k-型卡拉胶/聚乙烯吡咯烷酮共混水凝胶的辐射制备及性质研究

采用辐射技术制备了κ-型卡拉胶(KC)/聚乙烯基吡咯烷酮(PVP)共混水凝胶,研究了共混凝胶内KC含量、PVP的分子量和辐照剂量等对KC/PVP共混水凝胶性质的影响.实验发现,KC与高分子量的PVP(k-90)共混后在一定剂量范围内辐照可得到高强度、高溶胀行为的KC/PVP共混水凝胶,随着共混凝胶内KC含量的增加,凝胶强度及溶胀性能均显著提高.分析表明,KC与高分子量的PVP共混后,在较低剂量下KC的降解被抑制,从而获得一种由物理交联的KC和化学交联的PVP形成的互穿网络(IPN)凝胶.     

Effect of kappa-carrageenan on the properties of poly(N-vinyl pyrrolidone)/kappa-carrageenan blend hydrogel synthesized by γ-radiation technology

A series of hydrogels in the form of rods were prepared from kappa-carrageenan (KC) and poly (N-vinyl pyrrolidone) (PVP) by gamma radiation with ⁶⁰Co γ source at room temperature. The properties of the prepared hydrogels, such as the gel strength, gel fraction and swelling behavior were investigated. Incorporation of KC into the PVP/water system increased obviously the gel strength and equilibrium degree of swelling (EDS) of PVP hydrogel. The experimental analyses showed that the crosslinking reaction of PVP was quicker than the degradation of KC at a low dose (less than 30 kGy), and the degradation of KC was inhibited in the PVP/KC mixture system. So an interpenetrating polymer network (IPN) hydrogel composed of PVP (a chemical crosslinking network) and KC (a physical crosslinking network) was proposed here. The existence of different classes of water in this IPN system was shown by water melting curves using DCS.     

Swelling,elasticity and structure of hydrogels prepared via bis-macromonomers of poly(ethylene oxide)

The effect of swelling on the shear modulus was studied for hydrogels prepared by radical polymerization of methacrylate-terminated poly(ethylene oxide) (PEO) bis-macromonomers of different molecular weight. Gels made of long chains (M = 12000 or 6000) display classical softening upon swelling, whereas gels made of shorter chains (M = 4000 or 2000) remain rigid or even stiffen. The abnormal behaviour is explained by a specific character of network junctions presented by polymethacrylate chains in which each unit is linked with a PEO network chain. It is assumed that the interactions among densely grafted PEO chains result in their stretching on polymerization and non-affine deformation on swelling, which stiffen the gel. This is verified by the data on copolymer (macromonomers - 2-hydroxyethyl methacrylate) gels that have lesser densities of PEO chains attached to the junctions and show weaker stiffening on swelling. The osmotic pressure of gels was estimated from the swelling pressure and shear modulus. Similar to the mixing pressure of equivalent PEO solutions, it varies as the 9/4 power of polymer concentration. At the same time, it is lower than the mixing pressure. This indicates that the junctions make only quantitative changes in the osmotic properties of macromonomer chains.     

层状水凝胶仿生软骨的制备与性能

采用超声分散、高压加热共融、冷冻-熔融和γ射线辐照交联成型工艺制备层状水凝胶仿生软骨材料, 系统讨论了PVP添加量和辐照剂量对材料的凝胶含量、晶态结构及抗压缩弹性模量的影响, 观察和研究了层状水凝胶的微观结构. 研究结果表明, 随着PVP的质量分数(0-40%)和辐照剂量(0-60 kGy)的增加, 层状水凝胶的凝胶含量呈上升趋势; 其晶态结构在质量分数为20%的PVP和10 kGy辐照剂量下最完善; 其力学性能在质量分数为20%的PVP和20 kGy辐照剂量下最佳; PVP的加入改善了水凝胶的微观形貌, 有利于材料表面润滑性能的提高; 层状水凝胶层间渗透结合, 自然过渡, 形成结构良好的仿生软骨材料.     

Radiation synthesis of superabsorbent polyethylene oxide/tragacanth hydrogel

A new superabsorbent hydrogel has been prepared from tragacanth and polyethylene oxide (PEO) by gamma radiation at room temperature. Tragacanth solutions with different concentrations (1%, 3% and 5%) have been blended with 5% aqueous solution of PEO at a ratio of 1:1 and irradiated at doses 5–20 kGy. The properties of the prepared composite hydrogels were evaluated in terms of the gel fraction and the swelling behavior. An unexpected growth of the gel fraction was observed in PEO/tragacanth hydrogels irradiated at 5 kGy. Incorporation of 5% tragacanth into the aqueous PEO increased significantly the swelling percent of the hydrogels to more than 14,000% and thus makes it a superabsorbent material.     

