Jason A. Burdick

Most tissues of the human body present hierarchical fibrillar extracellular matrices that have a strong influence over their physicochemical properties and biological behavior. Of great interest is the introduction of this fibrillar structure to hydrogels, particularly due to the water‐rich composition, cytocompatibility and tunable properties of this class of biomaterials. Here, the main bottom‐up fabrication strategies for the design and production of hierarchical biomimetic fibrillar hydrogels and their most representative applications in the fields of tissue engineering and regenerative medicine are reviewed. For example, the controlled assembly/arrangement of peptides, polymeric micelles, cellulose nanoparticles (NPs), and magnetically responsive nanostructures, among others, into fibrillar hydrogels is discussed, as well as their potential use as fibrillar‐like hydrogels (e.g., those from cellulose NPs) with key …

Volumetric additive manufacturing (VAM) is an emerging layerless method for the rapid processing of reactive resins into 3D structures, where printing is much faster (seconds) than other lithography and direct ink writing methods (minutes to hours). As a vial of resin rotates in the VAM process, patterned light exposure defines a 3D object and then resin that has not undergone gelation can be washed away. Despite the promise of VAM, there are challenges with the printing of soft hydrogel materials from non‐viscous precursors, including into multi‐material constructs. To address this, we use sacrificial gelatin to modulate resin viscosity to support the cytocompatible VAM printing of macromers based on poly(ethylene glycol), hyaluronic acid (HA), and polyacrylamide. After printing, gelatin is removed by washing at an elevated temperature. To print multi‐material constructs, the gelatin‐containing resin is used as a …

Janus kinase (JAK) inhibitors are approved for many dermatologic disorders, but their use is limited by systemic toxicities including serious cardiovascular events and malignancy. To overcome these limitations, injectable hydrogels are engineered for the local and sustained delivery of baricitinib, a representative JAK inhibitor. Hydrogels are formed via disulfide crosslinking of thiolated hyaluronic acid macromers. Dynamic thioimidate bonds are introduced between the thiolated hyaluronic acid and nitrile‐containing baricitinib for drug tethering, which is confirmed with 1H and 13C nuclear magnetic resonance (NMR). Release of baricitinib is tunable over six weeks in vitro and active in inhibiting JAK signaling in a cell line containing a luciferase reporter reflecting interferon signaling. For in vivo activity, baricitinib hydrogels or controls are injected intradermally into an imiquimod‐induced mouse model of psoriasis …

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 …

Many cell types require direct cell–cell interactions for differentiation and function; yet, this can be challenging to incorporate into 3‐dimensional (3D) structures for the engineering of tissues. Here, a new approach is introduced that combines aggregates of cells (spheroids) with similarly‐sized hydrogel particles (microgels) to form granular composites that are injectable, undergo interparticle crosslinking via light for initial stabilization, permit cell–cell contacts for cell signaling, and allow spheroid fusion and growth. One area where this is important is in cartilage tissue engineering, as cell–cell contacts are crucial to chondrogenesis and are missing in many tissue engineering approaches. To address this, granular composites are developed from adult porcine mesenchymal stromal cell (MSC) spheroids and hyaluronic acid microgels and simulations and experimental analyses are used to establish the importance of …

INTRODUCTION: Changes in the tumor microenvironment arbitrated by a stiffened ECM are associated with tumor aggression and enable increased propensity towards metastasis. For instance, in vitro (2D) studies have implicated ECM properties in EAC progression. However, these studies are limited by the lack of 3D intercellular interactions, underscoring the need for physiologically relevant 3D culture models, such as patient-derived organoids (PDOs), that better recapitulate human cancer and its microenvironment to elucidate underlying mechanisms. Engineered hydrogels are an evolving and important component of 3D organoid culture systems, especially to introduce tunable physicochemical matrix signals that have been investigated in tumor progression and metastasis. Furthermore, PDOs have become an attractive pre-clinical in vitro model to study cancer biology and evaluate response to therapeutics …

For tissues to develop and maintain their function, cells must orchestrate their behaviour by generating and transmitting contractile forces. These forces are transmitted to their surrounding matrix or neighbouring cells via adhesion complexes. How tissues reach a force-balance is often assumed to involve intercellular stresses counterbalancing those in the substrate. However, experimental findings indicate that dampening focal adhesions can increase intercellular stresses. As the ECM is rarely uniform in composition or mechanical properties, it is important to understand how focal adhesions alter stress transmission and the force-balance of a tissue. To address this, we confined monolayers on disk or ring adhesive patterns to alter how they were bound to the substrate. Traction force microscopy and laser ablations of cell-cell junctions were used to examine stresses across epithelial monolayers whilst modulating substrate stiffness. We show that monolayers reach different force-balance states depending on focal adhesion distribution, with intercellular stresses not correlated with overall traction stresses on rings. Using an active matter model to examine the force-balance dynamics, we reveal that tissues reach a force-balance by generating non-uniform patterns of contractility linked to adhesion patterning. This work highlights the importance of considering the position and mechanical properties of cell-ECM and cell-cell attachments to capture the mechanical landscape of living tissues.

The majority of 3D-printed engineered living materials are printed on flat surfaces limiting the complexity and size of the materials. Additionally, the interplay between microbial cell density and hydrogel matrix stiffness has been shown to impact the final mechanical properties of 3D-printed microbial hydrogel composites. However, since these inks of materials are typically extremely soft, they require crosslinking as they are 3D printed. Therefore, the final mechanical properties of these materials are fixed in the 3D printing process. We will overcome these challenges, by utilizing a 3D support media that fixes the ink into place allowing for the cells to grow before crosslinking. Here, we 3D print photocrosslinkable methacrylated hyaluronic acid and Escherichia coli into a 3D support media swollen with liquid growth media. We show how crosslinking after incubating the 3D printed impacts the final cell density and …