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1.
An apparatus is described that enables the application of continuous pure moment loads to multi-segment spine specimens. This loading apparatus allows continuous cycling of the spine between specified flexion and extension (or right and left lateral bending) maximum load endpoints. Using a six-degree-of-freedom load cell and three-dimensional optoelectronic stereophotogrammetry, characteristic displacement versus load hysteresis curves can be generated and analyzed for different spinal constructs of interest. Unlike quasi-static loading, the use of continuous loading permits the analysis of the spine's behaviour within the neutral zone. This information is of particular clinical significance given that the instability of a spinal segment is related to its flexibility within the neutral zone. Representative curves for the porcine lumbar spine in flexion-extension and lateral bending are presented to illustrate the capabilities of this system.  相似文献   

2.
An increasing number of tissue banks have begun to focus on gamma irradiation and freeze-thaw in the reconstruction of anterior cruciate ligaments using allografts. The purpose of this study was to evaluate the biomechanical properties of human tendons after exposure to gamma radiation and repeated freeze-thaw cycles and to compare them with fresh specimens. Forty flexor digitorum superficialis tendons were surgically procured from five fresh cadavers and divided into four groups: fresh tendon, gamma irradiation, freeze-thaw and gamma irradiation+freeze-thaw. The dose of gamma irradiation was 25 kGy. Each freeze-thaw cycle consisted of freezing at -80 °C for 7 day and thawing at 25 °C for 6 h. These tendons underwent 4 freeze-thaw cycles. Biomechanical properties were analyzed during load-to-failure testing. The fresh tendons were found to be significantly different in ultimate load, stiffness and ultimate stress relative to the other three groups. The tendons of the gamma+freeze-thaw group showed a significant decrease in ultimate load, ultimate stress and stiffness compared with the other three groups. Gamma irradiation and repeated freezing-thawing (4 cycles) can change the biomechanical properties. However, no significant difference was found between these two processes on the effect of biomechanical properties. It is recommended that gamma irradiation (25 kGy) and repetitive freeze-thaw cycles (4 cycles) should not be adopted in the processing of the allograft tendons.  相似文献   

3.
荒漠区冻融交替显著改变土壤温度和水分条件,并进一步影响荒漠植物种子萌发.为解析荒漠土壤冻融过程对植物种子萌发的影响,本研究以古尔班通古特沙漠4种典型短命植物[东方旱麦草(Eremopyrum orientale)、卵果鹤虱(Lappula patula)、尖喙拢牛儿苗(Erodiumoxyrrhychum)和条叶庭荠(...  相似文献   

4.
Regarding cryoablation for the malignant lung tumors, multiple trials of the freeze-thaw process have been made, and we considered it necessary to view and analyze the freeze-thaw process as a freeze-thaw sequence. We caused the sequence in a porcine lung in vivo by using an acicular, cylindrical stainless-steel probe as the heat source for the freeze-thaw sequence and cooling to -150 °C with super high-pressure argon gas by causing the Joule-Thomson effect phenomenon at the tip of the probe. In this experiment, we examined the sequence by measuring the temperature and using the isothermal curve and the freezing function. As a result, it was demonstrated that the freezing characteristics considerably differed in the first sequence and the second sequence from those of non-aerated organs such as liver and kidney. In our experiments on porcine lung, thermal properties were considered to change as the bleeding caused by the first thawing infiltrated in the lung parenchyma, and it was confirmed that the frozen area in the second cycle was dramatically enlarged as compared with the first cycle (when a similar sequence is continuously repeated, we say it as cycle). This paper provides these details.  相似文献   

