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The majority of contemporary medical implants are fabricated from metals such as steel, titanium alloys, cobalt-chromium alloys, magnesium-based alloys, tantalum, nickel-titanium alloys, platinum-based alloys, etc. However, due to the increasing number of implantations, the incidence rate of implant-associated infections (IAIs) as a side effect also boosted. To our good fortune, plasma technology offers an exciting tool to enhance the antimicrobial effectiveness of such metals.
What is Plasma Coating?
Plasma coating is a method of depositing a thin film on the surface of a material by using plasma technology to improve the surface properties or introduce new functionality. Plasma is an ionized gas that consists of ions, electrons, and neutral particles with high reactivity and energy. During plasma coating, the coating material is activated by plasma so that it gets deposited on the substrate surface in the form of atoms or ions and creates a dense and uniform coating.
Plasma technology has come a long way to being a widely usable and multifunctional tool. With this technology, it is feasible to fabricate and use antimicrobial coatings on the surface of various materials at low temperature and without the use of any chemical solvents or special substrate materials. With the help of plasma-assisted methods, strongly customized surface modification can be achieved by grafting chemical functional groups or nanoscale-thick coatings with high antimicrobial activities. Among the different antimicrobial agents utilized via plasma-based techniques, metal and metal oxide nanoparticles of size between 5 and 200 nanometers have exhibited significant bactericidal effects against microorganisms and bacteria.
What Are the Benefits of Plasma Coating?
Plasma treatment can significantly alter the physicochemical properties of metal surfaces. Surface chemical composition, roughness, wettability, surface charge, and crystallinity, for example, are all important parameters in the biological response of medical materials. Plasma surface modification has been shown to be an extremely effective method of creating antimicrobial surfaces. Plasma treatment not only enhances the adhesion of antimicrobial coatings but also results in antimicrobial effects in metal implants.
How Is Plasma Technology Used for Coating?
The process of coating object surfaces using vacuum-plasma technology is similar in rudimentary steps to other coating processes but possesses a certain unique peculiarity of operations and advantages.
1. Surface Cleaning and Activation
Cleaning Treatment
In practice, the object surface needs to be cleaned as an essential step to ensure coating quality. The application of a vacuum environment is efficient in removing dust, grease, and other impurities from the surface. The conventional cleaning techniques are plasma cleaning technology, where high-energy plasma beams bombard the surface to decompose and expel organic contaminants, resulting in a clean surface.
Activation Treatment
After cleaning, the surface needs to be activated in order to enhance coating adhesion. Plasma activation subjects the surface to high-energy particles (ions, electrons, and free radicals) in order to generate chemical and physical changes on the surface to enhance active sites. The process enhances not just coating adhesion but also coating uniformity and density.
2. Introduction of Monomer and Coating Deposition
Selection and Introduction of Monomer
Antimicrobial monomers such as silver nitrate (AgNO₃) are introduced into the vacuum chamber, where they become degraded or activated in the plasma environment to form antimicrobial active compounds. Silver (Ag) is also being used extensively in medical devices, textiles, electronics, and other uses due to its enhanced antimicrobial action. Silver excepted, other commonly used antimicrobial monomers are copper (Cu), zinc (Zn), and their oxides, which exhibit better antimicrobial action at the nanoscale.
Coating Deposition Methods
Plasma-supported deposition methods, such as plasma-enhanced chemical vapor deposition (PECVD) and physical vapor deposition (PVD), enable the deposition of highly uniform and dense nanoscale coatings on the surface of products. These coatings not only have excellent antimicrobial activity but also impart some additional functionality, such as corrosion resistance and wear resistance, to enhance the product’s lifespan.
3. Post-Treatment and Product Removal
Process Gas Exhaust and Ventilation Treatment
After completing the deposition of the coating, the process gases in the vacuum chamber must be pumped out completely. This step ensures that the surface of the coating is free from residual gas contamination, maintaining the high purity of the product. Following proper ventilation re-establishes ambient atmospheric conditions, rendering the environment safe for the operators and the product.
Strict Industrial Hygiene Standards
During product removal, rigorous industrial hygiene practices are adhered to. Aseptic operations and multistage filtration ensure the high degree of sterility of the final product along with antimicrobial activity for applications requiring high levels such as medical and food packaging.