Viscoelastic Matrix Research Articles

Plasticity of 3D Hydrogels Predicts Cell Biological Behavior.

Under 3D culture conditions, cells tend to spread, migrate, and proliferate better in more viscoelastic and plastic hydrogels. Here, we present evidence that the improved cell behavior is facilitated by the lower steric hindrance of a more viscoelastic and plastic matrix with weaker intermolecular bonds. To determine intermolecular bond stability, we slowly insert semispherical tipped needles (100-700 μm diameter) into alginate dialdehyde-gelatin hydrogels and measure stiffness, yield strength, plasticity, and the force at which the surface ruptures (puncture force). To tune these material properties without affecting matrix stiffness, we precross-link the hydrogels with CaCl2 droplets prior to mixing in NIH/3T3 fibroblasts and final cross-linking with CaCl2. Precross-linking introduces microscopic weak spots in the hydrogel, increases plasticity, and decreases puncture force and yield strength. Fibroblasts spread and migrate better in precross-linked hydrogels, demonstrating that intermolecular bond stability is a critical determinant of cell behavior under 3D culture conditions.

Interpenetrating Polymer Network Hydrogels with Tunable Viscoelasticity and Proteolytic Cleavability to Direct Stem Cells In Vitro.

The dynamic nature of cellular microenvironments, regulated by the viscoelasticity and enzymatic cleavage of the extracellular matrix, remains challenging to emulate in engineered synthetic biomaterials. To address this, a novel platform of cell-instructive hydrogels is introduced, composed of two concurrently forming interpenetrating polymer networks (IPNs). These IPNs consist of the same basic building blocks - four-armed poly(ethylene glycol) and the sulfated glycosaminoglycan (sGAG) heparin - are cross-linked through either chemical or physical interactions, allowing for precise and selective tuning of the hydrogel's stiffness, viscoelasticity, and proteolytic cleavability. The studies of the individual and combined effects of these parameters on stem cell behavior revealed that human mesenchymal stem cells exhibited increased spreading and Yes-associated protein transcriptional activity in more viscoelastic and cleavable sGAG-IPN hydrogels. Furthermore, human induced pluripotent stem cell (iPSC) cysts displayed enhanced lumen formation, growth, and pluripotency maintenance when cultured in sGAG-IPN hydrogels with higher viscoelasticity. Inhibition studies emphasized the pivotal roles of actin dynamics and matrix metalloproteinase activity in iPSC cyst morphology, which varied with the viscoelastic properties of the hydrogels. Thus, the introduced sGAG-IPN hydrogel platform offers a powerful methodology for exogenous stem cell fate control.

A novel in-situ fibrillation enhancement strategy to achieve super-elastic green foam with enhanced biodegradation

Driven by concerns about the escalating environmental pollution caused by the widespread use of plastic products, there is considerable interest in developing high-performance biodegradable materials. Poly(butylene adipate-co-terephthalate) (PBAT) foams are recognized as a highly sought-after candidate for alleviating plastic pollution, distinguished by their admirable biodegradability and flexibility. However, the extensive applications of PBAT foam are considerably constrained by inadequate melt strength and inherent shrinkage. Herein, a pioneering and scalable strategy, combining the shear-induced in-situ fibrillation process with microcellular foaming, was devised to achieve lightweight and super-resilient PBAT/poly(tetrafluoroethylene) (PTFE) foams. Thanks to the heterogeneous nucleation effect and complex tangled physical networks induced by in-situ nano-fibrillated PTFE, the crystallization and viscoelasticity of PBAT matrix experienced a dramatic enhancement, further bolstering its foaming capabilities and suppressing the shrinkage process. More importantly, the synergy of reduced foam density and reinforcement effect of PTFE nanofibrils played a crucial role in improving the remarkable compression of PBAT/PTFE foams. These foams showed a maximum increase of 40.2 % in strength and 16.3 % in resilience compared to pure PBAT foams. Moreover, the thermal insulation and soil degradation capability of PBAT/PTFE foams were substantially enhanced, achieving 10.3 % biodegradation after just 2 months. This innovative strategy offers a promising avenue for developing high-performance eco-friendly biocomposites.

