Showing papers on "Self-healing hydrogels published in 1984"
TL;DR: Physical properties such as number average molecular weight Mn, specific hydrates and changing diffusion coefficient of crystalline/rubbery hydrogels based on poly(ethylene glycol) Mn 3 000-8 000 which affect the diffusion of drugs through the water swollen matrix and across the polymer boundary are discussed.
241 citations
Journal Article•
TL;DR: Erosion mechanisms are divided into three types and drug release within each type is described and four distinct polymer systems within this category are under development.
Abstract: Erosion mechanisms are divided into three types and drug release within each type is described. Type I erosion involves hydrolysis of hydrogels and these are useful in the controlled release of macromolecules entangled within their network structure. Type II erosion involves solubilization of water-insoluble polymers by reactions involving groups pendant from the polymer backbone. Of particular interest are polymers that solubilize by ionization of carboxylic acid groups, and the utilization of those systems is described. Type III erosion involves cleavage of hydrolytically labile bonds within the polymer backbone and four distinct polymer systems within this category are under development. One system involves the diffusion of drugs from a reservoir through a bioerodible membrane, another system utilizes microcapsules, a third system utilizes monolithic devices, and the fourth system utilizes drugs chemically bound to a bioerodible polymer.
213 citations
TL;DR: The applicability of the present concept and process has been demonstrated experimentally with the release of oxprenolol hydrochloride from hydrogel beads based on 2-hydroxyethyl methacrylate polymerized with a polymeric cross-linking agent.
123 citations
01 Jan 1984
TL;DR: When a biologically imcompatible material is in contact with blood, there takes place thrombus formation on it via a rapid adsorption of plasma proteins and the subsequent adhesion of platelets.
Abstract: When a biologically imcompatible material is in contact with blood, there takes place thrombus formation on it via a rapid adsorption of plasma proteins and the subsequent adhesion of platelets. Numerous approaches to supress the adhesion of blood components onto synthetic surfaces have been studied and hydrogels are found to be useful.
116 citations
TL;DR: The results indicate that a constant-rate of drug release can be achieved, via a specific sigmoidal drug concentration distribution without the need to have a saturated drug reservoir as in a membrane-reservoir system.
107 citations
TL;DR: In this article, a semi-crystalline hydrogel of crosslinked poly(ethylene oxide) was swollen with a solution of prostaglandin in an organic solvent at room temperature, thus avoiding contact with water or heat, both of which degrade the PGE2.
51 citations
Patent•
03 May 1984
TL;DR: In this paper, two thermoplastic uncrosslinked polymers, one hydrophobic and the other hydrophilic, and having a micro-phase separated morphology are described.
Abstract: Novel hydrogel compositions, comprised of a blend of two thermoplastic uncrosslinked polymers, one of which is hydrophobic, and the other hydrophilic, and having a microphase separated morphology are described. These hydrogel compositions are useful as devices for controlling the release rate of bioactive agents, such as therapeutic drugs, antimicrobials, contraceptive agents, or the like, in a biological environment. Depending upon the chemical nature of the agent to be released, its rate of release can be controlled by appropriate selection of the polymeric components of the blend and their relative ratios.
50 citations
TL;DR: Soft hydrophilic intraocular lenses made of an aminopolyamide and a hydroxyethylmethylmethacrylate hydrogel polymer were implanted in cats and followed for six weeks and observation of corneal microvilli may indicate a mild adverse reaction to the hydrogels, possibly from impurities.
48 citations
Patent•
10 Jan 1984TL;DR: In this paper, the crosslinking is carried out by a reaction of a polyfunctional isocyanate with the polyoxyethylene in solution in a non-aqueous solvent.
Abstract: The hydrogels consist essentially of the polyurethane of polyoxyethylene. The crosslinking is carried out by a reaction of a polyfunctional isocyanate with the polyoxyethylene in solution in a non-aqueous solvent. Transparent hydrogels are obtained, having a high swelling ratio in the presence of water and good mechanical properties.
43 citations
Patent•
06 Apr 1984
TL;DR: In this paper, a contact lens is prepared by casting, preferably spin casting, hydrophilic gels in a plastic mold, preferably polypropylene in the presence of a surface active agent.
Abstract: Hydrogels, e.g. hydrogel contact lens are prepared by casting, preferably spin casting, hydrophilic gels in a plastic mold, preferably polypropylene in the presence of a surface active agent.
