Detergent-Enzymatic Decellularization of Swine Blood Vessels: Insight on Mechanical Properties for Vascular Tissue Engineering

An overview of the production of tissue extracellular matrix and decellularization process

Thousands of patients need an organ transplant yearly, while only a tiny percentage have this chance to receive a tissue/organ transplant. Nowadays, decellularized animal tissue is one of the most widely used methods to produce engineered scaffolds for transplantation. Decellularization is defined as physically or chemically removing cellular components from tissues while retaining structural and functional extracellular matrix (ECM) components and creating an ECM-derived scaffold. Then, decellularized scaffolds could be reseeded with different cells to fabricate an autologous graft. Effective decellularization methods preserve ECM structure and bioactivity through the application of the agents and techniques used throughout the process. The most valuable agents for the decellularization process depend on biological properties, cellular density, and the thickness of the desired tissue. ECM-derived scaffolds from various mammalian tissues have been recently used in research and preclinical applications in tissue engineering. Many studies have shown that decellularized ECM-derived scaffolds could be obtained from tissues and organs such as the liver, cartilage, bone, kidney, lung, and skin. This review addresses the significance of ECM in organisms and various decellularization agents utilized to prepare the ECM. Also, we describe the current knowledge of the decellularization of different tissues and their applications.

Nerve regeneration using decellularized tissues: challenges and opportunities

In tissue engineering, the decellularization of organs and tissues as a biological scaffold plays a critical role in the repair of neurodegenerative diseases. Various protocols for cell removal can distinguish the effects of treatment ability, tissue structure, and extracellular matrix (ECM) ability. Despite considerable progress in nerve regeneration and functional recovery, the slow regeneration and recovery potential of the central nervous system (CNS) remains a challenge. The success of neural tissue engineering is primarily influenced by composition, microstructure, and mechanical properties. The primary objective of restorative techniques is to guide existing axons properly toward the distal end of the damaged nerve and the target organs. However, due to the limitations of nerve autografts, researchers are seeking alternative methods with high therapeutic efficiency and without the limitations of autograft transplantation. Decellularization scaffolds, due to their lack of immunogenicity and the preservation of essential factors in the ECM and high angiogenic ability, provide a suitable three-dimensional (3D) substrate for the adhesion and growth of axons being repaired toward the target organs. This study focuses on mentioning the types of scaffolds used in nerve regeneration, and the methods of tissue decellularization, and specifically explores the use of decellularized nerve tissues (DNT) for nerve transplantation.

Biomimetic tri-layered small-diameter vascular grafts with decellularized extracellular matrix promoting vascular regeneration and inhibiting thrombosis with the salidroside

Small-diameter vascular grafts (SDVGs) are urgently required for clinical applications. Constructing vascular grafts mimicking the defining features of native arteries is a promising strategy. Here, we constructed a tri-layered vascular graft with a native artery decellularized extracellular matrix (dECM) mimicking the component of arteries. The porcine thoracic aorta was decellularized and milled into dECM powders from the differential layers. The intima and media dECM powders were blended with poly (L-lactide-co-caprolactone) (PLCL) as the inner and middle layers of electrospun vascular grafts, respectively. Pure PLCL was electrospun as a strengthening sheath for the outer layer. Salidroside was loaded into the inner layer of vascular grafts to inhibit thrombus formation. In vitro studies demonstrated that dECM provided a bioactive milieu for human umbilical vein endothelial cell (HUVEC) extension adhesion, proliferation, migration, and tube-forming. The in vivo studies showed that the addition of dECM could promote endothelialization, smooth muscle regeneration, and extracellular matrix deposition. The salidroside could inhibit thrombosis. Our study mimicked the component of the native artery and combined it with the advantages of synthetic polymer and dECM which provided a promising strategy for the design and construction of SDVGs.

History, progress and future challenges of artificial blood vessels: a narrative review

Cardiovascular disease serves as the leading cause of death worldwide, with stenosis, occlusion, or severe dysfunction of blood vessels being its pathophysiological mechanism. Vascular replacement is the preferred surgical option for treating obstructed vascular structures. Due to the limited availability of healthy autologous vessels as well as the incidence of postoperative complications, there is an increasing demand for artificial blood vessels. From synthetic to natural, or a mixture of these components, numerous materials have been used to prepare artificial vascular grafts. Although synthetic grafts are more appropriate for use in medium to large-diameter vessels, they fail when replacing small-diameter vessels. Tissue-engineered vascular grafts are very likely to be an ideal alternative to autologous grafts in small-diameter vessels and are worthy of further investigation. However, a multitude of problems remain that must be resolved before they can be used in biomedical applications. Accordingly, this review attempts to describe these problems and provide a discussion of the generation of artificial blood vessels. In addition, we deliberate on current state-of-the-art technologies for creating artificial blood vessels, including advances in materials, fabrication techniques, various methods of surface modification, as well as preclinical and clinical applications. Furthermore, the evaluation of grafts both in vivo and in vitro, mechanical properties, challenges, and directions for further research are also discussed.

Biochemical Aspects of Scaffolds for Cartilage Tissue Engineering; from Basic Science to Regenerative Medicine

Chondral defects are frequent and important causes of pain and disability. Cartilage has limited self-repair and regeneration capacity. The ideal approach for articular cartilage defects is the regeneration of hyaline cartilage with sustainable symptom-free constructs. Tissue engineering provides new strategies for the regeneration of functional cartilage tissue through optimized scaffolds with architectural, mechanical, and biochemical properties similar to the native cartilage tissue. In this review, the basic science of cartilage structure, interactions between proteins, stem cells, as well as biomaterials, scaffold characteristics and fabrication methods, as well as current and potential therapies in regenerative medicine will be discussed mostly from a biochemical point of view. Furthermore, the recent trends in scaffold-based therapies and supplementary factors in cartilage tissue engineering will be considered.

Improving Biocompatibility of Polyester Fabrics through Polyurethane/Gelatin Complex Coating for Potential Vascular Application

Medical apparatus and instruments, such as vascular grafts, are first exposed to blood when they are implanted. Therefore, blood compatibility is considered to be the critical issue when constructing a vascular graft. In this regard, the coating method is verified to be an effective and simple approach to improve the blood compatibility as well as prevent the grafts from blood leakage. In this study, polyester fabric is chosen as the substrate to provide excellent mechanical properties while a coating layer of polyurethane is introduced to prevent the blood leakage. Furthermore, gelatin is coated on the substrate to mimic the native extracellular matrix together with the improvement of biocompatibility. XPS and FTIR analysis are performed for elemental and group analysis to determine the successful coating of polyurethane and gelatin on the polyester fabrics. In terms of blood compatibility, hemolysis and platelet adhesion are measured to investigate the anticoagulation performance. In vitro cell experiments also indicate that endothelial cells show good proliferation and morphology on the polyester fabric modified with such coating layers. Taken together, such polyester fabric coated with polyurethane and gelatin layers would have a promising potential in constructing vascular grafts with expected blood compatibility and biocompatibility without destroying the basic mechanical requirements for vascular applications.

Small-diameter artery decellularization: Effects of anionic detergent concentration and treatment duration on porcine internal thoracic arteries

Engineered replacement materials have tremendous potential for vascular applications where over 400,000 damaged and diseased blood vessels are replaced annually in the United States alone. Unlike large diameter blood vessels, which are effectively replaced by synthetic materials, prosthetic small-diameter vessels are prone to early failure, restenosis, and reintervention surgery. We investigated the differential response of varying 0%-6% sodium dodecyl sulfate and sodium deoxycholate anionic detergent concentrations after 24 and 72 h in the presence of DNase using biochemical, histological, and biaxial mechanical analyses to optimize the decellularization process for xenogeneic vascular tissue sources, specifically the porcine internal thoracic artery (ITA). Detergent concentrations greater than 1% were successful at removing cytoplasmic and cell surface proteins but not DNA content after 24 h. A progressive increase in porosity and decrease in glycosaminoglycan (GAG) content was observed with detergent concentration. Augmented porosity was likely due to the removal of both cells and GAGs and could influence recellularization strategies. The treatment duration on the other hand, significantly improved decellularization by reducing DNA content to trace amounts after 72 h. Prolonged treatment times reduced laminin content and influenced the vessel's mechanical behavior in terms of altered circumferential stress and stretch while further increasing porosity. Collectively, DNase with 1% detergent for 72 h provided an effective and efficient decellularization strategy to be employed in the preparation of porcine ITAs as bypass graft scaffolding materials with minor biomechanical and histological penalties.

