Lipase-catalysed stereoselective esterifications using gelatin-based hydrogels

A hydrogel stable in an organic solvent has been developed. This pseudo-solid aqueous gel (PAG) consists of only native gelatin and water, and has been used for immobilization of enzymes. A relatively high amount of gelatin is required in order to obtain stable gels. PAGs containing the enzyme Candida antarctica lipase (SP 525) were successfully used in catalysing the esterification of R/S-(±)-2-octanol and hexanoic acid in hexane. The conversions as well as the enantiomeric excess values of the product, R-(−)-2-octyl hexanoate, were high and comparable to those obtained with microemulsion-based gels. The PAGs containing immobilized lipase gave reproducible results and may be re-used several times. The gels are easy to prepare and use, non-toxic and biocompatible. The PAGs retain their integrity in organic solvents and may be used in preparative-scale synthesis of organic compounds.     

Physical properties of glycosaminoglycan hydrogels

The chemical composition of glycosaminoglycan (GAG) hydrogels was found to have a profound effect on the physical properties of gels. Hyaluronan (HA) and chondroitin sulfate (CS) were each modified with adipic dihydrazide (ADH) with carbodiimide chemistry. The resulting polymer was crosslinked with various concentrations of poly(ethylene glycol) dialdehyde (PEG‐diald) to produce a series of hydrogels. The physical properties of these GAG hydrogels varied in a concentration‐dependent fashion. Maximal crosslinking was observed at a theoretical crosslinking of 50% for the HA‐ADH‐PEG‐diald hydrogels and 75% for the CS‐ADH‐PEG‐diald hydrogels. Adding PEG‐diald beyond the optimum for crosslinking prolonged the in vitro enzymatic degradation time of the hydrogels. The swelling of the crosslinked GAG hydrogels was correlated with the amount of PEG‐diald used rather than with the crosslinking density. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4344–4356, 2004     

Studies of sodium humate/polyacrylamide/clay hybrid hydrogels. I. Swelling and rheological properties of hydrogels

A type of novel hybrid hydrogels from sodium humate (SH), polyacrylamide (PAM), and hydrophilic Laponite clay were prepared using potassium persulfate (KPS) as the initiator and N,N′-methylenebisacrylamide (MBA) as the cross-linker. The structures of the hydrogels were characterized by field emission scanning electron microscope and FTIR. Their swelling properties, swelling mechanism and rheological properties were also investigated. Experiments show that the composite is heterogeneous in the PAM/SH hydrogel system, while the clay collaborates with SH and improves the network structure of PAM/SH/clay hydrogel. High water-absorbing capability is shown for both hydrogel systems. Han plot proves that clay and SH are compatible with PAM for PAM/SH/clay hydrogels.     

医用水凝胶力学性能的研究进展

水凝胶是一类由亲水性聚合物链通过多种交联机制而形成的三维网络结构,具有良好的生物相容性、降解性及可调节的力学性能,广泛用于医药领域。针对不同的临床应用场景,水凝胶需要具备不同的力学性能,但目前尚无统一、系统的量化评价标准,无法针对不同临床应用需求特异性地调节水凝胶性能,限制了此类制剂应用。本文系统总结了医用水凝胶的临床应用及相应的力学性能要求、力学性能的表征手段及调节方法,并对医用水凝胶的发展现状进行总结和展望,希望为医用水凝胶力学性能的研究和发展提供理论基础。     

Mechanical properties and transition temperatures of cross-linked oriented gelatin

This study is an extension of previous work on cellulosics [(1994)Colloid Polym Sci 272: 284, 393] that showed that unusually good mechanical properties can be obtained by drying a swollen network of semirigid chains in a state of strain. This novel approach is applied in this investigation to gelatin, because of its attractive environmental characteristics but poor mechanical properties in the unmodified form. Since drawing of non-crosslinked gelatin is not practical, crosslinking by formaldehyde was used, followed by swelling, drawing and drying at fixed length. Mechanical tests were performed in static and dynamic modes. In this way improvements of Young's modulusE, and stress at break _b were determined as a function of gelatin concentration during drying. An increase inE and _b up to 2–3 times, and in the dynamic modulusE up to 6 times, was obtained when the draw ratio reached 4–5, after whichE, E, and _b were found to decrease. Such behavior is explained by the highest orientation being achieved at =4–5, as proved by x-ray analysis. At =10–20 the orientation is lost due to relaxation of chain segments, which is preceded by partial destroying of the network structure (chemical and physical), possibly via chain scission, but probably mostly by the pulling out of chains from crystallites. In any case, the mechanical properties become poor again.The improvements reported above were referred to the undrawn but crosslinked gelatin. Compared to the starting isotropic non-crosslinked material, the improvement is slightly higher. The observation that the improvements are less than those obtained for the cellulosics is explained by the coexistence of interpenetrating chemical and physical networks, which is typical of gelatin. This structural feature drastically reduces the orientability of the chains and the improvements that can be expected in the mechanical properties.     

