辐照对rhBMP-2骨诱导活性的影响

目的探讨不同剂量γ射线辐照对基因重组人骨形态发生蛋白2(rhBM P-2)骨诱导活性的影响及胶原载体的作用。方法以胶原海绵为载体制成rhBM P-2胶原复合物,分为4类:(Ⅰ)对照组:复合物未辐照;(Ⅱ)复合物辐照组:剂量为15、20、25和50kGy;(Ⅲ)载体辐照组:胶原载体接受50kGy辐照,然后复合未辐照的rhBM P-2;(Ⅳ)BM P辐照组:将rhBM P-2辐照25和50kGy,然后复合于胶原载体。各类BM P胶原复合物植入大鼠股骨肌袋内,术后2周和4周取出包块,进行大体、X线和组织学观察,通过组织形态分析对成骨进行定量分析。结果术后2周,复合物辐照15、20和25kGy组与对照组包块的大体、X线和组织学所见相似,包块内见大量未成熟的编织骨,成骨定量分析见20kGy组与对照组差异无统计学意义;复合物辐照25kGy组新生骨量明显低于复合物辐照15kGy组(P<0.05);复合物辐照50kGy和BM P辐照组无新骨形成。术后4周,各组均出现含有骨髓的成熟骨组织,其中复合物辐照25kGy组与对照组相似;复合物辐照50kGy组有成熟骨但数量较少;载体辐照和BM P辐照组新生骨量明显少于对照组。结论20和25kGy剂量辐照对rhBM P-2骨诱导活性没有影响或仅有一过性抑制;在辐照过程中,胶原载体对BM P具有保护作用。     

γ-射线辐照对α-淀粉酶和糖化酶的影响

本文研究了α-淀粉酶和葡萄糖苷的γ-辐照现象。剂量为0.5kGy时,活性分别提高5%和10%,用于山芋淀粉的酶促水解,生成的还原糖增加,剂量达5kGy和50kGy时,题示酶的活性分别开始下降。用差示扫描量热法(DSC)研究了辐照的热性质,其⊿H随剂量升高而减小,实验数据表明辐照技术可用于酒精发酵和酶制剂工业。     

γ-射线辐照甘薯淀粉对酶促水解的影响

用10至500kGy的γ-射线辐照淀粉,酶水解产生的还原糖和淀粉的碘亲和力,随剂量增加而增大;淀粉溶液的酸度和粘度随之降低。用X-衍射法研究了辐照淀粉的结晶结构,以及辐照对淀粉中微生物存活率的影响。这些结果可作为γ-辐照技术应用于无蒸煮酒精发酵的基础研究。     

HIFU消融MR T2WI不同信号子宫肌瘤的临床疗效及安全性分析

目的探讨HIFU对MR T2WI不同信号子宫肌瘤的消融效果及安全性。方法对156例患者共210个子宫肌瘤行HIFU消融治疗。根据术前MR T2WI表现分为低信号组、等信号组、高信号组及混杂信号组,比较各组间术前肌瘤体积、术中消融治疗参数(声源功率、辐照时间、治疗剂量及治疗强度)、能效因子、术后消融率、肌瘤缩小率及术中、术后不良反应发生率的差异。结果 4组间术前肌瘤体积(χ~2=14.720,P=0.002)、术中辐照时间(F=10.422,P0.001)、治疗剂量(χ~2=30.973,P0.001)、能效因子(F=3.953,P=0.009)、消融率(F=4.313,P=0.006)差异均有统计学意义。低信号组术前肌瘤体积明显小于高信号组(P=0.032)及混杂信号组(P=0.029);高信号组术中辐照时间明显长于低信号组(P0.001)及混杂信号组(P=0.006),治疗剂量明显大于低信号组(P0.001)、等信号组(P=0.023)及混杂信号组(P=0.013)。高信号组能效因子明显高于且消融率明显低于低信号组(P=0.016、0.003)、等信号组(P=0.012、0.006)及混杂信号组(P=0.002、0.003)。术中及术后均无严重并发症发生,且4组间放射痛、皮肤烫伤、治疗区疼痛等术中不良反应及阴道排液、下腹部疼痛、骶尾部疼痛等术后不良反应差异均无统计学意义(P均0.05)。结论 HIFU治疗对MR T2WI不同信号的子宫肌瘤均安全、有效。但其中高信号肌瘤消融难度较大,术后疗效相对较差。     

