Synergetic effect of freeze-drying and gamma irradiation on the mechanical properties of human cancellous bone

Abstract

Freeze-drying and irradiation are common process used by tissue banks to preserve and sterilize bone allografts. Freeze dried irradiated bone is known to be more brittle. Whether bone brittleness is due to irradiation alone, temperature during irradiation or to a synergetic effect of the freeze-drying-irradiation process was not yet assessed. Using a left-right femoral head symmetry model, 822 compression tests were performed to assess the influence of sequences of a 25 kGy irradiation with and without freeze-drying compared to the unprocessed counterpart. Irradiation of frozen bone did not cause any significant reduction in ultimate strength, stiffness and work to failure. The addition of the freeze-drying process before or after irradiation resulted in a mean drop of 35 and 31% in ultimate strength, 14 and 37% in stiffness and 46 and 37% in work to failure. Unlike irradiation at room temperature, irradiation under dry ice of solvent-detergent treated bone seemed to have no detrimental effect on mechanical properties of cancellous bone. Freeze-drying bone without irradiation had no influence on mechanical parameters, but the addition of irradiation to the freeze-drying step or the reverse sequence showed a detrimental effect and supports the idea of a negative synergetic effect of both procedures. These findings may have important implications for bone banking.

Irradiation Does Not Modify Mechanical Properties of Cancellous Bone Under Compression

“…In the current study, the difference in yield strain and the relationships between bone volume fraction and both Young's modulus and yield stress between groups was small (the effect of irradiation in the analysis of covariance was less than 5% of that in the control group, as indicated by the coefficient associated with irradiation in the generalized least squares model; Table 3) and a priori power was 0.99 to detect a 20% effect, supporting our conclusion that there is no effect of gamma radiation sterilization on these parameters. Our study confirms that the lack of effect of gamma irradiation on cancellous bone stiffness and strength observed in prior studies [3,5,11,12,14,19,31] was not the result of confounding variability in bone volume fraction or density among specimens [3,5,11,12,14,19,31].…”

“…In cortical bone, gamma radiation at typical sterilization doses causes reductions in ultimate strength [20], bending strength [13], work to fracture [2,20], fatigue life [1], and resistance to fatigue crack growth [26]. High doses of gamma irradiation (more than 51 kGy) impair cancellous bone strength and elastic modulus (Young's modulus) [3], whereas lower doses have not been associated with impaired elastic modulus or ultimate strength [3,5,11,12,14,19,31]. Although the density of cancellous bone is the single most important factor influencing cancellous bone strength and stiffness [24], prior studies of the effects of irradiation on cancellous bone have either not accounted for variation in density of the cancellous bone specimens [5,12,19,31] or have studied a relatively small range in cancellous bone density [3,14].…”

“…High doses of gamma irradiation (more than 51 kGy) impair cancellous bone strength and elastic modulus (Young's modulus) [3], whereas lower doses have not been associated with impaired elastic modulus or ultimate strength [3,5,11,12,14,19,31]. Although the density of cancellous bone is the single most important factor influencing cancellous bone strength and stiffness [24], prior studies of the effects of irradiation on cancellous bone have either not accounted for variation in density of the cancellous bone specimens [5,12,19,31] or have studied a relatively small range in cancellous bone density [3,14]. Because strength and stiffness of cancellous bone are related to the density raised to a power near 2.0 [24], a 10% difference in density among specimens can generate a 20% difference in strength or stiffness, suggesting small differences in density within a group increase the variability in studies, making it difficult to observe an effect of irradiation.…”

Comparative Biomechanical and Microstructural Analysis of Native versus Peracetic Acid-Ethanol Treated Cancellous Bone Graft

“…According to these findings, significant differences in failure stress and elastic modulus, compared to control samples, were found for gamma-irradiated human cancellous bone specimens with 60 kGy [21]. At a dose of 30 kGy no differences were observed between irradiated human cancellous bone and control [21, 44]. Knaepler and coworkers found that irradiation of porcine cancellous bone with 10 kGy did not impair the stability, whereas a dose of 25 kGy led to a reduction of stability to approximately 65% in uniaxial compression [37].…”

Radiation sterilization of tissue allografts: A review

“…Biocompatibility, osteogenic capacity, biomechanical strength and architecture are all important factors in the successful incorporation of graft bone and can determine the speed of recovery. Sterilization by gamma irradiation has been demonstrated to decrease osteogenic potential by reducing biocompatibility through the production of peroxidized lipids [71] , as well as diminishing the biomechanical stability of the bone [72,73] .…”