Effects of mechanical properties of gelatin methacryloyl hydrogels on encapsulated stem cell spheroids for 3D tissue engineering

An optofluidic system for the concentration gradient screening of oocyte protection drugs

Oocytes protective drug screening is essential for the treatment of reproductive diseases. However, few studies construct the oocyte in vitro drug screening microfluidic systems because of their enormous size, scarcity, and sensitivity to the culture environment. Here, we present an optofluidic system for oocyte drug screening and state analysis. The system consists of two parts: an open-top drug screening microfluidic chip and an optical Fourier filter analysis part. The open-top microfluidic chip anchors single oocyte with hydrogel and allows nutrient and gas environment updating which is essential for oocyte culturing. The optical filter analysis part is used to accurately analyse the status of oocytes. Based on this system, we found that fluorene-9-bisphenol (BHPF) damaged the oocyte spindle in a dose-dependent manner, a high dose of melatonin (10-3 M) effectively reduces the percentage of abnormally arranged chromosomes of oocytes exposed to 40 μM BHPF. This optofluidic system shows great promise for the culture of oocytes and demonstrates the robust ability for convenient multi-concentration oocytes drug screening. This technology may benefit further biomedicine and reproductive toxicology applications in the lab on a chip community.

Enhanced hepatotoxicity assessment through encapsulated HepG2 spheroids in gelatin hydrogel matrices: Bridging the gap from 2D to 3D culture

Conventional 2D drug screening often fails to accurately predict clinical outcomes. We present an innovative approach to improve hepatotoxicity assessment by encapsulating HepG2 spheroids in gelatin hydrogel matrices with different mechanical properties. Encapsulated spheroids exhibit sustained liver-specific functionality, enhanced expression of drug-metabolizing enzymes, and increased drug sensitivity compared to 2D cultures. The platform detects critical variations in drug response, with significant differences in IC50 values between 2D and spheroid cultures ranging from 1.3-fold to > 13-fold, particularly for acetaminophen. Furthermore, drug-metabolizing enzyme expression varies across hydrogel concentrations, suggesting a role for matrix mechanical properties in modulating hepatocyte function. This novel spheroid-hydrogel platform offers a transformative approach to hepatotoxicity assessment, providing increased sensitivity, improved prediction, and a more physiologically relevant environment. The use of such advanced in vitro models can accelerate drug development, reduce animal testing, and contribute to improved patient safety and clinical outcomes.

Microfluidics single-cell encapsulation reveals that poly-l-lysine-mediated stem cell adhesion to alginate microgels is crucial for cell-cell crosstalk and its self-renewal

Microfluidic cell encapsulation has provided a platform for studying the behavior of individual cells and has become a turning point in single-cell analysis during the last decade. The engineered microenvironment, along with protecting the immune response, has led to increasingly presenting the results of practical and pre-clinical studies with the goals of disease treatment, tissue engineering, intelligent control of stem cell differentiation, and regenerative medicine. However, the significance of cell-substrate interaction versus cell-cell communications in the microgel is still unclear. In this study, monodisperse alginate microgels were generated using a flow-focusing microfluidic device to determine how the cell microenvironment can control human bone marrow-derived mesenchymal stem cells (hBMSCs) viability, proliferation, and biomechanical features in single-cell droplets versus multi-cell droplets. Collected results show insufficient cell proliferation (234 % and 329 %) in both single- and multi-cell alginate microgels. Alginate hydrogels supplemented with poly-l-lysine (PLL) showed a better proliferation rate (514 % and 780 %) in a comparison of free alginate hydrogels. Cell stiffness data illustrate that hBMSCs cultured in alginate hydrogels have higher membrane flexibility and migration potency (Young's modulus equal to 1.06 kPa), whereas PLL introduces more binding sites for cell attachment and causes lower flexibility and migration potency (Young's modulus equal to 1.83 kPa). Considering that cell adhesion is the most important parameter in tissue engineering, in which cells do not run away from a 3D substrate, PLL enhances cell stiffness and guarantees cell attachments. In conclusion, cell attachment to PLL-mediated alginate hydrogels is crucial for cell viability and proliferation. It suggests that cell-cell signaling is good enough for stem cell viability, but cell-PLL attachment alongside cell-cell signaling is crucial for stem cell proliferation and self-renewal.

