Showing papers by "Lina Zhang published in 2016"

High-Strength and High-Toughness Double-Cross-Linked Cellulose Hydrogels: A New Strategy Using Sequential Chemical and Physical Cross-Linking

Abstract: Polysaccharide-based hydrogels have multiple advantages because of their inherent biocompatibility, biodegradability, and non-toxicic properties. The feasibility of using polysaccharide-based hydrogels could be improved if they could simultaneously fulfill the mechanical property and cell compatibility requirements for practical applications. Herein, the construction of double-cross-linked (DC) cellulose hydrogels is described using sequential chemical and physical cross-linking, resulting in DC cellulose hydrogels that are mechanically superior to single-cross-linked cellulose hydrogels. The formation and spatial distribution of chemically cross-linked domains and physically cross-linked domains within the DC cellulose hydrogels are demonstrated. The molar ratio of epichlorohydrin to anhydroglucose units of cellulose and the concentration of the aqueous ethanol solution are two critical parameters for obtaining mechanically strong and tough DC cellulose hydrogels. The mechanical properties of the DC cellulose hydrogels under loading-unloading cycles are described using compression and tension models. The possible toughening mechanism of double-cross-linking is discussed.

Ultra-Stretchable and Force-Sensitive Hydrogels Reinforced with Chitosan Microspheres Embedded in Polymer Networks.

Abstract: An ultra-stretchable and force-sensitive hydrogel with surface self-wrinkling microstructure is demonstrated by in situ synthesizing polyacrylamide (PAAm) and polyaniline (PANI) in closely packed swollen chitosan microspheres, exhibiting ultra-stretchability (>600%), high sensitivity (0.35 kPa-1 ) for subtle pressures (<1 kPa), and can detect force in a broad range (102 Pa-101 MPa) with excellent electrical stability and rapid response speed, potentially finding applications for E-skin.

High-Flexibility, High-Toughness Double-Cross-Linked Chitin Hydrogels by Sequential Chemical and Physical Cross-Linkings.

Abstract: High-flexibility, high-toughness double-cross-linked (DC) chitin hydrogels are prepared through a sequential chemical and physical cross-linkings strategy. The incorporation of chemically and physically cross-linked domains imbues the DC chitin hydrogels with relatively high stiffness, high toughness, and toughness recoverability.

Quaternized Chitosan/Poly(acrylic acid) Polyelectrolyte Complex Hydrogels with Tough, Self-Recovery, and Tunable Mechanical Properties

Abstract: Quaternized chitosan (QCh) was homogeneously synthesized by reacting chitosan with 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC) in alkali/urea aqueous solution for the first time. The structure and solution properties of QCh were characterized by using element analysis, FT-IR, 13C NMR, SEC-LLS, rheology, viscometer, and ξ-potential measurements. Subsequently, polyelectrolyte complex (PEC) hydrogels were constructed by in situ polymerization of acrylic acid (AA) monomers in the concentrated QCh solution. The structure and mechanical behavior of the prepared hydrogels were systematic studied. Because of the high charge density and solubility of QCh, strong electrostatic interactions were formed in the hydrogels and endowed them tough with self-recovery properties. The mechanical behavior of the hydrogels was accurately tuned from stiff and viscoelastic to soft and elastic by changing the poly(acrylic acid) (PAA) content. The regulation mechanism relied on the remarkable difference in the chai...

Strong and Rapidly Self-Healing Hydrogels: Potential Hemostatic Materials

Abstract: Benzaldehyde-terminated telechelic four-armed polyethylene glycol (PEG-BA) is synthesized and cross-linked with carboxymethyl chitosan (CMC) to form dynamic hydrogels with strong mechanical performance. The gelation temperature and time, mechanical performance, and self-healing behaviors are systematically investigated. The hydrogels have good storage modulus up to 3162.06 ± 21.06 Pa, comparable to conventional bulk hydrogels. The separated alternate hydrogel lines connect together to become an integrated hydrogel film after 5 min at room temperature without any external intervention. This is due to the dynamic equilibrium between the Schiff base linkages and the aldehyde groups of PEG-BA and amine groups on CMC backbone. The hydrogel shows excellent cytocompatibility and the cell viability is as high as 90.7 ± 6.8% after 2 d 3D encapsulation in the hydrogel. In vivo tests indicate that the hydrogels can effectively stop bleeding when the hydrogel is directly injected into a rabbit liver incision. The total blood loss is reduced from 0.65 ± 0.10 g to 0.29 ± 0.11 g, and the hemostasis time is decreased from 167 ± 21 s to 120 ± 10 s, when compared to a gauze treatment with physical compression. These self-healing hydrogels have potential to be used as a novel hemostatic material.

