's mechanical properties and degradation rate Anna Morawska-Chochół a,⁎, Jan Chłopek a, Barbara Szaraniec a, Patrycja Domalik-Pyzik a, Ewa Balacha a, Maciej Boguń b, Rafael Kucharski c,d a

AGH University of Science and Technology, Faculty of Materials Science and Ceramics, Department of Biomaterials, al. A. Mickiewicza 30, 30-059 Krakow, Poland Lodz University of Technology, Faculty of Material Technologies and Textile Design, Department of Material and Commodity Sciences and Textile Metrology, ul. Żeromskiego 116, 90-924 Lodz, Poland c Association “HEALTH”, ul. Kosciuszki 191, 40-525 Katowice, Poland d IEE-Group, Hannover, Germany b

a r t i c l e

i n f o

Article history: Received 28 July 2014 Received in revised form 5 November 2014 Accepted 23 February 2015 Available online 25 February 2015 Keywords: Intramedullary nails Biodegradable composites Injection moulding Hot pressing Forming from solution

a b s t r a c t When it comes to the treatment of long bone fractures, scientists are still investigating new materials for intramedullary nails and different manufacturing methods. Some of the most promising materials used in the field are resorbable polymers and their composites, especially since there is a wide range of potential manufacturing and processing methods. The aim of this work was to select the best manufacturing method and technological parameters to obtain multiphase, and multifunctional, biodegradable intramedullary nails. All composites were based on a poly(L-lactide) matrix. Either magnesium alloy wires or carbon and alginate fibres were introduced in order to reinforce the nails. The polylactide matrix was also modified with tricalcium phosphate and gentamicin sulfate. The composite nails were manufactured using three different methods: forming from solution, injection moulding and hot pressing. The effect of each method of manufacturing on mechanical properties and degradation rate of the nails was evaluated. The study showed that injection moulding provides higher uniformity and homogeneity of the particle-modified polylactide matrix, whereas hot pressing favours applying higher volume fractions of fibres and their better impregnation with the polymer matrix. Thus, it was concluded that the fabrication method should be individually selected dependently on the nail's desired phase composition. © 2015 Elsevier B.V. All rights reserved.

1. Introduction The obvious advantages of intramedullary osteosynthesis, such as: a good stabilization of bone fragments guaranteeing elasticity of the fixation, minimal damage of the surrounding tissue and low surgical risk, make it a significant and valuable method of long bone fracture treatment [1–6]. Metals are frequently used for intramedullary nails, e.g. stainless steel and titanium alloys [7]. Metal implants, however, have to be removed from the organism after they have fulfilled their task. Therefore, a patient needs another surgical intervention, which involves negative medical and financial consequences. Moreover, although the mechanical strength of metallic nails is fully satisfactory for bone stabilization (the bending strength of stainless steel 316L is in the range of 240–770 MPa), their Young's modulus is too high in relation to the bone's (E = 193 GPa for 316L and E = 110–114 GPa

⁎ Corresponding author. E-mail address: [email protected] (A. Morawska-Chochół).

http://dx.doi.org/10.1016/j.msec.2015.02.043 0928-4931/© 2015 Elsevier B.V. All rights reserved.

for Ti6Al–4V, while E = 10–40 GPa for bone) [8,9]. This significant disproportion causes stress shielding and inadvisable changes in natural bone biomechanics, that can further lead to bone resorption and cause bone fracture [10]. Taking all these factors into account, it is clear that resorbable nails can be endowed with more desired mechanical properties creating better internal fixation devices. In the field of resorbable biomaterials, there is a large selection of medically approved degradable polymers [11–15]. However, due to the low strength of the pure polymers, a polymer-based reinforced composite would be more appropriate for use in intramedullary nails. The greatest advantage of composites is the fact that their properties can be easily tailored to required specifications therefore, it is possible to obtain composite nails of mechanical parameters fitted to the bone properties. A gradual transfer of load from the biodegradable nails to the bone, without stress shielding, should allow proper bone healing with the added benefit of no necessary additional surgery for implant removal. One of the first attempts at applying resorbable materials for intramedullary osteosynthesis was undertaken by Saikku-Bäckström et al. in 2004 [16]. The tests involved using a copolymer of 96% Llactide and 4% D-lactide (PLA96). The work was performed using

