去细胞人羊膜基质的制备及免疫原性

目的制备去细胞人羊膜基质(AHAM)并分析其移植至小鼠体内后的免疫反应,评价去细胞人羊膜基质作为细胞移植支架的免疫原性。方法利用胰蛋白酶-EDTA消化人羊膜(HAM),去除人羊膜上皮细胞,制备新鲜去细胞人羊膜基质;新鲜去细胞人羊膜基质置于含硫酸软骨素及甘油的冷冻保护液中,-80℃保存;使用前经PBS复水处理后即冷冻去细胞人羊膜基质;免疫细胞化学分析去细胞人羊膜基质中人类白细胞抗原的表达情况;将冷冻的去细胞人羊膜基质移植至BALB/c小鼠肝脏内4周后,分析脾脏组织中CD4~+、CD8~+T淋巴细胞比例的变化。结果新鲜及冷冻保存后的去细胞人羊膜基质均不表达人类白细胞抗原;冷冻的去细胞人羊膜基质移植至小鼠体内后,脾脏组织中CD4~+、CD8~+T淋巴细胞无明显变化。结论去细胞人羊膜基质的免疫原性较低,移植后不会引起由T细胞介导的特异性排斥反应,可以作为免疫安全性的生物支架用于疾病的细胞移植治疗。     

人羊膜细胞在Ⅰ型胶原基质中的三维培养研究

将人羊膜间质细胞种入Ⅰ型胶原三维基质中,羊膜上皮细胞接种在基质的表面,构建人羊膜细胞/Ⅰ型胶原基质复合物以模拟人体羊膜组织结构,为其用于修复胎膜破口的研究做准备。采用罗丹明-鬼笔环肽荧光染色剂特异性标记胞浆中的微丝(F-actin)结构,观察细胞在三维基质中的细胞形态;扫描电镜和透射电镜法观察羊膜上皮细胞和间质细胞在三维培养中的超微结构。结果显示人羊膜上皮细胞和间质细胞在Ⅰ型胶原基质的复合培养中生长良好,显示出与体内羊膜细胞的相似性。以上结果提示,Ⅰ型胶原蛋白有望应用在羊膜细胞组织工程,三维细胞基质培养系统有望为胎膜早破提供新的研究方法和治疗手段。     

新鲜与保存羊膜移植与小梁切除后的瘢痕组织增生

背景:目前新鲜羊膜在眼表疾病方面得到了广泛应用,并且取得了抗纤维组织增生、抑制新生血管形成及减轻炎症反映等方面的满意疗效,但在青光眼方面的应用还未见报道。目的:观察新鲜羊膜移植对小梁切除术后瘢痕组织的抑制作用,并与保存羊膜对比。方法:将36只新西兰大白兔按随机数字表法分为3组,新鲜羊膜组和保存羊膜组分别进行新鲜羊膜移植、保存羊膜移植联合小梁切除术,空白组行单纯小梁切除术。分别于移植后1,2,3,4周检查滤过泡的形态和功能,用链酶亲和素免疫组织化学法检测滤过泡周围组织中血小板衍生生长因子的含量。结果与结论:新鲜羊膜组和保存羊膜组移植后滤过泡轻微隆起,有较好的滤过功能;观察病理组织切片表明滤过道内成纤维细胞增生较少,瘢痕组织也比较疏松。空白组滤过道被增生的纤维组织代替,成纤维细胞比较多。免疫组化结果显示,新鲜羊膜组和保存羊膜组的血小板衍生生长因子的表达少于空白组,新鲜羊膜组的表达少于保存羊膜组。提示新鲜羊膜和保存羊膜能改善滤过泡功能,减少瘢痕形成,维持滤过道的通畅,并且新鲜羊膜的作用效果优于保存羊膜。     

羊膜基质/聚丙烯复合补片的制备及其生物相容性评价

制备脱细胞羊膜基质, 运用物理方法将其复合于临床用聚丙烯补片, 以形成具有更好组织相容性的生物补片。通过细胞培养, 以聚丙烯膜为对照, 评价复合生物补片的细胞相容性;通过动物皮下植入实验, 以评价复合补片的组织相容性。结果表明, 复合补片羊膜基质表面上的成纤维细胞生长和形态均好于聚丙烯表面, 细胞增殖较快, 增殖率超过聚丙烯表面的50%。动物实验显示, 复合补片周围增生少, 无明显纤维包膜形成, 初期在植入周围有淋巴细胞等炎性细胞浸润, 随着羊膜逐渐降解, 4周时可见毛细血管新生;而对于聚丙烯材料, 植入处纤维包囊明显, 炎性情况也较严重。经羊膜基质复合的聚丙烯补片具有良好的细胞和组织相容性。     

