Conductivities and dielectric constant measurements in water at 25 °C have been made on the amphiphilics sodium n-dodecyl sulfate, n-dodecyltrimethylammonium bromide, and chlorpromazine hydrochloride. By using the conductivity/concentration data, critical micelle concentrations (cmc) have been determined by applying the Williams definition and two forms of the Phillips method. This first Phillips form consists of an approximation to Gaussians of the second derivative of the conductivity/concentration data followed by two consecutive integrations. The second form, which is proposed here, consists of the application of a combination of the Runge-Kutta numerical integrations method and the Levenberg-Marquardt leastsquares fitting algorithm. The proposed method permits the determination of the cmc in systems with low aggregation numbers and with slow variations of physical property/concentration curves allowing the determination of the so-called second cmc. A comparative study with results obtained by dielectric constant measurements has been carried out. With this new technique, the cmc's (first and second) are directly obtained as singular points in the dielectric constant/concentration curves, and thus, this technique is an alternative to the determination of cmc's from conductivities.

Dynamic light scattering and electrophoretic mobility measurements have been used to characterize the size, size distribution and zeta potentials (zeta-potentials) of egg yolk phosphatidylcholine (EYPC) liposomes in the presence of monovalent ions ( Na(+) and K(+)). To study the stability of liposomes the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory has been extended by introducing the hydrated radius of the adsorbed ions onto the liposome surfaces. The decrease of liposome size is explained on the basis of the membrane impermeability to some ions which generate osmotic forces, which leads to evacuate water from liposome inside.

Hyaluronic acid (HA) and gelatin (Gel) are major components of the extracellular matrix of different tissues, and thus are largely appealing for the construction of hybrid hydrogels to combine the favorable characteristics of each biopolymer, such as the gel adhesiveness of Gel and the better mechanical strength of HA, respectively. However, despite previous studies conducted so far, the relationship between composition and scaffold structure and physico-chemical properties has not been completely and systematically established. In this work, pure and hybrid hydrogels of methacroyl-modified HA (HAMA) and Gel (GelMA) were prepared by UV photopolymerization and an extensive characterization was done to elucidate such correlations. Methacrylation degrees of ca. 40% and 11% for GelMA and HAMA, respectively, were obtained, which allows to improve the hydrogels’ mechanical properties. Hybrid GelMA/HAMA hydrogels were stiffer, with elastic modulus up to ca. 30 kPa, and porous (up to 91%) compared with pure GelMA ones at similar GelMA concentrations thanks to the interaction between HAMA and GelMA chains in the polymeric matrix. The progressive presence of HAMA gave rise to scaffolds with more disorganized, stiffer, and less porous structures owing to the net increase of mass in the hydrogel compositions. HAMA also made hybrid hydrogels more swellable and resistant to collagenase biodegradation. Hence, the suitable choice of polymeric composition allows to regulate the hydrogels´ physical properties to look for the most optimal characteristics required for the intended tissue engineering application.

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