Biodegradable Grafts Research Articles

BIOLOGICAL PROSTHESES FOR CARDIOVASCULAR SURGERY – A HALF-CENTURY HISTORY AND DEVELOPMENT PROSPECTS

HighlightsSurgical correction of cardiovascular deformities is inextricably linked with the use of prostheses. The development and clinical testing of biological prostheses has been conducted under the guidance of the Member of Russian Academy of Sciences Leonid Barbarash at the Kuzbass Cardiology Center for more than 50 years. The uniqueness of the developed products lies in the use of a new biological tissue preservative – ethylene glycol diglycidyl ether, and an integrated approach involving the development and manufacture of products, study of long-term replacement outcome, causes of prosthetic dysfunction and genetic aspects of the use of bioprostheses in patients. AbstractThis article highlights the main achievements in the development of biological prostheses for cardiovascular surgery under the leadership of the Member of Russian Academy of Sciences L.S. Barbarash since the 1980s. Throughout this period, Leonid Barbarash and his team have developed and mass-produced various designs of bioprosthetic heart valves and tissue preservation methods, arterial grafts, and patches. The article presents the results of developing next-generation vascular biodegradable grafts capable of complete remodeling and stimulating endothelialization after the implantation into the vascular bed. Moreover, we conducted a series of genetic studies evaluating the significance of gene polymorphisms of various pathogenetic pathways involved in the pathological calcification of native heart valves and their prostheses.

Off-the-Shelf Synthetic Biodegradable Grafts Transform In Situ into a Living Arteriovenous Fistula in a Large Animal Model.

Current vascular access options require frequent interventions. In situ tissue engineering (TE) may overcome these limitations by combining the initial success of synthetic grafts with long-term advantages of autologous vessels by using biodegradable grafts that transform into autologous vascular tissue at the site of implantation. Scaffolds (6 mm-Ø) made of supramolecular polycarbonate-bisurea (PC-BU), with a polycaprolactone (PCL) anti-kinking-coil, are implanted between the carotid artery and jugular vein in goats. A subset is bio-functionalized using bisurea-modified-Stromal cell-derived factor-1α (SDF1α) derived peptides and ePTFE grafts as controls. Grafts are explanted after 1 and 3 months, and evaluated for material degradation, tissue formation, compliance, and patency. At 3 months, the scaffold is resorbed and replaced by vascular neo-tissue, including elastin, contractile markers, and endothelial lining. No dilations, ruptures, or aneurysms are observed and grafts are successfully cannulated at termination. SDF-1α-peptide-biofunctionalization does not influence outcomes. Patency is lower in TE grafts (50%) compared to controls (100% patency), predominantly caused by intimal hyperplasia. Rapid remodeling of a synthetic, biodegradable vascular scaffold into a living, compliant arteriovenous fistula is demonstrated in a large animal model. Despite lower patency compared to ePTFE, transformation into autologous and compliant living tissue with self-healing capacity may have long-term advantages.

Off-the-shelf, heparinized small diameter vascular graft limits acute thrombogenicity in a porcine model

Thrombogenicity poses a challenge to the clinical translation of engineered grafts. Previously, small-diameter vascular grafts (sdVG) composed of fibrin hydrogel microfiber tubes (FMT) with an external poly(ε-caprolactone) (PCL) sheath supported long-term patency in mice. Towards the development of an sdVG with off-the-shelf availability, the FMT's shelf stability, scale-up, and successful conjugation of an antithrombotic drug to the fibrin scaffold are reported here. FMTs maintain mechanical stability and high-water retention after storage for one year in a freezer, in a refrigerator, or at room temperature. Low molecular weight heparin-conjugated fibrin scaffolds enabled local and sustained delivery during two weeks of enzymatic degradation. Upscaled fabrication of sdVGs provides natural biodegradable grafts with size and mechanics suitable for human application. Implantation in a carotid artery interposition porcine model exhibited no rupture with thrombi prevented in all heparinized sdVGs (n = 4) over 4–5 weeks. Remodeling of the sdVGs is demonstrated with endothelial cells on the luminal surface and initial formation of the medial layer by 4–5 weeks. However, neointimal hyperplasia at 4–5 weeks led to the stenosis and occlusion of most of the sdVGs, which must be resolved for future long-term in vivo assessments. The off-the-shelf, biodegradable heparinized fibrin sdVG layer limits acute thrombogenicity while mediating extensive neotissue formation as the PCL sheath maintains structural integrity. Statement of significanceTo achieve clinical and commercial utility of small-diameter vascular grafts as arterial conduits, these devices must have off-the-shelf availability for emergency arterial bypass applications and be scaled to a size suitable for human applications. A serious impediment to clinical translation is thrombogenicity. Treatments have focused on long-term systemic drug therapy, which increases the patient's risk of bleeding complications, or coating grafts and stents with anti-coagulants, which minimally improves patient outcomes even when combined with dual anti-platelet therapy. We systematically modified the biomaterial properties to develop anticoagulant embedded, biodegradable grafts that maintain off-the-shelf availability, provide mechanical stability, and prevent clot formation through local drug delivery.

