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Ruobing Bai's picture

Fatigue fracture of tough hydrogels

Dear colleagues,

Attached please find our new paper "Fatigue fracture of tough hydrogels" published on Extreme Mechanics Letters.

 

Fatigue fracture of tough hydrogels

Ruobing Bai, Quansan Yang, Jingda Tang, Xavier P. Morelle, Joost Vlassak, Zhigang Suo

Jinxiong Zhou's picture

Predicting origami-inspired programmable self-folding of hydrogel trilayers

Imitating origami principles in active or programmable materials opens the door for development
of origami-inspired self-folding structures for not only aesthetic but also functional purposes. A
variety of programmable materials enabled self-folding structures have been demonstrated across
various fields and scales. These folding structures have finite thickness and the mechanical
properties of the active materials dictate the folding process. Yet formalizing the use of origami

Xuanhe Zhao's picture

Tough Soft Wet Adhesion

Tough bonding of hydrogels to diverse non-porous surfaces

Hyunwoo Yuk, Teng Zhang,Shaoting Lin, German Alberto Parada & Xuanhe Zhao

Nature Materials (2015) doi:10.1038/nmat4463

A design strategy for tough bonding of hydrogels to diverse solids.

Hydraulic Fracture and Toughening of a Brittle Layer Bonded to a Hydrogel

AbstractBrittle materials propagate opening cracks under tension. When stress increases beyond a critical magnitude, then quasistatic crack propagation becomes unstable. In the presence of several precracks, a brittle material always propagates only the weakest crack, leading to catastrophic failure. Here, we show that all these features of brittle fracture are fundamentally modified when the material susceptible to cracking is bonded to a hydrogel, a common situation in biological tissues.

linst06's picture

3D Printing of Highly Stretchable and Tough Hydrogels into Complex, Cellularized Structures

Sungmin Hong, Dalton Sycks, Hon Fai Chan, Shaoting Lin, Gabriel P. Lopez, Farshid Guilak, Kam W. Leong, Xuanhe Zhao, Advanced Materials, 27, 4035-4040, 2015. 

 

Cai Shengqiang's picture

Drying-induced cavitation in a constrained hydrogel

Cavitation can be often observed in soft materials. Most previous studies were focused on cavitation in an elastomer, which is under different mechanical loadings. In this paper, we investigate cavitation in a constrained hydrogel induced by drying. With taking account of surface tension and chemo-mechanics of gels, we calculate the free energy of the system as a function of cavity size. The free energy landscape shows double-well structure, analogous to first-order phase transition.  Above the critical humidity, a cavity inside the gel is tiny.

Zhigang Suo's picture

The toughest hydrogel in the world

The class started today.  I'll be teaching fracture mechanics this semester.  I'll be mostly using the class notes I wrote in 2010, but will post updated ones. 

In today's class I covered "Trouble with linear elastic theory of strength."  I have just posted updated notes of the lecture.  The new notes begin with the follwoing paragraphs.

Widusha Illeperuma's picture

Force and stroke of a hydrogel actuator

Hydrogels that undergo a volume phase transition in response to an
external stimulus are of great interest because of their possible use as
actuator materials. The performance of an actuator material is normally
characterized by its force–stroke curve, but little is known about the
force–stroke behavior of hydrogels. We use the theory of the ideal
elastomeric gel to predict the force–stroke curves of a
temperature-sensitive hydrogel and introduce an experimental method for
measuring the curve. The technique is applied to PNIPAm hydrogels with
low cross-link densities. The maximum force generated by the hydrogel
increases with increasing cross-link density, while the maximum stroke

Wei Hong's picture

Modeling mechano-chromatic lamellar gels

Consisting of alternating swelling and nonswelling polymeric layers (SLs and NLs), lamellar gels are 1D photonic crystals with tunable optical properties.  The lamellar structure induces a constraint between the SLs and the NLs, resulting in an anisotropic swelling behavior coupled with deformation.

