The application of plastic compression to modulate fibrin hydrogel mechanical properties

Sclerostin Antibody-Loaded Dense Collagen Hydrogels Promote Critical-Size Bone Defect Repair

The management of extensive bone loss remains a clinical challenge. Numerous studies are underway to develop a combination of biomaterials, biomolecules, and stem cells to address this challenge. In particular, the systemic administration of antibodies against sclerostin, a regulator of bone formation, was recently shown to enhance the bone repair efficiency of dense collagen hydrogels (DCHs) hosting murine dental pulp stem cells (mDPSCs). The aim of the present study was to assess whether these antibodies, encapsulated and released from DCHs, could promote craniofacial bone repair by the local inhibition of sclerostin. In vitro studies showed that antibody loading modified neither the hydrogel structure nor the viability of seeded mDPSCs. When implanted in a mouse calvaria critical-size bone defect, antibody-loaded DCHs showed repair capabilities similar to those of acellular unloaded DCHs combined with antibody injections. Importantly, the addition of mDPSCs provided no further benefit. Altogether, the local delivery of antisclerostin antibodies from acellular dense collagen scaffolds is highly effective for bone repair. The drastic reduction in the required amount of antibody compared to systemic injection should reduce the cost of the procedure, making the strategy proposed here a promising therapeutic approach for large bone defect repair.

Mineralization of Bone Extracellular Matrix-like Scaffolds Fabricated as Silk Sericin-Functionalized Dense Collagen–Fibrin Hybrid Hydrogels

The design of hydrogels that combine both the biochemical cues needed to direct seeded cellular functions and mineralization to provide the structural and mechanical properties approaching those of mineralized native bone extracellular matrix (ECM) represents a significant challenge in bone tissue engineering. While fibrous hydrogels constituting of collagen or fibrin (and their hybrids) can be considered as scaffolds that mimic to some degree native bone ECM, their insufficient mechanical properties limit their application. In the present study, an automated gel aspiration–ejection (automated GAE) method was used to generate collagen–fibrin hybrid gel scaffolds with micro-architectures and mechanical properties approaching those of native bone ECM. Moreover, the functionalization of these hybrid scaffolds with negatively charged silk sericin accelerated their mineralization under acellular conditions in simulated body fluid and modulated the proliferation and osteoblastic differentiation of seeded MC3T3-E1 pre-osteoblastic cells. In the latter case, alkaline phosphatase activity measurements indicated that the hybrid gel scaffolds with seeded cells showed accelerated osteoblastic differentiation, which in turn led to increased matrix mineralization. In summary, the design of dense collagen–fibrin hybrid gels through an automated GAE process can provide a route to tailoring specific biochemical and mechanical properties to different types of bone ECM-like scaffolds, and can provide a model to better understand cell–matrix interactions in vitro for bioengineering purposes.

Type 1 diabetes and engineering enhanced islet transplantation

The development of new therapeutic approaches to treat type 1 diabetes mellitus (T1D) relies on the precise understanding and deciphering of insulin-secreting β-cell biology, as well as the mechanisms responsible for their autoimmune destruction. β-cell or islet transplantation is viewed as a potential long-term therapy for the millions of patients with diabetes. To advance the field of insulin-secreting cell transplantation, two main research areas are currently investigated by the scientific community: (1) the identification of the developmental pathways that drive the differentiation of stem cells into insulin-producing cells, providing an inexhaustible source of cells; and (2) transplantation strategies and engineered transplants to provide protection and enhance the functionality of transplanted cells. In this review, we discuss the biology of pancreatic β-cells, pathology of T1D and current state of β-cell differentiation. We give a comprehensive view and discuss the different possibilities to engineer enhanced insulin-secreting cell/islet transplantation from a translational perspective.

An overview of substrate stiffness guided cellular response and its applications in tissue regeneration

Cell-matrix interactions play a critical role in tissue repair and regeneration. With gradual uncovering of substrate mechanical characteristics that can affect cell-matrix interactions, much progress has been made to unravel substrate stiffness-mediated cellular response as well as its underlying mechanisms. Yet, as a part of cell-matrix interaction biology, this field remains in its infancy, and the detailed molecular mechanisms are still elusive regarding scaffold-modulated tissue regeneration. This review provides an overview of recent progress in the area of the substrate stiffness-mediated cellular responses, including 1) the physical determination of substrate stiffness on cell fate and tissue development; 2) the current exploited approaches to manipulate the stiffness of scaffolds; 3) the progress of recent researches to reveal the role of substrate stiffness in cellular responses in some representative tissue-engineered regeneration varying from stiff tissue to soft tissue. This article aims to provide an up-to-date overview of cell mechanobiology research in substrate stiffness mediated cellular response and tissue regeneration with insightful information to facilitate interdisciplinary knowledge transfer and enable the establishment of prognostic markers for the design of suitable biomaterials.

