生物材料玻璃化保存液的热分析

在玻璃化超低温保存生物材料的研究中,低温保护剂的热分析对玻璃化溶液的优化和保存方案的选择具有重要的指导意义.本文以渗透性低温保护剂二甲基亚砜和丙二醇以及非渗透性保护剂聚乙烯醇作为研究对象,利用差式扫描量热法对聚乙烯醇/二甲基亚砜/丙二醇体系进行升温和降温实验,考察了体系的结晶特性、玻璃化转变特性、聚乙烯醇的浓度等因素对体系热性能参数的影响.     

加热方式对真空冷冻干燥热质传递机理的影响

1引言真空冷冻干燥（简称真空冻干）是多孔介质在低温低压下相变界面移动的耦合传热传质过程，其数学模型带有典型的非线性，难于精确求解［‘，2］。从应用上而言，真空冻干具有设备投资高，能耗大，干燥时间长的缺点。能量的供应即加热方式、升华水汽的流动条件、物料的输运性质是影响真空冻干性能的主要因素间。本文以牛肉的真空冷冻干燥过程为例，建立过程的非稳态数学模型，利用数值求解的结果，结合实验分析，研究了通过千层的辐射加热和通过冻结层的导热加热条件下真空冻干过程中传热传质的机理，分析了加热方式对缩短干燥时间的影响…     

冷冻干燥中升华过程界面的微CT观察及气固相变分析

采用微CT扫描成像、图像重构及灰度值分析技术对冷冻干燥中升华过程界面及气固相变进行实验观察与分析。采用高斯误差函数拟合,计算得到冰的平均灰度值为154。在后续灰度值比价分析中,固体物料苹果本身的灰度值高于冰的灰度值,从而可以分析冰晶的移动特性。从直接扫描图像和重构图像,均可看到升华界面的移动是一个立体的移动,由它所包裹的冻结区逐渐向物料几何中心收缩。对比冻结物料和冻干物料的灰度值曲线,可见刚开始灰度值较低的冰区,在冻干结束后变成灰度值相对较高的孔疏区。     

加热方式对真空冷冻干燥过程的影响

以平板状饱和牛肉为对象，对不同供热方法下冷冻干燥过程的传热传质进行了数值计算与实验研究，分析比较了表面加热与微波加热两种供热方式对冻干过程的影响，为冻干过程中供热方式的选择提供了理论依据及分析方法。     

低温真空冷冻干燥室内温度特性的研究

真空冷冻干燥设备广泛应用于药品、食品等的干燥领域,该干燥方式能避免药品、微生物等产生变性或失去生物活力,但是能耗较大,且干燥室内的温度在真空条件下,比较难于控制。文中从三个方面对其温度特性进行了实验研究:真空度对温度特性的影响;板面温度对于冻干瓶内温度控制的影响;保护气对于冻干瓶内温度控制的影响。     

PVA栅绝缘层浓度对P3HT有机场效应晶体管性能的影响

采用溶液制备法制备了用PVA作为绝缘层、P3HT作为有源层的有机场效应晶体管,,研究了不同浓度PVA栅绝缘层对器件性能的影响。实验结果显示,以质量分数为8%的PVA溶液制备的栅绝缘层具有最好的性能,器件的场效应迁移率为0.31 cm²·V^-1·s^-1,阈值电压为-6 V。进一步分析了PVA栅绝缘层浓度对器件性能提高的原因,结果表明,对于制备溶液化的有机场效应晶体管,选取合适的PVA栅绝缘层浓度非常重要。     

一种冷冻干燥装置用平板换热器的特性研究

在冷冻干燥过程的真空环境中,冻干物料放置在隔板上,热量通过隔板传递到物料中。平板换热器既作隔板,又作蒸发器。通过实验,研究了在真空条件下的表面换热特性及管内阻力特性,并分析了混合工质的配比对于平板换热器降温特性的影响。     

流化床冷冻干燥气体制冷循环工质的比较研究

氩气、氮气来源于空气,都不与药品中热敏性成分起反应。吸附式流化床冷冻干燥设备简单、节能,而且冻干产品品质与真空冷冻干燥接近。分析了应用在流化床冷冻干燥装置上的制冷循环,对氩气、氮气作为工质应用于该系统的性能进行计算,在此基础上,进行了比较研究。     

