Showing papers on "Self-healing hydrogels published in 1997"
TL;DR: The network structure and the thermodynamic nature of the components of these networks play a key role in their diffusional behavior, molecular mesh size changes (especially in environmentally responsive hydrogels), and the associated molecular stability of the incorporated bioactive agents.
Abstract: Recent developments include the use of water-swollen, crosslinked biomedical polymers as carriers for the delivery of drugs, peptides and proteins, as targeting agents for site-specific delivery, or as components for preparation of protein or enzyme conjugates. The network structure and the thermodynamic nature of the components of these networks play a key role in their diffusional behavior, molecular mesh size changes (especially in environmentally responsive hydrogels), and the associated molecular stability of the incorporated bioactive agents.
406 citations
TL;DR: New polyvalent hydrazide cross-linkers were synthesized, characterized, and used to prepare hydrazid cross-linked hydrogels derived from hyaluronic acid (HA) with different chemical and physical properties.
274 citations
TL;DR: The release kinetics of a model protein, Immunoglobulin G, from dex-(lactate)HEMA hydrogels were investigated and shown to be dependent on both the DS and the initial water content of the gel.
Abstract: Dextran hydrogels were prepared by radical polymerization of aqueous solutions of glycidyl methacrylate-derivatized dextran (dex-MA), hydroxyethyl methacrylate-derivatized dextran (dex-HEMA), and HEMA−oligolactate-derivatized dextran (dex-lactateHEMA), using potassium peroxydisulfate and N,N,N‘,N‘-tetramethylethylenediamine (TEMED) as the initiating system. Dex-MA hydrogels only degraded under extreme conditions (100 °C, pH 1−3), whereas hydrogels derived from dex-HEMA or dex-lactateHEMA degraded fully at pH 7.2 and 37 °C, due to hydrolysis of the lactate and/or carbonate esters in the cross-links. The degradation time of these gels can be tailored from 2 days to more than 2 months by varying the nature of the spacer, the degree of substitution1 of dextran (DS), and the initial water content of the hydrogels. The release kinetics of a model protein, Immunoglobulin G, from dex-(lactate)HEMA hydrogels were investigated and shown to be dependent on both the DS and the initial water content of the gel. Under ...
234 citations
TL;DR: In this article, 15 or 20% aqueous polyvinyl alcohol (PVA) hydrogels were prepared using repeated cycles of freezing for 6 or 12 hours at − 20 °C and thawing for 2 hours at 25 °C.
232 citations
Patent•
05 Nov 1997TL;DR: In this article, a prepolymer of an aliphatic polyoxaester having a polymerizable end group that may be used to produce hydrogels, surgical devices such as sutures, suture with attached needles, molded devices, and the like.
Abstract: The present invention describes a prepolymer of an aliphatic polyoxaester having a polymerizable end group that may be used to produce hydrogels, surgical devices such as sutures, sutures with attached needles, molded devices, and the like.
232 citations
TL;DR: In this paper, the authors defined the controlling parameters affecting transport of drugs and proteins through poly(acrylic acid), PAA, and poly(ACrylic acid-co-2-hydroxyethyl methacrylate), P(AA co-HEMA), which ultimately defined the mesh size available for solute diffusion, and demonstrated that at the lowest ratio of solute radius to polymer mesh size, solute/polymer interactions were a dominant factor in hindering the diffusion process.
222 citations
TL;DR: The electrical conductivity of poly(hydroxyethyl acrylate) PHEA, hydrogels was studied by means of dielectric relaxation spectroscopy in wide ranges of frequency (5 Hz-2 GHz), temperature (173 −363 K) and water content (0.065 −0.46 g of water per gram of dry material) as mentioned in this paper.
214 citations
Patent•
24 Oct 1997
TL;DR: In this article, a method for reducing the electrode impedance of implantable biosensors by coating the surface of the biosensor with a uniform hydrogel which allows unimpeded water movement around the sensor is provided.