Quantification of adhesion of mesenchymal stem cells spread on decellularized vein scaffold

Purpose:

To evaluate methods that improve adipose-derived stem cells (ASCs) population in decellularized biological venous scaffold for tissue engineering in blood vessels, a model in rabbits.

Methods:

The ASC was expanded until the third passage. Inferior vena cava (IVC) was submitted to the decellularization process using 1% sodium dodecyl sulfate (SDS) or 2% sodium deoxycholate (SD) to compose 12 study groups (G): pure SD or SDS, exposed or not to 1% TritonX-100 (TX-100) and exposed or not to poly-l’lysine and laminin (PL). Scaffolds were covered with 1 × 10⁵ or 1 × 10⁶ ASCs diluted in 10 μL Puramatrix™. The histological analysis was done by cell counting in hematoxylin and eosin (HE) and nuclei count in immunofluorescence (IF) with 4’,6-Diamidine-2’-phenylindole dihydrochloride (DAPI).

Results:

The study of groups in HE and IF showed similar results. For both analyses,IVC-SD-1 × 10⁶ ASC and IVC-SD-PL-1 × 10⁶ ASC provided the best results. The IF technique showed better sensitivity than HE, with a weak agreement between them.

Conclusions:

Decellularizing agent and the number of ASC influence scaffolds cellularization response and the best protocols as those ones using SD with or without the addition of PL.

Tissue-Engineered Vascular Graft with Co-Culture of Smooth Muscle Cells and Human Endothelial Vein Cells on an Electrospun Poly(lactic-co-glycolic acid) Microtube Array Membrane

Coronary artery disease is one of the major diseases that plagues today’s modern society. Conventional treatments utilize synthetic vascular grafts such as Dacron^® and Teflon^® in bypass graft surgery. Despite the wide adaptation, these synthetic grafts are often plagued with weaknesses such as low hemocompatibility, thrombosis, intimal hyperplasia, and risks of graft infection. More importantly, these synthetic grafts are not available at diameters of less than 6 mm. In view of these challenges, we strived to develop and adapt the electrospun Poly Lactic-co-Glycolic Acid (PLGA) Microtube Array Membrane (MTAM) vascular graft for applications smaller than 6 mm in diameter. Homogenously porous PLGA MTAMs were successfully electrospun at 5.5–8.5 kV under ambient conditions. Mechanically, the PLGA MTAMs registered a maximum tensile strength of 5.57 ± 0.85 MPa and Young’s modulus value of 1.134 ± 0.01 MPa; while MTT assay revealed that seven-day Smooth Muscle Cells (SMCs) and Human Umbilical Vein Endothelial Cells (HUVECs) registered a 6 times and 2.4 times higher cell viability when cultured in a co-culture setting in medium containing α-1 haptaglobulin. When rolled into a vascular graft, the PLGA MTAMs registered an overall degradation of 82% after 60 days of cell co-culture. After eight weeks of culturing, immunohistochemistry staining revealed the formation of a monolayer of HUVECs with tight junctions on the surface of the PLGA MTAM, and as for the SMCs housed within the lumens of the PLGA MTAMs, a monolayer with high degree of orientation was observed. The PLGA MTAM registered a burst pressure of 1092.2 ± 175.3 mmHg, which was sufficient for applications such as small diameter blood vessels. Potentially, the PLGA MTAM could be used as a suitable substrate for vascular engineering.

Post-decellularization techniques ameliorate cartilage decellularization process for tissue engineering applications

Due to the current lack of innovative and effective therapeutic approaches, tissue engineering (TE) has attracted much attention during the last decades providing new hopes for the treatment of several degenerative disorders. Tissue engineering is a complex procedure, which includes processes of decellularization and recellularization of biological tissues or functionalization of artificial scaffolds by active cells. In this review, we have first discussed those conventional steps, which have led to great advancements during the last several years. Moreover, we have paid special attention to the new methods of post-decellularization that can significantly ameliorate the efficiency of decellularized cartilage extracellular matrix (ECM) for the treatment of osteoarthritis (OA). We propose a series of post-decellularization procedures to overcome the current shortcomings such as low mechanical strength and poor bioactivity to improve decellularized ECM scaffold towards much more efficient and higher integration.

Design of Perfused PTFE Vessel-Like Constructs for In Vitro Applications

Tissue models mimic the complex 3D structure of human tissues, which allows the study of pathologies and the development of new therapeutic strategies. The introduction of perfusion overcomes the diffusion limitation and enables the formation of larger tissue constructs. Furthermore, it provides the possibility to investigate the effects of hematogenously administered medications. In this study, the applicability of hydrophilic polytetrafluoroethylene (PTFE) membranes as vessel-like constructs for further use in perfused tissue models is evaluated. The presented approach allows the formation of stable and leakproof tubes with a mean diameter of 654.7 µm and a wall thickness of 84.2 µm. A polydimethylsiloxane (PDMS) chip acts as a perfusion bioreactor and provides sterile conditions. As proof of concept, endothelial cells adhere to the tube's wall, express vascular endothelial cadherin (VE-cadherin) between neighboring cells, and resist perfusion at a shear rate of 0.036 N m^-2 for 48 h. Furthermore, the endothelial cell layer delays significantly the diffusion of fluorescently labeled molecules into the surrounding collagen matrix and leads to a twofold reduced diffusion velocity. This approach represents a cost-effective alternative to introduce stable vessel-like constructs into tissue models, which allows adapting the surrounding matrix to the tissue properties in vivo.

Extracellular Matrix for Small-Diameter Vascular Grafts

To treat coronary heart disease, coronary artery bypass grafts are used to divert blood flow around blockages in the coronary arteries. Autologous grafts are the gold standard of care, but they are characterized by their lack of availability, low quality, and high failure rates. Alternatively, tissue-engineered small-diameter vascular grafts made from synthetic or natural polymers have not demonstrated adequate results to replace autologous grafts; synthetic grafts result in a loss of patency due to thrombosis and intimal hyperplasia, whereas scaffolds from natural polymers are generally unable to support the physiological conditions. Extracellular matrix (ECM) from a variety of sources, including cell-derived, 2D, and cannular tissues, has become an increasingly useful tool for this application. The current review examines the ECM-based methods that have recently been investigated in the field and comments on their viability for clinical applications.

Decellularization of porcine carotid arteries using low-concentration sodium dodecyl sulfate

BACKGROUND

The decellularized scaffold is a promising material for producing tissue-engineered vascular grafts (TEVGs) because of its complex, native-like three-dimensional structure and mechanical properties. Sodium dodecyl sulfate (SDS), one of the most commonly used decellularization reagents, appears to be more effective than other detergents for removing cells from dense tissues. The concentrations of SDS used in previous studies and their effects on decellularization are not consistent.

METHODS

In this study, porcine carotid arteries were decellularized using detergent-based protocols using Triton X-100 followed by SDS at different concentrations and exposing time. Cell removal efficiency and composition were evaluated by histological analysis, and DNA and collagen quantification. Ultrastructure, mechanical properties, pore size distribution, and in vivo biocompatibility of decellularized arteries were also evaluated.

