Synthesis and structure of temperature-sensitive nanocapsules (original) (raw)
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American Journal of Drug Delivery, 2005
To develop and characterize a new class of temperature-sensitive hydrogel microspheres composed Abstract of poly(N-isopropylacrylamide)/poly(ethylene glycol) diacrylate (PNIPAAm/PEG-DA). Methods: The PNIPAAm/PEG-DA hydrogel microspheres were fabricated in two aqueous systems as a result of polymer/polymer immiscibility. Both PNIPAAm and PEG-DA were used as the precursors; the PEG-DA was also used as a cross-linker for the formation of the hydrogel microspheres. Bovine serum albumin was used as the model protein drug to examine the effects of the thermo-responsive properties of the hydrogel microspheres on the release of a protein at two different temperatures (22°C and 37°C). Results: The hydrated PNIPAAm/PEG-DA hydrogel microspheres exhibited a swollen diameter of 50μm, with a narrow particle-size distribution. Scanning electron microscopy and environmental scanning electron microscopy observations revealed that, upon swelling, the resulting hydrogel microspheres had a regular spherical and rough surface morphology. The lower critical solution temperature (LCST) of the PNIPAAm/PEG-DA hydrogel microspheres was around 29.1°C, based on differential scanning calorimetric data. The release of BSA from the hydrogel microspheres at 37°C was slower than that at 22°C because of the thermo-responsive nature of PNIPAAm at temperatures above its LCST. Conclusions: We believe that these kinds of PNIPAAm/PEG-DA hydrogel microspheres may have wide applications as promising drug delivery systems, because of their intelligent nature upon external temperature change.
Polymer International, 2006
Macroporous poly(N-isopropylacrylamide) (PNIPA) hydrogels were synthesized by free-radical crosslinking polymerization in aqueous solution from N-isopropylacrylamide monomer and N,N-methylenebis (acrylamide) crosslinker using poly(ethylene glycol) (PEG) with three different number-average molecular weights of 300, 600 and 1000 g mol −1 as the pore-forming agent. The influence of the molecular weight and amount of PEG pore-forming agent on the swelling ratio and network parameters such as polymer-solvent interaction parameter (χ) and crosslinking density (ν E ) of the hydrogels is reported and discussed. Scanning electron micrographs reveal that the macroporous network structure of the hydrogels can be adjusted by applying different molecular weights and compositions of PEG during polymerization. At a temperature below the volume phase transition temperature, the macroporous hydrogels absorbed larger amounts of water compared to that of conventional PNIPA hydrogels, and showed higher equilibrated swelling ratios in aqueous medium. Particularly, the unique macroporous structure provides numerous water channels for water diffusion in or out of the matrix and, therefore, an improved response rate to external temperature changes during the swelling and deswelling process. These macroporous PNIPA hydrogels may be useful for potential applications in controlled release of macromolecular active agents.
Journal of Polymer Research, 2014
Thermoresponsive colloidal microgels were prepared by precipitation copolymerization of N-isopropylacrylamide (NIPAM) and N-hydroxyethylacrylamide (HEAM) with various concentrations of a cross-linker in the presence of an anionic surfactant, sodium dodecylsulphate (SDS). The volume phase transition temperature (VPTT) of the prepared microgels was studied by dynamic light scattering (DLS), ultraviolet-visible spectroscopy (UV-vis) and proton nuclear magnetic resonance ( 1 H-NMR) spectroscopy. In addition, atomic force microscopy (AFM) was used to characterize the polydispersity and morphology of the microgels. Results indicated that poly(NIPAMco-HEAM) microgels are spherical and monodisperse. VPTTs of microgels determined by DLS and UV-vis methods are almost the same and very close to the human body temperature, presenting the microgels as candidates for biomedical application. The temperature at which the phase transition occurred is nearly independent of the cross-linking density, whereas the transition range is deeply influenced by temperature. Also, the SDS concentration was increased to decrease the average hydrodynamic size of the microgels, due to the electrostatic repulsion between the charged particles during the polymerization process. 1 H-NMR spectra of the microgels show a decrease in peak intensity with an increased temperature due to a reduction in molecular mobility of the polymer segments. Release rates of propranolol from microgels are deeply influenced by temperature; below the VPTT at 25°C, the drug is rapidly released at a rate comparable to that of a free drug, whereas above the VPTT (37 and 42°C), a fraction of the drug is mechanically expulsed in the first five min, followed by a prolonged release.