Marker-Independent Monitoring of in vitro and in vivo Degradation of Supramolecular Polymers Applied in Cardiovascular in situ Tissue Engineering.

The equilibrium between scaffold degradation and neotissue formation, is highly essential for in situ tissue engineering. Herein, biodegradable grafts function as temporal roadmap to guide regeneration. The ability to monitor and understand the dynamics of degradation and tissue deposition in in situ cardiovascular graft materials is therefore of great value to accelerate the implementation of safe and sustainable tissue-engineered vascular grafts (TEVGs) as a substitute for conventional prosthetic grafts. In this study, we investigated the potential of Raman microspectroscopy and Raman imaging to monitor degradation kinetics of supramolecular polymers, which are employed as degradable scaffolds in in situ tissue engineering. Raman imaging was applied on in vitro degraded polymers, investigating two different polymer materials, subjected to oxidative and enzymatically-induced degradation. Furthermore, the method was transferred to analyze in vivo degradation of tissue-engineered carotid grafts after 6 and 12 months in a sheep model. Multivariate data analysis allowed to trace degradation and to compare the data from in vitro and in vivo degradation, indicating similar molecular observations in spectral signatures between implants and oxidative in vitro degradation. In vivo degradation appeared to be dominated by oxidative pathways. Furthermore, information on collagen deposition and composition could simultaneously be obtained from the same image scans. Our results demonstrate the sensitivity of Raman microspectroscopy to determine degradation stages and the assigned molecular changes non-destructively, encouraging future exploration of this techniques for time-resolved quality assessment of in situ tissue engineering processes.

Evaluation of the biocompatibility and antimicrobial properties of biodegradable vascular grafts of various polymer composition with atrombogenic and antimicrobial drug coating

Creation of vascular grafts with atrombogenic and antimicrobial coating is a very important area.Objective: to evaluate the biocompatibility and antimicrobial properties of biodegradable vascular grafts of various polymer compositions with atrombogenic and antimicrobial drug coating.Materials and methods. Modification of the surface of the biodegradable vascular grafts was performed through complexation with polyvinylpyrrolidone, which was polymerized with polymer scaffold surface by means of ionizing radiation at 10 and 15 kGy. Physical and mechanical properties, as well as hemocompatibility were evaluated. Bacteriological studies were carried out using test strains of gram-negative and gram-positive microorganisms: Klebsiella pneumoniae spp. ozaena No. 5055, Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 25923, Proteus mirabillis ATCC3177, Pseudomonas aeruginosa.Results. There was no influence of modifying manipulations with ionizing radiation on the physical and mechanical characteristics of biodegradable prostheses. Vascular grafts with atrombogenic and antimicrobial coatings exhibited atrombogenic properties upon contact with blood, reducing platelet aggregation by 5–7 times (p < 0.05). Also decrease in adhesion and platelets deformation index was found on the surface of drug-eluting scaffolds (for PCL-based prostheses, the latter decreased by 1.9 times relative to unmodified counterparts (p < 0.05), for PHBV/PCL-based prostheses – by 1.3 times relative to unmodified counterparts and 1.5 times relative to scaffolds with polyvinylpyrrolidone (p < 0.05). Bacteriological studies revealed a local inhibitory effect in the place where scaffolds with cationic amphiphile were applied on agar. No growth retardation zones were identified. Polymeric composition of the scaffolds and the used dose of ionizing radiation did not lead to a difference in the bacteriostatic properties of the scaffolds with amphiphile.Conclusion. A full cycle of surface modification of biodegradable polymer prostheses based on both PCL and РHBV/PCL composition resulted in significant increase in the atrombogenic and antimicrobial properties of prostheses and did not worsen the physical-mechanical and biocompatible properties of the structures being developed.

