Hydrogels based on seafood chitin: From extraction to the development.

Chitin is extensively applied in vast applications due to its excellent biological properties, such as biodegradable and non-toxic. About 50 % of waste generated during seafood processing is chitin. Conventionally, chitin is extracted via chemical method. However, it has many shortcomings. Many novel extraction methods have emerged, including enzymatic hydrolysis, microbial fermentation, ultrasonic or microwave-assisted, ionic liquids, and deep eutectic solvents. Chitin and its derivatives-based hydrogels have attracted much attention due to their excellent properties. Nevertheless, they all have many limitations. Therefore, the preparation and application of chitin and its derivatives-based hydrogels are still facing great challenges. This review focuses on the challenges and prospects for sustainable chitin extraction from seafood waste and the preparation and application of chitin and its derivatives-based hydrogels. First section summarizes the mechanism and application of several methods of extracting chitin. The different extraction methods were evaluated from the aspects of yield, degree of acetylation, and protein and mineral residuals. The shortcomings of the extraction methods are also discussed. Next section summarizes the preparation and application of chitin and its derivatives-based hydrogels. Overall, we hope this mini-review can provide a practical reference for selecting chitin extraction methods from seafood and applying chitin and its derivatives-based hydrogels.

Crystallization, thermal and mechanical properties of stereocomplexed poly(lactide) with flexible PLLA/PCL multiblock copolymer.

In this work, the synthesized PLLA/PCL multi-block copolymers with different compositions were introduced into a stereocomplexed poly(lactide) (sc-PLA) matrix to accelerate the stereocomplexation of PLA enantiomers and improve its inherent brittleness. The PLLA/PCL multi-block copolymers were in different compositions to adjust the molecular weight of the PLLA block. The structure, molecular weight, crystallization behavior, crystal structure and thermal stability of PLLA/PCL multi-block copolymers were investigated. The results indicated that PLLA/PCL multi-block copolymers with controllable structure and composition were successfully synthesized. On this basis, the blends of sc-PLA and PLLA/PCL multi-block copolymers were prepared by solution casting, and characterized. The results revealed that the introduction of PLLA/PCL multi-block copolymers promoted the stereocomplexation of the PLA enantiomers during the melting crystallization process to obtain a complete stereocomplexed material. But the presence of the PCL block leads to a decrease in the melting temperature of the stereocomplex and difficulty in homogeneous nucleation. Compared with sc-PLA, the elongation at break of the blends was significantly improved and their tensile strengths were only slightly reduced. And the thermal stability and mechanical properties of the blends could be adjusted by controlling the content and composition of PCL/PLLA multi-block copolymers. These results revealed that the degree of stereocomplexation and toughness of sc-PLA were improved, which may expand the application fields of PLA-based materials.

Immobilization on magnetic PVA/SA@Fe3O4 hydrogel beads enhances the activity and stability of neutral protease.

Enzyme immobilization technology has a key role in improving the stability of enzyme reaction systems and biocatalyst utilization rates. In this study, polyvinyl alcohol/sodium alginate@Fe3O4 (PVA/SA@Fe3O4) magnetic immobilized-enzyme hydrogel beads were prepared. Their structure and morphology were characterized by scanning electron microscopy, surface area and porosity analyses, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and a vibrating sample magnetometer. The capability of PVA/SA@Fe3O4 to adsorb neutral protease was investigated with variations in composition, temperature, pH, stirring speed, enzyme concentration, and crosslinking concentration. The optimal parameters of the immobilization process were determined by response surface methodology (3% neutral protease, 4% crosslinking at 200 rpm, 45 °C and pH 7.2), under which an immobilization rate of 41.98 mg/g was obtained. The thermal stability, acid-base stability, and reusability of the immobilized enzyme were improved significantly. After seven cycles, the immobilized enzyme activity remained at 30.8% that of the initial enzyme activity. The results indicate that the immobilization of NP onto magnetic PVA/SA@Fe3O4 hydrogel beads improves enzyme efficiency, giving this process potential industrial applications.

The synthetic progestin norethindrone causes thyroid endocrine disruption in adult zebrafish.