Chemistry of Materials, 2012
We report on nanothin multilayer hydrogels of cross-linked poly(N-vinylcaprolactam) (PVCL) that exhibit distinctive and reversible thermoresponsive behavior. The single-component PVCL hydrogels were produced by selective cross-linking of PVCL in layer-by-layer films of PVCL-NH 2 copolymers assembled with poly(methacrylic acid) (PMAA) via hydrogen bonding. The degree of the PVCL hydrogel film shrinkage, defined as the ratio of wet thicknesses at 25°C to 50°C, was demonstrated to be 1.9±0.1 and 1.3±0.1 for the films made from PVCL-NH 2 -7 and PVCL-NH 2 -14 copolymers, respectively. No temperature-responsive behavior was observed for non-cross-linked two-component films due to the presence of PMAA. We also demonstrated that temperature-sensitive PVCL capsules of cubical and spherical shapes could be fabricated as hollow hydrogel replicas of inorganic templates. The cubical (PVCL) 7 capsules retained their cubical shape when temperature was elevated from 25°C to 50°C exhibiting 21±1% decrease in the capsule size. Spherical hydrogel capsules demonstrated similar shrinkage of 23±1%. The temperature-triggered capsule size changes were completely reversible. Our work opens new prospects for developing biocompatible and nanothin hydrogel-based coatings and containers for temperate-regulating drug delivery, cellular uptake, sensing, and transport behavior in microfluidic devices.
Polym. Chem., 2014
A synthetic method for thermoresponsive, glycerol based nanogels has been developed. The nanogels were synthesized by nanoprecipitation of the orthogonally functionalized macromonomers and their gelation in water. The crosslinking points were generated by strain promoted azide-alkyne cycloaddition which enabled the in situ encapsulation of Doxorubicin HCl. The mild and surfactant free reaction conditions make these nanogels ideal candidates for biomedical applications.
Langmuir, 2012
Novel thermal-and pH-responsive hollow nanocapsules (HNCaps) were fabricated through the grafting of a thiol-end capped PNIPAAm-b-PAA by thiol-ene "click" reaction onto PMMA HNCaps. The lowest critical solution temperature (LCST) of the fabricated HNCaps was obtained as 38-40°C. The fabricated nanosystem was loaded with doxorubicin hydrochloride (Dox), and its drug loading and encapsulation efficiencies were obtained as 62 and 53%, respectively. The in vitro stimuliresponsive drug release behavior of the fabricated nanomedicine was investigated extensively. The anticancer activity of the drug-loaded HNCaps was evaluated using MTT assay against MCF7 cells. The results exhibited excellent potential of nanosystem as a drug delivery system (DDS) for cancer chemotherapy. Novel thermal-and pH-responsive poly(methyl metacrylate)-grafted-[poly(N-isopropylacrylamideblock-acrylic acid)] hollow nanocapsules were fabricated as "smart" anticancer drug delivery system (DDS).
Fast-responsive porous thermoresponsive microspheres for controlled delivery of macromolecules
International journal of pharmaceutics, 2009
Porous thermoresponsive microspheres with a homogeneous dimension and distribution of the pores are synthesized by an original method. Poly(N-isopropylacrylamide-co-acrylamide) (poly(NIPAAm-co-AAm)) copolymer was obtained as a thermoresponsive material with a lower critical solution temperature (LCST) under physiologic-like conditions (i.e., at 37 degrees C and pH 7.4, 50mM phosphate buffer). Semitelechelic oligomers of NIPAAm (ONIPAAm) were also synthesized in the presence of 3-mercaptopropionic acid (MPA) (chain transfer molecule) which acts as a pore-forming agent. Poly(NIPAAm-co-AAm) and ONIPAAm were solubilized in acidified aqueous solution, dispersed in a mineral oil, and transformed in stable microspheres by crosslinking the amide group with glutaraldehyde at temperatures below and above the LCST of the oligomers, and always below the LCST of the polymer. Microspheres obtained at temperatures below the LCST of ONIPAAm are characterized by a homogeneous porous structure with a...
Journal of Polymer Research, 2011
In this study, thermo-sensitive terpolymer hydrogels based on N-tert-butylacrylamide (NtBAAm), Nisopropylacrylamide (NIPAAm) and N-vinyl pyrrolidone (NVP) were successfully photopolymerised and characterised. 1-hydroxy-cyclohexylphenylketone (Irgacure 184) and 2-hydroxy-2-methyl-1-phenyl-propanone (Irgacure 2959) were used as light-sensitive initiators to initiate the reactions. Chemical structures of the hydrogels were confirmed using Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy. The hydrogels were also characterised using modulated differential scanning calorimetry (MDSC) for their glass transition and phase transition temperatures. A single glass transition temperature (T g ) was observed, further confirming successful formation of a terpolymer. The hydrogels were thermo-responsive, exhibiting a decrease in lower critical solution temperature (LCST) as the NtBAAm weight ratio was increased. Pulsatile swelling studies indicated that the hydrogels had thermo-reversible properties and the swelling properties were dependent on test temperature, monomer feed ratios and crosslinker content. The proposed hydrogel system could find applications in a broader field of gel/drug interaction, for the development of controlled release and targeted delivery devices.