ISSN:0007-1641    

DOI:10.1002/pi.4980180102

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractA discussion of the properties of that class of materials known as ‘hydrogels’ must make particular reference to (i) a working definition of what is meant by a ‘gel’, (ii) the manner in which this relates to the underlying macromolecular structure, and (iii) how these properties are affected by the presence of water within the macromolecular network. The first point is answered by providing an operational definition of a gel, which depends on the mechanical response of the material to oscillatory shear. This type of behaviour is shown to be quantitatively related to the degree of connectivity of the network. The chemical aspects of the problem address the relationship between this and the degree of reaction achieved by those chemical or physical features responsible for crosslinking. Finally, the swelling properties of such materials are discussed, and how these are complicated by the non‐ideal thermodynamic properties of the solv

ISSN:0007-1641    

DOI:10.1002/pi.4980180103

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractSynthetic hydrogels are a versatile range of materials which are of value in several biomedical applications, particularly those where permeability is important. Because the equilibrium water content of the gel governs permeability processes and has a marked influence on other important properties, the permeability requirements of a material often influence other aspects of its behaviour. The design of hydrogels for contact lenses demands an understanding of these interrelationships and thus provides a valuable basis for extending hydrogel design to other applications.

ISSN:0007-1641    

DOI:10.1002/pi.4980180104

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThe gel structures formed by naturally occurring polysaccharides, eitherin vivo(in, for example, plant tissue) orin vitroafter extraction and purification, are normally crosslinked by extended intermolecular ‘junction zones’ of conformationally ordered chains. Formation and disruption of these ordered structures under biologically and industrially relevant conditions of extensive hydration may be monitored and characterised by a variety of physical techniques, in conjunction with x‐ray analysis at atomic resolution in the condensed phase by fibre diffraction. Interconnecting regions of residual disorder, necessary for solubilisation of the gel network, may be introduced by structural irregularities or block character in the primary seq

ISSN:0007-1641    

DOI:10.1002/pi.4980180105

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractSynthetic polymer hydrogels have many proven and potential biomedical applications as wound coverings, drug delivery systems, surgical prostheses, contact lenses and in extracorporeal circuitry. Their success in long‐term contact with biological fluids and cellular tissue depends upon their interfacial properties in such environments, and in turn, upon their physical and chemical nature. One approach to defining requirements for interfacial events at polymer surfacesin vivois to investigate cell adhesion behaviour on these materials in culture, and to correlate this behaviour with polymer structure and theories ofin vivobiocompatibility. At the same time, polymer hydrogels provide the opportunity to extend existing cell culture systems for the study of environmental cues for cell behaviour under normal and pathological circumstance

ISSN:0007-1641    

DOI:10.1002/pi.4980180106

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractStudies of the diffusion of globular proteins and dextran fractions within polysaccharide and poly‐acryamide gels by laser light scattering are described. Gels of stiff polysaccharide chains scatter light which exhibits little spectral broadening, since apart from a small amount of structural relaxation they are almost stationary at a molecular level. Well defined diffusion coefficient of compact macromolecules within these gels can be measured. However, gels of relatively flexible polymers such as polyacrylamide are highly mobile at a molecular level, and scatter light which is spectrally broadened by the diffusion of fluctuations in acrylamide concentration. In this case there is a complex interaction between the two diffusion coefficients, with the diffusing compact macromolecules dominating at low gel concentrations, and the diffusing gel fluctuations dominating at high gel concentrations where they tend to control the movement of the compact macromolecule

ISSN:0007-1641    

DOI:10.1002/pi.4980180107

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThe characteristics of the commercially available grades of polyvinylpyrrolidone are discussed, specifically in relation to the provenance of these materials, and the validity of the molecular weights quoted for them in the manufacturers and suppliers literature.

ISSN:0007-1641    

DOI:10.1002/pi.4980180108

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractChemically modified derivatives of the copolymeric poloxamer surfactants have been polymerised to form crosslinked, swelling hydrogels. Mixtures of derivatives of poloxamers 188 and 181 form gels which show increased swelling with increased content of the more hydrophilic poloxamer 188. The rate of release of benzoic andp‐hydroxybenzoic acids also increases with increasing content of poloxamer 188. Release rate data have been analysed in terms of the swelling controlled release model for these hydrogel

ISSN:0007-1641    

DOI:10.1002/pi.4980180109

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractRates and extents of cure are determined using differential scanning calorimetry in the isothermal mode over the temperature range 170–220°C, and from d.s.c. scans at various heating rates. The isothermal data are consistent with an autocatalytic mechanism at conversions up to about 20–30%. Data from d.s.c. scans fit a simple kinetic model which indicates that the apparent activation energy (E) for cure increases with increasing conversion, consistent with an increasing degree of diffusion control. At low levels of conversion the isothermal and dynamic data both provide estimates forEof about 70 kJ mol−1. The heat of cure is about 105 kJ mol−1epoxide, and is constant over a wide range of amine concentration. This indicates that any parallel or competing processes which occur must have the same heat of

ISSN:0007-1641    

DOI:10.1002/pi.4980180110

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThe curing reaction was monitored by differential scanning calorimetry scans at various heating rates and from isothermal experiments in the range 130–170°C. The catalysed isothermal cure is an initially rapid reaction which approximates to first‐order kinetics. Above about 30% conversion there is a transition to a much slower first‐order reaction. The differential scanning calorimetry scans show multiple exotherm peaks, indicative of a complex reaction. However, data at a given conversion can be described by a simple general kinetic model. The heat of reaction shows a decreasing trend with increasing catalyst concent

ISSN:0007-1641    

DOI:10.1002/pi.4980180111

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY