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Biofilm Resistant Surfaces and Coatings on Implants: A Review
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 18 (2019) 4847–4853
www.materialstoday.com/proceedings
ICMPC-2019
Biofilm Resistant Surfaces and Coatings on Implants: A Review P S V V S Narayanaa*, P S V V Sriharib a
b
Assistant Professor, Aditya Engineering College, Surampalem 533437, India Assistant Professor, Aditya College of Engineering and Technology, Surampalem 533437, India
Abstract The study of microbes in and around us that have a drastic affect on human health plays a vital role in medicine. Bacterial infections kill millions of people in the world. The structured formation of bacterial communities, known as biofilms, is the major cause of bacterial infections. Nosocomial infections are caused by biofilms due to their pathogenic nature. Biofilms contribute about 80% and 65% to chronic and microbial infections respectively. The adhesion of bacteria to implant surface is the source of biofilm formation. Therefore, the surface characteristics of the implant material dictate the host cells association and response. Biofilms are resistant to antibiotics, disinfectants, and the human immune system. Implants surface modifications play a vital role in improving their biocompatibility and anti-infection properties. Providing antibacterial and adhesion resistant surface coating acts as a novel approach to combat biofilms. This review presents the process of biofilm formation on different implants and the next generation of surface modification techniques to enhance biocompatibility and antimicrobial functionality using surface engineering and nanobiotechnology. © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 9th International Conference of Materials Processing and Characterization, ICMPC-2019 Keywords: Biofilm; implants; surface modification; antibacterial coatings; antibacterial surfaces
1. Introduction The replacement, or enhancement, and support of a body structure is done by use of an implant. Orthopedics, cardiovascular surgery, urology, dental, neurosurgery, plastic and reconstructive surgery all utilize implants to some extent. The reasons for their use are varied such as to replace worn, damaged or diseased part of the anatomy; to
* Corresponding author. Tel.: +91-9966-966-053. E-mail address: [email protected] 2214-7853 © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 9th International Conference of Materials Processing and Characterization, ICMPC-2019
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correct a deformity; to improve the function of an organ, etc. The major biomaterials that are in use are metals and alloys, composites, polymers, ceramics, and glasses (Table 1). Table 1. Data on existing implants. Implant
Materials
Use
Peritoneal catheter
Silicone, polyurethane
Peritoneal dialysis
Urinary catheter
Latex, silicone, nylon, Polyethylene terephthalate
Empty bladder
Central venous catheter
Silicone, polyvinylchloride, polyethylene
Administrate fluids or medication
Coronary stents
Cobalt-chromium, titanium alloy, Magnesium alloy
Reduce blockages in coronary arteries
Ventricular assist device
Titanium alloy, ceramics, polyurethane
Cardiac circulation assisting device
Cardiac pacemakers
Titanium alloy, polyurethane, silicone
Regulate heartbeat
Mechanical heart valve
Titanium alloys, graphite, polyester, pyrolytic carbon, cobalt-chromium
Valvular heart disease
Vascular grafts
Polytetrafluorethylene, polyethylene terephthalate
Reroute blood flow
Hip/knee implants
Stainless steel, titanium alloy, cobalt-chromium alloys, polyethylene, ceramics
Hip/knee replacement
Fracture fixation devices
Polymers, titanium alloys, stainless steel, cobaltchromium-magnesium alloys
Repair fractured bones
Dental implants
Titanium, cobalt-chromium alloy, alumina, zirconia, bioglass
Reconstruct teeth
Pelvic organ prolapse mesh
Polypropylene, polytetrafluoroethylene, polyester
Support pelvic floor
Cochlear implants
Titanium, platinum, silicone, polytetrafluoroethylene
Artificial electric hearing
Contact lenses
Polymethylmethacrylate, polyhydroethylmethacrylate, silicone
Correct vision
Intraocular lenses
Polymethylmethacrylate, silicone, acrylic
Replace eye’s natural lenses
Penile implants
Silicone
Treat erectile dysfunction
Breast implants
Silicone
Breast augmentation and reconstruction
Sutures
Nylon, silk, polydioxanone, steel wire, polypropylene
Close wound or surgical incision
P.S.V.V.S Narayana and P.S.V.V. Srihari/ Materials Today: Proceedings 18 (2019) 4847–4853
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2. Biofilm and its formation Biofilm is a 3D bacterial community encased within extracellular polymeric substances (EPS) secreted matrix. The growth exhibited by biofilms are distant from free floating or planktonic bacteria. The matrix of biofilm consists of 3% by weight with proteins, extracellular DNA, lipids, polysaccharides, and remaining 97% water. Bacteria in a biofilm are up to 600 times less susceptible to disinfectants and up to 1000 times less vulnerable to antibiotics compared to planktonic counterparts [1]. The dangerous pathogens that can produce biofilm consists of Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter sp. collectively known as ESKAPE pathogens. The bacteria adhesion and colonization on implant surfaces are mediated by factors like types of pathogens, physicochemical properties, surface morphometry, and environmental conditions. The factors mediating bacterial adhesion on implants are shown in Fig.1.
Fig. 1. Factors affecting biofilm formation.
The development of biofilm is a process and has 4 – stages: (1) Bacterial adhesion, (2) Biofilm formation, (3) Biofilm maturation, and (4) Biofilm dispersal [2]. Stage 1: biofilm adhesion. Bacteria that are floating freely attach to an abiotic surface immediately after encountering it. The adhesion of bacteria to the surface is affected by many physiochemical factors like surface hydrophobicity, van der Waals forces, ionic and polar interactions. The formation of a conditioning film after insertion due to absorption of host proteins such as fibronectin, lamnin, vitronectin, and fibrinogen during arthroplasty enhances bacterial adhesion through interactions between host proteins and bacterial proteins. At the end of this stage, a monolayer of bacteria adheres tightly to the binding sites. Stage 2: biofilm formation. A microcolony which is cellular aggregate formed by local multiplication of bacteria in the monolayer starts in this stage. Several multilayers of bacteria forms organized structure by a self – secreted extracellular polymeric substance matrix. The polysaccharide intercellular adhesion (PIA) and adhesive matrix molecules (MSCRAMMs) mediate this process. The cell to cell adhesion in staphulococi is due to accumulation – associated protein (Aap), staphylococcus aures surface protein G (SasG), protein A, and extracellular matrix protein (Emp). There is a chance for eradication of biofilm in this stage since it is unstable. Stage 3: biofilm maturation. The microcolonies turn to macrocolonies by rapid development and adaptation of cells in microcolonies. Flagellae, glycocalyx, fimbriae, exopolysaccharides and pili regulation helps to achieve biofilm maturation. The shear force produced by flowing body fluids on biofilm and surfactant peptides determine the shape and maturation of biofilm. SarA, SigB, and RsbU like gene regulators and luxS quorum – sensing systems
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regulate the maturation stage. The strength of surface attachment is determined by all these factors. After maturation biofilms are very hard to eradicate. Stage 4: biofilm dispersal. Detachment of bacteria from biofilm makes them free to float in the surrounding body fluids returning them to planktonic mode. This causes the spreading of infection. The dispersion causes further local invasion or selection of new sites and initiates a new cycle. This stage is controlled by Agr and proteases. These four stages are shown in Fig. 2.
Fig. 2. Stages of biofilm formation [3].
3. Biofilm-associated infections Bacterial biofilms in the form of a device associated and non-device associated infections contribute about 65% of all bacterial infections. The clinical infections associated with bacterial adhesion to implants are dental caries, chronic otitis media, cystic fibrosis lung infection, periodontitis, chronic rhinosinusitis, chronic wounds, urinary tract infections, recurrent tonsillitis, device-related infections etc. The device associated infections are related to medical devices, abiotic and foreign materials that are implanted into the body. The incidence of device associated biofilm infections with common used implants and medical devices over their lifetime are: 33% for urinary catheter; 2-10% for central venous catheter; 3-5% for peritoneal catheter; 1-4% for mechanical heart valve; 13-80% for ventricular assist device; less than 0.1% for coronary stents; 0.1-20% for cardiac pacemakers; 1-6% for vascular grafts; 01% for contact lenses; 0.1-0.5% for intraocular lenses; 0.5-4% for knee and hip implants; 5- 8% for dental implants; 2-5% for penile implants; 0-8% for pelvic organ prolapse mesh; 14-17% for cochlear implants; 1-2.5% for breast implants; unknown for sutures [3]. Single or multiple different species of bacteria can form biofilms. Contamination of urinary catheter is due to microbial cellular attachment of E. coli, Proteus mirabilis, Enterococcus faecalis and other gram negative bacteria. The central venous catheter is contaminated by S. aureus, Klebriella pneumoniae, S. epidermidis, and Enterobacter species. S. aureus, P. aeuruginosa, and Candida species cause peritoned catheter biofilm formation. Prosthetic valve endocarditis is caused due to biofilm formation on mechanical heart valves by Candida species, S. aureus, and Enterococcus species. S. aureus and P. aeruginosa are the causes for the biofilm formation in ventricular assist devices. Coronary stents are contaminated by S. aureus, P. aeruginosa, and Candida species. S. aureus, Candida and streptococcus species causes biofilm formation in cardiac pacemakers. Biofilm formation in vascular grafts is due to S. aureus, S. epidermidis, P. aeruginosa, and Enterobacter species. Candida, Serratia, and Proteus species adhere to contact lenses and causes biofilms on them. S. epidermidis causes intraocular lenses biofilm infections. Hip and knee implants are affected by S. aureus and Enterobacteriaceae. Biofilms on dental implants are formed by Actinomyces, Streptococcus, and Prevotella species [3]. The bacterial contamination of implants causes host immune system to react not only to bacteria but also recognize biomaterial surface as a foreign body. This reaction starts an inflammatory response. Non – device associated infections are caused due to the entry of bacteria into the bloodstream through trauma or from previous infections. In the case of Periodontitis, which is a gums disease, the biofilm formation is due to poor oral hygiene. It is caused by P. aerobicus and Fusobacterium which leads to soft tissue damage and even tooth loss. Bacteria entry into the bones causes Osteomyelitis. Light microscopy, electron microscopy, fluorescence microscopy, fluorescence in situ hybridization are some methods to detect biofilms.
