The application of a thermoresponsive chitosan/β-GP gel to enhance cell repopulation of decellularized vascular scaffolds

Photo-induced universal modification of small-diameter decellularized blood vessels with a hemocompatible peptide improves in vivo patency

Decellularized vessels (DVs) have the potential to serve as available grafts for small-diameter vascular (<6 mm) reconstruction. However, the absence of functional endothelia makes them likely to trigger platelet aggregation and thrombosis. Luminal surface modification is an efficient approach to prevent thrombosis and promote endothelialization. Previously, we identified a hemocompatible peptide, HGGVRLY, that showed endothelial affinity and antiplatelet ability. By conjugating HGGVRLY with a phenylazide group, we generated a photoreactive peptide that can be modified onto multiple materials, including non-denatured extracellular matrices. To preserve the natural collagen of DVs as much as possible, we used a lower ultrahydrostatic pressure than that previously reported to prepare decellularized grafts. The photoreactive HGGVRLY peptide could be modified onto DV grafts via UV exposure for only 2 min. Modified DVs showed improved endothelial affinity and antiplatelet ability in vitro. When rat abdominal aortas were replaced with DVs, modified DVs with more natural collagen demonstrated the highest patent rate after 10 weeks. Moreover, the photoreactive peptide remained on the lumen surface of DVs over two months after implantation. Therefore, the photoreactive peptide could be efficiently and sustainably modified onto DVs with more natural collagens, resulting in improved hemocompatibility. STATEMENT OF SIGNIFICANCE: We employed a relatively lower ultrahydrostatic pressure to prepare decellularized vessels (DVs) with less denatured collagens to provide a more favorable environment for cell migration and proliferation. The hemocompatibility of DV luminal surface can be enhanced by peptide modification, but undenatured collagens are difficult to modify. We innovatively introduce a phenylazide group into the hemocompatible peptide HGGVRLY, which we previously identified to possess endothelial affinity and antiplatelet ability, to generate a photoreactive peptide. The photoreactive peptide can be efficiently and stably modified onto DVs with more natural collagens. DV grafts modified with photoreactive peptide exhibit enhanced in vivo patency. Furthermore, the sustainability of photoreactive peptide modification on DV grafts within bloodstream is evident after two months of transplantation.

Hydrogel Tissue Bioengineered Scaffolds in Bone Repair: A Review

Large bone defects due to trauma, infections, and tumors are difficult to heal spontaneously by the body's repair mechanisms and have become a major hindrance to people's daily lives and economic development. However, autologous and allogeneic bone grafts, with their lack of donors, more invasive surgery, immune rejection, and potential viral transmission, hinder the development of bone repair. Hydrogel tissue bioengineered scaffolds have gained widespread attention in the field of bone repair due to their good biocompatibility and three-dimensional network structure that facilitates cell adhesion and proliferation. In addition, loading natural products with nanoparticles and incorporating them into hydrogel tissue bioengineered scaffolds is one of the most effective strategies to promote bone repair due to the good bioactivity and limitations of natural products. Therefore, this paper presents a brief review of the application of hydrogels with different gel-forming properties, hydrogels with different matrices, and nanoparticle-loaded natural products loaded and incorporated into hydrogels for bone defect repair in recent years.

The application of composite scaffold materials based on decellularized vascular matrix in tissue engineering: a review

Decellularized vascular matrix is a natural polymeric biomaterial that comes from arteries or veins which are removed the cellular contents by physical, chemical and enzymatic means, leaving only the cytoskeletal structure and extracellular matrix to achieve cell adhesion, proliferation and differentiation and creating a suitable microenvironment for their growth. In recent years, the decellularized vascular matrix has attracted much attention in the field of tissue repair and regenerative medicine due to its remarkable cytocompatibility, biodegradability and ability to induce tissue regeneration. Firstly, this review introduces its basic properties and preparation methods; then, it focuses on the application and research of composite scaffold materials based on decellularized vascular matrix in vascular tissue engineering in terms of current in vitro and in vivo studies, and briefly outlines its applications in other tissue engineering fields; finally, it looks into the advantages and drawbacks to be overcome in the application of decellularized vascular matrix materials. In conclusion, as a new bioactive material for building engineered tissue and repairing tissue defects, decellularized vascular matrix will be widely applied in prospect.

