Cesar A. Barbero

Synergistic effect of polyaniline coverage and surface microstructure on the inhibition of Pseudomonas aeruginosa biofilm formation

Biofilm Formation is a survival strategy for microorganisms to adapt to their environment. Microbial cells in biofilm become tolerant and resistant to antibiotics and immune responses, increasing the difficulties for the clinical treatment of microbial infections. The surface chemistry and the micro/nano-topography of solid interfaces play a major role in mediating microorganism activity and adhesion. The effect of the surface chemical composition and topography on the adhesion and viability of Pseudomonas aeruginosa was studied. Polymeric (polyethylene terephthalate) surfaces were covered with a conducting polymer (polyaniline, PANI) film by in-situ polymerization and microstructured by Direct Laser Interference Patterning (DLIP). The viability of Pseudomonas aeruginosa on the different surfaces was investigated. The physicochemical properties of the surfaces were characterized by water contact angle measurements, scanning electron microscopy and atomic force microscopy. Bacterial biofilms were imaged by atomic force and scanning electron microscopies. The bacterial viability decreased on PANI compared with the substrate (polyethylene terephthalate) and it decreased even more upon micro-structuring the PANI films. In addition, the biofilm reduction could be improved using polymers with different chemical composition and/or the same polymer with different topographies. Both methods presented diminish the bacterial attachment and biofilm formation. These findings present a high impact related to materials for biomedical engineer applications regarding medical devices, as prostheses or catheters.

Bioethanol production by reusable Saccharomyces cerevisiae immobilized in a macroporous monolithic hydrogel matrices

Performance of yeasts on industrial processes can be dramatically improved by immobilization of the biocatalyst. The immobilization of Saccharomyces cerevisiae inside monolithic macroporous hydrogels were produced by in-situ polymerization of acrylamide around a live yeast suspension under cryogelation conditions. Preculture of the yeasts was not necessary and this innovative and simple procedure is amenable to scaling-up to industrial production. The yeasts were efficiently retained in monolithic hydrogels, presenting excellent mechanical properties and high cell viability. Macroporous hydrogels showed a fast mass transport allowing the hydrogel-yeast complexes achieved similar ethanol yield and productivity than free yeasts, which is larger than those reached with yeasts immobilized in compact hydrogels. Moreover, the same yeasts were able to maintain its activity by up to five reaction cycles with a cell single batch during fermentation reactions.

Synthesis and characterization of GO-hydrogels composites

The preparation of poly(N-isopropylacrylamide) (PNIPAm) hydrogel nanocomposites containing graphene oxide (GO) and GO plus carbon nanotubes (CNT) in the polymer network is communicated. This one-pot preparation methods include the dispersion of GO (or GO plus CNT) in a solution of monomers and the subsequent polymerization. The texture of the nanocomposites was studied using scanning electron microscopy (SEM), where very compact surfaces are observed suggesting good dispersion of GO sheets and CNTs within the polymer matrix. The presence of GO inside the polymer network diminished the equilibrium swelling values and increased the elastic modulus up to 162 % with respect to the pure gel. Similar results were observed for the composite with CNT. Furthermore, the electrical resistivity of PNIPAm-GO diminishes as the applied compression force increases, being 50 % lower than hydrogel without GO. Moreover, the electrochemical properties of the hydrogels, evaluated by cyclic voltammetry, indicate highly reversible electrical charge/discharge response. In order to apply these materials for antibiotic delivery, the absorption of tetracycline (tet) is evaluated and the nanocomposites showed better absorption capability and improved antibiotic delivery. Preliminary results suggest that tet loaded PNIPAm-GO and PNIPAM-GO-CNT display antimicrobial activity against the Pseudomonas aeruginosa turning these materials as potential candidates for biomedical applications.

Photothermally enhanced bactericidal activity by the combined effect of NIR laser and unmodified graphene oxide against Pseudomonas aeruginosa

The manuscript shows the application of unmodified graphene oxide (GO) as a photothermally susceptible material to trigger antibacterial effects. The synthesis and characterization of unmodified GO easily dispersed in aqueous solutions is also shown. High GO concentrations in the dark and low GO concentrations irradiated with near infrared light (NIR) produced death in nosocomial bacterium (Pseudomonas aeruginosa). It is demonstrated that GO dispersion in the dark produced a dose-dependent increase in the antibacterial action at concentrations up to 120 μg/mL. On the other hand, by using much lower concentrations (c.a. 2 μg/mL) of GO (non toxic in the dark) and irradiating with near-infrared radiation during 15 min, a degree of mortality of 98.49% was observed. The P. aeruginosa treated with GO and irradiated exhibited DNA fragmentation due to the physical damage of cell membranes. The GO 2 μg/mL dispersions proved favorable, since they do not induce cell death in the dark, whereas the combination with NIR light triggers the damage to the cell membranes. This characteristic is clearly an advantage in comparison with traditional antibacterial nanomaterials (such as nanoparticles), which induce cell killing due to the nanoparticles toxicity per se. Furthermore, this work provides a novel treatment for combating bacterial nosocomial infections without the use of antibiotics, opening a new area of clinical application via simple photothermal therapy.

Poly(N-isopropylacrylamide) Crosslinked Gels as Intrinsic Amphiphilic Materials. Swelling Properties Used to Build Novel Interphases

The hydrophilic nature of hydrogels allows their swelling in aqueous solutions. In that way, any substance loaded inside the gel is exposed to the aqueous media and could be released if it is soluble in water. However, only substances that are soluble in water can be loaded inside a gel, which can be swelled only in water. In this work, we studied the swelling of poly( N-isopropylacrylamide) (PNIPAM) gels in nonaqueous solvents and their solutions with water. PNIPAM gels swell strongly in highly polar solvents, but they do not swell in slightly polar solvents (e.g., toluene). However, it is possible to swell the gel in mixtures containing toluene. The observed properties of PNIPAM gels allow describing them both as solvogels or amphigels. When the loaded substance is soluble in one solvent (e.g., water) and not in another (e.g., chloroform), the substance is not released but exposed to the new media. As a proof of concept, a colorimetric pH sensor active in CHCl3 and a Cu1+ sensor in water were built. Moreover, using a ternary solution containing toluene linear polystyrene can be loaded inside the gel, making a semi-interpenetrated network. Because PNIPAM swells in water and solvents immiscible in water, a liquid/liquid interphase can be set inside a gel. A near-infrared absorbing dye (soluble in CHCl3) is loaded in only half of a thermoresponsive PNIPAM gel. Upon near-infrared irradiation, only the region where the dye is loaded heats up driving the phase transition of PNIPAM.