Showing papers on "Self-healing hydrogels published in 2001"
4,511 citations
TL;DR: Development of environmentally sensitive hydrogels with a wide array of desirable properties can be made is a formidable challenge, however, if the achievements of the past can be extrapolated into the future, it is highly likely that responsive hydrogelWith such properties can been made.
4,216 citations
TL;DR: These results demonstrated how alginate gel and gel/cell systems could be formulated with controlled structure, gelation rate, and mechanical properties for tissue engineering and other biomedical applications.
1,350 citations
1,014 citations
TL;DR: The biological activities of these materials can be tailored to meet the requirements of a given tissue engineering application by creating a mixture of various bioactive PEG derivatives prior to photopolymerization.
699 citations
TL;DR: A review of patents and literature reveals an evolution in materials technologies driven by an increased understanding of the physiological needs of the cornea, beginning with the first hydrogel lenses developed by Wichterle, followed by a variety of high water hydrogels.
675 citations
TL;DR: The use of these degradable alginate‐derived hydrogels greatly improved cartilage‐like tissue formation in vivo, as compared toAlginate hydrogel, which degraded with a rate depending on the pH and temperature of the solution.
Abstract: Alginate has been widely used in a variety of biomedical applications including drug delivery and cell transplantation. However, alginate itself has a very slow degradation rate, and its gels degrade in an uncontrollable manner, releasing high molecular weight strands that may have difficulty being cleared from the body. We hypothesized that the periodate oxidation of alginate, which cleaves the carbon-carbon bond of the cis-diol group in the uronate residue and alters the chain conformation, would result in promoting the hydrolysis of alginate in aqueous solutions. Alginate, oxidized to a low extent (approximately 5%), degraded with a rate depending on the pH and temperature of the solution. This polymer was still capable of being ionically cross-linked with calcium ions to form gels, which degraded within 9 days in PBS solution. Finally, the use of these degradable alginate-derived hydrogels greatly improved cartilage-like tissue formation in vivo, as compared to alginate hydrogels.
605 citations
TL;DR: The compressive tangent modulus varied with biomaterial formulation and was found to be statistically strain magnitude and rate dependent and shear mechanical properties of a novel PVA hydrogel were characterized.
600 citations
TL;DR: Findings demonstrate that biomaterials may be designed to control bone development from transplanted cells, as well as demonstrate that adhesion ligands covalently coupled to hydrogel carriers would allow one to control pre-osteoblast cell attachment, proliferation, and differentiation.
Abstract: There is significant interest in the development of injectable carriers for cell transplantation to engineer bony tissues. In this study, we hypothesized that adhesion ligands covalently coupled to hydrogel carriers would allow one to control pre-osteoblast cell attachment, proliferation, and differentiation. Modification of alginate with an RGDcontaining peptide promoted osteoblast adhesion and spreading, whereas minimal cell adhesion was observed on unmodified hydrogels. Raising the adhesion ligand density increased osteoblast proliferation, and a minimum ligand density (1.5-15 femtomoles/cm2) was needed to elicit this effect. MC3T3-E1 cells demonstrated increased osteoblast differentiation with the peptide-modified hydrogels, as confirmed by the up-regulation of bone-specific differentiation markers. Further, transplantation of primary rat calvarial osteoblasts revealed statistically significant increases of in vivo bone formation at 16 and 24 weeks with G4RGDY-modified alginate compared with unmodifie...
544 citations
TL;DR: The existence of an ion-mediated response breaks the long-held paradigm of the xylem as a system of inert pipes and suggests a mechanism by which plants may regulate their internal flow regime.
Abstract: Increasing concentrations of ions flowing through the xylem of plants produce rapid, substantial, and reversible decreases in hydraulic resistance. Changes in hydraulic resistance in response to solution ion concentration, pH, and nonpolar solvents are consistent with this process being mediated by hydrogels. The effect is localized to intervessel bordered pits, suggesting that microchannels in the pit membranes are altered by the swelling and deswelling of pectins, which are known hydrogels. The existence of an ion-mediated response breaks the long-held paradigm of the xylem as a system of inert pipes and suggests a mechanism by which plants may regulate their internal flow regime.
