زهرا گرگین کرجی

Enhanced bone tissue regeneration and improved osseointegration are among the most important goals in design of multi-functional orthopedic biomaterials. In this study, we used additive manufacturing (selective laser melting) to develop multi-functional porous nitinol that combines superelasticity with a rationally-designed micro-architecture and biofunctionalized surface. The rational design based on triply periodic minimal surfaces aimed to properly adjust the pore size, increase the surface area (thereby amplifying the effects of surface bio-functionalization), and resemble the curvature characteristics of trabecular bone. The surface of Additively Manufactured (AM) porous nitinol was bio-functionalized using polydopamine-immobilized rhBMP2 for better control of the release kinetics. The actual morphological properties of porous nitinol measured by micro-computed tomography (e.g. open/close porosity, and surface area) closely matched the design values. The superelasticity originated from the austenite phase formed in the nitinol porous structure at room temperature. Polydopamine and rhBMP2 signature peaks were confirmed by XPS and FTIR tests. The release of rhBMP2 continued until 28 days. The early-time and long-term release profiles were found to be adjustable independent of each other. In vitro cell culture showed improved cell attachment, cell proliferation, cell morphology (spreading, spindle-like shape), cell coverage as well as elevated levels of ALP activity and increased calcium content for bio-functionalized surfaces as compared to as-manufactured specimens. The demonstrated functionalities of porous nitinol could be used as a basis for deployable orthopaedic implants with rationally designed micro-architectures that maximize bone tissue regeneration performance by release of biomolecules with adjustable and well-controlled release profiles. Keywords: Shape memory alloys, additive manufacturing, Biomimetic topology, osteogenic coatings, and controlled re