Viscoelastic Matrix Research Articles

Matrix viscoelasticity controls spatiotemporal tissue organization.

Biomolecular and physical cues of the extracellular matrix environment regulate collective cell dynamics and tissue patterning. Nonetheless, how the viscoelastic properties of the matrix regulate collective cell spatial and temporal organization is not fully understood. Here we show that the passive viscoelastic properties of the matrix encapsulating a spheroidal tissue of breast epithelial cells guide tissue proliferation in space and in time. Matrix viscoelasticity prompts symmetry breaking of the spheroid, leading to the formation of invading finger-like protrusions, YAP nuclear translocation and epithelial-to-mesenchymal transition both in vitro and in vivo in a Arp2/3-complex-dependent manner. Computational modelling of these observations allows us to establish a phase diagram relating morphological stability with matrix viscoelasticity, tissue viscosity, cell motility and cell division rate, which is experimentally validated by biochemical assays and in vitro experiments with an intestinal organoid. Altogether, this work highlights the role of stress relaxation mechanisms in tissue growth dynamics, a fundamental process in morphogenesis and oncogenesis.

Viscoelastic Liquid Matrix with Faster Bulk Relaxation Time Reinforces the Cell Cycle Arrest Induction of the Breast Cancer Cells via Oxidative Stress

The reactivating of disseminated dormant breast cancer cells in a soft viscoelastic matrix is mostly correlated with metastasis. Metastasis occurs due to rapid stress relaxation owing to matrix remodeling. Here, we demonstrate the possibility of promoting the permanent cell cycle arrest of breast cancer cells on a viscoelastic liquid substrate. By controlling the molecular weight of the hydrophobic molten polymer, poly(ε-caprolactone-co-D,L-lactide) within 35-63 g/mol, this study highlights that MCF7 cells can sense a 1000 times narrower relaxation time range (80-290 ms) compared to other studies by using a crosslinked hydrogel system. We propose that the rapid bulk relaxation response of the substrate promotes more reactive oxygen species generation in the formed semi-3D multicellular aggregates of breast cancer cells. Our finding sheds light on the potential role of bulk stress relaxation in a viscous-dominant viscoelastic matrix in controlling the cell cycle arrest depth of breast cancer cells.

Strain softening of natural rubber composites filled with carbon black and aramid fiber

Engineered rubber vulcanizates may contain a low content of short fibers and a high content of nanoparticles while the effects of the different fillers on the softening behavior are not yet explored. Herein, influences of carbon black (CB) and short aramid fiber (AF) on the Payne and Mullins effects of natural rubber composites are investigated for the first time by creating master curves of dynamic modulus or dissipation energy with respect to the straining responses of the matrix. It is revealed that the composite vulcanizates demonstrate the Payne effect characterized by decay of storage modulus, weak overshoot of loss modulus, and very weak high-order harmonics; this effect is mainly dominated by the rubber matrix experiencing microscopic strain amplitude enlarged by the filler. The composite vulcanizates exhibit the Mullins effect that becomes increasingly marked with increasing filler loading and is partially recovered by thermal annealing at relatively high temperatures. The energy dissipation during cyclic tensions is rooted in the viscoelastic deformation of the matrix and the filler-rubber interfacial debonding. The former is marked at room temperature where the rubber phase undergoes a crystallization-melting process during loading-unloading. The latter being marked in the presence of a small content of AF causes yieldinglike deformation for the virgin composites at low tensile strains, and its contribution to the softening is not recoverable during thermal annealing. The results show that the viscoelastic matrix is of importance in controlling the softening of the composite vulcanizates, which will be of guiding significance to conduct research studies on high-performance rubber composites products.

