Oxygen inhibition of free-radical polymerization is the dominant mechanism behind the “mold effect” on hydrogels

Simič, Rok; Mandal, Joydeb; Zhang, Kaihuan; Spencer, Nicholas D.

doi:10.1039/d1sm00395j

Cited by 52 publications

(37 citation statements)

References 33 publications

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“…Once the microgels are created via a straightforward emulsion polymerization, our composites are fabricated by mixing the ingredients together, briefly degassing, and then shaping with a mold, or via extrusion. In contrast, chemically crosslinked gels typically require oxygen-free conditions [21], polyvinyl alcohol gels require freeze-thaw [39] or annealing and re-swelling [15], and polyampholyte and double network gels require dialysis or re-swelling steps [13,40]. Furthermore, the mechanical properties of our composites vary surprisingly little as they swell.…”

Section: Discussionmentioning

confidence: 99%

“…The resulting materials show fracture properties that compete with (and can actually outperform) the toughest available hydrogels, while their stiffness is surprisingly constant as they swell. The preparation method is not oxygen-sensitive (unlike many hydrogel syntheses [21]), and is based on materials such as silicones and polyurethanes -common sealants with good adhesive properties. We show that the materials are highly adaptable, as they can be straightforwardly formed into complex geometries with non-uniform structures.…”

Section: Introductionmentioning

confidence: 99%

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Hydroelastomers: soft, tough, highly swelling composites

Moser¹,

Feng²,

Yaşa³

et al. 2022

Preprint

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Inspired by the cellular design of plant tissue, we present a new approach to make versatile, tough, highly water-swelling composites. We embed highly swelling hydrogel particles inside tough, water-permeable, elastomeric matrices. The resulting composites, which we call hydroelastomers, show little softening as they swell, and have excellent fracture properties that match those of the best-performing, tough hydrogels. Our composites are straightforward to fabricate, based on commercial materials, and can easily be molded or extruded to form shapes with complex swelling geometries. Furthermore, there is a large design space available for making hydroelastomers, since one can use any hydrogel as the dispersed phase in the composite, including hydrogels with stimuliresponsiveness. These features should make hydroelastomers excellent candidates for use in soft robotics and swelling-based actuation, or as shape-morphing materials, while also being useful as hydrogel replacements in a wide range of other fields.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Hydroelastomers: soft, tough, highly swelling composites

Moser¹,

Feng²,

Yaşa³

et al. 2022

Preprint

View full text Add to dashboard Cite

show abstract

“…Once the microgels are created via emulsion polymerization, our composites are fabricated by mixing the ingredients together, briefly degassing, and then shaping with a mold, or via extrusion. In contrast, chemically crosslinked gels typically require oxygen-free conditions, 7 polyvinyl alcohol gels require freeze–thaw 44 or annealing and re-swelling, 15 and polyampholyte and double network gels require dialysis or re-swelling steps. 13,45…”

Section: Discussionmentioning

confidence: 99%

“…The limited adoption of hydrogels is, in large part, due to various drawbacks of common, bulk-produced hydrogels. For example, simple synthetic hydrogels typically have low stretchability, are brittle 6 , and are not straightforward to fabricate as they rely on free-radical polymerization, which is oxygen sensitive 7 . Hy-drogels can also be tricky to adhere to most surfaces 8 , and will normally dehydrate in air 9 .…”

Section: Introductionmentioning

confidence: 99%

Hydroelastomers: soft, tough, highly swelling composites

et al. 2022

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“…While it would be ideal if this soft surface layer were homogeneous, providing a clear laminate structure, that is unlikely due to its formation at the interface between the prepolymer solution and a mold. The process of chemical cross-linking could involve effects from the surface energy of the mold material, adsorbed species on the mold, and the depletion of available polymer and cross-linker as the synthesis comes to completion . Thus, this soft surface layer also has a gradient of density from the bulk out to the most superficial polymer chains extending into an aqueous bath (Figure B).…”

Section: Introductionmentioning

confidence: 99%

Soft Contact Mechanics with Gradient-Stiffness Surfaces

2022

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The stiffness in the top surface of many biological entities like cornea or articular cartilage, as well as chemically cross-linked synthetic hydrogels, can be significantly lower or more compliant than the bulk. When such a heterogeneous surface comes into contact, the contacting load is distributed differently from typical contact models. The mechanical response under indentation loading of a surface with a gradient of stiffness is a complex, integrated response that necessarily includes the heterogeneity. In this work, we identify empirical contact models between a rigid indenter and gradient elastic surfaces by numerically simulating quasi-static indentation. Three key case studies revealed the specific ways in which (I) continuous gradients, (II) laminate-layer gradients, and (III) alternating gradients generate new contact mechanics at the shallow-depth limit. Validation of the simulation-generated models was done by micro- and nanoindentation experiments on polyacrylamide samples synthesized to have a softer gradient surface layer. The field of stress and stretch in the subsurface as visualized from the simulations also reveals that the gradient layers become confined, which pushes the stretch fields closer to the surface and radially outward. Thus, contact areas are larger than expected, and average contact pressures are lower than predicted by the Hertz model. The overall findings of this work are new contact models and the mechanisms by which they change. These models allow a more accurate interpretation of the plethora of indentation data on surface gradient soft matter (biological and synthetic) as well as a better prediction of the force response to gradient soft surfaces. This work provides examples of how gradient hydrogel surfaces control the subsurface stress distribution and loading response.

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Oxygen inhibition of free-radical polymerization is the dominant mechanism behind the “mold effect” on hydrogels

Abstract: Hydrogel surfaces are of great importance in numerous applications ranging from cell-growth studies and hydrogel-patch adhesion to catheter coatings and contact lenses. A common method to control the structure and...

Cited by 52 publications

References 33 publications

Hydroelastomers: soft, tough, highly swelling composites

Hydroelastomers: soft, tough, highly swelling composites

Hydroelastomers: soft, tough, highly swelling composites

Soft Contact Mechanics with Gradient-Stiffness Surfaces

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