Chitin Nanocrystals Research Articles

Interactions of chitin nanocrystals with β-lactoglobulin at the oil–water interface, studied by drop shape tensiometry

Particle stabilized emulsions have been gaining increasing attention in the past few years, because of their unique interfacial properties. However, interactions between food grade particles and other surfactants at the interface still need to be understood. In this research, the interfacial properties of chitin nanocrystals (ChN) were studied in the presence of a surface active milk protein, β-lactoglobulin (β-lg), often used to stabilize oil-in-water emulsions. ChN were prepared by acid hydrolysis of chitin. At low pH (pH 3), ChN and β-lg do not interact, as demonstrated by light scattering measurements, and both components carry positive charge. The properties of the interface were tested using drop shape tensiometry. Addition of ChN or β-lg to the aqueous phase reduced the interfacial tension, and β-lg adsorption was characterized with an increase in the interfacial elasticity. When β-lg was added to a solution containing 0.1% ChN, the film elasticity increased first and then decreased with increasing β-lg concentration. The mixed film elasticity was the highest at a combination of 0.1% ChN+0.01% β-lg, when both molecules were simultaneously added to the aqueous phase. On the other hand, when β-lg was added after ChN, the protein did not affect the properties of the interface, indicating that the ChN (0.1%) equilibrated film was stable and that protein–protein interactions, normally resulting in an increase in the film elasticity, did not occur.

Effect of soluble polysaccharides addition on rheological properties and microstructure of chitin nanocrystal aqueous dispersions

Mixtures of chitin nanocrystal aqueous dispersions (at pH 3.0) with soluble polysaccharides of varying molecular features were examined rheologically and microscopically, under different conditions of biopolymer concentration, ionic strength, pH and temperature. The addition of non-adsorbing polysaccharides (guar gum, locust bean gum and xanthan) as well as oppositely charged (κ-carrageenan) to a chitin nanocrystal dispersion, resulted in a network formation and the gel strength increased with the chitin nanocrystal concentration. In contrast, the chitin nanocrystal – chitosan or – pullulan mixed dispersions did not show any network formation (tanδ>1) at the concentration range examined. An increase in ionic strength and pH also resulted in an enhanced elasticity of the chitin nanocrystal–guar gum dispersions. Furthermore, an increase in the elastic modulus, which was irreversible upon cooling, was observed upon heating the chitin nanocrystal–polysaccharide mixed dispersions.

Thermo-mechanical properties of the composite made of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) and acetylated chitin nanocrystals

Acetylated chitin nanocrystals were prepared through surface modification, and biodegradable poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/chitin nanocrystals films were produced via solution-casting method. Transmission electron microscopy observations and X-ray diffraction profiles revealed that the rod-like morphology and crystal structure of chitin nanocrystals were maintained. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy results showed that the hydroxyl groups were partly replaced by the acetyl groups on the surface of chitin nanocrystals. The hydrophobic performance of the acetylated chitin nanocrystals was significantly increased according to the contact angle measurements. Differential scanning calorimeter results indicated that the influence of chitin nanocrystals on the crystallization behaviors of PHBV matrix was changed from suppression to assistance after the surface modification. Tensile test showed that the tensile strength and Young's modulus of PHBV/acetylated chitin nanocrystals composites were improved by 44% and 67%, comparing to the improvement of 24% and 43% for PHBV/chitin nanocrystals composites with the addition of 5.0wt.% nanocrystals into PHBV.

Chitin nanowhisker aerogels.

