Epoxy resin-based ultrafine dry powder coatings for implants

Ultrafine dry powder coating technology creates biocompatible polymeric coatings for implants. Nanoparticles (nTiO₂) modify flow to prevent agglomeration and create homogenous coatings. Since polyester-based coatings require the potentially harmful 1,3,5-triglycidyl isocyanurate (TGIC) curing agent, this study's objective was to develop alternative TGIC-free formulations. Epoxy and epoxy/polyester (1:1) hybrid mixtures were enriched with CaO (5% w/w) and nTiO₂ (0.5% w/w), as functional additives and flow modifiers, respectively. Epoxy-TiO₂ and Hybrid-TiO₂ mixtures were prepared with micron-sized TiO₂ (25% w/w) to enhance biocompatibility. Polymer chips and additives were combined in a high-shear mixer and passed through a sieve (35 µm) to yield ultrafine particles that were sprayed (20 kV) onto metal sheets and cured (200 °C). Particle size analyses showed that all formulations were ultrafine (D 0.5 < 35 µm), and epoxy/polyester/TiO₂ mixtures were the smallest (D 0.5 = 16.34 µm). Angles of repose, avalanche and resting indicated reduced flowability when epoxy was enriched with TiO₂ and/or polyester, although all formulae were highly flowable. Elemental mapping of coatings showed a predominance of carbon (C) and oxygen (O) from resin polymer, and elevated titanium (Ti) in the TiO₂ enriched surfaces. However, calcium (Ca) clusters were higher on the epoxy/polyester Hybrid coatings. Optical microscopy showed human mesenchymal cells (ATCC CRL-1486) attached and spread out, and Alizarin Red staining showed mineral deposits in 2–4 week cultures, particularly on epoxy/polyester/TiO₂ Hybrid surfaces. These epoxy resin-based formulations were effective TGIC-free substitutes for ultrafine dry powder coatings on implants.