Tuning porosity of macroporous hydrogels enables rapid rates of stress relaxation and promotes cell expansion and migration

Extracellular matrix (ECM) viscoelasticity broadly regulates cell behavior. While hydrogels can approximate the viscoelasticity of native ECM, it remains challenging to recapitulate the rapid stress relaxation observed in many tissues without limiting the mechanical stability of the hydrogel. Here, we develop macroporous alginate hydrogels that have an order of magnitude increase in the rate of stress relaxation as compared to bulk hydrogels. The increased rate of stress relaxation occurs across a wide range of polymer molecular weights (MWs), which enables the use of high MW polymer for improved mechanical stability of the hydrogel. The rate of stress relaxation in macroporous hydrogels depends on the volume fraction of pores and the concentration of bovine serum albumin, which is added to the hydrogels to stabilize the macroporous structure during gelation. Relative to cell spheroids encapsulated in bulk hydrogels, spheroids in macroporous hydrogels have a significantly larger area and smaller circularity because of increased cell migration. A computational model provides a framework for the relationship between the macroporous architecture and morphogenesis of encapsulated spheroids that is consistent with experimental observations. Taken together, these findings elucidate the relationship between macroporous hydrogel architecture and stress relaxation and help to inform the design of macroporous hydrogels for materials-based cell therapies.

Viscoelastic Hydrogel Modulates Phenotype of Macrophage-Derived Multinucleated Cells and Macrophage Differentiation in Foreign Body Reactions.

Biomaterial-induced macrophage-derived multinucleated cells (MNCs) are often observed at or near material implantation sites, yet their subtypes and roles in tissue repair and wound healing remain unclear. This study compares material-induced MNCs to cytokine-induced MNCs using both in vitro and in vivo models. 3D-embedded Raw264.7 cells and rat bone marrow-derived monocytes (BMDMs), with or without cytokines such as IL-4 and RANKL, were characterized for their MNC morphologies and subtypes via in situ immunocytochemistry and flow cytometry. Macrophage polarization and osteoclastic differentiation were assessed through NO production, arginase activity, and tartrate-resistant acid phosphatase levels. 3D matrix-induced MNCs expressed the same phenotypic heterogeneity as the IL-4 and RANK-treated ones. 3D matrix-induced MNCs displayed the same phenotypic heterogeneity as those treated with IL-4 and RANKL. A high viscoelastic matrix (1006.48 ± 92.29 Pa) induced larger populations of proinflammatory and osteoclast-like MNCs, whereas a low viscoelastic matrix (38.61 ± 7.56 Pa) supported active differentiation and gene expression across pro-, anti-inflammatory, and osteoclast-like macrophages. Matrix viscoelasticity also influenced the effects of IL-4 and RANKL on macrophage-derived MNC polarization. In an in vivo subcutaneous implantation model, medium to high viscoelastic matrices exhibited higher populations of CD86+ and RANK+ MNCs, while low viscoelastic matrices showed higher populations of CD206+ MNCs. These findings suggest that matrix viscoelasticity modulates macrophage differentiation and MNC phenotype, with low viscoelastic matrices potentially favoring anti-inflammatory MNCs and macrophage differentiation suitable for subcutaneous implantation.

The transient dynamic wave process in unidirectional composites

The propagation of nonstationary waves in unidirectional composite material is simulated by finite-element analysis. The composite material is explicitly formulated, i.e., discrete, stiff, elastic inclusions uniformly distributed in a viscoelastic matrix are modeled. An original procedure rooted in the linear Boltzmann–Volterra equations accounts for the viscoelastic effects in the matrix behavior. The chosen approach involves finite-element simulations of the transient wave process in two indicative configurations to study the effects attributed to wave scattering by the inclusions. The transient wave propagation in the unidirectional composite material and a viscoelastic specimen without inclusions are compared. Peculiarities in the numerical results due to the finite-element algorithm employed are decoupled from the output that reveals purely mechanical phenomena. For this purpose, the transient wave propagation in a one-dimensional elastic continuum, for which the exact analytical solution is well known, is effectively obtained by finite-element analysis. Furthermore, based on the unidirectional composite a homogenized model is defined by applying the mixture rule. An additional comparison between the composite containing discrete inclusions and the analogous homogenized material provides a basis to assess the output of models obtained by implementing a self-consistent scheme in a broader context.

