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Return to Story: Regional Focus: Biodegradable Implants Support Bone Growth
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Research on the implants is being performed by a collaborative, interdisciplinary team from Ruhr-University Bochum and the Duisburg-Essen University. Adapting existing research on titanium implants, the group seeks to develop techniques to accurately shape and implant the biodegradable materials. Once perfected, the procedure could be used to treat cranial defects resulting from osseous tumours, infectious lesions, traumatic injury, and congenital deformities—conditions that are now treated using prefabricated titanium implants.
Although titanium can be precisely formed and made biocompatible, the implants are merely tolerated by the body. Biodegradable implants, on the other hand, would dissolve completely in less than two years. Composed of inner and outer layers, “the implant’s inner structure would be replaced with bone in the first 12 months after surgery,” explains researcher Michael Wehmöller, who has researched implants at Ruhr-University since 1994.
Through the use of bone morphogenetic protein-2 (BMP-2), the most powerful of the osseous morphogenetic proteins, the body can accept the total degeneration of implants. Once the outer layer of the implant loses its structural function—approximately 18 months after surgery—the resulting bone growth would be strong enough to preserve the skull’s structural integrity.
In addition to its aesthetic value, the procedure would minimize the need for additional surgeries; and because the implants are replaced with natural bone, it is possible that they would be suitable for children who are still growing. If the material were implanted in growing children, the newly formed bone would be likely to grow at the same rate as the surrounding bone to maintain structural support in the skull, according to Wehmöller. “This is my gut instinct, and has not yet been observed,” he adds.
The research is still in a preliminary phase. “We cannot say if everything will work as we have imagined, but the first results of our research are extremely encouraging,” Wehmöller says. The group’s first experiment demonstrated the effectiveness of the implants in eight 12-month-old sheep. Surgical templates were used to create artificial skull defects that measured 4.5 ×6.5 cm. Composed of polylactides, calcium phosphate, and calcium carbonate, the implants are prepared in a single mould using a combination of processing techniques. Using robots, the defects were filled with the implants. At 2-, 9-, 12-, and 18-month intervals, the animals were examined using CT-scans, autopsy, and microscopy. Through the use of BMP-2, the formation of new bone in the dural layer of the meninges corresponded to the degradation of the porous inner layer of the implants. With the skull contour stabilized by the compact outer layer of poly-L-lactide, the experiment supported the feasibility of bioimplants greater than 20 cm diam in size for individual craniectomy and cranioplasty.
Wehmöller stresses that more research must be completed before the procedure can be used widely. “The research project is planned to last four years,” he explains. “A parallel or subsequent clinical trial will be needed for general approval.” Although the implants cannot be mass-produced, Wehmöller feels that the procedure should capture the attention of the med-tech industry: “The implants definitely have potential to profit the field of medical technology, because of the demand for new technology to fabricate implants to custom specifications.”
