Increasing salinity of fibrinogen solvent generates stable fibrin hydrogels for cell delivery or tissue engineering

Vascularization of PEGylated fibrin hydrogels increases the proliferation of human iPSC-cardiomyocytes

Studies have long sought to develop engineered heart tissue for the surgical correction of structural heart defects, as well as other applications and vascularization of this tissue has presented a challenge. Recent studies suggest that vascular cells and a vascular network may have regenerative effects on implanted cardiomyocytes (CM) and nearby heart tissue separate from perfusion of oxygen and nutrients. The goal of this study was to test whether vascular cells or a formed vascular network in a fibrin-based hydrogel would alter the proliferation of human iPSC-derived CM. First, vascular network formation in a slowly degrading PEGylated fibrin hydrogel was optimized by altering the cell ratio of human umbilical vein endothelial cells to human dermal fibroblasts, the inclusion of growth factors, and the total cell concentration. An endothelial to fibroblast ratio of 5:1 and a total cell concentration of 1.1 × 106 cells/mL without additional growth factors generated robust vascular networks while minimizing the number of cells required. Using this optimized system, human iPSC-derived CM were cultured on hydrogels without vascular cells, hydrogels with unorganized encapsulated vascular cells, or hydrogels with encapsulated vascular cells organized into networks for 7 days. CM proliferation and gene expression were assayed following 7 days of culture on the hydrogels. The presence of vascular cells in the hydrogel, whether unorganized or in vascular networks, significantly increased CM proliferation compared to an acellular hydrogel. Hydrogels with unorganized vascular cells resulted in lower CM maturity evidenced by decreased expression of cardiac troponin t (TNNT2), myosin light chain 7, and phospholamban compared to hydrogels without vascular cells and hydrogels with vascular networks. Altogether, this study details a robust method of forming rudimentary vascular networks in a fibrin-based hydrogel and shows that a hydrogel containing endothelial cells and fibroblasts can induce proliferation in adjacent CM, and these cells do not hinder CM gene expression when organized into a vascular network.

An In Vitro Characterization of a PCL-Fibrin Scaffold for Myocardial Repair

Each year in the United States approximately 10,000 babies are born with a complex congenital heart defect (CHD) requiring surgery in the first year of after birth. Several of these operations require the implantation of a full-thickness heart patch; however, the current patch materials available to pediatric heart surgeons are exclusively non-living and non-degradable, which do not grow with the patient and are prone to fail due to an inability to integrate with the heart. In this work, the goal was to develop a full-thickness, tissue engineered myocardial patch (TEMP) that is made from biodegradable components, strong enough to withstand the mechanical forces of the heart wall, and able to integrate with the heart and drive neotissue formation. Here, a thick and porous electrospun PCL scaffold filled with high-salt PEGylated fibrin was developed. The scaffold was found to be mechanically sufficient for heart wall repair. Vascular cells were able to infiltrate more than halfway through the scaffold in static culture within three weeks. The scaffold maintained pluripotent stem cells for at least four days, supports viable iPSC-derived cardiomyocytes, and fostered tissue thickening in vitro. The TEMP developed here and tested in vitro is promising for the repair of structural CHD and will next be assessed in situ.

A scalable human iPSC-based neuromuscular disease model on suspended biobased elastomer nanofiber scaffolds

Many devastating neuromuscular diseases currently lack effective treatments. This is in part due to a lack of drug discovery platforms capable of assessing complex human neuromuscular disease phenotypes in a scalable manner. A major obstacle has been generating scaffolds to stabilise mature contractile myofibers in a multi-well assay format amenable to high content image (HCI) analysis. This study describes the development of a scalable human induced pluripotent stem cell (iPSC)-neuromuscular disease model, whereby suspended elastomer nanofibers support long-term stability, alignment, maturation, and repeated contractions of iPSC-myofibers, innervated by iPSC-motor neurons in 96-well assay plates. In this platform, optogenetic stimulation of the motor neurons elicits robust myofiber-contractions, providing a functional readout of neuromuscular transmission. Additionally, HCI analysis provides rapid and automated quantification of axonal outgrowth, myofiber morphology, and neuromuscular synapse number and morphology. By incorporating amyotrophic lateral sclerosis (ALS)-related TDP-43G298Smutant motor neurons and CRISPR-corrected controls, key neuromuscular disease phenotypes are recapitulated, including weaker myofiber contractions, reduced axonal outgrowth, and reduced number of neuromuscular synapses. Treatment with a candidate ALS drug, the receptor-interacting protein kinase-1 (RIPK1)-inhibitor necrostatin-1, rescues these phenotypes in a dose-dependent manner, highlighting the potential of this platform to screen novel treatments for neuromuscular diseases.

