Development and in vivo evaluation of small-diameter vascular grafts engineered by outgrowth endothelial cells and electrospun chitosan/poly(ε-caprolactone) nanofibrous scaffolds

The influence of physical and spatial substrate characteristics on endothelial cells

Cardiovascular diseases are a main cause of death worldwide, leading to a growing demand for medical devices to treat this patient group. Central to the engineering of such devices is a good understanding of the biology and physics of cell-surface interactions. In existing blood-contacting devices, such as vascular grafts, the interaction between blood, cells, and material is one of the main limiting factors for their long-term durability. An improved understanding of the material's chemical- and physical properties as well as its structure all play a role in how endothelial cells interact with the material surface. This review provides an overview of how different surface structures influence endothelial cell responses and what is currently known about the underlying mechanisms that guide this behavior. The structures reviewed include decellularized matrices, electrospun fibers, pillars, pits, and grated surfaces.

Preparation and performance of random- and oriented-fiber membranes with core-shell structures via coaxial electrospinning

The cells and tissue in the human body are orderly and directionally arranged, and constructing an ideal biomimetic extracellular matrix is still a major problem to be solved in tissue engineering. In the field of the bioresorbable vascular grafts, the long-term functional prognosis requires that cells first migrate and grow along the physiological arrangement direction of the vessel itself. Moreover, the graft is required to promote the formation of neointima and the development of the vessel walls while ensuring that the whole repair process does not form a thrombus. In this study, poly (l-lactide-co-ε-caprolactone) (PLCL) shell layers and polyethylene oxide (PEO) core layers with different microstructures and loaded with sodium tanshinone IIA sulfonate (STS) were prepared by coaxial electrospinning. The mechanical properties proved that the fiber membranes had good mechanical support, higher than that of the human aorta, as well as great suture retention strengths. The hydrophilicity of the oriented-fiber membranes was greatly improved compared with that of the random-fiber membranes. Furthermore, we investigated the biocompatibility and hemocompatibility of different functional fiber membranes, and the results showed that the oriented-fiber membranes containing sodium tanshinone IIA sulfonate had an excellent antiplatelet adhesion effect compared to other fiber membranes. Cytological analysis confirmed that the functional fiber membranes were non-cytotoxic and had significant cell proliferation capacities. The oriented-fiber membranes induced cell growth along the orientation direction. Degradation tests showed that the pH variation range had little change, the material mass was gradually reduced, and the fiber morphology was slowly destroyed. Thus, results indicated the degradation rate of the oriented-fiber graft likely is suitable for the process of new tissue regeneration, while the random-fiber graft with a low degradation rate may cause the material to reside in the tissue for too long, which would impede new tissue reconstitution. In summary, the oriented-functional-fiber membranes possessing core-shell structures with sodium tanshinone IIA sulfonate/polyethylene oxide loading could be used as tissue engineering materials for applications such as vascular grafts with good prospects, and their clinical application potential will be further explored in future research.

Development and Preliminary Testing of Porcine Blood-Derived Endothelial-like Cells for Vascular Tissue Engineering Applications: Protocol Optimisation and Seeding of Decellularised Human Saphenous Veins

Functional endothelial cells (EC) are a critical interface between blood vessels and the thrombogenic flowing blood. Disruption of this layer can lead to early thrombosis, inflammation, vessel restenosis, and, following coronary (CABG) or peripheral (PABG) artery bypass graft surgery, vein graft failure. Blood-derived ECs have shown potential for vascular tissue engineering applications. Here, we show the development and preliminary testing of a method for deriving porcine endothelial-like cells from blood obtained under clinical conditions for use in translational research. The derived cells show cobblestone morphology and expression of EC markers, similar to those seen in isolated porcine aortic ECs (PAEC), and when exposed to increasing shear stress, they remain viable and show mRNA expression of EC markers similar to PAEC. In addition, we confirm the feasibility of seeding endothelial-like cells onto a decellularised human vein scaffold with approximately 90% lumen coverage at lower passages, and show that increasing cell passage results in reduced endothelial coverage.

Mitomycin-Treated Endothelial and Smooth Muscle Cells Suitable for Safe Tissue Engineering Approaches

In our previous study, we showed that discarded cardiac tissue from the right atrial appendage and right ventricular myocardium is an available source of functional endothelial and smooth muscle cells for regenerative medicine and tissue engineering. In the study, we aimed to find out what benefits are given by vascular cells from cardiac explants used for seeding on vascular patches engrafted to repair vascular defects in vivo. Additionally, to make the application of these cells safer in regenerative medicine we tested an in vitro approach that arrested mitotic division to avoid the potential tumorigenic effect of dividing cells. A tissue-engineered construction in the form of a patch based on a polycaprolactone-gelatin scaffold and seeded with endothelial and smooth muscle cells was implanted into the abdominal aorta of immunodeficient SCID mice. Aortic patency was assessed using ultrasound, MRI, immunohistochemical and histological staining. Endothelial and smooth muscle cells were treated with mitomycin C at a therapeutic concentration of 10 μg/ml for 2 h with subsequent analysis of cell proliferation and function. The absence of the tumorigenic effect of mitomycin C-treated cells, as well as their angiogenic potential, was examined by injecting them into immunodeficient mice. Cell-containing patches engrafted in the abdominal aorta of immunodeficient mice form the vessel wall loaded with the appropriate cells and extracellular matrix, and do not interfere with normal patency. Endothelial and smooth muscle cells treated with mitomycin C show no tumorigenic effect in the SCID immunodeficient mouse model. During in vitro experiments, we have shown that treatment with mitomycin C does not lead to a decrease in cell viability. Despite the absence of proliferation, mitomycin C-treated vascular cells retain specific cell markers, produce specific extracellular matrix, and demonstrate the ability to stimulate angiogenesis in vivo. We pioneered an approach to arresting cell division with mitomycin C in endothelial and smooth muscle cells from cardiac explant, which prevents the risk of malignancy from dividing cells in vascular surgery. We believe that this approach to the fabrication of tissue-engineered constructs based on mitotically inactivated cells from waste postoperative material may be valuable to bring closer the development of safe cell products for regenerative medicine.