5.
Corneal cryopreservation with dextran.   总被引:3,自引:0,他引:3  
Different methods of corneal cryopreservation have been introduced, those employing intracellular cryoprotectants such as Me2SO or glycerol being the most widely favored. We investigated the influence of several freeze-thaw trauma variables on the survival of porcine endothelial monolayers when employing the extracellular cryoprotective agent dextran. We first examined the effects of various dextran concentrations and then, having ascertained the optimal concentration, further investigated the influence of fetal calf serum (FCS) concentration in the cryopreservation medium, the cooling rate, the thawing temperature, and the length of the preincubation in the freezing medium prior to cryopreservation. The numerical densities of endothelial cells were determined at dissection in hypoosmotic balanced salt solution and after organ culture by staining with alizarin red S and trypan blue. Morphological evaluation was not performed directly after thawing but after a subsequent organ culture at 37 degrees C to detect latent cell damage after freeze-thaw trauma. Our data revealed that corneas cryopreserved in minimal essential medium containing 10% dextran but lacking FCS, preincubated for 3 h, frozen at a cooling rate of 1 degrees C/min, and thawed at 37 degrees C incurred the lowest cell losses (22.4%, SD +/- 3.8). We conclude that dextran is an effective cryoprotectant for freezing of porcine corneas. However, variations between species in the results of cryopreservation require further investigation of an in vivo animal model and studies with human corneas before its clinical use can be recommended.  相似文献   

6.
The effect of various thawing velocities on the motility and acrosomal maintenance of ram spermatozoa frozen at 20 degrees C/min (optimal) or 2 degrees C/min (suboptimal) was studied. The freeze-thaw motility and the percentage of intact acrosomes of spermatozoa frozen at 20 degrees C/min increased progressively with the thawing velocity. In semen frozen at 2 degrees C/min, motility of spermatozoa and the percentage of intact acrosomes declined drastically when the thawing velocity obtained in air at 20 degrees C was increased by thawing in water at 20 degrees C. Thawing at higher temperatures markedly increased both motility and acrosomal preservation, but the best results with semen frozen at 2 degrees C/min were lower than those obtained with semen frozen at 20 degrees C/min. The optimal freeze-thaw conditions for semen protected by 4% glycerol were freezing at 20 degrees C/min and thawing in water at 60 or 80 degrees C for 8 or 5 sec, respectively. Semen collected from rams exposed to a decreasing photoperiod exhibited higher motility after freezing and thawing than those exposed to an increasing photoperiod. However, there was no effect on acrosomal preservation after freezing at 20 degrees C/min.  相似文献   

7.
Tian JH  Wu ZH  Liu L  Cai Y  Zeng SM  Zhu SE  Liu GS  Li Y  Wu CX 《Theriogenology》2006,66(2):439-448
The objective was to determine the effects of various methods of oocyte activation and sperm pretreatment on development of porcine embryos derived from in vitro-matured oocytes and intracytoplasmic sperm injection (ICSI). The second polar body was extruded in the majority (>78.4%) of in vitro-matured (IVM) oocytes 4h after electrical pulse activation. In embryos generated by ICSI and sham-ICSI, a combination of an electrical pulse, with various chemical activators 4 h later, improved (P < 0.05) blastocyst formation rate compared to activation only with a pulse. Treatment with 6-dimethylaminopurine (DMAP) after electrical activation significantly increased the oocyte activation rate. The effects of exposure of sperm to repeated freeze-thaw cycles (without cryoprotectant) on oocyte activation and the effects of sperm pre-incubated with dithiothreitol (DTT) or Triton X-100 on early embryo development were also examined. Blastocyst formation rates after ICSI did not differ between motile sperm and those rendered immotile by one-time freezing and thawing without cryoprotectant. However, sperm rendered immotile by three cycles of freezing/thawing without cryoprotectant had a significantly lower blastocyst formation rate. Although oocytes injected with sperm pre-incubated with Triton X-100 had a higher normal fertilization rate than those pre-incubated with DTT or one-time frozen/thawed sperm, rates of blastocyst formation and cell numbers were similar among the three groups. In conclusion, various methods of oocyte activation and sperm preparation significantly affected the developmental capacity of early porcine embryos derived from IVM and ICSI.  相似文献   

