Porous structured metallic implants are preferable as bone graft substitutes due to their faster tissue integration mediated by bone in-growth and vascularization. The porous scaffolds/implants should also mimic the graded structure of natural bone to ensure a match of mechanical properties. This article presents a method for designing a graded porous structured acetabular implant and identifies suitable parameters for manufacturing the model through additive manufacturing. The design method is based on slice-wise modification to ensure continuity of gradation. Modification of the slices was achieved through the binary image processing route. A geodesic dome-type design was adopted for developing the acetabular cup model from the graded porous structure. The model had a solid shell with the target porosity and pore size gradually changing from 65% and 950 µm, respectively, in the inner side to 75% and 650 µm, respectively, towards the periphery. The required dimensions of the unit structures and the combinations of pore structure and strut diameter necessary to obtain the target porosity and pore size were determined analytically. Suitable process parameters were identified to manufacture the model by Direct Metal Laser Sintering (DMLS) using Ti6Al4V powder after carrying out a detailed experimental study to minimize the variation of surface roughness and warping over different build angles of the strut structures. Dual-contour scanning was implemented to simplify the scan strategy. The minimum diameter of struts that could be manufactured using the selected scanning strategy and scanning parameters was found to be 375 µm. Finally, the model was built and from the micro-CT data, the porosities and pore sizes were found to be closely conforming to the designed values. The stiffness of the structures, as found from compression testing, was also found to match with that of human trabecular bone well. Further, the structure exhibited compliant bending-dominated behaviour under compressive loading.

Nickel-Titanium alloy (Nitinol) is an excellent shape memory alloy (SMA) for Micro electro-mechanical systems (MEMS) particularly in biomedical applications owing to its three excellent features like shape memory effect (SME), superelasticity, and biocompatibility. The fabrication of micro features on Nitinol SMAs through conventional machining has been challenging due to its temperature-dependent material transformation properties. Micro electrochemical machining (micro-ECM), a nonconventional machining method for conductive material irrespective of strength and hardness has the potential for microfeature fabrication on Nitinol. This study presents the investigation on electrochemical dissolution behavior of Nitinol in different electrolytes for micro-ECM. The in uence of electrolytes on the nature of dissolution of Nitinol has been studied by fabricating microchannels in three levels of parameters containing applied voltage and electrolyte concentration. The rst three electrolytes were all aqueous neutral electrolytes i.e. sodium chloride (NaCl), sodium nitrate (NaNO 3 ), and sodium bromide (NaBr). For profound analysis of dissolution behavior and its in uence on machining performance, potentiodynamic polarization (PDP) tests of Nitinol were performed in aqueous NaCl, aqueous NaNO 3, and aqueous NaBr solutions. The PDP tests that are conducted here are cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The three aqueous solutions were utilized for microchannel fabrication in Nitinol through micro ECM in three levels of parameters out of which aqueous NaNO 3 was successful in fabricating microchannel. Then nonaqueous electrolyte of ethylene glycol-based NaNO 3 has been used to fabricate microchannels with lower depth overcut (DOC), width overcut (WOC), and length overcut (LOC) with respect to aqueous NaNO 3 electrolyte.

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