不同冻存方法对羊膜超微结构和上皮细胞活性的影响

背景：羊膜冻存方法众多,对羊膜超微结构和生物活性的影响不一,目前尚无有效的冻存方法。 目的：比较不同冻存方法对羊膜超微结构和活性影响的研究,探寻更为理想的冻存方法。 方法：将新鲜羊膜采用深低温和玻璃化冻存法保存,分别于冻存后3,6个月复苏羊膜,以新鲜羊膜组织为对照组,比较羊膜的超微结构差异、羊膜上皮细胞离体氧分压和乳酸脱氢酶活性。 结果与结论：不同冻存方法保存的羊膜超微结构有明显改变,但玻璃化冻存对其超微结构的影响相对较小;与新鲜羊膜相比较,深低温冻存组3,6个月羊膜的乳酸脱氢酶灰度值和氧分压明显降低(P < 0.05);玻璃化冻存组6个月后的羊膜乳酸脱氢酶灰度值和氧分压明显降低(P < 0.05),而玻璃化冻存组3个月后的上述检测结果与新鲜羊膜相比差异无显著性意义(P > 0.05)。结果证实,羊膜的玻璃化冻存技术优于深低温冻存技术,不仅维持了羊膜的超微结构,而且保持了羊膜上皮细胞的功能和活性。 中国组织工程研究杂志出版内容重点：组织构建;骨细胞;软骨细胞;细胞培养;成纤维细胞;血管内皮细胞;骨质疏松;组织工程全文链接：     

新鲜羊膜与脱细胞羊膜修复腱鞘缺损预防肌腱粘连北大核心

背景:羊膜独有的结构可阻止某些物质通过,能保证包裹内组织正常营养供应,而且具有抗粘连、组织相容性好、炎性反应轻、纤维包裹少及可降解等特性。目的:比较新鲜羊膜及脱细胞羊膜修复腱鞘缺损,预防肌腱粘连和促进肌腱愈合的作用。方法:取60只雄性来亨鸡,制作双足第三足趾制备肌腱及腱鞘损伤模型,随机分为3组修复,新鲜羊膜组采用新鲜人羊膜修复腱鞘缺损,脱细胞羊膜组采用人脱细胞羊膜修复腱鞘缺损,对照组不做腱鞘修复。修复后进行第三足趾组织学观察及生物力学测试。结果与结论:①组织学观察:修复后2周,3组均存在充血水肿及炎症反应,新鲜羊膜组最轻,对照组最严重,3组水肿及炎症反应随时间延长逐渐减轻。修复12周,各组假鞘较修复后4周明显成熟,新鲜羊膜组及脱细胞羊膜组假鞘表面细胞致密层状排列整齐,表面光滑;对照组假鞘表面细胞排列紊乱,结构松散,可见表面纤维组织突出假鞘表面;②生物力学测试:脱细胞羊膜组、新鲜羊膜组修复后4,8,12周的肌腱滑动距离均大于对照组(P<0.05),前2组间比较差异无显著性意义;脱细胞羊膜组、新鲜羊膜组修复后4,8周的肌腱最大拉伸断裂强度高于对照组(P<0.05),且新鲜羊膜组高于脱细胞羊膜组(P<0.05),3组修复后12周的肌腱最大拉伸断裂强度无差异;③结果表明:新鲜羊膜和脱细胞羊膜均可用于重建腱鞘缺损,预防肌腱粘连,新鲜羊膜在促进早期肌腱愈合方面优于脱细胞羊膜。     

不同冻存方法对羊膜超微结构和上皮细胞活性的影响（英文）

背景:羊膜冻存方法众多,对羊膜超微结构和生物活性的影响不一,目前尚无有效的冻存方法。目的:比较不同冻存方法对羊膜超微结构和活性影响的研究,探寻更为理想的冻存方法。方法:将新鲜羊膜采用深低温和玻璃化冻存法保存,分别于冻存后3,6个月复苏羊膜,以新鲜羊膜组织为对照组,比较羊膜的超微结构差异、羊膜上皮细胞离体氧分压和乳酸脱氢酶活性。结果与结论:不同冻存方法保存的羊膜超微结构有明显改变,但玻璃化冻存对其超微结构的影响相对较小;与新鲜羊膜相比较,深低温冻存组3,6个月羊膜的乳酸脱氢酶灰度值和氧分压明显降低(P0.05);玻璃化冻存组6个月后的羊膜乳酸脱氢酶灰度值和氧分压明显降低(P0.05),而玻璃化冻存组3个月后的上述检测结果与新鲜羊膜相比差异无显著性意义(P0.05)。结果证实,羊膜的玻璃化冻存技术优于深低温冻存技术,不仅维持了羊膜的超微结构,而且保持了羊膜上皮细胞的功能和活性。     