8.
Freeze-thaw tolerance and clues to the winter survival of a soil community   总被引:2,自引:0,他引:2  
Although efforts have been made to sample microorganisms from polar regions and to investigate a few of the properties that facilitate survival at freezing or subzero temperatures, soil communities that overwinter in areas exposed to alternate freezing and thawing caused by Foehn or Chinook winds have been largely overlooked. We designed and constructed a cryocycler to automatically subject soil cultures to alternating freeze-thaw cycles. After 48 freeze-thaw cycles, control Escherichia coli and Pseudomonas chlororaphis isolates were no longer viable. Mixed cultures derived from soil samples collected from a Chinook zone showed that the population complexity and viability were reduced after 48 cycles. However, when bacteria that were still viable after the freeze-thaw treatments were used to obtain selected cultures, these cultures proved to be >1,000-fold more freeze-thaw tolerant than the original consortium. Single-colony isolates obtained from survivors after an additional 48 freeze-thaw cycles were putatively identified by 16S RNA gene fragment sequencing. Five different genera were recognized, and one of the cultures, Chryseobacterium sp. strain C14, inhibited ice recrystallization, a property characteristic of antifreeze proteins that prevents the growth of large, potentially damaging ice crystals at temperatures close to the melting temperature. This strain was also notable since cell-free medium derived from cultures of it appeared to enhance the multiple freeze-thaw survival of another isolate, Enterococcus sp. strain C8. The results of this study and the development of a cryocycler should allow further investigations into the biochemical and soil community adaptations to the rigors of a Chinook environment.  相似文献   

9.
Traumatic injuries of the spine are mostly the consequence of rapid overload e.g. impact loading. In vitro investigations on this topic usually encompass biomechanical testing using frozen/thawed specimens and employ quasi-static loading conditions. It is generally accepted that a freezing/thawing cycle does not alter mechanical properties for slow loading rates. However, this has never been investigated for high impact velocities. In order to assess the effects of freezing/thawing and the influence of different impact velocities, we loaded 27 fresh and 15 frozen/thawed cadaveric rabbit spinal segments (intervertebral disc with one third of the adjacent vertebrae) with different impact energies and velocities using a custom-made, dropped-weight loading device. Endplate fractures were assessed by micro-CT scans. Specimen dimensions (disk, bone, and total height) and vertebrae bone density (BV/TV) were compared pre- and post-trauma. Energy absorption by spinal segments was quantified by measuring the initial ball rebound. We found that freezing/thawing increased endplate fracture frequency and decreased the energy absorption of the segments. Higher impact velocities increased the energy absorption, while higher impact energy increased both energy absorption and fracture frequency. Two conclusions are drawn: first, under impact loading, freezing alters permanently the biomechanical response, and second, for different impact velocities, different fracture initiation mechanisms apply. Therefore, quasi-static loading of frozen/thawed spinal segments is not a valid model for traumatic endplate injuries. However, caution should be exercised in extrapolating these findings to human vertebrae until tests on larger vertebrae are performed.  相似文献   

10.
Rodent models are commonly used to investigate tendon healing, with the biomechanical and structural properties of the healed tendons being important outcome measures. Tendon storage for later testing becomes necessary when performing large experiments with multiple time-points. However, it is unclear whether freezing rodent tendons affects their material properties. Thus the aim of this study was to determine whether freezing rat Achilles tendons affects their biomechanical or structural properties. Tendons were frozen at either −20 °C or −80 °C directly after harvesting, or tested when freshly harvested. Groups of tendons were subjected to several freeze-thaw cycles (1, 2, and 5) within 3 months, or frozen for 9 months, after which the tendons were subjected to biomechanical testing. Additionally, fresh and thawed tendons were compared morphologically, histologically and by transmission electron microscopy. No major differences in biomechanical properties were found between fresh tendons and those frozen once or twice at −20 °C or −80 °C. However, deterioration of tendon properties was found for 5-cycle groups and both long-term freezing groups; after 9 months of freezing at −80 °C the tear resistance of the tendon was reduced from 125.4 ± 16.4N to 74.3 ± 18.4N (p = 0.0132). Moreover, tendons stored under these conditions showed major disruption of collagen fibrils when examined by transmission electron microscopy. When examined histologically, fresh samples exhibited the best cellularity and proteoglycan content of the enthesis. These properties were preserved better after freezing at −80 °C than after freezing at −20 °C, which resulted in markedly smaller chondrocytes and less proteoglycan content. Overall, the best preservation of histological integrity was seen with tendons frozen once at −80 °C. In conclusion, rat Achilles tendons can be frozen once or twice for short periods of time (up to 3 months) at −20 °C or −80 °C for later testing. However, freezing for 9 months at either −20 °C or −80 °C leads to deterioration of certain parameters.  相似文献   

