Breath figure templated self-assembly of surface-acylated cellulose nanowhiskers confined as honeycomb films

The self-assembly of cellulose nanowhiskers (CNWs) in confined geometries provides a powerful method for the fabrication of novel structures. Herein, ordered honeycomb microporous films were first prepared with surface-acylated CNWs (CNWs-SU) through the breath figure method. Resulting films showed highly porous order over large regions and the iridescent color was only displayed by their rims, which is different from traditional dish-cast CNW films showing the iridescent color over the whole area. This is mainly due to the condensation of water droplets forming three-dimensional (3D) geometry, which forced CNWs-SU to self-assemble into cholesteric architectures in confined geometry and resulted in the iridescent color of the rims after drying. The mechanism was further studied by investigating the critical influencing factors, primarily the concentration of CNW-SU suspensions, the relative humidity of the atmosphere and the surface-attached moieties. In particular, CNW-SU suspensions with a concentration of 3 mg/mL at the relative humidity of 75% preferentially formed honeycomb films with uniform pores. Too low or too high concentrations of CNW-SU suspensions or relative humidity are not preferable for uniform porous films. CNWs-SU with further immobilized octadecane or fluoroalkyl groups on their surface strongly affected the formation of uniform porous films because of higher hydrophobicity and accompanying inhomogeneous condensation of water droplets. This work provides a novel method to study the interactions of CNWs beyond the planar geometry and the formation of uniform porous films solely with CNWs with structural colors open up interesting possibilities for broad application in photonic nanomaterials. Graphic abstract

Extraction and Characterization of Cellulose Nanowhiskers from TEMPO Oxidized Sisal Fibers

Cellulose nanowhiskers as one kind of renewable and biocompatible nanomaterials evoke much interest because of its versatility in various applications. Herein, the sisal cellulose nanowhiskers with length of 100–500 nm, ultrathin diameter of 6–61 nm, high crystallinity of 74.74 % and C6 carboxylate groups converted from C6 primary hydroxyls were prepared via a 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)/NaBr/NaClO system selective oxidization combined with mechanical homogenization. The effects of sodium hydroxide concentration in alkali pretreatment on the final sisal cellulose nanowhiskers were explored. It was found that with the increase of sodium hydroxide concentration, the sisal fiber crystalline type would change from cellulose I to cellulose II. The versatile sisal cellulose nanowhiskers would be particularly useful for applications in the nanocomposites as reinforcing phase, as well as in tissue engineering, filtration, pharmaceutical and optical industries as additives.

Breath figure templated self-assembly of surface-acylated cellulose nanowhiskers confined as honeycomb films

The self-assembly of cellulose nanowhiskers (CNWs) in confined geometries provides a powerful method for the fabrication of novel structures. Herein, ordered honeycomb microporous films were first prepared with surface-acylated CNWs (CNWs-SU) through the breath figure method. Resulting films showed highly porous order over large regions and the iridescent color was only displayed by their rims, which is different from traditional dish-cast CNW films showing the iridescent color over the whole area. This is mainly due to the condensation of water droplets forming three-dimensional (3D) geometry, which forced CNWs-SU to self-assemble into cholesteric architectures in confined geometry and resulted in the iridescent color of the rims after drying. The mechanism was further studied by investigating the critical influencing factors, primarily the concentration of CNW-SU suspensions, the relative humidity of the atmosphere and the surface-attached moieties. In particular, CNW-SU suspensions with a concentration of 3 mg/mL at the relative humidity of 75% preferentially formed honeycomb films with uniform pores. Too low or too high concentrations of CNW-SU suspensions or relative humidity are not preferable for uniform porous films. CNWs-SU with further immobilized octadecane or fluoroalkyl groups on their surface strongly affected the formation of uniform porous films because of higher hydrophobicity and accompanying inhomogeneous condensation of water droplets. This work provides a novel method to study the interactions of CNWs beyond the planar geometry and the formation of uniform porous films solely with CNWs with structural colors for diverse potential applications.

Facile Preparation of All Cellulose Self-reinforced Nanocomposites from Bamboo Shoot Fibers

Herein, a novel and facile fabrication method of self-reinforced all cellulose nanocomposite based on 2,2,6,6-tetramethylpiperidine-1-oxy (TEMPO) mediated oxidized bamboo shoot shell fibers was introduced. The composites were thoughtfully characterized. Cellulose nanowhiskers from the bamboo shoot fibers with the diameter of 60–90 nm and a large number of micropores were evenly distributed on the surface of the nanocomposite. Compared with the original fiber, the crystallinity of the composites increased, while the thermal stability decreased. The composite also showed good mechanical property and dimensional stability. It provides a promising and convenient route to obtain firm sheet-materials with micro- or nano- structures from nature cellulose fibers.

