Super‐macroporous dextran cryogels via UV‐induced crosslinking: synthesis and characterization

Cryogenic treatment and UV irradiation were exploited for the preparation of super‐macroporous cryogels from non‐modified high‐molar‐mass dextran. The photo‐crosslinking process was initiated by (4‐benzoylbenzyl)trimethylammonium chloride and N,N′‐methylenebisacrylamide (BAAm) was used as a crosslinking agent. Gel fraction yield and degree of swelling of the dextran cryogels were determined gravimetrically. Cryogel morphology and mechanical properties were studied using environmental scanning electron microscopy and dynamic rheological measurements, respectively. The effects of dextran concentration in the initial polymer solution, polymer molar mass and BAAm content on the crosslinking efficacy, physico‐mechanical properties and morphology of the cryogels were evaluated. The dextran cryogels were assessed as carriers of the model water‐soluble drug metoprolol. © 2017 Society of Chemical Industry     

Dextran microgels loaded with ZnO QDs: pH‐triggered degradation under acidic conditions

We demonstrated an extremely facile way to fabricate inorganic–organic microgels with pH sensitivity and fluorescence. Aqueous dextran microgels are crosslinked by ZnO quantum dots (QDs). The ZnO@Dextran microgels were synthesized by simply mixing amino‐modified ZnO (ZnO QDs) with carboxymethyl dextran (CMD) while stirring. The hybrid microgels showed an average diameter of ～5 μm and strong fluorescence under ultraviolet (365 nm) irradiation. Up to 79.3 wt % of ZnO QDs were loaded into microgels. The ZnO QDs crosslinkage in the hybrid microgels structure enabled the microgels to degrade under mild acidic environment due to pH sensitivity of ZnO QDs. After loading of doxorubicin (Dox), the microgels were used as drug carriers for pH‐controlled release of Dox. The degradation of the microgels and the release of loaded cargos could be monitored by detecting fluorescence intensity of the microgels. Moreover, owing to the cytotoxicity of ZnO QDs at their destination, drug‐loaded ZnO@Dextran microgels can be used for synergistic therapy. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45831.     

Studies of the esterification of dextran: routes to bioactive polymers and graft copolymers

Problems associated with the esterification of dextran as a means of coupling bioactive molecules or introduction of functionality suitable for graft polymerization are considered. In particular, the importance of eliminating side-reactions which incorporate into dextran unwanted residues, e.g. groups containing nitrogen, is emphasized and practical techniques for minimizing this are described. We have developed a formamide-based solvent suitable for esterification with the aid of dicyclohexyl carbodiimide (DCC) and carbonyl di-imidazole (CDI) as coupling agents. The preferred catalyst is p-pyrrolidinopyridine. CDI has the advantage of enabling dimethylsulphoxide to be used as solvent for dextran and other hydroxylic polymers without inducing oxidation of hydroxyl groups. This coupling agent is flexible and offers a choice of two routes to esterification, each having its merits. We have optimized conditions for coupling by use of butyric acid as model. Esterification of dextran has been employed in the preparation of soluble bioactive macromolecules by coupling the anti-platelet agent (I) and also in the synthesis of graft copolymers via introduction of 2-bromopropionate groups. Crosslinking of dextran and the polymerization of dipyridamole have been effected by use of CDI.     

Combined Effects of Confinement and Macromolecular Crowding on Protein Stability

Confinement and crowding have been shown to affect protein fates, including folding, functional stability, and their interactions with self and other proteins. Using both theoretical and experimental studies, researchers have established the independent effects of confinement or crowding, but only a few studies have explored their effects in combination; therefore, their combined impact on protein fates is still relatively unknown. Here, we investigated the combined effects of confinement and crowding on protein stability using the pores of agarose hydrogels as a confining agent and the biopolymer, dextran, as a crowding agent. The addition of dextran further stabilized the enzymes encapsulated in agarose; moreover, the observed increases in enhancements (due to the addition of dextran) exceeded the sum of the individual enhancements due to confinement and crowding. These results suggest that even though confinement and crowding may behave differently in how they influence protein fates, these conditions may be combined to provide synergistic benefits for protein stabilization. In summary, our study demonstrated the successful use of polymer-based platforms to advance our understanding of how in vivo like environments impact protein function and structure.     

