Fibrin: a versatile scaffold for tissue engineering applications

Biofunctionalization of ADA-GEL Hydrogels Based on the Degree of Cross-Linking and Polymer Concentration Improves Angiogenesis

The creation of bioartificial tissues is a promising option for the reconstruction of large-volume defects. The vascularization of tissue engineering constructs, as well as the material properties of the carrier matrix, are important factors for successful clinical application. In this regard, hydrogels are promising biomaterials, providing an extracellular matrix-like milieu that enables the possibility of cell transplantation and de novo tissue formation. Furthermore, biofunctionalization allows for a certain fine-tuning of angiogenic properties. This study aims to investigate vascularization and tissue formation of highly cross-linked alginate dialdehyde (ADA) and gelatin (GEL). This highly cross-linked network is created using a dural cross-linking mechanism combining ionic (Ca2+ ions) and enzymatic (human transglutaminase (hTG)) cross-linking, resulting in reduced swelling and moderate degradation rates. Vascularization of the ADA-GEL-hTG constructs is induced surgically using arteriovenous (AV) loops. Biocompatibility, tissue formation, and vascularization are analyzed by histology and X-ray microscopy. After only 2 weeks, vascularization of the ADA-GEL-hTG constructs is already present. After 4 weeks, both de novo tissue formation and vascularization of the ADA-GEL-hTG matrix increase. In conclusion, ADA-GEL-hTG-based hydrogels are shown to be promising scaffold materials for tissue engineering applications.

Macrophage and osteosarcoma cell crosstalk is dependent on oxygen tension and 3D culture

Osteosarcoma (OS), the most common form of primary bone cancer in young adults, has had no improvements in clinical outcomes in 50 years. This highlights a critical need to advance mechanistic understanding of OS to further therapeutic discovery, which will only be possible with accurate models of the disease. Compared to traditional monolayer studies and preclinical models, in vitro models that better replicate the three-dimensional (3D) bone marrow microenvironment will facilitate methodical investigations of the events and factors that drive OS progression. Herein, we use fibrin-alginate interpenetrating network (FA IPN) hydrogels to model the hematological bone marrow environment. We interrogated the effects of oxygen tension, 3D culture, and macrophage phenotype on OS behavior and specifically examine the immunomodulatory crosstalk between OS and macrophages. We observe that OS is more sensitive to oxygen tension when cultured in 3D. Specifically, both highly and less metastatic OS exhibit decreased changes in DNA content over time in 3D, but then demonstrate diverging behaviors in heterotypic culture with macrophages. OS response to macrophages differs as a function of metastatic potential, where highly metastatic OS shows increased immunosuppression that varies with oxygen tension but relies on direct coculture conditions. To our knowledge, this is among the first work to report the effects of 3D culture on the interplay between OS and macrophages in a coculture microenvironment. Together, these data introduce FA IPNs as a promising platform for cancer research and emphasize the importance of novel models for the mechanistic study of OS.

Applications of Platelet-Rich Fibrin (PRF) Membranes Alone or in Combination with Biomimetic Materials in Oral Regeneration: A Narrative Review

Platelet-rich fibrin (PRF) membranes are a biomaterial derived from the patient's own blood, used in different medical and dental areas for their ability to promote healing, tissue regeneration, and reduce inflammation. They are obtained by centrifuging the blood, which separates the components and concentrates the platelets and growth factors in a fibrin matrix. This material is then moulded into a membrane that can be applied directly to tissues. The use of these PRF membranes is often associated with the use of different biomimetic materials such as deproteinized bovine bone mineral (DBBM), β-tricalcium phosphate (β-TCP), enamel matrix derivative (EMD), and hydroxyapatite (HA). Different indications of PRF membranes have been proposed, like alveolar ridge preservation, alveolar ridge augmentation, guided tissue regeneration (GTR), and sinus floor augmentation. The aim of this narrative review is to check the state-of-the-art and to analyze the existing gaps in the use of PRF membranes in combination with biomimetic materials in alveolar ridge preservation, alveolar ridge augmentation, guided tissue regeneration (GTR), and sinus floor augmentation.

Blood Plasma, Fibrinogen or Fibrin Biomaterial for the Manufacturing of Skin Tissue-Engineered Products and Other Dermatological Treatments: A Systematic Review

The use of blood plasma, fibrinogen or fibrin, a natural biomaterial, has been widely studied for the development of different skin tissue-engineered products and other dermatological treatments. This systematic review reports the preclinical and clinical studies which use it alone or combined with other biomaterials and/or cells for the treatment of several dermatological conditions. Following the PRISMA 2020 Guidelines, 147 preclinical studies have revealed that the use of this biomaterial as a wound dressing or as a monolayer (one cell type) skin substitute are the preferred strategies, mainly for the treatment of excisional or surgical wounds. Moreover, blood plasma is mainly used alone although its combination with other biomaterials such as agarose, polyethylene glycol or collagen has also been reported to increase its wound healing potential. However, most of the 17 clinical reviewed evaluated its use for the treatment of severely burned patients as a wound dressing or bilayer (two cell types) skin substitute. Although the number of preclinical studies evaluating the use of blood plasma as a dermatological treatment has increased during the last fifteen years, this has not been correlated with a wide variety of clinical studies. Its safety and wound healing potential have been proved; however, the lack of a standard model and the presence of several approaches have meant that its translation to a clinical environment is still limited. A higher number of clinical studies should be carried out in the coming years to set a standard wound healing strategy for each dermatological disease.

Platelet-Rich Plasma Loaded Alginate-Based Injectable Hydrogel for Meniscal Tear Repair: In Vivo Evaluation in Lapine Model

Platelet-rich plasma (PRP) has been employed for orthopedic applications for decades due to the abundance of bioactive cues/growth factors that ameliorate the proliferation and migration of relevant cells involved in tissue repair/regeneration. In this work, PRP was incorporated into injectable compositions of alginate-based hydrogel and evaluated in vitro and in vivo. In vitro tests revealed that PRP addition promoted cell adhesion, cell proliferation, and distribution of seeded fibrochondrocytes on the hydrogel. Further, the DNA quantification and sGAG estimation confirmed the production of fibrocartilage-specific extracellular matrix, predominantly type 1 collagen and sGAG. For in vivo evaluation, tears were created surgically in the rabbit menisci and were filled with injectable hydrogel. Sham and hydrogel without PRP were used as controls. Histopathological evaluation after 3 months of implantation revealed that the healing was partial for sham control, but complete for hydrogel without PRP. The hydrogel served as the scaffold for fibrocartilage tissue regeneration. On the other hand, PRP-incorporated hydrogel showed good healing with low signs of inflammation as evidenced by histology and biochemical content. The healing was complete, and the nature of the regenerated tissues was very close to native tissue indicating that alginate-based hydrogel is a promising candidate for meniscal tissue repair.

Structurally sophisticated 3D-printed PCL-fibrin hydrogel meniscal scaffold promotes in situ regeneration in the rabbit knee meniscus

A meniscus injury is a common cartilage disease of the knee joint. Despite the availability of various methods for the treatment of meniscal injuries, the poor regenerative capacity of the meniscus often necessitates resection, leading to the accelerated progression of osteoarthritis. Advances in tissue engineering have introduced meniscal tissue engineering as a potential treatment option. In this study, we established the size of a standardized meniscal scaffold using knee Magnetic Resonance Imaging (MRI) data and created a precise Polycaprolactone (PCL) scaffold utilizing 3-Dimensional (3D) printing technology, which was then combined with Fibrin (Fib) hydrogel to form a PCL-Fib scaffold. The PCL scaffold offers superior biomechanical properties, while the Fib hydrogel creates a conducive microenvironment for cell growth, supporting chondrocyte proliferation and extracellular matrix (ECM) production. Physical and chemical characterization, biocompatibility testing, and in vivo animal experiments revealed the excellent biomechanical properties and biocompatibility of the scaffold, which enhanced in situ meniscal regeneration and reduced osteoarthritis progression. In conclusion, the integration of 3D printing technology and the Fib hydrogel provided a supportive microenvironment for chondrocyte proliferation and ECM secretion, facilitating the in situ regeneration and repair of the meniscal defect. This innovative approach presents a promising avenue for meniscal injury treatment and advances the clinical utilization of artificial meniscal grafts.

