Melt blending of poly(lactic acid) with biomedically relevant polyurethanes to improve mechanical performance.

Minimally invasive surgery procedures are of utmost relevance in clinical practice. However, the associated mechanical stress on the material poses a challenge for new implant developments. In particular PLLA, one of the most widely used polymeric biomaterials, is limited in its application due to its high brittleness and low elasticity. In this context, blending is a conventional method of improving the performance of polymer materials. However, in implant applications and development, material selection is usually limited to the use of medical grade polymers. The focus of this work was to investigate the extent to which blending poly-l-lactide (PLLA) with low contents of a selection of five commercially available medical grade polyurethanes leads to enhanced material properties. The materials obtained by melt blending were characterized in terms of their morphology and thermal properties, and the mechanical performance of the blends was evaluated taking into account physiological conditions. From these data, we found that mixing PLLA with Pellethane 80A is a promising approach to improve the material's performance, particularly for stent applications. It was found that PLLA/Pellethane blend with 10% polyurethane exhibits considerable plastic deformation before fracture, while pure PLLA fractures with almost no deformation. Furthermore, the addition of Pellethane only leads to a moderate reduction in elongation at yield and yield stress. In addition, dynamic mechanical analysis for three different PLLA/Pellethane ratios was performed to investigate thermally induced shape retention and shape recovery of the blends.

Micro Injection Molding of Drug-Loaded Round Window Niche Implants for an Animal Model Using 3D-Printed Molds.

A novel approach for the long-term medical treatment of the inner ear is the diffusion of drugs through the round window membrane from a patient-individualized, drug-eluting implant, which is inserted in the middle ear. In this study, drug-loaded (10 wt% Dexamethasone) guinea pig round window niche implants (GP-RNIs, ~1.30 mm × 0.95 mm × 0.60 mm) were manufactured with high precision via micro injection molding (µIM, Tmold = 160 °C, crosslinking time of 120 s). Each implant has a handle (~3.00 mm × 1.00 mm × 0.30 mm) that can be used to hold the implant. A medical-grade silicone elastomer was used as implant material. Molds for µIM were 3D printed from a commercially available resin (TG = 84 °C) via a high-resolution DLP process (xy resolution of 32 µm, z resolution of 10 µm, 3D printing time of about 6 h). Drug release, biocompatibility, and bioefficacy of the GP-RNIs were investigated in vitro. GP-RNIs could be successfully produced. The wear of the molds due to thermal stress was observed. However, the molds are suitable for single use in the µIM process. About 10% of the drug load (8.2 ± 0.6 µg) was released after 6 weeks (medium: isotonic saline). The implants showed high biocompatibility over 28 days (lowest cell viability ~80%). Moreover, we found anti-inflammatory effects over 28 days in a TNF-α-reduction test. These results are promising for the development of long-term drug-releasing implants for human inner ear therapy.