Synthetic Vascular Prostheses Research Articles

The Influence of Weaving Technologies on the Integral Characteristics of Synthetic Vascular Prostheses.

Ten vascular prostheses manufactured at the Science and Technology Park of the BNTU "Polytechnic" (Minsk, Republic of Belarus) have been analyzed. The prostheses differed in the type of weaving, duration and temperature of thermal fixation during crimping. Three samples had a single-layer structure and 7 samples had a double-layer structure. Tests for water permeability, resistance to radial bending, and porosity of the prostheses have been performed. The single-layer woven prostheses have demonstrated a low level of water permeability: the best result was shown by sample No.1: 80 [77.1; 80.5] ml/min/cm2. A strong direct correlation was revealed for these prostheses: the larger the pore diameter, the greater permeability (r=0.778; p=0.05). The single-layer woven prostheses appeared to be most resistant to radial bending, samples No.1 and 3 had no deformations at the minimum radius of the cylinder (r<4 mm), sample No.2 showed deformation on the cylinder with r=5 mm. For the single-layer prostheses, a strong negative correlation was noted (r=‒0.97; p=0.04) between the density of the warp threads and the kinking radius.All double-layer prostheses have demonstrated higher water permeability and weak resistance to deformation during radial bending. Samples No.4 and 8 were found to have minimum and maximum water permeability of 276.5 [258.3; 288.4] and 538.8 [533.3; 564.3] ml/min/cm2, respectively. The minimum kinking radius (7 mm) was shown by samples No.9 and 10. The worst results were demonstrated by sample No.6, which was deformed with minimal bending. Samples with ordinary plain weave have a low level of water permeability and high resistance to radial deformation, which makes them look most promising for the application in vascular surgery.

Influence of γ-Radiation on Mechanical Stability to Cyclic Loads Tubular Elastic Matrix of the Aorta.

A significant drawback of the rigid synthetic vascular prostheses used in the clinic is the mechanical mismatch between the implant and the prosthetic vessel. When placing prostheses with radial elasticity, in which this deficiency is compensated, the integration of the graft occurs more favorably, so that signs of cell differentiation appear in the prosthesis capsule, which contributes to the restoration of vascular tone and the possibility of vasomotor reactions. Aortic prostheses fabricated by electrospinning from a blend of copolymers of vinylidene fluoride with hexafluoropropylene (VDF/HFP) had a biomechanical behavior comparable to the native aorta. In the present study, to ensure mechanical stability in the conditions of a living organism, the fabricated blood vessel prostheses (BVP) were cross-linked with γ-radiation. An optimal absorbed dose of 0.3 MGy was determined. The obtained samples were implanted into the infrarenal aorta of laboratory animals-Landrace pigs. Histological studies have shown that the connective capsule that forms around the prosthesis has signs of high tissue organization. This is evidenced by the cells of the fibroblast series located in layers oriented along and across the prosthesis, similar to the orientation of cells in a biological arterial vessel.

Development of a vascular substitute produced by weaving yarn made from human amniotic membrane

Because synthetic vascular prostheses perform poorly in small-diameter revascularization, biological vascular substitutes are being developed as an alternative. Although their in vivo results are promising, their production involves long, complex, and expensive tissue engineering methods. To overcome these limitations, we propose an innovative approach that combines the human amniotic membrane (HAM), which is a widely available and cost-effective biological raw material, with a rapid and robust textile-inspired assembly strategy. Fetal membranes were collected after cesarean deliveries at term. Once isolated by dissection, HAM sheets were cut into ribbons that could be further processed by twisting into threads. Characterization of the HAM yarns (both ribbons and threads) showed that their physical and mechanical properties could be easily tuned. Since our clinical strategy will be to provide an off-the-shelf allogeneic implant, we studied the effects of decellularization and/or gamma sterilization on the histological, mechanical, and biological properties of HAM ribbons. Gamma irradiation of hydrated HAMs, with or without decellularization, did not interfere with the ability of the matrix to support endothelium formation in vitro. Finally, our HAM-based, woven tissue-engineered vascular grafts (TEVGs) exhibited clinically relevant mechanical properties. Thus, this study demonstrates that human, completely biological, allogeneic, small-diameter TEVGs can be produced from HAM, thereby avoiding costly cell culture and bioreactors.