Anomalous temperature dependent stiffness evolution in hydrogels

• A water-filled cavity model simulates the mechanical response of a hydrogel. • The model predicts the temperature-dependent viscoelastic response accurately. • The polymer and water dominant behaviours result in an anomaly in elastic response. We investigate the anomalous stiffness evolution of a hydrogel with an increase in temperature and provide an insight into the underlying mechanism through a finite element model. The continuum model considers the interplay between the water-filled fluid cavity, the surrounding viscoelastic chitosan matrix, and the temperature. It is observed that in the low-temperature regime (30 °C to 70 °C), water cavity volume fractions play a dominant role, while at higher temperatures (70 °C to 200 °C), the polymer viscoelastic properties govern the macroscopic stiffness of the system.

REVIEW ARTICLE Engineering bio-inks for 3D bioprinting cell mechanical microenvironment.

144Three-dimensional (3D) bioprinting has become a promising approach to constructing functional biomimetic tissues for tissue engineering and regenerative medicine. In 3D bioprinting, bio-inks are essential for the construction of cell microenvironment, thus affecting the biomimetic design and regenerative efficiency. Mechanical properties are one of the essential aspects of microenvironment, which can be characterized by matrix stiffness, viscoelasticity, topography, and dynamic mechanical stimulation. With the recent advances in functional biomaterials, various engineered bio-inks have realized the possibility of engineering cell mechanical microenvironment in vivo. In this review, we summarize the critical mechanical cues of cell microenvironments, review the engineered bio-inks while focusing on the selection principles for constructing cell mechanical microenvironments, and discuss the challenges facing this field and the possible solutions for them.

Effect of organic matrix viscoelasticity on indentation recovery behavior in a crossed-lamellar structure of mollusk shell

Mollusk shells are known for their excellent mechanical properties from the complex hierarchical microstructures consisting of calcium carbonate and a small quantity of organic matrix. To investigate the influence of the adhesive organic matrix on the microscopic indentation properties of crossed-lamellar structure in the Cymbiola nobilis (C. nobilis) shell, Vicker`s indentation tests were performed on the specimens with different states (wet, fresh, and calcined at 180°C and 300°C). It is found that the hardness of specimens decreases in this order, which is mainly attributed to the decreased interface bonding strength induced by the loss of moisture and the melting of organic matrix with increasing heat-treatment temperature. Additionally, the indentations of WET, RT and 180°C specimens show a partial recovery with extending time of repose, reflecting a characteristic of viscoelasticity. There is no recovery in 300°C specimen since the molten organic matrix loses its elasticity. The effects of organic matrix on the hardness and indentation recovery behavior of different specimens come from the changes in its elasticity and the interface bonding strength.

The effects of different types of periodontal ligament material models on stresses computed using finite element models

Finite element (FE) method has been used to calculate stress in the periodontal ligament (PDL), which is crucial in orthodontic tooth movement. The stress depends on the PDL material property, which varies significantly in previous studies. This study aimed to determine the effects of different PDL properties on stress in PDL using FE analysis. A 3-dimensional FE model was created consisting of a maxillary canine, its surrounding PDL, and alveolar bone obtained from cone-beam computed tomography scans. One Newton of intrusion force was applied vertically to the crown. Then, the hydrostatic stress and the von Mises stress in the PDL were computed using different PDL material properties, including linear elastic, viscoelastic, hyperelastic, and fiber matrix. Young's modulus (E), used previously from 0.01 to 1000 MPa, and 3 Poisson's ratios, 0.28, 0.45, and 0.49, were simulated for the linear elastic model. The FE analyses showed consistent patterns of stress distribution. The high stresses are mostly concentrated at the apical area, except for the linear elastic models with high E (E>15 MPa). However, the magnitude varied significantly from -14.77 to -127.58 kPa among the analyzed patients. The E-stress relationship was not linear. The Poisson's ratio did not affect the stress distribution but significantly influenced the stress value. The hydrostatic stress varied from -14.61 to -95.48 kPa. Different PDL material properties in the FE modeling of dentition do not alter the stress distributions. However, the magnitudes of the stress significantly differ among the patients with the tested material properties.

