The structural amphiphilicity of cellulose nanocrystals characterized from their cohesion parameters

Does pervasive interconnected network of cellulose nanocrystals in nanocomposite membranes address simultaneous mechanical strength/water permeability/salt rejection improvement?

In this research work, we investigated the effect of two cellulose nanocrystal (CNC)-related parameters, namely aspect ratio and loading content on the mechanical and desalination performance of a cellulose diacetate (CDA) model membrane system. Dispersion of high aspect ratio (HAR) CNCs in the CDA resulted in different types of nanoassembly, represented by evaluating the mechanical efficacy coefficient (CFE), viscoelastic responses and separation performance of the nanocomposite membranes. Accordingly, 0.15 and 0.25 wt% showed random isolated dispersion and tight polymer-nanorod network, while 0.50 and 0.75 wt% conformed to nanorods' pervasive interconnected network (PIN) through side-by-side aggregation and intensive bundle alignment, respectively. Specifically, the nanocomposite membrane containing 0.50 wt% HAR-CNCs simultaneously demonstrated improved mechanical strength along with mitigated water permeability/salt rejection tradeoff for brackish water desalination. This concurrent boosting was attributed to the effective mechanical reinforcement mechanism induced by the percolating network along with its partial aggregation-caused bi-continuous and electrostatically-controlled nano-pathways, orchestrating the separation tradeoff. It confirmed our hypothesis that a nanocomposite membrane with metamaterial characteristic could be obtained via manipulating the dispersion state of CNC rods in the CDA, triggering coincided optimization of mechanical strength and desalination performance.

Evaluation of Surface Free Energy Inducing Interfacial Adhesion of Amphiphilic Cellulose Nanofibrils

Cellulose nanofibrils (CNFs) have been studied extensively over the past decade. Their applications, e.g., as fillers for nanocomposites, stabilizers for Pickering emulsions, and scaffolds for cell culture, are mostly dictated by interfacial adhesion. In general, the individual surface free energy values of the constituents of a material correlate with its adsorption and desorption behaviors. In the present study, we estimated the surface free energy values of thin films composed of CNFs using traditional contact angle methods based on the Wenzel equation and van Oss-Chaudhury-Good theory. The accuracy and utility of the estimated surface free energy values were verified by close matching between the obtained adhesion energy values and the actual interfacial adsorption behaviors of the CNFs. Therefore, the evaluated surface energy values are expected to be a feasible tool for designing of interfacial interactions between CNF surfaces and other materials.

Ice recrystallization inhibition effect of cellulose nanocrystals at constant and cycling temperatures

Understanding the effects of ice recrystallization inhibitors at varying temperatures is critical for evaluating their applications. We studied the ice recrystallization inhibition (IRI) effects of cellulose nanocrystals (CNCs) at constant and cycling temperatures. A splat assay using a 3.0 % sucrose solution showed that the IRI effect of 0.2 % CNCs decreased with increasing temperatures from -10 °C to -2 °C; the IRI effects of 0.5 % and 1.0 % CNCs remained unchanged for an increase in temperature from -10 °C to -4 °C but decreased at the temperature of -2 °C. A sandwich assay using a 25.0 % sucrose solution revealed that IRI effects increased with increasing temperatures, except in the presence of 0.2 % and 0.5 % CNCs at -5 °C and - 4 °C. A sandwich assay using a 35.0 % sucrose solution revealed that better IRI effects were observed at higher temperatures at all CNCs concentrations. At cycling temperatures, CNCs were inactive for storage times for ≤2 h, regardless of the rate, holding time, and amplitude of temperature fluctuation, but were active for storage times of 2 and 10 days. The IRI effects of CNCs at different temperatures may be related to the coverage of CNCs on ice surface, diffusion rate of CNCs to ice surface, and types of ice recrystallization.

