Exploring the relationship between nanoscale dynamics and macroscopic rheology in natural polymer gums.

We report a study connecting the nanoscale and macroscale structure and dynamics of Acacia mearnsii gum as probed by small-angle X-ray scattering (SAXS), X-ray photon correlation spectroscopy (XPCS) and rheology. Acacia gum, in general, is a complex polysaccharide used extensively in industry. Over the analyzed concentration range (15 to 30 wt%) the A. mearnsii gum is found to have a gel-like linear rheology and to exhibit shear thinning flow behavior under steady shear. The gum solutions exhibited a steadily increasing elastic modulus with increasing time after they were prepared and also the emergence of shear thickening events within the shear thinning behavior, characteristic of associative polymers. XPCS measurements using gold nanoparticles as tracers were used to explore the microscopic dynamics within the biopolymer gels and revealed a two-step relaxation process with a partial decay at inaccessibly short times, suggesting caged motion of the nanoparticles, followed by a slow decay at later delay times. Non-diffusive motion evidenced by a compressed exponential line shape and an inverse relationship between relaxation time and wave vector characterizes the slow dynamics of A. mearnsii gum gels. Surprisingly, we have determined that the nanometer-scale mean square displacement of the nanoparticles showed a close relationship to the values predicted from the macroscopic elastic properties of the material, obtained through the rheology experiments. Our results demonstrate the potential applicability of the XPCS technique in the natural polymers field to connect their macroscale properties with their nanoscale structure and dynamics.

pH stimulus-responsive hybrid nanoparticles: A system designed for follicular delivery of brazilian plant-derived 5-alpha-reductase enzyme inhibitors.

The 5-alpha-reductase enzyme, present in pilosebaceous units, plays a crucial role in the appearance of cutaneous hyperandrogenism manifestations (hirsutism, acne, and androgenetic alopecia). Its inhibition is an excellent strategy to reverse these conditions. Given the limitations of existing treatments, with transient effects and delayed therapeutic response, as well as the possibility of causing undesirable side effects, this study sought to develop new drug delivery systems to overcome these limitations. In other words, innovative stimuli-responsive hybrid nanoparticles were synthesized using silica/natural polysaccharides, encapsulating 5-alpha-reductase enzyme inhibitors derived from the plant Stryphnodendron adstringens (Mart.) Coville (commonly known as 'Barbatimão'). Silica core was synthesized by the modified Stöber method. The pH responsive polysaccharides used to coat the porous silica cores were chitosan, and sodium alginate, this coating was carried out using the Layer-by-Layer technique. The hybrid nanoparticles were characterized at molecular and physical-chemical levels. Furthermore, encapsulation efficiency, pH-dependent release behavior, and cytotoxicity were evaluated. Amorphous mesoporous structure with adequate size for follicular delivery (between 300 and 600 nm) in addition to effective phytocompound loading capacity, above 80 % was obtained. Based on the release studies, it was possible to observe pH responsiveness. The ethyl acetate fraction (EAF) obtained from "Barbatimão" bark extract was released in a controlled and more efficient manner by the alginate-coated nanoparticle (SNP_EAF_SA) at pH 7.4, which corresponds to the pH at the deepest area of hair follicles. Furthermore, SNP_EAF_SA proved to be less cytotoxic compared to EAF and chitosan-coated hybrid nanoparticles (SNP_EAF_CH). Characterization, release, and cytotoxicity results indicate that SNP_EAF_SA is a promising system for on-demand follicular delivery of antiandrogenic actives contained in EAF.

Skin interaction, permeation, and toxicity of silica nanoparticles: Challenges and recent therapeutic and cosmetic advances.

