Effects of freezing rates and cryoprotectant on thermal expansion of articular cartilage during freezing process

The intact articular cartilage has not yet been successfully preserved at low temperature most likely due to the volume expansion from water to ice during freezing. The objective of this current study focuses on examining thermal expansion behavior of articular cartilage (AC) during freezing from 0 degree C to -100 degree C. Thermo Mechanical Analysis (TMA) was used to investigate the effects of different concentrations of dimethyl sulphoxide (DMSO) (0%, 10%, 30% and 60% v/v) and different freezing rates (1 C/min, 3 C/min and 5 C/min). The results showed that: (1) the inhomogeneous thermal expansion (or contraction) presents due to inhomogeneous water distributions in articular cartilage during freezing, which also may be the most likely reason that the matrix has been damaged in cryopreserved intact articular cartilage; (2) at the phase transition temperature range, the maximum thermal strain change value for 5C/min is approximately 1.45 times than that for 1 C/min, but the maximum thermal expansion coefficient of the later is about six times than that of the former; (3) the thermal expansion coefficient decreases with increasing cooling rate at the unfrozen temperature region, but some opposite results are obtained at the frozen temperature region; (4) the higher the DMSO concentration is, at the phase change temperature region, the smaller the thermal strain change as well as the maximum thermal expansion coefficient are, but DMSO concentration exhibits little effect on the thermal expansion coefficient at both unfrozen and frozen region. Once the DMSO concentration increasing enough, e.g. 60% v/v, the thermal strain decreases linearly and smoothly without any abrupt change due to little or no ice crystal forms (i.e. vitrification) in frozen articular cartilage. This study may improve our understanding of the thermal expansion (or contraction) behavior of cryopreserved articular cartilage and it may be useful for the future study on cryopreservation of intact articular cartilage.

The cryopreservation of a tissue engineered dermal replacement by programmed freezing

Long-term storag of engineered bio-artificial tissues is required to ensure the off-the-shelf availability to clinicians due to their long production cycle. Cryopreservation is likely the choice for long-term preservation. This study investigated the effects of dimethyl sulfoxide (DMSO) concentrations, cooling rates, cryoprotectant medium treatment methods and seeding on the cell viability of a tissue-engineered dermal substitute. The dermal fibroblast was cultured on a polyglycolic acid (PGA) scaffolding at 37degree C and a 5% CO<inf>2</inf>atmosphere for 14 days, and dermal slices (10&#215;3&#215;1.5mm) were used in the experimental group. The freezing was carried out in a computer-controlled programmable freezer at 0.5degree C/min, 1degree C/min and 2degree C/min in1.4M, 2.1M and 2.8M DMSO from 4degree C to -60degree C and then plunged into the liquid nitrogen tank immediately. After 24th of cryopreservation, the samples wereped in removed from liquid nitrogen and placed at room temperature in air for 0.5-1min, prior to submergence in a water bath at 37 degree C. viability of fresh control and cryopreserved dermal slices were determined with our modification of the MTT (3-[4,5-Dimethythiazol-2-yl] -2,5-diphenyltetrazolium bromide) assay. The effects of two cryoprotectant medium treatment methods and seeding (at -7degree C)on cell viability were also assessed. A cryopreservation protocol of 1degree C/min in 1.4M DMSO from 4degree C to -60degree C, and seeding at -7degree C proved optimal for this tissue-engineered dermal replacement, provided the dermal slice was transferred into the cryopreservation bag containing 1mL 1.4M DMSO bag and hold for 15min at 4degree C prior to freezing.

Role of nitric oxide in hemorrhagic shock-induced bacterial translocation

BACKGROUND

Hemorrhagic shock-induced bacterial translocation is an etiologic factor in the pathogenesis of multiple system organ damage. Excessive production of nitric oxide (NO) during hemorrhagic shock may lead to cellular injury and gut barrier failure that promotes bacterial translocation. We investigated the effect of aminoguanidine (AG) and N(G)-nitro-l-arginine methyl ester (l-NAME), both inhibitors of NO synthase, on hemorrhagic shock- induced bacterial translocation in the rat.

