N. Gabilondo

Starch and cellulose nanocrystals together into thermoplastic starch bionanocomposites.

In the present work, thermoplastic maize starch based bionanocomposites were prepared as transparent films, plasticized with 35% of glycerol and reinforced with both waxy starch (WSNC) and cellulose nanocrystals (CNC), previously extracted by acidic hydrolysis. The influence of the nanofiller content was evaluated at 1 wt.%, 2.5 wt.% and 5 wt.% of WSNC. The effect of adding the two different nanoparticles at 1 wt.% was also investigated. As determined by tensile measurements, mechanical properties were improved at any composition of WSNC. Water vapour permeance values maintained constant, whereas barrier properties to oxygen reduced in a 70%, indicating the effectiveness of hydrogen bonding at the interphase. The use of CNC or CNC and WSNC upgraded mechanical results, but no significant differences in barrier properties were obtained. A homogeneous distribution of the nanofillers was demonstrated by atomic force microscopy, and a shift of the two relaxation peaks to higher temperatures was detected by dynamic mechanical analysis.

Biocompatible hydrogel nanocomposite with covalently embedded silver nanoparticles.

Bionanocomposite materials, combining the properties of biopolymers and nanostructured materials, are attracting interest of the wider scientific community due to their potential application in design of implants, drug delivery systems, and tissue design platforms. Herein, we report on the use of maleimide-coated silver nanoparticles (Ag NPs) as cocross-linkers for the preparation of a bionanocomposite gelatin based hydrogel. Diels-Alder cycloaddition of benzotriazole maleimide (BTM) functionalized Ag NPs and furan containing gelatin in combination with additional amide coupling resulted in stable and biocompatible hybrid nanocomposite. The storage moduli values for the hydrogel are nearly three times higher than that of control hydrogel without NPs indicating a stabilizing role of the covalently bound NPs. Finally, the swelling and drug release properties of the materials as well as the biocompatibility and toxicity tests indicate the biomedical potential of this type of material.

Diels-Alder "click" chemistry for the cross-linking of furfuryl-gelatin-polyetheramine hydrogels†

This paper deals with the design of biopolymeric hydrogels after the chemical cross-linking of gelatin through the Diels–Alder (DA) reaction. Furan modified gelatin (Gel-FGE) was prepared by the reaction of furfuryl glycidyl ether with the free amino groups present in the gelatin. A Jeffamine®-based bismaleimide was employed as a cross-linking agent and the influence of the amount of cross-linker used on the final hydrogel properties was studied. The DA and retro-DA reactions were followed by ultraviolet spectroscopy and the final properties of the hydrogel assessed. Scanning Electron Microscopy was used to analyze the structure of the final material and rheology studies confirmed the formation of a chemically cross-linked network. The swelling behavior in response to external stimuli such as pH and salt concentration was also studied. By virtue of the DA “click” reaction, biopolymer-based cross-linked hydrogels, with promising properties for biomedical applications, were obtained in a simple one step procedure free of catalysts, additives or coupling agents.

Effect of maleimide-functionalized gold nanoparticles on hybrid biohydrogels properties

The role of well-dispersed gold nanoparticles as cross-linking agents in nanocomposite hydrogel formation was studied. Maleimide-coated gold nanoparticles were synthesized and used for Diels–Alder cycloaddition with furan modified gelatin. Hydrogel formation was aided by additional amide coupling of the modified gelatin with chondroitin sulfate. The cross-linking ability of the functionalized nanoparticles was evaluated and the final hydrogel properties were compared to those of a hybrid hydrogel containing inert-linker coated gold nanoparticles. The storage modulus of the nanoparticle cross-linked nanocomposites was 2.5–3 times compared to the controls. The presence of nanoparticles also affected the swelling properties, resulting in lower swelling ratios due to the formation of the more cross-linked structures. Conducted drug delivery experiments and the study of the light irradiation on the drug release behavior revealed promising features for the applications of nanocomposite polymer for drug delivery.

Designing hydrogel nanocomposites using TiO2 as clickable cross-linkers

Titanium dioxide (TiO2) nanoparticles with clickable functional groups were prepared to allow for the Diels–Alder “click” reaction with a furan-modified pigskin gelatin. Bifunctional dopamine-maleimide linker was employed for TiO2 functionalization with maleimide group. The obtained nanoparticles were characterized using TEM, Zeta potential and FTIR spectroscopy. Functional nanoparticles were subsequently used, together with chondroitin sulphate, as cross-linkers for gelatin hydrogels. Hydrogel controls with bare TiO2 and without nanoparticles were prepared for comparison. The swelling and rheological properties of the nanocomposite hydrogels confirmed the formation of the covalently linked heterogeneous networks. An increase in the storage moduli values was recorded when using maleimide-coated nanoparticles. At the same time, the swelling of the network was significantly reduced indicating the formation of more cross-linked networks. The participation of the surface attached maleimide functional groups through the Diels–Alder cycloaddition was thus confirmed. In addition, hydrogels responded to electrostatic forces as observed by electrostatic force microscopy.