499 citations
TL;DR: Two photocrosslinkable polysaccharides composed of alginate and hyaluronan are described that upon photolysis form soft, flexible, and viscoelastic hydrogels that are relevant for biomedical applications such as sealing wounds and reconstructing soft tissues.
Abstract: In situ photopolymerization is an exciting new technique for tissue engineering. Two photocrosslinkable polysaccharides composed of alginate and hyaluronan are described that upon photolysis form soft, flexible, and viscoelastic hydrogels. The degree of methacrylate modification and thus covalent affects mechanical properties such as swelling, compression, and creep compliance. Significant swelling is observed in aqueous solution; these hydrogels can swell up to 14 times their dry weight. Both hydrogels exhibit low phase angles and (G*) values indicative of viscoelastic materials. The hyaluronan based hydrogel is stronger and more resilient than the corresponding alginate gel. SEM and AFM studies on both hydrogels show smooth and uniform surfaces at the macroscopic level with salient features observed only on the nanometer scale. Rapid polymerization by an optical trigger allows for controlled in situ photopolymerization in a minimally invasive manner, indicating that these hydrogels are relevant for biomedical applications such as sealing wounds and reconstructing soft tissues.
TL;DR: Three-dimensional, cross-linked PEG hydrogel microstructures were immobilized on the surface and changes in fluorescence were also observed for immobilized fluorophore labeled acetylcholine esterase upon the addition of acetyl acholine.
Abstract: The fabrication of hydrogel microstructures based upon poly(ethylene glycol) diacrylates, dimethacrylates, and tetraacrylates patterned photolithographically on silicon or glass substrates is described. A silicon/silicon dioxide surface was treated with 3-(trichlorosilyl)propyl methacrylate to form a self-assembled monolayer (SAM) with pendant acrylate groups. The SAM presence on the surface was verified using ellipsometry and time-of-flight secondary ion mass spectrometry. A solution containing an acrylated or methacrylated poly(ethylene glycol) derivative and a photoinitiator (2,2-dimethoxy-2-phenylacetophenone) was spin-coated onto the treated substrate, exposed to 365 nm ultraviolet light through a photomask, and developed with either toluene, water, or supercritical CO2. As a result of this process, three-dimensional, cross-linked PEG hydrogel microstructures were immobilized on the surface. Diameters of cylindrical array members were varied from 600 to 7 micrometers by the use of different photomasks, while height varied from 3 to 12 micrometers, depending on the molecular weight of the PEG macromer. In the case of 7 micrometers diameter elements, as many as 400 elements were reproducibly generated in a 1 mm2 square pattern. The resultant hydrogel patterns were hydrated for as long as 3 weeks without delamination from the substrate. In addition, micropatterning of different molecular weights of PEG was demonstrated. Arrays of hydrogel disks containing an immobilized protein conjugated to a pH sensitive fluorophore were also prepared. The pH sensitivity of the gel-immobilized dye was similar to that in an aqueous buffer, and no leaching of the dye-labeled protein from the hydrogel microstructure was observed over a 1 week period. Changes in fluorescence were also observed for immobilized fluorophore labeled acetylcholine esterase upon the addition of acetyl acholine.
TL;DR: Highly crosslinked hydrogel spheres were fabricated using UV photopolymerization of poly(ethylene glycol) diacrylate and pentaerythritol triacylate with 2,2'-dimethoxy-2-phenyl-acetophenone (DMPA) as the photoinitiator to simulate delivery of a model protein drug.
TL;DR: A new chemical cross-linking scheme was utilized for the formation of degradable poly(ethylene glycol) hydrogels suitable for the delivery of protein drugs, and it was observed that about 65% of the incorporated protein was released with zero-order kinetics over a period of about 4 days.