Effect of the Interactions between Oppositely Charged Cellulose Nanocrystals (CNCs) and Chitin Nanocrystals (ChNCs) on the Enhanced Stability of Soybean Oil-in-Water Emulsions

Chitin nanocrystals (ChNCs) and cellulose nanocrystals (CNCs) have been recently used to stabilize emulsions; however, they generally require significant amounts of salt, limiting their applicability in food products. In this study, we developed nanoconjugates by mixing positively charged ChNCs and negatively charged CNCs at various ChNC:CNC mass ratios (2:1, 1:1, and 1:2), and utilized them in stabilizing soybean oil-water Pickering emulsions with minimal use of NaCl salt (20 mM) and nanoparticle (NP) concentrations below 1 wt%. The nanoconjugates stabilized the emulsions better than individual CNC or ChNC in terms of a reduced drop growth and less creaming. Oppositely charged CNC and ChNC neutralized each other when their mass ratio was 1:1, leading to significant flocculation in the absence of salt at pH 6. Raman spectroscopy provided evidence for electrostatic interactions between the ChNCs and CNCs, and generated maps suggesting an assembly of ChNC bundles of micron-scale lengths intercalated by similar-size areas predominantly composed of CNC. The previous measurements, in combination with contact angles on nanoparticle films, suggested that the conjugates preferentially exposed the hydrophobic crystalline planes of CNCs and ChNCs at a 1:1 mass ratio, which was also the best ratio at stabilizing soybean oil-water Pickering emulsions.

Tunable two-step shape and dimensional changes with temperature of a PNIPAM/CNC hydrogel

PNIPAM (poly(N-isopropylacrylamide)), a well-studied thermo-responsive polymer, undergoes conformational transition around 32 °C. On the other hand, cellulose nanocrystals (CNCs), as a promising and biocompatible material, has rarely been introduced to the PNIPAM-based fibrous hydrogel system. CNCs' impact on the temperature responsive behaviors of hydrogels, either in single layer or bilayer hydrogel systems, is yet to be investigated. In this work, stable well dispersed PNIPAM/CNC suspensions (with various CNC proportions) are prepared and electrospun into nanofiber membranes. The corresponding hydrogels are then obtained via UV-induced crosslinking. CNCs are found to exert a significant constraint effect on hydrogel swelling when it exceeded 5 wt% but a negligible effect on contraction. The difference between hydrogels with various CNC proportions regarding their temperature responsive behaviors is utilized to fabricate bilayer hydrogels. These bilayer samples are capable of generating 3D geometries when they come into contact with water for the first time via anisotropic swelling between the two layers and changing their dimension reversibly in the following swelling and contraction. In addition, these geometries are found to be highly tunable via the finely tuned thickness ratio between the two layers. This promising feature would significantly extend the application of these materials in tissue engineering where a controllable geometry of the culture substrate is of great importance.

Antimicrobial Activity of Cellulose Based Materials

Biomaterials available for a wide range of applications are generally polysaccharides. They may have inherent antimicrobial activity in the case of chitosan. However, in order to have specific functionalities, bioactive compounds must be immobilized or incorporated into the polymer matrix, as in the case of cellulose. We studied materials obtained by functionalizing cellulose with quaternary ammonium salts: dodecyl-trimethyl-ammonium bromide (DDTMABr), tetradecyl-trimethyl-ammonium bromide (TDTMABr), hexadecyl-trimethyl ammonium chloride (HDTMACl), some phosphonium salts: dodecyl-triphenyl phosphonium bromide (DDTPPBr) and tri n-butyl-hexadecyl phosphonium bromide (HDTBPBr) and extractants containing sulphur: 2-mercaptobenzothiazole (MBT) and thiourea (THIO). Cel-TDTMABr material, whose alkyl substituent chain conformation was shortest, showed the best antimicrobial activity for which, even at the lowest functionalization ratio, 1:0.012 (w:w), the microbial inhibition rate is 100% for Staphylococcus aureus, Escherichia coli, and Candida albicans. Among the materials obtained by phosphonium salt functionalization, Cel-DDTPPBr showed a significant bactericidal effect compared to Cel-HDTBPBr. For instance, to the same functionalization ratio = 1:0.1, the inhibition microbial growth rate is maximum in the case of Cel-DDTPPBr for Staphylococcus aureus, Escherichia coli, and Candida albicans. At the same time, for the Cel-HDTBPBr material, the total bactericidal effect is not reached even at the functionalization ratio 1:0.5. This behavior is based on the hydrophobicity difference between the two extractants, DDTPPBr and HDTBPBr. Cel-MBT material has a maximum antimicrobial effect upon Staphylococcus aureus, Escherichia coli, and Candida albicans at functionalized ratio = 1:0.5. Cel-THIO material showed a bacteriostatic and fungistatic effect, the inhibition of microbial growth being a maximum of 76% for Staphylococcus aureus at the functionalized ratio = 1:0.5. From this perspective, biomaterials obtained by SIR impregnation of cellulose can be considered a benefit to be used to obtain biomass-derived materials having superior antimicrobial properties versus the non-functional support.