Micropatterned fibrin scaffolds increase cardiomyocyte alignment and contractility for the fabrication of engineered myocardial tissue

Cardiovascular disease is the leading cause of death in the United States, which can result in blockage of a coronary artery, triggering a myocardial infarction (MI), scar tissue formation in the myocardium, and ultimately heart failure. Currently, the gold-standard solution for total heart failure is a heart transplantation. An alternative to total-organ transplantation is surgically remodeling the ventricle with the implantation of a cardiac patch. Acellular cardiac patches have previously been investigated using synthetic or decellularized native materials to improve cardiac function. However, a limitation of this strategy is that acellular cardiac patches only reshape the ventricle and do not increase cardiac contractile function. Toward the development of a cardiac patch, our laboratory previously developed a cell-populated composite fibrin scaffold and aligned microthreads to recapitulate the mechanical properties of native myocardium. In this study, we explore micropatterning the surfaces of fibrin gels to mimic anisotropic native tissue architecture and promote cellular alignment of human induced pluripotent stem cell cardiomyocytes (hiPS-CM), which is crucial for increasing scaffold contractile properties. hiPS-CMs seeded on micropatterned surfaces exhibit cellular elongation, distinct sarcomere alignment, and circumferential connexin-43 staining at 14 days of culture, which are necessary for mature contractile properties. Constructs were also subject to electrical stimulation during culture to promote increased contractile properties. After 7 days of stimulation, contractile strains of micropatterned constructs were significantly higher than unpatterned controls. These results suggest that the use of micropatterned topographic cues on fibrin scaffolds may be a promising strategy for creating engineered cardiac tissue.

Development and Optimisation of Hydrogel Scaffolds for Microvascular Network Formation

Traumatic injuries are a major cause of morbidity and mortality worldwide; however, there is limited research on microvascular traumatic injuries. To address this gap, this research aims to develop and optimise an in vitro construct for traumatic injury research at the microvascular level. Tissue engineering constructs were created using a range of polymers (collagen, fibrin, and gelatine), solvents (PBS, serum-free endothelial media, and MES/NaCl buffer), and concentrations (1-5% w/v). Constructs created from these hydrogels and HUVECs were evaluated to identify the optimal composition in terms of cell proliferation, adhesion, migration rate, viability, hydrogel consistency and shape retention, and tube formation. Gelatine hydrogels were associated with a lower cell adhesion, whereas fibrin and collagen ones displayed similar or better results than the control, and collagen hydrogels exhibited poor shape retention; fibrin scaffolds, particularly at high concentrations, displayed good hydrogel consistency. Based on the multipronged evaluation, fibrin hydrogels in serum-free media at 3 and 5% w/v were selected for further experimental work and enabled the formation of interconnected capillary-like networks. The networks formed in both hydrogels displayed a similar architecture in terms of the number of segments (10.3 ± 3.21 vs. 9.6 ± 3.51) and diameter (8.6446 ± 3.0792 μm vs. 7.8599 ± 2.3794 μm).

