Mechanical properties and cytocompatibility of dense and porous Zn produced by laser powder bed fusion for biodegradable implant applications

In this work, the macrotexture of dense Zn produced by laser powder bed fusion (LPBF) was studied and the mechanical properties for different tensile bar orientations were measured. The compressive strength of LPBF Zn scaffolds with five different unit cells was measured for a relative density of 20-51%. In addition, the response of mesenchymal stem cells to the LPBF Zn scaffolds was studied. The elastic modulus and yield strength of dense LPBF Zn were 110.0 +/- 0.2 GPa and 78.0 +/- 0.4 MPa, respectively in the vertical and 81.0 +/- 0.4 GPa and 55.0 +/- 0.7 MPa in the horizontal direction. This could be explained by the preferential orientation of the < 0001 > direction in the building plane. For LPBF Zn scaffolds, the plateau stress for the different unit cells varied between 8 and 33 MPa for a 30% relative density. Calcein staining, lactate production and DNA measurements over a 13-day period showed that mesenchymal stem cell viability was low for Zn scaffolds. This work forms a basis for further research into the LPBF texture formation of metals with hexagonal crystal structure, guides implant designers in scaffold unit cell and relative density selection and motivates further research into the cytocompatibility of LPBF Zn. Statement of Significance Laser powder bed fusion (LPBF) is a manufacturing technology which allows the seamless combination of porous and non-porous volumes in a metallic implant and is used in the orthopedic manufacturing industry today. The production of highly dense Zn with LPBF has been described earlier, but the mechanical properties of the resulting material have not been studied in detail yet. This study is the first to report on (i) the influence of different scanning strategies on the macrotexture of dense LPBF Zn and the resulting anisotropy of its mechanical properties, (ii) the relationship between the relative density and strength for LPBF Zn scaffolds with five different unit cells and (iii) the in vitro response of mesenchymal stem cells to these scaffolds. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.