Numerical Simulation for Durability of a Viscoelastic Polymer Material Subjected to Variable Loadings Fatigue Based on Entropy Damage Criterion.

This study aims to explore the impact of load history on the premature failure of the viscoelastic polymer matrix in carbon-fiber-reinforced plastics (CFRPs) using a method based on the concept of fracture fatigue entropy (FFE). A user-defined subroutine (UMAT) developed by the authors in previous studies was incorporated to apply the FFE damage criterion using ABAQUS software. Several variable-amplitude load modes, including frequent load amplitude changes and intermittent interruptions, were designed based on the conventional linear damage accumulation method (Palmgren-Miner rule), and the fatigue life under these loadings was obtained via numerical simulations. The results show that both frequent amplitude changes and even brief pauses in loading can accelerate damage accumulation, leading to premature failure of the polymer matrix. In these scenarios, the fatigue life ranged from 33.6% to 91.9% of the predictions made using the Palmgren-Miner rule, which shows significant variation and highlights cases in which the predicted fatigue life falls far short of expectations. This study offers a more practical and reliable approach for predicting fatigue life under complex loading conditions. Since the accuracy of the FFE criterion has been comprehensively validated in previous studies, this research focuses on its application to predict failure under variable loading conditions.

A novel mechanistic model for predicting shrinkage kinetics in plant-based foods by integrating solid matrix mobility and viscoelasticity

Deformation during drying is a major physical change influencing drying kinetics and final product quality. Therefore, accurate prediction of shrinkage kinetics is essential for determining the optimal drying conditions for these foods. Shrinkage kinetics is greatly influenced by their structural mobility (rubbery-glassy transition) and viscoelastic properties. The current deformation models lack a comprehensive integration of structural mobility and viscoelasticity concepts, resulting in limitation in attaining insights on physiochemical state variations and viscoelastic stresses developed during drying. In order to overcome this limitation, this study proposes a novel mechanistic shrinkage model that combines solid matrix mobility-based shrinkage velocity and viscoelasticity consideration, incorporating variable mechanical properties to simulate deformation arising from moisture loss and pressure gradient respectively. Comparison between predicted drying kinetics and shrinkage evolution with experimental observation yielded close agreement, achieving low mean absolute error values. As the drying process progressed, a distinct anisotropic shrinkage pattern emerged, which is attributed to varied structural mobility based on temperature and moisture distribution across the food sample. Notably, shrinkage driven by moisture loss significantly outweighed that induced by pressure, exerting a predominant influence on overall volume change. Furthermore, the model demonstrated heightened sensitivity to water transport parameters compared to mechanical factors, which indicates the significance of moisture dynamics in shaping the drying process. Combined consideration of physiochemical changes and viscoelastic concept in the developed deformation model extends new possibility towards optimizing the drying process as well as quality aspect evaluation.

Matrix Viscoelasticity Tunes the Mechanobiological Behavior of Chondrocytes.

In articular cartilage, the pericellular matrix acting as a specialized mechanical microenvironment modulates environmental signals to chondrocytes through mechanotransduction. Matrix viscoelastic alterations during cartilage development and osteoarthritis (OA) degeneration play an important role in regulating chondrocyte fate and cartilage matrix homeostasis. In recent years, scientists are gradually realizing the importance of matrix viscoelasticity in regulating chondrocyte function and phenotype. Notably, this is an emerging field, and this review summarizes the existing literatures to the best of our knowledge. This review provides an overview of the viscoelastic properties of hydrogels and the role of matrix viscoelasticity in directing chondrocyte behavior. In this review, we elaborated the mechanotransuction mechanisms by which cells sense and respond to the viscoelastic environment and also discussed the underlying signaling pathways. Moreover, emerging insights into the role of matrix viscoelasticity in regulating chondrocyte function and cartilage formation shed light into designing cell-instructive biomaterial. We also describe the potential use of viscoelastic biomaterials in cartilage tissue engineering and regenerative medicine. Future perspectives on mechanobiological comprehension of the viscoelastic behaviors involved in tissue homeostasis, cellular responses, and biomaterial design are highlighted. Finally, this review also highlights recent strategies utilizing viscoelastic hydrogels for designing cartilage-on-a-chip.

