Low oxygen concentrations impair tissue development in tissue-engineered cardiovascular constructs

Cardiovascular tissue engineering has shown considerable progress, but in vitro tissue conditioning to stimulate the development of a functional extracellular matrix still needs improvement. We investigated the environmental factor oxygen concentration for its potential to increase the amount of collagen and collagen cross-links, and therefore improve tissue quality. Cardiovascular tissue engineered (TE) constructs, made of rapidly degrading PGA/P4HB scaffold seeded with human vascular-derived cells, were cultured at 7%, 4%, 2%, 0.5% O(2) for 4 weeks and compared to control cultures at 21% O(2). Tissue properties were evaluated by measuring the extracellular matrix production and mechanical behavior. The culture environment was monitored closely and the oxygen gradient throughout the constructs was simulated with a theoretical model. TE constructs cultured at 21%, 7% and 4% O(2) showed dense and homogeneous tissue formation with comparable strength, stiffness, collagen and collagen cross-link content. At 2% O(2), collagen content and stiffness decreased, whereas at 0.5% O(2), hardly any tissue was formed. Overall, tissue properties deteriorated at the lowest oxygen concentrations, opposing our hypothesis that was based on previous culture at low oxygen concentrations. Further research will focus on establishing the balance between applied oxygen conditions (concentration and exposure time) and optimal tissue outcome.     

Water-soluble argatroban for antithrombogenic surface coating of tissue-engineered cardiovascular tissues

Argatroban is a powerful synthetic anticoagulant, but due to its water-insoluble nature, it is unsuitable for use as a coating material to reduce the thrombogenic potential of natural or tissue-engineered blood-contacting cardiovascular tissues. On the other hand, anionic compounds could adsorb firmly onto connective tissues. Therefore, in this study, an anionic form of argatroban was prepared by neutralization from its alkaline solution, dialysis, and freeze-drying. The subsequently obtained argatroban derivative could be easily dissolved in water. Analysis of the surface chemical composition showed that the water-soluble argatroban (WSA) could be adsorbed on the entire surface of tissue-engineered connective tissue sheets composed mainly of collagen. Adsorption was achieved on immersion of the tissue-engineered connective tissue sheet in a saline/WSA solution for only 30 s without any change in the mechanical properties of the tissue-engineered sheets. Complete surface adsorption (ca., 1 mg/cm(2) ) was obtained at WSA concentrations of over 5 mg/mL. WSA adsorption was maintained for at least 7 days with rinsing. Blood coagulation was significantly prevented on the WSA-adsorbed surfaces in acute in vitro experiments. The coating was applied to in vivo tissue-engineered vascular grafts (biotubes) or tri-leaflet tissues (biovalves) under development, ensuring a high likelihood of nonthrombogenicity of their blood-contacting surfaces with high patency, at least in the subchronic phase. It appears that WSA satisfies the initial requirements for a biocompatible aqueous coating material for use in natural or tissue-engineered tissues.     

A novel pulsatile,laminar flow bioreactor for the development of tissue-engineered vascular structures

Exposure of vascular cell-seeded, tubular, biodegradable polymers to pulsatile flow conditions has been proposed as a method to develop tissue-engineered blood vessels by "maturing" structural integrity, and increasing collagen content, suture retention, burst pressure, and tissue formation. These in vitro tissue-engineered arteries demonstrate contractile responses to pharmacologic agents and express markers of vascular differentiation. Current methods to induce pulsatile flow in a bioreactor system are limited by the creation of nonphysiologic pressure waveforms and noncompliant reservoirs to house the tissue-engineered vascular constructs. We have developed a novel method for the in vitro development of tubular vascular structures by using a mechanical ventilator to induce pulsatile, laminar flow into a fluid column, resulting in pressurized waveforms similar to mammalian physiology. The vascular constructs are housed in semicompliant tubing to facilitate an additional variable of circumferential stretch as a potential signaling mechanism. This approach more closely approximates mammalian physiology and we hypothesize that it will facilitate mechanical signaling necessary for the development of tissue-engineered vessels for clinical applications.     