RESULTS

The DNA content of decellularized scaffolds treated with 0.3% SDS for 72 h or 0.5% SDS for 48 h was significantly less than that treated with 1% SDS for 30 h. There was a significant loss of soluble collagen after treatment with 1% SDS relative to native arteries. The extensive loss of elastin and glycosaminoglycans was observed in decellularized arteries treated with 0.5% SDS or 1% SDS. The basement membrane and biomechanics were also damaged by these two protocols. Moreover, decellularized scaffolds became more porous with many large pores after treatment with 0.3% SDS.

CONCLUSION

Low-concentration SDS could be a suitable choice for artery decellularization. Decellularized porcine carotid arteries, prepared using Triton X-100 followed by 0.3% SDS, may be a promising biological scaffold for TEVGs.

Bioreactivity of decellularized animal, plant, and fungal scaffolds: perspectives for medical applications

Numerous biomedical applications imply supportive materials to improve protective, antibacterial, and regenerative abilities upon surgical interventions, oncotherapy, regenerative medicine, and others. With the increasing variability of the possible sources, the materials of natural origin are among the safest and most accessible biomedical tools. Animal, plant, and fungal tissues can further undergo decellularization to improve their biocompatibility. Decellularized scaffolds lack the most reactive cellular material, nuclear and cytoplasmic components, that predominantly trigger immune responses. At the same time, the outstanding initial three-dimensional microarchitecture, biomechanical properties, and general composition of the scaffolds are preserved. These unique features make the scaffolds perfect ready-to-use platforms for various biomedical applications, implying cell growth and functionalization. Decellularized materials can be repopulated with various cells upon request, including epithelial, endothelial, muscle and neuronal cells, and applied for structural and functional biorepair within diverse biological sites, including the skin and musculoskeletal, cardiovascular, and central nervous systems. However, the molecular and cellular mechanisms behind scaffold and host tissue interactions remain not fully understood, which significantly restricts their integration into clinical practice. In this review, we address the essential aspects of decellularization, scaffold preparation techniques, and its biochemical composition and properties, which determine the biocompatibility and immunogenicity of the materials. With the integrated evaluation of the scaffold profile in living systems, decellularized animal, plant, and fungal scaffolds have the potential to become essential instruments for safe and controllable biomedical applications.

Porcine carotid arteries decellularized with a suitable concentration combination of Triton X-100 and sodium dodecyl sulfate for tissue engineering vascular grafts

Tissue engineering vascular grafts (TEVGs) constructed by decellularized arteries have the potential to replace autologous blood vessels in bypass surgery for patients with cardiovascular disease. There are various methods of decellularization without a standard protocol. Detergents approaches are simple, and easy control of experimental conditions. Non-ionic detergent Triton X-100 and ionic detergent sodium dodecyl sulfate (SDS) are the most commonly used detergents. In this study, we used Triton X-100 and SDS with different concentrations to decellularize porcine carotid arteries. After that, we investigated the acellular effect and mechanical properties of decellularized arteries to find a promising concentration combination for decellularization. Results showed that any detergents' combination would damage the inherent structure of extracellular matrix, and the destruction increased with the increase of detergents' concentration. We concluded that the decellularization approach of 0.5% Triton X-100 for 24 h combined with 0.25% SDS for 72 h could help to obtain decellularized arteries with minimum destruction. This protocol may be able to prepare a clinically suitable vascular scaffold for TEVGs.

Riboflavin-mediated photooxidation to improve the characteristics of decellularized human arterial small diameter vascular grafts

Vascular grafts with a diameter of less than 6 mm are made from a variety of materials and techniques to provide alternatives to autologous vascular grafts. Decellularized materials have been proposed as a possible approach to create extracellular matrix (ECM) vascular prostheses as they are naturally derived and inherently support various cell functions. However, these desirable graft characteristics may be limited by alterations of the ECM during the decellularization process leading to decreased biomechanical properties and hemocompatibility. In this study, arteries from the human placenta chorion were decellularized using two distinct detergents (Triton X-100 or SDS), which differently affect ECM ultrastructure. To overcome biomechanical strength loss and collagen fiber exposure after decellularization, riboflavin-mediated UV (RUV) crosslinking was used to uniformly crosslink the collagenous ECM of the grafts. Graft characteristics and biocompatibility with and without RUV crosslinking were studied in vitro and in vivo. RUV-crosslinked ECM grafts showed significantly improved mechanical strength and smoothening of the luminal graft surfaces. Cell seeding using human endothelial cells revealed no cytotoxic effects of the RUV treatment. Short-term aortic implants in rats showed cell migration and differentiation of host cells. Functional graft remodeling was evident in all grafts. Thus, RUV crosslinking is a preferable tool to improve graft characteristics of decellularized matrix conduits.

Selection of biological prosthesis for abdominal wall repair on the basis of in vitro biocompatibility determination

Research on prostheses for repairing abdominal wall defects has progressed through past decades for developing an ideal prosthesis. The study was designed to compare different extracellular matrix (ECM) derived biological prostheses as alternate to conventional synthetic polymeric prostheses for the repair of full thickness abdominal wall defects. Five biological scaffolds derived from bovine diaphragm, bovine aorta, bovine gall bladder, porcine gall bladder, and rabbit skin were prepared and screened for their in vitro biocompatibility. Decellularized ECMs were subjected to various biocompatibility analyses, namely, water absorption potential, matrix degradation analysis, biomechanical testing, and cytocompatibility analysis. Though the rabbit skin displayed maximum biomechanical strength, due to its rapid degradation, it failed to fulfill the criteria of an ideal prosthesis. ECMs derived from bovine diaphragm and aorta were found to be superior than others based upon hydration and matrix degradation analysis, with best scores for bovine diaphragm followed by bovine aorta. The bovine diaphragm and aorta also displayed sufficient biomechanical strength, with diaphragm being the second highest (next to rabbit skin), in biomechanical strength followed by aorta. None of the biological prosthesis revealed any cytotoxicity. Thus, bovine diaphragm and aorta derived ECM fulfill the necessary criteria for their use as biological prosthesis. Because these prostheses are biocompatible, apart from their low cost, ease of availability, and simple preparation, they present a potential alternative to synthetic prosthesis for repair of abdominal wall defects, especially in veterinary patients.

Antigen removal process preserves function of small diameter venous valved conduits, whereas SDS-decellularization results in significant valvular insufficiency

Chronic venous disease (CVD) is the most common reported chronic condition in the United States, affecting more than 25 million Americans. Regardless of its high occurrence, current therapeutic options are far from ideal due to their palliative nature. For best treatment outcomes, challenging cases of chronic venous insufficiency (CVI) are treated by repair or replacement of venous valves. Regrettably, the success of venous valve transplant is dependent on the availability of autologous venous valves and hindered by the possibility of donor site complications and increased patient morbidity. Therefore, the use of alternative tissue sources to provide off-the-shelf venous valve replacements has potential to be extremely beneficial to the field of CVI. This manuscript demonstrates the capability of producing off-the-shelf fully functional venous valved extracellular matrix (ECM) scaffold conduits from bovine saphenous vein (SV), using an antigen removal (AR) method. AR ECM scaffolds maintained native SV structure-function relationships and associated venous valves function. Conversely, SDS decellularization caused significant changes to the collagen and elastin macromolecular structures, resulting in collagen fibril merging, elimination of fibril crimp, amalgaming collagen fibers and fragmentation of the inner elastic lamina. ECM changes induced by SDS decellularization resulted in significant venous valve dysfunction. Venous valved conduits generated using the AR approach have potential to serve as off-the-shelf venous valve replacements for CVI. STATEMENT OF SIGNIFICANCE: Retention of the structure and composition of extracellular matrix (ECM) proteins within xenogeneic scaffolds for tissue engineering is of crucial importance, due to the undeniable effect ECM proteins can impose on repopulating cells and function of the resultant biomaterial. This manuscript demonstrates that alteration or elimination of ECM proteins via commonly utilized decellularization approach results in complete disruption of venous valve function. Conversely, retention of the delicate ECM structure and composition of native venous tissue, using an antigen removal tissue processing method, results in preservation of native venous valve function.