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4. Antibacterial biomaterial strategies Infection-resistant biomaterials have become a modern way to prevent nosocomial infections. Depending on the specific clinical application, the infection resistant biomaterials have to be made. The biocompatibility, infection resistance, and tissue interactions have to be kept in mind for selecting and specifying the properties of the antiinfective biomaterials [4]. Biomaterials and surfaces enhanced with bactericidal, or fouling resistance or antibiofilm activities are the new strategies to add infection resistant properties. Infections associated with biomaterials can be prevented by using many approaches. In the past, scientists concentrated only on material selection to prevent infections. This includes changing bulk composition, implant dimension, and surface topology. This practice has become obsolete in the present day. From the vast literature, it can be seen that the change in surface topology, implant dimension, and material did not affect bacterial growth significantly. These days proteins, polymers, and a bone graft – based are being used to combat infections due to biofilms. These technologies use localized drug delivery systems. The localized drug delivery is the best solution to systemic toxicity and concentrates only in the area of the implant. The antibiotic resistance of bacteria in biofilm causes the localized drug delivery a challenging task. Therefore, elimination or inhibiting the biofilm formation acts as novel strategies in the production of infection resistant biomaterials. Bacterial interference, bacteriophages, dispersal agents, biofilm resistant surface modifications and coatings are novel strategies to prevent biofilm formation on implants [5]. Fibrin glue, collagen sponges, and gelatin are the drug delivery sources in protein-based materials. Collagen sponges are mostly used as drug delivery vehicles in orthopedic implants. Fibrin glue is used as a sealant whereas gelatin is used along with other modes of drug delivery. The major drawback of the protein-based drug delivery is that they release a large amount of drug initially rather than a sustained release after 7 days. In bone graft materials, antibiotics are mixed with a demineralized bone matrix, calcium sulfate, and bone graft for localized antibiotic delivery. The majority of the drug, approximately 70%, is released after 24 hours and after 7 days drug delivery becomes negligible. The unfavorable release kinetics of bone graft based drug delivery is set back compared to other vehicles. Synthetic based drug delivery makes use of synthetic materials for controlled and sustained release of the drug. Non-biodegradable polymethyl methacrylate (PMMA) is the popular synthetic antibiotic carrier. Less than half amount of drug release than the total incorporated, and undesirable early burst are the limitations of nonbiodegradable synthetic drug delivery. Biodegradable polymer matrices can overcome these limitations but these are still in the investigational stage [6]. Growth inhibition or causing biofilm detachment by making bacteria inside biofilm return to free-floating (planktonic) form is achieved by dispersal agents. Cis-2-Decenoic acid, nitric oxide, D amino acids along with some peptides and enzymes are some identified dispersal agents. Fatty acids dispersal agents sustained released is a challenge as they are difficult to incorporate into existing delivery vehicles. Bacteriophages are the viruses that have the ability to penetrate into a biofilm and prey on bacterial cells and constituents of biofilm-like polysaccharides. Bacteriophages are very difficult in clinical usage as phages have to be customized according to the pathogen causing biofilm. Competition for resources in the same environment can lead a bacteria to inhibit one another. This phenomenon is used as a working principle for bacteria interference. Bacterial interference with use of probiotic bacteria is a new method to fight pathogenic infections associated with biomaterials [7]. 5. Antibacterial surfaces Despite a different number of techniques available to fight bacterial infections on implants, due to their limitations and complexity in design and use the quest for new bacterial resistant surfaces is growing rapidly. The development in nanobiotechnology, nanomedicine, and nanofabrication techniques are integral components of the next generation of biomaterials. The concept behind the fabrication of bacteria resistant surfaces is to eliminate bacterial attachment to the surface or substantially reduce biofilm formation. Depending on the affect of surfaces on the biological system in contact with them, the bacteria resistant surfaces are categorized as antibiofouling or bactericidal. The phenomenon of cellular disruption causing cell death on contact with the surface of the implant is used by bactericidal surfaces. Antibiofouling surfaces provide unfavorable chemical and topographical properties on their surfaces which may prevent or resist bacterial adhesion to the surface. Some bacterial resistant surfaces can
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provide both antibiofouling and bactericidal properties. Antibacterial surfaces can be produced either artificially surface or from a biomimetic surface. Many surfaces in nature like shark skin, fish scale, plant leaves, spider silk, insect wings, and gecko foot possess bacterial colonization resistance. Superhydrophobicity, low-adhesion, and selfcleaning are the biofouling resistant characteristics that are identified from these natural surfaces. Colocasia esculenta (Taso) leaves when immersed in water shows antibacterial fouling character. The nanostructures on the wings of Psaltoda claripennis (Cicada) are bactericidal to P. aeruginosa. The mechanical rupture of bacterial cells on the nanopatterns od Cicada wings causes cell death. This type of mechanism can be used in the design of bactericidal surfaces. The nanopillars on the Cicada wings stretch cell membrane causing cell rupture. Antimicrobial peptides (AMPs), Ceropin A, observed on moths has microbial resistance. They form pores, disintegrate cell membrane, attack cell cytoplasm, and metabolic activity when an inhibitory concentration is reached [8]. Nanoparticles and polymers are used in the fabrication of artificial antibacterial surfaces. These surfaces have biofouling resistance or bactericidal in nature. Silver nanoparticles and polymers are some artificially produced bacteria resistant surfaces. Surface polymerization, functionalization, derivatization, and surface topography modification are the emerging methods for the fabrication of bacterial resistant surfaces. Surface chemistry modification is used in polymerization, functionalization, and derivatization. Physicomechanical changes of the surfaces are regarded as surface topography modification. Atom radical transfer and covalent bonding processes are used in the polymerization of the surface. Hydrophobic quaternary ammonium salts’ polycations when covalently bonded to a surface exhibit bactericidal properties. Nylon, glass, polyethylene and polyethylene terypthalate upon addition of hydrophobic quaternary ammonium salts exhibited antibacterial nature. The molecular proportion and weights of dopants in the polymerization of a surface using a covalent bonding process are very difficult to control. Atom transfer radical polymerization (ATRP) can overcome these problems. ATRP is highly controlled and can be customized to produce permanent antibacterial surfaces. Bacteria resistant polycationic polymers cause cell lysis and death by disrupting bacteria membrane negative charge. Physicochemical adsorption of antibacterial agents (like polymers, peptides, and enzymes) on substrate surfaces is used to produce antibacterial surface by using immobilization approach [9]. Introduction of hydrophobic, long chain, positively charged coating and functional groups are used in the modification of surfaces in surface functionalization or derivatization. Polymerization, plasma treatment, and covalent linkage are used in surface functionalization. Nanomaterials such as carbon nanotubes are the modern materials used in functionalization of surfaces. Morphometry and chemistry of the surfaces are modified by using plasma assisted surface treatment. Plasma-assisted surface treatment produces surfaces with better biocompatibility and antibacterial surfaces. Micro- and nanoscale porosity and surface roughness play a major role in controlling bacteria adhesion [10]. This type of modification falls under surface topography modification. Nanopatterns, nanospikes, and nanopillars exhibit antibacterial and biofilm formation prevention characteristics by using physicomechanical changes of the surfaces [11] [12]. 6. Antibacterial coatings Biocompatible coatings can improve the antibacterial performance of functionalized surfaces and can satisfy mechanical, chemical, tribological, and other requirements in biological environments. Materials’ bulk properties in clinical applications are almost optimized. Thin films on implants can be customized to give desired functions without affecting bulk properties of base materials. Contact-killing, anti-adhesion, and agent release are the major strategies for antibacterial coatings [13]. The release-based antibacterial coatings kill the attached and surrounding planktonic bacteria through leeching loaded antibacterial compounds. Antibiotics, antimicrobial peptides, enzymes, organic cationic compounds, organic non-cationic compounds, inorganic compounds, metallic and nonmetallic elements are used as release-based antibacterial coatings. Disrupting cellular signaling pathways and the chemistry of cells are major functions of release-based coatings. There are three approaches to controlling release kinetics in release-based coatings namely passive, active and bacteria triggered. Dendrimers, nanotubes, nanocapsules, and nanowires are incorporated in antibacterial coatings to control release kinetics. Passive release agent based biomaterial coating repels the bacteria and does not actively kill or interact with bacteria. Hydrophobic or hydrophilic repulsion, electrostatic repulsion, and low surface energy are the reaction mechanisms of passive antibacterial coatings. The active agent based release coatings use stimuli-responsive materials. These kill the
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bacteria that adhere to the coating surface. These coatings use electrostatic interaction or biocidal interactions to kill the bacteria. Rupture of the cell wall by electrostatic interaction or destruction of the cytoplasmic membrane causes the bacteria death upon adhesion. The metabolic activities of bacteria produce acidic substance into the surrounding environment leading to pH drop [14]. The bacteria-triggered release uses this pH response to release antibacterial agents. Another type of bacteria-triggered release used enzymes released by bacteria as triggers. Contact-killing coatings also use release-based materials for killing bacteria. Anti-adhesion or bacteria repelling coatings use surface topography modification to prevent adhesion of bacteria. 7.