How to explain the beneficial effects of leukocyte- and platelet-rich fibrin

The survival of an organism relies on its ability to repair the damage caused by trauma, toxic agents, and inflammation. This process involving cell proliferation and differentiation is driven by several growth factors and is critically dependent on the organization of the extracellular matrix. Since autologous platelet concentrates (APCs) are fibrin matrices in which cells, growth factors, and cytokines are trapped and delivered over time, they are able to influence that response at different levels. The present review thoroughly describes the molecular components present in one of these APCs, leukocyte- and platelet-rich fibrin (L-PRF), and summarizes the level of evidence regarding the influence of L-PRF on anti-inflammatory reactions, analgesia, hemostasis, antimicrobial capacity, and its biological mechanisms on bone/soft tissue regeneration.

Injectable Hydrogels for Liver: Potential for Clinical Translation

Injectable hydrogels are a sub-type of hydrogels which can be delivered into the host in a minimally invasive manner. They can act as carriers to encapsulate and deliver cells, drugs or active biomolecules across several disease conditions. Polymers, either synthetic or natural, or even a combination of the two, can be used to create injectable hydrogels. Clinically approved injectable hydrogels are being used as dressings for burn wounds, bone and cartilage reconstruction. Injectable hydrogels have recently gained tremendous attention for their delivery into the liver in pre-clinical models. However, their efficacy in clinical studies remains yet to be established. In this article, we describe principles for the design of these injectable hydrogels, delivery strategies and their potential applications in facilitating liver regeneration and ameliorating injury. We also discuss the several constraints related to translation of these hydrogels into clinical settings for liver diseases and deliberate some potential solutions to combat these challenges.

3D Bioprinting and Artificial Intelligence-Assisted Biofabrication of Personalized Oral Soft Tissue Constructs

Regeneration of oral soft tissue defects, including mucogingival defects associated with the recession or loss of gingival and/or mucosal tissues around teeth and implants, is crucial for restoring oral tissue form, function, and health. This study presents a novel approach using three-dimensional (3D) bioprinting to fabricate individualized grafts with precise size, shape, and layer-by-layer cellular organization. A multicomponent polysaccharide/fibrinogen-based bioink is developed, and bioprinting parameters are optimized to create shape-controlled oral soft tissue (gingival) constructs. Rheological, printability, and shape-fidelity assays, demonstrated the influence of thickener concentration and print parameters on print resolution and shape fidelity. Artificial intelligence (AI)-derived tool enabled streamline the iterative bioprinting parameter optimization and analysis of the interaction between the bioprinting parameters. The cell-laden polysaccharide/fibrinogen-based bioinks exhibited excellent cellular viability and shape fidelity of shape-controlled, full-thickness gingival tissue constructs over the 18-day culture period. While variations in thickener concentrations within the bioink minimally impact the cellular organization and morphogenesis (gingival epithelial, connective tissue, and basement membrane markers), they influence the shape fidelity of the bioprinted constructs. This study represents a significant step toward the biofabrication of personalized soft tissue grafts, offering potential applications in the repair and regeneration of mucogingival defects associated with periodontal disease and dental implants.

Harnessing the power of bioprinting for the development of next-generation models of thrombosis

Thrombosis, a leading cause of cardiovascular morbidity and mortality, involves the formation of blood clots within blood vessels. Current animal models and in vitro systems have limitations in recapitulating the complex human vasculature and hemodynamic conditions, limiting the research in understanding the mechanisms of thrombosis. Bioprinting has emerged as a promising approach to construct biomimetic vascular models that closely mimic the structural and mechanical properties of native blood vessels. This review discusses the key considerations for designing bioprinted vascular conduits for thrombosis studies, including the incorporation of key structural, biochemical and mechanical features, the selection of appropriate biomaterials and cell sources, and the challenges and future directions in the field. The advancements in bioprinting techniques, such as multi-material bioprinting and microfluidic integration, have enabled the development of physiologically relevant models of thrombosis. The future of bioprinted models of thrombosis lies in the integration of patient-specific data, real-time monitoring technologies, and advanced microfluidic platforms, paving the way for personalized medicine and targeted interventions. As the field of bioprinting continues to evolve, these advanced vascular models are expected to play an increasingly important role in unraveling the complexities of thrombosis and improving patient outcomes. The continued advancements in bioprinting technologies and the collaboration between researchers from various disciplines hold great promise for revolutionizing the field of thrombosis research.

Evaluation of plant-derived biomaterials for the development of tissue-engineered corneal substitutes

Corneal blindness affects over 10 million patients worldwide. Due to the limited supply of donor corneas and frequent graft failure, bioengineered alternatives are crucial. To overcome drawbacks associated with corneal substitutes from synthetic biomaterials, fabrication from plant-derived biomaterials is a potential alternative. Herein, soy protein and glutenin in combination with different crosslinkers were evaluated for fabrication of corneal substitutes. Optical, mechanical, and biochemical properties of fabricated constructs and control rabbit corneas were evaluated in vitro. Soy protein crosslinked with peroxidase/H202 possessed transparency and mechanical properties comparable to controls, although their water content and biocompatibility were inferior. In contrast, soy protein crosslinked with tannic acid showed similar water content, tensile strength, and biocompatibility as rabbit corneas; however, these constructs displayed significantly lower transparency and higher strain to failure. Finally, glutenin cross-linked using formaldehyde showed excellent transparency, strain to failure, and biocompatibility, however; they exhibited significantly lower water content and tensile strength than controls. This study is the first to establish CIELAB color values for the rabbit cornea, allowing quantitative optical evaluation of tissue-engineered substitutes. Thus, a crosslinking strategy utilizing plant-derived proteins for fabrication of constructs with properties comparable to rabbit corneas is a promising direction for development of tissue-engineered corneal substitutes.

Implantable 3D printed hydrogels with intrinsic channels for liver tissue engineering

This study presents the design, fabrication, and evaluation of a general platform for the creation of three-dimensional printed devices (3DPDs) for tissue engineering applications. As a demonstration, we modeled the liver with 3DPDs consisting of a pair of parallel millifluidic channels that function as portal-venous (PV) and hepatobiliary (HB) structures. Perfusion of medium or whole blood through the PV channel supports the hepatocyte-containing HB channel. Device computer-aided design was optimized for structural stability, after which 3DPDs were 3D printed in a polyethylene(glycol) diacrylate photoink by digital light processing and evaluated in vitro. The HB channels were subsequently seeded with hepatic cells suspended in a collagen hydrogel. Perfusion of 3DPDs in bioreactors enhanced the viability and function of rat hepatoma cells and were maintained over time, along with improved liver-specific functions. Similar results were observed with primary rat hepatocytes, including significant upregulation of cytochrome p450 activity. Additionally, coculture experiments involving primary rat hepatocytes, endothelial cells, and mesenchymal stem cells in 3DPDs showed enhanced viability, broad liver-specific gene expression, and histological features indicative of liver tissue architecture. In vivo implantation of 3DPDs in a rat renal shunt model demonstrated successful blood flow through the devices without clot formation and maintenance of cell viability. 3D printed designs can be scaled in 3D space, allowing for larger devices with increased cell mass. Overall, these findings highlight the potential of 3DPDs for clinical translation in hepatic support applications.