Biofabrication of small diameter tissue-engineered vascular grafts

Current clinical treatment strategies for the bypassing of small diameter (<6 mm) blood vessels in the management of cardiovascular disease frequently fail due to a lack of suitable autologous grafts, as well as infection, thrombosis, and intimal hyperplasia associated with synthetic grafts. The rapid advancement of 3D printing and regenerative medicine technologies enabling the manufacture of biological, tissue-engineered vascular grafts (TEVGs) with the ability to integrate, remodel, and repair in vivo, promises a paradigm shift in cardiovascular disease management. This review comprehensively covers current state-of-the-art biofabrication technologies for the development of biomimetic TEVGs. Various scaffold based additive manufacturing methods used in vascular tissue engineering, including 3D printing, bioprinting, electrospinning and melt electrowriting, are discussed and assessed against the biomechanical and functional requirements of human vasculature, while the efficacy of decellularization protocols currently applied to engineered and native vessels are evaluated. Further, we provide interdisciplinary insight into the outlook of regenerative medicine for the development of vascular grafts, exploring key considerations and perspectives for the successful clinical integration of evolving technologies. It is expected that continued advancements in microscale additive manufacturing, biofabrication, tissue engineering and decellularization will culminate in the development of clinically viable, off-the-shelf TEVGs for small diameter applications in the near future. STATEMENT OF SIGNIFICANCE: Current clinical strategies for the management of cardiovascular disease using small diameter vessel bypassing procedures are inadequate, with up to 75% of synthetic grafts failing within 3 years of implantation. It is this critically important clinical problem that researchers in the field of vascular tissue engineering and regenerative medicine aim to alleviate using biofabrication methods combining additive manufacturing, biomaterials science and advanced cellular biology. While many approaches facilitate the development of bioengineered constructs which mimic the structure and function of native blood vessels, several challenges must still be overcome for clinical translation of the next generation of tissue-engineered vascular grafts.

Novel reinforcement of corrugated nanofiber tissue-engineered vascular graft to prevent aneurysm formation for arteriovenous shunts in an ovine model

Objective

Many patients who require hemodialysis treatment will often require a prosthetic graft after multiple surgeries. However, the patency rate of grafts currently available commercially has not been satisfactory. Tissue engineering vascular grafts (TEVGs) are biodegradable scaffolds created to promote autologous cell proliferation and functional neotissue regeneration and, accordingly, have antithrombogenicity. Therefore, TEVGs can be an alternative prosthesis for small diameter grafts. However, owing to the limitations of the graft materials, most TEVGs are rigid and can easily kink when implanted in limited spaces, precluding future clinical application. Previously, we developed a novel corrugated nanofiber graft to prevent graft kinking. Reinforcement of these grafts to ensure their safety is required in a preclinical study. In the present study, three types of reinforcement were applied, and their effectiveness was examined using large animals.

Methods

In the present study, three different reinforcements for the graft composed of corrugated poly-ε-caprolactone (PCL) blended with poly(L-lactide-co-ε-caprolactone) (PLCL) created with electrospinning were evaluated: 1) a polydioxanone suture, 2) a 2-0 polypropylene suture, 3) a polyethylene terephthalate/polyurethane (PET/PU) outer layer, and PCL/PLCL as the control. These different grafts were then implanted in a U-shape between the carotid artery and jugular vein in seven ovine models for a total of 14 grafts during a 3-month period. In evaluating the different reinforcements, the main factors considered were cell proliferation and a lack of graft dilation, which were evaluated using ultrasound examinations and histologic and mechanical analysis.

Results

No kinking of the grafts occurred. Overall, re-endothelialization was observed in all the grafts at 3 months after surgery without graft rupture or calcification. The PCL/PLCL grafts and PCL/PLCL grafts with a polydioxanone suture showed high cell infiltration; however, they had become dilated 10 weeks after surgery. In contrast, the PCL/PLCL graft with the 2-0 suture and the PCL/PLCL graft covered with a PET/PU layer did not show any graft expansion. The PCL/PLCL graft covered with a PET/PU layer showed less cell infiltration than that of the PCL/PLCL graft.

Conclusions

Reinforcement is required to create grafts that can withstand arterial pressure. Reinforcement with suture materials has the potential to maintain cell infiltration into the graft, which could improve the neotissue formation of the graft.

In our basic science research study, we investigated tissue engineered vascular grafts for arteriovenous shunts. Our grafts were created with poly-ε-caprolactone and poly(L-lactide-co-ε-caprolactone) and designed with corrugated walls to avoid graft kinking. The grafts were implanted between the carotid artery and external jugular vein in a U-shape using an ovine model. To withstand the high pressure of blood on the arterial system, two types of reinforcement were applied to these tissue engineering vascular grafts. Because reinforcement of the graft could interfere with cell infiltration into the tissue engineering vascular grafts, the methods and material of reinforcement were investigated, in addition to the mechanical properties of the graft.

Failure Analysis of TEVG's I: Overcoming the Initial Stages of Blood Material Interaction and Stabilization of the Immune Response

Vascular grafts (VG) are medical devices intended to replace the function of a diseased vessel. Current approaches use non-biodegradable materials that struggle to maintain patency under complex hemodynamic conditions. Even with the current advances in tissue engineering and regenerative medicine with the tissue engineered vascular grafts (TEVGs), the cellular response is not yet close to mimicking the biological function of native vessels, and the understanding of the interactions between cells from the blood and the vascular wall with the material in operative conditions is much needed. These interactions change over time after the implantation of the graft. Here we aim to analyze the current knowledge in bio-molecular interactions between blood components, cells and materials that lead either to an early failure or to the stabilization of the vascular graft before the wall regeneration begins.

The performance of heparin modified poly(ε-caprolactone) small diameter tissue engineering vascular graft in canine-A long-term pilot experiment in vivo

Long-term in vivo observation in large animal model is critical for evaluating the potential of small diameter tissue engineering vascular graft (SDTEVG) in clinical application, but is rarely reported. In this study, a SDTEVG is fabricated by the electrospinning of poly(ε-caprolactone) and subsequent heparin modification. SDTEVG is implanted into canine's abdominal aorta for 511 days in order to investigate its clinical feasibility. An active and robust remodeling process was characterized by a confluent endothelium, macrophage infiltrate, extracellular matrix deposition and remodeling on the explanted graft. The immunohistochemical and immunofluorescence analysis further exhibit the regeneration of endothelium and smooth muscle layer on tunica intima and tunica media, respectively. Thus, long-term follow-up reveals viable neovessel formation beyond graft degradation. Furthermore, the von Kossa staining exhibits no occurrence of calcification. However, although no TEVG failure or rupture happens during the follow-up, the aneurysm is found by both Doppler ultrasonic and gross observation. Consequently, as-prepared TEVG shows promising potential in vascular tissue engineering if it can be appropriately strengthened to prevent the occurrence of aneurysm.