Conclusions
The use of medical devices and implants are rapidly growing everyday. Fouling of implants and other medical devices by bacteria is a major economic burden. Almost every implant used today are susceptible to bacterial contamination. The adhesion of bacteria to the implant surfaces causing biofilm formation is the major source of implant-related infections. Due to the inefficiency of antibiotics in dealing with biofilms lead to the emergence of new strategies to fight biofilms. The change in bulk properties of implant materials became obsolete in biofilm eradication. Presently, advanced antibiotic delivery methods are in use to prevent biofilm formation. However, these antibiotic delivery methods have shown many limitations. This paved the way for the paradigm-shifting developments to prevent or treat biofilm formation. Bactericidal and biofouling resistant surfaces and coatings have shown promising results in reducing biofilm formation. Study of challenges like tissue integration, short-term applications, the toxicity of the released coatings, and stability of coatings have to be done to guide future strategies for developing anti-infective biomaterials. Acknowledgements None. References [1] Carlo Renata Arciola, Davide Campoccia, Lucio Montanaro, Implant infections: adhesion, biofilm formation and immune evasion, Nature Reviews Microbiology, 2018, pp. 397-409. [2] Thomas Bjarnsholt, Maria Alhede, Morten Alhede, Steffen R. Eickhardt-Sørensen, Claus Moser, Michael Kühl, Peter Østrup Jensen, Niels Høiby, The in vivo biofilm, Trends in Microbiology, Cell Press, 2013. [3] Mario Salwiczek, Yue Qu, James Gardiner, Richard A.Strugnell, Trevor Lithgow, Keith M. McLean, Helmut Thissen, Emerging rules for effective antimicrobial coatings, Trends in Biotechnology, Cell Press, 2014, pp. 82-90. [4] Jacqueline L.Harding, Melissa M.Reynolds, Combating medical device fouling, Trends in Biotechnology, Cell Press, 2014, pp. 140-146. [5] Sarita R. Shah, Alexander M. Tatara, Rena N. D'Souza, Antonios G. Mikos, F. Kurtis Kasper, Evolving strategies for preventing biofilm on implantable materials, Materials Today, 2013, pp. 177-182. [6] Davide Campoccia, Lucio Montanaro, Carla Renata Arciola, A review of the biomaterials technologies for infection-resistant surfaces, Biomaterials, 2013, pp. 8533-8554. [7] Christophe Beloin, Stéphane Renard, Jean-Marc Ghigo, David Lebeaux, Novel approaches to combat bacterial biofilms, Current Opinion in Pharmacology, 2014, pp. 61-68. [8] Jafar Hasan, Russell J. Crawford, Elena P. Ivanova, Antibacterial surfaces: the quest for a new generation of biomaterials, Trends in Biotechnology, Cell Press, 2013, pp. 295-304. [9] Davide Campoccia, Lucio Montanaro, Carla Renata Arciola, A review of the clinical implications of anti-infective biomaterials and infectionresistant surfaces, Biomaterials, 2013. [10] Rajbi rKaur, Song Liu, Antibacterial surface design – Contact kill, Progress in Surface Science, 2016, pp. 136-153. [11] Mariekevan de Lagemaat, Arjen Grotenhuis, Betsyvan de Belt-Gritter, Steven Roest, Ton J.A. Loontjens, Henk J. Busscher, Henny C.van der Mei, Yijin Ren, Comparison of methods to evaluate bacterial contact-killing materials, Acta Biomaterialia, 2017, pp. 139-147. [12] Abinash Tripathy, Prosenjit Sen, Bo Su, Wuge H. Briscoe, Natural and bioinspired nanostructured bactericidal surfaces, Advances in Colloid and Interface Science, 2017, pp. 85-104. [13] M.Cloutier, D. Mantovani, F. Rose, Antibacterial Coatings: Challenges, Perspectives, and Opportunities, Trends in Biotechnology, Cell Press, 2015. [14] C. Adlhart, J. Verran, N.F. Azevedo, H. Olmez, M.M. Keinänen-Toivola, I. Gouveia, L.F. Melo, F. Crijns, Surface modifications for antimicrobial effects in the healthcare setting: a critical overview, Journal of Hospital Infection, 2018, pp. 239-249.
