Small-diameter Vascular Prostheses Research Articles

Development and performance evaluation of a novel elastic bacterial nanocellulose/polyurethane small caliber artificial blood vessels

There is an increasing demand for small-diameter blood vessels. Currently, there is no clinically available small-diameter artificial vessel. Bacterial nanocellulose (BNC) has vast potential for applications in artificial blood vessels due to its good biocompatibility. At the same time, medical polyurethane (PU) is a highly elastic polymer material widely used in artificial blood vessels. This study reports a composite small-diameter BNC/PU conduit using a non-solvent-induced phase separation method with the highly hydrophilic BNC tube as the skeleton and the hydrophobic polycarbonate PU as the filling material. The results revealed that the compliance and mechanical matching of BNC/PU tubes were higher than BNC tubes; the axial/radial mechanical strength, burst pressure, and suture strength were significantly improved; the blood compatibility and cell compatibility were also excellent. The molecular and subcutaneous embedding tests showed that the composite tubes had lighter inflammatory reactions. The results of the animal substitution experiments showed that the BNC/PU tubes kept blood flow unobstructed without tissue proliferation after implantation in rats for 9 months. Thus, the BNC/PU small-diameter vascular prosthesis had the potential for long-term patency and acted as an ideal material for small-diameter vessels.

Paracrine cross-talk between human adipose tissue-derived endothelial cells and perivascular cells accelerates the endothelialization of an electrospun ionomeric polyurethane scaffold

The ex vivo endothelialization of small diameter vascular prostheses can prolong their patency. Here, we demonstrate that heterotypic interactions between human adipose tissue-derived endothelial cells and perivascular cells can be exploited to accelerate the endothelialization of an electrospun ionomeric polyurethane scaffold. The scaffold was used to physically separate endothelial cells from perivascular cells to prevent their diffuse neo-intimal hyperplasia and spontaneous tubulogenesis, yet enable their paracrine cross-talk to accelerate the integration of the endothelial cells into a temporally stable endothelial lining of a continuous, elongated, and aligned morphology. Perivascular cells stimulated endothelial basement membrane protein production and suppressed their angiogenic and inflammatory activation to accelerate this biomimetic morphogenesis of the endothelium. These findings demonstrate the feasibility and underscore the value of exploiting heterotypic interactions between endothelial cells and perivascular cells for the fabrication of an endothelial lining intended for small diameter arterial reconstruction. Statement of SignificanceAdipose tissue is an abundant, accessible, and uniquely dispensable source of endothelial cells and perivascular cells for vascular tissue engineering. While their spontaneous self-assembly into microvascular networks is routinely exploited for the vascularization of engineered tissues, it threatens the temporal stability of an endothelial lining intended for small diameter arterial reconstruction. Here, we demonstrate that an electrospun polyurethane scaffold can be used to physically separate endothelial cells from perivascular cells to prevent their spontaneous capillary morphogenesis, yet enable their cross-talk to promote the formation of a stable endothelium. Our findings demonstrate the feasibility of engineering an endothelial lining from human adipose tissue, poising it for the rapid ex vivo endothelialization of small diameter vascular prostheses in an autologous, patient-specific manner.

Tissue-Engineered Constructions for the Needs of Cardiovascular Surgery: Possibilities of Personalization and Prospects for Use (Problem Article)

In the market for products for the needs of cardiovascular surgery, there is still no effective vascular prosthesis with a diameter of less than 4 mm, despite the continuous increase in the incidence of atherosclerosis and the increase in the number of surgical operations to restore blood flow in the affected arteries. At the same time, vascular tissue engineering has diverse methodological approaches for the development of effective functionally active small-diameter vascular prostheses suitable for adaptive growth and regeneration in situ. An important aspect is the possibility of personalizing the created prostheses not only by taking into account the individual anatomy of the patients vascular bed, but also by using autologous components to create such a prosthesis, which can be obtained directly from the recipient. The presented problematic article reflects the main results on the creation of biodegradable vascular prostheses of small diameter, obtained at the Research Institute of the Research institute for complex issues of cardiovascular diseases (Kemerovo). The functionality of the prostheses was provided both through the incorporation of biologically active components with proangiogenic potential for the purpose of complete remodeling in situ, and the formation of cell-populated vascular prostheses using autologous cells and proteins from patients with coronary heart disease. In the future, these vascular prostheses can cover the clinical need for elective and emergency cardiovascular surgery, neuro- and microsurgery, and military field vascular surgery.

