Elaine Armelin

Study on the degradability of poly(ester amide)s derived from the α-amino acids glycine, and l-alanine containing a variable amide/ester ratio

Abstract Two series of poly(ester amide)s prepared from sebacic acid and different ratios of 1,12-dodecanediamine and a diamine that contains both α-amino acid residues and ester groups have been synthesized and characterized. In order to maintain hydrogen bonding interactions, two diamines with the same number of main chain atoms were selected. The series differ on the nature of the α-amino acid residue: glycine or l -alanine. The calorimetric analysis shows that melting temperatures increase as the amide/ester ratio does. Polymers derived from l -alanine show lower crystallinities and melting temperatures than those constituted by glycine units. Hydrolytic and enzymatic degradabilities of both series of poly(ester amide)s have also been studied. The ratio and nature of α-amino acid residues in the chemical repeat unit greatly affect the degradation rate.

Cellular Adhesion, Proliferation and Viability on Conducting Polymer Substrates

This work reports a comprehensive study about cell adhesion and proliferation on the surface of different electroactive substrates formed by pi-conjugated polymers. Biological assays were performed considering four different cellular lines: two epithelial and two fibroblasts. On the other hand, the electroactivity of the three conducting systems was determined in physiological conditions. Results indicate that the three substrates behave as a cellular matrix, even though compatibility with cells is larger for PPy and the 3-layered system. Furthermore, the three polymeric systems are electro-compatible with the cellular monolayers.

Nanostructured conducting polymer for dopamine detection

In this work, we demonstrate the ability of poly(N-methylpyrrole) to form nanostructures and to detect very low concentrations of dopamine, an important neurotransmitter. Poly(N-methylpyrrole) hollow particles of controlled thickness have been prepared using the layer-by-layer assembly technique and polystyrene core-shell particles as templates, which are subsequently eliminated to yield free-standing hollow microspheres with a layer thickness of 30 nm. The morphology and composition of these structures have been evaluated by scanning electron microscopy, transmission electron microscopy, FTIR, Raman and X-ray photoelectron spectroscopies. Results demonstrate that intact hollow spheres can be obtained controlling the number of polymer deposition cycles. Furthermore, two kind of sensors were constructed by immobilizing poly(N-methylpyrrole)/Au nanocomposites and poly(N-methylpyrrole) nanomembranes on the surface of a glassy carbon electrode. Electrochemical techniques were employed to evaluate the ability of poly(N-methylpyrrole) to absorb/immobilize dopamine molecules. It was found that systems based on this conducting polymer are highly sensitive to the neurotransmitter concentration, presenting a very fast response even when the concentration of the dopamine is very low.

Study on the degradability of poly(ester amide)s related to nylons and polyesters 6,10 or 12,10

A series of random poly(ester amide)s with different chemical compositions and derived from sebacoyl dichloride, 1,6-hexanediamine and 1,6-hexanediol was synthesized and characterized. In addition, a poly(ester amide) with equal ratio of 1,12-dodecanediamine and 1,12-dodecanediol units was prepared. All these poly(ester amide)s were obtained by interfacial polymerization with high yields. Thermal behavior, mechanical properties, crystallinity and degradability were studied and compared with the parent polyesters (6,10 and 12,10) and nylons (6,10 and 12,10). The new poly(ester amide)s were hydrolyzable, the degradation rate depending on the ester/amide ratio and the methylene content of the diol or diamine units. On the contrary, they were not degraded with proteolytic enzymes. This observation contrasts with the behavior of related poly(ester amide)s that include α- amino acid units in their composition.

Towards sustainable solid-state supercapacitors: electroactive conducting polymers combined with biohydrogels

Solid-state organic electrochemical supercapacitors (OESCs) have been fabricated using poly(3,4-ethylenedioxythiophene) (PEDOT) electrodes, a biohydrogel as electrolyte system, and polyaniline fibers as redox additive. The effectivity of sodium alginate, κ-carrageenan, chitosan and gelatin hydrogels as electrolytic media has been evaluated considering different criteria. Results indicate that κ-carrageenan-based hydrogel is the most suitable to perform as electrolyte due to the appropriate combination of properties: mechanical stability, ease of preparation, lack of water leaking, and good medium for the electrochemical response of PEDOT electrodes. Cyclic voltammetry and galvanostatic charge–discharge assays indicate that OESCs based on PEDOT electrodes and κ-carrageenan hydrogel as electrolyte exhibits a good supercapacitor response in terms of specific capacitance, cycling stability, small leakage current and low self-discharging tendency. On the basis of these good properties, four OESC devices were assembled in series and used to power a red LED, confirming that, in addition to advantageous characteristics (e.g. elimination of liquid leaking and enhancement of the device compactness), the designed biohydrogel-containing OESC exhibits potential for practical applications. On the other hand, preliminary assays have been performed loading the κ-carrageenan hydrogel with polyaniline nanofibers, which act as a redox additive. OESC devices prepared using such loaded biohydrogel have been found to be very promising and, therefore, future work is oriented towards the improvement of their design.

Bioactive and electroactive response of flexible polythiophene:polyester nanomembranes for tissue engineering

Properties of free-standing nanomembranes prepared by blending poly(3-thiophene methyl acetate) and poly(tetramethylene succinate), a soluble polythiophene derivative and a biodegradable polyester, respectively, have been examined. The outstanding flexibility and robustness of the nanomembranes floating in ethanol have been demonstrated through aspiration in pipette/release/shape recovery cycles, which were repeated without cracking the film. The blend retains the electrochemical properties (i.e. oxidation and reduction processes) of the individual conducting polymer in both physiological and organic environments. Hydrolytic and enzymatic degradation assays show that the degradation of the polyester domains produces the detachment of the conducting polymer domains. The cellular viability, which has been studied using four different cellular lines, is significantly higher for the blend than for the polyester, indicating that the former material is a potential bioactive platform for tissue engineering. Finally, the electrobioactivity of the individual materials and the blend coated with cellular monolayers shows some dependence on the cellular line.

