Showing papers on "Self-healing hydrogels published in 1992"

Hydrogels: swelling, drug loading, and release.

Abstract: Hydrogels have been used by many investigators in controlled-release drug delivery systems because of their good tissue compatibility and easy manipulation of swelling level and, thereby, solute permeability The desired kinetics, duration, and rate of solute release from hydrogels are limited to specific conditions, such as hydrogel properties, amount of incorporated drug, drug solubility, and drug-polymer interactions This review summarizes the compositional and structural effects of polymers on swelling, loading, and release and approaches to characterize solute release behavior in a dynamic state A new approach is introduced to compensate drug effects (solubility and loading) with the release kinetics by varying the structure of heterogeneous polymers Modulated or pulsatile drug delivery using functional hydrogels is a recent trend in hydrogel drug delivery

Hydrogel compositions and methods of use

Abstract: Biocompatible, biodegradable, hydrogels are prepared from a backbone bonded to a cross-linking agent. Suitable backbones include proteins and polysaccharides, e.g,, albumin, polymannuronic acid, or polygalacturonic acid. Suitable cross-linking agents include polyvalent derivatives of polyethylene or polyalkylene glycol. These hydrogel compositions may be loaded with diagnostic labels, e.g,, radiopaque, paramagnetic, or superparamagnetic materials, or therapeutic drugs, e.g., chemotherapeutic drugs, antibiotics, or cells that produce therapeutic agents. This invention also relates to methods of use of such hydrogels for imaging during interventional procedures of a patient.

Synthesis and characterization of thermally reversible macroporous poly(N‐isopropylacrylamide) hydrogels

Abstract: Thermally reversible poly(N-isopropylacrylamide) (PNIPAAm) hydrogels having macroporous structures were prepared by a new method These gels have large pore volumes, large average pore sizes and faster macromolecule permeation rates in comparison to conventional PNIPAAm conventional hydrogels Compared with conventional PNIPAA hydrogels, the macroporous PNIPAAm gels have higher swelling ratios at temperatures below the LCST and exhibit faster deswelling and reswelling rates The deswelling rates are especially rapid

Wettable silicone hydrogel compositions and methods for their manufacture

Abstract: Improved silicone-containing hydrogels are disclosed with enhanced wettability comprising a silicone-containing monomer, hydrophilic monomers, and a relatively non-polar ring-containing monomer able to be converted to a highly polar amino acid upon hydration.

Chemistry and physics of “agricultural” hydrogels

Abstract: Superabsorbent polymer hydrogels can swell to absorb huge volumes of water or aqueous solutions. This property has led to many practical applications of these new materials, in particular, in agriculture for improving water retention of soils and the water supply of plants. This article reviews methods of superabsorbent gel synthesis, measurements and treatment of their properties, as well as their effects in soil and on plant growth. The thermodynamic approach used to describe the swelling behavior of polymer networks proves to be quite helpful in modelling the hydrogel efficiency as a water-absorbing additive.

Synthesis and characterization of pH- and/or temperature-sensitive hydrogels

Abstract: A series of pH-sensitive hydrogels that exhibit volume phase transition phenomena have been synthesized in aqueous solution and characterized with respect to their dynamic swelling behaviors. Positively charged hydrogels were prepared by copolymerizing varying ratios of N-isopropylacrylamide and NN′-dimethylaminopropylmethacrylamide. The hydrogels based on a temperature-sensitive hydrogel demonstrate a large change of equilibrium swelling in response to small variations of pH and/or temperature. These hydrogels exhibit different lower critical solution temperature (LCST) ranges depending on the environmental pH values. Below their LCST, they exhibit small and broad pH sensitivities normally observed in most hydrophilic polyelectrolyte gels, but above their LCST, they exhibit sharp pH dependent phase transition behaviors. The pH-dependent phase transition is strongly affected by temperature, while the temperature-dependent transition is, in turn, largely influenced by the pH. As the temperature is raised, the transitional degree of gel swelling change becomes sharper and larger, and the phase transition pH value shifts to a lower pH. It was also found that swelling is faster than deswelling for these cationic hydrogels, which suggests the existence of a water diffusion barrier during the deswelling. The swelling kinetics of initially dry and glassy gels were strongly dependent on both the pH value and temperature.

Hydrogels for site-specific drug delivery to the colon: in vitro and in vivo degradation.

Abstract: Novel hydrogels based on N,N-dimethylacrylamide, N-t-butylacrylamide, and acrylic acid cross-linked with azoaromatic compounds of varying length and electron density of the azo bond were synthesized. The cross-links are degradable by microbial azoreductases present predominantly in the colon, and the gels appear to be suitable for colon-specific drug delivery. The degradability in vitro and in vivo was found to be related to the degree of swelling of the gels. The higher the degree of swelling, the higher the degradability. However, structural and electronic factors were also shown to influence reduction of azo bonds.

