Simultaneous nano- and microscale structural control of injectable hydrogels via the assembly of nanofibrous protein...

Injectable hydrogels are advantageous as tissue regeneration scaffolds, as they can be delivered through a minimally invasive injection and seamlessly integrate with the target tissues. However, an important shortcoming of current injectable hydrogels is the lack of simultaneous control over their micro- and nanoscale structures. In this article, the authors report a strategy for developing injectable hydrogels that integrate a fibrous nanostructure and porous microstructure. The hydrogels are prepared by using novel nanofibrous microparticles as the building blocks. The protein based nanofibrous microparticles, fabricated by a spray freezing technology, can be injected through a syringe-needle system. A cell-compatible photocuring process can be deployed to connect the microparticles and form a mechanically robust hydrogel scaffold. The inter-particle voids combined to form the interconnected micropores and the diameter of the nanofibers (100-300 nm) closely mimics that of the native extracellular matrix. Compared to the non-porous hydrogels and non-fibrous hydrogels, the microparticle annealed nanofibrous (MANF) hydrogels potently enhance the osteogenic-marker expression (ALP, Runx2, OCT and BSP) and mineralization of human mesenchymal stem cells in vitro. MANF hydrogels also facilitate cell infiltration and enhance neovasculization in a subcutaneous implantation model in vivo. The capacity of MANF hydrogels to promote bone regeneration is investigated in a calvarial bone repair model. MANF hydrogels demonstrate significant higher bone regeneration after 8 weeks, indicating the significant role of microporosity and nanofibrous architecture in bone regeneration.