Design of functionalized cellulosic honeycomb films: site-specific biomolecule modification via "click chemistry"

Value-added materials from naturally abundant polymers such as cellulose are of significant importance. In particular, cellulosic open-framework structures with controlled chemical functionality of the internal surface have great potential in many biosensor applications. Although various cellulose derivatives can form porous honeycomb structured materials, solubility issues and problems with film formation exist. To address this, we have generated robust cellulosic open-framework structures that can be post-functionalized through site-specific modification. Regioselectively modified amphiphilic cellulose azides, 3-O-azidopropoxypoly(ethylene glycol)-2,6-di-O-thexyldimethylsilyl cellulosics, were synthesized, and honeycomb-patterned films were readily produced by the simple breath figures method. Changing the degree of polymerization (DP) of the pendent ethylene glycol (EG(DP)) groups from 22 to 4 increased the corresponding honeycomb film pore diameters from ~1.2 to ~2.6 μm, enabling the potential tuning of pore size. Moreover, these novel azido-functionalized honeycomb films were easily functionalized using Cu(I)-catalyzed alkyne-azide [2 + 3] cycloaddition reaction; biotin was "clicked" onto the azide functionalized cellulosic honeycomb films without any effect to the film structure. These results indicate this system may serve as a platform for the design and development of biosensors.     

Micropatterned thin film honeycomb materials from regiospecifically modified cellulose

Thin film honeycomb materials were prepared from regioselectively modified celluloses. The method uses water condensation at the surface of a cellulosic solution as an ordered template to form honeycomb structures. Pore size and distribution is controlled by several factors, one of which is the hydrophilicity of the cellulosic used. The amphiphilic nature of the celluloses was modified with varying lengths of ethylene glycol side chains using 2,6-thexyldimethylsilyl cellulose. It was found that the side chains do affect the honeycomb formation, with longer ethylene glycol chains leading to increased pore uniformity but having little influence on the pore size.     

Transparent cellulose films with high gas barrier properties fabricated from aqueous alkali/urea solutions

Transparent and bendable regenerated cellulose films prepared from aqueous alkali (NaOH or LiOH)/urea (AU) solutions exhibit high oxygen barrier properties, which are superior to those of conventional cellophane, poly(vinylidene chloride), and poly(vinyl alcohol). Series of AU cellulose films are prepared from different cellulose sources (cotton linters, microcrystalline cellulose powder, and softwood bleached kraft pulp) for different dissolution and regeneration conditions. The oxygen permeabilities of these AU cellulose films vary widely from 0.003 to 0.03 mL μm m(-2) day(-1) kPa(-1) at 0% relative humidity depending on the conditions used to prepare the films. The lowest oxygen permeability is achieved for the AU film prepared from 6 wt % cellulose solution by regeneration with acetone at 0 °C. The oxygen permeabilities of the AU cellulose films are negatively correlated with their densities, and AU films prepared from solutions with high cellulose concentrations by regeneration in a solvent at low temperatures generally have low oxygen permeabilities. The AU cellulose films are, therefore, promising biobased packaging materials with high-oxygen barrier properties.     

Green composite films prepared from cellulose,starch and lignin in room-temperature ionic liquid

A series of novel biobased composite films derived from cellulose, starch and lignin were prepared from an ionic liquid (IL), 1-allyl-3-methylimidazolium chloride (AmimCl) by coagulating in a nonsolvent condition. The ionic liquid can be recycled with a high yield and purity after the green film was prepared. The uniform design method was applied to investigate mechanical properties of the biobased composite films. The effect of each component and their associated interactive effects were investigated. The experimental results showed that contents of cellulose, lignin and starch had a significant influence on the mechanical properties of composite films. The composite films showed relatively excellent mechanical properties in dry and wet states owing to the mutual property supplement of different components. The composite films were characterized via FT-IR, X-ray diffraction (XRD) and scanning electron microscope (SEM). Their thermal stability and gas permeability were also investigated, and the results showed that the composite films had good thermal stability and high gas barrier capacity and give a CO₂:O₂ permeability ratio close to 1.     

