[Development of Shuttle Adsorbents between the Bottom and Surface of Water for the Adsorption of Pollutants].

For various pollutants with different specific gravity values, adsorbents having similar specific gravity values as those of target pollutants are necessary to achieve enough contact time. The purpose of this work is to introduce a self-vertical migration system to adsorbents for wastewater treatment. An alginate hydrogel composite with controlled specific gravity and buoyancy was successfully developed, which can first sink to the bottom of water and then float up on the surface after the adsorption. The alginate hydrogel composite was prepared using an alginate solution containing both glucose and yeast. In an experiment, the obtained beads first sank. However, 30 min later, most of them floated up to the water surface, where carbon dioxide was generated in the fermentation process. This behavior was repeated several times during the fermentation process, causing the beads to float. To confirm the efficiency of this unique property, the removal of cesium ions was demonstrated in a water column using Prussian Blue modified alginate gel beads with a repeated vertical migration system. The adsorbent showed a faster removal of cesium than the other adsorbents without the proposed system. We believe that the proposed system can be applied to treat large volumes of wastewater that cannot be stirred or pumped. Therefore, the novel adsorbent developed in this study is expected to significantly contribute to environmental remediation.

Potential applications of alginate oligosaccharides for biomedicine - A mini review.

Extensive research on marine algae, especially on their health-promoting properties, has been conducted. Various ingredients with potential biomedical applications have been discovered and extracted from marine algae. Alginate oligosaccharides are low molecular weight alginate polysaccharides present in cell walls of brown algae. They exhibit various health benefits such as anti-inflammatory, anti-microbial, anti-oxidant, anti-tumor and immunomodulation. Their low-toxicity, non-immunogenicity, and biodegradability make them an excellent material in biomedicine. Alginate oligosaccharides can be chemically or biochemically modified to enhance their biological activity and potential in pharmaceutical applications. This paper provides a brief overview on alginate oligosaccharides characteristics, modification patterns and highlights their vital health promoting properties.

3D printed double-network alginate hydrogels containing polyphosphate for bioenergetics and bone regeneration.

Low mechanical strength, poor processability, and low bioactivity of hydrogels limit their application in bone tissue engineering severely. Herein, a new 3D-printable, osteoinductive, and bioenergetic-active double-network (DN) hydrogel containing sodium alginate (SA), poly (ethylene glycol) diacrylate (PEGDA), and sodium polyphosphate (PolyP) was developed via a two-step method. The synergy of the covalent cross-linking network and the ionic cross-linking network improves the mechanical properties of the hydrogel. And the pre-gel with Ca2+ has better 3D printing performance to print complex tissue engineering scaffolds than common hydrogels. In addition, the incorporation of PolyP into DN hydrogel matrix significantly improves the bioactivity of hydrogels. The bioenergetic effect of PolyP improves adenosine triphosphate content of cells significantly to promote cell activities such as migration. The in vitro osseointegration investigation suggests that the orthophosphate monomer units, which are degradation fragments of PolyP, provide enough phosphoric acid units for the formation of calcium phosphate and accelerate the osteogenic differentiation of cells greatly. Therefore, the proposed printable, bioenergetic-active, osteoinductive DN hydrogel is potential to solve the problems of complex tissue engineering scaffolds and be applied in energy-crucial bone tissue regeneration.

Ecofriendly flame-retardant composite aerogel derived from polysaccharide: Preparation, flammability, thermal kinetics, and mechanism.

Bio-based aerogel (polysaccharide cryogel) have led to a growing interest because of eco-friendliness, sustainability and excellent thermal insulation properties. Herein, we report an eco-friendly strategy to construct lightweight and porous sodium alginate/carboxymethyl cellulose/chitosan polysaccharide-based composite aerogels (SCC-B) by freeze-drying and post-cross-linking technology. The ester cross-linking of polysaccharide component achieved strong web-like entangled structure when using 1,2,3,4-butanetetracarboxylic acid and sodium hypophosphite as eco-friendly co-additives, meanwhile significantly improved flame retardancy of SCC-B due to phosphorylation. The thermal kinetic behavior of SCC-B was investigated by Flynn-Wall-Ozawa and Kissinger models. Results indicated that peak heat release rate and total heat release of SCC-B decreased from 30 W/g to 20 W/g and 15 kJ/g to 10 kJ/g, respectively. Furthermore, the second-degree burn time of SCC-B reached up to 87.1 s under heat exposure of 11.3 kW/m2. These characteristics combine to suggest hopeful prospects for use of SCC-B in the fields of fire-protection clothing as a renewable flame-retardant material.