Glutaraldehyde Cross-Linking of Salt-Induced Fibrinogen Hydrogels

Covalent cross-linking is a common strategy to improve the mechanical properties of biological polymers. The most prominent field of application of such materials is in medicine, for example, in the form of bioprinting, drug delivery, and wound sealants. One biological polymer of particular interest is the blood clotting protein fibrinogen. In the natural process, fibrinogen polymerizes to fibrous hydrogel fibrin. Although the material shows great potential, its costs are very high due to the required enzyme thrombin. Recently, we introduced several approaches to trigger a thrombin-free fibrillogenesis of fibrinogen to a fibrin-like material. Inspired by the natural pathway of blood clotting in which covalent cross-linking stabilizes the clot, this "pseudofibrin" is now developed even further by covalently cross-linking the fibers. In particular, the effect of inexpensive glutaraldehyde on fiber morphology, rheological properties, and irreversible gel dissolution is investigated. Additionally, new insights into the reaction kinetics between fibrinogen and glutaraldehyde are gained. It could be shown that the fibrous structure of pseudofibrin can be retained during cross-linking and that glutaraldehyde significantly improves rheological properties of the hydrogels. Even more important, cross-linking with glutaraldehyde can prevent dissolution of the gels at elevated temperatures.

Effect of oxidized Bletilla striata polysaccharide on fibrin hydrogel formation and its application in wound healing dressing

Wound healing is influenced by various factors, including oxidative damage, bacterial infection, and inadequate angiogenesis, which collectively contribute to a protracted healing process. In this work, we designed innovative multifunctional hydrogels based on fibrin integrated with Bletilla striata polysaccharides (BSP) or oxidated Bletilla striata polysaccharides (OBSP) for use as wound dressings. The preliminary structure and bioactivity of BSP and OBSP were investigated. The effect of polysaccharides on the self-assembly process of fibrin hydrogels were also evaluated. BSP and OBSP significantly altered the initial fibrin fibrillogenesis and the ultimate structure of the fibrin network. Relative to pure fibrin hydrogel, the incorporation of BSP and OBSP enhanced water swelling and retention, and decelerated the degradation of hydrogels in PBS. Furthermore, BSP and OBSP augmented the antioxidant, antibacterial, and anti-inflammatory properties of fibrin hydrogels, with OBSP demonstrating superior performance in these aspects. Through the development of a murine wound model, it was observed that the wound healing efficacy of hydrogels incorporating BSP and OBSP surpassed that of the pure fibrin group. Notably, the hydrogel formulated with 25 mg/mL OBSP exhibited the most pronounced therapeutic effect, achieving a healing rate approaching 100 %. Consequently, fibrin-OBSP composite hydrogels demonstrate significant potential as wound dressings.

Biomolecule-based hydrogels as delivery systems for limbal stem cell transplantation: A review

Limbal stem cell deficiency (LSCD) is a complex disease of the cornea resulting from dysfunction and/or loss of limbal stem cells (LSCs) and their niche. Most patients with LSCD cannot be treated by conventional corneal transplants because the donor tissue lacks the LSCs necessary for corneal epithelial regeneration. Successful treatment of LSCD depends on effective stem cell transplantation to the ocular surface for replenishment of the LSC reservoir. Thus, stem cell therapies employing carrier substrates for LSCs have been widely explored. Hydrogel biomaterials have many favorable characteristics, including hydrophilicity, flexibility, cytocompatibility, and optical properties suitable for the transplantation of LSCs. Therefore, due to these properties, along with the necessary signals for stem cell proliferation and differentiation, hydrogels are ideal carrier substrates for LSCD treatment. This review summarizes the use of different medical-type hydrogels in LSC transplantation from 2001 to 2024. First, a brief background of LSCD is provided. Then, studies that employed various hydrogel scaffolds as LSC carriers are highlighted to provide a multimodal strategic reference for LSCD treatment. Finally, an analysis of prospective future developments and challenges in the field of hydrogels as LSC carriers for treating LSCD is presented.

Highly aligned myotubes formation of piscine satellite cells in 3D fibrin hydrogels of cultured meat

Currently, various cultured meat products, including chicken, beef and pork, have been developed. However, established methods for production cultured fish meat with highly aligned myotubes are still lack. In this study, we introduced a culture method based on high-biocompatibility fibrin hydrogels with an easy-to-use tissue mold for obtaining cultured fish fillets that closely mimicked the structure of natural fish fillets. Results showed that highly aligned myotubes were observed within the muscle bundles culturing in the tissue mold. The myotube fusion index was also increased to 72.65 %. Furthermore, key differentiation genes (desmin, myosin light chain kinase, myocilin) were up-regulated in the tissue mold group. Transcriptomic analysis further supported the effectiveness of method in promoting myoblast fusion. Stiffness of the muscle bundles was also positively impacted by the tissue mold. Ultimately, sensory and nutritional characteristics of natural and cultured fish fillets were compared, revealing that cultured fish fillets prepared from the tissue mold was closer to natural fish fillets in sensory characteristic, and there were still some gaps with natural fish fillets in nutritional characteristic. Overall, our findings suggest that optimizing culture methods can help bridge some gaps between natural meat and cultured meat, facilitating the development of cultured fish meat.

Bio-printing method as a novel approach to obtain a fibrin scaffold settled by limbal epithelial cells for corneal regeneration

Treatment of Limbal Stem Cell Deficiency (LSCD), based on autologous transplantation of the patient's stem cells, is one of the few medical stem cell therapies approved by the European Medicines Agency (EMA). It relies on isolating and culturing in vivo Limbal Epithelial Stem Cells (LESC) and then populating them on the fibrin substrate, creating a scaffold for corneal epithelial regeneration. Such a solution is then implanted into the patient's eye. The epithelial cell culture process is specific, and its results strongly depend on the initial cell seeding density. Achieving control of the density and repeatability of the process is a desirable aim and can contribute to the success of the therapy. The study aimed to test bioprinting as a potential technique to increase the control over LESCs seeding on a scaffold and improve process reproducibility. Cells were applied to 0.5 mm thick, flat, transparent fibrin substrates using extrusion bioprinting; the control was the traditional manual application of cells using a pipette. The use of 3D printer enabled uniform coverage of the scaffold surface, and LESCs density in printed lines was close to the targeted value. Moreover, printed cells had higher cell viability than those seeded traditionally (91.1 ± 8.2% vs 82.6 ± 12.8%). The growth rate of the epithelium was higher in bioprinted samples. In both methods, the epithelium had favorable phenotypic features (p63 + and CK14 +). 3D printing constitutes a promising approach in LSCD therapy. It provides favorable conditions for LESCs growth and process reproducibility. Its application may lead to reduced cell requirements, thereby to using fewer cells on lower passages, which will contribute to preserving LESCs proliferative potential.

Innovations in 3D ovarian and follicle engineering for fertility preservation and restoration

In-vitro maturation (IVM) is the process of cultivating early-stage follicles from the primordial to the antral stage and facilitating the maturation of oocytes outside the body within a supportive environment. This intricate procedure requires the careful coordination of various factors to replicate the natural ovarian conditions. Advanced techniques for IVM are designed to mimic the natural ovarian environment and enhance the development of follicles. Three-dimensional (3D) culture systems provide a more biologically relevant setting for follicle growth compared to traditional two-dimensional (2D) cultures. Traditional culture systems, often fail to support the complex process of follicle development effectively. However, modern engineered reproductive tissues and culture systems are making it possible to create increasingly physiological in-vitro models of folliculogenesis. These innovative methods are enabling researchers and clinicians to better replicate the dynamic and supportive environment of the ovary, thereby improving the outcomes of IVM offering new hope for fertility preservation and treatment. This paper focuses on the routine 3D culture, and innovative 3D culture of ovary and follicles, including a tissue engineering scaffolds, microfluidic (dynamic) culture system, organ-on-chip models, EVATAR system, from a clinical perspective to determine the most effective approach for achieving in-vitro maturation of follicles. These techniques provide critical support for ovarian function in various ovarian-associated disorders, including primary ovarian insufficiency (POI), premature ovarian failure (POF), ovarian cancer, and age-related infertility.

