Swelling-induced Deformation Research Articles

Controlled swelling-induced shape change of soft gel filled structures

Gels are polymers that can imbibe large amounts of solvent and generate large volumetric deformations in a process commonly termed swelling. The swelling-induced deformations can be harnessed to produce pressure against surrounding elastic elements, and therefore lead to spatial shape changes without the need for an external energy source. In the present paper, we consider a thin cylindrical elastic tube that encapsulates a gel and deforms in response to the swelling-induced forces. It is expected that by controlling the spatial stiffness distribution of the tube, the deformed swelling-induced shape can be programmed. We exploit this simple idea to obtain controlled shape change driven by the large volumetric expansion of gels. To this end, we train a machine learning algorithm through many FE simulations that enable solving the inverse problem: for any prescribed swelling-induced target shape, the algorithm provides the spatial stiffness distribution of the thin tube. The results confirm that precise controlled shape change is achievable by exploiting the large swelling-induced volumetric deformations in an autonomous manner (i.e. without the need for any external energy source). This work paves the way for new perspectives in the design of shape-change systems based on the simple yet proper elastic distribution of confining structures.

Swelling-induced deformation electronic signal of MXene hydrogel for cancer detection

A reactive-oxygen-species-responsive (ROS-responsive) conductive hydrogel sensor is developed for cancer detection using degradable TiO2/MXene-integrated polymer dots (PD-MX/TiO2) that could generate heat and control conductivity. During contact between hydrogel and H2O2, the loaded MXene (MX) is oxidized, resulting in formation of TiO2 and a change in MX dimensional conformation, conductivity, and light-to-heat generation. Interestingly, the presence of visible light accelerates this process owing to photocatalytic properties of TiO2. Furthermore, the resistivity of hydrogel changes from 27.5 to 72.0 and 48.1 kΩ after H2O2 treatment and visible-light irradiation, respectively. The hydrogel exhibits a distinct resistance signal during its deformation at x, y, and z axes of the three-dimensional axis, with a mean signal of 22.2%, 15.3%, and 7.2%, respectively. The in vitro analysis of cancer cells displays a distinguishable detection result for CHO-K1, HeLa, and PC-3, exhibiting electrical resistance of 62.9, 123.8, and 121.7 kΩ, respectively. Furthermore, light-to-heat conversion in the PD-MX/TiO2 Hydrogel decreases to 9.7 °C (HeLa) and 9.7 °C (PC-3) compare to that of the normal cells (17.3 °C). It is demonstrated that the hydrogel could be used for direct diagnosis when linked with a wireless apparatus, thus facilitating accurate and rapid evaluation of cancer microenvironment.

Microscale investigation of the anisotropic swelling of cartilage tissue and cells in response to hypo-osmotic challenges.

Tissue swelling represents an early sign of osteoarthritis, reflecting osmolarity changes from iso- to hypo-osmotic in the diseased joints. Increased tissue hydration may drive cell swelling. The opposing cartilages in a joint may swell differently, thereby predisposing the more swollen cartilage and cells to mechanical injuries. However, our understanding of the tissue-cell interdependence in osmotically loaded joints is limited as tissue and cell swellings have been studied separately. Here, we measured tissue and cell responses of opposing patellar (PAT) and femoral groove (FG) cartilages in lapine knees exposed to an extreme hypo-osmotic challenge. We found that the tissue matrix and most cells swelled during the hypo-osmotic challenge, but to a different extent (tissue: <3%, cells: 11%-15%). Swelling-induced tissue strains were anisotropic, showing 2%-4% stretch and 1%-2% compression along the first and third principal directions, respectively. These strains were amplified by 5-8 times in the cells. Interestingly, the first principal strains of tissue and cells occurred in different directions (60-61° for tissue vs. 8-13° for cells), suggesting different mechanisms causing volume expansion in the tissue and the cells. Instead of the continuous swelling observed in the tissue matrix, >88% of cells underwent regulatory volume decrease to return to their pre-osmotic challenge volumes. Cell shapes changed in the early phase of swelling but stayed constant thereafter. Kinematic changes to tissue and cells were larger for PAT cartilage than for FG cartilage. We conclude that the swelling-induced deformation of tissue and cells isanisotropic. Cells actively restored volume independent of the surrounding tissues and seemed to prioritize volume restoration over shape restoration. Our findings shed light on tissue-cell interdependence in changing osmotic environments that is crucial for cell mechano-transduction in swollen/diseased tissues.

