应用胶原支架构建组织工程心脏瓣膜的初步研究

目的 探讨应用胶原支架构建组织工程心脏瓣膜的可行性。方法 行兔皮下包埋实验。分别于4、6、8、12周观察材料的生物相容性和降解率。将犬主动脉壁间质细胞和主动脉内皮细胞种植于胶原膜上，进而将此瓣叶植入犬腹主动脉内3个月，观察材料吸收和瓣叶结构的变化。结果 胶原膜呈网孔状结构，孔径107μm。皮下包埋实验显示，材料生物相容性好，完全降解时间为12周。体内实验显示，材料于12周末被间质细胞合成的细胞外基质所取代，瓣叶表面有内皮细胞覆盖。结论 以胶原膜为支架构建组织工程心脏瓣膜是可行的，但材料在强度和组织相容性方面尚需改进。     

应用猪主动脉去细胞瓣膜支架体外构建组织工程心脏瓣膜

目的　探讨应用猪去细胞瓣膜支架体外构建组织工程心脏瓣膜的可行性。　方法　采用去垢剂、渗透压改变和核酸酶消化的方法制备猪主动脉瓣去细胞瓣膜支架 (实验组 ) ,用去内皮细胞主动脉瓣作对照 (对照组 ) ,并对两组含水量、可溶性蛋白含量、热皱缩温度、力学性能和组织相容性进行测定。培养犬主动脉壁间质细胞和内皮细胞 ,将其种植于实验组去细胞支架上 ,观察细胞生长情况 ,并测定内皮细胞合成前列环素的功能。　结果　实验组瓣膜细胞成分完全从瓣膜中去除 ,与对照组新鲜瓣膜相比 ,含水量增高 (P<0 .0 5 ) ,可溶性蛋白含量减少 (P<0 .0 5 ) ,热皱缩温度和抗张强度无明显变化。实验组瓣膜组织相容性试验显示 ,材料组织相容性好 ,体内降解时间为 10周 ;犬主动脉壁间质细胞和内皮细胞在瓣膜表面生长良好 ,内皮细胞具有合成分泌前列环素的功能。　结论　采用去垢剂、渗透压改变和核酸酶消化的方法制备猪主动脉瓣去细胞瓣膜支架 ,在去除细胞和可溶性蛋白质的同时保持了瓣叶的基本结构和力学性能 ;以其为支架体外构建组织工程心脏瓣膜的细胞不仅能在材料表面生长 ,还能合成、分泌血管活性物质 ,是具有生理功能的组织工程心脏瓣膜。     

去细胞和戊二醛处理对猪主动脉瓣内源性逆转录病毒影响的比较

我们应用聚合酶链反应(PCR)及逆转录．聚合酶链反应(RT-PCR)方法对去细胞猪瓣、猪外周血、犬腹主动脉内移植去细胞猪瓣1个月后外周血，并同时对经戊二醛处理猪主动脉瓣加以对照研究．探讨这两种方法对猪内源性逆转录病毒(PERV)的影响。     

血流力学对组织工程心脏瓣膜种子细胞形态及功能的影响

目的观察血流力学对组织工程心脏瓣膜种子细胞形态及功能的影响。方法从犬骨髓中分离得到骨髓间充质细胞（MSCs），经DiI标记后接种于去细胞猪主动脉瓣膜支架，培养7d后将所得瓣叶种植于犬腹主动脉内，术后4、8、12周取材，进行HE染色、天狼猩红染色、免疫组织化学染色及超微电镜检查等，观察细胞生长、形态及功能变化。设体外培养组为对照组。结果接种骨髓间充质细胞的去细胞猪主动脉瓣膜支架，移植于犬腹主动脉内后，仍可检测到所种植细胞，细胞生长良好。与对照组比较，细胞形态有所伸长，整体上沿流体方向改变形态，同时，瓣叶组织中Ⅰ、Ⅲ型胶原含量明显增加，并充满中性和酸性黏多糖。结论构建组织工程心脏瓣膜时，血流力学对种子细胞维持形态、保持功能起着重要作用。     

