The effects of test environment and cyclic stretching on the failure properties of human patellar tendons

There is a need to document the mechanical properties of patellar tendon allografts used for reconstructive surgery of the damaged anterior cruciate ligament, especially the effects of irradiation sterilization. The purpose of this study was to investigate the influences of in vitro test environment and low-level cyclic stretching prior to failure tests on nonirradiated and irradiated human graft tissues. Bilateral patellar tendons were split and each half processed accordingly. Some graft tissues were stretched cyclically at 2.5 mm deformation before failure. Experiments were performed in a 37 degrees C saline bath or with tissues moistened with a drip of the same. The irradiated grafts relaxed less and generated less slack length in the drip environment than the nonirradiated controls. Cyclic stretching did not alter failure characteristics of either graft tissue. While no significant differences in the tensile responses or failure characteristics were noted for irradiated and nonirradiated grafts in the drip, in the bath environment the nonirradiated tissues had greater strength and modulus. This resulted in there being a significant difference between irradiated and nonirradiated tissue responses in a heated saline bath environment. These experimental results exemplify the need to control in vitro test environments in the evaluation of various sterilization and preservation protocols for soft tissue allografts.     

Microstructurally based model analysis of gamma-irradiated tendon allografts.

A mathematical model of the collagenous microstructure of tendon was used to analyze the mechanical responses of gamma-irradiated patellar tendon allografts and nonirradiated controls. The model was fit to tensile test response curves from 10 pairs of allografts. Donors ranged in age from 16-64 years (six males, four females). The model indicated a decrease in elastic modulus of irradiated tendon collagen. It also suggested a significant increase in the degree and range of collagen fiber crimping following gamma irradiation. The model results agree with the literature and histological observations. The model fit the experimental response curves well and provided a structurally based, objective method of quantitatively studying the mechanical response of tendons and the consequences of irradiation sterilization.     

Sterilization of HIV with irradiation: relevance to infected bone allografts.

BACKGROUND: Bone allograft banks commonly sterilize frozen bone by irradiation. The dose-response relationship for HIV is calculated and the dose required to inactivate the bioburden of virus that may be present in allograft bone is determined. METHODS: A virus titre experiment is performed using irradiated frozen HIV. The virus is maintained on dry ice (approximately -70 degrees C) and is exposed to a cobalt 60 source with 0-40 kGy irradiation at 5 kGy intervals. Lymphocyte cell cultures are exposed to serial dilutions of the irradiated virus. The virus titre is quantified by cytological changes of HIV infection and p24 immunofluorescence. RESULTS: There is a linear relationship between the virus titre and the radiation dose delivered. The inactivation rate of irradiated virus was 0.1134 log10 tissue culture infective doses 50/mL per kGy (95% confidence intervals, 0.1248-0.1020). The irradiation dose required to inactivate the HIV bioburden in allograft bone is 35 kGy. The irradiation dose required to achieve a sterility assurance level of 10(-6) is 89 kGy. This dose exceeds current recommendations for sterilizing medical products and the current practice of many bone banks. CONCLUSIONS: It is concluded that gamma irradiation should be disregarded as a significant virus inactivation method for bone allografts.     

STERILIZATION OF HIV WITH IRRADIATION: RELEVANCE TO INFECTED BONE ALLOGRAFTS

Background : Bone allograft banks commonly sterilize frozen bone by irradiation. The dose–response relationship for HIV is calculated and the dose required to inactivate the bioburden of virus that may be present in allograft bone is determined. Methods : A virus titre experiment is performed using irradiated frozen HIV. The virus is maintained on dry ice (approximately –70°C) and is exposed to a cobalt 60 source with 0–40 kGy irradiation at 5 kGy intervals. Lymphocyte cell cultures are exposed to serial dilutions of the irradiated virus. The virus titre is quantified by cytological changes of HIV infection and p24 immunofluorescence. Results : There is a linear relationship between the virus titre and the radiation dose delivered. The inactivation rate of irradiated virus was 0.1134 log₁₀ tissue culture infective doses ₅₀/mL per kGy (95% confidence intervals, 0.1248–0.1020). The irradiation dose required to inactivate the HIV bioburden in allograft bone is 35 kGy. The irradiation dose required to achieve a sterility assurance level of 10^–6 is 89 kGy. This dose exceeds current recommendations for sterilizing medical products and the current practice of many bone banks. Conclusions : It is concluded that gamma irradiation should be disregarded as a significant virus inactivation method for bone allografts.     