Synthesis of a pH-responsive nano-cellulose/sodium alginate/MOFs hydrogel and its application in the regulation of water and N-fertilizer.

In order to circumvent the water eutrophication caused by nitrogen loss in agriculture, slow-release and high-water containing fertilizers have captured much attention. Considering the unstable release of traditional slow-released fertilizers, novel strategies need to be designed to meet the steady release of fertilizers. Herein, by integrating cellulose-based hydrogel with MIL-100(Fe), a pH-sensitive Cellulose/MOFs hydrogel (CAM) with a high surface area (45.25 m2/g) was devised. The volume changes and the water adsorption of the hydrogels were uncovered from pH 3 to pH 11, where the highest water adsorption (100 g/g) was achieved at pH 11. Besides, a pH-sensitive urea slow release fertilizer (U-CAM) was also designed. The urea release of the U-CAM at pH 11 was much slower than that of the U-CAM at pH 3, which indicated its potential application in arid regions. In parallel with a favorable water-holding capacity, the totally loss of the soil moisture loaded with U-CAM was slowed down by 18 days as compared with the pure soil. The positive effect of the U-CAM on the growth of wheat was indexed with the germination rate, number of tillers, photosynthetic rate and chlorophyll content of the crop, which verified their further application in irrigating farming.

Adsorption of 4-Nitrophenol on calcium alginate-multiwall carbon nanotube beads: Modeling, kinetics, equilibriums and reusability studies.

In this study calcium alginate-multiwall carbon nanotube (CA/MWCNTs) was synthesized using (CA) calcium alginate and multiwall carbon nanotube (MWCNTs), and its efficiency in adsorption of 4-Nitrophenol (4-NP) in aqueous solution was studied. The structure and properties of the synthesized adsorbent were investigated using scanning electron microscope (SEM), thermal gravimetric analysis (TGA), Fourier transform infrared (FTIR), and X-ray diffraction (XRD). The experimental design was performed using Box-Behnken design (BBD) in which variables pH, CA/MWCNTs, and temperature were examined. The results of the effect of temperature on the removal efficiency of 4-NP showed that the adsorption efficiency decreases with increasing temperature. The results of nonlinear isotherm and kinetics models showed that Langmuir and pseudo-second-order models were more consistent than other models. The maximum adsorption capacity of 4-NP in this study by CA, MWCNTs, and CA/MWCNTs was 136, 168.4, and 58.8 mg/g, respectively, which indicates that the use of MWCNTs on CA could increase the adsorption capacity. The results of reuse of the synthesized adsorbent at 4-NP removal also showed that after 5 reuse of the adsorbent, the removal of 4-NP using CA/MWCNTs is reduced by about 10%, which shows that the synthesized adsorbent can be used several times to adsorb contaminants without significant reduction in the efficiency.

Hydroxyapatite-reinforced alginate fibers with bioinspired dually aligned architectures.

Biological materials have excellent mechanical properties due to their organized structures from nano- to macro-scale. Artificial manufacture of materials with anisotropic microstructures still remains challenging. We described a stress-induced method to fabricate anisotropic alginate fibers. Organic-inorganic composite fibers were obtained by incorporating aligned hydroxyapatite (HAP) nanowires into the alginate fiber. Detailed structural characterization revealed the bone-like structure of the HAP-reinforced alginate fibers. Tensile test results showed that the maximum Young's modulus and tensile strength were 4.3 GPa and 153.8 MPa, respectively. A multiscale reinforcing mechanism is proposed after the discussion of the structure-property relationship: highly ordered and compacted nanofibrils aligned along the longitudinal direction at the microscale, and two kinds of alginate gels with different mechanical behaviors at the nanoscale coexisted (acidic alginate gel and calcium-alginate gel). This work validates the effectiveness of the bioinspired fabrication strategy, which inspires further manufacturing and optimization of materials for diverse applications.

Single-Step Synthesis of Alginate Microgels Enveloped with a Covalent Polymeric Shell: A Simple Way to Protect Encapsulated Cells.

