Project

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Hydrogel adhesion at small scales

Applicant Style Robert
Number 172827
Funding scheme Project funding (Div. I-III)
Research institution Departement Materialwissenschaft ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Mechanical Engineering
Start/End 01.04.2017 - 31.03.2021
Approved amount 251'050.00
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All Disciplines (2)

Discipline
Mechanical Engineering
Material Sciences

Keywords (4)

Solid surface stress; Hydrogel; Contact mechanics; Adhesion

Lay Summary (German)

Lead
Hydrogele sind eines der wichtigsten weichen Materialien, nicht nur weil sie Bausteine der neuesten innovativen Technologien sind, sondern auch weil unsere Körper zum grössten Teil aus Hydrogelen bestehen. Trotz der Allgegenwärtigkeit dieser Gele überraschen sie immer noch mit ihren Verhalten. Vor Kurzem wurde z.B. gezeigt, dass Hydrogele, auf welchen ein feines Pulver verteilt ist, aneinanderhaften. Hydrogele ohne Pulver täten dies normalerweise nicht. Zusätzlich wurde bewiesen, dass gerade weil die Hydrogele so weich sind, die Oberflächenspannung eine viel grössere Rolle spielt als erwartet. Dies drückt sich in deren Klebrigkeit und Verformungsverhalten aus. In diesem Projekt erforschen wir, wie Hydrogele haften und sich verformen. Die Ergebnisse werden zu weiteren Entwicklungen in mehreren Bereichen, von Wundversorgung bis zur Mikroindentierung auf Weichgewebe, führen.
Lay summary

Als Hauptziel untersuchen wir zu Beginn, wie kleine Prüfköpfe an Gelen haften und wie dieses Verhalten von der etablierten Theorie abweicht. Danach werden wir die Oberflächenspannung direkt messen, um deren Rolle im Haften besser zu verstehen. Dadurch werden wir neue Theorien entwickeln können, um das Verhalten weicher Hydrogele genauer vorauszusagen.

Unsere Ergebnisse werden von allgemeiner Bedeutung sein. Durch unsere Experimente werden wir zeigen wie die Oberflächenspannung eines Hydrogels von dessen Eigenschaften abhängt. Des Weiteren werden wir ein Grundverständnis der Haftung dieser Gele entwickeln. Dadurch unterstützen wir die Entwicklung besserer Klebstoffe für weiche Materialien, die z.B. in flexibler Elektronik oder biomimetischen Materialien eingesetzt werden können. Zusätzlich können Forscher die entwickelte Theorie verwenden, um die mechanischen Eigenschaften weicher Materialien präzise zu untersuchen.

Direct link to Lay Summary Last update: 13.04.2017

Lay Summary (English)

Lead
Hydrogels are one of the most important soft materials, both because of their use in cutting-edge soft technology, and because they make up most of our bodies. However due to their softness, they can behave very differently to how we’d expect. For example, recent work has shown how two pieces of soft tissue can be glued together simply by spreading a dry powder at their surfaces and then holding them together. Other work has shown that the surface tension of a hydrogel (something typically overlooked), can control how it sticks to surfaces, and how it responds when indented. In this project, we will investigate how hydrogels adhere and deform. This will advance many fields, from closing wounds in surgery, to microindentation of soft tissue, to creating soft composites for new technology.
Lay summary

As major goals, firstly we will investigate how small indenters stick to hydrogels, and how this differs from what we usually expect from established theory. Secondly, we will directly measure the surface tension of hydrogels, so that we can understand when it will be important for hydrogel adhesion. These will allow us to develop new rules that accurately describe how soft materials adhere together and deform.

 

Our results will be broadly relevant. We will develop a basic understanding of how hydrogels adhere together and deform. This will help develop better adhesives for soft materials (for applications like surgery, flexible electronics, and creating soft, ‚biomimetic‘ materials). Our work will also allow scientists to accurately measure the mechanical properties of small amounts of soft materials (e.g. in understanding the microstructure of our bodies). Furthermore, it will provide the first direct measurements of surface tensions in hydrogels and how these vary with gel properties.