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Substrate stiffness physically determines cell fate and tissue development.

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Rational design of scaffolds requires the understanding of cell-matrix interactions.

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Substrate stiffness depends on scaffold molecular-constituent-structure interaction.

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Substrate stiffness-mediated cellular responses vary in different tissues.

Transluminal compression increases mechanical stability, stiffness and endothelialization capacity of fibrin-based bioartificial blood vessels

Fibrin is used successfully as a biological matrix in various bioengineering approaches. Its unique combination of autologous availability, hemocompatibility and biological activity makes it an almost ideal matrix material for vascular tissue engineering. However, clinical application of fibrin-based bioartificial blood vessels is still limited due to insufficient mechanical stability and stiffness of fibrin matrices. Biomechanical properties of fibrin-based constructs can potentially be modified by adjusting matrix density. Thus, as an attempt to optimize strength and elasticity of fibrin matrices for vascular tissue engineering applications, we developed a simple and reproducible method for transluminal compression of small-diameter fibrin-based vessels: After initial polymerization of high-concentration fibrin matrices in a vascular mold, vessels were compressed using an intraluminal angioplasty balloon. Vessels compacted with different pressures were compared for ultimate strength, elastic and structural properties and cellularization capacity. Transluminal compression increased fibrin network density and facilitated rapid production of homogenous vessels with a length of 10 cm. Compared to non-compressed controls, compacted fibrin vessels showed superior maximal burst pressure (199.8 mmHg vs. 94.0 mmHg), physiological elastic properties similar to the elastic behavior of natural arteries and higher luminal endothelial cell coverage (98.6% vs. 34.6%). Thus, transluminal compaction represents a suitable technique to enhance biomechanical properties of fibrin-based bioartificial vessels while preserving the biological advantages of this promising biomaterial.

Polymeric Hydrogel Scaffolds: Skin Tissue Engineering and Regeneration

Tissue engineering is a novel regenerative approach in the medicinal field that promises the regeneration of damaged tissues. Moreover, tissue engineering involves synthetic and natural biomaterials that facilitate tissue or organ growth outside the body. Not surprisingly, the demand for polymer-based therapeutical approaches in skin tissue defects has increased at an effective rate, despite the pressing clinical need. Among the 3D scaffolds for tissue engineering and regeneration approaches, hydrogel scaffolds have shown significant importance for their use as 3D cross-linked scaffolds in skin tissue regeneration due to their ideal moisture retention property and porosity biocompatibility, biodegradable, and biomimetic characteristics. In this review, we demonstrated the choice of ideal biomaterials to fabricate the novel hydrogel scaffolds for skin tissue engineering. After a short introduction to the bioactive and drug-loaded polymeric hydrogels, the discussion turns to fabrication and characterisation techniques of the polymeric hydrogel scaffolds. In conclusion, we discuss the excellent wound healing potential of stem cell-loaded hydrogels and Nano-based approaches to designing hydrogel scaffolds for skin tissue engineering.

Tissue-engineered vascular microphysiological platform to study immune modulation of xenograft rejection

Most of the vascular platforms currently being studied are lab-on-a-chip types that mimic capillary networks and are applied for vascular response analysis in vitro. However, these platforms have a limitation in clearly assessing the physiological phenomena of native blood vessels compared to in vivo evaluation. Here, we developed a simply fabricable tissue-engineered vascular microphysiological platform (TEVMP) with a three-dimensional (3D) vascular structure similar to an artery that can be applied for ex vivo and in vivo evaluation. Furthermore, we applied the TEVMP as ex vivo and in vivo screening systems to evaluate the effect of human CD200 (hCD200) overexpression in porcine endothelial cells (PECs) on vascular xenogeneic immune responses. These screening systems, in contrast to 2D in vitro and cellular xenotransplantation in vivo models, clearly demonstrated that hCD200 overexpression effectively suppressed vascular xenograft rejection. The TEVMP has a high potential as a platform to assess various vascular-related responses.

Composition and Mechanism of Three-Dimensional Hydrogel System in Regulating Stem Cell Fate