11.
Although efforts have been made to sample microorganisms from polar regions and to investigate a few of the properties that facilitate survival at freezing or subzero temperatures, soil communities that overwinter in areas exposed to alternate freezing and thawing caused by Foehn or Chinook winds have been largely overlooked. We designed and constructed a cryocycler to automatically subject soil cultures to alternating freeze-thaw cycles. After 48 freeze-thaw cycles, control Escherichia coli and Pseudomonas chlororaphis isolates were no longer viable. Mixed cultures derived from soil samples collected from a Chinook zone showed that the population complexity and viability were reduced after 48 cycles. However, when bacteria that were still viable after the freeze-thaw treatments were used to obtain selected cultures, these cultures proved to be >1,000-fold more freeze-thaw tolerant than the original consortium. Single-colony isolates obtained from survivors after an additional 48 freeze-thaw cycles were putatively identified by 16S RNA gene fragment sequencing. Five different genera were recognized, and one of the cultures, Chryseobacterium sp. strain C14, inhibited ice recrystallization, a property characteristic of antifreeze proteins that prevents the growth of large, potentially damaging ice crystals at temperatures close to the melting temperature. This strain was also notable since cell-free medium derived from cultures of it appeared to enhance the multiple freeze-thaw survival of another isolate, Enterococcus sp. strain C8. The results of this study and the development of a cryocycler should allow further investigations into the biochemical and soil community adaptations to the rigors of a Chinook environment.  相似文献   

12.
《Reproductive biology》2020,20(1):75-80
Refreezing of sperm samples would provide the possibility of performing more cycles of fertility treatments. Although the effect of repeated cycles of freezing on sperm quality was studied, the effect of the length of the time interval between each freeze-thaw cycle has not been reported. Hence, we assessed the effect of incubation time on the sperm quality of thawed sperm after repeated freezing.One-hundred samples of potential sperm donations with normal sperm quality were evaluated. The fresh semen samples were analyzed and cryopreserved in liquid nitrogen until use. After thawing, the samples were divided randomly to two groups and reanalyzed for motility, vitality, and DNA fragmentation. They were incubated at room temperature and reanalyzed after either 90 min (group A) or 180 min (group B) of incubation, and once again after a repeated cycle of freezing and thawing.Our results showed that the sperm parameters of fresh samples of both groups were similar. After one freeze-thaw cycle, both groups still had comparable values. At the end of their respective incubation time periods, however, there was a significant difference in the mean values of the assessed parameters between the two groups (p < 0.01). An additional freeze-thaw cycle further exacerbated those differences, with group B undergoing an even more substantial decline (p < 0.001).Our data suggest that thawed human spermatozoa sustain a significant decline in sperm parameters in association with longer incubation time, which is further exacerbated by an additional freeze-thaw cycle.  相似文献   

