Ovijit Chaudhuri

Mechanical confinement of cells in 3D hydrogel scaffolds mediates cell fate and activity across a wide range of biological processes. Many cells secrete a nascent matrix within the hydrogel niche, which provides important biological signals to the cells but also obstructs direct cell-hydrogel interactions, making it unclear how the cells sense hydrogel confinement and carry out mechanotransduction. Here, we show that chondrocytes sense the solid stress arising from the accumulation of the nascent matrix in the hydrogel niche, which is mediated by hydrogel viscoelasticity and plasticity. We show that solid stresses elicit a wide range of pathophysiological responses, most notably an inflammatory response associated with cartilage osteoarthritis and injury, alongside a striking progenitor-like migratory response where the chondrocytes leverage mitosis to breach their nascent matrix and migrate to escape confinement. Our findings establish the role of the nascent matrix as an important transducer of mechanical confinement and illustrate how emergent solid stresses can drive chondrocyte pathology.

Lytic bacteriophages, viruses that lyse (kill) bacteria, hold great promise for treating infections, including wound infections caused by antimicrobial-resistant Pseudomonas aeruginosa. However, dosing and delivery strategies for phage therapy remain underdeveloped. In a mouse wound infection model specifically designed to evaluate the treatment of established infections—a critical gap in existing preclinical models—we investigated the impact of administration route, dose, and frequency on phage therapy efficacy. In this model, topical, but not systemic, delivery reduced wound bacterial burden. In vitro and in vivo data revealed rapid emergence of phage resistance and suggested potential benefit of using high and repeated doses. Building on these insights, we developed HydroPhage, a phage-containing hyaluronan-based hydrogel formed with dynamic covalent crosslinks that delivers high-titer phages over one week. Here, we show that sustained hydrogel-based delivery is a practical and effective approach for topical phage application.

Hydrogels that recapitulate the dynamic mechanical cues of native extracellular matrix are powerful tools that can be leveraged for tissue engineering. Despite growing recognition that cues such as stress relaxation and plasticity modulate cell–matrix interactions, the influence of these properties on mesenchymal stromal cell (MSC) chondrogenesis has yet to be elucidated across a broad range of relaxation timescales and in the absence of confounding biochemical cues. Here, we report the adaptable sliding hydrogel (ASG) with tunable stress relaxation and plasticity as a novel MSC cell niche. By incorporating reversible hydrazone crosslinks into polyethylene glycol (PEG)–based sliding hydrogels (SG), ASG achieves a wide range of tunable stress relaxation and plasticity that are distinct from other dynamic hydrogels used for MSC chondrogenesis. Notably, increasing stress relaxation and plasticity in ASG promotes rapid and robust cartilage formation by human MSCs and supports long-term cell viability. Mechanistically, ASG facilitates local matrix remodeling and enables MSCs to form “pericellular pockets” in 3D that correlate with enhanced nascent extracellular matrix deposition and reorganization, integrin signaling, and nuclear dynamics. Overall, the ASG platform provides a tunable, synthetic microenvironment that helps probe the relationship between dynamic mechanical cues and stem cell fate and informs next-generation material design within the field of tissue engineering.

Cell division within mechanically confining extracellular matrices (ECMs) is a key regulator of tissue morphogenesis and cancer progression. Although the intracellular force generation mechanisms that drive volumetric growth and mitotic elongation are well characterized, how ECMs resist these forces remains poorly understood. Unlike linearly elastic materials, fibrillar ECMs exhibit nonlinear and viscoelastic behaviors that fundamentally alter how they oppose cell generated stresses. Using a fiber level computational model, we dissected the origins of ECM mediated mechanical confinement during mitosis. We identified three distinct modes of resistance: compressive resistance at the cell poles, shear resistance from a pericellular shell, and tensile resistance at the cell equator. The relative contributions of these modes depended on fiber architecture and connectivity; however, shear resistance from the pericellular shell, which was pre-tensed by volumetric growth during G1, consistently dominated as the primary mechanical barrier to mitotic elongation. These findings suggest that the pericellular shell functions as a natural mechanical checkpoint on cell division within collagen rich microenvironments. Notably, a finite element continuum model, despite being the most widely used framework for tissue mechanics, failed to reproduce these behaviors, underscoring the necessity of fiber resolution approaches. We propose that overcoming this mechanical checkpoint is a critical step in cancer progression, enabling cells to divide within the dense stromal matrices characteristic of metastatic tumors.