Measuring the Proton Conductivity of Ion-Exchange Membranes Using Electrochemical Impedance Spectroscopy and Through-Plane Cell

The role of the incorporation of conducting polymer (CP), doped with different sulfonic acid organic molecules, in polystyrene (PS) and high-impact polystyrene (HIPS) with poly(styrene-ethylene-butylene) (SEBS) triblock copolymer has been investigated. Two factors associated with this model membrane system are addressed: (i) the influence of the presence of a low concentration of doped conducting polymer and (ii) the influence of the membrane preparation method. Membrane characterization and bulk conductivity measurements allowed the conclusion that proton conductivity has been promoted by the addition of CP; the best results were achieved for PAni-CSA, in either PS/SEBS or HIPS/SEBS blends. Additionally, the water uptake only decreased with the addition of PAni-doped molecules compared to the pure copolymer, without loss of ion-exchange capacity (IEC). Electrodialysis efficiency for HIPS/SEBS (before annealing) is higher than that for HIPS/SEBS (after annealing), indicating that membrane preparation method is crucial. Finally, through-plane cell arrangement proved to be an effective, quick, and time-saving tool for studying the main resistance parameters of isolating polymers, which is useful for application in industry and research laboratories working with membranes for electrodialysis or fuel cells.

Biodegradable free-standing nanomembranes of conducting polymer:polyester blends as bioactive platforms for tissue engineering

The present study reports the fabrication of free-standing nanomembranes with semiconducting and biodegradable properties. Nanomembranes have been prepared by spin-coating mixtures of a semiconducting polythiophene derivative, poly(3-thiophene methyl acetate), and a biodegradable polyester, poly(tetramethylene succinate). Both the roughness and thickness of the nanomembranes, which ranged from 3 to 20 nm and from 20 to 80 nm, respectively, were precisely controlled through the spin-coater speed and the solvent evaporation properties. Nanomembranes made of conducting polymer/polyester blends, which are able to retain the properties of the individual polymers, are stable in air and in ethanol solution for more than one year, facilitating their manipulation. Enzymatic degradation essays indicated that the ultra-thin films are biodegradable due to the presence of the aliphatic polyester. Interestingly, adhesion and proliferation assays with epithelial cells revealed that the behavior of the blend as cellular matrix is superior to that of the two individual polymers, validating the use of the nanomembranes as bioactive substrates for tissue regeneration.

Poly(2-thiophen-3-yl-malonic acid), a polythiophene with two carboxylic acids per repeating unit.

A new substituted polythiophene derivative bearing malonic acid, poly(2-thiophen-3-yl-malonic acid), has been prepared and characterized using a strategy that combines both experimental and theoretical methodologies. The chemical structure of this material has been investigated using FTIR and (1)H NMR, and its molecular conformation has been determined using quantum mechanical calculations. Interestingly, the arrangement of the inter-ring dihedral angles was found to depend on the ionization degree of the material, that is, on the pH, which has been found completely soluble in aqueous base solution. Thus, the preferred anti-gauche conformation changes to syn-gauche when the negatively charged carboxylate groups transforms into neutral carboxylic acid. UV-vis experiments and quantum mechanical calculations on model systems with a head-to-tail regiochemistry showed that the lowest pi-pi* transition energy is 2.25 and 2.39 eV for the negatively charged and the neutral polymer, respectively. These values are slightly larger than those previously reported for other polythiophenes with bulky polar side groups. The polymer presents a good thermal stability with a decomposition temperature above 215 degrees C and an electrical conductivity of 10(-5) S/cm, which is characteristic of semiconductor materials. Scanning electron microscopy micrographs showed that, after doping, the surface of this material displays regular distribution pores with irregular sizes. This surface suggests that poly(2-thiophen-3-yl-malonic acid) is a candidate for potential applications such as selective membranes for electrodialysis, wastewater treatment, or ion-selective membranes for biomedical uses.

Selective detection of dopamine combining multilayers of conducting polymers with gold nanoparticles

Electrodes based on the combination of three-layered films formed by two different conducting polymers and gold nanoparticles have been developed for the selective voltammetric determination of dopamine in mixtures with ascorbic acid and uric acid and human urine samples with real interferents. Voltammetric studies of solution mixtures indicate that electrodes formed by alternated layers of poly(3,4-ethylenedioxithiophene) (internal and external layer) and poly(N-methylpyrrole) (intermediate layer) show the best performance in terms of sensitivity and resolution. Furthermore, the sensitivity of such three-layered electrodes increases only slightly after coating its surface with gold nanoparticles (AuNPs), indicating that the catalytic effect typically played by AuNPs in the oxidation of dopamine is less effective in this case. Electrochemical pretreatments based on the application of consecutive oxidation-reduction cycles to electrodes before the detection process have been found to improve the selectivity without altering the sensitivity. On the other hand, the flux of dopamine to the three-layered surface increases linearly with the scan rate. The detection limit for these electrodes is around 10 μM DA in mixtures with uric acid, ascorbic acid, and cetaminophen, decreasing to 2-3 μM in the absence of such interferents. The utility of three-layered electrodes as sensors has also been demonstrated by determining DA in human samples with real interferents.