Radioprotection of Tendon Tissue via Crosslinking and Free Radical Scavenging

Ionizing radiation could supplement tissue bank screening to further reduce the probability of diseases transmitted by allografts if denaturation effects can be minimized. It is important, however, such sterilization procedures be nondetrimental to tissues. We compared crosslinking and free radical scavenging potential methods to accomplish this task in tendon tissue. In addition, two forms of ionizing irradiation, gamma and electron beam (e-beam), were also compared. Crosslinkers included 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and glucose, which were used to add exogenous crosslinks to collagen. Free radical scavengers included mannitol, ascorbate, and riboflavin. Radioprotective effects were assessed through tensile testing and collagenase resistance testing after irradiation at 25 kGy and 50 kGy. Gamma and e-beam irradiation produced similar degenerative effects. Crosslinkers had the highest strength at 50 kGy, EDC treated tendons had 54% and 49% higher strength than untreated, for gamma and e-beam irradiation respectively. Free radical scavengers showed protective effects up to 25 kGy, especially for ascorbate and riboflavin. Crosslinked samples had higher resistance to collagenase and over a wider dose range than scavenger-treated. Of the options studied, the data suggest EDC precrosslinking or glucose treatment provides the best maintenance of native tendon properties after exposure to ionizing irradiation. One or more of the authors (MGD) have received funding from the Musculoskeletal Transplant Foundation Peer Reviewed Scientific Grants Program (January–December 2005).     

Improved Tendon Radioprotection by Combined Cross-linking and Free Radical Scavenging

Allograft safety is a great concern owing to the risk of disease transmission from nonsterile tissues. Radiation sterilization is not used routinely because of deleterious effects on the mechanical integrity and stability of allograft collagen. We previously reported several individual cross-linking or free radical scavenging treatments provided some radioprotective effects for tendons. We therefore asked whether a combination of treatments would provide an improved protective effect after radiation exposure regarding mechanical properties and enzyme resistance. To address this question we treated 90 rabbit Achilles tendons with a combination of cross-linking (1-ethyl-3-[3-dimethyl aminopropyl] carbodiimide [EDC]) and one of three scavenging regimens (mannitol, ascorbate, or riboflavin). Tendons then were exposed to one of three radiation conditions (gamma or electron beam irradiation at 50 kGy or unsterilized). Combination-treated tendons (10 per group) had increases in mechanical properties and higher resistance to collagenase digestion compared with EDC-only and untreated tendons. Irradiated tendons treated with EDC-mannitol, -ascorbate, and -riboflavin combinations had comparable strength to native tendon and had averages of 26%, 39%, and 37% greater, respectively, than those treated with EDC-only. Optimization of a cross-linking protocol and free radical scavenging cocktail is ongoing with the goal of ensuring sterile allografts through irradiation while maintaining their structure and mechanical properties.     

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

Background Gamma irradiation has been widely used for sterilization of bone allografts. However, gamma irradiation alters proteins. This is favorable when it reduces immunogenicity, but is undesirable when osteoinductive proteins are damaged. Although the effect of gamma irradiation on BMPs has been studied, the effect of irradiation on the process of incorporation of morselized bone chips remains unclear. We studied the effects of sterilization by gamma irradiation on the incorporation of impacted morselized allografts.

Methods Bone chambers with impacted allografts, rinsed impacted allografts, allografts that were rinsed and subsequently irradiated, and an empty control were implanted in proximal medial tibiae of goats. Incorporation was evaluated using histology and histomorphometry.

