Human fibroblast-derived ECM as a scaffold for vascular tissue engineering

Extracellular matrix-derived materials for tissue engineering and regenerative medicine: A journey from isolation to characterization and application

Biomaterial choice is an essential step during the development tissue engineering and regenerative medicine (TERM) applications. The selected biomaterial must present properties allowing the physiological-like recapitulation of several processes that lead to the reestablishment of homeostatic tissue or organ function. Biomaterials derived from the extracellular matrix (ECM) present many such properties and their use in the field has been steadily increasing. Considering this growing importance, it becomes imperative to provide a comprehensive overview of ECM biomaterials, encompassing their sourcing, processing, and integration into TERM applications. This review compiles the main strategies used to isolate and process ECM-derived biomaterials as well as different techniques used for its characterization, namely biochemical and chemical, physical, morphological, and biological. Lastly, some of their applications in the TERM field are explored and discussed.

Atherosclerotic three-layer nanomatrix vascular sheets for high-throughput therapeutic evaluation

In vitro atherosclerosis models are essential to evaluate therapeutics before in vivo and clinical studies, but significant limitations remain, such as the lack of three-layer vascular architecture and limited atherosclerotic features. Moreover, no scalable 3D atherosclerosis model is available for making high-throughput assays for therapeutic evaluation. Herein, we report an in vitro 3D three-layer nanomatrix vascular sheet with critical atherosclerosis multi-features (VSA), including endothelial dysfunction, monocyte recruitment, macrophages, extracellular matrix remodeling, smooth muscle cell phenotype transition, inflammatory cytokine secretion, foam cells, and calcification initiation. Notably, we present the creation of high-throughput functional assays with VSAs and the use of these assays for evaluating therapeutics for atherosclerosis treatment. The therapeutics include conventional drugs (statin and sirolimus), candidates for treating atherosclerosis (curcumin and colchicine), and potential gene therapy (miR-146a-loaded liposomes). The high efficiency and flexibility of the scalable VSA functional assays should facilitate drug discovery and development for atherosclerosis.

Bioprinting Methods for Fabricating In Vitro Tubular Blood Vessel Models

Dysfunctional blood vessels are implicated in various diseases, including cardiovascular diseases, neurodegenerative diseases, and cancer. Several studies have attempted to prevent and treat vascular diseases and understand interactions between these diseases and blood vessels across different organs and tissues. Initial studies were conducted using 2-dimensional (2D) in vitro and animal models. However, these models have difficulties in mimicking the 3D microenvironment in human, simulating kinetics related to cell activities, and replicating human pathophysiology; in addition, 3D models involve remarkably high costs. Thus, in vitro bioengineered models (BMs) have recently gained attention. BMs created through biofabrication based on tissue engineering and regenerative medicine are breakthrough models that can overcome limitations of 2D and animal models. They can also simulate the natural microenvironment in a patient- and target-specific manner. In this review, we will introduce 3D bioprinting methods for fabricating bioengineered blood vessel models, which can serve as the basis for treating and preventing various vascular diseases. Additionally, we will describe possible advancements from tubular to vascular models. Last, we will discuss specific applications, limitations, and future perspectives of fabricated BMs.

Poly(ε-Caprolactone) Substrates with Micro/Nanohierarchical Patterned Structures for Cell Culture

A simple, efficient and controllable one-step template method is proposed to fabricate poly(ε-caprolactone) substrates with micro/nanohierarchical patterned structures. Two kinds of geometric patterns with and without nanowires, i.e., hexagonal and strip with controllable island size and spacing are designed and fabricated. Furthermore, the influence of geometric patterns, island size, island spacing, and patterned nanowires (pNW) on the growth behavior of MG-63 cells is studied in terms of cell density, distribution, proliferation, morphogenesis, and cellular alignment. It is found that MG-63 cells prefer to adhere and grow on the substrate with smaller island size or spacing. Moreover, unlike the hexagonal structure, the strip structure can guide cellular alignment on its surface. In addition, the microisland structures and the pNW play different roles in promoting cell proliferation, distribution, and morphogenesis. It is concluded that the growth behavior of MG-63 cells can be well controlled by precisely adjusting the micro/nanostructure of the substrate surface. A simple and effective method is provided here for the regulation of cell growth behavior.

Repair of the Urethral Mucosa Defect Model Using Adipose-Derived Stem Cell Sheets and Monitoring the Fate of Indocyanine Green-Labeled Sheets by Near Infrared-II

Treatment of urethral mucosa defects is a major challenge in urology. Synthetic materials or autologous mucosa does not provide satisfactory treatment options for long-term or large urethral mucosa defects. In response to this problem, we used autologous adipose-derived stem cells (ADSCs) to synthesize cell sheets in vitro for repairing urethral mucosa defect models. In order to monitor the localization and distribution of cell sheets in vivo, cells and sheets were labeled with indocyanine green (ICG) and the second near-infrared (NIR-II) fluorescence imaging was performed. ICG-based NIR-II imaging can successfully track ADSCs and sheets in vivo up to 8 W. Then, rabbit urethral mucosa defect models were repaired with ICG-ADSCs sheets. At 3 months after operation, retrograde urethrography showed that ADSC sheets could effectively repair urethral mucosa defect and restore urethral patency. Histological analysis showed that in ADSC sheet groups, continuous epithelial cells covered the urethra at the transplantation site, and a large number of vascular endothelial cells could also be seen. In the cell-free sheet group, there was no continuous epithelial cell coverage at the repair site of the urethra, and the expression of pro-inflammatory factor TNF-α was increased. It shows that the extracellular matrix alone without cells is not suitable for repairing urethral defects. Surviving ADSCs in the sheets may play a key role in the repair process. This study provides a new tracing method for tissue engineering to dynamically track grafts using an NIR-II imaging system. The ADSC sheets can effectively restore the structure and function of the urethra. It provides a new option for the repair of urethral mucosa defects.

Effect of Decellularized Extracellular Matrix Bioscaffolds Derived from Fibroblasts on Skin Wound Healing and Remodeling

The mammalian tissue extracellular matrix (ECM) has been used as a scaffold to facilitate the repair and reconstruction of numerous tissues. However, the material properties of decellularized ECM (dECM) from in vitro cell cultures and the effect of these properties on wound remodeling remain unclear. To elucidate its biological activity, we extracted dECM from human lung fibroblasts, fabricated it into a patch, and applied it to a full-thickness skin wound. The fibroblast-derived dECM (fdECM) maintained the content of collagen Ⅰ, collagen Ⅳ, and elastin, and the extraction process did not damage its critical growth factors. The fdECM-conjugated collagen patch (COL-fdECM) facilitated wound contraction and angiogenesis in the proliferative phase when applied to the in vivo full-thickness skin wound model. Moreover, the COL-fdECM treated wound showed increased regeneration of the epidermal barrier function, mature collagen, hair follicle, and subepidermal nerve plexus, suggesting qualitative skin remodeling. This therapeutic efficacy was similarly observed when applied to the diabetic ulcer model. fdECM was shown to help remodel the tissue by regulating fibroblast growth factors, matrix metalloproteinases, and tissue inhibitors of metalloproteinases via the p38 and ERK signaling pathways in an in vitro experiment for understanding the underlying mechanism. These results provide a biological basis for cell-derived ECM as a multi-functional biomaterial applicable to various diseases.