Biofabrication of tissue engineering vascular systems

Cardiovascular disease (CVD) is the leading cause of death among persons aged 65 and older in the United States and many other developed countries. Tissue engineered vascular systems (TEVS) can serve as grafts for CVD treatment and be used as in vitro model systems to examine the role of various genetic factors during the CVD progressions. Current focus in the field is to fabricate TEVS that more closely resembles the mechanical properties and extracellular matrix environment of native vessels, which depends heavily on the advance in biofabrication techniques and discovery of novel biomaterials. In this review, we outline the mechanical and biological design requirements of TEVS and explore the history and recent advances in biofabrication methods and biomaterials for tissue engineered blood vessels and microvascular systems with special focus on in vitro applications. In vitro applications of TEVS for disease modeling are discussed.

Review: Tissue Engineering of Small-Diameter Vascular Grafts and Their In Vivo Evaluation in Large Animals and Humans

To date, a wide range of materials, from synthetic to natural or a mixture of these, has been explored, modified, and examined as small-diameter tissue-engineered vascular grafts (SD-TEVGs) for tissue regeneration either in vitro or in vivo. However, very limited success has been achieved due to mechanical failure, thrombogenicity or intimal hyperplasia, and improvements of the SD-TEVG design are thus required. Here, in vivo studies investigating novel and relative long (10 times of the inner diameter) SD-TEVGs in large animal models and humans are identified and discussed, with emphasis on graft outcome based on model- and graft-related conditions. Only a few types of synthetic polymer-based SD-TEVGs have been evaluated in large-animal models and reflect limited success. However, some polymers, such as polycaprolactone (PCL), show favorable biocompatibility and potential to be further modified and improved in the form of hybrid grafts. Natural polymer- and cell-secreted extracellular matrix (ECM)-based SD-TEVGs tested in large animals still fail due to a weak strength or thrombogenicity. Similarly, native ECM-based SD-TEVGs and in-vitro-developed hybrid SD-TEVGs that contain xenogeneic molecules or matrix seem related to a harmful graft outcome. In contrast, allogeneic native ECM-based SD-TEVGs, in-vitro-developed hybrid SD-TEVGs with allogeneic banked human cells or isolated autologous stem cells, and in-body tissue architecture (IBTA)-based SD-TEVGs seem to be promising for the future, since they are suitable in dimension, mechanical strength, biocompatibility, and availability.

Selection of different endothelialization modes and different seed cells for tissue-engineered vascular graft

Tissue-engineered vascular grafts (TEVGs) have enormous potential for vascular replacement therapy. However, thrombosis and intimal hyperplasia are important problems associated with TEVGs especially small diameter TEVGs (<6 mm) after transplantation. Endothelialization of TEVGs is a key point to prevent thrombosis. Here, we discuss different types of endothelialization and different seed cells of tissue-engineered vascular grafts. Meanwhile, endothelial heterogeneity is also discussed. Based on it, we provide a new perspective for selecting suitable types of endothelialization and suitable seed cells to improve the long-term patency rate of tissue-engineered vascular grafts with different diameters and lengths.

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The material, diameter and length of tissue-engineered vascular graft are all key factors affecting its long-term patency.

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Endothelialization strategies should consider the different diameters and lengths of tissue-engineered vascular grafts.

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Cell heterogeneity and tissue heterogeneity should be considered in the application of seed cells.

The effect of pore diameter on neo-tissue formation in electrospun biodegradable tissue-engineered arterial grafts in a large animal model

To date, there has been little investigation of biodegradable tissue engineered arterial grafts (TEAG) using clinically relevant large animal models. The purpose of this study is to explore how pore size of electrospun scaffolds can be used to balance neoarterial tissue formation with graft structural integrity under arterial environmental conditions throughout the remodeling process. TEAGs were created with an outer poly-ε-caprolactone (PCL) electrospun layer and an inner sponge layer composed of heparin conjugated 50:50 poly (l-lactide-co-ε-caprolactone) copolymer (PLCL). Outer electrospun layers were created with four different pore diameters (4, 7, 10, and 15 µm). Fourteen adult female sheep underwent bilateral carotid artery interposition grafting (n = 3-4 /group). Our heparin-eluting TEAG was implanted on one side (n = 14) and ePTFE graft (n = 3) or non-heparin-eluting TEAG (n = 5) on the other side. Twelve of the fourteen animals survived to the designated endpoint at 8 weeks, and one animal with 4 µm pore diameter graft was followed to 1 year. All heparin-eluting TEAGs were patent, but those with pore diameters larger than 4 µm began to dilate at week 4. Only scaffolds with a pore diameter of 4 µm resisted dilation and could do so for up to 1 year. At 8 weeks, the 10 µm pore graft had the highest density of cells in the electrospun layer and macrophages were the primary cell type present. This study highlights challenges in designing bioabsorbable TEAGs for the arterial environment in a large animal model. While larger pore diameter TEAGs promoted cell infiltration, neotissue could not regenerate rapidly enough to provide sufficient mechanical strength required to resist dilation. Future studies will be focused on evaluating a smaller pore design to better understand long-term remodeling and determine feasibility for clinical use. STATEMENT OF SIGNIFICANCE: In situ vascular tissue engineering relies on a biodegradable scaffold that encourages tissue regeneration and maintains mechanical integrity until the neotissue can bear the load. Species-specific differences in tissue regeneration and larger mechanical forces often result in graft failure when scaling up from small to large animal models. This study utilizes a slow-degrading electrospun PCL sheath to reinforce a tissue engineered arterials graft. Pore size, a property critical to tissue regeneration, was controlled by changing PCL fiber diameter and the resulting effects of these properties on neotissue formation and graft durability was evaluated. This study is among few to report the effect of pore size on vascular neotissue formation in a large animal arterial model and also demonstrate robust neotissue formation.

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

Objective

Prosthetic 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.

Methods

TEVGs 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.

Results

All 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.

Conclusions

Our novel corrugated nanofiber vascular graft displayed neotissue formation without kinking in large animal model.

This basic science research article reported tissue-engineered vascular grafts for arteriovenous shunt procedures. Nanofibrous grafts were electrospun with polyglycolic acid and poly-ε-caprolactone with a corrugated wall design to prevent graft kinking. The tissue-engineered vascular grafts were then implanted in U-shape between the carotid artery and the external jugular vein of an ovine model. This graft had 87.5% patency rate and did not display significant kinking. Overall, re-endothelialization was observed in the grafts one month after the surgeries without graft rupture, calcification or aneurysmal change. This graft is a promising alternative to small diameter prosthetic grafts.

