Microinterfaces in biopolymer-based bicontinuous hydrogels guide rapid 3D cell migration

Semi-synthetic fibrous fibrin composites promote 3D microvascular assembly, survival, and host integration of endothelial cells without mesenchymal cell support

Vasculogenic assembly of 3D capillary networks remains a promising approach to vascularizing tissue-engineered grafts, a significant outstanding challenge in tissue engineering and regenerative medicine. Current approaches for vasculogenic assembly rely on the inclusion of supporting mesenchymal cells alongside endothelial cells, co-encapsulated within vasculo-conducive materials such as low-density fibrin hydrogels. Here, we established a material-based approach to circumvent the need for supporting mesenchymal cells and report that the inclusion of synthetic matrix fibers in dense (>3 mg mL-1) 3D fibrin hydrogels can enhance vasculogenic assembly in endothelial cell monocultures. Surprisingly, we found that the addition of non-cell-adhesive synthetic matrix fibers compared to cell-adhesive synthetic fibers best encouraged vasculogenic assembly, proliferation, lumenogenesis, a vasculogenic transcriptional program, and additionally promoted cell-matrix interactions and intercellular force transmission. Implanting fiber-reinforced prevascularized constructs to assess graft-host vascular integration, we demonstrate additive effects of enhanced vascular network assembly during in vitro pre-culture, fiber-mediated improvements in endothelial cell survival and vascular maintenance post-implantation, and enhanced host cell infiltration that collectively enabled graft vessel integration with host circulation. This work establishes synthetic matrix fibers as an inexpensive alternative to sourcing and expanding secondary supporting cell types for the prevascularization of tissue constructs.

Precision repair of zone-specific meniscal injuries using a tunable extracellular matrix-based hydrogel system

Meniscus injuries present significant therapeutic challenges due to their limited self-healing capacity and the diverse biological and mechanical properties across the tissue. Conventional repair strategies do not replicate the complex zonal characteristics within the meniscus, resulting in suboptimal outcomes. In this study, we introduce an innovative fetal/adult and stiffness-tunable meniscus decellularized extracellular matrix (DEM)-based hydrogel system designed for precision repair of heterogeneous, zonal-dependent meniscus injuries. By synthesizing fetal and adult DEM hydrogels, we identified distinct cellular responses, including that hydrogels with adult meniscus-derived DEM promote more fibrochondrogenic phenotypes. The incorporation of methacrylated hyaluronic acid (MeHA) further refined the mechanical properties and injectability of the DEM-based hydrogels. The combination of fetal and adult DEM with MeHA allowed for precise tuning of stiffness, influencing cell differentiation and closely mimicking native tissue environments. In vivo tests confirmed the biocompatibility of hydrogels and their integration with native meniscus tissues. Furthermore, advanced 3D bioprinting techniques enabled the fabrication of hybrid hydrogels with biomaterial and mechanical gradients, effectively emulating the zonal properties of meniscus tissue and enhancing cell integration. This study represents a significant advance in meniscus tissue engineering, providing a promising platform for customized regenerative therapies across a range of heterogeneous fibrous connective tissues.

Regulation of cell migration by extracellular matrix mechanics at a glance

Cell migration occurs throughout development, tissue homeostasis and regeneration, as well as in diseases such as cancer. Cells migrate along two-dimensional (2D) surfaces or interfaces, within microtracks, or in confining three-dimensional (3D) extracellular matrices. Although the basic mechanisms of 2D migration are known, recent studies have elucidated unexpected migration behaviors associated with more complex substrates and have provided insights into their underlying molecular mechanisms. Studies using engineered biomaterials for 3D culture and microfabricated channels to replicate cell confinement observed in vivo have revealed distinct modes of migration. Across these contexts, the mechanical features of the surrounding microenvironment have emerged as major regulators of migration. In this Cell Science at a Glance article and the accompanying poster, we describe physiological contexts wherein 2D and 3D cell migration are essential, report how mechanical properties of the microenvironment regulate individual and collective cell migration, and review the mechanisms mediating these diverse modes of cell migration.

Guiding Oligodendrocyte Progenitor Cell Maturation Using Electrospun Fiber Cues in a 3D Hyaluronic Acid Hydrogel Culture System

The current lack of therapeutic approaches to demyelinating disorders and injuries stems from a lack of knowledge surrounding the underlying mechanisms of myelination. This knowledge gap motivates the development of effective models to study the role of environmental cues in oligodendrocyte progenitor cell (OPC) maturation. Such models should focus on determining, which factors influence OPCs to proliferate and differentiate into mature myelinating oligodendrocytes (OLs). Here, we introduce a hyaluronic acid (HA) hydrogel system composed of cross-linked HA containing encapsulated HA fibers with swollen diameters similar to mature axons (2.7 ± 0.2 μm). We tuned hydrogel storage moduli to simulate native brain tissue (200-2000 Pa) and studied the effects of fiber presence on OPC proliferation, metabolic activity, protein deposition, and morphological changes in gels of intermediate storage modulus (800 ± 0.3 Pa). OPCs in fiber-containing gels at culture days 4 and 7 exhibited a significantly greater number of process extensions, a morphological change associated with differentiation. By contrast, OPCs in fiber-free control gels maintained more proliferative phenotypes with 2.2-fold higher proliferation at culture day 7 and 1.8-fold higher metabolic activity at culture days 4 and 7. Fibers were also found to influence extracellular matrix (ECM) deposition and distribution, with more, and more distributed, nascent ECM deposition occurring in the fiber-containing gels. Overall, these data indicate that inclusion of appropriately sized HA fibers provides topographical cues, which guide OPCs toward differentiation. This HA hydrogel/fiber system is a promising in vitro scheme, providing valuable insight into the underlying mechanisms of differentiation and myelination.