两种去细胞人心脏瓣膜的免疫原性分析

目的应用组织工程学方法去除人同种心脏瓣膜(HV)的内皮细胞成分或全部细胞成分,比较两种去细胞HV的免疫原性变化。方法采用低渗液-去污剂(1%Triton)-核酸酶[1μg/ml核糖核酸酶(RNase)和10μg/ml去氧核糖核酸酶(DNase)]去细胞法去除HV表面的内皮细胞成分,保留间质细胞及细胞外基质结构的完整性;采用低渗液-去污剂(1%去氧胆酸)-核酸酶[20μg/ml RNase和200μg/ml DNase]去细胞法去除HV组织中所有细胞成分,保留完整的细胞外基质。免疫组织化学方法测定HLA-DR抗原在HV组织中的表达;行大鼠皮下移植试验,组织学评价及定性、定量分析组织的钙化程度。结果免疫组织化学结果证实HV去内皮细胞和去全部细胞后组织中HLA-DR抗原表达均下降,但去全部细胞HV的HLA-DR抗原表达下降更为显著。大鼠皮下移植实验结果表明深低温液氮保存HV和去内皮细胞HV组织中有大量炎性细胞浸润,以淋巴细胞为著,管壁组织更为显著;去全部细胞HV炎性反应较轻,仅组织边缘有少量炎性细胞浸润。钙盐染色深低温液氮保存HV和去内皮细胞HV组织中可见钙盐沉积,呈现大量黑色颗粒,管壁组织更为显著;而去全部细胞HV组织中钙盐沉积极少。原子吸收光谱法定量分析结果表明去全部细胞HV组织中钙离子含量明显低于去内皮细胞HV和深低温液氮保存HV(P0.05),后两者差异无统计学意义(P0.05)。结论去全部细胞HV组织免疫原性显著下降,移植后炎性反应和组织钙化程度显著减轻。去内皮细胞HV组织免疫原性及移植后炎性反应有所下降,但移植后组织钙化程度仍显著增高,且管壁组织钙盐含量增高较瓣叶组织更加显著,提示组织中大量的间质细胞可能是参与HV移植后免疫反应、导致HV移植后钙化毁损的主要组织成份。     

人心脏瓣膜间质细胞体外培养的生物学特性

近年来 ,对心脏瓣膜间质细胞的形态学和生长率的研究结果报道不一 ,而且所采用的细胞体外培养系统仍多利用猪心脏瓣膜间质细胞作为细胞模型[1] ,所得结果如推广于人类 ,无疑存在着种属差异。因此 ,我们对人主动脉瓣间质细胞进行体外培养研究 ,观察其形态和生长动力学特征。一、材料和方法1.组织来源 :人主动脉瓣组织取自脑死亡、无心血管病变及结缔组织疾病的健康成年男性患者。将主动脉瓣沿瓣叶交界切开 ,瓣叶游离部位心室面和主动脉面用刀片轻轻刮除 ,以消除瓣叶内皮细胞。所切除瓣叶用不含血清的ＤＭＥＭ (Ｇｉｂｃｏ公司 )培养液洗涤后 …     

人骨髓基质干细胞构建组织工程心脏瓣膜的研究

目的探讨人骨髓基质干细胞种植在去细胞猪主动脉瓣叶上体外构建组织工程心脏瓣膜的可行性。方法经1%TritonX100、0.01%胰酶0.02%EDTA、DNaseI及RNaseI处理制备去细胞猪主动脉瓣叶支架,测定瓣叶去细胞前、后的生物力学特性;人骨髓基质干细胞体外分离、培养、扩增后种植在去细胞瓣叶表面,观察细胞生长情况。结果猪主动脉瓣叶去细胞后获得完整无细胞的纤维网状支架,瓣叶去细胞前、后的断裂强度和断裂伸长率差异无统计学意义(P>0.05);体外培养的人骨髓基质干细胞(MSCs)在去细胞瓣叶表面形成一层基本连续的细胞层。结论去除细胞成分的猪主动脉瓣叶组织是一种良好的纤维支架,可以用于构建组织工程心脏瓣膜;人骨髓基质干细胞种植在去细胞猪主动脉瓣叶上构建组织工程心脏瓣膜是可行的。     