3D Bioprinting of Engineered Living Materials with Extracellular Electron Transfer Capability for Water Purification.

Attention is widely drawn to the extracellular electron transfer (EET) process of electroactive bacteria (EAB) for water purification, but its efficacy is often hindered in complex environmental matrices. In this study, the engineered living materials with EET capability (e-ELMs) were for the first time created with customized geometric configurations for pollutant removal using three-dimensional (3D) bioprinting platform. By combining EAB and tailored viscoelastic matrix, a biocompatible and tunable electroactive bioink for 3D bioprinting was initially developed with tuned rheological properties, enabling meticulous manipulation of microbial spatial arrangement and density. e-ELMs with different spatial microstructures were then designed and constructed by adjusting the filament diameter and orientation during the 3D printing process. Simulations of diffusion and fluid dynamics collectively showcase internal mass transfer rates and EET efficiency of e-ELMs with different spatial microstructures, contributing to the outstanding decontamination performances. Our research propels 3D bioprinting technology into the environmental realm, enabling the creation of intricately designed e-ELMs and providing promising routes to address the emerging water pollution concerns.

The importance of a full chemo-poro-mechanical coupling for the modeling of subcutaneous injections

Modeling of subcutaneous injections in soft adipose tissue – a common way to administer pharmaceutical medication – is a challenging multiphysics problem which has recently attracted the attention of the engineering community, as it could help optimize medical devices and treatments. The underlying continuum mechanics of this process is complex and involves finite strain poro-mechanics – where a viscous fluid, containing different charged species, is injected into a porous viscoelastic matrix and absorbed by blood and lymph vessels – as well as electrochemistry, that generates osmotic pressure due to electrical charges attached to the tissue. In this paper, we present a chemo-mechanical model of subcutaneous injections that accounts for the diffusion of electrically charged chemical species – contained in the interstitial fluid – into the tissue, blood and lymph vessels. This work provides the methodology to derive a general theory accounting for the electro-chemo-poro-mechanical couplings in a thermodynamically consistent framework, avoiding phenomenological biases or inconsistencies likely to arise in the derivation of nonlinear theories with many couplings. To motivate its use for the modeling of subcutaneous injections, it is complemented by a simplified, linearized boundary value problem that illustrates the importance of considering these couplings for the prediction of subcutaneous injections key performance indicators.

High-strength, impact-resistant PP/PTFE composite foam with enhanced surface appearance achieved through mold-opening microcellular injection molding

Poor surface appearance and decreased mechanical performance are critical factors limiting the broad application of Microcellular injection molding (MIM) in foamed polymer products. Herein, in-situ polytetrafluoroethylene (PTFE) nanofibrils reinforced polypropylene (PP) foams with high strength, impact resistance, and enhanced surface quality were prepared by mold opening microcellular injection molding (MOMIM). PTFE nanofibers with different diameters were introduced into the PP matrix via twin screw extrusion and significantly enhanced the crystallinity and viscoelasticity of the PP matrix with the enhancement being more pronounced for the finer PTFE fibers. High-density oriented cellular structures were formed in the MOMIM PP/PTFE foams owing to the heterogeneous nucleation of PTFE and the stretching effect of the mold opening process. The optimum MOMIM PP/PTFE foam fabricated possesses a high cell orientation angle close to 90° and a large cell aspect ratio of 5.3, which reached a 34.37 % increase in tensile strength and a 73.08 % increase in impact strength owing to the synergetic effects of the PTFE network and the highly oriented fine cell structure, which effectively dissipated the tensile stress and impact stress by cell wall twisting and folding deformation. Furthermore, the MOMIM PP/PTFE foam showed a significantly enhanced surface quality compared to the MIM foam due to the reduced dragging flow in MOMIM, which greatly hindered cell rupture on the foam surface. Therefore, this work provides insights into the MOMIM of polymer composites containing fibrous fillers and the enhancement of tensile properties, impact resistance, and surface quality of foam products.