Interpenetrating networks of fibrillar and amorphous collagen promote cell spreading and hydrogel stability

Hydrogels composed of collagen, the most abundant protein in the human body, are widely used as scaffolds for tissue engineering due to their ability to support cellular activity. However, collagen hydrogels with encapsulated cells often experience bulk contraction due to cell-generated forces, and conventional strategies to mitigate this undesired deformation often compromise either the fibrillar microstructure or cytocompatibility of the collagen. To support the spreading of encapsulated cells while preserving the structural integrity of the gels, we present an interpenetrating network (IPN) of two distinct collagen networks with different crosslinking mechanisms and microstructures. First, a physically self-assembled collagen network preserves the fibrillar microstructure and enables the spreading of encapsulated human corneal mesenchymal stromal cells. Second, an amorphous collagen network covalently crosslinked with bioorthogonal chemistry fills the voids between fibrils and stabilizes the gel against cell-induced contraction. This collagen IPN balances the biofunctionality of natural collagen with the stability of covalently crosslinked, engineered polymers. Taken together, these data represent a new avenue for maintaining both the fiber-induced spreading of cells and the structural integrity of collagen hydrogels by leveraging an IPN of fibrillar and amorphous collagen networks. STATEMENT OF SIGNIFICANCE: Collagen hydrogels are widely used as scaffolds for tissue engineering due to their support of cellular activity. However, collagen hydrogels often undergo undesired changes in size and shape due to cell-generated forces, and conventional strategies to mitigate this deformation typically compromise either the fibrillar microstructure or cytocompatibility of the collagen. In this study, we introduce an innovative interpenetrating network (IPN) that combines physically self-assembled, fibrillar collagen-ideal for promoting cell adhesion and spreading-with covalently crosslinked, amorphous collagen-ideal for enhancing bulk hydrogel stability. Our IPN design maintains the native fibrillar structure of collagen while significantly improving resistance against cell-induced contraction, providing a promising solution to enhance the performance and reliability of collagen hydrogels for tissue engineering applications.

Collagen-Based Scaffolds for Volumetric Muscle Loss Regeneration

Volumetric muscle loss (VML) is a serious problem in healthcare that requires innovative solutions. Collagen and its derivatives are promising biomaterials for muscle tissue replacement due to their high biocompatibility, biodegradability, and lack of toxicity. This review comprehensively discusses collagen from various sources, its structural characteristics, cross-linking methods to obtain hydrogels, and approaches to incorporating various therapeutic molecules to create a biocomposite system with controlled release. Collagen-based scaffolds are promising constructs in tissue engineering and regenerative medicine. They can both perform their function independently and act as a depot for various biologically active substances (drugs, growth factors, genetic material, etc.). Collagen-based scaffolds for muscle volume restoration are three-dimensional constructs that support cell adhesion and proliferation and provide controlled release of therapeutic molecules. Various mechanical and biological properties of scaffolds can be achieved by cross-linking agents and bioactive molecules incorporated into the structure. This review highlights recent studies on collagen-based hydrogels for restoration of volumetric muscle loss.

Engineering and Monitoring the Sustained Release of Extracellular Vesicles from Hydrogels for In Vivo Therapeutic Applications

Extracellular vesicles (EVs) are gaining interest in regenerative medicine and biomaterials have been shown to extend EV bioavailability following delivery. Here, we report the labeling of both hydrogels and EVs to better understand hydrogel design for sustained EV release into tissues. Shear-thinning hydrogels were engineered using guest-host (i.e., adamantane-cyclodextrin) modifications to hyaluronic acid (GH), as well as GH hydrogels with the addition of gelatin crosslinked via transglutaminase (GH+Gel) to temporally control hydrogel properties. When labeled with a near-IR dye and injected into rat myocardial tissue, the GH+Gel hydrogel was retained (>14 days) longer than the GH hydrogel alone (~7 days), likely due to the added gelatin network. To overcome challenges associated with common EV labeling methods, we utilized a highly versatile metabolic labeling methodology via the incorporation of Ac4ManNAz during EV synthesis to introduce azide groups that could then be reacted with DBCO-dyes. When injected in saline, EVs were cleared within 24 hours in hearts; however, hydrogels enhanced EV retention, with levels based on hydrogel degradation behavior, namely >14 days for GH+Gel hydrogel and ~7 days for GH hydrogel alone. These findings support the use of hydrogels in EV therapies to help retain their presence at desired tissue sites.