40 citations
Patent•
28 Dec 1984TL;DR: The improved polymeric hydrogel suitable for use in forming soft contact lenses is described in this article, which is improved by means of its resistance to the formation of calcium, lipid and protein deposits thereon.
Abstract: The improved polymeric hydrogel suitable for use in forming soft contact lenses is described. The hydrogel is improved by means of its resistance to the formation of calcium, lipid and protein deposits thereon. This resistance is achieved by means of covalent modification of the hydrogel with a surfactant.
TL;DR: In this article, spherulite formation of the hydrogels prepared from pure monomer and mixtures of the modified monomers were studied using optical and scanning electron microscopy, which revealed different states of heterogeneity in the various crosslinked gels.
TL;DR: Work reported here shows that, contrary to reports in the literature, hydrogels made from pure poly(2-hydroxyethyl methacrylate), pHEMA, at crosslinker content greater than 0.15 mol % do not swell above the usual equilibrium values of 39-42% water content in aqueous urea solution.
Abstract: Work reported here shows that, contrary to reports in the literature, hydrogels made from pure poly(2-hydroxyethyl methacrylate), pHEMA, at crosslinker content greater than 0.15 mol % do not swell above the usual equilibrium values of 39-42% water content in aqueous urea solution. However, hydrogels containing small (impurity) amounts of methacrylic acid (MAA) do swell dramatically (approximately 90%) in dilute urea solution, but not directly due to the urea. The urea decomposes to produce ammonium ions, thus raising the pH of the solution. Ionization of MAA occurs above pH 6, causing electrostatic interactions within the gel. The grossly swollen state of these gels represents an internal equilibrium among forces due to rubber elasticity, polymer-polymer/solvent affinity, and electrostatic interactions.
TL;DR: The ultrastructure of developing cell attachment sites was studied and fully formed cell substratum attachment sites were not observed when either elastin-HEMA hydrogels or hydrogel polymerized in the absence of protein were employed.
TL;DR: A cell for electrochemically measuring dissolved oxygen permeability coefficients (P d ) has been constructed and tested successfully with Teflon ® FEP membranes of previously established P d values.
01 Jan 1984
TL;DR: In this article, the authors investigated the influence of gel structure on the diffusion characteristics of solutes through poly(2-hydroxyethyl methacrylate) (polyHEMA) hydrogels and found that diffusion mechanism was influenced by the nature of the water within the gel, and the average pore size of the network.
Abstract: Drug release kinetics from polymer implants in vivo are influenced by the rate of drug diffusion within the polymer, and by the nature of the medium surrounding the implant. Our previous work has investigated the influence of gel structure on the diffusion characteristics of solutes through poly(2-hydroxyethyl methacrylate) (polyHEMA) hydrogels (1). The diffusion mechanism was found to be influenced by the nature of the water within the gel, and the average pore size of the network. Sorption of solutes was reported to have a marked effect on network structure (2).
TL;DR: Comportement mecanique de gels polyelectrolytiques en vue d'obtenir des informations sur le role des charges electriques portees par les monomeres and le polymere sur la formation du reseau as mentioned in this paper.
Abstract: Comportement mecanique de gels polyelectrolytiques en vue d'obtenir des informations sur le role des charges electriques portees par les monomeres et le polymere sur la formation du reseau
Journal Article•
TL;DR: The growth and collagen synthesis by human embryonic lung fibroblasts (IMR-90) and endothelial cells on collagen-HEMA hydrogels and tissue culture plastic were examined and differences in protein synthesis were observed.
Abstract: Hydroxyethylmethacrylate (HEMA) hydrogels have a peculiar crater-like topography which renders them ideal for studying cell-to-substrate contact formation. Cultured rabbit aortic smooth muscle cells (SMC) were grown on collagen-HEMA hydrogels, and the ultrastructure of developing cell attachment sites was studied. By 3 hours after cell seeding, both the rounded and spreading SMC appeared anchored to the hydrogel via extra-cellular connective tissue-like material. The fully formed attachment site present at 5-8 day was characterized by large bundles of intracellular myofilaments inserting onto areas of increased electron density along the plasmalemmal membrane. Large amounts of extracellular connective tissue-like material also appeared attached to the areas of increased electron density. Fully formed cell substratum attachment sites were not observed when either elastin-HEMA or hydrogels polymerized in the absence of protein were employed. The growth and collagen synthesis by human embryonic lung fibroblasts (IMR-90) and endothelial cells on collagen-HEMA hydrogels and tissue culture plastic were also examined. Although the two cell types grew equally well on the two surfaces, differences in protein synthesis were observed. The procollagen Type I and III ratio synthesized by the fibroblasts remained the same while the ratio synthesized by the endothelial cells varied even though their morphology appeared similar. The fibroblasts synthesized less collagen when grown on collagen-HEMA hydrogels (this effect may be related to age), while the amount of collagen synthesized by the endothelial cells grown on the two surfaces was similar.