ScienceDirect Materials Today: Proceedings 18 (2019) 4847–4853
www.materialstoday.com/proceedings
ICMPC-2019
Biofilm Resistant Surfaces and Coatings on Implants: A Review P S V V S Narayanaa*, P S V V Sriharib a
b
Assistant Professor, Aditya Engineering College, Surampalem 533437, India Assistant Professor, Aditya College of Engineering and Technology, Surampalem 533437, India
Abstract The study of microbes in and around us that have a drastic affect on human health plays a vital role in medicine. Bacterial infections kill millions of people in the world. The structured formation of bacterial communities, known as biofilms, is the major cause of bacterial infections. Nosocomial infections are caused by biofilms due to their pathogenic nature. Biofilms contribute about 80% and 65% to chronic and microbial infections respectively. The adhesion of bacteria to implant surface is the source of biofilm formation. Therefore, the surface characteristics of the implant material dictate the host cells association and response. Biofilms are resistant to antibiotics, disinfectants, and the human immune system. Implants surface modifications play a vital role in improving their biocompatibility and anti-infection properties. Providing antibacterial and adhesion resistant surface coating acts as a novel approach to combat biofilms. This review presents the process of biofilm formation on different implants and the next generation of surface modification techniques to enhance biocompatibility and antimicrobial functionality using surface engineering and nanobiotechnology. © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 9th International Conference of Materials Processing and Characterization, ICMPC-2019 Keywords: Biofilm; implants; surface modification; antibacterial coatings; antibacterial surfaces
1. Introduction The replacement, or enhancement, and support of a body structure is done by use of an implant. Orthopedics, cardiovascular surgery, urology, dental, neurosurgery, plastic and reconstructive surgery all utilize implants to some extent. The reasons for their use are varied such as to replace worn, damaged or diseased part of the anatomy; to
* Corresponding author. Tel.: +91-9966-966-053. E-mail address: [email protected] 2214-7853 © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 9th International Conference of Materials Processing and Characterization, ICMPC-2019
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P.S.V.V.S Narayana and P.S.V.V. Srihari/ Materials Today: Proceedings 18 (2019) 4847–4853
correct a deformity; to improve the function of an organ, etc. The major biomaterials that are in use are metals and alloys, composites, polymers, ceramics, and glasses (Table 1). Table 1. Data on existing implants. Implant
Materials
Use
Peritoneal catheter
Silicone, polyurethane
Peritoneal dialysis
Urinary catheter
Latex, silicone, nylon, Polyethylene terephthalate
Empty bladder
Central venous catheter
Silicone, polyvinylchloride, polyethylene
Administrate fluids or medication
Coronary stents
Cobalt-chromium, titanium alloy, Magnesium alloy
Reduce blockages in coronary arteries
Ventricular assist device
Titanium alloy, ceramics, polyurethane
Cardiac circulation assisting device
Cardiac pacemakers
Titanium alloy, polyurethane, silicone
Regulate heartbeat
Mechanical heart valve
Titanium alloys, graphite, polyester, pyrolytic carbon, cobalt-chromium
Valvular heart disease
Vascular grafts
Polytetrafluorethylene, polyethylene terephthalate
Reroute blood flow
Hip/knee implants
Stainless steel, titanium alloy, cobalt-chromium alloys, polyethylene, ceramics
Hip/knee replacement
Fracture fixation devices
Polymers, titanium alloys, stainless steel, cobaltchromium-magnesium alloys
Repair fractured bones
Dental implants
Titanium, cobalt-chromium alloy, alumina, zirconia, bioglass
Reconstruct teeth
Pelvic organ prolapse mesh
Polypropylene, polytetrafluoroethylene, polyester
Support pelvic floor
Cochlear implants
Titanium, platinum, silicone, polytetrafluoroethylene
Artificial electric hearing
Contact lenses
Polymethylmethacrylate, polyhydroethylmethacrylate, silicone
Correct vision
Intraocular lenses
Polymethylmethacrylate, silicone, acrylic
Replace eye’s natural lenses
Penile implants
Silicone
Treat erectile dysfunction
Breast implants
Silicone
Breast augmentation and reconstruction
Sutures
Nylon, silk, polydioxanone, steel wire, polypropylene
Close wound or surgical incision
P.S.V.V.S Narayana and P.S.V.V. Srihari/ Materials Today: Proceedings 18 (2019) 4847–4853
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2. Biofilm and its formation Biofilm is a 3D bacterial community encased within extracellular polymeric substances (EPS) secreted matrix. The growth exhibited by biofilms are distant from free floating or planktonic bacteria. The matrix of biofilm consists of 3% by weight with proteins, extracellular DNA, lipids, polysaccharides, and remaining 97% water. Bacteria in a biofilm are up to 600 times less susceptible to disinfectants and up to 1000 times less vulnerable to antibiotics compared to planktonic counterparts [1]. The dangerous pathogens that can produce biofilm consists of Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter sp. collectively known as ESKAPE pathogens. The bacteria adhesion and colonization on implant surfaces are mediated by factors like types of pathogens, physicochemical properties, surface morphometry, and environmental conditions. The factors mediating bacterial adhesion on implants are shown in Fig.1.
Fig. 1. Factors affecting biofilm formation.