Microgels of biopolymers such as alginate are widely used to encapsulate cells and other biological payloads. Alginate is an attractive material for cell encapsulation because it is nontoxic and convenient: spherical alginate gels are easily created by contacting aqueous droplets of sodium alginate with divalent cations such as Ca2+. Alginate chains in the gel become cross-linked by Ca2+ cations into a 3-D network. When alginate gels are placed in a buffer, however, the Ca2+ cross-links are eliminated by exchange with Na+, thereby weakening and degrading the gels. With time, encapsulated cells are released into the external solution. Here, we describe a simple solution to the above problem, which involves forming alginate gels enveloped by a thin shell of a covalently cross-linked gel. The shell is formed via free-radical polymerization using conventional monomers such as acrylamide (AAm) or acrylate derivatives, including polyethylene glycol diacrylate (PEGDA). The entire process is performed in a single step at room temperature (or 37 °C) under mild, aqueous conditions. It involves combining the alginate solution with a radical initiator, which is then introduced as droplets into a reservoir containing Ca2+ and monomers. Within minutes of either simple incubation or exposure to ultraviolet (UV) light, the droplets are converted into alginate-polymer microcapsules with a core of alginate and a shell of the polymer (AAm or PEGDA). The microcapsules are mechanically more robust than conventional alginate/Ca2+ microgels, and while the latter swell and degrade when placed in buffers or in chelators like sodium citrate, the former remain stable under all conditions. We encapsulate both bacteria and mammalian cells in these microcapsules and find that the cells remain viable and functional over time. Lastly, a variation of the synthesis technique is shown to generate multilayered microcapsules with a liquid core surrounded by concentric layers of alginate and AAm gels. We anticipate that the approaches presented here will find application in a variety of areas including cell therapies, artificial cells, drug delivery, and tissue engineering.

A double-network polysaccharide-based composite hydrogel for skin wound healing.

Effective wound dressings are of great significance in preventing infections and promoting wound healing. However, most existing hydrogel dressings have an inadequacy in either mechanical performance, biological activities, or versatilities. Here we presented a double-network cross-linked polysaccharide-based hydrogel composed of collagen peptide-functionalized carboxymethyl chitosan (CS) and oxidized methacrylate sodium alginate (SA). The hydrogel possessed interconnected porous morphologies, suitable swelling ratios, excellent mechanical properties, and favorable biocompatibility. Meanwhile, the in vivo studies using a mouse full-thickness skin defect model showed that the double-network CS/SA hydrogel significantly accelerated wound healing by regulating the inflammatory process, promoting collagen deposition, and improving vascularization. Therefore, the functionalized double-network hydrogel should be a potential candidate as wound dressings.

The composite microbeads of alginate, carrageenan, gelatin, and poly(lactic-co-glycolic acid): Synthesis, characterization and Density Functional Theory calculations.

Binary (AC, AG), ternary (ACG, ACP, AGP), quaternary (ACGP) composite beads of alginate (A), carrageenan (C), gelatin (G), and poly (lactic-co-glycolic acid) (P) were prepared. The dried beads had a 700 µm average diameter. The microspheres with and without P were characterized by FT-IR, TGA/DTA, SEM, and PZC analysis. The results proved that the features of the composites were completely different from their bare components. Density Functional Theory (DFT) calculations were performed at the B3LYP/6-311++G** level to enlighten the elementary physical and chemical properties of A, C, P, and G compounds. The vibrational modes obtained by calculations were compared with those observed in the FT-IR spectra. The Frontier Molecular Orbital (FMO) analyses showed that the component G was the softer and had smaller energy gap than the other components and vice versa for component P. NBO (Natural Bond Orbital) analyses implied that the n → П* (resonance) interactions for components A, G, and P contributed to the lowering of the molecular stabilization, whereas that the n → σ* (anomeric) interactions were responsible for decreasing of the stabilization of the component. From the obtained results, these kinds of components can be hoped the promising materials for usage in the many scientific fields, especially in medicine and in drug design.

Copper-Free Azide-Alkyne Cycloaddition for Peptide Modification of Alginate Hydrogels.