Patent•
11 Jan 1984
TL;DR: In this paper, the crosslinking is carried out by a reaction of a polyfunctional isocyanate with the polyoxyethylene in solution in a non-aqueous solvent.
Abstract: The hydrogels consist essentially of the polyurethane of polyoxyethylene. The crosslinking is carried out by a reaction of a polyfunctional isocyanate with the polyoxyethylene in solution in a non-aqueous solvent. Transparent hydrogels are obtained, having a high swelling ratio in the presence of water and good mechanical properties.
TL;DR: It should be emphasized in the literature that a proper distribution of hydrophilic and hydrophobic regions on a biopolymer interface many The International Journal Of Artificial Organs / Vol.
Abstract: Hydrophilic polymer gels, called hydrogels, are a broad class of polymeric materials that swell in water as much as 30 to 95%, but do not dissolve therein. Owing to the high amounts of water absorbed, hydrogels exhibit good biocompatibility. Hydrogels were first introduced as useful biomaterials by Wichterle and Lim (1) who developed the most common hydrogel, namely 2-hydroxyethyl metacrylate (HEMA). Hydrogels may be prepared by different procedures, as by polymerization of hydrophilic monomers or by chemical modification of existing polymers. Several types of monomers may be used to produce hydrogels, as hydroxyalkyl methacrylates, acrylamid derivatives, acrylic acid derivatives, methylene-bis-acrylamide, pyridine, crotonic acid, 2,4 pentadiene -1-01, sodium styrene sulfonate, amminoethyl methacrylate propylene, glycol methacrylate, etc. (2). Hydrophilic polymers like HEMA are water-swollen gels which have only poor mechanical properties and therefore, their application in pure state is very limited. They must have adequate number of hydrophilic groups to allow swelling (no dissolution) in water, but this decreases their mechanical stabilities. Therefore, the hydrophilic monomers are usually copolymerized with hydrophobic monomers. The hydrophilicity of hydrogels, hence, can be modified by use of less water soluble monomers (e.g., methyl methacrylate) for control of the mechanical strength and the degree of swelling. Hydrophilic monomers are mixed with hydrophobic ones in different ratios to yield hydrogels with a wide range of water content. It should be emphasized in the literature that a proper distribution of hydrophilic (both neutral and charged) and hydrophobic regions on a biopolymer interface many The International Journal Of Artificial Organs / Vol. 7 no. 5, 1984/ p.p, 283-288
01 Jan 1984
TL;DR: The aim of this model is to elucidate the possible mechanisms of cell adhesion and protein adsorption, and to use this knowledge for the development of non-thrombogenic biocompatible implant materials.
Abstract: Hydrogels elicit a low cellular adhesion in vitro when measured by platelet adhesion tests under static conditions (1,2). A thermodynamic model has been described which predicts the level of cellular adhesion and protein adsorption to a range of polymer surfaces (3,4). The aim of this model is to elucidate the possible mechanisms of cell adhesion and protein adsorption, and to use this knowledge for the development of non-thrombogenic biocompatible implant materials.
TL;DR: In this paper, a study of diffusion in hydrogels and aqueous polymer solutions by a fluorescence quenching method was conducted and it was found that the kinetics of this process are monoexponential.
Abstract: As a result of a study of diffusion in hydrogels and aqueous polymer solutions by a fluorescence quenching method, it has been found that the kinetics of this process are monoexponential. This indicates the homogeneity of the medium surrounding the fluorophor. The value of the quenching rate constant monotonically decreases with increase of polymer concentration in the gel, up to 60%. With a further increase to 70%, it sharply decreases which evidently is due to the system approaching the glass transition point. For a fixed polymer concentration, the quenching rate constant increase in the order, polyacrylamide gel, polyvinyl alcohol gel, polyethylene glycol solution.