Matrix Viscoelasticity Decouples Bubble Growth and Mobility in Coarsening Foams.

Pressure-driven coarsening triggers bubble rearrangements in liquid foams. Our experiments show that changing the continuous phase rheology can alter these internal bubble dynamics without influencing the coarsening kinetics. Through bubble tracking, we find that increasing the matrix yield stress permits bubble growth without stress relaxation via neighbor-switching events, promoting more spatially homogeneous rearrangements and decoupling bubble growth from mobility. This eventually leads to a structural change that directly impacts the foam mechanical and stability properties, essential for applications in various technological and industrial contexts.

Numerical Relaxation Analysis of Carbon Fiber Reinforced Polymers

AbstractCarbon fiber reinforced polymers are widely used to manufacture aerospace deployable structures. These structures are folded in launch configuration and then deployed in space for operational activities. Since the stowage of deployable structures in folded configuration occurs for long time, the understanding of the viscoelastic properties of the material is essential to predict the structural behavior during both the deployment phase and the operational life. In this work, numerical relaxation analysis is performed on the representative volume element (RVE) of a carbon fiber reinforced polymer using a homogenization approach at the microscale. This aims to predict the effects of matrix viscoelasticity on the structural performance of a deployable structure.

Finite element modeling of ultrasonic attenuation and dispersion in graded multilayer polymer composites

In this paper, finite element models of ultrasonic wave propagation in Cu–PMMA composites are established. The effects of second-phase particles, ultrasonic properties, and graded interfaces on the ultrasonic propagation behavior are investigated, and the contributions of particle-independent scattering, particle interactions, and matrix viscoelasticity to the ultrasonic attenuation are quantitatively evaluated. The results show that there is no obvious coupling between particle scattering and matrix viscoelasticity in Cu–PMMA composites, and the longitudinal wave speed has little effect with the variation of particle size, ultrasonic frequency, and graded interface, while the variation of the acoustic attenuation coefficient is related to the disorder of ultrasonic energy propagation direction. In the intra-layer uniform model, with the increase in Cu particle size and ultrasonic frequency, the scattering effect of Cu particles on the ultrasonic waves is enhanced, resulting in a significant increase in the acoustic attenuation coefficient. In the inter-layer graded multilayer model, there is a strong reverse energy propagation between the layers, causing the acoustic attenuation coefficient to increase significantly.

Schiff base crosslinked hyaluronic acid hydrogels with tunable and cell instructive time-dependent mechanical properties

The dynamic interplay between cells and their native extracellular matrix (ECM) influences cellular behavior, imposing a challenge in biomaterial design. Dynamic covalent hydrogels are viscoelastic and show self-healing ability, making them a potential scaffold for recapitulating native ECM properties. We aimed to implement kinetically and thermodynamically distinct crosslinkers to prepare self-healing dynamic hydrogels to explore the arising properties and their effects on cellular behavior. To do so, aldehyde-substituted hyaluronic acid (HA) was synthesized to generate imine, hydrazone, and oxime crosslinked dynamic covalent hydrogels. Differences in equilibrium constants of these bonds yielded distinct properties including stiffness, stress relaxation, and self-healing ability. The effects of degree of substitution (DS), polymer concentration, crosslinker to aldehyde ratio, and crosslinker functionality on hydrogel properties were evaluated. The self-healing ability of hydrogels was investigated on samples of the same and different crosslinkers and DS to obtain hydrogels with gradient properties. Subsequently, human dermal fibroblasts were cultured in 2D and 3D to assess the cellular response considering the dynamic properties of the hydrogels. Moreover, assessing cell spreading and morphology on hydrogels having similar modulus but different stress relaxation rates showed the effects of matrix viscoelasticity with higher cell spreading in slower relaxing hydrogels.