Control of in vitro tissue-engineered bone-like structures using human mesenchymal stem cells and porous silk scaffolds

Natural bone consists of cortical and trabecular morphologies, the latter having variable pore sizes. This study aims at engineering different bone-like structures using scaffolds with small pores (112-224 microm) in diameter on one side and large pores (400-500 microm) on the other, while keeping scaffold porosities constant among groups. We hypothesized that tissue engineered bone-like structure resulting from silk fibroin (SF) implants is pre-determined by the scaffolds' geometry. To test this hypothesis, SF scaffolds with different pore diameters were prepared and seeded with human mesenchymal stem cells (hMSC). As compared to static seeding, dynamic cell seeding in spinner flasks resulted in equal cell viability and proliferation, and better cell distribution throughout the scaffold as visualized by histology and confocal microscopy, and was, therefore, selected for subsequent differentiation studies. Differentiation of hMSC in osteogenic cell culture medium in spinner flasks for 3 and 5 weeks resulted in increased alkaline phosphatase activity and calcium deposition when compared to control medium. Micro-computed tomography (microCT) detailed the pore structures of the newly formed tissue and suggested that the structure of tissue-engineered bone was controlled by the underlying scaffold geometry.     

Ultrastructure abnormalities in proteoglycans, collagen fibrils, and elastic fibers in normal and myxomatous mitral valve chordae tendineae.

Normal and myxomatous chordae tendineae were studied using light and electron microscopy, to assess the alterations in the appearance and mutual arrangement of proteoglycans, collagen fibrils, and elastic fibers. Specific staining with ruthenium red and cuprolinic blue in a critical electrolyte concentration mode were used to localize proteoglycans. Fresh tissues were fixed in glutaraldehyde containing the cationic dyes and embedded into Spurr resin. Semithin sections of LR White (London Resin Co., Basingstoke, U.K.)-embedded tissue were used for histochemistry. In normal chordae tendineae, the fibrosa comprised close-packed collagen fibrils intermixed with elastic fibers. These were surrounded by a thin layer of elastic fibers and collagen fibrils, both of which were closely associated with proteoglycans. In myxomatous chordae tendineae, alterations were observed in the connective tissue. Proteoglycans were more abundant and were distributed throughout the tissue. The outermost layer was transformed into an undifferentiated electron-dense mass surrounding the central fibrosa, which contained degraded elastic fibers and collagen fibrils. Collagen fibrils had faint banding or lacked a banding pattern altogether. Spaces between collagen fibrils were occupied by abnormal proteoglycans or proteoglycan aggregates. Elastic fibers showed varying degrees of degeneration and were occasionally replaced by electron-lucent spaces containing microfibrils. Accumulation of abnormal proteoglycan was also observed around degenerated elastic fibres and collagen fibrils.     

Current status of tissue engineering for cardiovascular structures

Various vascular and valvlular grafts are commonly used in the treatment of cardiovascular disease. Current prosthetic or bioprosthetic materials lack growth potential, and therefore, subsequent replacement further defeats the concept of primary repair early in pediatric cardiac patients. Tissue engineering is a new discipline that offers the potential to create replacement structures from autologous cells and biodegradable polymer scaffolds. Because tissue-engineering constructs contain living cells, they may have the potential for growth, self-repair, and self-remodeling. Cardiac valve leaflets and large conduits in the pulmonary ciruulation have been made with this tissue-engineering approach in lambs. Venous conduits were also created in dogs. Mixed cell populations of endothelial cells and fibroblasts were isolated from explanted peripheral arteries or vein. A synthetic biodegradable scaffold con-sisting of polyglactin and polyglycolic acid fibers was seeded in vitro with mixed cultured cells. After one week, these autologous cell/polymer constructs were reimplanted in animals. Each animal was then followed periodically by echocardiography and angiography. The animals were sacrificed, and the implanted tissues were examined histologically, biochemically, and biomechanically. A 4-hydroxyproline assay was performed to evaluate the collagen content. The implanted conduit diameters increased as the animals grew during the study period. Histologically, the biodegradable polymer scaffold was completely degraded. Collagen analysis of the constructs showed the development of an extracellular matrix. Immunohistochemical staining demonstrated elastin fiber in the matrix and factor VIII on the inner surface of the conduits. In conclusion, a tissue-engineering approach to constructing cardiovascular structures is feasible using cells of either arterial or venous origin. In these tissue-engineered autografts, transplanted autologous cells generated the proper matrix over the polymer scaffold under physiologic conditions.     