Molecular mechanisms of esophageal epithelial regeneration following repair of surgical defects with acellular silk fibroin grafts

Constructive remodeling of focal esophageal defects with biodegradable acellular grafts relies on the ability of host progenitor cell populations to repopulate implant regions and facilitate growth of de novo functional tissue. Intrinsic molecular mechanisms governing esophageal repair processes following biomaterial-based, surgical reconstruction is largely unknown. In the present study, we utilized mass spectrometry-based quantitative proteomics and in silico pathway evaluations to identify signaling cascades which were significantly activated during neoepithelial formation in a Sprague Dawley rat model of onlay esophagoplasty with acellular silk fibroin scaffolds. Pharmacologic inhibitor and rescue experiments revealed that epithelialization of neotissues is significantly dependent in part on pro-survival stimuli capable of suppressing caspase activity in epithelial progenitors via activation of hepatocyte growth factor receptor (c-MET), tropomyosin receptor kinase A (TrkA), phosphoinositide 3-kinase (PI3K), and protein kinase B (Akt) signaling mechanisms. These data highlight the molecular machinery involved in esophageal epithelial regeneration following surgical repair with acellular implants.

Corrugated nanofiber tissue-engineered vascular graft to prevent kinking for arteriovenous shunts in an ovine model

ObjectiveProsthetic grafts are often needed in open vascular procedures. However, the smaller diameter prosthetic grafts (<6 mm) have low patency and often result in complications from infection. Tissue-engineered vascular grafts (TEVGs) are a promising replacement for small diameter prosthetic grafts. TEVGs start as a biodegradable scaffold to promote autologous cell proliferation and functional neotissue regeneration. Owing to the limitations of graft materials; however, most TEVGs are rigid and easily kinked when implanted in limited spaces, which precludes clinical application. We have developed a novel corrugated nanofiber graft to prevent kinking. MethodsTEVGs with corrugated walls (5-mm internal diameter by 10 cm length) were created by electrospinning a blend of poly-ε-caprolactone and poly(L-lactide-co-caprolactone). The biodegradable grafts were then implanted between the carotid artery and the external jugular vein in a U-shape using an ovine model. TEVGs were implanted on both the left and right side of a sheep (n = 4, grafts = 8). The grafts were explanted 1 month after implantation and inspected with mechanical and histologic analyses. Graft patency was confirmed by measuring graft diameter and blood flow velocity using ultrasound, which was performed on day 4 and every following week after implantation. ResultsAll sheep survived postoperatively except for one sheep that died of acute heart failure 2 weeks after implantation. The graft patency rate was 87.5% (seven grafts out of eight) with one graft becoming occluded in the early phase after implantation. There was no significant kinking of the grafts. Overall, endothelial cells were observed in the grafts 1 month after the surgeries without graft rupture, calcification, or aneurysmal change. ConclusionsOur novel corrugated nanofiber vascular graft displayed neotissue formation without kinking in large animal model.

