Joaquín Antonio González

Antimicrobial Activity of Starch Hydrogel Incorporated with Copper Nanoparticles

In order to obtain an antimicrobial gel, a starch-based hydrogel reinforced with silica-coated copper nanoparticles (Cu NPs) was developed. Cu NPs were synthesized by use of a copper salt and hydrazine as a reducing agent. In order to enhance Cu NP stability over time, they were synthesized in a starch medium followed by a silica coating. The starch hydrogel was prepared by use of urea and water as plasticizers and it was treated with different concentrations of silica-coated copper nanoparticles (Si-Cu NPs). The obtained materials were characterized by Fourier transform infrared (FT-IR) spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, scanning electron microscopy (SEM), and rheometry. FT-IR and EPR spectra were used for characterization of Cu NPs and Si-Cu NPs, confirming that a starch cap was formed around the Cu NP and demonstrating the stability of the copper nanoparticle after the silica coating step. SEM images showed Cu NP, Si-Cu NP, and hydrogel morphology. The particle size was polydisperse and the structure of the gels changed along with particle concentration. Increased NP content led to larger pores in starch structure. These results were in accordance with the rheological behavior, where reinforcement by the Si-Cu NP was seen. Antimicrobial activity was evaluated against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacterial species. The hydrogels were demonstrated to maintain antimicrobial activity for at least four cycles of use. A dermal acute toxicity test showed that the material could be scored as slightly irritant, proving its biocompatibility. With these advantages, it is believed that the designed Si-Cu NP loaded hydrogel may show high potential for applications in various clinical fields, such as wound dressings and fillers.

Chitin hybrid materials reinforced with graphene oxide nanosheets: chemical and mechanical characterisation

Chitin hybrid materials reinforced with graphene oxide nanosheets (nGO) have been prepared. The chitin : nGO ratio ranged from proportions where chitin was the main component to ones where nGO exceeded chitin. SEM and TEM images showed that high proportions of nGO may result in nanosheet association. FTIR, 13C solid-state NMR and DSC analyses showed that the interaction among the components would not involve the formation of new molecular bonds. nGO was shown to act as a filler that induces structural rearrangements in chitin which lead to new hydrogen bonds among the chains. The mechanical stability proved to be higher when the nGO content in the hybrid was similar to or higher than that of chitin. The rheological behaviour of the material was shown to become more solid-like with increasing nGO content. The nGO did not interfere with lysozyme activity on chitin chains, indicating that these materials would be biodegradable.

Antimicrobial surface functionalization of PVC by a guanidine based antimicrobial polymer.

Abstract Antimicrobial polyvinyl chloride (PVC) plastic was obtained by covalent bonding of poly hexamethylenediamine guanidine hydrochloride (PHMG), a guanidine based antimicrobial polymer. This was achieved by grafting mercaptopropyltrimethoxysilane onto PVC, followed by aminopropyltriethoxysilane. Glutaraldehyde is a bifunctional crosslinker that was bonded to the free amine groups found in the treated PVC on one side and PHMG on the other. The treated PVC samples were characterized by FT-IR and XPS, showing that the PVC samples were successfully modified. Energy Dispersive X-ray spectroscopy showed the spatial distribution of the elements Si and S, indicating that the coatings were homogeneous. The resulting PVC samples showed high antimicrobial activity against Gram-positive and Gram-negative bacteria. Furthermore, the biofilm formation was negligible in comparison with the untreated material. The coating elusion assay indicated that its antimicrobial ability was achieved via direct contact rather than a controlled release mechanism.

Sustainable and smart keratin hydrogel with pH-sensitive swelling and enhanced mechanical properties

Protein based hydrogels are a very interesting type of biomaterials with many probed strengths related to their source and chemical structure. Biocompatibility and biodegradability are accompanied by affordability when it comes to low cost sources. The main keratin source is agroindustrial waste, such as feathers, horns, hooves, hair and wool. Thus, the main cost of keratin hydrogels derives from their processing. Here is presented a new strategy for the obtaining of a keratin hydrogel with enhanced mechanical properties using low cost reagents. This keratin hydrogel is stiff enough to allow handling without special cares and also presenting a reversible pH-responsive behavior. The minimum swelling is observed at low pH due to a collapsed and disordered protein network with water tightly adsorbed to the hydrophilic sites. The swelling rises significantly above pH6 and the maximum swelling appears above pH8 where an expanded network allows water to enter to the pores.