Novel amphiphilic dextran copolymers nanoparticles for delivery of doxorubicin

In this work, a novel biodegradable amphiphilic copolymer based on dextran and 1,2‐dipalmitoyl‐sn‐glycero‐3‐phosphoethanolamine (DPPE) was successfully prepared. The amphiphilic copolymer may self‐assemble into polymeric micelles in an aqueous solution. Fluorescence spectroscopy, dynamic light scattering (DLS), and a transmission electron microscope (TEM) method confirmed the formation of copolymeric micelles. To estimate the feasibility as novel drug carriers, doxorubicin (DOX) was incorporated into polymeric nanoparticles. The DOX‐loaded nanoparticles exhibited greater antitumor effect than free DOX for HeLa celles, suggesting that the dextran/DPPE nanoparticles have great potential as a tumor targeting drug carrier. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Surface active and rheological properties of lipids of different origins at the polymer/water interface

In recent years, intensive investigations on the synthesis of polymer suspensions containing microspheres of various diameters with a narrow size distribution have been carried out for their use as bioligand carriers in immunoassay. In this context, lipids are rather promising, because they exhibit surface-active properties and are used as SAS during the synthesis of polymer suspensions; at the same time, lipids containing phosphatidylcholine have a property to interact specifically with a C-reactive peptide [1–3]. These properties of the lipids are reasonable to use for the creation of test systems for the definition of a C-reactive peptide by the latex agglutination reaction method (LAR), in which the polymeric microspheres containing phosphatidylcholine on their surface are used as bioligand carriers.     

Modification of polysaccharides: Degradation and graft copolymerization onto dextran

A water soluble muco-polysaccharide, “dextran”, was subjected to selective degradation and graft copolymerized with acrylamide and methylmethacrylate. Using ceric ions as initiator a low molecular weight model dextran and dextran-g-poly(acrylamide) as well as dextran-g-poly(methylmethacrylate) copolymers were prepared. The selective chain degradation and the graft copolymerizations were carried out at varying concentrations of Ce(IV) and monomer and varying temperatures. The course of degradative chain cleavage has been followed by viscometry. The low molecular weight model dextran and the copolymers were purified by usual methods. Their physical and chemical properties were tested and compared with the base. The energy of activation for the chain degradation and other related thermodynamic parameters have been evaluated.     

Leuconostoc dextransucrase and dextran: production,properties and applications

This review covers the production, properties and applications of the biopolysaccharide dextran; this biopolymer can be produced via fermentation either with Leuconostoc mesenteroides strains and other lactic acid bacteria or with certain Gluconobacter oxydans strains. The former strains convert sucrose into dextran with the dextransucrase enzyme whereas the latter convert maltodextrins into dextran with the dextran dextrinase enzyme. Emphasis is mainly focused on Leuconostoc strains as producer organisms of dextransucrase and dextran types. In addition to industrial fermentation processes producing the enzymes and/or the dextrans, biocatalysis principles are also being developed, whereby enzyme preparations convert sucrose or maltodextrins, respectively, into (oligo)dextrans. The chemical and physical properties of different dextrans are discussed in detail, together with the characteristics and molecular mode of action of dextransucrase. Subsequently, useful applications of dextran and some problems associated with undesirable formation of dextran are outlined. Copyright © 2005 Society of Chemical Industry     

Reproducible,biocompatible medical materials from biologically derived polysaccharides: Processing and Characterization