Cellulose Amphiphilic Materials: Chemistry, Process and Applications

In the last decade, amphiphilic cellulose (AC) is emerging as attractive biomaterial for different therapeutic use, due to its unique chemical and physical properties. Using it as alternative to synthetic polymers, AC opens up new avenues to prepare new bio-sustainable materials with low impact in the cellular environment. Herein, most recent methods to synthesize and processing AC materials from different sources—i.e., cellulose nanofibers, bacterial cellulose, cellulose derivatives—will be discussed. By an accurate optimization of morphology and surface chemistry, it is possible to develop innovative amphiphilic platforms, promising for a wide range of biomedical applications, from drug delivery to molecular/particle adsorption.

Effect of solvent type on the dispersion quality of spray-and freeze-dried CNCs in PLA through rheological analysis

Polylactide (PLA) nanocomposites with spray-and freeze-dried cellulose nanocrystals (i.e., SCNC and FCNC) were prepared through solution casting using four different solvents: tetrahydrofuran (THF), chloroform (CHL), dimethylformamide (DMF), and dimethyl sulfoxide (DMSO). Small amplitude oscillatory shear rheological analysis was extensively employed to explore the CNC dispersion quality in PLA. Overall, the rheological properties differences of PLA/SCNC and PLA/FCNC nanocomposites were not very significant. Moreover, the use of THF and CHL did not lead to a proper dispersion of CNCs in PLA due to their low dielectric constants. On the other hand, while the use of DMF was effective on the enhancement of CNC dispersion, DMSO could more dramatically lead to such enhancement due to its higher dielectric constant. The percolation threshold in PLA/SCNC nanocomposites prepared with DMF and DMSO was predicted around 1.52 and 0.12 wt% CNC, respectively. The crystallization behavior of PLA/nanocomposites prepared with DMF and DMSO were also explored.

Cellulose nanocrystals produced using recyclable sulfuric acid as hydrolysis media and their wetting molecular dynamics simulation

Cellulose nanocrystals (CNCs) were successfully produced with good nanoscales and dispersibility, using a recycled sulfuric acid (H₂SO₄) hydrolysis process. This method, at the cost of an overall 25% increase in the hydrolysis time, could significantly reduce the dosage of H₂SO₄ by approximately 40% without affecting the per-batch yield and performance of CNCs. The obtained CNCs with an average diameter of 6.0-6.5 nm and an average length of 126-134 nm, were successfully applied in the preparation of oil-in-water (O/W) Pickering emulsions via high-pressure homogenization. The emulsions exhibited good storage stability when the concentration of CNC was 1.0 wt%. Further, understanding the wetting behaviors of surface modified CNCs with solvent is critical for the functional designing of Pickering emulsion. Hence, we gained insights into the wetting of hydrophobic and hydrophilic surfaces of sulfate modified CNCs with water and organic solvent (hexadecane) droplets, using molecular dynamic simulation. The results showed that both surfaces had hydrophilic as well as lipophilic properties. Although the sulfate-grafted surface was more hydrophilic than unmodified CNC, substantial local wetting heterogeneities appeared for both solvents. It provides a deeper understanding of the interfacial interactions between modified CNCs and solvent molecules at the molecular level.