BMSC-derived extracellular matrix better optimizes the microenvironment to support nerve regeneration

A favorable microenvironment plays an important role in nerve regeneration. Extracellular matrix (ECM) derived from cultured cells or natural tissues can facilitate nerve regeneration in the presence of various microenvironmental cues, including biochemical, spatial, and biomechanical factors. This study, through proteomics and three-dimensional image analysis, determines that the components and spatial organization of the ECM secreted by bone marrow mesenchymal cells (BMSCs) are more similar to acellular nerves than those of the ECMs derived from Schwann cells (SCs), skin-derived precursor Schwann cells (SKP-SCs), or fibroblasts (FBs). ECM-modified nerve grafts (ECM-NGs) are engineered by co-cultivating BMSCs, SCs, FBs, SKP-SCs with well-designed nerve grafts used to bridge nerve defects. BMSC-ECM-NGs exhibit the most promising nerve repair properties based on the histology, neurophysiology, and behavioral analyses. The regeneration microenvironment formed by the ECM-NGs is also characterized by proteomics, and the advantages of BMSC-ECM-NGs are evidenced by the enhanced expression of factors related to neural regeneration and reduced immune response. Together, these findings indicate that BMSC-derived ECMs create a more superior microenvironment for nerve regeneration than that by the other ECMs and may, therefore, represent a potential alternative for the clinical repair of peripheral nerve defects.

Bio-assembling and Bioprinting for Engineering Microvessels from the Bottom Up

Blood vessels are essential in transporting nutrients, oxygen, metabolic wastes, and maintaining the homeostasis of the whole human body. Mass of engineered microvessels is required to deliver nutrients to the cells included in the constructed large three-dimensional (3D) functional tissues by diffusion. It is a formidable challenge to regenerate microvessels and build a microvascular network, mimicking the cellular viabilities and activities in the engineered organs with traditional or existing manufacturing techniques. Modular tissue engineering adopting the "bottom-up" approach builds one-dimensional (1D) or two-dimensional (2D) modular tissues in micro scale first and then uses these modules as building blocks to generate large tissues and organs with complex but indispensable microstructural features. Building the microvascular network utilizing this approach could be appropriate and adequate. In this review, we introduced existing methods using the "bottom-up" concept developed to fabricate microvessels including bio-assembling powered by different micromanipulation techniques and bioprinting utilizing varied solidification mechanisms. We compared and discussed the features of the artificial microvessels engineered by these two strategies from multiple aspects. Regarding the future development of engineering the microvessels from the bottom up, potential directions were also concluded.

Three-dimensional endothelial cell incorporation within bioactive nanofibrous scaffolds through concurrent emulsion electrospinning and coaxial cell electrospraying

Nanofibrous scaffolds hold great promise in tissue engineering owing to their extracellular matrix (ECM)-mimicking architectures. Electrospinning, with its ease for producing nanofibrous scaffolds, has therefore been widely employed for various tissue engineering applications. However, electrospun nanofibrous scaffolds have faced the inherent challenge of three-dimensional (3D) cell distribution due to the small sizes of interconnected pores in these scaffolds when conventional approach of scaffold fabrication with subsequent cell seeding is adopted, which severely limits their applications in repairing/regenerating human body tissues with thick and vascularized structures. In this study, we demonstrate a method to directly place living endothelial cells within bioactive nanofibrous scaffolds in 3D through concurrent emulsion electrospinning and coaxial cell electrospraying. Using this concurrent manufacturing method, endothelial cells are encapsulated in hydrogel microspheres and deposited along with vascular endothelial growth factor (VEGF)-containing nanofibers in the scaffold fabrication process, resulting in nanofibrous scaffolds with 3D embedded cell-encapsulated microspheres. After selective disruption of the hydrogel microspheres, the encapsulated endothelial cells are released, yielding bioactive nanofibrous scaffolds with tissue-like 3D cell-incorporated nanofibrous structures. It is shown that cell viability is well preserved (>98%) during the concurrent manufacturing process and that a deep cell distribution (~100 μm) through the scaffold thickness has been achieved. With combined structural and biochemical cues via the 3D cell-incorporated architectures, endothelial cells can freely stretch, display enhanced intercellular connections, and maintain the phenotype in the bioactive nanofibrous scaffolds. Our investigations offer a promising platform technology for creating bioactive nanofibrous scaffolds with 3D cell incorporation and for overcoming inherent problems of electrospun nanofibrous scaffolds, which should open new avenues for biomanufacturing tissue-mimicking constructs with vascularized structures and complex anatomy. STATEMENT OF SIGNIFICANCE: Electrospun nanofibrous scaffolds face challenges in three-dimensional (3D) cell incorporation and vascularization. Enhancing cell penetration via enlarged interconnected pores is a common strategy to address that. However, there are conflicts between cell penetration and structural integrity for scaffolds formed using such strategy, as deep cell penetration, if possible, can only achieve in highly loose architectures. In this investigation, we demonstrate a concurrent emulsion electrospinning and coaxial cell electrospraying technique, realizing 3D endothelial cell incorporation in electrospun nanofibrous scaffolds independent of cell penetration. Our technology appropriately addresses the conflict between deep 3D cell incorporation and structural integrity. In the scaffolds, the 3D incorporated endothelial cells show well-preserved viability, phenotype and functions, implying improved vascularization potential.

Challenges and Possibilities of Cell-Based Tissue-Engineered Vascular Grafts

There is urgent demand for biologically compatible vascular grafts for both adult and pediatric patients. The utility of conventional nonbiodegradable materials is limited because of their thrombogenicity and inability to grow, while autologous vascular grafts involve considerable disadvantages, including the invasive procedures required to obtain these healthy vessels from patients and insufficient availability in patients with systemic atherosclerosis. All of these issues could be overcome by tissue-engineered vascular grafts (TEVGs). A large body of evidence has recently emerged in support of TEVG technologies, introducing diverse cell sources (e.g., somatic cells and stem cells) and novel fabrication methods (e.g., scaffold-guided and self-assembled approaches). Before TEVG can be applied in a clinical setting, however, several aspects of the technology must be improved, such as the feasibility of obtaining cells, their biocompatibility and mechanical properties, and the time needed for fabrication, while the safety of supplemented materials, the patency and nonthrombogenicity of TEVGs, their growth potential, and the long-term influence of implanted TEVGs in the body must be assessed. Although recent advances in TEVG fabrication have yielded promising results, more research is needed to achieve the most feasible methods for generating optimal TEVGs. This article reviews multiple aspects of TEVG fabrication, including mechanical requirements, extracellular matrix components, cell sources, and tissue engineering approaches. The potential of periodic hydrostatic pressurization in the production of scaffold-free TEVGs with optimal elasticity and stiffness is also discussed. In the future, the integration of multiple technologies is expected to enable improved TEVG performance.

