Insight into the Viscous and Adhesive Contributions to Hydrogel Friction

Shoaib, Tooba; Espinosa‐Marzal, Rosa M.

doi:10.1007/s11249-018-1045-7

Cited by 34 publications

(45 citation statements)

References 56 publications

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“…A dependence of friction on sliding velocity has been reported in many subsequent studies and over a wide range of conditions. Although these studies have also shown that hydrogel friction also varies with the chemical composition of the polymer [20][21][22], monomer and crosslinking concentrations [23,24], and surface roughness [25,26], a detailed description of these results is out of the scope of this review.…”

Section: Property Equationmentioning

confidence: 99%

“…However, MD simulations of the tribological performance of neutral polymer (dextran) brushes against a hard wall recently showed a good agreement with experiments only after consideration of an effective polymer-wall attraction that leads to intermittent contact between polymer chains and wall [45]. The direct contact between the polymer and a solid surface has also been observed either directly via imaging [46,47] or indirectly through the measured stick-slip [23,24]. This reminds us that the existence of a thin film is not universal, but strongly depends on the chemical interactions between the polymer and the solid countersurface.…”

Section: Hydration Lubricationmentioning

confidence: 99%

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Advances in Understanding Hydrogel Lubrication

Shoaib

Espinosa‐Marzal

2020

Colloids and Interfaces

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Since their inception, hydrogels have gained popularity among multiple fields, most significantly in biomedical research and industry. Due to their resemblance to biological tribosystems, a significant amount of research has been conducted on hydrogels to elucidate biolubrication mechanisms and their possible applications as replacement materials. This review is focused on lubrication mechanisms and covers friction models that have attempted to quantify the complex frictional characteristics of hydrogels. From models developed on the basis of polymer physics to the concept of hydration lubrication, assumptions and conditions for their applicability are discussed. Based on previous models and our own experimental findings, we propose the viscous-adhesive model for hydrogel friction. This model accounts for the effects of confinement of the polymer network provided by a solid surface and poroelastic relaxation as well as the (non) Newtonian shear of a complex fluid on the frictional force and quantifies the frictional response of hydrogels-solid interfaces. Finally, the review delineates potential areas of future research based on the current knowledge.

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Section: Property Equationmentioning

confidence: 99%

Section: Hydration Lubricationmentioning

confidence: 99%

Advances in Understanding Hydrogel Lubrication

Shoaib

Espinosa‐Marzal

2020

Colloids and Interfaces

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“… 1 – 4 , 6 However, CoF measurement results greatly depend on the testing conditions, which can make the replication and interpretation of results difficult. 6 , 7 In addition, kinetic friction force does not reflect the adhesion force between two surfaces, which fundamentally distinguishes the CoF measurement from the adhesive strength measurement of cornea epithelium against SCLs. 8 Therefore, we present a customized device to directly measure the adhesive strength at the corneal epithelial cells/SCLs interface through relaxation experiments and suggest a new parameter, the residual modulus, as a candidate material property complementary to CoF for screening and developing contact lens formulations.…”

Section: Introductionmentioning

confidence: 99%

Tuning Corneal Epithelial Cell Adhesive Strength with Varying Crosslinker Content in Silicone Hydrogel Materials

Liu

Scales

Fuller

2020

Trans. Vis. Sci. Tech.

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To quantify the effect of silicone hydrogel crosslink density on the adhesion at corneal epithelial cells/silicone hydrogel contact lens interface. Methods: A custom-built rheometer, referred to as the live cell monolayer rheometer, was used to measure the adhesive strengths between corneal epithelial cell monolayers and silicone hydrogel lens surfaces. The resulting stress relaxations of senofilcon Aderived silicone hydrogel materials with varying crosslinking densities and delefilcon A were tested. Senofilcon Alike materials labeled L1, L2, L3, L4, and L5 contained crosslinker concentrations of 1.2, 1.35, 1.5, 1.65, and 1.8 wt%, respectively. The residual modulus measured from the live cell monolayer rheometer provided a direct indication of adhesive attachment. Results: Within the senofilcon-derived series, the adhesive strength shows a surprising minimum with respect to crosslink density. Specifically, L1 (1.20%) has the highest adhesive strength of 39.5 ± 11.2 Pa. The adhesive strength diminishes to a minimum of 11.2 ± 2.1 Pa for L3, whereafter it increases to 14.5 ± 2.5 Pa and 18.1 ± 5.1 Pa for L4 and L5, respectively. The delefilcon A lens exhibits a comparable adhesive strength of 27.8 ± 6.3 Pa to L1. Conclusions: These results demonstrated that increasing the crosslink density has a nonmonotonic influence on the adherence of lenses to mucin-expressing corneal epithelial cells, which suggests a competition mechanism at the cell/lens interface. Translational Relevance: Because the adhesiveness of contact lenses to ocular tissues may impact the comfort level for lens wearers and affect ease of removal, this study suggests that lens adhesion can be optimized through the control of crosslink density.

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“…The measurements associated with these theories have identified a speed-independent regime at sliding speeds slow enough to avoid viscous drag penalties (Fig. 2) [41,47,48].…”

Section: Hydrogel Self-mated 'Gemini' Frictionmentioning

confidence: 99%

“…Some groups are also beginning to consider this fluid drainage during sliding from the near-surface region in a 'hydrodynamic' sense, in which the fluid motion controls the deformation, and thus the friction response [42,[73][74][75]. Finally, the combination of speed-dependent effects and surface adhesions has been considered in detail at the nanoscale [47].…”

Section: Fast-and Slow-sliding Speeds Regimesmentioning

confidence: 99%

Review: Friction and Lubrication with High Water Content Crosslinked Hydrogels

et al. 2020

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As soft aqueous hydrogels have moved from new materials to the basis for real engineered devices in the last 20 years, their surface friction and lubrication are emerging as critical aspects of their function. The flexibility to alter and augment their mechanical and surface properties through control of the crosslinked 3D polymer networks has produced materials with diverse surface behaviors, even with the relatively simple composition of a single monomer and crosslink chemistry. Correspondingly with new understandings of the bulk behavior of hydrogels has been the identification of the mechanisms that govern the lubricity and frictional response under dynamic sliding conditions. Here we review these efforts, closely examining and identifying the internal and external influences that drive tribological response in high water content crosslinked hydrogels. The roles of surface structure, elasticity, contact response, charge, water interaction and water flow are addressed here as well as current synthesis and testing methods. We also collect open questions as well as the future needs to fully understand and exploit the surface properties of hydrogels for sliding performance.

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Insight into the Viscous and Adhesive Contributions to Hydrogel Friction

Cited by 34 publications

References 56 publications

Advances in Understanding Hydrogel Lubrication

Advances in Understanding Hydrogel Lubrication

Tuning Corneal Epithelial Cell Adhesive Strength with Varying Crosslinker Content in Silicone Hydrogel Materials

Review: Friction and Lubrication with High Water Content Crosslinked Hydrogels

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