医用聚丙烯酰胺水凝胶(奥美定)细胞毒性研究

目的　评价医用聚丙烯酰胺水凝胶 (奥美定 )中可滤出成分是否对细胞产生潜在的毒性。方法　采用细胞毒性试验中的琼脂覆盖法 ,通过直接放置样品和放置样品浸提液载片两种方法 ,对三批不同生产日期的奥美定进行测试研究。结果　直接放置样品组 ,测试样品下均出现部分细胞脱色 ,其余细胞微着色 ,未见细胞溶解R =0 .5 / 0 ,放置样品浸提液载片组与浸提介质对照组相同R =0 / 0。结论　奥美定无细胞毒性     

异种脱钙骨基质颗粒的生物相容性实验研究

目的 评价制备的异种脱钙骨基质(demineralized bone matrix,DBM)植入体内的生物相容性,为进一步实验研究和临床应用提供依据.方法 取猪四肢长管状骨皮质骨经理化处理后,制备脱脂脱钙(材料A)和脱脂脱钙去细胞(材料B)两种粒径为250～810 μm的DBM颗粒和浸提液,骨颗粒脱脂脱钙后测钙、磷含量.采用标准的毒理学方法进行急性毒性实验、皮肤刺激实验、热原实验、溶血实验、细胞毒性实验和肌肉植入实验.结果 未脱钙皮质骨钙、磷含量分别为(189.09±3.12)mg/g和(124.73±2.87)mg/g:DBM颗粒的钙、磷含量分别为(3.48±0.09)mg/g和(3.46±0.07)mg/g;DBM颗粒钙、磷含量分别为未脱钙皮质骨的1.87%和2.69%.急性毒性实验:各组小鼠活动正常,7 d内小鼠无死亡,各组动物未见中毒症状或不良反应;7 d后各组小鼠体重日平均增加差异无统计学意义(P>0.05).皮内刺激实验观察显示,注射材料A、B浸提液和生理盐水处无明显红斑、水肿和皮肤坏死,极轻微刺激.热原实验两组动物体温升高最高均为0.4℃,符合<0.6℃的国家标准.材料A浸提液的溶血率为1.14%,材料B为0.93%,符合<5%的国家标准.异种DBM的细胞毒性为0～1级.肌肉内植入实验显示动物术后生存良好,各植入部位均未见组织坏死、积液及化脓感染.术后不同时间点植入材料A、B组局部细胞免疫定量评分比较差异无统计学意义(P>0.05).结论 DBM颗粒的毒性程度为无毒,皮肤无刺激,无热原性,溶血率<5%,对细胞无明显毒性,具有良好的生物相容性和一定的骨诱导性.     

医用聚丙烯酰胺水凝胶（奥美定）细胞毒性研究

目的　评价医用聚丙烯酰胺水凝胶（奥美定）中可滤出成分是否对细胞产生潜在的毒性。方法　采用细胞毒性试验中的琼脂覆盖法,通过直接放置样品和放置样品浸提液载片两种方法,对三批不同生产日期的奥美定进行测试研究。结果　直接放置样品组,测试样品下均出现部分细胞脱色,其余细胞微着色,未见细胞溶解R=0.5/0,放置样品浸提液载片组与浸提介质对照组相同R=0/0。结论　奥美定无细胞毒性。     