TL;DR: Findings indicate that the growth factor immobilized to the acidic gelatin hydrogel through ionic interaction was released in vivo as a result of hydrogels degradation.
Abstract: To develop a carrier for the controlled release of biologically-active growth factors, biodegradable hydrogels were prepared through glutaraldehyde cross-linking of gelatin with isoelectric points (IEP) of 5.0 and 9.0, i.e. 'acidic' and 'basic' gelatins, respectively. Radioiodinated growth factors were used to investigate their sorption and desorption from the hydrogel of both types of gelatin. Basic fibroblast growth factor (bFGF) and transforming growth factor-beta1 (TGF-beta1) were well sorbed with time to the acidic gelatin hydrogel, while less sorption was observed for the basic gelatin hydrogel. This could be explained in terms of the electrostatic interaction between the growth factors and the acidic gelatin. However, bone morphogenetic protein-2 (BMP-2) and vascular endothelial growth factor (VEGF), though their IEPs are higher than 7.0, were sorbed to the acidic gelatin hydrogel to a smaller extent than the two other growth factors. Under in vitro non-degradation conditions, approximately 20% of the incorporated bFGF and TGF-beta1 was desorbed from the hydrogels within the initial 40 min, followed by no further substantial desorption, whereas large initial desorption was observed for BMP-2 and VEGF. When implanted in the back subcutis of mice, gelatin hydrogels were degraded over time. Each growth factor was retained in vivo being incorporated in the acidic gelatin hydrogel: the smaller the in vitro desorption amount from the hydrogel, the longer the in vivo retention time. The in vivo profile of bFGF and TGF-beta1 retention was in good accordance with that of the hydrogel. These findings indicate that the growth factor immobilized to the acidic gelatin hydrogel through ionic interaction was released in vivo as a result of hydrogel degradation.
TL;DR: In this paper, a macroporous temperature-sensitive poly(N-isopropylacrylamide) (PNIPAAm) hydrogels have been successfully synthesized by using poly(ethylene glycol) (PEG) as the pore-forming agent.
Abstract: Macroporous temperature-sensitive poly(N-isopropylacrylamide) (PNIPAAm) hydrogels have been successfully synthesized by using poly(ethylene glycol) (PEG) as the pore-forming agent. Scanning electron microscope graphs reveal that the macroporous network structure of the hydrogels can be adjusted by applying different molecular weights of PEG during the polymerization reaction. The surface roughness of the hydrogels is also investigated using atomic force microscopy, and the results indicate that the surface of the PEG-modified gel is much rougher compared to that of the conventional PNIPAAm gel. The newly invented macroporous hydrogels exhibit much better properties as temperature-sensitive intelligent polymers. For instance, at a temperature below the lower critical solution temperature (LCST), they absorb larger amounts of water and show obviously higher equilibrated swelling ratios in the aqueous medium. Particularly, due to their unique macroporous structure, the PEG-modified hydrogels show a tremendou...
TL;DR: The results suggest that photocrosslinked hydrogels are promising scaffolds for tissue engineering cartilage as cell viability is readily maintained; uniform cell seeding is easy to achieve: and the biochemical content of the extracellular matrix is not compromised as the scaffold thickness is increased from 2 to 8 mm.
TL;DR: In conclusion, photoencapsulation of microspheres in PEO‐based hydrogels provides a method to deliver molecules such as growth factors in porous hydrogel systems to enhance the ability to engineer tissues.
TL;DR: By covalently attaching the important cell adhesion protein fibronectin onto the PVA hydrogel surface, the rate of fibroblast attachment and proliferation was dramatically improved, and promoted two-dimensional cell migration.
