Shape-changing material for filling bone defects

In a breakthrough, researchers have developed a "self-fitting" material that expands with warm salt water to precisely fill bone defects and also acts as a scaffold for new bone growth.

To develop a better material, the researchers made a shape-memory polymer (SMP) that moulds itself precisely to the shape of the bone defect without being brittle.

It also supports the growth of new bone mass.

The team made a porous SMP foam resembling a stiff sponge, with many interconnected pores to allow bone cells to migrate in and grow.

Upon heating to 60 degrees Celsius, the SMP becomes very soft and malleable.

"During surgery to repair a bone defect, a surgeon could warm the SMP to that temperature and fill in the defect with the softened material," said Melissa Grunlan from Texas A&M University.

"Then, as the SMP is cooled to body temperature, it would resume its former stiff texture and 'lock' into place," she noted.

The researchers also coated the SMPs with polydopamine, a sticky substance that helps lock the polymer into place by inducing formation of a mineral that is found in bone.

"It may also help osteoblasts, the cells that produce bone, to adhere and spread throughout the polymer. The SMP is biodegradable, so that eventually the scaffold will disappear, leaving only new bone tissue behind," Grunlan explained.

Currently, the most common method for filling bone defects in the head, face or jaw is autografting.

The problem is that the autograft is a rigid material that is very difficult to shape into irregular defects.

To test whether the SMP scaffold could support bone cell growth, the researchers seeded the polymer with human osteoblasts.

After three days, the polydopamine-coated SMPs had grown about five times more osteoblasts than those without a coating.

The team described their approach at the 248th national meeting and exposition of the American Chemical Society (ACS) this week.