Machine Design

New bone substitute will be ceramic

Sandia researchers have devised a ceramic prosthetic device that may replace the standard method of bone replacement.

Sandia researcher Joe Cesarano admires the perfect fit of his team's robocasted implant set in the jawbone of a manufactured skull.

The device is a scaffoldlike structure, a layered mesh that's stronger than bone, yet porous enough to let newly grown bone and blood vessels weave their way through it. It's made mainly of hydroxyapatite, a material that's approved by the FDA for bodily implants.

Traditional bone replacement involves removing good bone from one area to replace a damaged section in another. But the Sandia-patented process, called robocasting, eliminates the need to extract good bone as a replacement. A computer-controlled machine dispenses liquefied ceramic pastes to form shapes of varying complexity along a prearranged path. To create simulated bone scaffolding, the machine dispenses a hydroxyapatite mixture in crosslaid slivers each about as thick and as far apart as the diameters of 10 human hairs.

“Bone, blood vessels, and collagen love to grow into a structure with pores of that size (500 microns),” says Sandia scientist Joe Cesarano. “The material becomes a hard-tissue scaffold for promoting new bone growth,” he adds. The paste must be strong enough to set in place without drooping. The scaffolds are set in wax and machined to exactly the right shape by studying CAT scan results.

But while CAT scans accurately delineate diseased material, it doesn't show what the bone would have looked like when it was healthy. This information initially came from a surgeon working with computer programmers to create the dimensions of what was missing. “There is nothing inherently expensive about either the materials or the process,” says Cesarano.

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