PVA-based polymers as coatings for soft tissue implant

INTRODUCTION Rapid progress in the biomedical field has contributed to the development of biocompatible materials. However, for implant, the interface between the device and human body can be critical. In fact, the performance of a material, in a biological environment, is conditioned by both its surface properties and the combination of physico-chemical and mechanical properties that are required for a specific application. To improve the properties of materials in biomedical applications and allow a better interaction of the medical device with the biological system surrounding it, often, polymeric coatings are applied. A successful coating must be biocompatible, non-toxic and sterilizable, have sufficient mechanical properties, be durable under conditions of use and adhere to the device. Many methods have already been used to enhance adhesion, including plasma treatment, surface functionalization, mechanical roughening and the use of a primer applied between the substrate and polymer coating. Hydrophilic coatings, prepared using polymers with functional groups able to absorb water, such as amino, hydroxyl or carboxyl groups, are widely used to produce coatings on metallic or plastic substrates. Interestingly, coatings based on hydrogels can provide additional advantages such as good biocompatibility, good wetting and low friction. Their soft nature makes them excellent candidates as coating for soft tissue implants. The aim of this study is to evaluate the adhesion properties of poly(vinyl alcohol) (PVA)/gelatin blends and poly(vinylalcohol-co-acrylic acid) P(VA-co-AA) copolymers for their potential use as polymer coatings. EXPERIMENTAL METHODS PVA and gelatin (gel) solutions, blended at 80/20 weight ratio, were physically crosslinked after eight freezing-thawing cycles in order to obtain stable hydrogels. P(VA-co-AA) copolymers were prepared in our labs by radical polimeriization in water, starting from vinyl acetate and acrylic acid monomers. Samples of P(VA-co-AA) both in film form and hydrogel were obtained by casting solution or freezing/thawing method, respectively. The P(VA-co-AA) films were then crosslinked by thermal treatment (DHT). A series of samples was prepared after deposition on metallic supports. The physico-chemical and mechanical characterization was performed using DSC, FT-IR Chemical Imaging and DMA. Adhesion durability of the support was evaluated after immersion of the coating/support in water at room temperature, the day number before delamination was measured. RESULTS AND DISCUSSION Thermal analysis, performed on dried samples, showed no substantial differences of melting temperature for both samples in film or hydrogel form with respect to pure PVA. Enthalpy values resulted significantly lower than for both samples and both forms. The values of elastic modulus measured in wet condition resulted for all the samples in the range of values of soft tissues (0.5-2MPa). FT-IR Chemical Imaging showed a homogeneous coating of the samples deposited on the support (Fig 1). Fig 1. Optical image, chemical map and spectrum of the PVA-gel coating Durability test showed a better coating adhesion for the samples in film form with respect to gel samples (Fig 2). In particular, the highest value of durability was measured for the copolymer in form of film. Fig 2 Durability results for PVA-based samples CONCLUSION The preliminary results suggest a possible use of the synthetised copolymer as primer to improve the adhesion between PVA-based hydrogel on metallic support. ACKNOWLEDGMENTS The authors would like to thank the MIUR-MISE-Regione Toscana (Bando PAR FAS 2007-2013 Linea d'Azione 1.1 -Azione 1.1.2 BANDO FAS SALUTE 2014) for financial support.