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intramedullary nails with SR-PLA96 applied together with Kirschner wires, which were implanted in the fractures of the femoral bone neck of large animals (sheep). The manufacturing and processing methods used in creating polymer composites are key in the control of mechanical properties. Such parameters as homogeneity, interphase bond strength, and distribution of modifiers can be changed depending on the type, volume fraction, and properties of applied additives [17,18]. On the other hand, the form of modifiers can determine the processing method. The more diversified the phases in the composite, the more difficult the choice of an optimal processing method and its specific parameters [17]. This work constitutes an attempt at the development of intramedullary nails made of resorbable polylactide reinforced with resorbable magnesium alloy wires or long fibres (alginate and carbon fibres were used). All the applied phases demonstrate the ability of full or partial (in the case of carbon fibres) degradation. It has already been proven by the authors that carbon fibres, after their fragmentation, are able to assimilate with the bone tissue and, moreover, stimulate its growth (the apatite's nucleation begins at the surface of the fibres) [19–23]. Another group of material that were applied were magnesium alloys, which are becoming more and more popular among researchers in the fields of orthopaedics and bone surgery [24–28]. The most important merits of magnesium alloys are: superior mechanical properties to polymers (higher strength and Young's modulus with value similar to that of bone), as well as biocompatibility and biodegradation in the environment of a living organism. The polylactide matrix was also modified with tricalcium phosphate and gentamicin sulfate. These additives are responsible for biological properties described in the authors' previous work [29]. In this work, different multiphase, biodegradable intramedullary nails were manufactured using three various methods. The applied methods were: forming from solution, injection moulding and hot pressing. Authors focused on assessing the influence of the particular fabrication method and its technological parameters on the mechanical properties and degradation behaviour of the nails. 2. Materials 2.1. Initial materials The following materials were used to manufacture composite nails:

− tricalcium phosphate (TCP) — Sigma-Aldrich® (Ca3(PO4)2 ≥ 96.0%); − gentamicin sulfate (GS — gemtamicini sulfas) — Interforum Pharma wholesaler in Krakow. 2.2. Composites Two main groups of composite nails can be specified: I. PLA reinforced with Mg alloy wires • PLA/Mg/GS • PLA/MgII/GS II. PLA reinforced with CF and Alg fibres — to map the anatomic structure of the bone, the fully degradable alginate fibres were placed inside the intramedullary nails, while the partially degradable carbon fibres were placed outside • • • •

PLA/CF PLA/CF/Alg PLA/CF/Alg/GS PLA/CF/Alg/TCP/GS

➢ Pure PLA nails and PLA modified with TCP and GS were tested as reference • PLA • PLA/TCP/GS 3. Methods 3.1. Fabrication methods Three different methods were used to manufacture designed composite nails: forming from solution (S), injection moulding (IM) and hot pressing (HP). The nails were fabricated in two sizes: • small nails suitable for rabbit femoral bone — 2.5 mm in diameter, 100 mm long; • large nails suitable for human forearm bone — 4.5 mm in diameter, 150 mm long.

− poly-L-lactide (PLA) — Ingeo™ 3051D, NatureWorks® LLC; − long carbon fibres (CF) — Toho Tenax America, HTS 5631 (tensile strength of 4.3 GPa, Young's modulus of 238 GPa and elongation of 1.8%); − long calcium alginate fibres (Alg) — Department of Material and Commodity Sciences and Textile Metrology of Lodz University of Technology. The fibres were formed by the wet solution method applying a 7.4% sodium alginate solution in water. The solidification and tension process was performed in a 3% CaCl2 bath (fibre diameter of 17 μm, tensile strength of 220.8 MPa, Young's modulus of 12.7 GPa); − magnesium alloy wires (Mg) — Leibniz University of Hannover, Institute of Materials Science. The wires differed in diameter and a composition of an alloy:

3.1.1. Forming from solution Polymer solution was prepared by dissolving PLA in dichloromethane CH2Cl2 (POCH) (40 g/100 ml), and then adding gentamicin sulfate distributed in 100 ml of the same solvent. In the next step alginate fibres were preliminary saturated with the PLA + GS solution and pulled through 1 mm cylindrical form to create the nail's core. After the solvent evaporated, a carbon outer layer was formed — alginate core was covered with uniaxially oriented carbon fibre rovings. The whole sample was then saturated with the polymer solution and pulled through a 2.5 mm cylindrical form (it was repeated three times). Samples were left overnight to allow the solvent to evaporate and after that samples were cut into 100 mm nails (2.5 mm in diameter). Nails of the following phase composition were obtained by forming from solution: PLA + CF + Alg + GS (S) — polylactide matrix modified with carbon fibres (20 wt.%), calcium alginate fibres (20 wt.%) and gentamicin (12 mg per implant) (Fig. 1A).

• MgII — dMgII = 0.97 mm, magnesium alloy with the content of: aluminium 3%, lithium 9%, and calcium up to 1%; • MgIII — dMgIII = 0.5 mm, magnesium alloy containing the main elements: aluminium 5.5–6.5%, zinc 0.8–1.5% and the trace elements up to 1%: lithium, rare earth metals (an alloy addition obtained as rare earth metal ore), and calcium;

3.1.2. Injection moulding Using the injection moulding method, pure polymer or polymer with tricalcium phosphate nanoparticles and/or gentamicin powder (dependent of the nails' phase composition) was plasticized at 160– 170 °C and then injected in a vertical screw injection moulder (MULTIPLAS).

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Fig. 1. Real photographs of the nails: PLA + CF + Alg + GS (S) nail (A), PLA + CF + Alg (IM) nail (B) and PLA + Mg (IM) nail (C). Please note that B and C were taken for a nail without GS in order to highlight the arrangement of the reinforcement phase.

3.1.2.1. Nails dedicated to rabbit femoral bone. Small nails (2.5 mm in diameter, 100 mm long) of the following phase composition were obtained by injection moulding: 1) PLA (IM) — polylactide nail, reference sample 2) PLA + CF + Alg + GS (IM) — polylactide matrix modified with carbon fibres (10 wt.%), calcium alginate fibres (10 wt.%) and gentamicin (12 mg per implant) (Fig. 1B)

Two etched (as described previously) and twisted MgII wires were placed in the form, then the PLA granulate mixed with GS was added. The sample was heated to 145 °C and pressed under 5 MPa in a hydraulic press. 3) PLA + CF (HP) — polylactide matrix modified with 1D carbon fibres (40 wt.%)

Alginate (inner) and carbon fibre (outer layer) cores were prepared by saturating the fibres with the PLA + GS solution (prepared as above) and drawing through a 1 mm cylindrical form. Prepared cores were then placed in a 2.5 mm in diameter mould and the injection moulding of homogenized polymer granulate/gentamicin powder was performed.

The carbon fibre rovings were interlayered with the polymer granulate in the form, which was then heated to 165 °C and pressed under 5 MPa in a hydraulic press.

3) PLA + Mg + GS (IM) — polylactide matrix modified with MgII and MgIII wires and gentamicin (12 mg per implant) (Fig. 1C)

The calcium alginate fibres and carbon fibre rovings were interlayered with the polymer granulate in the form. In the next step the form was heated to 165 °C and samples were pressed under 5 MPa in a hydraulic press.

The first step in the fabrication of the Mg-modified nails was etching of the magnesium alloy wires. The wires were immersed in an etching solution (19 g 100% acetic acid, 5 g sodium nitrate (V), 100 ml distilled water) for 30 s, then rinsed with distilled water and dried in a dryer for 20 min at 70 °C. The MgIII wire was then twisted around a MgII wire and they were both placed in the mould, completing the injection process. 3.1.2.2. Nails dedicated to human forearm bone. Large nails (4.5 mm in diameter, 150 mm long) of the following phase composition were obtained by injection moulding: 1) PLA + TCP + GS (IM) — polylactide matrix modified with tricalcium phosphate (5 wt.%) and gentamicin (20 wt.%) 2) PLA + MgII + GS (IM) — polylactide matrix modified with two twisted MgII wires and gentamicin (20 wt.%). Two etched (as described previously) and twisted MgII wires were placed in the mould. A mixture of polymer granulate and gentamicin powder was injected. 3.1.3. Hot pressing Large nails (4.5 mm in diameter, 150 mm long; suitable for a human forearm bone) of the following phase composition were obtained by hot pressing. 1) PLA + TCP + GS (HP) — polylactide matrix modified with tricalcium phosphate (5 wt.%) and gentamicin (20 wt.%) The PLA granulate mixed with TCP and GS was poured into the form and heated to 145 °C. The forms were then pressed under 5 MPa in a hydraulic press. 2) PLA + MgII + GS (HP) — polylactide matrix modified with two twisted MgII wires and gentamicin (20 wt.%)