无白蛋白受体鼠中源于移植肝非实质细胞的肝细胞功能研究

目的研究F344大鼠来源的肝非实质细胞(LNPCs)能否驻存于γ射线全身照射的先天性无白蛋白大鼠(F344alb)的骨髓,进而转化为产白蛋白肝细胞。方法研究分为5组：无细胞移植和γ射线全身照射组(组I,n=5)；接受γ射线全身照射,无细胞移植(组Ⅱ,n=5)；移植1×10~7 LNPCs,无γ射线全身照射(组Ⅲ,n=5)；γ射线全身照射后移植1×10~7 LNPCs(组Ⅳ,n=5)；γ射线全身照射后移植1×10~7骨髓细胞(BMCs,组Ⅴ,n=5),8周后,处死大鼠。肝脏切片行白蛋白免疫染色,检测呈多于6个白蛋白阳性簇状分布的肝细胞群中提取的DNA和血清中自蛋白的水平。结果(1)生存率：接受LNPCs移植的γ射线全身照射F344alb(组Ⅳ)平均存活率83．3%,而仅γ射线全身照射的F344alb存活率为20．0%(组Ⅱ),同时接受BMCs移植的γ射线全身照射F344alb平均存活率的的达100．0%(组Ⅴ)。(2)白蛋白阳性肝细胞呈多于6个的簇状分布仅发现于γ射线全身照射后接受LNPCs或BMCs移植的肝切片中(组Ⅳ和组Ⅴ)。(3)从F344alb受体(组Ⅳ和组Ⅴ)骨髓细胞及肝脏切片中微切的呈多于6个白蛋白阳性簇状分布的肝细胞群中提取的DNA中可检测到正常的白蛋白基因序列。(4)组Ⅳ和组Ⅴ血清中白蛋白水平显著升高。结论F344来源的肝非实质细胞能驻存于γ射线全身照射的F344alb的骨髓,进而在肝内转化为产白蛋白肝细胞。     

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。     

大鼠和家兔辐照灭菌去抗原—自溶同种骨移植片骨移植研究

利用大鼠颅骨钻孔移植和家兔尺骨缺损移植实验观察经不同方法制备的去抗原-自溶同种骨移植片(AAA)骨的愈合效果,并与自体骨、新鲜同种骨、不脱灰AAA骨及异种骨相比较,结果发现脱灰AAA骨具有较好的骨诱导活性;25kGy剂量的辐照可以明显降低移植大鼠颅骨的愈合效果,但对家兔影响甚小。辐照AAA骨的愈合效果明显优于新鲜同种骨。     

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.     

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).     

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.     

Gamma irradiation and ethylene oxide in the sterilization of native reindeer bone morphogenetic protein extract.

BACKGROUND AND AIMS: For human use, it is necessary to sterilize bone morphogenetic proteins (BMPs), in order to reduce the risk of infections and associated complications. We compared the effects of ethylene oxide and gamma irradiation in the sterilization of native reindeer BMP extract with regard to bone induction in the Balb/C mouse thigh muscle pouch model. MATERIALS AND METHODS: BMP extract, sterilized with ethylene oxide gas (Steri-Vac 4XL, temperature 29 degrees C, exposure time 4 h, ethylene oxide concentration 860 mg/l), or gamma irradiation at doses of 3.15 MRad was administered in implants containing 5 or 10 mg of BMP extract with collagen carrier. Non-sterilized collagen implants served as controls. New bone formation was evaluated based on the incorporation of Ca45 and radiographically three weeks after implantation. RESULTS: The collagen was not able to induce new bone visible in radiographs. The mean Ca45 incorporation in the gamma sterilized group containing 5 mg of BMP extract was 30% (p = 0.04) and that containing 10 mg of BMP extract was 60% (p = 0.02) higher than seen in the corresponding ethylene oxide sterilized groups. The mean new bone areas were 45% higher in the gamma sterilized groups than in the corresponding ethylene oxide sterilized groups, but the differences were not significant. The mean optical density of new bone in the gamma sterilized group containing 5 mg of BMP extract was 75% (p = 0.00) and in that containing 10 mg of BMP extract was 70% (p = 0.00) higher than seen in the corresponding ethylene oxide sterilized groups. CONCLUSION: Native reindeer BMP extract is more sensitive to the effects of ethylene oxide gas sterilization than gamma irradiation. These results suggest that gamma irradiation is recommendable for the sterilization of BMP extracts.     

