Showing papers on "Self-healing hydrogels published in 1988"

Solute diffusion in swollen membranes. IX. Scaling laws for solute diffusion in gels

Abstract: A scaling law was developed for the diffusion coefficient of spheroidal and ellipsoidal solutes in nonporous, equilibrium-swollen hydrogels. The law relates the solute diffusion coefficient to the solute size, the gel mesh size, and the gel equilibrium volume degree of swelling. The law was verified by appropriate data of low and high molecular weight solute diffusion through hydrogels such as swollen networks of poly(vinyl alcohol), poly(2-hydroxyethyl methacrylate), cellulose, and others. An additional scaling law was developed which relates the rate of release of a small or large molecule from an equilibrium swollen hydrogel with time and with morphological characteristics of the polymeric network.

pH-Dependent Swelling and Solute Diffusion Characteristics of Poly(Hydroxyethyl Methacrylate–CO–Methacrylie Acid) Hydrogels

Abstract: Poly(hydroxyethyl methacrylate-co-methacrylic acid) hydrogels can swell extensively in a high-pH medium where the carboxyl groups are ionized. The swelling equilibrium is a strong function of the methacrylic acid composition of the polymer and pH of the medium. The nonionized gel structure was found to be rather insensitive to the amount of cross-linker, tetraethylene glycol dimethacrylate (TEGDMA), incorporated, within the range of 0.5 to 3%. This result is supportive of the existence of secondary interactions that shield the effect of covalent cross-links. Phenylpropanolamine (PPA) was used as a probe solute to study the diffusion characteristics of the poly(HEMA-co-MA) gels. Its diffusion coefficient in the swollen matrices of different methacrylic acid compositions at various pH's was measured via a desorption method. It is evident that these diffusion coefficients follow Yasuda's free volume theory, which expresses an exponential relationship between the solute diffusivity in a swollen polymer membrane and the reciprocal of the membrane hydration. Although interactions exist between PPA and the hydrogel matrix, these interactions are not significant enough to perturb the free volume relationship established. This observation can be explained by the high ionic strength of the system.

Thermally reversible polyurethane hydrogels and cosmetic, biological and medical uses

Abstract: Thermally reversible polyurethane hydrogels are formed by adding water to a gel forming hydrophilic polyurethane polymer produced by reacting under anhydrous conditions a non-aromatic organic diisocyanate with a glycol component in an NCO/OH mole weight ratio of from about 0.900/1 to about 0.980/1, the glycol component having a number average molecular weight of from about 1000 to 3500 wherein the percentage by weight of the diisocyanate in the reaction mixture is from about 7% to about 20%. The hydrogels are solids at room temperature but liquify at higher temperatures such as body temperature and therefore are useful as carriers for the protection, delivery and sustained release of a variety of active agents including pharmaceuticals, cosmetics, living cells and organisms.

Permeation of nickel through human skin in vitro--effect of vehicles.

Abstract: SUMMARY The effect of the vehicle on the permeation rate of nickel ions through excised human skin was evaluated. Different hydrogels were compared with the standard patch test in petrolatum. A hydroxypropyl methylcellulose gel seemed to be the most promising alternative to petrolatum. It gave high bioavailability of the nickel and had good film forming properties leaving the nickel spread across the skin surface as a thin film without microscopically detectable crystals. The content of nickel in the various skin layers after cutaneous application was determined, and nickel was found to accumulate in the epidermis, probably due to epidermal binding. A significant amount of nickel was found also in the dermis. Occlusion and application of higher nickel concentrations increased the transport rate and must be considered in patch testing using this hydrogel. We conclude that nickel permeation is highly dependent of the choice of vehicle and the vehicle should, therefore, be an important consideration in patch testing with nickel.

Hydrogels for buccal drug delivery: properties relevant for muco-adhesion.

Abstract: In order to develop a muco-adhesive hydrogel for buccal drug delivery it is necessary to understand fully the properties determining adhesiveness as well as mechanisms involved. In this study we measured glass transition temperatures, water contact angles and the peel- and shear detachment forces from porcine oral mucosa, of acrylic acid and butyl acrylate copolymers. The contact angle maximizes at 50% butyl acrylate content. The glass transition temperature decreases from 0% to 100% butyl acrylate. There seems to exist a certain combination of contact angle and glass transition temperature which is related to adhesiveness. This strongly suggests that, in order to obtain a muco-adhesive hydrogel, at least two properties have to be optimized: (1) the polarity of the polymer surface and (2) the molecular mobility of the polymer groups.

Thermal Behavior of Poly Hydroxy Ethyl Methacrylate (pHEMA) Hydrogels

Abstract: The freezing and melting behavior of water in poly hydroxy ethyl methacrylate (pHEMA) hydrogels of different cross-linker and water contents was investigated in relation to the glass transition temperature (Tg) of the gels. After prolonged cooling at −15°C a constant amount of 1.7 mol water per monomeric unit did not freeze, regardless of both the cross-linker and the water content of the gels. At this water content and temperature, pHEMA gels were below their Tg, and the water molecules were prevented from diffusing to the ice crystals formed in the gel. Therefore, the inability of part of the water in pHEMA gels to freeze is not a thermodynamic phenomenon but is caused by kinetic factors.