去细胞猪主动脉瓣叶的获取和内皮细胞的种植

目的　探讨猪主动脉瓣叶去细胞后作为组织工程心脏瓣膜支架的可行性。　方法　经胰酶 - EDTA、表面活性剂和核酸酶处理 ,去除猪主动脉瓣叶的细胞成分 ,测定瓣叶去细胞前、后的生物力学特性 ,并在其表面种植新生牛主动脉内皮细胞 (BAECs) ;分别行大鼠皮下包埋实验。　结果　猪主动脉瓣叶中的细胞成分能完全去除 ,获得完整无细胞的纤维网状支架 ,断裂强度和断裂伸长率无明显变化 ;种植的 BAECs在去细胞瓣叶表面可形成一层连续的细胞层 ,其分泌前列环素 (PGI2 )的能力同直接种植在 2 4孔板中的比较 ,差异无统计学意义 (P>0 .0 5 )。　结论　猪主动脉瓣去细胞后获得的纤维支架可以用来构建组织工程瓣膜 ,适宜于血管内皮细胞的生长。     

基于内皮祖细胞构建的组织工程静脉体内初步评价

目的探讨基于犬骨髓源内皮祖细胞和猪脱细胞动脉基质构建的组织工程静脉植入体内的可行性。方法实验犬（n=8）骨髓体外扩增获取内皮祖细胞,荧光标记后将其种植于猪脱细胞动脉基质,体外构建组织工程静脉。以未种植细胞的脱细胞基质为对照（n=4）,将其置换自体犬下腔静脉,术后10d、4周、12周造影后取材检测。结果实验（对照）组在第10天、4周、12周的通畅率分别为7／7（2／4）、6／6（2／2）和4／4（1／2）。相关检测提示实验组移植血管腔面覆盖汇合的内皮细胞,部分为种植的细胞,部分为新形成的内皮细胞,中层有成纤维细胞和α-actin阳性细胞出现。通畅的对照组腔面由假内膜覆盖。结论基于自体内皮祖细胞和脱细胞动脉基质构建组织工程静脉是可行的,但需要进一步改进和观察。     

去细胞组织工程同种心脏瓣膜的免疫学特征

目的构建去细胞的组织工程同种心脏瓣膜,探讨其免疫学特性变化。方法取液氮保存的人同种主动脉带瓣管道,采用低渗液-去污剂(1％去氧胆酸,1％DOA)-核酸酶[20mg／L核糖核酸酶(RNase)和200 mg／L去氧核糖核酸酶(DNase)]去细胞法去除同种心脏瓣膜、管壁组织及肌肉中所有的细胞成分,保留完整的细胞外基质,构建去细胞的组织工程同种心脏瓣膜;采用免疫组织化学方法测定HLA-DR抗原在同种心脏瓣膜组织中的表达;行大鼠皮下移植试验,评价组织学变化及Van Kosaa银染色法定性分析、原子吸收光度计法定量分析组织的钙化程度。结果去细胞同种心脏瓣膜的白细胞抗原-DR(HLA-DR)表达较深低温液氮保存同种心脏瓣膜(HVA)显著下降;大鼠皮下移植8周后,去细胞同种心脏瓣膜组织中的炎性细胞浸润显著减少,定性分析表明去细胞组瓣叶和管壁组织中呈黑色颗粒的钙盐沉积较深低温液氮组显著下降,尤管壁组织更为显著;定量分析亦表明去细胞瓣叶和管壁组织的钙化程度显著下降(瓣叶:去细胞组0．83±0．17 mg／ g,深低温液氮组[(1．39±0．26)mg／g,P<0．05];管壁:去细胞组(2．35±2．58)mg／g,深低温液氮组[(42．66±7．46)mg／g,P<0．05)]。结论去细胞同种心脏瓣膜的免疫原性显著下降,有望减轻移植后免疫反应,延长同种心脏瓣膜的使用寿命。     

两种细胞洗涤剂制备脱细胞同种生物带瓣管道支架的研究

目的比较去氧胆酸钠(deoxycholic acid, DOA)和十二烷基硫酸钠(sodium dodecylsulphate, SDS)两种细胞洗涤剂制备脱细胞的同种生物带瓣管道(homograft bioprosthetic tube valved, HBTV)支架的效果,为体外构建组织工程瓣(tissue-engineering heart valve, TEHV)提供同种生物瓣支架材料. 方法对同种带瓣主动脉管道和带瓣肺动脉管道,分别用含0.5% DOA或0.03% SDS的Tris低渗缓冲液共同孵育48 h,脱去经液氮保存、具有活性的HBTV表面的内皮细胞,固定剂固定后分别进行HE、胶原纤维和弹力纤维染色的光镜观察,以及扫描电镜观察,摄片. 结果两种洗涤剂均完全地脱去了HBTV表面的内皮细胞,中心部位的成纤维细胞有部分存留;细胞外基质,如胶原纤维和弹力纤维等均较完整地保留下来,其形态结构与脱细胞前无明显改变. 结论 0.03%～0.1% SDS或0.5% DOA的低渗缓冲液对制备HBTV脱内皮细胞支架效果均较佳,有利于HBTV再内皮化时种植细胞的黏附和扩增,可进一步应用于体外构建TEHV的研究.对于脱主动脉壁的细胞,SDS浓度应增至0.1%为佳.     

