Mechanical property characterization of electrospun recombinant human tropoelastin for vascular graft biomaterials

The development of vascular grafts has focused on finding a biomaterial that is non-thrombogenic, minimizes intimal hyperplasia, matches the mechanical properties of native vessels and allows for regeneration of arterial tissue. In this study, the structural and mechanical properties and the vascular cell compatibility of electrospun recombinant human tropoelastin (rTE) were evaluated as a potential vascular graft support matrix. Disuccinimidyl suberate (DSS) was used to cross-link electrospun rTE fibers to produce a polymeric recombinant tropoelastin (prTE) matrix that is stable in aqueous environments. Tubular 1 cm diameter prTE samples were constructed for uniaxial tensile testing and 4 mm small-diameter prTE tubular scaffolds were produced for burst pressure and cell compatibility evaluations from 15 wt.% rTE solutions. Uniaxial tensile tests demonstrated an average ultimate tensile strength (UTS) of 0.36 ± 0.05 MPa and elastic moduli of 0.15 ± 0.04 and 0.91 ± 0.16 MPa, which were comparable to extracted native elastin. Burst pressures of 485 ± 25 mm Hg were obtained from 4 mm internal diameter scaffolds with 453 ± 74 μm average wall thickness. prTE supported endothelial cell growth with typical endothelial cell cobblestone morphology after 48 h in culture. Cross-linked electrospun rTE has promising properties for utilization as a vascular graft biomaterial with customizable dimensions, a compliant matrix and vascular cell compatibility.     

Engineered composite tissue as a bioartificial limb graft

The loss of an extremity is a disastrous injury with tremendous impact on a patient's life. Current mechanical prostheses are technically highly sophisticated, but only partially replace physiologic function and aesthetic appearance. As a biologic alternative, approximately 70 patients have undergone allogeneic hand transplantation to date worldwide. While outcomes are favorable, risks and side effects of transplantation and long-term immunosuppression pose a significant ethical dilemma. An autologous, bio-artificial graft based on native extracellular matrix and patient derived cells could be produced on demand and would not require immunosuppression after transplantation. To create such a graft, we decellularized rat and primate forearms by detergent perfusion and yielded acellular scaffolds with preserved composite architecture. We then repopulated muscle and vasculature with cells of appropriate phenotypes, and matured the composite tissue in a perfusion bioreactor under electrical stimulation in vitro. After confirmation of composite tissue formation, we transplanted the resulting bio-composite grafts to confirm perfusion in vivo.     

Application of a vascular graft material (Solcograft-P) in experimental surgery

The implantation and post-implantation behaviour of a Solcograft-P vascular prosthesis in the aortic, aorto-iliac, carotid and vena caval positions in dogs was studied up to 100 d post-surgery in order to assess the suitability of this vascular material for use in man. Solcograft-P is prepared from the carotid arteries of calves by crosslinking the collagen stroma using adipyl dichloride. During the postoperative follow-up period of 3 month, 100% of the aortal grafts, 80% of the aorto-iliac bypasses, 60% of the vena caval grafts and 35% of the carotid implants remained patent. The biochemical properties of the Solcograft-P are better than those of Solcograft, its predecessor. The intimal lining was consistently smooth and homogeneous in grafts of biological origin, and no aneurysm was observed. Infection and early thrombosis occured no more frequently than with other grafts. The new Solcograft-P, crosslinked via ester and amide groups, seems to represent a real improvement over Solcograft. Our results suggest that Solcograft-P should prove valuable in various cases of reconstructive vascular surgery of the lower limb, especially when the autologous vena saphena magna is not available, and its mechanical properties may well prove suitable for both arterial and venous replacement.     