Direct link to Lay Summary Last update: 13.04.2017

Responsible applicant and co-applicants

Employees

Publications

Publication
Transient supramolecular assembly of a functional perylene diimide controlled by a programmable pH cycle
Panzarasa Guido, Torzynski Alexandre L., Sai Tianqi, Smith-Mannschott Katrina, Dufresne Eric R. (2020), Transient supramolecular assembly of a functional perylene diimide controlled by a programmable pH cycle, in Soft Matter, 16(3), 591-594.
Supramolecular assembly by time-programmed acid autocatalysis
Panzarasa Guido, Sai Tianqi, Torzynski Alexandre L., Smith-Mannschott Katrina, Dufresne Eric R. (2020), Supramolecular assembly by time-programmed acid autocatalysis, in Molecular Systems Design & Engineering.
Liquid-Liquid Phase Separation in an Elastic Network
Style Robert W., Sai Tianqi, Fanelli Nicoló, Ijavi Mahdiye, Smith-Mannschott Katrina, Xu Qin, Wilen Lawrence A., Dufresne Eric R. (2018), Liquid-Liquid Phase Separation in an Elastic Network, in Physical Review X, 8(1), 011028-011028.

Collaboration

Group / person Country
Types of collaboration
Soft Matter Physics Laboratory, Sungkyunkwan University Korean Republic (South Korea) (Asia)
- Exchange of personnel

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
Wetting on Soft or Microstructured Surfaces Talk given at a conference Surface stresses in soft gels 11.04.2019 Bad Honnef, Germany Style Robert;
Liquids @ Interfaces Poster Surface stresses in soft solids 22.10.2018 Bordeaux, France Style Robert;
GRS Soft Condensed Matter Physics (Soft Matter in and out of Equilibrium) Poster Adhesion on soft hydrogels 13.08.2017 Colby-Sawyer College, United States of America Smith-Mannschott Katrina;
GRS and GRC Science of Adhesion (Molecular Insight to Understand Fracture and Adhesion) Poster Adhesion on soft hydrogels 22.07.2017 South Hadley, United States of America Smith-Mannschott Katrina;


Abstract

Hydrogels are one of the most important classes of soft materials due to their versatility and use across many fields.For example, they are one of nature's fundamental building blocks and they are widely used in fields ranging from tissue engineering to drug delivery, diapers, contact lenses, stretchable electronics, friction reduction, and novel stimuli-responsive materials. Across all of their uses, their adhesive and contact behaviour is crucial. For example, in surgery wounds in soft tissue need to be glued shut quickly, effectively and without toxicity. Useful soft composites and coatings require hydrogels to be well-gripped or bonded to other materials. Drugs can be targeted to specific parts of the body by understanding how drug-loaded particles adhere to natural hydrogels in the body.Our scientific understanding of hydrogel adhesion and contact currently relies heavily on classical contact mechanics.However, our recent work has shown that classical contact and adhesion results are likely to fail at small scales in soft hydrogels.This is for several reasons.For example, the gel's surface stress (the equivalent of a liquid's surface tension) should become important for contact areas smaller than a critical elastocapillary lengthscale; this will significantly reduce a hydrogel's adhesion.Furthermore, there can be significant phase separation of a hydrogel in contact zones, which will also modify contact behaviour.The role of such effects has not yet been experimentally studied, despite wide usage of classical contact mechanics in modelling small-scale hydrogel adhesion.Thus this project has two key aims:1) To characterise small-scale contact and adhesion in hydrogels, in particular investigating how adhesive behaviour deviates from classical predictions.2) To directly measure the surface stress of hydrogels, and use this to develop new models describing how surface stresses affect hydrogel adhesion/indentation results.We will achieve our aims with a series of experiments that build upon our established expertise.We will develop hydrogel substrates that are marked with fluorescent nanobeads, and indent these with spherical silica particles with a range of sizes.Using confocal microscopy and direct imaging, we can precisely track the embedded nanobeads as the hydrogel adheres to and conforms around the silica particles.Thus we can accurately characterise particle adhesion while changing parameters such as the type of hydrogel, its degree of swelling, and stiffness.We will also use a nano-indenter to characterise the indentation behaviour of small particles.These experiments will allow us to infer the surface stress of the hydrogel.Finally, we will use the experiments to derive laws that describe small-scale adhesive behaviour in soft hydrogels that can be used in modelling, and interpretation of indentation experiments.Our results will be broadly relevant.For example, from a fundamental science perspective, our work will measure hydrogel surface stresses and how they depend on parameters such as osmotic pressure and gel swelling for the first time.Our work will also quantify how hydrogel adhesion is modified at small scales.This will be useful for many applications, including guiding optimisation of new, nano-particle-based hydrogel adhesion techniques.Furthermore, many experimentalists rely on nano-indentation techniques to measure local properties of hydrogels and similar biological material (e.g. through Atomic Force Microscopy).Currently, interpretation of such data relies on potentially-flawed theory, and our work will provide correct expressions that will enable accurate measurements.
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