- A method is needed to enable cortical bone allografts to be sterilized with radiation without detriment to their mechanical properties and biointegration
- Massachusetts General hospital researchers incorporated vitamin E into large, structural allografts as a radioprotectant through diffusion and supercritical carbon dioxide homogenization
- The resulting grafts had superior mechanical properties, cytocompatibility and host bone–allograft unionization rates compared with allografts that were only irradiated
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In the U.S., about half of bone grafting procedures make use of cadaveric bone allografts, which can be contaminated with bacteria and viruses. Sterilization of these allografts is often done with ionizing radiation, which can reduce its mechanical strength and delay its union with the host bone.
To improve the mechanical properties of irradiated cortical bone allografts, Jeremy V. Suhardi, MD, a former student at Massachusetts General Hospital, and Ebru Oral, PhD, associate director of biomaterials in the Harris Orthopedic Laboratory at Mass General, and colleagues propose using vitamin E as a radioprotectant. They describe their method in the Journal of Biomedical Materials Research, Part B: Applied Biomaterials.
Study Rationale and Methods
Vitamin E is a natural antioxidant whose main biological role is to prevent oxidation of cell membranes through free radical scavenging. The researchers' hypothesis was that vitamin E would protect bone by sparing collagen cross-links from scission by free radicals.
They compared samples of bovine tibia that were only irradiated with samples that were treated with vitamin E using one of three methods:
- Method 1: Immersion in vitamin E emulsion for two weeks
- Method 2: Immersion in vitamin E for six hours, followed by homogenization in supercritical carbon dioxide for 24 hours to increase the rate of vitamin E diffusion
- Method 3: Immersion in genipin, a collagen cross-linking agent, for two weeks followed by method 2
The researchers also extracted bone from 15 rats, treated five samples with each of the three methods and implanted them into other rats.
Sterilization: The vitamin E–treated allografts did not interfere with radiation-mediated killing of bacteria.
Potential for tissue damage: Compared with irradiated-only grafts, vitamin E–treated allografts were mechanically stronger and were less cytotoxic to osteoclasts and osteoblasts. Method 3 was no more effective than method 2 in promoting mechanical strength, presumably because vitamin E was so effective in protecting collagen structure that additional cross-linking was unnecessary.
Unionization: In rats, allografts that were vitamin E–treated were faster to integrate with host bone than irradiated-only allografts were.
Incorporating vitamin E into bone allografts through diffusion and supercritical carbon dioxide homogenization is feasible for efficient and uniform radioprotection of bone allografts that will undergo sterilization. The processing of other types of bone grafts, such as cancellous chips, would also be possible with this method, and diffusion times would be even shorter for smaller samples.
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