Cardiac tissue engineering for myocardial infarction treatment

Myocardial infarction is one of the major causes of morbidity and mortality worldwide. Current treatments can relieve the symptoms of myocardial ischemia but cannot repair the necrotic myocardial tissue. Novel therapeutic strategies based on cellular therapy, extracellular vesicles, non-coding RNAs and growth factors have been designed to restore cardiac function while inducing cardiomyocyte cycle re-entry, ensuring angiogenesis and cardioprotection, and preventing ventricular remodeling. However, they face low stability, cell engraftment issues or enzymatic degradation in vivo, and it is thus essential to combine them with biomaterial-based delivery systems. Microcarriers, nanocarriers, cardiac patches and injectable hydrogels have yielded promising results in preclinical studies, some of which are currently being tested in clinical trials. In this review, we cover the recent advances made in cellular and acellular therapies used for cardiac repair after MI. We present current trends in cardiac tissue engineering related to the use of microcarriers, nanocarriers, cardiac patches and injectable hydrogels as biomaterial-based delivery systems for biologics. Finally, we discuss some of the most crucial aspects that should be addressed in order to advance towards the clinical translation of cardiac tissue engineering approaches.

Decellularization of Porcine Carotid Arteries: From the Vessel to the High-Quality Scaffold in Five Hours

The use of biologically derived vessels as small-diameter vascular grafts in vascular diseases is currently intensely studied. Vessel decellularization provides a biocompatible scaffold with very low immunogenicity that avoids immunosuppression after transplantation. Good scaffold preservation is important as it facilitates successful cell repopulation. In addition, mechanical characteristics have to be carefully evaluated when the graft is intended to be used as an artery due to the high pressures the vessel is subjected to. Here, we present a new and fast decellularization protocol for porcine carotid arteries, followed by investigation of the quality of obtained vessel scaffolds in terms of maintenance of important extracellular matrix components, mechanical resistance, and compatibility with human endothelial cells. Our results evidence that our decellularization protocol minimally alters both the presence of scaffold proteins and their mechanical behavior and human endothelial cells could adhere to the scaffold in vitro. We conclude that if a suitable protocol is used, a high-quality decellularized arterial scaffold of non-human origin can be promptly obtained, having a great potential to be recellularized and used as an arterial graft in transplantation medicine.

Accelerated tissue regeneration in decellularized vascular grafts with a patterned pore structure

Decellularized tissue is expected to be utilized as a regenerative scaffold. However, the migration of host cells into the central region of the decellularized tissues is minimal because the tissues are mainly formed with dense collagen and elastin fibers. This results in insufficient tissue regeneration. Herein, it is demonstrated that host cell migration can be accelerated by using decellularized tissue with a patterned pore structure. Patterned pores with inner diameters of 24.5 ± 0.4 μm were fabricated at 100, 250, and 500 μm intervals in the decellularized vascular grafts via laser ablation. The grafts were transplanted into rat subcutaneous tissue for 1, 2, and 4 weeks. All the microporous grafts underwent faster recellularization with macrophages and fibroblast cells than the non-porous control tissue. In the case of non-porous tissue, the cells infiltrated approximately 50% of the area four weeks after transplantation. However, almost the entire area was occupied by the cells after two weeks when the micropores were aligned at a distance of less than 250 μm. These results suggest that host cell infiltration depends on the micropore interval, and a distance shorter than 250 μm can accelerate cell migration into decellularized tissues.