Silica nanoparticles (SNPs) received more attention with the emergence of nanotechnology with the aim and promise of becoming innovative drug delivery systems. They have been fulfilling this objective with excellence and nowadays they play a central role in biomedical applications. New SNPs application routes are being explored such as the epidermal, dermal, and transdermal routes. With that, novel models of synthesis, functionalization, and applications constantly appear. However, it is essential that such innovations are accompanied by in-depth studies on permeation, biodistribution, metabolization, and elimination of the generated by-products. Such studies are still incipient, if not rare. This article reviews significant findings on SNPs and their skin interactions. An extensive literature review on SNPs synthesis and functionalization methodologies was performed, as well as on the skin characteristics, skin permeation mechanisms, and in vivo toxicity assessments. Furthermore, studies of the past 5 years on the main therapeutic and cosmetic products employing SNPs, with greater emphasis on in vivo and ex vivo studies were included.

Biocompatible gum arabic-gold nanorod composite as an effective therapy for mistreated melanomas.

Advanced melanoma patients that are not included in common genetic classificatory groups lack effective and safe therapeutic options. Chemotherapy and immunotherapy show unsatisfactory results and devastating adverse effects for these called triple wild-type patients. New approaches exploring the intrinsic antitumor properties of gold nanoparticles might reverse this scenario as a safer and more effective alternative. Therefore, we investigated the efficacy and safety of a composite made of gum arabic-functionalized gold nanorods (GA-AuNRs) against triple wild-type melanoma. The natural polymer gum arabic successfully stabilized the nanorods in the biological environment and was essential to improve their biocompatibility. In vivo results obtained from treating triple wild-type melanoma-bearing mice showed that GA-AuNRs remarkably reduced primary tumor growth by 45%. Furthermore, GA-AuNRs induced tumor histological features associated with better prognosis while also reducing superficial lung metastasis depth and the incidence of intrapulmonary metastasis. GA-AuNRs' efficacy comes from their capacity to reduce melanoma cells ability to invade the extracellular matrix and grow into colonies, in addition to a likely immunomodulatory effect induced by gum arabic. Additionally, a broad safety investigation found no evidence of adverse effects after GA-AuNRs treatment. Therefore, this study unprecedentedly reports GA-AuNRs as a potential nanomedicine for advanced triple wild-type melanomas.

Gold nanocolloid-protein interactions and their impact on ß-sheet amyloid fibril formation.

The influence of the presence of small molecules and nanoparticles on the mechanism of amyloid fibril formation has attracted attention because amyloid protein fibrils are associated with degenerative diseases. Here, we studied the interaction between gold nanoparticles (AuNPs) and a model protein (lysozyme). Both the formation of amyloid fibrils in the presence of gold nanoparticles, as well as the interaction between lysozyme and the amyloid fibrils with AuNPs, were investigated to gain an understanding of the distinct behaviour of lysozyme in its fibrillar and globular form. It was observed that the presence of AuNPs delayed the unfolding of α-helixes present in the globular lysozyme and the formation of the amyloid fibrils. However, the addition of AuNPs was also associated with a larger amount of ß-sheet structures in the system once equilibrium was reached. Furthermore, the results showed that the driving force of the interaction between AuNPs and lysozyme in its fibrillar and globular forms was significantly different, and that the interaction of AuNPs with the preformed lysozyme amyloid fibrils led to a structural change in the protein.

Correction: Stability of gum Arabic-gold nanoparticles in physiological simulated pHs and their selective effect on cell lines.

[This corrects the article DOI: 10.1039/C5RA24858B.].

Physical-chemical characteristics and potential use of a novel alginate/zein hydrogel as the sorption phase for polar organic compounds.

A novel alginate based hydrogel was successfully prepared and tested for the solid phase microextraction of medium-to-high polarity compounds, when supported in a polypropylene (PP) fiber. Pure alginate when added onto the surface of the PP fiber, resulted in a significant improvement in the extraction efficiency of the analytes (except for ß-estradiol). The alginate hydrogel was modified upon the incorporation of a small amount of zein, a corn protein. Interestingly, the alginate/zein-supported hydrogel was capable of successfully extracting compounds with low partition constant (Kow), such as 17-α-ethinyl estradiol, progesterone and estriol, since the initial water uptake decreased dramatically in this gel, therefore, leaving the alginate hydroxyl groups more available to interact with the polar compounds. In conclusion, this paper presents the preparation of a simple, low cost, reusable, and efficient sorption phase for the extraction of polar compounds with different polarities in aqueous samples, which is a current technological challenge in developing efficient wastewater treatment.

