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Implant

In order for an implant designed and fabricated in this way to be available for general clinical use, a number of important questions must be answered. One of these questions relates to biocompatibility - will the body react adversely to the material and will the device serve its intended function? The choice of hydroxyapatite was made in part because of its successful use in a number of clinical applications. Its long-term compatibility with body tissue in these applications is now well-established. Its chemical similarity to the natural mineral of bone makes it an attractive candidate for our research.

The task of developing a device for bone replacement in the mandible carries with it the additional requirement of high strength. The pressure transmitted through the teeth to the mandible during chewing can exceed 400 pounds per square inch. Consequently we have designed the scaffold for this application to exceed the strength of the natural bone it replaces. Current research is directed toward understanding the change in strength that occurs as the scaffold is broken down over time in the body and is built up by ingrowth of new bone tissue. The purpose is to ensure that adequate strength is maintained throughout the period of bone remodeling.


Credit: Dr. Russ Jamison, Materials Science and Engineering, University of Illinois at Urbana-Champaign

For laboratory testing we use model scaffolds like that shown here in
order to precisely control the conditions. The diameter of each rod in
this image is approximately 300 microns.

 

The encouragement of ingrowth of bone and vascular tissue into the scaffold is in fact an essential function of the device at the microscopic level. It is known that bone cells attach to hydroxyapatite surfaces (a property known as “osteoconductivity”). Our research is directed to understanding the ways in which these cells migrate and attach to the scaffold. We do this by studying scaffolds of various designs immersed in “simulated body fluid” in the laboratory. An example is shown below.

Credit: Dr. Russ Jamison, Materials Science and Engineering, University of Illinois at Urbana-Champaign

Test scaffolds are seeded with bone cells in the laboratory
using simulated body fluid. The cells in this picture are too
small to be seen.

 

We modify the surfaces of the scaffolds during fabrication to influence these “cell-scaffold” interactions. The example shown below demonstrates that bone cells attach to the scaffold surfaces in distinctive ways according to surface characteristics of the scaffold. Of particular interest now is the influence of micron-scale porosity that we create during fabrication on cell attachment and function.

Credit: Dr. Russ Jamison, Materials Science and Engineering, University of Illinois at Urbana-Champaign

Bone cells attach to scaffolds by extending cell processes to the surface.
In this case the processes engage microscopic pores in the surface
after three days in simulated body fluid.




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