Starch-based hydrogels for environmental applications: A review.

Water sources have become extremely scarce and contaminated by organic and inorganic industrial and agricultural pollutants as well as household wastes. Poisoning water resources by dyes and metals is a problem because contaminated water can leak into subsurface and surface sources, causing serious contamination and health problems. Therefore, developing wastewater treatment technologies is valuable. Today, hydrogels have attracted considerable attention owing to their broad applications. Hydrogels are polymeric network compositions with significant water-imbibing capacity. Hydrogels have potential applications in diverse fields such as biomedical, personal care products, pharmaceuticals, cosmetics, and biosensors. They can be prepared by using natural (biopolymers) and synthetic polymers. Synthetic polymer-based hydrogels obtained from petrochemicals are not environmentally benign; thus, abundant plant-based polysaccharides are found as more suitable compounds for making biodegradable hydrogels. Polysaccharides with many advantages such as non-toxicity, biodegradability, availability, inexpensiveness, etc. are widely employed for the preparation of environmentally friendly hydrogels. Polysaccharides-based hydrogels containing chitin, chitosan, gum, starch (St), etc. are employed to remove pollutants, metals, and dyes. Among these, St has attracted a lot of attention. St can be mixed with other compounds to make hydrogels, which remove dyes and metal ions to variable degrees of efficiency. Although St has numerous advantages, it suffers from drawbacks such as low stability, low water solubility, and fast degradability in water which limit its application as an environmental adsorbent. As an effective way to overcome these weaknesses, various modification approaches to form starch-based hydrogels (SBHs) employing different compounds have been reported. The preparation methods and applications of SBH adsorbents in organic dyes, hazardous materials, and toxic ions elimination from water resources have been comprehensively discussed in this review.

A guanosine/konjac glucomannan supramolecular hydrogel with antioxidant, antibacterial and immunoregulatory properties for cutaneous wound treatment.

Developing naturally-derived wound dressing materials with intrinsic therapeutic effects is desirable for the clinical applications. Recently, guanosine-based supramolecular G-quadruplex (G4) hydrogel exhibited great potential in preparing biological materials due to its simple fabrication method and responsive gel networks. However, the weak mechanical properties and the consequent burst release of bioactive molecules restrict its clinical applications. Herein, we found that konjac glucomannan (KGM) with immunoregulatory effect did not affect the self-assembly of G-quadruplexes and thus effectively enhancing the mechanical properties of G4 hydrogel. Aloin, as a model drug, was in situ loaded into gel networks, finally obtaining the G4/Aloin-KGM hydrogel. This hydrogel exhibited porous morphology, swelling ability and hemostatic capability. Boronate bonds in G4 networks and aloin collectively endowed the hydrogel with excellent antioxidant performance. Meanwhile, aloin also provided outstanding in vitro and in vivo bactericidal ability. The wounds treated with this biocompatible hydrogel demonstrated faster regeneration of epithelial and dermal tissues, and the whole wound healing stages were accelerated by promoting collagen deposition, facilitating macrophage polarization towards M2 phenotype, down-regulating the expression level of IL-6, and up-regulating the expression level of IL-10, CD31 and α-SMA.

Body temperature-induced adhesive hyaluronate/gelatin-based hybrid hydrogel dressing for promoting skin regeneration.

Skin wound management faces significant clinical challenges, including continuous bacterial infection and inflammation. Therefore, developing removable hydrogel dressings with intrinsic multifunctional properties is highly desirable. In this study, a body temperature-induced adhesive and removable hydrogel was designed to treat skin defect wounds. The HA/Gel-R-Ag hybrid gel was prepared by incorporating a silver ion-crosslinked sulfhydryl hyaluronate/gelatin-based polymeric gel network into a supramolecular rhein gel network, thereby significantly enhancing its mechanical properties. Temperature-responsive gelatin chains give the hybrid gel reversible tissue adhesiveness and detachment, thus avoiding secondary injury to wounds when changing the hydrogels. The hybrid gel exhibited excellent bactericidal ability owing to the antibacterial capacity of the silver ions and rhein. Moreover, both HA and rhein endowed the hybrid gel with immunoregulatory effects by promoting macrophage polarization from pro-inflammatory M1 phenotype to anti-inflammatory M2 phenotype. In a full-thickness skin defect mouse mode, this porous, degradable, and biocompatible HA/Gel-R-Ag hybrid gel boosted skin regeneration by inhibiting inflammation and promoting collagen deposition and angiogenesis. It is thus a simple method for widening the application range of mechanically weak rhein gels and providing a promising wound dressing material with multiple intrinsic functions for treating skin wounds.

