组织工程心脏瓣膜研究进展

目前组织工程心脏瓣膜研究已在支架的选材、种子细胞的选择、种子细胞的种植与瓣膜构建方法三个方面取得进展，并已构建出三种代表性组织工程心脏瓣膜。对它们各自的特点进行综述。     

组织工程心脏瓣膜种子细胞:来源及应用

背景:应用机械瓣和生物瓣行瓣膜置换是治疗终末期瓣膜病的有效手段,然而他们的临床应用受到多个因素的限制。具备生物活性的组织工程心脏瓣膜有潜力克服机械瓣和生物瓣的不足,选择适宜的种子细胞是组织工程心脏瓣膜研究的一个重要方面,许多成熟的体细胞和干细胞已被用于构建组织工程心脏瓣膜,然而尚未获得理想的结果。目的:以构成瓣膜的细胞成分为基础,对用于构建组织工程心脏瓣膜的种子细胞、体外细胞种植方法的研究进行综述。方法:由第一作者基于PubMed数据库和万方数据库应用计算机检索2000年1月至2012年12月相关的文章,英文检索词为"Tissue engineering,Heart valves,Cell",中文检索词为"组织工程,心脏瓣膜,细胞",优选文章内容与组织工程心脏瓣膜种子细胞直接相关,具备针对性和权威性,发表在权威杂志的文章共39篇进行综述。结果与结论:瓣膜的细胞成分主要是内皮细胞和间质细胞,早期人们常用内皮细胞和成纤维细胞构建组织工程瓣膜,随着干细胞研究的深入,应用搏动性生物反应器种植间充质干细胞具有构建的组织工程瓣膜的潜力。     

脂肪间充质干细胞分化为内皮细胞并体外构建组织工程心脏瓣膜

背景：组织工程心脏瓣膜是利用组织工程技术将种子细胞种植于瓣膜支架上所构建的一种人工瓣膜,目前国内外研究主要集中于种子细胞来源及支架选择上。 目的：探讨人脂肪间充质干细胞体外向内皮细胞诱导分化后的细胞作为种子细胞,脱细胞猪主动脉瓣膜作为支架体外构建组织工程心脏瓣膜的可行性。 方法：利用吸脂术采集脂肪组织,分离、培养脂肪间充质干细胞,流式细胞仪鉴定细胞表型;免疫细胞化学方法及RT-PCR检测细胞分化标志物;应用Triton X-100联合胰蛋白酶的方法制备脱细胞猪主动脉瓣支架,将体外培养扩增的诱导分化后的内皮细胞种植于支架上构建组织工程心脏瓣膜,光镜及电镜下观察组织工程心脏瓣膜的组织学结构。 结果与结论：脂肪组织分离培养的脂肪间充质干细胞向内皮细胞诱导分化后表达CD31、CD34、CD144、Ⅷ因子和内皮型一氧化氮合成酶等内皮细胞特异性抗原;脱细胞猪主动脉瓣膜支架脱细胞完全,弹力纤维及胶原纤维保持完整;构建的组织工程心脏瓣膜可见支架上排列连续的单细胞层。提示脂肪间充质干细胞在体外向内皮细胞诱导分化后已初步具有内皮细胞功能,在脱细胞猪主动脉瓣膜支架上生长良好,可以在体外初步构建组织工程心脏瓣膜。     

组织工程心脏瓣膜的构建：现状与前景

背景：目前临床上应用的心脏生物瓣和机械瓣都存在一些缺陷和不足,而组织工程心脏瓣膜有可能避免这些问题的出现,成为瓣膜替代物的理想选择。 目的：探讨构建组织工程心脏瓣膜的实验研究进展。 方法：应用数据库检索的方法分析关于组织工程心脏瓣膜的实验研究文献,组织工程心脏瓣膜的三大要素为种子细胞、支架材料和细胞种植。 结果与结论：心脏瓣膜修复和置换是目前治疗心脏瓣膜性疾病的主要外科手段。目前,主要用于构建组织工程心脏瓣膜的种子细胞有血管内皮细胞、内皮祖细胞以及骨髓间充质干细胞等。经脱细胞处理的支架具有良好的生物力学性能和组织相容性,细胞种植后支架表面会形成一层连续的细胞层,其构建的组织工程心脏瓣膜是可行的。组织工程心脏瓣膜有着良好的应用前景,但目前还有很多问题需要解决,还处于研究的初级阶段。 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：     