Polylysine Enriched Matrices: A Promising Approach for Vascular Grafts

Cardiovascular diseases represent the leading cause of death in developed countries. Modern surgical methods show poor efficiency in the substitution of small-diameter arteries (<6 mm). Due to the difference in mechanical properties between the native artery and the substitute, the behavior of the vessel wall is a major cause of inefficient substitutions. The use of decellularized scaffolds has shown optimal prospects in different applications for regenerative medicine. The purpose of this work was to obtain polylysine-enriched vascular substitutes, derived from decellularized porcine femoral and carotid arteries. Polylysine acts as a matrix cross-linker, increasing the mechanical resistance of the scaffold with respect to decellularized vessels, without altering the native biocompatibility and hemocompatibility properties. The biological characterization showed an excellent biocompatibility, while mechanical tests displayed that the Young's modulus of the polylysine-enriched matrix was comparable to native vessel. Burst pressure test demonstrated strengthening of the polylysine-enriched matrix, which can resist to higher pressures with respect to native vessel. Mechanical analyses also show that polylysine-enriched vessels presented minimal degradation compared to native. Concerning hemocompatibility, the performed analyses show that polylysine-enriched matrices increase coagulation time, with respect to commercial Dacron vascular substitutes. Based on these findings, polylysine-enriched decellularized vessels resulted in a promising approach for vascular substitution.

Characterization of a heparinized decellularized scaffold and its effects on mechanical and structural properties

Decellularization is a promising approach in tissue engineering to generate small-diameter blood vessels. However, some challenges still exist. We performed two decellularization phases to develop an optimal decellularized scaffold and analyze the relationship between the extracellular matrix (ECM) composition and mechanical properties. In decellularization phase I, we tested sodium dodecylsulfate (SDS), Triton X-100 (TX100) and trypsin at different concentrations and exposure times. In decellularization phase II, we systematically compared five combined decellularization protocols based on the results of phase I to identify the optimal method. These protocols tested cell removal, ECM preservation, mechanical properties, and residual cytotoxicity. We further immobilized heparin to optimal decellularized scaffolds and determined its anticoagulant activity and mechanical properties. The combined decellularization protocol comprising treatment with 0.5% SDS followed by 1% TX100 could completely remove the cellular contents and preserve the mechanical properties and ECM architecture better. In addition, the heparinized decellularized scaffolds not only had sustained anticoagulant activity, but also similar mechanical properties to native vessels. In conclusion, heparinized decellularized scaffolds represent a promising direction for small-diameter vascular grafts, although further in vivo studies are needed.

Polycaprolactone/gelatin degradable vascular grafts simulating endothelium functions modified by nitric oxide generation

Aim: Host remolding with scaffolds degradation and rapid formation of a complete endothelium, are prospective solutions for improving performance of small diameter vascular grafts. Materials & methods: For this purpose, microfibrous polycaprolactone (PCL)/gelatin scaffolds were prepared by electrospinning and subsequently functionalized with heparin and organoselenium-immobilized polyethyleneimine for nitric oxide generation through layer-by-layer self-assembly. Results: Our results showed that modified PCL/gelatin grafts had strong catalytic nitric oxide generation capacity and facilitated the enhanced attachment of endothelial cells, compared with control scaffold groups. Meanwhile, the modified grafts exhibited good hemocombatility, rapid endothelialization and smooth muscle cell regeneration. Conclusion: Modification of biodegradable scaffolds, proposed in this work, could enhance biological functions of vascular grafts and provides new strategies for the construction of small diameter vascular grafts.

Small Diameter Xenogeneic Extracellular Matrix Scaffolds for Vascular Applications

Currently, despite the success of percutaneous coronary intervention (PCI), coronary artery bypass graft (CABG) remains among the most commonly performed cardiac surgical procedures in the United States. Unfortunately, the use of autologous grafts in CABG presents a major clinical challenge as complications due to autologous vessel harvest and limited vessel availability pose a significant setback in the success rate of CABG surgeries. Acellular extracellular matrix (ECM) scaffolds derived from xenogeneic vascular tissues have the potential to overcome these challenges, as they offer unlimited availability and sufficient length to serve as "off-the-shelf" CABGs. Unfortunately, regardless of numerous efforts to produce a fully functional small diameter xenogeneic ECM scaffold, the combination of factors required to overcome all failure mechanisms in a single graft remains elusive. This article covers the major failure mechanisms of current xenogeneic small diameter vessel ECM scaffolds, and reviews the recent advances in the field to overcome these failure mechanisms and ultimately develop a small diameter ECM xenogeneic scaffold for CABG. Impact Statement Currently, the use of autologous vessel in coronary artery bypass graft (CABG) is common practice. However, the use of autologous tissue poses significant complications due to tissue harvest and limited availability. Developing an alternative vessel for use in CABG can potentially increase the success rate of CABG surgery by eliminating complications related to the use of autologous vessel. However, this development has been hindered by an array of failure mechanisms that currently have not been overcome. This article describes the currently identified failure mechanisms of small diameter vascular xenogeneic extracellular matrix scaffolds and reviews current research targeted to overcoming these failure mechanisms toward ensuring long-term graft patency.

Fabrication Techniques for Vascular and Vascularized Tissue Engineering

Impaired or damaged blood vessels can occur at all levels in the hierarchy of vascular systems from large vasculatures such as arteries and veins to meso- and microvasculatures such as arterioles, venules, and capillary networks. Vascular tissue engineering has become a promising approach for fabricating small-diameter vascular grafts for occlusive arteries. Vascularized tissue engineering aims to fabricate meso- and microvasculatures for the prevascularization of engineered tissues and organs. The ideal small-diameter vascular graft is biocompatible, bridgeable, and mechanically robust to maintain patency while promoting tissue remodeling. The desirable fabricated meso- and microvasculatures should rapidly integrate with the host blood vessels and allow nutrient and waste exchange throughout the construct after implantation. A number of techniques used, including engineering-based and cell-based approaches, to fabricate these synthetic vasculatures are herein explored, as well as the techniques developed to fabricate hierarchical structures that comprise multiple levels of vasculature.

Shear-resistant hydrogels to control permeability of porous tubular scaffolds in vascular tissue engineering

Aiming to perfuse porous tubular scaffolds for vascular tissue engineering (VTE) with controlled flow rate, prevention of leakage through the scaffold lumen is required. A gel coating made of 8% w/v alginate and 6% w/v gelatin functionalized with fibronectin was produced using a custom-made bioreactor-based method. Different volumetric proportions of alginate and gelatin were tested (50/50, 70/30, and 90/10). Gel swelling and stability, and rheological, and uniaxial tensile tests reveal superior resistance to the aggressive biochemical microenvironment, and their ability to withstand physiological deformations (~10%) and wall shear stresses (5-20 dyne/cm²). These are prerequisites to maintain the physiologic phenotypes of vascular smooth muscle cells and endothelial cells (ECs), mimicking blood vessels microenvironment. Gels can induce ECs proliferation and colonization, especially in the presence of fibronectin and higher percentages of gelatin. The custom-designed bioreactor enables the development of reproducible and homogeneous tubular gel coating. The permeability tests show the effectiveness of tubular scaffolds coated with 70/30 alginate/gelatin gel to occlude wadding pores, and therefore prevent leakages. The synthesized double-layered tubular scaffolds coated with alginate/gelatin gel and fibronectin represent both promising substrate for ECs and effective leakproof scaffolds, when subjected to pulsatile perfusion, for VTE applications.

