In the field of regenerative medicine, one of the current areas of interest involves the use of scaffolding-like materials that a patient's own cells can be "seeded" onto. As the cells grow and populate the material, they gradually replace it, until all that remains is a solid piece of tissue or bone. Now, scientists at Houston's Rice University have taken that concept a step further, using a polymer that is liquid at room temperature, but that solidifies into a scaffold when injected into patients' bodies.

The Rice team created a hydrogel containing a polymer known as poly(N-isopropylacrylamide), which has also recently been put forward as a "reversible glue" for temporarily sealing eye injuries while patients are in transit. As long as it's kept below body temperature, the polymer remains in a liquid state. Once heated by the body, however, it becomes a semi-solid.

The scientists envision the gel being injected into the body in areas where bone has been lost to injury or disease. As it solidifies, it will fill the void, providing a scaffold for cells from the adjacent natural bone to grow into.

In the case of some other "thermogelling polymers," however, they expel their own water content while solidifying. This causes them to shrink to as little as one-third their original size, thus negating their whole void-filling function. The team got around that problem by adding chemical cross-linkers to the gel. These stabilize the material, keeping it from shrinking as it sets.

As an added benefit, the bonds formed by the cross-links are gradually degraded by alkaline phosphatase, which occurs in high levels when new bone is being formed. This means that as natural bone grows into the material, the material itself will disintegrate to make way for the bone. It's believed that the rate of degradation could be tweaked to allow for different bone growth rates, as they vary between individuals and different parts of the body.

A paper on the research was recently published in the journal Biomacromolecules.

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