Skull putty
Repairing bones might one day be as easy as applying putty. Lutolf et al. edge closer to this goal with a type of bone-healing matrix, consisting of a few peptides, some polyethelyne glycol and a bone morphogenic protein (BMP). BMPs induce the differentiation of bone progenitor cells, but when administered in solution, BMPs quickly dissipate. To build a BMP-infused scaffold, the researchers covalently linked polyethylene glycol to two peptides: an integrin-binding motif to attract cells to the scaffold, and a substrate for matrix metalloproteinase, an enzyme secreted by fibroblasts. The investigators then infused this scaffold with BMP-2. Migration of cells into the scaffold prompted cleavage of the metalloproteinase substrate – which weakened the scaffold. This weakening caused release of BMP-2, prompting bone formation, they report in the May 1 Nature Biotechnology. The technique efficiently regenerated bone in a rat model of cranial healing. Eventually, the entire scaffold degraded, replaced with bone. In principle, such a scaffold could incorporate different types of proteins, for medical applications such as repair of tissues other than bone.
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