Abstract
INTRODUCTION: There is an ever-evolving need of customized, anatomic-specific grafting materials for bone surgery. More specifically, biocompatible and osteoconductive materials, that may be reconfigured in shape dynamically through the application of an external stimulus. The objective of this study was to assess – 1) the biocompatibility of gel-cast Poly-D, L-lactic acid (PLA)/β-Tricalcium Phosphate (TCP), 2) the material’s rheological properties (for 3D printing via Direct Inkjet Writing (DIW)), 3) the shape memory characteristics of 3D printed constructs. The purpose of this study was to establish a basis for the development of DIW based Shape Memory Polymer Ceramic Composites (SMPCC) for potential use in bone regenerative applications through minimally invasive treatment modalities.METHODS: SMPCC gels of PLA (Mw = 160 kDa) and β-TCP were prepared of different w/w ratios (100/0, 90/10, 80/20, 70/30, 60/40 and 50/50), through polymer dissolution in acetone (15% w/v). Biocompatibility was analyzed through Presto Blue assays, Osteoblast differentiation and successive calcification was quantified through Alizarin Red Staining. qPCR was performed to quantify the expression of osteogenic markers (Runx2 and Col). Rule of Mixtures and Finite Element models helped estimate mechanical strength of the materials used in this study. Rheological properties of the gels were measured to determine shear thinning and shape retention capabilities. Gels were then extruded through a custom-built DIW printer. Space filling cuboids of the polymer-ceramic material were printed and subjected to thermomechanical characterization to measure shape fixity (Rf) and shape recovery (Rr) ratios through 5 successive shape memory cycles.RESULTS: A significant increase in cellular viability and calcification were observed with the addition of β-TCP particles within the polymer matrix at all time-points relative to pure (100%) PLA (positive control). The SMPCC colloidal gels exhibited shear thinning capabilities for extrusion through a small orifice. Additionally, SMPCC gels exhibited quick stress relaxation for shape retention immediately post-extrusion through a deposition nozzle. Shape Memory Effect (SME) was observed in the 3D printed space filling cuboids. SME was repeatable up to 4 shape memory effect cycles after which significant permanent deformation was observed in the constructs.CONCLUSION: The DIW technique in conjunction with the polymer dissolution method allowed for 3D printing of SMPCC constructs without the need for thermal loading. The SMPCC were biocompatible and capable of exhibiting SME without a significant loss in thermomechanical properties after being subjected to multiple shape memory cycles. While further research on scaffold macro/micro geometries, and engineered porosities are warranted, this study suggests that the application of this SMPCC material and 3D printing workflow to produce customized, patient specific bone scaffolds/grafts/membranes is feasible. Furthermore, it serves as a steppingstone towards the potential of minimizing damage to the operating site with smaller incisions, lesser pain, shorter hospital stays and fewer complications post-surgery.