Seven million people suffer bone fractures annually in the U.S. Musculoskeletal conditions cost $215 billion/year. These numbers are increasing dramatically as the population ages. Calcium phosphate cement (CPC) can be molded and set in-situ to form hydroxyapatite, is osteoconductive, and can be resorbed and replaced by new bone. However, the low strength of CPC limits its use to non-stress locations. The parent grant investigates compositional and microstructural tailoring to improve injectability, strength and resorption;optimizes chitosan content;develops non-rigid CPC with high-strain and anti-washout;models growth factor release as a function of pore volume fraction and time;and performs animal study on CPC resorption and the effects of microstructural design, and animal study on bone regeneration and the effects of single and multiple growth factors and MSCs delivered. However, the parent grant does not include the use of electrospun nanofibers, nor human umbilical cord mesenchymal stem cells (hUCMSCs). The objectives of this competitive revision supplement are to: (1) Develop novel, injectable nanofiber-CPC scaffolds with increased load-bearing capability and enhanced stem cell attachment and function for bone repair;(2) establish relationships between nanofibers and scaffold properties, and between nanofibers and stem cell attachment, proliferation, differentiation, and in vivo bone regeneration;(3) determine whether hUCMSCs are more superior than adult bone marrow-derived hMSCs in bone regeneration, when delivered via nanofiber-CPC scaffold. Aim 1 will develop electrospun nanofiber-CPC as injectable, load-bearing, and bioactive scaffold. Aim 2 will study the effect of nanofiber-CPC scaffold on hMSC and hUMCSC proliferation and differentiation. Aim 3 will investigate the effects of hMSC and hUCMSC delivery via nanofiber-CPC on bone regeneration in animal model. This project is expected to demonstrate, for the first time, that hUCMSCs delivered via novel nanofiber-CPC scaffold are more superior in osteogenesis and bone regeneration, than bone marrow-derived hMSCs. These findings will potentially have a highly significant impact on stem cell-based tissue engineering and future clinical treatments. The new injectable, strong and macroporous nanofiber-CPC scaffolds with stem cell and growth factor delivery are expected to have a wide range of dental, craniofacial and orthopedic applications, with greatly enhanced bone regeneration to improve the health and quality of life for millions of people. PUBLIC HEALTH RELEVANCE: This project will develop the first injectable, moderate load-bearing, macroporous, bone-mimicking nanofiber-apatite scaffolds with stem cell and multiple growth factor delivery, and will study bone regeneration in animal model. Potential applications include dental, craniofacial and orthopedic repairs. They include maxillofacial reconstruction using the moldable scaffold to achieve shaping and esthetics, and minimally-invasive surgeries such as filling and strengthening osteoporotic bone lesions at risk for fracture, with greatly enhanced bone healing and regeneration to improve the health and quality of life for millions of people.