新型人工机械心脏瓣膜疲劳磨损实验研究

为检验新型瓣膜的疲劳磨损特性,采用TH-2200型人工心瓣疲劳寿命测试仪对聚甲醛瓣叶的双叶心脏瓣膜进行加速疲劳实验,并对疲劳后的瓣膜进行扫描电镜检测,发现该瓣膜经4×108次疲劳测试后,瓣环无明显磨损,瓣叶转动灵活,心瓣正常工作,但在瓣环枢轴坑的部分位置发现少量粘附的聚甲醛颗粒,尺寸约0.1~1μm,瓣叶总磨损率为0.681%。虽然新型瓣膜疲劳实验证明了瓣膜结构设计合理,能够满足国家标准要求的疲劳寿命,但是仍需要对瓣叶材料表面进行处理,进一步提高瓣叶的耐磨性。     

人工生物心脏瓣膜

市场背景人体心脏有4枚瓣膜,它们与心脏舒缩同步开关,达到控制血液流向的目的。由于各种不同的原因,诸如风心病(慢性风湿性心内膜炎)、老年性瓣膜损坏或瓣膜先天性缺陷等均可能导致瓣膜功能的异常。一旦心瓣膜受损,尤其是瓣膜病变严重的患者,人工瓣膜的替换将成为惟一有效的治疗,其成功率可达98.5%以上。心脏瓣膜病是最常见的心脏病,其发病占整个心脏病的一半。据2003年的统计资料,全世界每年接受换瓣手术的病人已从10年前的10万增加到30万。2003年全世界人工心脏瓣膜产业总额由2002年的8亿美元增加到9.1亿美元,增长了12%(2002年以前每年平…     

人工心脏瓣膜的现状与发展

自1960年Harken和Starr第一次成功将人工瓣膜植入人体心脏以来，人工瓣膜在几十年内经历了几代的发展，出现了多种材料与实施方法，为人造瓣膜治疗瓣膜性心脏病提供了越来越有效、安全以及方便的器械及技术支持。     

机械三叶心瓣模型的定常流实验研究

对机械人工三叶心脏瓣膜的模型进行定常流测试,并与QT型双叶瓣膜进行比较。通过使用Soildworks2005中的插件COSMOSFloWorks2005作为定常流测试的模拟软件,分别在定常流5L/min、10L/min、15L/min不同流量,不同开启角度79°、83°、87°下,测试出三叶瓣膜的跨瓣压差。测试实验结果表明三叶瓣膜跨瓣压差的确远小于双叶瓣膜,而且血流动力表现优于双叶瓣,符合瓣膜的设计要求。     

国产人工心脏瓣膜综述

人工心脏瓣膜是指可植入心脏内代替心脏瓣膜,具有天然心脏瓣膜功能的人工器官。当心脏瓣膜病变严重而不能采用瓣膜分离手术或修补手术来恢复或改善瓣膜功能时,则须采用人工心脏瓣膜置换术。     

新型人工曲面机械双叶瓣体外脉动流实验

自体心脏瓣膜为无神经元控制,在多物理场因素引导下,血液流动场、瓣膜和腱索之间相互作用运动,保持血流单向流动。经临床研究表明,患者植入瓣膜后的瓣膜并发症及患者生存率,与瓣膜结构、血流流场密切相关,对此评价瓣膜的血流动力学性能对改进瓣膜结构具有重要作用。自制新型曲面双叶型机械瓣膜,通过理论解析和瞬态流固耦合模拟分析讨论瓣膜最大开启时瓣膜的血流动力学性能;并在体外动态仿真环境下,对曲面型双叶瓣膜进行血流动力学测试,采用Vivitest脉动流实验平台测量,通过测试瓣膜压力、开口面积、返流量等物理量来衡量瓣膜在主动脉位置的使用性能。最后研究同St.Jude双叶瓣和国内GK瓣等同类机械瓣的动力学性能作对照,根据评价结果前瞻性地研究双叶曲面机械瓣结构性能。结果表明,研制的新型曲面瓣膜具有优良的血流动力学特性。     