Waterproof breathable layers - A review

Waterproof breathable layers (WPBLs) can be classified into two large groups of hydrophilic nonporous and hydrophobic porous layers. These layers (e.g., fabrics, films, membranes, and meshes) can be produced by various continuous and non-continuous processes such as coating, laminating, film stretching, casting, etc. The most common methods for production, characterization, and testing of WPBLs are presented and discussed in light of recent publications. The materials with high level of waterproofness and breathability are often used in outerwear for winter sports, sailing apparel, raincoats, military/police jackets, backpacks, tents, cargo raps, footwear and etc. WPBLs can also be used for other specialized applications such as membrane distillation, oil-water filtration, and wound dressing. These applications are discussed by presenting several good examples. The main challenge in the production of these layers is to compromise between waterproofness and breathability with opposing nature. The related research gaps, challenges, and future outlook are highlighted to shed more light on the topic.

Concise Review: Patency of Small-Diameter Tissue-Engineered Vascular Grafts: A Meta-Analysis of Preclinical Trials

Several patient groups undergoing small‐diameter (<6 mm) vessel bypass surgery have limited autologous vessels for use as grafts. Tissue‐engineered vascular grafts (TEVG) have been suggested as an alternative, but the ideal TEVG remains to be generated, and a systematic overview and meta‐analysis of clinically relevant studies is lacking. We systematically searched PubMed and Embase databases for (pre)clinical trials and identified three clinical and 68 preclinical trials ([>rabbit]; 873 TEVGs) meeting the inclusion criteria. Preclinical trials represented low to medium risk of bias, and binary logistic regression revealed that patency was significantly affected by recellularization, TEVG length, TEVG diameter, surface modification, and preconditioning. In contrast, scaffold types were less important. The patency was 63.5%, 89%, and 100% for TEVGs with a median diameter of 3 mm, 4 mm, and 5 mm, respectively. In the group of recellularized TEVGs, patency was not improved by using smooth muscle cells in addition to endothelial cells nor affected by the endothelial origin, but seems to benefit from a long‐term (46–240 hours) recellularization time. Finally, data showed that median TEVG length (5 cm) and median follow‐up (56 days) used in preclinical settings are relatively inadequate for direct clinical translation. In conclusion, our data imply that future studies should consider a TEVG design that at least includes endothelial recellularization and bioreactor preconditioning, and we suggest that more standard guidelines for testing and reporting TEVGs in large animals should be considered to enable interstudy comparisons and favor a robust and reproducible outcome as well as clinical translation.

Fabrication of Kidney Proximal Tubule Grafts Using Biofunctionalized Electrospun Polymer Scaffolds

The increasing prevalence of end-stage renal disease and persistent shortage of donor organs call for alternative therapies for kidney patients. Dialysis remains an inferior treatment as clearance of large and protein-bound waste products depends on active tubular secretion. Biofabricated tissues could make a valuable contribution, but kidneys are highly intricate and multifunctional organs. Depending on the therapeutic objective, suitable cell sources and scaffolds must be selected. This study provides a proof-of-concept for stand-alone kidney tubule grafts with suitable mechanical properties for future implantation purposes. Porous tubular nanofiber scaffolds are fabricated by electrospinning 12%, 16%, and 20% poly-ε-caprolactone (PCL) v/w (chloroform and dimethylformamide, 1:3) around 0.7 mm needle templates. The resulting scaffolds consist of 92%, 69%, and 54% nanofibers compared to microfibers, respectively. After biofunctionalization with L-3,4-dihydroxyphenylalanine and collagen IV, 10 × 106 proximal tubule cells per mL are injected and cultured until experimental readout. A human-derived cell model can bridge all fiber-to-fiber distances to form a monolayer, whereas small-sized murine cells form monolayers on dense nanofiber meshes only. Fabricated constructs remain viable for at least 3 weeks and maintain functionality as shown by inhibitor-sensitive transport activity, which suggests clearance capacity for both negatively and positively charged solutes.

Biological effects different diameters of Tussah silk fibroin nanofibers on olfactory ensheathing cells

Transplantation of olfactory ensheathing cells (OECs) has potential for treating spinal cord and brain injury. However, they are void of an extracellular matrix to support cell growth and migration. Engineering of tissue to mimic the extracellular matrix is a potential solution for neural repair. Tussah silk fibroin (TSF) has good biocompatibility and an Arg-Gly-Asp tripeptide sequence. A small number of studies have assessed the effect of the diameter of TSF nanofibers on cell adhesion, growth and migration. In the present study, TSF nanofibers with a diameter of 400 and 1,200 nm were prepared using electrospinning technology; these were then used as scaffolds for OECs. The structure and morphology of the TSF nanofibers were characterized by scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy. An inverted-phase contrast microscope and SEM were used to observe the morphology of OECs on the TSF nanofibers. The effect on the adhesion of the cells was observed following crystal violet staining. The phenotype of the cells and the maximum axon length on the scaffolds were evaluated by immunostaining for nerve growth factor receptor p75. Cell proliferation and viability were assessed by an MTT assay and a Live/Dead reagent kit. The migration efficiency of OECs was observed using live-cell microscopy. The results indicated that a 400-nm TSF fiber scaffold was more conducive to OEC adhesion, growth and migration compared with a 1,200-nm TSF scaffold. The phenotype of the OECs was normal, and no difference in OEC phenotype was observe when comparing those on TSF nanofibers to those on PLL. The present study may provide guidance regarding the preparation of tissue-engineered materials for neural repair.

Tissue Engineering at the Blood-Contacting Surface: A Review of Challenges and Strategies in Vascular Graft Development

Tissue engineered vascular grafts (TEVGs) are beginning to achieve clinical success and hold promise as a source of grafting material when donor grafts are unsuitable or unavailable. Significant technological advances have generated small-diameter TEVGs that are mechanically stable and promote functional remodeling by regenerating host cells. However, developing a biocompatible blood-contacting surface remains a major challenge. The TEVG luminal surface must avoid negative inflammatory responses and thrombogenesis immediately upon implantation and promote endothelialization. The surface has therefore become a primary focus for research and development efforts. The current state of TEVGs is herein reviewed with an emphasis on the blood-contacting surface. General vascular physiology and developmental challenges and strategies are briefly described, followed by an overview of the materials currently employed in TEVGs. The use of biodegradable materials and stem cells requires careful control of graft composition, degradation behavior, and cell recruitment ability to ensure that a physiologically relevant vessel structure is ultimately achieved. The establishment of a stable monolayer of endothelial cells and the quiescence of smooth muscle cells are critical to the maintenance of patency. Several strategies to modify blood-contacting surfaces to resist thrombosis and control cellular recruitment are reviewed, including coatings of biomimetic peptides and heparin.