Biological Functions of Macromolecular Protein Hydrogels in Constructing Osteogenic Microenvironment

Irreversible bone defects resulting from trauma, infection, and degenerative illnesses have emerged as a significant health concern. Structurally and functionally controllable hydrogels made by bone tissue engineering (BTE) have become promising biomaterials. Natural proteins are able to establish connections with autologous proteins through unique biologically active regions. Hydrogels based on proteins can simulate the bone microenvironment and regulate the biological behavior of stem cells in the tissue niche, making them candidates for research related to bone regeneration. This article reviews the biological functions of various natural macromolecular proteins (such as collagen, gelatin, fibrin, and silk fibroin) and highlights their special advantages as hydrogels. Then the latest research trends on cross-linking modified macromolecular protein hydrogels with improved mechanical properties and composite hydrogels loaded with exogenous micromolecular proteins have been discussed. Finally, the applications of protein hydrogels, such as 3D printed hydrogels, microspheres, and injectable hydrogels, were introduced, aiming to provide a reference for the repair of clinical bone defects.

Nucleic acid-responsive smart systems for controlled cargo delivery

Stimulus-responsive delivery systems allow controlled, highly regulated, and efficient delivery of various cargos while minimizing side effects. Owing to the unique properties of nucleic acids, including the ability to adopt complex structures by base pairing, their easy synthesis, high specificity, shape memory, and configurability, they have been employed in autonomous molecular motors, logic circuits, reconfigurable nanoplatforms, and catalytic amplifiers. Moreover, the development of nucleic acid (NA)-responsive intelligent delivery vehicles is a rapidly growing field. These vehicles have attracted much attention in recent years due to their programmable, controllable, and reversible properties. In this work, we review several types of NA-responsive controlled delivery vehicles based on locks and keys, including DNA/RNA-responsive, aptamer-responsive, and CRISPR-responsive, and summarize their advantages and limitations.

Employing novel biocompatible composite scaffolds with bioglass 58S and poly L-lactic acid for effective bone defect treatment

BACKGROUND

Bioglass materials have gained significant attention in the field of tissue engineering due to their osteoinductive and biocompatible properties that promote bone cell differentiation. In this study, a novel composite scaffold was developed using a sol-gel technique to combine bioglass (BG) 58 S with a poly L-lactic acid (PLLA).

METHODS AND RESULTS

The physiochemical properties, morphology, and osteoinductive potential of the scaffolds were investigated by X-ray diffraction analysis, scanning electron microscopy, and Fourier-transform infrared spectroscopy. The results showed that the SiO2-CaO-P2O5 system was successfully synthesized by the sol-gel method. The PLLA scaffolds containing BG was found to be osteoinductive and promoted mineralization, as demonstrated by calcium deposition assay, upregulation of alkaline phosphatase enzyme activity, and Alizarin red staining data.

CONCLUSIONS

These in vitro studies suggest that composite scaffolds incorporating hBMSCs are a promising substitute material to be implemented in bone tissue engineering. The PLLA/BG scaffolds promote osteogenesis and support the differentiation of bone cells, such as osteoblasts, due to their osteoinductive properties.

Recent Advances in Hydrogel-Based 3D Bioprinting and Its Potential Application in the Treatment of Congenital Heart Disease

Congenital heart disease (CHD) is the most common birth defect, requiring invasive surgery often before a child's first birthday. Current materials used during CHD surgery lack the ability to grow, remodel, and regenerate. To solve those limitations, 3D bioprinting is an emerging tool with the capability to create tailored constructs based on patients' own imaging data with the ability to grow and remodel once implanted in children with CHD. It has the potential to integrate multiple bioinks with several cell types and biomolecules within 3D-bioprinted constructs that exhibit good structural fidelity, stability, and mechanical integrity. This review gives an overview of CHD and recent advancements in 3D bioprinting technologies with potential use in the treatment of CHD. Moreover, the selection of appropriate biomaterials based on their chemical, physical, and biological properties that are further manipulated to suit their application are also discussed. An introduction to bioink formulations composed of various biomaterials with emphasis on multiple cell types and biomolecules is briefly overviewed. Vasculogenesis and angiogenesis of prefabricated 3D-bioprinted structures and novel 4D printing technology are also summarized. Finally, we discuss several restrictions and our perspective on future directions in 3D bioprinting technologies in the treatment of CHD.

Magnetic fibrin nanofiber hydrogel delivering iron oxide magnetic nanoparticles promotes peripheral nerve regeneration

Peripheral nerve injury is a debilitating condition that have a profound impact on the overall quality of an individual's life. The repair of peripheral nerve defects continues to present significant challenges in the field. Iron oxide magnetic nanoparticles (IONPs) have been recognized as potent nanotools for promoting the regeneration of peripheral nerves due to their capability as biological carriers and their ability to template the hydrogel structure under an external magnetic field. This research used a fibrin nanofiber hydrogel loaded with IONPs (IONPs/fibrin) to promote the regeneration of peripheral nerves in rats. In vitro examination of PC12 cells on various concentrations of IONPs/fibrin hydrogels revealed a remarkable increase in NGF and VEGF expression at 2% IONPs concentration. The biocompatibility and degradation of 2% IONPs/fibrin hydrogel were assessed using the in vivo imaging system, demonstrating subcutaneous degradation within a week without immediate inflammation. Bridging a 10-mm sciatic nerve gap in Sprague Dawley rats with 2% IONPs/fibrin hydrogel led to satisfactory morphological recovery of myelinated nerve fibers. And motor functional recovery in the 2% IONPs/fibrin group was comparable to autografts at 6, 9 and 12 weeks postoperatively. Hence, the composite fibrin hydrogel incorporating 2% IONPs exhibits potential for peripheral nerve regeneration.

Cascade encapsulation of antimicrobial peptides, exosomes and antibiotics in fibrin-gel for first-aid hemostasis and infected wound healing

Wounding is one of the most common healthcare problems. Bioactive hydrogels have attracted much attention in first-aid hemostasis and wound healing due to their excellent biocompatibility, antibacterial properties, and pro-healing bioactivity. However, their applications are limited by inadequate mechanical properties. In this study, we first prepared edible rose-derived exosome-like nanoparticles (ELNs) and used them to encapsulate antimicrobial peptides (AMP), abbreviated as ELNs(AMP). ELNs(AMP) showed superior intracellular antibacterial activity, 2.5 times greater than AMP, in in vitro cell infection assays. We then prepared and tested an FDA-approved fibrin-gel of fibrinogen and thrombin encapsulating ELNs(AMP) and novobiocin sodium salt (NB) (ELNs(AMP)/NB-fibrin-gels). The fibrin gel showed a sustained release of ELNs(AMP) and NB over the eight days of testing. After spraying onto the skin, the formulation underwent in situ gelation and developed a stable patch with excellent hemostatic performance in a mouse liver injury model with hemostasis in 31 s, only 35.6 % of the PBS group. The fibrin gel exhibited pro-wound healing properties in the mouse-infected skin defect model. The thickness of granulation tissue and collagen of the ELNs(AMP)/NB-fibrin-gels group was 4.00, 6.32 times greater than that of the PBS group. In addition, the ELNs(AMP)/NB-fibrin-gels reduced inflammation (decreased mRNA levels of TNF-α, IL-1β, IL6, MCP1, and CXCL1) at the wound sites and demonstrated a biocompatible and biosafe profile. Thus, we have developed a hydrogel system with excellent hemostatic, antibacterial, and pro-wound healing properties, which may be a candidate for next-generation tissue regeneration with a wide clinical application for first-aid hemostasis and infected wound healing.

Rapid Self-Assembly Mini-Livers Protect Mice Against Severe Hepatectomy-Induced Liver Failure

The construction of bioartificial livers, such as liver organoids, offers significant promise for disease modeling, drug development, and regenerative medicine. However, existing methods for generating liver organoids have limitations, including lengthy and complex processes (taking 6-8 weeks or longer), safety concerns associated with pluripotency, limited functionality of pluripotent stem cell-derived hepatocytes, and small, highly variable sizes (typically ≈50-500 µm in diameter). Prolonged culture also leads to the formation of necrotic cores, further restricting size and function. In this study, a straightforward and time-efficient approach is developed for creating rapid self-assembly mini-livers (RSALs) within 12 h. Additionally, primary hepatocytes are significantly expanded in vitro for use as seeding cells. RSALs exhibit consistent larger sizes (5.5 mm in diameter), improved cell viability (99%), and enhanced liver functionality. Notably, RSALs are functionally vascularized within 2 weeks post-transplantation into the mesentery of mice. These authentic hepatocyte-based RSALs effectively protect mice from 90%-hepatectomy-induced liver failure, demonstrating the potential of bioartificial liver-based therapy.

