Spongy polymer developed to fill holes in bones

The shape-memory polymer is soft when heated, but turns stiff as it cools
The shape-memory polymer is soft when heated, but turns stiff as it cools
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The shape-memory polymer is soft when heated, but turns stiff as it cools
The shape-memory polymer is soft when heated, but turns stiff as it cools

Whether they're the result of injuries, surgery or birth defects such as cleft palate, missing sections of bone in the skull or jaw can certainly affect someone's appearance. Although there are some methods of filling in such gaps, they have limitations that limit their application. A newly-developed foam-like material, however, may be able to succeed where other approaches have failed.

Usually, bone defects in the head, face or jaw are filled using either bone harvested from another part of the patient's body (such as the hip), or a material such as bone putty.

Harvested bone must be carved to fit into the hole, and ensuring a good fit can be difficult given the rigid consistency of the material. Additionally, complications can arise at the site from which the bone was taken. Putty is certainly more malleable, although it can become brittle once it sets, and its non-porous structure doesn't allow the body's adjacent bone cells to grow into it.

Created by a Texas A&M University team led by Dr. Melissa Grunlan, the new material is what's known as a shape-memory polymer or SMP. It's made from linked molecules of poly(ε-caprolactone), which is described as "an elastic, biodegradable substance that is already used in some medical implants." It's also coated in a sticky polymer called polydopamine.

When heated to 140ºF (60ºC), the SMP becomes soft and spongy, and can easily be pushed in to fill gaps in bone. As it cools to body temperature, however, it reverts to its usual stiff consistency. This essentially locks it into the hole, plus the polydopamine helps anchor it by inducing the formation of a mineral that is naturally found in bone.

Once the SMP is in place and solidified, its porous structure provides a scaffolding for the patient's own bone cells to grow into – a process that the scientists believe may be aided by the polydopamine. Also, because the material is biodegradable, the idea is that over time it will be entirely replaced by natural bone. In these ways, it's quite similar to scaffolding-like materials being developed at institutes such as Rice University, the University of Southampton, and the Fraunhofer Institute for Laser Technology.

The Texas A&M SMP has already been tested in vitro, with animal tests and human trials planned to take place down the road. Grunlan and her team presented their research this week at the 248th National Meeting & Exposition of the American Chemical Society.

Source: ACS

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