Showing papers on "Self-healing hydrogels published in 1987"

Hydrogels in Medicine and Pharmacy

Abstract: Hydrogels in medicine and pharmacy , Hydrogels in medicine and pharmacy , کتابخانه مرکزی دانشگاه علوم پزشکی تهران

Mechanisms of mucoadhesion of poly(acrylic acid) hydrogels.

Abstract: It has been proposed that mucoadhesives which adhere to the gastric mucus layer may be used to prolong gastric retention time of oral dosage forms Preliminary studies, using acrylic hydrogels, have established that the density of carboxyl groups on the polymer chain is important for mucoadhesion To understand the role(s) of the carboxyl groups in mucoadhesion, acrylic acid–aerylamide random copolymers [P(AA-co-AM)] were synthesized, and the adhesion strength of the cross-linked polymers to the gastric mucus layer was examined as a function of the pH, initial concentration of the cross-linking agent, degree of swelling, and carboxyl-group density From the study on mucoadhesion of various P(AA-co-AM), it was found that at least 80% of the vinyl groups of the polymer must possess carboxyl groups in the protonated form The dependence of mucoadhesion on pH and carboxyl-group density suggests that mucoadhesion occurs through hydrogen bonding In addition, the density of the cross-linking agent significantly affects mucoadhesion As the density of the cross-linking agent is lowered, the mucoadhesive strength increases, although the density of carboxyl groups in the test surface area is reduced It is concluded that for mucoadhesion to occur, polymers must have functional groups that are able to form hydrogen bonds above the critical concentration (80% for vinyl polymers), and the polymer chains should be flexible enough to form as many hydrogen bonds as possible

Specificity and biological activity of the protein deposited on the hydrogel surface. Relationship of polymer structure to biofilm formation.

Abstract: The in-situ lens-bound protein layer (LBPL) was characterized on hydrogels of varying water content and ionic-binding capacity. The LBPL proved to be critically dependent on the ionic binding capacity of a given hydrogel. On nonionic polymers the LBPL invariably was thin and largely insoluble. Histochemical staining allowed the detection of all major types of tear proteins. Amino acid analysis revealed a variable composition. Extractable protein proved devoid of active lysozyme. Electrophoresis of pooled samples revealed a variable mixture of acidic, neutral, and basic bands. To what extent variability is dependent on tear film composition and lens structure awaits use of more sensitive analytic procedures. On anionic hydroxyethylmethacrylate copolymer lenses, the LBPL proved radically different. Here the LBPL invariably was much thicker and composed primarily of loosely bound protein. Electrophoresis and enzymatic analysis revealed a homogenous layer consisting primarily of lysozyme much of which retains enzymatic activity. The amino acid analysis of the insoluble protein suggests a similar composition. Specificity of deposition can be attributed to ionic affinity. Conformational integrity can be attributed partly to the unique stability of lysozyme. Electrophoresis of a pooled anionic lens extract revealed an unknown, highly mobile, basic protein. This presumably represents the selective accumulation of a highly basic trace or transient constituent of the tear film. The specificity and biological activity of the LBPL on the anionic lens may modify hydrogel biocompatibility affecting risk of spoilage, microbial colonization, and propensity to trigger an inflammatory and immune response.

Cell responses to biomaterials I: Adhesion and growth of vascular endothelial cells on poly(hydroxyethyl methacrylate) following surface modification by hydrolytic etching

Abstract: Hydrogels of poly(hydroxyethyl methacrylate) (polyHEMA) homopolymer do not normally support the attachment and growth of mammalian cells. By altering the surface it has been possible to dramatically change this cell–substratum interaction so that vascular endothelial cells can attach and completely populate a poly HEMA surface. While this can be achieved by copolymerisation of polyHEMA with methacrylic acid or diethylaminoethyl methacrylate, it is most conveniently achieved by brief treatment of polyHEMA hydrogel with concentrated sulphuric acid. The resultant creation of surface—COOH groups, revealed by electron spectroscopy for chemical analysis, is consistent with the hydrolytic formation of methacrylic acid on the surface layer. Surface—COOH groups created by treatment with chloric or hydrofluoric acids were not effective. Following sulfuric acid treatment, cell adhesion and growth on polyHEMA hydrogel were better than on Teflon and approached those attained on glow–discharge-treated polystyrene. The capacity of acid-treated polyHEMA to adsorb albumin or fibronectin was of the order of 100-fold or 10-fold lower respectively than either polystyrene, Teflon, or segmented polyurethane. Hydrolytic “etching” in this way is proposed as an efficient means of expanding the use of polyHEMA hydrogel as a biomaterial without modifying the overall physicochemical properties of the bulk of the material.

