Hybrid Coatings Based on Polyvinylpyrrolidone/Polyethylene Glycol Enriched with Collagen and Hydroxyapatite: Incubation Studies and Evaluation of Mechanical and Physiochemical Properties

Coating materials offers an intriguing solution for imparting inert implants with additional bioactive characteristics without changing underlying parameters such as mechanical strength. Metallic implants like endoprostheses or polymeric implants can be coated with a thin layer of bioactive film capable of stimulating bone-forming cells to proliferate or release a drug. However, irrespective of the final implantation site of such a coating biomaterial, it is necessary to conduct detailed mechanical and physicochemical in vitro analyses to determine its likely behavior under biological conditions. In this study, polymeric and composite coatings with hydroxyapatite obtained under UV light underwent incubation tests in four different artificial biological fluids: simulated body fluid (SBF), artificial saliva, Ringer's fluid, and water (as the reference fluid). The potentiometric and conductometric properties, sorption capacity, and degradation rate of the coatings were examined. Furthermore, their hardness, modulus of elasticity, and deformation were determined. It was demonstrated that the coatings remained stable in SBF liquid at a pH value of around 7.4. In artificial saliva, the greatest degradation of the polymer matrix (ranging between 36.19% and 39.79%) and chipping of hydroxyapatite in the composite coatings were observed. Additionally, the effect of ceramics on sorption capacity was determined, with lower capacity noted with higher HA additions. Moreover, the evaluation of surface morphology supported by elemental microanalysis confirmed the appearance of new apatite layers on the surface as a result of incubation in SBF. Ceramics also influenced mechanical aspects, increasing hardness and modulus of elasticity. For the polymer coatings, the value was 11.48 ± 0.61, while for the composite coating with 15% ceramics, it increased more than eightfold to a value of 93.31 ± 11.18 N/mm². Based on the conducted studies, the effect of ceramics on the physicochemical as well as mechanical properties of the materials was determined, and their behavior in various biological fluids was evaluated. However, further studies, especially cytotoxicity analyses, are required to determine the potential use of the coatings as biomaterials.