4) PLA + CF + Alg (HP) — polylactide matrix modified with 1D calcium alginate fibres (20 wt.%) and 1D carbon fibres (20 wt.%)

5) PLA + CF + Alg + TCP + GS (HP) — polylactide matrix modified with 1D calcium alginate fibres (20 wt.%), 1D carbon fibres (20 wt.%), tricalcium phosphate (5 wt.%) and gentamicin (20 wt.%) The calcium alginate fibres and carbon fibre rovings were interlayered with the polymer granulate mixed with TCP particles and GS powder. In the next step the form was heated to 165 °C and samples were pressed under 5 MPa in a hydraulic press. 3.2. Test methods 3.2.1. In vitro degradation study The nails were incubated in distilled water at 37 °C for 12 weeks. Mass to volume ratio was set to 1 g/50 ml. The tests included the measurements of pH (Elmetron CP-411, 0.01 pH accuracy) and conductivity (Elmetron CC-411, 0.1 μS/cm accuracy) changes of the incubation fluids. All tests were triplicated. Mass changes of the nails were also analyzed. Samples were weighed on RADWAG PS 360/C/2 (± 0.001 g). Mass loss values were calculated according to the following equation: ML ¼

Wi −Wd  100% Wi

where: mass loss [%] initial weight [g] dry weight [g] The measurements were taken after 24, 48 and 96 h in the first week and then — once per week. ML Wi Wd

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Fig. 2. Changes of the pH (A) and ion conductivity (B) during 12-week incubation of nails in distilled water.

3.2.2. Mechanical tests The mechanical properties (bending strength and Young's modulus) of the obtained nails were determined using the three point bending test according to the PN-EN ISO 14125:2001 and PN-EN ISO 178. The tests were performed on a universal testing machine Zwick 7000 type 1435, compatible with the TestXpert v.8.1 program, with the deformation rate of 2 mm/min. The mechanical tests were conducted on initial samples as well as on samples after 8 and 12 weeks of incubation. Summary statistics were calculated and are presented as the median value. The error bars represent standard deviations. 3.2.3. Microstructure analysis Scanning Electron Microscopy (SEM) was used to observe the microstructure of the obtained composite materials, the distribution of their phases and the state of interphases, as well as the changes in microstructure taking place during incubation. The tests were performed using Nova 200 NanoSEM electron microscope (FEI Company) on initial samples and those incubated in distilled water for 8 and 12 weeks.

and 150 mm in length, which corresponds to the dimensions of intramedullary nails used in a human forearm bone. In order to assess the influence of the preparation method on the properties of the implant, large nails adapted to a forearm bone were also produced by injection moulding. The technological parameters (temperature, plasticization time in high temperature methods, solution concentration and homogenization technique in the forming from the solution method) were selected experimentally. The difficulties were as follows: the presence of bubbles in the hot pressing method, the degradation of the polymer manifested by increased brittleness as a result of too high temperature of the process, the agglomeration of fillers, the difficulty to impregnate fibres, excessive shrinkage and bubbles appearing while solvent vaporized in the forming from the solution method. Due to the occurring difficulties, it was not possible to obtain all the phase contents of the nails in the particular methods. The work presents the results achieved once the technology was optimized.