Diagnosis and Successful Surgical Treatment of Ascending Aorta Valved Conduit Rupture

Prosthetic infection is the most common complication after aortic replacement with a synthetic vascular prosthesis or a valved conduit (VC); in this case, aortic valve (AV) rupture occurs in 0.1-1.3% of patients. The cause of valve rupture is not only infective endocarditis; ascending aortic aneurysm and obvious calcification of the native AV are also known risk factors. The paper describes a clinical case of a 49-year-old patient examined and treated in Petrovsky Russian Scientific Center of Surgery. Eighteen years after primary surgical intervention for aortic stenosis, AV reprosthesis and ascending aorta VC replacement were performed according to the Bentall - De Bono procedure modified by Kouchoukos. In 2021, computed tomographic aortography has revealed that in the presence of infective endocarditis, there is aortic prosthetic rupture to form a paraprosthetic fistula and a pseudoaneurysm cavity. The results of instrumental studies are comparable with intraoperative data. The clinical case is of interest due to the rare occurrence of complications and to the significant role of multislice computed tomography during examination and postoperative monitoring.

Fabrication of heparinized small diameter TPU/PCL bi-layered artificial blood vessels and in vivo assessment in a rabbit carotid artery replacement model

Increasingly growing problems in vascular access for long-term hemodialysis lead to a considerable demand for synthetic small diameter vascular prostheses, which usually suffer from some drawbacks and are associated to high failure rates. Incorporating the concept of in situ tissue engineering (TE) into synthetic small diameter blood vessels, for example, thermoplastic poly(ether urethane) (TPU) ones, could provide an alternative approach for vascular access that profits from the advantages of excellent mechanical properties of synthetic polymer materials (early cannulation) and unique biointegration regeneration of autologous neovascular tissues (long-term fistulae). In this study, a kind of heparinized small diameter (d = 2.5 mm) TPU/poly(ε-caprolactone) (TPU/PCL-Hep) bi-layered blood vessels was electrospun with an inner layer of PCL and an outer layer of TPU. Afterward, the inner surface heparinization was conducted by coupling H2N-PEG-NH2 to the corroded PCL layer and then heparin to the attached H2N-PEG-NH2 via the EDCI/NHS chemistry. Herein a heparinized PCL inner layer could not only inhibit thrombosis, but also provide sufficient space for the neotissue regeneration via biodegradation with time. Meanwhile, a TPU outer layer could confer the vascular access the good mechanical properties, such as flexibility, viability and fitness of elasticity between the grafts and host blood vessels as evidenced by the adequate mechanical properties, such as compliance (4.43 ± 0.07%/ 100 mmHg), burst pressure (1447 ± 127 mmHg) and suture retention strength (1.26 ± 0.07 N) without blood seepage after implantation. Furthermore, a rabbit carotid aortic replacement model for 5 months was demonstrated 100% animal survival and 86% graft patency. Puncture assay also revealed the puncture resistance and self-sealing (hemostatic time < 2 min). Histological analysis highlighted neotissue regeneration, host cell infiltration and graft remodeling in terms of extracellular matrix turnover. Altogether, these results showed promising aspects of small diameter TPU/PCL-Hep bi-layered grafts for hemodialytic vascular access applications.

Tobramycin Supplemented Small-Diameter Vascular Grafts for Local Antibiotic Delivery: A Preliminary Formulation Study.