Alginate, a biocompatible polymer naturally derived from algae, is widely used as a synthetic analogue of the extracellular matrix in tissue engineering. Integrin-binding peptide motifs, including RGD, a derivative of fibronectin, are typically grafted to the alginate polymer through carbodiimide reactions between peptide amines and alginate uronic acids. However, lack of chemo-selectivity of carbodiimide reactions can lead to side reactions that lower peptide bioactivity. To overcome these limitations, we developed an approach for copper-free, strain-promoted azide-alkyne cycloaddition (SPAAC)-mediated conjugation of azide-modified adhesive peptides (azido-cyclo-RGD, Az-cRGD) onto alginate. Successful conjugation of azide-reactive cyclooctynes onto alginates using a heterobifunctional crosslinker was confirmed by azido-coumarin fluorescent assay, NMR, and through click reactions with azide-modified fluorescent probes. Compared to cyclo-RGD peptides directly conjugated to alginate polymers with standard carbodiimide chemistry, Az-cyclo-RGD peptides exhibited higher bioactivity, as demonstrated by cell adhesion and proliferation assays. Finally, Az-cRGD peptides enhanced the effects of recombinant bone morphogenetic proteins on inducing osteogenesis of osteoblasts and bone marrow stromal stem cells in 3D alginate gels. SPAAC-mediated click approaches for peptide-alginate bioconjugation overcome the limitations of previous alginate bioconjugation approaches and potentially expand the range of ligands that can be grafted to alginate polymers for tissue engineering applications.

Construction and research on size and phase 'fixed-point remodelling' intelligent drug delivery system.

It is important to enhance penetration depth of nanomedicine and realise rapid drug release simultaneously at targeted tumour for improving anti-tumour efficiency of chemotherapeutic drugs. This project employed sodium alginate (Alg) as matrix material, to establish tumour-responsive nanogels with particle size conversion and drug controlled release functions. Specifically, tumour-targeting peptide CRGDK was conjugated with Alg first (CRGDK-Alg). Then, doxorubicin (DOX) was efficiently encapsulated in CRGDK-FeAlg nanogel during the cross-linking process (CRGDK-FeAlg/DOX). This system was closed during circulation. Once reaching tumour, the particle size of nanogels was reduced to ∼25 nm, which facilitated deep penetration of DOX in tumour tissues. After entering tumour cells, the size of nanogels was further reduced to ∼10 nm and DOX was released simultaneously. Meanwhile, FeAlg efficiently catalysed H2O2 to produce •OH by Fenton reaction, achieving local chemodynamic therapy without O2 mediation. Results showed CRGDK-FeAlg/DOX significantly inhibited tumour proliferation in vivo with V/V0 of 1.13 after treatment, significantly lower than that of control group with V/V0 of 4.79.

Nanoparticles integrating natural and synthetic polymers for in vivo insulin delivery.

The aims of the current study were to develop insulin-loaded nanoparticles comprised of various polymers at different compositions, and to evaluate their ability to lower blood glucose levels in diabetic rats following subcutaneous and oral administrations. Several combinations of natural and synthetic polymers have been utilized for preparation of nanoparticles including, chitosan, alginate, albumin and Pluronic. Nanosized (170 nm-800 nm) spherical particles of high encapsulation efficiency (15-52%) have been prepared. Composition and ratios between the integrated polymers played a pivotal role in determining size, zeta potential, and in vivo hypoglycemic activity of particles. After subcutaneous and oral administration in diabetic rats, some of the insulin-loaded nanoparticles were able to induce much higher hypoglycemic effect as compared to the unloaded free insulin. For instance, subcutaneous injection of nanoparticles comprised of chitosan combined with sodium tripolyphosphate, Pluronic or alginate/calcium chloride, resulted in comparable hypoglycemic effects to free insulin, at two-fold lower dose. Nanoparticles were well-tolerated after oral administration in rats, as evidenced by by measuring levels of alanine aminotransferase, aspartate aminotransferases, albumin, creatinine and urea. This study indicates that characteristics and delivery efficiency of nanomaterials can be controlled via utilizing several natural/synthetic polymers and by fine-tuning of combination ratio between polymers.

Long-term antibacterial composite via alginate aerogel sustained release of antibiotics and Cu used for bone tissue bacteria infection.