Fluorine containing soft contact lens hydrogels

Abstract: An improved soft contact lens material, existing as a hydrogel, is formed by a polymer containing a fluorinated monomer, a hydroxyalkyl ester of acrylic or methacrylic acid, and an N-vinyl lactam. The polymer may also contain other hydrophilic and/or hard hydrophobic monomers, crosslinking agents, and uv-absorbing agents. Contact lenses made of these combinations have high water of hydrations, are highly wettable, have extremely high oxygen permeabilities and are resistant to protein deposits and other forms of attached debris.

Synthesis and characterization of hydrogels from graft copolymers

Abstract: Graft copolymers of well-defined structure composed of a 2,3-dihydroxypropyl methacrylate backbone and uniform molecular weight polystyrene branches were prepared by the macromonomer method and studied for their application as hydrogels utilizing their microdomain structure. Film specimens prepared by solution casting of the graft copolymer swelled immediately in water to form stable hydrogels which were characterized by measuring the equilibrium degree of swelling and the oxygen permeability in water. Swelling behavior of the hydrogel was also characterized by the small angle X-ray scattering (SAXS) measurement. It is clearly shown that the microphase separated structure of the graft copolymers is considerably regular and the swelling behavior and the oxygen permeability coefficient of hydrogels can be well-controlled by both the architecture of preformed graft copolymers and the microdomain structure in the cast specimens.

Swelling and Mechanical Properties of Cellulose Hydrogels Part VI. Dynamic Mechanical Properties

Abstract: Etude a 20, 50 et 80°C, d'hydrogels sous compression uniaxiale pour une teneur en eau variant entre 0,14 g/g et 5 g/g

An alternative method of determining the water content of hydrogels

Abstract: Teneur en eau du xerogel polymethacrylate d'hydroxy-2 ethyle gonfle dans une solution aqueuse tres diluee de Bleu Dextran BD 2000

Process for the preparation of a hydrogel which is largely free from monomers

Abstract: A polymer hydrogel substantially free from monomers and oligomers is prepared by contacting a previously prepared polymer hydrogel with a single-phase mixture of water and a solvent and then separating the mixture of water and solvent from the hydrogel.

Temperature dependence of the contact angle at the polymer-water interface

Abstract: Contact angle measurements on polymer hydrogels were performed at various temperatures, and we obtained the dispersive ( γ s d ) and nondispersive ( γ s p ) components of the surface tension of polymer hydrogel at each temperature. Utilizing the temperature dependence values of γ s d and γ s p , we obtained the surface entropies of polymer hydrogels. The polymer hydrogels used were isotactic and syndiotactic poly(2-hydroxyethyl methacrylate) (HEMA), poly(2-hydroxyethyl methacrylate + aminoethyl methacrylate) (HEMA + AEMA), poly(2-hydroxyethyl methacrylate + N -vinyl pyrrolidone) (HEMA + VP), poly(2-hydroxyethyl methacrylate + methyl methacrylate) (HEMA + MMA), poly(2-hydroxyethyl methacrylate + methoxyethyl methacrylate) (HEMA + MEMA), and poly(2-hydroxyethyl methacrylate + methoxyethoxyethyl methacrylate) (HEMA + MEEMA), respectively. The contact angles were also measured by using droplets of water-immiscible liquids under conditions in which the polymer hydrogel was fully hydrated.

Crystal growth in syndiotactic poly(vinyl alcohol) hydrogels

Abstract: Aqueous solutions of syndiotacticity-rich poly(vinyl alcohol) (s-PVA) form gels easily. The optimum condition of growth of the calcium tartrate crystal formed by diffusing calcium chloride into hydrogels containing tartaric acid was studied with use ofs- PVA of a syndiotacticity of 56 % and a degree of polymerization of 1460. The crystal grew in the gel of the concentrations of 2 % s-PVA and of 0.5 N tartaric acid at pH=4. The relation between the formation of Liesegang rings and shear modulus of a gel was studied by diffusing silver nitrate into gels containing potassium chromate. The distance between rings decreased with increasing shear modulus of a gel in the range from 670 to 7500 dyne/cm2. The Liesegang rings were not formed for the shear modulus gel for 280 and 16200 dyne/cm2.