A Novel Dual-Permanent-Magnet Mechanical Antenna for Pipeline Robot Localization and Communication.

The demand for pipeline inspection has promoted the development of pipeline robots and associated localization and communication technologies. Among these technologies, ultra-low-frequency (30-300 Hz) electromagnetic waves have a significant advantage because of their strong penetration, which can penetrate metal pipe walls. Traditional low-frequency transmitting systems are limited by the size and power consumption of the antennas. In this work, a new type of mechanical antenna based on dual permanent magnets was designed to solve the above problems. An innovative amplitude modulation scheme that involves changing the magnetization angle of dual permanent magnets is proposed. The ultra-low-frequency electromagnetic wave emitted by the mechanical antenna inside the pipeline can be easily received by the antenna outside to localize and communicate with the robots inside. The experimental results showed that when two N38M-type Nd-Fe-B permanent magnets with a volume of 3.93 cm3 each were used, the magnetic flux density reached 2.35 nT at 10 m in the air and the amplitude modulation performance was satisfactory. Additionally, the electromagnetic wave was effectively received at 3 m from the 20# steel pipeline, which preliminarily verified the feasibility of using the dual-permanent-magnet mechanical antenna to achieve localization of and communication with pipeline robots.

Schiff base modified starch: A promising biosupport for palladium in Suzuki cross-coupling reactions.

Starch can be used in diverse fields because it is a readily available, non-toxic polysaccharide with adaptable functionality and biodegradability. In this study, taking the aforementioned characteristics into consideration, we designed a modified starch (Starch-SB), which serves as supporting material for palladium stabilization. This new air and moisture-stable robust palladium composite [Starch-SB-Pd(II)] was characterized by FT-IR, XRD, TGA, XPS, SEM, EDX, TEM, CP/MAS 13C NMR, and ICP-MS analytical techniques. The catalytic studies exhibit high activity (up to 99 %) and stability in Suzuki cross-coupling reactions for this starch supported catalytic system under mild conditions (lower reaction temperature and green solvents) because of the cooperative interactions of multifunctional capturing sites on starch (Schiff base, hydroxy and amine groups) with palladium species. The experiments on reusability demonstrate that Starch-SB-Pd(II), which was prepared from functionalized starch, could be readily recycled several cycles through centrifugation. Moreover, we proposed a possibly multifunctional complex structure. This work presents an appealing and intriguing pathway for the utilization of polysaccharide as crucial support in green chemical transformations.

Enzymatic one-pot preparation of carboxylmethyl chitosan-based hydrogel with inherent antioxidant and antibacterial properties for accelerating wound healing.

Facile preparation of multifunctional hydrogel wound dressings with inherent versatile properties is highly desirable in practical healthcare. Here, a biocompatible hydrogel was designed and fabricated via mild enzymatic crosslinking and polymerization. We first designed an enzymatic system containing horseradish peroxidase (HRP), H2O2, and the macromolecular initiator-acetoacetyl polyvinyl alcohol (PVA-ACAC), which can generate active PVA-ACAC carbon radicals via HRP-mediated oxidation by H2O2. Trimethylammonium chloride (Q), methacryloyl (MA) and phenol (Ph)-grafted carboxymethyl chitosan (Ph-QCMCS-MA) was then synthesized. HRP catalyzes the oxidation of phenol groups to achieve the fast phenol crosslinking, and PVA-ACAC carbon radicals initiate the polymerization of MA groups simultaneously, finally obtaining the target PPQM gel. The quaternary ammonium and phenol groups endow the PPQM gel with excellent antibacterial and antioxidant properties, respectively. This multifunctional hydrogel, which has additional adhesive and hemostatic properties, could promote wound healing processes in an in vivo full-thickness skin defect experiment by reducing the generation of pro-inflammatory cytokines (IL-6) and upregulating anti-inflammatory factors (IL-10) and angiogenesis-related cytokines (VEGF and α-SMA). As a result, it could be used as competitive wound dressings.

