Chunyu Chang

Novel hydrogels prepared via direct dissolution of chitin at low temperature: structure and biocompatibility

Chitin is produced by a number of living organisms in lower plant and animal kingdoms, and possesses natural biocompatibility. However, its dissolution is very difficult in the most common solvents. In the present work, chitin was dissolved completely in 8 wt% NaOH/4 wt% urea aqueous solution via the freezing/thawing method to prepare transparent solutions without derivatization, as supported by 13C NMR. Subsequently, hydrogels were prepared directly from the chitin solution in the NaOH/urea aqueous system, for the first time, maintaining the attractive structure and properties of chitin. Two kinds of chitin hydrogels were obtained through physical or chemical cross-linking by using epichlorohydrin (ECH) in the NaOH/urea aqueous system. The rheological measurements revealed that the formation of chitin hydrogels by chemical cross-linking was a rapid gelation process (within 1 min), leading to perfect hydrogels. The chitin hydrogels exhibited a uniformly porous morphology, low crystallinity, good mechanical strength, and high swelling ratio. Furthermore, the results of a 293T cell viability assay indicated their excellent biocompatibility and safety. The chitin hydrogels may find wide use in bio-applications, as a result of the more stable structure and better compatibility of chitin than that of its derivatives, such as chitosan.

Strongly fluorescent hydrogels with quantum dots embedded in cellulose matrices

Hydrogels having strong fluorescence were fabricated successfully, for the first time, from cellulose and quantum dots (QDs) in a NaOH/urea aqueous system via a mild chemical cross-linking process. The CdSe/ZnS nanoparticles were embedded firmly in the cellulose matrices, as a result of strong interactions between the CdSe/ZnS nanoparticles and cellulose after hydrolysis of the QDs ligands. The results from FTIR spectra, transmission electron microscopy, scanning electron microscopy and photoluminescence (PL) spectra revealed that the cellulose networks in the hydrogels played an important role in the protection of the CdSe/ZnS structure and preservation of the quantum dots characteristics. The cellulose–QDs hydrogels exhibited strong PL emission and nearly pure color from green to red, depending on the size of the QDs. Moreover, the hybrid hydrogels possessed a good transparence and compressive strength. This work provides a new pathway for the construction of safe and biocompatible biopolymer–QDs hydrogels with a high efficiency of PL emission.

High strength films with gas-barrier fabricated from chitin solution dissolved at low temperature

The fabrication of pure chitin materials remains a challenge due to the difficult dissolution and regeneration of chitin. It has been a stumbling block for chitin research and utilization. In this work, chitin was dissolved completely in 11 wt% NaOH–4 wt% urea aqueous solution via the freezing/thawing method without derivatization, as supported by 13C NMR spectra. The pure regenerated chitin films with high strength were successfully prepared from the transparent chitin solution by coagulating with ethanol or 45 wt% dimethylacetamide (DMAc) aqueous solution. The influences of the interactions between the chitin solution and coagulants on the structure and properties of the chitin films were investigated by UV, FT-IR spectra, scanning electron microscopy, X-ray diffraction, nitrogen adsorption isotherms, thermo-gravimetric analysis and tensile testing, indicating the good coagulating condition. The dissolution and regeneration of chitin was confirmed to be an entirely physical processes. The chitin films possessed homogeneous structure, high optical transmittance (87% at 800 nm), moderate thermal stability, as well as excellent tensile strength (up to 111 MPa). Moreover, these chitin films had good gas barrier properties (0.003 barrer for oxygen permeability), indicating great potentials in the materials field. This work would open up a completely new avenue with green technology to investigate the most intransigent chitin.

Biocompatible cellulose-based superabsorbent hydrogels with antimicrobial activity

Current superabsorbent hydrogels commercially applied in the disposable diapers have disadvantages such as weak mechanical strength, poor biocompatibility, and lack of antimicrobial activity, which may induce skin allergy of body. To overcome these hassles, we have developed novel cellulose based hydrogels via simple chemical cross-linking of quaternized cellulose (QC) and native cellulose in NaOH/urea aqueous solution. The prepared hydrogel showed superabsorbent property, high mechanical strength, good biocompatibility, and excellent antimicrobial efficacy against Saccharomyces cerevisiae. The presence of QC in the hydrogel networks not only improved their swelling ratio via electrostatic repulsion of quaternary ammonium groups, but also endowed their antimicrobial activity by attraction of sections of anionic microbial membrane into internal pores of poly cationic hydrogel leading to the disruption of microbial membrane. Moreover, the swelling properties, mechanical strength, and antibacterial activity of hydrogels strongly depended on the contents of quaternary ammonium groups in hydrogel networks. The obtained data encouraged the use of these hydrogels for hygienic application such as disposable diapers.

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

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.

