Tailoring of cellular mechanical microenvironments to rescue age-related impairments in bone regeneration

Aging impairs both the responsiveness of bone cells to mechanical loading and the success of bone healing following injury. Growing evidence indicates that these two phenomena are related: local mechanical cues present in the cellular microenvironment (“mechanical microenvironment”) regulate numerous aspects of bone healing, including recruitment and osteoblastic differentiation of marrow stromal cells (MSCs). Importantly, studies by multiple groups of investigators have indicated that aged cells remain mechanosensitive, but require higher stimulus magnitudes. Therefore, the focus of this project is on directly manipulating the mechanical microenvironment during bone healing, via customization of the architecture of additively manufactured (AM), osteoinductive, bioceramic scaffolds, in order to identify how the cellular responses to local mechanical cues differ with age. The hypothesis of this work is that tailoring of cellular mechanical microenvironments through advanced AM scaffold design can rescue age-related impairments in bone regeneration. This work builds on preliminary data demonstrating use of an innovative AM method to print mechanically robust ceramic scaffolds of exceptionally tunable architectures with high porosity (>80%) and pore sizes large enough to facilitate vascularization and osteogenesis in vivo. In Aim 1, we will compare the osteogenic responses of young (12-week-old) vs. mature (77-week-old) vs. aged (104-week-old) murine MSCs to the mechanical microenvironment within mechanically loaded scaffolds in vitro. The local mechanical cues present in these scaffolds will be determined using finite element modeling and mechanical testing, and the cellular responses evaluated using a novel combination of techniques including spatial assessment of the progression of osteogenesis at the single-cell level. Aim 2 will leverage these analytical tools as well, and will compare the bone regeneration responses to tailored mechanical microenvironments within scaffolds implanted in young and aged mice. Together, these two aims address an area of high clinical need and will fill critical gaps in knowledge regarding age-related changes in bone mechano- responsiveness during healing. The outcomes of this work will lay the foundation for a new generation of bone repair technologies that can accommodate alterations in cell behavior with aging and harness cell mechano-sensitivity to promote osteogenic differentiation, bone tissue formation, and ultimately, restoration of bone function following injury.