Functionalized chitosan as a novel support for stabilizing palladium in Suzuki reactions.

Chitosan is a versatile polysaccharide in different domains due to facile modification and good biodegradability. In this paper, taking advantage of such functional properties, we have developed a stabilizer agent [OCMCS-SB] produced from chitosan, and palladium was successfully immobilized on this designed stabilizer [OCMCS-SB-Pd(II)]. The obtained complex was illuminated by 13C CP-MAS NMR, FT-IR, TGA, XRD, XPS, SEM, TEM and ICP-OES analyses. Due to the interactions of primary hydroxyl groups on chitosan, Schiff base and carboxy groups, the Pd complex showed excellent reactivity (up to 99 %) and stability towards Suzuki reactions in eco-friendly medium. Subsequently, the reusability experiments for OCMCS-SB-Pd(II) formed from chitosan were examined in five consecutive cycles, which showed no appreciable decrease in activity. Furthermore, a reasonably trifunctional complex structure was proposed. The present bio-based system offers a promising approach in utilizing such biopolymers in organic transformations.

Controlled synthesis of Cu-based SAPO-18/34 intergrowth zeolites for selective catalytic reduction of NOx by ammonia.

Cu-based SAPO-18, SAPO-18/34 intergrowth and SAPO-34 zeolites were applied for the selective catalytic reduction of NOx by ammonia (NH3-SCR) catalysts. Comprehensive characterization results revealed that the SAPO-18/34 with higher amount and strength of acid sites could facilitate the generation of more isolated copper ions (Cu2+ and Cu+) and suppress the formation of CuOx, which might account for the fact that intergrowth crystal structure of Cu-SAPO-18/34 exhibited higher fresh NH3-SCR activity, more robust hydrothermal durability and better SO2-resistance ability than that Cu-SAPO-18 and Cu-SAPO-34. In situ DRIFTS results provided the formation of reaction intermediates, such as -NH2, NH4+, NO3-, NO2-, etc. Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) reaction mechanisms were both involved in Cu-based SAPO-18 and SAPO-18/34 intergrowth zeolites, but the L-H mechanism dominated the NH3-SCR reaction, in addition, Cu-SAPO-34 only followed "L-H" mechanism.

Salen-based hypercrosslinked polymer-supported Pd as an efficient and recyclable catalyst for C-H halogenation.

In this work, we report the first use of a salen-based hypercrosslinked polymer-supported Pd catalyst to carry out C-H halogenation. This catalyst can effectively catalyze C-H bromination and chlorination even better than its homogeneous counterpart Pd(OAc)2. It also showed excellent reusability without loss of catalytic activity for ten cycles. A broad substrate scope was explored and moderate to excellent yields were obtained.

Design and synthesis of amine-functionalized cellulose with multiple binding sites and their application in CC bond forming reactions.

