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Focus on Safety:
Biomechanical Impacts on Sterilized Allograft Bio-implants
A number of studies have been conducted regarding the effects of sterilization on bio-implants. For example, studies have shown that uncontrolled gamma irradiation of freeze-dried or hydrated samples at room temperature negatively affects biomechanical tissue properties. In contrast, irradiated deep-frozen bone allografts seem to be less brittle than similar grafts irradiated at room temperature. Tissue banks have incorporated this finding into the development of improved sterilization methods for allograft tissue and now carry out sterilization at low temperatures.
Allowash XG® sterilization and its biomechanical effect
There is another component in complete sterilization: Allowash XG, a patented and proprietary sterilization process that removes greater than 99 percent of bone marrow and blood elements from the internal bone matrix. But how does it affect the biomechanical properties of bio-implants?
Soft Tissue Sterilization
In one research study, soft tissue grafts were examined after processing with Allowash XG, which includes a terminal sterilization step on dry ice. Several graft types were divided into groups, one of which was gamma irradiated at a targeted absorbed dose of 18 kGy, which is the sterilizing dose for Allowash XG. Allowash-processed (non-irradiated) grafts served as experimental controls. The tensile strength of fascia lata, anterior tibialis tendons, and semitendinosis tendons irradiated at both the target absorbed doses was statistically comparable to the matched grafts in the control group. The tensile strength of patellar ligaments irradiated at the target absorbed dose of 18 kGy was likewise statistically comparable to the matched controls.
Donor Age as a Variable
In another study based on donor age, tensile testing was performed on tendons that were randomly assigned to a single-strand or double-strand configuration. Both non-irradiated and gamma-irradiated tissue were evaluated, and no statistically significant differences were observed for ultimate load to failure, stiffness, stress, or displacement at failure for single strand tibialis tendons between Allowash-processed (non-irradiated) and Allowash XG-processed (gamma-irradiated) tissue.
Structural Effects
Separate studies on the mechanical strength of structural bio-implants observed that, among all three VertiGraft® bio-implant types, no statistically significant differences were found between irradiated and control grafts when tested in axial compression and compressive shear. And in studies of large, durable load-bearing grafts, the results for all three types tested (25 mm femoral rings, 14 mm cancellous dowels, and 20 mm fibular segments) revealed no statistically significant difference between gamma-irradiation sterilized and non-irradiated tissue.
Conclusion
Taken as a whole, peer-reviewed literature, pre-clinical testing, and clinical outcome data all indicate that, when performed under controlled conditions regarding temperature as well as irradiation dose setting, the Allowash XG process does not adversely affect the biomechanical properties of tissues needed for their intended clinical applications.
To read the complete, annotated white paper summarizing these results, please click here.
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