Polyvinylidene fluoride (PVDF) as a biomaterial: From polymeric raw material to monofilament vascular suture

Abstract

This study identified the effects of various manufacturing processes on the crystalline microstructure, mechanical properties, and biocompatibility of a polyvinylidene fluoride (PVDF) suture. To achieve this, changes in the crystalline microstructure and the tensile behavior of PVDF monofilaments were monitored in vitro after different thermal processing, coloration, and sterilization treatments. In addition, the in vivo biocompatibility of the manufactured and sterilized PVDF suture was assessed by using it to anastomose a preclotted polyester vascular prosthesis as a thoracoabdominal bypass in a series of dogs. The tissue response was followed by histologic and scanning electron microscopy over implantation periods ranging from 4 h to 6 months. Differential scanning calorimetry and infrared spectroscopy (FTIR-ATR) showed that thermal processing and the addition of a coloring agent had a direct effect on modifying the crystalline microstructure and hence changing the mechanical properties. For example, thermal processing converted some of the alpha phase into the beta and gamma polymorphs, whereas coloration led only to a major increase in the beta-to-alpha ratio. The tensile properties were found to be optimized when the relative proportion of the beta and gamma phases combined compared to the alpha form gave rise to an FTIR A509/A532 absorption ratio between 4.0 and 4.5. Sterilization was found to cause some modifications to the crystalline microstructure near the surface of the monofilaments, but it did not change their mechanical properties. Pathologic examination of the anastomotic regions after different periods of implantation revealed a minimal cellular response, with no mineralization, intimal hyperplasia, or excessive fibrous tissue reaction. This good biocompatibility, together with other desirable characteristics such as ease of manipulation and satisfactory mechanical strength, makes PVDF an attractive alternative monofilament suture material for cardiovascular surgery.