Production of bioactive cellulose films reconstituted from ionic liquids

A new method for introducing enzymes into cellulosic matrixes which can be formed into membranes, films, or beads has been developed using a cellulose-in-ionic-liquid dissolution and regeneration process. Initial results on the formation of thin cellulose films incorporating dispersed laccase indicate that active enzyme-encapsulated films can be prepared using this methodology and that precoating the enzyme with a second, hydrophobic ionic liquid prior to dispersion in the cellulose/ionic liquid solution can provide an increase in enzyme activity relative to that of untreated films, presumably by providing a stabilizing microenvironment for the enzyme.     

Ionic liquid-based preparation of cellulose-dendrimer films as solid supports for enzyme immobilization

Surface-active cellulose films for covalent attachment of bioactive moieties were achieved by codissolution of cellulose with polyamidoamine (PAMAM) dendrimers in an ionic liquid followed by regeneration of the composite as a film. Different generations of PAMAM were used for the formation of cellulose-dendrimer composites, as well as films with the dendrimer covalently bonded to the cellulose by means of the linker 1,3-phenylene diisocyanate. Surface characterization, thermal stability, and utility for immobilization of laccase were determined. The presence of the dendrimer amino groups was confirmed by detailed characterization of the films' surfaces. These modified films exhibit acceptable thermal stability, comparable to that of other regenerated cellulose films, but the number of active functional groups on the surface is much smaller than the theoretical amount expected. Films made with 1,3-phenylene diisocyanate as linker for covalently bound cellulose and dendrimers exhibit a better performance for immobilization of laccase than those prepared by simple mixing of the cellulose and dendrimer. In general, a linear correspondence between the dendrimer generation within the films and the specific activity of immobilized laccase in such films was not observed.     

Superhydrophobicity of cellulose triacetate fibrous mats produced by electrospinning and plasma treatment

Nano/micro-fibrous cellulose triacetate (CTA) mats were prepared by electrospinning a fixed concentration of CTA with different methylene chloride (MC)/ethanol (EtOH) ratios and with various concentrations of CTA at a fixed MC/EtOH 80/20 (v/v) ratio. All of the electrospun CTA mats had a high water contact angle (WCA) compared to the CTA cast film. At a solvent composition of 80/20 (v/v) and 5 wt.% CTA concentration, the CTA mat without plasma treatment had good surface roughness and electrospinning processability, and its WCA was 142°. To further improve its hydrophobicity, the CTA fibrous mat electrospun from the 5 wt.% solution of CTA was treated with a CF₄ plasma for various times. Superhydrophobicity could be obtained after the CF₄ plasma treatment. The WCA of the CTA mat reached as high as 153° after plasma treatment for 60 s.     

Cell transfer printing from patterned poly(ethylene glycol)-oleyl surfaces to biological hydrogels for rapid and efficient cell micropatterning

Cell transfer printing from patterned poly(ethylene glycol)-oleyl surfaces onto biological hydrogel sheets is investigated herein, as a new cell stamping method for both cell microarray and tissue engineering. By overlaying a hydrogel sheet on the cells immobilized on the poly(ethylene glycol)-oleyl surface and successively peeling it off, the immobilized cells were transferred onto a hydrogel sheet because the adhesive interaction between the cells and the hydrogel was stronger than that between the cells and the poly(ethylene glycol)-oleyl surface. Four types of human cell could be efficiently transferred onto a rigid collagen sheet. The transfer printing ratios, for all cells, were above 80% and achieved within 90 min. A cell microarray was successfully prepared on a collagen gel sheet using the present stamping method. We have also demonstrated that the transferred pattern of endothelial cells is transformed to the patterned tube-like structure on the reconstituted basement membrane matrix. Finally, the patterns of two types of endothelial cell are shown to be easily prepared on the matrix, and the desired tube-like structures, including the orderly pattern of the two different cells, were formed spontaneously. Thus, the present poly(ethylene glycol)-oleyl coated substrates are useful for rapid and efficient cell stamping, in the preparation of multi-cellular pattern on extracellular matrices.     

