We've actually been hearing a lot about "bioscaffolds" lately.
In a nutshell, they're three-dimensional pieces of biocompatible material that are implanted within the body, and that have a microstructure similar to that of the surrounding tissue. Over time, cells from that tissue migrate into the scaffold, colonizing it and reproducing. Eventually, they entirely replace the material, forming pure muscle, bone, cartilage or other tissue.
That said, pre-producing such bioscaffolds and then implanting them in muscle is quite challenging. With that in mind, scientists at the University of Connecticut developed a prototype handheld 3D printer to do the job.
It starts by depositing a gelatin-based hydrogel directly into the unwanted gap within the muscle. An integrated ultraviolet light causes that gel to cure into a bioscaffold made up of tiny muscle-like fibers, which readily adheres to the adjacent muscle tissue – no sutures are required. Muscle cells then move into the scaffolding.
In lab tests, the device proved to be effective at treating volumetric muscle loss injuries in mice.