Complex and robust tissue self-organization requires defined initial conditions and dynamic boundaries—neighbouring tissues and extracellular matrix that actively evolve to guide morphogenesis. A major challenge in tissue engineering is identifying material properties that are compatible with controlling initial culture conditions while mimicking dynamic tissue boundaries. Here we describe a highly tunable granular biomaterial, MAGIC matrix, that supports both long-term bioprinting and gold-standard tissue self-organization. We identify that significant stress relaxation at the long timescales and large deformation magnitudes relevant to self-organization is required for optimal morphogenesis. We apply optimized MAGIC matrices toward precise extrusion bioprinting of saturated cell suspensions directly into three-dimensional culture. Carefully controlling initial conditions for tissue growth yields dramatic increases in organoid reproducibility and complexity across multiple tissue types, enabling high-throughput generation of organoid arrays and perfusable three-dimensional microphysiological systems. Our results identify key biomaterial parameters for optimal organoid morphogenesis and lay the foundation for fabricating more complex and reproducible self-organized tissues.

Cell migration is pivotal in cancer metastasis, where cells navigate the extracellular matrix (ECM) and invade distant tissues. While the ECM is viscoelastic, exhibiting time-dependent stress relaxation, its influence on cell migration remains poorly understood. Here, we employ an integrated experimental and modeling approach to investigate filopodial cancer cell migration on viscoelastic substrates and uncover a striking transition from sub-diffusive to super-diffusive behavior driven by the substrate’s viscous relaxation timescale. Conventional motor-clutch based migration models fail to capture these anomalous migration modes, as they overlook the complex adhesion dynamics shaped by broad distribution of adhesion lifetimes. To address this, we develop a glassy motor-clutch model that incorporates the rugged energy landscape of adhesion clusters, where multiple metastable states yield long-tailed adhesion timescales. Our model reveals that migration dynamics are governed by the interplay between cellular and substrate timescales: slow-relaxing substrates prolong trapping, leading to sub-diffusion, while fast-relaxing substrates promote larger steps limiting trapping, leading to super-diffusion. Additionally, we uncover the role of actin polymerization and contractility in modulating adhesion dynamics and driving anomalous migration. These findings establish a mechanistic framework linking substrate viscoelasticity to cell motility, with implications for metastasis and cancer progression.

T cells adeptly migrate through soft tissues to target aberrant cells and regulate immunity. However, how they establish migration paths in confining nanoporous extracellular matrices (ECMs), and why they often fail to do so in dense ECMs that occur during fibrosis and around tumors, remain unclear. Here, we studied T cell migration in confining collagen-rich hydrogels spanning a range of stiffness, viscoelasticity, mechanical plasticity, and shear strength. Strikingly, only shear strength—the stress required for material failure—correlated strongly with migration, challenging the long-held focus on stiffness and pore size in cell motility. During migration, T cells extend actin-rich, finger-like protrusions into the ECM, which then undergo divergent breaststroke-like motion. Thus, T cells tear apart confining matrices using breaststroke-like motion to generate migration paths.

Circulating monocytes are recruited to the tumor microenvironment, where they can differentiate into macrophages that mediate tumor progression. To reach the tumor microenvironment, monocytes must first extravasate and migrate through the type-1 collagen rich stromal matrix. The viscoelastic stromal matrix around tumors not only stiffens relative to normal stromal matrix, but often exhibits enhanced viscous characteristics, as indicated by a higher loss tangent or faster stress relaxation rate. Here, we studied how changes in matrix stiffness and viscoelasticity impact the three-dimensional (3D) migration of monocytes through stromal-like matrices. Interpenetrating networks of type-1 collagen and alginate, which enable independent tunability of stiffness and stress relaxation over physiologically relevant ranges, were used as confining matrices for 3D culture of monocytes. Increased stiffness and faster stress relaxation independently enhanced the 3D migration of monocytes. Migrating monocytes have an ellipsoidal or rounded wedge-like morphology, reminiscent of amoeboid migration, with accumulation of actin at the trailing edge. Matrix adhesions were dispensable for monocyte migration in 3D, but migration did require actin polymerization and myosin contractility. Mechanistic studies indicate that actin polymerization at the leading edge generates protrusive forces that open a path for the monocytes to migrate through in the confining viscoelastic matrices. Taken together, our findings implicate matrix stiffness and stress relaxation as key mediators of monocyte migration and reveal how monocytes use pushing forces at the leading edge mediated by actin polymerization to generate migration paths in confining viscoelastic matrices.