经食管三维超声心动图应用于风湿性二尖瓣成形术中的效果评估

目地:评价经食管三维超声心动图应用于风湿性心脏瓣膜病二尖瓣成形术中的效果。方法:回顾性分析2012年1月-2015年4月在我院心外科被诊断为风湿性二尖瓣关闭不全并行二尖瓣成形术的35例患者的临床资料,采用经食管三维超声心动图观察瓣膜形态、瓣下腱索及瓣环情况,同时用软件计算二尖瓣三维结构参数,评估手术成功率。结果:瓣环面积、瓣环周长、瓣叶面积、前叶面积、后叶面积、脱垂高度、脱垂容积和瓣叶非平面夹角均较术前明显缩小(P0.05),而前叶角度和后叶角度较术前明显增大(P0.05)。经食管三维超声心动图监测二尖瓣成形术,本组35例一次性成功33例,成功率为94.3%,2例术中发现3级反流后改行二尖瓣人工置换术。结论 :经食管三维超声心动图是风湿性二尖瓣成形术成功的关键,具有极高的应用价值。     

人工生物瓣膜血流动力学行为的有限元分析

使用脉动工作站检测生物瓣膜在近似生理条件下的血流动力学特性,结合有限元分析研究了生物瓣膜在心动周期过程中的微观应力和应变情况,寻求一种快速评价人工心脏瓣膜结构—力学性能间关系的方法。结果表明,生物瓣膜(Edwards #2625)在体外脉动流检测条件下的平均跨瓣压差为10.8 mmHg、有效开口面积为2.0 cm~2、返流百分比为8.4%,均符合ISO-5840国际检测标准。生物瓣膜有限元模拟结果揭示其在收缩期最大主应力达到425 kPa,应力集中在弯曲变形严重的腹部以及瓣叶缝合边;舒张期最大主应力为1.46 MPa,应力集中在瓣叶缝合边的两侧。在脉动检测的不同时间点,瓣膜有限元模型开口面积均与实验条件下样品的开口面积近似,证明了有限元模拟结果的可靠性。本文提出的体外脉动流检测实验与有限元仿真计算相结合的方法,为评价人工心脏瓣膜的结构—力学性能间关系提供一种高效可靠的途径。     

先天性二尖瓣狭窄(瓣膜型)超声心动图

本文报告先天性二尖瓣狭窄(5例)超声心动图特征。胸骨旁长轴切面:(1)二尖瓣轻度增厚,瓣叶冗长,瓣缘卷曲(2)舒张期瓣尖开放呈圆拱顶状,且位置较低,接近乳头肌(3)腱索显著缩短(4)左室腔内肌性或纤维性条束错综交织,甚可影响二尖瓣的开放。二尖瓣短轴切面:(1)能探测到瓣叶的切面数增多(2)二尖瓣口与乳头肌见于同一切面(3)二尖瓣口面积缩小、偏心,偏向左室后壁(4)二乳头肌发育不良,乳头肌间距离缩小。超声的心动图可对先天性与风湿性二尖瓣狭窄作出鉴别。先天性二尖瓣狭窄(瓣膜型)超声心动图@易维佳$上海市胸科医院 @谢松伟$上海市胸科医院…     

食品包装材料生态化发展下的非石油基降解塑料

目前常用的非石油基降解塑料可分为全淀粉型、化学(人工)合成型和天然高分子(以淀粉为主)与合成高分子共混型3种类型。淀粉基生物降解塑料能完全生物降解,制成的薄膜具有良好的透明度、柔韧性、抗张强度,不溶于水,无毒,故市场占有率高,被广泛应用于食品包装、食品容器和一次性餐饮具等;聚乳酸生物降解塑料力学性能与聚丙烯相似,并具有与聚苯乙烯相似的光泽度、清晰度和加工性,同时具有无毒、无刺激性、强度高、易加工成型和优良的生物相容性等特点,是一种能够真正实现生态和经济双重效益的、发展速度最快的生物降解塑料;聚丁二酸丁二醇酯生物降解塑料综合性能优良,性价比合理,故在食品包装、一次性餐具、药品包装瓶、生物医用高分子材料以及汽车零部件等领域均具有良好的应用前景。非石油基降解塑料作为包装材料是必然趋势,其得到广泛应用的关键在于提高材料的改性技术与控制成本,同时须保证其对人体无毒无害,强调个性化,并注重提高市场接受度。     

Novel transcatheter aortic heart valves exhibiting excellent hemodynamic performance and low-fouling property