Fermentation of a skim milk concentrate with Streptococcus thermophilus and chymosin: structure, viscoelasticity and syneresis of gels

Fermentation of a reconstituted skim milk concentrate (8% protein) was investigated to elucidate the effects of various fermentation parameters on the structural, rheological and visual (wheying-off) properties of the resulting gels (pH 4.60). Fermentation trials were performed with non-exocellular polysaccharide-producing strains of Streptococcus thermophilus at various fermentation temperatures and at various chymosin levels. Oscillatory vane rheometry carried out on the intact gels (at 4 °C) showed that the level of chymosin had a significant impact on the gel strength (storage modulus G′). This can be explained by the arrangement of casein micelles into more compact aggregates and the enhanced fusion of aggregated casein micelles as revealed by transmission electron microscopy for the gels fermented with chymosin. Wheying-off of the stirred gels as measured by a centrifugation test (at 4 °C) and pore size of the intact gel structures investigated by scanning electron microscopy both increased with increasing level of chymosin and increasing fermentation temperature (resulting in an increase in acidification rate). A higher level of syneresis (wheying-off) is explained by the larger pore size, since larger pores present a lower resistance to the outflow of whey from the gel.     

基于光聚合星型PEG-b-PCL大分子单体可生物降解水凝胶的合成及表征

以辛酸亚锡为催化剂 ,通过星型聚乙二醇 (PEG)引发ε 己内酯 (CL)开环聚合 ,制备了PEG b PCL嵌段共聚物 ,进一步以丙烯酸酯封端 ,合成了 3种水溶性大分子单体 .以 2 ,2 二甲氧基 2 苯基苯乙酮为引发剂 ,在紫外光作用下 ,大分子单体在水中由于胶束的形成能够迅速聚合形成水凝胶 .利用1 H NMR、FTIR、DSC、TGA、ESEM、凝胶含量、溶胀比等分析测试手段对大分子单体及其形成的水凝胶进行了表征 .结果表明 ,干胶迅速吸水而达到溶胀平衡 ,水凝胶具有较大的溶胀比和高的水含量 ;随着PEG臂数的增加 ,干胶的熔融峰顶温度下降 ,凝胶的溶胀比减小 ;ESEM图片上清晰地表明水凝胶的网络结构     

Use of electron beam for the production of hydrogel dressings

The electron beam irradiation technique has been utilized to prepare hydrogel wound dressings. The composition of the dressings is based on polyvinylpyrrolidone (PVP), poly(ethylene glycol) (PEG), and agar. Increasing the irradiation dose leads to an increase in the gel fraction; this increase is due to increased crosslink density. The gel fraction% decreases as the PEG concentration increases. The maximum swelling% decreases with increasing the irradiation dose, but increases with increasing the PEG concentration. This relationship can be utilized to modify the gel properties as gel fraction% and maximum swelling of the hydrogel. The prepared dressings could be considered as a good barrier against microbes.     

K-型卡拉胶/聚乙烯吡咯烷酮共混水凝胶的辐射合成

采用辐射技术合成了K 型卡拉胶 (KC) /聚乙烯吡咯烷酮 (PVP)共混水凝胶 ,研究了天然高分子KC、单体N 乙烯基吡咯烷酮 (N VP)、交联剂二甲基丙烯酸十四甘醇酯 ( 1 4G) ,辐照剂量以及剂量率等对辐射合成的KC/PVP共混水凝胶性质的影响 .实验发现 ,KC与适当比例的N VP共混后在一定剂量范围内辐照可得到高强度、高溶胀行为的KC/PVP共混水凝胶 ,随着共混凝胶内KC含量的相对增加 ,凝胶强度及溶胀性的能均显著提高 ,但合成该共混凝胶的最佳剂量却相对提前 ;加入 1 4G后降低了KC/PVP共混凝胶辐射合成最佳剂量 ,同时使KC/PVP共混凝胶的强度进一步提高 ;剂量、剂量率对KC/PVP共混凝胶的性质亦有很大的影响 .分析表明 ,KC与N VP共混后 ,在较低剂量下KC的降解被抑制 ,从而获得一种由物理交联的KC和化学交联的PVP形成的互穿网络 (IPN)凝胶     

