What Are Orthopedic Implants?
Orthopedic implants are designed device that helps to replace a bone, joint, or cartilage due to losing a limb, congenital disabilities, or breaking a leg. The most common types of orthopedic implants are plates, screws, and prostheses. The orthopedic implants are made up of titanium and titanium alloys.
What Happens to Orthopedic Implants?
People suffer from various bone defects caused by conditions like sports injury, osteoporosis, and some accidents that, in turn, seriously impact the quality of life. In recent years, there has been an increasingly high demand for orthopedic implants. Implant-related orthopedic infection is a common issue in clinical orthopedics, either caused by premature implant failure or postoperative implant complication. The implant-related infections are mainly due to the biofilm formation in the implants. Once a biofilm is formed in the implant, it is challenging to eliminate it, which also leads to chronic infections. Antibiotics may not be effective on biofilms; instead, they can cause severe issues like cytotoxicity and delayed bone degeneration. Therefore, frequent implant replacement is needed once implant-related infections occur. It is essential to stop the biofilm formation in the implants; this can be achieved by incorporating antibacterial coatings.
What Is the Role of Antibacterial Coatings in Orthopedic Implants?
Based on the implants' excellent surface and chemical structure, the surface coating technique can help achieve antibacterial effects without affecting the material's properties. This surface coating technique may also help achieve other surface properties of the material, such as scratch resistance, corrosion resistance, wear resistance, and suitable wettability.
The antimicrobial coatings on the implants have also helped progress the strategies to improve the implants. Three approaches have designed the antimicrobial coatings on the surface of implants. They are anti-adhesion, contact-killing, and releasing types. The antimicrobial words are expanded from antibiotics, metal ions, low molecular organic compounds, and nanoparticles to synthetic or natural polymers.
Antimicrobial coatings must be bioactive and biocompatible as their primary role is osseointegration. The orthopedic implant surface should stimulate proper adhesion of the host cell and growth by preventing the colonization of bacteria and adhesion of it.
It is tough to balance antimicrobial properties and biocompatibility as the surface of the implants, which stimulates host cell adhesion, also helps bacteria involved in some of the adhesive mechanisms on the host cell. The antimicrobial coatings that prevent implant-related infection by bacteria repelling or anti-adhesion limit the host cell adhesion and will not stimulate the integration of the body tissues.
Thus, a lack of bacteria-repelling, anti-adhesion, or bactericidal activity can contaminate the surface and lead to toxicity. Therefore it is essential to maintain the bioactivity and biocompatibility of the coatings to prevent infections.
How Does Infection Occur in Orthopedic Implants?
An ideal orthopedic implant should possess bioactivity, biocompatibility, durability, hardness, wear resistance, corrosion resistance, and the same elastic modulus as the human bone. Various infections and aseptic loosening may affect it, which may be a significant cause of implant failure. The biocompatibility and bioactivity of the implant surface facilitate host cell adhesion but also cause infections by the growth and adhesion of microorganisms.
Infections in orthopedic implants are caused by the colonization and adhesion of bacteria during surgeries or in the postoperative period. Replacement surgeries treat these infections. Chronic and acute infections of the implants may also cause death.
Bacterial adhesion, growth, and colonization into the biofilms are the primary causes* of implant-related infections. The biofilm primarily comprises bacterial colonies and extracellular polymeric substances like proteins, DNA (deoxyribonucleic acid), and polysaccharides.
Biofilm usually forms in five stages: reversible bacterial adhesion, irreversible adhesion, initial biofilm formation, biofilm maturation, and release of toxins and free bacteria.
In the first stage, the bacteria can move freely, stack, and gather on the implant's surface when the bacterial adhesion is reversible.
In the second stage, due to the adsorption of specific and nonspecific interaction between the proteins and bacteria on the implant surface, it tends to begin the intercellular adhesion and proliferation by gradually secreting the extracellular polymers causing bacterial adhesion to be irreversible, which in turn cause restriction in the bacterial movements due to restraints of the secretion.
In the third stage, the constant reproduction of bacteria on the implant surface forms multi-layers of bacteria to colonize, forming a biofilm.
In the fourth stage, the tiny colonies formed in the third stage progress to form large colonies, forming an exact three-dimensional matrix structure called bacterial biofilm.
In the fifth stage, when the bacteria reproduce, the bacteria in the already formed biofilm release and prepare to colonize, which in turn causes a chronic infection.
What Are the Antimicrobial Coatings Used in Orthopedic Implants?
The antimicrobial coatings that are used to prevent implant-related orthopedic infections are
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Adhesion-resistant coatings.
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Contact bactericidal coatings.
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Release type of antibacterial coatings.
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Antibiotics release antibacterial coatings.
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Metal ions release antibacterial coatings.
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Non-metallic ions release antibacterial coatings.
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Synergistic multi-mechanism antibacterial coatings.
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Multifunctional antibacterial coatings.
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Smart antibacterial coatings.
In addition, DAC hydrogel, gentamicin PLLA coatings, iodine coatings, and silver coatings are used to prevent implant-related infections in orthopedic surgeries.
In addition to this, common hydrophobic and hydrophilic antibacterial coatings are also used in orthopedic implants.
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Common Hydrophobic Antibacterial Coatings - Hydrophobic antibacterial coatings on orthopedic implants aim to prevent bacterial adhesion and infection. Common materials include silver nanoparticles, titanium dioxide, and hydrophobic polymers. These coatings create a hostile environment for bacteria, hindering biofilm formation. They often exhibit sustained release of antibacterial agents, enhancing long-term efficacy. These coatings improve implant success rates by reducing infection risks in orthopedic surgeries.
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Common Hydrophilic Antibacterial Coatings - Hydrophilic antibacterial coatings on orthopedic implants are designed to enhance osseointegration while preventing infections. Common coatings include hydroxyapatite, silver nanoparticles, and antibiotics like vancomycin or gentamicin. These materials create a favorable environment for bone growth while exerting antimicrobial properties, reducing the risk of postoperative infections.
Conclusion
Implant-related infections cause the most vexing problem in the medical field, as they can negatively affect the clinical use of implants. In such circumstances, the application and development of several antimicrobial coatings help solve the problem created by implant-related infections. The coatings mentioned in the article are currently applied to orthopedic implants depending on their functions and mechanisms. Antimicrobial coatings play an essential role in preventing implant-related infections. So, an ideal orthopedic implant must be coated with multi-functional and innovative antimicrobial coatings. Thus, antimicrobial coatings help to achieve and progress the clinical use of orthopedic implants.