Transcatheter aortic heart valves (TAHVs) have been widely used for aortic valve replacements, with less trauma and lower clinical risk compared with traditional surgical heart valve replacements. In the present study, composites of poly(ethylene glycol) diacrylate (PEGDA) hydrogels and anisotropic high-shrinkage polyethylene terephthalate/polyamide6 (PET-PA6) fabric (PEGDA/PET-PA6) were fabricated as artificial heart valve leaflets. Dynamic mechanical analyses (DMA) indicated that PEGDA/PET-PA6 composites possessed anisotropic mechanical properties (i.e., storage moduli ～23.30 ± 1.36 MPa parallel to the aligned fabric fibers and ～9.68 ± 0.90 MPa perpendicular to the aligned fibers at 1 Hz) that were comparable to aortic valve leaflets. The PEGDA/PET-PA6 composites with smooth surfaces were highly hydrophilic (contact angle ～41.6° ± 3.8°) and had low-fouling properties without platelet adhesion, suggesting a low risk of thrombogenicity when they interacted with blood. Furthermore, transcatheter aortic heart valves were fabricated using nitinol self-expanding frames and PEGDA/PET-PA6 composites as artificial leaflets, which presented excellent hemodynamic performance with a large orifice area (1.75 cm²) and low regurgitation (3.41%), thus meeting the requirements of ISO 5840-3 standard. Therefore, PEGDA/PET-PA6 composites had suitable mechanical properties, good biocompatibility, and low-fouling properties, indicating that they might be used for TAHVs in the future.     

Biologically Inspired Scaffolds for Heart Valve Tissue Engineering via Melt Electrowriting

Heart valves are characterized to be highly flexible yet tough, and exhibit complex deformation characteristics such as nonlinearity, anisotropy, and viscoelasticity, which are, at best, only partially recapitulated in scaffolds for heart valve tissue engineering (HVTE). These biomechanical features are dictated by the structural properties and microarchitecture of the major tissue constituents, in particular collagen fibers. In this study, the unique capabilities of melt electrowriting (MEW) are exploited to create functional scaffolds with highly controlled fibrous microarchitectures mimicking the wavy nature of the collagen fibers and their load‐dependent recruitment. Scaffolds with precisely‐defined serpentine architectures reproduce the J‐shaped strain stiffening, anisotropic and viscoelastic behavior of native heart valve leaflets, as demonstrated by quasistatic and dynamic mechanical characterization. They also support the growth of human vascular smooth muscle cells seeded both directly or encapsulated in fibrin, and promote the deposition of valvular extracellular matrix components. Finally, proof‐of‐principle MEW trileaflet valves display excellent acute hydrodynamic performance under aortic physiological conditions in a custom‐made flow loop. The convergence of MEW and a biomimetic design approach enables a new paradigm for the manufacturing of scaffolds with highly controlled microarchitectures, biocompatibility, and stringent nonlinear and anisotropic mechanical properties required for HVTE.     

Cylindrical Bending and Vibration of Polar Material Laminates

This article considers a plane strain problem, which is known in conventional linear elasticity as cylindrical bending of simply supported plates and cross-ply laminates. By considering fibrous composites containing fibers resistant to bending, it formulates and solves corresponding polar elasticity equations governing the static and dynamic behavior of beam-like components made of a homogeneous or layered transversely isotropic material; each layer has embedded a single family of fibers. Fiber bending stiffness is accounted for through involvement of an extra elastic modulus, which, unlike its conventional elasticity counterparts that have dimensions of stress, has dimensions of force. Its involvement in the analysis implies existence of some intrinsic material area or length parameter, which may be associated, for instance, with fiber thickness of fiber spacing. A considerable amount of relevant numerical results are presented for thick beam components made of either homogeneous or two-layered transversely isotropic material. For the static bending problem, these include a detailed presentation of through-thickness distributions of displacements, stresses, as well as couple-stress. For the dynamic problem, attention is focused on the influence that fiber bending stiffness exerts on fundamental frequency parameters.     

Characterization of the anisotropic materials capable of exhibiting an isotropic Young or shear or area modulus

By means of the decomposition of an anisotropic elastic tensor into symmetric traceless tensors, the general intrinsic expressions involving no redundant elastic coefficients are obtained for the orientation distribution functions of the Young, shear and area moduli of an anisotropic material. Necessary and sufficient conditions are established for each of these moduli to be isotropic. It is found that an anisotropic material exhibiting an isotropic Young or shear or area modulus can be only either transversely isotropic or orthotropic.     

Composite materials whose phases have partially equal elastic moduli

Hill [J. Mech. Phys. Solids 11 (1963) 357, 12 (1964) 199] discovered that, regardless of its microstructure, a linearly elastic composite of two isotropic phases with identical shear moduli is isotropic and has the effective shear modulus equal to the phase ones. The present work generalizes this result to anisotropic phase composites by showing and exploiting the fact that uniform strain and stress fields exist in every composite whose phases have certain common elastic moduli. Precisely, a coordinate-free condition is given to characterize this specific class of elastic composites; an efficient algebraic method is elaborated to find the uniform strain and stress fields of such a composite and to obtain the structure of the effective elastic moduli in terms of the phase ones; sufficient microstructure-independent conditions are deduced for the orthogonal group symmetry of the effective elastic moduli. These results are applied to elastic composites consisting of isotropic, transversely isotropic and orthotropic phases.     