组织工程心脏瓣膜的研究进展

组织工程心脏瓣膜(tissue engineering heart valve,TEHV)理论上能克服机械瓣及生物瓣的不足,具有广阔的发展前景.目前组织工程心脏瓣膜的研究主要集中在瓣膜支架材料的选取及制备、种子细胞的选择和种子细胞的种植及培养等三方面.本文将分别就这三方面研究进展进行介绍,分析目前存在的问题,并对其应用进行展望.     

组织工程心脏瓣膜及干细胞应用前景

组织工程心脏瓣膜是一种具有活力、能够自我修复和增生的人工瓣膜。理想的组织工程心脏瓣膜由于具有优良的血流动力学特征,低或甚至无免疫反应,不需要长期抗凝治疗以及耐用性好等特性,能够很好地克服目前临床上使用的机械瓣和生物瓣的缺点。综述了近年来国外组织工程心脏瓣膜在生物材料、培养环境和种子细胞等方面的新进展,并展望了干细胞作为种子细胞的应用前景。     

组织工程化心脏瓣膜的研究进展

心脏瓣膜置换术是外科治疗瓣膜性心脏病的主要方法，但目前临床应用的人工瓣膜的远期效果尚不满意。近年来，随着组织工程学技术的进展，利用培养的自身组织细胞种植于支架材料表面，体外重新构建理想的心脏瓣膜植物日益成为研究热点。本文简述了心脏瓣膜工程的定义，细胞支架材料的选择，种子细胞的培养、种植方法以及组织工程化心脏瓣膜的评估，并指出下一步研究中尚需解决的问题。     

血液流体动力学研究与生物反应器在组织工程化心脏瓣膜构建的应用

由于目前临床应用的心脏瓣膜替代物各有其固有的不足，探索以合适的方法构建具有生长活性的组织工程化心脏瓣膜一直是该领域各国学者研究报道的焦点。心脏瓣膜生物反应器模拟了心脏瓣膜在体内所处的血流动力学环境，并具有传质功能，所以在TEHV构建中除了要有足够健康的种子细胞和理想的生物支架材料，生物反应器是不可缺少的。对血液流动力研究进展，心脏瓣膜生物反应器的原理、构造与设计，生物反应器在心脏瓣膜组织工程中的应用范围进行了逐一概述。     

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。     

Design and manufacture of a polyvinyl alcohol (PVA) cryogel tri-leaflet heart valve prosthesis

Although current artificial heart valves are life sustaining medical devices, improvements are still necessary to address deficiencies. Bioprosthetic valves have a compromised fatigue life, while mechanical valves have better durability but are prone to thromboembolic complications. A novel, one-piece, tricuspid valve, consisting of leaflets, stent and sewing ring, made entirely from the hydrogel, polyvinyl alcohol cryogel (PVA-C), has been developed and demonstrated. This valve has three thin leaflets attached to a cylindrical stent. In order to approximate the complex shape of the surface of the natural heart valve leaflets, two different geometries have been proposed: revolution about an axis of a hyperboloid shape and revolution about an axis of an arc subtending (joining) two straight lines. The parameters of both geometries were examined based on a compromise between avoiding sharp curvature of leaflets and minimization of the central opening of the valve when closed. The revolution of an arc subtending two straight lines was selected as the preferred geometry since it has the benefit of a smaller central opening when the value of the maximum curvature for the leaflets is the same for each valve geometry. A cavity mold has been designed and constructed to form the PVA-C heart valve. The three leaflets were formed and integrated into the stent and sewing ring in a single process. Prototype heart valves were manufactured in the mold from a solution of PVA and water, by controlled freezing and thawing cycles.     

