Being able to precisely characterize the mechanical properties of soft microparticles is essential for numerous situations from the understanding of the flow of biological fluids to the development of soft micro-robots. Here we present a simple measurement technique for the Poisson's ratio of soft micron-sized hydrogels in the presence of a surrounding liquid. This methods relies on the measurement of the deformation in two orthogonal directions of a rectangular hydrogel slab compressed uni-axially inside a microfluidic channel. Due to the in situ character of the method, the sample does not need to be dried, allowing for the measurement of the mechanical properties of swollen hydrogels. Using this method we determine the Poisson's ratio of hydrogel particles composed of polyethylene glycol (PEG) and varying solvents fabricated using a lithography technique. The results demonstrate with high precision the dependence of the hydrogel compressibility on the solvent fraction and character. The method, easy to implement, can be adapted for the measurement of a variety of soft and biological materials.
This review focuses on a microparticle-producing technique widely used for its efficacy in controlling physicochemical properties: droplet-based microfluidics. The review describes the various strategies applied under this technique, and the size, shape, concentration, stability and mechanical properties of the alginate hydrogel microparticles obtained.
Hydrogels are widespread soft materials, which can serve a wide range of applications. The control over the viscoelastic properties of the gel is of paramount importance. Ongoing environmental issues have raised the consumer's concern towards the use of more sustainable materials, including hydrogels. However, are greener materials compatible with high functionality? In a safe-by-design approach, this work demonstrates that functional hydrogels with in situ responsivity of their elastic properties by external stimuli can be developed from entirely ``sustainable'' components, a biobased amphiph…
An unusual type of mechanical behavior was registered while studying the swollen hydrogel compositions "cellulose-polyacrylamide" in the conditions of multiple cyclic compression tests with the broad variation of the deformation speed. While increasing the deformation speed the clearly seen inversion of the positions of compression and decompression parts of the cyclic stress-strain curves was detected. While carrying out the cyclic compression tests with relatively low deformation speed (about 100-200 % of the initial sample's height per minute) the well defined hysteresis of the stress-strai…
In situ observation of precipitation or phase separation induced by solvent addition is important in studying its dynamics. Combined with optical and fluorescence microscopy, microfluidic devices have been leveraged in studying the phase separation in various materials including biominerals, nanoparticles, and inorganic crystals. However, strong scattering from the subphases in the mixture is problematic for in situ study of phase separation with high temporal and spatial resolution. In this work, we present a quasi-2D microfluidic device combined with total internal reflection microscopy as a…
The current understanding of motility through body shape deformation of microorganisms and the knowledge of fluid flows at the microscale provides ample examples for mimicry and design of soft microrobots. In this work, a two-dimensional spiral is presented that is capable of rotating by non-reciprocal curling deformations. The body of the microswimmer is a ribbon consisting of a thermo-responsive hydrogel bilayer with embedded plasmonic gold nanorods. Such a system allows fast local photothermal heating and non-reciprocal bending deformation of the hydrogel bilayer under non-equilibrium condi…
Encapsulation of chemicals using polymer membranes enables to control their transport and delivery for applications such as agrochemistry or detergency. To rationalize the design of polymer capsules, it is necessary to understand how the membranes' mechanical properties control the transport and release of the cargo. In this article, we use microfluidics to produce model polymer capsules and study in situ their behavior in controlled elongational flows. Our model capsules are obtained by assembling polymer mono and hydrogen-bonded bilayers at the surface of an oil droplet in water. We also use…
Biological hydrogels have been increasingly sought after as e.g. wound dressings or scaffolds for regenerative medicine, due to their inherent biofunctionality in biological environments. Especially in moist wound healing, the ideal material should absorb large amounts of wound exudate whilst remaining mechanically competent in-situ. Despite their large hydration, however, current biological hydrogels still leave much to be desired in terms of mechanical properties in physiological conditions. To address this challenge, a multi-scale approach is presented for the synthetic design of cyto-compa…
Linear poroelastic response of thin permeable gel films
Ecole des Ponts Paris Tech（巴黎路桥学校）；Université Gustave Eiffel（居斯塔夫埃菲尔大学）；CNRS（法国国家科学研究中心）；ESPCI Paris（巴黎物理化工国立高等学院）；Université PSL（巴黎文理研究大学）；Institut Pierre-Gilles de Gennes（皮埃尔-吉勒·德热纳研究所）；Univ. Bordeaux（波尔多大学）；LOMA（光学与分子力学实验室）
Spatial control of wettability is key to many applications of microfluidic devices, ranging from double emulsion generation to localized cell adhesion. A number of techniques, often based on masking, have been developed to produce spatially-resolved wettability patterns at the surface of poly(dimethylsiloxane) (PDMS) elastomers. A major impediment they face is the natural hydrophobic recovery of PDMS: hydrophilized PDMS surfaces tend to return to hydrophobicity with time, mainly because of diffusion of low molecular weight silicone species to the surface. Instead of trying to avoid this phenom…
Design and modelling of compliant mechanisms with invertible Poisson's ratio effect for growing biological cells
Department of Mechanical and Aerospace Engineering, Indian Institute of Technology Hyderabad（印度理工学院海德拉巴分校机械与航空航天工程系）；School of Mechanical Sciences, Indian Institute of Technology Goa（印度理工学院果阿分校机械科学学院）