Cell-Derived Extracellular Matrix for Tissue Engineering and Regenerative Medicine

Cell-derived extracellular matrices (CD-ECMs) captured increasing attention since the first studies in the 1980s. The biological resemblance of CD-ECMs to their in vivo counterparts and natural complexity provide them with a prevailing bioactivity. CD-ECMs offer the opportunity to produce microenvironments with costumizable biological and biophysical properties in a controlled setting. As a result, CD-ECMs can improve cellular functions such as stemness or be employed as a platform to study cellular niches in health and disease. Either on their own or integrated with other materials, CD-ECMs can also be utilized as biomaterials to engineer tissues de novo or facilitate endogenous healing and regeneration. This review provides a brief overview over the methodologies used to facilitate CD-ECM deposition and manufacturing. It explores the versatile uses of CD-ECM in fundamental research and therapeutic approaches, while highlighting innovative strategies. Furthermore, current challenges are identified and it is accentuated that advancements in methodologies, as well as innovative interdisciplinary approaches are needed to take CD-ECM-based research to the next level.

Use of bioactive extracellular matrix fragments as a urethral bulking agent to treat stress urinary incontinence

Injection of urethral bulking agents is a low-risk, minimally invasive surgical procedure to treat stress urinary incontinence (SUI). In this study, we developed a promising injectable bulking agent comprising extracellular matrix fragments of adipose-derived stem cell sheets (ADSC ECM) and investigated its effectiveness in urethral bulking therapy. The structural integrity and proteins of ADSC sheet ECM were well retained in decellularized ADSC ECM fragments. To locate transplanted ADSC ECM fragments, they were labeled with ultrasmall super-paramagnetic iron oxide nanoparticles, which enabled in vivo monitoring after implantation in a SUI rat model for up to 4 weeks. When ADSC ECM fragments were injected into the rat urethra, they became fully integrated with the surrounding tissue within 1 week. Four weeks after transplantation, host cells had regenerated within the ADSC ECM fragment injection area. Moreover, new smooth muscle tissue had formed around the ADSC ECM fragments, as confirmed by positive staining of myosin. These results indicate that injection of ECM fragments may be a promising minimally invasive approach for treating SUI.

Considerations in the Development of Small-Diameter Vascular Graft as an Alternative for Bypass and Reconstructive Surgeries: A Review

BACKGROUND

Current design strategies for small diameter vascular grafts (< 6 mm internal diameter; ID) are focused on mimicking native vascular tissue because the commercially available grafts still fail at small diameters, notably due to development of intimal hyperplasia and thrombosis. To overcome these challenges, various design approaches, material selection, and surface modification strategies have been employed to improve the patency of small-diameter grafts.

REVIEW

The purpose of this review is to outline various considerations in the development of small-diameter vascular grafts, including material choice, surface modifications to enhance biocompatibility/endothelialization, and mechanical properties of the graft, that are currently being implanted. Additionally, we have taken into account the general vascular physiology, tissue engineering approaches, and collective achievements of the authors in this area. We reviewed both commercially available synthetic grafts (e-PTFE and PET), elastic polymers such as polyurethane and biodegradable and bioresorbable materials. We included naturally occurring materials by focusing on their potential application in the development of future vascular alternatives.

CONCLUSION

Until now, there are few comprehensive reviews regarding considerations in the design of small-diameter vascular grafts in the literature. Here-in, we have discussed in-depth the various strategies employed to generate engineered vascular graft due to their high demand for vascular surgeries. While some TEVG design strategies have shown greater potential in contrast to autologous or synthetic ePTFE conduits, many are still hindered by high production cost which prevents their widespread adoption. Nonetheless, as tissue engineers continue to develop on their strategies and procedures for improved TEVGs, soon, a reliable engineered graft will be available in the market. Hence, we anticipate a viable TEVG with resorbable property, fabricated via electrospinning approach to hold a greater potential that can overcome the challenges observed in both autologous and allogenic grafts. This is because they can be mechanically tuned, incorporated/surface-functionalized with bioactive molecules and mass-manufactured in a reproducible manner. It is also found that most of the success in engineered vascular graft approaching commercialization is for large vessels rather than small-diameter grafts used as cardiovascular bypass grafts. Consequently, the field of vascular engineering is still available for future innovators that can take up the challenge to create a functional arterial substitute.

From arteries to capillaries: approaches to engineering human vasculature

From micro-scaled capillaries to millimeter-sized arteries and veins, human vasculature spans multiple scales and cell types. The convergence of bioengineering, materials science, and stem cell biology has enabled tissue engineers to recreate the structure and function of different hierarchical levels of the vascular tree. Engineering large-scale vessels has been pursued over the past thirty years to replace or bypass damaged arteries, arterioles, and venules, and their routine application in the clinic may become a reality in the near future. Strategies to engineer meso- and microvasculature have been extensively explored to generate models to study vascular biology, drug transport, and disease progression, as well as for vascularizing engineered tissues for regenerative medicine. However, bioengineering of large-scale tissues and whole organs for transplantation, have failed to result in clinical translation due to the lack of proper integrated vasculature for effective oxygen and nutrient delivery. The development of strategies to generate multi-scale vascular networks and their direct anastomosis to host vasculature would greatly benefit this formidable goal. In this review, we discuss design considerations and technologies for engineering millimeter-, meso-, and micro-scale vessels. We further provide examples of recent state-of-the-art strategies to engineer multi-scale vasculature. Finally, we identify key challenges limiting the translation of vascularized tissues and offer our perspective on future directions for exploration.

The use of tissue-engineered skin to demonstrate the negative effect of CXCL5 on epidermal ultraviolet radiation-induced cyclobutane pyrimidine dimer repair efficiency

BACKGROUND

Ultraviolet radiation (UVR) is responsible for keratinocyte cancers through the induction of mutagenic cyclobutane pyrimidine dimers (CPDs). Many factors influence CPD repair in epidermal keratinocytes, and a better understanding of those factors might lead to prevention strategies against skin cancer.

OBJECTIVES

To evaluate the impact of dermal components on epidermal CPD repair efficiency and to investigate potential factors responsible for the dermal-epidermal crosstalk modulating UVR-induced DNA damage repair in keratinocytes.

METHODS

A model of self-assembled tissue-engineered skin containing human primary keratinocytes and fibroblasts was used in this study.