Design of polyphosphazene hydrogels with improved structural properties by use of star-shaped multithiol crosslinkers

The feasibility of using a star-shaped crosslinker to produce a hydrogel with controlled mechanical properties and degradation rates was investigated. The aqueous blends of functional polymers and crosslinkers formed a solution at low temperature and a hydrogel with desired mechanical properties at body temperature. The introduction of star-shaped crosslinkers affected the microscopic and macroscopic properties of the hydrogel. The fabricated hydrogels could be suitable for many potential biomedical applications because of their injectability, tunable mechanical properties, controlled degradation rate and gel formation under physiological conditions.     

Swelling behaviors, tensile properties and thermodynamic studies of water sorption of 2-hydroxyethyl methacrylate/epoxy methacrylate copolymeric hydrogels

A series of copolymeric hydrogels based on 2-hydroxyethyl methacrylate (HEMA) and epoxy methacrylate (EMA) were synthesized by bulk polymerization. Swelling behaviors and tensile properties of hydrogels were studied. Dynamic swelling behaviors of copolymeric hydrogels indicate that the swelling process of these polymers follows Fickian behavior. The equilibrium water content (EWC) decreased and volume fraction of polymer in hydrogel (?₂) increased with EMA content increasing due to its hydrophobicity. The increase of ionic strength of swelling medium or temperature results in a decrease in EWC and an increase in values of ?₂. Young’s modulus and tensile strength of hydrogels, as well as effective crosslink density (v_e), increased as EMA content increased or ionic strength of swelling medium increased, attributing to increasing interaction between hydrophobic groups and polymer-polymer interaction with an increase in EMA content or in ionic strength. The polymer-solvent interaction parameter χ reflecting thermodynamic interaction was also studied. As EMA content, ionic strength of swelling medium or temperature increased, the values of χ increased. The values of χ and its two components χ_H and χ_S varied with increasing T. The negative values and trend of the enthalpy and entropy of dilution derived from values of χ_S and χ_H, could be explained on the basis of structuring of water through improved hydrogen bonding and hydrophobic interaction.     

Pectin- and gelatin-based film: effect of gamma irradiation on the mechanical properties and biodegradation

Agricultural by-products, pectin and gelatin, were used to prepare a biodegradable film. The film casting solution including the pectin and gelatin was irradiated at 0, 10, 20, and 30 kGy to investigate the irradiation effect on the mechanical properties of the film. The tensile strength of the 10 kGy-irradiated film was the highest among the treatments but the elongation at break, water vapour permeability, and swelling ratio were the lowest. Hunter color L^*- and a^*-values decreased but the b^*-value increased as the irradiation dose increased. The total organic carbon content produced from the Paenibacillus polymyxa and Pseudomonas aeruginosa also showed that the film of 10 kGy-irradiated was lower than those of 0, 20, and 30 kGy-irradiated films. In conclusion, irradiation of the film casting solution at 10 kGy increased the mechanical properties of the pectin and gelatin based film. To manufacture the film by agricultural by-products, however, the irradiation dose of the film casting solution should be determined to achieve better mechanical properties.     

Effects of synthesis-solvent on swelling and elastic properties of poly(N-isopropylacrylamide) hydrogels

Thermosensitive N-isopropylacrylamide (NIPA) hydrogels were synthesized by a free radical copolymerization with N,N′-methylenebisacrylamide (MBAA) in four solvents: water, ethanol, acetone and N,N-dimethylformamide. The swelling and elastic properties of the hydrogels were affected by the synthesis-solvents; the hydrogels (e.g. NIPA/MBAA = 1000/50 mol/m³-pre-gel solution) synthesized in water have smaller swelling volume and larger shear modulus at 10 °C than those synthesized in amphiphilic solvents. The network structure of hydrogels was estimated in terms of the conversion and two sorts of effective crosslinking density based on the Flory theory and the concentration of crosslinker. The hydrogels synthesized in water can have the microscopic inhomogeneous network arising from the entanglement of polymer chains, while the hydrogels synthesized in amphiphilic solvents can have the homogeneous network arising from the polymer concentration lower than the pre-gel solution and can be similar in network structure to the lightly crosslinked hydrogel synthesized in water.     