Abstract: Methods for reducing the electrode impedance of implantable biosensors by coating the surface of the biosensor with a uniform hydrogel which allows unimpeded water movement around the sensor are provided. The surface coatings are compositions which are biocompatible and are capable of water uptake of at least 120% of their weight, more preferably at least 200% of their weight. Upon the uptake of water, the hydrogels used in the present invention will also swell and provide a layer of water around the electrodes to which the hydrogels are attached. The hydrogels can be prepared from (a) a diisocyanate, (b) a hydrophilic polymer which is a hydrophilic diol, a hydrophilic diamine, or a combination thereof, and optionally, (c) a chain extender.
207 citations
TL;DR: In this paper, the influence of a non-uniform external magnetic field on the shape of gel tubes and the possibility to induce elongation and contraction by means of a magnetic field gradient produced by an electromagnet have been demonstrated.
201 citations
TL;DR: Gels formed by cross-linking functionalized poly(ethylene glycol) (PEG) and a lysine-containing polypeptide through the action of a natural tissue enzyme, transglutaminase hold potential for forming highly hydrated networks around living cells.
Abstract: We demonstrate formation of a hydrogel network by cross-linking functionalized poly(ethylene glycol) (PEG) and a lysine-containing polypeptide through the action of a natural tissue enzyme, transglutaminase. The enzyme reaction rate using a PEG-modified peptide substrate is the same as the reaction rate for free substrate. Both the ratio and total concentration of the two macromers determine whether gelation will occur and the nature of the gel which forms. Under suitable conditions, clear gels form and swell to give a final composition which is 90% water. Diffusion coefficients of small proteins and albumin in the gel are comparable to those in free solution. Gelation proceeds under mild conditions and thus these gels hold potential for forming highly hydrated networks around living cells.
186 citations
TL;DR: It was concluded that a gel composition and an applied stimuli (T, pH, pH/T), determined the gel swelling/deswelling kinetics and the release profiles.
TL;DR: The possibility that the glucose-sensitive phase-reversible hydrogels can be used to regulate the insulin release as a function of the free glucose concentration in the environment is demonstrated.
Patent•
30 Jun 1997
TL;DR: Shaped medical devices, e.g. stents, having improved mechanical properties and structural integrity are disclosed in this paper, which are composed of shaped polymeric hydrogels which are both ionically and non-ionically cross-linked and which exhibit improved structural integrity after selective removal of the cross-linking ions.
Abstract: Shaped medical devices, e.g. stents, having improved mechanical properties and structural integrity are disclosed. The devices commprise shaped polymeric hydrogels which are both ionically and non-ionically cross-linked and which exhibit improved structural integrity after selective removal of the cross-linking ions. Process for making such devices are also disclosed wherein an ionically cross-linkable polymer is both ionically and non-ionically crosslinked to form a shaped medical device. When implanted in the body, selective in-vivo stripping of the cross-linking ions produces a softer, more flexible implant having improved structural integrity.
TL;DR: It was shown by FTIR analysis that by a proper selection of the polymerization conditions, hydrogels could be obtained in which more than 95% of the methacrylate groups had reacted within 20 min and was dependent on the amount of dextranase in the gel.
TL;DR: In this article, a semi-interpenetrating polymer network (semi-IPN) composed of crosslinked chitosan with glutaraldehyde and silk fibroin was prepared.
Abstract: A novel natural polymer blend, namely, a semi-interpenetrating polymer network (semi-IPN) composed of crosslinked chitosan with glutaraldehyde and silk fibroin was prepared. The FTIR spectra of the semi-IPN manifested that the chitosan and silk fibroin had a strong hydrogen-bond interaction and formed an interpolymer complex. The semi-IPN showed good pH sensitivity and ion sensitivity. According to the different swelling ratios of the semi-IPN in the buffer solution with different pH values or the AlCl3 aqueous solution with different concentrations, the semi-IPN could swell and shrink while being put alternately into different pH buffer solutions or AlCl3 aqueous with different concentrations. The semi-IPN could also act as an ''artificial muscle'' because its swelling-shrinking behavior exhibited a fine reversibility. q 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2257-2262, 1997
TL;DR: The gelatin hydrogel is a promising matrix for effective induction of biological activity of bFGF for bone regeneration in skull and sinus defects and does not interfere with bone regeneration at the skull defect because of their disappearance during biodegradation.