Augmented active constrained layer damping of beams using graphite reinforced viscoelastic composite material

This paper deals with the use of viscoelastic composite material (VECM) for the constrained layer of an active constrained layer damping (ACLD) treatment for enhanced damping characteristics due to contributions of extensional strains in addition to transverse shear strain. The proposed VECM layer is composed of graphite fibers reinforced in a conventional viscoelastic matrix. The bending analysis of the overall beam is carried out and contributions of extensional and shear strains for damping behavior are found out. The effects of changing various geometric parameters of the present VECM layer on the control performance of the ACLD treatment have also been evaluated and presented.

Viscoelastic modeling of the stress relaxation behavior for the bionic extracellular matrix polymer scaffold

Viscoelasticity of the extracellular matrix (ECM) plays a critical part in controlling cell behavior. However, the structure-related viscoelasticity of the synthetic ECM and its mechanism are rarely reported. Due to its high tissue similarity, synthetic ECM with structural anisotropy and viscoelasticity holds a great promise for structure and function correlation studies. Here, we reported a series of synthetic composite hydrogel-based ECM with different levels of anisotropic orientation and viscoelastic properties through recently developed post-treatment procedures (the confined pre-strain stretching and drying procedure, the soaking salt solution procedure, and the synergetic sequences of two procedures). Further, by establishing a multimode Maxwell viscoelastic mechanic model, the stress relaxation behavior of the bionic ECM with different levels of anisotropic orientation and viscoelastic properties was simulated successfully. The characteristic viscoelastic parameters of the bionic ECM could also be calculated exactly. This study presented a novel viscoelastic mechanic model for mimicking the key ECM features of the synthetic ECM with anisotropic structure and viscoelasticity properties.

Wave attenuation in viscoelastic hierarchical plates

Phononic crystals (PCs) are periodic structures obtained by the spatial arrangement of materials with contrasting properties, which can be designed to efficiently manipulate mechanical waves. Plate structures can be modeled using the Mindlin–Reissner plate theory and have been extensively used to analyze the dispersion relations of PCs. Although the analysis of the propagating characteristics of PCs may be sufficient for simple elastic structures, analyzing the evanescent wave behavior becomes fundamental if the PC contains viscoelastic components. Another complication is that increasingly intricate material distributions in the unit cell of PCs with hierarchical configuration may render the calculation of the complex band structure (i.e., considering both propagating and evanescent waves) prohibitive due to excessive computational workload. In this work, we propose a new extended plane wave expansion formulation to compute the complex band structure of thick PC plates with arbitrary material distribution using the Mindlin–Reissner plate theory containing constituents with a viscoelastic behavior approximated by a Kelvin–Voigt model. We apply the method to investigate the evanescent behavior of periodic hierarchically structured plates for either (i) a hard purely elastic matrix with soft viscoelastic inclusions or (ii) a soft viscoelastic matrix with hard purely elastic inclusions. Our results show that for (i), an increase in the hierarchical order leads to a weight reduction with relatively preserved attenuation characteristics, including attenuation peaks due to locally resonant modes that present a decrease in attenuation upon increasing viscosity levels. For (ii), changing the hierarchical order implies in opening band gaps in distinct frequency ranges, with an overall attenuation improved by an increase in the viscosity levels.

Supercritical carbon dioxide foaming for ultra-low dielectric loss perfluorinated foam