Building Blood Vessels with Vascular Progenitor Cells

Vascular progenitor cells have been identified from perivascular cell fractions and peripheral blood and bone marrow mononuclear fractions. These vascular progenitors share the ability to generate some of the vascular lineages, including endothelial cells, smooth muscle cells, and pericytes. The potential therapeutic uses for vascular progenitor cells are broad and relate to stroke, ischemic disease, and to the engineering of whole organs and tissues that require a vascular component. This review summarizes the best-characterized sources of vascular progenitor cells and discusses advances in 3D printing and electrospinning using blended polymers for the creation of biomimetic vascular grafts. These advances are pushing the field of regenerative medicine closer to the creation of small-diameter vascular grafts with long-term clinical utility.

Performance of marrow stromal cell-seeded small-caliber multilayered vascular graft in a senescent sheep model

Failure of small-caliber grafts, used as bypass or reconstructive grafts in cardiovascular treatments, is often caused by thrombosis and stenosis. We have developed a multilayered, compliant graft with an electrospun heparin-encapsulated core and collagen-chitosan shell. Herein, the performances of acellular and cell-seeded grafts were evaluated in adult sheep for preclinical assessment. Allogeneic ovine marrow stroma cells (MSCs) were uniformly attached to the lumen of cell-seeded grafts. Interposition grafts were used for carotid arteries. Four grafts were tested for each type. Upon implantation, all grafts successfully restored perfusion and rhythmically deformed under pulsatile arterial flow. Weekly ultrasonography and Doppler revealed that all grafts remained patent for perfusion during the course of one-month study. No formation of blood clots or other complications were found. The diameter of graft lumen did not vary significantly over the time or with the graft type, while narrowing at anastomosis and significant thickening of graft wall were found in both types of grafts. More significant neotissue formation was found at anastomotic sections of acellular controls compared to cell-seeded grafts. Results from histological and immunofluorescent analyses revealed moderate intimal hyperplasia (IH) at anastomosis. When compared to cell-seeded grafts, acellular controls presented thicker IH composed of α-smooth muscle actin positive cells and ground substances, which correlated with reduced and more disturbing flow. IH was thickest at anastomosis and tapered off to a minimum in the mid-section. Few PECAM-positive cells appeared on cell-seeded grafts but not acellular controls. Additionally, lesser graft thickening was found in cell-seed grafts, which might be associated with the function of stromal cells in altering the fibrotic process during tissue repair. Results suggest that MSCs held the potential to reduce hyperplasia and improve healing in an aged, large animal model for vascular grafting.

Review of Vascular Graft Studies in Large Animal Models

As the incidence of cardiovascular disease continues to climb worldwide, there is a corresponding increase in demand for surgical interventions involving vascular grafts. The current gold standard for vascular grafts is autologous vessels, an option often excluded due to disease circumstances. As a result, many patients must resort to prosthetic options. While widely available, prosthetic grafts have been demonstrated to have inferior patency rates compared with autologous grafts due to inflammation and thrombosis. In an attempt to overcome these limitations, many different materials for constructing vascular grafts, from modified synthetic nondegradable polymers to biodegradable polymers, have been explored, many of which have entered the translational stage of research. This article reviews these materials in the context of large animal models, providing an outlook on the preclinical potential of novel biomaterials as well as the future direction of vascular graft research.

Versatility of Chitosan-Based Biomaterials and Their Use as Scaffolds for Tissue Regeneration

Chitosan is a naturally occurring polysaccharide obtained from chitin, present in abundance in the exoskeletons of crustaceans and insects. It has aroused great interest as a biomaterial for tissue engineering on account of its biocompatibility and biodegradation and its affinity for biomolecules. A significant number of research groups have investigated the application of chitosan as scaffolds for tissue regeneration. However, there is a wide variability in terms of physicochemical characteristics of chitosan used in some studies and its combinations with other biomaterials, making it difficult to compare results and standardize its properties. The current systematic review of literature on the use of chitosan for tissue regeneration consisted of a study of 478 articles in the PubMed database, which resulted, after applying inclusion criteria, in the selection of 61 catalogued, critically analysed works. The results demonstrated the effectiveness of chitosan-based biomaterials in 93.4% of the studies reviewed, whether or not combined with cells and growth factors, in the regeneration of various types of tissues in animals. However, the absence of clinical studies in humans, the inadequate experimental designs, and the lack of information concerning chitosan's characteristics limit the reproducibility and relevance of studies and the clinical applicability of chitosan.

Chitosan-Poly(caprolactone) Nanofibers for Skin Repair

Dermal wounds, both acute and chronic, represent a significant clinical challenge and therefore the development of novel biomaterial-based skin substitutes to promote skin repair is essential. Nanofibers have garnered attention as materials to promote skin regeneration due to the similarities in morphology and dimensionality between nanofibers and native extracellular matrix proteins, which are critical in guiding cutaneous wound healing. Electrospun chitosan-poly(caprolactone) (CPCL) nanofiber scaffolds, which combine the important intrinsic biological properties of chitosan and the mechanical integrity and stability of PCL, were evaluated as skin tissue engineering scaffolds using a mouse cutaneous excisional skin defect model. Gross assessment of wound size and measurement of defect recovery over time as well as histological evaluation of wound healing showed that CPCL nanofiber scaffolds increased wound healing rate and promoted more complete wound closure as compared with Tegaderm, a commercially available occlusive dressing. CPCL nanofiber scaffolds represent a biomimetic approach to skin repair by serving as an immediately available provisional matrix to promote wound closure. These nanofiber scaffolds may have significant potential as a skin substitute or as the basis for more complex skin tissue engineering constructs involving integration with biologics.

Endothelial and smooth muscle cells derived from human cardiac explants demonstrate angiogenic potential and suitable for design of cell-containing vascular grafts

Background

Endothelial and smooth muscle cells are considered promising resources for regenerative medicine and cell replacement therapy. It has been shown that both types of cells are heterogeneous depending on the type of vessels and organs in which they are located. Therefore, isolation of endothelial and smooth muscle cells from tissues relevant to the area of research is necessary for the adequate study of specific pathologies. However, sources of specialized human endothelial and smooth muscle cells are limited, and the search for new sources is still relevant. The main goal of our study is to demonstrate that functional endothelial and smooth muscle cells can be obtained from an available source—post-surgically discarded cardiac tissue from the right atrial appendage and right ventricular myocardium.