Three-dimensional (3D) hydrogel systems integrating different types of stem cells and scaffolding biomaterials have an important application in tissue engineering. The biomimetic hydrogels that pattern cell suspensions within 3D configurations of biomaterial networks allow for the transport of bioactive factors and mimic the stem cell niche in vivo, thereby supporting the proliferation and differentiation of stem cells. The composition of a 3D hydrogel system determines the physical and chemical characteristics that regulate stem cell function through a biological mechanism. Here, we discuss the natural and synthetic hydrogel compositions that have been employed in 3D scaffolding, focusing on their characteristics, fabrication, biocompatibility, and regulatory effects on stem cell proliferation and differentiation. We also discuss the regulatory mechanisms of cell-matrix interaction and cell-cell interaction in stem cell activities in various types of 3D hydrogel systems. Understanding hydrogel compositions and their cellular mechanisms can yield insights into how scaffolding biomaterials and stem cells interact and can lead to the development of novel hydrogel systems of stem cells in tissue engineering and stem cell-based regenerative medicine. Impact statement Three-dimensional hydrogel system of stem cell mimicking the stemcell niche holds significant promise in tissue engineering and regenerative medicine. Exactly how hydrogel composition regulates stem cell fate is not well understood. This review focuses on the composition of hydrogel, and how the hydrogel composition and its properties regulate the stem cell adhesion, growth, and differentiation. We propose that cell-matrix interaction and cell-cell interaction are important regulatory mechanisms in stem cell activities. Our review provides key insights into how the hydrogel composition regulates the stem cell fate, untangling the engineering of three-dimensional hydrogel systems for stem cells.

3D Perfusable Hydrogel Recapitulating the Cancer Dynamic Environment to in Vitro Investigate Metastatic Colonization

Metastasis is a dynamic process involving the dissemination of circulating tumor cells (CTCs) through blood flow to distant tissues within the body. Nevertheless, the development of an in vitro platform that dissects the crucial steps of metastatic cascade still remains a challenge. We here developed an in vitro model of extravasation composed of (i) a single channel-based 3D cell laden hydrogel representative of the metastatic site, (ii) a circulation system recapitulating the bloodstream where CTCs can flow. Two polymers (i.e., fibrin and alginate) were tested and compared in terms of mechanical and biochemical proprieties. Computational fluid-dynamic (CFD) simulations were also performed to predict the fluid dynamics within the polymeric matrix and, consequently, the optimal culture conditions. Next, once the platform was validated through perfusion tests by fluidically connecting the hydrogels with the external circuit, highly metastatic breast cancer cells (MDA-MB-231) were injected and exposed to physiological wall shear stress (WSS) conditions (5 Dyn/cm2) to assess their migration toward the hydrogel. Results indicated that CTCs arrested and colonized the polymeric matrix, showing that this platform can be an effective fluidic system to model the first steps occurring during the metastatic cascade as well as a potential tool to in vitro elucidate the contribution of hemodynamics on cancer dissemination to a secondary site.

Contraction of fibrin-derived matrices and its implications for in vitro human skin bioengineering

It is well-known that fibroblasts play a fundamental role in the contraction of collagen and fibrin hydrogels when used in the production of in vitro bilayered skin substitutes. However, little is known about the contribution of other factors, such as the hydrogel matrix itself, on this contraction. In this work, we studied the contraction of plasma-derived fibrin hydrogels at different temperatures (4, 23, and 37°C) in an isotonic buffer (phosphate-buffered saline). These types of hydrogels presented a contraction of approximately 30% during the first 24 hr, following a similar kinetics irrespectively of the temperature. This kinetics continued in a slowed down manner to reach a plateau value of 40% contraction after 10-15 days. Contraction of commercial fibrinogen hydrogels was studied under similar conditions and the kinetics was completed after 8 hr, reaching values between 20 and 70% depending on the temperature. We attribute these substantial differences to a modulatory effect on the contraction due to plasma proteins which are initially embedded in, and progressively released from, the plasma-based hydrogels. The elastic modulus of hydrogels measured at a constant frequency decreased with increasing temperature in 7-day gels. Rheological measurements showed the absence of a strain-hardening behavior in the plasma-derived fibrin hydrogels. Finally, plasma-derived fibrin hydrogels with and without human primary fibroblast and keratinocytes were prepared in transwell inserts and their height measured over time. Both cellular and acellular gels showed a height reduction of 30% during the first 24 hr likely due to the above-mentioned intrinsic fibrin matrix contraction.

Hybrid elastin-like recombinamer-fibrin gels: physical characterization and in vitro evaluation for cardiovascular tissue engineering applications

In the field of tissue engineering, the properties of the scaffolds are of crucial importance for the success of the application. Hybrid materials combine the properties of the different components that constitute them. In this study hybrid gels of Elastin-Like Recombinamer (ELR) and fibrin were prepared with a range of polymer concentrations and ELR-to-fibrin ratios. The correlation between SEM micrographs, porosities, swelling ratios and rheological properties was discussed and a poroelastic mechanism was suggested to explain the mechanical behavior of the hybrid gels. Applicability as scaffold materials for cardiovascular tissue engineering was shown by the realization of cell-laden matrixes which supported the synthesis of collagens as revealed by immunohistochemical analysis. As a proof of concept, a tissue-engineered heart valve was fabricated by injection moulding and cultivated in a bioreactor for 3 weeks under dynamic conditions. Tissue analysis revealed the production of collagen I and III, fundamental proteins for cardiovascular constructs.