Engineering of poly(caprolactone) and poly(glycerol sebacate) small-diameter vascular prosthesis with quercetin.

The fabrication of biodegradable, bioabsorbable, and biocompatible vascular scaffolds with enhanced mechanical and biological properties that are able to modulate local inflammation and induce endothelialization after surgical implant is still a challenge. In this work, a fibrous scaffold, made of poly(ε-caprolactone) and poly(glycerol sebacate), was fabricated to be potentially used as a small-diameter graft in vascular surgery. The novelty of this research is represented by the direct incorporation of quercetin, a well-known antioxidant compound with several biologicalproperties, into a polymeric scaffold obtaining a vascular construct able to modulate two key factors involved in postsurgical inflammation, matrix metalloproteinase-9 and endothelial nitric oxide synthase. For its production, an electrospinning apparatus, a solution made of the two polymers (both 20% (w/v), mixed at the ratio 1:1 (v/v)), and free quercetin (0.05% (w/v))were used. Scanning electron and atomic force microscopies were employed to investigate the morphological properties of the fabricated electrospun scaffolds. Furthermore, physicochemical properties, includingFourier-transform infrared spectroscopy, mass loss, fluid uptake, quercetin release, mechanical properties, and biological activity of the scaffolds were studied. The expression of matrix metalloproteinase-9, tissue inhibitor of metalloproteinase-1, and of endothelial nitric oxide synthase was evaluated when the quercetin-functionalized scaffold was exposed to human endothelial cells treated with tumor necrosis factor-α. The results of this study confirmed the feasibility of incorporating free quercetin during the electrospinning process to impart biological properties to small-diameter vascular prostheses.

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.

Silk-based bilayered small diameter woven vascular conduits for improved mechanical and cellular characteristics

A major impediment to the development of small diameter vascular grafts is to achieve an optimal balance between its mechanical properties and cellular response. To address this, the technique of cylindrical weaving has been combined with electrospinning to fabricate a seamless bilayered conduit (∼3 mm) having an inner cell-friendly nanofibrous layer of poly(caprolactone)/collagen and an outer mechanically compliant woven silk layer. Mechanical characteristics such as burst strength, suture retention, compliance and leak resistance were found to be improved for this bilayered conduit when compared to the commercial standard. In-vitro studies revealed that the lumen of the conduit was non-hemolytic and could support adhesion and viability of endothelial cells. Overall, our studies suggest that the proposed bilayer construct could be a suitable candidate for small diameter vascular prosthesis.

Vascular Polyurethane Prostheses Modified with a Bioactive Coating-Physicochemical, Mechanical and Biological Properties.

This study describes a method for the modification of polyurethane small-diameter (5 mm) vascular prostheses obtained with the phase inversion method. The modification process involves two steps: the introduction of a linker (acrylic acid) and a peptide (REDV and YIGSR). FTIR and XPS analysis confirmed the process of chemical modification. The obtained prostheses had a porosity of approx. 60%, Young’s Modulus in the range of 9–11 MPa, and a water contact angle around 40°. Endothelial (EC) and smooth muscle (SMC) cell co-culture showed that the surfaces modified with peptides increase the adhesion of ECs. At the same time, SMCs adhesion was low both on unmodified and peptide-modified surfaces. Analysis of blood-materials interaction showed high hemocompatibility of obtained materials. The whole blood clotting time assay showed differences in the amount of free hemoglobin present in blood contacted with different materials. It can be concluded that the peptide coating increased the hemocompatibility of the surface by increasing ECs adhesion and, at the same time, decreasing platelet adhesion. When comparing both types of peptide coatings, more promising results were obtained for the surfaces coated with the YISGR than REDV-coated prostheses.