Swelling Equilibria for Acrylamide-Based Polyampholyte Hydrogels

Abstract: Polyampholyte hydrogels were prepared by copolymerizing acrylamide with methacryamidopropyl trimethylammonium chloride and sodium styrenesulfonate. The total nominal charge density of the hydrogels was held constant at 4.7±0.1 mol% (dry basis). While the molar ratio of anionic to cationic moeties was varied. The swelling of hydrogels in water showed increasing insensitivity to ionic strength as the molar ratio of anionic to cationic moieties approached unity. Donnan membrane equilibria qualitatively explain the experimental results

Adhesive hydrogels having extended use lives and process for the preparation of same

Abstract: This invention relates to a non-stringy adhesive hydrophilic gel comprising an aqueous mixture of a radiation crosslinkable water-soluble polymer, at least one humectant effective to extend the moisture retaining characteristics of the gel and which inhibits the ability of radiant energy to crosslink the water-soluble polymer, a pharmacologically active agent, and a crosslinking promoter effective to counteract the crosslinking inhibitory effect of humectant. The aqueous mixture is exposed to radiant energy effective to provide a non-stringy adhesive cohesive homogeneous hydrophilic gel that has an extended in-use lifetime. The gels can be formed into PATCHES for long term application of the pharmacologically active agent to a patient.

Entrapment of microbial cells within polyurethane hydrogel beads with the advantage of low toxicity

Abstract: A new method is described for the entrapment of microbial cells in polyurethane (PUR) hydrogel beads. This hydrogel is produced from a hydrophilic pre-polymer blocked with bisulphite by adjusting the pH between 4 and 6.5. Bisulphite-blocked isocyanate has a substantially lower toxicity against living cells than unblocked (conventional) isocyanates. The poly(carbamoylsulfonate) (PCS) hydrogels have optimal elastic properties and therefore can be used for a matrix of biocatalysts in an agitated reactor as well as in a fluid-bed reactor. The results of ethanol fermentation ofSaccharomyces cerevisiae entrapped in PCS hydrogel beads, and of the denitrification activity of immobilizedParacoccus denitrificans are promising. In contrast, entrapped cells in conventional PUR hydrogels didn’t show any activity.

Study on PVA hydrogel crosslinked by epichlorohydrin

Abstract: Poly(vinyl alcohol) hydrogel was prepared by using epichlorohydrin as a crosslinking agent. The molecular weight between crosslinks was calculated. The swelling behavior, as well as mechanical properties, of the hydrogels were examined by weighing and tensile testing, respectively. Values of equilibrium water content of more than 95% were reached while Young's modulus and tensile strength of the hydrogels were about 105 dyn/cm2. Crystallization was introduced by drying the hydrogels at 90°C. The dried hydrogel samples were used for swelling kinetic study, then reequilibrated with water and subjected again to tensile testing. Due to the formation of microcrystalline domains in the PVA hydrogel network after annealing, hydrogels with greatly enhanced Young's modulus, tensile strength, and elongation at break were obtained and their equilibrium water content values remained still high, i.e., 87 and 93%. © 1992 John Wiley & Sons, Inc.

Hydrogels based on water-soluble poly(ether urethanes) derived from L-lysine and poly(ethylene glycol)

Abstract: Water-soluble poly(ether urethanes) (M w up to 170 000) have been prepared by the copolymerization of bis(succinimidyl) carbonate derivatives of poly(ethylene glycol) (PEG) with L-lysine (Lys) in a strictly alternating fashion. The pendent carboxylic acid groups were used in crosslinking reactions. The resulting hydrogels formed transparent, highly swollen films. At an equilibrium water content of about 80 %, these films exhibited a relatively high degree of tensile strength ranging from 0.26 to 1.09 MPa.

Transparent poly(vinyl alcohol) hydrogel with high water content and high strength

Abstract: To develop a transparent poly(vinyl alcohol) (PVA) hydrogel with high water content and high strength, we studied the physical gelation of PVA solutions and found that low temperature crystallization of PVA solutions in mixed solvents consisting of water and a water-miscible organic solvent yields transparent gels. The strength and transparency of the PVA hydrogel is dependent on both the type of organic solvent and the mixing ratio of water/organic solvent. A mixed solvent from water/dimethyl sulfoxide resulted in the highest transparency and the highest tensile strength among the water/organic solvent combination studied. A plausible mechanism is proposed for the formation of transparent and strong hydrogels on the basis of the results obtained.

Porous structure and rheological properties of hydrogels of highly water‐absorptive cellulose graft copolymers

Abstract: The porous structures of the highly swollen hydrogels of cellulose—acrylamide graft copolymers were studied by the solute exclusion technique. For these hydrogels, the cumulative volume of pores up to 560 A in pore width was between 450 and 850 mL/g, and was between 20 and 30% of the total pore volume. With an increasing in the amount of crosslinker added in the grafting procedure, the cumulative pore volume up to 560 A decreased. Furthermore, larger pores shrunk preferentially. In the range of concentration from 0.003 to 0.3%, the viscosity of the hydrogels increased remarkably with an increase in concentration. The concentration dependence of the viscosity showed a transition at about 0.03%, which corresponded to the reciprocal of the water retention values for each copolymer. At concentrations over 3%, fluidity of the hydrogels was lost and the water swollen copolymers became viscoelastic. This dynamic viscoelasticity remained essentially unchanged in the temperature range of 20 to 80°C. The dynamic viscoelasticity was dependent on the concentration, but the concentration dependence was smaller than that of the viscosity. The larger the amount of the crosslinker added, the larger the value of dynamic modulus became.