Peripheral artery occlusive disease is an emerging cardiovascular disease characterized by the blockage of blood vessels in the limbs and is associated with dysfunction, gangrene, amputation, and a high mortality risk. Possible treatments involve by-pass surgery using autologous vessel grafts, because of the lack of suitable synthetic small-diameter vascular prosthesis. One to five percent of patients experience vascular graft infection, with a high risk of haemorrhage, spreading of the infection, amputation and even death. In this work, an infection-proof vascular graft prototype was designed and manufactured by electrospinning 12.5% w/v poly-L-lactic-co-glycolic acid solution in 75% v/v dichloromethane, 23.8% v/v dimethylformamide and 1.2% v/v water, loaded with 0.2% w/wPLGA. Polymer and tobramycin concentrations were selected after viscosity and surface tension and after HPLC-UV encapsulation efficiency (EE%) evaluation, respectively. The final drug-loaded prototype had an EE% of 95.58% ± 3.14%, with smooth fibres in the nanometer range and good porosity; graft wall thickness was 291 ± 20.82 μm and its internal diameter was 2.61 ± 0.05 mm. The graft’s antimicrobic activity evaluation through time-kill assays demonstrated a significant and strong antibacterial activity over 5 days against Staphylococcus aureus and Escherichia coli. An indirect cell viability assay on Normal Human Dermal Fibroblasts (NHDF) confirmed the cytocompatibility of the grafts.

КЛИНИКО-ДЕМОГРАФИЧЕСКАЯ ХАРАКТЕРИСТИКА ПАЦИЕНТОВ И ФАКТОРЫ РИСКА ИНФИЦИРОВАНИЯ ИСКУССТВЕННЫХ СОСУДИСТЫХ ПРОТЕЗОВ ПОСЛЕ РЕКОНСТРУКТИВНЫХ ОПЕРАЦИЙ НА АОРТО-ПОДВЗДОШНО-БЕДРЕННОМ СЕГМЕНТЕ

Objective: to study the clinical and demographic characteristics of patients and risk factors, to analyze their influence on the frequency of infection of artificial vascular prostheses in the aortoiliac-femoral segment. Material and methods. We analyzed 609 medical records of inpatient patients who had undergone vascular reconstructive interventions on the aortoiliac-femoral segment using a synthetic vascular prosthesis. The article presents the clinical and demographic characteristics of patients with lesions of the aortoiliac-femoral segment. The frequency of conduit infection in various major diseases, surgical approaches, types of bypass surgery (prosthetics), types of artificial vascular prosthesis was analysed. Results. The patients who developed lesions of the aortoiliac-femoral segment were mostly males (94.6%), urban residents (78%), unemployed (68.6%), those with chronic obliterating diseases of the arteries of the lower extremities (72.7%) and coronary heart disease (59.4%). The incidence of vascular prostheses in patients with chronic obliterating diseases of the arteries of the lower extremities was 5.5%, and in those with an aneurysm of the infrarenal abdominal aorta – 1.2%. Conclusion. The pattern of developing artificial vascular prosthesis infection has been established. Infection of conduits occurs statistically significantly more often in patients with chronic obliterating diseases of the arteries of the lower extremities than in those with an aneurysm of the infrarenal abdominal aorta.

The Effect of Mechanical Compatibility and of Thrombogenicity on the Ingrowth of a New Synthetic Vascular Prosthesis (Experimental Study).

Common disadvantages of modern synthetic vascular prostheses are thrombogenicity and lack of biomechanical compatibility with the prothesized vessel. To elucidate the role of these factors in the prosthesis integration, prostheses specimens were made by the electrospinning from the known materials: polycaprolactone, polyurethane and a mixture of fluorine-containing synthetic rubber FKM-26 with fluoroplastic F-26. The germination of the prostheses was compared with standard e-PTFE prosthesis in the pigs infrarenal aorta. The elastic properties of prostheses were studied by elastometry under the physiological range of loads. The thrombogenicity of the materials was determined by the number of platelets adhered to material surface exposed to native blood. The patency of the prostheses was checked by aortography. The germination of prostheses was assessed in the histological examination. It was shown that, with this set of materials, biomechanical compatibility turned out to be a more important factor of integration than the material thrombogenicity.