Clinical results of the HDS vascular access graft for hemodialysis

A total of 104 HDS vascular access grafts were implanted in patients with end-stage renal failure. Fortyseven grafts were cannulated within 7 days after implantation (early cannulation), and 57 grafts were cannulated after postoperative day 7 (late cannulation). Comparison of primary and secondary patency rates showed no significant difference between the early and late cannulation groups. The results indicate that early cannulation of the HDS graft is safe and does not adversely affect patency.     

小口径微孔聚氨酯人造血管生物力学性能研究

目的分析小口径聚氨酯人造血管的微观形态,探讨聚氨酯人造血管管壁厚度对其渗透性能和拉伸强度的影响。方法通过在直径为4mm玻璃棒模具上复合均匀厚度的聚氨酯膜,并加入一定量的致孔剂,研制出具有微观多孔结构的小口径聚氨酯人造血管。采用扫描电镜表征其微观多孔结构,根据ISO7198国际标准设计了一套人造血管渗透性能的测试装置来测试其水渗透性能,并通过INSTRON万能强力仪(型号:5566)测试其拉伸强度。结果小口径的聚氨酯人造血管的内、外表面以及截面均呈微孔结构,微孔的大小在100μm以下,大小和分布比较均匀,并且随着人造血管壁厚度的增加,其渗透性能逐渐减小,拉伸强度先增大后减小,实验测试结果均与国外研究在同一范围。结论用聚氨酯材料研制的小口径人造血管在部分生物力学性能方面能满足人体血管置换要求。     

The performance of a small-calibre graft for vascular reconstructions in a senescent sheep model

There is an acute clinical need for small-calibre (<6 mm) vascular grafts for surgery. The aim of this study was to evaluate the long-term performance of a small-calibre graft produced from a nanocomposite biomaterial, polyhedral oligomeric silsesquioxane poly(carbonate-urea)urethane (POSS-PCU), in a large animal model following Good Manufacturing Practice (GMP) and Good Laboratory Practice (GLP) protocols. Grafts were characterised and implanted into the left carotid artery (LCA) of senescent sheep (n = 11) for a period of 9 months. In vivo compliance and blood flow rates were measured using ultrasound wall tracking software and a Transonic flow meter. Graft patency and degree of intimal hyperplasia (IH) were examined at the study end point. Seven of the POSS-PCU grafts were free from thrombosis, IH, calcification and aneurysmal dilation, with 4 occluding within 14 days. All of the ePTFE controls (n = 4) were found to be occluded by day 32. The lumen of the patent POSS-PCU grafts was free from any cellular deposits, whilst perigraft tissue could be seen to be infiltrating into the body of the graft from the adventitia. No significant differences were detected between the blood flow rates (p = 0.3693) and compliance (p = 0.9706) of the POSS-PCU grafts and the native artery, either post-operatively or after 9 months implantation. Small-calibre vascular grafts produced from POSS-PCU offer a viable option for the clinical use in revascularisation procedures with a patency rate of 64%.     

Bilayered vascular grafts based on silk proteins

A major block in the development of small diameter vascular grafts is achieving suitable blood vessel regeneration while minimizing the risk of thrombosis, intimal hyperplasia, suture retention, and mechanical failure. Silk-based tubular vessels for tissue engineering have been prepared by molding, dipping, electrospinning, or gel spinning, however, further studies are needed to improve the mechanical and blood compatibility properties. In the present study a bilayered vascular graft based on silk fibroin (SF) was developed. The graft was composed of an inner silk fiber-reinforced SF tube containing heparin and a highly porous SF external layer. Compared with previously fabricated SF tubes the fiber-reinforcement provided a comparable or higher mechanical strength, burst pressure, and suture retention strength, as well as mechanical compliance, to saphenous veins for vascular grafts. Heparin release was sustained for at least 1 month, affording blood compatibility to the grafts. The outer layer of the grafts prepared through lyophilization had a highly porous structure in which the macropore walls were composed of nanofibers similar to extracellular matrix, which offered an excellent environment for cell growth. In vitro studies showed good cytocompatibility and hemocompatibility.     