Micro-Nanostructured Polyaniline Assembled in Cellulose Matrix via Interfacial Polymerization for Applications in Nerve Regeneration

Abstract: Conducting polymers have emerged as frontrunners to be alternatives for nerve regeneration, showing a possibility of the application of polyaniline (PANI) as the nerve guidance conduit. In the present work, the cellulose hydrogel was used as template to in situ synthesize PANI via the limited interfacial polymerization method, leading to one conductive side in the polymer. PANI sub-micrometer dendritic particles with mean diameter of ∼300 nm consisting of the PANI nanofibers and nanoparticles were uniformly assembled into the cellulose matrix. The hydrophobic PANI nanoparticles were immobilized in the hydrophilic cellulose via the phytic acid as “bridge” at presence of water through hydrogen bonding interaction. The PANI/cellulose composite hydrogels exhibited good mechanical properties and biocompatibility as well as excellent guiding capacity for the sciatic nerve regeneration of adult Sprague–Dawley rats without any extra treatment. On the basis of the fact that the pure cellulose hydrogel was an inert...

Construction of cellulose/nanosilver sponge materials and their antibacterial activities for infected wounds healing

Abstract: Antibacterial sponges with the silver nanoparticles (Ag NPs) were constructed by freeze-drying of cellulose composite hydrogels, which were prepared in NaOH/urea aqueous system with cooling, where the interconnecting pores of the sponge not only were used as micro-reactors to synthesize Ag nanoparticles but also inhibited the aggregation of Ag NPs. The Ag nanoparticles with size range from 4 to 50 nm, depending on the AgNO3 concentration, were uniformly immobilized in the cellulose/nanosilver sponges. The cellulose/nanosilver composite materials exhibited excellent antibacterial activities. Further, in vivo tests confirmed that the composite sponges had an ability to accelerate infected wound healing, as a result of the existence of the antibacterial Ag nanoparticles and absorbing capacity for wound exudate. The experimental data strongly encouraged the use of cellulose/nanosilver composite sponge as antibacterial materials, especially in case of serious wound infection. The composite cellulose sponge containing Ag nanoparticles provided an alternative material for the application of the infected wound healing.

Natural Materials Assembled, Biodegradable, and Transparent Paper-Based Electret Nanogenerator

Abstract: Developing eco-friendly and low-cost electronics is an effective strategy to address the electronic waste issue. In this study, transparent cellulose nanopaper (T-paper) and polylactic acid (PLA) electret were used to construct a biodegradable and transparent paper-based electret nanogenerator. The nanogenerator could be assembled with paper products to form a self-powered smart packaging system without impairing the appearance, due to the high transparency and desirable output performance. Furthermore, the self-degradation property in the natural soil of the nanogenerator is demonstrated, indicating that the nanogenerator is recycled and will not pollute the environment. We anticipate that this study will provide new insights to develop eco-friendly power source and paper-based electronics.

Tough and Cell-Compatible Chitosan Physical Hydrogels for Mouse Bone Mesenchymal Stem Cells in Vitro.

Abstract: Most hydrogels involve synthetic polymers and organic cross-linkers that cannot simultaneously fulfill the mechanical and cell-compatibility requirements of biomedical applications. We prepared a new type of chitosan physical hydrogel with various degrees of deacetylation (DDs) via the heterogeneous deacetylation of nanoporous chitin hydrogels under mild conditions. The DD of the chitosan physical hydrogels ranged from 56 to 99%, and the hydrogels were transparent and mechanically strong because of the extra intra- and intermolecular hydrogen bonding interactions between the amino and hydroxyl groups on the nearby chitosan nanofibrils. The tensile strength and Young’s modulus of the chitosan physical hydrogels were 3.6 and 7.9 MPa, respectively, for a DD of 56% and increased to 12.1 and 92.0 MPa for a DD of 99% in a swelling equilibrium state. In vitro studies demonstrated that mouse bone mesenchymal stem cells (mBMSCs) cultured on chitosan physical hydrogels had better adhesion and proliferation than tho...

