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 47,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Temperature-sensitive diblock copolymers, poly(N-isopropylacrylamide)-b-poly(D,L-lactide) (PNIPAAm-b-PLA) with different PNIPAAm contents were synthesized and utilized to fabricate microspheres containing bovine serum albumin (BSA, as a model protein) by a water-in-oil-in-water double emulsion solvent evaporation process. XPS analysis showed that PNIPAAm was a dominant component of the microspheres surface. BSA was well entrapped within the microspheres, and more than 90% encapsulation efficiency was achieved. The in vitro degradation behavior of microspheres was investigated using SEM, NMR, FTIR, and GPC. It was found that the microspheres were erodible, and polymer degradation occurred in the PLA block. Degradation of PLA was completed after 5 months incubation in PBS (pH 7.4) at 37 degrees C. A PVA concentration of 0.2% (w/v) in the internal aqueous phase yielded the microspheres with an interconnected porous structure, resulting in fast matrix erosion and sustained BSA release. However, 0.05% PVA produced the microspheres with a multivesicular internal structure wrapped with a dense skin layer, resulting in lower erosion rate and a biphasic release pattern of BSA that was characterized with an initial burst followed by a nonrelease phase. The microspheres made from PNIPAAm-b-PLA with a higher portion of PNIPAAm provided faster BSA release. In addition, BSA release from the microspheres responded to the external temperature changes. BSA release was slower at 37 degrees C (above the LCST) than at a temperature below the LCST. The microspheres fabricated with PNIPAAm-b-PLA having a 1:5 molar ratio of PNIPAAm to PLA and 0.2% (w/v) PVA in the internal aqueous phase provided a sustained release of BSA over 3 weeks in PBS (pH 7.4) at 37 degrees C.
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PMID:Preparation and characterization of temperature-sensitive poly(N-isopropylacrylamide)-b-poly(D,L-lactide) microspheres for protein delivery. 1460 9

This work was focused on the investigation of temperature and pH-responsive polymeric composite membranes and their permeability to proteins and peptides in response to environmental stimuli. The composite membranes were prepared from nanoparticles of poly(N-isopropylacrylamide-co-methacrylic acid) of various NIPAAm:MAA ratios dispersed in a matrix of a hydrophobic polymer. N-Benzoyl-L-tyrosine ethyl ester HCl, momany peptide, Leuprolide, vitamin B(12), insulin, and lysozyme were used as model solutes. The morphology of the membranes was examined with SEM and permeation of the solutes was measured using side-by-side diffusion cells at varied temperatures and pH. Permeability of the solutes across the membranes increased with increasing temperature or particle concentration, while decreased with increasing pH and molecular size of the solutes. Membranes containing nanoparticles of more NIPAAm units exhibited higher thermal sensitivity, and those with higher MAA content showed more pH responsiveness, which was in line with the temperature and pH-responsive volume change of the nanoparticles. The change in permeability was quickly detected following the application of the stimuli. These results and partition study using vitamin B(12) supported the proposed gel-pore mechanism of solute permeation through these composite membranes.
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PMID:Temperature and pH-responsive polymeric composite membranes for controlled delivery of proteins and peptides. 1511 Apr 79

Micropatterned cross-linked film making up a temperature-responsive component has been fabricated through the following two steps: layer-by-layer electrostatic assembly of photosensitive nitrodiazoresin (NDR) and a thermosensitive copolymer of poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPA-AA)), and subsequent selective exposure to UV light through a photomask followed with development in sodium dodecyl sulfate (SDS) aqueous solution. The irradiated regions of the film are retained due to the formed covalently linked structure, whereas the unirradiated parts of the film are removed fully from the substrate in SDS solution. The well-defined micropatterns were characterized with field-emission scanning electron spectroscopy (FE-SEM) and atomic force microscopy (AFM).
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PMID:Micropatterned self-assembled film based on temperature-responsive poly(N-isopropylacrylamide-co-acrylic acid). 1527 54