Decellularization of rat aortic valve allografts reduces leaflet destruction and extracellular matrix remodeling

OBJECTIVES: Decellularization of aortic valve allografts in advance of transplantation is a promising approach to overcome immune-induced early graft failure. In this study the effects of in vitro cell extraction on extracellular matrix molecules and in vivo remodeling of decellularized aortic valves were investigated in a heterotopic aortic valve rat implantation model. METHODS: Rat aortic valve conduits were decellularized by a 2-step detergent-enzymatic extraction method involving sodium dodecyl sulfate in combination with RNase and DNase. Cellular and acellular allogeneic (2x, n = 4) and syngeneic valve grafts (2x, n = 3) were grafted infrarenally into the descending aorta for 21 days. Immunohistochemical techniques were used to study extracellular matrix constitution (elastin, collagen, fibronectin, and chondroitin sulfate) and cellular infiltration. RESULTS: The decellularization procedure resulted in a complete loss of all cellular structures from the entire valve conduit with minimal damage to the extracellular matrix. All transplanted cellular allografts became deformed, swollen, and acellular with major changes in extracellular matrix structure. The transplanted decellularized allografts, however, retained normal preserved valve leaflets comparable to transplanted cellular and acellular syngeneic grafts. With the exception of cellular syngeneic grafts, all other grafts showed retrovalvular thrombi. CONCLUSIONS: Damage to the valves caused by decellularization technique is much less than the damage caused by the recipient's immune response. In vitro removal of viable cells in (cryopreserved) homografts may decrease graft failure. Seeding with autologous or major histocompatibility complex-matched donor endothelial cells will be necessary to diminish damage induced by an absent blood-tissue barrier.     

Tissue engineered heart valves: autologous cell seeding on biodegradable polymer scaffold

We previously reported on the successful creation of tissue-engineered valve leaflets and the implantation of these autologous tissue leaflets in the pulmonary valve position. Mixed cell populations of endothelial cells and fibroblasts were isolated from explanted ovine arteries. Endothelial cells were selectively labeled with an acetylated low-density lipoprotein marker and separated from fibroblasts using a fluorescent activated cell sorter. A synthetic biodegradable scaffold consisting of polyglycolic acid fibers was seeded first with fibroblasts then subsequently coated with endothelial cells. Using these methods, autologous cell/polymer constructs were implanted in 6 animals. In 2 additional control animals, a leaflet of polymer was implanted without prior cell seeding. In each animal, using cardiopulmonary bypass, the right-posterior leaflet of the pulmonary valve was resected completely and replaced with an engineered valve leaflet with (n = 6) or without (n = 2) prior cultured cell seeding. After 6 h and 1, 6, 7, 9, and 11 weeks, the animals were sacrificed and the implanted valve leaflets were examined histologically, biochemically, and biomechanically. Animals receiving leaflets made from polymer without cell seeding were sacrificed and examined in a similar fashion after 8 weeks. In the control animals, the acellular polymer leaflets were degraded completely leaving no residual leaflet tissue at 8 weeks. The tissue-engineered valve leaflet persisted in each animal in the experimental group; 4-hydroxyproline analysis of the constructs showed a progressive increase in collagen content. Immunohistochemical staining demonstrated elastin fibers in the matrix and factor VIII on the surface of the leaflet. The cell labeling experiments demonstrated that the cells on the leaflets had persisted from the in vitro seeding of the leaflets. In the tissue-engineered heart valve leaflet, transplanted autologous cells generated proper matrix on the polymer scaffold in a physiologic environment at a period of 8 weeks after implantation.     