A comparative high-resolution physicochemical analysis of commercially available fibrin sealants: Impact of sealant osmolality on biological performance

Fibrin sealants are well-established components of the surgical toolbox, especially in procedures that harbor a high risk of perioperative bleeding. Their widespread use as hemostats, sealants or tissue-adhesives in various surgical settings has shown that the choice of the appropriate sealant system affects the clinical outcome. While many studies have compared the hemostatic efficiency of fibrin sealants to that of other natural or synthetic sealants, there is still limited data on how subtle differences in fibrin sealant formulations relate to their biological performance. Here, we performed an in-depth physicochemical and biological characterization of the two most commonly used fibrin sealants in the US and Europe: TISSEEL™ ("FS") and VISTASEAL™/VERASEAL™ ("FS+Osm"). Our chemical analyses demonstrated differences between the two sealants, with lower fibrinogen concentrations and supraphysiological osmolality in the FS+Osm formulation. Rheological testing revealed FS clots have greater clot stiffness, which strongly correlated with network density. Ultrastructural analysis by scanning electron microscopy revealed differences between FS and FS+Osm fibrin networks, the latter characterized by a largely amorphous hydrogel structure in contrast to the physiological fibrillar network of FS. Cytocompatibility experiments with human fibroblasts seeded on FS and FS+Osm fibrin networks, or cultured in presence of sealant extracts, revealed that FS+Osm induced apoptosis, which was not observed with FS. Although differential sealant osmolality and amounts of fibrinogen, as well as the presence of Factor XIII or additives such as antifibrinolytics, may explain the mechanical and structural differences observed between the two fibrin sealants, none of these substances are known to cause apoptosis at the respective concentrations in the sealant formulation. We thus conclude that hyper osmolality in the FS+Osm formulation is the primary trigger of apoptosis-a mechanism that should be evaluated in more detail, as it may affect the cellular wound healing response in situ.

Assembling a supramolecular 3D network with tuneable mechanical properties using adamantylated cross-linking agents and β-cyclodextrin-modified hyaluronan

Hydrogels based on the supramolecular host-guest concept can be prepared if at least one constituent is a polymer chain modified with supramolecular host or guest (or both) units. Low-molecular-weight multitopic counterparts can also be used, however, guest molecules in the role of cross-linking agents are seldom reported, although such an approach offers wide-ranging possibilities for tuning the system properties via easily achievable structural modifications. In this paper, a series of adamantane-based star-like guest molecules was used for cross-linking of two types of β-cyclodextrin-modified hyaluronan (CD-HA). The prepared 3D supramolecular networks were characterised using nuclear magnetic resonance, titration calorimetry and rheological measurements to confirm the formation of the host-guest complexes between adamantane moieties and β-cyclodextrin units, including their typical properties such as self-healing and dynamic nature. The results indicate that the nature of the cross-linker (amides versus esters) has a greater impact on mechanical properties than the length of the guest's arms. In addition, the results show that the length of the HA polymer chain is more important than the degree of modification with supramolecular units. In conclusion, it was proven that the modular concept employing low-molecular-weight cross-linking guests is valuable for the formulation of supramolecular networks, including hydrogels.

Technological advances in fibrin for tissue engineering

Fibrin is a promising natural polymer that is widely used for diverse applications, such as hemostatic glue, carrier for drug and cell delivery, and matrix for tissue engineering. Despite the significant advances in the use of fibrin for bioengineering and biomedical applications, some of its characteristics must be improved for suitability for general use. For example, fibrin hydrogels tend to shrink and degrade quickly after polymerization, particularly when they contain embedded cells. In addition, their poor mechanical properties and batch-to-batch variability affect their handling, long-term stability, standardization, and reliability. One of the most widely used approaches to improve their properties has been modification of the structure and composition of fibrin hydrogels. In this review, recent advances in composite fibrin scaffolds, chemically modified fibrin hydrogels, interpenetrated polymer network (IPN) hydrogels composed of fibrin and other synthetic or natural polymers are critically reviewed, focusing on their use for tissue engineering.

pH and Thrombin Concentration Are Decisive in Synthesizing Stiff, Stable, and Open-Porous Fibrin-Collagen Hydrogel Blends without Chemical Cross-Linker

