Evaluating the Cytotoxicity of Commercial Materials for Additive Manufacturing of Soft Tissues

The rapid growth of additive manufacturing technologies continues to drive the commercial development of standardized materials to streamline the process. Despite the growing range of available materials, few still achieve a balance between flexibility and biocompatibility. Here, we evaluated the cytotoxicity of Formlabs Biomed Elastic 50A, Biomed Flexible 80A, and Biomed Durable resin using normal human dermal fibroblasts and human mesenchymal stromal cells. The sol fraction of the crosslinked and uncrosslinked materials was measured to determine the amount of leachable components in the polymer network. Following ISO 10993-5 guidelines, cytotoxicity was evaluated through direct, indirect, or extract testing for 24 h. All three materials did not elicit a cytotoxic response when assessed through fluorescence imaging and LDH assay. In each test, cells showed similar viability as cells cultured with a known noncytotoxic control, polycaprolactone, and showed significantly higher viability compared to a cytotoxic control, a polyurethane film containing 0.1% zinc diethyldithiocarbamate (ZDEC). Post-processing parameters were shown to minimize the effects of cytotoxicity when post-treated with an isopropyl alcohol wash, UV post-curing, or ethanol sterilization. Overall, the Formlabs Biomed Elastic 50A, Biomed Flexible 80A, and Biomed Durable resins were shown to exhibit minimal cytotoxicity after printing and post-processing. Further, the presented findings can be adapted to standardize in vitro testing of a wide range of commercial photocurable resins for tissue-interfacing parts.