RESULTS

We showed that CPD repair in keratinocytes is positively influenced by the presence of a dermis. We investigated the secretome and found that the cytokine CXCL5 is virtually absent from the culture medium of reconstructed skin, compared with media from fibroblasts and keratinocytes alone. By modulating CXCL5 levels in culture media of keratinocytes, we have shown that CXCL5 is an inhibitor of CPD repair.

CONCLUSIONS

This work outlines the impact of the secreted dermal components on epidermal UVR-induced DNA damage repair and sheds light on a novel role of CXCL5 in CPD repair.

Elastin-like recombinamers in collagen-based tubular gels improve cell-mediated remodeling and viscoelastic properties

The partial substitution of collagen with elastin-like recombinamers in tubular gels improves cell-mediated remodeling, elastic moduli and strength during maturation.

Integrins expressed on the surface of human endometrial stromal cells derived from a female patient experiencing spontaneous abortion

Here, as a basic study in revealing the correlation between extracellular matrix components and spontaneous abortion, we defined the types of integrins expressed on the surface of endometrial stromal (ES) cells retrieved from the uterus of a patient experiencing spontaneous abortion. For these, the types of integrin subunits in the ES cells retrieved from a woman with spontaneous abortion were identified at the transcriptional and translational levels, and functional assay was conducted for confirming the combinations of integrin α and β subunits. Among the genes encoding 25 integrin subunits, significantly high transcription was seen in integrins α₁, α₂, α₃, α₄, α₅, α_V, β₁, β₃, and β₅. Translation of integrins α₁, α₃, α₅, α_V, and β₁ on the cell surface was detected in almost all ES cells, whereas integrins α₂, α₄, β₃, and β₄ were expressed translationally only in some ES cells. Subsequently, ES cells showed significantly increased adhesion to collagen I, laminin, fibronectin, and vitronectin, and functional blocking of integrin α₁, α₃, α₅, and α_V significantly inhibited adhesion to these molecules. These results demonstrated that active heterodimers composed of integrins α₁β₁, α₃β₁, α₅β₁, and α_Vβ₁ were co-localized on the surface of ES cells derived from a patient experiencing spontaneous abortion.

Hyaluronic acid as a macromolecular crowding agent for production of cell-derived matrices

Cell-derived matrices (CDMs) provide an exogenous source of human extracellular matrix (ECM), with applications as cell delivery vehicles, substrate coatings for cell attachment and differentiation, and as biomaterial scaffolds. However, commercial application of CDMs has been hindered due to the prolonged culture time required for sufficient ECM accumulation. One approach to increasing matrix deposition in vitro is macromolecular crowding (MMC), which is a biophysical phenomenon that limits the diffusion of ECM precursor proteins, resulting in increased ECM accumulation at the cell layer. Hyaluronic acid (HA), a natural MMC highly expressed in vivo during fetal development, has been shown to play a role in ECM production, but has not been investigated as a macromolecule for increasing cell-mediated ECM deposition in vitro. In the current study, we hypothesized that HA can act as a MMC, and increase cell-mediated ECM production. Human dermal fibroblasts were cultured for 3, 7, or 14 days with 0%, 0.05%, or 0.5% high molecular weight HA. Ficoll 70/400 was used as a positive control. SDS-PAGE, Sircol, and hydroxyproline assays indicated that 0.05% HA-treated cultures had significantly higher mean collagen deposition at 14 days, whereas Ficoll 70/400-treated cultures had significantly lower collagen production compared to the HA and untreated controls. However, fluorescent immunostaining of ECM proteins and quantification of mean gray values did not indicate statistically significant differences in ECM production in HA or Ficoll 70/400-treated cultures compared to untreated controls. Raman imaging (a marker-free spectral imaging method) indicated that HA increased ECM deposition in human dermal fibroblasts. These results are consistent with decreases in CDM stiffness observed in Ficoll 70/400-treated cultures by atomic force microscopy. Overall, these results indicate that there are macromolecule- and cell type- dependent effects on matrix assembly, turnover, and stiffness in cell-derived matrices. STATEMENT OF SIGNIFICANCE: Cell-derived matrices (CDMs) are versatile biomaterials with many regenerative medicine applications, including as cell and drug delivery vehicles and scaffolds for wound healing and tissue regeneration. While CDMs have several advantages, their commercialization has been limited due to the prolonged culture time required to achieve CDM synthesis in vitro. In this study, we explored the use of hyaluronic acid (HA) as a macromolecular crowder in human fibroblast cell cultures to support production of CDM biomaterials. Successful application of macromolecular crowding will allow development of human cell-derived, xeno-free biomaterials that re-capitulate the native human tissue microenvironment.

Polyurethane End-Capped by Tetramethylpyrazine-Nitrone for Promoting Endothelialization Under Oxidative Stress

Thrombus and restenosis are two main factors that cause the failure of vascular implants. Constructing a functional and confluent layer of endothelial cells (ECs) is considered an ideal method to prevent these problems. However, oxidative stress induced by the disease and implantation can damage ECs and hinder the endothelialization of implants. Thus, developing biomaterials that can protect ECs adhesion and proliferation from oxidative stress is urgently needed for the rapid endothelialization of vascular implants. In this work, a novel polyurethane (PU-TBN) is synthesized by employing tetramethylpyrazine-nitrone (TBN) as end-group to endow polymers with dual functions of antioxidant activity and promoting endothelialization. Common PU without TBN is also prepared to be control. Compared to PU, PU-TBN significantly promotes human umbilical vein endothelial cells (HUVECs) adhesion and proliferation, where cells spread well and a confluent endothelial layer is formed. PU-TBN also shows obvious free radical scavenging activity, and thus effectively attenuates oxidative stress to protect HUVECs from oxidative apoptosis. Moreover, PU-TBN exhibits enhanced antiplatelets effect, excellent biocompatibility, and similar mechanical properties to PU. These characteristics can endow PU-TBN with great potential to be used as vascular implants or coatings of other materials for rapid endothelialization under complex oxidative stress environment.