Natural polysaccharides like chitosan and dextran have garnered considerable interest in biomedical applications due to their biocompatibility, biodegradability, and nontoxicity. Nonetheless, the development of a reproducible class of medical devices from these materials is challenging and has had limited success. Chitosan and dextran are inherently variable and synthesis using these materials is prone to inconsistencies. In this study, we put forward a robust product development regimen that allows these natural materials to be developed into a reproducible class of biomaterials. First, an array of validated characterization methods (Proton Nuclear Magnetic Resonance, titrations, Ultraviolet spectroscopy, Size Exclusion Chromatography—Multi-Angle Light Scattering, Size Exclusion Chromatography—Refractive Index, and proprietary methods) were developed that allowed rigorous specifications to be set for unprocessed chitosan and dextran, chitosan and dextran intermediates, and chemically modified materials—acrylated chitosan (aCHN) and oxidized dextran (oDEX). Second, a robust and reproducible synthesis scheme involving various in-process controls was developed to chemically modify the unprocessed polysaccharides. Third, purification methods to remove byproducts and low-molecular-weight impurities for both aCHN and oDEX were developed. The study presents a viable strategy for converting variable, natural materials into a reproducible class of biomaterials that can be applied in various biomedical applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48454.     

Effects of denaturing agents on the molecular association of dextran. I. Aqueous solutions

Molecular association of aqueous dextran solutions have been investigated by viscosimetric measurements. Intrinsic viscosities of different concentrations of aqueous solutions of dextran with a variety of denaturing agents have been determined. Intrinsic viscosity numbers and Huggins constants of dextran solutions decreased with the addition of denaturing agents. The reducing effect of denaturing agents on the intrinsic viscosities and Huggins constants decreased in the order guanidinium sulfate > guanidinium carbonate > guanidinium chloride > thiourea > urea. The effect of temperature on the intrinsic viscosities of dextran and dextran denaturing agent solutions have also been investigated. A small change in the intrinsic viscosity values was observed for dextran in 1M of guanidinium carbonate and sulfate solutions with the increase of the temperature from 25 to 40 °C. Aqueous dextran solutions, however, showed a significant decrease in the intrinsic viscosities in the same temperature range. © 1995 John Wiley & Sons, Inc.     

Modification of poly(ethylene terephthalate) surface with attached dextran macromolecules

BACKGROUND: Peroxidation of a poly(ethylene terephthalate) (PET) surface clears the path to the formation of biospecific polymeric layers on it. The goal of this work was the modification of a PET surface with oligoperoxides with further grafting of dextran macromolecules to this peroxidated surface. RESULTS: Novel oligoperoxides with a good affinity to PET were synthesized. They are capable of attaching to the PET surface, due to the decomposition of peroxide groups via the formation of free radicals. The alterations in surface energy and its components as a result of surface modification as well as changes in topography of the PET surface were determined. The degree of modification of the PET surface can reach 68% and depends on the following: the method of oligoperoxide and dextran deposition; the concentration of both oligoperoxide and dextran in the initial solution; and the temperature at which the modification is carried out. CONCLUSION: A new method of PET surface activation has been developed. The attachment of dextran macromolecules to modified PET surfaces is confirmed. Copyright © 2009 Society of Chemical Industry     

Determination of thermodynamic interaction in mixed polymer solutions by a rapid and precise osmotic method. The system dextran/polyvinylpyrrolidone/water

An accurate and simple osmotic method for determination of thermodynamic interaction in ternary solutions (polymer A/polymer B/solvent) is described. The equipment consists of a membrane osmometer of a special design with small chambers and a pressure-sensing device to monitor the pressure difference across the membrane. A procedure has been developed to measure osmotic pressures up to rather high concentrations in both quasi-binary and quasi-ternary systems. The osmotic method is compared with results from light scattering. Different methods are utilized to extract ordinary virial coefficients as well as mixed virial coefficients from the primary data. The system dextran/polyvinylpyrrolidone/water (two different molecular weights of dextran) was chosen as a model.     