Growth factor-eluting hydrogels for management of corneal defects

With 1.5-2.0 million new cases annually worldwide, corneal injury represents a common cause of vision loss, often from irreversible scarring due to surface corneal defects. In this study, we assessed the use of hepatocyte growth factor (HGF) loaded into an in situ photopolymerizable transparent gelatin-based hydrogel for the management of corneal defects. In vitro release kinetics showed that, in regard to the total amount of HGF released over a month, 55 ± 11% was released during the first 24 h, followed by a slow release profile for up to one month. The effect of HGF was assessed using an ex vivo model of pig corneal defect. After three days of organ culture, epithelial defects were found to be completely healed for 89% of the corneas treated with HGF, compared to only 11% of the corneas that had fully re-epithelialized when treated with the hydrogel without HGF. The thickness of the epithelial layer was found to be significantly higher for the HGF-treated group compared to the group treated with hydrogel without HGF (p = 0.0012). Finally, histological and immunostaining assessments demonstrated a better stratification and adhesion of the epithelial layer in the presence of HGF. These results suggest that the HGF-loaded hydrogel system represents a promising solution for the treatment of persistent corneal defects at risk of scarring.

Chitosan Hydrogel Enhances the Therapeutic Efficacy of Bone Marrow-Derived Mesenchymal Stem Cells for Myocardial Infarction by Alleviating Vascular Endothelial Cell Pyroptosis

Supplemental Digital Content is Available in the Text.

Myocardial infarction (MI) is one of the higher mortality rates, and current treatment can only delay the progression of the disease. Experiments have shown that cell therapy could improve cardiac function and mesenchymal stem cells (MSCs)-based therapies provide a great promising approach in the treatment of MI. However, low cell survival and engraftment restricts the successful application of MSCs for treating MI. Here, we explored whether co-transplantation of a chitosan (CS) thermosensitive hydrogel with bone marrow-derived MSCs (BMSCs) could optimize and maximize the therapeutic of BMSCs in a mouse model of MI. The fate of transplanted BMSCs was monitored by bioluminescence imaging, and the recovery of cardiac function was detected by echocardiogram. Our results proved that CS hydrogel enhanced the BMSCs' survival and the recovery of cardiac function by protecting the vascular endothelial cells. Further studies revealed that the increased number of vascular endothelial cells was due to the fact that transplanted BMSCs inhibited the inflammatory response and alleviated the pyroptosis of vascular endothelial cells. In conclusions, CS hydrogel improved the engraftment of transplanted BMSCs, ameliorated inflammatory responses, and further promoted functional recovery of heart by alleviating vascular endothelial cell pyroptosis.

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.

Enhancing medial layer recellularization of tissue-engineered blood vessels using radial microchannels

Aim: Cell repopulation of tissue-engineered vascular grafts (TEVGs) from decellularized arterial scaffolds is limited by dense concentric tunica media layers which impede cells migrating radially between the layers. We aimed to develop and validate a new microneedle device to modify decellularized carotid arteries with radial microchannels to enhance medial layer repopulation. Material & methods: Modified decellularized porcine arteries were seeded with rat mesenchymal stem cells using either standard longitudinal injection, or a dual vacuum-perfusion bioreactor. Mechanical tests were used to assess the arterial integrity following modification. Results & conclusion: The method herein achieved radial recellularization of arteries in vitro without significant loss of mechanical integrity, Thus, we report a novel method for successful radial repopulation of decellularized carotid artery-based tissue-engineered vascular grafts.

Thermoresponsive polysaccharides and their thermoreversible physical hydrogel networks

Thermoresponsive polymers have been used extensively for various applications including food additives, pharmaceutical formulations, therapeutic delivery, cosmetics and environmental remediation, to mention a few. Many thermoresponsive polymers have the ability to form physical hydrogel networks in response to temperature changes, which are particularly useful for emerging biomedical applications, including cell therapies, drug delivery systems, tissue engineering, wound healing and 3D bioprinting. In particular, the use of polysaccharides with thermoresponsive properties has been of interest due to their wide availability, versatile functionality, biodegradability, and in many cases, inherent biocompatibility. Naturally thermoresponsive polysaccharides include agarose, carrageenans and gellan gum, which exhibit upper critical solution temperatures, transitioning from a solution to a gel state upon cooling. Arguably, this limits their use in biomedical applications, particularly for cell encapsulation as they require raised temperatures to maintain a solution state that may be detrimental to living systems. Conversely, significant progress has been made over recent years to develop synthetically modified polysaccharides, which tend to exhibit lower critical solution temperatures, transitioning from a solution to a gel state upon warming. Of particular interest are thermoresponsive polysaccharides with a lower critical solution temperature in between room temperature and physiological temperature, as their solutions can conveniently be manipulated at room temperature before gelling upon warming to physiological temperature, which makes them ideal candidates for many biological applications. Therefore, this review provides an introduction to the different types of thermoresponsive polysaccharides that have been developed, their resulting hydrogels and properties, and the exciting applications that have emerged as a result of these properties.

