Showing papers on "Self-healing hydrogels published in 2002"
TL;DR: The composition and synthesis of hydrogels, the character of their absorbed water, and permeation of solutes within their swollen matrices are reviewed to identify the most important properties relevant to their biomedical applications.
5,173 citations
TL;DR: It is timely to summarize the polymeric systems that undergo sol-gel transitions, particularly due to temperature, with emphasis on the underlying transition mechanisms and potential delivery aspects.
2,048 citations
TL;DR: In this overview, different chemical and physical crosslinking methods used for the design of biodegradable hydrogels are summarized and discussed.
1,674 citations
TL;DR: This review highlights the use of hydrogels (a class of polymeric systems) in controlled drug delivery, and their application in stimuli- responsive, especially pH-responsive, drug release.
1,593 citations
TL;DR: Advantages of photopolymerization of hydrogels are presented, the photoinitiators and materials in current use are described and the applications that have been investigated are summarized.
1,591 citations
TL;DR: The biomolecule-sensitive hydrogels reviewed in this paper are expected to contribute significantly to the exploration and development of newer generations of intelligent biomaterials and self-regulated drug delivery systems.
1,278 citations
TL;DR: The focus of this article is to review molecular imprinting within hydrogels and discuss recent efforts on analyte-responsive intelligent gels, specifically suggesting the possibility of utilizing molecular imprinted strategies to impart analyte specificity and responsiveness within these systems.
1,111 citations
TL;DR: Poly(ethylene glycol) (PEG) hydrogels were investigated as encapsulation matrices for osteoblasts to assess their applicability in promoting bone tissue engineering and a concentration dependence of RGD groups was observed, with increased osteoblast attachment and spreading with higher RGD concentrations.
1,018 citations
TL;DR: With the incorporation of degradable linkages into the network, gel properties with an initially high K (350 kPa) and final high q (7.9) were obtained, which allowed for increased type II collagen synthesis coupled with a homogenous distribution of GAGs.
Abstract: When using hydrogel scaffolds for cartilage tissue engineering, two gel properties are particularly important: the equilibrium water content (q, equilibrium swelling ratio) and the compressive modulus, K. In this work, chondrocytes were photoencapsulated in degrading and nondegrading poly(ethylene glycol)-based hydrogels to assess extracellular matrix (ECM) formation as a function of these gel properties. In nondegrading gels, the glycosaminoglycan (GAG) content was not significantly different in gels when q was varied from 4.2 to 9.3 after 2 and 4 weeks in vitro. However, gels with a q of 9.3 allowed GAGs to diffuse throughout the gels homogenously, but a q < or = 5.2 resulted in localization of GAGs pericellularly. Interestingly, in the moderately crosslinked gels with a K of 360 kPa, an increase in type II collagen synthesis was observed compared with gels with a higher (960 kPa) and lower (30 kPa) K after 4 weeks. With the incorporation of degradable linkages into the network, gel properties with an initially high K (350 kPa) and final high q (7.9) were obtained, which allowed for increased type II collagen synthesis coupled with a homogenous distribution of GAGs. Thus, a critical balance exists between gel swelling, mechanics, and degradation in forming a functional ECM.
843 citations
TL;DR: Characterization of the gelation process, from the molecular level up through the macroscopic properties of the material, suggests that by linking the intramolecular folding of small designed peptides to their ability to self-assemble, responsive materials can be prepared.
Abstract: A general peptide design is presented that links the pH-dependent intramolecular folding of β-hairpin peptides to their propensity to self-assemble, affording hydrogels rich in β-sheet. Chemical responsiveness has been specifically engineered into the material by linking intramolecular folding to changes in solution pH, and mechanical responsiveness, by linking hydrogelation to self-assembly. Circular dichroic and infrared spectroscopies show that at low pH individual peptides are unstructured, affording a low-viscosity aqueous solution. Under basic conditions, intramolecular folding takes place, affording amphiphilic β-hairpins that intermolecularly self-assemble. Rheology shows that the resulting hydrogel is rigid but is shear-thinning. However, quick mechanical strength recovery after cessation of shear is observed due to the inherent self-assembled nature of the scaffold. Characterization of the gelation process, from the molecular level up through the macroscopic properties of the material, suggests ...
812 citations
TL;DR: Diblock copolypeptide amphiphiles containing charged and hydrophobic segments are synthesized and shape-specific supramolecular assembly is integral to the gelation process, and provides a new class of peptide-based hydrogels with potential for applications in biotechnology.
