Laponite® and Laponite®-PEO hydrogels with enhanced elasticity in phosphate-buffered saline

Hydrogels of the synthetic clay Laponite® and Laponite®-poly (ethylene oxide) (PEO) have long been studied as model systems to understand fundamental aspects of colloidal disks and colloid-polymer systems. More recently, these systems have been explored for a variety of biomedical applications. However, there is limited information in the literature on the fundamental properties of Laponite and Laponite-polymer gels at pH<9. Here, we report the rheological behavior of Laponite and Laponite-PEO systems at biologically relevant conditions (e.g. physiological pH and ionic strength) and examine the effect of phosphate-buffered saline on the properties of the gel. Our results show that the elastic modulus of both Laponite and Laponite-PEO gels increases dramatically, in some cases by one order of magnitude or more, after immersing gels in phosphate-buffered saline. This may be due to an enhanced edge-face interaction between particles in buffered solutions, which would promote a long-lasting network structure of clay particles. These results are relevant to the design of clay-polymer gels and nanocomposites hydrogels for biomaterials applications.