Synthetic progestin norethindrone (NET) widely used in oral contraceptives, hormonal therapy and livestock farming has been detected in various aquatic ecosystems. Recent studies have shown that NET can cause thyroid endocrine disruption in amphibians. However, studies are still lacking on thyroid axis of fish. In the present study, we investigated thyroid hormone levels (T3 and T4) and transcriptional patterns of 15 genes of the hypothalamic-pituitary-thyroid axis (HPT axis) in adult zebrafish that were exposed to solvent control and three measured concentrations of NET (7, 84 and 810 ng/L) for 90 days. The results indicated that NET significantly lowered T3 and T4 levels in both female and male zebrafish. Transcriptional expression profiles of some of the HPT-axis related genes were disrupted. Specifically, the expression levels of tshb and pax8 have increased significantly while dio2 and ugt1ab have decreased in females. In male, however, tshb expression levels were increased while ttr, ugt1ab, thra and thrb were decreased. The overall results demonstrate that NET disrupts thyroid endocrine system by interfering at multiple sites along HPT axis in adult zebrafish.

Novel Ternary Heterogeneous Reduction Graphene Oxide (RGO)/BiOCl/TiO2 Nanocomposites for Enhanced Adsorption and Visible-Light Induced Photocatalytic Activity toward Organic Contaminants.

Herein, we describe a simple and cost-effective design for the fabrication of a novel ternary RGO/BiOCl/TiO2 nanocomposites through a simple hydrothermal process. The prepared nanocomposites were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (UV-vis DRS) and N2 adsorption-desorption analysis. Organic contaminants-such as methylene blue (MB), methyl orange (MO), rhodamine B (RhB) and amido black-10B (AB-10B)-were employed as the target pollutants to evaluate the adsorption capacity and photocatalytic activity of RGO/BiOCl/TiO2 nanocomposites. From experimental data, it was also found that the amount of TiO2 impressed the photocatalytic performance, and the nanocomposites with 10% of TiO2 showed the best photocatalytic activity. The improved photocatalytic performance may be mainly due to the narrow band gap, and the charge separation and migration of RGO. Moreover, good recyclability was obtained from RGO/BiOCl/TiO2 nanocomposites, and scavenger tests indicated that photogenerated holes were the main active species in the reaction system. Therefore, the prepared RGO/BiOCl/TiO2 nanocomposites have broad applications foreground in pollutants purification.

The progestin norethindrone alters growth, reproductive histology and gene expression in zebrafish (Danio rerio).

The aim of this study was to assess the long-term effects of synthetic progestin norethindrone (NET) on the growth, reproductive histology, and transcriptional expression profiles of genes associated with the hypothalamic-pituitary-gonadal (HPG) axis and germ cells in adult zebrafish. Adult zebrafish were exposed to 7, 84 and 810 ng/L NET for 90 days. The results showed that exposure to 810 ng/L NET caused a significant decrease in growth of females and males. The ovary weight and GSI was significantly reduced by NET at concentrations of 84 or 810 ng/L, which came along with the delay of ovary maturation in females. However, NET at all treatments resulted in acceleration of sperm maturation in males. In the ovaries of females, a strong inhibition of cyp19a1a gene was observed following exposure to NET at 810 ng/L. Similarly, NET at the highest treatment led to a significant down-regulation of cyp17, cyp19a1a, vasa, nanos1, dazl and dmc1 genes in the testes of males. Taken together, the overall results demonstrated that NET could impact growth and gonadal maturation, with significant alterations of transcriptional expression genes along HPG axis and germ cells.

Tough, stretchable and compressive alginate-based hydrogels achieved by non-covalent interactions.