Results Histology revealed evidence of bone graft incorporation, which proceeded in a similar way in unprocessed, rinsed, and both rinsed and irradiated bone grafts. After 12 weeks, no difference in bone and tissue ingrowth was found between the unprocessed, the rinsed, and the rinsed and subsequently irradiated allografts. The amount of unresorbed graft remnant was highest in the unprocessed bone grafts.

Interpretation We conclude that sterilization with gamma irradiation does not influence the incorporation of impacted rinsed bone allografts.     

Irradiation-sterilization of rat bone matrix gelatin

Bone matrix gelatin induces bone formation in muscle, and when implanted orthotopically it improves bone repair. Co-60 sterilization of bone gelatin impairs the protein-bound induction mechanisms. Gelatin samples nonirradiated or irradiated by 25 or 50 kGy were implanted into a pouch in the abdominal wall of Sprague-Dawley rats, as well as into a 7-mm calvarial defect. Evaluation was done by histologic studies, histomorphometry of orthotopic implants, and determination of alkaline phosphatase in ectopic implants. Gelatin irradiated with 50 kGy was absorbed in the muscle bed without evidence of any specific host reaction. Irradiation of 25 kGy led to histologically confirmed ectopic bone formation, but the wet weight of the explants was only half that of the nonirradiated control samples. Alkaline phosphatase activity was equal in both of these groups. With orthotopic implantation, neither a histologic nor a morphometric effect was seen with 25 kGy. Loss of osteoinduction with 25-kGy irradiation is apparently masked by osteoconductive mechanisms with orthotopic implantation.     

Sterilization by gamma radiation impairs the tensile fatigue life of cortical bone by two orders of magnitude.

Cortical bone grafts are utilized frequently for skeletal reconstruction, spinal fusion and tumor surgery. Due to its efficacy and convenience terminal sterilization by gamma radiation is often essential to minimize disease transmission and infection. However, the impairment in the material properties of bone tissue secondary to gamma radiation sterilization is a concern since the mechanical functionality of a bone graft is of primary importance. While the extent of this impairment is well investigated for monotonic loading conditions, there does not seem to exist any information on the effects of gamma radiation sterilization on cortical bone's fatigue properties, the physiologically relevant mode of loading. In this study we investigated the degradation in the high-cycle and low-cycle tensile fatigue lives of cortical bone tissue secondary to gamma radiation sterilization at a dose of 36.4 kGy which approximately falls in the higher end of the standard dose range used in tissue banking. The high-cycle and the low-cycle fatigue tests were conducted under load control at initial strain levels of 0.2% and 0.4%, respectively. Monotonic tensile tests were also conducted to compare the impairment of fatigue properties with the impairment of monotonic properties. Results demonstrated that the impairment in both the high-cycle and the low-cycle fatigue lives were two orders of magnitude following sterilization, a change much more pronounced than that observed for monotonic loading. In conclusion, the results suggest that the impairment of the mechanical function of gamma radiation sterilized allografts is even worse in fatigue than monotonically. Therefore, grafts should be designed to minimize functional strains and avoid stress raisers to prevent premature fatigue failures.     

Complications of irradiated allografts in orthopaedic tumor surgery

Massive structural allografts used for replacement of bone defects after removal of bone tumors have several complications, including fracture, infection, and nonunion. To decrease the rate of infection, irradiation of selected allografts before their implantation was performed. This study evaluated the complications in patients with these irradiated grafts. Twenty-four patients were identified who had received allografts from 1987 through 1991 that were irradiated before implantation. The dosage of radiation was between 10 kGy and 30 kGy. The mean length of followup of the patients was 5 years (range, 2-9 years). These grafts were compared with a control group of grafts that were not irradiated but were implanted during the same time and used for similar diagnostic problems with defects of similar size. The outcomes of the groups differed significantly only in the incidence of allograft fracture. These findings indicate that high-dose irradiation to bone allografts is associated with a higher rate of fracture than are similar reconstructions using nonirradiated allografts.     