The development of biofilm is a process and has 4 – stages: (1) Bacterial adhesion, (2) Biofilm formation, (3) Biofilm maturation, and (4) Biofilm dispersal [2]. Stage 1: biofilm adhesion. Bacteria that are floating freely attach to an abiotic surface immediately after encountering it. The adhesion of bacteria to the surface is affected by many physiochemical factors like surface hydrophobicity, van der Waals forces, ionic and polar interactions. The formation of a conditioning film after insertion due to absorption of host proteins such as fibronectin, lamnin, vitronectin, and fibrinogen during arthroplasty enhances bacterial adhesion through interactions between host proteins and bacterial proteins. At the end of this stage, a monolayer of bacteria adheres tightly to the binding sites. Stage 2: biofilm formation. A microcolony which is cellular aggregate formed by local multiplication of bacteria in the monolayer starts in this stage. Several multilayers of bacteria forms organized structure by a self – secreted extracellular polymeric substance matrix. The polysaccharide intercellular adhesion (PIA) and adhesive matrix molecules (MSCRAMMs) mediate this process. The cell to cell adhesion in staphulococi is due to accumulation – associated protein (Aap), staphylococcus aures surface protein G (SasG), protein A, and extracellular matrix protein (Emp). There is a chance for eradication of biofilm in this stage since it is unstable. Stage 3: biofilm maturation. The microcolonies turn to macrocolonies by rapid development and adaptation of cells in microcolonies. Flagellae, glycocalyx, fimbriae, exopolysaccharides and pili regulation helps to achieve biofilm maturation. The shear force produced by flowing body fluids on biofilm and surfactant peptides determine the shape and maturation of biofilm. SarA, SigB, and RsbU like gene regulators and luxS quorum – sensing systems
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regulate the maturation stage. The strength of surface attachment is determined by all these factors. After maturation biofilms are very hard to eradicate. Stage 4: biofilm dispersal. Detachment of bacteria from biofilm makes them free to float in the surrounding body fluids returning them to planktonic mode. This causes the spreading of infection. The dispersion causes further local invasion or selection of new sites and initiates a new cycle. This stage is controlled by Agr and proteases. These four stages are shown in Fig. 2.
Fig. 2. Stages of biofilm formation [3].
3. Biofilm-associated infections Bacterial biofilms in the form of a device associated and non-device associated infections contribute about 65% of all bacterial infections. The clinical infections associated with bacterial adhesion to implants are dental caries, chronic otitis media, cystic fibrosis lung infection, periodontitis, chronic rhinosinusitis, chronic wounds, urinary tract infections, recurrent tonsillitis, device-related infections etc. The device associated infections are related to medical devices, abiotic and foreign materials that are implanted into the body. The incidence of device associated biofilm infections with common used implants and medical devices over their lifetime are: 33% for urinary catheter; 2-10% for central venous catheter; 3-5% for peritoneal catheter; 1-4% for mechanical heart valve; 13-80% for ventricular assist device; less than 0.1% for coronary stents; 0.1-20% for cardiac pacemakers; 1-6% for vascular grafts; 01% for contact lenses; 0.1-0.5% for intraocular lenses; 0.5-4% for knee and hip implants; 5- 8% for dental implants; 2-5% for penile implants; 0-8% for pelvic organ prolapse mesh; 14-17% for cochlear implants; 1-2.5% for breast implants; unknown for sutures [3]. Single or multiple different species of bacteria can form biofilms. Contamination of urinary catheter is due to microbial cellular attachment of E. coli, Proteus mirabilis, Enterococcus faecalis and other gram negative bacteria. The central venous catheter is contaminated by S. aureus, Klebriella pneumoniae, S. epidermidis, and Enterobacter species. S. aureus, P. aeuruginosa, and Candida species cause peritoned catheter biofilm formation. Prosthetic valve endocarditis is caused due to biofilm formation on mechanical heart valves by Candida species, S. aureus, and Enterococcus species. S. aureus and P. aeruginosa are the causes for the biofilm formation in ventricular assist devices. Coronary stents are contaminated by S. aureus, P. aeruginosa, and Candida species. S. aureus, Candida and streptococcus species causes biofilm formation in cardiac pacemakers. Biofilm formation in vascular grafts is due to S. aureus, S. epidermidis, P. aeruginosa, and Enterobacter species. Candida, Serratia, and Proteus species adhere to contact lenses and causes biofilms on them. S. epidermidis causes intraocular lenses biofilm infections. Hip and knee implants are affected by S. aureus and Enterobacteriaceae. Biofilms on dental implants are formed by Actinomyces, Streptococcus, and Prevotella species [3]. The bacterial contamination of implants causes host immune system to react not only to bacteria but also recognize biomaterial surface as a foreign body. This reaction starts an inflammatory response. Non – device associated infections are caused due to the entry of bacteria into the bloodstream through trauma or from previous infections. In the case of Periodontitis, which is a gums disease, the biofilm formation is due to poor oral hygiene. It is caused by P. aerobicus and Fusobacterium which leads to soft tissue damage and even tooth loss. Bacteria entry into the bones causes Osteomyelitis. Light microscopy, electron microscopy, fluorescence microscopy, fluorescence in situ hybridization are some methods to detect biofilms.