Electrospun scaffolds for tissue engineering of vascular grafts

There is a growing demand for off-the-shelf tissue engineered vascular grafts (TEVGs) for the replacement or bypass of damaged arteries in various cardiovascular diseases. Scaffolds from the decellularized tissue skeletons to biopolymers and biodegradable synthetic polymers have been used for fabricating TEVGs. However, several issues have not yet been resolved, which include the inability to mimic the mechanical properties of native tissues, and the ability for long-term patency and growth required for in vivo function. Electrospinning is a popular technique for the production of scaffolds that has the potential to address these issues. However, its application to human TEVGs has not yet been achieved. This review provides an overview of tubular scaffolds that have been prepared by electrospinning with potential for TEVG applications.     

Effect of a flow-streamlining implant at the distal anastomosis of a coronary artery bypass graft

Intimal thickening in the coronary artery bypass graft (CABG) distal anastomosis has been implicated as the major cause of restenosis and long-term graft failure. Several studies point to the interplay between nonuniform hemodynamics including disturbed flows and recirculation zones, wall shear stress, and long particle residence time as possible etiologies. The hemodynamic features of two anatomic models of saphenous-vein CABGs were studied and compared. One simulated an anastomosis with both diameter and compliance mismatch and a curvature at the connection, analogous to the geometry observed in a conventional cardiothoracic procedure. The other, simulated an anastomosis with a flow stabilizing anastomotic implant connector which improves current cardiothoracic procedures by eliminating the distal vein bulging and curvature. Physiologic flow conditions were imposed on both models and qualitative analysis of the flow was performed with dye injection and a digital camera. Quantitative analysis was performed with laser Doppler velocimetry. Results showed that the presence of the bulge at the veno-arterial junction, contributed to the formation of accentuated secondary structures (helices), which progress into the flow divider and significantly affect radial velocity components at the host vessel up to four diameters downstream of the junction. The model with the implant, achieved more hemodynamically efficient conditions on the host vessel with higher mean and maximum axial velocities and lower radial velocities than the conventional model. The presence of the sinus may also affect the magnitude and shape of the shear stress at locations where intimal thickening occurs. Thus, the presence of the implant creates a more streamlined environment with more primary and less secondary flow components which may then inhibit the development of intimal thickening, restenosis, and ultimate failure of the saphenous vein graft. © 2002 Biomedical Engineering Society. PAC2002: 8780Rb, 8719Rr, 8719Uv, 8763Lk, 8719Xx, 4262Be, 4780+v, 8710+e     

Compositional and microstructural design of highly bioactive P2O5-Na2O-CaO-SiO2 glass-ceramics

Bioactive glasses having chemical compositions between 1Na₂O-2CaO-3SiO₂ (1N2C3S) and 1.5Na₂O-1.5CaO-3SiO₂ (1N1C2S) containing 0, 4 and 6 wt.% P₂O₅ were crystallized through two stage thermal treatments. By carefully controlling these treatments we separately studied the effects on the mechanical properties of two important microstructural features not studied before, crystallized volume fraction and crystal size. Fracture strength, elastic modulus and indentation fracture toughness were measured as a function of crystallized volume fraction for a constant crystal size. Glass-ceramics with a crystalline volume fraction between 34% and 60% exhibited a three-fold improvement in fracture strength and an increase of 40% in indentation fracture toughness compared with the parent glass. For the optimal crystalline concentration (34% and 60%) these mechanical properties were then measured for different grain sizes, from 5 to 21 μm. The glass-ceramic with the highest fracture strength and indentation fracture toughness was that with 34% crystallized volume fracture and 13 μm crystals. Compared with the parent glass, the average fracture strength of this glass-ceramic was increased from 80 to 210 MPa, and the fracture toughness from 0.60 to 0.95 MPa.m^1/2. The increase in indentation fracture toughness was analyzed using different theoretical models, which demonstrated that it is due to crack deflection. Fortunately, the elastic modulus E increased only slightly; from 60 to 70 GPa (the elastic modulus of biomaterials should be as close as possible to that of cortical bone). In summary, the flexural strength of our best material (215 MPa) is significantly greater than that of cortical bone and comparable with that of apatite-wollastonite (A/W) bioglass ceramics, with the advantage that it shows a much lower elastic modulus. These results thus provide a relevant guide for the design of bioactive glass-ceramics with improved microstructure.     

