Engineering 3D in vitro Models to Mimic the Impact of Aging on Delayed Bone Healing and Inflammation

Aging is accompanied by a decline in the ability to heal bone injuries, which poses a public health risk, as the elderly are more likely to sustain bone injuries. Understanding how aging affects mesenchymal stem cells (MSCs) and macrophages—key players in bone healing—can guide the development of treatments to address this decline. However, existing modalities to study bone healing in the context of aging each have flaws: animal models are expensive and lack tunability, while 2D cultures lack physiological relevance and fail to capture in vivo cellular behavior. Tissue-engineered 3D models, which use biomaterials to replicate physiological environments, provide a cost-effective and tunable alternative. However, no such model exists to study bone healing in the context of aging. This study seeks to establish a 3D in vitro model that can recapitulate key features of bone healing in the context of aging. Macroporous microribbon hydrogels were used as a scaffold to culture primary mouse MSCs and macrophages taken from young and aged mice. MSC osteogenic potential was assessed through mineralization and matrix deposition, while macrophage inflammatory polarization was evaluated via ELISA for inflammatory cytokines and qPCR for inflammatory markers. The model recapitulated age-related declines in MSC osteogenic potential, increased macrophage inflammatory polarization, and the impact of aging on stem cell-immune cell crosstalk and circulatory signaling on MSC osteogenesis and macrophage inflammation. This novel model provides a physiologically relevant platform to mechanistically study the effects of aging on bone healing and evaluate potential therapeutic strategies.