Evaluations for surrounding tissue incorporation after implantation of synthetic vascular prostheses in animal models.

Incorporation of surrounding tissues after implantation of synthetic vascular prostheses potentially varies in accordance with implanted prostheses. To evaluate post-implant tissue incorporation, we examined surgical, histological and ultrastructural findings after implantation in animal models. Three types of commercially available prostheses were tested (Gelweave™; Group G, J Graft SHIELD NEO®; Group J and Triplex®; Group T). Prostheses were implanted into Sprague-Dawley rats subcutaneously or sutured on abdominal aorta of Japanese white rabbits. The tissues were surgically examined for adhesion and were subjected to histological evaluations for cellular and tissue infiltration and ultrastructural observations by scanning electron microscopy (SEM). Group G exhibited less tendency in adhesion formation in early phase (rat: G vs J, P < 0.0001; G vs T, P < 0.0001/rabbit: G vs J, P < 0.0001; G vs T, P = 0.059). In late phase, Group J showed highest adhesion (rat: G vs J, P = 0.0004; J vs T, P = 0.015/rabbit: G vs J, P = 0.0015; J vs T, P = 0.0044). In group G, a gap was observed between implants and surrounding tissues forming capsulation, whereas other groups exhibited tissue infiltration inside of the implants wall which were also confirmed by SEM. The tissue permeation toward the implants and adhesion was positively correlated (P < 0.0001). Surrounding tissue conformation varied in accordance with the type of prostheses. It is desirable to elucidate characteristics of each prosthesis to select suitable grafts for each patient to achieve a better surgical outcome.

Outcome of Prosthetic Arteriovenous Graft in Lower Limb for Hemodialysis

Background: The burden of chronic kidney disease and the incidence of end-stage renal disease in India are continuously increasing. For each of these patients, adequate vascular access for dialysis is essential for survival. Access to patients' blood can come in the form of a catheter, native arteriovenous fistula (AVF), or prosthetic graft. It is apparent that the number of new “incident” patients and “prevalent” patients will continue to increase, requiring stable forms of vascular access. An alternative to autologous AVF is placement of a synthetic vascular graft prosthesis. Methods: This is a retrospective study which aims to evaluate the outcome of 10 consecutive patients with arteriovenous grafts (AVGs) made for hemodialysis in patients with exhaustive veins/failed AVFs with central venous catheters (CVCs) in situ. Results: The mean age of patients in our study was 54 years. The primary patency rate of AVGs was 50% and 30%, whereas the secondary patency rate was found to be 80% and 60% at 6 months and 1 year, respectively. Conclusion: AVGs can be used as an alternative to AVFs with acceptable results.

Prosthetic repair of the aorta with a cadaveric homograft for infection of bifurcated synthetic vascular prosthesis

Infection of arterial vascular grafts is a rare but utterly severe complication in vascular surgery. Therapeutic policy in patients with graft infection has not been standardized, to be determined individually. One of the variants of surgical treatment is considered to be repeat aortic repair using a cadaveric graft. Presented in the article is a clinical case report concerning a 60-year-old male patient previously subjected to aortofemoral bifurcation bypass grafting with stage IV ischaemia of lower limbs according to the Pokrovsky-Fontaine classification. In the early postoperative period the events of critical ischaemia were not arrested. Due to the presence of a block of the femoropopliteal segment, as the second stage 3 days after the primary operation, the patient underwent autovenous femoropopliteal bypass grafting with a reversed autovein above the knee-joint fissure. The clinical course of critical ischaemia of the limb was relieved. During subsequent 8 months of follow up his state remained stable. Eight months after the primary operation he developed purulent discharge from the postoperative scar on the left femur. In the setting of the Purulent Surgery Department, the patient was emergently subjected to opening and drainage of the abscess of the postoperative scar. On the bottom of the wound there was a freely lying branch of a synthetic vascular prosthesis. Computed tomography revealed infection of the entire synthetic prosthesis and aneurysms of distal anastomoses. Given extremely high risk for the development of arrosive haemorrhage, a decision was made on operative treatment - repeat prosthetic repair of the abdominal aorta with a cadaveric allograft. At the Vascular Department of the Clinic of Faculty Surgery, laparotomy was performed, with removal of the infected graft, followed by debridement of the retroperitoneal space and repeat aortofemoral bifurcation prosthetic repair of the abdominal aorta with a cadaveric allograft. The wound healed with first intention. There was no evidence of infectious process relapse. The patient was discharged on postoperative day 15 in a satisfactory condition. The duration of follow up amounted to 6 months. The control examination showed that the pain-free walking distance was 500 m. Doppler ultrasonography demonstrated that the graft was functioning, with no signs of either anastomotic aneurysms or suppuration of the retroperitoneal space.