Elastic and strength properties of canine long bones

Summary The mechanical properties of canine long bones have been determined. The mean and standard deviation of the maximum load supported by six fresh canine femurs in 3-point bending was 1366±253 N. In all cases, the bones sustained a considerable amount of plastic deformation before failure. The modulus of elasticity (GN/m²), ultimate tensile stress (MN/m²) and yield stress (MN/m²) were 13·86, 108·3 and 88·3 for six humeral specimens and 13·88, 142·1 and 104·0 for 13 tibial specimens, respectively. The tibial specimens showed a statistically significant higher ultimate strength than the humeral specimens.     

Patient-derived endothelial progenitor cells improve vascular graft patency in a rodent model

Late outgrowth endothelial progenitor cells (EPCs) derived from the peripheral blood of patients with significant coronary artery disease were sodded into the lumens of small diameter expanded polytetrafluoroethylene (ePTFE) vascular grafts. Grafts (1 mm inner diameter) were denucleated and sodded either with native EPCs or with EPCs transfected with an adenoviral vector containing the gene for human thrombomodulin (EPC + AdTM). EPC + AdTM was shown to increase the in vitro rate of graft activated protein C (APC) production 4-fold over grafts sodded with untransfected EPCs (p < 0.05). Unsodded control and EPC-sodded and EPC + AdTM-sodded grafts were implanted bilaterally into the femoral arteries of athymic rats for 7 or 28 days. Unsodded control grafts, both with and without denucleation treatment, each exhibited 7 day patency rates of 25%. Unsodded grafts showed extensive thrombosis and were not tested for patency over 28 days. In contrast, grafts sodded with untransfected EPCs or EPC + AdTM both had 7 day patency rates of 88-89% and 28 day patency rates of 75-88%. Intimal hyperplasia was observed near both the proximal and distal anastomoses in all sodded graft conditions but did not appear to be the primary occlusive failure event. This in vivo study suggests autologous EPCs derived from the peripheral blood of patients with coronary artery disease may improve the performance of synthetic vascular grafts, although no differences were observed between untransfected EPCs and TM transfected EPCs.     

Modeling the transmural stress distribution during healing of bioresorbable vascular prostheses

Little attention has been given to the stresses within the wall of bioresorbable vascular prostheses and how they might affect the resorption process. We modeled the graft “complex” (inner tissue capsule, residual graft, and outer tissue capsule) as a three-layered compound tube under internal pressure. Using this biomechanical model, we studied the effects of alterations in the geometry (i. e., radius and thickness) and mechanical properties of each stratum on the overall transmural stress distribution. Hypothetical simulations were performed to investigate the possible-sequence of and alterations in the radial and circumferential stresses during the resorption process. Our results suggest that early in the resorption phase, the inner tissue capsule is subjected to compressive hoop stresses and concentrated, largemagnitude compressive radial stresses. This distribution gives way to the more typical distribution for a thick-walled tube when equilibration (i.e., complete resorption) is approached. The prediction of the compressive stresses in the pseudo-intima during early resorption parallels findings of an elevated mitotic index in that region at that time. This leads to a new hypothesis, namely, that compressive stresses, both in-plane and out-of-plane with respect to the regenerated vascular cells, participate in the resorption process of bioresorbable vascular grafts by modulating elevated cellular proliferative activity and may play an important role in other aspects of vascular cell biology. Results of recent experimentation support this hypothesis.     