Fibrin, a scaffold material for islet transplantation and pancreatic endocrine tissue engineering

Fibrin is derived from fibrinogen during injury to produce a blood clot and thus promote wound repair. Composed of different domains, including Arg-Gly-Asp amino acid motifs, fibrin is used extensively as a hydrogel and sealant in the clinic. By binding to cell surface receptors like integrins and acting as a supportive 3D scaffold, fibrin has been useful in promoting cell differentiation, proliferation, function, and survival. In particular, fibrin has been able to maintain islet cell architecture, promote beta cell insulin secretion, and islet angiogenesis, as well as inducing a protective effect against cell death. During islet transplantation, fibrin improved neovascularization and islet function. These improvements resulted in reduced number of transplanted islets necessary to reverse diabetes. Therefore, fibrin, as a biocompatible and biodegradable scaffold, should be considered during subcutaneous islet transplantation and beta cell expansion in vitro to ensure maintenance of islet cell function, proliferation, and survival to develop effective cell-based therapies for the treatment of diabetes.

A fibrin/hyaluronic acid hydrogel for the delivery of mesenchymal stem cells and potential for articular cartilage repair

Background

Osteoarthritis (OA) is a degenerative joint disease affecting approximately 27 million Americans, and even more worldwide. OA is characterized by degeneration of subchondral bone and articular cartilage. In this study, a chondrogenic fibrin/hyaluronic acid (HA)-based hydrogel seeded with bone marrow-derived mesenchymal stem cells (BMSCs) was investigated as a method of regenerating these tissues for OA therapy. This chondrogenic hydrogel system can be delivered in a minimally invasive manner through a small gauge needle, forming a three-dimensional (3D) network structure in situ. However, an ongoing problem with fibrin/HA-based biomaterials is poor mechanical strength. This was addressed by modifying HA with methacrylic anhydride (MA) (HA-MA), which reinforces the fibrin gel, thereby improving mechanical properties. In this study, a range of fibrinogen (the fibrin precursor) and HA-MA concentrations were explored to determine optimal conditions for increased mechanical strength, BMSC proliferation, and chondrogenesis potential in vitro.

Results

Increased mechanical strength was achieved by HA-MA reinforcement within fibrin hydrogels, and was directly correlated with increasing HA-MA concentration. Live/dead staining and metabolic assays confirmed that the crosslinked fibrin/HA-MA hydrogels provided a suitable 3D environment for BMSC proliferation. Quantitative polymerase chain reaction (qPCR) of BMSCs incubated in the fibrin/HA-MA hydrogel confirmed decreased expression of collagen type 1 alpha 1 mRNA with an increase in Sox9 mRNA expression especially in the presence of a platelet lysate, suggesting early chondrogenesis.

Conclusion

Fibrin/HA-MA hydrogel may be a suitable delivery method for BMSCs, inducing BMSC differentiation into chondrocytes and potentially aiding in articular cartilage repair for OA therapy.

Fibrinogen and fibrin based micro and nano scaffolds incorporated with drugs, proteins, cells and genes for therapeutic biomedical applications

Over the past two decades, many types of natural and synthetic polymer-based micro- and nanocarriers, with exciting properties and applications, have been developed for application in various types of tissue regeneration, including bone, cartilage, nerve, blood vessels, and skin. The development of suitable polymers scaffold designs to aid the repair of specific cell types have created diverse and important potentials in tissue restoration. Fibrinogen (Fbg)- and fibrin (Fbn)-based micro- and nanostructures can provide suitable natural matrix environments. Since these primary materials are abundantly available in blood as the main coagulation proteins, they can easily interact with damaged tissues and cells through native biochemical interactions. Fbg- and Fbn-based micro and nanostructures can also be consecutively furnished/or encapsulated and specifically delivered, with multiple growth factors, proteins, and stem cells, in structures designed to aid in specific phases of the tissue regeneration process. The present review has been carried out to demonstrate the progress made with micro and nanoscaffold applications and features a number of applications of Fbg- and Fbn-based carriers in the field of biomaterials, including the delivery of drugs, active biomolecules, cells, and genes, that have been effectively used in tissue engineering and regenerative medicine.

Stem cell maintenance in a different niche

To overcome the difficulty of controlling stem cell fate and function in applications to regenerative medicine, a number of alternative approaches have been made. Recent reports demonstrate that a non-cellular niche modulating the biophysical microenvironment with chemical factors can support stem cell self-renewal. In our previous studies, early establishment was executed to optimize biophysical factors and it was subsequently found that the microgeometry of the extracellular matrix made huge differences in stem cell behavior and phenotype. We review here a three-dimensional, non-cellular niche designed to support stem cell self-renewal. The characteristics of stem cells under the designed system are further discussed.