Showing papers on "Self-healing hydrogels published in 1979"

Blood‐compatibility‐water‐content relationships for radiation‐grafted hydrogels

Abstract: A series of radiation-grafted hydrogels with water contents ranging from 10% to 90% have been prepared When evaluated by the vena cava ring test, increasing amounts of adherent thrombus were found in rings with lower graft water contents Using a baboon arteriovenous shunt evaluation system, platelet thromboembolic consumption was found to be directly proportional to graft water content Hydrogels studied by the renal embolus ring test were found to cause numerous infarcts in the kidneys of test animals Results from these studies do not support “water-content-blood-compatibility” hypotheses which have been suggested for hydrogels Results obtained with a series of hydrophilic-hydrophobic copolymers suggest that a balance of polar and apolar sites at a polymer-surface may be important for blood compatibility The significance of results from the three evaluation systems used is discussed

Water binding properties of hydrogel polymers for reverse osmosis and related applications

Abstract: Differential scanning calorimetry (DSC) has been used in the study of a series of hydrogels in an attempt to correlate water binding and transport properties. DSC and oxygen transport studies were carried out on a series of styrene-2-hydroxyethyl methacrylate copoly-mers. The transport of dissolved oxygen through those copolymers that contained no freezing water was found to be negligible in comparison to those in which both freezing and non-freezing water was present. This correlates well with the observation that the dense layer of asymmetric cellulose acetate reverse osmosis membranes was found to contain little or no free water. On this basis, the use of DSC in the design of a hydrogel that contains little or no freezing water (to promote salt rejection) with a reasonably high total water content (to maximise water flux) for use in reverse osmosis, is described. The resultant copolymer of acrylamide, methacrylic acid and styrene has a total equilibrium water content (30 per cent) that is twice that of a typical dense cellulose acetate used in reverse osmosis and a very low (< 1 per cent) freezing water content. Examination of the fine structure of the melting endotherms and freezing exotherms associated with various hydrogels shows several interesting features which are interpreted in terms of the existence of a continuum of water states. These range from water that is unaffected by its polymeric environment to water (on average two or less molecules per monomer repeat unit) that is hydrogen bonded to functional groups in the polymer.

Cationic hydrogels based on hydroxyalkyl acrylates and methacrylates

Abstract: Novel cationic hydrogels, containing basic (cationic) groups in their molecular structure, and processes for their preparation are described. These novel hydrogels are three-dimensional polymer networks, having good water permeability and mechanical properties, and are obtained by simultaneous polymerization and crosslinking, in the presence of a polymerization catalyst, such as an organic peroxide, azobisisobutyronitrile or other free radical polymerization catalyst, of a mixture of (a) hydroxyalkyl acrylate or methacrylate, (b) a cationic monomer - usually an ester of acrylic or methacrylic acid with an amino alcohol, the terminal amino group of which may be quaternized, such as dimethylaminoethyl methacrylate or acrylate and the quaternized derivatives thereof, and (c) a cross-linking agent, such as glycol diacrylate or dimethacrylate; if desired there may also be present (d) one or more additional monomers, usually an acrylic monomer such as an alkyl acrylate or methacrylate, acrylamides etc. (although other monomers such as vinyl acetate, styrene, etc. may also be used) which is copolymerizable with (a), (b) and (c). The thus obtained cationic hydrogels are useful for combining, by reaction or complexing, with materials having an opposite charge; such as acidic or anionic agricultural chemicals (insecticides, herbicides, fungicides, plant growth regulators, etc.), germicides, pharmaceuticals, cosmetics, hormones, enzymes, flavors, fragrances, antiperspirants, metals and the like, both to recover such acidic or anionic materials from an aqueous medium and for purifying water containing them, and also for the preparation of a complex or other combination of the cationic hydrogel with such materials which may be useful per se or from which the complexed or combined acidic or anionic material may be slowly or controllably released.

Natural protein polymer hydrogels

Abstract: Natural protein hydrogel structures formed from natural proteins having molecular weights not exceeding 100,000 by dissolving the protein in an aqueous acidic solution, crosslinking the protein, and air drying to a moisture content not exceeding 10 percent The air dried structure may or may not be bleached with an aqueous solution of an oxidizing agent and thoroughly washed with water The washed structure is dehydrated by treatment with a water-miscible organic solvent, washed with water, and redried to a moisture content of not more than 10 percent The structures may be in the form of soft contact lenses, films, fibers, and prosthetics

Microscopic determination of the penetration of proteins and polysaccharides into poly(hydroxyethyl methacrylate) and similar hydrogels

Abstract: Ultraviolet and light microscopy were used to measure the depth of penetration of fluoresce-in-labeled dextrans, serum albumin, and lysozyme into hydrogels. Proteins were visualized by a staining technique. Hydroxyethyl methacrylate was bulk polymerized (PHEMA, 37.7% H2O) and solution polymerized (PHEMA, 41.05–42.90% H2O); poly(glyceryl methacrylate) was solution polymerized (PGMA, 76.0–84.8% H2O); and poly(GMA-co-methyl methacrylate) was bulk polymerized [P(GMA/MMA), 41.5% H2O]. Dextrans of up to 150,000 mol wt and lysozyme penetrated PHEMA hydrogels; dextrans, but not proteins, penetrated P(GMA/MMA) hydrogels. Albumin penetrated only in the higher hydrated PGMA hydrogels. The porosity of PHEMA hydrogels is at least as large as 30 A (the smaller axis of lysozyme); the porosity of P(GMA/MMA) hydrogels is at least 19 A (the thickness of the rodlike dextran molecules of 150,000 mol wt). The PGMA hydrogels have a porosity of at least 50 A, which is the size of the smallest axis of serum albumin.