Determination of ovalbumin sensing response of protein-imprinted bilayered hydrogel strips via measurement of mechanically driven bending angles based on swelling-induced deformation.

Novel detection method has been developedto explore changes in mechanical bending angles on a bilayer of polyethylene terephthalate (PET) and molecularly imprinted polymer (MIP). For an ovalbumin (OVA)-imprinted hydrogel layer, functional monomers were employed to achieve sufficient binding effect in the polymer matrix. The OVA amount added in the MIP precursor solution and the dimensions of OVA-imprinted hydrogel (MIH) strips were controlled to maximize the change in bending angles as an OVA sensing response within a valid detection range. The sensing behaviors were determined by monitoring the difference in the bending angles via protein adsorption based on the swelling-induced deformation of the OVA-extracted hydrogel (E-MIH) strip. The equilibrium adsorption capacity of the E-MIH strip was calculated via the Bradford protein assay. The detection limit, quantification limit, and imprinting factor were calculated. To compare the selectivity coefficients, the adsorption behaviors of three proteins were investigated. Finally, the reusability of the E-MIH strip was explored via repeated adsorption and extraction. Based on the results, the E-MIH strips demonstrated a promising protein sensing platform monitoring mechanical bending angles affected by swelling deformation.

A nonlinear mechanics model of soft network metamaterials with unusual swelling behavior and tunable phononic band gaps

Soft mechanical metamaterials with negative swelling responses represent a class of man-made materials with specially engineered micro-architectures, which are attractive for applications in areas such as biomedical engineering, aerospace and microelectronics. These soft mechanical metamaterials are usually constructed with laminated filaments that serve as building block structures in periodic lattices, with capabilities to convert hydraulic deformations of active materials into large bending deformations of the filamentary microstructures. The previous studies mainly relied on massive calculations of finite element analyses (FEA) as the core process of metamaterial designs to achieve targeted mechanical properties. The FEA calculations could, however, be very cumbersome and time-consuming, especially when the micro-architecture involves a large number of complex microstructures. This paper introduces a theoretical model that can predict accurately the swelling-induced deformations in such soft mechanical metamaterials consisting of sandwiched horseshoe microstructures. This model takes into account the evident shape change of sandwiched cross section observed in experiments, during the hydration process. Experimental and computational studies on mechanical metamaterials with a wide range of microstructure geometries were carried out to validate the developed model. These results unveil the significant role of out-of-plane deformations on the swellability of the mechanical metamaterials. The theoretical model sheds light on the essential microstructure-property relationship, which could serve as a reference of metamaterial designs to achieve desired swelling behavior. Furthermore, we leverage the active control of microstructure geometry during hydration to offer tunable phononic band structures, with potential applications in noise/vibration control and wave mitigation.

Biomimetic Janus Paper with Controllable Swelling for Shape Memory and Energy Conversion

Being inspired by the “seismonastic reaction” of Mimosa pudica, an asymmetric swelling system was constructed to induce the controllable directional deformation of filter paper. In this work, multifunctional biomimetic Janus paper was facilely fabricated via depositing poly(vinylidene fluoride) (PVDF) on one side of Qualitative Filter Paper (QFP), the permeation of polymer solutions within filter paper was well controlled during fabrication. The wetting and swelling behavior of the prepared Janus paper were detected. The Janus paper showed controllable swelling-induced deformations in water. Both the degree and orientation of the deformation were fully investigated. On the one hand, the degree of deformation depends on the gradient wettability and hygroscopicity of the Janus paper, on the other hand, the orientation of deformation is related to the storage and release of stress. Additionally, the steady deformation during swelling endows the Janus paper with novel shape memory property both under idling and loading conditions. The Janus paper was also applied to achieve reversible energy conversion from the swelling potential energy to mechanical potential energy.

