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Cooking Up Bone Replacement
Illustrations by Jennifer Fairman
Each year, birth defects, trauma or surgery leave some 200,000 people in the United States in need of replacement bones in the head or face. Traditionally, the best treatment required surgeons to remove part of a patient’s fibula, cut it into the general shape needed and implant it in the right location. But this procedure not only creates leg trauma but also falls short—because the relatively straight fibula can’t be shaped to fit the subtle curves of the face very well.
This has led researchers like biomedical engineer Warren Grayson to look to 3-D printing, or so-called additive manufacturing, which creates 3-D objects from a digital\computer file by piling on successive, ultrathin layers of materials. The process excels at making extremely precise structures—including anatomically accurate ones—from plastic, but “cells placed on plastic scaffolds need some instructional cues to become bone cells,” says Grayson. “The ideal scaffold is another piece of bone, but natural bones can’t usually be reshaped very precisely.”
So he and his team set to work whipping up a new “recipe” for replacement bone, reported last spring in ACS Biomaterials Science & Engineering. By following this recipe, you’ll end up with composite material that combines the strength and printability of plastic with the biological “information” contained in natural bone.
A. 8 grams pulverized natural bone (from about 4 cow knees)
B. 19 grams polycaprolactone (PCL), biodegradable polyester
C. 24 milliliters fibrinogen with adipose-derived stem cells
D. 6 milliliters thrombin
E. Nutritional broth
Once you’ve got the hang of cooking up bone replacement, you can give it a try. For first-time cooks, it’s best to start with mice.
Voila! By implanting your new scaffolding laden with stem cells, the mice should experience new bone growth in their mandible—at least 50 percent more bone growth after 12 weeks, compared to a scaffold made with pure PCL.
The amount of growth varies, says Grayson: “In our experiments, the 70 percent scaffold encouraged bone formation much better than the 30 percent scaffold, but the 30 percent scaffold is stronger. Since there wasn’t a difference between the two scaffolds in healing, we are investigating further to figure out which blend is best overall.”