改性聚乙二醇水凝胶在组织工程心脏瓣膜中的应用研究

目的 探索改性聚乙二醇(PEG)水凝胶在改善种子细胞和去细胞生物材料支架的复合中的效果.方法 猪主动脉瓣进行去细胞处理后分两组(n=8),A组:山羊自体骨髓间充质干细胞(BMSCs)作为种子细胞包裹于改性PEG水凝胶中贴附于去细胞猪主动脉瓣;B组:单纯种植BMSCs于去细胞猪主动脉瓣;并随机取两组中的8只山羊自身主动脉瓣为对照组(C组).A、B组静态培养7 d后,植入细胞供体羊的腹主动脉内;16周后取材进行形态学、组织学、B超、扫描和透射电镜观察以及生物力学检测.结果 在张力强度[(12.9±1.3)MPa对(8.8±0.4)MPa]、内皮细胞覆盖率(84.6%对14.8%)、附壁血栓形成率(0/8对8/8)等方面A组明显优于B组(P<0.05).生物力学强度A组和C组差异无统计学意义.BMSCs于体内微环境下向内皮细胞和肌成纤维细胞分化.结论 利用改性PEG水凝胶复合去细胞生物支架材料以及自体间充质干细胞构建组织工程瓣膜具有可行性.它可进一步改善种子细胞和支架材料之间的复合关系,并保护种子细胞在动脉流环境下的生长和分化.     

Aortic valve graft implantation in rats: a new functional model

BACKGROUND: Allograft heart valves used in cardiac surgery often fail at an unacceptable rate. Immune mechanisms contribute to this failure, but adequate and functional small-animal valve models to characterize this phenomenon are lacking. The objective of this study was to create native aortic valve insufficiency in recipient rats to provide for a functional abdominal aortic valve graft implant. METHODS: Lewis recipient rats underwent single-leaflet injury of their native aortic valve through a right carotid catheter injury. Animals were allowed to recover for 28 days, at which time a Lewis aortic valve graft was implanted infrarenally. Echocardiography with color flow Doppler scanning was performed before aortic injury, 1 week after aortic injury, and after abdominal implantation of a valve graft in animals with native aortic insufficiency. RESULTS: After aortic valve injury, all animals had moderate-to-severe aortic insufficiency with a significant increase in diastolic and systolic left ventricular dimensions. Color flow Doppler scanning revealed diastolic aortic flow reversal from the aortic valve extending to the infrarenal abdominal aorta. Aortic valve grafts were then implanted infrarenally in animals with created aortic valve insufficiency and resulted in 100% patency and preservation of leaflets at 4 weeks after implantation. Leaflet motion of the abdominal graft was visualized by means of M-mode echocardiography. CONCLUSION: Compensated native aortic insufficiency results in aortic diastolic flow reversal distal to the infrarenal aorta, thus allowing normal motion of the infrarenal allograft leaflets. This functional model will provide an opportunity to investigate the role of immunologic valve injury in the failure of valve allografts.     

Cell characterization of porcine aortic valve and decellularized leaflets repopulated with aortic valve interstitial cells: the VESALIO Project (Vitalitate Exornatum Succedaneum Aorticum Labore Ingenioso Obtenibitur)

BACKGROUND: Heart valve bioprostheses for cardiac valve replacement are fabricated by xeno- or allograft tissues. Decellularization techniques and tissue engineering technologies applied to these tissues might contribute to the reduction in risk of calcification and immune response. Surprisingly, there are few data on the cell phenotypes obtained after cellularizing these naturally-derived biomaterials in comparison to those expressed in the intact valve. METHODS: Aortic valve interstitial cells (VIC) were used to repopulate the corresponding valve leaflets after a novel decellularization procedure based on the use of ionic and nonionic detergents. VIC from leaflet microexplants at the third passage were utilized to repopulate the decellularized leaflets. Intact, decellularized and repopulated valve leaflets and cultured VIC were examined by immunocytochemical procedures with a panel of antibodies to smooth muscle and nonmuscle differentiation antigens. Intact and cellularized leaflets were also investigated with Western blotting and transmission electron microscopy, respectively. RESULTS: Myofibroblasts and smooth muscle cells (SMC) were mostly localized to the ventricularis of the leaflet whereas fibroblasts were dispersed unevenly. Cultured VIC were comprised of myofibroblasts and fibroblasts with no evidence of endothelial cells and SMC. Two weeks after VIC seeding into decellularized leaflets, grafted cells were found penetrating the bioscaffold. The immunophenotypic and ultrastructural properties of the grafted cells indicated that a VIC heterogeneous mesenchymal cell population was present: fibroblasts, myofibroblasts, SMC, and endothelial cells. CONCLUSIONS: VIC seeding on detergent-treated valve bioscaffolds has the cellular potential to reconstruct a viable aortic valve.     