Suture retention strength of P(LLA-CL) tissue-engineered vascular grafts

The suture retention strength of artificial vascular grafts is a key mechanical property that affects the function of the grafts. Different from the conventional method of testing the suture retention strength, this study simulated the actual suturing state of vascular scaffolds approximately and investigated the effect of graft type, graft wall thickness, and number of stitches on the suture retention strength of poly(l-lactide-co-ε-caprolactone) P(LLA-CL) vascular grafts. The results showed that the P(LLA-CL) tissue-engineered vascular scaffolds have excellent suture performance and, when the graft wall thickness is greater than 0.24 mm, the suture retention strength will meet the vascular transplantation standard. Under the same conditions, the greater the number of stitches, the more uniform the force of the anastomosis and then the greater the suture retention strength. This experiment provides a more comprehensive and accurate suture retention strength value for the application of P(LLA-CL) tissue engineered vascular grafts, which helps to guide the further optimization of tissue-engineered vascular grafts to meet specific mechanical performance requirements.

A method that simulates the actual suture status of a vascular graft provides a more consistent suture retention strength.

Systematic in vitro comparison of decellularization protocols for blood vessels

Decellularization of native blood vessels is a promising technology to generate 3D biological scaffolds for vascular grafting. Blood vessel decellularization has been performed in previous studies under various experimental conditions, that complicates comparison and optimization of suitable protocols. The goal of this work was to systematically compare the decellularization and recellularization efficacy of 5 different protocols utilizing the detergents sodium dodecyl sulfate (SDS), sodium deoxycholate (SDC), CHAPS and TritonX-100 together with DNA-removing enzymes on porcine vena cava in a perfusion bioreactor setup. Additionally, we tested the effect of DNase on the extracellular matrix (ECM) properties. We found that all protocols could efficiently decellularize blood vessels. Mechanical strength, collagen preservation and ECM integrity were similar among all tested detergents, yet TritonX protocols required long-term DNase application for complete decellularization. However, TritonX-based protocols showed the greatest recellularization efficacy with HUVECs in vitro. Furthermore, we developed a novel protocol for TritonX which improved recellularization and reduced total process time and ECM stiffness compared to previous protocols. SDS, SDC and CHAPS based protocols had a lower recellularization potential. In conclusion, decellularization of blood vessels can be achieved with all tested reagents, but TritonX treated ECM can be most efficiently recellularized with endothelial cells.

Multi-stage bioengineering of a layered oesophagus with in vitro expanded muscle and epithelial adult progenitors

A tissue engineered oesophagus could overcome limitations associated with oesophageal substitution. Combining decellularized scaffolds with patient-derived cells shows promise for regeneration of tissue defects. In this proof-of-principle study, a two-stage approach for generation of a bio-artificial oesophageal graft addresses some major challenges in organ engineering, namely: (i) development of multi-strata tubular structures, (ii) appropriate re-population/maturation of constructs before transplantation, (iii) cryopreservation of bio-engineered organs and (iv) in vivo pre-vascularization. The graft comprises decellularized rat oesophagus homogeneously re-populated with mesoangioblasts and fibroblasts for the muscle layer. The oesophageal muscle reaches organised maturation after dynamic culture in a bioreactor and functional integration with neural crest stem cells. Grafts are pre-vascularised in vivo in the omentum prior to mucosa reconstitution with expanded epithelial progenitors. Overall, our optimised two-stage approach produces a fully re-populated, structurally organized and pre-vascularized oesophageal substitute, which could become an alternative to current oesophageal substitutes.

Combining decellularised scaffolds with patient-derived cells holds promise for bioengineering of functional tissues. Here the authors develop a two-stage approach to engineer an oesophageal graft that retains the structural organisation of native oesophagus.

Decellularized and Secured Porcine Arteries with NaOH-based Process: Proof of Concept

BACKGROUND

There is a need for small caliber vascular prosthesis. Synthetic grafts are hindered by thrombogenicity and rapid occlusion. Decellularized matrices could be an alternative. We assessed in vitro and in vivo the biocompatibility of porcine artery treated with a chemical/physical process for decellularization and graft securitization with non/conventional pathogens inactivation.

METHODS

Porcine carotid arteries (PCA) were treated. First, biopsies (n = 4/tissue) were performed before/after treatment to assess decellularization (hematoxylin and eosin/-4',6-diamidino-2-phenylindole/DNA/Miller). Second, 5 rats received an abdominal aortic patch of decellularized PCA (DPCA). Four pigs received subcutaneous DPCA implants (n = 2/pig). Half were explanted at day 15 and half at day 30. Finally, 2 pigs received DPCA (n = 2) and polytetrafluoroethylene prosthesis (n = 1), respectively, as carotid interposition. Implants were removed at day 30. Inflammation (CD3 and CD68 immunostaining) calcifications (von Kossa staining), remodeling (hematoxylin and eosin), and vascular characterization (CD31 and alpha-smooth muscle actin immunofluorescent staining) were investigated.

RESULTS

Ninety-five percentage of decellularization was obtained without structural deterioration. No death occurred. Low inflammatory reaction was found in the 2 models for DPCA. Acquisition of vascular identity was confirmed in the rodent and porcine models. Similarity between native PCA and DPCA was observed after 30 days. In contrast, polytetrafluoroethylene graft showed severe calcifications, higher CD3 reaction, and higher intimal hyperplasia (P < 0.05).

CONCLUSIONS

The physical and chemical process ensures decellularization of carotid porcine arteries and their in vivo remodeling with the presence of an endothelium and smooth-muscle-like cells as well as a low level of inflammatory cells.

Triton X-100 combines with chymotrypsin: A more promising protocol to prepare decellularized porcine carotid arteries

BACKGROUND

Morbidity and mortality of cardiovascular diseases are increasing in recent years. To solve these problems, vascular transplantation has become a common approach. Decellularization has been a hot spot of tissue engineering to prepare vessel substitutes for vascular transplantation. However, there is no established canonical protocol for decellularization thus far.

OBJECTIVE

To further understand the decellularization effect of decellularization protocols and the causal relationship between decellularization and mechanical properties.

METHODS

Three decellularization protocols including two chemical protocols based on SDS and Trypsin respectively and a combination of Triton X-100 with chymotrypsin were adopted to obtain decellularized porcine carotid arteries in our study. After decellularization, histological analysis, scanning electron microscopy and mechanical tests were performed to evaluate their efficiency on removing of cellular components, retention of extracellular matrix and influence on mechanical properties.

RESULTS

All these decellularization protocols used in our study were efficient to remove cellular components. However, SDS and trypsin performed more disruptive effect on ECM structure and mechanical properties of native arteries while Triton X-100 combines with chymotrypsin had no significant disruptive effect.

CONCLUSIONS

Compared with decellularization protocols based on SDS and trypsin, Triton X-100 combines with chymotrypsin used in our study may be a more promising protocol to prepare decellularized porcine carotid arteries for vascular tissue engineering applications.

Novel Approach Toward the Generation of Tissue Engineered Heart Valve by Using Combination of Antioxidant and Detergent: A Potential Therapy in Cardiovascular Tissue Engineering

To develop decellularized heart valve scaffold from porcine for heart valve regeneration. Porcine heart valves were decellularized with unique optimized approach by using 1% sodium dodecyl sulfate solution and 5% dimethyl sulfoxide for the first time. Effect of decellularization process on scaffold were characterized by hematoxylin-eosin, 4',6-diamidino-2-phenylindole, Masson's trichrome, alcian blue staining and scanning electron microscopy for extracellular matrix (ECM) analysis in scaffold. The results showed that developed protocol for decellularization of heart valve scaffold shown complete removal of all cellular components, without changing the properties of ECM. The developed protocol was successfully used for heart valve ECM scaffolds development from porcine. The developed protocol seems to be promising solution for the heart valve tissue engineering application.