A study of the deformation behaviour of veneers resulting from water storage (A methodological approach for determining the swelling characteristic using the example of European beech veneer)

This article discusses the swelling-induced deformation behaviour of veneers. Impregnation tests were performed to assess the influences on the unrestrained deformation of veneers. Among others, the tests focused on a comparison of the swelling-induced deformation in consideration of influences caused by the manufacturing process for different anatomical orientations (tangential or radial veneer). For this, samples of European beech veneer (Fagus sylvatica L.) were measured under a microscope and categorised into groups of tangentially or radially sampled veneers based on the anatomical characteristics. In addition, manufacture-specific damage was documented during the slicing process and also considered for the assessment. As a result of these tests, it was proven that the influence of near-surface damage caused by the manufacture on the unrestrained deformation of veneers was significantly dominant.

Finite element method for coupled diffusion-deformation theory in polymeric gel based on slip-link model

A polymeric gel is an aggregate of polymers and solvent molecules, which can retain its shape after a large deformation. The deformation behavior of polymeric gels was often described based on the Flory-Rehner free energy function without considering the influence of chain entanglements on the mechanical behavior of gels. In this paper, a new hybrid free energy function for gels is formulated by combining the Edwards-Vilgis slip-link model and the Flory-Huggins mixing model to quantify the time-dependent concurrent process of large deformation and mass transport. The finite element method is developed to analyze examples of swelling-induced deformation. Simulation results are compared with available experimental data and show good agreement. The influence of entanglements on the time-dependent deformation behavior of gels is also demonstrated. The study of large deformation kinetics of polymeric gel is useful for diverse applications.

Swelling–twist interaction in fiber-reinforced hyperelastic materials: the example of azimuthal shear

We study how fiber-reinforced materials will naturally undergo swelling deformations in which a relatively greater stretch occurs transverse to the fibers than in the fiber direction. This means that a pattern of initially curved fibers prior to swelling will tend to straighten out as swelling proceeds. This can lead to swelling-induced deformations with a high degree of localized shearing and significant overall twisting. Such a process is examined for a plane strain swelling deformation that combines twist with radial expansion. Analytical results are obtained for both types: small and large swelling. Of particular interest is the relation of the extensible fiber theory to a theory for inextensible fibers. We examine the extent to which the former approaches the latter in the limit as the fibers are taken to be progressively stiffer.

Swelling-Induced Deformation of Spherical Latex Particles

Experimental evidence is presented showing that the direct formation of anisotropic colloidal polymer particles via aqueous heterophase polymerization is essentially controlled by the entropy gain of the linear fraction in the semi-interpenetrating network of the seed particles during swelling. Anisotropic particles are produced via photoinitiated polymerization, allowing swelling and polymerization to take place at the same temperature. These experiments prove that the temperature effect on rubber elasticity is, if at all, only of minor importance for the formation of anisotropic polymer particles. The major significance of swelling of the seed particles for the whole process is underlined by additional studies with optical microscopy and model simulations.

Anisotropic swelling of thin gel sheets.

We describe the anisotropic swelling within the Flory-Rehner thermodynamic model through an extension of the elastic component of the free-energy, which takes into account the oriented hampering of the swelling-induced deformations due to the presence of stiffer fibers. We also characterize the homogeneous free-swelling solutions of the corresponding anisotropic stress-diffusion problem, and discuss an asymptotic approximation of the key equations, which allows us to explicitly derive the anisotropic solution of the problem. We propose a proof-of-concept of our model, realizing thin bilayered gel sheets with layers having different anisotropic structures. In particular, for seedpod-like sheets, we observe and quantitatively measure the helicoid versus ribbon transition determined by the aspect ratio of the composite sheet.

Swelling-induced and controlled curving in layered gel beams.

