Showing papers on "Self-healing hydrogels published in 1986"

Thermodynamic interactions in copolymeric hydrogels

Abstract: Preparation de xerogels acrylate de butyle/N-vinylpyrrolidone avec de petites quantites de reticulants par copolymerisation radiochimique et gonflement dans l'eau

Crosslinked poly(sodium acrylate) hydrogels

Abstract: Samples of poly(acry1ic acid) (PAA) neutralized to varying degrees with sodium hydroxide were subjected to γ-irradiation to yield insoluble crosslinked polyacrylate hydrogels. The efficiency of crosslinking was found to be dependent on the degree of neutralization of the sample and the concentration of the irradiated polymer solution. The extent of water uptake of the gel was shown to be related to the degree of neutralization by titration of acid groups within the gel subsequent to cross-linking. Lightly crosslinked gels exhibited a maximum degree of swelling at a particular neutralization level. This was ascribed to a maximum in the long-range forces exerted cooperatively by the polymeric charges. The presence of simple electrolyte ions reduces swelling by screening these forces.

Synthetic hydrogels as drug delivery systems

Abstract: Hydrogels are widely studied materials for the preparation of sustained release drug dosage forms. Their soft, tissue-like consistency and their high biocompatibility in a number of applications make them promising candidates for this purpose. The water and the polymer in the gel form intricate structures and much research has been devoted to the elucidation of these structures, and of the interactions involved in their formation. Simple, drug-loaded hydrogels normally give a matrix-type delivery profile, in which the release rate is proportional to the square root of time; a number of approaches has been used to change this profile to other types of delivery, for instance to zero-order release. A number of in vivo tests using hydrogel delivery systems has given favourable results.

Characterization of the cross-linked structure of hydrogels.

Abstract: The theoretical study of a hydrogel network has the purpose of revealing the structure and configuration of its chains by use of appropriate theoretical models. Characterization of the hydrogel network structure is a complex procedure because of the many types of possible networks, including, regular, irregular, loosely cross-linked, highly cross-linked, and imperfect networks. In order to determine the cross-linking density of a hydrogel, use is made of mainly two theories, the equilibrium swelling theory and the rubber elasticity theory. If an uncross-linked polymer is soluble in or thermodynamically compatible with a liquid penetrant, then the same polymer when cross-linked will be swollen by this liquid. When a cross-linked network acting as an elastomer is stretched, it reaches an equilibrium strain while the stress remains constant. The analysis of the cross-linked structure of hydrogels can be done by a variety of experimental techniques, prominent among which are swelling and mechanical tests.

Fundamentals of Hydrogels and Gelation

Abstract: A 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 solvent water.

Swelling properties of copolymeric hydrogels prepared by gamma irradiation

Abstract: Crosslinked xerogels in the form of rods have been prepared to > 99.9% conversion by the γ-ray initiated copolymerization in vacuo ob n-butyl acrylate (BA) with N-vinyl-2-pyrrolidone (VP) in the presence and absence of a crosslinking agent. Thin (about 0.5 mm) disks were swollen in water at 21°C, the final equilibrium swelling being the true water content only for copolymers of high BA content. At low-medium BA content, swelling was accompanied by the release of a small water-soluble fraction, leading to a slightly reduced apparent value for the water content. True water contents could be obtained more rapidly by prior Soxhlet extraction with boiling water. For xerogels containing > about 75% VP by weight, the resultant hydrogels had water contents > about 80%. The influences of dose, dose rate copolymer composition, and concentration of crosslinker on the water content, sol fraction, and extension ratio were investigated. A high level of reproducibility in properties of the hydrogels was obtained by numerous replicate experiments. The feasibility of scaling up the preparation to produce long (60 cm) xerogel rods of uniform properties has been demonstrated. For these copolymers, swelling in several common organic solvents generally exceeds that in water.

Synthetic Hydrogels as Substrata for Cell Adhesion Studies

Abstract: Synthetic 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 surfaces in vivo is to investigate cell adhesion behaviour on these materials in culture, and to correlate this behaviour with polymer structure and theories of in vivo biocompatibility. 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 circumstances.

The Role of Permeability and Related Properties in the Design of Synthetic Hydrogels for Biomedical Applications

Abstract: Synthetic 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.

Polyacetal hydrogels formed from divinyl ethers and polyols

Abstract: A therapeutic composition comprising a therapeutic macromolecular agent incorporated in cross-linked polyacetal.