Injectable poloxamer/graphene oxide hydrogels with well‐controlled mechanical and rheological properties

Although significant progress has been made in the design and application of injectable hydrogels for biomedical applications, concurrent control of rheological and mechanical properties of injectable hydrogels has remained as an open challenge to the researchers. In this work, we introduce and put into practice a photo‐curable poloxamer (also known as Pluronic)/graphene oxide (Plu/GO) injectable hydrogel with well‐controlled rheological and mechanical properties. Acrylate group was anchored to hydrogel structure to endow photo‐crosslinking ability through decelerating degradation rate of poloxamer hydrogels after injection. It was found that the modified Plu remains stable in biological media for a long‐term period without significant weight loss. Rheological properties of hydrogels were also carried out as essential prerequisite for an ideal injectability via frequency sweep, flow curve, recovery, and yield stress before and after modification, signifying shear‐thinning behavior of Plu/GO hydrogels with high recoverability. The viscosity of shear‐thinning‐like hydrogels dropped at higher shear stress, which facilitated injection process. Moreover, mechanical behavior of Plu was optimized by manipulating the content of Plu, degree of modification with reactive precursor, curing, and particularly incorporation of GO without deteriorating effects on rheological behavior of Plu.     

DNA hydrogels formed of bended DNA scaffolds and properties study

In recent years,DNA supramolecular hydrogels have attracted much attention due to their injectability,biocompatibility,responsiveness and self-healing properties.In this work,we designed a linear DNA brick containing one duplex with two cytosine (C)-rich sequence on both ends.This brick can first assemble to form duplex under pH 8 condition.After adjusting the pH to 5,the C-rich sequence tends to form intermolecular i-motif structure,which joins the linear DNA molecules together to form interlocked cyclic structures and yield the DNA hydrogel.By adjusting the length and bending curvature of the duplex part of the molecule,one can change the basic unit of the hydrogel structure to tune the properties of the DNA hydrogel.     

温度敏感聚(N-异丙基丙烯酰胺)/聚(乙烯醇)水凝胶的制备及性能研究

聚 (N -异丙基丙烯酰胺 ) (PNIPA)水凝胶具有温度敏感性 ,其在 33℃左右有一个相转变温度或较低临界溶解温度 (L CST) [1,2 ] .当外界温度低于 LCST时 ,PNIPA水凝胶吸水溶胀 ;而当外界温度高于L CST时 ,PNIPA水凝胶剧烈收缩失水 ,发生相分离 .这种相分离特性应用于药物的控制释放 [3] .固定化酶[4 ] 和循环吸收剂 [5] 等领域 .然而 ,通常的 PNIPA水凝胶是通过化学键交联而成的三维网络聚合物 ,很难发生解体或进行生物降解 ,其在某些特定场合 (如药物的体内释放等 )受到一定限制 .聚乙烯醇 (PVA)的亲水性和生物相容性较好 ,是…     

Synthesis and properties of pH and temperature sensitive P(NIPAAm-co-DMAEMA) hydrogels

In order to investigate the influence of the continuous alkylamide sequence having pH sensitive unit on the temperature sensitivity of poly(N-isopropylacrylamide) (PNIPAAm)-based hydrogel, a monomer, N-(2-(dimethylamino) ethyl)-methacrylamide (DMAEMA), having an ethylamide group as well as an aliphatic tertiary amino group, was designed and synthesized. Hydrogels based on NIPAAm and DMAEMA were prepared via free radical polymerization. The resulted P(NIPAAm-co-DMAEMA) hydrogels were characterized in terms of maximum swelling ratio, swelling kinetics, temperature response kinetics, and effect of pH. The data obtained show that the novel hydrogels have the strong desire to respond to external temperature and pH stimuli. Importantly, because the P(NIPAAm-co-DMAEMA) hydrogels have the continuous alkylamide sequence containing isopropylamide pendant groups from PNIPAAm and ethylamide pendant groups from PDMAEMA, the incorporation of DMAEMA moiety not only provides the pH sensitivity, but also maintains the thermal properties of P(NIPAAm-co-DMAEMA) hydrogels, even as the molar percentage of DMAEMA moiety reaches 14 mol%.     