Methods

Heterogeneous primary cell cultures were enzymatically isolated from cardiac explants and then grown in specific endothelial and smooth muscle growth media on collagen IV-coated surfaces. The population of endothelial cells was further enriched by immunomagnetic sorting for CD31, and the culture thus obtained was characterized by immunocytochemistry, ultrastructural analysis and in vitro functional tests. The angiogenic potency of the cells was examined by injecting them, along with Matrigel, into immunodeficient mice. Cells were also seeded on characterized polycaprolactone/chitosan membranes with subsequent analysis of cell proliferation and function.

Results

Endothelial cells isolated from cardiac explants expressed CD31, VE-cadherin and VEGFR2 and showed typical properties, namely, cytoplasmic Weibel-Palade bodies, metabolism of acetylated low-density lipoproteins, formation of capillary-like structures in Matrigel, and production of extracellular matrix and angiogenic cytokines. Isolated smooth muscle cells expressed extracellular matrix components as well as α-actin and myosin heavy chain. Vascular cells derived from cardiac explants demonstrated the ability to stimulate angiogenesis in vivo. Endothelial cells proliferated most effectively on membranes made of polycaprolactone and chitosan blended in a 25:75 ratio, neutralized by a mixture of alkaline and ethanol. Endothelial and smooth muscle cells retained their functional properties when seeded on the blended membranes.

Conclusions

We established endothelial and smooth muscle cell cultures from human right atrial appendage and right ventricle post-operative explants. The isolated cells revealed angiogenic potential and may be a promising source of patient-specific cells for regenerative medicine.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-017-1156-1) contains supplementary material, which is available to authorized users.

Preparation and characterization of carbon nanofibrous/hydroxyapatite sheets for bone tissue engineering

Critical size bone defects are orthopedic defects that will not heal without intervention or that will not completely heal over the natural life time of the animal. Although bone generally has the ability to regenerate completely however, critical defects require some sort of scaffold to do so. In the current study we proposed a method to obtain a carbon nanofibrous/Hydroxyapatite (HA) bioactive scaffold. The carbon nanofibrous (CNF) nonwoven fabrics were obtained by the use of the electrospinning process of the polymeric solution of poly acrylonitrile "PAN" and subsequent stabilization and carbonization processes. The CNFs sheets were functionalized by both hydroxyapatite (HA) and bovine serum albumin (BSA). The HA was added to the electrospun solution, but in case of (BSA), it was adsorbed after the carbonization process. The changes in the properties taking place in the precursor sheets were investigated using the characterization methods (SEM, FT-IR, TGA and EDX). The prepared materials were tested for biocompatibility via subcutaneous implantation in New Zealand white rabbits. We successfully prepared biocompatible functionalized sheets, which have been modified with HA or HA and BSA. The sheets that were functionalized by both HA and BSA are more biocompatible with fewer inflammatory cells of (neutrophils and lymphocytes) than ones with only HA over the period of 3weeks.

Perivascular cells and tissue engineering: Current applications and untapped potential

The recent development of tissue engineering provides exciting new perspectives for the replacement of failing organs and the repair of damaged tissues. Perivascular cells, including vascular smooth muscle cells, pericytes and other tissue specific populations residing around blood vessels, have been isolated from many organs and are known to participate to the in situ repair process and angiogenesis. Their potential has been harnessed for cell therapy of numerous pathologies; however, in this Review we will discuss the potential of perivascular cells in the development of tissue engineering solutions for healthcare. We will examine their application in the engineering of vascular grafts, cardiac patches and bone substitutes as well as other tissue engineering applications and we will focus on their extensive use in the vascularization of engineered constructs. Additionally, we will discuss the emerging potential of human pericytes for the development of efficient, vascularized and non-immunogenic engineered constructs.

Preclinical study of patient-specific cell-free nanofiber tissue-engineered vascular grafts using 3-dimensional printing in a sheep model

BACKGROUND

Tissue-engineered vascular grafts (TEVGs) offer potential to overcome limitations of current approaches for reconstruction in congenital heart disease by providing biodegradable scaffolds on which autologous cells proliferate and provide physiologic functionality. However, current TEVGs do not address the diverse anatomic requirements of individual patients. This study explores the feasibility of creating patient-specific TEVGs by combining 3-dimensional (3D) printing and electrospinning technology.

METHODS

An electrospinning mandrel was 3D-printed after computer-aided design based on preoperative imaging of the ovine thoracic inferior vena cava (IVC). TEVG scaffolds were then electrospun around the 3D-printed mandrel. Six patient-specific TEVGs were implanted as cell-free IVC interposition conduits in a sheep model and explanted after 6 months for histologic, biochemical, and biomechanical evaluation.

RESULTS

All sheep survived without complications, and all grafts were patent without aneurysm formation or ectopic calcification. Serial angiography revealed significant decreases in TEVG pressure gradients between 3 and 6 months as the grafts remodeled. At explant, the nanofiber scaffold was nearly completely resorbed and the TEVG showed similar mechanical properties to that of native IVC. Histological analysis demonstrated an organized smooth muscle cell layer, extracellular matrix deposition, and endothelialization. No significant difference in elastin and collagen content between the TEVG and native IVC was identified. There was a significant positive correlation between wall thickness and CD68⁺ macrophage infiltration into the TEVG.

CONCLUSIONS

Creation of patient-specific nanofiber TEVGs by combining electrospinning and 3D printing is a feasible technology as future clinical option. Further preclinical studies involving more complex anatomical shapes are warranted.

Tissue-Engineered Small Diameter Arterial Vascular Grafts from Cell-Free Nanofiber PCL/Chitosan Scaffolds in a Sheep Model

Tissue engineered vascular grafts (TEVGs) have the potential to overcome the issues faced by existing small diameter prosthetic grafts by providing a biodegradable scaffold where the patient’s own cells can engraft and form functional neotissue. However, applying classical approaches to create arterial TEVGs using slow degrading materials with supraphysiological mechanical properties, typically results in limited host cell infiltration, poor remodeling, stenosis, and calcification. The purpose of this study is to evaluate the feasibility of novel small diameter arterial TEVGs created using fast degrading material. A 1.0mm and 5.0mm diameter TEVGs were fabricated with electrospun polycaprolactone (PCL) and chitosan (CS) blend nanofibers. The 1.0mm TEVGs were implanted in mice (n = 3) as an unseeded infrarenal abdominal aorta interposition conduit., The 5.0mm TEVGs were implanted in sheep (n = 6) as an unseeded carotid artery (CA) interposition conduit. Mice were followed with ultrasound and sacrificed at 6 months. All 1.0mm TEVGs remained patent without evidence of thrombosis or aneurysm formation. Based on small animal outcomes, sheep were followed with ultrasound and sacrificed at 6 months for histological and mechanical analysis. There was no aneurysm formation or calcification in the TEVGs. 4 out of 6 grafts (67%) were patent. After 6 months in vivo, 9.1 ± 5.4% remained of the original scaffold. Histological analysis of patent grafts demonstrated deposition of extracellular matrix constituents including elastin and collagen production, as well as endothelialization and organized contractile smooth muscle cells, similar to that of native CA. The mechanical properties of TEVGs were comparable to native CA. There was a significant positive correlation between TEVG wall thickness and CD68⁺ macrophage infiltration into the scaffold (R² = 0.95, p = 0.001). The fast degradation of CS in our novel TEVG promoted excellent cellular infiltration and neotissue formation without calcification or aneurysm. Modulating host macrophage infiltration into the scaffold is a key to reducing excessive neotissue formation and stenosis.