Abstract: Hydrogels have been used in biology and medicine for many years, and they possess many properties that make them advantageous for tissue engineering applications. Their high water content and tissue-like elasticity are similar to the native extracellular matrix of many tissues. In this work, we investigated the potential of a modified poly(vinyl alcohol) (PVA) hydrogel as a biomaterial for tissue engineering applications. First, the ability of NIH3T3 fibroblast cells to attach to PVA hydrogels was evaluated. Because of PVA's extremely hydrophilic nature, important cell adhesion proteins do not adsorb to PVA hydrogels, and consequently, cells are unable to adhere to the hydrogel. By covalently attaching the important cell adhesion protein fibronectin onto the PVA hydrogel surface, the rate of fibroblast attachment and proliferation was dramatically improved, and promoted two-dimensional cell migration. These studies illustrate that a fibronectin-modified PVA hydrogel is a potential biomaterial for tissue engineering applications.
Patent•
02 Feb 2001
TL;DR: In this article, a method for forming tissue-adherent hydrogels using substantially dry precursors is described. But the method is not suitable for the use of blood vessels.
Abstract: Compositions and methods are provided for forming tissue-adherent hydrogels using substantially dry precursors. The dehydrated precursors are premixed prior to in situ therapy and utilize naturally-occurring body fluids as an aqueous environment that initiates transformation, which causes dissolution and nearly simultaneous crosslinking of the precursors, thus forming an insoluble hydrogel implant. The dehydrated precursor-based hydrogels may be used as sealants for fluid leaks from tissue, as adherent drug delivery depots, as means for augmenting and/or supporting tissue, and as means for serving a variety of other useful medical and surgical purposes.
TL;DR: Comb-type graft hydrogels are composed of crosslinked alginate network and grafted with poly(N-isopropylacrylamide) (PNIPAAm) as mentioned in this paper.
TL;DR: These peptide-modified P(NIPAAm-co-AAc) hydrogels serve as useful tools for studying cell-material interactions within 3D structures and have the potential to be used as injectable scaffolds for tissue engineering applications.
TL;DR: In this article, the PVA/PVP blended hydrogel has a water content in the range between 60% and 80% and water absorption between 40% and 250% and the water vapor transmission rate value (WVTR) varies between 50 and 200 g/m2/h.
TL;DR: The results suggest that the core--shell architecture is a powerful one for the design of colloidal "smart gels" with tunable properties and the formation of a thin, stable skin layer at the particle exterior during the early stages of particle collapse is the rate limiting factor in particle deswelling.
Abstract: Thermoresponsive, core--shell poly-N-isopropylacrylamide (p-NIPAm) nanoparticles (microgels) have been synthesized by seed and feed precipitation polymerization, and the influence of chemical differentiation between the core and shell polymers on the phase transition kinetics and thermodynamics has been examined. The results suggest that the core--shell architecture is a powerful one for the design of colloidal "smart gels" with tunable properties. To examine these materials, differential scanning calorimetry (DSC), (1)H NMR, and temperature-programmed photon correlation spectroscopy (TP-PCS) have been employed. These measurements show that the addition of small concentrations of a hydrophobic monomer (butyl methacrylate, BMA) into the particle shell produces large decreases in the rate of thermo-induced particle collapse. Conversely, these low levels of hydrophobic modification do not perturb the thermodynamics of the particle phase transition. When these results are examined in light of previous studies of macroscopic hydrogels, they suggest that the formation of a thin, stable skin layer at the particle exterior during the early stages of particle collapse is the rate limiting factor in particle deswelling. Finally, the hydrophobicity (BMA content) of the shell determines the magnitude of the hydrogel collapse rate, while the thickness of the BMA containing region does not impact the observed kinetics. Together, these results suggest that control over the kinetics of microgel deswelling events can be accomplished simply by modification of the particle periphery, and therefore do not require homogeneous modification of the entire polymer structure.
TL;DR: In this paper, the state of the miscibility of the blend hydrogel films was examined over the entire composition range by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA).
TL;DR: In this paper, the properties of semi-IPNIPN hydrogels with poly(N-isopropylacrylamide) (PNIPAAm) chains were studied at several temperatures.
