Adriana F. Lubambo

Electrospinning of commercial guar-gum: Effects of purification and filtration

Guar gums of two different commercial sources were successfully electrospun on both mica and copper tape at several concentrations starting from 1% (w/w). The electrospun fibers formed with the raw materials were not uniform and presented aggregates and beads within the fibers. Two different purification procedures and a filtration sequence with different pore size membranes were applied to enhance galactomannan solution homogeneity and solubility. The consequence was improved fiber morphology. We observed that the precipitation step, within the purification procedure, produced changes in the molar mass distribution and yielded different fiber diameter. Furthermore, spherical aggregates between fibers and within them disappeared after the sequential filtration. The resulting electrospun fiber diameter decreased with membrane pore diameter reduction. We conclude that the filtration process is responsible for molecular disentanglement, as well as disaggregation, which leads to improved electrospun galactomannan fiber morphology.

Diamond thermal expansion measurement using transmitted X-ray back-diffraction.

The linear thermal expansion coefficient of diamond has been measured using forward-diffracted profiles in X-ray backscattering. This experimental technique is presented as an alternative way of measuring thermal expansion coefficients of solids in the high-resolution Bragg backscattering geometry without the intrinsic difficulty of detecting the reflected beam. The temperature dependence of the lattice parameter is obtained from the high sensitivity of the transmitted profiles to the Bragg angle variation with temperature. The large angular width of the backscattering profiles allows the application of this technique to mosaic crystals with high resolution. As an application of this technique the thermal expansion coefficient of a synthetic type-Ib diamond (110) single crystal was measured from 10 to 300 K. Extremely low values (of the order of 1 x 10(-7) +/- 5 x 10(-7)) for the linear thermal expansion coefficient in the temperature range from 30 to 90 K are in good agreement with other reported measurements.

Adsorption of protein glnB of Herbaspirillum seropedicae on Si(111) investigated by AFM and XPS

The protein GlnB-Hs (GlnB of Herbaspirillum seropedicae) in diazotroph micro-organisms signalizes levels of nitrogen, carbon, and energy for a series of proteins involved in the regulation of expression and control of the activity of nitrogenase complex that converts atmospheric nitrogen in ammonia, resulting in biological nitrogen fixation. Its structure has already been determined by X-ray diffraction, revealing a trimer of (36 kDa) with lateral cavities having hydrophilic boundaries. The interactions of GlnB-Hs with the well-known Si(111) surface were investigated for different incubation times, protein concentrations in initial solution, deposition conditions, and substrate initial state. The protein solution was deposited on Si(111) and dried under controlled conditions. An atomic force microscope operating in dynamic mode shows images of circular, linear, and more complex donut-shaped protein arrangement, and also filament types of organization, which vary from a few nanometers to micrometers. Apparently, the filament formation was favored because of protein surface polarity when in contact with the silicon surface, following some specific orientation. The spin-coating technique was successfully used to obtain more uniform surface covering.

Tuning protein GlnB-Hs surface interaction with silicon: FTIR-ATR, AFM and XPS study.

Herbaspirillum seropedicae GlnB (GlnB-Hs) is a signal transduction protein involved in the control of nitrogen, carbon and energetic metabolism. The adsorption of GlnB-Hs deposited by spin coating on hydrophilic and hydrophobic silicon forms a thin layer that was characterized using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared attenuated total reflectance spectroscopy (FTIR-ATR). AFM allowed the identification of globular, face-up donut like array of protein on hydrophilic silicon substrate, favoring deprotonated residues to contact the silicon oxide surface. Over hydrophobic silicon, GlnB-Hs adopts a side-on conformation forming a filament network, avoiding the contact of protonated residues with silicon surface. XPS allowed us to determine the protonated and non-protonated states of nitrogen 1s (N 1s). The FTIR-ATR measurements provided information about protein secondary structure and its conservation, after surface adsorption.

Nanometric organisation in blends of gellan/xyloglucan hydrogels

Mixtures of gellan gum (GL) and a xyloglucan (XGJ) extracted from Hymenaea courbaril seeds were prepared in a solution of 0.15 mol L(-1) NaCl. Rheology measurements revealed that 2.4 g L(-1) pure GL formed a brittle hydrogel, and GL-XGJ blends showed improved pseudoplastic character with higher XGJ contents. SAXS analyses showed that the Rg dimensions ranged from 1.3 to 4.9 nm, with larger values occurring as the amount of XGJ increased, and diffusion tests indicated that better diffusion of methylene blue dye was obtained in the network with a higher XGJ content. AFM topographic images of the films deposited onto mica revealed fewer heterogeneous surfaces with increased XGJ contents. The water contact angle revealed more hydrophobic character on all of the films, and the wettability decreased with increasing amounts of XGJ. Therefore, the demonstrated benefit of using XGJ blends is the production of a soft material with improved interface properties.