Viscoelastic hydrogels regulate adipose-derived mesenchymal stem cells for nucleus pulposus regeneration

Low back pain is a leading cause of disability worldwide, often attributed to intervertebral disc (IVD) degeneration with loss of the functional nucleus pulposus (NP). Regenerative strategies utilizing biomaterials and stem cells are promising for NP repair. Human NP tissue is highly viscoelastic, relaxing stress rapidly under deformation. However, the impact of tissue-specific viscoelasticity on the activities of adipose-derived stem cells (ASC) remains largely unexplored. Here, we investigated the role of matrix viscoelasticity in regulating ASC differentiation for IVD regeneration. Viscoelastic alginate hydrogels with stress relaxation time scales ranging from 100 s to 1000s were developed and used to culture human ASCs for 21 days. Our results demonstrated that the fast-relaxing hydrogel significantly enhanced ASCs long-term cell survival and NP-like extracellular matrix secretion of aggrecan and type-II collagen. Moreover, gene expression analysis revealed a substantial upregulation of the mechanosensitive ion channel marker TRPV4 and NP-specific markers such as SOX9, HIF-1α, KRT18, CDH2 and CD24 in ASCs cultured within the fast-relaxing hydrogel, compared to slower-relaxing hydrogels. These findings highlight the critical role of matrix viscoelasticity in regulating ASC behavior and suggest that viscoelasticity is a key parameter for novel biomaterials design to improve the efficacy of stem cell therapy for IVD regeneration. Statement of significanceSystematically characterized the influence of tissue-mimetic viscoelasticity on ASC. NP-mimetic hydrogels with tunable viscoelasticity and tissue-matched stiffness. Long-term survival and metabolic activity of ASCs are substantially improved in the fast-relaxing hydrogel. The fast-relaxing hydrogel allows higher rate of cell protrusions formation and matrix remodeling. ASC differentiation towards an NP-like cell phenotype is promoted in the fast-relaxing hydrogel, with more CD24 positive expression indicating NP committed cell fate. The expression of TRPV4, a molecular sensor of matrix viscoelasticity, is significantly enhanced in the fast-relaxing hydrogel, indicating ASC sensing matrix viscoelasticity during cell development. The NP-specific ECM secretion of ASC is considerably influenced by matrix viscoelasticity, where the deposition of aggrecan and type-II collagen are significantly enhanced in the fast-relaxing hydrogel.

3D identification and characterization of force chains in asphalt concrete based on continuum mesomechanics

Force chains occurring within particle assemblies have been extensively investigated based on granular mechanics; however, research on their identification and characterization in asphalt concrete, where coarse aggregates are dispersed in a viscoelastic asphalt mortar matrix, has been still very limited due to the lack of identifying criteria. A three-dimensional (3D) finite element (FE) simulation-based method was proposed to identify and characterize force chains of asphalt concrete from a continuum mesomechanics perspective. Stress concentration regions within the asphalt mortar matrix were treated as the main load-transfer regions (MLRs) between coarse aggregates. The MLRs were identified by a local detection method that inspects whether an asphalt mortar element is highly stressed in its local region. The load-transfer aggregates were then determined if their effective contact areas, i.e., the asphalt mortar elements sharing the nodes with aggregate elements, were found simultaneously containing an MLR, thereby enabling force chain identification. The compressive force chains in several 3D asphalt concrete mesostructures were determined and quantitatively characterized. The results indicate that the proposed method can effectively identify the force chains in asphalt concrete and their characteristics can be used to quantitatively evaluate the aggregate skeleton.