Biocompatible Human Placental Extracellular Matrix Derived Hydrogels

Solubilizing extracellular matrix (ECM) materials and transforming them into hydrogels has expanded their potential applications both in vitro and in vivo. In this study, hydrogels are prepared by decellularization of human placental tissue using detergent and enzymes and by the subsequent creation of a homogenized acellular placental tissue powder (P-ECM). A perfusion-based decellularization approach is employed using detergent and enzymes. The P-ECM with and without gamma irradiation is then utilized to prepare P-ECM hydrogels. Physical and biological evaluations are conducted to assess the suitability of the P-ECM hydrogels for biocompatibility. The decellularized tissue has significantly reduced cellular content and retains the major ECM proteins. Increasing the concentration of P-ECM leads to improved mechanical properties of the P-ECM hydrogels. The biocompatibility of the P-ECM hydrogel is demonstrated through cell proliferation and viability assays. Notably, gamma-sterilized P-ECM does not support the formation of a stable hydrogel. Nonetheless, the use of HCl during the digestion process effectively decreases spore growth and bacterial bioburden. The study demonstrates that P-ECM hydrogels exhibit physical and biological attributes conducive to soft tissue reconstruction. These hydrogels establish a favorable microenvironment for cell growth and the need for investigating innovative sterilization methods.

Polyethylene glycol crosslinked decellularized single liver lobe scaffolds with vascular endothelial growth factor promotes angiogenesis in vivo

BACKGROUND

Improving the mechanical properties and angiogenesis of acellular scaffolds before transplantation is an important challenge facing the development of acellular liver grafts. The present study aimed to evaluate the cytotoxicity and angiogenesis of polyethylene glycol (PEG) crosslinked decellularized single liver lobe scaffolds (DLSs), and establish its suitability as a graft for long-term liver tissue engineering.

METHODS

Using mercaptoacrylate produced by the Michael addition reaction, DLSs were first modified using N-succinimidyl S-acetylthioacetate (SATA), followed by cross-linking with PEG as well as vascular endothelial growth factor (VEGF). The optimal concentration of agents and time of the individual steps were identified in this procedure through biomechanical testing and morphological analysis. Subsequently, human umbilical vein endothelial cells (HUVECs) were seeded on the PEG crosslinked scaffolds to detect the proliferation and viability of cells. The scaffolds were then transplanted into the subcutaneous tissue of Sprague-Dawley rats to evaluate angiogenesis. In addition, the average number of blood vessels was evaluated in the grafts with or without PEG at days 7, 14, and 21 after implantation.

RESULTS

The PEG crosslinked DLS maintained their three-dimensional structure and were more translucent after decellularization than native DLS, which presented a denser and more porous network structure. The results for Young's modulus proved that the mechanical properties of 0.5 PEG crosslinked DLS were the best and close to that of native livers. The PEG-VEGF-DLS could better promote cell proliferation and differentiation of HUVECs compared with the groups without PEG cross-linking. Importantly, the average density of blood vessels was higher in the PEG-VEGF-DLS than that in other groups at days 7, 14, and 21 after implantation in vivo.

CONCLUSIONS

The PEG crosslinked DLS with VEGF could improve the biomechanical properties of native DLS, and most importantly, their lack of cytotoxicity provides a new route to promote the proliferation of cells in vitro and angiogenesis in vivo in liver tissue engineering.

Harvest of Cell-Only Muscle Fibers Using Thermally Expandable Hydrogels with Adhesive Patterns

Muscle tissue engineering has been the focus of extensive research due to its potential for numerous medical applications, including ex vivo actuator development and clinical treatments. In this study, we developed a method for harvesting muscle fiber in a floatable and translocatable manner utilizing thermally expandable hydrogels with a chemically patterned polydopamine (PD) layer generated by microcontact printing (μCP). The μCP of PD on the hydrogel facilitated the formation of stripe patterns with varying widths of printed/nonprinted area (50/50, 100/100, and 200/200 μm). The spatially controlled adhesion of C2C12 myoblasts on the PD patterns produced clearly distinguishable muscle fibers, and translocated muscle fibers exhibited preserved extracellular matrix and junction proteins. Furthermore, the development of anisotropic arrangements and mature myotubes within the fibers suggests the potential for functional control of engineered muscle tissues. Overall, the muscle fiber harvesting method developed herein is suitable for both translocation and floating and is a promising technique for muscle tissue engineering as it mimics the structure-function relationship of natural tissue.

