Clustering and Self‐Recovery of Slanted Hydrogel Micropillars

Lee, Hyemin; Kim, Jun‐Hyun; Wu, Guang; Lee, Hae-Min; Kim, Jaekyoung; Kwon, Dokyeong; Yang, Shu; Kim, Chang‐Koo; Yoon, Hyunsik

doi:10.1002/admi.201801142

Cited by 8 publications

(11 citation statements)

References 24 publications

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“…Such an energy-based approach has an advantage in that the model does not require the direction of forces, such as adhesion force and bending force of the micropillars. [22,23] We analyze one type of cluster as an example: four micropillars cluster at the center. As the micropillars are symmetric, we first analyze two of them (Figure 3a).…”

Section: Modeling Of Clustering Transitionmentioning

confidence: 99%

“…To determine these two components, we measure contact angles of two known liquids: glycerin and ethylene glycol. The surface energy of the hydrogel is measured as 174 AE 23 mJ m À2 at 20 C and 151 AE 9 mJ m À2 at 80 C. Whereas calculating adhesion energy by using van der Waals force requires values that are hard to be measured, such as the Hamaker constant, atomic arrangement between two surfaces, and cut-off distance, [22,23] we use reliable the surface tension of liquids and contact angles that can be easily measured.…”

Section: Modeling Of Clustering Transitionmentioning

confidence: 99%

“…[9] The micropillars can be temporarily de-clustered by combing or drying them, but they will eventually cluster in water because the de-clustered state is still metastable. [22,23] Consequently, whereas clustering has shown various functions, de-clustering has been rarely studied.…”

Section: Introductionmentioning

confidence: 99%

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Clustering Transition in Thermo‐Responsive Micropillars

et al. 2022

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Clustering of high‐aspect‐ratio micropillars is a common phenomenon in nature, and has been utilized to build complex and large‐scale microarchitectures. To induce the clustering, the micropillars should be prepared to be metastable, so that they cluster under perturbation, such as the drying of water. Consequently, once micropillars cluster, they cannot de‐cluster spontaneously. This article shows that the micropillars of thermo‐responsive hydrogels can cluster and de‐cluster spontaneously and reversibly by changing the temperature. This behavior is called clustering transition. When the temperature is low, the micropillars swell and become soft. When the temperature is high, the micropillars de‐swell and become stiff. This phase transition alters the lowest energy state of the system, resulting in a reversible clustering transition. To demonstrate, high‐aspect‐ratio micropillars of poly(N‐isopropylacrylamide‐co‐acrylamide) hydrogels are fabricated through a soft‐molding technique. The micropillars show the clustering transition, and the behavior is studied using a thermodynamic model. By controlling the temperature, the micropillars grip and release microparticles on‐demand.

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Section: Modeling Of Clustering Transitionmentioning

confidence: 99%

Section: Modeling Of Clustering Transitionmentioning

confidence: 99%

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Clustering Transition in Thermo‐Responsive Micropillars

et al. 2022

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“…High-aspect-ratio pillars (HAPs) are ideal structures for the fabrication of functional surfaces owing to their structural characteristics. − For instance, pillars formed in a uniform array exhibit a straight or clustered shape based on the elastic modulus of the material used. , When the elastic modulus of the material of the pillars is high, the structures remain straight, and when the elastic modulus is low, they form clusters readily. This is because HAPs made of low-elastic-modulus materials, such as elastomers, are intrinsically unstable.…”

Section: Introductionmentioning

confidence: 99%

“…Nevertheless, they can be made to exhibit new functionalities by adjusting the degree of aggregation of the pillars. For example, clustered pillars can be exploited to trap tiny particles or used as tissue scaffolds to guide stem cell differentiation. , Therefore, the ability to maintain the straight shape of high-aspect-ratio pillars and the ability to control their clustering behavior are both important factors.…”

Section: Introductionmentioning

confidence: 99%

Capillary-Induced Clustering of Thermoresponsive Micropillars

Choi

Lim

Kim

et al. 2021

ACS Appl. Mater. Interfaces

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In this study, we demonstrate the controllable clustering of thermoresponsive high-aspect-ratio hydrogel pillars by modulating the elastic modulus of the materials. Generally, high-aspect-ratio polymeric pillars readily cluster owing to the effect of capillary force and adhesion. However, this unstable behavior hinders the implementation of various functionalities such as wetting, adhesion, and energy harvesting on surfaces with such pillars. Conversely, clustering behavior may be required in the case of digital microfluidic platforms that grip tiny particles or perform biological and chemical analyses. Therefore, it is necessary to develop a reliable method for controlling the clustering behavior. To this end, we fabricate high-aspect-ratio pillars that exhibit capillary-induced clustering behavior based on the cross-linker density of the thermoresponsive hydrogel and the temperature of the surrounding environment. Through experimental and theoretical analyses, a criterion for controlling the clustering and recovery behavior of the fabricated pillars is determined. The established criterion is employed to fabricate a smart mobile camera lens cover that can produce blurred and deblurred images based on optical variations resulting from the clustering and recovery of the pillars. The results of this study can be used to fabricate high-aspect-ratio polymeric pillars for use in diverse applications.

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3D Printing of Strong and Tough Double Network Granular Hydrogels

Hirsch

Charlet

Amstad

2020

Adv Funct Materials

113

127

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Many soft natural tissues display a fascinating set of mechanical properties that remains unmatched by manmade counterparts. These unprecedented mechanical properties are achieved through an intricate interplay between the structure and locally varying the composition of these natural tissues. This level of control cannot be achieved in soft synthetic materials. To address this shortcoming, a novel 3D printing approach to fabricate strong and tough soft materials is introduced, namely double network granular hydrogels (DNGHs) made from compartmentalized reagents. This is achieved with an ink composed of microgels that are swollen in a monomer‐containing solution; after the ink is additive manufactured, these monomers are converted into a percolating network, resulting in a DNGH. These DNGHs are sufficiently stiff to repetitively support tensile loads up to 1.3 MPa. Moreover, they are more than an order of magnitude tougher than each of the pure polymeric networks they are made from. It is demonstrated that this ink enables printing macroscopic, strong, and tough objects, which can optionally be rendered responsive, with high shape fidelity. The modular and robust fabrication of DNGHs opens up new possibilities to design adaptive, strong, and tough hydrogels that have the potential to advance, for example, soft robotic applications.

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Clustering and Self‐Recovery of Slanted Hydrogel Micropillars

Cited by 8 publications

References 24 publications

Clustering Transition in Thermo‐Responsive Micropillars

Clustering Transition in Thermo‐Responsive Micropillars

Capillary-Induced Clustering of Thermoresponsive Micropillars

3D Printing of Strong and Tough Double Network Granular Hydrogels

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