Visceral debranching in hybrid surgery of thoracoabdominal aortic aneurysms

Presented herein is a review of the literature dedicated to the method of visceral debranching, i. e., switching of the visceral and renal branches of the abdominal aorta to its intact portion, using synthetic vascular prostheses as the first stage of hybrid surgical treatment of thoracoabdominal aortic aneurysms prior to endovascular aortic aneurysm repair. This is accompanied and followed by describing the history of the problem, operative technique, results of studies, as well as the data from registries and meta-analyses. Also discussed are the main complications of the method and measures of their prevention. We conclude that hybrid surgery of the thoracoabdominal portion of the aorta is a promising method in a particular cohort of patients, especially those at high surgical risk of 'open' aortic surgery.

Fractal dimension analysis: A new tool for analyzing colony-forming units

The gold standard for quantifying bacteria both in routine diagnostics and in research is plating followed by count of colony-forming units (CFU). But, manual CFU counting on plates is time-consuming and subjective. We evaluated fractal dimension as a new methodology for evaluating CFU. Twenty fragments of expanded polytetrafluoroethylene (ePTFE) synthetic vascular prosthesis and 20 silicone prostheses were embedded in bacterial suspensions and incubated. The prostheses were then sown in solid culture medium and incubated for 48 h. Petri dishes were photographed and analyzed by fractal dimension. There was correlation between the number of CFU in manual counting and the fractal dimension analysis (p = 0.0001). We demonstrated that fractal dimension is a useful method for microbiological analyses in researches. It makes CFU analysis easier and faster and can be used regardless of the culture medium.•Petri dishes with different bacterial colonies were photographed with a digital camera under natural light.•The images were binarized and analyzed with ImageJⓇ's “fractal dimension” tool.•Fractal dimension analysis showed to be a good tool for evaluating the amount of colony-forming unit.

The Effect of Mechanical Properties of Synthetic Prostheses Made by Electrospinning on the Results of Experimental Implantation in the Infrarenal Abdominal Aorta