Tissue-Penetrating Ultrasound-Triggered Hydrogel for Promoting Microvascular Network Reconstruction

The microvascular network plays an important role in providing nutrients to the injured tissue and exchanging various metabolites. However, how to achieve efficient penetration of the injured tissue is an important bottleneck restricting the reconstruction of microvascular network. Herein, the hydrogel precursor solution can efficiently penetrate the damaged tissue area, and ultrasound triggers the release of thrombin from liposomes in the solution to hydrolyze fibrinogen, forming a fibrin solid hydrogel network in situ with calcium ions and transglutaminase as catalysts, effectively solving the penetration impedance bottleneck of damaged tissues and ultimately significantly promoting the formation of microvascular networks within tissues. First, the fibrinogen complex solution is effectively permeated into the injured tissue. Second, ultrasound triggered the release of calcium ions and thrombin, activates transglutaminase, and hydrolyzes fibrinogen. Third, fibrin monomers are catalyzed to form fibrin hydrogels in situ in the damaged tissue area. In vitro studies have shown that the fibrinogen complex solution effectively penetrated the artificial bone tissue within 15 s after ultrasonic triggering, and formed a hydrogel after continuous triggering for 30 s. Overall, this innovative strategy effectively solved the problem of penetration resistance of ultrasound-triggered hydrogels in the injured tissues, and finally activates in situ microvascular networks regeneration.

Harnessing Macromolecular Chemistry to Design Hydrogel Micro- and Macro-Environments

Cell encapsulation within three-dimensional hydrogels is a promising approach to mimic tissues. However, true biomimicry of the intricate microenvironment, biophysical and biochemical gradients, and the macroscale hierarchical spatial organizations of native tissues is an unmet challenge within tissue engineering. This review provides an overview of the macromolecular chemistries that have been applied toward the design of cell-friendly hydrogels, as well as their application toward controlling biophysical and biochemical bulk and gradient properties of the microenvironment. Furthermore, biofabrication technologies provide the opportunity to simultaneously replicate macroscale features of native tissues. Biofabrication strategies are reviewed in detail with a particular focus on the compatibility of these strategies with the current macromolecular toolkit described for hydrogel design and the challenges associated with their clinical translation. This review identifies that the convergence of the ever-expanding macromolecular toolkit and technological advancements within the field of biofabrication, along with an improved biological understanding, represents a promising strategy toward the successful tissue regeneration.

Biological scaffold as potential platforms for stem cells: Current development and applications in wound healing

Wound repair is a complex challenge for both clinical practitioners and researchers. Conventional approaches for wound repair have several limitations. Stem cell-based therapy has emerged as a novel strategy to address this issue, exhibiting significant potential for enhancing wound healing rates, improving wound quality, and promoting skin regeneration. However, the use of stem cells in skin regeneration presents several challenges. Recently, stem cells and biomaterials have been identified as crucial components of the wound-healing process. Combination therapy involving the development of biocompatible scaffolds, accompanying cells, multiple biological factors, and structures resembling the natural extracellular matrix (ECM) has gained considerable attention. Biological scaffolds encompass a range of biomaterials that serve as platforms for seeding stem cells, providing them with an environment conducive to growth, similar to that of the ECM. These scaffolds facilitate the delivery and application of stem cells for tissue regeneration and wound healing. This article provides a comprehensive review of the current developments and applications of biological scaffolds for stem cells in wound healing, emphasizing their capacity to facilitate stem cell adhesion, proliferation, differentiation, and paracrine functions. Additionally, we identify the pivotal characteristics of the scaffolds that contribute to enhanced cellular activity.

Three-Dimensional Cultivation a Valuable Tool for Modelling Canine Mammary Gland Tumour Behaviour In Vitro

Cell cultivation has been one of the most popular methods in research for decades. Currently, scientists routinely use two-dimensional (2D) and three-dimensional (3D) cell cultures of commercially available cell lines and primary cultures to study cellular behaviour, responses to stimuli, and interactions with their environment in a controlled laboratory setting. In recent years, 3D cultivation has gained more attention in modern biomedical research, mainly due to its numerous advantages compared to 2D cultures. One of the main goals where 3D culture models are used is the investigation of tumour diseases, in both animals and humans. The ability to simulate the tumour microenvironment and design 3D masses allows us to monitor all the processes that take place in tumour tissue created not only from cell lines but directly from the patient's tumour cells. One of the tumour types for which 3D culture methods are often used in research is the canine mammary gland tumour (CMT). The clinically similar profile of the CMT and breast tumours in humans makes the CMT a suitable model for studying the issue not only in animals but also in women.

Bringing innovative wound care polymer materials to the market: Challenges, developments, and new trends

The development of innovative products for treating acute and chronic wounds has become a significant topic in healthcare, resulting in numerous products and innovations over time. The growing number of patients with comorbidities and chronic diseases, which may significantly alter, delay, or inhibit normal wound healing, has introduced considerable new challenges into the wound management scenario. Researchers in academia have quickly identified promising solutions, and many advanced wound healing materials have recently been designed; however, their successful translation to the market remains highly complex and unlikely without the contribution of industry experts. This review article condenses the main aspects of wound healing applications that will serve as a practical guide for researchers working in academia and industry devoted to designing, evaluating, validating, and translating polymer wound care materials to the market. The article highlights the current challenges in wound management, describes the state-of-the-art products already on the market and trending polymer materials, describes the regulation pathways for approval, discusses current wound healing models, and offers a perspective on new technologies that could soon reach consumers. We envision that this comprehensive review will significantly contribute to highlighting the importance of networking and exchanges between academia and healthcare companies. Only through the joint of these two actors, where innovation, manufacturing, regulatory insights, and financial resources act in harmony, can wound care products be developed efficiently to reach patients quickly and affordably.

Enhancing Adhesion of Fibrin-Based Hydrogel to Polythioether Polymer Surfaces

The development of stable (bio)hybrid constructs composed of scaffolds and (bio)matrices is a major challenge in the field of tissue engineering. In the present work, the adhesion of fibrin-based hydrogels to the surface of polythioether-based polymers relevant to the 3D printing of polymer scaffolds produced by thiol-ene click chemistry was investigated. Adhesion properties were characterized by single-lap tensile shear testing. Both the sample preparation and the test method were optimized for the analysis of fibrin gel bonding to the polythioether surface. Our experimental results show that even without further modification, an adhesion between the fibrin hydrogel and polythioether is substantial, with an adhesion strength of 4.9 ± 1.0 kPa. To further improve the bonding, linear functional poly(N-vinylpyrrolidone-co-glycidyl methacrylate) (PVP-co-GMA) copolymers were used that are known for covalently binding to fibrin. The maximum adhesion strength in our study was found to be 18.4 ± 3.4 kPa. The pure PVP-co-GMA copolymers also demonstrate covalent binding to the thiol-ene-based polymers with a maximum adhesion strength of 32.2 ± 2.7 kPa. Therefore, compared to pure fibrin, the presence of copolymer coating both on the polythioether surface and in the fibrin gel led to a significant increase of the adhesion strength by a factor of 1.6.