A randomized clinical trial of a human acellular dermal matrix demonstrated superior healing rates for chronic diabetic foot ulcers over conventional care and an active acellular dermal matrix comparator

This study compared the efficacy and safety of a human acellular dermal matrix (ADM), D-ADM, with a conventional care arm and an active comparator human ADM arm, GJ-ADM, for the treatment of chronic diabetic foot ulcers. The study design was a prospective, randomized controlled trial that enrolled 168 diabetic foot ulcer subjects in 13 centers across 9 states. Subjects in the ADM arms received one application but could receive one additional application of ADM if deemed necessary. Screen failures and early withdrawals left 53 subjects in the D-ADM arm, 56 in the conventional care arm, and 23 in the GJ-ADM arm (2:2:1 ratio). Subjects were followed through 24 weeks with major endpoints at Weeks 12, 16, and 24. Single application D-ADM subjects showed significantly greater wound closure rates than conventional care at all three endpoints while all applications D-ADM displayed a significantly higher healing rate than conventional care at Week 16 and Week 24. GJ-ADM did not show a significantly greater healing rate over conventional care at any of these time points. A blinded, third party adjudicator analyzed healing at Week 12 and expressed "strong" agreement (κ = 0.837). Closed ulcers in the single application D-ADM arm remained healed at a significantly greater rate than the conventional care arm at 4 weeks posttermination (100% vs. 86.7%; p = 0.0435). There was no significant difference between GJ-ADM and conventional care for healed wounds remaining closed. Single application D-ADM demonstrated significantly greater average percent wound area reduction than conventional care for Weeks 2-24 while single application GJ-ADM showed significantly greater wound area reduction over conventional care for Weeks 4-6, 9, and 11-12. D-ADM demonstrated significantly greater wound healing, larger wound area reduction, and a better capability of keeping healed wounds closed than conventional care in the treatment of chronic DFUs.

Preparation and characterization of small-diameter decellularized scaffolds for vascular tissue engineering in an animal model

BACKGROUND

The development of a suitable extracellular matrix (ECM) scaffold is the first step in vascular tissue engineering (VTE). Synthetic vascular grafts are available as an alternative to autologous vessels in large-diameter arteries (>8 mm) and medium-diameter arteries (6-8 mm). In small-diameter vessels (<6 mm), synthetic vascular grafts are of limited use due to poor patency rates. Compared with a vascular prosthesis, natural tissue ECM has valuable advantages. Despite considerable progress in recent years, identifying an optimal protocol to create a scaffold for use in small-diameter (<6 mm) fully natural tissue-engineered vascular grafts (TEVG), remains elusive. Although reports on different decellularization techniques have been numerous, combination of and comparison between these methods are scarce; therefore, we have compared five different decellularization protocols for making small-diameter (<6 mm) ECM scaffolds and evaluated their characteristics relative to those of fresh vascular controls.

RESULTS

The protocols differed in the choice of enzymatic digestion solvent, the use of non-ionic detergent, the durations of the individual steps, and UV crosslinking. Due to their small diameter and ready availability, rabbit arteria carotis were used as the source of the ECM scaffolds. The scaffolds were subcutaneously implanted in rats and the results were evaluated using various microscopy and immunostaining techniques.

CONCLUSIONS

Our findings showed that a 2 h digestion time with 1× EDTA, replacing non-ionic detergent with double-distilled water for rinsing and the application of UV crosslinking gave rise to an ECM scaffold with the highest biocompatibility, lowest cytotoxicity and best mechanical properties for use in vivo or in situ pre-clinical research in VTE in comparison.

Decellularization Strategies for Regenerative Medicine: From Processing Techniques to Applications

As the gap between donors and patients in need of an organ transplant continues to widen, research in regenerative medicine seeks to provide alternative strategies for treatment. One of the most promising techniques for tissue and organ regeneration is decellularization, in which the extracellular matrix (ECM) is isolated from its native cells and genetic material in order to produce a natural scaffold. The ECM, which ideally retains its inherent structural, biochemical, and biomechanical cues, can then be recellularized to produce a functional tissue or organ. While decellularization can be accomplished using chemical and enzymatic, physical, or combinative methods, each strategy has both benefits and drawbacks. The focus of this review is to compare the advantages and disadvantages of these methods in terms of their ability to retain desired ECM characteristics for particular tissues and organs. Additionally, a few applications of constructs engineered using decellularized cell sheets, tissues, and whole organs are discussed.

Cell-free vascular grafts: Recent developments and clinical potential

Recent advances in vascular tissue engineering have led to the development of cell-free grafts that are available off-the-shelf for on demand surgery. Challenges associated with cell-based technologies including cell sourcing, cell expansion and long-term bioreactor culture motivated the development of completely cell-free vascular grafts. These are based on decellularized arteries, decellularized cultured cell-based tissue engineered grafts or biomaterials functionalized with biological signals that promote in situ tissue regeneration. Clinical trials undertaken to demonstrate the applicability of these grafts are also discussed. This comprehensive review summarizes recent developments in vascular graft technologies, with potential applications in coronary artery bypass procedures, lower extremity bypass, vascular injury and trauma, congenital heart diseases and dialysis access shunts, to name a few.

Diameter and thickness-related variations in mechanical properties of degraded arterial wall in the rat xenograft model

The purpose of this study was to evaluate the diameter and thickness-related variations in mechanical properties of degraded arterial wall. To this end, ring tests were performed on 31 samples from the rat xenograft model of abdominal aortic aneurysm (AAA) and failure properties were determined. An inverse finite element method was then employed to identify the material parameters of a hyperelastic and incompressible strain energy function. Correlations with outer diameter and wall thickness of the rings were examined. Furthermore, we investigated the changes in mechanical properties between the grafts, which consist in guinea pig decellularized aortas, native murine aortas and degraded aortas (AAAs). Decellularized aortas presented a significantly lower ultimate strain associated with a higher stiffening rate compared to native aortas. AAAs exhibited a significantly lower ultimate stress than other groups and an extensible-but-stiff behavior. The proposed approach revealed correlations of ultimate stress and material parameters of aneurysmal aortas with outer diameter and thickness. In particular, the negative correlations of the material parameter accounting for the response of the non-collagenous matrix with diameter and thickness (r=-0.67 and r=-0.73, p<0.001) captured the gradual loss of elastin with dilatation observed in histology (r=-0.97, p<0.001). Moreover, it exposed the progressive weakening of the wall with enlargement and thickening (r=-0.64 and r=-0.69, p<0.001), suggesting that wall thickness and diameter may be indicators of rupture risk in the rat xenograft model.

Development of an in-process UV-crosslinked, electrospun PCL/aPLA-co-TMC composite polymer for tubular tissue engineering applications

Cardiovascular diseases remain the largest cause of death worldwide, and half of these deaths are the result of failure of the vascular system. Tissue engineering promises to provide new, and potentially more effective therapeutic strategies to replace damaged or degenerated vessels with functional vessels. However, these engineered vessels have substantial performance criteria, including vessel-like tubular shape, structure and mechanical property slate. Further, whether implanted without or with prior in vitro culture, such tubular scaffolds must provide a suitable environment for cell adhesion and growth and be of sufficient porosity to permit cell colonization. This study investigates the fabrication of slowly degradable, composite tubular polymer scaffolds made from polycaprolactone (PCL) and acrylated l-lactide-co-trimethylene carbonate (aPLA-co-TMC). The addition of acrylate groups permits the 'in-process' formation of crosslinks between aPLA-co-TMC chains during electrospinning of the composite system, exemplifying a novel process to produce multicomponent, elastomeric electrospun polymer scaffolds. Although PCL and aPLA-co-TMC were miscible in a co-solvent, a criteria for electrospinning, due to thermodynamic incompatibility of the two polymers as melts, solvent evaporation during electrospinning drove phase separation of these two systems, producing 'core-shell' fibres, with the core being composed of PCL, and the shell of crosslinked elastomeric aPLA-co-TMC. The resulting elastic fibrous scaffolds displayed burst pressures and suture retention strengths comparable with human arteries. Cytocompatibility testing with human mesenchymal stem cells confirmed adhesion to, and proliferation on the three-dimensional fibrous network, as well as alignment with highly-organized fibres. This new processing methodology and resulting mechanically-robust composite scaffolds hold significant promise for tubular tissue engineering applications.

