Hybrid hydrogel based on stereocomplexPDLA/PLLAand gelatin for bone regeneration

Natural bone is a perfect combination of dense shell cortical bone and porous core spongiosa. Inspired by this gradient structure, we prepared a double-layered hydrogel with stereocomplex PDLA-PEG-PDLA and PLLA-PEG-PLLA as the inner porous core and gelatin/nano hydroxyapitite as the outer strengthen shell. Crosslinking of gelatin with natural crosslinker genipin made the shell available for early supporting and the inner physical hydrogel facilitated new bone formation. Successful synthesis of PDLA-PEG-PDLA (or PLLA-PEG-PLLA) was confirmed by(1)H NMR (stands for nuclear magnetic resonance) spectra. The procedure of composite scaffold was monitored with scanning electron microscopy and fourier-transform infrared spectroscopy. In vitro test with mouse preosteoblast MC3T3-E1 cells found that the obtained hybrid hydrogels could improve cell adhesion, proliferation, calcium deposition, and upregulate osteogenesis-related gene expression. Further in vivo experiment on rat calvarial defects also confirmed the capacity of the as-prepared scaffold to accelerate new bone formation. The above data suggested that this core-shell hydrogel helpful for nutrient transportation, bony bridging, and osteoconductivity. But how to control the degradation process of the hydrogel and match with new bone formation still remained challenging.