Abstract: Protein-based hydrogels are used for many applications, ranging from food and cosmetic thickeners to support matrices for drug delivery and tissue replacement. These materials are usually prepared using proteins extracted from natural sources, which can give rise to inconsistent properties unsuitable for medical applications. Recent developments have utilized recombinant DNA methods to prepare artificial protein hydrogels with specific association mechanisms and responsiveness to various stimuli. Here we synthesize diblock copolypeptide amphiphiles containing charged and hydrophobic segments. Dilute solutions of these copolypeptides would be expected to form micelles; instead, they form hydrogels that retain their mechanical strength up to temperatures of about 90 degrees C and recover rapidly after stress. The use of synthetic materials permits adjustment of copolymer chain length and composition, which we varied to study their effect on hydrogel formation and properties. We find that gelation depends not only on the amphiphilic nature of the polypeptides, but also on chain conformations--alpha-helix, beta-strand or random coil. Indeed, shape-specific supramolecular assembly is integral to the gelation process, and provides a new class of peptide-based hydrogels with potential for applications in biotechnology.
TL;DR: For two different types of poly(N-isopropylacrylamide) (PNIPA) hydrogels, the effects of crosslinker contents on various physical properties were investigated in this article.
Abstract: For two different types of poly(N-isopropylacrylamide) (PNIPA) hydrogels, i.e., nanocomposite type PNIPA hydrogels (NC gel) and conventional chemically cross-linked PNIPA hydrogels (OR gel), the effects of cross-linker contents on various physical properties were investigated. In NC gels composed of a unique organic (PNIPA)/inorganic (clay) network, the inorganic clay acts as a multifunctional cross-linker in place of an organic cross-linker (BIS) as used in OR gels. In NC gels, which generally exhibit extraordinary mechanical toughness, the tensile moduli and tensile strengths are almost proportional to the clay content (Cclay), while the elongation at break tends to decrease slightly with increasing Cclay. On the other hand, in OR gels, which always exhibit weak and brittle natures, there was no detectable change in properties on altering the concentration of BIS (CBIS). The deswelling rate was affected markedly by the cross-linker content in both gels though in opposite directions. On increasing cross-...
TL;DR: A new family of nanoscale materials on the basis of dispersed networks of cross-linked ionic and nonionic hydrophilic polymers is being developed, one example is the nanosized cationic network ofcross-linked poly(ethylene oxide) and polyethyleneimine, PEO-cl-PEI nanogel, which has a potential of enhancing oral and brain bioavailability of oligonucleotides.
TL;DR: The rapid gelation of the HA-DTPH solution under physiological conditions was achieved, which demonstrated the capacity for in situ cell encapsulation, and release of blue dextran from cross-linked films was used as a model for drug release.
TL;DR: For the first time, hydrogel scaffolds with a designed external shape and a well-defined internal pore structure were prepared by this RP process and the versatile application potential of new hydrogels was demonstrated in cell culture.
TL;DR: Several types of drug delivery systems using hydrogels are discussed that showed pulsed and/or pulsatile drug delivery characteristics and thermal stimuli-regulated pulsed drug release is established through the design of drug Delivery devices, hydrogel, and micelles.
TL;DR: Intrinsically cell non-adhesive PVA hydrogels were functionalized with the cell-adhesion peptide RGDS and found to support the attachment and spreading of fibroblasts in a dose-dependent manner, and suggest that photopolymerizable PVA Hydrogels are promising for tissue engineering applications.
TL;DR: A degradation mechanism assuming pseudo first-order hydrolysis kinetics and accounting for the structure of the crosslinked networks successfully predicted the experimentally observed trends in these properties with degradation, and the application of these macromers as in situ forming hydrogel constructs for cartilage tissue engineering is demonstrated.
TL;DR: The development of a photopatterning technique that allows localized photoencapsulation of live mammalian cells to control the tissue architecture and the combination of microfabrication approaches with photopolymerizable biomaterials will have implications in tissue engineering, elucidating fundamental structure–function relationships of tissues, and formation of immobilized cell arrays for biotechnological applications.