We describe swelling-driven curving in originally straight and non-homogeneous beams. We present and verify a structural model of swollen beams, based on a new point of view adopted to describe swelling-induced deformation processes in bilayered gel beams, that is based on the split of the swelling-induced deformation of the beam at equilibrium into two components, both depending on the elastic properties of the gel. The method allows us to: (i)determine beam stretching and curving, once assigned the characteristics of the solvent bath and of the non-homogeneous beam, and (ii) estimate the characteristics of non-homogeneous flat gel beams in such a way as to obtain, under free-swelling conditions, three-dimensional shapes. The study was pursued by means of analytical, semi-analytical and numerical tools; excellent agreement of the outcomes of the different techniques was found, thus confirming the strength of the method.

Swelling dynamics of a thin elastomeric sheet under uniaxial pre-stretch

It has been demonstrated experimentally that pre-stretch affects the swelling of an elastomeric membrane when it is exposed to a solvent. We study theoretically the one-dimensional swelling of a pre-stretched thin elastomeric sheet, bonded to an impermeable rigid substrate, to quantify the influence of pre-stretch. We show that the solvent uptake increases when pre-stretch increases, both at equilibrium and during the swelling transient, where it exhibits two different scaling regimes. The coupling between the solvent uptake and pre-stretch may be practically exploited to design soft actuators where the swelling-induced deformations can be controlled by varying the pre-stretch.

Swelling-induced deformations: a materials-defined transition from macroscale to microscale deformations

Swelling-induced deformations are common in many biological and industrial environments, and the shapes and patterns that emerge can vary across many length scales. Here we present an experimental study of a transition between macroscopic structural bending and microscopic surface creasing in elastomeric beams swollen non-homogeneously with favorable . We show that this transition is dictated by the materials and geometry of the system, and we develop a simple scaling model based on competition between bending and swelling energies that predicts if a given droplet would deform a polymeric structure macroscopically or microscopically. We demonstrate how proper tuning of materials and geometry can generate instabilities at multiple length scales in a single structure.

J044023 母材上に拘束されたハイドロゲル層の膨潤に伴う大変形応答([J044-02]ソフトマター・イノベーション(2))

J044023 母材上に拘束されたハイドロゲル層の膨潤に伴う大変形応答([J044-02]ソフトマター・イノベーション(2))

Swelling-induced instabilities in microscale, surface-confined poly(N-isopropylacryamide) hydrogels

A hydrogel is a three-dimensional hyperelastic polymer network that swells to a specific volume upon exposure to a penetrating solvent. If mechanical constraints interfere with the swelling process, anisotropic compressive stresses are generated, which may manifest in local or global instabilities. Herein, we employ confocal microscopy for the in situ, three-dimensional study of micron-scale hydrogels that are pinned to a solid substrate. Depending on the initial geometry of the hydrogel, four general modes of swelling-induced deformation were found: lateral differential swelling, local sinusoidal edge buckling, bulk sinusoidal buckling, and surface creasing. The transition between local edge buckling and bulk buckling is consistent with linear elastic theory; however, linear theory cannot be used to predict many details of the swollen structures. Whereas global buckling has a well-defined wavelength that depends on height of the hydrogel structure, edge buckling appears to be independent of height and depends on sample history. Moreover, edge buckling can appear in globally buckled structures, suggesting two different mechanisms for the two instabilities.

Inhomogeneous swelling of a gel in equilibrium with a solvent and mechanical load

A network of polymers can imbibe a large quantity of a solvent and swell, resulting in a gel. The swelling process can be markedly influenced by a mechanical load and geometric constraint. When the network, solvent, and mechanical load equilibrate, inside the gel the chemical potential of the solvent is homogeneous, but the concentration of the solvent and the deformation of the network can be inhomogeneous. We use the chemical potential of the solvent and the deformation gradient of the network as the independent variables of the free-energy function, and show that the boundary value problem of the swollen gel is equivalent to that of a hyperelastic solid. We implement this approach in the finite-element package, ABAQUS, and analyze examples of swelling-induced deformation, contact, and bifurcation. Because commercial software like ABAQUS is widely available, this work may provide a powerful tool to study complex phenomena in gels.