Preparation of dextran cryogels for separation processes of binary dye and pesticide mixtures from aqueous solutions

We present mechanically strong macroporous, squeezable dextran cryogels as a column filling material for the removal and separation of binary organic dye and pesticide mixtures from aquatic medium. Dextran cryogels were prepared from aqueous solutions of dextran of various molecular weights (MWs) in the presence of 20 to 50 mol% divinyl sulfone (DVS) as a cross-linker at −18°C. The cryogels have interconnected irregular pores of 100 μm in sizes, and exhibit 69-84% reversible squeezability without damaging the 3D dextran network. Their total open pore volumes (6.3-10 mL g⁻¹), weight swelling ratios in water (1380%-2200%), and mechanical parameters could easily be adjusted by both DVS mol% and MW of dextran. Dextran cryogel with the highest modulus (3.8 ± 0.5 MPa), compressive stress (8 ± 2 MPa) and plateau stress (0.46 ± 0.04 MPa) was obtained at 50 mol% DVS using dextran with a MW of 15 to 25 kg·mol⁻¹. Dextran cryogels are hydrolysable at pH = 1 and 9 but stable at 7.4 independent on both the degree of cross-linking and MW of dextran. At below 50 mol% DVS, they are blood compatible and possess slight thrombogenic effect with blood clotting index value of 98% ± 5%. They are also capable to separate binary dye and pesticide mixtures from aqueous solutions via ionic interactions.     

TiO2纳米结构作为载体在药物缓控释传递系统的应用

TiO₂纳米结构以其生物相容性好、机械强度高、耐热耐腐蚀等优点,在药物缓控释传递系统载体应用方面引起广泛关注。结合近几年研究报道,本文将单一和功能化TiO₂纳米结构作为药物缓控释载体进行分类,简述了制备方法、结构表征、载药方法、释药机理等,分析了功能化TiO₂纳米结构修饰结合外界刺激响应在药物缓控释系统的应用。结果表明,相比单一结构,功能化修饰后的TiO₂纳米结构具有载药率高、缓控释效果明显、生物相容性好等优点;功能化修饰结合外界刺激响应,进一步提升药物缓控释效果;而相比单一和双重刺激响应,多重刺激响应能够更好地实现局部靶向释药。最后预测该纳米结构作为药物缓控释传递系统载体的研究发展方向并指出目前实现临床应用所面临的问题。     

pH-Sensitive performance of dextran–poly(acrylic acid) copolymer and its application in controlled in vitro release of ibuprofen

Dextran–poly(acrylic acid) copolymers (D-A) are prepared through copolymerizing of acrylic acid (AA) with dextran. Their structural properties and performances are characterized using various methods. The results indicate that the carboxyl groups of poly(acrylic acid) strongly interact with the proton acceptors of glucose units in dextran, and the effects of AA/dextran molar ratio on the pH sensitivity of obtained copolymers are remarkable. The D-A copolymer shows a smart pH response, specifically, shrinkage in a low pH medium and swelling at high pH. The potential application of D-A copolymer as a drug delivery matrix is explored using ibuprofen as a model drug.     

Synthesis and characterization of new dextran‐acrylamide gels

Dextran‐acrylamide gels were synthesized in a single step reaction by using 4,4′‐azobis(4‐cynovaleric acid) as bi‐functional initiator at 60°C. Corresponding acrylamide (AaM) gels in the absence of dextran were also prepared for comparison. Several parameters such as reaction period (6, 12, and 24 h), monomer and crosslinker concentrations were varied and their effects on the properties of gels were investigated. Gels were characterized by their mechanical and swelling behaviors and in terms of structural changes using SEM. It was observed that swelling degree decreased by increasing the monomer concentration due to formation of more crosslinking points that cause tighter network structure. Mechanical measurements showed that elastic modulus of AaM gels was higher than that of dextran‐AaM gel which indicating the importance of dextran concentration on the flexibility of the network. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Insight on the periodate oxidation of dextran and its structural vicissitudes

