Effects of tissue preservation on murine bone mechanical properties

Murine bone specimens are used extensively in skeletal research to assess the effects of environmental, physiologic and pathologic factors on their mechanical properties. Given the destructive nature of mechanical testing, it is normally performed as a terminal procedure, where specimens must be preserved without affecting their mechanical properties. To this end, we aimed to study the effects of tissue preservation (freezing and formalin fixation) on the elastic and viscoelastic mechanical properties of murine femur and vertebrae. A total of 120 femurs and 180 vertebral bodies (L3–L5) underwent non-destructive cyclic loading to assess their viscoelastic properties followed by mono-cyclic loading to failure to assess their elastic properties. All specimens underwent re-hydration in 0.9% saline for 30 min prior to mechanical testing. Analysis indicated that stiffness, modulus of elasticity, yield load, yield strength, ultimate load and ultimate strength of frozen and formalin-fixed femurs and vertebrae were not different from fresh specimens. Cyclic loading of both femurs and vertebrae indicated that loss, storage and dynamic moduli were not affected by freezing. However, formalin fixation altered their viscoelastic properties. Our findings suggest that freezing and formalin fixation over a 2-week period do not alter the elastic mechanical properties of murine femurs and vertebrae, provided that specimens are re-hydrated for at least half an hour prior to testing. However, formalin fixation weakened the viscoelastic properties of murine bone by reducing its ability to dissipate viscous energy. Future studies should address the long-term effects of both formalin fixation and freezing on the mechanical properties of murine bone.     

The high frequency properties of brain tissue

Computer modeling is becoming increasingly important in the realm of brain biomechanics and injury. New computer simulations range from modeling of brain surgery, a low frequency, high strain event, to predicting injury as a result of an impact to the head, a high frequency event with varying strain magnitudes. This range of modeling efforts requires characterization of the tissue over as wide a frequency and strain range as possible. Research done to date has concentrated on the low frequency properties of the tissue. Complex compression and complex shear moduli have been measured at frequencies up to 350 Hz. Impact modeling requires use of frequency data at significantly higher frequencies than these. The "wave-in-a-tube" ultrasonic method was applied to brain tissue to determine mechanical properties at frequencies between 100 kHz and 10 MHz. Of these properties, only complex bulk modulus |K*| is fairly invariant (2133 MPa) with respect to frequency. Complex shear and complex Young's moduli vary with frequency and approach an asymptotic upper limit. Some variation in complex Poisson's ratio was also observed.     

A comprehensive experimental study on material properties of human brain tissue

A comprehensive study on the biomechanical response of human brain tissue is necessary to investigate traumatic brain injury mechanisms. Published brain material property studies have been mostly performed under a specific type of loading, which is insufficient to develop accurate brain tissue constitutive equations. In addition, inconsistent or contradictory data in the literature made it impossible for computational model developers to create a single brain material model that can fit most, if not all, experimental results.     

Effects of high temperature on reproduction

The significance of seasonal fluctuations in the components of the reproductive cycle is complex. In mammals, high environmental temperature may cause delayed puberty, delayed onset of sexual season, irregularity in cycle length, duration of estrus, ovulation rate, frequency of anovulatory estrus,morphological abnormalities in ova, fetal size and semen characteristics. High temperatures, in birds, may affect rate of egg laying, egg weight, shell quality, fertility, size of blastoderm and hatchability. Animals have developed effective thermoregulatory mechanisms for the testis. The effects of extremes of temperatures on reproduction vary with the species,breed, age, stage of reproductive cycle,period of temperature exposure, nature of temperature fluctuation and altitude. Effects of low temperature on reproduction have been little studied.

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Zusammenfassung Die Bedeutung von jahreszeitlichen Schwankungen der Komponenten im Fortpflanzungszyklus ist komplex. Bei SÄugetieren kann hohe Temperatur eine verspÄtere PubertÄt bewirken, spÄten Beginn der Brunst, UnregelmÄssigkeiten in der ZykluslÄnge,Oestrusdauer, Ovulationsrate und HÄufigkeit von anovulatorischen Oestrus, morphologische AbnormalitÄten der Eier, der Fötengrösse und des Samens.Bei Vögeln können hohe Temperaturen die LegetÄtigkeit, Eigewicht, SchalenqualitÄt, Fruchtbarkeit, Grösse des Blastoderms und Ausbrütbarkeit beeinflussen. Tiere haben wirksame thermoregulatorische Mechanismen für die Hoden entwickelt.Die Einflüsse von Temperaturextremen auf die Fortpflanzung variiert mit der Tierart, Zucht, Alter,Stadium im Fortpflanzungszyklus, Temperatureinwirkungszeit, Art der Temperaturschwankungen und Höhe. Die Bedeutung niedriger Temperatur für die Fortpflanzung ist noch wenig untersucht.