Abstract: Recent advances in tissue engineering have leveraged progress in both polymer chemistry and cell biology. For example, photopolymerizable biomaterials have been developed that can be used to photoencapsulate cells in peptide-derivatized hydrogel networks. While these materials have been useful in bone, cartilage and vascular tissue engineering, they have limited applicability to more complex tissues that are characterized by precise cell and tissue organization (e.g., liver, kidney). Typically, the tissue shape has been defined solely by the container used for photopolymerization. In this paper, we describe the use of photolithographic techniques to broaden the capability of photopolymerizable PEG-based biomaterials by inclusion of structural features within the cell/hydrogel network. Specifically, we describe the development of a photopatterning technique that allows localized photoencapsulation of live mammalian cells to control the tissue architecture. In this study, we optimized the effect of ultraviolet (UV) exposure and photoinitiator concentration on both photopatterning resolution and cell viability. With regard to photopatterning resolution, we found that increased UV exposure broadens feature size, while photoinitiator concentration had no significant effect on patterning resolution. Cell viability was characterized using HepG2 cells, a human hepatoma cell line. We observed that UV exposure itself did not cause cell death over the doses and time scale studied, while the photoinitiator 2,2-dimethoxy-2-phenyl-acetophenone was itself cytotoxic in a dose-dependent manner. Furthermore, the combination of UV and photoinitiator was the least biocompatible condition presumably due to formation of toxic free radicals. The utility of this method was demonstrated by photopatterning hydrogels containing live cells in various single layer structures, patterns of multiple cellular domains in a single “hybrid” hydrogel layer, and patterns of multiple cell types in multiple layers simulating use in a tissue engineering application. The combination of microfabrication approaches with photopolymerizable biomaterials will have implications in tissue engineering, elucidating fundamental structure–function relationships of tissues, and formation of immobilized cell arrays for biotechnological applications.
TL;DR: New models to predict the swelling/deswelling of hydrogels in buffered pH solutions are developed and are found to predictThe swelling/ Deswelling processes accurately.
Abstract: The widespread application of ionic hydrogels in a number of applications like control of microfluidic flow, development of muscle-like actuators, filtration/separation and drug delivery makes it important to properly understand these materials. Understanding hydrogel properties is also important from the standpoint of their similarity to many biological tissues. Typically, gel size is sensitive to outer solution pH and salt concentration. In this paper, we develop models to predict the swelling/deswelling of hydrogels in buffered pH solutions. An equilibrium model has been developed to predict the degree of swelling of the hydrogel at a given pH and salt concentration in the solution. A kinetic model has been developed to predict the rate of swelling of the hydrogel when the solution pH is changed. Experiments are performed to characterize the mechanical properties of the hydrogel in different pH solutions. The degree of swelling as well as the rate of swelling of the hydrogel are also studied through experiments. The simulations are compared with experimental results and the models are found to predict the swelling/deswelling processes accurately.
TL;DR: The unique acid sensitivity of the acetal cross-linker should make it a useful synthetic intermediate in the design of acid-sensitive drug or gene delivery systems.
Abstract: A new acid-labile acetal cross-linker was synthesized and used to prepare protein-loaded hydrogels and microgels. This cross-linker undergoes an acid-catalyzed degradation with a half-life of 5.5 m...
TL;DR: Antibiotic hydrogels based on a vancomycin (Van) derivative, formed by self-assembling Van-pyrene in water, using the pi-pi interaction of pyrene moieties and hydrogen bonding of Vans, promise a new way to make novel biomaterials.
Abstract: Antibiotic hydrogels based on a vancomycin (Van) derivative, formed by self-assembling Van-pyrene (1) in water, using the pi-pi interaction of pyrene moieties and hydrogen bonding of Vans, promise a new way to make novel biomaterials.
TL;DR: A new rapid prototyping (RP) technology was developed at the Freiburg Materials Research Center to meet the demands for desktop fabrication of hydrogels, including especially its potential for tissue engineering.
Abstract: Scaffolds are of great importance for tissue engineering because they enable the production of functional living implants out of cells obtained from cell culture. These scaffolds require individual external shape and well defined internal structure with interconnected porosity. The problem of the fabrication of prototypes from computer assisted design (CAD) data is well known in automotive industry. Rapid prototyping (RP) techniques are able to produce such parts. Some RP techniques exist for hard tissue implants. Soft tissue scaffolds need a hydrogel material. No biofunctional and cell compatible processing for hydrogels exists in the area of RP. Therefore, a new rapid prototyping (RP) technology was developed at the Freiburg Materials Research Center to meet the demands for desktop fabrication of hydrogels. A key feature of this RP technology is the three-dimensional dispensing of liquids and pastes in liquid media. The porosity of the scaffold is calculated and an example of the data conversion from a volume model to the plotting path control is demonstrated. The versatile applications of the new hydrogel scaffolds are discussed, including especially its potential for tissue engineering.