Effects of spent tea leaf powder on the properties and functions of cellulose green composite films

Abstract: The aim of the present work was to develop novel bio-based polymer composite films with improved tensile and thermal properties. In this work, cellulose and spent tea leaf powder (STLP) were used as the matrix and filler respectively in the preparation of biocomposite films. To make cellulose solution, cotton linters were dissolved in pre-cooled aqueous solution of 8 wt.% Lithium hydroxide and 15 wt.% urea. Tea is an important beverage of household and hotels and spent tea leaves form a conjugal solid waste. STLP was added to cellulose solution in 5–25 wt.% of weight of cellulose. The cellulose and cellulose/STLP composite films were prepared by regeneration method using ethyl alcohol coagulation bath. The dry films were characterized by optical microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and tensile tests. The effect of STLP loading on the properties of the cellulose/STLP composite films was studied. The results indicated that the composite films had higher tensile properties and thermal stability than the cellulose matrix. The dye adsorption ability of cellulose and cellulose/STLP composites in wet form was also studied. It was observed that the composite wet films had higher dye adsorption capacity than the matrix. Results of this study indicated STLP to be a promising green filler for polymer matrices.

Anti-tumor effect of β-glucan from Lentinus edodes and the underlying mechanism

Abstract: β-Glucans are well known for its various bioactivities, but the underlying mechanism has not been fully understood. This study focuses on the anti-tumor effect and the potential mechanism of a branched β-(1, 3)-glucan (LNT) extracted from Lentinus edodes. The in vivo data indicated that LNT showed a profound inhibition ratio of ~75% against S-180 tumor growth, even significantly higher than the positive control of Cytoxan (~54%). Interestingly, LNT sharply promoted immune cells accumulation into tumors accompanied by cell apoptosis and inhibition of cell proliferation during tumor development. Furthermore, LNT not only up-regulated expressions of the tumor suppressor p53, cell cycle arrestin p21 and pro-apoptotic proteins of Bax and caspase 3/9, but also down-regulated PARP1 and anti-apoptotic protein Bcl-2 expressions in tumor tissues. It was first found that LNT initiated p53-dependent signaling pathway to suppress cell proliferation in vitro, and the caspase-dependent pathway to induce cell apoptosis in vivo. The underlying anti-tumor mechanism was proposed that LNT activated immune responses to induce cell apoptosis through caspase 3-dependent signaling pathway and to inhibit cell proliferation possibly via p53-dependent signaling pathway in vivo. Besides, LNT inhibited angiogenesis by suppressing VEGF expression, leading to slow progression of tumors.

Facile construction of carbon dots via acid catalytic hydrothermal method and their application for target imaging of cancer cells

Abstract: To solve the problem of high temperature or long reaction time in hydrothermal synthesis of carbon dots (CDs), a novel method based on the promoting carbonization by hydrochloric acid as catalysis was developed in present work. The acid catalyzed carbon dots (ACDs) were prepared facilely from tryptophan and phenylalanine at 200 °C for 2 h. In our findings, the acids could promote significantly the formation of the ACDs’ carbon core, as a result of the accelerating of the carbonization due to the easy deoxidation. The ACDs showed an average size of 4.8 nm, and consisted of high carbon crystalline core and various surface groups. The ACDs exhibited good optical properties and pH-dependent photoluminescence (PL) intensities. Furthermore, the ACDs were safe and biocompatible. The experimental results demonstrated that such new ACDs were connected with DNA-aptamer by EDC/NHS reaction maintaining both the bright fluorescence and recognizing ability on the cancer cells, which so could be served as an effective PL sensing platform. The resultant DNA-aptamer with ACDs (DNA-ACDs) could stick to human breast cancer cells (MCF-7) specifically, and exhibited high sensitivity and selectivity, indicating the potential applications in the cancer cells targeted imaging fields.

Construction of controllable size silver nanoparticles immobilized on nanofibers of chitin microspheres via green pathway

Abstract: In the present work, nanofibrous chitin microsphere (NCM) was prepared via sol–gel transition from a chitin solution dissolved in a NaOH/urea aqueous system at low temperatures. Ag nanoparticles (AgNPs) were synthesized via an in situ reduction of silver nitrate using trisodium citrate dehydrate and were immobilized on chitin nanofibers to obtain composite microspheres that consist of nanofibers and AgNPs (NCM-Ag). The size of AgNPs could be controlled in the range of 10 to 70 nm, depending on the concentration of AgNO3. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) analyses showed that the chitin nanofibers have a strong affinity toward AgNPs, resulting from the interaction between the acetamino group of chitin and the AgNPs. The NCM-Ag exhibited a perfect nanoporous structure and high surface area, as well as high stability in organic solvents. Moreover, in the catalytic epoxidation of olefin (particularly, the conversion of styrene to styrene epoxide), NCM-Ag exhibited an excellent selectivity of up to 90%. Converting chitin powder into chitin microspheres using an environmentally friendly technique is a green process, which is beneficial for the large-scale synthesis of industrial products. More importantly, this work provides a green synthetic pathway for the construction of size-controlled noble metal nanoparticles immobilized on nanofiber support, which have a wide range of potential applications.