Microelectronic is developing towards high frequency (GHz) and high speed (Gpbs), putting forward high requirements for low dielectric materials. The most efficient method for fabricating low dielectric materials is the incorporation of air into matrix via supercritical CO2 foaming. Herein, a low dielectric thermoplastic perfluorinated polymer is selected to be the matrix and another low dielectric perfluorinated polymer which is capable to form in-situ nanofibrils is selected to regulate the matrix viscoelasticity. Supercritical CO2 foaming method is then applied to introduce a large amount of low dielectric air into nanofibrill modified perfluorinated polymer. Owing to supercritical CO2 as a residue-free foaming agent (residue impurities in matrix originated from foaming agent would increase dielectric loss significantly at GHz) and its strong interaction with perfluorinated polymer (ensure large expansion ratio of the obtained foams to introduce a large amount of low dielectric air in matrix), the lowest dielectric loss of 0.00015 (among the existing polymeric materials) is then obtained by supercritical CO2 foaming of in-situ nanofibril modified perfluorinated polymer. Furthermore, the hydrophobic and oilphobic properties of the perfluorinated polymer were enhanced by supercritical CO2 foaming to form a cellular structure; simultaneously, the corrosion resistance to strong alkali and V0 flame retarding properties of the ultra-low dielectric foam were maintained resulted from the perfluorinated cell walls. Therefore, such superior comprehensive performance of this ultra-low dielectric perfluorinated foam made from supercritical CO2 foaming enables it the best alternative for the next-generation high-frequency (GHz to THz) and high-speed (sub Tbps) signal transmission substrate in electronics.

Investigation of the Mechanical Properties for Polymer Reinforced by Nanoparticles with Considering Viscoelasticity of the Matrix

Investigation of the Mechanical Properties for Polymer Reinforced by Nanoparticles with Considering Viscoelasticity of the Matrix

A machine learning accelerated inverse design of underwater acoustic polyurethane coatings

Here we propose a detailed protocol to enable an accelerated inverse design of acoustic coatings for underwater sound attenuation application by coupling Machine Learning and an optimization algorithm with Finite Element Models (FEM). The FEMs were developed to obtain the realistic performance of the polyurethane (PU) acoustic coatings with embedded cylindrical voids. The frequency dependent viscoelasticity of PU matrix is considered in FEM models to substantiate the impact on absorption peak associated with the embedded cylinders at low frequencies. This has been often ignored in previous studies of underwater acoustic coatings, where usually a constant frequency-independent complex modulus was used for the polymer matrix. The key highlight of the proposed optimization framework for the inverse design lies in its potential to tackle the computational hurdles of the FEM when calculating the true objective function. This is done by replacing the FEM with an efficiently computable surrogate model developed through a Deep Neural Network. This enhances the speed of predicting the absorption coefficient by a factor of 4.5 times 10^3 compared to FEM model and is capable of rapidly providing a well-performing, sub-optimal solution in an efficient way. A significant, broadband, low-frequency attenuation is achieved by optimally configuring the layers of cylindrical voids. This is accomplished by accommodating attenuation mechanisms, including Fabry–Pacute{e}rot resonance and Bragg scattering of the layers of voids. Furthermore, the proposed protocol enables the inverse and targeted design of underwater acoustic coatings through accelerating the exploration of the vast design space compared to time-consuming and resource-intensive conventional trial-and-error forward approaches.

Mechanical checkpoint regulates monocyte differentiation in fibrotic niches.

Myelofibrosis is a progressive bone marrow malignancy associated with monocytosis, and is believed to promote the pathological remodelling of the extracellular matrix. Here we show that the mechanical properties of myelofibrosis, namely the liquid-to-solid properties (viscoelasticity) of the bone marrow, contribute to aberrant differentiation of monocytes. Human monocytes cultured in stiff, elastic hydrogels show proinflammatory polarization and differentiation towards dendritic cells, as opposed to those cultured in a viscoelastic matrix. This mechanically induced cell differentiation is blocked by inhibiting a myeloid-specific isoform of phosphoinositide 3-kinase, PI3K-γ. We further show that murine bone marrow with myelofibrosis has a significantly increased stiffness and unveil a positive correlation between myelofibrosis grading and viscoelasticity. Treatment with a PI3K-γ inhibitor in vivo reduced frequencies of monocyte and dendritic cell populations in murine bone marrow with myelofibrosis. Moreover, transcriptional changes driven by viscoelasticity are consistent with transcriptional profiles of myeloid cells in other human fibrotic diseases. These results demonstrate that a fibrotic bone marrow niche can physically promote a proinflammatory microenvironment.