In this study, two alginate-based hydrogels with good mechanical strength, toughness and resilience were synthesized by hydrophobic interaction and coordination bonding. Sodium alginate/poly(acrylamide) semi-interpenetrating network (NaAlg/PAM semi-IPN) hydrogels were first synthesized through the micelle copolymerization of acrylamide and stearyl methacrylate in the presence of sodium alginate, then calcium alginate/poly(acrylamide) double network (CaAlg/PAM DN) hydrogels were prepared by immersing the as-prepared NaAlg/PAM semi-IPN hydrogels in a CaCl2 solution. FT-IR and XPS results revealed NaAlg/PAM semi-IPN hydrogels and CaAlg/PAM DN hydrogels were successfully synthesized through non-covalent interactions. The tensile strength of CaAlg/PAM DN hydrogels could reach 733.6 kPa, and their compressive strengths at 80% strain are significantly higher than those of the corresponding NaAlg/PAM semi-IPN hydrogels, which is attributed to the alginate network crosslinked by Ca2+. The dual physically crosslinked CaAlg/PAM DN hydrogels can achieve fast self-recovery, and good fatigue resistance, which is mainly assigned to energy dissipation through dynamic reversible non-covalent interactions in both networks. The self-healing ability, swelling behavior and morphology of the synthesized alginate-based hydrogels were also evaluated. This study offers a new avenue to design and construct hydrogels with high mechanical strength, high toughness and fast self-recovery properties, which broadens the current research and application of hydrogels.

Crystallization and Properties of Poly(lactide)/Poly(δ-valerolactone) Alternating Supramolecular Copolymers Adjusted by Stereocomplexation.

The crystallization behavior of a series of synthesized polylactide (PLA)/poly(δ-valerolactone) (PVL) supramolecular copolymers with 2-ureido-4[1H]-pyrimidinone (UPy) groups is investigated by differential scanning calorimetry and X-ray diffraction. The stereocomplexation of PLA-based supramolecular polymers (SMPs) is strongly related to the block length, L/D ratios, and the UPy groups. Both the increase of the PLA block length and the self-complementary hydrogen bonding of the UPy end groups restrain the crystallization of the PVL blocks. The stereocomplexation of PLA-SMPs is greatly promoted by UPy groups, while the homocrystallization of PLA is constrained. The dynamic mechanical analysis indicated that the enhanced stereocomplexation would lead to higher thermal resistance and mechanical properties of PLA-based SMPs.

Biodegradable Poly(acrylic acid-co-acrylamide)/Poly(vinyl alcohol) Double Network Hydrogels with Tunable Mechanics and High Self-healing Performance.

We proposed a novel strategy in the fabrication of biodegradable poly(acrylic acid-co-acrylamide)/poly(vinyl alcohol) (P(AAc-co-Am)/PVA) double network (DN) hydrogels with good mechanical and self-healing properties. In the DN hydrogel system, P(AAc-co-Am) polymers form a network through the ionic coordinates between -COO- and Fe3+ and hydrogen bonding between -COOH and -CONH2, while another network is fabricated by the complexation between PVA and borax. The influences of the composition on the rheological behaviors and mechanical properties of the synthesized DN hydrogels were investigated. The rheological measurements revealed that the viscoelasticity and stiffness of the P(AAc-co-Am)/PVA DN hydrogels increase as the acrylamide and Fe3+ concentrations increase. At 0.05 mmol of Fe3+ and 50% of acrylamide, tensile strength and elongation at break of P(AAc-co-Am)/PVA DN hydrogels could reach 329.5 KPa and 12.9 mm/mm, respectively. These properties arise from the dynamic reversible bonds existed in the P(AAc-co-Am)/PVA DN hydrogels. These reversible bonds also give good self-healing properties, and the maximum self-healing efficiency of P(AAc-co-Am)/PVA DN hydrogels is up to 96.4%. The degradation test of synthesized DN hydrogels was also conducted under simulated physiological conditions and the weight loss could reach 74% in the simulated intestinal fluid. According to the results presented here, the synthesized P(AAc-co-Am)/PVA DN hydrogels have a potential application prospect in various biomedical fields.

Superhydrophobic foam prepared from high internal phase emulsion templates stabilised by oyster shell powder for oil-water separation.

