The influence of chemical polishing of titanium scaffolds on their mechanical strength and in-vitro cell response

Abstract

Selective Laser Melting (SLM) is a powder-bed-based additive manufacturing method, using a laser beam, which can be used to produce metallic scaffolds for bone regeneration. However, this process also has a few disadvantages. One of its drawbacks is the necessity of post-processing in order to improve the surface finish. Another drawback lies in the removal of unmelted powder particles from the build. In this study, the influence of chemical polishing of SLM fabricated titanium scaffolds on their mechanical strength and in vitro cellular response was investigated. Scaffolds with bimodal pore size (200 μm core and 500 μm shell) were fabricated by SLM from commercially pure titanium powder and then chemically treated in HF/HNO3 solutions to remove unmelted powder particles. The cell viability and mechanical strength were compared between as-made and chemically-treated scaffolds. The chemical treatment was successful in the removal of unmelted powder particles from the titanium scaffold. The Young's modulus of the fabricated cellular structures was of 42.7 and 13.3 GPa for as-made and chemically-treated scaffolds respectively. These values are very similar to the Young's modulus of living human bone. Chemical treatment did not affect negatively cell proliferation and differentiation. Additionally, the chemically-treated scaffolds had a twofold increase in colonization of osteoblast cells migrating out of multicellular spheroids. Furthermore, X-ray computed microtomography confirmed that chemically-treated scaffolds met the dimensions originally set in the CAD models. Therefore, chemical-treatment can be used as a tool to cancel the discrepancies between the designed and fabricated objects, thus enabling fabrication of finer structures with regular struts and high resolution.