A COMPARATIVE STUDY OF CELLULOSE NANOWHISKERS (CNWs) AND CELLULOSE NANOFIBERS (CNFs)

Cellulose nanowhiskers (CNWs) from plant biomass are of considerable interest, primarily due to their low density, biodegradability, mechanical strength, economic output, and renewability. Here, a new pretreatment method has been developed to produce CNWs based on supercritical CO2 and ethanol. The raw material was micro-fibrillated cellulose (MFC) and experimental factors were controlled to enhance the properties of CNWs produced using a ball-milling technique following supercritical CO2 pretreatment. Cellulose nanofibers (CNFs) were also prepared using a high-pressure Microfluidizer©. A comparative study was conducted of the properties of the raw materials, the CNWs and the CNFs. The solid yields of P-MFC after supercritical CO2 pretreatment gradually decreased, along with the temperature and the reaction time. Scanning electron microscopy (SEM) images of the CNWs and CNFs show that the morphology of the CNWs was basically acicular, while that of the CNFs was mainly soft fibrous. Thermogravimetric analysis results suggest that the thermal stability of the CNWs was substantially higher than those of the CNFs and the raw material. XRD results indicate that the crystallinity showed an initial increasing trend and then declined with increasing temperature and reaction time, and the crystallinity value of CNWs was higher than that of CNFs. The smaller CNWs became rougher and had a larger surface area.

Design, Synthesis, and Biological Evaluation of Camptothecin Loaded Biotinylated Cellulose Nanowhiskers as Anticancer Agents

Objective: Using biotinylated cellulose nanowhiskers (CNWs), we designed and synthesized a Glutathione (GSH) sensitive- Camptothecin (CPT) prodrug for selective CPT delivery (compound 12). Methods: CPT-biotin (compound 9), was synthesized by direct conjugation of CPT to the biotin via GSH sensitive linkage to evaluate the role of CNWs in compound 12. The chemical structures of the synthesized prodrugs were confirmed by FT-IR, 1H NMR, 13C NMR, and ESI-MS, while the nanoparticles were characterized by DLS and TEM. Results: The in-vitro drug release assay demonstrated that only 18.6% of CPT was released from the nano conjugate under GSH stimulation at micromolar level (100 μM), while 83.1% accumulative release rate was achieved under GSH stimulation at millimolar level (10 mM). The in-vitro cytotoxicity assay (MTT assay) demonstrated that compound 9showed higher inhibition ratios on biotin positive cells, MCF-7, and HepG2, and lower cytotoxicity on biotin negative, CHO. Compound 12 showed good activity against MCF-7, HepG2, and much lower cytotoxicity on CHO. Conclusion: This work demonstrates CPT-biotinylated cellulose nanowhiskers for selective chemotherapy and may have the potential to be used for cancer targeting.

Extraction and Characterization of Cellulose and Cellulose Nanowhiskers from Almond Shell Biomass, Metal Removal and Toxicity Analysis

Almond shell is a major agro-industry waste. Cellulose is the major crystalline component of naturally porous almond shell biomass. In this study, cellulose (ASC) was isolated from almond shell (AS) by the dewaxing-alkali treatment-bleaching method, and nanocrystalline cellulose (ASN) was obtained by sulphuric acid hydrolysis of the obtained ASC. Separation efficiency was confirmed by X-ray diffraction and IR absorption studies. ASC exhibited predominantly microporous monolithic structures under a scanning electron microscope. Its porosity resulted in significant absorption of Cu(II) and Pb(II) ions when applied as an absorbent in their solutions. Transmission electron microscopy and atomic force microscopy revealed the formation of ASN nanowhiskers with an average length and diameter of 170 nm and 20 nm, respectively. Zeta potential of -32.4 mV suggested good colloidal dispersibility of the nanowhiskers. No hemolytic toxicity to erythrocyte cells was recorded, which suggested the potential applicability of the obtained nanomaterial in foods and pharmaceuticals. Remarkably high crystallinity and thermal resistance observed from calorimetry and thermogravimetry studies indicated enhanced density of the crystalline moiety during synthesis. ASC and ASN can be developed as effective metal absorption substrates and reinforcement agents in heat-resistant composite materials.

Cellulosic Nanowhiskers: Preparation and Drug Delivery Applications

: Nanomaterials have applications in almost every field and among them, green nanomaterials have various biological applications. Green nanomaterials are specifically useful for drug and DNA delivery applications. Considering that cellulose is the most abundant and easily available biomolecules, and it has been used for preparing greener cellulose nanomaterials. Cellulosic nanowhiskers are a cost-effective and green alternative to chemical non-viral gene delivery systems. Cellulose nanowhiskers are commonly extracted from plant sources, and they are generally prepared by sulfuric and hydrochloric acid hydrolysis of plant cellulose. In this review, the topic of cellulose nanowhiskers as green biocompatible materials for gene and drug delivery is discussed with several practical examples.