Intelligent hydrogels, particularly poly(N-isopropylacrylamide) (PNIPAAm)-based hydrogels, have attracted extensive interest because the soft wet hydrogels can change their shapes in response to the small changes of environmental factors like temperature. In order to fully make use of this unique property of PNIPAAm-based hydrogels, the response rates of the PNIPAAm hydrogels have to be improved since the dynamics property is critical to certain applications of this material. In this paper, the thermo-sensitive PNIPAAm hydrogels were successfully synthesized by carrying out the polymerization of N-isopropylacrylamide monomer in vacuum (-100 kPa) at room temperature (22 degrees C). The resultant hydrogel has tremendously improved shrinking rate as well as the large volume changes upon temperature stimulation when comparing with the normal PNIPAAm hydrogel. The SEM micrographs revealed that the improved properties were attributed to the macroporous network structure generated during the synthesis under vacuum.
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PMID:Thermoresponsive hydrogel with rapid response dynamics. 1534 49

A thermo-responsive comb-like polymer with chitosan as the backbone and pendant poly(N-isopropylacrylamide) (PNIPAM) groups has been synthesized by grafting PNIPAM-COOH with a single carboxy end group onto chitosan through amide bond linkages. The copolymer exhibits reversible temperature-responsive soluble-insoluble characteristics with the lower critical solution temperature (LCST) being at around 30 degrees C. Results from SEM observations confirm a porous 3D hydrogel structure with interconnected pores ranging from 10 to 40 microm at physiological temperature. A preliminary in vitro cell culture study has demonstrated the usefulness of this hydrogel as an injectable cell-carrier material for entrapping chondrocytes and meniscus cells. The hydrogel not only preserves the viability and phenotypic morphology of the entrapped cells but also stimulates the initial cell-cell interactions.
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PMID:Thermo-responsive chitosan-graft-poly(N-isopropylacrylamide) injectable hydrogel for cultivation of chondrocytes and meniscus cells. 1712 21

New smart surface-modified polypropylene (PP) was prepared for improving the loading and the sustained delivery of vancomycin and, thus, reducing the risk of biofilm formation when used as component of biomedical devices. Isothermal titration calorimetry (ITC) served for screening the most suitable monomers for grafting; the drug preferentially bonding to ionized acrylic acid (AAc). A net-PP-g-PNIPAAm-inter-net-PAAc was synthesized by first grafting and cross-linking of N-isopropylacrylamide onto PP films and then interpenetrating a second network by redox polymerization and cross-linking of AAc. PP-g-PAAc slabs were prepared by grafting AAc and, optionally, cross-linking. The amount and composition of grafted polymer (FTIR-ATR), morphology (SEM), temperature- and pH-responsiveness (swelling measurements), thermal behavior (DSC), friction coefficient (rheometry), drug loading and release rate, and effect against methicillin-resistant Staphylococcus aureus (MRSA) biofilms (modified robbins device) were evaluated. Grafting of AAc notably decreased the friction coefficient from 0.28+/-0.03 to 0.05+/-0.02 and enhanced the vancomycin loading (up to 2.5mg/cm(2)). Drug-loaded films showed a pH-dependent release rate, sustaining the release in pH 7.4 aqueous media at 37 degrees C for several hours. All drug-loaded films reduced biofilm formation by MRSA; the anti-biofilm effect being statistically significant (91.7% reduction, alpha<0.05) for PP-g-PAAc with the thinnest grafting layer.
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PMID:Polypropylene grafted with smart polymers (PNIPAAm/PAAc) for loading and controlled release of vancomycin. 1857 53

In this work we try to develop a new thermal gelling injectable scaffold for three-dimensional cell culture. Instead of using linear, branched, or grafted macromolecules, thermosensitive microgel particles or microspheres are used as building blocks for the construction of the macroscopic hydrogel scaffold. As a proof of concept, thermosensitive poly(N-isopropylacrylamide-co-2-hydroxyethyl methacrylate) (P(NIPAM-HEMA)) microgel particles were synthesized, which present a volume phase transition temperature (VPTT) at about 29 degrees C. Rheological test shows that the concentrated P(NIPAM-HEMA) microgel dispersion is colloidally stable when heated above its VPTT, indicating hydrophobic interaction alone can not induce thermal gelation of the dispersion. In the presence of a low concentration of CaCl(2), however, with the introduction of additional ionic cross-linking, the microgel dispersion gelates and forms macroscopic hydrogel. Gelation temperature of the microgel dispersion decreases with increasing ionic strength. SEM observation reveals that the resultant bulky gel has an interconnected porous microstructure. 293T cells, a human cell line, were encapsulated inside the hydrogel by simple mixing with the microgel dispersion at room temperature and heating to 37 degrees C. MTT (3-[4,5-dimethylthiazol-2-yl]-3,5-diphenyl tetrazolium bromide) assays reveal that the cells are viable and proliferate inside the 3D scaffold.
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PMID:In situ gelation of P(NIPAM-HEMA) microgel dispersion and its applications as injectable 3D cell scaffold. 1936 98

