Showing papers on "Self-healing hydrogels published in 1977"

Crosslinked poly(vinyl alcohol) hydrogels as swollen elastic networks

Abstract: Transparent crosslinked PVA hydrogels were prepared by electron beam irradiation of aqueous solutions under nitrogen. These weak hydrogels, upon swelling at 30°C in water, showed low elastic moduli (up to 50 psi), low ultimate tensile strength (up to 4 psi), and low extensibility to break (not higher than 85%). Values of the molecular weight between crosslinks Mc were calculated from swelling and from tensile experiments. In fact, two values of Mc were calculated for each swelling experiment, (a) allowing for observed variation in the polymer–solvent interaction parameter χ1 with concentration, and (b) fixing χ1 = 0.494 according to literature data. The correlation of the Mc obtained from tensile data with the Mc obtained from swelling data, by (a) or (b), was approximately linear and gave the same per cent agreement.

Development of semicrystalline poly(vinyl alcohol) hydrogels for biomedical applications.

Abstract: Swollen crosslinked poly(vinyl alcohol) (PVA) networks were developed and tested as potential biomaterials. They were prepared by electron-beam irradiation of aqueous PVA solutions at various temperatures and doses of irradiation. These materials were characterized by low mechanical properties and especially by low elongation at break and ultimate tensile strength. Reinforcement was achieved by a two-stage dehydration-annealing process, introducing crystallites in the polymeric network. Improved mechanical properties were achieved due to the presence of this crystalline PVA phase. Due to their structure, these hydrogels are proposed to be used as biomembranes for selective transport of macromolecules and as biomaterials for synthetic articular cartilage applications. Surface heparinization was accomplished by reacting heparin to the hydroxyl groups of the PVA surface, through covalent acetal bridges.

Polyelectrolyte hydrogels and methods of their preparation

Abstract: A predetermined mass comprising an acrylate salt and acrylamide is exposed to a controlled intensity and dose of ionizing radiation effecting simultaneous cross-linking and polymerization thereof to form a polyelectrolyte hydrogel. The resulting hydrogel is an insoluble hydrophilic copolymer which can contain or when dried absorb large quantities of aqueous fluids.

Hydrophilic copolymer of N,N-di(C{HD 1{L -C{HD 2{L alkyl)acrylamide cross-linked with a glycidyl ester

Abstract: A hydrophilic copolymer of an N,N-di(C1-C2 alkyl)acrylamide is disclosed. The copolymer is formed by reacting, based on 100 parts, from about 20-80 parts of a C1-C2 alkyl substituted acrylamide, about 10-80 parts of a C1-C4 alkyl acrylate, methacrylate, or combinations of acrylate and methacrylate, and about 2-20 parts of a glycidyl ester of acrylic, methacrylic or crotonic acid. The resulting copolymerization product can be equilibrated with water or other aqueous solutions to form hydrogels useful in forming shaped hydrogel articles. One particular shaped article which can be formed is a hydrophilic contact lens. A process for forming the hydrogels is also disclosed.

Control of the Pilocarpine Release Rate Through Hydrogels by Plasma Treatment

Abstract: The rate of release of an aqueous solution of pilocarpine hydrochloride sequestered in hydrogel-type materials can be reduced by plasma treatment of the polymer surface. Two plasma techniques were used. The first involves exposure of the hydrogel to the effects of a glow discharge sustained in argon, a process known as CASING. (Crosslinking by Active Species of Inert Gases). The second technique involves the deposition of a thin film by plasma polymerization of organic gases. The gases used in this study were ethane, ethylene and tetrafluoroethylene. Hydrogels were prepared by photopolymerization of 2-hydroxymethyl methacrylate (HEMA), and copolymerization of HEMA with methyl acrylate. The CASING treatment was found to be least effective. The most successful method was the plasma polymerization of tetrafluoroethylene, which yielded an order of magnitude reduction in the flux rate of pilocarpine with a film thickness of 0.25μ;m. Polymerization conditions bringing about a crack-resistant film were critical ...

Reactions of human platelets with microspheres of poly(hydroxymethyl methacrylate) and polyacrylamide

Abstract: We have studied the contact interaction of platelets with hydrogels. In the form of microspheres, 0.6–1.0 μ, poly (glycol methacrylate) (poly HEMA) and poly (methyl methacrylate) beads cause platelets to aggregate at concentrations of about 108 beads/ml. Polyacrylamide and (20/80) poly (acrylamide–HEMA) copolymer were ineffective in aggregating platelets. The admixture of 20% methacrylate to polyHEMA rendered the beads inactive. Blood plasma components other than fibrinogen were found essential to the interaction of the beads with platelets. Near-infrared spectra of the hydrogels polyacrylamide and polyHEMA showed the water hydrogen bonds to be the same for both and different from those in pure water. The monomer HEMA is an inhibitor of platelet aggregation and the release reaction at levels of 0.1%. It is concluded that the two hydrogels have different blood compatibilities, which depend more on the network structures than the water structures in the respective gels.

Kinetics of the crystallization of crosslinked poly(vinyl alcohol) films by slow evaporation of hydrogels

Abstract: The kinetics of crystallization of polymer-diluent mixtures with the restraint of polymeric chains with finite molecular weighty are of particular interest in the case of dehydration of swollen polymeric networks. The scope of this communication is to study the nucleation and crystal growth of plasticized crosslinked polymeric systems in terms of drying theories and to predict the behavior of structurally defined polymeric networks under well monitored drying conditions. Crosslinked hydrogels prepared by electron beam irradiation of aqueous PVA solutions were dehydrated at 25 ± 1°C under drying conditions of varying relative humidity of the environment. The degree of crystallinity was a function of crosslinking density, water (or polymer) weight fraction and evaporation rate. For low evaporation rates, the degree of crystallinity and the crystallization rate were affected by the average distance between crosslinks in the network and by the difference in initial polymer weight fraction of the material. At higher evaporation rates these effects were significantly minimized. Depending on the drying conditions, nucleation started at induction times varying between 15–115 hours and always at polymer weight content above 75%. A kinetic model of the results is presented and discussed.

Polymeric materials in the physiological environment

Abstract: The interactions between natural and synthetic materials and blood components are analyzed with emphasis on the interdependence between biomaterials research and development and ultimate applications. Two new synthetic polymers, perfluorobutyryl ethylcellulose and polyalkylsulfone, that combine desirable blood compatibility and gas-to-blood transfer rates are discussed in terms of their potential usefulness for membrane oxygenators. Among the several hydrogels, polyacrylamide covalently grafted onto segmented polyether-urethane substrates showed essentially no platelet adhesion and adsorbed the least plasma proteins in comparison to other systems. Polymeric composites having stiffness, anisotropies that approximate living tissues, and the ability to culture cells and hence to maintain a living cellular interface between flowing blood and microfiber substrates, are expected to expand the horizons for biomaterials in prosthetic applications.

Structure and properties of primary polymer particles of freshly precipitated Cr3+ hydrogels

Abstract: 1. Freshly precipitated hydrogels of Cr3+ have a number of structural hydroxyl groups per single cation corresponding to chromium hydroxide Cr(OH)3. 2. Freshly precipitated hydrogels of Cr3+ contain water in molecular form, both in the structure of the plane polymer layer and in the interlayer space of the polymer particles. 3. The authors suggest a mechanism for the formation of polymer particles in precipitates of Cr3+ hydrogels, and propose a structural model for them.