Endothelialization and patency of RGD-functionalized vascular grafts in a rabbit carotid artery model

To address the growing demand of small-diameter vascular grafts for cardiovascular disease, it is necessary to develop substitutes with bio-functionalities, such as anticoagulation, rapid endothelialization, and smooth muscle regeneration. In this study, the small-diameter tubular grafts (2.2 mm) were fabricated by electrospinning of biodegradable polymer polycaprolactone (PCL) followed by functional surface coating with an arginine-glycine-aspartic acid (RGD)-containing molecule. The healing characteristics of the grafts were evaluated by implanting them in rabbit carotid arteries for 2 and 4 weeks. Results showed that at both time points, all 10 of the RGD-modified PCL grafts (PCL-RGD) were patent, whereas 4 of the 10 non-modified PCL grafts were occluded due to thrombus formation. Scanning electron microscopy (SEM) data showed abundant platelets adhering on the surface of the midportion of the PCL grafts. In contrast, only few platelets were observed on the PCL-RGD surface, suggesting that RGD modification significantly improved the hemocompatibility of the PCL grafts. Histological analysis demonstrated enhanced cell infiltration and homogeneous distribution within the PCL-RGD grafts in comparison with the PCL grafts. Furthermore, immunofluorescence staining also showed a 3-fold increase of endothelial coverage of the PCL-RGD grafts than that of PCL grafts at those two time points. After 4-week implantation, 65.3 ± 7.6% of the surface area of the PCL-RGD grafts was covered by smooth muscle cell layer, which is almost 23% more than that on the PCL grafts. The present study indicates that RGD-modified PCL grafts exhibit an improved remodeling and integration capability in revascularization.     

Characteristics and prognosis in patients with prosthetic vascular graft infection: a prospective observational cohort study

Prosthetic vascular graft infection (PVGI) is a devastating complication, with a mortality rate of up to 75%, which is especially caused by aortic graft infection. The purpose of this study was to evaluate factors associated with in-hospital mortality of patients with definite graft infection, and with long-term outcome. We reviewed medical records of 85 patients treated for PVGIs defined by positive bacterial culture of intraoperative specimens or blood samples, and/or clinical, biological and radiological signs of infection. In-hospital patient mortality was defined as any death occurring during the initial treatment of the graft infection. Cure was defined as the absence of evidence of relapsing infection during long-term follow-up (≥1 year). Eighty-five patients (54 aortic and 31 limb graft infections) treated by surgical debridement and removal of the infected prosthesis (n=41), surgical debridement without removal of prosthesis (n=34) or antimicrobial treatment without surgery (n=10) were studied. The only microbiological difference observed between patients with early (occurring within 4 months after surgery) vs. late PVGI and between those with aortic vs. limb PVGI was the incidence of PVGI caused by Staphylococcus aureus, which was greater in patients with limb PVGI. Overall cure was observed in 93.2% of 59 patients with a follow-up of a minimum of 1 year. Overall in-hospital mortality was 16.5% (n=14). Two variables were independently associated with mortality: age >70 years (OR 9.1, 95% CI 1.83-45.43, p 0.007) and aortic graft infection (OR 5.6, 95% CI 1.1-28.7, p 0.037).     

电疗交流电对人体植入金属Ti6AL4V在模拟体液中的腐蚀作用

为探索中、低频电疗植入体内金属的腐蚀作用,本文在模拟体液中研究了1-1000Hz和不同电流幅值对Ti6LV交流电腐蚀。增大电流幅值或减小交流电频率将使Ti6LV从钝态转变到生成膜状态以至发生孔蚀。交流电波形对腐蚀也有一定影响。     