Abstract: Hydrogels of a semiinterpenetrated polymer network, semi-IPN [based on cross-linked polyacrylamide (PAAm) having poly(N-isopropylacrylamide) (PNIPAAm) inside], were synthesized, and their properties, such as swelling ratio and compressing elastic moduli, were studied at several temperatures. Equilibrium swelling ratios of semi-IPN markedly decreased due to the presence of less hydrophilic PNIPAAm chains. The semi-IPN presented a greater elastic modulus when compared to the cross-linked PAAm hydrogel. The values of apparent cross-linking density were determined from the mechanical compression measurements, made at temperatures that ranged from 25 to 40 °C. The presence of PNIPAAm chains on the network increases the polymer volume fraction of the swollen gel. At 25 °C the effect induces the formation of physical entanglements, increasing the apparent cross-linking density and then enlarging the compressing elastic modulus. Above 32 °C, the LCST of PNIPAAm in water, semi-IPN hydrogels presented higher values...
TL;DR: This system takes advantage of stimuli-responsive release of encapsulated salts from liposomes to trigger the self-assembly of a 16amino acid peptide, and shows that the induction of self- assembly by gentle warming or by exposure to near-infrared light results in rapid gelation of peptide/liposome suspensions into highly cross-linked, fibrillar,â-sheet hydrogels.
Abstract: Self-assembling systems present attractive platforms for engineering stimulus-responsive materials with controlled nanoand microstructures. Recent efforts to design such systems include synthetic block copolymers, 1a proteins that self-assemble into hydrogels via leucine zipper motifs, 1b cyclic peptides that selfassemble into nanotubes, 1c-e and peptides that form fibrillar â-sheet networks. 1f-i Here we demonstrate systems that selfassemble from fluid precursors into highly cross-linked peptide hydrogels in response to thermal or photochemical triggering. Our system takes advantage of stimuli-responsive release of encapsulated salts from liposomes to trigger the self-assembly of a 16amino acid peptide. We show that the induction of self-assembly by gentle warming or by exposure to near-infrared light results in rapid gelation of peptide/liposome suspensions into highly cross-linked, fibrillar,â-sheet hydrogels. The ability to trigger rapid sol -gel transformations of peptide solutions via physiologically benign stimuli (temperature, light) may lead to the development of new injectable materials for drug delivery, wound healing, and tissue engineering applications. The 16-amino acid peptide consists of alternating hydrophobic and hydrophilic residues: H 2N-(FEFEFKFK)2-COOH, (FEK16). We chose to investigate FEK16 because several related peptides with alternating hydrophobic -hydrophilic residues are known to self-assemble intoâ-sheet structures, often in an ionic-strengthdependent manner. 1f,2 â-sheet structure is favored by the strictly alternating hydrophobic -hydrophilic primary structure of the peptide, which positions all hydrophobic side chains on one side of theâ-sheet and all hydrophilic side chains on the other. 3 Saltinduced self-assembly of this peptide may be driven by the shielding of electrostatic repulsive forces with increasing ion concentrations, allowing attractive hydrophobic and van der Waals forces to dominate. 2d
Patent•
22 Mar 2001TL;DR: In this paper, a wettable silicone hydrogel made by including a high molecular weight hydrophilic polymer into the mixture of the silicone monomer mix is presented, which is entrapped in the hydrogels with little or no covalent bonding between it and the matrix.
Abstract: A wettable silicone hydrogel made by including a high molecular weight hydrophilic polymer into the silicone hydrogel monomer mix is presented. The hydrophilic polymer is entrapped in the hydrogel with little or no covalent bonding between it and the hydrogel matrix.
TL;DR: Importantly, the proteins were quantitatively released from the gels and with full preservation of the enzymatic activity of lysozyme, emphasizing the protein-friendly preparation method of theprotein-loaded stereocomplex hydrogel.