BIODEGRADABLE VASCULAR GRAFT MODIFIED BY RGD-PEPTIDES: EXPERIMENTAL RESEARCH

Research goals. To study the effectiveness of RGD-peptide modification of the small-diameter biodegradable vascular grafts depending on the type of a linker and RGD configuration.Material and Methods. Tubular scaffolds with a diameter of 1.5 and 4.0 mm were produced by electrospinning from polyhydroxybutyrate/valerate (PHBV) and polycaprolactone (PCL). The PHBV/PCL grafts were modified with RGD peptides. In vitro experiments showed the degree of erythrocyte hemolysis and adhesion of the platelets and endothelial cells when in contact with a modified surface. The physico-mechanical properties and the structure of graft surface were studied before and after modification. The PHBV/PCL and PHBV/PCL/RGD vascular grafts were implanted into the abdominal aorta of rats for the periods of 1 and 3 months. Explant samples were studied using confocal microscopy and histological methods.Results. The results of physical and mechanical tests showed a significant decrease in the strength properties of the PHBV/PCL/RGD grafts relative to the unmodified analogs. A significant increase in platelet aggregation was found in the modified grafts. The level of adhesion of the endothelial cells on the modified surfaces was higher than that on the unmodified surfaces. Shortterm implantation of the grafts for 1 and 3 months showed that the modified grafts had higher patency and a less tendency to calcification compared with the unmodified grafts. Immunofluorescence study demonstrated the significant superiority of the modified vascular grafts in terms of stimulating the formation of a mature endothelial monolayer. A longer linker of 4,7,10-trioxa-1,13-tridecane diamine was found to increase the bioavailability of RGD peptides; the use of RGDK and c[RGDFK] for surface modification of the grafts stimulated early endothelialization of the internal surface of the implants and reduced the prosthetic wall calcification tendency, which together increased the patency of the implanted grafts.Conclusion. In short-term implantation of biodegradable vascular grafts modified with RGD peptides, the grafts with RGDK and c[RGDFK], attached to the surface of the prostheses through the 4,7,10-triox-1,13-tridecane diamine linker, showed the best results in terms of endothelial adhesion and maintenance of the viability of the endothelial cells in vitro and endothelialization in vivo; these grafts had high patency after implantation into the bloodstream of small laboratory animals and a less tendency to calcification.

BIODEGRADABLE VASCULAR GRAFT REINFORCED WITH A BIODEGRADABLE SHEATH

Background. Tissue-engineered vascular grafts can be reinforced by a biostable or biodegradable polymer sheath. A combination of electrospinning, routinely used for fabrication of biodegradable tubular grafts, and the layer-by-layer coating allows forming a polymeric sheath ensuring long-term integrity and high biocompatibility of the vascular grafts after the implantation. Aim To evaluate mechanical properties and in vivo performance of biodegradable small-diameter vascular grafts with a reinforcing sheath.Methods. Tubular grafts (4 mm diameter) were fabricated from poly(3-hydroxybutyrate-co3-hydroxyvalerate) and poly(ε-caprolactone) by emulsion electrospinning with the incorporation of vascular endothelial growth factor (VEGF) into the inner third of the graft and basic fibroblast growth factor (bFGF) along with stromal cell-derived factor-1α (SDF-1α) into the outer two thirds of the graft wall. Poly(ε-caprolactone) sheath was formed by the layer-by-layer coating. Upon graft fabrication, scanning electron microscopy was performed to assess the grafts’ surface, tensile testing allowed evaluating mechanical properties. The samples were implanted into the ovine carotid artery (n = 5 animals) for 12 months with the subsequent histological examination.Results. Sintering temperature of 160°C during the extrusion allowed effective and delicate merging of poly(ε-caprolactone) coating with the outer surface of the poly(3hydroxybutyrate-co-3-hydroxyvalerate)/poly(ε-caprolactone) tubular graft. The thickness of poly(ε-caprolactone) fiber was 380–400 μm, the increment of the reinforcing filament was 1 mm. The reinforcing sheath led to a 3-fold increase in durability and elastic modulus of the vascular grafts. At the 12-months follow-up, the grafts reported retained integrity. No signs of inflammation or calcification were found.Conclusion. The poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and poly(ε-caprolactone) vascular grafts with hierarchically incorporated growth factors and the reinforced poly(ε-caprolactone) spiral sheath demonstrated improved mechanical properties while retaining integrity and high biocompatibility after the long-term implantation into the ovine carotid artery.

Preventing collapsing of vascular scaffolds: The mechanical behavior of PLA/PCL composite structure prostheses during in vitro degradation.

The success of blood conduit replacement with synthetic graft is highly dependent on the architecture, and mechanical properties of the graft, especially for biodegradable grafts serving as scaffolds for in-situ tissue engineering. Particularly, the property of the radial compression recovery represents a critical to keep the patency during biointegration. Bi-component composite vascular grafts (cVG) made of polylactic acid (PLA) fabric and polycaprolactone (PCL) were developed with superior mechanical properties. In this research, the compressive and tensile properties of the prototypes were characterized when they were subjected to accelerated degradation. In addition, the prepared cVG were analyzed by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and wide angle X-ray diffraction (WAXD) to illustrate the gradual loss of mechanical properties. The results demonstrated that the cVG retained the circular cross-section even through its tensile strength decreased during degradation. The cVG samples containing a high percentage of PLA fibers lost their tensile strength faster, while the samples with lower PLA percentage lost the compressive resistance strength more quickly. This unique fabric-based composite biodegradable vascular prosthesis with an outstanding radical compression recovery could be a good candidate for in-situ formation of tissue engineered vascular graft.