TL;DR: The synthesis and characterization of ABA triblock copolymers from polyester hard segments and poly(ethylene oxide) [PEO] soft segments as well as their biological and degradation properties will be discussed.
TL;DR: The GAG hydrogel films provide a highly hydrated, peri-cellular environment in which assembly of other matrix components can readily occur, and presentation of growth and differentiation factors, and cell migration can readily occurred.
TL;DR: A brief introduction and recent developments in the area of stimulus-responsive hydrogels, particularly those that respond to temperature and pH, and their applications in drug delivery are provided.
Abstract: Recently, there has been a great deal of research activity in the development of stimulus-responsive polymeric hydrogels. These hydrogels are responsive to external or internal stimuli and the response can be observed through abrupt changes in the physical nature of the network. This property can be favorable in many drug delivery applications. The external stimuli can be temperature, pH, ionic strength, ultrasonic sound, electric current, etc. A majority of the literature related to the development of stimulus-responsive drug delivery systems deals with temperature-sensitive poly(N-isopropyl acrylamide) (pNIPAAm) and its various derivatives. However, acrylic-based pH-sensitive systems with weakly acidic/basic functional groups have also been widely studied. Quite recently, glucose-sensitive hydrogels that are responsive to glucose concentration have been developed to monitor the release of insulin. The present article provides a brief introduction and recent developments in the area of stimulus-responsive hydrogels, particularly those that respond to temperature and pH, and their applications in drug delivery.
TL;DR: Protein-graft-poly(ethylene glycol) hydrogels represent a new and versatile class of biomimetic hybrid materials that hold clinical promise in serving as implants to promote wound healing and tissue regeneration.
TL;DR: The design and preparation of novel biodegradable hydrogels developed by the free radical polymerization of acrylamide and acrylic acid, and some formulations with bis-acrylamides, in the presence of a corn starch/ethylene-co-vinyl alcohol copolymer blend (SEVA-C), is reported.
TL;DR: The selective collapse of the more hydrophobic blocks above the lower critical solution temperature was employed to drive the thermo-reversible self-assembly of elastin-mimetic diblock and triblock copolymer into protein-based nanoparticles and nano-textured hydrogels, respectively.
TL;DR: The results suggest that the material properties of OPF-based hydrogels can be altered by changing the molecular weight of PEG used in synthesis and that multilayered OPF hydrogel constructs can be produced, with each layer having distinct mechanical properties.
Abstract: This study was designed to determine the effect of changes in poly(ethylene glycol) (PEG) molecular weight on swelling and mechanical properties of hydrogels made from a novel polymer, oligo(poly(ethylene glycol) fumarate) (OPF), recently developed in our laboratory. Properties of hydrogels made from OPF with initial PEG molecular weights of 860, 3900, and 9300 were examined. The PEG 3900 formulation had a tensile modulus of 23.1 +/- 12.4 kPa and percent elongation at fracture of 53.2 +/- 13.7%; the PEG 9300 formulation had similar tensile properties (modulus: 16.5 +/- 4.6 kPa, elongation: 76.0 +/- 26.4%). However, the PEG 860 gels had a significantly higher modulus (89.5 +/- 50.7 kPa) and a significantly smaller percent elongation at fracture (30.1 +/- 6.4%), when compared with other formulations. Additionally, there were significant differences in percent swelling between each of the formulations. Molecular weight between crosslinks (M(c)) and mesh size were calculated for each OPF formulation. M(c) increased from 2010 +/- 116 g/mol with PEG 860 to 6250 +/- 280 g/mol with PEG 9300. Mesh size calculations showed a similar trend (76 +/- 2 A for PEG 860 to 160 +/- 6 A for PEG 9300). It was also found that these hydrogels could be laminated if a second layer was added before the first had completely crosslinked. Mechanical testing of these laminated gels revealed that the presence of an interfacial area did not significantly alter their tensile properties. These results suggest that the material properties of OPF-based hydrogels can be altered by changing the molecular weight of PEG used in synthesis and that multilayered OPF hydrogel constructs can be produced, with each layer having distinct mechanical properties.