Fibrin-collagen hydrogel blends exhibit high potential for tissue engineering applications. However, it is still unclear whether the underlying cross-linking mechanisms are of chemical or physical nature. It is here hypothesized that chemical cross-linkers play a negligible role and that instead pH and thrombin concentration are decisive for synthetizing blends with high stiffness and hydrolytic stability. Different fibrin-collagen formulations (pure and with additional transglutaminase) are used and the blends' compaction rate, hydrolytic stability, compressive strength, and hydrogel microstructure are investigated. The effect of thrombin concentration on gel compaction is examined and the importance of pH control during synthesis observed. It is revealed that transglutaminase impairs gel stability and it is deduced that fibrin-collagen blends mainly cross-link by mechanical interactions due to physical fibril entanglement as opposed to covalent bonds from chemical cross-linking. High thrombin concentrations and basic pH during synthesis reduce gel compaction and enhance stiffness and long-term stability. Scanning electron microscopy reveals a highly interpenetrating fibrous network with unique, interconnected open-porous microstructures. Endothelial cells proliferate on the blends and form a confluent monolayer. This study reveals the underlying cross-linking mechanisms and presents enhanced fibrin-collagen blends with high stiffness, hydrolytic stability, and large, interconnected pores; findings that offer high potential for advanced tissue engineering applications.

A biomimetic three-layered fibrin gel/PLLA nanofibers composite as a potential scaffold for articular cartilage tissue engineering application

Developing an engineered scaffold inspired by structural features of healthy articular cartilage (AC) has attracted much attention. In this study, the design and fabrication of a three-layered fiber/hydrogel scaffold in which each layer replicates the organization of a pertinent layer of AC tissue is aimed. To this end, electrospun poly L-lactic acid (PLLA) nanofibers are prepared and fragmented into nano/micro cylinders via aminolysis. Three-layers of the scaffold in which continuous fibrous layer, fibrin gel incorporated by chopped fibers and fibrin gel embedded by cylindrical aligned fibrous mat perpendicular to articulating surface, respectively served as an upper, middle and bottom layers, are prepared. The layers' physicomechanical characteristics are comprehensively evaluated. Results show that optimized electrospinning set up results in the smallest fibers diameter of 367±317 nm and successful aminolysis provides amine-functionalized chopped nanofibers with a mean length of 1.65±1.2 µm. Static mechanical analysis of the layers demonstrates that Young tensile modulus of the upper layer is 152± 17 MPa while compressive moduli of the middle and bottom layers are 38±4 and 79± 6 KPa, respectively. Assessing mechanical parameters under dynamic loading also shows that adding fibrous part in the composite scaffold layers enhances viscoelastic behavior of fibrin gel. Also, incorporation of 0.25% chopped fibers into the fibrin matrix notably enhances the equilibrium water content; however, it increases in-vitro weigh loss rate from 6% to 10.5% during a seven-day period. cytocompatibility analysis confirms that all layers possess acceptable cytocompatibility. In a conclusion, the designed three-layered composite structure successfully mimics the physicomechanical as well as microstructural features of AC and could be suggested as a potential scaffold for this tissue regeneration.

A defined heat pretreatment of gelatin enables control of hydrolytic stability, stiffness, and microstructural architecture of fibrin-gelatin hydrogel blends

Fibrin-gelatin hydrogel blends exhibit high potential for tissue engineering in vitro applications. However, the means to tailor these blends in order to control their properties, thus opening up a broad range of new target applications, have been insufficiently explored. We hypothesized that a controlled heat treatment of gelatin prior to blend synthesis enables control of hydrolytic swelling and shrinking, stiffness, and microstructural architecture of fibrin-gelatin based hydrogel blends while providing tremendous long-term stability. We investigated these hydrogel blends' compressive strength, in vitro degradation stability, and microstructure in order to test this hypothesis. In addition, we examined the gel's ability to support endothelial cell proliferation and stretching of encapsulated smooth muscle cells. This research showed that a controlled heat pretreatment of the gelatin component strongly influenced the stiffness, swelling, shrinking, and microstructural architecture of the final blends regardless of identical gelatin mass fractions. All blends offered high long-term hydrolytic stability. In conclusion, the results of this study open the possibility to use this technique in order to tune low-concentrated, open-porous fibrin-based hydrogels, even in long-term tissue engineering in vitro experiments.