Therapeutic Potential of Human-Derived Endothelial Colony-Forming Cells in Animal Models

PURPOSE OF REVIEW

Tissue regeneration requires proper vascularization. In vivo studies identified that the endothelial colony-forming cells (ECFCs), a subtype of endothelial progenitor cells that can be isolated from umbilical cord or peripheral blood, represent a promising cell source for therapeutic neovascularization. ECFCs not only are able to initiate and facilitate neovascularization in diseased tissue but also can, by acting in a paracrine manner, contribute to the creation of favorable conditions for efficient and appropriate differentiation of tissue-resident stem or progenitor cells. This review outlines the progress in the field of in vivo regenerative and tissue engineering studies and surveys why, when, and how ECFCs can be used for tissue regeneration.

RECENT FINDINGS

Reviewed literature that regard human-derived ECFCs in xenogeneic animal models implicates that ECFCs should be considered as an endothelial cell source of preference for induction of neovascularization. Their neovascularization and regenerative potential is augmented in combination with other types of stem or progenitor cells. Biocompatible scaffolds prevascularized with ECFCs interconnect faster and better with the host vasculature. The physical incorporation of ECFCs in newly formed blood vessels grants prolonged release of trophic factors of interest, which also makes ECFCs an interesting cell source candidate for gene therapy and delivery of bioactive compounds in targeted area.

SUMMARY

ECFCs possess all biological features to be considered as a cell source of preference for tissue engineering and repair of blood supply. Investigation of regenerative potential of ECFCs in autologous settings in large animal models before clinical application is the next step to clearly outline the most efficient strategy for using ECFCs as treatment.

Synthesis and characterization of polycaprolactone urethane hollow fiber membranes as small diameter vascular grafts

The design of bioresorbable synthetic small diameter (<6mm) vascular grafts (SDVGs) capable of sustaining long-term patency and endothelialization is a daunting challenge in vascular tissue engineering. Here, we synthesized a family of biocompatible and biodegradable polycaprolactone (PCL) urethane macromers to fabricate hollow fiber membranes (HFMs) as SDVG candidates, and characterized their mechanical properties, degradability, hemocompatibility, and endothelial development. The HFMs had smooth surfaces and porous internal structures. Their tensile stiffness ranged from 0.09 to 0.11N/mm and their maximum tensile force from 0.86 to 1.03N, with minimum failure strains of approximately 130%. Permeability varied from 1 to 14×10(-6)cm/s, burst pressures from 1158 to 1468mmHg, and compliance from 0.52 to 1.48%/100mmHg. The suture retention forces ranged from 0.55 to 0.81N. HFMs had slow degradation profiles, with 15 to 30% degradation after 8weeks. Human endothelial cells proliferated well on the HFMs, creating stable cell layer coverage. Hemocompatibility studies demonstrated low hemolysis (<2%), platelet activation, and protein adsorption. There were no significant differences in the hemocompatibility of HFMs in the absence and presence of endothelial layers. These encouraging results suggest great promise of our newly developed materials and biodegradable elastomeric HFMs as SDVG candidates.

Mass spectrometric imaging of in vivo protein and lipid adsorption on biodegradable vascular replacement systems

Cardiovascular diseases present amongst the highest mortality risks in Western civilization and are frequently caused by arteriosclerotic vessel failure. Coronary artery and peripheral vessel reconstruction necessitates the use of small diameter systems that are mechanically stress-resistant and biocompatible. Expanded polytetrafluorethylene (ePTFE) is amongst the materials used most frequently for non-degradable and bio-degradable vessel reconstruction procedures, with thermoplastic polyurethanes (TPU) representing a promising substitute. The present study describes and compares the biological adsorption and diffusion occurring with both materials following implantation in rat models. Gel electrophoresis and thin-layer chromatography, combined with mass spectrometry and mass spectrometry imaging, were utilized to identify the adsorbed lipids and proteins. The results were compared with the analytes present in native aorta tissue. It was revealed that both polymers were severely affected by biological adsorption after 10 min in vivo. Proteins associated with cell growth and migration were identified, especially on the luminal graft surface, while lipids were found to be located on both the luminal and abluminal surfaces. Lipid adsorption and cholesterol diffusion were found to be correlated with the polymer modifications identified on degradable thermoplastic urethane graft samples, with the latter revealing extensive cholesterol adsorption. The present study demonstrates an interaction between biological matter and both graft materials, and provides insights into polymer changes, in particular, those observed with thermoplastic urethanes already after 10 min in vivo exposure. ePTFE demonstrated minor polymer modifications, whereas several different polymer signals were observed for TPU, all were co-localized with biological signals.

Effect of a Novel Stent on Re-Endothelialization, Platelet Adhesion, and Neointimal Formation

AIM

Vascular endothelial-cadherin (VE-cadherin) is specifically expressed by outgrowth endothelial cells (OECs). Zwitterionic stent showed high antifouling and excellent blood compatibility. Therefore, we hypothesized that anti-VE-cadherin antibody-coated zwitterionic stents (VE-cad-Z stents) would promote re-endothelialization, reduce neointimal formation, and resist thrombus.

METHODS

VE-cad-Z stents were examined using platelet adhesion test, platelet activation, and OEC capture ability in vitro. In vivo effect of VE-cad-Z stents on re-endothelialization, thrombus-resistance, and neointima hyperplasia was investigated in left common carotid arteries of rabbits (n=15).