Effect of low and high methoxyl citrus pectin on the properties of polypyrrole based electroactive hydrogels.

Electroactive hydrogels were prepared using commercial citric pectin, either raw (PC) or purified through dialysis (dPC), and chemically synthesized polypyrrole (PPy). 1H NMR analyses showed that PC is a low methoxyl pectin (degree of methoxylation, DM=46%) and dPC is a high methoxyl pectin (DM=77%). The pyrrole polymerization was monitored through UV-vis spectroscopy and both samples were observed to be good stabilizers for PPy in aqueous medium. The dispersions were used to prepare the hydrogels h-PC-PPy and h-dPC-PPy. The hydrogel h-dPC-PPy has a higher swelling index (SI≈25%) at pH 1.2 than the hydrogel h-PC-PPy (SI≈7%). Contrastingly, at pH 6.8 both hydrogels lost their mechanical integrity. Raman spectroscopy revealed that PPy is more oxidized in h-PC-PPy. Nevertheless, both hydrogels are electroactive and therefore can be considered for applications in which the control of the degree of swelling is desired.

Surface interactions of gold nanorods and polysaccharides: From clusters to individual nanoparticles.

Gold nanorods (AuNRs) are suitable for constructing self-assembled structures for the development of biosensing devices and are usually obtained in the presence of cetyltrimethylammonium bromide (CTAB). Here, a sulfated chitosan (ChiS) and gum arabic (GA) were employed to encapsulate CTAB/AuNRs with the purpose of studying the interactions of the polysaccharides with CTAB, which is cytotoxic and is responsible for the instability of nanoparticles in buffer solutions. The presence of a variety of functional groups such as the sulfate groups in ChiS and the carboxylic groups in GA, led to efficient interactions with CTAB/AuNRs as evidenced through UV-vis and FTIR spectroscopies. Electron microscopies (HR-SEM and TEM) revealed that nanoparticle clusters were formed in the GA-AuNRs sample, whereas individual AuNRs, surrounded by a dense layer of polysaccharides, were observed in the ChiS-AuNRs sample. Therefore, the presented work contributes to the understanding of the driving forces that control the surface interactions of the studied materials, providing useful information in the building-up of gold self-assembled nanostructures.

Native and structurally modified gum arabic: exploring the effect of the gum's microstructure in obtaining electroactive nanoparticles.

Electroactive nanoparticles combining gum arabic (GA) and polyaniline (PANI) were prepared by chemical synthesis. The gum consists of highly branched anionic polysaccharides with some protein content. GA was structurally modified by Smith controlled degradation, in order to reduce its degree of branching (GAD), aiming the elucidation of the relationship between the structure and the properties of complex polysaccharides. The modification was studied by SEC, GC-MS, (13)C NMR and colorimetric methods. GAD has lower molecular mass, lower degree of branching and lower uronic acid content. Besides it is enriched in galactose and protein when compared with GA. The obtained composites (GA-PANI and GAD-PANI) were thoroughly characterized. Although the use of both polysaccharides (GA and GAD) produced highly stable electroactive nanoparticles, the best combination of properties was achieved for GA-PANI. The sample GAD was not able to prevent the occurrence of crosslinking between PANI chains, possibly due to its lower microstructural complexity which diminishes the occurrence of hydrogen bonds between the polymers.

A tailored biocatalyst achieved by the rational anchoring of imidazole groups on a natural polymer: furnishing a potential artificial nuclease by sustainable materials engineering.

Foreseeing the development of artificial enzymes by sustainable materials engineering, we rationally anchored reactive imidazole groups on gum arabic, a natural biocompatible polymer. The tailored biocatalyst GAIMZ demonstrated catalytic activity (>10(5)-fold) in dephosphorylation reactions with recyclable features and was effective in cleaving plasmid DNA, comprising a potential artificial nuclease.