Viscoelastic stiffening of gelatin hydrogels for dynamic culture of pancreatic cancer spheroids

The tumor microenvironment (TME) in pancreatic adenocarcinoma (PDAC) is a complex milieu of cellular and non-cellular components. Pancreatic cancer cells (PCC) and cancer-associated fibroblasts (CAF) are two major cell types in PDAC TME, whereas the non-cellular components are enriched with extracellular matrices (ECM) that contribute to high stiffness and fast stress-relaxation. Previous studies have suggested that higher matrix rigidity promoted aggressive phenotypes of tumors, including PDAC. However, the effects of dynamic viscoelastic matrix properties on cancer cell fate remain largely unexplored. The focus of this work was to understand the effects of such dynamic matrix properties on PDAC cell behaviors, particularly in the context of PCC/CAF co-culture. To this end, we engineered gelatin-norbornene (GelNB) based hydrogels with a built-in mechanism for simultaneously increasing matrix elastic modulus and viscoelasticity. Two GelNB-based macromers, namely GelNB-hydroxyphenylacetic acid (GelNB-HPA) and GelNB-boronic acid (GelNB-BA), were modularly mixed and crosslinked with 4-arm poly(ethylene glycol)-thiol (PEG4SH) to form elastic hydrogels. Treating the hybrid hydrogels with tyrosinase not only increased the elastic moduli of the gels (due to HPA dimerization) but also concurrently produced 1,2-diols that formed reversible boronic acid-diol bonding with the BA groups on GelNB-BA. We employed patient-derived CAF and a PCC cell line COLO-357 to demonstrate the effect of increasing matrix stiffness and viscoelasticity on CAF and PCC cell fate. Our results indicated that in the stiffened environment, PCC underwent epithelial-mesenchymal transition. In the co-culture PCC and CAF spheroid, CAF enhanced PCC spreading and stimulated collagen 1 production. Through mRNA-sequencing, we further showed that stiffened matrices, regardless of the degree of stress-relaxation, heightened the malignant phenotype of PDAC cells. Statement of significanceThe pancreatic cancer microenvironment is a complex milieu composed of various cell types and extracellular matrices. It has been suggested that stiffer matrices could promote aggressive behavior in pancreatic cancer, but the effect of dynamic stiffening and matrix stress-relaxation on cancer cell fate remains largely undefined. This study aimed to explore the impact of dynamic changes in matrix viscoelasticity on pancreatic ductal adenocarcinoma (PDAC) cell behavior by developing a hydrogel system capable of simultaneously increasing stiffness and stress-relaxation on demand. This is achieved by crosslinking two gelatin-based macromers through orthogonal thiol-norbornene photochemistry and post-gelation stiffening with mushroom tyrosinase. The results revealed that higher matrix stiffness, regardless of the degree of stress relaxation, exacerbated the malignant characteristics of PDAC cells.

Matrix viscoelasticity promotes liver cancer progression in the pre-cirrhotic liver.

Type 2 diabetes mellitus is a major risk factor for hepatocellular carcinoma (HCC). Changes in extracellular matrix (ECM) mechanics contribute to cancer development1,2, and increased stiffness is known to promote HCC progression in cirrhotic conditions3,4. Type 2 diabetes mellitus is characterized by an accumulation of advanced glycation end-products (AGEs) in the ECM; however, how this affects HCC in non-cirrhotic conditions is unclear. Here we find that, in patients and animal models, AGEs promote changes in collagen architecture and enhance ECM viscoelasticity, with greater viscous dissipation and faster stress relaxation, but not changes in stiffness. High AGEs and viscoelasticity combined with oncogenic β-catenin signalling promote HCC induction, whereas inhibiting AGE production, reconstituting the AGE clearance receptor AGER1 or breaking AGE-mediated collagen cross-links reduces viscoelasticity and HCC growth. Matrix analysis and computational modelling demonstrate that lower interconnectivity of AGE-bundled collagen matrix, marked by shorter fibre length and greater heterogeneity, enhances viscoelasticity. Mechanistically, animal studies and 3D cell cultures show that enhanced viscoelasticity promotes HCC cell proliferation and invasion through an integrin-β1-tensin-1-YAP mechanotransductive pathway. These results reveal that AGE-mediated structural changes enhance ECM viscoelasticity, and that viscoelasticity can promote cancer progression in vivo, independent of stiffness.