Synthesis of stimuli–responsive chitosan–based hydrogels by Diels–Alder cross–linking `click´ reaction as potential carriers for drug administration

Stimuli-responsive chitosan-based hydrogels for biomedical applications using the Diels-Alder reaction were prepared. Furan modified chitosan (Cs-Fu) was cross-linked with polyetheramine derived bismaleimide at different equivalent ratios in order to determine the effect in the swelling and release properties on the final CsFu:BMI hydrogels. The Diels Alder cross-linking reaction was monitored by UV-vis spectroscopy and rheological measurements. Both the sol-gel transition value and the final storage modulus for the different formulations were similar and close to 40 min and 400 Pa, respectively. On the contrary, the swelling degree was found to be strongly dependent on the amount of bismaleimide, mainly in acidic medium, where the increased cross-linking reduced the swelling value in 25%, but maintaining the sustained drug release in the simulated gastrointestinal environment. Our study suggested that these DA-cross-linked chitosan hydrogels could be potential carriers for targeted drug administration.

Polymerization of Formaldehyde and Phenol at Different Pressures

Phenol-formaldehyde resole resins were investigated as regards their cure behaviour using both atmospheric and high-pressure conditions. Results obtained using Fourier transform infrared spectroscopy and solid-state 13C (cross-polarization/magic angle spinning) nuclear magnetic resonance showed different polymerization pathways of the resin into the usually used differential scanning calorimetry pressure resistant crucibles and under atmospheric pressure. Under high pressure conditions a competition between oxidation and polymerization reactions was detected, leading to less methylene bridge formation and more remaining free ortho -positions, with a consequent lower degree of polymerization.

Design of reusable novel membranes based on bacterial cellulose and chitosan for the filtration of copper in wastewaters

This study has been carried out to design novel, environmentally friendly membranes by in situ and ex situ routes based on bacterial cellulose (BC) as a template for the chitosan (Ch) as functional entity for the elimination of copper in wastewaters. Two routes led to bionanocomposites with different aspect and physico-chemical properties. The mechanical behaviour in wet state, strongly related to crystallinity and water holding capacity, resulted to be very different depending on the preparation route although the Ch content was very similar: 35 and 37 wt% for the in situ and ex situ membranes, respectively. The morphological characterization suggested a better incorporation of the Ch into BC matrix through the in situ route. The cooper removal capacity of these membranes was analyzed and in situ prepared membrane showed the highest values, about 50%, for initial concentrations of 50 and 250 mg L-1. Moreover the reusability of the membranes was assessed. This is the first time that the whole 3D nano-network BC membrane is used to provide physical integrity for chitosan to develop eco-friendly membranes with potential applications in heavy metal removal.

By-products of the cider production: an alternative source of nutrients to produce bacterial cellulose

In the present work a culture process to produce bacterial cellulose (BC) using by-products of the cider production from the Basque Country was investigated. The apple pomace was mixed with sugar cane (AR/SC medium) and the mixture was found to be a potential carbon source for Gluconacetobacter medellinensis strain ID13488 since higher cellulose production was observed with respect to the commercial Hestrin and Shramm medium (H–S). The culture media were characterized in terms of pH, oxygen and sugars consumption. The expression level of the operon bcs (genes involved in BC biosynthesis) in apple residue containing medium respect to standard H–S medium was determined. It was found that in AR/SC medium the expression levels of bcsA gene, wich is the first gene of the bcs operon, was increased in 1.5-fold respect to the H–S media which correlates with the fact that BC production in AR/SC media is higher than in H–S media. The physico-chemical and mechanical properties, microstructure, crystallinity and water holding capacity of the biosynthesized BC membranes were analyzed and it was found that, in general, the BC obtained from AR/SC medium presented superior properties than that obtained from H–S medium. In this study an economic method for BC production is proposed with suitable properties for many applications.

Modification of Pea Starch and Dextrin Polymers with Isocyanate Functional Groups

Pea starch and dextrin polymers were modified through the unequal reactivity of isocyanate groups in isophorone diisocyanate (IPDI) monomer. The presence of both urethane and isocyanate functionalities in starch and dextrin after modification were confirmed by Fourier transform infrared spectroscopy (FTIR) and 13C nuclear magnetic resonance (13C NMR). The degree of substitution (DS) was calculated using elemental analysis data and showed higher DS values in modified dextrin than modified starch. The onsets of thermal degradation and temperatures at maximum mass losses were improved after modification of both starch and dextrin polymers compared to unmodified ones. Glass transition temperatures (Tg) of modified starch and dextrin were lower than unmodified control ones, and this was more pronounced in modified dextrin at a high molar ratio. Dynamic water vapor sorption of starch and dextrin polymers indicated a slight reduction in moisture sorption of modified starch, but considerably lower moisture sorption in modified dextrin as compared to that of unmodified ones.