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4. Antibacterial biomaterial strategies Infection-resistant biomaterials have become a modern way to prevent nosocomial infections. Depending on the specific clinical application, the infection resistant biomaterials have to be made. The biocompatibility, infection resistance, and tissue interactions have to be kept in mind for selecting and specifying the properties of the antiinfective biomaterials [4]. Biomaterials and surfaces enhanced with bactericidal, or fouling resistance or antibiofilm activities are the new strategies to add infection resistant properties. Infections associated with biomaterials can be prevented by using many approaches. In the past, scientists concentrated only on material selection to prevent infections. This includes changing bulk composition, implant dimension, and surface topology. This practice has become obsolete in the present day. From the vast literature, it can be seen that the change in surface topology, implant dimension, and material did not affect bacterial growth significantly. These days proteins, polymers, and a bone graft – based are being used to combat infections due to biofilms. These technologies use localized drug delivery systems. The localized drug delivery is the best solution to systemic toxicity and concentrates only in the area of the implant. The antibiotic resistance of bacteria in biofilm causes the localized drug delivery a challenging task. Therefore, elimination or inhibiting the biofilm formation acts as novel strategies in the production of infection resistant biomaterials. Bacterial interference, bacteriophages, dispersal agents, biofilm resistant surface modifications and coatings are novel strategies to prevent biofilm formation on implants [5]. Fibrin glue, collagen sponges, and gelatin are the drug delivery sources in protein-based materials. Collagen sponges are mostly used as drug delivery vehicles in orthopedic implants. Fibrin glue is used as a sealant whereas gelatin is used along with other modes of drug delivery. The major drawback of the protein-based drug delivery is that they release a large amount of drug initially rather than a sustained release after 7 days. In bone graft materials, antibiotics are mixed with a demineralized bone matrix, calcium sulfate, and bone graft for localized antibiotic delivery. The majority of the drug, approximately 70%, is released after 24 hours and after 7 days drug delivery becomes negligible. The unfavorable release kinetics of bone graft based drug delivery is set back compared to other vehicles. Synthetic based drug delivery makes use of synthetic materials for controlled and sustained release of the drug. Non-biodegradable polymethyl methacrylate (PMMA) is the popular synthetic antibiotic carrier. Less than half amount of drug release than the total incorporated, and undesirable early burst are the limitations of nonbiodegradable synthetic drug delivery. Biodegradable polymer matrices can overcome these limitations but these are still in the investigational stage [6]. Growth inhibition or causing biofilm detachment by making bacteria inside biofilm return to free-floating (planktonic) form is achieved by dispersal agents. Cis-2-Decenoic acid, nitric oxide, D amino acids along with some peptides and enzymes are some identified dispersal agents. Fatty acids dispersal agents sustained released is a challenge as they are difficult to incorporate into existing delivery vehicles. Bacteriophages are the viruses that have the ability to penetrate into a biofilm and prey on bacterial cells and constituents of biofilm-like polysaccharides. Bacteriophages are very difficult in clinical usage as phages have to be customized according to the pathogen causing biofilm. Competition for resources in the same environment can lead a bacteria to inhibit one another. This phenomenon is used as a working principle for bacteria interference. Bacterial interference with use of probiotic bacteria is a new method to fight pathogenic infections associated with biomaterials [7]. 5. Antibacterial surfaces Despite a different number of techniques available to fight bacterial infections on implants, due to their limitations and complexity in design and use the quest for new bacterial resistant surfaces is growing rapidly. The development in nanobiotechnology, nanomedicine, and nanofabrication techniques are integral components of the next generation of biomaterials. The concept behind the fabrication of bacteria resistant surfaces is to eliminate bacterial attachment to the surface or substantially reduce biofilm formation. Depending on the affect of surfaces on the biological system in contact with them, the bacteria resistant surfaces are categorized as antibiofouling or bactericidal. The phenomenon of cellular disruption causing cell death on contact with the surface of the implant is used by bactericidal surfaces. Antibiofouling surfaces provide unfavorable chemical and topographical properties on their surfaces which may prevent or resist bacterial adhesion to the surface. Some bacterial resistant surfaces can
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provide both antibiofouling and bactericidal properties. Antibacterial surfaces can be produced either artificially surface or from a biomimetic surface. Many surfaces in nature like shark skin, fish scale, plant leaves, spider silk, insect wings, and gecko foot possess bacterial colonization resistance. Superhydrophobicity, low-adhesion, and selfcleaning are the biofouling resistant characteristics that are identified from these natural surfaces. Colocasia esculenta (Taso) leaves when immersed in water shows antibacterial fouling character. The nanostructures on the wings of Psaltoda claripennis (Cicada) are bactericidal to P. aeruginosa. The mechanical rupture of bacterial cells on the nanopatterns od Cicada wings causes cell death. This type of mechanism can be used in the design of bactericidal surfaces. The nanopillars on the Cicada wings stretch cell membrane causing cell rupture. Antimicrobial peptides (AMPs), Ceropin A, observed on moths has microbial resistance. They form pores, disintegrate cell membrane, attack cell cytoplasm, and metabolic activity when an inhibitory concentration is reached [8]. Nanoparticles and polymers are used in the fabrication of artificial antibacterial surfaces. These surfaces have biofouling resistance or bactericidal in nature. Silver nanoparticles and polymers are some artificially produced bacteria resistant surfaces. Surface polymerization, functionalization, derivatization, and surface topography modification are the emerging methods for the fabrication of bacterial resistant surfaces. Surface chemistry modification is used in polymerization, functionalization, and derivatization. Physicomechanical changes of the surfaces are regarded as surface topography modification. Atom radical transfer and covalent bonding processes are used in the polymerization of the surface. Hydrophobic quaternary ammonium salts’ polycations when covalently bonded to a surface exhibit bactericidal properties. Nylon, glass, polyethylene and polyethylene terypthalate upon addition of hydrophobic quaternary ammonium salts exhibited antibacterial nature. The molecular proportion and weights of dopants in the polymerization of a surface using a covalent bonding process are very difficult to control. Atom transfer radical polymerization (ATRP) can overcome these problems. ATRP is highly controlled and can be customized to produce permanent antibacterial surfaces. Bacteria resistant polycationic polymers cause cell lysis and death by disrupting bacteria membrane negative charge. Physicochemical adsorption of antibacterial agents (like polymers, peptides, and enzymes) on substrate surfaces is used to produce antibacterial surface by using immobilization approach [9]. Introduction of hydrophobic, long chain, positively charged coating and functional groups are used in the modification of surfaces in surface functionalization or derivatization. Polymerization, plasma treatment, and covalent linkage are used in surface functionalization. Nanomaterials such as carbon nanotubes are the modern materials used in functionalization of surfaces. Morphometry and chemistry of the surfaces are modified by using plasma assisted surface treatment. Plasma-assisted surface treatment produces surfaces with better biocompatibility and antibacterial surfaces. Micro- and nanoscale porosity and surface roughness play a major role in controlling bacteria adhesion [10]. This type of modification falls under surface topography modification. Nanopatterns, nanospikes, and nanopillars exhibit antibacterial and biofilm formation prevention characteristics by using physicomechanical changes of the surfaces [11] [12]. 6. Antibacterial coatings Biocompatible coatings can improve the antibacterial performance of functionalized surfaces and can satisfy mechanical, chemical, tribological, and other requirements in biological environments. Materials’ bulk properties in clinical applications are almost optimized. Thin films on implants can be customized to give desired functions without affecting bulk properties of base materials. Contact-killing, anti-adhesion, and agent release are the major strategies for antibacterial coatings [13]. The release-based antibacterial coatings kill the attached and surrounding planktonic bacteria through leeching loaded antibacterial compounds. Antibiotics, antimicrobial peptides, enzymes, organic cationic compounds, organic non-cationic compounds, inorganic compounds, metallic and nonmetallic elements are used as release-based antibacterial coatings. Disrupting cellular signaling pathways and the chemistry of cells are major functions of release-based coatings. There are three approaches to controlling release kinetics in release-based coatings namely passive, active and bacteria triggered. Dendrimers, nanotubes, nanocapsules, and nanowires are incorporated in antibacterial coatings to control release kinetics. Passive release agent based biomaterial coating repels the bacteria and does not actively kill or interact with bacteria. Hydrophobic or hydrophilic repulsion, electrostatic repulsion, and low surface energy are the reaction mechanisms of passive antibacterial coatings. The active agent based release coatings use stimuli-responsive materials. These kill the
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bacteria that adhere to the coating surface. These coatings use electrostatic interaction or biocidal interactions to kill the bacteria. Rupture of the cell wall by electrostatic interaction or destruction of the cytoplasmic membrane causes the bacteria death upon adhesion. The metabolic activities of bacteria produce acidic substance into the surrounding environment leading to pH drop [14]. The bacteria-triggered release uses this pH response to release antibacterial agents. Another type of bacteria-triggered release used enzymes released by bacteria as triggers. Contact-killing coatings also use release-based materials for killing bacteria. Anti-adhesion or bacteria repelling coatings use surface topography modification to prevent adhesion of bacteria. 7.