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.     

A novel application of high-dose (50 kGy) gamma irradiation for demineralized bone matrix: effects on fusion rate in a rat spinal fusion model

BACKGROUND CONTEXT: The safety of allograft material has come under scrutiny because of recent reports of allograft-associated bacterial and viral infections in tissue recipients. Gamma irradiation, although being one of the most effective ways of terminal sterilization, has been shown to affect the biomechanical properties of allograft bone. It may also have detrimental effects on the osteoinductivity of allograft material such as demineralized bone matrix (DBM) by the denaturation of proteins because of heat generated by irradiation. Sterilization of DBM material is an important variable in processing graft materials. This is considered to be one of the factors leading to different fusion rates observed with different commercially available DBM products, as the sterilization procedure itself may affect the osteoinductivity of the material. Currently, there is no ideal sterilization technique that limits the detrimental effect on osteoinductivity and fusion rates. PURPOSE: To evaluate the effects of a range of hydrogen peroxide exposures with or without the controlled high-dose gamma irradiation after processing with radioprotectant solutions (Clearant radiation sterilization procedure) on the fusion rates of human DBM. STUDY DESIGN: A prospective in vivo animal study. METHODS: Eighty mature athymic nude female rats were used for this study, which formed 10 equal groups. Human DBM exposed to hydrogen peroxide for different time periods (0, 1, 6, and 24 hours) was divided into two major subgroups. One group was further treated with controlled high-dose radiation using radioprotectants (radiation treated), whereas the other group was frozen immediately without specific treatment (non-radiation treated). Both radiation-treated and non-radiation-treated DBM material from each group of hydrogen peroxide exposure times were implanted between L4 and L5 transverse processes of the rats forming eight test groups including eight animals in each. The remaining 16 rats were divided into two additional groups to form negative (only decortication, n=8) and positive (bone morphogenetic protein [BMP]-2, n=8) control groups. The rats were evaluated for fusion by radiographs (2, 4, and 8 weeks), manual palpation (8 weeks), and histological analysis after sacrificing. Comparison of fusion rate among all groups was made using these three evaluation methods. RESULTS: Increasing the time period of hydrogen peroxide (0, 1, 6, or 24 hours) exposure for preparation of DBM from bone allograft did not affect the fusion rates significantly (p<.05), although there was a trend toward decreasing fusion rates with longer exposure times. When the hydrogen peroxide washed DBM preparations were also radiation treated, the resulting fusion rates were again not significantly different (p<.05). Agreement among fusion detection methods was found to be high. CONCLUSIONS: Hydrogen peroxide processing was not detrimental to fusion rates. The additional terminal sterilization technique with special gamma irradiation protocols (Clearant process) also did not decrease the fusion rates but could provide an additional margin of safety.     

Head penetration into Hylamer acetabular liner sterilized by gamma irradiation in air and in a nitrogen atmosphere

We reviewed 25 consecutive primary cementless total hip arthroplasties with Hylamer acetabular liners (Hylamer group) and 12 with conventional ultra-high molecular weight polyethylene (Enduron group). Two-dimensional penetration of the femoral head into the liner was determined from anteroposterior radiographs of the pelvis. Head penetration rate was 0.37 mm/y in the Hylamer group sterilized by gamma irradiation in air (n = 6; mean length of follow-up, 3 years), 0.21 mm/y in the Hylamer group sterilized by gamma irradiation in a nitrogen atmosphere (n = 19; mean length of follow-up, 2.7 years), and 0.11 mm/y in the Enduron group (n = 12; mean length of follow-up, 3.9 years). Osteolysis was identified in 6 of the 25 hips with Hylamer liners and 1 of the 12 hips with conventional liners. There was a positive linear correlation between period from production to operation and head penetration rate with Hylamer liner sterilized by gamma irradiation in air and no correlation in a nitrogen atmosphere. Rapid oxidation by irradiation in air might not be the main cause of high rate of wear in Hylamer liners.     

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.     

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.     

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.