A bioink blend for rotary 3D bioprinting tissue engineered small-diameter vascular constructs

3D bioprinted vascular constructs have gained increased interest due to their significant potential for creating customizable alternatives to autologous vessel grafts. In this study, we developed a new approach for biofabricating fibrin-based vascular constructs using a novel rotary 3D bioprinter developed in our lab. We formulated a new bioink by incorporating fibrinogen with gelatin to achieve a desired shear-thinning property for rotary bioprinting. The blending of heat-treated gelatin with fibrinogen turned unprintable fibrinogen into a printable biomaterial for vessel bioprinting by leveraging the favorable rheological properties of gelatin. We discovered that the heat-treatment of gelatin remarkably affects the rheological properties of a gelatin-fibrinogen blended bioink, which in turn influences the printability of the ink. Further characterizations revealed that not only concentration of the gelatin but the heat treatment also affects cell viability during printing. Notably, the density of cells included in the bioinks also influenced printability and tissue volumetric changes of the printed vessel constructs during cultures. We observed increased collagen deposition and construct mechanical strength during two months of the cultures. The burst pressure of the vessel constructs reached 1110 mmHg, which is about 52% of the value of the human saphenous vein. An analysis of the tensile mechanical properties of the printed vessel constructs unveiled an increase in both the circumferential and axial elastic moduli during cultures. This study highlights important considerations for bioink formulation when bioprinting vessel constructs. STATEMENT OF SIGNIFICANCE: There has been an increased demand for small-diameter tissue-engineered vascular grafts. Vascular 3D bioprinting holds the potential to create equivalent vascular grafts but with the ability to tailor them to meet patient's needs. Here, we presented a new and innovative 3D rotary bioprinter and a new bioink formulation for printing vascular constructs using fibrinogen, a favorable biomaterial for vascular tissue engineering. The bioink was formulated by blending fibrinogen with a more printable biomaterial, gelatin. The systematic characterization of the effects of heat treatment and gelatin concentration as well as bioink cell concentration on the printability of the bioink offers new insight into the development of printable biomaterials for tissue biofabrication.

Rapid fabrication of reinforced and cell-laden vascular grafts structurally inspired by human coronary arteries

Design strategies for small diameter vascular grafts are converging toward native-inspired tissue engineered grafts. A new automated technology is presented that combines a dip-spinning methodology for depositioning concentric cell-laden hydrogel layers, with an adapted solution blow spinning (SBS) device for intercalated placement of aligned reinforcement nanofibres. This additive manufacture approach allows the assembly of bio-inspired structural configurations of concentric cell patterns with fibres at specific angles and wavy arrangements. The middle and outer layers were tuned to structurally mimic the media and adventitia layers of native arteries, enabling the fabrication of small bore grafts that exhibit the J-shape mechanical response and compliance of human coronary arteries. This scalable automated system can fabricate cellularized multilayer grafts within 30 min. Grafts were evaluated by hemocompatibility studies and a preliminary in vivo carotid rabbit model. The dip-spinning-SBS technology generates constructs with native mechanical properties and cell-derived biological activities, critical for clinical bypass applications.

Tissue-derived microparticles reduce inflammation and fibrosis in cornea wounds

Biological materials derived from the extracellular matrix (ECM) of tissues serve as scaffolds for rebuilding tissues and for improved wound healing. Cornea trauma represents a wound healing challenge as the default repair pathway can result in fibrosis and scar formation that limit vision. Effective treatments are needed to reduce inflammation, promote tissue repair, and retain the tissue's native transparency and vision capacity. Tissue microparticles derived from cornea, cartilage and lymph nodes were processed and screened in vitro for their ability to reduce inflammation in ocular surface cells isolated from the cornea stroma, conjunctiva, and lacrimal gland. Addition of ECM particles to the media reduced expression of inflammatory genes and restored certain tear film protein production in vitro. Particles derived from lymph nodes were then applied to a rabbit lamellar keratectomy corneal injury model. Application of the tissue particles in a fibrin glue carrier decreased expression of inflammatory and fibrotic genes and scar formation as measured through imaging, histology and immunohistochemistry. In sum, immunomodulatory tissue microparticles may provide a new therapeutic tool for reducing inflammation in the cornea and ocular surface and promoting tissue repair. STATEMENT OF SIGNIFICANCE: Damaged cornea will result in scar tissue formation that impedes vision, and new therapies are needed to enhance wound healing in the cornea and to prevent fibrosis. We evaluated the effects of biological scaffolds derived extracellular matrix (ECM) during corneal wound healing. These ECM particles reduced inflammatory gene expression and restored tear film production in vitro, and reduced scar formation and fibrosis genes in the wounded cornea, when applied to in vivo lamellar keratectomy injury model. The immunomodulatory tissue microparticles may provide a new therapeutic tool for reducing inflammation in the cornea and ocular surface and promoting proper tissue repair.

Cell Seeding on UV-C-Treated 3D Polymeric Templates Allows for Cost-Effective Production of Small-Caliber Tissue-Engineered Blood Vessels

There is a strong clinical need to develop small-caliber tissue-engineered blood vessels for arterial bypass surgeries. Such substitutes can be engineered using the self-assembly approach in which cells produce their own extracellular matrix (ECM), creating a robust vessel without exogenous material. However, this approach is currently limited to the production of flat sheets that need to be further rolled into the final desired tubular shape. In this study, human fibroblasts and smooth muscle cells were seeded directly on UV-C-treated cylindrical polyethylene terephthalate glycol-modified (PETG) mandrels of 4.8 mm diameter. UV-C treatment induced surface modification, confirmed by Fourier-transform infrared spectroscopy (FTIR) analysis, was necessary to ensure proper cellular attachment and optimized ECM secretion/assembly. This novel approach generated solid tubular conduits with high level of cohesion between concentric cellular layers and enhanced cell-driven circumferential alignment that can be manipulated after 21 days of culture. This simple and cost-effective mandrel-seeded approach also allowed for endothelialization of the construct and the production of perfusable trilayered tissue-engineered blood vessels with a closed lumen. This study lays the foundation for a broad field of possible applications enabling custom-made reconstructed tissues of specialized shapes using a surface treated 3D structure as a template for tissue engineering.

Generating vascular conduits: from tissue engineering to three-dimensional bioprinting

Vascular disease - including coronary artery disease, carotid artery disease, and peripheral vascular disease - is a leading cause of morbidity and mortality worldwide. The standard of care for restoring patency or bypassing occluded vessels involves using autologous grafts, typically the saphenous veins or internal mammary arteries. Yet, many patients who need life- or limb-saving procedures have poor outcomes, and a third of patients who need vascular intervention have multivessel disease and therefore lack appropriate vasculature to harvest autologous grafts from. Given the steady increase in the prevalence of vascular disease, there is great need for grafts with the biological and mechanical properties of native vessels that can be used as vascular conduits. In this review, we present an overview of methods that have been employed to generate suitable vascular conduits, focusing on the advances in tissue engineering methods and current three-dimensional (3D) bioprinting methods. Tissue-engineered vascular grafts have been fabricated using a variety of approaches such as using preexisting scaffolds and acellular organic compounds. We also give an extensive overview of the novel use of 3D bioprinting as means of generating new vascular conduits. Different strategies have been employed in bioprinting, and the use of cell-based inks to create de novo structures offers a promising solution to bridge the gap of paucity of optimal donor grafts. Lastly, we provide a glimpse of our work to create scaffold-free, bioreactor-free, 3D bioprinted vessels from a combination of rat vascular smooth muscle cells and fibroblasts that remain patent and retain the tensile and mechanical strength of native vessels.