Injectable Extracellular Matrix-Inspired Hemostatic Hydrogel Composed of Hyaluronan and Gelatin with Shear-Thinning and Self-Healing

Injectable ECM-inspired hydrogels composed of hyaluronic acid and gelatin are biocompatible and potentially useful for various medical applications. We developed injectable hydrogels composed of monoaldehyde-modified hyaluronic acid (HA-mCHO) and carbohydrazide-modified gelatin (GL-CDH), "HA/GL gel", whose ratios of HA-mCHO to GL-CDH were different. The hydrogels exhibited gelation times shorter than 3 s. In addition, the hydrogels showed strong shear-thinning and self-healing properties, mainly because of the dynamic covalent bonding of Schiff bases between HA-mCHO and GL-CDH. This hydrogel degraded in the mice's peritoneum for a week and showed excellent biocompatibility. Moreover, the hydrogel showed a higher breaking strength than fibrin glue in the lap shear test of porcine skin. Finally, the hydrogels decreased bleeding to as low as fibrin glue without using thrombin and fibrinogen in a mouse liver bleeding model in both single- and double-barreled syringe administrations. HA/GL gels have the potential for excellent biocompatibility and hemostasis in clinical settings.

Investigation of background, novelty and recent advance of iron (II,III) oxide- loaded on 3D polymer based scaffolds as regenerative implant for bone tissue engineering: A review

Bone tissue engineering had crucial role in the bone defects regeneration, particularly when allograft and autograft procedures have limitations. In this regard, different types of scaffolds are used in tissue regeneration as fundamental tools. In recent years, magnetic scaffolds show promising applications in different biomedical applications (in vitro and in vivo). As superparamagnetic materials are widely considered to be among the most attractive biomaterials in tissue engineering, due to long-range stability and superior bioactivity, therefore, magnetic implants shows angiogenesis, osteoconduction, and osteoinduction features when they are combined with biomaterials. Furthermore, these scaffolds can be coupled with a magnetic field to enhance their regenerative potential. In addition, magnetic scaffolds can be composed of various combinations of magnetic biomaterials and polymers using different methods to improve the magnetic, biocompatibility, thermal, and mechanical properties of the scaffolds. This review article aims to explain the use of magnetic biomaterials such as iron (II,III) oxide (Fe2O3 and Fe3O4) in detail. So it will cover the research background of magnetic scaffolds, the novelty of using these magnetic implants in tissue engineering, and provides a future perspective on regenerative implants.

A Fibrin-Based Human Multicellular Gingival 3D Model Provides Biomimicry and Enables Long-Term In Vitro Studies

Collagen-type I gels are widely used for the fabrication of 3D in vitro gingival models. Unfortunately, their long-term stability is low, which limits the variety of in vitro applications. To overcome this problem and achieve better hydrolytic stability of 3D gingival models, fibrin-based hydrogel blends with increased long-term stability in vitro are investigated. Two different fibrin-based hydrogels are tested: fibrin 2.5% (w/v) and fibrin 1% (w/v)/gelatin 5% (w/v). Appropriate numbers of primary human gingival fibroblasts (HGFs) and OKG4/bmi1/TERT (OKG) keratinocytes are optimized to achieve a homogeneous distribution of cells under the assumed 3D conditions. Both hydrogels support the viability of HGFs and the stability of the hydrogel over 28 days. In vitro cultivation at the air-liquid interface triggers keratinization of the epithelium and increases its thickness, allowing the formation of multiple tissue-like layers. The presence of HGFs in the hydrogel further enhances epithelial differentiation. In conclusion, a fibrin-based 3D gingival model mimics the histology of native gingiva in vitro and ensures its long-term stability in comparison with the previously reported collagen paralogs. These results open new perspectives for extending the period within which specific biological or pathological conditions of artificial gingival tissue can be evaluated.

Fabrication of chitosan/fibrin-armored multifunctional silver nanocomposites to improve antibacterial and wound healing activities

A wound healing substitute promotes rapid tissue regeneration and protects wound sites from microbial contamination. The silver-based antiseptic frequently moist skin stains, burns and irritation, penetrates deep wounds and protects against pathogenic infections. Thus, we formulated a novel fibrin/chitosan encapsulated silver nanoparticle (CH:F:SPG-CH:SNP) composites bandage accelerating the polymicrobial wound healing. Electrospinning method was employed to form the nano-porous, inexpensive, and biocompatible smart bandages. The structural, functional, and mechanical properties were analyzed for the prepared composites. The biological capacity of prepared CH:F:SPG-CH:SNP bandage was assessed against NIH-3 T3 fibroblast and HaCaT cell lines. In vitro hemolytic assays using red blood cells were extensively studied and explored the low hemolytic effect (4.5 %). In addition, the improved drug delivery nature captured for the CH:F:SPG-CH:SNP composite bandage. Antibacterial experiments were achieved against Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus and Lactobacillus bulgaricus using zone inhibition method. Moreover, in-vivo wound healing efficacy of fabricated smart bandage was evaluated on the albino Wistar rats which revealed the significant improvement on the postoperative abdomen wounds.

Clots reveal anomalous elastic behavior of fiber networks

The adaptive mechanical properties of soft and fibrous biological materials are relevant to their functionality. The emergence of the macroscopic response of these materials to external stress and intrinsic cell traction from local deformations of their structural components is not well understood. Here, we investigate the nonlinear elastic behavior of blood clots by combining microscopy, rheology, and an elastic network model that incorporates the stretching, bending, and buckling of constituent fibrin fibers. By inhibiting fibrin cross-linking in blood clots, we observe an anomalous softening regime in the macroscopic shear response as well as a reduction in platelet-induced clot contractility. Our model explains these observations from two independent macroscopic measurements in a unified manner, through a single mechanical parameter, the bending stiffness of individual fibers. Supported by experimental evidence, our mechanics-based model provides a framework for predicting and comprehending the nonlinear elastic behavior of blood clots and other active biopolymer networks in general.

Development of Human-Derived Photocrosslinkable Gelatin Hydrogels for Tissue Engineering

Hydrogels are often used as biomimetic matrices for tissue regeneration. The source of the hydrogel is of utmost importance, as it affects the physicochemical characteristics and must be carefully selected to stimulate specific cell behaviors. Naturally derived polymeric biomaterials have inherent biological moieties, such as cell binding and protease cleavage sites, and thus can provide a suitable microenvironment for cells. Human-derived matrices can mitigate potential risks associated with the immune response and disease transmission from animal-derived biomaterials. In this article, we developed glycidyl methacrylate-modified human-derived gelatin (hGelGMA) hydrogels for use in tissue engineering applications. By adjusting the glycidyl methacrylate concentration in the reaction mixture, we synthesized hGelGMA with low, medium, and high degrees of modification referred to as hGelGMA-L, hGelGMA-M, and hGelGMA-H, respectively. The amount of polymeric networks in the hydrogels was increased proportionally with the degree of modification. This change has resulted in a decreasing trend in pore size, porosity, and consequent swelling ratio. Similarly, increasing the polymer concentration also exhibited slower enzymatic degradation. On the other hand, increasing the polymer concentration led to an improvement in mechanical properties, where the compressive moduli of hGelGMA-L, hGelGMA-M, and hGelGMA-H hydrogels have changed at 2.9 ± 1.0, 13.7 ± 0.9, and 26.4 ± 2.5 kPa, respectively. The cytocompatibility of hGelGMA was assessed by 3D encapsulation of human-derived cells, including human dermal fibroblasts (HDFs) and human mesenchymal stem cells (hMSCs), in vitro. Regardless of the degree of glycidyl methacrylate modification, the hGelGMA hydrogels preserved the viability of encapsulated cells and supported their growth and proliferation. HDF cells showed a higher metabolic activity in hGelGMA-H, while MSCs exhibited an increased metabolic activity when they were encapsulated in hGelGMA-M or hGelGMA-H. These results showed that photocrosslinkable human-derived gelatin-based hydrogels can be synthesized and their physical properties can be distinctly fine-tuned to different extents as a function of their degrees of modification depending on the needs of the target tissue. Due to its promising physical and biological properties, it is anticipated that hGelGMA can be utilized in a wide spectrum of tissue engineering applications.

