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Temperature-sensitive poly(N-isopropylacrylamide) (PNIPA) nanohydrogels were synthesized by nanoemulsion polymerization in water-in-oil systems. Several cross-linking degrees and the incorporation of acrylic acid as comonomer at different concentrations were tested to produce nanohydrogels with a wide range of properties. The physicochemical properties of PNIPA nanohydrogels, and their relationship with the swelling-collapse behaviour, were studied to evaluate the suitability of PNIPA nanoparticles as smart delivery systems (for active packaging). The swelling-collapse transition was analyzed by the change in the optical properties of PNIPA nanohydrogels using ultraviolet-visible spectroscopy. The thermodynamic parameters associated with the nanohydrogels collapse were calculated using a mathematical approach based on the van't Hoff analysis, assuming a two-state equilibrium (swollen to collapsed). A mathematical model is proposed to predict both the thermally induced collapse, and the collapse induced by the simultaneous action of two factors (temperature and pH, or temperature and organic solvent concentration). Finally, van't Hoff analysis was compared with differential scanning calorimetry. The results obtained allow us to solve the problem of determining the molecular weight of the structural repeating unit in cross-linked NIPA polymers, which, as we show, can be estimated from the ratio of the molar heat capacity (obtained from the van't Hoff analysis) to the specific heat capacity (obtained from calorimetric measurements).

We used temperature-sensitive poly(N-isopropylacrylamide) hydrogels as drug delivery systems, so changes in body temperature induced by pathogens could act like external stimuli to activate controlled release of the drugs incorporated in the hydrogel. In the distilled water combined release studies, we chose two model drugs: aminophylline and triamterene. The amount of drug released was measured by UV-Vis spectroscopy following the evolution of the absorption peaks of aminophylline (271 nm) and triamterene (365 nm). The maximum release time was greater for triamterene than for aminophylline at 37 °C, so these time-release profiles enabled the active ingredients to work over different periods of time. By increasing molar mass or solubility of the drug, we observed that the diffusion coefficient decreased. On the contrary, increasing hydrophobicity of the drug leads to a diffusion coefficient increase. The evolution of pore size distribution of hydrogels during loading and releasing was measured by quasi-elastic light scattering and by environmental electronic scanning microscope. When loading and releasing the drugs, the pore size of the hydrogel decreased and increased again without reaching the initial pore size of the hydrogel, respectively. We observed that the greater the concentration of drug loaded into the hydrogel, the greater the reduction in pore size.

Temperature-sensitive poly(N-isopropylacrylamide) (PNIPA) nanohydrogels were synthesized by nanoemulsion polymerization in water-in-oil systems. Several cross-linking degrees and the incorporation of acrylic acid as comonomer at different concentrations were tested to produce nanohydrogels with a wide range of properties. The physicochemical properties of PNIPA nanohydrogels, and their relationship with the swelling-collapse behaviour, were studied to evaluate the suitability of PNIPA nanoparticles as smart delivery systems (for active packaging). The swelling-collapse transition was analyzed by the change in the optical properties of PNIPA nanohydrogels using ultraviolet-visible spectroscopy. The thermodynamic parameters associated with the nanohydrogels collapse were calculated using a mathematical approach based on the van't Hoff analysis, assuming a two-state equilibrium (swollen to collapsed). A mathematical model is proposed to predict both the thermally induced collapse, and the collapse induced by the simultaneous action of two factors (temperature and pH, or temperature and organic solvent concentration). Finally, van't Hoff analysis was compared with differential scanning calorimetry. The results obtained allow us to solve the problem of determining the molecular weight of the structural repeating unit in cross-linked NIPA polymers, which, as we show, can be estimated from the ratio of the molar heat capacity (obtained from the van't Hoff analysis) to the specific heat capacity (obtained from calorimetric measurements).

SummaryItaconic acid has been polymerised in aqueous medium using potassium persulphate as initiator. An important dependence on the polymer yield with the initial pH of the reaction medium is observed. Polymers obtained on this work showed to be mainly atactic, with around 1.14 of polydispersity and molecular weight around 5 × 105 ,g/mol. All the Polymers synthesized were characterized by FTIR, 1H-NMR, 13C-NMR, gpc, thermogravimetry and acid number. Analysis of these materials seem to indicate a decrease of acidity related to the lost of one carboxylic group from the itaconic acid residue, probably due to intramolecular interactions when the monomer is incorporated into the polyiner growing chain.