Cellulose nanocrystals incorporated β-chitosan nanoparticles to enhance the stability and in vitro release of β-galactosidase

Beta-galactosidase (β-gal), catalyzing the transformation of lactose to glucose and galactose, had been encapsulated in β-chitosan nanoparticles (β-CS NPs) in previous work, but they were prone to aggregation and disscociation, resulting in poor bioavailability of β-gal. Herein, we developed cellulose nanocrystals (CNC, as stabilizers and fillers) stabilized β-gal loaded low molecular weight (LMW) β-CS NPs through ionic gelation technology to enhance enzyme activity and further control in vitro release of β-gal. Results showed that particle size and Zeta potential (ZP) of CNCs stabilized β-gal loaded CS NPs were 143.20 nm and -34.70 mV under the optimal conditions, respectively. Structural analysis were employed to study the incorporation of β-gal and CNC into β-CS NPs. In vitro release study conducted at pH 4.5 and 7.4 showed that both β-gal loaded β-CS NPs and CNC stabilized ones retained the release of β-gal for over 12 h. Moreover, CNC stabilized β-gal loaded β-CS NPs retained higher β-gal activity (81.23%) than that of controls (30%) within 2 h. Therefore, it was indicated that CNC incorporated β-CS NPs could serve as non-toxic and effective carriers of β-gal for the treatment of lactose intolerance.

Orienting Cellulose Nanocrystal Functionalities Tunes the Wettability of Water-Cast Films

Cellulose nanocrystal (CNC)-based materials display apparently erratic wetting behaviors with contact angle (CA) variations as large as 30° from sample to sample. This work hypothesizes that it is the orientation of CNC amphiphilic functionalities at the interface with air that causes the variability in CA. By exploiting relationships with the Hansen solubility parameter theory, a set of surface tension parameters is proposed for both the polar and the non-polar surfaces of cellulose I_β nanocrystals. These coefficients elucidate the wettability of CNC materials by establishing a correlation between the wetting properties of the air/sample interface and its chemical composition in terms of non-polar moieties. Advancing/receding CA experiments suggest that, while spin-coating CNC suspensions yield purely polar films, oven-casting them produces amphiphilic surfaces. We proposed a mechanism where the state of dispersion (individual or agglomerated) in which CNCs reach the air/water interface during casting is the determining factor: while individual nanocrystals find it more stable to orient their non-polar surfaces toward the interface, the aspect ratio of CNC agglomerates favors an orientation of their polar surfaces. This represents the first compelling evidence of CNC orientation at an interface and can be applied to Pickering emulsions and nanocomposites and to the production of CNC materials with tuned wettability.

Chemical affinity and dispersibility of boron nitride nanotubes

Boron nitride nanotubes (BNNTs) are electrically insulating nanoparticles that display highly competitive elastic modulus and thermal conductivity. Long presented as potential fillers for nanocomposite applications, their poor dispersibility in most commodity polymers has, however, limited their spread. In this work, the chemical affinity of purified BNNTs, measured in terms of Hansen solubility parameters (HSP), were obtained through sedimentation tests in a wide set of organic solvents, taking into account relative sedimentation time. The parameters obtained were {δ _d; δ _p; δ _h} = {16.8; 10.7; 14.7} ± {0.3; 0.9; 0.3} MPa^1/2, with a Hildebrand parameter, δ _t = 24.7 MPa^1/2 and a sphere radius of 5.4 MPa^1/2. The solubility parameters were determined considering complete dispersion of the purified nanomaterial, as well as the viscosity and density of the host solvent. These factors, combined with the high purity of the BNNTs, are crucial to minimize the uncertainty of the HSP characterization. Such refined values provide necessary insights both to optimize the solvent casting of unmodified BNNTs, and to orient the surface modification efforts that would be needed to integrate these nanomaterials into a wider range of host matrices.

Cellulose nanocrystals of variable sulfation degrees can sequester specific platelet lysate-derived biomolecules to modulate stem cell response

Cellulose nanocrystals can bind different patterns of platelet lysate-derived protein in a surface sulfation dependent manner. The potential to direct stem cell fate by solid-phase presentation of defined protein coronas is demonstrated.