Influence of the composition of milk-protein κ/ι-hybrid-carrageenan gels on product properties

κ/ι-Hybrid-types of carrageenan are often used for stabilisation of milk-based systems. However, real food systems vary in their composition, so it is of interest to investigate the influence of the product composition on the gel properties and storage stability. A response surface experimental design with four factors was analysed: casein:whey-protein ratio, concentration of carrageenan, KCl and CaCl₂ addition to the milk system. The characteristics of the gels were determined by oscillatory rheometry. In the statistical fitted model using all ingredients as parameters it was shown that the storage modulus G′ was linearly dependent on the minor ingredients KCl and CaCl₂. Non-linearity was seen for the influence of the concentration of carrageenan. As the total protein content was kept constant at 5%, the linear increase of G′ with higher casein amount can be explained by the known interactions between casein and carrageenan.     

Mechanical and Adhesive Properties of Ploy(ethylene glycerol) Diacrylate Based Hydrogels Plasticized with PEG and Glycerol

Using polyethylene glycol(PEG) or glycerol as the plasticizer, we synthesized the hydrogels from poly(ethylene glycol) diacrylate(PEGDA), polyvinylpyrrolidone(PVP) and poly(vinyl alcohol)(PVA) under UV radiation. The effects of different plasticizers on the mechanical properties and adhesion properties of the hydrogels were investigated. The results show that the plasticizer can improve the elongation and peeling force. The most pronounced changes in the tensile property of the hydrogels are due to the addition of glycerol followed by PEG, the lower the plasticizer's molecular weight, the greater its effect. The maximum peeling force is 0.317 or 0.257 N with PEG or glycerol as plasticizer, respectively, and their adhesion properties are due to the formation of hydrogen bonds.     

Rheological behavior of self-assembling PEG-beta-cyclodextrin/PEG-cholesterol hydrogels

The rheological properties of a recently developed self-assembling hydrogel system composed of beta-cyclodextrin (betaCD)- and cholesterol-derivatized 8-arm star-shaped poly(ethylene glycol) (PEG8) were investigated. To understand and predict the gel rheological properties, data fitting with the Maxwell model as well as comparing the system's concentration-dependent behavior with Cates' model for reversibly breaking chains were performed. To investigate the influence of the polymer architecture, networks were also prepared by replacing the cholesterol-derivatized 8-arm star-shaped PEG by linear bifunctional PEG-cholesterol or by using 4-arm instead of 8-arm polymers. Rheological analysis showed that the 8-arm polymer-based mixtures yielded tight viscoelastic networks, but their storage and loss moduli significantly deviated from those predicted by the Maxwell model. The scaling of the plateau moduli, relaxation times, and zero-shear viscosities with concentration for gels composed of 8-arm cholesterol- and betaCD-derivatized PEG followed a power law with exponents higher than predicted by Cates' model. On the other hand, hydrogels in which linear bifunctional PEG-cholesterol was used instead of 8-arm star-shaped PEG-cholesterol or which were based on 4-arm polymers showed a substantially better fit with the Maxwell model and reduced differences between empirical and Cates' theoretical scaling exponents. Rheological analysis also showed that the hydrogels were thermoreversible. At low temperatures, the gels showed viscoelastic behavior due to slow overall relaxation of the polymer chains. At higher temperatures, however, a reduced number of betaCD/cholesterol complexes and concomitant faster chain relaxation processes eventually led to liquid-like behavior. The relationship between temperature and the relaxation time was used to determine an activation energy of 46 kJ/mol for breaking and reptation of the polymers.     

The effect of added liposomes on the rheological properties of a hydrogel: a systematic study

Rheological characteristics of liposome-containing-hydrogels were studied. Sonicated unilamellar vesicles (SUV), prepared by probe sonication and multilamellar vesicles (MLV) prepared by thin film hydration were loaded in a hydrogel containing carbopol 974 NF and hydroxyethylcellulose (Natrosol 250 HX). Phosphatidylcholine (PC) or hydrogenated-PC (HPC) liposomes, plain or mixed with cholesterol (chol) were used. Static (steady-stress sweep-tests) and dynamic (frequency sweep-tests) rheological measurements were carried out. All gels had a shear thinning behaviour (fitted well by Cross model). Zero-rate shear viscosity and power law index values, revealed that PC liposome addition in the hydrogel had minimum effect on its rheological properties even at the highest lipid concentration used (20 mg/ml). Oppositely, HPC (or HPC/chol) liposome addition resulted in significant modulations of the same rheological characteristics (which increased with increasing lipid concentration). HPC liposomes also caused a significant increase in gel relaxation time, which indicates that the elastic character of the gel strengthens as HPC liposome concentration increases. Concluding, liposome composition (membrane rigidity) and lipid concentration, but not liposome size, seem to be very important factors that determine the rheological modulations caused by liposome addition in gels.     