Abstract: Biodegradable gelatin hydrogels incorporating basic fibroblast growth factor (bFGF) were evaluated for their efficacy in bone regeneration using a rabbit model. Hydrogels with water contents of 85% and 98% were prepared using chemical crosslinking of gelatin with an isoelectric point of 4.9 in aqueous solution and, after freeze drying, were impregnated with an aqueous solution of bFGF to obtain bFGF-incorporated gelatin hydrogels. When they were implanted into bone defects measuring 6 mm in diameter in rabbit skulls (six animals/group), complete closure of the defect was observed at 12 weeks after implantation, regardless of the water content of the hydrogels. In contrast, bFGF did not enhance bone regeneration when applied to the skull defect in solution with phosphate-buffered saline (PBS). Also, gelatin hydrogels lacking bFGF were not effective in inducing bone formation, with fibrous tissue growing into the defect instead, similar to the skull defect seen in control rabbits treated with PBS. This indicates that the presence of hydrogels did not interfere with bone regeneration at the skull defect, probably because of their disappearance during biodegradation. It is concluded that the gelatin hydrogel is a promising matrix for effective induction of biological activity of bFGF for bone regeneration in skull and sinus defects.
01 Jan 1997
TL;DR: In this paper, surface modification of polyurethaneureas via Oligomeric end groups Incorporated During Synthesis is discussed, and a Reactive Surface with Stimuli-Sensitivity toward Temperature and pH is presented.
Abstract: Surface Modification of Polymers for Biomedical Applications: Chemical, Biological, and Surface Analytical Challenges.- A Creation of an Intelligent Surface - The Design of a Reactive Surface with Stimuli-Sensitivity toward Temperature and pH.- In Situ Surface Modification of Contact Lens Polymers.- Surface Modification of Segmented Polyurethaneureas via Oligomeric End Groups Incorporated During Synthesis.- XPS and SSIMS Characterization of Surfaces Modified by Plasma Deposited Oligo(glyme) Films.- Deposition of Fluorocarbon Films by Remote RF Glow Discharges.- Plasma Copolymerization of Tetrafluoroethylene and Chlorotrifluoroethylene.- Preparation of Plasma Polymerized Tetramethylhydrocyclotetrasiloxane Membrane on Microporous Hollow Fibers.- Plasma Treatments of Polymers by NH3-H2 RF Glow Discharges: Coupling Plasma and Surface Diagnostics.- Surface Characterization of Fiber-Supported Hydrogels.- XPS Analysis of Plasma-Treated Silicone Rubber.- Assaying for Primary Amines on Modified Polymer Surfaces Using TIRF Spectoscopy.- Surface Tension Analysis of PBT and PET Fibre-Based Leukodepletion Filters.- The Self-Assembly and Inhibition of Protein Adsorption by Thiolated Dextran Monolayers at Hydrophobic Metal Surfaces.- Hydrolysis of a Neutral Hydrogel and Biomolecule Attachment to Increase Cell Adhesion and Migration.- Surface Attachment of Functional Peptides by Electrochemical Polymerization.- Covalently Attached Thin Coatings Comprising Saccaride and Alkylene Oxide Segments.- Heparin Immobilization onto Sol-Gel Derived Organic-Inorganic Hybrid Network.- Covalent Surface Attachment of Polysaccharides via Bifunctional Epoxides.- Thermal Recovery of Cells Cultured on Poly(N-Isopropylacrylamide) Surface-Grafted Polystyrene Dishes.- Grafting of PEO via the Williamson Ether Synthesis onto Polymeric Surfaces and Their Affinity for Proteins.- Four Protein-Friendly Approaches to Polymer Surface Metallization Using Monolayers of Gold Nanoparticles.- Contributors.