Effects of modified cellulose nanocrystals on the barrier and migration properties of PLA nano-biocomposites

The aim of this paper is to report the impact of the addition of cellulose nanocrystals on the barrier properties and on the migration behaviour of poly(lactic acid), PLA, based nano-biocomposites prepared by the solvent casting method. Their microstructure, crystallinity, barrier and overall migration properties were investigated. Pristine (CNC) and surfactant-modified cellulose nanocrystals (s-CNC) were used, and the effect of the cellulose modification and content in the nano-biocomposites was investigated. The presence of surfactant on the nanocrystal surface favours the dispersion of CNC in the PLA matrix. Electron microscopy analysis shows the good dispersion of s-CNC in the nanoscale with well-defined single crystals indicating that the surfactant allowed a better interaction between the cellulose structures and the PLA matrix. Reductions of 34% in water permeability were obtained for the cast films containing 1wt.% of s-CNC while good oxygen barrier properties were detected for nano-biocomposites with both 1wt.% and 5wt.% of modified and un-modified cellulose nanocrystals, underlining the improvement provided by cellulose on the PLA films. Moreover, the migration level of the studied nano-biocomposites was below the overall migration limits required by the current normative for food packaging materials in both non-polar and polar simulants.     

Metallization and Biopatterning on Ultra-Flexible Substrates via Dextran Sacrificial Layers

Micro-patterning tools adopted from the semiconductor industry have mostly been optimized to pattern features onto rigid silicon and glass substrates, however, recently the need to pattern on soft substrates has been identified in simulating cellular environments or developing flexible biosensors. We present a simple method of introducing a variety of patterned materials and structures into ultra-flexible polydimethylsiloxane (PDMS) layers (elastic moduli down to 3 kPa) utilizing water-soluble dextran sacrificial thin films. Dextran films provided a stable template for photolithography, metal deposition, particle adsorption, and protein stamping. These materials and structures (including dextran itself) were then readily transferrable to an elastomer surface following PDMS (10 to 70∶1 base to crosslinker ratios) curing over the patterned dextran layer and after sacrificial etch of the dextran in water. We demonstrate that this simple and straightforward approach can controllably manipulate surface wetting and protein adsorption characteristics of PDMS, covalently link protein patterns for stable cell patterning, generate composite structures of epoxy or particles for study of cell mechanical response, and stably integrate certain metals with use of vinyl molecular adhesives. This method is compatible over the complete moduli range of PDMS, and potentially generalizable over a host of additional micro- and nano-structures and materials.     

Novel regenerated cellulose films prepared by coagulating with water: Structure and properties

Regenerated films were successfully prepared from cellulose/NaOH/urea solution by coagulating with water at temperature from 25 to 45 °C. The results of solid ¹³C NMR, wide angle X-ray diffraction, scanning electron microscopy (SEM) and tensile testing revealed that the cellulose films possessed homogeneous structure and cellulose II crystalline, similar to that prepared previously by coagulating with 5 wt% H₂SO₄. By changing the coagulation temperature from 25 to 45 °C, tensile strength of the films was in the range of 85-139 MPa. Interestingly, the RC35 film coagulated at 35 °C exhibited the highest tensile strength (σ_b = 139 MPa). The inclusion complex associated with cellulose, NaOH and urea hydrates in the cellulose solution were broken by adding water (non-solvent), leading to the self-association of cellulose to regenerate through rearrangement of the hydrogen bonds. This work provided low-cost and “green” pathway to prepare cellulose films, which is important in industry.     