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Resume L'importance des fluctuations saisonnières sur le cycle de reproduction est complexe. Chez les mammifères, une température élevée peut causer un retard de la puberté et du rut des irrégularités de la durée du cycle et de l'oestrus ainsi que de la fréquence des ovulations; les cycles anovulatoires, les anomalies morphologiques de l'oeuf, de la semence et les variations de la grandeur fétale sont plus frequents. Chez les oiseaux les hautes températures peuvent influencer la ponte, le poids de l'oeuf, la qualité de la coquille, la fertilité, la grandeur de blastoderme et la tendance à couver. Les animaux ont développé des mécanismes thermorégulateurs efficaces pour les testicules. Les influences des extrÊmes de température sur la reproduction varient avec l'espèce, la race, l'âge,le stade du cycle de reproduction, la nature et la durée des différences de température et l'altitude. L'influence des basses températures sur la reproduction n'a pas encore été bien étudiée.

     

Alpha-tocopherol in the brain tissue preservation of stroke-prone spontaneously hypertensive rats

Oxidative stress has an important role in neuronal damage during cerebral ischemia and can lead to cognitive and behavioral impairment. Alpha-tocopherol, a powerful antioxidant, may be able to preserve neuronal tissue and circumvent neurological deficits. Thus, this study aimed to investigate the influence of alpha-tocopherol in the preservation of brain tissue and the maintenance of memory formation in stroke-prone spontaneously hypertensive rats (SHRSP). To achieve this aim, twenty-four 15-week-old male SHRSP rats were separated into the following four groups (n?=?6 each) that received different treatments over a 4-week period: the alpha-tocopherol group, the control group, the L-NAME group, and the L-NAME?+?alpha-tocopherol group. We evaluated the physiological parameters (body weight, diuresis, and food and water intake), an oxidative stress marker (malondialdehyde levels), and neurological responses (the Morris Water Maze and Novel Objects Recognition tests). Afterwards, the brains were removed for histopathological analysis and quantification of the number of cells in the hippocampus. Statistically, the alpha-tocopherol group demonstrated better results when compared to all groups. The data indicated a reduction in oxidative stress and the preservation of neurological responses in groups treated with alpha-tocopherol. In contrast, the L-NAME group exhibited increased malondialdehyde levels, impairment of neurological responses, and several hippocampus tissue injuries. The others groups exhibited nerve tissue changes that were restricted to the glial nodes. No significant alterations were observed in the physiologic parameters. Based on these findings, we suggest that alpha-tocopherol can prevent stroke, preserve the structure of the hippocampus, and maintain both memory and cognition functions.     

Mechanical properties of brain tissue in tension

This paper contains experimental results of in vitro, uniaxial tension of swine brain tissue in finite deformation as well as proposes a new hyper-viscoelastic constitutive model for the brain tissue. The experimental results obtained for two loading velocities, corresponding to strain rates of 0.64 and 0.64 x 10(-2)s(-1), are presented. We believe that these are the first ever experiments of this kind. The applied strain rates were similar to those applied in our previous study, focused on explaining brain tissue properties in compression. The stress-strain curves are convex downward for all extension rates. The tissue response stiffened as the loading speed increased, indicating a strong stress-strain rate dependence. Swine brain tissue was found to be considerably softer in extension than in compression. Previously proposed in the literature brain tissue constitutive models, developed based on experimental data collected in compression are shown to be inadequate to explain tissue behaviour in tension. A new, non-linear, viscoelastic model based on the generalisation of the Ogden strain energy hyper-elastic constitutive equation is proposed. The new model accounts well for brain tissue deformation behaviour in both tension and compression (natural strain in <-0.3,0.2>) for strain rates ranging over five orders of magnitude.     

Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin exposure on bone material properties

Dioxins are known to decrease bone strength, architecture and density. However, their detailed effects on bone material properties are unknown. Here we used nanoindentation methods to characterize the effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on nanomechanical behaviour of bone matrix.Pregnant rats were treated with a single intragastric dose of TCDD (1 μg/kg) or vehicle on gestational day 11. Tibias of female offspring were sampled on postnatal day (PND) 35 or 70, scanned at mid-diaphysis with pQCT, and evaluated by three-point bending and nanoindentation.TCDD treatment decreased bone mineralization (p<0.05), tibial length (p<0.01), cross-sectional geometry (p<0.05) and bending strength (p<0.05). Controls showed normal maturation pattern between PND 35 and 70 with decreased plasticity by 5.3% and increased dynamic hardness, storage and complex moduli by 26%, 13% and 12% respectively (p<0.05), while similar maturation was not observed in TCDD-exposed pups.In conclusion, for the first time, we demonstrate retardation of bone matrix maturation process in TCDD-exposed animals. In addition, the study confirms that developmental TCDD exposure has adverse effects on bone size, strength and mineralization. The current results in conjunction with macromechanical behaviour suggest that reduced bone strength caused by TCDD is more associated with the mineralization and altered geometry of bones than with changes at the bone matrix level.     