Results of long-term patency of small-diameter biodegradable vascular prostheses with atrombogenic drug coating of sheep model

Background. Preclinical tests of biodegradable small diameter vascular prostheses on a sheep model have been carried out.Aim. To assess the results of long-term patency and remodeling of biodegradable vascular prostheses based on polyhydroxybutyrate / valerate and polycaprolactone with an atrombogenic drug coating in a large laboratory animal model.Methods. We researched vascular prostheses made of polyhydroxybutyrate / valerate and polycaprolactone (PHBV/PCL) 4 mm in diameter with layer-by-layer vascular endothelial growth factor incorporated into the polymer framework, the main fibroblast growth factor, chemoattractant molecule containing SDF-1a (GFmix) surface, and additional modifying drug surface heparin and iloprost (PHBV/PCL/ GFmix/Heparin/Iloprost). Animals with implanted synthetic Gore-Tex vascular grafts with a diameter of 4 mm were included into a comparison group.Results. After one day of implantation it was revealed that the patency of biodegradable PHBV/PCL/GFmix/Heparin/Iloprost prostheses was 62.5%, while synthetic Gore-Tex prostheses were thrombosed in 100% of cases. At the same time, after 18 months of implantation, the patency of biodegradable vascular PHBV/PCL/ GFmix/Heparin/Iloprost prostheses decreased to 50%. Passable drug-eluting polymer grafts were completely resorbed after 18 months of implantation, and aneurysmically expanded newly formed vascular tissue was formed in their place.Conclusion. Vascular prostheses made of polyhydroxybutyrate/valerate and polycaprolactone showed better long-term patency results than synthetic prostheses used in the clinical practice. However, the strengthening of the external framework of the prostheses is required in order to prevent the formation of aneurysms.

Development of personalized cell-populated vascular graft in vitro

Aim. To create a personalized cell-populated small-diameter vascular prosthesis in a pulsating bioreactor.Methods. Tubular grafts were made by electrospinning from mixtures of biodegradable polymers, poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(εcaprolactone) (PCL). The inner surface is modified with fibrin. Tubular scaffolds were colonized with cultured colony-forming endothelial cells and grown under static conditions for 2 days. Then, the cell-populated prostheses continued to be cultivated for 5 days in a pulsating bioreactor system with a final shear stress of 2.85 dynes/cm².Results. The advantages of the cultivation of cell-populated vascular prostheses in a pulsating bioreactor have been revealed. The selected mode of cultivation of cellpopulated vascular prostheses under conditions of a pulsating flow with a shear stress of 2.85 dynes/cm² did not have a damaging effect on the integrity of the endothelial monolayer. Moving unidirectional mechanical stimuli of chaotic orientation fibers of F-actin changed to a predominant orientation in the direction of flow, and also increased the expression of F-actin, Talin focal adhesion protein, and specific endothelial markers CD309, CD31, vWF.Conclusion. The creation of a personalized cell-populated small-diameter vascular prosthesis with a functional endothelial monolayer is possible due to the use of autologous endothelial cells, autologous fibrin, and cultivation under conditions of a pulsating flow.

Results of long-term permeability of small-diameter vascular prostheses modified by pro-angiogenic factors and athrombogenic drug coating (model of large laboratory animals)

Developed for bypass surgery, tissue-engineered vascular grafts should remain passable after implantation and have high rate of endothelialization to ensure long-term patency, atrombogenicity and biocompatibility. This study was aimed at assessing the long-term patency of polyhydroxybutyrate/valerate (PHBV)/polycaprolactone (PCL) vascular grafts modified by pro-angiogenic factors and athrombogenic drug coating in a large laboratory animal model.

Advancing tissue-engineered vascular grafts via their endothelialization and mechanical conditioning.

Tissue engineering has garnered significant attention for its potential to address the predominant modes of failure of small diameter vascular prostheses, namely mid-graft thrombosis and anastomotic intimal hyperplasia. In this review, we described two main features underpinning the promise of tissue-engineered vascular grafts: the incorporation of an antithrombogenic endothelium, and the generation of a structurally and biomechanically mimetic extracellular matrix. From the early attempts at the in-vitro endothelialization of vascular prostheses in the 1970s through to the ongoing clinical trials of fully tissue-engineered vascular grafts, the historical advancements and unresolved challenges that characterize the current state-of-the-art are summarized in a manner that establishes a guide for the development of an effective vascular prosthesis for small diameter arterial reconstruction. The importance of endothelial cell purity and their arterial specification for the prevention of both diffuse neointimal hyperplasia and the accelerated development of atherosclerotic lesions is delineated. Additionally, the need for an extracellular matrix that recapitulates both the composition and structure of native elastic arteries to facilitate the protracted stability and patency of an engineered vasoactive conduit is described. Finally, the capacity of alternative sources of cells and mechanical conditioning to overcome these technical barriers to the clinical translation of an effective small diameter vascular prosthesis is discussed. In conclusion, this review provides an overview of the historical development of tissue-engineered vascular grafts, highlighting specific areas warranting further research, and commentating on the outlook of a clinically feasible and therapeutically efficacious vascular prosthesis for small diameter arterial reconstruction.

