Papers by Keyword: Hydrogel

Abstract: The Poly N-Isopropyl acrylamide (PNIPA) gels were prepared in different synthesis media by crosslinking with acrylate monomers with varying chain length. The microstructural characterization in terms of the free volume fractions and distributions were studied using positron annihilation lifetime spectroscopy (PALS). The equilibrium swelling of the PNIPA in distilled water was measured. An attempt has been made to understand the correlations between microscopic free volumes and the equilibrium swelling of the gels. The free volume fraction of the gels prepared in Dimethyl formamide (DMF) was directly correlated with swelling while it varied inversely with chain length of the crosslinker. The microstructure of the gels was found to be very sensitive to the solvent/medium used for polymerization. Our studies show that the swelling property is influenced by the free volumes, chain relaxation as well as the chemical nature of the cross linkers.

Abstract: Calcium phosphatepolymer composites have been produced for bone-repairing. We have focused development of composites by a crystal growth technique in a hydrogel matrix, that is regarded as gel-mediated processing. Under the gel-mediated condition, reaction temperature is one of the major parameter to determine microstructure of the precipitated crystals. In the present study, we investigated effects of the reaction temperature on formation of calcium phosphates through gel-mediated processing where double diffusion technique was applied. Crystalline phases of calcium phosphate formed in the hydrogel were varied from octacalcium phosphate (OCP) to hydroxyapatite (HAp) with increasing the reaction temperature. OCP crystals formed at 4 and 40 °C had granular or spherical shape, while HAp crystals formed at 80 °C had rod shape. The HAp crystals were composed of a large number of fibrous crystals. The rod-shaped HAp crystals were oriented in the direction of ion diffusion. Formation of oriented HAp crystals was generated by increase in diffusion rate of ions in the hydrogel matrix after increasing reaction temperature in gel-mediated processing.

Abstract: The unusual amino acid 3,4-dihydroxyphenylalanine with a catechol side chain is believed to impart both adhesive and cohesive characteristics of mussel adhesive proteins. Inspired by the pH-tunable coordination between catechol moiety and Fe³⁺, responsible for the high extensibility and self-healing properties of the cuticle of mussel byssal threads, we report the synthesis of a dopamine modified Pluronic F68 block copolymer (PluF68-Dopa) with high coupling efficiency and utilization of catechol-Fe³⁺ interactions to yield cross-linking hydrogels with enhanced mechanical strength and self-healing properties. Ultraviolet-visible spectroscopy was used to identify PluF68-Dopa-Fe³⁺ complex species via pH control in dilution solution. At lower pH, concentrated PluF68-Dopa-Fe³⁺ mixture remained a fluid, whereas at higher pH an elastomeric gel immediately formed. PluF68-Dopa-Fe³⁺ cross-linked hydrogels are not only pH-responsive but also possess self-healing properties due to the reversible bond interactions between catechol moiety and Fe³⁺. These new biomimetic materials are expected to have potential biomedical and engineering applications.

Abstract: Abstract. Hydrogels based on poly (N-vinyl-2-pyrrolidone) (PVP) obtained by ionizing radiation are sterile, biocompatible can be used as topics dressings. Due to the high degree of hydration of the gel, it has a low mechanical strength, which is one of the biggest problems in its application. The objective of this work was to study the properties of the hydrogel based on PVP / sodium alginate containing pseudoboehmites nanoparticles treated with octadecylamine for pharmaco applications, order drug release when immobilized on a matrix of PVP/sodium alginate/pseudoboehmite. Pseudoboehmite nanoparticles were obtained by sol-gel route, from aluminum nitrate and ammonia as precursors, and subsequently were treated with octadecylamine. The hydrogels based on PVP/sodium alginate/pseudoboehmite treated were prepared by ionizing radiation with doses of 30 and 35kGy. The characterization of hydrogels obtained was made by means of thermomechanical (tensile tests, DTA and TG) and physicochemical (swelling, sol-gel fraction) tests. The results obtained showed that the hydrogel based only on PVP and sodium alginate showed highest tensile strength. The presence of pseudoboehmite in the hydrogels decreases the formation of crosslinks, while the presence of PEG in the agar and causes a decrease in Tg of the polymer matrix.