TL;DR: Results showed that increasing the NIPAAm concentration in the copolymers or terpolymers resulted in a higher degree of temperature-sensitive swelling, and synthesis of a terpolymer in which segments rich in N-isopropylacrylamide were distributed within P(AA-co-HEMA) chains led to hydrogels displaying increased temperature sensitivity.
Abstract: Controlled release devices were designed which respond to changes in pH and temperature by reversibly swelling and deswelling to control release of streptokinase. Copolymer hydrogels composed of N-isopropylacrylamide (NIPAAm) and methacrylic acid (MAA) as well as terpolymer hydrogels containing NIPAAm, acrylic acid (AA), and 2-hydroxyethyl methacrylate (HEMA) were synthesized. Hydrogels containing NIPAAm display a change in swelling behavior across the lower critical solubility temperature of PNIPAAm, whereas hydrogels with MAA and AA swelled only at high pH values due to the ionization of carboxylic pendant groups. HEMA was chosen as a third component to add mechanical strength and integrity to the hydrogel. Pulsatile pH- and temperature-dependent swelling studies were performed to determine the extent and rate at which the hydrogels swell in response to changing conditions. Results showed that increasing the NIPAAm concentration in the copolymers or terpolymers resulted in a higher degree of temperature...
TL;DR: It appears that hydrogels synthesized by a polymer-polymer reaction degraded at a slightly faster rate than their analogues synthesizing by cross-linking of polymeric precursors, which was compared with those of a linear azopolymer and a low-molecular-weight azosubstrate respectively.
TL;DR: The water content of these polyvinyl alcohol (PVA) hydrogels was studied as a function of polymer molecular weight, the acetate, (meth)acrylate, and methacrylamide contents and irradiation conditions as mentioned in this paper.
Abstract: Poly(vinyl alcohol) (PVA) was partially modified by polymer analogous reaction with acrylic and methacrylic acid and with 2-vinyl-4,4-dimethyl-azlactone to obtain water-soluble polymers with pendant (meth)acrylate and acrylamide groups. Aqueous solutions of these polymers were crosslinked by UV-irradiation within seconds to form transparent networks with potential for use in contact lenses. The water content of these hydrogels was studied as a function of polymer molecular weight, the acetate, (meth)acrylate, and methacrylamide contents and irradiation conditions. The hydrogels showed good mechanical properties, even at low crosslinker (<5 mol %) and high water contents (60–80%). The formation kinetics and stability of aggregates, investigated by combined GPC/light-scattering measurements of samples annealed and/or stored at different temperatures (−20 to 100°C), give insight into PVA secondary structures. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3603–3611, 1997
TL;DR: Bulk diffusion of linear polymers such as PEG (adhesion promoter) incorporated into polymer networks (hydrogels) was an effective technique for enhancing gel/gel adhesion in various applications including polymer/mucus interactions in mucoadhesion and development of muco adhesion controlled drug delivery systems.
Abstract: The fracture energy required to separate layers of hydrogel films was investigated to evaluate the impact of bulk polymer diffusion on hydrogel/hydrogel adhesion and to obtain molecular information on the fracture energy in polymer mucoadhesion. Poly(ethylene glycol) (PEG) was incorporated in a hydrogel and was used as an adhesion promoter. The influence of PEG molecular weight and contact time on PEG diffusion across the hydrogel/hydrogel interface was investigated by using tensiometric studies and near-field FTIR microscopy. These experiments indicated that linear PEG diffusion enhanced the adhesion between the two hydrogel layers. The enhanced adhesion could not be explained by surface wetting phenomena alone. These results indicated that bulk diffusion of linear polymers such as PEG (adhesion promoter) incorporated into polymer networks (hydrogels) was an effective technique for enhancing gel/gel adhesion in various applications including polymer/mucus interactions in mucoadhesion and development of mucoadhesive controlled drug delivery systems.
TL;DR: In this article, the mechanical properties of bio-artificial materials prepared using poly(vinyl alcohol), poly(acrylic acid) (PAA) as synthetic components, and collagen (SC), gelatin, starch, hyaluronic acid (HA) and dextran as biological components, were investigated by dynamic mechanical thermal analysis.
