Cell membrane (CellMem) coating has emerged as a biomimetic strategy to modify polymeric nanoparticles for drug delivery applications. Compared to using individual ligands, CellMem coating has unique advantages in biomimicry by borrowing the entire ligand repertoire contained in the cell membrane. Our lab has recently explored combining CellMem coating with macroporous scaffolds for enhancing tissue regeneration via immunomodulation. We demonstrated that coating of macroporous gelatin microribbon (µRB) scaffolds with CellMem from primed mesenchymal stem cells (pMSCs) induced regenerative immune response and enhanced bone healing in a mouse disease model. While our previous study demonstrates the promise of CellMem-coated µRB scaffolds for regeneration, it was limited to using cells from young donors and in a young disease model, yet patients needing therapies are mostly aged population. Aging is known to be associated with excessive inflammation and delayed healing. As such, the goal of this proposal is to determine optimal CellMem coating for enhancing bone regeneration in aging via targeting immunomodulation and to elucidate how varying CellMem coating modulates MSC/immune cell crosstalk. We propose to use allogeneic CellMem isolated from young donors due to their more abundant supply and more potent functionality than CellMem from aged donors. We choose CellMem from pMSCs and M1 Mφ due to their immunomodulatory functions and ability to scavenge inflammatory cytokines, respectively. We hypothesize that varying the ratio of MSC/ Mφ CellMem coating will modulate Mφ polarization and MSC osteogenesis in vitro. We further hypothesize that cells from young and aged donors would require a different optimal ratio of CellMem coating. To test these hypotheses, we will assess the effects of varying ratios of CellMem coating on individual cell types and MSC/immune cell crosstalk in vitro using cells from young and aged donors. We devised a tri- culture model (MSC/ Mφ/T cells) to better mimic the complex cellular crosstalk in vivo. Lead formulations that result in robust bone formation in the tri-culture model will be validated in vivo using young and aged mouse critical-sized bone defect models. Our team has a long track record of productive collaborations and this project will integrate our complementary expertise in biomaterials, immunology, bone biology, aged animal models, tissue engineering, mass cytometry, and single-cell sequencing. This project will pioneer the translation of CellMem- coated scaffolds for enhanced regeneration in aging and elucidate the underlying mechanisms through the use of a tri-culture model and high-dimensional assays.