兔主动脉冻结过程中未冻水份额的研究

利用差示扫描量热仪(DSC)技术中的分步扫描(Stepwise scanning)法,研究了不同浓度的低温保护剂对主动脉血管冻结过程中未冻水份额的影响。研究结果表明:分步扫描量热技术可以用于血管材料冻结过程中未冻水份额的定量研究,而且具有较高楠度;随着低温保护剂二甲亚砜(DMSO)浓度的增大,血管的初始冻结点温度呈线性降低,但其冻结过程的未冻水份额显著增大,这是由于高浓度DMSO具有很强水合能力所致。     

冻干溶液的低温显微研究与热分析

利用低温显微系统研究了叔丁醇水溶液降温时的晶体形态,并利用差示扫描量热法(DSC)研究了溶液的反玻璃化结晶。低温显微实验表明:叔丁醇／水溶液结晶形状、大小与叔丁醇的浓度有关,浓度为10％时形成粗大的针状结晶, 有利于升华速率的提高。DSC实验表明:10％叔丁醇／10％蔗糖／水三元溶液的临界复温速率为250℃／min左右。     

Freeze-drying of human platelets: influence of intracellular trehalose and extracellular protectants

Freeze-drying is an ideal alternative for long-term preservation of platelets in blood banks. Intracellular trehalose is believed to be an effective lyoprotectant for preserving cells during freeze-drying. In this study, 13 mM intracellular trehalose was loaded into human platelets through fluid-phase endocytosis pathway. Bovine serum albumin and trehalose were used as extracellular protectants. The effects of intracellular trehalose and extracellular protectants on freeze-dried platelets were studied respectively. The results showed 13 mM intracellular trehalose was beneficial to freeze-dried human platelets, but only slightly enhanced the protection afforded by extracellular protectants. Loaded with 13 mM intracellular trehalose, platelets were freeze-dried in a formulation of 1 percent bovine serum albumin and 1 percent trehalose, 40 days later, the survival rate of rehydrated platelets was about 85 percent, the morphology of rehydrated platelets was intact and the aggregation percentage with thrombin (1 U/ml) was 97.3 percent.     

Study on the Electrospinnability of Polyvinyl Alcohol Solutions by Using Water/N,N-dimethylacetamide or Water/N,N-dimethylformamide as Solvents

The electrospinning of poly(vinyl alcohol) (PVA) (99% hydrolysis degree) aqueous solution with added organic solvents N, N-dimethylacetamide (DMAc) or N, N-Dimethylformamide (DMF) was investigated. After the addition of the organic solvents to the PVA aqueous solutions, the surface tension and conductivity decreased and the viscosity significantly increased, which caused an improved electrospinnability of the PVA solutions. The micro-structures of the three solutions were investigated by dynamic light scattering (DLS), differential scanning calorimetry (DSC) and dynamic viscoelastic measurements. The DLS data revealed that the swelling of the PVA coils was slightly increased but the overlaps of PVA coils decreased greatly after one of the organic solvents was added to the aqueous solution. The DSC data showed both the water-rich phase and PVA-rich phase were destroyed and the solution became more homogenous after the addition due to the interaction between the organic solvent and water. Viscoelastic data showed there was an obvious difference in the storage modulus behavior between the aqueous solutions and the water/solvents solutions. These changes in the micro-structure and properties were the reason for the improved electrospinnability of the PVA solution. According to scanning electron microscopy (SEM), the average diameter of the electrospun PVA nanofibers was about 308 nm for the DMF/water system, and 255 nm for the DMAC/water system, as compared with uneven diameter nanofibers for the water system.     

Effect of various freezing solutions on cryopreservation of mesenchymal stem cells from different animal species

The objective of this study is to compare the effects of different well defined freezing solutions with a reduced concentration of dimethylsulfoxide (DMSO) combined with polyethylene glycol (PEG) and/or trehalose on cryopreservation of mesenchymal stem cells (MSCs) from mice, rats and calves. Post-thaw cell viability, proliferation capacity and differentiation potential of MSCs from different species were assessed after cryopreservation with the conventional slow freezing method. Although the post-thaw viabilities and metabolic activities varied among the different species, satisfactory results were obtained with 5 percent (v/v) DMSO, 2 percent (w/v) PEG, 3 percent (w/v) trehalose and 2 percent (w/v) bovine serum albumin (BSA) as the freezing solution. Our results showed that mouse MSCs were more robust to cryopreservation compared with rat and bovine MSCs.     