辐照灭菌冷冻干燥羊膜修复碱烧伤

背景：经辐照灭菌的冷冻干燥羊膜便于保存和使用,但羊膜经这种方式处理后其活性是否会降低、其临床疗效是否会受到影响至今仍鲜有报道。 目的：观察辐照灭菌后的冷冻干燥羊膜对兔角膜碱烧伤的修复作用。 方法：取健康成年白兔9只,均用1 mol/L 氢氧化钠烧伤角膜后,左侧眼设为羊膜组植入辐照灭菌后的冷冻干燥的羊膜,右侧眼设为对照组不植入羊膜。植入后30 d内裂隙灯显微镜每日观察角膜透明度、角膜新生血管及角膜上皮修复情况。 结果与结论：羊膜植入后30 d,羊膜组角膜透明度、新生血管及角膜上皮修复情况明显优于对照组(P < 0.05),角膜上皮愈合好,基质纤维排列更为整齐,炎细胞浸润程度轻,新生血管更少。结果证实,兔角膜碱烧伤后植入辐照灭菌后的冷冻干燥羊膜可减轻角膜炎性反应,促进角膜上皮修复,减少角膜新生血管形成。     

交联剂对脱细胞膀胱基质生物力学性能的影响

目的 研究不同交联剂对猪脱细胞膀胱基质的组织结构影响,并比较其生物力学性能,为盆底修复替代材料的选择提供依据.方法 采用表面活性剂+酶消化法去除新鲜猪膀胱的细胞成分,将脱细胞膀胱基质随机分为3组,A组经0.25％戊二醛交联,B组经0.625％京尼平交联,C组未交联.对各组材料进行HE染色,观察纤维的变化情况.使用生物力学性能测试系统检测抗拉强度、断裂伸长率、弹性模量,并进行统计学分析.结果 京尼平交联脱细胞膀胱基质后呈深蓝色,保持了天然组织构架的完整,纤维更加致密.戊二醛交联脱细胞膀胱基质后呈浅黄色,纤维排列紊乱且有断裂.新鲜猪膀胱经上述三种方法处理后,其弹性模量增大、断裂伸长率减小,而其中京尼平交联处理的脱细胞膀胱基质力学性能与新鲜膀胱组织更为相近.结论 京尼平交联的脱细胞膀胱基质组织结构的形态佳,同时较大限度地保留膀胱组织的力学性能,可能是较理想的盆底重建材料.     

不同脱细胞方法对猪尾纤维环生物力学特性及组织结构的影响

目的探讨不同脱细胞处理方法对猪尾椎间盘纤维环生物力学特性及组织结构的影响,为构建组织工程纤维环提供实验依据。方法取新鲜猪尾纤维环60个,随机分为4组,每组15个。Triton X-100组(A组):先将纤维环放入Tris-HCl低渗缓冲液中振荡48 h,再用TritonX-100、DNaseⅠ和RNase A对纤维环脱细胞处理;SDS组(B组):将纤维环冻融3次,接着用SDS、DNaseⅠ和RNase A对纤维环脱细胞处理;胰蛋白酶组(C组):用含胰蛋白酶、DNaseⅠ和RNase A的Tris缓冲液对纤维环脱细胞处理;对照组(D组):纤维环不做任何处理。采用HE染色与扫描电镜方法,观察各组脱细胞情况以及纤维环超微结构的变化;采用生物化学和生物力学方法检测各组纤维环的胶原含量、氨基葡聚糖(GAG)含量及力学参数。结果与对照组比较,HE染色及扫描电镜可见A、B、C 3组均无细胞残留;A组纤维环超微结构未见破坏,C组纤维环超微结构可见轻度破坏,B组纤维环超微结构可见明显破坏。A、B、C 3组纤维环胶原含量与对照组比较无统计学差异(P>0.05),但GAG含量均明显低于对照组(P<0.05)。A、C两组的力学参数(极限载荷、极限应力、韧度、弹性模量、断裂功耗)与对照组无统计学差异(P>0.05),B组上述力学参数均低于对照组(P<0.05)。结论 Triton X-100组处理后的猪尾椎间盘纤维环无细胞残留,结构无破坏,基质成分及力学性能保存良好,适合于构建组织工程纤维环。     

