Synthesis and Characterization of Zwitterionic Polymer Brush Functionalized Hydrogels with Ionic Responsive Coefficient of Friction

Abstract

Freeze–thaw poly­(vinyl alcohol) hydrogels (PVA-H) offer great potential for several biomedical applications due to their biomimetic mechanical properties and biocompatibility. Despite these advantages, the use of PVA-H for load bearing applications has been limited due to poor performance in boundary lubrication compared to natural tissue such as articular cartilage. Recently, zwitterionic polymer brushes have been shown to act as effective boundary lubricants on rigid substrates; however, to the best of our knowledge, the synergistic effects of zwitterionic brushes coupled with the biomimetic fluid load support exhibited by hydrogels have not been reported. We report here on our investigation involving the synthesis and characterization of two unique types of polymer brush functionalized PVA hydrogels. The zwitterionic polymers that were compared contained either [2-(methacryloyloxy)­ethyl]­dimethyl-3-sulfopropyl­ammonium hydroxide, PMEDSAH, or 2-methacryloyl­oxyethyl­phosphoryl­choline, PMPC, repeating units. Both hydrogels coated with zwitterionic polymers were found to be cytocompatible. We report further on micrometer-scale surface properties via water contact angle goniometry, surface roughness measurements, and scanning electron microscopy. Finally, the impact of brush functionalization on the mechanics of the tribologically enhanced gels is reported with comparison to natural articular cartilage within the context of Hertzian contact theory.

Superlubricity of pH-responsive hydrogels in extreme environments

“… Gong et al (1999a) and others demonstrated that the friction coefficients of polyelectrolyte hydrogels depend on their charge density and the charge of the sliding countersurface ( Oogaki et al, 2009 ; Ahmed et al, 2014 ). When the countersurface and hydrogel have the same charge, friction decreases with increasing surface charge density due to greater electrostatic repulsion between the two sliding interfaces and the formation of a solvent layer ( Yoo et al, 1997 ; Gong et al, 1999a ; Oogaki et al, 2009 ; Ahmed et al, 2014 ; Osaheni et al, 2020 ; Wang et al, 2020 ). Models have been developed to predict the thickness of this fluid layer, which depend on variables such as contact pressures and swelling ratios ( Gong et al, 1999a ; Sokoloff, 2010 ; Sokoloff, 2012 ; Sokoloff, 2013 ; Erbaş and Olvera De La Cruz, 2016 ; Tai et al, 2019 ).…”

“…Previous studies have demonstrated that glass has a negative surface charge density in water ( Behrens and Grier, 2001 ) and that surface charge density increases with increasing pH ( Shah et al, 1996 ; Gong et al, 1999b ). Since friction is a systems property and is dependent on the countersurface material, having a negatively charged countersurface such as glass will lead to electrostatic interactions between the charged hydrogel surfaces ( Osaheni et al, 2020 ). At pH = 0.35, neither the glass probe nor P(AAm- co- AA) hydrogel should have any charge, justifying the high friction coefficients.…”

Construction and Tribological Properties of Biomimetic Cartilage-Lubricating Hydrogels

“…Thus, lubrication properties are crucial to the PVA hydrogels when targeting cartilage replacement. Recently, several investigations have focused on the friction property of PVA hydrogels blended with highly hydrophilic polymers (such as polyethylene glycol, poly([2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide), poly(2-methacryloyloxyethyl phosphorylcholine), etc., which indicated that these polymers, acting as lubricants, could facilitate a reduction in the friction of hydrogels via hydration lubrication [ 24 , 25 , 26 , 27 , 28 ]. However, to date, there have been very few studies regarding simultaneously improving the friction and wear of PVA hydrogels to treat articular cartilage defects.…”

Articular Cartilage-Inspired Hybrid Double-Network Hydrogels with a Layered Structure and Low Friction Properties

“…4 On the basis of mechanism of hydration and lubrication, the addition of hydration molecules can effectively reduce the interfacial friction, which is the general principle for designing water-based lubricating materials. However, in some cases, traditional hydration lubrication cannot meet the multidimensional requirements of specific friction systems, such as intelligent friction control, 5 arthritis synergistic treatment, 6 and bionic lubrication. 7 The emergence of functional hydration lubrication makes it possible to solve these problems.…”