Periodate oxidized dextran has been widely studied in a broad range of biotechnological applications, regardless of this, usually little attention is paid to the oxidation extension consequences on the properties of the final modified dextran. Based on a bidimensional NMR analysis, we suggest that the two aldehydes groups, resulting from the periodate oxidation, are not fully reactive with N-nucleophiles, under certain pH conditions. The aldehyde group bonded to C₃ appeared to be the only prone to react. The other aldehyde might be arrested in more stable hemiacetal structures. The hemiacetals are also responsible for oxidized dextran crosslinking, interfering in simple processing steps, such as dissolution and solubility, as well as increasing the viscosity of the solutions. The molecular weight variation on the oxidized samples can be followed by dynamic mechanical thermal analysis in consequence of the variation of glass transition temperature with the molecular weight, which was corroborated by the onset temperature of the thermal degradation.     

Super-macroporous composite cryogels based on biodegradable dextran and temperature-responsive poly(N-isopropylacrylamide)

This contribution describes the fabrication of super-macroporous cryogels comprising an interpenetrating network of biodegradable dextran and temperature-responsive poly(N-isopropylacrylamide) (PNIPAAm) segments. Cryogels were prepared from nonmodified dextran and N-isopropylacrylamide (NIPAAm) via cryogenic treatment of their aqueous solutions and subsequent irradiation with Ultraviolet light. The weight ratio of the two precursors was varied in order to find out the proper conditions for producing cryogels of high gel fraction yield and favorable physico-mechanical properties. Temperature-responsive behavior and enhanced elastic modulus were established for cryogel materials containing ≥50 wt% PNIPAAm. Scanning electron microscopy study revealed an open-porous structure of cryogels below and above the temperature of volume phase transition. Such morphology featured a very quick response of the material to temperature changes. The capability of dextran/PNIPAAm cryogels for instant release of water-soluble substances was demonstrated as well.     

汽车尾气净化催化剂载体

叙述了汽车尾气净化对其催化剂载体的要求, 讨论了几种已用于汽车尾气净化的催化剂载体, 比较了各种载体的性能。认为堇青石陶瓷蜂窝状载体是目前较为适合的汽车尾气净化催化剂载体。     

The preparation and filtration characteristics of Dextran-MnO2 gel particles

Different kinds of Dextran-MnO₂ gel particles are prepared in different conditions, depending on variables such as the molecular weight of dextran and formation temperature. Some physical properties and filtration characteristics of these gel particles are measured and discussed. Although the mean sizes of these gel particles are very close to each other, their filtration characteristics are far different due to their mechanical strength and compressibility. A typical filtration curve of gel particles can be divided into three regions, and a retardation cake compression during the filtration can be observed from the curve. The particle formation temperature has a trivial effect on their mechanical strength. An increase in formation temperature leads to only a slight decrease in particle size. On the other hand, gel particles are formed by using dextrans with three different molecular weights - 70,000 (sample A), 500,000 (sample B) and 2,000,000 Da (sample C) - and are used in filtration experiments. The results show that the molecular weight of dextran plays a major role in determining particle mechanical strength; the sequence of particle hardness is sample B > sample A > sample C. The dynamic analysis method proposed by Hwang and Hseuh [K.J. Hwang, C.L. Hseuh, J. Membr. Sci. 214 (2003) 259] is employed to estimate the local cake properties in a filter cake, e.g., solid compressive pressure, porosity and specific filtration resistance. Because sample C has the highest compressibility, it constructs a cake with the lowest porosity and the highest specific filtration resistance; and consequently, the lowest filtration rate. Although the mechanical strength of sample B is higher than that of sample A, its wider particle size distribution results in lower cake porosity and higher filtration resistance, as well as a lower filtration rate. It could be said that the filtration rate decreases with an increase in the molecular weight of dextran.