Angiogenesis in tissue-engineered small intestine

Tissue-engineered intestine offers promise as a potential novel therapy for short bowel syndrome. In this study we characterized the microvasculature and angiogenic growth factor profile of the engineered intestine. Twenty-three tissue-engineered small intestinal grafts were harvested from Lewis rat recipients 1 to 8 weeks after implantation. Architectural similarity to native bowel obtained from juvenile rats was assessed with hematoxylin and eosin-stained sections. Capillary density, measured after immunohistochemical staining for CD34, was expressed as number of capillaries per 1000 nuclei. Vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) tissue levels were measured by ELISA and normalized to total protein. Over the 8-week period cysts increased in volume (0.5 cm(3) at week 1 versus 12.6 cm(3) at week 8) and mass (1.30 +/- 0.29 versus 9.74 +/- 0.3 g; mean +/- SEM). Muscular and mucosal layers increased in thickness, but capillary density remained constant (82.95 +/- 4.81 capillaries per 1000 nuclei). The VEGF level was significantly higher in juvenile rat bowel than in engineered cyst (147.6 +/- 23.9 versus 42.3 +/- 3.4 pg/mg; p < 0.001). Tissue bFGF levels were also higher (315 +/- 65.48 versus 162.3 +/- 15.09 pg/mg; p < 0.05). The mechanism driving angiogenesis differs in engineered intestine and in normal bowel. VEGF and bFGF delivery may prove useful for bioengineering of intestine.     

Ultrastructure of PkC(II/III)-immunopositive structures in rat primary visual cortex

Summary In the primary visual cortex of adult rats the cellular and subcellular distribution of protein kinase C isozymes II and III (PkCII/III) was examined by immunohistochemical methods with a monoclonal antibody against PkCII/III. Strong PkC(II/III)-immunoreactivity was found in neurons and astrocytes. Immunopositive neurons exhibited morphological features characteristic for both pyramidal and non-pyramidal cells. They were distributed in layers II through VI but were concentrated in layers II/III. At the electron microscopic level immunoprecipitate was found predominantly in distinct regions of the somata, except the nuclei, and only a few labeled dendrites and axons were seen. Two different patterns of cytoplasmic immunoreactivity could be distinguished. In most neurons, PkC(II/III)-staining was confined to cytoplasmic spots associated with the Golgi complex, while a few neurons exhibited additional labeling in the vicinity of the cell membrane. Moreover, PkC(II/III)-immunoreactivity was present in numerous astroglial processes and in the perikaryal cytoplasm of a subpopulation of astrocytes.Present data provide morphological indications for specifie functions of PkC isozymes II and III in neurons as well as in astrocytes.     

Optimized growth conditions for tissue engineering of human cardiovascular structures

Optimized in vitro formation of strong tissue is a prerequisite for tissue engineering of cardiovascular structures, such as heart valves and blood vessels. This study evaluates different growth media additives as to cell proliferation, extracellular matrix formation, and mechanical characteristics. Biodegradable polymers were seeded with human vascular myofibroblasts. Group A was cultured with standard medium, groups B, C, and D were in addition supplemented with ascorbate, fibroblast growth factor (bFGF), and both respectively. Analysis included histology, electron microsocopy, mechanical testing, and biochemical assays for cell proliferation (DNA) and extracellular matrix (collagen). DNA content increased in all groups, showing significantly more cells in group C and D after 14d. Collagen increased in all groups, except for C. Morphology showed viable, layered cellular tissue, with collagen fibrils after 2w, most pronounced in B and D. Mechanical properties decreased initially, stabilizing after 2w. In conclusion, standard nutrient media were efficient for seeded human vascular cells cultured on biodegradable meshes. Supplementation with bFGF+ascorbate resulted in enhanced early cell proliferation and structurally more mature tissue formation.     

体外构建血管化组织工程心肌

目的:探讨体外构建血管化组织工程心肌的可行性。方法:大鼠骨髓间充质干细胞以浓度为10μmol/L的5-氮胞苷诱导为心肌细胞并用DAPI标记、骨髓源内皮祖细胞以内皮细胞培养基EGM2-MV定向诱导为内皮细胞并用CM-dil标记。标记后的心肌细胞与内皮祖细胞按2:1比例,以4×10~6个/ml的密度种植于Matrigel基质胶支架上。同种密度心肌细胞种植为对照组。对复合体形态、细胞分布等进行观察。结果:H-E染色及荧光显微镜观察可见两组复合体的细胞分布均匀,生长状态良好;单纯心肌细胞种植组可见细胞黏附聚集生长,并未出现网状结构,而2:1混合培养组24 h后可见内皮细胞相互连接成网状结构,出现典型的成血管现象,且形成的血管样结构明显多于对照组;心肌细胞凋亡数较对照组少。结论:骨髓源性心肌细胞与骨髓源性内皮细胞联合种植于Matrigel基质胶共培养,可于体外成功构建血管化组织工程心肌。     