Biomaterials are the key to unlock spheroid function and therapeutic potential

Spheroids are three-dimensional cell aggregates that mimic fundamental aspects of the native tissue microenvironment better than single cells, making them a promising platform for the study of tissue development and therapeutics. Spheroids have been investigated for decades as models in cancer research, yet we have only just scratched the surface of their potential clinical utility in cell-based therapies. Like many cells, spheroids commonly exhibit a loss of key attributes upon implantation, motivating the need for strategies to regulate their function in situ. Biomaterials offer numerous opportunities to preserve spheroid function and guide spheroid behavior by tailoring the local microenvironment.

Gelatin Methacryloyl Hydrogel, from Standardization, Performance, to Biomedical Application

Gelatin methacryloyl (GelMA), a photocurable hydrogel, is widely used in 3D culture, particularly in 3D bioprinting, due to its high biocompatibility, tunable physicochemical properties, and excellent formability. However, as the properties and performances of GelMA vary under different synthetic conditions, there is a lack of standardization, leading to conflicting results. In this study, a uniform standard is established to understand and enhance GelMA applications. First, the basic concept of GelMA and the density of the molecular network (DMN) are defined. Second, two properties, degrees of substitution and ratio of solid content, as the main measurable parameters determining the DMN are used. Third, the mechanisms and relationships between DMN and its performance in various applications in terms of porosity, viscosity, formability, mechanical strength, swelling, biodegradation, and cytocompatibility are theoretically explained. The main questions that are answered: what does performance mean, why is it important, how to optimize the basic parameters to improve the performance, and how to characterize it reasonably and accurately? Finally, it is hoped that this knowledge will eliminate the need for researchers to conduct tedious and repetitive pre-experiments, enable easy communication for achievements between groups under the same standard, and fully explore the potential of the GelMA hydrogel.

3D-biofabricated chondrocyte-laden decellularized extracellular matrix-contained gelatin methacrylate auxetic scaffolds under cyclic tensile stimulation for cartilage regeneration

Three-dimensional (3D) hydrogel constructs can mimic features of the extracellular matrix (ECM) and have tailorable physicochemical properties to support and maintain the regeneration of articular cartilage. Various studies have shown that mechanical cues affect the cellular microenvironment and thereby influence cellular behavior. In this study, we fabricated an auxetic scaffold to investigate the effect of 3D tensile stimulation on chondrocyte behavior. Different concentrations of decellularized extracellular matrix (dECM) were mixed with fish gelatin methacrylate (FGelMa) and employed for the preparation of dECM/FGelMa auxetic bio-scaffolds using 3D biofabrication technology. We show that when human chondrocytes (HCs) were incorporated into these scaffolds, their proliferation and the expression of chondrogenesis-related markers increased with dECM content. The function of HC was influenced by cyclic tensile stimulation, as shown by increased production of the chondrogenesis-related markers, collagen II and glycosaminoglycans, with the involvement of the yes-associated protein 1 signaling pathway. The biofabricated auxetic scaffold represents an excellent platform for exploring interactions between cells and their mechanical microenvironment.

Engineered biomaterials to guide spheroid formation, function, and fabrication into 3D tissue constructs

Cellular spheroids are aggregates of cells that are being explored to address fundamental biological questions and as building blocks for engineered tissues. Spheroids possess distinct advantages over cellular monolayers or cell encapsulation in 3D natural and synthetic hydrogels, including direct cell-cell interactions and high cell densities, which better mimic aspects of many tissues. Despite these advantages, spheroid cultures often exhibit uncontrollable growth and may be too simplistic to mimic complex tissue structures. To address this, biomaterials are being leveraged to further expand the use of cellular spheroids for biomedical applications. In this review, we provide an overview of recent studies that utilize engineered biomaterials to guide spheroid formation and function, as well as their fabrication into tissues for use as tissue models and for therapeutic applications. First, we describe biomaterial strategies that allow the high-throughput fabrication of homogeneously-sized spheroids. Next, we summarize how engineered biomaterials are introduced into spheroid cultures either internally as microparticles or externally as hydrogel microenvironments to influence spheroid behavior (e.g., differentiation, fusion). Lastly, we discuss a variety of biofabrication strategies (e.g., 3D bioprinting, melt electrowriting) that have been used to develop macroscale tissue models and implantable constructs through the guided assembly of spheroids. Overall, the goal of this review is to provide a summary of how biomaterials are currently being engineered and leveraged to support spheroids in biomedical applications, as well as to provide a future outlook of the field. STATEMENT OF SIGNIFICANCE: Cellular spheroids are becoming increasingly used as in vitro tissue models or as 'building blocks' for tissue engineering and repair strategies. Engineered biomaterials and their processing through biofabrication approaches are being leveraged to structurally support and guide spheroid processes. This review summarizes current approaches where such biomaterials are being used to guide spheroid formation, function, and fabrication into tissue constructs. As the field is rapidly expanding, we also provide an outlook on future directions and how new engineered biomaterials can be implemented to further the development of biofabricated spheroid-based tissue constructs.