Pulmonary type II cell lamellar body ultrastructure preserved by rapid freezing and freeze drying

Lamellar body ultrastructure was examined in cultured type II alveolar epithelial cells processed by a method of rapid freezing and freeze drying in the absence of both chemical fixation and solvent dehydration. This method of specimen preparation was chosen to optimize the retention of soluble substances within the type II cell. The use of cultured cell aggregates in which type II cells line the free surface facilitated the effectiveness of rapid freezing for the preservation of lamellar body fine structure. Lamellar bodies of frozen/frozen dried type II cells showed none of the often profound lipid extraction artifact produced by conventional processing. Instead they exhibited a substructure with noteworthy characteristics in common with lamellar bodies processed by resin dehydration lipid retention methods (Stratton, 1976). Importantly, the lamellae of frozen/frozen dried lamellar bodies were contiguous, with no interlamellar space, as is commonly observed in solvent-processed (extracted) specimens. The dimensions of lamellar components in frozen/frozen dried lamellar bodies were, however, different from published values for resin-dehydrated lipid-retained specimens. Lamellar width and the widths of component phospholipid head and fatty acid tail regions in frozen/frozen dried lamellar bodies were approximately 35% smaller than values reported for resin-dehydrated lamellar bodies. This difference was attributed to shrinkage of lamellar components as water was removed from the unfixed tissue during the freeze-drying process. Lamellar bodies preserved by rapid freezing/freeze drying to optimize the in situ retention of intracellular components possess closely adherent concentric membranous lamellae. This supports the contention that the widely appreciated lamellar pattern of the pulmonary lamellar body represents the in vivo molecular organization of intracellular surfactant phospholipids.     

离体大鼠胰腺去细胞生物支架的制备与鉴定

目的 通过离体灌注加浸泡的方法制备大鼠胰腺去细胞生物支架(PDBC),为胰岛和胰腺的组织工程研究提供新型天然生物支架. 方法 健康成年大鼠20只,以物理冻融及灌注洗脱法(脱氧胆酸钠+ DNAase),采用胆管、胰管联合逆向在体灌流法获取胰腺去细胞生物支架.并通过基因组DNA定量定性分析,组织化学染色、免疫荧光组织化学染色、荧光积分吸光度分析、透射电镜观察等进一步测定细胞残留以及观察去细胞支架,如胶原IV、纤维连接蛋白和层黏连蛋白等成分的保留. 结果 DNA定性分析显示,实验组未见明显DNA条带,对照组DNA条带可达100bp,定量检测实验组DNA残留不足对照组的5％;组织化学染色和透射电镜观察均表明,去细胞支架无细胞残留,细胞外支架连续性完好,脉管支架保存完整;免疫荧光结果表明,胶原蛋白、弹性蛋白等细胞外支架成分保留较完整,未见明显细胞核成分残留. 结论 运用冻融加浸泡灌注制备的胰腺去细胞生物支架,细胞去除彻底,细胞外支架保留完好.     

冷冻干燥法对人精子DNA的影响

目的探讨冷冻干燥法用于人类精子保存的安全性。方法取健康志愿者合格精液40份，平均分为4组，其中3组分别加入不同的冻干保护剂（ETBS；ETBS＋海藻糖：ETBS＋海藻糖＋蛋黄）后给予冷冻干燥处理，在4℃冰箱中保存3周；1组作为新鲜精液对照组。对4组标本分别以原位缺口末端标记（TUNEL）法和彗星试验进行DNA断裂精子百分率检测。结果ETBS、ETBS＋海藻糖、ETBS＋海藻糖＋蛋黄组和新鲜精液组DNA断裂精子百分率以TUNEL法检测，分别为（6．39±1．46）％、（5．75±1．29）％、（5．20±1．38）％、（4．94±1．86）％；以彗星试验检测，分别为（6．48±1．58）％、（5．83±1．48）％、（5．28±1．42）％、（5．12±1．65）％。冷冻干燥保存后的各组与新鲜精液相比较，DNA断裂精子百分率差异均无统计学意义（P〉0．05）。结论以ETBS或ETBS加海藻糖、蛋黄为保护剂的冷冻干燥法对人精子DNA无明显损伤，可有效地保护人精子的DNA。     

Synthesis of superporous hydrogels: hydrogels with fast swelling and superabsorbent properties.