The use of heparin, bFGF, and VEGF 145 grafted acellular vascular scaffold in small diameter vascular graft

We aim to test the application of heparin, bFGF, and VEGF 145 grafted acellular vascular scaffold in small diameter vascular graft. The amount of bFGF and VEGF 145 were determined by ELISA. Femoral artery transplantation was performed. Mechanical strength of acellular vascular scaffolds was determined. Angiography was performed for blood vessel patency. Factor VIII and α2-actin expression was detected by immunohistochemistry. bFGF and VEGF 145 had stable release at 60 and 70 days in vitro, and the release rate of VEGF 145 was slightly slower than that of bFGF. After transplantation, 9 months of the vascular patency rate was 100% at 1, 3, and 9 months, and, was up to 90% at 18 months, while the patency rate in group with grafted heparin only at 1-month was 60%, at 3-month was 40%, at 9-month was 15%, and at 18-month was 10%. The blood vessels taken after 18 months had no significant difference in the mechanical properties between the transplanted and the natural vessels. Positive expression of factor VIII and α2-actin was observed. The heparinized and bFGF and VEGF 145 grafted allogeneic vascular acellular scaffolds are preliminarily obtained, which show good biocompatibility and patency and are of great importance for small diameter vascular graft. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 00B: 000-000, 2018. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 672-679, 2019.

Polymersome–hydrogel composites with combined quick and long-term antibacterial activities

Intrinsically antibacterial polymersomes loaded with antibiotics were incorporated into hydrogels, exhibiting quick and long-acting antibacterial activity.

Comprehensive mechanical characterization of PLA fabric combined with PCL to form a composite structure vascular graft

Vascular grafts made by tissue engineering processes are prone to buckling and twisting, which can impede blood flow and lead to collapse of the vessel. These vascular conduits may suffer not only from insufficient tensile strength, but also from vulnerabilities related to compression, torsion, and pulsatile pressurization. Aiming to develop a tissue engineering-inspired blood conduit, composite vascular graft (cVG) prototypes were created by combining a flexible polylactic acid (PLA) knitted fabric with a soft polycaprolactone (PCL) matrix. The graft is to be populated in-situ with cellular migration and proliferation into the device. Comprehensive characterizations probed the relationship between structure and mechanical properties of the different cVG prototypes. The composite grafts exhibited major improvements in mechanical characteristics compared to single-material devices, with particular improvement in compression and torsional resistance. A commercial expanded polytetrafluoroethylene (ePTFE) vascular graft was used as a control against the proposed composite vascular grafts. CVG devices showed high tensile strength, high bursting strength, and improved suture retention. Compression, elastic recovery, and compliance were similar to those for the ePTFE graft.

Cell-microenvironment interactions and architectures in microvascular systems

In the past decade, significant advances have been made in the design and optimization of novel biomaterials and microfabrication techniques to generate vascularized tissues. Novel microfluidic systems have facilitated the development and optimization of in vitro models for exploring the complex pathophysiological phenomena that occur inside a microvascular environment. To date, most of these models have focused on engineering of increasingly complex systems, rather than analyzing the molecular and cellular mechanisms that drive microvascular network morphogenesis and remodeling. In fact, mutual interactions among endothelial cells (ECs), supporting mural cells and organ-specific cells, as well as between ECs and the extracellular matrix, are key driving forces for vascularization. This review focuses on the integration of materials science, microengineering and vascular biology for the development of in vitro microvascular systems. Various approaches currently being applied to study cell-cell/cell-matrix interactions, as well as biochemical/biophysical cues promoting vascularization and their impact on microvascular network formation, will be identified and discussed. Finally, this review will explore in vitro applications of microvascular systems, in vivo integration of transplanted vascularized tissues, and the important challenges for vascularization and controlling the microcirculatory system within the engineered tissues, especially for microfabrication approaches. It is likely that existing models and more complex models will further our understanding of the key elements of vascular network growth, stabilization and remodeling to translate basic research principles into functional, vascularized tissue constructs for regenerative medicine applications, drug screening and disease models.