Abstract: Intrinsically conducting polymers are of great interest for a large number of applications. But among major drawbacks are their low solubility in common solvents and their poor mechanical properties. Elaboration of composites associating a matrix, bringing its mechanical properties, and polyaniline, as the conducting polymer is a way of overcoming these disadvantages. Chitosan-graft-polyaniline copolymers were synthesized by simple oxidative method. The grafting reaction was quite total and it was found that the copolymers crosslinked to yield a composite hydrogel in which the polyaniline was homogeneously embedded. The conductivity of precursor (block copolymer) and gels was found to be larger than 10-2 S.cm-1. The composite gels were characterized in terms of swelling and rheological properties. They can be classified as "superabsorbent" hydrogels and the swelling is reversible. The composite gels were then successfully used as actuators.

Abstract: Over the last ten years, microfluidic technologies have gained considerable importance. However, realising highly integrated microsystems is a major challenge, which so far has only been solved insufficiently. Here, we present an innovative approach to fabricate low-cost, integrable mi- crofluidic platforms. As active elements, photopolymerised hydrogels based on Poly(N-isopropylacrylamide) (PNIPAAm) are introduced. PNIPAAm is temperature-sensitive. Heated in water above its lower crit- ical solution temperature (LCST), it reversibly changes from a swollen to a shrunken state (volume change in the order of 90%) and can, via an electrothermic interface, be employed as electrothermally switchable actuator. Varying specific parameters in the swelling agent, for example varying its alco- hol concentration, can shift the LCST. So not only micropumps or microvalves, but also valves with an appointed threshold value, so-called chemostats or chemical transistors, can be realised. Using the example of a microchip performing enzymatic endpoint analyses, we investigate characteristic be- haviour of active elements based on PNIPAAM and show the ability of integrating different fluidic operations like fluid transportation, metering, valving and mixing into one fully polymeric microchip.

Abstract: The lab-on-a-chip (LOC) technology was expected to influence our every day live in a similarly fundamental way as integrated circuits have. Unfortunately, this demand has not been met yet. The cause therefore lies in the complexity of microelectromechanical systems (MEMS), which form the base of the current LOC technology. We present a new concept of LOC which are based on fluidic microchemomechanical systems (μCMS). During the fabrication process, these μCMS are preprogrammed by monolithic integration of special active components. These active components are holding chemical energy that can be transformed at least once into mechanical energy and thus provide a timed and quantitative exactly defined fluidic function. With our simple and inexpensive fabrication method combined with the above mentioned advantages of the invented μCMS, new and better LOC technology can be developed.

Abstract: A novel kind of supramolecular structrued hydrogels were fabricated by Diels-Alder click reaction between furan-functionalized polypseudorotaxanes and polymeric dienophiles. Firstly, polypseudorotaxanes were prepared by supramolecular self-assembly of furan-terminated poly(ethylene glycol)(PEG) and α-cyclodextrins (CDs) in water. And polymeric dienophiles were synthesized by a coupling reaction between copolymer of hydroxyethyl methacrylate and N,N-dimethyl acrylamide and N-maleoyl alanine (AMI). The supramolecular structured hydrogels were prepared by Diels-Alder reaction in water.

Abstract: The thermo-responsive hydrogels poly(N-isopropylacrylamide) (PNIPAm) were synthesized by frontal polymerization (FP) in dimethylsulfoxide (DMSO) and ethanol mixture. The effects of composition of synthesis-solvent on FP feature and porous morphologies as well as their response behavior of the final products were studied. PNIPAm hydrogel synthesized in mixture exhibited a porous structure, which was responsible for its higher swelling ratio. Moreover, an improvement in swelling capability of the final PNIPAm hydrogel was found when the ethanol content in mixed media was elevated. The approach, frontal polymerization in mixed solvent, reported here provides a promising option to synthesize porous intelligent hydrogels PNIPAm.

Abstract: In this paper, the cross-linking injection hydrogel were synthesized by EDC crosslinker and Carboxymethyl chitosan (CMCS)/Human-like collagen (HLC). Cytotoxicity was assessed by Methylthiazolydiphenyl-tetrazolium bromide (MTT) assay which indicated that the hydrogels was non-toxic to the BHK21 cell .Chondrocyct-encapsulation of this hydrogel were studied in order to asses the cells compatibility of the injection gel. The result showed that the material has no cytotoxicity to the cells and promoted cell adhesion and proliferation. Injected those hydrogels into mice subcutaneous , the following parameters were evaluated: inflammatory response, vascularization, new hypoderm generation. After 2,4,12,and 24 weeks of healing, the rats were sacrilifced suggested that gels in animals did not induce inflammation obvious, vessel bestrid the material after 4 weeks injection, new hypoderm generated in 12 weeks and packaged the hydrogels after 24 weeks. Consequently the gels are promised for the application in the biomaterials area.