Subpopulations of dermal skin fibroblasts secrete distinct extracellular matrix: implications for using skin substitutes in the clinic

Background

While several commercial dermoepidermal scaffolds can promote wound healing of the skin, the achievement of complete skin regeneration still represents a major challenge.

Objectives

To perform biological characterization of self‐assembled extracellular matrices (ECMs) from three different subpopulations of fibroblasts found in human skin: papillary fibroblasts (Pfi), reticular fibroblasts (Rfi) and dermal papilla fibroblasts (DPfi).

Methods

Fibroblast subpopulations were cultured with ascorbic acid to promote cell‐assembled matrix production for 10 days. Subsequently, cells were removed and the remaining matrices characterized. Additionally, in another experiment, keratinocytes were seeded on the top of cell‐depleted ECMs to generate epidermal‐only skin constructs.

Results

We found that the ECM self‐assembled by Pfi exhibited randomly oriented fibres associated with the highest interfibrillar space, reflecting ECM characteristics that are physiologically present within the papillary dermis. Mass spectrometry followed by validation with immunofluorescence analysis showed that thrombospondin 1 is preferentially expressed within the DPfi‐derived matrix. Moreover, we observed that epidermal constructs grown on DPfi or Pfi matrices exhibited normal basement membrane formation, whereas Rfi matrices were unable to support membrane formation.

Conclusions

We argue that inspiration can be taken from these different ECMs, to improve the design of therapeutic biomaterials in skin engineering applications.

What's already known about this topic?

There are several types of skin fibroblasts within the dermis that can be defined by their spatial location: papillary fibroblasts (Pfi), reticular fibroblasts (Rfi) and dermal papilla fibroblasts (DPfi).

Extracellular matrix (ECM) composition is distinct with regard to composition and architecture within the papillary, reticular and hair follicle dermis in vivo.

When skin is injured, dermal replacement substitutes used for tissue repair do not reflect the heterogeneity observed within the skin dermis.

What does this study add?

Self‐assembled ECMs from different subpopulations of skin fibroblasts can be generated in vitro.

Cell‐assembled ECMs made in vitro from Pfi, Rfi and DPfi reflect dermal heterogeneity seen in vivo and are morphologically, functionally and compositionally distinct from one another.

Inspiration should be taken from cell‐assembled ECMs from distinct fibroblast subpopulations, to improve the design of therapeutic biomaterials in skin engineering applications.

What is the translational message?

Cell‐assembled ECMs from DPfi and Pfi, but not Rfi, can support formation of a basement membrane in adjacent keratinocytes in vitro.

Inspiration should be taken from cell‐assembled ECMs from distinct fibroblast subpopulations, to improve the design of therapeutic biomaterials in skin engineering applications.

Linked Comment: https://doi.org/10.1111/bjd.16773.

https://doi.org/10.1111/bjd.16946 available online

https://goo.gl/Uqv3dl

Current Strategies for the Manufacture of Small Size Tissue Engineering Vascular Grafts

Occlusive arterial disease, including coronary heart disease (CHD) and peripheral arterial disease (PAD), is the main cause of death, with an annual mortality incidence predicted to rise to 23.3 million worldwide by 2030. Current revascularization techniques consist of angioplasty, placement of a stent, or surgical bypass grafting. Autologous vessels, such as the saphenous vein and internal thoracic artery, represent the gold standard grafts for small-diameter vessels. However, they require invasive harvesting and are often unavailable. Synthetic vascular grafts represent an alternative to autologous vessels. These grafts have shown satisfactory long-term results for replacement of large- and medium-diameter arteries, such as the carotid or common femoral artery, but have poor patency rates when applied to small-diameter vessels, such as coronary arteries and arteries below the knee. Considering the limitations of current vascular bypass conduits, a tissue-engineered vascular graft (TEVG) with the ability to grow, remodel, and repair in vivo presents a potential solution for the future of vascular surgery. Here, we review the different methods that research groups have been investigating to create TEVGs in the last decades. We focus on the techniques employed in the manufacturing process of the grafts and categorize the approaches as scaffold-based (synthetic, natural, or hybrid) or self-assembled (cell-sheet, microtissue aggregation and bioprinting). Moreover, we highlight the attempts made so far to translate this new strategy from the bench to the bedside.

Recent Progress in Vascular Tissue-Engineered Blood Vessels

Cardiovascular disease is the number one cause of death in the U.S and results in the loss of approximately one million lives and more than 400 billion U.S. dollars for treatments every year. Recently, tissue engineered blood vessels have been studied and developed as promising replacements for treatment with autologous veins. Here, we summarize the cell sources and methods to make tissue-engineered blood vessels (TEBVs), the recent progress in TEBV related research, and also the recent progress in TEBV related clinical studies.

Effect of Simulated Microgravity Conditions on Differentiation of Adipose Derived Stem Cells towards Fibroblasts Using Connective Tissue Growth Factor

Background: Mesenchymal stem cells (MSCs) are multipotent cells able to differentiating into a variety of mesenchymal tissues including osteoblasts, adipocytes and several other tissues. Objectives: Differentiation of MSCs into fibroblast cells in vitro is an attractive strategy to achieve fibroblast cell and use them for purposes such as regeneration medicine. The goal of this study was investigate the simulated microgravity effect on differentiation of Adipose Derived Stem Cells (ADSCs) to fibroblasts. Materials and Methods: To fibroblast differentiation 100 ng.mL^-1 of connective tissue growth factor (CTGF), and for simulation microgravity, 2D clinostat was used. After isolation the human ADSCs from adipose, cells were passaged, and at passages 3 they were used for characterization and subsequent steps. After 7 days of CTGF and simulated microgravity treatment, proliferation, and differentiation were analyzed collectively by MTT assay, quantitative PCR analyses, and Immunocytochemistry staining. Results: MTT assay revealed that CTGF stimulate the proliferation but simulated microgravity didn't have statistically significant effect on cell proliferation. In RNA level the expression of these genes are investigated: collagen type I (COLI), elastin (ELA), collagen type III (ColIII), Matrix Metalloproteinases I(MMP1), Fibronectin 1 (FN1), CD44, Fibroblast Specific protein (FSP-1), Integrin Subunit Beta 1 (ITGB1), Vimentin (VIM) and Fibrillin (FBN). We found that expression of ELN, FN1, FSP1, COL1A1, ITGB1, MMP1 and COL3A1 in both condition, and VIM and FBN1 just in differentiation medium in normal gravity increased. In protein level the expression of COL III and ELN in simulated microgravity increased. Conclusions: These findings collectively demonstrate that the simulated microgravity condition alters the marker fibroblast gene expression in fibroblast differentiation process.