Effects of annealing and the addition of PEG on the PVA based hydrogel by gamma ray

Poly(vinyl alcohol) (PVA) is an interesting material with good biocompatibility, high elasticity and hydrophilic characteristics. PVA hydrogels have been formed through chemical crosslinking with aldehyde, photopolymerization and physical crosslinking with freeze-thawing. In this study, crosslinked hydrogels based on PVA, and poly(ethylene glycol) (PEG) were prepared by gamma-ray irradiation, and then annealed at 120 °C. The properties of a hydrogel such as gel fraction, swelling behavior, gel strength as a function of PEG content and annealing time were investigated. Also, the thermal behaviors were examined by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The gel fraction decreases with an increase in PEG content and decrease in annealing time. The tensile strength increases with an increase in annealing time. The thermal behaviors have shown different patterns according to the annealing time. The improved properties suggest that PVA/PEG blend hydrogel can be a good candidate for applications in the articular cartilage.     

Macroporous Poly(Acrylamide) Hydrogels: Swelling and Shrinking Behaviors

Macroporous poly(acrylamide) hydrogels have been synthesized by using poly(ethylene glycol) (PEG) with three different molecular weights as the pore‐forming agent. Scanning electron microscope graphs reveal that the macroporous network structure of the hydrogels can be adjusted by applying different molecular weights of PEG during the polymerization reaction. The swelling ratios of the PEG‐modified hydrogels were much higher than those for the same type of hydrogel prepared via conventional method. However, the swelling/deswelling ratios of the PEG‐modified hydrogels were affected slightly by the change in the amount of the PEG. Scanning electron microscopy experiments, together with swelling ratio studies, reveal that the PEG‐modified hydrogels are characterized by an open structure with more pores and higher swelling ratio, but lower mechanical strength, compared the conventional hydrogel. PAAm has potential applications in controlled release of macromolecular active agents.     

New neutral and ionic poly(ethylene oxide) networks by radical polymerization

New opportunities resulting from a turn to radical polymerization in the synthesis of poly(ethylene oxide) (PEO) networks are discussed and exemplified. Several series of such networks have been prepared by radical homo‐ and copolymerization in aqueous media of “macromonomers”, i.e. partly methacrylated poly(ethylene glycol) (PEG) of varied molecular weight (MW ≅ 2000‐12000) and functionality (f_n ≅ 1.25‐1.8). This family of gels as a whole has the volume swelling degree Q in the range of 10 to 200 ml/ml. The hydrogels are characterized by means of Q, elastic modulus, swelling pressure, and with the use of some probes. The swelling behaviour of neutral hydrogels of this kind is briefly resumed. The multifunctional junctions formed in the propagation reaction of methacrylate end groups determine their main peculiarity. Anomalous elastic behaviour of the swollen networks prepared at high concentration of polymer has been observed and attributed to the network chains stretching of the same nature as in polymer stars or brushes. The junctions' functionality (F ≈ 20‐300) is evaluated from these data as well as from MW of the soluble models of network junctions. The PEO networks with charged units in junctions have been obtained by copolymerization of macromonomers with some ionic (meth)acrylic monomers. These gels display all the polyelectrolyte features, e.g. enhanced Q values in water (up to 50‐70) and, contrary to neutral PEO gels, the strong dependence on salt content. However, the osmotic contribution of mobile ions into swelling is shown to be low due to localization of charges in the junctions. The hydrogels that combine PEO and polymethacrylic acid chains capable of interpolymer complexation have been prepared and studied. They show much higher swelling in pure water (Q up to 200), strong deswelling by NaCl, and very sharp drop in swelling (ca. two order in Q) at pH ≈ 4.5‐5.5 due to complexation.     