Cryopreservation of umbilical cord blood-derived mesenchymal stem cells without dimethyl sulfoxide

Cryopreservation of umbilical cord blood-derived mesenchymal stem cells (UCB-derived MSCs) is crucial step for its clinical applications in cell transplantation therapy. In the cryopreservation of MSCs, dimethyl sulfoxide has been widely used as a cryoprotectant (CPA). However, it has been proved that DMSO has toxic side effects to human body. In this study, DMSO-free CPA solutions which contained ethylene glycol (EG), 1, 2-propylene glycol (PG) and sucrose as basic CPAs, supplemented with polyvinyl alcohol (PVA) as an additive, were developed for the cryopreservation of UCB-derived MSCs. The cryopreservation of UCB-derived MSCs was achieved by vitrification via plunging into liquid nitrogen and by programmed freezing via an optical-DSC system respectively. The viability of thawed UCB-derived MSCs was tested by trypan blue exclusion assay. Results showed that the viability of thawed UCB-derived MSCs was enhanced from 71.2% to 95.4% in the presence of PVA for vitrification, but only < 10% to 45% of viability was found for programmed freezing. These results indicate that PVA exerts a beneficial effect on the cryopreservation of UCB-derived MSCs and suggest the vitrification in combination with the dimethyl sulfoxide free CPA solutions supplemented with PVA would be an efficient protocol for the cryopreservation of UCB-derived MSCs.     

Effect of tetrasodium tripolyphosphate on the freeze-concentrated glass-like transition temperature of sugar aqueous solutions

The freeze-concentrated glass-like transition temperatures (Tg2), so-called ante-melting temperature or ice-melting temperature of tripolyphosphate-sugar aqueous solutions prepared with various sugars (ribose, sorbitol, glucose, maltose, sucrose, and trehalose) were investigated by using differential scanning calorimetry to evaluate the effect of tetrasodium tripolyphosphate on the Tg2 of sugar aqueous solutions. The Tg2 of tripolyphosphate-sugar aqueous solutions were higher than those of tripolyphosphate or sugar aqueous solutions and converged in a narrow temperature range of 238 to 243 K. Furthermore, a study of the Tg2 of tripolyphosphate-glucose aqueous solutions adjusted to various ratios indicated that the Tg2 increment depended on the ratio and that another glass-like transition appeared at a temperature below the Tg2 by increasing the ratio of tripolyphosphate. The drastic increase in the Tg2 of sugars with the addition of tripolyphosphate will be useful for improving the cryostabilization of biomaterials.     

Intracellular sugars improve survival of human red blood cells cryopreserved at -80 degrees C in the presence of polyvinyl pyrrolidone and human serum albumin

Cryopreservation with impermeable protectants has great significance on storage of human red blood cells. It has become feasible to use glycerol free cryopreservation for human red blood cells. This study focuses on the effect of intracellular trehalose or glucose on human red blood cells cryopreserved in the presence of polymer. Red blood cells were cryopreserved for 48 h-72 h at -80 degrees C. The data showed that the loading efficiency of glucose was significantly higher than that of trehalose, but trehalose loading process induced more hemolysis than glucose loading process. Compared with the other groups, the combination of intracellular glucose, PVP, and human serum albumin can significantly decrease the percent hemolysis after cryopreservation (P<0.01). However, the percent hemolysis induced by intracellular trehalose was less than that induced by extracellular trehalose, but the difference was not significant (P<0.05). The adenosine 5'-triphosphate (ATP) level and 2,3-diphosphoglycerate (2,3-DPG) level of cryopreserved red blood cells were significantly less than those of fresh red blood cells. However, sugars can provide certain protection for ATP and 2, 3-DPG compared with red blood cells cryopreserved in the absence of sugars. The protection of glucose on the metabolic function was more than that of trehalose. Cryopreservation can increase the percentage of cells with exposed phosphatidylserine (PS), but the ability of trehalose to maintain PS normal distribution is higher than that of glucose. Furthermore, intracellular sugars can protect membrane integrity of cryopreserved red blood cells, although a small portion of cells appeared spherocytic or echinocytic shape. Finally, most membrane proteins of cryopreserved red blood cells were similar to the membrane proteins of fresh red blood cells, but trehalose can result in loss of glyceraldehyde phosphate dehydrogenase (GAPD) and peroxiredoxin 2. In conclusion, it is feasible to cryopreserve red blood cells using polymer, human albumin and sugars as main protectants. The cryoprotective effect of glucose may be better than that of trehalose in the presence of PVP and human serum albumin, because sugar loading process causes more cell injuries in case of trehalose compared to glucose, and these injuries in turn manifest themselves during subsequent cryopreservation and thawing. In the future, finding an approach to decrease the injuries during trehalose loading process still is critical.     