RESULTS

In vitro, VE-cad-Z stents showed better platelet-resistance and OEC-capture ability (DNA concentration: 297.23±22.71 versus 67.49±15.26 ng/µL, P＜0.01). In vivo, VE-cad-Z stents exhibited better patency rate than bare metal stents (BMS) (15/15 versus 12/15), and it significantly reduced platelet adhesion and neointima formation (neointima area: 1.13±0.05 versus 1.00±0.05mm(2), P＜0.01 and 3.04±0.11versus 1.05±0.06mm(2), P＜0.01, at 3 and 30 days, respectively; % stenosis: 20.99±0.98 versus 18.72±0.97, P＜0.01 and 56.46±2.20 versus 19.45±1.24, P＜0.01, at 3 and 30 days, respectively).

CONCLUSION

These data suggested that VE-cad-Z stents could specifically capture OECs, consequently promote endothelial healing, and also reduce platelet adhesion and neointima formation.

Characterization and preparation of bio-tubular scaffolds for fabricating artificial vascular grafts by combining electrospinning and a 3D printing system

The last decade has seen artificial blood vessels composed of natural polymer nanofibers grafted into human bodies to facilitate the recovery of damaged blood vessels. However, electrospun nanofibers (ENs) of biocompatible materials such as chitosan (CTS) suffer from poor mechanical properties. This study describes the design and fabrication of artificial blood vessels composed of a blend of CTS and PCL ENs and coated with PCL strands using rapid prototyping technology. The resulting tubular vessels exhibited excellent mechanical properties and showed that this process may be useful for vascular reconstruction.

Tissue engineering vascular grafts a fortiori: looking back and going forward

INTRODUCTION

Cardiovascular diseases such as coronary heart disease often necessitate the surgical repair using conduits. Although autografts still remain the gold standard, the inconvenience of harvesting and/or insufficient availability in patients with atherosclerotic disease has given impetus to look into alternative sources for vascular grafts.

AREAS COVERED

There are four main techniques to produce tissue-engineered vascular grafts (TEVGs): i) biodegradable synthetic scaffolds; ii) gel-based scaffolds; iii) decellularised scaffolds and iv) self-assembled cell-sheet-based techniques. The first three techniques can be grouped together as scaffold-guided approach as it involves the use of a construct to function as a supportive framework for the vascular graft. The most significant advantages of TEVGs are that it possesses the ability to grow, remodel and respond to environmental factors. Cell sources for TEVGs include mature somatic cells, stem cells, adult progenitor cells and pluripotent stem cells.

EXPERT OPINION

TEVG holds great promise with advances in nanotechnology, coupled with important refinements in tissue engineering and decellularisation techniques. This will undoubtedly be an important milestone for cardiovascular medicine when it is eventually translated to clinical use.

Tissue engineered scaffolds for an effective healing and regeneration: reviewing orthotopic studies

It is commonly stated that tissue engineering is the most promising approach to treat or replace failing tissues/organs. For this aim, a specific strategy should be planned including proper selection of biomaterials, fabrication techniques, cell lines, and signaling cues. A great effort has been pursued to develop suitable scaffolds for the restoration of a variety of tissues and a huge number of protocols ranging from in vitro to in vivo studies, the latter further differentiating into several procedures depending on the type of implantation (i.e., subcutaneous or orthotopic) and the model adopted (i.e., animal or human), have been developed. All together, the published reports demonstrate that the proposed tissue engineering approaches spread toward multiple directions. The critical review of this scenario might suggest, at the same time, that a limited number of studies gave a real improvement to the field, especially referring to in vivo investigations. In this regard, the present paper aims to review the results of in vivo tissue engineering experimentations, focusing on the role of the scaffold and its specificity with respect to the tissue to be regenerated, in order to verify whether an extracellular matrix-like device, as usually stated, could promote an expected positive outcome.

Electrospinning of biomimetic scaffolds for tissue-engineered vascular grafts: threading the path

Tissue-engineered vascular grafts (TEVGs) offer an alternative to synthetic grafts for the surgical treatment of atherosclerosis and congenital heart defects, and may improve graft patency and patient outcomes after implantation. Electrospinning is a versatile manufacturing process for the production of fibrous scaffolds. This review aims to investigate novel approaches undertaken to improve the design of electrospun scaffolds for TEVG development. The review describes how electrospinning can be adapted to produce aligned nanofibrous scaffolds used in vascular tissue engineering, while novel processes for improved performance of such scaffolds are examined and compared to evaluate their effectiveness and potential. By highlighting new drug delivery techniques and porogenic technologies, in addition to analyzing in vitro and in vivo testing of electrospun TEVGs, it is hoped that this review will provide guidance on how the next generation of electrospun vascular graft scaffolds will be designed and tested for the potential improvement of cardiovascular therapies.

Fabrication and characteristics of chitosan sponge as a tissue engineering scaffold

Cells, growth factors, and scaffolds are the three main factors required to create a tissue-engineered construct. After the appearance of bovine spongiform encephalopathy (BSE), considerable attention has therefore been focused on nonbovine materials. In this study, we examined the properties of a chitosan porous scaffold. A porous chitosan sponge was prepared by the controlled freezing and lyophilization of different concentrations of chitosan solutions. The materials were examined by scanning electron microscopy, and the porosity, tensile strength, and basic fibroblast growth factor (bFGF) release profiles from chitosan sponge were examined in vitro. The morphology of the chitosan scaffolds presented a typical microporous structure, with the pore size ranging from 50 to 200 μm. The porosity of chitosan scaffolds with different concentrations was approximately 75–85%. A decreasing tendency for porosity was observed as the concentration of the chitosan increased. The relationship between the tensile properties and chitosan concentration indicated that the ultimate tensile strength for the sponge increased with a higher concentration. The in vitro bFGF release study showed that the higher the concentration of chitosan solution became, the longer the releasing time of the bFGF from the chitosan sponge was.

Vessel bioengineering

The development of vascular bioengineering has led to a variety of novel treatment strategies for patients with cardiovascular disease. Notably, combining biodegradable scaffolds with autologous cell seeding to create tissue-engineered vascular grafts (TEVG) allows for in situ formation of organized neovascular tissue and we have demonstrated the clinical viability of this technique in patients with congenital heart defects. The role of the scaffold is to provide a temporary 3-dimensional structure for cells, but applying TEVG strategy to the arterial system requires scaffolds that can also endure arterial pressure. Both biodegradable synthetic polymers and extracellular matrix-based natural materials can be used to generate arterial scaffolds that satisfy these requirements. Furthermore, the role of specific cell types in tissue remodeling is crucial and as a result many different cell sources, from matured somatic cells to stem cells, are now used in a variety of arterial TEVG techniques. However, despite great progress in the field over the past decade, clinical effectiveness of small-diameter arterial TEVG (<6mm) has remained elusive. To achieve successful translation of this complex multidisciplinary technology to the clinic, active participation of biologists, engineers, and clinicians is required.