Strategies to capitalize on cell spheroid therapeutic potential for tissue repair and disease modeling

Cell therapies offer a tailorable, personalized treatment for use in tissue engineering to address defects arising from trauma, inefficient wound repair, or congenital malformation. However, most cell therapies have achieved limited success to date. Typically injected in solution as monodispersed cells, transplanted cells exhibit rapid cell death or insufficient retention at the site, thereby limiting their intended effects to only a few days. Spheroids, which are dense, three-dimensional (3D) aggregates of cells, enhance the beneficial effects of cell therapies by increasing and prolonging cell-cell and cell-matrix signaling. The use of spheroids is currently under investigation for many cell types. Among cells under evaluation, spheroids formed of mesenchymal stromal cells (MSCs) are particularly promising. MSC spheroids not only exhibit increased cell survival and retained differentiation, but they also secrete a potent secretome that promotes angiogenesis, reduces inflammation, and attracts endogenous host cells to promote tissue regeneration and repair. However, the clinical translation of spheroids has lagged behind promising preclinical outcomes due to hurdles in their formation, instruction, and use that have yet to be overcome. This review will describe the current state of preclinical spheroid research and highlight two key examples of spheroid use in clinically relevant disease modeling. It will highlight techniques used to instruct the phenotype and function of spheroids, describe current limitations to their use, and offer suggestions for the effective translation of cell spheroids for therapeutic treatments.

Free radical-scavenging composite gelatin methacryloyl hydrogels for cell encapsulation

Gelatin methacryloyl (GelMA) hydrogels have been widely used for cell encapsulation in tissue engineering due to their cell adhesiveness and biocompatibility. However, free radicals generated during gelation decrease the viability of the encapsulated cells by increasing intracellular oxidative stress, so appropriate strategies for scavenging free radicals need to be developed. To meet that need, we developed composite GelMA hydrogels incorporating nanofiber particles (EF) coated with epigallocatechin-gallate (EGCG). The GelMA composite hydrogels were successfully fabricated and had a storage modulus of about 5 kPa, which is similar to that of pristine GelMA hydrogel, and the drastic free radical scavenging activity of EGCG was highly preserved after gelation. In addition, human adipose-derived stem cells encapsulated within our composite hydrogels had better viability (about 1.5 times) and decreased intracellular oxidative stress (about 0.3 times) compared with cells within the pristine GelMA hydrogel. We obtained similar results with human dermal fibroblasts and human umbilical vein endothelial cells, indicating that our composite hydrogels are suitable for various cell types. Furthermore, we found that the ability of the encapsulated cells to spread and migrate increased by 5 times within the composite hydrogels. Collectively, our results demonstrate that incorporating EF into GelMA hydrogels is a promising way to enhance cell viability by reducing free-radical-derived cellular damage when fabricating 3D tissue ex vivo. STATEMENT OF SIGNIFICANCE: Gelatin methacryloyl (GelMA) hydrogels have been widely applied to various tissue engineering applications because of their biocompatibility and cell interactivity. However, free radicals generated during the GelMA hydrogel fabrication decrease the viability of encapsulated cells by elevating intracellular oxidative stress. Here, we demonstrate radical scavenging GelMA hydrogels incorporating epigallocatechin-gallate (EGCG)-coated nanofiber particles (EF). The composite GelMA hydrogels are successfully fabricated, maintaining their mechanical properties, and the viability of encapsulated human adipose-derived stem cells is greatly improved after the gelation, indicating that our composite GelMA hydrogel alleviates damages from free radicals. Collectively, the incorporation of EF within GelMA hydrogels may be a promising way to enhance the viability of encapsulated cells, which could be applied to 3D tissue fabrication.