Decellularization of porcine articular cartilage explants and their subsequent repopulation with human chondroprogenitor cells

Engineering tissues with comparable structure, composition and mechanical functionality to native articular cartilage remains a challenge. One possible solution would be to decellularize xenogeneic articular cartilage in such a way that the structure of the tissue is maintained, and to then repopulate this decellularized matrix with human chondroprogenitor cells that will facilitate the reconstitution, maintenance and eventual turnover of the construct following implantation. The overall objective of this study was to develop a protocol to efficiently decellularize porcine articular cartilage grafts and to identify a methodology to subsequently repopulate such explants with human chondroprogenitor cells. To this end, channels were first introduced into cylindrical articular cartilage explants, which were then decellularized with a combination of various chemical reagents including sodium dodecyl sulfate (SDS) and nucleases. The decellularization protocol resulted in a ~90% reduction in porcine DNA content, with little observed effect on the collagen content and the collagen architecture of the tissue, although a near-complete removal of sulfated glycosaminoglycans (sGAG) and a related reduction in tissue compressive properties was observed. The introduction of channels did not have any detrimental effect on the biochemical or the mechanical properties of the decellularized tissue. Next, decellularized cartilage explants with or without channels were seeded with human infrapatellar fat pad derived stem cells (FPSCs) and cultured chondrogenically under either static or rotational conditions for 10 days. Both channeled and non-channeled explants supported the viability, proliferation and chondrogenic differentiation of FPSCs. The addition of channels facilitated cell migration and subsequent deposition of cartilage-specific matrix into more central regions of these explants. The application of rotational culture appeared to promote a less proliferative cellular phenotype and led to an increase in sGAG synthesis within the explants. Rotational culture also appeared to promote higher cell viability and led to a more even distribution of cells within the channels of decellularized explants. To conclude, this study describes an effective protocol for the decellularization of porcine articular cartilage grafts and a novel methodology for the partial recellularization of such explants with human stem cells. Decellularized soft tissue explants that maintain their native collagen architecture may represent promising scaffolds for musculoskeletal tissue engineering applications.

Development of decellularized scaffolds for stem cell-driven tissue engineering

Organ transplantation is an effective treatment for chronic organ dysfunctioning conditions. However, a dearth of available donor organs for transplantation leads to the death of numerous patients waiting for a suitable organ donor. The potential of decellularized scaffolds, derived from native tissues or organs in the form of scaffolds has been evolved as a promising approach in tissue-regenerative medicine for translating functional organ replacements. In recent years, donor organs, such as heart, liver, lung and kidneys, have been reported to provide acellular extracellular matrix (ECM)-based scaffolds through the process called 'decellularization' and proved to show the potential of recellularization with selected cell populations, particularly with stem cells. In fact, decellularized stem cell matrix (DSCM) has also emerged as a potent biological scaffold for controlling stem cell fate and function during tissue organization. Despite the proven potential of decellularized scaffolds in tissue engineering, the molecular mechanism responsible for stem cell interactions with decellularized scaffolds is still unclear. Stem cells interact with, and respond to, various signals/cues emanating from their ECM. The ability to harness the regenerative potential of stem cells via decellularized ECM-based scaffolds has promising implications for tissue-regenerative medicine. Keeping these points in view, this article reviews the current status of decellularized scaffolds for stem cells, with particular focus on: (a) concept and various methods of decellularization; (b) interaction of stem cells with decellularized scaffolds; (c) current recellularization strategies, with associated challenges; and (iv) applications of the decellularized scaffolds in stem cell-driven tissue engineering and regenerative medicine. Copyright © 2015 John Wiley & Sons, Ltd.