Evaluation of 3D-Printed Biostable and Bioresorbable Elastomeric Thermoplastics for Medical Implant Applications

Abstract

In many instances of soft tissue applications, implants based on compliant polymers have proven to exhibit superior performance over those based on stiffer polymers. Combined with the capability of 3D-printing to create complex structures, many innovative implants based on compliant polymers can be envisioned. However, current literature on 3D-printed compliant polymers is limited. The motivation behind this work is to contribute to the development of 3D-printed biomedical implants that are based on compliant, elastomeric polymer for soft tissue applications. The two aims that comprise this work look to shed light on two particularly sparse areas of study, the fatigue of elastomeric 3D-printed architected structures and the structure-property relationship of 3D-printed bioresorbable elastomeric polymer. The two aims are: 1) to investigate the behavior and durability of 3D-printed polycarbonate urethane (PCU) porous membrane under cyclic loading, and 2) to study the structure-property relationships of 3D-printed poly(L-lactide-co-ε-caprolactone).In the first aim, the mechanical properties of bulk PCU of various grades were first characterized, followed by a comprehensive dimensional and mechanical characterization of 3D-printed PCU membranes of two different pore shapes, square and bowtie. In addition to the PCU membranes, a PCU-PETG laminate membrane were also studied. The strong dependence of bulk 3D-printed PCU’s mechanical properties on its testing environment were first shown via monotonic tensile testing. Tests of samples printed with various raster angles showed differences in the defect tolerance of each PCU grade. Cyclic loading of printed PCU membrane shows a strong dependence of fatigue performance on membrane shape and loading orientation. In certain configurations, PCU membrane exhibited comparable performance to commercial polypropylene mesh. However, the PCU membranes also showed an undesirable ratcheting under cyclic loading. A PCU-PETG laminate membrane was then shown as one approach to minimize ratcheting. In the second aim, the impact of 3D-printing and annealing processes toward PLCL morphology is first evaluated. Then, the hydrolytic degradation profile of both annealed and unannealed 3D-printed PLCL scaffolds is studied. The results show that printed samples were initially fully amorphous. Subsequent aging and annealing process induced significant change in morphology via crystallization and in turn affected its physical properties. However, degradation behavior was largely unaffected by the annealing induced crystallization.In summary, we first demonstrated the potential of PCU membranes for use in prolapse mesh application by evaluating their mechanical properties, particularly their fatigue behavior. Then, we demonstrated the structure-property relationship of 3D-printed PLCL scaffolds, with a focus on the impact of the fabrication process on degradation behavior. The results shown here should contribute well to further development of elastomeric 3D-printed implant devices.