Tuning Fe3O4 nanoparticle dispersion through pH in PVA/guar gum/electrospun membranes.

Polyvinyl Alcohol (PVA)/guar gum (GG) membranes with different loads of paramagnetic iron oxide Fe3O4 nanoparticles were successfully electrospun using both non-alkaline and alkaline stock solutions. The nanoparticle homogeneity distribution was clearly enhanced in fibers obtained from alkaline stock solutions. This is mainly due to the interaction between GG and the metallic ion, which also leads to further dispersion of remained uncoated nanoparticles in the mixture. It was also noticed that GG favors nanoparticle stability in the mixture and contributes to nanoparticle encapsulation. X-ray results showed that all membranes were semi-crystalline. FTIR-ATR spectra showed that Fe-O absorption band intensity improved with increasing nanoparticle load, reaching saturation at 3.5mg/ml Fe3O4 concentration under alkaline conditions. VSM analyses showed that the nanoparticles are paramagnetic and were successfully incorporated by the fibers. In vitro biocompatibility tests using L929 cells indicates adequate levels of cytotoxicity and cell adhesion/proliferation assays for both membranes obtained from non-alkaline and alkaline stock solutions. Therefore, they have potential for biomedical applications as biodegradable wound dressing.

Dewetting pattern and stability of thin xyloglucan films adsorbed on silicon and mica

Thin polysaccharide films prepared with xyloglucan (XG), a neutral polysaccharide extracted from the seeds of Guibourtia hymenifolia were prepared by spin-coating and drop deposition under pH3, pH5 and pH12, on silicon and mica substrates. Atomic force microscopy (AFM) images show flat nanoporous matrices with additional grain-like structures on both mica and silicon for pH 3 and pH 5. However, X-ray photoelectron spectroscopy (XPS) and Auger spectra of these adsorbed biopolymers prepared under alkaline condition (pH 12) reveal that Na(+) ions from the solution interact with the mica substrate surface and with XG forming chemical bonds. Both XPS and Auger results suggest XG depolymerisation during adsorption, caused by an alkaline ss-base catalyzed degradation mechanism, which is consistent with the more basic character of the mica surface under these conditions. Thus, the polysaccharide diffusion is inhibited during dewetting due to the surface bonding. On the other hand, the interaction of Na(+) in solution with the silicon surface is weaker, favoring its interaction with the polysaccharide, conserving the overall polymer structure of XG and allowing the biopolymer to slip and diffuse during dewetting, forming the final branched fractal structure.

Physicochemical and in vitro biocompatibility of films combining reconstituted bacterial cellulose with arabinogalactan and xyloglucan.

Reconstituted cellulose films were generated using residual bacterial cellulose membranes mechanically defibrillated (RBC fibrils) recycled following wound dressing production via a dry-cast process. Arabinogalactan (AG) extracted from Pereskia aculeata leaves and/or a xyloglucan (GHXG) from Guibourtia hymenifolia seeds were incorporating into the RBC at various compositions, and new films were created using the same process. Biocomposite properties were evaluated by scanning electron microscopy, contact angle (CA), and X-ray diffraction measurements. The attachment and proliferation of murine L929 fibroblasts on RBC and RBC/Hydrocolloids (HD) were also evaluated. RBC films with 20-30% GHXG replacement improved film stability and the inclusion of HD increased microfiber aggregation and reduced porous regions. Changes in the hydrophilic characteristics were also observed and owing to the adhesion effect the inclusion of HD on RBC led to a statistically significant effect of the mechanical properties of films. The RBC/AG films supported L929 adhesion similar to that observed for commercial bacterial cellulose, indicating their potential use for biomedical applications.

AFM characterization of spin coated carboxylated polystyrene nanospheres/xyloglucan layers on mica and silicon

Self-assembled nano-arrays have a potential application as solid-phase diagnostics in many biomedical devices. The easiness of its production is directly connected to manufacture cost reduction. In this work, we present self-assembled structures starting from spin coated thin films of carboxylated polystyrene (PSC) and xyloglucan (XG) mixtures on both mica and silicon substrates. AFM images showed PSC nanospheres on top of a homogeneous layer of XG, for both substrates. The average nanosphere diameter fluctuated for a constant speed and it was likely to be independent of the component proportions on the mixture within a range of 30-50% (v/v) PSC. It was also observed that the largest diameters were found at the center of the sample and the smallest at the border. The detected nanospheres were also more numerous at the border. This behavior presents a similarity to spin coated colloidal dispersions. We observed that the average nanosphere diameter on mica substrates was bigger than the nanosphere diameters obtained on top of silicon substrates, under the same conditions. This result seems to be possibly connected to different mixture-surface interactions.