Spheroid-Hydrogel-Integrated Biomimetic System: A New Frontier in Advanced Three-Dimensional Cell Culture Technology

BACKGROUND

Despite significant advances in three-dimensional (3D) cell culture technologies, creating accurate in vitro models that faithfully recapitulate complex in vivo environments remains a major challenge in biomedical research. Traditional culture methods often fail to simultaneously facilitate critical cell-cell and cell-extracellular matrix (ECM) interactions while providing control over mechanical and biochemical properties.

SUMMARY

This review introduces the spheroid-hydrogel-integrated biomimetic system (SHIBS), a groundbreaking approach that synergistically combines spheroid culture with tailored hydrogel technologies. SHIBS uniquely bridges the gap between traditional culture methods and physiological conditions by offering unprecedented control over both cellular interactions and environmental properties. We explore how SHIBS is revolutionizing fields ranging from drug discovery and disease modeling to regenerative medicine and basic biological research. The review discusses current challenges in SHIBS technology, including reproducibility, scalability, and high-resolution imaging, and outlines ongoing research addressing these issues. Furthermore, we envision the future evolution of SHIBS into more sophisticated organoid-hydrogel-integrated biomimetic systems and its integration with cutting-edge technologies such as microfluidics, 3D bioprinting, and artificial intelligence.

KEY MESSAGES

SHIBS represents a paradigm shift in 3D cell culture technology, offering a unique solution to recreate complex in vivo environments. Its potential to accelerate the development of personalized therapies across various biomedical fields is significant. While challenges persist, the ongoing advancements in SHIBS technology promise to overcome current limitations, paving the way for more accurate and reliable in vitro models. The future integration of SHIBS with emerging technologies may revolutionize biomimetic modeling, potentially reducing the need for animal testing and expediting drug discovery processes. This comprehensive review provides researchers and clinicians with a holistic understanding of SHIBS technology, its current capabilities, and its future prospects in advancing biomedical research and therapeutic innovations.

BACKGROUND

Despite significant advances in three-dimensional (3D) cell culture technologies, creating accurate in vitro models that faithfully recapitulate complex in vivo environments remains a major challenge in biomedical research. Traditional culture methods often fail to simultaneously facilitate critical cell-cell and cell-extracellular matrix (ECM) interactions while providing control over mechanical and biochemical properties.

SUMMARY

This review introduces the spheroid-hydrogel-integrated biomimetic system (SHIBS), a groundbreaking approach that synergistically combines spheroid culture with tailored hydrogel technologies. SHIBS uniquely bridges the gap between traditional culture methods and physiological conditions by offering unprecedented control over both cellular interactions and environmental properties. We explore how SHIBS is revolutionizing fields ranging from drug discovery and disease modeling to regenerative medicine and basic biological research. The review discusses current challenges in SHIBS technology, including reproducibility, scalability, and high-resolution imaging, and outlines ongoing research addressing these issues. Furthermore, we envision the future evolution of SHIBS into more sophisticated organoid-hydrogel-integrated biomimetic systems and its integration with cutting-edge technologies such as microfluidics, 3D bioprinting, and artificial intelligence.

KEY MESSAGES

SHIBS represents a paradigm shift in 3D cell culture technology, offering a unique solution to recreate complex in vivo environments. Its potential to accelerate the development of personalized therapies across various biomedical fields is significant. While challenges persist, the ongoing advancements in SHIBS technology promise to overcome current limitations, paving the way for more accurate and reliable in vitro models. The future integration of SHIBS with emerging technologies may revolutionize biomimetic modeling, potentially reducing the need for animal testing and expediting drug discovery processes. This comprehensive review provides researchers and clinicians with a holistic understanding of SHIBS technology, its current capabilities, and its future prospects in advancing biomedical research and therapeutic innovations.

Microinterfaces in biopolymer-based bicontinuous hydrogels guide rapid 3D cell migration

Cell migration is critical for tissue development and regeneration but requires extracellular environments that are conducive to motion. Cells may actively generate migratory routes in vivo by degrading or remodeling their environments or instead utilize existing extracellular matrix microstructures or microtracks as innate pathways for migration. While hydrogels in general are valuable tools for probing the extracellular regulators of 3-dimensional migration, few recapitulate these natural migration paths. Here, we develop a biopolymer-based bicontinuous hydrogel system that comprises a covalent hydrogel of enzymatically crosslinked gelatin and a physical hydrogel of guest and host moieties bonded to hyaluronic acid. Bicontinuous hydrogels form through controlled solution immiscibility, and their continuous subdomains and high micro-interfacial surface area enable rapid 3D migration, particularly when compared to homogeneous hydrogels. Migratory behavior is mesenchymal in nature and regulated by biochemical and biophysical signals from the hydrogel, which is shown across various cell types and physiologically relevant contexts (e.g., cell spheroids, ex vivo tissues, in vivo tissues). Our findings introduce a design that leverages important local interfaces to guide rapid cell migration.