We present an X-ray photon correlation spectroscopy (XPCS) study of dynamic transitions in an anisotropic colloid-polymer dispersion with multiple arrested states. The results provide insight into the mechanism for formation of repulsive glasses, attractive glasses, and networked gels of colloids with weakly adsorbing polymer chains. In the presence of adsorbing polymer chains, we observe three distinct regimes: a state with slow dynamics consisting of finite particles and clusters, for which interparticle interactions are predominantly repulsive; a second dynamic regime occurring above the saturation concentration of added polymer, in which small clusters of nanoparticles form via a short-range depletion attraction; and a third regime above the overlap concentration in which dynamics of clusters are independent of polymer chain length. The observed complex dynamic state diagram is primarily governed by the structural reorganization of a nanoparticle cluster and polymer chains at the nanoparticle-polymer surface and in the concentrated medium, which in turn controls the dynamics of the dispersion. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 752–760

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. Copyright © 2015 John Wiley & Sons, Ltd.

A major limitation of current soft biomaterials for tissue engineering and cell encapsulation is inadequate transport of oxygen to cells and tissues. Oxygen transport is a challenge in nearly all aqueous hydrogel biomaterials. Here, we report the effective diffusivity of oxygen in alginate-based hydrogels containing stable perfluorocarbon (PFC) emulsions. Incorporation of 7% perfluorooctyl bromide into the alginate gels was found to increase oxygen permeability by a factor of three. Our work also demonstrates that the increase in oxygen transport is largely due to improved oxygen solubility in PFC-containing gels. Although promising, this improved oxygen transport comes with a trade-off in terms of mechanical robustness. This must be carefully considered in future development of PFC-containing hydrogels for biomedical devices. Copyright © 2014 John Wiley & Sons, Ltd.

Terminal, or postprocessing, sterilization of composite biomaterials is crucial for their use in wound healing and tissue-engineered devices. Recent research has focused on optimizing traditional biomaterial formulations to create better products for commercial and academic use which incorporate hydrophobic compounds or secondary gel networks. To use a hydrogel in a clinical setting, terminal sterilization is necessary to ensure patient safety. Lyophilization, gamma-irradiation, and ethylene oxide treatment all have negative consequences when applied to alginate scaffolds for clinical use. Here, we aim to find alternative terminal sterilization methods for alginate and alginate-based composite hydrogels which maintain the structure of composite alginate networks for use in biomedical applications. A thorough investigation of the effect of common sterilization methods on swollen alginate-based hydrogels has not been reported and therefore, this work examines autoclaving, ethanol washing, and ultraviolet light as sterilization techniques for alginate and alginate/Pluronic® F68 composite hydrogels. Preservation of structural integrity is evaluated using shear rheology and analysis of water retention, and efficacy of sterilization is determined via bacterial persistence within the hydrogel. Results indicate that ethanol sterilization is the best method of those investigated because ethanol washing results in minimal effects on mechanical properties and water retention and eliminates bacterial persistence. Furthermore, this study suggests that ethanol treatment is an efficacious method for terminally sterilizing interpenetrating networks or other composite hydrogel systems. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 102B: 877–884, 2014.