In this paper, poly(styrene-divinylbenzene) foams were synthesized using a high internal phase emulsion (HIPE) technique with Span 80 and with 900 °C calcined oyster shell powder as a co-emulsifier, 2,2'-azobisisobutyronitrile (AIBN) as an initiator and deionized water as the dispersing phase. SEM images revealed that the materials possess a hierarchical porous structure of nano/micro size, which resulted in saturated oil adsorption in only half a minute. The dispersing phase amount was investigated for its effect on adsorption. The optimized foams have 24.8-58.3 g g-1 adsorbencies for several organic solvents, and they demonstrated superhydrophobicity and excellent oleophilicity with the water contact angle (WCA) even close to 149° and oil contact angle approaching 0°. Moreover, the foams displayed high oil retention under pressure. The adsorption-centrifugation cycling results indicated high repeatability of the recovered foams. All of these features predicted the potential applications of superhydrophobic foams in oil-water separation.

Crystallization, rheology and mechanical properties of the blends of poly(l-lactide) with supramolecular polymers based on poly(d-lactide)-poly(ε-caprolactone-co-δ-valerolactone)-poly(d-lactide) triblock copolymers.

In this study, we investigated the blending of poly(l-lactide) (PLLA) with supramolecular polymers based on poly(d-lactide)-poly(ε-caprolactone-co-δ-valerolactone)-poly(d-lactide) (PDLA-PCVL-PDLA) triblock copolymers as an efficient way to modify PLLA. The supramolecular polymers (SMP) were synthesized by the terminal functionalization of the PDLA-PCVL-PDLA copolymers with 2-ureido-4[1H]-pyrimidinone (UPy). The structure, thermal properties and rheological behavior of the synthesized supramolecular polymers were studied; we found that the formation of the UPy dimers expanded the molecular chain of the polymer and the incorporation of the UPy groups suppressed the crystallization of polymers. In addition, the synthesized supramolecular polymers had a low glass transition temperature of about -50 °C, showing the characteristics of elastomers. On this basis, superior properties such as a fast crystallization rate, high melt strength, and toughness of fully bio-based, i.e., PLA-based materials were achieved simultaneously by blending PLLA with the synthesized supramolecular polymers. In the PLLA/SMP blends, PLLA could form a stereocomplex with its enantiomeric PDLA blocks of supramolecular polymers, and the stereocomplex crystals with the cross-linking networks reinforced the melt strength of the PLLA/SMP blends. The influences of the SMP composition and the SMP content in the PLLA matrix on crystallization and mechanical properties were analyzed. The supramolecular polymers SMP0.49 and SMP1.04 showed a reverse effect on the crystallization of PLLA. Tensile tests revealed that the lower content of the synthesized supramolecular polymers could achieve toughening of the PLLA matrix. Therefore, the introduction of supramolecular polymers based on PDLA-PCVL-PDLA is an effective way to control the crystallization, rheology and mechanical properties of PLLA.

Preparation of a porous superhydrophobic foam from waste plastic and its application for oil spill cleanup.

In order to cope with the increasing oil spill accidents and the intentional discharge of oily wastewater, a new oil-adsorbing material with superhydrophobicity and reusability is needed. In this paper, waste plastic was used to fabricate an alveolate polystyrene (PS) foam to reduce secondary pollution. The PS foam was synthesized from a high internal phase Pickering emulsion (HIPPE) technique in a one-step process. The emulsion was stabilized by a co-Pickering system of Span 80 surfactant and SiO2 particles. To explain the super stability of the HIPPE, a novel model of the water-in-oil droplet was promoted. The obtained SiO2@PS foam exhibited a multi-order-porous structure, and displayed superhydrophobicity and superoleophilicity. It can selectively remove various oily contaminants from water with a high adsorption capacity of 20.4-58.1 g g-1 at a fast rate. The oil-adsorbed material can be reused by simple centrifugation, and no more than a 1% decline was obtained in the oil adsorption after 10 cycles. Therefore, the SiO2@PS foam has a great potential application in oily water treatment.

Competitive Stereocomplexation and Homocrystallization Behaviors in the Poly(lactide) Blends of PLLA and PDLA-PEG-PDLA with Controlled Block Length.