Comb-shaped graft copolymers with cellulose side-chains prepared via click chemistry

Comb-shaped copolymers with cellobiose acetate or cellulose triacetate (CTA) side-chains, PPMA-g-(CTA2-C15) and PPMA-g-(CTA13-C15), were prepared by grafting N-(15-azidopentadecanoyl)-2,3,6-tri-O-acetyl-4-O-(2,3,4,6-tetra-O-acetyl-β-d-glucopyranosyl)-β-d-glucopyranosylamine (CTA2-C15-N₃) and N-(15-azidopentadecanoyl)-tri-O-acetyl-β-cellulosylamine (CTA13-C15-N₃, number average degree of polymerization (DP_n) = 13) onto poly(2-propyn-1-yl methacrylate) (PPMA, weight average degree of polymerization (DP_w, X + Y = 5.59 × 10²)) via “click chemistry”. The copolymers were characterized by ¹H, ¹³C and two-dimensional NMR and size exclusion chromatography-multi-angle laser light scattering (SEC-MALS) measurements. The numbers of CTA side-chains (X) of PPMA-g-(CTA2-C15) and PPMA-g-(CTA13-C15) were calculated as 4.03 × 10² and 2.45 × 10², respectively. Copolymers with cellulosic side-chains, PPMA-g-(CELL2-C15) and PPMA-g-(CELL13-C15), were successfully obtained after deacetylation of PPMA-g-(CTA2-C15) and PPMA-g-(CTA13-C15), respectively. X-ray diffraction measurements revealed that PPMA-g-(CELL13-C15) showed crystalline pattern of cellulose II, which is believed to have anti-parallel orientation.     

Chiral nematic ordering of polysaccharides

In this paper, evidence for the chiral nematic (cholesteric) self-ordering of cellulose-derived materials is reviewed. A wide range of cellulose derivatives, and some other polysaccharides, form chiral nematic phases, both in concentrated solution and in the melt. Solid films and gels retaining the chiral nematic ordering of the polymer chains may be prepared from these liquid crystalline phases. Optical and electron microscopic techniques may be used to elucidate the helicoidal structure of chiral nematic cellulosics in the liquid crystalline phase, and of the films, gels and solids prepared from such phases. Remarkably, dilute aqueous suspensions of cellulose crystallites prepared by acid degradation also show chiral nematic order; the order is preserved in dry films prepared from the suspensions. The structure of some of these samples prepared in vitro shows a marked resemblance to structures observed in vivo.     

Changes in the molecular orientation and tensile properties of uniaxially drawn cellulose films

Cellulose films were prepared by dissolving lyocell fibers in LiCl/N,N-dimethylacetamide solvent and subsequently coagulating and drying them under ambient conditions. To introduce preferred orientation, the films were uniaxially drawn under air-dry and rewetted conditions, respectively. Preferred orientation was determined by birefringence measurements and by wide-angle X-ray scattering. Mechanical properties were characterized by means of tensile tests with films conditioned to standard temperatures and humidity. Drawing resulted in the substantial reorientation of cellulose, whereby the molecular chains in the amorphous regions exhibited clearly stronger reorientation than the crystalline fraction. The average degree of orientation was comparable to orientation achieved in spun cellulose fibers. Wet-drawing resulted in improved tensile strength and modulus of elasticity but reduced elongation at break. The mechanical properties of wet-drawn films are competitive with regard to cellophane and melt-blown cellulose films, particularly considering their high modulus of elasticity of up to 26 GPa, which is also comparable to values obtained for industrially produced cellulose fibers.     

New nanocomposite materials reinforced with flax cellulose nanocrystals in waterborne polyurethane

New nanocomposite films were prepared from a suspension of cellulose nanocrystals as the filler and a polycaprolactone-based waterborne polyurethane (WPU) as the matrix. The cellulose nanocrystals, prepared by acid hydrolysis of flax fiber, consisted of slender rods with an average length of 327 +/- 108 nm and diameter of 21 +/- 7 nm, respectively. After the two aqueous suspensions were mixed homogeneously, the nanocomposite films were obtained by casting and evaporating. The morphology, thermal behavior, and mechanical properties of the films were investigated by means of attenuated total reflection Fourier transform infrared spectroscopy, wide-angle X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, and tensile testing. The results indicated that the cellulose nanocrystals could disperse in the WPU uniformly and resulted in an improvement of microphase separation between the soft and hard segments of the WPU matrix. The films showed a significant increase in Young's modulus and tensile strength from 0.51 to 344 MPa and 4.27 to 14.86 MPa, respectively, with increasing filler content from 0 to 30 wt %. Of note is that the Young's modulus increased exponentially with the filler up to a content of 10 wt %. The synergistic interaction between fillers and between the filler and WPU matrix played an important role in reinforcing the nanocomposites. The superior properties of the new nanocomposite materials could have great potential applications.     