In vivo repopulation of xenogeneic and allogeneic acellular valve matrix conduits in the pulmonary circulation

BACKGROUND: Approaches to in vivo repopulation of acellularized valve matrix constructs have been described recently. However, early calcification of acellularized matrices repopulated in vivo remains a major obstacle. We hypothesised that the matrix composition has a significant influence on the onset of early calcification. Therefore, we evaluated the calcification of acellularized allogenic ovine (AVMC) and xenogenic porcine (XVMC) valve matrix conduits in the pulmonary circulation in a sheep model. METHODS: Porcine (n = 3) and sheep (n = 3) pulmonary valve conduits were acellularized by trypsin/EDTA digestion and then implanted into healthy sheep in pulmonary valve position using extracorporeal bypass support. Transthoracic echocardiography (TTE) was performed at 12 and 24 weeks after the implantation. The animals were sacrificed at week 24 or earlier when severe calcification of the valve conduit became evident by TTE. The valves were examined histologically and biochemically. RESULTS: All AVMC revealed severe calcification after 12 weeks with focal endothelial cell clustering and no interstitial valve tissue reconstitution. In contrast, after 24 weeks XVMC indicated mild calcification on histologic examination (von Kossa staining) with histologic reconstitution of valve tissue and confluent endothelial surface coverage. Furthermore, immunohistologic analysis revealed reconstitution of surface endothelial cell monolayer (von Willebrand factor), and interstitial myofibroblasts (Vimentin/Desmin). CONCLUSIONS: Porcine acellularized XVMC are resistant to early calcification during in vivo reseeding. Furthermore, XVMC are repopulated in vivo with valve-specific cell types within 24 weeks resembling native valve tissue.     

Experimental in vitro endothelialization of cardiac valve leaflets.

This study reports our results with vitro endothelialization of fresh nonpreserved homograft valve leaflets compared with mild alternatively preserved valves and valves treated by preservation procedures commonly used for commercially available tissue valves. In vitro lining of biological heart valves with cultured autologous endothelial cells might help prevent the detrimental effects of degeneration on valve durability. To investigate the growth characteristics of endothelial cells on valve bioprostheses, three different methods of storage and preservation were compared. After precoating with fibronectin and seeding of 4.4 x 10(4) endothelial cells/cm2 onto the different leaflet surfaces, primary adherence, growth kinetics, morphology, and maintenance of monolayer integrity were studied over a period of 10 days. On valve leaflet surfaces of group 1 (fresh nonpreserved homograft valve leaflets) and group 2 (mild alternatively preserved valves), endothelial cells grew to persistent monolayers between days 6 and 10. In contrast, endothelial cell proliferation with monolayer growth could not be achieved on the group 3 leaflets (preserved like commercially available biological valve prostheses). In that group, no viable endothelial cells could be found on the valve surfaces 2 days after seeding. These results demonstrate the theoretical feasibility of endothelializing biological heart valve leaflets in vitro if they are not preserved and stored according to commonly used procedures. Provided such an endothelium can withstand the mechanical forces after implantation in vivo, in vitro endothelialization might contribute either to the development of new biological heart valves for modern cardiac surgery or to the improvement of clinical results with homograft valve transplants.     

Computed tomography detects tissue formation in a stented engineered heart valve

Tissue-engineered heart valves (TEHV) are being explored as an alternative to conventional heart valve prostheses. Using the classic tissue engineering paradigm, a stented tri-leaflet valve is fabricated. Subsequently, the construct is implanted into the pulmonary position in a sheep. Follow-up by means of computed tomography, magnetic resonance imaging, and echocardiography was used to assess tissue formation. After 4 weeks, the scaffold of the TEHV has degraded and new tissue is formed. However, small areas without tissue formation were present at macroscopic inspection. This phenomenon was only visible on computed tomographic images. Therefore, computed tomography appears a promising technique for in vivo follow-up of tissue formation in tissue-engineered heart valves.