Anisotropic effective moduli of microcracked materials under antiplane loading

This study focuses on the prediction of the anisotropic effective elastic moduli of a solid containing microcracks with an arbitrary degree of alignment by using the generalized self-consistent method (GSCM). The effective elastic moduli pertaining to anti-plane shear deformation are discussed in detail. The undamaged solid can be isotropic as well as anisotropic. When the undamaged solid is isotropic, the GSCM can be realized exactly. When the undamaged solid is anisotropic it is difficult to provide an analytical solution for the crack opening displacement to be used in the GSCM, thus an approximation of the GSCM is pursued in this case. The explicit expressions of coupled nonlinear equations for the unknown effective moduli are obtained. The coupled nonlinear equations are easily solved through iteration.     

A novel approach via combination of electrospinning and FDM for tri-leaflet heart valve scaffold fabrication

In this paper, a novel combination method of electrospinning and rapid prototyping (RP) fused deposition modeling (FDM) is proposed for the fabrication of a tissue engineering heart valve (TEHV) scaffold. The scaffold preparation consisted of two steps: tri-leaflet scaffold fabrication and heart valve ring fabrication. With the purpose of mimicking the anisotropic mechanical properties of the natural heart valve leaflet, electrospun thermoplastic polyurethane (ES-TPU) was introduced as the tri-leaflet scaffold material. ES-TPU scaffolds can be fabricated to have a well-aligned fiber network, which is important for applications involving mechanically anisotropic soft tissues. We developed ES-TPU scaffolds as heart valve leaflet materials under variable speed conditions and measured fiber alignment by fast Fourier transform (FFT). By using FFT to assign relative alignment values to an electrospun matrix, it is possible to systematically evaluate how different processing variables affect the structure and material properties of a scaffold. TPU was suspended at certain concentrations and electrospun from 1,1,1,3,3,3-hexafluoro-2-propanol onto rotating mandrels (200–3000 rpm). The scaffold morphological property and mechanical anisotropic property are discussed in the paper as a function of fiber diameter and mandrel RPM. The induction of varying degrees of anisotropy imparted distinctive material properties to the electrospun scaffolds. A dynamic optimum design of the heart valve ring graft was constructed by FDM. Fabrication of a 3D heart valve ring was constructed using pro-engineer based on optimum hemodynamic analysis and was converted to an STL file format. The model was then created from PCL which was sewed and glued with electrospun nanofibrous leaflets. This proposed method was proven as a promising fabrication process in fabricating a specially designed graft with the correct physical and mechanical properties.     

Micromechanical effective elastic moduli of continuous fiber-reinforced composites with near-field fiber interactions

A higher-order micromechanical framework is presented to predict the overall elastic deformation behavior of continuous fiber-reinforced composites with high-volume fractions and random-fiber distributions. By taking advantage of the probabilistic pair-wise near-field interaction solution, the interacting eigenstrain is analytically derived. Subsequently, by making use of the Eshelby equivalence principle, the perturbed strain within a continuous circular fiber is accounted for. Further, based on the general micromechanical field equations, effective elastic moduli of continuous fiber-reinforced composites are constructed. An advantage of the present framework is that the higher-order effective elastic moduli of composites can be analytically predicted with relative simplicity, requiring only material properties of the matrix and fibers, the fiber?Cvolume fraction and the microstructural parameter ??. Moreover, no Monte Carlo simulation is needed for the proposed methodology. A series of comparisons between the analytical predictions and the available experimental data for isotropic and anisotropic fiber reinforced composites illustrate the predictive capability of the proposed framework.     

Atomic force microscopy of electrospun organic-inorganic lipid nanofibers

An organic-inorganic hybridization strategy has been proposed to synthesize polymerizable lipid-based materials for the creation of highly stable lipid-mimetic nanostructures. We employ atomic force microscopy (AFM) to analyze the surface morphology and mechanical property of electrospun cholesteryl-succinyl silane (CSS) nanofibers. The AFM nanoindentation of the CSS nanofibers reveals elastic moduli of 55.3?±?27.6 to 70.8?±?35 MPa, which is significantly higher than the moduli of natural phospholipids and cholesterols. The study shows that organic-inorganic hybridization is useful in the design of highly stable lipid-based materials.