Conclusions
The use of medical devices and implants are rapidly growing everyday. Fouling of implants and other medical devices by bacteria is a major economic burden. Almost every implant used today are susceptible to bacterial contamination. The adhesion of bacteria to the implant surfaces causing biofilm formation is the major source of implant-related infections. Due to the inefficiency of antibiotics in dealing with biofilms lead to the emergence of new strategies to fight biofilms. The change in bulk properties of implant materials became obsolete in biofilm eradication. Presently, advanced antibiotic delivery methods are in use to prevent biofilm formation. However, these antibiotic delivery methods have shown many limitations. This paved the way for the paradigm-shifting developments to prevent or treat biofilm formation. Bactericidal and biofouling resistant surfaces and coatings have shown promising results in reducing biofilm formation. Study of challenges like tissue integration, short-term applications, the toxicity of the released coatings, and stability of coatings have to be done to guide future strategies for developing anti-infective biomaterials. Acknowledgements None. References [1] Carlo Renata Arciola, Davide Campoccia, Lucio Montanaro, Implant infections: adhesion, biofilm formation and immune evasion, Nature Reviews Microbiology, 2018, pp. 397-409. [2] Thomas Bjarnsholt, Maria Alhede, Morten Alhede, Steffen R. Eickhardt-Sørensen, Claus Moser, Michael Kühl, Peter Østrup Jensen, Niels Høiby, The in vivo biofilm, Trends in Microbiology, Cell Press, 2013. [3] Mario Salwiczek, Yue Qu, James Gardiner, Richard A.Strugnell, Trevor Lithgow, Keith M. McLean, Helmut Thissen, Emerging rules for effective antimicrobial coatings, Trends in Biotechnology, Cell Press, 2014, pp. 82-90. [4] Jacqueline L.Harding, Melissa M.Reynolds, Combating medical device fouling, Trends in Biotechnology, Cell Press, 2014, pp. 140-146. [5] Sarita R. Shah, Alexander M. Tatara, Rena N. D'Souza, Antonios G. Mikos, F. Kurtis Kasper, Evolving strategies for preventing biofilm on implantable materials, Materials Today, 2013, pp. 177-182. [6] Davide Campoccia, Lucio Montanaro, Carla Renata Arciola, A review of the biomaterials technologies for infection-resistant surfaces, Biomaterials, 2013, pp. 8533-8554. [7] Christophe Beloin, Stéphane Renard, Jean-Marc Ghigo, David Lebeaux, Novel approaches to combat bacterial biofilms, Current Opinion in Pharmacology, 2014, pp. 61-68. [8] Jafar Hasan, Russell J. Crawford, Elena P. Ivanova, Antibacterial surfaces: the quest for a new generation of biomaterials, Trends in Biotechnology, Cell Press, 2013, pp. 295-304. [9] Davide Campoccia, Lucio Montanaro, Carla Renata Arciola, A review of the clinical implications of anti-infective biomaterials and infectionresistant surfaces, Biomaterials, 2013. [10] Rajbi rKaur, Song Liu, Antibacterial surface design – Contact kill, Progress in Surface Science, 2016, pp. 136-153. [11] Mariekevan de Lagemaat, Arjen Grotenhuis, Betsyvan de Belt-Gritter, Steven Roest, Ton J.A. Loontjens, Henk J. Busscher, Henny C.van der Mei, Yijin Ren, Comparison of methods to evaluate bacterial contact-killing materials, Acta Biomaterialia, 2017, pp. 139-147. [12] Abinash Tripathy, Prosenjit Sen, Bo Su, Wuge H. Briscoe, Natural and bioinspired nanostructured bactericidal surfaces, Advances in Colloid and Interface Science, 2017, pp. 85-104. [13] M.Cloutier, D. Mantovani, F. Rose, Antibacterial Coatings: Challenges, Perspectives, and Opportunities, Trends in Biotechnology, Cell Press, 2015. [14] C. Adlhart, J. Verran, N.F. Azevedo, H. Olmez, M.M. Keinänen-Toivola, I. Gouveia, L.F. Melo, F. Crijns, Surface modifications for antimicrobial effects in the healthcare setting: a critical overview, Journal of Hospital Infection, 2018, pp. 239-249.