Additively manufactured stochastic and gyroid scaffold design towards osseointegration and bone regeneration in a rabbit femur model

The design of scaffolds has evolved overtime from simple geometries such as non-porous structures to more advanced lattice-based structures such as triply periodic minimal surfaces (TPMS). This evolution brought along better response to implants in terms of compatibility and promotion of cell ingrowth. The use of novel designs like stochastic designs, impart the user with the ability to locally control the porosity of the scaffold and thus fine tune its functional and structural properties like stiffness and porosity gradient. Stochastic structures with locally controlled porosity better replicate the microstructural complexity of natural tissues. In this paper, the versatility of the stochastic scaffold design approach was tested by mimicking the porosity gradient of a bone in all three axes (labelled as uniaxial, biaxial and triaxial) and successfully printing them using multiple different 3D printing processes. These designs were then tested for cell viability in vitro and since all functionally graded scaffolds along with the relatively simpler uniform porosity design displayed positive results, the stochastic scaffold with uniform porosity was selected for in vivo studies involving a rabbit femur model along with a solid cylinder and gyroid TPMS structure as controls. The titanium alloy samples used for in vivo testing were evaluated for their mechanical properties which were in the range of the native trabecular bone and supported statistically significant cell growth. The scaffolds elicited minimal immune responses in vivo on implantation in rabbits and effectively supported bone growth and integration without significant adverse effects. While the performance differences between porous designs were minimal, the stochastic scaffolds demonstrated slightly superior scores and staining results compared to gyroid scaffolds.