Synthesis and Viscoelastic Properties of Hydrophobically Modified Hydrogels

Summary: We report the synthesis and characterization of a family of hydrophobically modified hydrogels designed to have an improved fracture resistance. A backbone of poly(acrylic acid) (PAA) was functionalized with double bonds and hydrophobic groups. The functionalized PAA was then crosslinked with a dithiol. The chemical structure of the gels was characterized with a combination of NMR, titration methods and rheological techniques. The crosslinked structure of the hydrogel was found to be dependent on the polymer concentration only, while the dissipative properties of the gel increased strongly at all frequencies, with the introduction of hydrophobic groups which formed reversible associations. We expect these viscoelastic hydrogels to display dramatically different properties from the unmodified hydrogels when stretched and fractured.     

Sustained release drug delivery using supramolecular hydrogels of the triblock copolymer PCL–PEG–PCL and α-cyclodextrin

Supramolecular hydrogels (SMGel) have attracted much attention as a drug and gene delivery system in recent years. In this study, SMGels based on the tri-block copolymer of poly-ε-caprolactone–polyethylene glycol–poly-ε-caprolactone (PCL–PEG–PCL) and α-cyclodextrin (α-CD) were prepared and evaluated for the delivery of two model drugs, naltrexone hydrochloride and vitamin B₁₂. Tri-block copolymers were synthesized easily in 15 min by ring-opening polymerization using the microwave irradiation technique, and their structures were determined by gel permeation chromatography and nuclear magnetic resonance methods. SMGels composed of various concentrations of the copolymer and α-CD were prepared and characterized for their rheological behaviour, their gel formation time and in vitro drug release profile. The results indicated that copolymers with a PCL to PEG ratio of 1:4 are suitable for SMGel preparation. The most viscose system with good syringeability was prepared by mixing 12 % wt α-CD and 10 % wt of copolymer. The gelation was found to occur within a minute after mixing. The viscosity of the hydrogel systems was determined as a function of shear rate. Finally, in vitro B₁₂ release through the hydrogel systems was studied. Up to 80 % of Vitamin B₁₂ was released through this system during a period of 20 days. Rheological evaluation revealed that the hydrogel has shear thinning properties, and the system regained its ground rheological state in a time dependent manner. Polymer concentration did not affect the drug release profiles. Finally, it was concluded that such systems are appropriate drug delivery systems due to their ability to provide a controlled drug release profile and their shear thinning thixotropic behaviour, which makes them syringeable and injectable.     

Studies on interpolymer self-organisation behaviour of protoporphyrin IX bound poly(carboxylic acid)s with complimentary polymers by means of fluorescence techniques

Covalently bound protoporphyrin IX was used as a fluorophore to investigate the interpolymer complex formation between the poly(carboxylic acid)s, PMAA/PAA and poly(N-vinyl pyrrolidone), PVP, poly(ethylene oxide), PEO or poly(ethylene glycol), PEG. Absorption and emission spectral properties of protoporphyrin IX bound to PAA, PMAA and PVP have been studied. Protoporphyrin IX in poly(MAA-co-PPIX) was found to be present in the dimer or higher aggregated form at low pH due to the environmental restriction imposed by the polymer whereas in the case of poly(AA-co-PPIX) and poly(VP-co-PPIX), PPIX exists in monomeric form. The fluorescence intensity and lifetime of PPIX bound to poly(carboxylic acid)s increase on complexation through hydrogen bonding with PVP, PEO and PEG due to the displacement of water molecules in the vicinity of the PPIX. Poly(MAA-co-PPIX) shows longer fluorescence lifetime due to the more compact interpolymer complexation as compared to poly(AA-co-PPIX) due to the enhanced hydrophobicity of PMAA. Poly(VP-co-PPIX) shows a decrease in the fluorescence lifetime on complexation with PMAA or PAA due to the hydrophilic and microgel like environment of the fluorophore bound to PVP. The contrasting behaviour of the same polymer adduct with respect to the site of the fluorophore is interpreted to be due to the solvent structure which determines the environment of the fluorophore.     

Rheological properties of poly(ethylene glycol) solutions and gels

By the interaction of a water–glycol solution of poly(ethylene glycol) (PEG) with calcium chloride dihydrate, a gel was produced. It was determined that, below a certain shear rate, this gel is a Newtonian fluid; however, above a certain shear rate, which depends on the gel viscosity, the properties of this gel are anomalous: the gel flow instantaneously completely stops. The viscosity of the gels was found to exponentially increase with increasing concentration of the cross-linking metal at constant PEG concentration. The density of the gels linearly increases with increasing concentration of the cross-linking metal at constant PEG concentration.