Autophagy regulates odontoblast differentiation by suppressing NF-κB activation in an inflammatory environment

Abstract: Odontoblasts are derived from dental papilla mesenchymal cells and have an important role in defense against bacterial infection, whereas autophagy can recycle long-lived proteins and damaged organelles to sustain cellular homeostasis. Thus, this study explores the role of autophagy in odontoblast differentiation with lipopolysaccharide (LPS) stimulation in vitro and the colocalization of p-NF-κB and LC3 in caries teeth. The odontoblasts differentiation was enhanced through LPS stimulation, and this outcome was reflected in the increased number of mineralized nodules and alkaline phosphatase (ALP) activity. The expression levels of the autophagy markers LC3, Atg5, Beclin1 and TFE3 increased time dependently, as well along with the amount of autophagosomes and autophagy fluxes. This result suggests that autophagy was enhanced in odontoblasts cultured with mineralized-induced media containing LPS. To confirm the role of autophagy in differentiated odontoblasts with LPS stimulation, chloroquine (CQ) or rapamycin were used to either block or enhance autophagy. The number of mineralized nodules decreased when autophagy was inhibited, but this number increased with rapamycin treatment. Phosphorylated nuclear factor-κB (NF-κB) expression was negatively related to autophagy and could inhibit odontoblast differentiation. Furthermore, p-NF-κB and LC3 colocalization could be detected in cells stimulated with LPS. The nucleus translocation of p-NF-κB in odontoblasts was enhanced when autophagy was inhibited by Atg5 small interfering RNA. In addition, the colocalization of p-NF-κB and LC3 in odontoblasts and sub-odontoblastic layers was observed in caries teeth with reactionary dentin. Therefore, our findings provide a novel insight into the role of autophagy in regulating odontoblast differentiation by suppressing NF-κB activation in inflammatory environments.

Spherical nanocomposite particles prepared from mixed cellulose–chitosan solutions

Abstract: Novel cellulose–chitosan nanocomposite particles with spherical shape were successfully prepared via mixing of aqueous biopolymer solutions in three different ways. Macroparticles with diameters in the millimeter range were produced by dripping cellulose dissolved in cold LiOH/urea into acidic chitosan solutions, inducing instant co-regeneration of the biopolymers. Two types of microspheres, chemically crosslinked and non-crosslinked, were prepared by first mixing cellulose and chitosan solutions obtained from freeze thawing in LiOH/KOH/urea. Thereafter epichlorohydrin was applied as crosslinking agent for one of the samples, followed by water-in-oil (W/O) emulsification, heat induced sol–gel transition, solvent exchange, washing and freeze-drying. Characterization by X-ray photoelectron spectroscopy, total elemental analysis, and Fourier transform infrared spectroscopy confirmed the prepared particles as being true cellulose–chitosan nanocomposites with different distribution of chitosan from the surface to the core of the particles depending on the preparation method. Field emission scanning electron microscopy and laser diffraction was performed to study the morphology and size distribution of the prepared particles. The morphology was found to vary due to different preparation routes, revealing a core shell structure for macroparticles prepared by dripping, and homogenous nanoporous structure for the microspheres. The non-crosslinked microparticles exhibited a somewhat denser structure than the crosslinked ones, which indicated that crosslinking restricts packing of the chains before and under regeneration. From the obtained volume-weighted size distributions it was found that the crosslinked microspheres had the highest median diameter. The results demonstrate that not only the mixing ratio and distribution of the two biopolymers, but also the morphology and nanocomposite particle diameters are tunable by choosing between the different routes of preparation.