13.
Spinal injuries are a great cost to society and the afflicted individuals. It is well known that most spinal injuries are not bony fractures but rather soft tissue lesions falling in the 'subfailure' region. For the clinical diagnosis of spinal injuries, abnormal motion patterns under physiological loads are considered an important factor. The purpose of the present study was to determine the onset and progression of spinal injury, and compare the sensitivity of three motion parameters: neutral zone (NZ), elastic zone (EZ), and range of motion (ROM). Spinal injury was defined as a significant increase in any of the three motion parameters. A repeatable high-speed flexion-compression load vector was applied individually to six porcine cervical spine specimens. Several impacts of increasing severity were applied to each specimen. After each impact, flexion-extension motion was measured. Neutral zone was the residual deformation from the neutral position to the position under zero load at the start of the final load cycle. Elastic zone was the displacement from zero load to the maximum load on the final load cycle. Range of motion was the sum of the neutral and elastic zones. The first significant increase in motion was determined by the neutral zone parameter with few observable anatomic lesions on the specimens. This was the onset of spinal injury. The next significant motion increase was also determined by the neutral zone parameter. After this motion increase, termed the progression of injury, ligament ruptures were observed in some specimens. It was concluded that the neutral zone was the most sensitive motion parameter in defining the onset and progression of spinal injury.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

14.
Over a ten-month period 736 embryos were collected from 103 cows induced to superovulate. Embryos were frozen in 10% glycerol and, after thawing, 655 appeared viable and were transferred nonsurgically to synchronous recipients. When embryos did not appear degenerative before freezing and transfers were performed within 3 hr of thawing, 40% of the embryos resulted in pregnancies. If embryos showed signs of degeneration before freezing, only 27% resulted in pregnancies after thawing and transfer. Similarly, when non-degenerative embryos were kept in Casou straws for more than 3 hr after thawing, fewer produced pregnancies (25%) following transfer. The number of embryos frozen in each vial ranged from one to 18 and this had no significant effect on success. By selecting embryos to be frozen and transferring them soon after thawing, the proportion of embryos surviving the freeze-thaw process can be very high.  相似文献   

15.
The paper investigates both fresh porcine spleen and liver and the possible decomposition of these organs under a freeze-thaw cycle. The effect of tissue preservation condition is an important factor which should be taken into account for protracted biomechanical tests. In this work, tension tests were conducted for a large number of tissue specimens from twenty pigs divided into two groups of 10. Concretely, the first group was tested in fresh state; the other one was tested after a freeze-thaw cycle which simulates the conservation conditions before biomechanical experiments. A modified Fung model for isotropic behavior was adopted for the curve fitting of each kind of tissues. Experimental results show strong effects of the realistic freeze-thaw cycle on the capsule of elastin-rich spleen but negligible effects on the liver which virtually contains no elastin. This different behavior could be explained by the autolysis of elastin by elastolytic enzymes during the warmer period after thawing. Realistic biomechanical properties of elastin-rich organs can only be expected if really fresh tissue is tested. The observations are supported by tests of intestines.  相似文献   

16.
The effects of single and repeated freezing and thawing of Setaria lutescens seeds in liquid nitrogen were investigated. One freeze to ?196 °C followed by a slow thaw, increased seed germination from 40 to 70%, but additional freeze-thaw cycles reduced germination to 30%. Using a scanning electron microscope, evidence was produced that seed coat cracking did not cause either initial increased, or subsequent reduced germination. Observations with a transmission electron microscope revealed that disruption of the integrity of lipid bodies accompanied increased damage from repeated freezing at ?196 °C and thawing. Repeated freezing and thawing of seeds stored in liquid nitrogen should be done with care to avoid loss of the germplasm.  相似文献   

17.
In vitro tests on the biomechanical properties of human spines are often performed using fresh frozen specimens. However, this carries the risk of pathogen transfer from specimen to the worker and the specimens can only be used for a limited amount of time. Human spinal specimens embalmed with formaldehyde carry an almost absent risk of transfer of pathogens and can be stored and used for a long time, but the tissue properties are strongly affected making this method inapplicable for biomechanical testing. In this study, a new embalming technique called Fix for Life (F4L), which claims to preserve the tissue properties, was tested. The range of motion (ROM) and stiffness of six fresh human spinal specimens was measured using a spinal motion simulator before and after F4L embalming. After F4L embalming, spinal stiffness increased in flexion-extension by 230%, in lateral bending by 284% and in axial rotation by 271%. ROM decreased by 46% in flexion-extension, 56% in lateral bending and 54% in axial rotation. In conclusion, based on this study, F4L does not maintain physiological spinal biomechanical properties, and we propose that this method should not be used for biomechanical studies. Nevertheless, the method may be an alternative to formaldehyde fixation in situations such as training and education because the effect on spinal biomechanics is less detrimental than formaldehyde and tissue color is maintained.  相似文献   