Biomolecules based hydrogels and their potential biomedical applications: A comprehensive review

The need for biocompatible drug carriers has been significantly increased from the past few years. Researchers show great interest in the development of more versatile and sophisticated biomaterials based drug carriers. Hydrogels are beneficial drug carriers and easily release the controlled amount of drug at target site due to its tunable structure. The hydrogels made-up of potent biological macromolecules including collagen, gelatin, fibrin, elastin, fibroin, chitosan, starch, alginate, agarose and carrageenan have been proven as versatile biomaterials. These are three-dimensional polymeric networks, synthesized by crosslinking of hydrophilic polymers. The biological macromolecules based hydrogels containing therapeutic substances are used in a wide range of biomedical applications including wound healing, tissue engineering, cosmetics and contact lenses. However, many aspects related to hydrogels such as the mechanism of cross-linking and molecular entanglement are not clear. So, there is a need to do more research and exploration toward the extensive and cost-effective use of hydrogels. The present review article elaborately discusses the biomolecules based hydrogels and their possible biomedical applications in different fields.

Enhancing differentiation of menstrual blood-derived stem cells into female germ cells using a bilayer amniotic membrane and nano-fibrous fibroin scaffold

Three-dimensional nanofiber scaffolds offer a promising method for simulating in vivo conditions within the laboratory. This study aims to investigate the influence of a bilayer amniochorionic membrane/nanofibrous fibroin scaffold on the differentiation of human menstrual blood mesenchymal stromal/stem cells (MenSCs) into female germ cells. MenSCs were isolated and assigned to four culture groups: (i) MenSCs co-cultured with granulosa cells (GCs) using the scaffold (3D-T group), (ii) MenSCs using the scaffold alone (3D-C group), (iii) MenSCs co-cultured only with GCs (2D-T group), and (iv) MenSCs without co-culture or scaffold (2D-C group). Both MenSCs and GCs were independently cultured for two weeks before co-culturing was initiated. Flow cytometry was employed to characterize MenSCs based on positive markers (CD73, CD90, and CD105) and negative markers (CD45 and CD133). Additionally, flow cytometry and immunocytochemistry were used to characterize the GCs. Differentiated MenSCs were analyzed using real-time PCR and immunostaining. The real-time PCR results demonstrated significantly higher levels of VASA expression in the 3D-T group compared to the 3D-C, 2D-T, and 2D-C groups. Similarly, the SCP3 mRNA level in the 3D-T group was notably elevated compared to the 3D-C, 2D-T, and 2D-C groups. Moreover, the expression of GDF9 was significantly higher in the 3D-T group when compared to the 3D-C, 2D-T, and 2D-C groups. Immunostaining results revealed a lack of signal for VASA, SCP3, or GDF9 markers in the 2D-T group, while some cells in the 3D-T group exhibited positive staining for all these proteins. These findings suggest that the combination of a bilayer amniochorionic membrane/nanofibrous fibroin scaffold with co-culturing GCs facilitates the differentiation of MenSCs into female germ cells.

Hydrogel-Loaded Exosomes: A Promising Therapeutic Strategy for Musculoskeletal Disorders

Clinical treatment strategies for musculoskeletal disorders have been a hot research topic. Accumulating evidence suggests that hydrogels loaded with MSC-derived EVs show great potential in improving musculoskeletal injuries. The ideal hydrogels should be capable of promoting the development of new tissues and simulating the characteristics of target tissues, with the properties matching the cell-matrix constituents of autologous tissues. Although there have been numerous reports of hydrogels loaded with MSC-derived EVs for the repair of musculoskeletal injuries, such as intervertebral disc injury, tendinopathy, bone fractures, and cartilage injuries, there are still many hurdles to overcome before the clinical application of modified hydrogels. In this review, we focus on the advantages of the isolation technique of EVs in combination with different types of hydrogels. In this context, the efficacy of hydrogels loaded with MSC-derived EVs in different musculoskeletal injuries is discussed in detail to provide a reference for the future application of hydrogels loaded with MSC-derived EVs in the clinical treatment of musculoskeletal injuries.

Advances in tissue engineering and biofabrication for in vitro skin modeling

The global prevalence of skin disease and injury is continually increasing, yet conventional cell-based models used to study these conditions do not accurately reflect the complexity of human skin. The lack of inadequate in vitro modeling has resulted in reliance on animal-based models to test pharmaceuticals, biomedical devices, and industrial and environmental toxins to address clinical needs. These in vivo models are monetarily and morally expensive and are poor predictors of human tissue responses and clinical trial outcomes. The onset of three-dimensional (3D) culture techniques, such as cell-embedded and decellularized approaches, has offered accessible in vitro alternatives, using innovative scaffolds to improve cell-based models' structural and histological authenticity. However, these models lack adequate organizational control and complexity, resulting in variations between structures and the exclusion of physiologically relevant vascular and immunological features. Recently, biofabrication strategies, which combine biology, engineering, and manufacturing capabilities, have emerged as instrumental tools to recreate the heterogeneity of human skin precisely. Bioprinting uses computer-aided design (CAD) to yield robust and reproducible skin prototypes with unprecedented control over tissue design and assembly. As the interdisciplinary nature of biofabrication grows, we look to the promise of next-generation biofabrication technologies, such as organ-on-a-chip (OOAC) and 4D modeling, to simulate human tissue behaviors more reliably for research, pharmaceutical, and regenerative medicine purposes. This review aims to discuss the barriers to developing clinically relevant skin models, describe the evolution of skin-inspired in vitro structures, analyze the current approaches to biofabricating 3D human skin mimetics, and define the opportunities and challenges in biofabricating skin tissue for preclinical and clinical uses.

Cellular composition modifies the biological properties and stability of platelet rich plasma membranes for tissue engineering

Scaffolds should provide structural support for tissue regeneration, allowing their gradual biodegradation and interacting with cells and bioactive molecules to promote remodeling. Thus, the scaffold's intrinsic properties affect cellular processes involved in tissue regeneration, including migration, proliferation, differentiation, and protein synthesis. In this sense, due to its biological effect and clinical potential, Platelet Rich Plasma (PRP) fibrin could be considered a successful scaffold. Given the high variability in commercial PRPs formulations, this research focused on assessing the influence of cellular composition on fibrin membrane stability and remodeling cell activity. The stability and biological effect were evaluated at different time points via D-dimer, type I collagen and elastase quantification in culture media conditioned by Plasma Rich in Growth Factors - Fraction 1 (PRGF-F1), Plasma Rich in Growth Factors - Whole Plasma (PRGF-WP) and Leukocyte-rich Platelet Rich Plasma (L-PRP) membranes, and by gingival fibroblast cells seeded on them, respectively. Ultrastructure of PRP membranes was also evaluated. Histological analyses were performed after 5 and 18 days. Additionally, the effect of fibrin membranes on cell proliferation was determined. According to the results, L-PRP fibrin membranes degradation was complete at the end of the study, while PRGF membranes remained practically unchanged. Considering fibroblast behavior, PRGF membranes, in contrast to L-PRP ones, promoted extracellular matrix biosynthesis at the same time as fibrinolysis and enhanced cell proliferation. In conclusion, leukocytes in PRP fibrin membranes drastically reduce scaffold stability and induce behavioral changes in fibroblasts by reducing their proliferation rate and remodeling ability.

Bioinspired Collagen/Hyaluronic Acid/Fibrin-Based Hydrogels for Soft Tissue Engineering: Design, Synthesis, and In Vitro Characterization

A major challenge for future drug development comprises finding alternative models for drug screening. The use of animal models in research is highly controversial, with an ongoing debate on their ethical acceptability. Also, animal models are often poorly predictive of therapeutic outcomes due to the differences between animal and human physiological environments. In this study, we aimed to develop a biomimetic hydrogel that replicates the composition of skin for potential use in in vitro modeling within tissue engineering. The hydrogel was fabricated through the crosslinking of collagen type I, hyaluronic acid, four-arm PEG succinimidyl glutarate (4S-StarPEG), and fibrinogen. Various ratios of these components were systematically optimized to achieve a well-interconnected porosity and desirable rheological properties. To evaluate the hydrogel's cytocompatibility, fibroblasts were embedded within the matrix. The resulting hydrogel exhibited promising properties as a scaffold, also facilitating the growth of and proliferation of the cells. This biomimetic hydrogel holds great potential for tissue engineering applications, particularly in skin regeneration and cancer research. The study used melanoma spheroids fabricated using the 96-round bottom well plate method as a potential application. The results demonstrate that the developed hydrogels allowed the maintenance of spheroid integrity and viability, meaning it has a promising use as a three-dimensional in vitro model of melanoma for both tissue engineering and drug screening applications.