Swelling behavior of hydrogels containing phosphate groups

Abstract: Hydrogels containing phosphate groups were prepared by copolymerization of 2-methacryloyl-oxyethyl dihydrogen phosphate (phosmer) and various hydrophilic monomers [N,N-dimethyl-acrylamide (DMAAm), acrylic acid (AAc) and 2-hydroxyethyl methacrylate (HEMA)], and the swelling behavior was investigated. These hydrogels are thermo-sensitive. Phosmer-DMAAm and phosmer-HEMA hydrogel deswell with increasing temperature, but for the phosmer-AAc hydrogel the swelling ratio increases with temperature. Interestingly, the swelling ratio decreases with an increase in phosphate group content. This unusual behavior may arise from the phosphate group acting both as the functional group and the crosslinking agent.

Methods for the preparation of non-stringy adhesive hydrophilic gels

Abstract: A method is disclosed for the preparation of non-stringy hydrogels that are comprised of a homogeneous uniform mixture of water and at least one water-soluble high molecular weight polymer. Suitable mixtures may be derived from poly(ethylene oxide) and water or poly(vinyl pyrrolidone), a viscosity enhancing hydrophilic polymer and water, and further, may optionally contain an effective amount of a water-soluble electrolyte to provide conductive non-stringy materials. These polymeric mixtures are crosslinked by exposure to radiant energy to provide gel-like solids which are sufficiently tacky and adhesive to adhere to the subjects' skin and yet are substantially non-stringy and non-aggressive such that contact with such hydrogels imparts less discomfort to the user. In addition, the consumer utilizing the products of this invention would not experience the objectionable sticky, stringy sensation associated with existing adhesive gels.

Prosthesis with improved biocompatibility

Abstract: An injectable or implantable material for soft tissue augmentation comprising a hydrogel containing both hydrophobic and hydrophilic domains is prepared by copolymerizing a hydrophilic monomer, such as water soluble N-vinylpyrrolidone with non-water soluble monomers, such as N-vinyl carbazole, its derivatives, or a non-water soluble derivative of N-vinylpyrrolidone. Also suitable for injection into direct contact with body tissue are hydrogels prepared by cross-linking polyvinylpyrrolidone. The hydrogel may be either solid or composed of particles. The hydrogel may also be enclosed within a flexible porous or nonporous envelope.

A new hydrophilic polymer for biomaterial coatings with low protein adsorption.

Abstract: BIOPOL polyurethane polymers, an extension of the HYPOL Polymer series of foamable hydrophilic polymers, have been developed which exhibit improved performance for selected biomedical applications. Members of the BIOPOL polyurethane polymer series, with molecular weights in the range of 7000 to 30,000, are larger molecules than HYPOL polymers (MW less than 3000) and produce hydrogels, rather than foams, when mixed with water. The prototype material in this series, BIOPOL XP-5, is a liquid prepolymer which chain extends in water and forms a hydrogel which can contain greater than 85% water. The time required for polymerization with water was dependent on the prepolymer: water ratio. This prepolymer was coated onto silica and medical grade tubing and then cured in place with water to form a stable coating which was resistant to non-specific protein binding. In addition, soluble, isocyanate-free forms of the prepolymer were tested for toxicity and shown to produce no adverse effects when injected intravenously into mice or when applied to a chicken chorioallantoic membrane. BIOPOL polymers can be useful in applications where protein adsorption is an undesirable event.

Surface fixation of hydrogels. Heparin and glucose oxidase hydrogelated surfaces.

Abstract: The authors report a new photochemical technique for the fixation of hydrogels onto the surface of fabricated devices and sensors. The preparative method is based on two different types of photochemistry: photocross-linking due to intermolecular photodimerization of cinnamoyl groups, and photoinduced covalent bonding due to the photoreactivity of azido groups. The immobilization of heparin, useful as a thromboresistant coating, onto poly(ethylene terephthalate), and the immobilization of glucose oxidase onto the surface of a carbon fiber electrode, were demonstrated. In the former, immobilized heparin was found to be continuously released from the hydrogel, and the release rate was effectively controlled by the thickness of the hydrogel. In the latter, upon the addition of glucose, a spontaneous electrical response was observed to function as a glucose sensor. No delamination was found for either system after vigorous washing with water. Thus, durable surface hydrogelation, simultaneous immobilization of bioactive substances, and functioning of the systems were demonstrated.