We have been interested in the synthesis of hydrogels with fast swelling kinetics and superabsorbent properties. To increase the water absorption rate, interconnected pores were introduced to the hydrogels. Since the pore size in the dried hydrogels is in the order of hundreds of micrometers, these hydrogels are called "superporous" hydrogels. Superporous hydrogels were synthesized by crosslinking polymerization of various vinyl monomers in the presence of gas bubbles formed by the chemical reaction of acid and NaHCO3. The polymerization process was optimized to capture the gas bubbles inside the synthesized hydrogels. The use of the NaHCO3/acid system allowed easy control of timing for gelation and foam formation. We found that PF127 was the best foam stabilizer for most of the monomer systems used in our study. Scanning electron microscope (SEM) pictures showed interconnected pores forming capillary channels. The capillary channels, which were critical for fast swelling, were preserved during drying by dehydrating water-swollen hydrogels with ethanol before drying. The ethanol-dehydrated superporous hydrogels reached equilibrium swelling within minutes. The equilibrium swelling time could be reduced to less than a minute with the use of a wetting agent. In our study, water moisture was used as a wetting agent since the amount of moisture content in the dried hydrogels easily could be controlled. Preparation of superporous hydrogels using the right blowing system, foam stabilizer, drying method, and wetting agent makes it possible to reduce the swelling time to less than a minute regardless of the size of the dried gels. The superporous hydrogels can be used where fast swelling and superabsorbent properties are critical.     

The impact of hydration changes in fresh bio-tissue on THz spectroscopic measurements

We present a study of how residual hydration in fresh rat tissue samples can vastly alter their extracted terahertz (THz) optical properties and influence their health assessment. Fresh (as opposed to preserved) tissue most closely mimics in vivo conditions, but high water content creates many challenges for tissue handling and THz measurement. Our THz measurements of fresh tissue over time highlight the effect of tissue hydration on tissue texture and dimension, the latter directly influencing the accuracy of calculated optical properties. We then introduce lyophilization (freeze drying) as a viable solution for overcoming hydration and freshness problems. Lyophilization removes large amounts of water while retaining sample freshness. In addition, lyophilized tissue samples are easy to handle and their textures and dimensions do not vary over time, allowing for consistent and stable THz measurements. A comparison of lyophilized and fresh tissue shows for the first time that freeze drying may be one way of overcoming tissue hydration issues while preserving tissue cellular structure. Finally, we compare THz measurements from fresh tissue against necrotic tissue to verify freshness over time. Indeed, THz measurements from fresh and necrotic tissues show marked differences.     

灌注法制备离体大鼠心脏脱细胞基质

目的 探索制备离体大鼠心脏脱细胞生物支架材料的新方法,为心脏组织工程研究提供三维立体天然支架.方法 取30只成年SD大鼠心脏,运用冻融加化学萃取的组织工程学方法 (胰蛋白酶、十二烷基硫酸钠和曲拉通X-100)处理离体大鼠心脏,同时观察心脏大体形态及颜色变化,并对脱细胞支架进行基因组DNA分析;HE染色,免疫荧光法,扫描和透射电镜进一步检测鉴定脱细胞支架的生物学特征.结果 心脏脱细胞支架外观透明,包膜完整,维持心脏三维立体结构,肉眼可见心脏内脉管系统;脱细胞支架DNA残留量不及对照组的3%;HE染色、扫描和透射电镜结果 显示,心脏脱细胞生物支架去细胞彻底,细胞外基质网状结构保留完整;免疫荧光结果 表明,胶原、弹性蛋白等细胞外支架成分保留较完整,未见明显细胞核成分残留.结论 运用冻融加化学萃取法所制备的离体心脏脱细胞生物支架去细胞彻底,细胞外基质保留较完整,是较为理想的心脏三维立体生物支架材料.     

The effects of freeze drying and freeze drying additives on the prothrombin time and the international sensitivity index