Fracture resistance of gamma radiation sterilized cortical bone allografts.

Gamma radiation is widely used for sterilization of human cortical bone allografts. Previous studies have reported that cortical bone becomes brittle due to gamma radiation sterilization. This embrittlement raises concern about the performance of a radiation sterilized allograft in the presence of a stress concentration that might be surgically introduced or biologically induced. The purpose of this study was to investigate the effect of gamma radiation sterilization on the fracture resistance of human femoral cortical bone in the presence of a stress concentration. Fracture toughness tests of specimens sterilized at a dose of 27.5 kGy and control specimens were conducted transverse and longitudinal to the osteonal orientation of the bone tissue. The formation of damage was monitored with acoustic emission (AE) during testing and was histologically observed following testing. There was a significant decrease in fracture toughness due to irradiation in both crack growth directions. The work-to-fracture was also significantly reduced. It was observed that the ability of bone tissue to undergo damage in the form of microcracks and diffuse damage was significantly impaired due to radiation sterilization as evidenced by decreased AE activity and histological observations. The results of this study suggest that, for cortical bone irradiated at 27.5 kGy, it is easier to initiate and propagate a macrocrack from a stress concentration due to the inhibition of damage formation at and near the crack tip.     

Free radical scavenging alleviates the biomechanical impairment of gamma radiation sterilized bone tissue.

Terminal sterilization of bone allografts by gamma radiation is often essential prior to their clinical use to minimize the risk of infection and disease transmission. While gamma radiation has efficacy superior to other sterilization methods it also impairs the material properties of bone allografts, which may result in premature clinical failure of the allograft. The mechanisms by which gamma radiation sterilization damages bone tissue are not well known although there is evidence that the damage is induced via free radical attack on the collagen. In the light of the existing literature, it was hypothesized that gamma radiation induced biochemical damage to bone's collagen that can be reduced by scavenging for the free radicals generated during the ionizing radiation. It was also hypothesized that this lessening of the extent of biochemical degradation of collagen will be accompanied by alleviation in the extent of biomechanical impairment secondary to gamma radiation sterilization. Standardized tensile test specimens machined from human femoral cortical bone and specimens were assigned to four treatment groups: control, scavenger treated-control, irradiated and scavenger treated-irradiated. Thiourea was selected as the free radical scavenger and it was applied in aqueous form at the concentration of 1.5 M. Monotonic and cyclic mechanical tests were conducted to evaluate the mechanical performance of the treatment groups and the biochemical integrity of collagen molecules were assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The native mechanical properties of bone tissue did not change by thiourea treatment only. The effect of thiourea treatment on mechanical properties of irradiated specimens were such that the post-yield energy, the fracture energy and the fatigue life of thiourea treated-irradiated treatment group were 1.9-fold, 3.3-fold and 4.7-fold greater than those of the irradiated treatment group, respectively. However, the mechanical function of thiourea treated and irradiated specimens was not to the level of unirradiated controls. The damage occurred through the cleavage of the collagen backbone as revealed by SDS PAGE analysis. Irradiated specimens did not exhibit a noteworthy amount of intact alpha-chains whereas those irradiated in the presence of thiourea demonstrated intact alpha-chains. Results demonstrated that free radical damage is an important pathway of damage, caused by cleaving the collagen backbone. Blocking the activity of free radicals using the scavenger thiourea reduces the extent of damage to collagen, helping to maintain the mechanical strength of sterilized tissue. Therefore, free radical scavenger thiourea has the potential to improve the functional life-time of the allograft component following transplantation.     

