Investigation of bone matrix composition, architecture and mechanical properties reflect structure-function relationship of cortical bone in glucocorticoid induced osteoporosis.

Glucocorticoid induced osteoporosis (GIOP) is the most common negative consequence of long-term glucocorticoid treatment, leading to increased fracture risk followed by loss of mobility and high mortality risk. These biologically induced changes in bone quality at molecular level lead to changes both in bone matrix architecture and bone matrix composition. However, the quantitative details of changes in bone quality - and especially their link to reduced macroscale mechanical properties are still largely missing. In this study, a mouse model for glucocorticoid-induced osteoporosis (GIOP) was used to investigate mechanical and material alterations in bone cortex (natural nanocomposite) at different scale. By combining quantitative backscattered electron (qBSE) imaging, nanoindentation and high brilliance synchrotron X-ray nanomechanical imaging on a genetically modified mouse model of GIOP, we were able to quantify the local indentation modulus, mineralization distribution and the alterations of nanoscale structures and deformation mechanisms in the mid-diaphysis of femur, and relate them to the macroscopic mechanical changes. Our results showed clear and significant changes in terms of material quality of bone at nanoscale and microscale, which manifests itself in development of spatial heterogeneities in mineralization and indentation moduli across the bone organ, with potential implications for increased fracture risk.

Effect of Hatch Spacing on Melt Pool and As-built Quality During Selective Laser Melting of Stainless Steel: Modeling and Experimental Approaches.

In this study, a combined simulation and experimental approach is utilized to investigate the influence of hatch spacing on the microstructure and as-built quality of 316L stainless steel (SS) samples fabricated by selective laser melting (SLM). A three-dimensional finite element model (FEM) is employed to investigate heat transfer and melt pool during the SLM of 316L SS. The phase transformation and variation of the thermo-physical properties of the materials are considered in this model. The effects of hatch spacing (H) on the temperature field, microstructure and melt pool size, overlap rate, surface quality, and relative density during the SLM of 316L SS are investigated. The simulated results indicate that, as the hatch spacing increases, the depth increases and the width of the melt pool decreases. Meanwhile, with the increase of hatch spacing, the simulated temperature of the subsequent tracks falls below the melting temperature of the first track. Moreover, the microstructures were found to coarsen with the increasing hatch spacing due to the reduced cooling rate. The optimized hatch spacing and overlap rate between adjacent tracks were obtained from numerical simulations. Simulation results illustrate that, when the optimized hatch spacing of 100 µm is adopted, fully dense parts with a smooth surface can be fabricated by SLM, thus experimentally validating the simulation results.