Effects of Additive Manufacturing and Sterilization on Poly(p-Dioxanone) for Short-Term Application in the Intestinal Environment

Additive manufacturing of patient specific implants made of biodegradable polymers is receiving increasing attention in the medical sector, including the trend towards manufacturing at the point-of-care. Despite this, the changes of the polymer structure and their effects on mechanical properties and degradation behavior caused by the additive manufacturing process and subsequent sterilization are still insufficiently investigated, although of key relevance for the implant's functionality. In this study, poly(p-dioxanone) (PPDO) was processed by fused filament fabrication (FFF). The effects of manufacturing as well as two different low-temperature sterilization techniques, namely H₂O₂ plasma and gamma irradiation, on the polymer structure were evaluated. Additionally, PPDO degradation was investigated by immersing the processed samples in Sorensen's phosphate buffer (PB) with pH = 6.47 for 28 days to mimic implantation in intestinal milieu and evaluated at regular time intervals. Results showed that we were able to successfully print PPDO without influencing the polymer structure or cytocompatibility. No significant changes were detected for plasma-sterilized samples (PS) while gamma-sterilized (GS) ones significantly decreased molecular weight (M_w and M_n) and showed significant lower inherent viscosity (IV) compared with the (non-sterilized) control group after processing. During immersion in PB, a decrease in M_w, M_n, and mechanical strength occurred for all samples. However, GS samples were affected to a much higher extent compared with the other groups both in final values and timeline. A degradation plateau was seen for the tensile strength of NS and PS samples over the first 21 and 17 days, respectively, followed by a steady decrease. In contrast, for the GS samples, a drastic decrease in tensile strength occurred already during the first 14 days. There was no notable mass loss detected within the first 28 days of degradation for any of the sample groups. Based on these results, we conclude that FFF with subsequent plasma sterilization is a reliable process for manufacturing PPDO devices for short-term applications that require stable mechanical conditions within the first weeks of implantation to guarantee the time needed for tissue healing before degrading, as for example, in the case of intestinal compression anastomoses. Such requirement could not be met with gamma sterilization with the dose used, because of the too fast decrease in mechanical properties.