Objective:To investigate the effects of different particle sizes on the collagen structure of demineralized bone matrix (DBM) and the effectiveness of dry ice as an irradiation protectant in the procedure of gamma irradiation.Methods:DBM samples with different particle sizes (0.5-1.0 mm, 1.2-2.8 mm, 3.3-4.7 mm and 5.7-7.0 mm) were prepared, and sterilized with several doses of gamma irradiation (0 kGy, 15 kGy and 25 kGy) at room temperature. Additionally, another group of DBM samples were sterilized with 25 kGy gamma irradiation with protective agent. Changes in surface and characteristics of collagen were observed by using scanning electron microscope (SEM), Sodium dodecyl sulfatepolyacrylamide gel electrophoresis (SDS-PAGE), differential scanning calorimetry (DSC) and carbonyl content.Results:The color of collagen extract indicated that oxidative damage is directly related to irradiation dose. SEM showed that the gamma irradiation caused collagen structure disorder and fiber breakage. As the irradiation doses increased, the damage area significantly increased. When the particle size increased, the damage area tended to decrease. The DSC showed that the thermal denaturation temperature of 5.7-7 mm, 3.3-4.7 mm, 1.2-2.8 mm and 0.5-1.0 mm were 142.8℃, 97.3℃,84.3℃ and 83.9℃, respectively. The differences of the thermal denaturation temperatures among the four particle sizes were statistically significant ( F=0.560, P=0.650). Collagen structure was destroyed by gamma irradiation, resulting in a decrease in collagen molecular weight. While, large particle DBM had a tendency to resist radiation damage. There was a significant difference on the contents of carbonyl in collagen from same particle sizes of DBM with different irradiation dose. The carbonyl content gradually decreased with the increase of particle size, but the difference was not statistically significant ( F=0.560, P=0.650). Conclusion:The gamma irradiation and collagen oxidative damage have obvious dose-response relationship. With the increase of gamma irradiation dose, the degree of collagen damage increases. The sizes of DBM could affect the sensitivity of collagen to gamma irradiation. With the decrease of particle sizes, DBM particles are more susceptible to gamma irradiation damage. Additionally, dry ice, as a radiation protection agent, has a certain degree protection effect against radiation.

Objective To identify prognostic factors ofmotorfunctionafter surgery of metastatic spinal cord compression (MSCC).Methods The clinical data of 681 patients with spinal metastases from January 2008 to December 2017 were retrospectively analyzed.According to inclusion and exclusion criteria,a total of 206 patients with spinal metastatic were included.Postoperative neurological function was assessed using Frankel classification.The influence of age,gender,preoperative status,number of spine metastases,location of spinal metastases,visceral metastases,bone metastases,primary tumor type,interval from symptom to surgery,time of developing motor deficits,interval from primary tumor diagnosis to MSCC,preoperativethe Eastern Cooperative Oncology Group performance status (ECOG-PS),Karnofsky Performance score (KPS) and surgical procedures on postoperative function outcomes were explored.Results 140 (68.0％) patients were able to walk postoperatively compared with 88 (42.7％) patients preoperatively.Moreover,in 89.8％ of all patients,79 ambulatory patients maintained ambulation after treatment.The univariate analysis according to Ordered-logit model showed thatnumber of spine metastases,location of spinal metastases,preoperative ECOG-PS,preoperative KPS,interval from symptom to surgery and time of developing motor deficits were related with posttreatment motor functions.The multivariable analysis showed that number of spine metastases (OR=2.03;95％CI:1.12-3.33;P=0.04),preoperative ECOG-PS (OR=4.84;95％CI:2.42-8.15;P=0.038),interval from symptom to surgery (OR=3.78;95％CI:3.12-9.15;P=0.024),time of developing motor deficits(OR=2.75;95％CI:1.22-3.89;P=0.01) were independent prognostic factors for function outcomes.Conclusion 1-2 levels of metastasis,Interval from symptom to treatment ≥ 48 h,time of developing motor deficits ≥7 d,and ECOG-PS 1-2 can be considered as the most significant positive prognosticfactors for post-treatment ambulatory status.Spinal metastasis should have a higher priority,and immediate intervention should be started before the development of irreversible neurologic deficits.Increasing awareness of early symptoms and earlier screeningwith regular outpatient review might make a difference for patients with MSCC.Consequently,the identified prognostic factors can be considered as apreoperative assessment tool to predict the neurologic outcomeand guide clinical treatment for individual patients with MSCC.