The use of gum Arabic as "Green" stabilizer of poly(aniline) nanocomposites: a comprehensive study of spectroscopic, morphological and electrochemical properties.

Herein we show the synthesis and characterization of water dispersible composites formed by poly(aniline) and the natural polymer gum Arabic (GA), used as stabilizer. The materials were synthesized via a rapid and straightforward method and were fully characterized by different techniques such as UV-Vis, Raman, FTIR, TEM, SEM and cyclic voltammetry. TEM and SEM images revealed that the proportion of stabilizer highly influences the growth mechanism of the nanostructures. It was found spherical particles, elongated structures and large agglomerates at the lower, intermediate and at the higher GA amount, respectively. Accordingly to fluorescence spectra, different hydrophobic structures are formed depending on the GA amount in aqueous solutions, possibly acting as hosting sites for the PANI growth. In order to further study the PANI polymerization in the presence of GA, kinetics experiments were performed and showed that nucleation is the limiting step for the composite growth and a model is proposed. Spectroscopic experiments showed that the presence of GA affects the PANI conformation, avoiding the formation of phenazine structures which highly impairs the electroactivity of PANI. The material integrity is achieved by strong hydrogen bond interactions between PANI and GA as evidenced by the study of specific NH bands in FTIR and Raman analyses. The intensity of the hydrogen bonds decreased upon higher amounts of GA, probably due to steric impediment around the NH sites. Cyclic voltammograms showed a good electroactivity behavior of the modified electrodes presenting distinguishable diffusional processes through the adsorbed composites. By this way, we have thoroughly investigated the formation and properties of new conducting polymer composite materials. Taken into account the low toxicity of GA and the excellent dispersity in water, the materials can successfully be applied in bioelectrochemical applications or as green corrosion inhibitors.

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.

Property evaluations of dry-cast reconstituted bacterial cellulose/tamarind xyloglucan biocomposites.

We describe the mechanical defibrillation of bacterial cellulose (BC) followed by the dry-cast generation of reconstituted BC films (RBC). Xyloglucan (XGT), extracted from tamarind seeds, was incorporated into the defibrillated cellulose at various compositions, and new films were created using the same process. Microscopy and contact angle analyses of films revealed an increase in the microfibre adhesion, a reduced polydispersity in the diameters of the microfibrils and increased hydrophobic behaviour as a function of %XGT. X-ray diffraction analysis revealed changes to the crystallographic planes of the RBC and the biocomposite films with preferential orientation along the (110) plane. Compared with BC, RBC/XGT biocomposite with 10% XGT exhibited improvement in its thermal properties and in Young's modulus. These results indicated a reorganisation of the microfibres with mechanical treatment, which when combined with hydrocolloids, can create cellulose-based materials that could be applied as scaffolding for tissue engineering and drug release.

Structural characterization and emulsifying properties of polysaccharides of Acacia mearnsii de Wild gum.

Polysaccharides (GNF) from Acacia mearnsii de Wild gum exudates, collected from trees growing in the south of Brazil, were characterized ((13)C and HSQC NMR, GC-MS, colorimetric assays). A commercial gum arabic (GAC) was analyzed similarly and compared with GNF. There were differences, consistent with distinct behavior in tensiometry tests and as emulsion stabilizer. GNF had a higher protein content than GAC, with small differences in the monosaccharide composition, the greater one being the lower uronic acid content of GNF (4%), compared with GAC (17%). GNF had a much broader molecular mass distribution, M(w)/M(n), and a lower M(w). GNF was more efficient in lowering the surface tension of water and saline solutions and was more efficient in emulsifying castor oil droplets. Results were discussed taking into account structural and molecular differences between the studied gums. It was concluded that polysaccharides from A. mearnsii de Wild are candidates as substitutes of currently commercialized arabic gums (Acacia senegal and Acacia seyal) having, depending on their application, improved properties.