Wide pore alumina supports

Abstract: High surface area, wide-pore-containing porous aluminas are prepared by mulling together aluminum nitrate derived hydrogels with sodium aluminate derived hydrogels, extruding, drying and calcining at 500°-700° C.

Hydrogels containing siloxane comonomers

Abstract: Hydrogel polymeric material, suitable for preparing optical devices such as contact lenses. The material is of improved oxygen permeability and mechanical properties in comparison with conventional hydrogels. It comprises, in addition to the hydrogel material, from about 5% to about 60% by weight of a siloxane comonomer containing both an aromatic ring and vinyl functionality. Its cooperation and combination of performance characteristics with traditional hydrogel forming monomers provides a very useful polymeric material for making lenses of the soft hydrogel type.

Structural Analysis of Granular Silica Aerogels

Abstract: S.S. Kistler [1] announced as early as 1934, that aerogels are obtainable from colloidal substances in liquid form, i.e. gels, via supercritical drying. Often the starting materials for preparing alcogels and hydrogels are organic silicon compounds [2].

Short-term biocompatibility studies of hydrogel-grafted collagen copolymers

Abstract: Synthetic hydrogels are an interesting class of biomaterials. Hydrogels were prepared by the graft copolymerization of either HEMA and MMA or HEMA and GDMA onto soluble collagen using different cross linking agents. The tissue compatibility of these hydrogels was studied by implantation in rats. It was observed that there were no untoward rejection phenomena of these gels when implanted in vivo except for the typical healing process. The hydrogels were well tolerated and might well serve as good tissue equivalents.

Method for refining glyceride oils using partially dried amorphous silica hydrogels

Abstract: Adsorbents comprising partially dried amorphous silica hydrogels having a moisture content of at least about 25 wt % and an average pore diameter of about 60 Angstroms or less are useful in processes for the removal of trace contaminants, specifically phospholipids and associated metal ions, from glyceride oils. Treatment of the partially dried hydrogels with organic acid increases their adsorption capacity for these trace contaminants.

Hydrogels of quadrol methacrylate polymers

Abstract: Acrylate and methacrylate monoesters and diesters having the following formula (I) ##STR1## wherein R1, R2, R3 are as defined in the specification, are disclosed. These monomers are polymerizable into hydrogel polymers which are extremely hydrophilic. These hydrogel polymers are useful in the preparation of wound dressings. These polymers form complexes with polyvalent metal ions such as Ca, Mg, Mn and Cu, and possess macrophage stimulating activity in addition to the useful properties possessed by other acrylate and methacrylate hydrogel polymers.

The gamma-ray-induced crosslinking of polyacrylamide

Abstract: The gamma-ray-induced crosslinking of polyacrylamide was carried out under various conditions. The molecular weight of the polymer before inrradiation was found to be the most important factor for crosslinking. When polymers have low molecular weights such as 80,000, the intensity of radiation, the external pressure applied, and the water content of the polymer powder became important for crosslinking. Although the polycrylamide hydrogel can be obtained directly by irradiating the monomer, it was obtained more conveniently by the irradiation of monomer—polymer mixtures. The hydrogels obtained by the radiation with a dose of over 50 kgray, absorb water by 1000–1500 wt %.

Hydrogels in controlled drug delivery

Abstract: Hydrogels are water-insoluble but water-swellable polymers made by a variety of chemical methods utilizing both natural and synthetic polymer backbones. They can be prepared in a wide-variety of physical forms such as foams, films, sheets, beads, powders, tubes and blocks. Thermoplastic and thermosetting forms are known and they present a very versatile class of materials capable of considerable development. The natural hydrogel material gelatin has been used in pharmaceutical formulation for more than a century and is well known in the form of soft or hard-gelatin capsules. The modern synthetic hydrogel polymers have a broad capability for specific synthetic design and the skills of polymer scientists in tailor-making the polymers and devices utilizing them will lead to a considerably expanded use of these reproducible materials in the future. This introductory presentation will be restricted to these synthetic hydrogels.

The Effect of a Rate Controlling Membrane on Release from Polyhema Hydrogels

Abstract: The possibility of laminating a non-permeable, perforated membrane onto a polymer matrix providing zero-order drug release kinetics has been reported. The work we have undertaken involves an assessment of the suitability of poly(2-hydroxyethylmethacrylate) (polyHEMA) as the matrix in such a system. PolyHEMA hydrogels were prepared by the radiation polymerization of HEMA monomer solutions of different initial water contents. Membranes were laminated during the polymerization process. In Vitro release rates of substituted benzoic acids from laminates were determined.