Reinforced Modification of PEEK and its Applications

聚醚醚酮（PEEK）作为一种特种热塑性工程塑料,在许多工程领域有着广泛的应用。采用不同手段改性聚醚醚酮,改善其热学性能、力学性能、摩擦学性能和加工性能等,有利于降低生产成本和进一步拓展其应用范围。本文从化学改性和纤维增强、无机填充、表面改性、与有机共混等物理改性两个方面综述了近年来国内外聚醚醚酮改性研究进展情况,以及对其在工业领域、电子电器领域、航空领域、汽车领域和医学领域中的应用作了简单的概括,最后展望了聚醚醚酮改性研究开发问题及解决方法。     

Mechanical properties and transition temperatures of crosslinked-oriented gelatin

 This second part of a systematic study of the properties of crosslinked-oriented gelatin involves the effects of orientation and water content on the glass transition temperature T _g and on the melting behavior. The samples were the same as those in the preceding study, and their transition temperatures were determined by both differential scanning calorimetry and dynamic mechanical thermal analysis. The crosslinked gelatin which had been room-conditioned showed two transition temperatures: the lower one was attributed to T _g of the water-plasticized gelatin, and the higher one was interpreted as T _g of dried gelatin superimposed by melting. A rather unusual situation arose because of the fact that the T _g and melting temperatures T _m (217 and 230 ^°C, respectively) are so similar. Using water as plasticizer not only decreases T _g but produces imperfect crystallites which melt below the T _g of the system. The presence of the amorphous phase in the glassy state would presumably make it essentially impossible to define a melting point or crystallization temperature in the normal manner, as an equilibrium between crystalline and amorphous phases. Received: 8 October 1996 Accepted: 2 November 1995     

Fabrication and chemical crosslinking of electrospun <Emphasis Type="Italic">trans</Emphasis>-polyisoprene nanofiber nonwoven

In this work, the optimal electrospinning conditions of trans-polyisoprene (TPI) solutions were evaluated nevertheless its lower glass transition temperature than the room temperature. Subsequently, chemical crosslinking of TPI nonwovens was firstly investigated by vulcanizing at high temperatures in the case of the persistence of nanofiber structure. For this purpose, curing agents of TPI were embedded in TPI nanofibers by co-electrospinning, and then a protect layer was coated on TPI nanofibers by filtering gelatin solution going through TPI nonwoven before the vulcanization at 140?160 °C. The results showed that the vulcanization of TPI fibrous nonwoven at high temperatures did not destroy the fiber morphology. Interestingly, TPI fibrous nonwovens after vulcanization showed excellent mechanical properties (~17 MPa of tensile strength) that could be comparable to or even higher than that of some bulk rubber materials.     

Preparation and surface properties of the polysiloxane material modified with fluorocarbon side chains

The novel polysiloxane material modified with fluorocarbon side chains was synthesized. FTIR, FNMR were used to characterize the copolymer structure. The emulsion of the modified polysiloxane was prepared. The reflectance spectrum of the dyed polyester fabric treated with the polymer was also discussed. The effect of the modified polysiloxane on the color fastness of the dyed polyester fabric was investigated. The results show that the novel polysiloxane material modified with fluorocarbon side chains had excellent surface activity. It did not affect the shade of color and the fastnesses of the dyed fabrics and could improve the handle of fabrics. The treated fabric with the modified polysiloxane showed excellent repellency to water.     

Influence of the monomer properties on the rheological behavior of chemically crosslinked hydrogels

The rheological behavior of two hydrogels, poly(sodium acrylate) and polyacrylamide gels, synthesized in the presence of the same crosslinking agent molecule, N,N′-methylene bis-acrylamide, has been investigated. The variation of the norm of the complex shear modulus |G*| vs. the monomer concentration (sodium acrylate or acrylamide) exhibited a different power law, depending on the nature of the monomer molecule. This discrepancy was ascribed to the influence of the properties of the monomer molecules on the crosslinked structure of the gelified networks. The analysis of the experimental results have allowed the suggestion that the elasticity exponent value was dependent on the length and on the conformation of the polymer chains connecting the junctions points of the network. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2535–2541, 1997     

Ion exchange and ion transport properties of sulfonated organically modified silica hydrogels

Sulfonated ormosil hydrogels (~80% water) were prepared using tetramethyl orthosilicate as a silica precursor and 2(4-chlorosulfonylphenyl)ethyltrichlorosilane to provide sulfonate functionality for ion-exchange and ion conductivity. Ruthenium(III) hexamine was used as a redox probe in electrochemical studies performed on porous carbon fibre paper electrodes impregnated with the gel. The gel-modified electrodes extracted Ru(NH₃)₆³⁺ from solutions in 0.1 M CF₃CO₂Na_(aq) with a partition coefficient of ~36, and with ~100% of the sulfonate sites being accessible for ion exchange. The Ru(NH₃)₆^3+/2+ couple exhibited reversible and facile electrochemistry in the gel, with a Ru(NH₃)₆²⁺ diffusion coefficient of 4.9×10^–8 cm² s^–1 determined by chronoamperometry. This is an order of magnitude higher than the mobility of this complex in Nafion. The hydrogel-modified electrodes were stable for days, and could be repeatedly loaded with Ru(NH₃)₆³⁺.Special Issue to celebrate the 70^th birthday of Professor Zbigniew Galus