The research aims to study the effect of circumferential compliance of synthetic vascular prostheses on their healing during implantation in the infrarenal abdominal aorta of pigs. In an experiment, 12 pigs were implanted with blood vessel prostheses in the infrarenal abdominal aorta. The prostheses possessed elastic characteristics obtained by a tensile testing machine, and differed in circumferential compliance: rigid (polycaprolactone [PCL]); less compliant than the native aorta (polyurethane [PU]); comparable in compliance to the native aorta (copolymer of vinylidene fluoride with hexafluoropropylene) before (FKM) and after radiation treatment (FKM-γ). The implanted prostheses compliance was measured by aortography during the first 3days and 1month after implantation, the condition of the prosthesis capsule was evaluated by macroscopic preparations and histologic examination. Pulsation on PCL prostheses was nonexistent immediately after implantation. On PU prostheses, slight pulsation was noted during the first 3days and disappeared after 1month. On FKM prostheses, although pulsation persisted after 1month, a significant expansion of prostheses was also recorded as a result of fatigue plastic deformation. On FKM-γ prostheses, pulsation comparable in magnitude with aortic pulsation was present 1month after implantation with no change in the size of the prosthesis. Macroscopic preparations reveal significant differences in the formed connective tissue capsule. The PCL prosthesis capsule is thick, narrowing the lumen of the vessel from the outside. The outer surface of PU prostheses is covered with a thinner uniform fibrous capsule. The inner surface of the FKM and FKM-γ prostheses is covered with a thin layer of smooth whitish tissue. The FKM prosthesis, unlike the FKM-γ prosthesis, is sharply expanded. In all cases, moderate aortic expansion was observed distal to the prosthesis. According to the histologic data, the outer and inner capsules of PCL prostheses are covered with a thick layer of fibrous tissue with signs of productive inflammation and foci of calcification. PU prostheses are surrounded by a thick connective tissue capsule partially endothelialized from the inside; the outer capsule is randomly populated with fibroblastic cells. FKM prostheses have a thin outer capsule where smooth muscle cells are visible, mainly oriented along and across the prosthesis axis; the inner capsule is thin and completely covered with a layer of endothelial cells from the side of the lumen. A layered structure is visible in the prosthesis capsule of FKM-γ, and the fibroblast cells in each layer of the capsule are oriented along or across the prosthesis axis, similar to the structure of a natural arterial vessel. The inner surface of the prosthesis is completely endothelialized. The healing and degree of inflammation in a capsule of blood vessel prostheses implanted in the infrarenal abdominal aorta of pigs depend on the degree of their circumferential compliance. Although maintaining pulsations, the cellular structure of the capsule is characterized by a greater degree of differentiation and approaches the structure of the native arterial wall.

Biocompatibility of Small-Diameter Vascular Grafts in Different Modes of RGD Modification.

Modification with Arg-Gly-Asp (RGD) peptides is a promising approach to improve biocompatibility of small-calibre vascular grafts but it is unknown how different RGD sequence composition impacts graft performance. Here we manufactured 1.5 mm poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/poly(ε-caprolactone) grafts modified by distinct linear or cyclic RGD peptides immobilized by short or long amine linker arms. Modified vascular prostheses were tested in vitro to assess their mechanical properties, hemocompatibility, thrombogenicity and endothelialisation. We also implanted these grafts into rat abdominal aortas with the following histological examination at 1 and 3 months to evaluate their primary patency, cellular composition and detect possible calcification. Our results demonstrated that all modes of RGD modification reduce ultimate tensile strength of the grafts. Modification of prostheses does not cause haemolysis upon the contact with modified grafts, yet all the RGD-treated grafts display a tendency to promote platelet aggregation in comparison with unmodified counterparts. In vivo findings identify that cyclic Arg-Gly-Asp-Phe-Lys peptide in combination with trioxa-1,13-tridecanediamine linker group substantially improve graft biocompatibility. To conclude, here we for the first time compared synthetic small-diameter vascular prostheses with different modes of RGD modification. We suggest our graft modification regimen as enhancing graft performance and thus recommend it for future use in tissue engineering.

Graft-type antithrombogenic MPC polymers as the surface modifier on the small-diameter vascular prostheses of segmented polyurethane

