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Resumé. 2014 Abstract. 2014 A study of the surface tension of semi-dilute polymer solutions in theta solvent conditions is presented. Theoretical predictions are given for the two cases when the interface is attractive or repulsive. The Cahn approach for the interfacial tension is used in order to calculate the interfacial tension in the mean field theory of polymer solutions. The measurements, were performed on two polymer theta solvent systems : polydimethylsiloxanebromocyclohexane at 29 °C and polystyrene-cyclohexane at 34°C for the attractive and repulsive cases respectively. The well-known ring method was used. The agreement between theory and experiments is good. The theoretical predictions and the results are compared with those obtained in good solvent case that we reported.in a previous paper. The transition 03B8 solvent-good solvent is studied for the attractive system.

Cell-laden hydrogel microspheres have shown encouraging outcomes in the fields of drug delivery, tissue engineering or regenerative medicine. Beyond the classical single coating with polycations, many other different coating designs have been reported with the aim of improving mechanical properties and in vivo performance of the microspheres. Among the most common strategies are the inclusion of additional polycation coatings and the covalent bonding of the semi-permeable membranes with biocompatible crosslinkers such as genipin. However, it remains challenging to characterize the effects of the interactions between the polycations and the hydrogel microspheres over time in vitro. Here we use a force spectroscopy-based simultaneous topographical and mechanical characterization to study polymer-to-polymer interactions in alginate microspheres with different coating designs, maintaining the hydrogels in liquid. In addition to classical topography parameters, we explored, for the first time, the evolution of peak/valley features along the z axis via thresholding analysis and the cross-correlation between topography and stiffness profiles with resolution down to tens of nanometers. Thus, we demonstrated the importance of genipin crosslinking to avoid membrane detachment in alginate microspheres with double polycation coatings. Overall, this methodology could improve hydrogel design rationale and expedite in vitro characterization, therefore facilitating clinical translation of hydrogel-based technologies.