Is it Possible to Create Readily Available Tissue-Engineered Vascular Grafts Without Using Cells?

Introduction - In modern vascular surgery remains the problem of small-diameter vascular grafts. Autologous or synthetic vascular grafts are used routinely for arterial bypass in patients with cardiovascular disease. However, some patients either lack suitable autologous tissue or cannot receive synthetic grafts. Such patients could benefit from a vascular graft produced by tissue engineering. Currently, there are a number of techniques to receipt such artificial vessel, some of which are already in clinical trials. The method of using acellular biodegradable scaffold suggests that host cells can regenerate new vascular wall in situ, thats allows to overcome the scalability issue and make the grafts available off-the-shelf. The aim of the study is a comprehensive assessment of bioresorbable prosthesis from L-polylactide (PLA), and determining the possibility of its use as acellular vascular graft available off-the-shelf. Methods - Tubular grafts were obtained by the electrospinning method, (1.2 mm inner diameter) on the basis of nonwoven nano- and microfiber biodegradable polymer PLA. Mechanical characteristics such as tensile strength ,Young’s modulus E, and tensile deformation at break ofthe samples were determined using a UTS 10 universaltesting machine (Germany). Porosity parameters were determined by mercury porosimetry and BET method. Cytology analyses were performed with nanofibersfrom PLA and culture of mesenchymal stem cellsobtained from adipose tissue (ASCs). To assess the degree of cell adhesion toPLA grafts investigated materials were placed insquare-hole board (Nunc, USA). Investigation of barrier propertiesof tubular grafts were carried out on a developed laboratory setup. Obtained grafts were implanted in the abdominal aorta of rats (n=18). Follow-up was 16 months. The material was subjected to histological examination, electron microscopy, immunohistochemistry CD 31 +. After 14 months implantation angiography was performed (n=1). Results - During the operations and by the results of the investigation physical and mechanical properties it has been shown that obtained grafts are suitable for sewing in the bloodstream. For grafts from L-polylactide the pore volume was 78% and the surface area per gram of polymer 3.6 m2 (S BET).Investigation of adhesion and proliferation of mesenchymal stem cells derived from adipose tissue of rats showed safety and biocompatibility of used materials. All grafts formed neointima, with no signs of hyperplasia in the areas of anastomoses. Patency for PLA grafts 88% (n = 18). After 16 months (n=3) histology shows total resorption of PLA fibers, new vascular wall consist of connecctive tissue with endotelial lining, but all zone of reconstruction was presented by aneurysm. Conclusion - Small diameter vascular prostheses with high porosity obtained by electrospinning from PLA have sufficient exploitation mechanical properties. In in vivo experiments proved its safety, biocompatibility. Received patency rates are satisfactory for grafts with small diameter. Low mechanical properties of the connective tissue formed in the area of reconstruction have led to the formation of aneurysms. To sum up, the need for the introduction of cells in the wall of the graft in vitro before implantation is not in doubt.

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.

Improved endothelialization of small-diameter ePTFE vascular grafts through growth factor therapy.