The inverse emulsion copolymerization of acrylamide (AM) with dimethylaminoethylacrylate methyl chloride (Q9) using redox initiation with low surfactant concentration in an isoparaffinic solvent has been studied. The kinetics of conversions of inverse-emulsion polymerizations were investigated by HPLC method. It was an interesting way to know rapidly the conversion of each monomer with high reproducibility. In all experiments the monomer concentration was 25% respect the total weight or higher and the experiments were carried out at 50∘C.The effects of initiator concentration, composition of the monomer mixture and monomer concentration on the polymerization conversion and viscosity of copolymers solutions have been examined. For copolymer characterization, the results of viscosity were compared with commercial copolymer viscosities.The formulations with 3,000 ppm of initiator were the most interesting of all copolymer compositions since they presented very high conversions and their viscosities were higher than those of commercial copolymer solutions. The analysis of monomer concentration was carried out with 3,000 ppm and the conversion and viscosity were higher when the monomer concentration was increased.

Folate-targeted poly[(p-nitrophenyl acrylate)-co-(N-isopropylacrylamide)] nanohydrogel (F-SubMG) was loaded with 5-fluorouracil (5-FU) to obtain low (16.3 ± 1.9 μg 5-FU/mg F-SubMG) and high (46.8 ± 3.8 μg 5-FU/mg F-SubMG) load 5-FU-loaded F-SubMGs. The complete in vitro drug release took place in 8 h. The cytotoxicity of unloaded F-SubMGs in MCF7 and HeLa cells was low; although it increased for high F-SubMG concentration. The administration of 10 μM 5-FU by 5-FU-loaded F-SubMGs was effective on both cellular types. Cell uptake of F-SubMGs took place in both cell types, but it was higher in HeLa cells because they are folate receptor positive. After subcutaneous administration (28 mg 5-FU/kg b.w.) in Wistar rats, F-SubMGs were detected at the site of injection under the skin. Histological studies indicated that the F-SubMGs were surrounded by connective tissue, without any signs of rejections, even 60 days after injection. Pharmacokinetic study showed an increase in MRT (mean residence time) of 5-FU when the drug was administered by drug-loaded F-SubMGs.

Temperature-sensitive poly(N-isopropylacrylamide) (PNIPA) nanohydrogels were synthesized by nanoemulsion polymerization in water-in-oil systems. Several cross-linking degrees and the incorporation of acrylic acid as comonomer at different concentrations were tested to produce nanohydrogels with a wide range of properties. The physicochemical properties of PNIPA nanohydrogels, and their relationship with the swelling-collapse behaviour, were studied to evaluate the suitability of PNIPA nanoparticles as smart delivery systems (for active packaging). The swelling-collapse transition was analyzed by the change in the optical properties of PNIPA nanohydrogels using ultraviolet-visible spectroscopy. The thermodynamic parameters associated with the nanohydrogels collapse were calculated using a mathematical approach based on the van't Hoff analysis, assuming a two-state equilibrium (swollen to collapsed). A mathematical model is proposed to predict both the thermally induced collapse, and the collapse induced by the simultaneous action of two factors (temperature and pH, or temperature and organic solvent concentration). Finally, van't Hoff analysis was compared with differential scanning calorimetry. The results obtained allow us to solve the problem of determining the molecular weight of the structural repeating unit in cross-linked NIPA polymers, which, as we show, can be estimated from the ratio of the molar heat capacity (obtained from the van't Hoff analysis) to the specific heat capacity (obtained from calorimetric measurements).

SummaryCopolymeric poly(acrylic acid-co-methyl methacrylate) hydrogels for three different compositions: (90/10), (80/20) and (60/40), have been studied. Drug release has been examined as a function of the hydrogel composition by HPLC (High Pressure Liquid Cromatography). The release experiments were carried out at 37 °C. The fraction of available drug release was linear in t1/2. The values of the diffusional coefficient (0.50

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