Abstract: Bioartificial polymeric materials represent a new class of polymeric materials based on blends of synthetic and natural polymers, designed with the purpose of producing new materials with enhanced properties with respect to the single components. The mechanical properties of bioartificial materials prepared using poly(vinyl alcohol) (PVA), poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA) as synthetic components, and collagen (SC), gelatin, starch, hyaluronic acid (HA) and dextran as biological components, were investigated by dynamic mechanical thermal analysis. The materials were prepared in the form of films or hydrogels and treated by glutaraldehyde (GTA) vapour or thermal dehydration in order to reduce their solubility in water. The results indicate that SC/PVA, gelatin/PVA and starch/PVA films behave as biphasic systems, showing good mechanical properties over a wide range of temperature. It was observed that the GTA procedure affects only the biological component of the SC/PVA and gelatin/PVA blends, whilst the thermal treatment influences mainly the synthetic polymer. In the case of HA/PVA hydrogels, a modulus variation was found with the HA content related to the organization degree and perfection of the PVA network structure. It seems evident that, in the experimental conditions used, dextran/PAA mixtures behave as miscible blends showing a glass transition intermediate between those of the pure components. With both untreated and GTA-treated gelatin/PMAA blends, it was not possible to evaluate the miscibility of the systems; it could only be affirmed that these materials show good mechanical properties over a wide range of temperature. © 1997 SCI.
TL;DR: In this paper, a temperature and pH-responsive drug delivery system was studied by using interpenetrating polymer network (IPN) hydrogels constructed with poly(acrylic acid) (PAAc) and poly(vinyl alcohol)(PVA), which showed pulsatile patterns in response to both pH and temperature.
Abstract: A temperature- and pH-responsive drug delivery system was studied by using interpenetrating polymer network (IPN) hydrogels constructed with poly(acrylic acid) (PAAc) and poly(vinyl alcohol) (PVA). The release of indomethacin incorporated into these hydrogels showed pulsatile patterns in response to both pH and temperature. Indomethacin diffused from the polymer matrices through the swelling and deswelling mechanism. The release amount increased at higher temperature because of the swelling caused by the dissociation of hydrogen bonding. The drastic change of drug release was achieved by alternating pH of the buffer solution and was attributed to the change of states of ionic groups within IPN hydrogels. The free water contents were calculated by using differential scanning calorimetry (DSC), and were proved to be the main factor in the swelling. These results demonstrated that the drug release could be controlled by the swelling/deswelling degree of IPN hydrogels as functions of pH and/or temperature. © 1997 John Wiley & Sons, Inc. J Appl Polm Sci 65: 685–693
TL;DR: In this article, the authors used free radical polymerization in aqueous solution of N-isopropylacrylamide (NIPA) and of NIPA with acrylic acid (AA), methacrylic acid (MAA), and 2-methyl-2-acryl-propanesulfonic acid (AMPS) as comonomers.
TL;DR: In this article, a polyvinyl alcohol (PVA) aqueous solution and thawing it slowly has high water content, excellent mechanical properties of high tensile strength, elongation and good shape recovery by elasticity.
Abstract: The hydrogel synthesized by freezing a polyvinyl alcohol (PVA) aqueous solution and thawing it slowly has high water content, excellent mechanical properties of high tensile strength, elongation and good shape recovery by elasticity. The PVA used had a degree of polymerization of 2500 and a degree of saponification of 99.5 mol%. The solution was obtained by dissolving 7.5 g of PVA in 80 g of water, this was frozen at −50°C for 3 h and then warmed up to room temperature over 10h. This freezing–thawing process was repeated once again and a hydrogel was synthesized. The hydrogel had a water content of about 90 wt%. Its tensile strength was 0.6 MPa and the elongation at break was 130%. The shape of the hydrogel which was deformed by an external force recovered in a short time when it was released from the force. This recovery had good persistence and repeatability. Applying these properties a strain sensor and a gas pressure sensor were tested. Furthermore, a PVA hydrogel rod containing polyacrylic acid was used as a bending actuator. This hydrogel had the ability to deform when direct current was applied.