COMPOSITE CONTRAST USING TO RESEARCH BIOLOGICAL OBJECTS BY SCANNING ELECTRON MICROSCOPY

The purpose . Мodification of scanning electron microscopy method in backscattered electrons to research biological samples with massive metal or mineral inclusions. Materials and methods . In the article the alternative method without cutting sections were supplied. Samples for researching (plates from NiTi surrounded by tissues after subcutal implantation, explanted stents, explanted epoxy covered xenoaortic bioprosthetic heart valves , explanted biodegradable vascular grafts from rats abdominal aorta) were embedded in epoxy risin, polymerized, made surface slices from blocks with samples, contrasted by uranyl acetate and lead citrate and researched in backscattered electrons. Results . By using the proposed method samples acquired composite contrast and subcellular structures had good visualization in scanning electron microscopy. Conclusion . Our research showed availability this method to research microstructural characteristics of contacts between hard material and biological tissues and to analyze cellular structure on implant- tissue border. Besides, this method is universal for researching different biological samples, and it has special advantages for research materials with volumetric metal and mineral inclusions. Another advantage of this method is ability to research samples with large square of surface, what can’t be made by using transmission electron microscopy method.

Biomaterials patterned with discontinuous microwalls for vascular smooth muscle cell culture: biodegradable small diameter vascular grafts and stable cell culture substrates

The medial layer of small diameter blood vessels contains circumferentially aligned vascular smooth muscle cells (vSMC) that possess contractile phenotype. In tissue-engineered constructs, these cellular characteristics are usually achieved by seeding planar scaffolds with vSMC, rolling the cell-laden scaffold into a tubular structure, and maturing the construct in a pulsatile bioreactor, a lengthy process that can take up to two months. During the maturation phase, the cells circumferentially orient, their contractile protein expression increases, and they obtain a contractile phenotype. Generating cell culture platforms that enable the rapid production of directionally oriented vSMC with increased contractile protein expression would be a major step forward for blood vessel tissue engineering and would greatly facilitate the in vitro study of vSMC biology. Previously, we developed a micropatterned cell culture surface that promotes orientation and contractile protein expression of vSMC. Herein, we explore two potential applications of this technology. First, we fabricate tubular and biodegradable scaffolds that possess the micropatterning on their exterior surface. When vSMC are seeded on these scaffolds, they initially proliferate in order to fill the microchannels and as confluence is reached the cells align in the direction of the micropatterning resulting in a biodegradable scaffold that is inhabited by circumferentially aligned vSMC within a week. Second, we illustrate that we can generate biostable cell culture surfaces that allow the in vitro study of the cells in a more contractile state. Specifically, we explore contractile protein expression of cells cultured on the micropatterned surfaces with the addition of soluble transforming growth factor beta one (TGFβ1).

Characterization and preparation of bioinspired resorbable conduits for vascular reconstruction

