Hydrogel that degrades as new bone tissues are formed

In what could ease the process of bone engineering, researchers at Rice University have created a hydrogel that instantly turns from liquid to semi-solid at close to body temperature - and then degrades at precisely the right pace.

The gel shows potential as a bioscaffold to support the regrowth of bone and other three-dimensional tissues in a patient's body using the patient's own cells to seed the process.

"This research describes the development of a novel thermogelling hydrogel for stem cell delivery that can be injected into skeletal defects to induce bone regeneration and that can be degraded and eliminated from the body as new bone tissue forms and matures," said Antonios Mikos, a professor at Rice University in the US.

A problem with thermogelling polymers is that once they harden, they begin to collapse and then force out water, said Brendan Watson, a graduate student at Rive University.

That process, known as syneresis, defeats the purpose of defining the space doctors hope to fill with new tissue.

The researchers solved the problem by adding chemical cross-linkers to the gel's molecules.

"These chemical crosslinks are attached by phosphate ester bonds, which can be degraded by catalysts - in particular, alkaline phosphatase - that are naturally produced by bone tissue," Watson said.

The catalysts are naturally present in your body at all times, in low levels. But in areas of newly-formed bone, they actually get to much higher levels, he added.

"So what we get is a semismart material for bone-tissue engineering. As new bone is formed, the gel should degrade more quickly in that area to allow even more space for bone to form," Watson said.

The study appeared in the journal Biomacromolecules.