The compressive material properties of the plantar soft tissue

The plantar soft tissue is the primary means of physical interaction between a person and the ground during locomotion. Dynamic loads greater than body weight are borne across the entire plantar surface during each step. However, most testing of these tissues has concentrated on the structural properties of the heel pad. The purpose of this study was to determine the material properties of the plantar soft tissue from six locations beneath: the great toe (subhallucal), the 1st, 3rd and 5th metatarsal heads (submetatarsal), the lateral midfoot (lateral submidfoot) and the heel (subcalcaneal). We obtained specimens from these locations from 11 young, non-diabetic donors; the tissue was cut into 2 cm x 2 cm blocks and the skin was removed. Stress relaxation experiments were conducted and the data were fit using the quasi-linear viscoelastic (QLV) theory. To determine tissue modulus, energy loss and the effect of test frequency, we also conducted displacement controlled triangle waves at five frequencies ranging from 0.005 to 10 Hz. The subcalcaneal tissue was found to have an increased relaxation time compared to the other areas. The subcalcaneal tissue was also found to have an increased modulus and decreased energy loss compared to the other areas. Across all areas, the modulus and energy loss increased for the 1 and 10 Hz tests compared to the other testing frequencies. This study is the first to generate material properties for all areas of the plantar soft tissue, demonstrating that the subcalcaneal tissue is different than the other plantar soft tissue areas. These data will have implications for foot computational modeling efforts and potentially for orthotic pressure reduction devices.     

Effects of high temperature on body temperature and hormonal adjustments in piglets

Effects of a high (33 degrees C) or thermoneutral (23 degrees C) temperature on body temperature and endocrine parameters were studied in weaned piglets. Rectal and skin temperatures were measured in four ad libitum fed animals per temperature during three weeks. After this acclimation period, 11 blood samples were withdrawn on a 24-h period. Over the acclimation period, rectal and skin temperatures were 0.6 and 2.9 degrees C higher, respectively, at 33 degrees C than at 23 degrees C (P < 0.01), this change occurring from the 1st day at 23 or 33 degrees C. A tendency of serum leptin concentrations to be lower after meals at 33 degrees C than at 23 degrees C was also displayed (P = 0.09). Plasmatic concentrations in Insulin-like growth factor I and thyroxine were decreased at 33 degrees C relative to 23 degrees C (P < 0.01 and P < 0.06, respectively), and triiodothyronine concentrations tended to be lower at 33 degrees C than at 23 degrees C (P = 0.1), which could account for the lower heat production and growth observed in pigs exposed to high temperatures.     

Enhancement of structural preservation and immunocytochemical staining in low temperature embedded pancreatic tissue

The recently developed low temperature embedding procedure with the resin Lowicryl K4M (Carlemalm E, Garavito M, Villiger W: Proc 7th Eur Cong Electron Microsc, 1980, p 656; Garavito M, Carlemalm E, Villiger W: Proc 7th Eur Cong Electron Microsc, 1980, p 658) was tested for its suitability for embedding of glutaraldehyde-fixed rat pancreatic tissue and for postembedding staining of thin sections with the protein A-gold (pAg) technique (Roth J, Bendayan M, Orci L: J Histochem Cytochem 26:1074, 1978) for amylase. Compared to conventional Epon embedding of glutaraldehyde fixed tissue, the low temperature embedding method with Lowicryl K4M resulted in a superior preservation of the general cellular fine structure, particularly in the Golgi apparatus. For low temperature embedded tissue, the quantitative evaluation of the immunocytochemical labeling for amylase showed a more specific staining of the rough endoplasmic reticulum, the Golgi apparatus, and the zymogen granules. This was due to a significant lowering of the background staining over all cellular organelles. The use of Lowicryl K4M at low temperature, due to the superior preservation, yields improved resolution and specificity in immunocytochemical postembedding staining.     

Effects of air movement on swine at high temperature

Sixty pigs were used to study the effects of air movement (0.05, 0.5, and 1.0 m/s) at constant air temperatures of either 5.6 or 11.1°C above optimum, and at 3 different weight ranges (36–50kg, 54–68 kg, and 73–86 kg) during the growing-finishing stages. An air velocity of 0.5 m/s produced significantly greater weight gain and feed conversion than did 0.05 m/s. An air velocity of 1.0 m/s produced intermediate results.     

