Coatings on orthopedic implants to overcome present problems and challenges: A focused review

Life of orthopedic implants is severely hampered by various factors including infections, corrosion, wearing, excessive inflammation, severe toxicity, poor osseointegration, and foreign body effects. Infection may cause prolonged suffering and may lead to death of patient. Corrosion and wear not only weaken the implants but also causes toxicity. The implants' material may be treated as pathogen by our immune system and causes chronic inflammation and foreign body reactions and ultimately this may result in poor osseointegration. The coating of biocompatible and bioactive material on the surface of implants is a local and most effective strategy to resolve these problems and enhance the life of implants. Coatings deliver biologicals at damage site directly, so work more precisely than orderly pharmacology action. This manuscript reviewed the current development in functional as well as protective coatings on titanium, cobalt-chromium, stainless steel, and magnesium based metallic and other non-metallic orthopedic implants. Ceramic based coatings like hydroxyapatite, titanium nitride, titanium oxynitride, titanium aluminum nitride, and oxides of Al, Si, Ta, Ti, Zn, Ce and Nb based coatings are observed to be effective as antimicrobial, anticorrosion and bioactive coatings. Polymer based coatings like polyethylene oxide, hydrophilic polymethacrylic acid, polyethylene glycol, poly(lactide-co-glycolide), and glycidyl methacrylate-based coatings are observed to be effective as antimicrobial and bioactive coatings. Bioactive molecules such as bisphosphonates and zoledronic based coatings are observed to be beneficial in mitigating foreign body effects. Coatings of various proteins and growth factors are proved to improve osseointegration. Hydroxyapatite based coatings are observed to be the most effective in controlling infection, corrosion, foreign body effects and improving osseointegration.