摘要:

in the first part of this article calorimetric studies on poly (hydroxy ethyl methacrylate) (PHEMA) are presented. In the past the irregular melting curves in this type of experiment have been interpreted as evidence for the existence of different types of water in these gels. The studies presented here demonstrate that the occurrence of a glass transition in the freezing hydrogels may be responsible for this irregular melting behavior, and that this behavior is not (necessarily) an indication for the existence of different types of water. In the second part results are shown of measurements of the mobility of water in hydrogels, made by relaxation NMR. These results indicate that very rapid interchange occurs between the water molecules, and they support the conclusion that the calorimetric data mentioned above are not indicative for the existence of different classes of water in hydrogels. These results are compared with data from other fields of science, especially from fundamental freeze drying studies, which support the alternative interpretation of the calorimetric measurements.

ISSN:0920-5063    

DOI:10.1163/156856294X00095

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A new type of soft contact lens was developed from the poly(vinyl alchol) (PVA) hydrogel prepared by a low temperature crystallization technique using a water-dimethyl sulfoxide mixed solvent. The PVA contact lens materials had a water content of 78% and a tensile strength of 50 kg/cm2, five times as strong as that of commercial poly(2-hydroxyethyl methacrylate) soft contact lens. The amount of proteins adsorbed to the PVA soft hydrogel material was half to one thirtieth of that of conventional soft contact lenses. Histological and scanning electron microscopic observation of rabbit eyes which had worn the PVA soft contact lens for 12 weeks showed no difference in corneal epithelium and cell arrangement in the corneal epithelium from the non-wearing eyes.

ISSN:0920-5063    

DOI:10.1163/156856294X00103

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A room-temperature-precipitable, activated terpolymer consisting of N-isopropylacrylamide (NIPAAm)/N n-butylacrylamide(nBAAm)/N acryloxysuccinimide(NASI) (LCST = 7-13°C) at a monomer feed ratio of 60:40:2.5, respectively, was prepared and conjugated to an antibody. The conjugate was evaluated in a novel cellulose acetate (CA) membrane-based immunoassay which utilizes the especially strong physical attachment of the polymer to CA to bind and concentrate the polymer attached protein onto the membrane. When compared in the CA membrane immunoassay to the antibody-poly(NIPAAm) conjugate prepared via anhydrous copolymerization of NIPAAm and NASI at the monomer feed ratio of 40 : 1, respectively, the performance of the NIPAAm/nBAAm/NASI terpolymer was superior to that of the NIPAAm/NASI copolymer (LCST = 32°C) when the studies were carried out at room temperature. However, the terpolymer and copolymer gave equivalent performance when the assay mixture was heated to 45°C. These results indicate the importance of the LCST of the polymer component of the Ab-polymer conjugate to its adsorption and binding on the CA membrane.

ISSN:0920-5063    

DOI:10.1163/156856294X00112

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

ABA block copolymers of polyethylene glycol and poly-DL-lactic acid were prepared by ring-opening polymerization of DL-dilactide with α,ω-dihydroxy polyethylene glycol,n, 1000 or 2000. The morphology of the resulting copolymers, with PEG : PLA ratios(mol/mol) of 1:2, 1: 3 and 1:4, was characterized by DSC and ESR spectroscopy. The rate of water uptake was biphasic, reflecting the contribution of two processes: rapid diffusion of water into the initially miscible PEG and PLA blocks; then a slower rate of hydration possibly due to phase separation and hydrolytic cleavage of the PLA blocks. The rate of hydrolytic degradation of the block copolymers in DI water at 37°C was measured by two methods: weight loss and colorimetric analysis of the carboxy end group concentration resulting from chain scission of PLA blocks. As a result of phase separation, the rate of scission of PLA blocks in the copolymers was similar to that of the PLA homopolymer. The more rapid onset of weight loss of the copolymers, relative to PLA, is attributed to the greater water solubility of PEG-PLA oligomers and their greater diffusivity in the more highly hydrated copolymers.

ISSN:0920-5063    

DOI:10.1163/156856294X00121

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

We present results of equilibrium swelling studies of the ionizable copolymer gel, methyl methacrylate/N,N-dimethylaminoethyl methacrylate 70/30 mol%, in buffered and unbuffered electrolyte solutions. The experimental conditions were designed to demonstrate the sensitivity of swelling in ionized gels to the electrolyte composition of the external solution. In general, gel swelling as a function of solution ionic strength is shown to be highly nonmonotonic and is particularly sensitive to the valence and concentrations of ions present in solution. A rigorous test of ideal Donnan equilibrium theory shows that the latter is unable to explain all the data in a self-consistent manner. However, a heuristic procedure based on the ideal Donnan theory can predict qualitatively the observed trends. While not quantitative, this heuristic approach provides considerable insight into the mechanisms underlying the swelling behavior under various solution conditions. Possible causes of nonideal behavior are discussed, and some observed specific ion effects are reported and discussed.

ISSN:0920-5063    

DOI:10.1163/156856294X00130

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Polymeric particles are produced by different polymerization techniques. Phase inversion (dispersion) polymerization is one of the recent techniques to obtain monosize polymeric microbeads in the size range of 1-50 μm. The size and monodispersity of these microbeads can be adjusted by using several solvent systems (e.g., alcohol-water mixtures) with different polarities and by changing the type and amount of monomer, initiator and stabilizer. Surfaces of these microbeads can be further modified by different techniques including coating with different copolymers. Monosize polymeric microbeads are widely used in medical and biological applications as carriers, such as in immunoassays and cell separation, in site-specific drug delivery systems, in nuclear medicine for diagnostic imaging, in studying the phagocytic process, in affinity separation of biological entities, etc. Here, some important aspects of the production of monosize microbeads based on polystyrene and their modified forms are briefly discussed, and some selected medical and biological applications are summarized.

ISSN:0920-5063    

DOI:10.1163/156856294X00149

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The permeation of macromolecules such as fluoroescein-labeled dextran fractions through thermally reversible hydrogels has been investigated. A permeation model has been formulated, which takes into account hydrogel porosity and tortuosity as well as the combined effect of a geometric restraint for a relatively large solute molecule at a pore entrance and the friction between solute molecules moving through the pores and pore walls. Based on this model, we have estimated the tortuosity and average pore size of a swollen hydrogel, poly(N-isopropylacrylamide) [poly(NIPAAm)] and a swollen heterogel, poly(N-isopropylacrylamide-co-vinyl-terminated dimethylsiloxane) [poly(NIPAAm-co-VTPDMS)]. The permeation data for dextran molecules up to the size of 43.5 Å in radius show good agreement with the values predicted from the model.

ISSN:0920-5063    

DOI:10.1163/156856294X00158

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Weakly crosslinked poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) gel was synthesized and the chemomechanical behaviors in the presence of N-alkylpyridinium chloride (CnPyCl n = 4, 12, 16) were studied. The principle of this behavior is based upon an electrokinetic molecular assembly reaction of surfactant molecules on the polymer gel caused by both electrostatic and hydrophobic interactions. Under an electric field PAMPS gel underwent significant and quick bending and the response could be controlled effectively by changing the alkyl chain length of the surfactant molecule, the salt concentration, and the current applied. The results allow us to consider that cooperative complex formation between PAMPS gel and CnPyCl is responsible for this effective chemomechanical behavior.

ISSN:0920-5063    

DOI:10.1163/156856294X00167

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor