Mesenchymal stem cell-loaded thermosensitive hydroxypropyl chitin hydrogel combined with a three-dimensional-printed poly(ε-caprolactone) /nano-hydroxyapatite scaffold to repair bone defects via osteogenesis, angiogenesis and immunomodulation

Chitin-derived hydrogels are commonly used in bone regeneration because of their high cell compatibility; however, their poor mechanical properties and little knowledge of the interaction between the materials and host cells have limited their practical application. Methods: To evaluate osteoinductivity and enhance the mechanical properties of a newly synthesized thermosensitive hydroxypropyl chitin hydrogel (HPCH), a mesenchymal stem cell (MSC)-encapsulated HPCH was infused into a three-dimensional-printed poly (ε-caprolactone) (PCL)/ nano-hydroxyapatite (nHA) scaffold to form a hybrid scaffold. The mechanical properties and cell compatibility of the scaffold were tested. The interaction between macrophages and scaffold for angiogenesis and osteogenesis were explored in vitro and in vivo. Results: The hybrid scaffold showed improved mechanical properties and high cell viability. When MSCs were encapsulated in HPCH, osteo-differentiation was promoted properly via endochondral ossification. The co-culture experiments showed that the hybrid scaffold facilitated growth factor secretion from macrophages, thus promoting vascularization and osteoinduction. The Transwell culture proved that MSCs modulated the inflammatory response of HPCH. Additionally, subcutaneous implantation of MSC-encapsulated HPCH confirmed M2 activation. In situ evaluation of calvarial defects confirmed that the repair was optimal in the MSC-loaded HPCH + PCL/nHA group. Conclusions: PCL/nHA + HPCH hybrid scaffolds effectively promoted vascularization and osteoinduction via osteogenesis promotion and immunomodulation, which suggests promising applications for bone regeneration.