Chitin nanowhiskers are structured into mesoporous aerogels by using the same benign process used previously in our group to make cellulose nanowhisker aerogels. The nanowhiskers are sonicated in water to form a hydrogel before solvent-exchange with ethanol and drying under supercritical CO2 (scCO2). Aerogels are prepared with various densities and porosities, relating directly to the initial chitin nanowhisker content. scCO2 drying enables the mesoporous network structure to be retained as well as allowing the gel to retain its initial dimensions. The chitin aerogels have low densities (0.043–0.113 g cm−3), high porosities (up to 97 %), surface areas of up to 261 m2 g−1, and mechanical properties at the high end of other reported values (modulus between 7 and 9.3 MPa). The aerogels were further characterized by using X-ray diffraction, BET analysis, electron microscopy, FTIR, and thermogravimetric analysis. Characterization showed that the rod-like crystalline nature of the nanowhiskers was retained during the aerogel production process, making the aerogel truly an assembled structure of chitin nanocrystals. These aerogels also showed the lowest reported shrinkage during drying to date, with an average shrinkage of only 4 %.

Nanocomposites of bacterial cellulose nanofibers and chitin nanocrystals: fabrication, characterization and bactericidal activity

An environmentally friendly approach was implemented for the production of nanocomposites with bactericidal activity, using bacterial cellulose (BC) nanofibers and chitin nanocrystals (ChNCs). The antibacterial activity of ChNCs prepared by acid hydrolysis, TEMPO-mediated oxidation or partial deacetylation of α-chitin powder was assessed and the structure of the ChNC nanoparticles was characterized by X-ray diffraction, atomic force microscopy, and solid-state 13C-NMR. The partially deacetylated ChNCs (D-ChNC) showed the strongest antibacterial activity, with 99 ± 1% inhibition of bacterial growth compared to control samples. Nanocomposites were prepared from BC nanofibers and D-ChNC by (i) in situ biosynthesis with the addition of D-ChNC nanoparticles in the culture medium of Acetobacter aceti, and (ii) post-modification by mixing D-ChNC with disintegrated BC in an aqueous suspension. The structure and mechanical properties of the BC/D-ChNC nanocomposites were characterized by Fourier transform infrared spectroscopy, elemental analysis, field-emission scanning electron microscopy, and an Instron universal testing machine. The bactericidal activity of the nanocomposites increased with the D-ChNC content, with a reduction in bacterial growth by 3.0 log units when the D-ChNC content was 50%. D-ChNC nanoparticles have great potential as substitutes for unfriendly antimicrobial compounds such as heavy metal nanoparticles and synthetic polymers to introduce antibacterial properties to cellulosic materials.

In vitrolipid digestion of chitinnanocrystal stabilized o/w emulsions

Chitin nanocrystals (ChN) have been shown to form stable Pickering emulsions. These oil-in-water emulsions were compared with conventional milk (whey protein isolate, WPI, and sodium caseinate, SCn) protein-stabilized emulsions in terms of their lipid digestion kinetics using an in vitro enzymatic protocol. The kinetics of fatty acid release were evaluated as well as the change in oil droplet size of the respective emulsions during lipid digestion. The interfacial pressure was measured by addition of the duodenal components using drop tensiometry and the electrical charge of the oil droplets was also assessed, in an attempt to relate the interfacial properties with the stability of the emulsions towards lipolysis. Lipid hydrolysis in the ChN-stabilized emulsion was appreciably slower and the plateau values of the total concentration of fatty acids released were much lower, compared to the WPI- and SCn-stabilized emulsions. Moreover, the ChN-stabilized emulsions were relatively stable to coalescence during lipid digestion, whereas the WPI- and SCn-stabilized emulsions exhibited a significant increase in their droplet size. On the other hand, no major differences were shown among the different emulsion samples in terms of their interfacial properties. The increased stability of the ChN-stabilized emulsions towards lipolysis could be attributed to several underlying mechanisms: (i) strong and irreversible adsorption of the chitin nanocrystals at the interface that might inhibit an extensive displacement of the solid particles by bile salts and lipase, (ii) network formation by the nanocrystals in the bulk (continuous) phase that may reduce lipid digestion kinetics, and (iii) the ability of chitin, and consequently of ChNs, to impair pancreatic lipase activity. The finding that ChNs can be used to impede lipid digestion may have important implications for the design and fabrication of structured emulsions with controlled lipid digestibility that could provide the basis for the development of novel products that may promote satiety, reduce caloric intake and combat obesity.

