Mimicking Nature: Effect of Architectural Design Inspired by Cancellous Bone on the Biological Response of hMSC Cultured on Titanium Scaffolds Fabricated by Laser Beam Powder Bed Fusion.

Bone tissue regeneration can be affected by various architectonical features of 3D porous scaffold, for example, pore size and shape, strut size, curvature, or porosity. However, the design of additively manufactured structures studied so far was based on uniform geometrical figures and unit cell structures, which often do not resemble the natural architecture of cancellous bone. Therefore, the aim of this study was to investigate the effect of architectonical features of additively manufactured (aka 3D printed) titanium scaffolds designed based on microtomographic scans of fragments of human femurs of individuals of different ages on in vitro response of human bone-derived mesenchymal stem cells (hMSC). Four different types of titanium scaffold (33Y, 48Y, 56Y, and 63Y, where the number indicates the age of the individual) were fabricated using laser beam powder bed fusion (PBF-LB) and characterized with respect to the dimensional features, permeability, and stiffness. hMSC were seeded onto the scaffolds and MTS, DNA, alkaline phosphatase, and alizarin red assays were used to study cell viability, proliferation, and osteogenic differentiation. Microcomputed tomography revealed that the largest average pore size was in scaffolds 63Y (543 ± 200 μm), which was nearly twice as large as the smallest pores in scaffolds 56Y. Moreover, scaffolds 63Y exhibited the highest porosity (~61%), while the other architectures had porosity of ~43%-44%. Scaffolds 63Y also had the lowest surface area-to-volume ratio (11.07 ± 0.05 mm), whereas scaffolds 56Y had the highest (14.80 ± 0.06 mm). Furthermore, scaffolds 33Y had the largest strut size (398 ± 124 μm), exceeding the size in scaffolds 56Y (the smallest strut size) by over 1.5 times. CFD simulations indicated that the hydraulic permeability was the highest for scaffolds 63Y (5.24 × 10 m; order of magnitude higher than in the other architectures). Stiffness of the investigated scaffolds, determined by finite element modeling, ranged from ~29 GPa (63Y) to ~60 GPa (56Y). This study demonstrates that the highest manufacturing accuracy in 3D printed structures based on architectural designs inspired by cancellous bone could be achieved when the structures were characterized by moderate strut sizes, the largest pores, and the highest porosity and permeability. The scaffold with the highest porosity and permeability (i.e., 63Y) yielded the lowest cell retention. Regarding the osteogenic differentiation, a correlation was found between the mineralization of the deposited extracellular matrix and the hydraulic permeability, pore size, and surface area-to-volume ratio but not the porosity.