Structure and properties of crosslinked hydrogels based on the polyelectrolyte complex polyacrylic acid-polyethyleneimine

Abstract: IR spectroscopy and potentiometric titration have been used to investigate the structure of crosslinked gels based on a polyelectrolyte complex of polyacrylic acid and branched polyethyleneimine. The dependence of their physical chemical properties on the ratio of the ionic and covalent bonds between the chains of the polyelectrolytes in aqueous and salt media has been studied. It is shown that by varying the nature and the ratio of the stabilizing gel-ionic, covalent and hydrogen bonds one may within wide limits change the properties of the hydrogels of the polyelectrolyte complex, their stability in different media, swelling capacity and permeability in relation to water and dissolved substances. The patterns found are in good agreement with the structure established in this work in the polyacrylic acid-polyethyleneimine complex.

Effect of temperature on structure and transport properties of hydrogels based on regenerated cellulose

Abstract: Structure of hydrogels based on regenerated cellulose and transport of non-electrolytes have been investigated at various temperatures. When the temperature of the surrounding solution is raised from 273 to 318–328 K the hydration H of the hydrogel decreases slowly. The apparent partition coefficient of urea between water and the swollen membrane varies between 0·5 and 0·9 within the temperature interval 293–323 K in accord with the changes in H . Interaction of urea with the cellulose matrix becomes stronger above328 K.

Study on the swelling behaviour of copolymer hydrogels

Abstract: The states of water in poly(N-vinylpyrrolidone-methylmethacrylate) and poly(N-vinylpyr-rolidone-2-hydroxyethyl methacrylate) hydrogels have been studied by means of DSC. The effect of polymer structure on equilibrium swelling extent of water has been examined. It was found' that the state of water and the water content in different hydrogels were dependent on the kind of monomer used, the component of copolymer, the sequence distribution of the monomer unit and the degree of crosslinking (including chemical and physical) to a great extent. The equilibrium water content of the hydrogel may be regarded as the sum of the different state of swollen water contents of the hydroge. Based on these, a semiempirical formula used to estimate the equilibrium water content of the copolymer hydrogels was presented.

Process for preparing hydrogels free of monomers

Abstract: Das Verfahren zur Herstellung eines weitgehend monomerenund oligomerenfreien Hydrogels ist dadurch gekennzeichnet, das das Hydrogel mit einem einphasigen Gemisch aus Wasser und einem Losungsmittel in Kontakt gebracht und danach das Gemisch aus Wasser und Losungmittel von dem Hydrogel abgetrennt wird. The process for producing a substantially monomerenund oligomerenfreien hydrogel is characterized in that the hydrogel is contacted with a single-phase mixture of water and a solvent into contact, and then the mixture of water and solvent is separated off from the hydrogel.

Use of Organic Cosolvents for Enhanced Leaching of HEMA/MAA Copolymers

Abstract: Leaching processes that use solvents to shrink and swell hydrogels by ionizing constituents of the gel and/or by solvating the hydrophobic regions with organic cosolvents were explored as a means to cleanse implantable hydrogels. 336 Gels of poly(2-hydroxyethyl methacrylate/methacrylic acid) (pHEMA/MAA) were chosen because of their common use as bio-materials; a composition having 2.5 mole % MAA and a cross-linker of tetraethylene glycol dimethacrylate (TEGDMA) at 0.15 mole % was used. Leaching solutions with pH 10 and 3, which lie above and below the dissociation point of the MAA moieties on the gel network, were used either alone or as 50% volume mixtures with ethanol or isopropanol. Execution of three shrink/swell cycles shows that as much as an 4% of additional material was lost from the gel compared to simple leaching in pH 6 water baths. Sequential exposure to acidic and basic aqueous alcohol solutions was shown to be a faster, but equivalent method of leaching as compared with sequential exposure to acid and base. A method for controlled swelling and shrinking was developed to allow delicate or irregularly shaped gel structures to be leached without damage due to stress associated with rapid swelling/shrinking.

Temporary Wound Covering: Effect of Chemical Modification

Abstract: Extensive skin loss resulting from thermal injuries poses traumatic and life threatening problems. The major causes of death are from bacterial infection and excessive fluid loss developed post-burn. Victims who manage to survive these early threats are, nonetheless, permanently damaged psychologically and physically by the disfiguring scars which arise from wound contraction. The absence of a template for cell propagation retards epithelialization and subsequent wound closure. Previous studies on hydrogels prepared from non-immunogenic dextran (mol. wt. 151,000) and impregnated with bacteriostatic agents have shown them to be effective in controlling infection. Therefore, it is desirable to modify these hydrogels such that they will also support the growth of cells. Since positively charged groups such as 2-diethyl-aminoethyl (DEAE) have been shown to facilitate cell attachment and growth in commercial microcarriers, we investigated the binding of DEAE groups onto preformed gels. A preliminary evaluation of the DEAD-treated hydrogels indicated that DEAE-binding significantly facilitates the propagation and growth of cells on the hydrogel surface.