Event Abstract Back to Event Graft-type antithrombogenic MPC polymers as the surface modifier on the small-diameter vascular prostheses of segmented polyurethane Yihua Liu1*, Yuuki Inoue2, Atsushi Mahara3, Sachiro Kakinoki3, Tetsuji Yamaoka3 and Kazuhiko Ishihara1, 2 1 School of Engineering, The University of Tokyo, Department of Bioengineering, Japan 2 School of Engineering, The University of Tokyo, Department of Materials Engineering, Japan 3 National Cerebral and Cardiovascular Center Research Institute, Japan Introduction: The foreign surfaces of cardiovascular biomedical devices always cause blood coagulation. The adherent endothelial cells protect the surfaces of synthetic vascular prostheses with diameter over 6 mm from blood coagulation. However, the applications of these vascular prostheses as small arteries (diameter: less than 2 mm) were failure due to limited thrombogenicity.The objective of this study is to develop an antithrombogenic surface modifier of the segmented polyurethane (SPU) by the graft-type 2-methacryloyloxyethyl phosphorylcholine (MPC) polymers. The SPU is widely used as biomedical materials because of its excellent mechanical properties. To achieve molecular interaction between MPC polymer and SPU even under the blood flow condition, the graft-type poly(MPC-co-2-ethylhexyl methacrylate (EHMA)) (graft-PMEH) was synthesized and hybridized with the SPU [1]. The affinity between poly(EHMA) segments and soft segments of SPU is a key intermiscibility in the SPU/graft-PMEH. Initial blood interactions were observed by passing through the SPU/graft-PMEH tubing [2]. Materials and methods: The graft-PMEH was synthesized by two different living radical polymerizations. The SPU/graft-PMEH membrane was prepared by a double-solution casting procedure. The surface elements of membranes were confirmed by X-ray photoelectron spectroscopy (XPS). Biocompatibility was evaluated by protein adsorption test from human plasma with gold-colloid labeled immunoassay, and human umbilical vein endothelial cells (HUVEC) adhesion assay. The SPU/graft-PMEH tubings (Φ2 mm, length 35 mm) were prepared with the similar procedure of membranes on a revolving stick. The tubing was directly connected to the living porcine blood vessel for 2 min. The samples were observed by scanning electron microscopy (SEM). Results: The phosphorus peak and nitrogen peak attributed to phosphorylcholine group of MPC unit were observed on the XPS in SPU/graft-PMEH membranes. Plasma proteins adsorbed in a dispersed pattern on the SPU surface. In contrast, the SPU/graft-PMEH membrane dramatically suppressed 90% amount of protein adsorption. Also, a little HUVEC could be adhered and no proliferation was observed. On the luminal surface of SPU/graft-PMEH tubing, blood cell adhesion was inhibited even after whole blood was passed through without anticoagulation (Fig.1). Discussion: The graft-PMEH shows a high stability on the SPU surface because that poly(EHMA) segments side chains promote intermiscibility with the soft segment domain of SPU. The graft-PMEH could prevent thrombus formation even after blood contacting without any anticoagulant. This is due to the nature of the MPC polymers, that is, high resistance to adsorption of proteins and adhesion of cells to obtain antithrombogenicity. Conclusion: The SPU/graft-PMEH combined with excellent blood compatibility, mechanical properties and non-endothelialization is a potential biomaterial for small diameter vascular prostheses. We would like to thank Dr Tomohiro Konno and Dr Kyoko Fukazawa from the University of Tokyo for their valuable and constructive discussions.; This work was financially supported by a Health and Labour Sciences Research Grant (Grant H24-018) from the Ministry of Health, Labour, and Welfare of Japan.

Scaffold-Free Tubular Tissues Created by a Bio-3D Printer Undergo Remodeling and Endothelialization when Implanted in Rat Aortae.

BackgroundSmall caliber vascular prostheses are not clinically available because synthetic vascular prostheses lack endothelial cells which modulate platelet activation, leukocyte adhesion, thrombosis, and the regulation of vasomotor tone by the production of vasoactive substances. We developed a novel method to create scaffold-free tubular tissue from multicellular spheroids (MCS) using a “Bio-3D printer”-based system. This system enables the creation of pre-designed three-dimensional structures using a computer controlled robotics system. With this system, we created a tubular structure and studied its biological features.Methods and ResultsUsing a “Bio-3D printer,” we made scaffold-free tubular tissues (inner diameter of 1.5 mm) from a total of 500 MCSs (2.5× 104 cells per one MCS) composed of human umbilical vein endothelial cells (40%), human aortic smooth muscle cells (10%), and normal human dermal fibroblasts (50%). The tubular tissues were cultured in a perfusion system and implanted into the abdominal aortas of F344 nude rats. We assessed the flow by ultrasonography and performed histological examinations on the second (n = 5) and fifth (n = 5) day after implantation. All grafts were patent and remodeling of the tubular tissues (enlargement of the lumen area and thinning of the wall) was observed. A layer of endothelial cells was confirmed five days after implantation.ConclusionsThe scaffold-free tubular tissues made of MCS using a Bio-3D printer underwent remodeling and endothelialization. Further studies are warranted to elucidate the underlying mechanism of endothelialization and its function, as well as the long-term results.

