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Zhibing Hu

Publications and source records attributed to Zhibing Hu.

13 recordsLinked to original sources
PubMed2007

Temperature-responsive semipermeable capsules composed of colloidal microgel spheres.

We present semipermeable, hollow capsules (colloidosomes) that expand and contract upon heating and cooling. The capsules are composed of micrometer-sized poly(N-isopropylacrylamide)-co-acrylic acid microgel particles, which exhibit a reversible size transition near 34 degrees C. The microgel particles assemble on the surfaces of water droplets in oil. Addition of the diblock copolymer poly(butadiene-b-N-methyl 4-vinyl pyridinium iodide) to the oil results in soft, elastic membranes of microgel particles that remain intact after the droplet interfaces are dissolved. Under heating, the capsules contract reversibly by 13% or irreversibly by 40% in radius. These stimulus-responsive colloidosomes might be useful for controlled release or as microscopic actuators.

Biocompatible Materials↗
PubMed2007

Photo-, thermally, and pH-responsive microgels.

Microgels with photo-, thermally, and pH-responsive properties in aqueous suspension have been synthesized and characterized using dynamic light scattering and UV-visible spectroscopy. The new route involved first preparing poly(N-isopropylacrylamide) (PNIPAM)-allylamine copolymer microgels and a spiropyran photochrome (SP) bearing a carboxylic acid group. Then the functionalized spiropyran was coupled to the microgel via an amide bond. The dark-equilibrated gel particles feature spiropyran molecules in the polar, merocyanine form. After irradiation of visible light, the particle size becomes smaller because spiropyran changes to the relatively nonpolar, closed spiro form. The PNIPAM-SP microgels undergo a volume phase transition in water from a swollen state to a collapsed state with increasing temperature under all light conditions. However, the transition temperature range of the PNIPAM-SP is much broader than that for the PNIPAM without SP. The PNIPAM-SP microgels are monodisperse and self-assemble into a crystalline lattice while in suspension. The UV-visible spectra of an aqueous suspension of PNIPAM-SP microgel in the dark-adapted, merocyanine form showed both an absorption peak around 512 nm due to the merocyanine (giving a reddish color to the suspension) and two sharp peaks from Bragg diffraction of colloidal crystallites. Upon visible irradiation, the 512-nm band bleached significantly due to spiropyran photoisomerization. The spiropyran photoisomerization and accompanying color changes of the suspension were reversible upon alternating dark, UV, and visible light irradiation. Due to the residues of amine groups, the swelling capability of PNIPAM-SP microgels reduces as the pH value is changed from 7 to 10.

Acrylic Resins↗
PubMed2006

Growth of columnar hydrogel colloidal crystals in water-organic solvent mixture.

A novel emulsion method has been demonstrated to grow columnar hydrogel colloidal crystals by mixing an aqueous suspension of poly-N-isopropylacrylamide-co-allylamine microgels with organic solvent, driven by the coalescence of micelles consisting of organic oil droplets coated by many microgels. This method leads to microgel colloidal crystals of several centimeters growing from the top to the bottom along the gravity direction. Both temperature and polymer concentration play critical roles for the formation of columnar crystals. A phase diagram has been determined, and it can be used as a guide to selectively grow different crystals, including columnar crystals and randomly oriented crystals, and enable the coexistence of columnar crystals and randomly oriented crystals.

Journal Article↗
PubMed2004

Physically bonded nanoparticle networks: a novel drug delivery system.

Monodispersed nanoparticles consisting of interpenetrating polymer networks (IPNs) of polyacrylic acid (PAAc) and poly(N-isopropylacrylamide) (PNIPAM) were prepared by a seed-and-feed method. The temperature-dependent viscosity measurement revealed that the IPN nanoparticle dispersions with polymer concentrations above 2.5 wt.% underwent an inverse thermoreversible gelation at about 33 degrees C. Dextran markers of various molecular weights as model macromolecular drugs were mixed with the IPN nanoparticle dispersion at room temperature. At body temperature, the dispersion became a gel. The drug release profiles were then measured using UV-Visible spectroscopy as a function of particle size and polymer concentration. The schematic structure of the nanoparticle network was proposed based on the experimental results. The drug delivery model presented here was significant because such a dispersion and a drug was mixed without chemical reaction at room temperature to form a drug delivery liquid. This liquid could be injected into a body to form in situ a gelled drug depot to release the drug slowly.

Drug Delivery Systems↗
PubMed2004

Crystallization kinetics of thermosensitive colloids probed by transmission spectroscopy.

The kinetics of crystallization of poly-N-isopropylacrylamide (PNIPAM) particles has been investigated using the UV-visible transmission spectroscopy. Since the particle size decreases with the increase in temperature, microgel dispersions of different volume fractions have been obtained by varying the temperature of a single sample. It is found that the rates of the change in crystallinity, the average crystallite size, and the number density of crystallites at the most rapid stage over a certain time interval at various temperatures can be described by the power-law relations. At 19 degrees C, the PNIPAM system behaves as a hard sphere system under microgravity. The hard sphere theory based on Monte Carlo simulation has been used as a reference point to compare with conventional hard spheres, soft spheres, and PNIPAM spheres.