高温对玉米螟赤眼蜂实验种群的影响

以米蛾卵为繁育寄主,组建了玉米螟赤眼蜂在26、29、32和35 ℃下的实验种群生命表,探讨了高温对玉米螟赤眼蜂生长和生殖的影响.结果表明,高温32 ℃～35 ℃对玉米螟赤眼蜂各虫态的生长发育有明显的抑制作用.卵 幼虫的存活率在26 ℃和29 ℃分别为 94.2%和88.6%,32 ℃时下降至80.2%,而35 ℃时仅为53.2%,蛹的存活率也表现出相应的下降趋势.玉米螟赤眼蜂羽化后12 h内的抱卵量、体长及卵粒大小随温度的升高而减少或变小.26 ℃时,玉米螟赤眼蜂羽化后0～12 h的抱卵量为37.9粒,随着温度的升高,抱卵量急剧下降,29 ℃、32 ℃和35 ℃的抱卵量分别为29.6、21.6和13.7粒.在26 ℃及29 ℃时,所有雌蜂均能进行正常交配和产卵,32 ℃时有6.7%的个体不产卵,至35 ℃时,则有60%的个体不能进行正常的生殖活动.     

Inverse identification of region-specific hyperelastic material parameters for human brain tissue

The identification of material parameters accurately describing the region-dependent mechanical behavior of human brain tissue is crucial for computational models used to assist, e.g., the development of safety equipment like helmets or the planning and execution of brain surgery. While the division of the human brain into different anatomical regions is well established, knowledge about regions with distinct mechanical properties remains limited. Here, we establish an inverse parameter identification scheme using a hyperelastic Ogden model and experimental data from multi-modal testing of tissue from 19 anatomical human brain regions to identify mechanically distinct regions and provide the corresponding material parameters. We assign the 19 anatomical regions to nine governing regions based on similar parameters and microstructures. Statistical analyses confirm differences between the regions and indicate that at least the corpus callosum and the corona radiata should be assigned different material parameters in computational models of the human brain. We provide a total of four parameter sets based on the two initial Poisson’s ratios of 0.45 and 0.49 as well as the pre- and unconditioned experimental responses, respectively. Our results highlight the close interrelation between the Poisson’s ratio and the remaining model parameters. The identified parameters will contribute to more precise computational models enabling spatially resolved predictions of the stress and strain states in human brains under complex mechanical loading conditions.

     

采后预温处理对草莓果实贮藏保鲜效果的影响

研究了采后预温处理对草莓果实贮藏保鲜的影响,结果表明,冷藏(5℃)条件下,贮前50℃预热处理30m in的果实腐烂率最低;室温贮藏(19℃~21℃)条件下,50℃预热处理30m in、5℃预冷处理30m in的果实腐烂率最低;贮藏前期,果实中超氧化物歧化酶(SOD)活性、丙二醛(MDA)含量不断上升,预热处理能明显提高果实的SOD活性;贮藏后期,果实SOD活性不断下降、MDA含量持续上升,预处理能显著抑制果实SOD活性的下降和MDA含量的增加。     

Effects of tissue storage and freezing on brain glutamate uptake

Glutamate uptake appears to be stable when measured in rat striatal synaptosomes from tissue stored for up to four hours post-mortem at 25°C. Between four and eight hours storage at room temperature there is a sharp 70% decrease in uptake. Freezing of tissue on dry ice, storage at 4°C for up to 7 days and at ?80°C for 5 days results in 20–30% residual glutamate uptake. Quantitatively similar data can be obtained in eight extrastriatal brain areas. Kinetic analysis of glutamate uptake in stored and frozen tissue reveals the loss of the majority of both sodium-dependent high affinity and temperature-sensitive low affinity sites (v_max-values) while the respective K_m-values are not significantly changed. Pharmacological properties of the high affinity uptake versus a number of specific and metabolic uptake inhibitors remain unaltered by the storage and freezing procedure. The tissue treatment chosen for the present study roughly corresponds with the preparation of human post-mortem brain tissue for enzyme-, receptor-binding- or neuro-transmitter assays. It therefore seems conceivable that meaningful uptake studies can be performed on human autopsy material, thus adding an important parameter to the battery of neurochemical markers already accessible for post-mortem $\text{in}$$\text{vitro}$ examination.     

Effects of low-molecular-weight aluminum complexes on brain tissue calcium homeostasis

The in vitro effects of low-molecular-weight aluminum complexes (citrate, lactate, and ATP complex) on the Ca²⁺ uptake and aluminum-induced lipid peroxidation of brain tissue show that the modification of the calcium homeostasis is determined by the nature of the ligand and that there is no correlation between the aluminum-induced lipid peroxidation and the Ca²⁺ uptake. The same characteristics have been shown by a similar study performed with Ehrlich carcinoma cells. The electrophoretic analyses of the aluminum lactate-albumin and aluminum lactate-ATP interactions indicate an aluminum transfer from the lactate to the albumin and ATP ligands. The increased Ca²⁺ uptake when ATP is present in the incubation medium with aluminum citrate and aluminum lactate corroborates the suggested mediator role of ATP in cellular calcium homeostasis modification induced by iron.