Laser Diagnostics of the Mesoscale Heterogeneity of Aqueous Solutions of Polar Organic Compounds

A mesoscale droplet phase, which is spontaneously formed in aqueous solutions of some polar organic compounds, has been experimentally investigated by methods of dynamic light scattering and laser phase microscopy. It is shown that tetrahydrofuran and tert-butanol aqueous solutions demonstrate a strong peak of light scattering intensity in the range of molecular concentrations of about 0.02 to 0.08, which corresponds to inhomogeneities with a characteristic size of about 100 nm. These liquid droplets are enriched with molecules of dissolved substance. A similar light scattering peak for aqueous solutions of glycerol and ethylene glycol is less pronounced. A theoretical model of the phase separation of binary solutions with twinkling (i.e., existing for a finite time) intermolecular hydrogen bonds is developed. The model predicts the existence of an additional low-concentration light scattering peak near the spinodal of the solution free of hydrogen bonds. A characterization of solutions according to the numerical values of twinkling hydrogen bond parameters is outlined.     

Influence of Position on the Microstructure of Carbon Black/Polyvinyl Alcohol Composite Obtained by the Directional Freeze-drying Process

Carbon black (CB)/polyvinyl alcohol (PVA) composites with porous structure were obtained by a directional freeze-drying process of their solution in water. The microstructures of this composite at different positions through the thickness were investigated. The study shows that the composite formed a lamellar structure at the lower surface of the specimen because of the basic crystallographic and crystal growth characteristics of ice. The composite near the top surface of the specimen showed an alignment direction of the ice vertical to the container's wall and the direction of solution lowering into the liquid nitrogen. The alignment direction deflects gradually and finally converges with the aligned direction grown from the bottom position near the middle part of the CB/PVA composite. The ice crystals grow very fast along the direction of temperature gradients, which results in that a small fraction of PVA solute was entrapped within the ice crystals, leading to the formation of trans-bridge lamellar structure near the top surface of the specimen. This result shows that the position in the sample has a great influence on the structure of the porous CB/PVA composite obtained by the directional freeze-drying process.     

The role of disaccharides for protein–protein interactions – a SANS study

ABSTRACT

The disaccharide trehalose has shown outstanding anti-aggregation properties for proteins, which are highly important for the possibility to treat neurodegenerative diseases, such as Alzheimer’s and Huntington’s disease. However, the role and mechanism of trehalose for such stabilising effects are still largely unknown, partly because a direct structural picture of how trehalose organises around proteins in an aqueous system is missing. Here we compare small-angle neutron scattering (SANS) data on myoglobin in aqueous solutions of either sucrose or trehalose, in order to investigate their effect on protein–protein interactions. We find that both trehalose and sucrose induces a well-defined protein–protein distance, which could explain why these inhibit protein–protein interactions and associated protein aggregation. It does not however explain the superior anti-aggregation effect of trehalose and suggests that the local solvent structures are highly important for explaining the protein stabilisation mechanism. In a broader perspective, these findings are important for understanding the role of sugars in biological stabilisation, and could provide a structural explanation for why trehalose is a promising candidate for the treatment of neurodegenerative and other protein aggregation related diseases.     

Fourier Self-Deconvolution Analysis of β-Sheet Contents in the Amide I Region of Hemoglobin Aqueous Solutions under Exposure to 900 MHz Microwaves and Bioprotective Effectiveness of Sugar and Salt Solutions

Spectroscopic Fourier self-deconvolution analysis was used to investigate β-sheet features in the secondary structure of hemoglobin under mobile phone microwaves at 900 MHz. To this end, four samples of hemoglobin in bidistilled water, sucrose, trehalose, and sodium chloride aqueous solutions were exposed for up to 4 hr to 900 MHz microwaves at an average H-field intensity of 42 mA/m. Quantitative spectral analyses highlighted significant increases in β-sheet contents in the Amide I region of hemoglobin samples in bidistilled water solution, but no appreciable change was observed in hemoglobin samples in sucrose, trehalose, and sodium chloride solutions. These results led us to conclude that mobile phone microwaves can denaturate hemoglobin in bidistilled water solution whereas sucrose, trehalose, and sodium chloride solutions produce a protective effect against microwaves, preserving the protein from unfolding.