The effect of gamma radiation sterilization on the fatigue crack propagation resistance of human cortical bone

BACKGROUND: Clinical evidence has suggested that the rate of fracture in allografts sterilized with gamma radiation may be higher than that in controls. Gamma radiation sterilization has been shown to affect the post-yield properties of bone but not the elastic modulus. Since most allograft fractures occur with subcritical loads during activities of daily living, it may be that the fatigue properties of irradiated allografts are diminished. In this study, the fatigue crack propagation behavior of cortical bone sterilized with gamma radiation was compared with that of gender and age-matched controls. We hypothesized that gamma radiation significantly reduces the resistance of cortical bone to fatigue crack growth. METHODS: Specimens for fatigue crack propagation testing were machined from four pairs of fresh-frozen human femora obtained from four individuals (a younger male, younger female, older male, and older female donor). Half of the specimens were sterilized with 31.7 kGy of gamma radiation. The specimens were cyclically loaded to failure in a servohydraulic testing system, and crack growth was monitored. The cyclic stress intensity factor and the fatigue crack growth rate were calculated to examine the kinetics of fatigue crack growth. Following testing, the damage zone around the fracture plane was analyzed histologically. RESULTS: The morphology and kinetics of crack growth in irradiated specimens differed from the control data. Overall, the irradiated bone was significantly less resistant to fatigue crack growth than was control tissue (p < 0.05). There was less microdamage associated with fracture in the irradiated specimens than in the control specimens, with the exception of the bone from the older female donor. CONCLUSIONS: Gamma radiation sterilization significantly reduces the fatigue crack propagation resistance of cortical bone. Irradiated specimens also demonstrate a smaller amount of microdamage along the fracture plane. These findings may be due to ultrastructural alterations in the collagen matrix caused by radiation. CLINICAL RELEVANCE: This study suggests that, despite having pre-yield mechanical properties that are similar to those of nonirradiated bone, gamma-radiation-sterilized allograft may be more predisposed to fracture even under the subcritical loads that occur during the activities of daily living.     

Microbiological safety and clinical efficacy of radiation sterilized amniotic membranes for treatment of second-degree burns

Amniotic membranes collected from the placentae of screened donors were processed and sterilized by gamma irradiation at 25 kGy. The sterility assurance level (SAL) of gamma irradiated amniotic membranes and clinical efficacy in second-degree burn wound healing were evaluated. Processed air-dried amniotic tissue from 159 batches of processing was checked for the bioburden level before sterilization. About 39% of the tissues had bioburden in the range of 10(1)-10(2)/100 cm(2) and 54.8% in the range of 10(2)-10(3)/100 cm(2). Based on the bioburden of the processed tissue prior to sterilization and the D(10) value of 2.3 kGy for the radiation resistant reference strain Bacillus pumilus, the sterility assurance level of the amniotic membranes irradiated at 25 kGy is found to be 10(-7) to 10(-11). The burn wound healing rate was compared between the radiation sterilized amniotic membranes and glycerol preserved amniotic membranes. Fifty patients with partial-thickness burns (up to 70% TBSA) were selected for the study. The scalds constituted 82% (41 patients) whereas flame burns accounted for 18% (9 patients). Various aspects like ease of application, patient comfort, development of fluid under the membrane, bacterial culture of drained fluid, rate of epithelialization, development of hypertrophic scars, keloids, unstable scars and restriction of joint movements were recorded with the application of gamma irradiated and glycerol preserved membranes. Radiation sterilized amniotic membranes had advantage over the glycerolized membranes with respect to the ease of application. Five patients with glycerol preserved membranes and four with gamma irradiated membranes developed fluid. The bacteriology of fluid showed Pseudomonas aeruginosa in four cases, Staphylococcus aureus in two cases, Escherichia coli in two cases and Acinetobacter in one case. The application of radiation sterilized amniotic membranes on the burn wound favoured epithelialization. In all the patients, membranes dessicated and separated in 10-14 days time leaving behind an epithelialized surface.     

Viruses adsorbed on musculoskeletal allografts are inactivated by terminal ethylene oxide disinfection.

