The role of salicylate as dopant in polypyrrole matrix deposited on biocompatible substrates

Abstract

Salicylates are used as nonsteroidalanti-inflammatory drugs (NSAIDs). The most commonly used and well-knownsalicylate (Sa) is aspirin. Several studies suggest that aspirin not onlyrelieves fever, inflammation, and pain, but also reduces the risk of stroke,heart attack, and some cancers. In our time, great efforts are being made toproduce metal implants with drug-releasing systems. It is important to deliverdrugs locally near the implanted material to achieve high efficacy oftherapeutic agents. In addition, coating the surface of the metallic implant toprotect it from corrosion is a widely studied topic. Polypyrrole (PPy) is aconductive polymer and a suitable material for biomedical applications withmany advantages such as its relatively easy electrosynthesis in aqueoussolutions, biocompatibility and good stability. Specifically, the Sa molecule plays a dualrole in the electrosynthesis of PPy on various biocompatible substrates. First,Sa acts as a dopant of the polymer and second, it is a promoter for theformation of rectangular microtubules. The microtubular structures provide alarge active surface area and, under certain experimental conditions, the Saanion can be released from the film. In this way, the anti-inflammatory effectof Sa can be exploited in the vicinity of the substrate. Another interestingfeature of Sa molecule is that it behaves as a passivating agent, inhibitingthe dissolution of active metals such as iron or magnesium and also allowing astable PPy formation. In addition, implant-related infections are a tragicproblem, and revision surgery is often required for individuals with severeinfections. To prevent this, surface modifications are also used. For example,the addition of metal ions such as Ag+, Cu2+, and Zn2+is suitable because they exert antimicrobial activity at the implant site. 316L Stainless Steel (316 LSS) is the most commonly used alloy for medical implants and was coated withSa-doped PPy with microtubular morphology to improve the corrosion properties.The PPy coating was able to immobilize silver and copper particles. Ti-6Al-4Vand Nitinol are Ti-based widely used biomaterials. PPy films were synthesizedfrom aqueous solution with Sa onto both alloys. The microstructured polymermatrix was used for the immobilization of Zn and Ag species, respectively.These modifications provide antimicrobial properties against Staphylococcus aureus. AZ91D is abiodegradable magnesium alloy used for temporary implants. To retard corrosion,the substrate was coated with a double film consisting of a molybdate-basedfilm and a PPy film obtained from a Sa solution. The duplex film was modifiedwith silver and exhibits good antibacterial activity against Escherichia coli. In the present chapter,the role of Sa concentration in the electroformation of PPy on different alloyssuch as 316L SS, Ti-6Al-4V, Nitinol, and AZ91D is investigated. The obtainedcorrosion protection of the coatings was analyzed in Ringer or artificialsaliva solutions and the role of Sa in immobilizing metals on PPy matrix forantibacterial properties was also studied.