Developing non-fouling and lubricious surface coatings for orthopedic implants
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Foreign body response (FBR) remains a persistent challenge limiting the longevity of medical devices. Upon implantation, non-specific protein adsorption on the implant surface can trigger FBR and result in fouling. This necessitates frequent replacements and surgical procedures. Biological host responses are influenced primarily by atomic-scale surface properties like wettability, roughness and cytotoxicity. This dissertation introduces robust and versatile surface modification techniques designed to suitably alter these properties to enhance biocompatibility, applicable to commercially available, industrial-strength materials used in orthopedic implants. Chemical modification via introduction of zwitterionic molecules is a proven strategy that greatly alters the thermodynamics of surface protein adsorption through strong interfacial hydration effects. This reduces non-specific protein adsorption and enhances surface lubricity through robust hydration layers and fluidity of adhered water. The techniques demonstrated herein use poly (sulfobetaine methacrylate) (pSBMA) due to its low cost and ease of synthesis relative to other zwitterionic molecules. In grafting these species on to implant surfaces, we leverage versatile chemical modification methods based on RFGD plasma and ARGET ATRP. The first part of this work thus focuses on surface modification protocols that involve surface activation using RFGD plasma deposition of HEMA, followed by macro-initiator covalent coupling and grafting pSBMA using ARGET ATRP (method 1). Next, we introduce a solvent free initiator for ARGET ATRP (method 2). A highly reactive bromoester, M3BP is deposited on the surface using RFGD plasma and used as initiator for synthesizing pSBMA coatings. Polyurethane and titanium are used as model substrates to demonstrate the versatility of these techniques. This dissertation also details the performance evaluation of the fabricated coatings, including quantification of surface composition, wettability, protein adsorption and lubricity, in addition to in vitro and in vivo studies. Surfaces prepared using methodology 1 achieve a 93% reduction in albumin adsorption and 95% reduction in the friction coefficients relative to bare surfaces. They are chemically robust, non-cytotoxic, and show good in vivo performance in mice and chicken models. Surfaces prepared using methodology 2 also exhibit comparable results for both protein adsorption and friction coefficients, while providing an alternative ARGET ATRP initiator chemistry that does not require harsh solvents and is compatible with various materials irrespective of surface chemistry or geometry. These results signify the potential of these techniques for substantially improving biocompatibility and represent a proof-of-concept for simple and reproducible surface modification techniques with applicability at scale, serving a critical complementary function in maximizing the longevity and performance of orthopedic implants.
- Chemical engineering