Journal Article↗
PubMed2004

Synthesis and self-assembly of nearly monodisperse nanoparticles of a naturally occurring polymer.

Nearly monodisperse nanoparticles have been synthesized based on a naturally occurring polymer of hydropropylcellulose (HPC) using precipitation polymerization method. It is found that when the polydispersity index value of the HPC nanoparticles is less than 1.10, the HPC particles can self-assemble into an ordered structure, displaying bright colors. UV-visible spectroscopy reveals that the color shifts to a lower wavelength as the interparticle distance decreases following the Bragg diffraction equation. The HPC nanoparticle assembly in water has been further stabilized by covalently bonding neighboring particles to form a three-dimensional network. This network contains a large amount of water similar to a conventional bulk gel but displays colors as a result of its ordered structure.

Biocompatible Materials↗
PubMed2004

Synthesis and light scattering study of microgels with interpenetrating polymer networks.

Monodispersed microgels composed of poly(acrylic acid) (PAAc) and poly(N-isopropylacrylamide) (PNIPAM) interpenetrating polymer networks (IPN) were synthesized by a two-step method, first preparing PNIPAM microgel and then polymerizing acrylic acid that interpenetrates into the PNIPAM network. The growth kinetics of the IPN particle formation was obtained by measuring the turbidity and particle hydrodynamic radius (Rh) as a function of reaction time. IPN and PNIPAM microgels were characterized and compared by dynamic and static light scattering techniques. The concentrated aqueous solutions of the PNIPAM-PAAc IPN microgels exhibit an inverse thermoreversible gelation. In contrast to polymer solutions of poly(NIPAM-co-AAc) that have the inverse thermoreversible gelation, our system can self-assemble into an ordered structure, displaying bright colors. Furthermore, IPN microgels undergo the reversible volume phase transitions in response to both pH and temperature changes associated with PAAc and PNIPAM networks, respectively.

Journal Article↗
PubMed2004

Controlled drug release from hydrogel nanoparticle networks.

Monodisperse nanoparticles of poly-N-isopropylacrylamide-co-allylamine (PNIPAM-co-allylamine) and PNIPAM-co-acrylic acid (PNIPAM-co-AA) were synthesized. The close-packed PNIPAM-co-allylamine and PNIPAM-co-AA nanoparticles were converted to three-dimensional gel networks by covalently crosslinking neighboring particles at room temperature and neutral pH using glutaric dialdehyde and adipic acid dihydrazide, respectively. Controlled release studies were conducted using dextran markers of various molecular weights as model macromolecular drugs. Release was quantified under various physical conditions, including a range of temperatures and dextran molecular weights. Dextran, entrapped in cavities in the nanoparticle network, was released with a rate regulated by their molecular weights and cavity size. No release from a conventional bulk PNIPAM gel, with high crosslinking density, was observed. The rate of release from the PNIPAM-co-allylamine network was temperature-dependent, being much faster at room temperature than that at human body temperature. In contrast, release of low molecular weight dextrans from the PNIPAM-co-AA network showed a temperature-independent release profile. These nanoparticle networks have several advantages over conventional bulk gels for controlling the release of high molecular weight biomolecules.

Acrylic Resins↗
PubMed2004

Tissue responses to thermally-responsive hydrogel nanoparticles.

Thermally-responsive hydrogel nanoparticles of poly(N-isopropylacrylamide) (PNIPAM) and hydroxypropyl cellulose (HPC) have been synthesized. The particle size has been correlated to surfactant concentration and polymer concentration using dynamic laser light scattering techniques. The tissue compatibility of these hydrogel nanoparticles has been evaluated by comparing with poly-L-lactic acid and polystyrene nanoparticles using a mouse implantation model. Our results suggested that both PNIPAM and HPC nanoparticles triggered lesser inflammatory and fibrotic responses among all nanoparticles tested. It is likely that these hydrogel nanoparticles may be suitable for tissue augmentation or drug-delivery devices.

Acrylic Resins↗
PubMed2003

Phase behavior of thermally responsive microgel colloids.

The phase behavior of poly-N-isopropylacrylamide (PNIPAM) nanoparticles dispersed in water is investigated using a thermodynamic perturbation theory combined with light-scattering and spectrometer measurements. It is shown how the volume transition of PNIPAM particles affects the interaction potential and determines a novel phase diagram that has not been observed in conventional colloids. Because both particle size and attractive potential depend on temperature, PNIPAM aqueous dispersion exhibits phase transitions at a fixed particle number density by either increasing or decreasing temperature.

Journal Article↗