Some Analytical Formulas for the Equilibrium States of a Swollen Hydrogel Shell

Dear Colleagues,
I wish to bring to you my recent work with my supervisor Hui-Hui Dai on "Some  Analytical Formulas for the Equilibrium States of a Swollen Hydrogel Shell". Below is the abstract and attached is the preprint of the article. I will very much appreciate your comments and suggestions.

Xuanhe Zhao's picture

Postdoctoral Position at Duke Soft Active Materials Laboratory

The Duke Soft Active Materials Laboratory directed by Prof Xuanhe Zhao is seeking a highly motivated postdoctoral fellow to study mechanics of polymers and hydrogels with applications in tissue regenerations. The work will be carried out in close collaboration with the Duke Orthopaedic Bioengineering Laboratory directed by Prof Farshid Guilak.

Rui Huang's picture

Swell induced surface instability of confined hydrogel layers

A previous work suggested a critical condition to form surface creases in elastomers and gels. For elastomers, the critical condition seems to have closed a gap between experimental observations (e.g., by bending a rubber block) and the classical instability analysis by Biot. For gels, however, experiments have observed a wide range of critical swelling ratios, from around 2 to 3.7. Here we present a linear perturbation analysis for swollen hydrogels confined on a rigid substrate, which predicts critical swelling ratios in a similar range.

Cai Shengqiang's picture

A theory of constrained swelling of a pH-sensitive hydrogel

Many engineering devices and natural phenomena involve gels that swell under the constraint of hard materials. The constraint causes a field of stress in a gel, and often makes the swelling inhomogeneous even when the gel reaches a state of equilibrium. To analyze inhomogeneous swelling of a pH-sensitive gel, we implement a finite element method in the commercial software ABAQUS.  The program is attached here.  Contact Shenqiang Cai (shqcai@gmail.com) for a description of the program.

Rui Huang's picture

Effect of constraint on swelling of hydrogels and formation of surface creases

Inspired by recent works by Wei Hong , Xuanhe Zhao, Zhigang Suo, and their coworkers, we started a project on hydrogels, with particular interest in various instability patterns observed in experiments. The attachment is our first manuscript on this subject. Through this work we hope to achieve the following:

Zhigang Suo's picture

Mechanics of Soft Active Materials

At the invitation of David Clarke on behalf of the UCSB/Los Alamos Institute of Multiscale Materials and Structures, I gave the following three lectures:

  1. Large deformation and instability in dielectric elastomers
  2. Large deformation and instability in swelling polymeric gels
  3. Mechanics and electrochemistry of polyelectrolyte gels

The abstracts follow, and the slides are attached at the end of this post.

Zhigang Suo's picture

Large deformation and instability in gels

I'm attaching slides of a talk that I gave yesterday at the Schlumberger-Doll Research Center.  In preparing the talk, I made liberal use of slides prepared by Wei Hong for his own presentations.  The talk is mainly based on the following papers:

Xuanhe Zhao's picture

Inhomogeneous and anisotropic equilibrium state of a swollen hydrogel containing a hard core

A polymer network can imbibe water from environment and swell to an equilibrium state. If the equilibrium is reached when the network is subject to external mechanical constraint, the deformation of the network is typically anisotropic, and the concentration of water inhomogeneous.  Such an equilibrium state in a network constrained by a hard core is modeled here with a nonlinear differential equation.  The presence of the hard core markedly reduces the concentration of water near the interface and causes high stresses.

Wei Hong's picture

Drying-induced bifurcation in a hydrogel-actuated nanostructure

Hydrogels have enormous potential for making adaptive structures in response to diverse stimuli.  In a structure demonstrated recently, for example, nanoscale rods of silicon were embedded vertically in a swollen hydrogel, and the rods tilted by a large angle in response to a drying environment (Sidorenko, et al., Science 315, 487, 2007).  Here we describe a model to show that this behavior corresponds to a bifurcation at a critical humidity, analogous to a phase transition of the second kind.

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