STATEMENT OF SIGNIFICANCE

Autologous small diameter blood vessel grafts are unsuitable solutions for vessel repair. Engineered solutions such as tubular biomaterial scaffolds however have substantial performance criteria to meet, including vessel-like tubular shape, structure and mechanical property slate. We detail herein an innovative methodology to co-electrospin and 'in-process' crosslink composite mixtures of Poly(caprolactone) and a newly synthesised acrylated-Poly(lactide-co-trimethylene-carbonate) to create elastomeric, core-shell nanofibrous porous scaffolds in a one-step process. This novel composite system can be used to make aligned scaffolds that encourage stem cell adhesion, growth and morphological control, and produce robust tubular scaffolds of tunable internal diameter and wall thickness that possess mechanical properties approaching those of native vessels, ideal for future applications in the field of vessel tissue engineering.

Decellularized human placenta chorion matrix as a favorable source of small-diameter vascular grafts

Biomaterials based on decellularized tissues are increasingly attracting attention as functional alternatives to other natural or synthetic materials. However, a source of non-cadaver human allograft material would be favorable. Here we establish a decellularization method of vascular tissue from cryopreserved human placenta chorionic plate starting with an initial freeze-thaw step followed by a series of chemical treatments applied with a custom-made perfusion system. This novel pulsatile perfusion set-up enabled us to successfully decellularize the vascular tissue with lower concentrations of chemicals and shorter exposure times compared to a non-perfusion process. The decellularization procedure described here lead to the preservation of the native extracellular matrix architecture and the removal of cells. Quantitative analysis revealed no significant changes in collagen content and a retained glycosaminoglycan content of approximately 29%. In strain-to-failure tests, the decellularized grafts showed similar mechanical behavior compared to native controls. In addition, the mechanical values for ultimate tensile strength and stiffness were in an acceptable range for in vivo applications. Furthermore, biocompatibility of the decellularized tissue and its recellularizationability to serve as an adequate substratum for upcoming recellularization strategies using primary human umbilical vein endothelial cells (HUVECs) was demonstrated. HUVECs cultured on the decellularized placenta vessel matrix performed endothelialization and maintained phenotypical characteristics and cell specific expression patterns. Overall, the decellularized human placenta vessels can be a versatile tool for experimental studies on vascularization and as potent graft material for future in vivo applications.

STATEMENT OF SIGNIFICANCE

In the US alone more than 1million vascular grafts are needed in clinical practice every year. Despite severe disadvantages, such as donor site morbidity, autologous grafting from the patient's own arteries or veins is regarded as the gold standard for vascular tissue repair. Besides, strategies based on synthetic or natural materials have shown limited success. Tissue engineering approaches based on decellularized tissues are regarded as a promising alternative to clinically used treatments to overcome the observed limitations. However, a source for supply of non-cadaver human allograft material would be favorable. Here, we established a decellularization method of vascular tissue from the human placenta chorionic plate, a suitable human tissue source of consistent quality. The decellularized human placenta vessels can be a potent graft material for future in vivo applications and furthermore might be a versatile tool for experimental studies on vascularization.

Arterial Decellularized Scaffolds Produced Using an Innovative Automatic System

There is still an unmet clinical need for small-caliber artery substitution. Decellularized scaffolds in tissue engineering represent a promising solution. We have developed an innovative system for the automatic decellularization of blood vessels, used to process pig arteries. The system is able to automatically drive a decellularization process in a safe and reliable environment, with complex time patterns, using up to three different decellularization solutions, and providing at the same time a physical stress to improve the decellularization. The decellularization of pig arteries was evaluated by means of histology, DNA quantification and mechanical testing. Outcomes showed scaffolds with no cellular or nuclear remnants and a well-preserved tissue structure, corroborated by mechanical properties similar to native tissue. Decellularized scaffolds were seeded on the inner layer with human endothelial cells and implanted as iliac artery replacement in 4 pharmacologically immune-compromised pigs. This chimeric model was performed as a very preliminary evaluation to investigate the performances of these scaffolds in vivo, and to investigate the fate of seeded cells. Recipients were sacrificed on day 14 and day 70 after surgery, and vessels were found to be patent and with no evidence of thrombi formation. The inner layer was covered by endothelial cells, and the migration of cells positive for α-smooth-muscle actin was observed from the outer layer towards the tunica media. Intriguingly, the endothelial cells on explanted vessels were entirely derived from the host while the seeded cells were lost. In conclusion, this work presents a novel tool for a safe and controlled production of arterial scaffolds, with good decellularization outcomes and a good performance in a short-term, large-animal implantation.

Decellularized biological matrices: an interesting approach for cardiovascular tissue repair and regeneration

The repair and replacement of blood vessels is one of the most challenging topics for biomedical research. Autologous vessels are preferred as graft materials, but they still have many issues to overcome: for instance, they need multiple surgical procedures and often patients may not have healthy and surgically valuable arteries useful as an autograft. A tissue-engineering approach is widely desirable to generate biological vascular prostheses. Recently, decellularization of native tissue has gained significant attention in the biomedical research field. This method is used to obtain biological scaffolds that are expected to maintain the complex three-dimensional structure of the extracellular matrix, preserving the biomechanical properties of the native tissues. The decellularizing methods and the biomechanical characteristics of these products are presented in this review. Decellularization of biological matrices induces the loss of major histocompatibility complex (MHC), which is expected to promote an immunological response by the host. All the studies showed that decellularized biomaterials possess adequate properties for xenografting. Concerning their mechanical properties, several studies have demonstrated that, although chemical decellularization methods do not affect the scaffolds' mechanical properties, these materials can be modified through different treatments in order to provide the desired mechanical characteristics, depending on the specific application. A short overview of legislative issues concerning the use of decellularized substitutes and future perspectives in surgical applications is also presented. Copyright © 2015 John Wiley & Sons, Ltd.

Biomimetic microstructural reorganization during suture retention strength evaluation of electrospun vascular scaffolds

Suture retention strength (SRS) is commonly used as a measure the ability of sutures to adhere implants to surrounding tissue. While SRS is widely employed, surprisingly its effects on graft microstructure have not been characterized. This is particularly germane to the broad utilization of electrospun implants in tissue engineering. These implants need to retain their initial nanoscale topography while simultaneously preserving clinically critical mechanical properties. We examined the suture-driven microstructural deformation of polycaprolactone electrospun to form both square and tubular SRS samples. The impact of fiber orientation (generally parallel or random orientation, orthogonally aligned) on the SRS of these vascular tissue equivalents was analyzed and compared to native and decellularized porcine vasculature. The initial state of the fiber clearly dictates the overall efficiency of scaffold utilization. SRS values for as-spun fibers at a thickness of 300 μm were found to be in the range of 1.59-4.78 N for the three orientations. Unexpectedly, random fibers provided the optimal SRS values based on both resistance to suture motion and the percentage of scaffold involvement. A "V-shaped" failure morphology is observed for both electrospun scaffolds and native tissue during SRS testing. Post-test fiber alignment in the tensile direction was visible in all initial fiber orientations similar to that of native tissue. These findings are significant as they allow us to employ new, counterintuitive biomimetic design criteria for nanofiber-based scaffolds in which reliable mechanical integration with the surrounding tissues via suture-based methods is important. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1525-1534, 2016.

