Mesh Size Control of Polymer Fluctuation Lubrication in Gemini Hydrogels

Urueña, Juan Manuel; Pitenis, Angela A.; Nixon, Ryan; Schulze, Kyle D.; Angelini, Thomas E.; Sawyer, W. Gregory

doi:10.1016/j.biotri.2015.03.001

Cited by 108 publications

(117 citation statements)

References 54 publications

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“…The lubrication of biological interfaces is undoubtedly one of the most complicated and challenging systems to theorists and experimentalists; in part, because biology is fundamentally alive, evolving, and dynamic. In many ways high water content synthetic gels parallel these interfaces, and recent work with hydrogels in matched (Gemini) configurations has shed some light on the basic dissipative mechanisms associated with aqueous lubrication [1][2][3]. In these experiments the assumptions have been that although submerged and predominately aqueous, they are self-lubricated in direct contact not under hydrodynamic or fluid film lubrication.…”

Section: Introductionmentioning

confidence: 99%

“…In spite of these differences, hydrogels remain a convenient and potentially very useful system for theoretical and experimental studies of aqueous lubrication. The ability to specify the water content, polymer concentration, and mesh size, while maintaining optical transparency with excellent long-term stability [8] makes hydrogels nearly ideal specimens for tribological studies that aim to explore the sensitivity of gel friction to perturbations in stress, speed, and other contact conditions including surface roughness, materials, and contact aging [1][2][3]9,10].…”

Section: Introductionmentioning

confidence: 99%

“…Hydrogels provide a unique platform in which to study aqueous lubrication. The mechanics of hydrogels are well studied, and a single parameter, mesh size ( ), determines the hydraulic permeability ( ) [23], osmotic pressure ( ) [24], elastic modulus (E) [24], and recently was found to be the dominant parameter in the scaling of friction coefficient ( ) [3]. As friction coefficient is almost always a system parameter, and not a material property, the mesh size control of friction is somewhat misleading.…”

Section: Introductionmentioning

confidence: 99%

“…However, it is an exciting concept that has revealed a surprising result: large mesh size and high water content hydrogels were the lowest friction systems under identical loads and sliding speeds for a wide variety of mesh sizes. Further, work exploring the response to Gemini hydrogel tribology over a wide range in sliding speeds has revealed transitions in behavior that are thought to be linked to the polymer relaxation times ( ) and the ratio of the mesh size to the sliding velocity ( /v) [2,3]. However, all of these previous studies were performed under constant load conditions.…”

Section: Introductionmentioning

confidence: 99%

“…All sliding experiments were performed completely submerged in ultrapure water in the Gemini configuration. The hydrogels were made from polyacrylamide ( ~7 nm) following a method previously used and characterized via small angle X-ray scattering (SAXS) as reported in [3].…”

Section: Introductionmentioning

confidence: 99%

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Normal Load Scaling of Friction in Gemini Hydrogels

et al. 2018

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Health and physiology are critically dependent on the ability of soft, permeable, and aqueous materials (e.g. cartilage, cells, and extracellular matrix) to provide lubrication over a wide range of speeds and contact stresses. Living cells and tissues present tremendous handling and experimental challenges for fundamental biotribology studies. Synthetic high water content hydrogels, designed to share similar mechanical and transport properties of biomaterials, can provide fundamental insights into the basic dissipative mechanisms associated with aqueous lubrication. Recent studies investigating the response of self-mated (Gemini) hydrogels to a wide range of sliding speeds under constant load conditions revealed transitions in friction behavior that may be associated with polymer relaxation time and contact time for a surface mesh during sliding (mesh size divided by the sliding speed). Here, the extent to which contact pressure and contact area affect hydrogel friction behavior was explored by changing the applied load over two orders of magnitude (0.1-20 mN) and the sliding speed over four orders of magnitude (10 m/s-100 mm/s). Oscillating pin-on-disk microtribological experiments were performed in ultrapure water for Gemini polyacrylamide hydrogels (average mesh size ~7 nm). Friction coefficient decreased across all ranges of sliding speed with increasing applied load, consistent with predictions of contact area scaling non-linearly with applied load and pressureindependent surface shear stresses. The contact area for Gemini hydrogel interfaces under these conditions has been shown to follow Hertzian contact mechanics theory, and supports the scaling of friction coefficient in the speed-independent regime that follows ~ Fn −1/3 .

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Normal Load Scaling of Friction in Gemini Hydrogels

et al. 2018

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Polymeric Hydrogels—A Promising Platform in Enhancing Water Security for a Sustainable Future

Loo

Vásquez

Athanassiou

et al. 2021

Adv Materials Inter

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anthropogenic activities that have led to saline intrusion and contamination of the existing freshwater sources, making the current approaches for water treatment even more difficult and costly. [2][3][4] This, in combination with the continuously rising global water demand, results in a rather pessimistic prediction that an additional 2000 billion m 3 of freshwater supply will be required by 2030 to meet the global demand, assuming no gains on the current state of water-production capacity and efficiency. [5,6] As the existing freshwater sources are being depleted, there is a growing need for utilization of a broader range of water sources beyond the conventional ones, that is, brackish water, seawater, wastewater, and atmospheric moisture. [7] On top of that, there is a call for a greater focus on enhancing water security, particularly for the poor and vulnerable populations, as water scarcity is more critical in these geographical regions due to the lack of access to conventional infrastructure and power sources to produce clean water. [1,8,9] This, in addition to the increasing intensity and frequency of climate-related disasters, present unique demands, such as simple and off-grid operations, for water technologies (WTs) that can be deployed to manage the constraints imposed by these circumstances. [10]

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Lubrication Mechanism of Surface‐Attached Hydrogel Layers in Sliding Contact

Bahrami

Houérou

Rühe

2022

Adv Materials Inter

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Swollen, surface‐attached hydrogel layers in sliding contact exhibit unusual friction properties. To study this phenomenon, hydrogel layers covalently bonded to solid substrates are generated by CH insertion crosslinking. Brief UV irradiation of thin layers of photoreactive prepolymers leads to simultaneous crosslinking of the polymer chains and attachment of the network to the substrate. As the surface‐attached hydrogel layers can only swell perpendicular to the surface, and the polymer subchains on the two sides of the friction pair cannot interpenetrate for entropic reasons, adhesion in such friction pairs is negligible. In this work, the tribological behavior of surface‐attached hydrogel pairs is investigated as a function of load and sliding velocity. It is observed that for very thin films, the indentation and accordingly the friction is a strong function of the film thickness and the role of the chain confinement on the lubrication of surface‐attached hydrogels is discussed. A model for the friction mechanism of such systems is developed.

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Mesh Size Control of Polymer Fluctuation Lubrication in Gemini Hydrogels

Cited by 108 publications

References 54 publications

Normal Load Scaling of Friction in Gemini Hydrogels

Normal Load Scaling of Friction in Gemini Hydrogels

Polymeric Hydrogels—A Promising Platform in Enhancing Water Security for a Sustainable Future

Lubrication Mechanism of Surface‐Attached Hydrogel Layers in Sliding Contact

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