Nanostructured Polyester Yarn Integration in Woven Vascular Implants

Woven synthetic vascular prosthesis consisting of polyester yarn, nanostructured particles of colloidal silver and polyurethane yarns and natural silk surgical thread were offered in the process of this scientific and practical activity. Previous scientific and practical experience of manufacturing various types of vascular prostheses was used in designing a new prosthesis. Advanced biomechanical and other properties used in the development of yarns were examined. The innovative structure of woven walls of prosthesis has normal biomechanical properties. Expressed antimicrobial activity of nanostructured wall of the prosthesis is an important indicator for the successful incorporation of synthetic implant in a living organism. These prostheses are capable of providing long-term normal physiologic hemodynamics in the recycled circulatory system.

Electrospun vascular grafts with improved compliance matching to native vessels

Coronary artery bypass grafting is one of the most commonly performed major surgeries in the United States. Autologous vessels such as the saphenous vein are the current gold standard for treatment; however, synthetic vascular prostheses made of expanded poly(tetrafluoroethylene) or poly(ethylene terephthalate) are used when autologous vessels are unavailable. These synthetic grafts have a high failure rate in small diameter (<4 mm) applications due to rapid reocclusion via intimal hyperplasia. Current strategies to improve clinical performance are focused on preventing intimal hyperplasia by fabricating grafts with compliance and burst pressure similar to native vessels. To this end, we have developed an electrospun vascular graft from segmented polyurethanes with tunable properties by altering material chemistry and graft microarchitecture. Relationships between polyurethane tensile properties and biomechanical properties were elucidated to select polymers with desirable properties. Graft thickness, fiber tortuosity, and fiber fusions were modulated to provide additional tools for controlling graft properties. Using a combination of these strategies, a vascular graft with compliance and burst pressure exceeding the saphenous vein autograft was fabricated (compliance = 6.0 ± 0.6%/mmHg × 10(-4) , burst pressure = 2260 ± 160 mmHg). This graft is hypothesized to reduce intimal hyperplasia associated with low compliance in synthetic grafts and improve long-term clinical success. Additionally, the fundamental relationships between electrospun mesh microarchitecture and mechanical properties identified in this work can be utilized in various biomedical applications.

Polyethylene terephthalate/chitosan tubular knits made by using a freeze-drying method

Biomaterials are commonly used in vitro or in vivo. Synthetic vascular prostheses, artificial bones, and artificial joints are used in vitro. Bone scaffolds demand components with good biocompatibility, mechanical strengths, and pore size. This allows the bone tissue to attach to and grow inside the bone scaffolds. Polyethylene terephthalate (PET) filaments and chitosan have good biocompatibility and are non-toxic. This study prepares biocompatible, porous, 1- and 2-layer three-dimensional PET/chitosan tubular knits by a freeze-drying method. PET plied yarns with three combinations of various denier (D) and coefficients of twist-150D/2, 225D/4, and 300D/3-are knitted into tubular knits with proper mechanical properties and porous structure. The resulting tubular knits are then alkali treated with 3 M sodium hydroxide (NaOH) reagent for 90 min, immersed in 1 wt% chitosan solution, and then freeze-dried, forming the porous PET/chitosan tubular knits. The functional group analysis and degradation of the alkali-treated chitosan films are first evaluated, and then the tensile strength, surface observation, pore size, and biocompatibility of the resulting PET/chitosan tubular knits are evaluated. The experimental result shows that 1- and 2-layer PET/chitosan tubular knits have desirable mechanical strength, stability, and biocompatibility antibacterial properties.