4.2. Injection moulding and forming from solution 4. Results and discussion 4.2.1. In vitro degradation study 4.1. Technological aspects The nails were manufactured using three methods: forming from solution, injection moulding and hot pressing. The first two methods were used to obtain smaller nails adapted to the dimensions of a rabbit's femoral bone (2.5 mm in diameter and 100 mm long). Due to the technological difficulties, it was impossible to obtain such small nails by hot pressing. Hence, the hot pressed nails were larger: 4.5 mm in diameter

4.2.1.1. Nails modified with magnesium alloy wires. Samples obtained by forming from solution and injection moulding were incubated in distilled water in 37 °C. The changes of incubation fluids' pH and conductivity values were analyzed. Significant differences in the behaviour of particularly fabricated materials in the water environment were noted (Fig. 2). The highest pH (Fig. 2A) was observed in the case of the samples modified with magnesium alloy wires obtained by injection moulding

Fig. 3. SEM images of cross-section of PLA + Mg + GS (IM) nails: initial (A), after 8 weeks (B), and after 12 weeks of incubation in distilled water (C).

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Fig. 4. SEM images of magnesium wire surface (Mg II): before etching and (A) after etching (B).

(PLA + Mg + GS(IM)). Already after the fourth day of incubation, the pH reached its maximum and maintained the pH = 10 level for the whole period of twelve weeks' incubation. Increases in conductivity values were also observed (Fig. 2B). Those significant changes resulted from the corrosion of magnesium and the release of Mg2 + ions of basic character [25]. Undoubtedly, such high pH level is unlikely to be reached in the living organism. The tests were performed in a closed environment, while typically in the body there is a constant flow of physiological fluids. Therefore, such a high increase of pH is not expected in vivo. Moreover, in the further stages of nail degradation, alkaline influence of Mg wires can balance the acidic products of PLA resorption. On the other hand, alkaline environment positively influences the antibacterial behaviour what was described in the authors' previous paper [29] and by other scientists [30]. Also, a number of in vitro and in vivo studies proved that alkaline pH connected with the use of Mg alloys has no unfavourable effect on cells [31,32] and even enhance bone formation [33]. The explanation should be found in bone physiology. After the injury, in the first stage of bone healing acidic pH causes bone resorption, but it is followed by the increase of pH value. The alkaline environment facilitates osteoblast activation and bone mineralization [34]. Despite significant pH and conductivity changes, the degradation of Mg wires – even after the 12th week of incubation – was not visible in the microstructure of the nails (Fig. 3). SEM cross-section images showed very good adhesion at the wire–matrix interphase in the case of Mg-reinforced nails. The incubation of the material in distilled water did not cause any significant changes in the character of the interphase. Both after 8 and 12 weeks, no cracks or fissures were observed, which could have appeared as a result of the polymer's degradation or the corrosion of Mg wires. Good adhesion was assured by etching the wire surface before the nail moulding. In this way, a significant change

in the wire surface microstructure was achieved (Fig. 4). The etching removed minor impurities, loosely bounded fragments and made the surface porous. Lack of microstructural changes proved that the degradation process was neither advanced nor rapid, and the PLA matrix properly protected the wires. The corrosion probably affected only those areas of wires that have not been covered properly with the polymer during the injection, e.g. their endings. 4.2.1.2. Nails modified with long carbon and alginate fibres. The pH changes observed for the carbon and alginate fibre-reinforced nails were not significant. A slight pH decrease (to the levels of 6–) was recorded only after the first incubation day and then pH remained at a neutral level. The initial decrease was a result of the gentamicin release, which was confirmed by Morawska-Chochol et al. [29]. Differences resulting from the type of fabrication method were visible in ion conductivity variations (Fig. 2B). The conductivity values changed the most in the case of PLA + CF + ALG + GS(S) nails formed from solution, whereas they were almost half as small in the case of analogical nails obtained by injection moulding (IM). This can be explained by the fact that the polymer matrix in nails formed from solution did not assure proper protection against degradation of alginate fibres. Particular fibrous phases were differently arranged depending on manufacturing methods of the nail. When forming from solution, the fibres were present in the whole PLA matrix volume. As a result, fibre–polymer matrix interphases were present not only in the volume of the nails, but also on their surface. This facilitated water diffusion into the nails and the release of degradation products into the environment. In contrast, the nails that were obtained by injection moulding had only a fibrous core and the outer layer was a compact polymer matrix. This made fluid penetration into the nails more difficult.

Fig. 5. SEM images of cross-section of PLA + CF + Alg + GS (S) nails: initial (A), after 8 weeks (B), and after 12 weeks of incubation in distilled water (C).

