Polymer to mend bones

A biodegradable polymer made with green solvents can mend broken thigh bones in mice, UK researchers have shown.

The sponge-like polylactic acid scaffold was coated with vascular endothelial growth factor protein and seeded with human bone marrow cells to mimic the biological factors that stimulate natural bone regrowth. After slowly delivering its contents, the polymer is metabolised by the body leaving no trace.

The breakthrough means the innovative polymer is a step closer to being used in hospitals. According to Richard Oreffo of Southampton University, who works on the team, human trials could be less than 5 years away.

Many researchers are working on similar systems because they promise to avoid the problems of harvesting bone grafts from patients and donors. But a key difficulty is how to make a polymer that's holey and sponge-like, but which also encapsulates a highly expensive and delicate protein or drug inside.

The solution Howdle's team has been developing over the last decade is to use supercritical carbon dioxide - a solvent with properties midway between those of a gas and a liquid. Formed under pressure, the supercritical fluid melts the polymer and allows any delicate protein to be mixed into it just above body temperature. When the pressure is released, carbon dioxide gas foams up this mixture, automatically forming the porous scaffold ready-coated with active drug or protein.