Valvular heart disease in patients with hypocomplementemic urticarial vasculitis syndrome associated with Jaccoud's arthropathy.

BACKGROUND: Since 1973, more than 75 patients with hypocomplementemic urticarial vasculitis syndrome (HUVS) were reported, but valvular heart disease does not seem to have been noted in these patients. Since 1993, however, five patients with HUVS accompanied by Jaccoud's arthropathy (JA) were found to have serious valvular heart disease. METHODS: To characterize the cardiac valvulopathy of the third patient with HUVS/JA to have undergone valve replacement, this study included the use of routine and special tissue stains, as well as immunohistochemical staining. We compared gross and histologic findings of this patient's valve to those of two other patients with this complex syndrome who underwent valve replacement. Pathologic findings of these latter two patients were described in separate earlier reports. RESULTS: Histologic examination of the resected valves in all three patients showed an acute necrotizing endocarditis and fibrin deposition on the surface of valve leaflets. Beneath the surfaces of the leaflets, there was evidence of chronic inflammation, consisting of lymphocytes and histiocytes. A fibrocalcific degenerative change was also present in all three valves. Positive staining for IgG, IgA, IgM, and light-chain determinant-bearing proteins was detected primarily at the valve surface in special studies of the aortic valve of the patient described in the current report. CONCLUSION: Patients with HUVS and associated JA should be evaluated for the presence of valvular heart disease. The latter is probably a nonrheumatic, inflammatory, and degenerative process, mediated by immune complex, as well as cellular immune mechanisms.     

An unusual complication associated with the Carpentier-Edwards porcine bioprosthesis

Primary tissue failure of bioprosthetic heart valves refers primarily to calcification of the leaflets of the bioprosthesis. A 75 year old patient underwent reoperation 15 years after mitral valve replacement with a Carpentier-Edwards porcine bioprosthesis. The extracted bioprosthetic valve was found to have one prolapsed leaflet and a small amount of calcification on all three leaflets without tear or perforation. The two commissures suspending the prolapsed leaflet were detached, causing mitral valve regurgitation.     

Effects of leaflet geometry on the flow field in three bileaflet valves when installed in a pneumatic ventricular assist device

Our group is currently developing a pneumatic ventricular assist device (PVAD). In this study, in order to select the optimal bileaflet valve for our PVAD, three kinds of bileaflet valve were installed and the flow was visualized downstream of the outlet valve using the particle image velocimetry (PIV) method. To carry out flow visualization inside the blood pump and near the valve, we designed a model pump that had the same configuration as our PVAD. The three bileaflet valves tested were a 21-mm ATS valve, a 21-mm St. Jude valve, and a 21-mm Sorin Bicarbon valve. The mechanical heart valves were mounted at the aortic position of the model pump and the flow was visualized by using the PIV method. The maximum flow velocity was measured at three distances (0, 10, and 30 mm) from the valve plane. The maximum flow velocity of the Sorin Bicarbon valve was less than that of the other two valves; however, it decreased slightly with increasing distance it the X-Y plane in all three valves. Although different bileaflet valves are very similar in design, the geometry of the leaflet is an important factor when selecting a mechanical heart valve for use in an artificial heart.     

组织工程心脏瓣膜支架材料的选择与应用

背景：支架材料的选择在组织工程心脏瓣膜中起着至关重要的作用,支架材料的选择也就影响着组织工程心脏瓣膜的构建效果。 目的：评价组织工程心脏瓣膜支架材料的的优缺点,并对其选择进行总结。 方法：以 “组织工程,心脏瓣膜,支架材料,生物相容性”,为中文关键词;以:“tissue engineering,heart valves, scaffold material, biocompatibility” 为英文关键词,采用计算机检索1993-01/2009-10相关文章。纳入与有关生物材料与组织工程心脏瓣膜的相关的文章;排除重复研究及Meta分析类文章。 结果与结论：人工合成高分子材料有更大的可控性,可预先塑性,大量制备,孔径和孔隙率较容易控制,成本低廉;天然生物材料和合成高分子材料都存在一定不足,将人工可降解材料与天然材料相结合构建瓣膜支架,发挥两者各自的优势构建出性能良好的组织工程心脏瓣膜。组织工程心脏瓣膜的研究前景广阔。但距离临床应用还有很长的路要走,相信随着研究的不断深入以及支架材料的不断优化对组织工程心脏瓣膜构建方法的改进,在不远的将来造福于广大心脏瓣膜病患者。     

