Author:
Chau Allison L.,Pugsley Conor D.,Miyamoto Madeleine E.,Tang Yongkui,Eisenbach Claus D.,Mates Thomas E.,Hawker Craig J.,Valentine Megan T.,Pitenis Angela A.
Abstract
AbstractPolyacrylamide hydrogels are widely used in biomedical applications due to their tunable mechanical properties and charge neutrality. Our recent tribological investigations of polyacrylamide gels have revealed tunable and pH-dependent friction behavior. To determine the origins of this pH-responsiveness, we prepared polyacrylamide hydrogels with two different initiating chemistries: a reduction–oxidation (redox)-initiated system using ammonium persulfate (APS) and N,N,N′N′-tetramethylethylenediamine (TEMED) and a UV-initiated system with 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone (Irgacure 2959). Hydrogel swelling, mechanical properties, and tribological behavior were investigated in response to solution pH (ranging from ≈ 0.34 to 13.5). For polyacrylamide hydrogels in sliding contact with glass hemispherical probes, friction coefficients decreased from µ = 0.07 ± 0.02 to µ = 0.002 ± 0.002 (redox-initiated) and from µ = 0.05 ± 0.03 to µ = 0.003 ± 0.003 (UV-initiated) with increasing solution pH. With hemispherical polytetrafluoroethylene (PTFE) probes, friction coefficients of redox-initiated hydrogels similarly decreased from µ = 0.06 ± 0.01 to µ = 0.002 ± 0.001 with increasing pH. Raman spectroscopy measurements demonstrated hydrolysis and the conversion of amide groups to carboxylic acid in basic conditions. We therefore propose that the mechanism for pH-responsive friction in polyacrylamide hydrogels may be credited to hydrolysis-driven swelling through the conversion of side chain amide groups into carboxylic groups and/or crosslinker degradation. Our results could assist in the rational design of hydrogel-based tribological pairs for biomedical applications from acidic to alkaline conditions.
Graphical abstract
Funder
National Science Foundation Graduate Research Fellowship Program
National Science Foundation
National Science Foundation CAREER
Publisher
Springer Science and Business Media LLC
Subject
Surfaces, Coatings and Films,Surfaces and Interfaces,Mechanical Engineering,Mechanics of Materials
Cited by
5 articles.
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