Effect of freeze‐drying and gamma irradiation on the mechanical properties of human cancellous bone

Abstract

Freeze-drying and gamma irradiation are commonly used for preservation and sterilization in bone banking. The cumulative effects of preparation and sterilization of cancellous graft material have not been adequately studied, despite the clinical importance of graft material in orthopaedic surgery. Taking benefit from the symmetry of the left and right femoral heads, the influence of lipid extraction followed by freeze-drying of a femoral head and a final 25-kGy gamma irradiation was determined, with the nonirradiated, nonprocessed counterpart as the control. Five hundred and fifty-six compression tests were performed (137 pairs for the first treatment and 141 pairs for the second). Mechanical tests were performed after 30 minutes of rehydration in saline solution. Freeze-dried femoral heads that had undergone lipid extraction experienced reductions of 18.9 and 20.2% in ultimate strength and stiffness, respectively. Unexpectedly, the work to failure did not decrease after this treatment. The addition of gamma irradiation resulted in a mean drop of 42.5% in ultimate strength. Stiffness of the processed bone was not modified by the final irradiation, with an insignificant drop of 24%, whereas work to failure was reduced by a mean of 71.8%. Freeze-dried bone was a bit less strong and stiff than its frozen control. Its work to failure was not reduced, due to more deformation in the nonlinear domain, and it was not brittle after 30 minutes of rehydration. Final irradiation of the freeze-dried bone weakened its mechanical resistance, namely by the loss of its capacity to absorb the energy (in a plastic way) and a subsequent greater brittleness.

On the effect of X-ray irradiation on the deformation and fracture behavior of human cortical bone

“…Within the fibrils, such molecular stretching competes with intermolecular sliding and breaking of weak and strong bonds between TC molecules, both sliding motions provide the basis for large plastic strains without catastrophic failure. 7 At the mineralized collagen fibril level, continuous glide between TC molecules and between hydroxyapatite (HA) particles and these molecules, initiated by slip at the HA-TC molecule interface, enables a large regime of dissipative deformation once plastic yielding begins. Such molecular behavior of the protein and mineral phases during large-scale deformation of the mineralized collagen fibrils, in addition to representing a mechanism of plasticity, provides for intrinsic toughening and enhanced fracture resistance through the formation of plastic zones around crack-like defects [77,78].…”

“…At the high dose end (>10 kGy), gamma irradiation is commonly used to terminally sterilize allograft tissues and bones [2][3][4][5], and has been proven to be very potent sterilization agent with the ability to effectively penetrate tissue. However, gamma irradiation is also known to adversely affect the mechanical and biological properties of tissue in a dose-dependent manner by degrading the collagen [6][7][8][9][10][11][12][13][14]. Specifically, gamma rays split polypeptide chains; in wet specimens, irradiation causes release of free radicals via radiolysis of water molecules that induces cross-linking reactions in collagen molecules [15][16][17].…”

“…This has resulted in the application of sterilization doses ranging from 25 to 35 kGy [16], although even at such a "standard dose" the effect of irradiation on the mechanical integrity of bone and tissue is still controversial. For doses up to 35 kGy, several studies [7,8,10,[18][19][20] have reported a significant effect on the post-yield properties of cortical bone, in particular significant reductions in plastic properties such as ultimate strength and work-of-fracture, but little effect on the elastic properties, i.e., stiffness and elastic limit. Conversely, other studies on bones and tendons [9,14,21,22] have claimed no significant reduction in biomechanical properties after similar doses.…”

Effect of sterilization by gamma radiation on nano-mechanical properties of teeth

“…In addition, it has successfully been applied for sterilization of bone allografts in orthopedic surgery [6;7]. However, the radiation doses used (25 to 40 kGy) often reduce the mechanical stability of the bone grafts which might cause the implant to fail [8][9][10].…”

Irradiation has no effect on the incorporation of impacted morselized bone: A bone chamber study in goats

“…Due to changes in mechanical properties of bone by gamma irradiation, it has been used with some caution in clinical practice-especially in load-bearing applications. Irradiated morselized bone was found to be less strong, less stiff and significantly more brittle than fresh-frozen control bone when tested in compression models (Cornu et al 2000). However, it has been shown that irradiated freeze-dried impacted grafts provide a more stable femoral reconstruction than fresh-frozen grafts when tested in a hip simulator (Cornu et al 2003).…”