Polymeric biomaterials for wound healing

Skin indicates a person's state of health and is so important that it influences a person's emotional and psychological behavior. In this context, the effective treatment of wounds is a major concern, since several conventional wound healing materials have not been able to provide adequate healing, often leading to scar formation. Hence, the development of innovative biomaterials for wound healing is essential. Natural and synthetic polymers are used extensively for wound dressings and scaffold production. Both natural and synthetic polymers have beneficial properties and limitations, so they are often used in combination to overcome overcome their individual limitations. The use of different polymers in the production of biomaterials has proven to be a promising alternative for the treatment of wounds, as their capacity to accelerate the healing process has been demonstrated in many studies. Thus, this work focuses on describing several currently commercially available solutions used for the management of skin wounds, such as polymeric biomaterials for skin substitutes. New directions, strategies, and innovative technologies for the design of polymeric biomaterials are also addressed, providing solutions for deep burns, personalized care and faster healing.

A Review of Patents and Innovative Biopolymer-Based Hydrogels

Biopolymers represent a great resource for the development and utilization of new functional materials due to their particular advantages such as biocompatibility, biodegradability and non-toxicity. "Intelligent gels" sensitive to different stimuli (temperature, pH, ionic strength) have different applications in many industries (e.g., pharmacy, biomedicine, food). This review summarizes the research efforts presented in the patent and non-patent literature. A discussion was conducted regarding biopolymer-based hydrogels such as natural proteins (i.e., fibrin, silk fibroin, collagen, keratin, gelatin) and polysaccharides (i.e., chitosan, hyaluronic acid, cellulose, carrageenan, alginate). In this analysis, the latest advances in the modification and characterization of advanced biopolymeric formulations and their state-of-the-art administration in drug delivery, wound healing, tissue engineering and regenerative medicine were addressed.

Dual-Crosslinking of Gelatin-Based Hydrogels: Promising Compositions for a 3D Printed Organotypic Bone Model

Gelatin-based hydrogels have emerged as a popular scaffold material for tissue engineering applications. The introduction of variable crosslinking methods has shown promise for fabricating stable cell-laden scaffolds. In this work, we examine promising composite biopolymer-based inks for extrusion-based 3D bioprinting, using a dual crosslinking approach. A combination of carefully selected printable hydrogel ink compositions and the use of photoinduced covalent and ionic crosslinking mechanisms allows for the fabrication of scaffolds of high accuracy and low cytotoxicity, resulting in unimpeded cell proliferation, extracellular matrix deposition, and mineralization. Three selected bioink compositions were characterized and the respective cell-laden scaffolds were bioprinted. Temporal stability, morphology, swelling, and mechanical properties of the scaffolds were thoroughly studied and the biocompatibility of the constructs was assessed using rat mesenchymal stem cells while focusing on osteogenesis. Experimental results showed that the composition of 1% alginate, 4% gelatin, and 5% (w/v) gelatine methacrylate, was found to be optimal among the examined, with shape fidelity of 88%, large cell spreading area and cell viability at around 100% after 14 days. The large pore diameters that exceed 100 µm, and highly interconnected scaffold morphology, make these hydrogels extremely potent in bone tissue engineering and bone organoid fabrication.

3D bioprinted liver tissue and disease models: Current advances and future perspectives

Three-dimensional (3D) bioprinting is a promising technology for fabricating complex tissue constructs with biomimetic biological functions and stable mechanical properties. In this review, the characteristics of different bioprinting technologies and materials are compared, and development in strategies for bioprinting normal and diseased hepatic tissue are summarized. In particular, features of bioprinting and other bio-fabrication strategies, such as organoids and spheroids are compared to demonstrate the strengths and weaknesses of 3D printing technology. Directions and suggestions, such as vascularization and primary human hepatocyte culture, are provided for the future development of 3D bioprinting.

Current advancements in bio-ink technology for cartilage and bone tissue engineering

In tissue engineering, the fate of a particular organ/tissue regeneration and repair mainly depends on three pillars - 3D architecture, cells used, and stimulus provided. 3D cell supportive structure development is one of the crucial pillars necessary for defining organ/tissue geometry and shape. In recent years, the advancements in 3D bio-printing (additive manufacturing) made it possible to develop very precise 3D architectures with the help of industrial software like Computer-Aided Design (CAD). The main requirement for the 3D printing process is the bio-ink, which can act as a source for cell support, proliferation, drug (growth factors, stimulators) delivery, and organ/tissue shape. The selection of the bio-ink depends upon the type of 3D tissue of interest. Printing tissues like bone and cartilage is always challenging because it is difficult to find printable biomaterial that can act as bio-ink and mimic the strength of the natural bone and cartilage tissues. This review describes different biomaterials used to develop bio-inks with different processing variables and cell-seeding densities for bone and cartilage 3D printing applications. The review also discusses the advantages, limitations, and cell bio-ink compatibility in each biomaterial section. The emphasis is given to bio-inks reported for 3D printing cartilage and bone and their applications in orthopedics and orthodontists. The critical/important performance and the architectural morphology requirements of desired bone and cartilage bio-inks were compiled in summary.

The use of commercial fibrin glue in dermal replacement material reduces angiogenic and lymphangiogenic gene and protein expression in vitro

BACKGROUND

Commercial fibrin glue is increasingly finding its way into clinical practice in surgeries to seal anastomosis, and initiate hemostasis or tissue repair. Human biological glue is also being discussed as a possible cell carrier. To date, there are only a few studies addressing the effects of fibrin glue on the cell-molecular level. This study examines the effects of fibrin glue on angiogenesis and lymphangiogenesis, as well as adipose-derived stem cells (ASCs) with a focus on gene and protein expression in scaffolds regularly used for tissue engineering approaches.

METHODS

Collagen-based dermal regeneration matrices (DRM) were seeded with human umbilical vein endothelial cells (HUVEC), human dermal lymphatic endothelial cells (LECs), or adipose-derived stem cells (ASC) and fixed with or without fibrin glue according to the experimental group. Cultures were maintained for 1 and 7 days. Finally, angiogenic and lymphangiogenic gene and protein expression were measured with special regard to subtypes of vascular endothelial growth factor (VEGF) and corresponding receptors using Multiplex-qPCR and ELISA assays. In addition, the hypoxia-induced factor 1-alpha (HIF1a) mediated intracellular signaling pathways were included in assessments to analyze a hypoxic encapsulating effect of fibrin polymers.

RESULTS

All cell types reacted to fibrin glue application with an alteration of gene and protein expression. In particular, vascular endothelial growth factor A (VEGFA), vascular endothelial growth factor B (VEGFB), vascular endothelial growth factor C (VEGFC), vascular endothelial growth receptor 1 (VEGFR1/FLT1), vascular endothelial growth receptor 2 (VEGFR2/KDR), vascular endothelial growth receptor 3 (VEGFR3/FLT4) and Prospero Homeobox 1 (PROX1) were depressed significantly depending on fibrin glue. Especially short-term fibrin effect led to a continuous downregulation of respective gene and protein expression in HUVECs, LECs, and ASCs.

CONCLUSION

Our findings demonstrate the impact of fibrin glue application in dermal regeneration with special regard to angiogenesis and lymphangiogenesis. In particular, a short fibrin treatment of 24 hours led to a decrease in gene and protein levels of LECS, HUVECs, and ASCs. In contrast, the long-term application showed less effect on gene and protein expressions. Therefore, this work demonstrated the negative effects of fibrin-treated cells in tissue engineering approaches and could affect wound healing during dermal regeneration.

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.