血管移植修复掌浅弓缺损的研究进展

目的 探讨不同部位血管移植修复掌浅弓血管缺损的研究进展。方法 以“vascular system injuries” “superficial palmar arch” “vascular grafting” “vein grafts” “arterial graft”和“血管系统损伤”“掌浅弓”“血管移植术”“静脉移植”“动脉移植”作为关键词,限定语言种类为英文和中文,在PubMed、中国知网和万方数据库检索2016年12月之前发表的有关掌浅弓缺损后应用血管移植修复的相关文献,进行归纳总结。结果 临床上对于严重外伤所致的掌浅弓缺损,主要采用浅静脉移植和小动脉移植两种方式进行重建。不同的修复方式具有不同的优缺点:足部静脉移植多采用端侧吻合的方式,可提供足够多的吻合口,但手术操作难度较大;Y型静脉移植多将移植血管串联桥接,优点是远端可提供多个吻合端口,但手术繁复,桥接后的血管远近端口径与受区血管口径相差较大;前臂静脉网移植可以解决供受区血管不匹配难题,但血管网解剖不恒定,增加了手术切取难度;手背静脉弓形态、口径与掌浅弓相近,手术切取及吻合操作均较容易,而瓣膜阻挡及手背瘢痕明显是其缺点;足背浅静脉弓移植修复掌浅弓缺损,可以解决供受区远、近端血管口径不匹配、数目不等难题,但瓣膜阻挡血流一直是困扰着临床的难题;小动脉移植修复掌浅弓缺损,临床效果可靠,缺点是对供区肌肉血供有一定影响。结论 应用血管移植可以重建缺损掌浅弓的连续性,恢复远端手指血液供应;不同部位血管移植修复缺损掌浅弓的手术方式及手术繁易程度存在差异,并均有一定缺陷;临床上寻找一种新的、适宜的血管供区,是血管移植重建掌浅弓缺损的研究方向。     

一种新的人工血管涂层及其实验研究

目的为克服目前使用的人工血管涂层材料性质普遍不稳定、不易提纯、交联用难且价格昂贵的缺陷,作者进行了人工血管丝素蛋白涂层的实验研究.材料和方法将丝素蛋白浸渍涂层涤纶人工血管内外壁并使用甲醛交联固定.通过血管壁渗水率、形态学以及力学性能等体外试验评价丝素蛋白涂层人工血管是否达到人工血管植入前标准.结果未涂层人工血管管壁渗水率通过丝素蛋白涂层降低了99%,达到植入时不漏血的目的.丝素蛋白涂层占重(117±22)mg/g显著低于较InterGardTM血管胶原涂层占重(302±23)mg/g(P＜0.05).结论丝素蛋白涂层人工血管可操控性好,渗水率低.同时在体外具备良好的生物降解性能.     

USPIO-labeled textile materials for non-invasive MR imaging of tissue-engineered vascular grafts

Non-invasive imaging might assist in the clinical translation of tissue-engineered vascular grafts (TEVG). It can e.g. be used to facilitate the implantation of TEVG, to longitudinally monitor their localization and function, and to provide non-invasive and quantitative feedback on their remodeling and resorption. We here incorporated ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles into polyvinylidene fluoride (PVDF)-based textile fibers, and used them to prepare imageable tissue-engineered vascular grafts (iTEVG). The USPIO-labeled scaffold materials were molded with a mixture of fibrin, fibroblasts and smooth muscle cells, and then endothelialized in a bioreactor under physiological flow conditions. The resulting grafts could be sensitively detected using T1-, T2- and T2*-weighted MRI, both during bioreactor cultivation and upon surgical implantation into sheep, in which they were used as an arteriovenous shunt between the carotid artery and the jugular vein. In vivo, the iTEVG were shown to be biocompatible and functional. Post-mortem ex vivo analyses provided evidence for efficient endothelialization and for endogenous neo-vascularization within the biohybrid vessel wall. These findings show that labeling polymer-based textile materials with MR contrast agents is straightforward and safe, and they indicate that such theranostic tissue engineering approaches might be highly useful for improving the production, performance, personalization and translation of biohybrid vascular grafts.