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A cell-imprinted poly(dimethylsiloxane)/hydroxyapatite nanocomposite substrate was fabricated to engage topographical, mechanical, and chemical signals to stimulate and boost stem cell osteogenic differentiation. The physicochemical properties of the fabricated substrates, with nanoscale resolution of osteoblast morphology, were probed using a wide range of techniques including scanning electron microscopy, atomic force microscopy, dynamic mechanical thermal analysis, and water contact angle measurements. The osteogenic differentiation capacity of the cultured stem cells on these substrates was probed by alizarin red staining, ALP activity, osteocalcin measurements, and gene expression analysis. The outcomes revealed that the concurrent roles of the surface patterns and viscoelastic properties of the substrate provide the capability of directing stem cell differentiation toward osteogenic phenotypes. Besides the physical and mechanical effects, we found that the chemical signaling of osteoinductive hydroxyapatite nanoparticles, embedded in the nanocomposite substrates, could further improve and optimize stem cell osteogenic differentiation.

A chitosan/alginate dialdehyde multilayered film was fabricated using the layer-by-layer assembly method. Besides electrostatic interaction that promotes alternate adsorption of the oppositely charged polyelectrolytes, the Schiff base reaction between the amine groups on chitosan and the aldehyde groups on alginate dialdehyde provides a covalently cross-linked film, which after reduction by sodium cyanoborohydride is stable under both acidic and alkaline conditions. Moreover, the cross-linked film is responsive to changes in pH and addition of multivalent salts. The structural properties of the multilayered film such as thickness, refractive index, and water content were examined using simultaneous quartz crystal microbalance with dissipation monitoring and spectroscopic ellipsometry.

Skin adhesives are polymer materials used for attaching medical devices to the skin. Probing the performance of such adhesives is of great interest for rational material formulation. Here, we present a perspiration simulator, which includes a skin mimicking gelatin substrate with controlled roughness and the ability to perspire with a tunable sweat rate. The setup was used for probing peel adhesion of adhesives under realistic wear conditions. Adhesives with indistinguishable rheological properties but different ability to absorb artificial sweat were evaluated. The rheological properties were fixed to decouple the bulk mechanical properties from events occurring at the substrate–adhesive interface. The effects of application pressure, dwell time, and perspiration were quantified for each adhesive formulation. Here, we found that sweat introduced at the substrate–adhesive interface restricts further bonding of the adhesives by limiting viscous flow. Water-absorbing skin adhesives were found to have significantly higher peel forces compared to nonabsorbing adhesives under sweating conditions where the adhesive could absorb the introduced sweat.

The effect of sodium fluoride, sodium trichloroacetate, and sodium thiocyanate on the stability and conformation of poly(N-isopropylacrylamide), in bulk solution and at the gold-aqueous interface, is investigated by differential scanning calorimetry, dynamic light scattering, quartz crystal microbalance, and atomic force microscopy. The results indicate a surface partitioning of the weakly hydrated anions, i.e., thiocyanate and trichloroacetate, and the findings are discussed in terms of anion-induced electrostatic stabilization. Although attractive polymer-ion interactions are suggested for thiocyanate and trichloroacetate, a salting-out effect is found for sodium trichloroacetate. This apparent contradiction is explained by a combination of previously suggested mechanisms for the salting-out effect by weakly hydrated anions.

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The Hofmeister series is a classification of ions regarding their ability to stabilize or destabilize aqueous solutions of proteins, polymers and other molecules which are partly miscible with water. In this study, we employ differential scanning calorimetry to investigate how the stability of aqueous solutions of poly(propylene oxide) is affected by mixtures of ions with different location in the Hofmeister series. Our results show that the Hofmeister effects of pure salt species are not always linearly additive and that the relative effect of some ions can be reversed depending on the composition of the salt mixture as well as by the absolute and relative concentration of the different species. We suggest that these results can lead to a better understanding of the potential role of the Hofmeister effect in regulation of biological processes, which does always take place in salt mixtures rather than solutions containing just single salt species.

Polyelectrolyte brushes have received extensive attention due to their swelling behavior in aqueous solutions, which is a result of their ionic nature and nonelectrostatic (polymer–polymer and polymer–solvent) interactions. While the nonelectrostatic contributions are typically assumed to be negligible compared to the ion osmotic pressure, we present herein a systematic investigation of how the nonelectrostatic interactions dramatically affect the swelling behavior of polyelectrolyte brushes. Using a modular synthesis procedure, polyelectrolyte brushes with similar chain lengths, grafting densities, and charge densities but with various side chains were synthesized. The swelling behaviors of the brushes were then thoroughly investigated as a function of grafting density and ionic strength using ellipsometry. A theoretical mean-field approach was also developed to quantify the contributions of the ion osmotic and nonelectrostatic effects. Accordingly, it was both experimentally and theoretically demonstrated how fundamentally different swelling behaviors can exist depending on the relative contributions of ion osmotic and nonelectrostatic effects. This new insight reveals new opportunities for applications of polyelectrolyte brushes based on their tunable hydrophobicity and provides new ideas for fundamental investigations of these systems.