We reported the synthesis of double thermo-responsive block copolymers comprised of a poly(N-isopropylacrylamide (NIPAAm)) block and a poly(NIPAAm-co-N-(hydroxymethyl)acrylamide (HMAAm)) block, which was synthesized using an atom transfer radical polymerization (ATRP) technique. The cloud point of the poly(NIPAAm-co-HMAAm) (NH) block could be easily controlled by altering the HMAAm content. Below the cloud point of polyNIPAAm (N) block, the block copolymers were completely dissolved. Between the cloud points of each block, the block copolymer formed the aggregate structure that could be constructed with the hydrated NH shell and the dehydrated N core. Moreover with increases in temperature, the diameter decreased due to the dehydration of the NH block shell. The response was completely reversible by changes in temperature, as confirmed by (1)H NMR, turbidity, and FE-SEM measurements.
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PMID:Assembly behavior of double thermo-responsive block copolymers with controlled response temperature in aqueous solution. 1944 85

A poly(N-isopropylacrylamide-co-ethylene dimethacrylate) (poly(NIPAAm-co-EDMA)) monolith was in situ prepared in the capillary and was investigated for in-tube solid-phase microextraction (SPME). NIPAAm, an acrylamide monomer with isopropyl group, was crosslinked with EDMA. PEG of 400-20,000 Da molecular weight and methanol were selected as the binary porogens. The porous structures of the resulting monoliths have been assessed by SEM, nitrogen adsorption-desorption, and pressure drop measurements. To investigate the extraction mechanism, several groups of model analytes (including neutral, acidic, and basic) were examined. The result showed that this monolithic material exhibited high extraction efficiencies for compounds under highly acidic and basic conditions, which was due to the hydrophobic interactions and excellent pH stability of the monolith. The equilibrium extraction time profiles were also monitored for model compounds to evaluate the extraction capacity of monolithic capillary. Finally, the developed monolith in-tube SPME-HPLC method was applied to the determination of three tricyclic antidepressants from urine samples.
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PMID:Preparation of a poly(N-isopropylacrylamide-co-ethylene dimethacrylate) monolithic capillary and its application for in-tube solid-phase microextraction coupled to high-performance liquid chromatography. 1960 42

Hollow silica nanospheres with mesoporous shells were successfully fabricated with a new one-pot strategy by using a thermosensitive polymer, poly(N-isopropylacrylamide) (PNIPAm), as a reversible template without the need of further calcination or chemical etching. By simply regulating the solution temperature with respect to the lower critical solution temperature (LCST) of PNIPAm, PNIPAm chains can reversibly form aggregates or dissolve in aqueous solution. The thermosensitive character makes PNIPAm chains behave as soft templates for the formation of core-shell silica nanospheres at elevated temperature (>LCST), and they will then diffuse out of the cores at lower temperature (<LCST), leading to the formation of hollow silica nanospheres. The TEM, SEM, XRD, and N(2) adsorption-desorption results indicate that the shells of such hollow silica nanospheres also contain large quantities of irregular mesopores. This new strategy was also tested with another thermosensitive polymer, poly(vinyl methyl ether) (PVME). However, only solid silica nanospheres with a broad size distribution were obtained when PVME was used. We speculated on the possible formation mechanism of hollow silica nanospheres with PNIPAm templates. The effects of the initial concentration of PNIPAm, the molecular weight of PNIPAm, and the pretreatment of silica precursor on the morphology and size of the resultant hollow silica nanospheres were also investigated. The PNIPAm soft templates were confirmed to be recyclable.
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PMID:One-pot preparation of hollow silica spheres by using thermosensitive poly(N-isopropylacrylamide) as a reversible template. 1976 Dec 58


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