In 1987 it was anticipated that unsterilized tissues would transmit virus diseases such as hepatitis and HIV-1 from infected donors so a freeze-drying process for musculoskeletal tissue was developed to include terminal ethylene oxide (EO) exposure for 14 h. We found no studies of EO efficacy when viruses were associated with human allografts so we studied the antiviral effect of terminal EO disinfection using all but the final freeze-drying phase of this clinical processing protocol (CPP). Specifically we looked at EO inactivation of HIV-1, a human hepatitis B surrogate and test viruses known to be highly resistant to disinfecting agents, including irradiation. Freeze-drying, ordinarily required after EO disinfection and part of the CPP, was not done. Suspensions of HIV-1, Bovine viral diarrhea, Reovirus type 3, Duck hepatitis B, Poliomyelitis and Canine parvovirus were adsorbed on glass, demineralized bone powder, and preprocessed strips of femoral cortex, iliac wedges, cancellous blocks and patellar bone-tendon-bone preparations and subjected to EO disinfection. Test viruses were inactivated at the end of 7 h of EO disinfection, providing a safety factor in the CPP of at least 100%. Because allografts can transmit viruses, terminal EO disinfection should provide safer musculoskeletal allografts than non-disinfected tissues or those irradiated with a standard irradiation dose. New spontaneously appearing viruses would probably be inactivated with this terminal EO disinfection but they and viral bioweapons will require individual validation to assure viral inactivation.     

γ射线照射对椎间盘生物学活性的影响

目的探讨γ射线照射处理异体椎间盘的可行性,同时进一步评估去细胞化椎间盘作为自然支架辅助生物学治疗椎间盘退变的性能。方法手术获取6例成熟比格犬的椎间盘,逐级冷冻保存,随机分为对照组及18kGy、25kGy、50kGy γ射线照射组（n=8）,处理各组椎间盘后进行细胞活性及生物力学检测并进行对比分析。结果椎间盘细胞活性与照射剂量成负相关,对照组纤维环及髓核细胞活性分别为92．6％、90．7％,18kGy照射组为76．5％、70．6％,25kGy照射组为52．7％、46．9％,50kGy照射组为18．3％、10．1％,各组间差异有统计学意义（P〈0．01）。不同组间椎间盘生物力学性能差异均无统计学意义（P〉0．05）,其中压缩、拉伸轴向力及左／右旋转扭力矩均维持在正常水平。结论优化γ射线照射可以作为异体椎间盘消毒灭菌的手段,但其确切效果有待体内实验进一步验证。去细胞化椎间盘具有较为理想的生物学及机械性能,有望作为自然支架用于椎间盘疾病的相关研究。     

Mechanical strength of cortical allografts with gamma radiation versus ethylene oxide sterilization

We investigated the effects of gamma irradiation versus ethylene oxide (ETO) sterilization on the mechanical strength of cortical bone grafts. Tibias were collected from cadavers of mature goats. Sixty test specimens were randomized into four groups: fresh (no processing), frozen (freezing at -70 degrees C), gamma-irradiated, and ETO-sterilized specimens. Torsion, three-point bending, and compression testing were separately performed with a material testing machine. Parameters studied included maximum stress, strain, deflection, extension, load, shear modulus, and E-modulus. Compared with findings for the fresh specimens, findings were as follows for gamma-irradiated specimens: maximal shear modulus, reduced by 48%; shear stress, by 55%; deflection, by 71%; bending stress, by 51%; bending strain, by 74%; extension, by 60%; and compression strain, by 50%. However, there were no reductions in those parameters for the frozen specimens or the ETO-sterilized specimens. These findings confirm that shear, bending, and compression strength of cortical allografts are weakened by gamma irradiation at room temperature. To maintain optimum mechanical properties, ETO sterilization of allografts is better than gamma sterilization, especially for cortical bone, because it is usually used in load-bearing settings.     

11 kGy gamma irradiated demineralized bone matrix enhances osteoclast activity

Background

Demineralized bone matrix (DBM) allografts are widely used in orthopaedic clinics. However, the biological impact on its osteoinductivity after its sterilization process by gamma irradiation is not well studied. Furthermore, little is known about the relationship between residual calcium levels on osteoinductivity.