Bone related-bacterial diseases including wound infections and osteomyelitis (OM) remain a serious problem accompanied with amputation in most severe cases. In this work, we report an exceptional effective antibacterial alginate aerogel, which consists of tigecycline (TGC) and octahedral Cu crystal as an organo-inorganic synergy platform for antibacterial and local infection therapy applications. The alginate aerogel could greatly prolong the release of copper ions and maintain effective antibacterial concentration over 18 days. The result of in-vitro experiments demonstrated that the alginate aerogel has an exceptional effective function on antibacterial activity. Cytotoxicity tests indicated that the alginate aerogel has low biological toxicity (average cell viability >75%). These remarkable results suggested that the alginate aerogel exhibits great potential for the treatment of OM, and has a prosperous future of application in bone tissue engineering.

3D printing of an integrated triphasic MBG-alginate scaffold with enhanced interface bonding for hard tissue applications.

Osteochondral defects affect both of cartilage and subchondral areas, thus it poses a significant challenge to simultaneously regenerate two parts in orthopedics. Tissue engineering strategy is currently regarded as the most promising way to repair osteochondral defects. This study focuses on developing a multilayered scaffold with enhanced interface bonding through 3D printing. One-shot printing process enables control over material composition, pore structure, and size in each region of the scaffold, while realizes seamlessly integrated construct as well. The scaffold was designed to be triphasic: a porous bone layer composed of alginate sodium (SA) and mesoporous bioactive glasses (MBG), an intermediate dense layer also composed of SA and MBG and a cartilaginous layer composed of SA. The mechanical strength including the interface adhesion strength between layers were characterized. The results indicated that SA crosslinking after 3D printing anchored different materials together and integrated all regions. Additional scaffold soaking in simulated body fluid (SBF) and cell culture medium induced apatite deposition and had weakened the compressive and tensile strengths, while no layer dislocation or delamination occurred.

In situ-synthesis of calcium alginate nano-silver phosphate hybrid material with high flame retardant and antibacterial properties.

In this study, we demonstrate the in-situ synthesis of a functional hybrid material of calcium alginate (CaAlg)/nano-silver phosphate (nano-Ag3PO4). The morphology of nano Ag3PO4 was in spherical shape with a diameter of 10-60 nm, and uniformly distributed in the continuous phase of CaAlg. The limiting oxygen index (LOI) of the hybrid material reached 61.4%, which was about 53.0% higher than that of CaAlg. In addition, its heat release rate, total heat release and smoke emission were much lower than those of CaAlg. The thermogravimetric analysis coupled with Fourier transform infrared analysis and pyrolysis-gas chromatography-mass spectrometry results indicate that the synthesized material released less flammable gas, compared to CaAlg, and the thermal mechanism of CaAlg/Ag3PO4 was proposed based on the data. Furthermore, the antibacterial rate of the hybrid material against common pathogens was >97%. This study prefigures the promising application of the marine polysaccharide functional materials in the field of the fire protection and epidemic prevention.

Exploring Endolysin-Loaded Alginate-Chitosan Nanoparticles as Future Remedy for Staphylococcal Infections.

Endolysins are a novel class of antibacterials with proven efficacy in combating various bacterial infections, in vitro and in vivo. LysMR-5, an endolysin derived from phage MR-5, demonstrated high lytic activity in our laboratory against multidrug-resistant S. aureus (MRSA) and S. epidermidis strains. However, endolysin and proteins in general are associated with instability and short in vivo half-life, consequently limiting their usage as pharmaceutical preparation to treat bacterial infections. Nanoencapsulation of endolysins could help to achieve better therapeutic outcome, by protecting the proteins from degradation, providing sustained release, thus could increase their stability, shelf life, and therapeutic efficacy. Hence, in this study, the feasibility of alginate-chitosan nanoparticles (Alg-Chi NPs) to serve as drug delivery platform for LysMR-5 was evaluated. LysMR-5-loaded nanoparticles were prepared by calcium ion-induced pre-gelation of alginate core and its complexation with chitosan. The formation of nanoparticles was confirmed on the basis of DLS, zeta potential, and electron microscopy imaging. The LysMR-5-loaded nanoparticles presented a hydrodynamic diameter of 276.5 ± 42, a PDI of 0.342 ± 0.02, a zeta potential - 25 mV, and an entrapment efficiency of 62 ± 3.1%. The potential ionic interaction between alginate, chitosan, and LysMR-5 was investigated by FT-IR and SEM-EDX analysis. Using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), nano-sized particles with characteristic morphology were seen. Different antibacterial assays and SDS-PAGE analysis showed no change in endolysin's structural integrity and bioactivity after entrapment. A direct antibacterial effect of blank Alg-Chi Nps, showing enhanced bactericidal activity upon LysMR-5 loading, was observed against S. aureus. At physiological pH (7.2), the release profile of LysMR-5 from Alg-Chi NPs showed a biphasic release and followed a non-Fickian release mechanism. The biocompatible nature as revealed by cytocompatibility and hemocompatibility studies endorsed their use as drug delivery system for in vivo studies. Collectively, these results demonstrate the potential of Alg-Chi NPs as nano-delivery vehicle for endolysin LysMR-5 and other therapeutic proteins for their use in various biomedical applications.