Cryopreservation of tissue-engineered epithelial sheets in trehalose

Tissue-engineered epidermal membranes are useful for clinical wound healing. To facilitate these products in the clinic, optimized storage methods need to be developed. We studied the efficiency of extracellular trehalose at various concentrations for cryopreserving human tissue-engineered epidermal membranes compared with that of dimethyl-sulfoxide (DMSO) used by most organ banks for cryopreserving skin grafts and artificial skin substitutes. Keratinocyte (KC) viability, proliferation and marker expression following cryopreservation in trehalose were examined with similar results to those using DMSO. Trehalose concentration (0.4m) was optimized according to the described cellular activities following cryopreservation. Artificial epidermal substitutes were then cryopreserved in trehalose at the optimized concentration. Cell viability, growth factor secretion and wound healing properties of cryopreserved artificial epidermal substitutes using nude mice were examined and compared with those of DMSO cryopreservation. Cryopreservation with trehalose enhanced human KC viability in suspension and artificial skin substitutes. In addition, trehalose cryopreservation provided fast recovery of EGF and TGF-β1 secretion by KCs after thawing. When transplanted into nude mice, trehalose-cryopreserved artificial skin repaired skin defects in a similar manner to that of a non-cryopreserved control. Moreover, trehalose-cryopreserved artificial skin resulted in engraftment and wound closure that was significantly enhanced compared with that of DMSO-cryopreserved epidermal membranes. The results indicate that the use of trehalose improves cryopreservation of tissue-engineered epithelial sheets.     

组织工程化软骨构建的研究进展

背景：组织工程学方法为关节软骨缺损的修复提供了新的治疗模式,具有广阔的应用前景。 目的：探究组织工程化软骨的构建方法、研究方向和应用前景。 方法：检索中国期刊全文数据库(CNKI:1991至2011年)和Web of Science(1991至2011年)数据库,检索词分别为“组织工程,软骨损伤,种子细胞,支架”和“Tissue Engineering,Cartilage Defects,Seed Cell,Scaffolds”,语言分别设为中文和英文。阅读文题和摘要进行筛选,选择具有原创性,论点论据可靠且分析全面,密切相关的文章,排除重复性研究以及质量较差文章。按纳入排除标准筛选后,共纳入30篇文章。 结果与结论：组织工程化软骨多以各种种子细胞与不同的支架材料进行复合,且在软骨缺损修复中体现了较好的应用价值,但应用于临床还有许多具体问题需要解决。     

组织工程心脏瓣膜细胞生物学研究进展

由于现有的机械瓣和生物瓣仍存在种种不足,如不具备生长性、需抗凝、易感染、不能生长和自我修复等。组织工程心脏瓣膜是一新兴的研究领域,涉及多门学科。构建组织工程心脏瓣膜应包括支架的制作、细胞的种植、瓣膜的体外培养和最终移植入人体。其中种植的细胞是组织工程心脏瓣膜的基本要素。就组织工程心脏瓣膜的细胞生物学研究进展做一综述。     

组织工程心脏瓣膜细胞生物学研究进展

由于现有的机械瓣和生物瓣仍存在种种不足，如不具备生长性、需抗凝、易感染、不能生长和自我修复等。组织工程心脏瓣膜是一新兴的研究领域，涉及多门学科。构建组织工程心脏瓣膜应包括支架的制作、细胞的种植、瓣膜的体外培养和最终移植人人体。其中种植的细胞是组织工程心脏瓣膜的基本要素。就组织工程心脏瓣膜的细胞生物学研究进展做一综述。     

Gene therapy in tissue-engineered blood vessels

Cardiovascular disease is the leading cause of morbidity and mortality in Western society. More than 1 million arterial bypass procedures are performed annually in the United States, where either autologous veins or synthetic grafts are used to replace arteries in the coronary or peripheral circulation. Tissue engineering of blood vessels from autologous cells has the potential to produce biological grafts for use in bypass surgery. Ex vivo development of vascular grafts also provides an ideal target of site-specific gene therapy to optimize the physiology of the developing conduit, and for the possible delivery of other therapeutic genes to a vascular bed of interest. In this article, we demonstrate that by using a novel retroviral gene delivery system, a target gene of interest can be specifically delivered to the endothelial cells of a developing engineered vessel. Further, we demonstrate that this technique results in stable incorporation of the delivered gene into the target endothelial cells for more than 30 days. These data demonstrate the utility of the retroviral gene delivery approach for optimizing the biologic phenotype of engineered vessels. This also provides the framework for testing an array of genes that may improve the function of engineered blood vessels after surgical implantation.     

