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Down to the Bone

February 09, 1999

Although modern medical technology is already well advanced, implants made of synthetic materials can cause problems: they may give rise to rejection reactions or loosen over time because the contact between the surrounding tissue and the implanted material is not good enough. A remarkable procedure developed by a team of chemists working with Horst Kessler of the Technical University of Munich, in cooperation with Merck-Biomaterials GmbH in Darmstadt, could prevent this in the future. They coat the implants with a layer of special peptides, which they adapted from natural models. These specifically attract bone cells, which then settle firmly on the implants.
Bones are not unchanging structures: they are constantly reshaped by bone-building and bone-dissolving cells known as "osteoblasts" and "osteoclasts". In this way, the body adapts to changing stresses. If these cells can be successfully lured onto the surface of a material, they can see to it that it is firmly anchored into the bone structure.
This is where Kessler and his co-workers come in. They use the fact that osteoblasts bear "integrins" on their surface. Integrins are proteins, which have a sort of docking station for other specific proteins; they are comparable to small snap fasteners, which help cells attach themselves to suitable surfaces. The Munich chemists have thus produced protein-like substances that exactly fit the osteoblast docking sites. They then use short molecular chains to attach these substances to the surfaces of sample solids made of the plastic, PMMA (polymethylmethacrylate) - a material often used in operating rooms.
In trials, when the researchers placed their coated plastic in a nutrient solution of osteoblasts, all of the bone cells attached themselves to the synthetic surface and couldn't be removed even by either washing or shaking. Within 22 days, the osteoblasts on the plastic even multiplied by about tenfold. Kessler now hopes that this biological coating can help fit "real" implants made of PMMA more firmly into the natural bone structure. It is also possible that other "healing" cells will be "attracted" by this technique.
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