Evaluation of process-induced residual stresses in orthogonal 3D woven composites via nonlinear finite element modeling validated by hole drilling experiments

Effects of matrix material constitutive model and presence of defects on development of manufacturing induced residual stresses are studied using Finite Element (FE) analysis in an orthogonal 3D woven composite. The residual stresses are assumed to arise from a difference in the coefficients of thermal expansion between the reinforcement and the matrix. Numerical results are compared with experimentally observed surface displacements resulting from blind hole drilling and measured via electronic speckle pattern interferometry. It is demonstrated that for accurate reproduction of the residual stress fields using FE modeling, viscoelastic matrix properties should be used and possible presence of cracks at the tow/matrix interface should not be neglected.

Microcellular foams simultaneous reinforcing and toughening strategy of combining nano-fibrillation network and supercritical solid-state foaming

Foams with excellent mechanical performance are extremely valuable, as playing a key role in structural materials. However, it is still a significant challenge to simultaneously strengthen and toughen foam materials. In this work, a novel strategy combining nano-fibrillation network and supercritical carbon dioxide (scCO 2 ) solid-state foaming was proposed as follows: 1) In designing micro-scale cellular structure, chain extension and fibrillation technologies were synergistically adopted to improve the matrix viscoelasticity for cell stability, scCO 2 solid-sate foaming was then adopted to improve cell nucleation and cell growth. The combination of the above technologies helps to obtain a microcellular foam with large expansion ratio and small cell size; 2) In designing nano-scale hierarchical structure of crystalline and multiphase, flexible fibrils were dispersed in cell walls to compensate for matrix's brittleness and hence increased the foam impact strength, the crystals in cell walls improved the bending strength of cell walls and hence increased the foam compression strength. Herein, the obtained microcellular foam has simultaneous improvements in compression strength from 1.7 MPa to 2.7 MPa and impact toughness from 0.26 kJ/m 2 to 0.46 kJ/m 2 while maintaining a low foam density of 0.13 g/cm 3 . • A novel strategy is firstly proposed to simultaneously strengthen and toughen foams. • Micro/nano structure is regulated by in-situ fibrillation and supercritical solid-state foaming. • Nano fibrils facilitate crystallization and hence improve foam compression strength. • Nano fibril network hinders crack propagation and hence improves foam toughness. • Micro cellular structure improves foam compression strength and toughness.

Multiscale modeling of viscoelastic behavior of unidirectional composite laminates and deployable structures

Due to the inherent viscoelasticity of constituent matrix and the possibility of long-term storage, space deployable structures made of composites are likely to exhibit relaxation in the stored strain energy, which may degrade their deployment performance. This paper presents a bottom-up finite element based multiscale computational strategy that bridges the experimentally measurable properties of constituent fibers and matrix to numerical predictions of viscoelastic behavior of composite laminates and general shell structures. A user-friendly RVE analysis plug-in tool is developed in Abaqus/CAE to rapidly estimate the effective orthotropic viscoelastic properties of unidirectional composites by taking as input the microstructure geometry as well as the known properties of fibers and matrix. Some benchmark problems were solved, and the accuracy and efficiency of the proposed plug-in tool were verified. Next, the strategy is shown to be applicable to model the viscoelastic behavior of macroscale composite laminates and deployable shell structures, by utilizing built-in functions in Abaqus to define the stacking sequence and accordingly update the material properties. In particular, the proposed multiscale strategy was employed to simulate the influence of modulus relaxation on the deployment dynamics of a composite tape-spring hinge, and good agreement was achieved as compared to reported experimental results.