AIM: To determine whether freezing, freeze drying protective additives, or freeze drying of plasma samples from patients on coumarin treatment and from normal individuals affects prothrombin times or the international sensitivity index (ISI) calibration. METHODS: The effect of the addition of the protective additives singly and combined on the prothrombin time of coumarin samples and normal samples before and after freeze drying was observed using high and low ISI reference thromboplastins. ISI values were also determined. RESULTS: Freezing caused a prolongation of prothrombin time in the normal plasma samples with both reagents, which was significant with the low ISI human. Prolongation (non-significant) of the prothrombin time in coumarin plasma samples occurred with the human reagent only. Significant prolongation of normal prothrombin time by some of the protective additives before and after freeze drying was observed with both thromboplastins but to a greater extent with the human. Significant prolongation of prothrombin time in coumarin plasma samples was observed, but again was more marked with human thromboplastin. An approximate ISI was determined on the 20 coumarin samples. The only marked ISI change was with the WHO human thromboplastin after freeze drying of plasma, where a decrease from 0.95 to 0.90 was observed, corresponding to a marked prothrombin ratio increase. CONCLUSIONS: Freeze drying additives and the freeze drying procedure prolong normal and coumarin prothrombin times, with low ISI thromboplastin. Less marked prolongations occurred with a high ISI rabbit reagent, coumarin samples showing more significant prolongations. Marked ISI change in freeze dried plasma was only recorded with the low ISI ECAA human reagent. Frozen normal plasma samples cannot be used with confidence for ISI calibrations.     

Repeated freeze-thawing of bone tissue affects Raman bone quality measurements

The ability to probe fresh tissue is a key feature to biomedical Raman spectroscopy. However, it is unclear how Raman spectra of calcified tissues are affected by freezing. In this study, six transverse sections of femoral cortical bone were subjected to multiple freeze∕thaw cycles and probed using a custom Raman microscope. Significant decreases were observed in the amide I and amide III bands starting after two freeze thaw cycles. Raman band intensities arising from proline residues of frozen tissue appeared consistent with fresh tissue after four cycles. Crystallinity values of bone mineral diminished slightly with freezing and were noticeable after only one freezing. Mineral carbonate levels did not deviate significantly with freezing and thawing. The authors recommend freezing and thawing bone tissue only once to maintain accurate results.     

The importance of "like to like" ISI calibrations with freeze dried plasmas. European Concerted Action on Anticoagulation.

AIM: To assess reliability of like to like and cross species calibrations using two types of certified freeze dried plasma calibrants--artificially depleted of vitamin K clotting factors, and from coumarin treated patients. METHODS: Six ECAA national control laboratories provided certified values for the freeze dried plasmas in terms of the human plain international reference preparation (IRP) (BCT/441) with the manual prothrombin time technique. Eight other ECAA national laboratories determined international sensitivity index (ISI) values in full fresh plasma same species and cross species WHO calibrations against a low ISI human IRP (BCT/441) of the ECAA low ISI human thromboplastin and high ISI ECAA rabbit thromboplastin. Parallel calibrations were performed using the certified values. RESULTS: Calibrations on fresh plasmas of the human ECAA reference thromboplastin (stated ISI = 0.95) gave ISI of 0.957 against the human IRP and 1.66 against the rabbit IRP. The ECAA rabbit (stated ISI = 1.67) gave an identical value on the fresh plasma calibration v the human IRP. With freeze dried depleted plasmas certified in terms of the human IRP, the ISI of the ECAA human was 1.01, but the ECAA rabbit (stated ISI = 1.67) gave a low ISI of 1.47. The freeze dried coumarin plasmas gave an ISI of 0.943 for the ECAA human but only 1.493 for the ECAA rabbit. CONCLUSIONS: Fresh plasmas give reliable ISI when calibrating thromboplastins in same species and cross species calibrations. Freeze dried plasmas certified in terms of a single IRP, whether artificially depleted or of coumarin plasma origin, cannot be used for calibration of dissimilar thromboplastins.     

Evaluation of collagen gel microstructure by scanning electron microscopy

We performed qualitative comparison of freeze drying and chemical drying as methods of preparing 3D wet specimens for scanning electron microscopy. Human fibroblasts immobilized in collagen gel were used as a model system. Specimens fixed with glutaraldehyde were frozen in liquid nitrogen and freeze-dried at low temperature in high vacuum. In parallel experiments, glutaraldehyde-fixed samples were dehydrated in ascending ethanol solutions, absolute ethanol, and 100% hexamethyldisilazane and then dried at room temperature. Scanning electron microscopy microphotographs of collagen fibers and cells were characterized by high resolution and the absence of collapsed or deformed structures even at high magnification (×50,000) for both chemical drying and high-vacuum freeze drying. However, high-vacuum freeze drying is superior to chemical drying for the investigation of the internal space of 3D scaffolds, because sample fracture can be prepared directly in liquid nitrogen. These techniques are a part of the sample preparation process for scanning electron microscopy and can also be used for studies of cell adhesion, morphology, and arrangement in wet specimens (3D gels and flexible tissue engineering scaffolds).