Soft tissues such as blood vessels possess mechanical behavior characterized by a ‘J-shaped’ stress-strain curve with a low-stiffness and a highly elastic zone. These biomechanical characteristics result in rapid endothelialization, smooth muscle cell regeneration, and aneurysm inhibition. The objective of this study was to fabricate biodegradable vascular grafts mimicking the mechanical properties of native arteries. Vascular grafts (inner diameter = 5.0 mm, length = 2.0 cm) were fabricated by dip coating poly(L-lactide-co-e-caprolactone) (PLCL) copolymers on polydioxanone (PDO) fibers. We used PDO fibers of different diameters to yield vascular grafts with a range of mechanical properties. Biomechanical properties, microstructure, and biocompatibility of the grafts were assessed using circumferential tensile testing, burst pressure measurement, scanning electron microscopy, and subcutaneous implantation, respectively. Vascular grafts possessed circumferential tensile strength and strain in the range of 4.07 to 5.98 MPa and 2.83 to 3.47 MPa, respectively, and were circumferentially stronger than expanded polytetrafluoroethylene (ePTFE) grafts. Burst pressure was physiologically relevant in the range of 1323.0 to 1736 kPa and water entry pressure was between 102.66 to 257.33 kPa. Mechanical properties of the grafts were also assessed in vivo after subcutaneous implantation in Sprague-Dawley rats for up to 8 weeks. Examination of the retrieved grafts indicated that the ‘J-shaped’ strain/stress curve was maintained for up to 3 week in PDO/PLCL vascular grafts. In contrast, ePTFE grafts did not maintain ‘J-shaped’ stress-strain behavior after in vivo implantation. Histological analysis demonstrated cellularization within PDO/PLCL grafts, whereas, PTFE grafts showed cellularization and neotissues mainly at the outer side. Our results suggest a new methodology for the fabrication of biodegradable vascular grafts with mechanical behaviour comparable to the native arteries that might avoid failure due to mechanical mismatch between the graft and native arteries.

DEVELOPMENT OF TISSUE ENGINEERED SMALL DIAMETER VASCULAR GRAFT FOR THE CARDIOVASCULAR SURGERY NEEDS

RICICD has large experience in the development of products for cardiovascular surgery, in particular, the bioprosthesis heart valves and blood vessels. Since 2010, under the leadership of the academician of RAS L. S. Barbarash researches to create bioresorbable vascular prostheses of small diameter began. The primary purpose – to create polymer structures with bio-directed action capable to replace individual structures of a living organism, in particular, of cardiovascular system. Scientific novelty of the problem lies in using a new approach for creation an organ directly in the patient’s body by biofunctional and bioresorbable features of polymer structures. The long-term patency of PCL vascular grafts and PHBV and PCL composition grafts had proved. The in vitro experiments had proved that growth factors incorporated into composition of biodegradable grafts retain their biological activity. The long-term in vivo experiments had demonstrated that vascular endothelial growth factor had accelerated endothelization and had improved vascular patency of biodegradable polymer grafts.

FEM Modelling and Experimental Analysis of Mechanical Properties of Artificial Blood Vessel

This article deals with a study and optimization of technology for a production of low-diameter biodegradable vascular grafts using modified electrospinning device. This production method allows preparation of grafts with diameter under 6 mm, which serve as carriers of tissue cells. Also their production and establishing of a simulation model, which describes their behaviour under internal pressure. For this purpose spinning device was created with a rotary collector, which allows obtaining the desired fiber orientation that is perpendicular to the axis of rotation. This orientation is necessary for the efficient proliferation of cells and future mechanical properties of artificial blood vessels. Formations created in this way were subjected to mechanical testing. Based on obtained data a suitable material model and FEM model of artificial vessels was established. These vessels were loaded with internal pressure corresponding with standard blood pressure in human body (120/80 mmHg). The results allow assessing the behaviour of the blood vessels during cultivation and proliferation of the cells in bioreactor. This is very important, because in bioreactor a medium, which pulsed under some pressure, is applied. Based on the obtained results were recommended optimization of production process, which led to suitable vessel properties.

Experimental noninferiority trial of synthetic small-caliber biodegradable versus stable vascular grafts

