Evaluation of a Medical Grade Thermoplastic Polyurethane for the Manufacture of an Implantable Medical Device: The Impact of FDM 3D-Printing and Gamma Sterilization.

Three-dimensional printing (3DP) of thermoplastic polyurethane (TPU) is gaining interest in the medical industry thanks to the combination of tunable properties that TPU exhibits and the possibilities that 3DP processes offer concerning precision, time, and cost of fabrication. We investigated the implementation of a medical grade TPU by fused deposition modelling (FDM) for the manufacturing of an implantable medical device from the raw pellets to the gamma (γ) sterilized 3DP constructs. To the authors' knowledge, there is no such guide/study implicating TPU, FDM 3D-printing and gamma sterilization. Thermal properties analyzed by differential scanning calorimetry (DSC) and molecular weights measured by size exclusion chromatography (SEC) were used as monitoring indicators through the fabrication process. After gamma sterilization, surface chemistry was assessed by water contact angle (WCA) measurement and infrared spectroscopy (ATR-FTIR). Mechanical properties were investigated by tensile testing. Biocompatibility was assessed by means of cytotoxicity (ISO 10993-5) and hemocompatibility assays (ISO 10993-4). Results showed that TPU underwent degradation through the fabrication process as both the number-averaged (Mn) and weight-averaged (Mw) molecular weights decreased (7% Mn loss, 30% Mw loss, p < 0.05). After gamma sterilization, Mw increased by 8% (p < 0.05) indicating that crosslinking may have occurred. However, tensile properties were not impacted by irradiation. Cytotoxicity (ISO 10993-5) and hemocompatibility (ISO 10993-4) assessments after sterilization showed vitality of cells (132% ± 3%, p < 0.05) and no red blood cell lysis. We concluded that gamma sterilization does not highly impact TPU regarding our application. Our study demonstrates the processability of TPU by FDM followed by gamma sterilization and can be used as a guide for the preliminary evaluation of a polymeric raw material in the manufacturing of a blood contacting implantable medical device.

The effect of hydration on the material and mechanical properties of cellulose nanocrystal-alginate composites.

Alginate is commonly used in the form of hydrogels in biomedical applications. It is known to be highly sensitive to liquid exposure and can degrade or solubilize easily. This study attempts to improve the mechanical and material properties in various humidity conditions and in liquid immersion of thin alginate films with the addition of unmodified and oxidized cellulose nanocrystals (CNCs, CNC-Ts). CNCs and CNC-Ts were added to alginate composites in varying amounts, and the material and mechanical properties were measured in dry, humid, and liquid conditions. It was shown that the properties can be enhanced with the addition of nanocellulose as tested by liquid uptake, and mechanical testing. These results suggest that the addition of TEMPO-oxidized nanocellulose crystals improves the performance and longevity of alginate when exposed to phosphate buffer solution (PBS) compared to deionized water. This improved performance was shown to have a limited effect on the adhesion of mesenchymal stem cells (MSCs) to the surface of the nanocomposites.