M. M. Castillo-Ortega

Preparation by coaxial electrospinning and characterization of membranes releasing (−) epicatechin as scaffold for tissue engineering

Optimal conditions for the preparation of a composite material of fibers of cellulose acetate (CA) and poly(vinyl pyrrolidone) (PVP), containing epicatechin (Epic) within the fiber CA/PVP-Epic/CA, were found. The morphology and physical/chemical properties of the fibrous membranes containing CA, PVP, and epicatechin were characterized using FTIR spectroscopy, thermal analysis, SEM, TEM, and natural weathering. Also, mechanical characterization of the fibers showed that tensile strength of the membrane was not affected by the presence of epicatechin within the fiber as compared with fibers without epicatechin. The effect of the medium on the release rate of epicatechin was also studied. The amount of epicatechin release was higher in water, 79.6%, and 31% in MesenCult medium. These results showed that these composite materials are recommended for cardiac tissue engineering; furthermore, using these materials allows precise release of the epicatechin in the damaged tissue.

Polyaniline Toluenesulfonates: X-Ray Diffraction and Electrical Conductivity

Abstract Two polyaniline toluenesulfonates with different crystallinities were synthesized by using iron(III) and copper(II) toluenesulfonates, respectively, as oxidative coupling agents. The toluenesulfonate obtained with the iron(III) salt showed well-defined X-ray powder diffraction peaks; the other toluenesulfonate showed a diffuse pattern. When the toluenesulfonate with the higher crystallinity was neutralized and then doped again with HCl, the resulting polyaniline chloride showed an X-ray pattern closely resembling that of the original toluenesulfonate. The diffraction patterns of the toluenesulfonate and the chloride can be interpreted by assuming an essentially identical crystal packing in the unit cell. Since the cell volumes of the two salts are almost identical, the counteranion with a larger molecular size has a closer contact with a polyaniline chain; the close intermolecular contact may enhance interchain diffusion of charge carriers.

Chemochromic properties of neutral polyaniline throughout cholesterol exposure

This paper presents a novel biosensing platform for cholesterol accomplished by the spin-coating deposition of neutral polyaniline on poly(methyl methacrylate) support and the subsequent covalent immobilization of cholesterol oxidase onto polyaniline surface. The polyaniline film entraps the enzyme and it also acts as an active layer for optical sensing of free cholesterol. The effects of immobilization process of the enzyme over the oxidation state of polyaniline backbone and the optimum pH and temperature conditions for immobilized cholesterol oxidase were studied. The sensibility of the system to cholesterol in concentrations equivalent to those present in human serum evidences its potentiality in an optical method simply based on chemochromic properties of polyaniline.

Synthesis by Emulsion Polymerization of Poly(butyl acrylate-co-silver acrylate) Ionomers and Evaluation of their Possible Applications

The synthesis by emulsion polymerization and the characterization by a battery of techniques of poly(butyl acrylate-co-silver acrylate) [poly(BuAc-co-AgAc)] ionomers are reported here. Reaction rates were fast and conversions around 90% were obtained in less than one hour, regardless of the initial ratio of butyl acrylate and silver acrylate employed (BuAc/AgAc = 90/10, 80/20, 70/30). Particle size was in the range of 176 to 200 nm, depending on the BuAc/AgAc ratio. Ionomers’ formation was corroborated by infrared spectroscopy and inferred by differential scanning calorimetry (DSC). DSC disclosed that the poly(BuAc-co-AgAc) has two glass transition temperatures: one at ca. −49°C due to relaxation of the ionomer backbone domains rich in BuAc and another ca. 35°C due to the relaxation of the backbone domains where the AgAc-units content was higher. Young moduli increased as the copolymers became richer in AgAc. Antibacterial tests against Escherichia coli with the 90/10 (BuAc/AgAc) ionomer revealed that the bacteria population diminishes from 5 log CFU/mL to less than 0.3 MPN/mL after one hour of contact with the ionomers. Also, we demonstrated that the ionomers are excellent compatibilizers for making semiconductive films of n-dodecylbenzene sulfonic acid-doped polyaniline (PANIDBSA)-poly(BuAc-co-AgAc) and poly(n-butyl methacrylate) (PBMA) blends. The electrical conductivity of the blend films, which were homogeneous, rose as the AgAc content in the films increased.

Enzyme mediated synthesis of polypyrrole in the presence of chondroitin sulfate and redox mediators of natural origin.

Polypyrrole (PPy) was synthesized by enzyme mediated oxidation of pyrrole using naturally occurring compounds as redox mediators. The catalytic mechanism is an enzymatic cascade reaction in which hydrogen peroxide is the oxidizer and soybean peroxidase, in the presence of acetosyringone, syringaldehyde or vanillin, acts as a natural catalysts. The effect of the initial reaction composition on the polymerization yield and electrical conductivity of PPy was analyzed. Morphology of the PPy particles was studied by scanning electron microscopy and transmission electron microscopy whereas the chemical structure was studied by X-ray photoelectron and Fourier transformed infrared spectroscopic techniques. The redox mediators increased the polymerization yield without a significant modification of the electronic structure of PPy. The highest conductivity of PPy was reached when chondroitin sulfate was used simultaneously as dopant and template during pyrrole polymerization. Electroactive properties of PPy obtained from natural precursors were successfully used in the amperometric quantification of uric acid concentrations. PPy increases the amperometric sensitivity of carbon nanotube screen-printed electrodes toward uric acid detection.

Preparation of Electrically Conductive Polymeric Membranes

Cellulose acetate porous membranes, coated with polyaniline, were chemically modified with polyelectrolytes to produce films of varying and controlled porosity and electrical conductivity. The highest electrical conductivity was obtained in membranes prepared with poly(styrene sulfonate) with large pore sizes. The electrical properties as well as scanning electron microscopy (SEM) images are discussed.