Chitin Whiskers: An Overview

Chitin is the second most abundant semicrystalline polysaccharide. Like cellulose, the amorphous domains of chitin can also be removed under certain conditions such as acidolysis to give rise to crystallites in nanoscale, which are the so-called chitin nanocrystals or chitin whiskers (CHWs). CHW together with other organic nanoparticles such as cellulose whisker (CW) and starch nanocrystal show many advantages over traditional inorganic nanoparticles such as easy availability, nontoxicity, biodegradability, low density, and easy modification. They have been widely used as substitutes for inorganic nanoparticles in reinforcing polymer nanocomposites. The research and development of CHW related areas are much slower than those of CW. However, CHWs are still of strategic importance in the resource scarcity periods because of their abundant availability and special properties. During the past decade, increasing studies have been done on preparation of CHWs and their application in reinforcing polymer nanocomposites. Some other applications such as being used as feedstock to prepare chitosan nanoscaffolds have also been investigated. This Article is to review the recent development on CHW related studies.

New chitin complexes and their anti-aging activity from inside out.

Nutritional and topical antioxidants and immuno-modulant compounds play a key role in maintaining healthy skin. However, little is known about the combined effects antioxidant cosmeceuticals and nutricosmetics can have on the appearance of aging skin. The clinical trial was designed to study the combined effects on skin hydration, superficial lipids, elasticity, peroxidation and global clinical appearance, of melatonin, Vit. E and Betaglucan (MEB) complexed with chitin nano-crystals administered both topically and orally. Clinical examinations were conducted by dermatologists. By a randomized placebo-controlled, 12 week multicenter study on 70 healthy subjects, affected with skin photo-aging, the anti-aging efficacy and tolerability of the combined activity of topical emulsion and oral hard capsules, containing MEB complexed with chitin nano-crystals (CN) was evaluated clinically and by biophysical non-invasive measurements at week 4,8 and 12. The effects of MEB intake resulted significantly higher (p<0.005) than placebo for all the parameters evaluated by biophysical and clinical measurements. The values resulted higher when the active ingredients MEB were complexed with CN, whether used topically, orally or a combination of both (p<0.05). The positive results, observed since week 4, were accompanied by no side-effects throughout the entire study. The combined topical and oral use of MEB was associated with reduced wrinkling, better skin appearance and general overall wellness. When MEB were complexed with CN, the obtained results were statistically more positive (p<0.05) for all the biophysical and clinical parameters considered.

Chitin nanocrystals grafted with poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and their effects on thermal behavior of PHBV.

Chemically modified chitin nanocrystals were synthesized by grafting poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) onto chitin backbone via chlorination. Acetyl amino group was maintained in the reaction. The chemical structure and morphology of PHBV grafted chitin nanocrystals were characterized by Fourier transform infrared, Transmission electron microscopy and X-ray photoelectron spectroscopy. Contact angle measurement showed that the lipophilicity of chitin was improved by the surface modification. The effects of original chitin and PHBV-graft-chitin nanocrystals on the crystallizing and melting behavior of PHBV were studied by differential scanning calorimeter (DSC). The results indicated that both unmodified and modified chitin nanocrystals suppressed crystallization of PHBV. The melt point of PHBV was increased after being mixed with nanofillers.