Straw is a green and promising material in nature. However, as is the case for all other biopolymers, straw have to face the challenge of underutilization thereby resulting in environmental and economic issues. To overcome these drawbacks, the urgent exploitation of straw is needed for its comprehensive utilization. In this paper, we chose cellulose as the straw model to prepare two amine ligands functionalized environmentally-friendly cellulose supported catalyst. The ethylenediamine functionalized cellulose catalyst (ADC) was effective in the reaction of aromatic aldehydes with nitromethane to synthesize nitroalkenes and 1,3­dinitroalkanes. Based on ADC, the diethylenetriamine functionalized cellulose (CL-DETA-Cl) could capture Pd firmly by virtue of the covalent bonding between diethylenetriamine functionalized cellulose and palladium nanoparticles. The synthesized catalyst (CL-DETA-Pd) was then illuminated by using FT-IR, TGA, XRD, TEM, ICP-OES and XPS. The multifunctional complex could catalyze the Suzuki-Miyaura reactions efficiently and prevented the metal leaching through the multiple capturing sites (hydroxyl and amine groups) with palladium. Also, the catalyst could be completely regenerated in a few cycles with simple centrifugation. This study will provide reliable foundation and extensive application way to further utilization of straw.

Differences in Zwitterionic Sulfobetaine and Carboxybetaine Dextran-Based Hydrogels.

Zwitterionic sulfobetaine (SB) and carboxybetaine (CB) have been extensively investigated for their noticeable antifouling properties. Both SB and CB have cationic and anionic groups in the molecule, but they differ in negatively charged groups. Molecular simulations have been conducted to investigate the different properties induced by structure changes. However, few studies have focused on the differences between SB and CB materials, especially zwitterionic polysaccharides. Two zwitterionic sulfobetaine and carboxybetaine dextran hydrogels were designed and used as models to compare their properties. Results showed that the equilibrium swelling ratios of the SB-DEX hydrogels were much higher than CB-DEX ones, and larger interior pores were observed in the SB-DEX hydrogels due to their higher hydrophilicity. The rheological storage modulus of the SB-DEX hydrogels was lower than that of CB-DEX ones as a result of higher water content of SB-DEX. These results were consistent with molecular modeling. Additionally, both CB-DEX and SB-DEX had remarkable biocompatibilities, and the in vitro release studies showed that the SB-DEX and CB-DEX hydrogels released DOX in a sustained manner under acidic condition (pH 5.0), indicating their promise as an effective drug-delivery system.

Antifouling zwitterionic dextran micelles for efficient loading DOX.

Polysaccharides derivatives are typical drug nanocarriers which are nontoxic and biodegradable. However, as is the case for all drug delivery systems, polysaccharides derivatives have to face the issue of protein fouling. In this paper, we present the design and synthesis of carboxybetaine-modified dextran-polycaprolactone (CB-Dex-PCL) copolymers as doxorubicin (DOX) nanocarriers. Results showed that DOX/CB-Dex-PCL micelles exhibited better cumulative release at the pH value of 5.2 than at the physiological pH of 7.4, which indicated potential applications in killing tumor cells while minimizing the toxicity to normal tissues. Additionally, antifouling properties of carboxybetaine functionalized dextran micelles were much better than that of unmodified dextran for fibrinogen and lysozyme as tested by ITC. Finally, cytotoxicity tests using Hela cells showed that CB-Dex-PCL and DOX-loaded micelles exhibited great biocompatibility. All the above observations indicated that CB-Dex-PCL micelles are potentially excellent drug carriers for the treatment of human cancerous tumors.

N-Methylimidazole functionalized carboxymethycellulose-supported Pd catalyst and its applications in Suzuki cross-coupling reaction.

In this paper, N-Methylimidazole functionalized carboxymethylcellulose-supported palladium nanoparticles (CMC-NHC-Pd) was synthesized and characterized by TEM, SEM, EDX, CP/MAS 13C NMR, FT-IR, TGA, XRD, and XPS analysis. The prepared nanoparticles can be used as an environmentally-friendly and trifunctional catalyst. The well-designed CMC supported palladium nanoparticles catalyst with polydentate ligands is also stable and efficient for Suzuki cross-coupling reactions under mild conditions through the cooperative interaction of trifunctional capturing sites with palladium, -COO-, -OH and N-Methylimidazole. This catalyst can be readily recovered by a few cycles of simple filtration. This work proposes a plausible trifunctional catalyst complex.