Fig. 4.

Photo images of 3D PCL-incorporated STH structures injected by a multineedle injecting system. a) A customized multineedle injecting device that can continuously and simultaneously inject multiple hydrogel types through the single head system. Each hydrogel syringe can be independently actuated by a separate pump. b–d) Stiffer hydrogels to deliver osteogenic cells (7STH50+PCL, blue) and softer hydrogels to deliver endothelial cells (6STH50+PCL, red) could be injected from the 3D injecting device without physical clogging, in both individual (b, c) and simultaneous (d) modes. e) Injected PCL incorporated STHs were sufficiently stable to maintain their dual-layer structures in an aqueous system. f–j) PCL-incorporated STHs could completely fill the complex empty spaces, including triangle, square, and star shaped void structures that were formed in transparent PDMS substrates. k–l) By using a porcine bone, we demonstrated that our injectable bone implant material could fill the defect sites of bone with any size and shape. Panels k and l show photo images of defect site in the porcine bone before and after injecting dual-layer structured STH, respectively.