Dual Physically Cross-Linked Nanocomposite Hydrogels Reinforced by Tunicate Cellulose Nanocrystals with High Toughness and Good Self-Recoverability

The weak mechanical properties of hydrogels usually limited their application in biomedical and industrial fields. Herein, we reported a nanocomposite network of poly(acrylic acid-co-acrylamide) (PAAAM) sequentially cross-linked by quaternized tunicate cellulose nanocrystals (Q-TCNCs) and Fe3+. Q-TCNCs acted as both interfacial compatible reinforcements and cross-linkers in the nanocomposite hydrogels to form loose cross-linking, whereas compact cross-linking was built by ionic coordination between Fe3+ and -COO- of PAAAM. The toughness of dual cross-linked hydrogel (D-Gel) was 340 times that of mono-cross-linked hydrogel (m-Gel), which was 10 times that of PAAAM hydrogel. Moreover, the nanocomposite hydrogels exhibited excellent self-recoverability after treating the stretched samples in FeCl3 aqueous solution. This work provided a universal strategy for construction of tough nanocomposite hydrogel reinforced with cellulose nanocrystals.

Tunicate cellulose nanocrystals reinforced nanocomposite hydrogels comprised by hybrid cross-linked networks

Cellulose nanocrystals are considered as promising biomass nanofillers for polymeric hydrogels, but poor interface compatibility between cellulose nanocrystals and hydrogel matrix usually reduces their reinforcement effect. Here, we reported a novel interface compatible nanocomposite hydrogel prepared by introducing quaternized tunicate cellulose nanocrystals (Q-TCNCs) into chemically cross-linked poly (acrylic acid) (PAA) networks. Q-TCNCs acted as both nanofillers and physical cross-linkers in the PAA networks, and the electrostatic interaction between the positive charges of Q-TCNCs and negative charges of PAA chains improved their interface compatibility. The nanocomposite hydrogels exhibited controllable swelling ratio and pH-sensitive swelling behaviors. The mechanical properties of hydrogels significantly increased after incorporation of Q-TCNCs. Moreover, the nanocomposite hydrogels exhibited partly recoverable ability due to the presence of reversible electrovalent bonds in the hydrogel networks.

Chitin/clay microspheres with hierarchical architecture for highly efficient removal of organic dyes

Numerous adsorbents have been reported for efficient removal of dye from water, but the high cost raw materials and complicated fabrication process limit their practical applications. Herein, novel nanocomposite microspheres were fabricated from chitin and clay by a simple thermally induced sol-gel transition. Clay nanosheets were uniformly embedded in a nanofiber weaved chitin microsphere matrix, leading to their hierarchical architecture. Benefiting from this unique structure, microspheres could efficiently remove methylene blue (MB) through a spontaneous physic-sorption process which fit well with pseudo-second-order and Langmuir isotherm models. The maximal values of adsorption capability obtained by calculation and experiment were 152.2 and 156.7 mg g-1, respectively. Chitin/clay microspheres (CCM2) could remove 99.99% MB from its aqueous solution (10 mg g-1) within 20 min. These findings provide insight into a new strategy for fabrication of dye adsorbents with hierarchical structure from low cost raw materials.

Deformation Drives Alignment of Nanofibers in Framework for Inducing Anisotropic Cellulose Hydrogels with High Toughness

Deformation-driven alignment of macromolecules or nanofibers leading to anisotropy is a challenge in functional soft materials. Here, tough cellulose hydrogels that exhibited deformation-induced anisotropy are fabricated by reacting cellulose with a small amount of epichlorohydrin (EPI) in LiOH/urea solution and subsequent treating with dilute acid. The loosely cross-linked network that was obtained via chemical cross-linking of cellulose with EPI as a large framework maintained the elasticity of hydrogels, whereas nanofibers produced by the acid treatment formed physical cross-linked networks through hydrogen bonds which could efficiently dissipated mechanical energy. Meanwhile, the nanofibers could further aggregate to form submicrobundles and participate in the formation of frameworks during the acid treatment. Under deformation, the nanofibers and submicrobundles in the physical networks synchronize easily to align with the large framework, generating the rapidly responsive birefringence behaviors with highly stable colors. Thus, the cellulose hydrogels possessing sensitively mechano-responsive behavior could be utilized as a dynamic light switch and a soft sensor to accurately detect small external force, respectively. This work opens a novel pathway to construct tough and mechanoresponsive hydrogels via a green conversion of natural polysaccharide.

Tunicate cellulose nanocrystal reinforced polyacrylamide hydrogels with tunable mechanical performance

Tunicate cellulose nanocrystals (TCNCs) are widely used as nanofillers for the reinforcements of polymeric materials because of their high aspect ratio and modulus. However, poor interfacial compatibility between TCNCs and polymer matrix always weakens the mechanical performance of nanocomposite materials. Herein, novel nanocomposite hydrogels composed of TCNCs and polyacrylamide (PAM) were generated by chemical crosslinking of PAM with TCNCs that worked as both multifunctional crosslinkers and interfacial compatible nanofillers. Our strategy for the preparation of hydrogels avoided using any toxic crosslinking agent. The morphology, swelling behavior, and mechanical properties of nanocomposite hydrogels could be tuned by varying the amount of initiator. This work provided a simple, universal, and sustainable method to synthesize nanocomposite hydrogels with tunable mechanical performance.Graphical abstract