Eggshell-based polymer helps implants fuse with living bone tissue
Scientists at the National University of Science and Technology Center for Composite Materials (NUST MISIS) in Russia are developing a new bioactive polymer-ceramic composite derived from common eggshells that can be used to treat skull injuries and other surgical bone procedures.
Bone is so common that it's easy to take for granted, but that doesn't mean that it isn't a remarkable material. One piece of evidence for this is that after over a century of intense effort, scientists haven't been able to come up with a synthetic version for surgical applications that works as well as the original.
A simple example of this is in cases where a section of the cranium needs to be replaced because of a fracture, or because of a congenital defect that leaves part of the skull dangerously thin, the usual procedure is to replace the damaged or defective section of bone with one made out of metal, plastic, or ceramic. But none of these are really up to the job.
Part of the problem is mechanical. The artificial plate may be too soft or too brittle, too pliable or too stiff, liable to altering its shape as temperatures change, or hard to shape and fit properly. Another is that most of these materials are bioinert. That is, they don't interact with living tissue. This is intentional because surgeons don't want to put implants in peoples' bodies that may cause infections or suffer tissue rejections. Unfortunately, it also means that these implants can't really become a part of the body and act more like a natural component.
To overcome this, the NUST MISIS team looked at a synthetic polymer called polymethylmethacrylate (PMMA) that is commonly used as a bone cement because of its strength and self-curing properties. Unfortunately, PMMA is less than optimal because it's bioinert, but the team changed this by adding a silicate bioceramic called diopside that is derived from eggshells.
According to the team, the diopside is relatively nontoxic, biodegradable, and can stimulate the growth of bone tissue in its vicinity, so the implant can eventually fuse with the bone instead of being merely cemented to it.
"Eggshells have health benefits such as bone mineralization and growth, treatment of osteoporosis and are therefore used as a bone graft," says Inna Bulygina, a iPhD student in Biomaterial Science at NUST MISIS. "We have adopted a cost-effective approach to recycling biowaste to improve the quality of life for patients with bone disease. For the production of composites, diopside obtained from eggshells was used."
The team produced a porous composite PMMA/diopside material by means of a solvent casting method, where a thermoplastic polymer is formed by repeatedly dipping a mold into a solution of the polymer, leaving layers of film behind. Different samples of the material were produced with 25, 50 and 75 percent proportions of diopside used.
"The samples containing 50 percent diopside have shown the best result – they have demonstrated a four-fold increase in compressive strength, and after four weeks of in vitro testing have shown a good ability to deposit bone minerals on their surface," says Rajan Choudhary, a postdoc student. "At the same time, we have found that the mechanical properties of the obtained porous composites correspond to the properties of the spongy bone of the human body."
The research was published in the Journal of Asian Ceramic Societies.