Cancer-associated fibroblasts regulate the biological behavior of cancer cells and stroma in gastric cancer

Gastric cancer (GC) is a frequently diagnosed type of cancer in China, and is associated with a high mortality rate. The biological behavior of GC requires investigation in order to provide an evidence base for the development of strategies to prevent and treat GC. For this purpose, the present review outlines the process of tumor microenvironment (TME) evolution, including the dynamic biological behavior of different types of cancer cell and stroma. Cancer-associated fibroblasts (CAFs) serve as prominent stromal cellular components in the GC TME, and exhibit an essential function in GC progression. In the present study, the function of CAFs in cancer cell proliferation, cell migration, invasion, extracellular matrix remodeling, pathological angiogenesis and immune cell infiltration were investigated. The studies discussed in the present review demonstrate that the cross-talk between CAF, cancer cells and tumor stroma promotes GC progression.

Comparative characteristics of laryngeal-resident mesenchymal stromal cell populations isolated from distinct sites in the rat larynx

BACKGROUND

Although tissue-resident mesenchymal stromal cells (MSCs) in the larynx have been described, their distinct characteristics and roles have not been thoroughly explored. Therefore, we investigated stem cell characteristics and regenerative potentials of single clonal populations isolated from rat epiglottic mucosa (EM), lamina propria (LP), and macula flava (MF) to determine whether they comprised laryngeal tissue-resident stem cells.

METHODS

Single clonal laryngeal cells were isolated following microdissection of the EM, LP, and MF from the rat larynx. Several clonal populations from the three laryngeal subsites were selected and expanded in vitro. We compared the stem cell characteristics of self-renewal and differentiation potential, as well as the cell surface phenotypes and gene expression profiles, of laryngeal MSC-like cells to that of bone marrow MSCs (BM-MSCs). We also investigated the regenerative potential of the laryngeal cells in a radiation-induced laryngeal injury animal model.

RESULTS

Self-renewing, clonal cell populations were obtained from rat EM, LP, and MF. EM-derived and LP-derived clonal cells had fibroblast-like features, while MF-resident clonal cells had stellate cell morphology and lipid droplets containing vitamin A. All laryngeal clonal cell populations had MSC-like cell surface marker expression (CD29, CD44, CD73, and CD90) and the potential to differentiate into bone and cartilage cell lineages; EM-derived and MF-derived cells, but not LP-derived cells, were also able to differentiate into adipocytes. Clonal cells isolated from the laryngeal subsites exhibited differential extracellular matrix-related gene expression. We found that the mesenchymal and stellate cell-related genes desmin and nestin were enriched in laryngeal MSC-like cells relative to BM-MSCs (P < 0.001). Growth differentiation factor 3 (GDF3) and glial fibrillary acidic protein (GFAP) transcript and protein levels were higher in MF-derived cells than in other laryngeal populations (P < 0.001). At 4 weeks after transplantation, laryngeal MF-derived and EM-derived cells contributed to laryngeal epithelial and/or glandular regeneration in response to radiation injury.

CONCLUSIONS

These results suggest that cell populations with MSC characteristics reside in the EM, LP, and MF of the larynx. Laryngeal MSC-like cells contribute to regeneration of the larynx following injury; further investigation is needed to clarify the differential roles of the populations in laryngeal tissue regeneration, as well as the clinical implications for the treatment of laryngeal disease.

In Vitro Evaluation of Essential Mechanical Properties and Cell Behaviors of a Novel Polylactic-co-Glycolic Acid (PLGA)-Based Tubular Scaffold for Small-Diameter Vascular Tissue Engineering

In this paper, we investigate essential mechanical properties and cell behaviors of the scaffolds fabricated by rolling polylactic-co-glycolic acid (PLGA) electrospinning (ES) films for small-diameter vascular grafts (inner diameter < 6 mm). The newly developed strategy can be used to fabricate small diameter vascular grafts with or without pre-seeded cells, which are two main branches for small diameter vascular engineering. We demonstrate that the mechanical properties of our rolling-based scaffolds can be tuned flexibly by the number of layers. For cell-free scaffolds, with the increase of layer number, burst pressure and suture retention increase, elastic tensile modulus maintains unchanged statistically, but compliance and liquid leakage decrease. For cell-containing scaffolds, seeding cells will significantly decrease the liquid leakage, but there are no statistical differences for other mechanical properties; moreover, cells live and proliferate well in the scaffold after a 6-day culture.

Aligned Nanofibrous Cell-Derived Extracellular Matrix for Anisotropic Vascular Graft Construction

There is a large demand for tissue engineered vascular grafts for the application of vascular reconstruction surgery or in vitro drug screening tissue model. The extracellular matrix (ECM) composition along with the structural and mechanical anisotropy of native blood vessels is critical to their functional performance. The objective of this study is to develop a biomimetic vascular graft recapitulating the anisotropic features of native blood vessels by employing nanofibrous aligned fibroblast-derived ECM and human mesenchymal stem cells (hMSCs). The nanotopographic cues of aligned ECM direct the initial cell orientation. The subsequent maturation under circumferential stress generated by a rotating wall vessel (RWV) bioreactor further promotes anisotropic structural and mechanical properties in the graft. The circumferential tensile strength is significantly higher than longitudinal strength in bioreactor samples. Expression of smooth muscle cell specific genes, α-smooth muscle actin and calponin, in hMSCs is greatly enhanced in bioreactor samples without any biochemical stimulation. In addition, employment of premade ECM and RWV bioreactor significantly reduces the graft fabrication time to three weeks. Mimicking the ECM composition, cell phenotype, structural and mechanical anisotropy, the vascular graft presented in this study is promising for vascular reconstruction surgery or in vitro tissue model applications.

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.

Hydrophilic cell-derived extracellular matrix as a niche to promote adhesion and differentiation of neural progenitor cells

Cell-derived extracellular matrix exhibits excellent adhesion performance for neural progenitor cell anchoring and residency, resulting in promoted proliferation of the stem cells to basal forebrain cholinergic neurons.

In Vivo Remodeling of Fibroblast-Derived Vascular Scaffolds Implanted for 6 Months in Rats

There is a clinical need for tissue-engineered small-diameter (<6 mm) vascular grafts since clinical applications are halted by the limited suitability of autologous or synthetic grafts. This study uses the self-assembly approach to produce a fibroblast-derived decellularized vascular scaffold (FDVS) that can be available off-the-shelf. Briefly, extracellular matrix scaffolds were produced using human dermal fibroblasts sheets rolled around a mandrel, maintained in culture to allow for the formation of cohesive and three-dimensional tubular constructs, and decellularized by immersion in deionized water. The FDVSs were implanted as an aortic interpositional graft in six Sprague-Dawley rats for 6 months. Five out of the six implants were still patent 6 months after the surgery. Histological analysis showed the infiltration of cells on both abluminal and luminal sides, and immunofluorescence analysis suggested the formation of neomedia comprised of smooth muscle cells and lined underneath with an endothelium. Furthermore, to verify the feasibility of producing tissue-engineered blood vessels of clinically relevant length and diameter, scaffolds with a 4.6 mm inner diameter and 17 cm in length were fabricated with success and stored for an extended period of time, while maintaining suitable properties following the storage period. This novel demonstration of the potential of the FDVS could accelerate the clinical availability of tissue-engineered blood vessels and warrants further preclinical studies.

