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- ItemSelf-Hydrophobization in a Dynamic Hydrogel for Creating Nonspecific Repeatable Underwater Adhesion(Weinheim : Wiley-VCH Verlag, 2020) Han, L.; Wang, M.; Prieto-López, L.O.; Deng, X.; Cui, J.Adhesive hydrogels are widely applied for biological and medical purposes; however, they are generally unable to adhere to tissues under wet/underwater conditions. Herein, described is a class of novel dynamic hydrogels that shows repeatable and long-term stable underwater adhesion to various substrates including wet biological tissues. The hydrogels have Fe3+-induced hydrophobic surfaces, which are dynamic and can undergo a self-hydrophobization process to achieve strong underwater adhesion to a diverse range of dried/wet substrates without the need for additional processes or reagents. It is also demonstrated that the hydrogels can directly adhere to biological tissues in the presence of under sweat, blood, or body fluid exposure, and that the adhesion is compatible with in vivo dynamic movements. This study provides a novel strategy for fabricating underwater adhesive hydrogels for many applications, such as soft robots, wearable devices, tissue adhesives, and wound dressings.
- ItemOn the afferrante-carbone theory of ultratough tape peeling(Niš : Univ., 2023) Ciavarella, Michele; McMeeking, Robert M.; Cricrì, GabrieleIn a simple and interesting theory of ultratough peeling of an elastic tape from a viscoelastic substrate, Afferrante and Carbone find that there are conditions for which the load for steady state peeling could be arbitrarily large in steady state peeling, at low angles of peeling-what they call "ultratough" peeling (Afferrante, L., Carbone, G., 2016, The ultratough peeling of elastic tapes from viscoelastic substrates, Journal of the Mechanics and Physics of Solids, 96, pp.223-234). Surprisingly, this seems to lead to toughness enhancement higher than the limit value observed in a very large crack in an infinite viscoelastic body, possibly even considering a limit on the stress transmitted. The Afferrante-Carbone theory seems to be a quite approximate, qualitative theory and many aspects and features of this "ultratough" peeling (e.g. conformity with the Rivlin result at low peel angles) are obtained also through other mechanisms (Begley, M.R., Collino, R.R., Israelachvili, J.N., McMeeking, R.M., 2013, Peeling of a tape with large deformations and frictional sliding, Journal of the Mechanics and Physics of Solids, 61(5), pp. 1265-1279) although not at “critical velocities”. Experimental and/or numerical verification would be most useful.
- ItemAdhesion of a cylindrical punch with elastic properties that vary radially(Amsterdam [u.a.] : Elsevier, 2023) Kossa, Attila; Hensel, René; McMeeking, Robert M.The adhesion of a rigid substrate and an adhered straight cylindrical punch with a non-homogeneous elastic modulus is analyzed. The stress distributions are obtained along the interface for various elastic modulus gradients. The calculations are performed in the commercial finite element software Abaqus using a user material (UMAT) subroutine to control the dependence of Young's modulus on the radial position. The UMAT code is shared in the paper. The results reveal that the decreasing elastic modulus toward the perimeter of the punch can be used to significantly reduce the normal stress magnitudes in the singularity domain, which leads to stronger adhesion. The increase in the adhesion strength is characterized numerically. The effect of Poisson's ratio is also analyzed.
- ItemFunctional surface microstructures inspired by nature – From adhesion and wetting principles to sustainable new devices(Amsterdam [u.a.] : Elsevier Science, 2021) Arzt, Eduard; Quan, Haocheng; McMeeking, Robert M.; Hensel, RenéIn the course of evolution nature has arrived at startling materials solutions to ensure survival. Investigations into biological surfaces, ranging from plants, insects and geckos to aquatic animals, have inspired the design of intricate surface patterns to create useful functionalities. This paper reviews the fundamental interaction mechanisms of such micropatterns with liquids, solids, and soft matter such as skin for control of wetting, self-cleaning, anti-fouling, adhesion, skin adherence, and sensing. Compared to conventional chemical strategies, the paradigm of micropatterning enables solutions with superior resource efficiency and sustainability. Associated applications range from water management and robotics to future health monitoring devices. We finally provide an overview of the relevant patterning methods as an appendix.
- ItemAnalytical and numerical results for the elasticity and adhesion of elastic films with arbitrary Poisson’s ratio and confinement(London [u.a.] : Taylor & Francis, 2022) Müller, Christian; Müser, Martin H.We present an approximate, analytical treatment for the linearly elastic response of a film with arbitrary Poisson's ratio (Formula presented.), which is indented by a flat cylindrical punch while resting on a rigid foundation. Our approach is based on a simple scaling argument allowing the vast changes of the elastomer’s effective modulus (Formula presented.) with the ratio of film height (Formula presented.) and indenter radius (Formula presented.) to be described with a compact, analytical expression. This yields exact asymptotics for large and small reduced film heights (Formula presented.), whereby it also reproduces the observation that (Formula presented.) has a pronounced minimum for (Formula presented.) at (Formula presented.). Using Green’s function molecular dynamics (GFMD), we demonstrate that the predictions for (Formula presented.) are reasonably correct and generate accurate reference data for effective modulus and pull-off force. GFMD also reveals that the nature of surface instabilities occurring during stable crack growth as well as the crack initiation itself depend sensitively on the way how continuum mechanics is terminated at small scales, that is, on parameters beyond the two dimensionless numbers (Formula presented.) and (Formula presented.) defining the continuum problem.