Cardiac valve replacement: a bioengineering approach

The second most common major heart operation in the western world is valve replacement. Any one of the four heart valves may become either so stenotic or regurgitant that it needs to be replaced in order to restore normal heart function. Although replacement surgery of dysfunctional heart valves has a very high success rate, it can provide the surgeon with a difficult decision regarding the choice of a suitable prosthesis for the individual patient. Over the years many different types of artificial heart valves have been devised. Surgeons typically deal with a heart valve replacement by installing a mechanical prosthesis or by using a bioprosthetic valve, hand-crafted from animal tissue. Least commonly, valves can be taken from human organ donors. Mechanical valve substitutes have a long fatigue life but the central flow occluders often induce blood cell trauma. Tissue substitutes have an unimpeded central orifice when open, cause minimal cell damage but have a relatively short fatigue life, especially in children where calcification may be a major problem. More recently alternative materials, such as polyurethane, have been used in artificial heart valve design while the new concept of tissue-engineering has enhanced the prospects towards an ideal cardiac valve replacement. Today's artificial valves are designed with a better understanding of the cardiovascular system with the aid of computers. Advances in computer software have allowed simulations of fluid flows through valve substitutes, both in cardiac flow simulators and the heart itself.     

Mechanical valve replacement in congenital heart defects in the era of international normalized ratio self-management

As the number of patients with congenital heart defects requiring heart valve replacement increases, the need for durable valve substitutes with good hemodynamic performance and a low incidence of complications becomes more apparent. The use of porcine xenografts is burdened with early fibrocalcific degeneration, whereas the use of mechanical heart valves led to an increased number of thromboembolic events, especially when implanted in the right side of the heart. We report on our experiences implanting bileaflet heart valves in congenital heart defects since the introduction of international normalized ratio (INR) self-management. The data of 68 long-term survivors (33 males, 35 females) who underwent mechanical heart valve replacement in congenital heart defect were reviewed. Patient age at the time of valve replacement ranged from 5 months to 61 years (mean 21 years). Underlying diagnoses were tetralogy of Fallot (n=33), morbus Ebstein (n=4), atrioventricular canal (n=13), truncus arteriosus communis (n=5), transposition of the great arteries (n=10), and congenitally corrected transposition of the great arteries (n=3). In all patients, bileaflet valves were implanted (St. Jude Medical n=40, Carbomedics n=28). Anticoagulation was performed using dicumarol (Marcumar) and INR self-management in all cases. The mean follow-up was 72 months (range 6-132 months; 409 patient-years). Valve thrombosis developed in 3 of 68 patients (4.4%, all three had tetralogy of Fallot, mean age 9.8 years) after a mean follow-up of 3.5 years. In two of these three patients, re-pulmonary valve replacement was necessary, whereas the third patient was treated by thrombolysis. From our experience, we conclude that mechanical heart valve replacement is a good therapy option with a low complication rate for patients with congenital heart defects requiring valve replacement, especially when INR self-management is performed.     

Cavitation phenomenon in monoleaflet mechanical heart valves with electrohydraulic total artificial heart

Recently, cavitation on the surface of mechanical heart valves has been studied as a cause of fractures occurring in implanted mechanical heart valves. In this study, to investigate the mechanism of cavitation bubbles associated with monoleaflet mitral valves in an electrohydraulic total artificial heart (EHTAH), and to select the best valves for our EHTAH system, we measured three parameters. First, an image was created of the cavitation bubbles using a high-speed camera. Second, pressure drop in the vicinity of the valve surface was measured using mini pressure sensor. Then, the closing of the valve was observed using a Laser displacement sensor. Most of the cavitation bubbles in the Medtronic Hall valve were observed at the edge of the valve stop. With the Omnicarbon valve, the cavitation bubbles were observed at the edge of the valve and on the inner side of the leaflet. On the other hand, cavitation bubbles were observed only on the inner side of the leaflet in Bj?rk-Shiley valve. Cavitation bubbles concentrated on the edge of the valve stop; the major cause of these cavitation bubbles was determined to be the squeeze flow. The formation of cavitation bubbles depended on the valve closing velocity and the valve leaflet geometry. From a viewpoint of squeeze flow, a low closing velocity and a small size of the valve stop could minimize cavitation.     