MATERIALS AND METHODS

Anesthetized male Sprague-Dawley rats were subjected to a hemorrhagic shock protocol for 30 min followed by intravenous injection (1 mL/kg body wt) with normal saline, AG (100 mg/kg), or l-NAME (10 mg/kg). Tissues/organs were examined histologically for damage and bacterial translocation. Plasma nitrate/nitrite was measured using a procedure based on the Griess reaction, and nitric oxide synthase (NOS) expression was determined immunohistochemically.

RESULTS

The shocked animals treated with saline died within 90 min, and deaths were associated with 100% bacterial translocation, increased tissue/organ damage, and elevated nitrate/nitrite production. In contrast, both AG and l-NAME increased the survival time of shocked rats to >72 h, abrogated bacterial translocation, reduced tissue/organ damage, and prevented excessive nitrate/nitrite production and upregulation of expression of endothelial NOS and inducible NOS.

CONCLUSIONS

Prevention of bacterial translocation by pharmacologic agents such as aminoguanidine and l-NAME could be an important therapeutic approach to lessen mortality rates following hemorrhagic shock.

Experimental measurement and theoretical analyses of the freezing-thawing processes around a probe

Both the experimental and the analytical studies of the freezing/thawing process around a cryosurgical cylinder probes in a simulative biological tissue are presented in this paper. The enthalpy method and the finite element scheme are applied to solve the multidimensional phase change problems in cryosurgery. A very good agreement is found between the computed solutions and the experimental results. The influences of different cooling-warming schemes of the probe on the ice ball development, the temperature variation, the axial and the radial temperature gradients inside the tissues, and the requirement of cooling power are analyzed

Influence of L-arginine, aminoguanidine, and NG-nitro-L-arginine methyl ester (L-name) on the survival rate in a rat model of hemorrhagic shock

Nitric oxide (NO) has been implicated in the pathophysiology of hemorrhagic shock. We investigated the influence of L-arginine (the precursor of NO synthesis), N(G)-nitro-L-arginine methyl ester (L-NAME) and aminoguanidine (AG) (inhibitors of NO synthase, with selectivity toward the constitutive and inducible isoforms, respectively) on the survival rate in a rat model of hemorrhagic shock. Anesthetized, male Sprague-Dawley rats (300-350 g) were subjected to hemorrhagic shock for 30 min followed by intravenous injection (1 mL/kg) with normal saline, L-arginine (30 mg/kg), L-NAME (10 mg/kg), L-NAME+L-arginine, AG (1, 10, 100 mg/kg) or AG (100 mg/kg)+L-arginine (n = 5 per group). Hemorrhagic shocked rats treated with saline died within 90 min. In contrast, L-NAME increased the survival time to >72 h in shocked rats. AG (1, 10, and 100 mg/kg) increased the survival time of shocked animals to 150 min, 230 min, and >72 h, respectively. Shocked rats treated with L-arginine died within 80 min, and those that received L-NAME+L-arginine and AG+L-arginine died within 120 min and 110 min, respectively. L-NAME and AG (dose dependently) reduced macroscopic and microscopic injuries, nitrate/nitrite, PGE2 and creatinine production, and inhibited GOT activity in shocked animals. L-arginine reversed the beneficial effects of AG and L-NAME, suggesting the involvement of NO in the pathophysiology of hemorrhagic shock.

Cryopreservation and transplantation of dog trachea

In order to meet the need of trachea transplantation for clinical application, it is important to research the methods of cryopreservation and transplantation of trachea. By the thermal analyses and thermal control techniques, combined with electron microscopy, the effects of cooling and warming rates with different concentrations of cryoprotective agents were studied. Also the transplantation technique was studied, eighty five percent (17/20) of the dogs were survival after the transplantation with cryopreserved tracheas.

Effects on rapid cooling of small samples in quenching

Rapid cooling of small samples is necessary both to cryofixation for electron microscopy and to vitrification for cryopreservation. Several effects on the cooling rates of small samples quenched into liquid nitrogen were studied, including the diameter of samples, the subcooling of liquid nitrogen, the quenching speed, and the quenching distance. The heat flux is 1.4 x 10(6) W/m2; the cooling rate is also up to 8200 K/s at the CHF point of boiling curves for sphere of diameter 0.287 mm quenching into subcooled liquid nitrogen. It is also found that if the time of sample moving inside the liquid nitrogen is not longer than the time required for forming stable vapor in the liquid, the quenching boiling heat transfer is not influenced by the quenching speed. Several equation for calculating heat flux of samples are also presented.