Effects of soft and hard magnetic particles on the mechanical performance of ultra-soft magnetorheological elastomers

Magnetorheological elastomers (MREs) mechanically respond to external magnetic stimuli by changing their mechanical properties and/or changing their shape. Recent studies have shown the great potential of MREs when manufactured with an extremely soft matrix and soft-magnetic particles. Under the application of an external magnetic field, such MREs present significant mechanical stiffening, and when the magnetic field is off, they show a softer response, being these alternative states fully reversible. Although soft-magnetic particles are suitable for their high magnetic susceptibility, they require the magnetic actuation to remain constant in order to achieve the magneto-mechanical stiffening. Here, we present an alternative solution based on hard-magnetic MREs to provide stiffening responses that can be sustained along time without the need of keeping the external magnetic field on. To this end, we manufacture novel extremely soft hard-magnetic MREs (stiffness in the order of 1 kPa) and characterise them under magneto-mechanical shear and confined magnetic expansion deformation modes, providing a comparison framework with the soft-magnetic counterparts. The extremely soft nature of the matrix allows for easily activating the magneto-mechanical couplings under external magnetic actuation. In this regard, we provide a novel approach by setting the magnetic actuation below the fully magnetic saturating field. In addition, free deformation tests provide hints on the microstructural transmission of torques from the hard-magnetic particles to the viscoelastic matrix, resulting in macroscopic geometrical effects and intricate shape-morphing phenomena.

Adaptive Self-Organization of Nanomaterials Enables Strain-Insensitive Resistance of Stretchable Metallic Nanocomposites.

Highly conductive and stretchable nanocomposites are promising material candidates for skin electronics. However, the resistance of stretchable metallic nanocomposites highly depends on external strains, often deteriorating the performance of fabricated electronic devices. Here, a material strategy for the highly conductive and stretchable nanocomposites comprising metal nanomaterials of various dimensions and a viscoelastic block-copolymer matrix is presented. The resistance of the nanocomposites can be well retained under skin deformations (<50% strain). It is demonstrated that silver nanomaterials can self-organize inside the viscoelastic media in response to external strain when their surface is conjugated with 1-decanethiol. Distinct self-organization behaviors associated with nanomaterial dimensions and strain conditions are found. Adopting the optimum composition of 0D/1D/2D silver nanomaterials can render the resistance of the nanocomposites insensitive to uniaxial or biaxial strains. As a result, the resistance can be maintained with a variance of <1% during 1000 stretching cycles under uniaxial and biaxial strains of <50% while a high conductivity of ≈31000 S cm-1 is achieved.

Dispersing swimming microalgae in self-assembled nanocellulose suspension: Unveiling living colloid dynamics in cholesteric liquid crystals

Active matter comprises individual energy-consuming components that convert locally stored energy into mechanical motion. Among these, liquid crystal dispersed self-propelled colloids have displayed fascinating dynamic effects and nonequilibrium behaviors. In this work, we introduce a new type of active soft matter based on swimming microalgae and lyotropic nanocellulose liquid crystal. Cellulose is a kind of biocompatible polysaccharide that nontoxic to living biological colloids. In contrast to microalgae locomotion in isotropic and low viscosity media, we demonstrate that the propulsion force of swimming microalgae can overcome the stabilizing elastic force in cholesteric nanocellulose liquid crystal, with the displacement dynamics (gait, direction, frequency, and speed) be altered by the surrounding medium. Simultaneously, the active stress and shear flow exerted by swimming microalgae can introduce local perturbation in surrounding liquid crystal orientation order. The latter effect yields hydrodynamic fluctuations in bulk phase as well as layer undulations, helicoidal axis splay deformation and director bending in the cholesteric assembly, which finally followed by a recovery according to the inherent viscoelasticity of liquid crystal matrix. Our results point to an unorthodox design concept to generate a new type of hybrid soft matter that combines nontoxic cholesteric liquid crystal and active particles, which are expected to open opportunities in biosensing and biomechanical applications.