Protein and lipid adsorption by acrylic hydrogels and their relation to water wettability

Abstract: Radiochemical techniques were applied to determine protein and lipid uptake by acrylic hydrogels. The water wettability of these gels was previously obtained by using contact angle goniometry and was found to depend mainly on the composition of the polymer matrix but not on the equilibrium water content. Three hydrogels, poly(hydroxyethyl acrylate), poly(glyceryl methacrylate), and poly(acrylamide), had approximately the same equilibrium water content, therefore the same approximate penetrability with respect to protein. The uptake of both the protein (bovine serum albumin) and the lipid (cholesteryl oleate) appeared to be directly related to the water–gel interfacial tension, whereas the ease of removal was inversely related to water wettability. A cationic preservative, benzalkonium chloride, increased the protein uptake somewhat for two of the hydrogels. Preexposure to proteinaceous solutions had a pronounced effect, increasing the lipid uptake by the hydrogels, with the exception of PGMA. The results obtained appear to support the minimum interfacial free-energy hypothesis of biocompatibility.

Characterization of homogeneous and pseudocomposite homopolymers and copolymers for articular cartilage replacement.

Abstract: Semicrystalline swollen polymeric networks are prime candidates for biomedical applications. Purity, controlled structure, easy preparation, non-biodegradability and improved mechanical properties are some of their most important characteristics. New articular cartilage simulants in the form of hydrogels with surface hydroxyl groups have been developed and characterized. The mechanical properties and physical behavior of these materials are described by high elastic moduli, ultimate tensile strength and elongation at break, low tear propagation resistance and excellent friction properties. Crystallinities vary between 15% and 35% and the crystallites are stable within the range of practical applications. The hydrogels show no permeability to hyaluronic acid and can be grafted with cationic monomers or polymers to form boundary lubricant layers. Techniques have also been developed for the preparation of deformable pseudocomposites consisting of layers of swollen semicrystalline and amorphous polymer.

Interpenetrating polymer networks for biological applications.

Abstract: The use of a sequential polymerization method for preparing interpenetrating polymer networks with biocompatible surfaces has been studied. A hydrogel monomer was made to undergo polymerization with simultaneous cross-link formation, in the presence of a swollen thermoplastic elastomer heterophase block copolymer. On removal of the swelling solvent, an interpenetrating network of the hydrogel and the thermoplastic elastomer was obtained, which absorbed water in the manner of a hydrogel, but had mechanical properties superior to hydrogels. The studies employed a poly(ether-urethane) block copolymer as the thermoplastic elastomer. The materials fabricated included samples in which the interpenetrating polymerization extended throughout the thermoplastic elastomer as well as samples in which the interpenetrating polymerization was confined to a region near the surface of the latter.

One and two component hydrogels, 3. Deswelling and compression measurements on one component hydrogels†‡

Abstract: The value of the Flory-Huggins interaction parameter for water and poly(N-vinyl-2-pyrrolidone)1 (PVP), networks is determined by combining uni-directional compression measurements in the swollen state with network deswelling measurements. It was found that the dependance of the parameter on crosslink density can be explained by considering the interaction of water with the crosslinking molecule, a very water insoluble compound. Moreover, it was found that the interaction parameter within the swelling range studied is independant of network concentration. The number of elastically effective network chains is overestimated by a substantial margin.

The behavior of three different types of materials in vitro and in the dynamic physiological environment: review and analyses of critical parameters.

Abstract: A comparative analysis of smooth-surfaced synthetic materials, gels, especially those based on polyacrylamide, and polyester flocked surfaces indicate profound differences between these three types of materials when in contact with blood. Although many smooth-surface materials adsorb fibrinogen in vitro, several of these perform well in vivo without polymerization of fibrinogen to fibrin leading to clot-formation apparently because of enzymatic reactions in the physiological environment. Polyacrylamide hydrogels adsorb little plasma proteins, show negligible platelet adhesion and activation. In contrast, polyester flocked (fibril) surface deposit large quantites of fibrinogen that polymerizes to fibrin with entrapped formed blood elements (clot). The thickness of this layer is difficult to control and the build-up continues to a thickness up to approximately 400 to 600 micron depending on the species. The danger of clot-fragmentation and flock-detachment especially during flexing makes these rough surfaces inferior in blood-contacting application, in comparison to the best current synthetic smooth-surfaced biomaterials, hydrogels, and chemically modified natural tissue components.

Process for producing hydrogels, catalysts consisting of such hydrogels having a metallic compound incorporated therein, and use thereof for olefin polymerization

Abstract: Inorganic hydrogels, e.g., silica-containing hydrogels, are contacted with contacting agents comprising oxygen-containing organic compounds and then dried to remove the liquid components therefrom. The contacting agent can also be an oxygen-containing organic compound in combination with a liquid hydrocarbon or an oxygen-containing compound in combination with a liquid hydrocarbon or an oxygen-containing compound in combination with a liquid hydrocarbon and a surfactant. The hydrogel can be treated with a catalytic metal compound prior to or during the contacting with the contacting agents in order to produce a composition after drying and calcining that is catalytically active for olefin polymerization. The treated hydrogel can also, after drying, be treated anhydrously with a catalytic metal compound to produce a composition that is active for 1-olefin polymerization upon calcination.