Synthesis and Characterization of Oxidized Polysaccharides for In Situ Forming Hydrogels.

Polysaccharides are widely used as building blocks of scaffolds and hydrogels in tissue engineering, which may require their chemical modification to permit crosslinking. The goal of this study was to generate a library of oxidized alginate (oALG) and oxidized hyaluronic acid (oHA) that can be used for in situ gelling hydrogels by covalent reaction between aldehyde groups of the oxidized polysaccharides (oPS) and amino groups of carboxymethyl chitosan (CMC) through imine bond formation. Here, we studied the effect of sodium periodate concentration and reaction time on aldehyde content, molecular weight of derivatives and cytotoxicity of oPS towards 3T3-L1 fibroblasts. It was found that the molecular weights of all oPs decreased with oxidation and that the degree of oxidation was generally higher in oHA than in oALG. Studies showed that only oPs with an oxidation degree above 25% were cytotoxic. Initial studies were also done on the crosslinking of oPs with CMC showing with rheometry that rather soft gels were formed from higher oxidized oPs possessing a moderate cytotoxicity. The results of this study indicate the potential of oALG and oHA for use as in situ gelling hydrogels or inks in bioprinting for application in tissue engineering and controlled release.

Preparation of alginate oligosaccharides and their biological activities in plants: A review.

Alginate oligosaccharide (AOS) is the degradation product of alginates extracted from brown algae. As a multifunctional oligomer, it has attracted widespread attention in plant research. Different methods of preparation generate AOS possessing diverse structural properties, and result in differences in AOS activity. In this review, the methods of preparation and characterization of AOS are briefly summarized, followed by a systematic introduction to the activity and mechanisms of AOS in plants. AOS can act as a growth promoter at different growth stages of plants. AOS also enhances resistance to pathogens, drought, salt, heavy metals and other stressors by triggering plant immunity, exerting bioactivity just like a pathogen-associated molecular pattern. In addition, AOS can regulate ABA biosynthesis and metabolite to preserve fruit quality and enhance shelf life. This review provides a comprehensive summary of the biological activity of AOS in plants, which will support research and the application of AOS treatments for plants in the future.

Injectable self-crosslinking hydrogels for meniscal repair: A study with oxidized alginate and gelatin.

Injectable in situ gelling hydrogels are viable treatment options for meniscal injuries occurring in athletes. The present study aims to develop an injectable hydrogel via borax complexation of oxidized alginate, followed by a self-crosslinking reaction with gelatin through a Schiff's base reaction. Gelation kinetics and degree of crosslinking could be controlled by changing the concentration of components and the formation of Schiff ;'s base formation was confirmed by Raman spectroscopy. The injectable alginate dialdehyde-gelatin (15ADA20G) hydrogel showed 423 ±â€¯20 % water uptake, had an average pore size of 48 µm and compressive strength 295 ±â€¯32 kPa. Phase contrast images, scanning electron micrographs and actin staining depicted adhesion, profuse proliferation, and distribution of fibrochondrocytes on the hydrogel demonstrating its cytocompatibility. Application of hydrogel at the pig meniscal tear ex vivo showed good integration with the host meniscal tissue. Further, the histology of 15ADA20G hydrogel filled meniscus showed retention of hydrogel in the close proximity of meniscal tear even after 3days in culture. The self-crosslinking injectable hydrogel offers a niche for the growth of fibrochondrocytes.