Thermotropic biphilic hydrogels and hydroplastics

Abstract: Novel hydrogels and hydroplastics are described which exhibit temperature dependent, reversible phase separations and clear-opaque transitions between 1° and 100° C. These materials consist of linear or crosslinked random copolymers of N,N-dimethylacrylamide with alkyl- and alkoxyalkyl acrylates. The water solubility and water swelling of these polymers is extremely temperature dependent; they show sharply defined clear to opaque transitions in their water swollen state and as soluble polymers show Lower Critical Solution Temperatures (LCST). They are useful in drug delivery systems, absorption and extraction processes and as qualitative thermometers, thermosensors and self-activating sunscreens, for example in greenhouses.

Experimental implantation of hydrogel into the bone.

Abstract: The present study deals with the application and possibilities of insoluble hydrophilic gels (poly(2-hydroxyethyl methacrylate)) as substitutes of bone tissue experimentally. Their biocompatibility is examined with regard to the porous qualities of the implant and to its chemical structure, and their behavior in the cancellous and compact bone is evaluated. It was found that the modifications of hydrogels used in the experiment are biocompatible, with the compatibility increasing in proportion to increasing porosity. The nonporous and microporous hydrogels are not compatible and are demarcated. The sintered macroporous gel is surrounded by a thin fibrin membrane. By adding methacrylic acid to the hydrogel surface, adhesion increases markedly. Marked destruction also appears in the polymer especially in the cancellous bone. By an active destruction of the polymer, no direct phagocytosis can be proved. Upon breakdown of the implant in the compact bone the activity of the macrophages is delayed. When the gel without methacrylic acid is used alone, destruction does not occur even after 193 days. When methacrylic acid is added to the polymer surface, destruction does occur and the implant is filled only by bone trabeculae.

Entrapping of acid phosphatase in poly(2‐hydroxyethyl methacrylate) matrices: Preparation and kinetic properties

Abstract: The present work was undertaken to determine the influence of immobilization of acid phosphatase by entrapment in poly(2-hydroxyethyl methacrylate) (poly-HEMA) gels on the rate and duration of p-nitrophenyl phosphate hydrolysis. This enzyme was selected as model system for the sake of comparison with other immobilization techniques studied previously making use of natural polymers. Under certain conditions, catalyst inactivation induced by chemical agents employed during polymerization was very low. Activity recovery in the enzymatically filled hydrogels depends on acid phosphatase loading and attains a maximum at 2 mg per gram of support. The use of low molecular weight linear polymers as matrix fillers is advisable. The best results were achieved with poly(ethylene oxide) PEG 1500, but PEG 6000 and poly(N-vinylpyrrolidone) PVP 10 000 are also effective. Bovine serum albumin (BSA) is useless. The highest value of activity recovery obtained was 24% that of free enzyme. Roughly 30% of enzyme is retained in active form in the hydrogel and works with an efficiency ranging from 97% to 90% depending on average particle size. The kinetic parameters Km and Ea suggest the presence of a combined diffusive and enzymatic reaction-controlling mechanism. Only a minor shift of optimum pH was observed. Both operational and storage stability are largely improved upon entrapping in hydrogels.

New type of hydrogel for controlled drug delivery.

Abstract: The new type of hydrogel system (which is known under the trademark HYPAN™), is described in some detail here, emphasizing its grades and those properties potentially useful in controlled drug deli...

Coprecipitated hydrogels in pressure tolerant gas diffusion electrodes

Abstract: Gas diffusion electrodes and gas-generating or consuming electrochemical cells utilizing the same are disclosed. The electrode comprises an electronically conductive and electrochemically active porous body defining respective gas and electrolyte contacting surfaces, with a substantially gas impermeable layer covering the electrolyte contacting surface. The layer comprises an electrolyte-insoluble, ionomeric ionically conductive hydrophilic hydrogel formed by coprecipitation between at least first and second precursor polymers.

Hydrogels with increased organic solvent soluble active agent loading capacity, their preparation and the use thereof

Abstract: An organic solvent soluble active agent containing water-insoluble hydrophilic hydrogel comprising a copolymer of (A) a water-soluble monoolefinic monomer or a mixture thereof optimally containing up to 50% thereof of one or more water-insoluble mono-olefinic monomers and (B) a terminally diolefinic hydrophobic macromer containing polypropylene oxide or polytetramethylene oxide units prepared in the presence of an effective macromer expanding amount of a macromer soluble compound of the formula R'--R"--O.sub.n R"' where R', R", R"' and n are as defined in the claims, hydrogels useful in the loading of such active agents, their preparation, and use are disclosed.

Uv absorbing vinyl monomers and polymers and ocular implants prepared therefrom

Abstract: Ultraviolet light absorbing, polymerizable phenothiazine and azaphenothiazine monomers, copolymers thereof and articles of manufacture, including lenses, optical devices, plastic films and hydrogels, constructed therefrom.

Thermally Stable Acrylic Polymer for Profile Modification Applications

Abstract: Profile modification is a process in which flooding water is diverted from highly permeable zones into less permeable oil-bearing layers within a subterranean reservoir. In recent years this has been achieved by the use of polymeric hydrogels in yhich the water-soluble polymer is cross-linked by a multivalent metal ion1. The latter may be generated in situ from a redox couple, e.g., sodium dichromate/sodium metabisulfite or as a complexed reagent, e.g., aluminum citrate. This enables the gelation process to be retarded until the aqueous polymer solution has been placed deep into the thief zone.