Fabrication of a trileaflet heart valve scaffold from a polyhydroxyalkanoate biopolyester for use in tissue engineering

Previously, we reported the implantation of a single tissue engineered leaflet in the posterior position of the pulmonary valve in a lamb model. The major problems with this leaflet replacement were the scaffold's inherent stiffness, thickness, and nonpliability. We have now created a scaffold for a trileaflet heart valve using a thermoplastic polyester. In this experiment, we show the suitability of this material in the production of a biodegradable, biocompatible scaffold for tissue engineered heart valves. A heart valve scaffold was constructed from a thermoplastic elastomer. The elastomer belongs to a class of biodegradable, biocompatible polyesters known as polyhydroxyalkanoates (PHAs) and is produced by fermentation (Metabolix Inc., Cambridge, MA). It was modified by a salt leaching technique to create a porous, three-dimensional structure, suitable for tissue engineering. The trileaflet heart valve scaffold consisted of a cylindrical stent (1 mm X 15 mm X 20 mm I.D.) containing three valve leaflets. The leaflets were formed from a single piece of PHA (0.3 mm thick), and were attached to the outside of the stent by thermal processing techniques, which required no suturing. After fabrication, the heart valve construct was allowed to crystallize (4 degrees C for 24 h), and salt particles were leached into doubly distilled water over a period of 5 days to yield pore sizes ranging from 80 to 200 microns. Ten heart valve scaffolds were fabricated and seeded with vascular cells from an ovine carotid artery. After 4 days of incubation, the constructs were examined by scanning electron microscopy. The heart valve scaffold was tested in a pulsatile flow bioreactor and it was noted that the leaflets opened and closed. Cells attached to the polymer and formed a confluent layer after incubation. One advantage of this material is the ability to mold a complete trileaflet heart valve scaffold without the need for suturing leaflets to the conduit. Second advantage is the use of only one polymer material (PHA) as opposed to hybridized polymer scaffolds. Furthermore, the mechanical properties of PHA, such as elasticity and mechanical strength, exceed those of the previously utilized material. This experiment shows that PHAs can be used to fabricate a three-dimensional, biodegradable heart valve scaffold.     

Tissue-engineered heart valve leaflets: an effective method of obtaining acellularized valve xenografts

To determine the most effective method of producing the acellularized xenograft heart valve leaflets, we compared pathological findings of the xenograft heart valve leaflets produced by three methods; freeze-thawing, Triton and NaCl-SDS treatment and further analyzed the pattern of endothelial cells seeded onto them. Materials and methods: Two pigs were sacrificed and three pulmonary valve leaflets were harvested from each animal. They were immediately stored in a tissue preservation solution and assigned in one of the three preparation methods for acellularization. Endothelial cells from the jugular vein of a goat were isolated and seeded onto the acellularized xenograft heart valve leaflets. Light and Electron microscopic analyses were performed. Result and conclusion: H & E stain showed that cells were almost absent in the leaflet treated with NaCl-SDS, while cells were partly present in the leaflets treated, one with Triton and the other Freeze-thawing. Transmission microscopic analyses showed cell-free matrix with well preserved collagen architecture under the seeded endothelial cells in the leaflets treated with NaCl-SDS. In conclusion, the valve leaflets treated with NaCl-SDS among three representative methods of acellularization of tissues (freeze-thawing, Triton X-100, and NaCl-SDS) showed the better results than the others in terms of the efficacy of decellularization and response to endothelial cell seeding.