Chitin based hybrid composites reinforced with graphene derivatives: a nanoscale study

In this work, we present two novel nanostructured hybrid materials based on a chitin matrix loaded with increasing amounts of graphene oxide and reduced graphene oxide nanosheets (nGO and rGO, respectively). Both kinds of material (Chi:nGO and Chi:rGO) were studied using different spectroscopic and rheological techniques with the aim of understanding the interaction mechanism between chitin and nGO/rGO and explaining how the type of filler and its proportion affects its reinforcement. The production of these hybrids represents not only the obtention of low-cost materials with mechanical resistance but also a good opportunity for developing materials with several applications according to their composition. The nGO and rGO were characterised through FT-IR and ESR for the determination of the oxidation degree of each nanofiller. Then, the hybrids were spectroscopically analysed with FT-IR, ESR and SAXS which demonstrated that the components do not interact through covalent bonding and the nanosheets are well-dispersed among the chitin matrix. Finally, a rheological behavior assay was performed and its results were analysed in terms of G′ and η*. In short, all the results allowed us to conclude that nGO acts as a more efficient reinforcer than rGO due to the higher amount of hydrogen bonding established with chitin.

Continuous flow adsorption of ciprofloxacin by using a nanostructured chitin/graphene oxide hybrid material

A novel nanostructured material was successfully developed by combining a chitin matrix with graphene oxide nanosheets (Chi:nGO) and then used for the continuous flow adsorption of ciprofloxacin. The spectroscopic characterization indicated that none covalent interaction between both components would be occurring and the introduction of nGO did not interfere in chitin nanostructure rearrangement during gelling and later drying. SEM images and Mercury Intrusion Porosimetry results showed a wide pore size distribution ranging from nano to micrometers. The continuous flow adsorption was observed to be dependent on the pH which affects the electrostatic interaction. The flow rate, Na+ concentration and water hardness were evaluated to describe the adsorption process. The resistance to alkali allowed to regenerate and reuse the column for subsequent adsorption cycles. Finally, ciprofloxacin spiked real water samples were assessed and the results confirmed that the medium pH was the main parameter that defines the adsorption behavior.

Dual antibacterial effect of immobilized quaternary ammonium and aliphatic groups on PVC

A coating comprising quaternary ammonium salts (QAS) and aliphatic moieties was formed on the poly(vinyl chloride) (PVC) surface in order to confer antibacterial activity. This was achieved by grafting mercaptopropyltrimethoxysilane onto PVC, followed by aminopropyltriethoxysilane. Betaine and dodecenyl succinic anhydride (DDSA) were bonded to free amine groups. The modified PVC samples were characterized by FT-IR, showing that the PVC surface was successfully coated. Energy dispersive X-ray spectroscopy showed the spatial distributions of the elements Si and S, indicating that the coatings were homogeneous. Betaine and DDSA coated PVC showed a better antibacterial performance than the controls. This antibacterial effect was extremely reinforced in betaine–DDSA modified PVC showing greater antibacterial activity than both treatments separately applied. Antibacterial activity against Acinetobacter baumannii, Pseudomonas aeruginosa, Staphylococcus aureus, and Bacillus subtilis was studied in the treated samples showing that the coating was effective against Gram positive and Gram negative species.

Phosphorus adsorption by a modified polyampholyte-diatomaceous earth material containing imidazole and carboxylic acid moieties: batch and dynamic studies

The aim of this study was to investigate phosphorus removal in water by using a polyampholyte obtained by the reaction of methacrylic acid, ethylene glycol diglycidyl ether and imidazole by a one step synthesis, mixed with diatomaceous earth. The material was characterized before and after phosphorus exposure using FT-IR, Raman, and solid state 31P-NMR and 13C-NMR spectroscopy concluding that the charged imidazole units were involved in the interaction between the phosphorus and the polyampholyte and that only the H2PO4− species was adsorbed. The point of zero charge value was 5.09. Concomitantly, the optimal pH for P adsorption was 5.0. As pH was increased, the polymer turned more negative, and the phosphate repulsion diminished the adsorption. In the batch experiments, the adsorption isotherms at pH values 5.0 and 7.0 were studied. The effects of different flow rates, P influent concentration and the interference of nitrate and sulfate in the breakthrough curves were studied. A shorter breakthrough time occurred at a higher flow rate. The q0 values not only increased from lower to higher influent levels but also showed a decrease in the presence of S and N as interferents demonstrating that there was a competition for the adsorption sites between those anions and the phosphate.

Innovative Immobilization Matrices.

We present a brief survey of some of the recent work of Professor Luis E. Díaz, performed together with his students and collaborators at the University of Buenos Aires. Dr Luis E. Díaz has been involved in research on biochemical and pharmaceutical sciences solving scientific and industry problems for over 40 years until he passed away. Prof. Díaz scientific interests included various topics from NMR spectroscopy to biomedicine but fundamentally he focused in various aspects of chemistry (analytical, organic, inorganic and environmental). This is not a complete survey but a sampling of prominent projects related to sol-gel chemistry with a focus on some of his recent publications.