Production of a Bilayered Self-Assembled Skin Substitute Using a Tissue-Engineered Acellular Dermal Matrix

Our bilayered self-assembled skin substitutes (SASS) are skin substitutes showing a structure and functionality very similar to native human skin. These constructs are used, in life-threatening burn wounds, as permanent autologous grafts for the treatment of such affected patients even though their production is exacting. We thus intended to shorten their current production time to improve their clinical applicability. A self-assembled decellularized dermal matrix (DM) was used. It allowed the production of an autologous skin substitute from patient's cells. The characterization of SASS reconstructed using a decellularized dermal matrix (SASS-DM) was performed by histology, immunofluorescence, transmission electron microscopy, and uniaxial tensile analysis. Using the SASS-DM, it was possible to reduce the standard production time from about 8 to 4 and a half weeks. The structure, cell differentiation, and mechanical properties of the new skin substitutes were shown to be similar to the SASS. The decellularization process had no influence on the final microstructure and mechanical properties of the DM. This model, by enabling the production of a skin substitute in a shorter time frame without compromising its intrinsic tissue properties, represents a promising addition to the currently available burn and wound treatments.

Sundew adhesive: a naturally occurring hydrogel

Bioadhesives have drawn increasing interest in recent years, owing to their eco-friendly, biocompatible and biodegradable nature. As a typical bioadhesive, sticky exudate observed on the stalked glands of sundew plants aids in the capture of insects and this viscoelastic adhesive has triggered extensive interests in revealing the implied adhesion mechanisms. Despite the significant progress that has been made, the structural traits of the sundew adhesive, especially the morphological characteristics in nanoscale, which may give rise to the viscous and elastic properties of this mucilage, remain unclear. Here, we show that the sundew adhesive is a naturally occurring hydrogel, consisting of nano-network architectures assembled with polysaccharides. The assembly process of the polysaccharides in this hydrogel is proposed to be driven by electrostatic interactions mediated with divalent cations. Negatively charged nanoparticles, with an average diameter of 231.9 ± 14.8 nm, are also obtained from this hydrogel and these nanoparticles are presumed to exert vital roles in the assembly of the nano-networks. Further characterization via atomic force microscopy indicates that the stretching deformation of the sundew adhesive is associated with the flexibility of its fibrous architectures. It is also observed that the adhesion strength of the sundew adhesive is susceptible to low temperatures. Both elasticity and adhesion strength of the sundew adhesive reduce in response to lowering the ambient temperature. The feasibility of applying sundew adhesive for tissue engineering is subsequently explored in this study. Results show that the fibrous scaffolds obtained from sundew adhesive are capable of increasing the adhesion of multiple types of cells, including fibroblast cells and smooth muscle cells, a property that results from the enhanced adsorption of serum proteins. In addition, in light of the weak cytotoxic activity exhibited by these scaffolds towards a variety of mammal cells, evidence is sufficient to propose that sundew adhesive is a promising nanomaterial worth further exploitation in the field of tissue engineering.

Advancing biomaterials of human origin for tissue engineering

Biomaterials have played an increasingly prominent role in the success of biomedical devices and in the development of tissue engineering, which seeks to unlock the regenerative potential innate to human tissues/organs in a state of deterioration and to restore or reestablish normal bodily function. Advances in our understanding of regenerative biomaterials and their roles in new tissue formation can potentially open a new frontier in the fast-growing field of regenerative medicine. Taking inspiration from the role and multi-component construction of native extracellular matrices (ECMs) for cell accommodation, the synthetic biomaterials produced today routinely incorporate biologically active components to define an artificial in vivo milieu with complex and dynamic interactions that foster and regulate stem cells, similar to the events occurring in a natural cellular microenvironment. The range and degree of biomaterial sophistication have also dramatically increased as more knowledge has accumulated through materials science, matrix biology and tissue engineering. However, achieving clinical translation and commercial success requires regenerative biomaterials to be not only efficacious and safe but also cost-effective and convenient for use and production. Utilizing biomaterials of human origin as building blocks for therapeutic purposes has provided a facilitated approach that closely mimics the critical aspects of natural tissue with regard to its physical and chemical properties for the orchestration of wound healing and tissue regeneration. In addition to directly using tissue transfers and transplants for repair, new applications of human-derived biomaterials are now focusing on the use of naturally occurring biomacromolecules, decellularized ECM scaffolds and autologous preparations rich in growth factors/non-expanded stem cells to either target acceleration/magnification of the body's own repair capacity or use nature's paradigms to create new tissues for restoration. In particular, there is increasing interest in separating ECMs into simplified functional domains and/or biopolymeric assemblies so that these components/constituents can be discretely exploited and manipulated for the production of bioscaffolds and new biomimetic biomaterials. Here, following an overview of tissue auto-/allo-transplantation, we discuss the recent trends and advances as well as the challenges and future directions in the evolution and application of human-derived biomaterials for reconstructive surgery and tissue engineering. In particular, we focus on an exploration of the structural, mechanical, biochemical and biological information present in native human tissue for bioengineering applications and to provide inspiration for the design of future biomaterials.

A strategy for rapid and facile fabrication of controlled, layered blood vessel-like structures

With the aid of fibrin glue, we wrap thin films into multi-layered tubes with a precisely-arranged cell distribution within 70 min.

Injectable SVF-loaded porcine extracellular matrix powders for adipose tissue engineering

This study provides a novel method in injectable tissue engineering which contains porcine extracellular matrix (ECM) powder scaffolds and stromal-vascular fraction (SVF) cells.

The Tissue-Engineered Vascular Graft-Past, Present, and Future

Cardiovascular disease is the leading cause of death worldwide, with this trend predicted to continue for the foreseeable future. Common disorders are associated with the stenosis or occlusion of blood vessels. The preferred treatment for the long-term revascularization of occluded vessels is surgery utilizing vascular grafts, such as coronary artery bypass grafting and peripheral artery bypass grafting. Currently, autologous vessels such as the saphenous vein and internal thoracic artery represent the gold standard grafts for small-diameter vessels (<6 mm), outperforming synthetic alternatives. However, these vessels are of limited availability, require invasive harvest, and are often unsuitable for use. To address this, the development of a tissue-engineered vascular graft (TEVG) has been rigorously pursued. This article reviews the current state of the art of TEVGs. The various approaches being explored to generate TEVGs are described, including scaffold-based methods (using synthetic and natural polymers), the use of decellularized natural matrices, and tissue self-assembly processes, with the results of various in vivo studies, including clinical trials, highlighted. A discussion of the key areas for further investigation, including graft cell source, mechanical properties, hemodynamics, integration, and assessment in animal models, is then presented.