A sponge-like polymer, polycaprolactone (PCL), could be used as a medical material to fill gaps in human bone and serve as a scaffold to promote new bone growth. Injuries, birth defects or removing tumors can create gaps in bone that are too large to heal naturally, and the polymer has the potential to improve upon the two most commonly used procedures to repair these bone gaps.
These two approaches are currently used to fill cranio-maxillofacial bone defects; each have their drawbacks. The first method is autografting, where surgeons harvest bone from somewhere else on the body and try to shape it to fit the bone defect. Melissa Grunlan, Ph.D., the leader of the polymer study, said this method is problematic because it is difficult to shape autografts into the shape of the irregular defects, and harvesting bone for the autograft can create complications in the part of the body where the bone was taken. The second approach is to use bone putty or cement to plug gaps. However, these materials become brittle as they harden, and they lack pores that would allow new bone cells to rebuild the damaged tissue.
Grunlan and her colleagues at Texas A&M University encourage a new approach that involves the use of a nonbrittle shape-memory polymer (SMP) that molds itself precisely to the shape of the bone defect and supports the growth of new bone tissue. The porous SMP foam is made by linking molecules of polycaprolactone, an elastic, biodegradable substance that is already used in some medical implants. The resulting material resembles a stiff sponge, with many interconnected pores that bone cells can migrate to and grow.
When heated to 140 F, the SMP becomes soft and malleable. During surgery to repair a bone defect, a surgeon would warm the SMP to that temperature and fill in the defect with the softened material. As the SMP cools to the body temperature, it returns to its former stiff texture and settles into place. The researchers also coated the SMPs with polydopamine, a sticky substance that helps lock the polymer into place by prompting formation of a mineral found in bone. It may also help osteoblasts, the cells that produce bone, to adhere and spread throughout the polymer. Over time, the biodegradable SMP scaffold eventually disappears, leaving only new bone tissue behind.