Oil-in-water emulsions stabilized by chitin nanocrystal particles

The aim of the present study was to investigate the oil-in-water emulsion stabilizing ability of chitin nanocrystals (colloidal rod-like particles) and the factors that may influence the properties of such systems. Chitin nanocrystal aqueous dispersions were prepared by acid hydrolysis of crude chitin from crab shells and oil-in-water emulsions were generated by homogenizing appropriate quantities of a chitin nanocrystal stock aqueous dispersion with corn oil, using an ultra-sonic homogenizer. The resulting emulsions were visually evaluated for their creaming behaviour upon storage. Additionally, the samples were studied with static light scattering, small deformation oscillatory rheometry and optical microscopy, under different conditions of nanocrystal concentration, ionic strength, pH and temperature. The chitin nanocrystals were proven quite effective in stabilizing o/w emulsions against coalescence, over a period of one month, as evidenced by static light experiments and microscopy, and this could be attributed to the adsorption of the nanocrystals at the oil–water interface. The rheological data provided evidence for network formation in the emulsions with increasing chitin nanocrystal concentration. Such a gel-like behaviour was attributed to an inter-droplet network structure and the formation of a chitin nanocrystal network in the continuous phase. The stability of the emulsions to creaming increased with an increase in nanocrystal concentration. Finally, by raising the temperature (20–74 °C), NaCl concentration (up to 200 mM) or pH (from 3.0 to 6.7) there was an enhancement of the emulsion elastic character and creaming stability.

From Waste Materials Skin-Friendly Nanostructured Products to Save Humans and the Environment

Waste material from the fishing industry disposed off-shore exceeds 250 billion tons/year, and it is considered hazardous due to its high perishability and polluting effect, both on land and sea. Considering the actual production of chitin, chitosan and oligosaccharides from crustaceons, it is understandable how difficult it is to eliminate all the waste material obtained from food industry, therefore the need for more innovation and creativity. With this in mind we propose an industrial use of the natural chitin nanocrystals (known as chitin-nanofibrils-CN) to produce innovative cosmetics, food supplements and protective films that can improve our way of living while saving the environment.

Mixed aqueous chitin nanocrystal–whey protein dispersions: Microstructure and rheological behaviour

Chitin nanocrystals (ChN) and whey protein isolate (WPI) aqueous dispersions (at pH 3.0) of different polymer concentrations were mixed and examined with small deformation oscillatory measurements and polarized optical microscopy, under different conditions of ionic strength and temperature. The ChN–WPI mixed dispersions displayed a gel-like behaviour with increasing either the ChN or the WPI concentration. The network formation could be attributed to phase separation phenomena, as evidenced by the micrographs obtained, due to thermodynamic incompatibility between the two components; i.e. the addition of WPI, as a globular biopolymer mixture, in a dispersion of rod-like particles (ChN) leads to the formation of ChN-rich and ChN-poor domains. Increasing ionic strength did not significantly affect the viscoelastic properties of the network. However, heating of the ChN–WPI mixed dispersions resulted in further increase of the elastic modulus, which was irreversible upon cooling.

Processing of Polymer Nanocomposites Reinforced with Polysaccharide Nanocrystals

Aqueous suspensions of polysaccharide (cellulose, chitin or starch) nanocrystals can be prepared by acid hydrolysis of biomass. The main problem with their practical use is related to the homogeneous dispersion of these nanoparticles within a polymeric matrix. Water is the preferred processing medium. A new and interesting way for the processing of polysaccharide nanocrystals-based nanocomposites is their transformation into a co-continuous material through long chain surface chemical modification. It involves the surface chemical modification of the nanoparticles based on the use of grafting agents bearing a reactive end group and a long compatibilizing tail.

Metastability of Nematic Gels Made of Aqueous Chitin Nanocrystal Dispersions

Chitin nanocrystal aqueous dispersions were prepared by acid hydrolysis of crude chitin from crab shells. The resulting dispersions were studied with small deformation oscillatory experiments and polarized optical microscopy under different conditions of nanocrystal concentration, ionic strength, pH, and temperature. The chitin nanocrystal dispersions exhibited a nematic gel-like behavior with increasing solids concentration. The appearance of nematic-like structures could be explained by the Onsager theory for parallel alignment of anisotropic particles on entropic terms, while the sol-gel transition could be attributed to associative interactions between the chitin nanocrystals. With increasing ionic strength and pH, such associative interactions were enhanced, because the repulsive forces due to the electrostatic charges were reduced and, thus, stronger gels were formed. Heating of the nanocrystal dispersions led to further increases in the storage modulus (G'), which were irreversible upon cooling; the rate of G' increase (dG'/dt) was dependent on temperature.

