(I-632) Mechanobiology At Work: Analysis of Surface Characteristic Induced by Physiological Load-induced Deformation of 3D Printed Truss Elements and Osteogenic Response of Mesenchymal Stem Sells
Director of Biomechanics Research Massachusetts General Hospital Newton, Massachusetts, United States
Introduction: Proprietary build themes have been developed to create a hierarchical surface roughness on a Ti truss-based implant using an Electron Beam Melting (EBM) technology. Given that MSCs respond to cues from their mechanical environment, this study evaluated how surface features influence MSC morphology, adhesion, clustering, and osteogenic differentiation.
Methods: Three different Ti hierarchical surface roughnesses were fabricated using the EBM: 1) Smooth Titanium (Smooth), and two proprietary 3D-printed (P3D) titanium surfaces, which consist of a hierarchical surface roughness that spans from the macro to nano-scale having lesser 2) P3D1 or greater 3) P3D2 surface roughness. Both 2D and 3D scan images showed the irregular 3D peaks and valleys on the P3D1 and P3D2.
Results: In static culture, as results of analysis by the areal method, P3D1 and P3D2 have similar surface roughness, and the height distribution of P3D2 is sharper compared with P3D1. Both cell area and aspect ratio were significantly lower on the P3D1 and P3D2 surfaces, compared to cells on smooth titanium, and RT-PCR analysis of BM conditions showed that COL-I was more highly expressed on smooth surfaces than on rough surfaces, while OCN expression was higher on the rough surfaces. Based on finite-element modeling and analysis, tensile strain distribution varied as expected across the surface of the material, with the distribution only slightly altered based on roughness (P3D2). High cell viability on the P3D2 surface was confirmed under the application of cyclic tensile strain. Dynamic loading enhanced all osteogenic gene expression compared to static culture conditions. BMP2 expression was considerably higher than the static baseline, with a significant increase between DLx1 and DLx2, while ALP, Runx2 and OPN showed amplified expression on DLx1 and leveled off after DL×2. Compared to the static control, OCN expression was higher with each loading event.
Conclusion : Here, when hMSCs were seeded on the rough Ti surfaces and exposed to physiologic dynamic loading, these loading events amplified the osteogenic expression indicating synergistic effects of the material microenvironment on differentiation and the macro environment through strain distribution enabled by the truss design. Future work will investigate how these mechanically primed cells enhance bone formation in vivo.