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Fig. 6. SEM images of cross-section of PLA + CF + Alg + GS (IM) nails: initial (A), after 8 weeks (B), and after 12 weeks of incubation in distilled water (C).

These conclusions are confirmed by the SEM images (Figs. 5, 6) — the microstructure of the nails formed from solution significantly loosened during incubation time. After 8 weeks, empty spaces appeared among the fibres in both carbon and alginate reinforced nails. The nails obtained by injection moulding were affected by such changes after 12 weeks of incubation. The above observations concerning the nail degradation were confirmed by their mass changes (Fig. 7). The highest decrease in mass value is visible for the PLA + CF + Alg + GS(S) nails formed from solution and it can be explained by the degradation of the alginate fibre core. In nails obtained by injection moulding (both with carbon and alginate fibres and with magnesium wires) mass loss values are significantly lower. As it was mentioned earlier, the microstructure of outer parts of those nails was much more compact, hence inner phases of composites were better protected from the influence of aqueous environment of incubation fluids.

4.2.2. Mechanical properties Mechanical tests indicated that each of the applied reinforcements positively influenced the mechanical properties of the nails (Fig. 8). The highest increase in strength values was observed for the PLA + Mg + GS(IM) and PLA + CF + Alg + GS(IM) nails obtained by injection moulding. However, significant scattering of results in the case of fibre-reinforced nails attests to the lack of repeatability. In the injection moulding method, the introduction of carbon fibres into the polymer matrix significantly improved the bending strength of the composite (the average increase of 70%, but considering the best obtained result — over 100%), as well as its Young's modulus (about 150% increase). The analogise composite obtained by forming from solution (PLA + CF + Alg + GS(S)) showed lesser improvement in mechanical parameters (strength increase of 20%), even though the fibre volume fractions were doubled as compared to the nails obtained by injection moulding. Most likely, it was a consequence of the sample forming technique and weak fibre–matrix interphases coming from insufficient impregnation of the fibres with polymer solution. Weak fibre–matrix interphase did not assure the appropriate transfer of stresses on the fibres and caused its rapid delamination. In contrast, good adhesion of the polylactide matrix to the Mg wire surface (discussed above and presented in Fig. 3) ensured stability of Mg-nail mechanical properties during the first 12 weeks of incubation. The decrease in mechanical parameters was observed only after this time period (Fig. 9). After the 8th week, the strength values of the PLA + CF + Alg + GS nails, independent of the forming method, were reduced by about 50%. This resulted from the degradation of alginate fibres in the nail core. Furthermore, the nails became deformed during incubation. Fig. 10 shows the photographs of macroscopic changes in the nails after 12 weeks of incubation in distilled water. The deformation was connected with the difficulty in the axial positioning of the core (containing the fibres) in

the PLA matrix, as it shifted during the injection to the bottom of the mould. 4.3. Injection moulding vs hot pressing The mechanical tests performed on hot pressed, larger-sized nails corresponding to nails used to stabilize forearm bone fractures showed a significant advantage of the composites reinforced with carbon fibres. With the addition of subsequent modifying phases, that is: alginate fibres, tricalcium phosphate nanoparticles and gentamicin particles, the strength of the nails decreased gradually. However, even the most complex composite nails (PLA + CF + Alg + TCP + GS nails) were still stronger (over 200 MPa) than the nails discussed above obtained by injection moulding or formed from solution (Fig. 11A). In the case of the nails with fibrous reinforcement, the bending strength was much higher than for bone tissue (120 MPa). This value should be sufficient to ensure long bone fracture stabilization [8]. To put that into context, the bending strength of a material traditionally used for the fabrication of intramedullary nails – stainless steel 316L – is in the range of 240–770 MPa [9]. The Young's modulus of the hot pressed nails (Fig. 11B) was close to the value of the Young's modulus of the bone (10–40 GPa) [8]. Whereas, in the case of the conventional metallic nails this parameter is significantly higher (E = 193 GPa for 316L and E = 110–114 GPa for Ti6Al–4V). Excessive Young's modulus of the metallic nails is in fact one of their main disadvantages, being the main cause of stress shielding and complications with fracture healing [35]. In the case of the other composites, the strength of nails obtained by injection moulding was higher, which was especially evident for the nails with Mg wires. This was connected with the more homogeneous distribution of ceramic and drug particles in the polymer matrix after

Fig. 7. Mass loss of nails during 12-week incubation in distilled water.