Cross-Linked Chitosan/Chitin Crystal Nanocomposites with Improved Permeation Selectivity and pH Stability

This study is aimed at developing and characterizing cross-linked bionanocomposites for membrane applications using chitosan as the matrix, chitin nanocrystals as the functional phase, and gluteraldehyde as the cross-linker. The nanocomposites' chemistry and morphology were examined by estimation of gel content, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and atomic force microscopy (AFM), whereby the occurrence of cross-linking and nanoscale dispersion of chitin in the matrix was confirmed. Besides, cross-linking and chitin whiskers content were both found to impact the water uptake mechanism. Cross-linking provided dimensional stability in acidic medium and significantly decreased the equilibrium water uptake. Incorporation of chitin nanocrystals provided increased permeation selectivity to chitosan in neutral and acidic medium.

Chitin Nanocrystals Prepared by TEMPO-Mediated Oxidation of α-Chitin

Chitin nanocrystals dispersed in water were successfully prepared by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) mediated oxidation of alpha-chitin in water at pH 10 under specific conditions, followed by ultrasonic treatment. When the amount of NaClO added as co-oxidant in the oxidation was 5.0 mmol/g of chitin, the weight percentage of the water-insoluble fraction in the TEMPO-oxidized chitin was 90%, and its carboxylate content reached 0.48 mmol/g. Since the TEMPO-oxidized chitin thus prepared had a crystallinity as high as that of the original alpha-chitin, the C6 carboxylate groups formed by TEMPO-mediated oxidation can be regarded as being present only on the chitin crystallite surfaces. No N-deacetylation occurred on the TEMPO-oxidized chitins. When the TEMPO-oxidized chitin was subjected to ultrasonic treatment in water, mostly individualized chitin nanocrystals were obtained, and the average nanocrystal length and width were 340 and 8 nm, respectively.

α-Chitin Nanocrystals Prepared from Shrimp Shells and Their Specific Surface Area Measurement

Alpha-chitin was isolated from shrimp shells. The chitin was subjected to extensive treatments of acid hydrolysis and mechanical disruption to yield nanocrystals. The goal of this article is to characterize alpha-chitin nanocrystals produced from shrimp shells in regard to crystallite properties and the specific surface area of the chitin nanoparticles. X-ray diffraction data indicate an increase in chitin crystallinity after hydrolysis, as less-ordered chitin domains are digested. Line broadening data were used to measure crystallite size and particle size in the hydrolyzed chitin nanocrystals. Dye adsorption with Congo red was used to measure the specific surface area of the particles, indicating values near 350 m2/g. This value was supported with calculations derived from X-ray crystallite size measurements. Particle surface area measurements were compared with similarly prepared cellulose nanocrystals.

A highly elastic constant-viscosity fluid

This study assessed the applicability of chitin nanocrystals prepared by 2, 2, 6, 6-Tetramethyl-1-Piperidine-1-oxyl radical (TEMPO)-mediated oxidation in traditional papermaking coating color systems. The α-chitin nanocrystals (CTNCs) with different carboxyl content, size, and morphology were prepared from crab shells by alkali pretreatment and TEMPO-mediated oxidation in the water at pH 10, and then the ratio of CTNCs to latex was applied to traditional coating color system to replace part of latex. The results showed that when the amount of NaClO added as co-oxidant in the oxidation was 15.0 mmol/g of chitin, the carboxyl content of alkali-pretreated CTNCs was up to 0.76 mmol/g. The amount of carboxyl groups presented a linear relation with the degree of individualization of nanocrystals and dispersion. When the ratio of latex to CTNCs was 90꞉10, the water retention value of the coating was 92% lower than that of the pure latex system, and the rheological property was better. The relationship between the addition amount of CTNCs and the surface strength and the coverage of coating layers were also studied, and results showed that when the ratio of latex to CTNCs was 95꞉5, the surface strength was the highest of 1.45 m/s, and the coverage of coating layers rate reached the highest of 78%.