Hypothesis

We hypothesize that low-dose gamma irradiation retains the osteoinducitivity properties of DBM and causes ectopic bone formation.

Materials and methods

A randomised animal trial was performed to compare tissue and molecular responses of low-dose (11 kGy) gamma irradiated and non-irradiated human DBM at 6 weeks post-intramuscular implantation using an athymic rat model. In addition, we correlated residual calcium levels and bone formation in gamma irradiated DBM.

Results

A modified haematoxylin and eosin stain identified ectopic bony capsules at all implanted sites with no significant difference on the amount of new bone formed between the groups. Statistically significantly lower ratio of alkaline phosphatase expression over tartrate-resistant acid phosphatase and/or cathepsin K expressions was found between the groups.

Discussion

This study found that low-dose gamma irradiated DBM, which provides a sterility assurance level of 10^?6 for bone allografts, retained osteoinductivity but exhibited significantly enhanced osteoclastic activity. Furthermore, this is the first study to find a positive correlation between residual calcium levels and bone formation in gamma irradiated DBM.     

Validation of 11 kGy as a Radiation Sterilization Dose for Frozen Bone Allografts

A radiation sterilization dose (RSD) of 25 kGy is deleterious to bone allografts. This study aimed to establish a lower RSD for bone allografts using method 1 of International Standard Organisation 11137.2:2006. This provides a database to select an RSD corresponding to an allograft's bioburden, given that the bioburden's gamma resistance is equal to or less than the standard. This can be verified by irradiating 100 allografts at a dose selected to provide a sterility assurance level of 10⁻². The bioburden of our allografts was 0, which prescribed a verification dose of 1.3 kGy. After irradiating 100 allografts, sterility tests returned no positive cultures. We therefore validated an RSD of 11 kGy for allografts with that bioburden. According to the standard, this RSD provides a sterility assurance level of 10⁻⁶ for bone allografts.     

Tendon allograft sterilized by peracetic acid/ethanol combined with gamma irradiation

Background

Research and clinical applications have demonstrated that the effects of tendon allografts are comparable to those of autografts when reconstructing injured tendons or ligaments, but allograft safety remains problematic. Sterilisation could eliminate or decrease the possibility of disease transmission, but current methods seldom achieve satisfactory sterilisation without affecting the mechanical properties of the tendon.

Hypothesis

Peracetic acid-ethanol in combination with low-dose gamma irradiation (PE-R) would inactivate potential deleterious microorganisms without affecting mechanical and biocompatible properties of tendon allograft.

Study design

Controlled laboratory design.

Methods

HIV, PPV, PRV and BVDV inactivation was evaluated. After verifying viral inactivation, the treated tendon allografts were characterised by optical microscopy, scanning electron microscopy and tensile testing, and the cytocompatibility was assessed with an MTT assay and by subcutaneous implantation.

Results

Effective and efficient inactivation of HIV, PPV, PRV and BVDV was observed. Histological structure and ultrastructure were unchanged in the treated tendon allograft, which also exhibited comparable biomechanical properties and good biocompatibility.

Conclusion

The preliminary results confirmed our hypothesis and demonstrated that the PE-R tendon allograft has significant potential as an alternative to ligament/tendon reconstruction.

Clinical relevance

Tendon allografts have been extensively used in ligament reconstruction and tendon repair. However, current sterilisation methods have various shortcomings, so PE-R has been proposed. This study suggests that PE-R tendon allograft has great potential as an alternative for ligament/tendon reconstruction.

What is known about this subject

Sterilisation has been a great concern for tendon allografts. However, most sterilisation methods cannot inactivate viruses and bacteria without impairing the mechanical properties of the tendon allograft.

What this study adds to existing knowledge

Peracetic acid/ethanol with gamma irradiation can effectively inactivate viruses and bacteria. Meanwhile, tendon allografts sterilised by this method maintain their physiological tendon structure, biomechanical integrity and good compatibility.