Patent•
15 Jan 1997
TL;DR: In this article, the subject copolymers comprised polyacrylamide backbones, where a portion of the acrylamides monomeric units comprised hydrogen bonding groups as N-substituents.
Abstract: Thermoreversible hydrogels comprising non-ionic, linear copolymers, and methods of their use in electrophoresis, are provided. The subject copolymers comprise polyacrylamide backbones, where a portion of the acrylamide monomeric units comprise hydrogen bonding groups as N-substituents. Combination of the subject copolymers with an aqueous phase provides thermoreversible hydrogels which find use as separation media in electrophoretic applications.
TL;DR: In this paper, a copolymerization reaction of poly(2-hydroxyethyl methacrylate) with 2-ethylhexyl acrylate, E, using AIBN as initiator was studied.
Abstract: Acrylic hydrogels based on 2-hydroxyethyl methacrylate, H, have been synthesized by copolymerization reaction of this monomer with 2-ethylhexyl acrylate, E, using AIBN as initiator. Reactivity ratios were estimated from copolymerization reactions carried out in solution and at low conversion, by using both linearization and nonlinearization methods. They were found to be rE = 0.29 and rH = 2.54. The swelling behavior of the hydrogels was studied by immersion of copolymer films prepared by bulk copolymerization, in water at different temperatures. Equilibrium water uptake was strongly dependent on composition and decreased with the E content in the copolymer. Fickian behavior was observed in all cases for reduced sorption coefficients lower than 0.4. The diffusion coefficient was found to decrease with increasing E content in the copolymer. A value of apparent activation energy for the diffusion process of 8.8 kJ/mol was obtained for poly(2-hydroxyethyl methacrylate); however, H/E copolymers did not obey t...
TL;DR: Enzymatically-degrading dextran hydrogels were investigated as matrices for the delayed release of proteins and the release of a model protein (IgG) was studied as a function of several factors including the concentration of deXTranase, the initial water content of the gel and the degree of GMA substitution determining the crosslink density of the Gel.
TL;DR: In this paper, it was found that the rate of gelation depends on the molecular weight and on the degree of oxidation of dextran, the type of gelatin and the reaction conditions.
Abstract: Hydrogels were prepared by reaction of gelatin with partial periodate oxidized dextran. It was found that the rate of gelation depends on the molecular weight and on the degree of oxidation of dextran, the type of gelatin and on the reaction conditions. Rheological measurements demonstrate that the gel strength is governed by two factors: chemical crosslinking by reaction with polyaldehyde and physical structuring of the gelatin. By proper selection of the reaction conditions, in particular storage temperature, the contribution of both processes to the final material strength can be varied. It was observed that short cryogenic treatment significantly enhances the chemical crosslinking.
Patent•
28 Oct 1997
TL;DR: In this article, a composition providing electrically conductive adhesive hydrogels used as skin contact adhesives and an electrical interface for disposable medical devices is presented, which are formed by free radical polymerization in the presence of water by ultraviolet curing with initiator and multifunctional cross-linking agent.
Abstract: A composition providing electrically conductive adhesive hydrogels used as skin contact adhesives and an electrical interface for disposable medical devices. The hydrogels are cationic acrylates and are made from acrylic esters of quaternary chlorides and/or sulfates or acrylic amides of quaternary chlorides. The present hydrogels are formed by free radical polymerization in the presence of water by ultraviolet curing with initiator and multifunctional cross-linking agent, and include a buffer system to prevent discoloration, hydrolysis of and improve shelf-life of the hydrogels. Other additives may be added to the hydrogels either before or after curing, depending on the intended end use. The present hydrogels hydrate a subject's skin, wet around skin surface hair and protect against burning of a subject due to electrical stimulation through the hydrogel. The hydrogels, cohesiveness enables direct hydrogel-to-hydrogel contact and storage, yet remain readily separable. The hydrogels may be presented in a formula which is noncorrosive to aluminum in contact therewith, and pass standards testing for biocompatibility and electrical properties.