BackgroundProsthetic vascular grafts in humans characteristically lack confluent endothelialization regardless of the duration of implantation. Use of high-porosity grafts has been proposed as a way to induce endothelialization through transgraft capillarization, although early experiments failed to show increased healing in man.ObjectivesWe hypothesized that transduction of tissues around the prosthetic conduit with vectors encoding VEGF receptor-2 (VEGFR2) ligands would augment transinterstitial capillarization and induce luminal endothelialization of high-porosity ePTFE grafts.MethodsFifty-two NZW rabbits received 87 ePTFE uni- or bilateral end-to-end interposition grafts in carotid arteries. Rabbits were randomized to local therapy with adenoviruses encoding AdVEGF-A165, AdVEGF-A109 or control AdLacZ and analyzed at 6 and 28 days after surgery by contrast-enhanced ultrasound and histology.ResultsAdVEGF-A165 and AdVEGF-A109 dramatically increased perfusion in perigraft tissues at 6 days (14.2 ± 3.6 or 16.7 ± 2.6-fold increases, P < 0.05 and P < 0.01). At 28 days, the effect was no longer significantly higher than baseline. At 6 days, no luminal endothelialization was observed in any of the groups. At 28 days, AdVEGF-A109- and AdVEGF-A165-treated animals showed enhanced ingrowth of transinterstitial capillaries (66.0 ± 13.7% and 77.4 ± 15.7% of graft thickness vs 44.7 ± 24.4% in controls, P < 0.05) and improved luminal endothelialization (11.2 ± 26.3% and 11.4 ± 22.2%, AdVEGF-A109 and AdVEGF-A165 vs 0% in controls, P < 0.05). No increased stenosis was observed in the treatment groups as compared to LacZ controls.ConclusionsThis study suggests that transient local overexpression of VEGFR2 ligands in the peri-implant tissues at the time of graft implantation is a novel strategy to increase endothelialization of high-porosity ePTFE vascular grafts and improve the patency of small-diameter vascular prostheses.

Improved endothelialization of small-diameter ePTFE grafts through growth factor therapy.

Background: Prosthetic vascular grafts in humans characteristically lack confluent endothelialization regardless the duration of implantation. Use of high-porosity grafts has been proposed as a way to induce endothelialization through transgraft capillarization, although early experiments failed to show increased healing in man. Objectives: We hypothesized that transduction of tissues around the prosthetic conduit with vectors encoding VEGF Receptor-2 (VEGFR2) ligands would augment transinterstitial capillarization and induce luminal endothelialization of high-porosity PTFE grafts. Methods: Fifty-two NZW rabbits received 87 ePTFE uni- or bilateral end-to-end interposition grafts in carotid arteries. Rabbits were randomized to local therapy with adenoviruses encoding AdVEGF-A165, AdVEGF-A109 or control AdLacZ and analyzed at 6 and 28d after surgery by contrast-enhanced ultrasound and histology. Results: AdVEGF-A165 and AdVEGF-A109 dramatically increased perfusion in perigraft tissues at 6d (14.2±3.6 or 16.7±2.6- fold increases, P&lt;0.05 and P&lt;0.01). At 28d the effect was no longer significantly higher than baseline. At 6d no luminal endothelialization was observed in any of the groups. At 28d, AdVEGF-A109 and AdVEGF-A165 treated animals showed enhanced ingrowth of transinterstitial capillaries (66.0±13.7% and 77.4±15.7% of graft thickness vs. 44.7±24.4% in controls, P&lt;0.05) and improved luminal endothelialization (11.2±26.3% and 11.4±22.2%, AdVEGF-A109 and AdVEGF-A165 vs. 0% in controls, P&lt;0.05). No increased stenosis was observed in the treatment groups as compared to LacZ controls. Conclusions: This study suggests that transient local overexpression of VEGFR2 ligands in the peri-implant tissues at time of graft implantation is a novel strategy to increase endothelialization of high-porosity ePTFE vascular grafts and improve the patency of small-diameter vascular prostheses.

Bioprinted gelatin hydrogel platform promotes smooth muscle cell contractile phenotype maintenance.

Three dimensional (3D) bioprinting has been proposed as a method for fabricating tissue engineered small diameter vascular prostheses. This technique not only involves constructing the structural features to obtain a desired pattern but the morphology of the pattern may also be used to influence the behavior of seeded cells. Herein, we 3D bioprinted a gelatin hydrogel microchannel construct to promote and preserve the contractile phenotype of vascular smooth muscle cells (vSMCs), which is crucial for vasoresponsiveness. The microchanneled surface of a gelatin hydrogel facilitated vSMC attachment and an elongated alignment along the microchannel direction. The cells displayed distinct F-actin anisotropy in the direction of the channel. The vSMC contractile phenotype was confirmed by the positive detection of contractile marker gene proteins (α-smooth muscle actin (α-SMA) and smooth muscle-myosin heavy chain (SM-MHC)). Having demonstrated the effectiveness of the hydrogel channels bioprinted on a film, the bioprinting was applied radially to the surface of a 3D tubular construct by integrating a rotating mandrel into the 3D bioprinter. The hydrogel microchannels printed on the 3D tubular vascular construct also orientated the vSMCs and strongly promoted the contractile phenotype. Together, our study demonstrated that microchannels bioprinted using a transglutaminase crosslinked gelatin hydrogel, could successfully promote and preserve vSMC contractile phenotype. Furthermore, the hydrogel bioink could be retained on the surface of a rotating polymer tube to print radial cell guiding channels onto a vascular graft construct.

