The state of the art in tissue engineering generally involves some form of biodegradable gel scaffolding material, a supply of patient-matched cells to populate that scaffold, and the delivery of a mix of proteins to induce growth and steer cells towards other desired behaviors. This effort to regrow sections of the skull is an example of the type:
A team of researchers repaired a hole in a mouse's skull by regrowing "quality bone," a breakthrough that could drastically improve the care of people who suffer severe trauma to the skull or face. The work was a resounding success, showing that a potent combination of technologies was able to regenerate the skull bone with supporting blood vessels in just the discrete area needed without developing scar tissue - and more rapidly than with previous methods. Injuries or defects in the skull or facial bones are very challenging to treat, often requiring the surgeon to graft bone from the patient's pelvis, ribs, or elsewhere. But if all goes well with this new approach, it may make painful bone grafting obsolete.
In the experiment, the researchers harvested skull cells from the mouse and engineered them to produce a potent protein to promote bone growth. They then used a hydrogel, which acted like a temporary scaffolding, to deliver and contain these cells to the affected area. It was the combination of all three technologies that proved so successful. Using calvaria or skull cells from the subject meant the body didn't reject those cells. The protein, BMP9, has been shown to promote bone cell growth more rapidly than other types of BMPs. Importantly, BMP9 also appeared to improve the creation of blood vessels in the area. Being able to safely deliver skull cells that are capable of rapidly regrowing bone in the affected site, in vivo as opposed to using them to grow bone in the laboratory, which would take a very long time, promises a therapy that might be more surgeon friendly, and not too complicated to scale up for the patients.
The scaffolding is a material based on citric acid and called PPCN-g, is a liquid that when warmed to body temperature becomes a gel-like elastic material. "When applied, the liquid, which contains cells capable of producing bone, will conform to the shape of the bone defect to make a perfect fit. It then stays in place as a gel, localizing the cells to the site for the duration of the repair. As the bone regrows, the PPCN-g is reabsorbed by the body. What we found is that these cells make natural-looking bone in the presence of the PPCN-g. The new bone is very similar to normal bone in that location. A reconstruction procedure will be a lot easier when you can harvest a few cells, make them produce the BMP9 protein, mix them in the PPCN-g solution, and apply it to the bone defect site to jump-start the new bone growth process where you want it."