Stereocomplex poly(lactide) (PLA) was obtained by solution blending of linear PLLA and PDLA-PEG-PDLA. Effects of the L/D ratios, PEG block, and PDLA block on stereocomplexation of the blends are systemically discussed. The full stereocomplex PLA can be acquired by solution blending when L/D ratios are in the range of 7/3⁻5/5. The experiment results demonstrated that the stereocomplex degree of PLLA/PDLA-PEG-PDLA prepared by melt blending was closely related to the PEG block and PDLA block. POM results indicated that the blends with high L/D ratio showed large disordered spherulites, and the typical Maltese cross pattern was observed as the L/D ratios decreased. The results of PEG block on the stereocomplexation of PLLA/PDLA-PEG-PDLA revealed that the PEG blocks possessed two sides: accelerating agent for the mobility of polymer chains and decreasing nucleation capacity due to their diluting effect. The effect of PDLA block on the stereocomplexation of the blends was also well investigated. The results showed that the crystallization of sc-crystallites and hc-crystallites in the PLLA/PDLA-PEG4k-PDLA blends with different PDLA blocks presents an obvious competition relationship, and this is not beneficial to the formation of sc-crystallites with increasing PDLA block. The melting behavior of PLLA/PDLA-PEG4k-PDLA with different PDLA blocks after isothermal crystallization showed that the blends could achieve full stereocomplex when the crystallization temperature exceeded 160 °C, and a crystallite with high perfection could be formed as the crystallization temperature increased. This study systemically investigated the effects of the L/D ratios, PEG block, PDLA block, and crystallization conditions on stereocomplex crystallization of PLLA/PDLA-PEG-PDLA blends, which can provide potential approaches to control the microstructure and physical performances of PLLA/PDLA-PEG-PDLA blends.

Preparation and adsorption property of xylan/poly(acrylic acid) magnetic nanocomposite hydrogel adsorbent.

Adsorbents based on natural polysaccharides have attracted increasing interest because of their low-cost and biodegradability, particularly, polysaccharide-based nanocomposite adsorbents. In this study the xylan/poly(acrylic acid) magnetic nanocomposite hydrogel adsorbent was prepared from wheat straw xylan and Fe3O4 nanoparticles, and its adsorption property was studied on methylene blue removal. The prepared hydrogel adsorbent had a semi-interpenetrating network structure and exhibited a macro-porous structure with interconnected porous channels. Super-paramagnetic characteristic behavior was observed from magnetic analysis using a vibrating sample magnetometer. The optimum condition for methylene blue adsorption on the adsorbent was found at pH 8 with an adsorbent dosage of 3g/L and an initial concentration of 400mg/L, and the removal percentage reached above 90%. The adsorption isotherm of methylene blue on the prepared hydrogel adsorbent was fitted to the Langmuir model, and the pseudo-second-order kinetic model could describe the adsorption process. All obtained results indicated that the prepared hydrogel adsorbent is promising for water treatment applications.

Hemicellulose-based pH-sensitive and biodegradable hydrogel for controlled drug delivery.

Hydrogels based on hemicellulose of wheat straw were prepared as a novel carrier for controlled drug delivery. The chemical structure and morphology of the hydrogels were characterised using FT-IR and SEM, respectively. The swelling ratios of the hydrogels were determined, and the results showed that the hydrogels were pH-responsive. The swelling kinetics of the hydrogels followed a Fickian diffusion process in media with a pH of 1.5, and water uptake was controlled collaboratively by hydrogel relaxation and water diffusion in media with pH values of 7.4 and 10.0. The degradation test of the hydrogels was conducted under simulated physiological conditions, and both hemicellulose content and the crosslinking density of the hydrogels were major factors that affected the biodegradability of the hemicellulose-based hydrogels. A comparison of the in vitro release of acetylsalicylic acid and theophylline indicated that the drug release was controlled both by the hydrogel and by the intrinsic character of the drug. According to the results presented here, hemicellulose-based hydrogels can be used in biomedical fields, especially for controlled drug release.

Chemical constituents from Delphinium chrysotrichum and their biological activity.

A new diterpene alkaloid named delphatisine C (1) has been isolated from aerial parts of Delphinium chrysotrichum along with three known norditerpenoid alkaloids delpheline (2), delbrunine (3), and delectinine (4). Their structures were characterized on the basis of their spectral data. All of them were determined by SRB assay for their cytotoxicity, and compound (1) showed significant cytotoxic activities (IC(50)=2.36 µmol/L) against the A549 cell line.