18.
谭波  吴福忠  杨万勤  余胜  刘利  王奥  杨玉莲 《生态学报》2012,32(21):6670-6678
川西亚高山/高山森林土壤通常具有明显的季节性冻融特征。为深入了解川西亚高山/高山森林冬季土壤生态过程,于2008年11月-2009年10月,在土壤初冻期、冻结期和融化期及生长季节,研究了不同海拔(3582 m、3292 m和3023 m)岷江冷杉林的土壤氧化还原酶活性及其对土壤冻融的响应。土壤冻结时间和冻融循环次数随海拔的增加而增加。冻融格局显著影响了土壤氧化还原酶活性,但不同土壤酶在不同海拔表现出明显差异。土壤过氧化物酶和脱氢酶活性受初冻期冻融循环和温度降低影响显著下降,而过氧化氢酶活性明显上升。3种土壤氧化还原酶活性在土壤温度相对稳定的冻结期变化不显著,但在融化期随着土壤温度急剧增加经历一个明显的活性高峰后快速降低,且冻结时间最长和冻融循环次数最多的3582 m变化更为显著。此外,海拔和土层的交互作用显著影响了过氧化物物活性,但对脱氢酶和过氧化氢酶活性不显著。脱氢酶活性与土壤温度极显著相关,但过氧化物酶和过氧化氢酶活性与土壤温度的相关性随海拔差异而不同。这些结果表明川西亚高山/高山森林冬季土壤氧化还原酶仍然具有较高的活性,但受到季节性冻融及其变化的显著影响。  相似文献   

19.
Formalin fixation strongly influences biomechanical properties of the spine   总被引:7,自引:0,他引:7  
As fresh human cadaveric spine specimens for in vitro testing are hard to obtain and carry a potential risk of infection, the possibility of using embalmed spine specimens has been considered. The cross-linking effect of formalin fixation, however, raises uncertainties regarding the biomechanical likeness of preserved specimens. They have been reported to be stiffer, but no quantitative data exist.

The purpose of this study was to determine the biomechanical differences between fresh and formalin-fixed spine specimens, using L1–2 motion segments from six 16-week-old calf spines. The range of motion and neutral zone were determined in flexion-/extension, left/right axial rotation, and right/left lateral bending.

The range of motion decreased in the formalin fixed specimens by as much as 80%, and the neutral zone by as much as 96%. The results of this study therefore imply that, for biomechanical testing, formalin-fixed specimens are not representative of the in vivo conditions.  相似文献   


20.
为了解季节性冻融及其变化对土壤动物群落特征的影响,于2008年11月-2009年10月的冬季(土壤冻融期、冻结期和融化期)及植被生长季节,研究了不同岷江冷杉(Abies faxoniana)林的大型土壤动物群落特征。共采集大型土壤动物10,763只,隶属于91科。冬季与生长季节土壤动物群落结构存在显著差异:冬季以长角毛蚊科幼虫和尖眼蕈蚊科幼虫为优势类群,大蚊科幼虫、苔甲科和蠓科幼虫等为常见类群;而生长季节以蚁科、隐翅甲科、长角毛蚊科幼虫和异蛩目为优势类群,原铗叭科、蝇科幼虫和石蜈蚣目等为常见类群。土壤动物群落个体密度、类群数量和多样性指数(H’)随冻融格局变化表现出先降低后升高的趋势,在土壤融化期达到了一个明显高峰值。冬季土壤动物以腐食性类群为主,捕食性和植食性功能类群在融化末期(4月25日)和生长季节初期(5月25日)显著增加。研究结果表明冻融循环和冻结作用显著影响土壤动物群落结构,季节转换过程中土壤动物群落的变化可能对深入认识冬季和生长季节生态过程的相互关系具有重要意义。  相似文献   

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