Evaluation of tissue-engineered vascular autografts

This study evaluated the endothelial function and mechanical properties of tissue-engineered vascular autografts (TEVAs) constructed with autologous mononuclear bone marrow cells (MN-BMCs) and a biodegradable scaffold using a canine inferior vena cava (IVC) model. MN-BMCs were obtained from a dog and seeded onto a biodegradable tubular scaffold consisting of polyglycolide fiber and poly(L-lactide-co-epsilon-caprolactone) sponge. This scaffold was implanted in the IVC of the same dog on the day of surgery. TEVAs were analyzed biochemically, biomechanically, and histologically after implantation. When TEVAs were explanted and stimulated with acetylcholine at 1 month, they produced nitrates and nitrites dose dependently. N(G)-nitro-L-arginine methylester significantly inhibited these reactions. With stimulation by acetylcholine, factor VIII-positive cells of TEVAs produced endothelial nitric oxide synthase proteins, and the ratio of endothelial nitric oxide synthase/s17 mRNA was similar among native IVC and TEVAs 1 and 3 months after implantation. TEVAs had biochemical properties and wall thickness similar to those of native IVC at 6 months after implantation, and tolerated venous pressure well without any problems such as calcification. The number of inflammatory cells in TEVAs and the ratio of CD4/s17 mRNA decreased significantly with time. These results indicate that TEVAs are a biocompatible material with functional endothelial cells and biomechanical properties and do not have unwanted side effects.     

组织工程化人工角膜的临床应用：距离还有多远？

背景：人工角膜是取代混浊角膜组织而用异质成形材料制成的一种特殊屈光装置,通过手术植入患眼,以取得一定视力。 目的：介绍近年来人工角膜研究进展。 方法：由第一作者用计算机检索万方医学网和Medline database数据库,检索词分别为“人工角膜、角膜移植、生物相容性、组织工程”和“keratoprosthesis, corneal transplantation, biocompatibility, tissue engineering”,对人工角膜移植的动物实验、临床进展、植入方式及生物相容性、并发症等方面进行探讨。 结果与结论：共检索到204篇文章,按纳入和排除标准对文献进行筛选,共纳入50篇文章。人工角膜的研制在近年来有了较大的进步,非组织工程化人工角膜在材料选择,处理和设计方式上有所创新,同时具有活性的组织工程化人工角膜的出现为人工角膜的研制开辟了一条新途径。 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：     

组织工程角膜内皮层移植的研究与应用

背景：组织工程角膜内皮可以克服角膜内皮移植的短缺并能够改善角膜内皮细胞的质量,其应用前景十分广阔。因此,寻找一种理想的重建角膜内皮方法是组织工程角膜研究领域的重要课题和研究热点。 目的：总结并讨论组织工程角膜内皮重建的研究进展。 方法：应用计算机检索PubMed 数据库(http://www.ncbi.nlm.nih.gov/PubMed)相关文章,检索时间为2000至2012年,检索词为“corneal endothelial cell,transplantation,tissue engineering”,并限定文章语言种类为英语,然后再从中筛选出与主题相关的部分文献。 结果与结论：初检得到163篇文章,按主题相关性对文献进一步筛选,最终纳入44篇文章。目前构建单层角膜内皮层的研究较多,也取得了巨大的成绩,但是仍没有一种材料或重建方式可以完全符合临床应用的组织工程的人角膜内皮。每一种材料和方法都各有优缺点,克服这些缺点以及观察在体内的长期影响是今后的发展方向。     

Imaging of cardiovascular structures using near-infrared femtosecond multiphoton laser scanning microscopy

Multiphoton imaging represents a novel and very promising medical diagnostic technology for the high-resolution analysis of living biological tissues. We performed multiphoton imaging to analyzed structural features of extracellular matrix (ECM) components, e.g., collagen and elastin, of vital pulmonary and aortic heart valves. High-resolution autofluorescence images of collagenous and elastic fibers were demonstrated using multifluorophore, multiphoton excitation at two different wavelengths and optical sectioning, without the requirement of embedding, fixation, or staining. Collagenous structures were selectively imaged by detection of second harmonic generation (SHG). Additionally, routine histology and electron microscopy were integrated to verify the observed results. In comparison with pulmonary tissues, aortic heart valve specimens show very similar matrix formations. The quality of the resulting three-dimensional (3-D) images enabled the differentiation between collagenous and elastic fibers. These experimental results indicate that multiphoton imaging with near-infrared (NIR) femtosecond laser pulses may prove to be a useful tool for the nondestructive monitoring and characterization of cardiovascular structures.