The degradation of gelatin/alginate/fibrin hydrogels is cell type dependent and can be modulated by targeting fibrinolysis

In tissue engineering, cell origin is important to ensure outcome quality. However, the impact of the cell type chosen for seeding in a biocompatible matrix has been less investigated. Here, we investigated the capacity of primary and immortalized fibroblasts of distinct origins to degrade a gelatin/alginate/fibrin (GAF)-based biomaterial. We further established that fibrin was targeted by degradative fibroblasts through the secretion of fibrinolytic matrix-metalloproteinases (MMPs) and urokinase, two types of serine protease. Finally, we demonstrated that besides aprotinin, specific targeting of fibrinolytic MMPs and urokinase led to cell-laden GAF stability for at least forty-eight hours. These results support the use of specific strategies to tune fibrin-based biomaterials degradation over time. It emphasizes the need to choose the right cell type and further bring targeted solutions to avoid the degradation of fibrin-containing hydrogels or bioinks.

Hydrogels: Properties and Applications in Biomedicine

Hydrogels are crosslinked polymer chains with three-dimensional (3D) network structures, which can absorb relatively large amounts of fluid. Because of the high water content, soft structure, and porosity of hydrogels, they closely resemble living tissues. Research in recent years shows that hydrogels have been applied in various fields, such as agriculture, biomaterials, the food industry, drug delivery, tissue engineering, and regenerative medicine. Along with the underlying technology improvements of hydrogel development, hydrogels can be expected to be applied in more fields. Although not all hydrogels have good biodegradability and biocompatibility, such as synthetic hydrogels (polyvinyl alcohol, polyacrylamide, polyethylene glycol hydrogels, etc.), their biodegradability and biocompatibility can be adjusted by modification of their functional group or incorporation of natural polymers. Hence, scientists are still interested in the biomedical applications of hydrogels due to their creative adjustability for different uses. In this review, we first introduce the basic information of hydrogels, such as structure, classification, and synthesis. Then, we further describe the recent applications of hydrogels in 3D cell cultures, drug delivery, wound dressing, and tissue engineering.

Biobased Elastomer Nanofibers Guide Light-Controlled Human-iPSC-Derived Skeletal Myofibers

Generating skeletal muscle tissue that mimics the cellular alignment, maturation, and function of native skeletal muscle is an ongoing challenge in disease modeling and regenerative therapies. Skeletal muscle cultures require extracellular guidance and mechanical support to stabilize contractile myofibers. Existing microfabrication-based solutions are limited by complex fabrication steps, low throughput, and challenges in measuring dynamic contractile function. Here, the synthesis and characterization of a new biobased nanohybrid elastomer, which is electrospun into aligned nanofiber sheets to mimic the skeletal muscle extracellular matrix, is presented. The polymer exhibits remarkable hyperelasticity well-matched to that of native skeletal muscle (≈11-50 kPa), with ultimate strain ≈1000%, and elastic modulus ≈25 kPa. Uniaxially aligned nanofibers guide myoblast alignment, enhance sarcomere formation, and promote a ≈32% increase in myotube fusion and ≈50% increase in myofiber maturation. The elastomer nanofibers stabilize optogenetically controlled human induced pluripotent stem cell derived skeletal myofibers. When activated by blue light, the myofiber-nanofiber hybrid constructs maintain a significantly higher (>200%) contraction velocity and specific force (>280%) compared to conventional culture methods. The engineered myofibers exhibit a power density of ≈35 W m-3 . This system is a promising new skeletal muscle tissue model for applications in muscular disease modeling, drug discovery, and muscle regeneration.