Small diameter electrospun silk fibroin vascular grafts: Mechanical properties, in vitro biodegradability, and in vivo biocompatibility

To overcome the drawbacks of autologous grafts currently used in clinical practice, vascular tissue engineering represents an alternative approach for the replacement of small diameter blood vessels. In the present work, the production and characterization of small diameter tubular matrices (inner diameter (ID)=4.5 and 1.5 mm), obtained by electrospinning (ES) of Bombyx mori silk fibroin (SF), have been considered. ES-SF tubular scaffolds with ID=1.5 mm are original, and can be used as vascular grafts in pediatrics or in hand microsurgery. Axial and circumferential tensile tests on ES-SF tubes showed appropriate properties for the specific application. The burst pressure and the compliance of ES-SF tubes were estimated using the Laplace's law. Specifically, the estimated burst pressure was higher than the physiological pressures and the estimated compliance was similar or higher than that of native rat aorta and Goretex® prosthesis. Enzymatic in vitro degradation tests demonstrated a decrease of order and crystallinity of the SF outer surface as a consequence of the enzyme activity. The in vitro cytocompatibility of the ES-SF tubes was confirmed by the adhesion and growth of primary porcine smooth muscle cells. The in vivo subcutaneous implant into the rat dorsal tissue indicated that ES-SF matrices caused a mild host reaction. Thus, the results of this investigation, in which comprehensive morphological and mechanical aspects, in vitro degradation and in vitro and in vivo biocompatibility were considered, indicate the potential suitability of these ES-SF tubular matrices as scaffolds for the regeneration of small diameter blood vessels.

Cells and stimuli in small-caliber blood vessel tissue engineering

The absence of successful solutions in treatments of small-caliber vessel diseases led to the Vascular Tissue Engineering approach to develop functional nonimmunogenic tissue engineered blood vessels. In this context, the choice of cells to be seeded and the microenvironment conditioning are pivotal. Biochemical and biomechanical stimuli seem to activate physiological regulatory pathways that induce the production of molecules and proteins stimulating stem cell differentiation toward vascular lineage and reproducing natural cross-talks among vascular cells to improve the maturation of tissue engineered blood vessels. Thus, this review focuses on (1) available cell sources, and (2) biochemical and biomechanical stimuli, with the final aim to obtain the long-term stability of the endothelium and mechanical properties suitable for withstanding physiological load.

Effect of Intensified Decellularization of Equine Carotid Arteries on Scaffold Biomechanics and Cytotoxicity

Decellularized equine carotid arteries (dEAC) are suggested to represent an alternative for alloplastic vascular grafts in haemodialysis patients to achieve vascular access. Recently it was shown that intensified detergent treatment completely removed cellular components from dEAC and thereby significantly reduced matrix immunogenicity. However, detergents may also affect matrix composition and stability and render scaffolds cytotoxic. Therefore, intensively decellularized carotids (int-dEAC) were now evaluated for their biomechanical characteristics (suture retention strength, burst pressure and circumferential compliance at arterial and venous systolic and diastolic pressure), matrix components (collagen and glycosaminoglycan content) and indirect and direct cytotoxicity (WST-8 assay and endothelial cell seeding) and compared with native (n-EAC) and conventionally decellularized carotids (con-dEAC). Both decellularization protocols comparably reduced matrix compliance (venous pressure compliance: 32.2 and 27.4% of n-EAC; p < 0.01 and arterial pressure compliance: 26.8 and 23.7% of n-EAC, p < 0.01) but had no effect on suture retention strength and burst pressure. Matrix characterization revealed unchanged collagen contents but a 39.0% (con-dEAC) and 26.4% (int-dEAC, p < 0.01) reduction of glycosaminoglycans, respectively. Cytotoxicity was not observed in either dEAC matrix which was also displayed by an intact endothelial lining after seeding. Thus, even intensified decellularization generates matrix scaffolds highly suitable for vascular tissue engineering purposes, e.g., the generation of haemodialysis shunts.

Decellularization of human dermis using non-denaturing anionic detergent and endonuclease: a review

Decellularized human dermis has been used for a number of clinical applications including wound healing, soft tissue reconstruction, and sports medicine procedures. A variety of methods exist to prepare this useful class of biomaterial. Here, we describe a decellularization technology (MatrACELL^®) utilizing a non-denaturing anionic detergent, N-Lauroyl sarcosinate, and endonuclease, which was developed to remove potentially immunogenic material while retaining biomechanical properties. Effective decellularization was demonstrated by a residual DNA content of ≤4 ng/mg of wet weight which represented >97 % DNA removal compared to unprocessed dermis. Two millimeter thick MatrACELL processed human acellular dermal matrix (MH-ADM) exhibited average ultimate tensile load to failure of 635.4 ± 199.9 N and average suture retention strength of 134.9 ± 55.1 N. Using an in vivo mouse skin excisional model, MH-ADM was shown to be biocompatible and capable of supporting cellular and vascular in-growth. Finally, clinical studies of MH-ADM in variety of applications suggest it can be an appropriate scaffold for wound healing, soft tissue reconstruction, and soft tissue augmentation.

An experimental study to replace the thoracic descending aorta for pigs with a self-made sutureless blood vessel

To simplify the procedure of blood vessel replacement operation and shorten the vascular anastomosis time, we developed a special artificial blood vessel which can be connected to native blood vessels without suture. The self-made sutureless blood vessel (SMSBV) was made from two titanium connectors and a Gore-Tex graft. To investigate blood compatibility and histocompatibility of the SMSBV, we carried thoracic descending aorta replacement using either SMSBV or Gore-Tex, respectively, in pigs. The aortic clamp time and the operative blood loss in the experimental group (using SMSBV) were less than those in the control group (using Gore-Tex). The whole blood hematocrit, platelet count, plasma soluble P-selectin, plasma free hemoglobin, and interleukins 2, 6 at each time point were not different significantly between the two groups. Light microscopy and transmission electron microscopy examination showed there were layers of vascular smooth muscle cells and endothelial cells adhered in the inner wall of artificial blood vessel without any signs of thrombosis. Based on the result, we have drawn the conclusion that the application of SMSBV can significantly shorten the vascular anastomosis time, reduce operative blood loss, and show good blood and tissue compatibility.

Decellularized matrices for cardiovascular tissue engineering

Cardiovascular disease (CVD) is one of the leading causes of death in the Western world. The replacement of damaged vessels and valves has been practiced since the 1950's. Synthetic grafts, usually made of bio-inert materials, are long-lasting and mechanically relevant, but fail when it comes to "biointegration". Decellularized matrices, instead, can be considered biological grafts capable of stimulating in vivo migration and proliferation of endothelial cells (ECs), recruitment and differentiation of mural cells, finally, culminating in the formation of a biointegrated tissue. Decellularization protocols employ osmotic shock, ionic and non-ionic detergents, proteolitic digestions and DNase/RNase treatments; most of them effectively eliminate the cellular component, but show limitations in preserving the native structure of the extracellular matrix (ECM). In this review, we examine the current state of the art relative to decellularization techniques and biological performance of decellularized heart, valves and big vessels. Furthermore, we focus on the relevance of ECM components, native and resulting from decellularization, in mediating in vivo host response and determining repair and regeneration, as opposed to graft corruption.

Vascular Tissue Engineering: Recent Advances in Small Diameter Blood Vessel Regeneration

Cardiovascular diseases are the leading cause of mortality around the globe. The development of a functional and appropriate substitute for small diameter blood vessel replacement is still a challenge to overcome the main drawbacks of autografts and the inadequate performances of synthetic prostheses made of polyethylene terephthalate (PET, Dacron) and expanded polytetrafluoroethylene (ePTFE, Goretex). Therefore, vascular tissue engineering has become a promising approach for small diameter blood vessel regeneration as demonstrated by the increasing interest dedicated to this field. This review is focused on the most relevant and recent studies concerning vascular tissue engineering for small diameter blood vessel applications. Specifically, the present work reviews research on the development of tissue-engineered vascular grafts made of decellularized matrices and natural and/or biodegradable synthetic polymers and their realization without scaffold.