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Fig. 8. Bending strength (A) and Young's modulus (B) of the nails dedicated to rabbits.

Fig. 9. Changes of implants' strength (A) and Young's modulus (B) after 8 and 12 weeks of incubation in distilled water.

Fig. 10. Examined materials after 12 weeks of incubation in distilled water: PLA + CF + Alg + GS(S) (A), PLA + CF + Alg + GS(IM) (B), and PLA + Mg + GS(IM) (C).

Fig. 11. Bending strength (A) and elastic modulus (B) of the nails dedicated to human forearm bone, obtained by hot pressing (HP) and injection moulding (IM).

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the injection. In contrast, in the hot pressing method, the particles formed agglomerates and despite the pressing, there were some local pores left. 5. Conclusions It was demonstrated that the fabrication method of polymer-based nails significantly affects their mechanical properties and degradation behaviour. With the first method, forming from solution, it was challenging to fabricate samples with reproducible properties. Injection moulding assured higher uniformity and homogeneity of the polymer matrix containing ceramic and antibiotic particles in the case of Mgreinforced nails. The final method — hot pressing, was the most applicable for the fibre-reinforced nails, as it allowed for using higher volume fractions of fibres and their better impregnation with the polymer matrix. This study showed that the fabrication method of novel polymer-based nails should be individually selected depending on desired phase composition of the nails. Acknowledgements This work was part of research project No. 4575/B/T02/2009/37 and was financially supported by the Ministry of Science and Higher Education. SEM photographs were taken by Magdalena Ziąbka from the Department of Ceramics and Refractories, Faculty of Materials Science and Ceramics, AGH University of Science and Technology, Krakow, Poland. References [1] M.R. Bong, K.J. Koval, K.A. Egol, The history of intramedullary nailing, Bull. NYU Hosp. Jt. Dis. 64 (3) (2006) 94–97. [2] I. Kempf, A. Grosse, G. Beck, Closed intramedullary nailing. Its application to comminuted fractures of the femur, J. Bone Joint Surg. Am. 67 (1985) 709–720. [3] C. Krettek, Intramedullary nailing, in: T.P. Rüedi, R.E. Buckley, C.G. Moran (Eds.), Principles of Fracture Management. Volume 1 — Principles, AO Publishing, Switzerland, 2007, pp. 257–287. [4] A. Krishan, C. Peshin, D. Singh, Intramedullary nailing and plate osteosynthesis for fractures of the distal metaphyseal tibia and fibula, J. Orthop. Surg. (Hong Kong) 17 (3) (2009) 317–320. [5] J. Marciniak, Biomaterial selection aspects of intramedullary osteosynthesis, in: J. Marciniak, W. Chrzanowski, A. Krauze (Eds.), Intramedullary Nailing in Osteosynthesis, Printing House of the Silesian University of Technology, Gliwice, 2008, pp. 89–124 (in polish). [6] I.A. Pilih, A. Čretnik, Historical overview and biomechanical principles of intramedullary nailing, Intramedullary Fracture Fixation, Medicinski Masečnik, Maribor, 2007. [7] J. Marciniak, W. Chrzanowski, A. Krauze, Intramedullary Nailing in Osteosynthesis, Printing House of the Silesian University of Technology, Gliwice, 2008. (in polish). [8] S. Weiner, W. Traub, H.D. Wagner, Lamellar bone: structure–function relations, J. Struct. Biol. 126 (1999) 241–255. [9] N. Kurgan, R. Varol, Mechanical properties of P/M 316L stainless steel materials, Powder Technol. 201 (2010) 242–247. [10] A.S. Brydone, D. Meek, S. Maclaine, Bone grafting, orthopaedic biomaterials, and the clinical need for bone engineering, Proc. Inst. Mech. Eng. H. 224 (2010) 1329–1343. [11] Y.H. An, S.K. Wollf, R.J. Friedman, Pre-clinical in vivo evaluation of orthopaedic bioabsorbable devices, Biomaterials 21 (2000) 2635–2652.

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