Accurate and continuous ultrasonography evaluation of small diameter vascular prostheses in vivo.

There is a large clinical requirement for novel vascular grafts; however, the development of novel vascular grafts has not been extremely successful to date. The most successful method for the continuous evaluation of vascular grafts in vivo remains unclear. Therefore, an optimal successive, non-invasive imaging modality is necessary for the study of vascular transplantation. In the present study, a common rabbit model of carotid artery defect was utilized. The patency and hemodynamic characteristics of implanted grafts was examined following surgery by color Doppler ultrasound in three modes, including B-mode, color flow map and pulse-Doppler examination. The results revealed that ultrasound had sufficient spatial resolution to generate clear images of the carotid artery of rabbits with or without the implanted grafts. Color Doppler ultrasound may be applied to evaluate and differentiate the patent, stenosis and occlusion of carotid arteries in rabbits with different vascular grafts implanted. Furthermore, color Doppler ultrasound is an optimal imaging modality for continuous evaluation in vivo. It is also possible for some quantitative analyses to be performed, including measuring the diameter of vascular lumens and the flow velocity of the region of interest. The present study suggests vascular ultrasound as the optimum choice for continuous surveillance of vascular prostheses in vivo, which may provide valuable information about the grafts in order to greatly shorten the experimental period.

Performance improvements of the BNC tubes from unique double-silicone-tube bioreactors by introducing chitosan and heparin for application as small-diameter artificial blood vessels

In order to improve property of bacterial nano-cellulose (BNC) to achieve the requirements of clinical application as small caliber vascular grafts, chitosan (CH) was deposited into the fibril network of the BNC tubes fabricated in unique Double-Silicone-Tube bioreactors. Heparin (Hep) was then chemically grafted into the BNC-based tubes using EDC/NHS crosslinking to improve performance of anticoagulation and endothelialization. Physicochemical and mechanical property, blood compatibility, and cytocompatibility were compared before and after compositing. The results indicated that strength at break was increased but burst pressure decreased slightly after compositing. Performance of the BNC tubes was improved remarkably after introducing chitosan and heparin. The EDC/NHS crosslinking catalyzed both amide bonds and ester bonds formation in the BNC/CH-Hep composites. Three-dimensional surface structure and roughness were firstly obtained and discussed in relation to the hemocompatibility of BNC-based tubes. This work demonstrates the heparinized BNC-based tubes have great potential in application as small-diameter vascular prosthesis.

Influence of PEG on heparin release of heparin-loading PCL/PEG vascular prosthesis membranes

Objective To investigate the influence of polyethylene glycol (PEG) on heparin release of heparin-loaded polycaprolactone/polyethylene glycol (PCL/PEG) membranes used in artificial vascular peosthesis. Methods Heparin-loaded PCL/PEG membrane samples with different PEG mass contents of 0, 0.5%, 10% and 15% were prepared by blending method and freeze-drying technology. The influence of PEG on heparin release was experimental studied in vitro. The influence of PEG on the structural characteristics of the samples were investigated by X-ray diffraction, Fourier transform infrared spectrum and differential scanning calorimeter. Results The addition of PEG reduced the heparin release resistance. The results showed that the average release rate of heparin in the first day and the release amount for 34 d were improved. Both these parameters increased with the increase of PEG mass content. The X-ray diffraction, Fourier transform infrared spectroscopy and differential scanning calorimetry showed that the crystallinity of PCL membrane was slightly enhanced by the addition of heparin, but the overall effect was not significant. In addition, the addition of heparin could promote the crystalline grain growth of PEG, and a common distribution of heparin and PEG in the matrix was observed. Conclusions The heparin release control can be achieved by adjusting the PEG mass content in heparin-loading PCL/PEG membranes prepared by blending method and freeze-drying technology. The proposed samples may have anticoagulant effect, which can be expected to be used as small-diameter artificial vascular prosthesis material. Key words: Heparinization; Blending; Sustained release; Vascular membrane material