Long-term evolution of polycaprolactone vascular prostheses has been investigated recently. The goal of this study was to evidence a noninferiority of such grafts compared with expanded polytetrafluoroethylene (ePTFE) implants in an aortic replacement model in the rat. Fourteen anesthetized Sprague-Dawley rats received an infrarenal aortic graft (biodegradable, n = 8; expanded polytetrafluoroethylene, n = 6) replacement (end to end; inner diameter, 2 mm). Biodegradable grafts (polycaprolactone) were produced by random micro-/nanofiber electrospinning. After a median survival of 16.5 months, in vivo ultrasonography and angiography as well as postexplantation microcomputed tomography, histomorphometry, immunohistochemistry, and scanning electron microscopy were performed. Patency was 100% for polycaprolactone and 67% for ePTFE. No aneurysmal dilatation or stenoses were found in either group. Compliance was significantly higher for polycaprolactone compared with ePTFE (8.2 ± 1.0%/100 mm Hg vs 5.7 ± 0.7%/100 mm Hg; P < .01), but markedly reduced compared with adjacent native aortas and the control group. Histologically, low cellular in-growth was found in ePTFE whereas polycaprolactone showed significantly greater homogenous cellularity, producing an autologous extracellular matrix (10.8% ± 4.0% vs 32.1% ± 9.2%, P < .0001). Morphometry showed 100% neo-endothelialization for both grafts with a totally confluent endothelial coverage for polycaprolactone grafts by scanning electron microscope. More intimal hyperplasia was found in ePTFE compared with polycaprolactone grafts. Calcification was higher in ePTFE than in polycaprolactone grafts (15.8% vs 7.0%, P = .04) and was absent in controls. Outcomes of synthetic biodegradable nanofiber polycaprolactone grafts are not inferior compared with the clinically used expanded polytetrafluoroethylene grafts after long-term implantation in the rat aorta. Moreover, these implants show better patency, compliance, endothelialization, and cell in-growth, and less intimal hyperplasia and calcification than their counterparts.

Micro-recanalization in a biodegradable graft for reconstruction of the vas deferens is enhanced by sildenafil citrate

This study investigated the effect of sildenafil citrate on micro-recanalization and neovascularization, which were previously demonstrated in a rat model using biodegradable grafts (BGs) for vas deferens reconstruction. A total of 24 male rats underwent bilateral vasectomy with removal of a 0.5-cm vasal segment and were randomly assigned to four groups. Groups 1 and 2 underwent immediate vasovasostomy. Groups 3 and 4 underwent interposition of a 0.5-cm BG in the vasal gap. Groups 1 and 3 were given 5 mg kg(-1) day(-1) oral sildenafil. Other groups were given placebo. Rats were housed with females 12 weeks postoperatively. Reconstructed vasal segments were harvested 16 weeks postoperatively and analyzed histologically. Fluid from the distal vasal stump was analyzed for motile sperm. Urine samples obtained 16 weeks postoperatively were analyzed for cGMP levels. cGMP levels in rats treated with sildenafil were significantly higher than in control rats. No pregnancies were sired by grafted groups. In all, 5/6 rats in group 1 and 3/6 rats in group 2 sired litters. No motile sperm were noted in the vasal fluid of the grafted groups. Motile sperm were noted in all rats in group 1 and in 5/6 rats in group 2. In addition, 29 and 4 microcanals were detected in the sildenafil and placebo groups, respectively (P = 0.023). No microcanal exceeded 3 mm in length. An average of 12 and 28 blood vessels per graft were noted in the placebo and sildenafil groups, respectively (P < 0.0001). In conclusion, sildenafil enhances micro-recanalization and neovascularization in BG used for vas deferens reconstruction, but does not increase the microcanal length after 16 weeks.

Micro-recanalization in a biodegradable graft for reconstruction of the vas deferens is enhanced by sildenafil citrate

OBJECTIVE: Micro-recanalization of the vas after vasectomy has been observed in humans and a similar process occurs using a biodegradable graft model in the rat. In the present study, we investigated the effect of oral sildenafil citrate on this process.DESIGN: Prospective, randomized study.MATERIALS AND METHODS: 12 male Sprague-Dawley rats underwent bilateral vasectomy followed by bilateral vasovasostomy with implantation of 5 mm biodegradable grafts; 6 were then given sildenafil citrate orally (5 mg/kg/d) for 16 weeks and 6 were given placebo. The reconstructed segments were then harvested and serially sectioned for histologic examination.RESULTS: Of the 14 grafts harvested to date, 8 were from the sildenafil group and 6 from the placebo group. A total of 20 microcanals have been observed in the sildenafil group (average of 5 per animal) and 2 in the placebo group (average of 0.67 per animal). Of the 22 microcanals, 19 were observed in the testicular side of the grafts and 3 in the abdominal side.CONCLUSIONS: Orally administered sildenafil citrate enhances the formation of microcanals in the reproductive tract following vasectomy in a rat model. OBJECTIVE: Micro-recanalization of the vas after vasectomy has been observed in humans and a similar process occurs using a biodegradable graft model in the rat. In the present study, we investigated the effect of oral sildenafil citrate on this process. DESIGN: Prospective, randomized study. MATERIALS AND METHODS: 12 male Sprague-Dawley rats underwent bilateral vasectomy followed by bilateral vasovasostomy with implantation of 5 mm biodegradable grafts; 6 were then given sildenafil citrate orally (5 mg/kg/d) for 16 weeks and 6 were given placebo. The reconstructed segments were then harvested and serially sectioned for histologic examination. RESULTS: Of the 14 grafts harvested to date, 8 were from the sildenafil group and 6 from the placebo group. A total of 20 microcanals have been observed in the sildenafil group (average of 5 per animal) and 2 in the placebo group (average of 0.67 per animal). Of the 22 microcanals, 19 were observed in the testicular side of the grafts and 3 in the abdominal side. CONCLUSIONS: Orally administered sildenafil citrate enhances the formation of microcanals in the reproductive tract following vasectomy in a rat model.

