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.

Ingredients

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
F. Beta-glycerophosphate

Directions

1. Start by mixing PCL, a biodegradable polyester used in making polyurethane (FDA-approved for other clinical uses), with increasing amounts of “bone powder,” made by pulverizing the porous bone inside cow knees after stripping it of cells. For best results, ensure that the percentage of bone powder falls somewhere between 30 and 70 percent by mass of the overall mixture. Mix well.

2. Next, it’s time to create the shape you need for your scaffold by using a 3-D printer to print your own scaffold. Heat the bone powder/ PCL mixture until the PCL melts. Once the mixture is pliable, extrude it using a nozzle to create a scaffold in the shape of the mandible bone you want to create.

3. Now it’s time to begin growing new bone! Suspend the stem cells in fibrinogen (the “liquid” version of fibrin). Just before seeding the cells, mix thrombin with the cells/fibrinogen, and then immediately seed that mixture onto the scaffold. (The thrombin causes the fibrinogen to turn from a liquid to a gel in about 30 seconds—it gels just after seeding the scaffolds, becoming fibrin—which helps hold the cells in place so that they do not pass through the pores of the scaffold.)

4. Now immerse your seeded scaffold in a beaker of nutritional broth (lacking pro-bone ingredients). Important: Be sure to include beta-glycerophosphate in your broth. This accelerates calcification and will enable the enzyme alkaline phosphatase to deposit calcium phosphate, the primary mineral in bone.

5. After three weeks, your new bone is nearly complete! It will show gene activity higher in three genes indicative of bone formation compared to cells grown on pure PCL scaffolds.

6. With the help of the beta-glycerophosphate, the cells on your scaffold will produce much more calcium per cell: 30 percent more calcium per cell on a scaffold using a 30 percent bone powder mixture, and twice as much calcium per cell on a scaffold using a 70 percent bone powder mixture.

Serving Suggestions

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.”