Anti-hepatoma activity of the stiff branched β-D-glucan and effects of molecular weight

Abstract: The water soluble β-(1 → 3)-D-glucan with short branches (AF1) isolated from Auricularia auricula-judae was successfully fractionated by ultrasonication into three fractions with different weight-average molecular weights (Mws). The results of static and dynamic laser light scattering, viscometry and atomic force microscopy confirmed that the AF1 samples adopted a stiff chain conformation in water, and the coexistence of individuals and aggregates occurred gradually with increasing concentration. The AF1 sample with the highest Mw easily self-entangled, and exhibited a strong shear rate-dependence of viscosity in water. The glucans displayed anti-hepatoma activity and significantly inhibited H22 tumour growth without cytotoxicity towards normal tissues. They displayed both molecular weight- and dosage-dependencies of anti-tumour activity, and the sample with an Mw of 7.7 × 105 at the dosage of 5 mg kg−1 exhibited the highest inhibition ratio of ∼77% against H22 tumour, even significantly higher than the positive control of cytoxan. The immunohistochemical and western blot analyses revealed that the AF1 glucans triggered cell apoptosis, indicated by the activation of caspase 3/9 and down-regulated tumour angiogenesis factors of VEGF and CD31. The underlying antitumor mechanism was suggested to induce tumour cell apoptosis and to inhibit angiogenesis in tumour tissues via enhancement of the immune-response. Taken together, the AF1 β-glucan was a potent natural drug candidate with high anti-cancer activities and less cytotoxicity, and the AF1 sample with a moderate molecular weight existed in aqueous solution as a more extended chain conformation, which plays an important role in activating immune responses.

Light weight, mechanically strong and biocompatible α-chitin aerogels from different aqueous alkali hydroxide/urea solutions

Abstract: Light weight and mechanically strong α-chitin aerogels were fabricated using the sol-gel/self-assembly method from α-chitin in different aqueous alkali hydroxide (KOH, NaOH and LiOH)/urea solutions. All of the α-chitin solutions exhibited temperature-induced rapid gelation behavior. 13C nuclear magnetic resonance (NMR) spectra revealed that the aqueous alkali hydrox- ide/urea solutions are non-derivatizing solvents for α-chitin. Fourier transform infrared (FT-IR), X-ray diffraction (XRD) and cross-polarization magic angle spinning (CP/MAS) 13C NMR confirmed that α-chitin has a stable aggregate structure after undergoing dissolution and regeneration. Subsequently, nanostructured α-chitin aerogels were fabricated by regeneration from the chitin solutions in ethanol and then freeze-drying from t -BuOH. These α-chitin aerogels exhibited high porosity (87% to 94%), low density (0.09 to 0.19 g/cm3), high specific surface area (419 to 535 m2/g) and large pore volume (2.7 to 3.8 cm3/g). Moreover, the α-chitin aerogels exhibited good mechanical properties under compression and tension models. In vitro studies showed that mBMSCs cultured on chitin hydrogels have good biocompatibility. These nanostructured α-chitin aerogels may be useful for various applications, such as catalyst supports, carbon aerogel precursors and biomedical materials.

Rapid dissolution of spruce cellulose in H 2 SO 4 aqueous solution at low temperature

Abstract: Dissolution of cellulose is the key challenge in its applications. It has been discovered that spruce cellulose with high molecular weight (4.10 × 105 g mol−1) can be dissolved in 64 wt% H2SO4 aqueous solution at low temperature within 2 min, and the cellulose concentration in solution can reach as high as 5 % (w/v). FT-IR spectra and XRD spectra proved that it is a direct solvent for cellulose rather than a derivative aqueous solution system. The cold H2SO4 aqueous solution broke the hydrogen bonds among cellulose molecules and the low temperature dramatically slowed down the hydrolysis, which led to the dissolution of cellulose. The resultant cellulose solution was relatively stable, and the molecular weight of cellulose only slightly decreased after storage at −20 °C for 1 h. Due to the high molecular weight of cellulose, cellulose solution could form regenerated films with good mechanical properties and transparency at low concentration (2 % w/v). This work has not only provided the new evidence of cellulose dissolution which facilitated the development of cellulose solvent, but also suggested a convenient way to directly transfer cellulose with high molecular weight into materials without structure modifications.

Fabrication of Hollow Materials by Fast Pyrolysis of Cellulose Composite Fibers with Heterogeneous Structures

Abstract: A facile method for the fabrication of inorganic hollow materials from cuprammonium cellulose composite filaments based on fast pyrolysis has been developed. Unlike Ostwald ripening, approaches based on the Kirkendall effect, and other template methods, this process yielded hollow materials within 100 s. The heterogeneous structure of the cellulose composite fibers and the gradient distribution of the metal oxides are the main reasons for the formation of the hollow structure. The diameter, wall thickness, and length of the hollow microfibers could be conveniently controlled. With their perfect morphology, these hollow structural materials have great potential for use in various fields.