Early microrecanalization of vas deferens following biodegradable graft implantation in bilaterally vasectomized rats

We evaluated a biodegradable graft for reconstruction of rat vasa deferentia with long obstructed or missing segments. A total of 47 Sprague-Dawley rats underwent bilateral vasectomy and were divided into groups according to length of the vas deferens affected (0.5, 1, 1.5 cm). After 8 weeks, poly-(D,L-lactide) (PDLA) grafts were used to reconnect the vas deferens. Grafts and adjoining vasa deferentia were excised 8 and 12 weeks later and evaluated microscopically. At 8 weeks, microscopic changes included a robust inflammatory response around the grafts. All grafts were still intact but in the early stages of degradation. No microtubules, indicative of vas deferens recanalization, were identified. One specimen showed evidence of healing and neovascularization at the interface zone between the vas deferens and the graft. At 12 weeks, grafts were further degraded but still present. Microscopic evaluation showed decreased inflammation. Seven specimens showed neovascularization at the interface zone; two of these showed distinct epithelialized vas deferens microcanals at the graft edges. One specimen showed a microcanal spanning the entire 0.5-cm graft. A time period of 8 weeks is not ample enough for vas deferens regeneration in the setting of a biodegradable PDLA graft; however, early evidence of re-growth was seen at 12 weeks. A longer healing time should permit further biodegradation of the graft, as well as re-growth and possible eventual reconnection of the vas deferens, allowing passage of sperm. These findings suggest a potential role for biodegradable grafts in the reconstruction of vas deferens with long obstructed segments.

Neoarteries grownin vivousing a tissue‐engineered hyaluronan‐based scaffold

Vascular tissue engineering has emerged as a promising technology for the design of an ideal, responsive, living conduit with properties similar to that of native tissue. The missing link in tissue-engineered blood vessels is elastin biosynthesis. Several biomaterials are currently used but few support elastin biosynthesis in a 3-D array. In previous studies, we demonstrated that a hyaluronan-based scaffold (HYAFF-11) grafted in the infrarenal rat aorta successfully guided the complete regeneration of a well-functioning small-diameter (2 mm) neoartery. The aim of the present study was to test the ability of HYAFF-11 biodegradable grafts to develop into neovessels of larger size (4 mm) in a porcine model, focusing on extracellular matrix (ECM) remodeling and elastin biosynthesis. HYAFF-11 tubes (diameter 4 mm, length 5 cm) were implanted in an end-to-end fashion in the common carotid artery. Grafts were analyzed for patency with a Duplex scan every 15 days. ECM components were evaluated by histological and molecular biological methods. All the animals survived the observation period without complications. Intimal hyperplasia (initiating at the anastomotic site) and graft thrombosis led to 3 cases of partial or complete occlusion, as demonstrated by histological examination. There were no signs of stenoses or aneurysms in the remaining grafts. After 5 months, the biomaterial was almost completely degraded and replaced by a neoartery segment composed of mature smooth muscle cells, collagen, and elastin fibers organized in layers and was completely covered on the luminal surface by endothelial cells (vWF(+)). Whereas in previous small animal studies, patency rates were not optimal, those obtained in the present study using hyaluronan-based grafts of larger size confirmed the ability of these constructs to guide the development of a well-functioning neoartery, with the remarkable additional attribute of facilitating the formation of organized layers of elastin fibers.