Atomic layer deposition of titanium dioxide on cellulose acetate for enhanced hemostasis

TiO₂ films may be used to alter the wettability and hemocompatibility of cellulose materials. In this study, pure and stoichiometric TiO₂ films were grown using atomic layer deposition on both silicon and cellulose substrates. The films were grown with uniform thicknesses and with a growth rate in agreement with literature results. The TiO₂ films were shown to profoundly alter the water contact angle values of cellulose in a manner dependent upon processing characteristics. Higher amounts of protein adsorption indicated by blurry areas on images generated by scanning electron microscopy were noted on TiO₂-coated cellulose acetate than on uncoated cellulose acetate. These results suggest that atomic layer deposition is an appropriate method for improving the biological properties of hemostatic agents and other blood-contacting biomaterials.     

Bacterial cellulose reinforced polyurethane-based resin nanocomposite: A study of how ethanol and processing pressure affect physical, mechanical and dielectric properties

Nanocomposite films of bacterial cellulose (10-50 wt%) and polyurethane-based resin were prepared and characterized for physical, mechanical and dielectric properties. It was observed that the bacterial cellulose swelled in ethanol, and that bacterial cellulose sheets prepared from fibre suspension in ethanol exhibited a relatively less dense structure in comparison to those processed from aqueous fibre suspension. Nanocomposites fabricated from ethanol suspension also showed inferior mechanical properties but superior dielectric properties. Higher amounts of free proton generated from ethanol can induce more dipole mechanism; therefore, there is higher mobility of proton localized along cellulose chain, indicating that higher dielectric constants can be obtained.     

蜜蜂巢脾抗氧化活性与抗菌活性的研究

以意蜂巢脾和中蜂巢脾为研究材料,分别采用水提法和醇提法处理,对获得的4种提取物,以DPPH.法测定自由基清除能力,福林酚法测定总酚含量,琼脂扩散法测定其对金黄色葡萄球菌和大肠杆菌的抑菌半径。结果表明,巢脾提取物具有一定的抗氧化活性和抑菌活性,且含有丰富的酚类化合物。除了对大肠杆菌的抑制作用外,巢脾水提液效果优于巢脾醇提液;除DPPH.清除能力外,意蜂巢脾效果优于中蜂巢脾效果;生物学活性呈现浓度依赖效应。本研究为巢脾在中医药领域的应用提供了一定的解释,并证明了巢脾是一种潜在的天然生物资源。     

A Comparative Study of Fibroblast Behaviors under Cyclic Stress Stimulus and Static Culture on 3D Patterned Matrix

Mechanical stress and patterned surface of the scaffolds has been recognized as a crucial factor in determining cell functionality and tissue development, which in turn can direct the cell responses. In this study, fibroblasts M-3T3 in three-dimensional (3D) honeycomb patterning Chitosan/Poly(L-Lactic Acid) (CS/PLLA) composites was stimulated by a 15% sinusoidal (1 Hz) strain applied by a biodynamic test instrument. The effects of mechanical stimulus on the cell proliferation and basic Fibroblast Growth Factor (bFGF) secretion were studied in comparison to the non-strain groups and blank control. Results show that fibroblasts are able to sense the mechanical stimulation and respond, resulting in a time dependent increase of bFGF secretion and promoting cell proliferation. Moreover, the cells seeded in the scaffolds showed a higher cell proliferation and bFGF secretion. These findings support the hypothesis that suitable mechanical stimulus has positive effect on fibroblasts, and such a 3D honeycomb patterned scaffold may play a positive role in regulating cell behaviors in vitro.