Microvascular development in the rat arteriovenous loop model in vivo-A step by step intravital microscopy analysis

The arteriovenous (AV) loop model is a key technique to solve one of the major problems of tissue engineering-providing adequate vascular support for a tissue construct of significant size. However, the molecular and cellular mechanisms of vascularization and factors influencing the generation of new tissue in the AV loop are still poorly understood. We previously established a novel intravital microscopy approach to study these events. In this study, we implanted our observation chamber filled with two types of hydrogels such as fibrin and methacrylate gelatin (GelMA) and performed intravital microscopy (IVM) on days 7, 14, and 21. Initial microvessel formation was observed in GelMA on day 14, while the vessel network showed clear indicators of network rearrangement and maturation on day 21. No visible microvessels were observed in fibrin. The chambers were explanted on day 21. Histological examination revealed higher numbers of microvessels in GelMA compared to fibrin, while the AV loop was thrombosed in all fibrin constructs, possibly due to matrix degradation. GelMA proved to be an ideal matrix for IVM studies in the AV loop model due to its slow degradation and transparency. This IVM model can be employed as a novel tool for live and thus faster comprehension of crucial events in the tissue regeneration process, which can improve tissue engineering application.

Sensing Alzheimer’s Disease Utilizing Au Electrode by Controlling Nanorestructuring

This paper reports the development of Alzheimer’s disease (AD) sensor through early detection of amyloid-beta (Aβ) (1–42) using simple nanorestructuring of Au sheet plate by oxidation-reduction cycle (ORC) via the electrochemical system. The topology of Au substrates was enhanced through the roughening and Au grains grown by a simple ORC technique in aqueous solutions containing 0.1 mol/L KCl electrolytes. The roughened substrate was then functionalized with the highly specific antibody β-amyloid Aβ (1–28) through HS-PEG-NHS modification, which enabled effective and direct detection of Aβ (1–42) peptide. The efficacy of the ORC method had been exhibited in the polished Au surface by approximately 15% larger electro-active sites compared to the polished Au without ORC. The ORC polished structure demonstrated a rapid, accurate, precise, reproducible, and highly sensitive detection of Aβ (1–42) peptide with a low detection limit of 10.4 fg/mL and a wide linear range of 10−2 to 106 pg/mL. The proposed structure had been proven to have potential as an early-stage Alzheimer’s disease (AD) detection platform with low-cost fabrication and ease of operation.

A Prevascularized Polyurethane-Reinforced Fibrin Patch Improves Regenerative Remodeling in a Rat Right Ventricle Replacement Model

Congenital heart defects (CHDs) affect 1 in 120 newborns in the United States. Surgical repair of structural heart defects often leads to arrhythmia and increased risk of heart failure. The laboratory has previously developed an acellular fibrin patch reinforced with a biodegradable poly(ether ester urethane) urea mesh that result in improved heart function when tested in a rat right ventricle wall replacement model compared to fixed pericardium. However, this patch does not drive significant neotissue formation. The patch materials are modified here and this patch is prevascularized with human umbilical vein endothelial cells and c-Kit⁺ human amniotic fluid stem cells. Rudimentary capillary-like networks form in the fibrin after culture of cell-encapsulated patches for 3 d in vitro. Prevascularized patches and noncell loaded patch controls are implanted onto full-thickness heart wall defects created in the right ventricle of athymic nude rats. Two months after surgery, defect repair with prevascularized patches results in improved heart function and the patched heart area exhibited greater vascularization and muscularization, less fibrosis, and increased M2 macrophage infiltration compared to acellular patches.

Vascularization in skin wound healing: where do we stand and where do we go?

Cutaneous healing is a highly complex process that, if altered due to, for example, impaired vascularization, results in chronic wounds or repaired neotissue of poor quality. Significant progress has been achieved in promoting neotissue vascularization during tissue repair/regeneration. In this review, we discuss the strategies that have been explored and how each one of them contributes to regulate vascularization in the context of cutaneous wound healing from two different perspectives - biomaterial-based and a cell-based approaches. Finally, we discuss the implications of these findings on the development of the 'next generation' approaches to target vascularization in wound healing highlighting the importance of going beyond its contribution to regulate vascularization and take into consideration the temporal features of the healing process and of different types of wounds.