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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).

In this work the synthesis of smart nanoparticles capable of respond to external stimulus (pH and temperature variations) is reported. To avoid post-polymerization modification, functionalized monomers able to respond to pH and temperature changes were and then polymerized. The synthesized monomers have the capability for coupling with folic acid which is the target molecule. For this reason their polymers can be used as targeted drug delivery systems. Smart polymeric nanoparticles were prepared by direct and inverse microemulsion polymerization of the synthesized monomers. The nanoparticles were charged with drugs and their release kinetic was studied.

Copolymeric nanohydrogels based on N-isopropylacrylamide, N-(pyridin-4-ylmethyl)acrylamide and tert-butyl-2-acrylamidoethyl carbamate, synthesized by microemulsion polymerization, were characterized using Fourier transform infrared spectroscopy and their size (38-52 nm) determined using quasielastic light scattering. Folic acid was covalently attached to the nanohydrogels (1.40 ± 0.07 mmol g−1). Tamoxifen (6.7 ± 0.2-7.3 ± 1.2 µg TMX mg−1 nanohydrogel), a hydrophobic anticancer drug, and 5-fluorouracil (7.7 ± 0.7-10.14 ± 1.75 µg 5-FU mg−1 nanohydrogel), a hydrophilic anticancer drug, were loaded into the nanohydrogels. Maximum in vitro TMX release (77-84% of loaded drug) depended on interactions of the drug with hydrophobic clusters of the nanogels; however, no nanogel/5-FU interactions allowed total release of the loaded drug. The cytotoxicity of unloaded nanohydrogels in MCF7, T47D and HeLa cells was low. Cell uptake of nanogels without bound folic acid took place in the three cell types by unspecific internalization in a time-dependent process. Cell uptake increased for folic acid-targeted nanohydrogels in T47D and HeLa cells, which have folate receptors. The administration of 10 and 30 µmol L−1 TMX by TMX-loaded nanogels and 10 µmol L−1 5-FU by 5-FU-loaded nanogels was effective on the three cell types, and the best results were obtained for folic acid-targeted nanohydrogels. Copyright © 2012 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

We used temperature-sensitive poly(Nisopropylacrylamide) 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. [ABSTRACT FROM AUTHOR]

The article reports on the synthesis and characterization of poly(butyl monoitaconate-co acrylamide) hydrogels to be used as drug release agents. The hydrogels were synthesized using four isomers of butanol. The authors also reported the influence of butyl monoitaconate isomery on swelling behavior and Young's and compression moduli. A decrease in the time for reaching swelling equilibrium was observed when butyl ramification was increased.

The article presents a study that synthesized poly(N-isopropylacrylamide) (PNIPA) nanohydrogels by inverse microemulsion for the controlled release of anti-tumour drugs. The anti-tumour drugs 5-fluorouracil (5-FU), methotrexate (MTX) and mitomycin C (MMC) were loaded into PNIPA nanogels using spray drying and freeze drying to obtain drug-loaded xerogels. Their effect on drug release was evaluated using mathematical modelling. The researchers concluded that drug release was quicker when spray drying was used than those obtained by freeze drying.

Hydrogels of acrylic acid and itaconic acid has been synthesized with different monomers ratios. The swelling process of the different xerogels immersed in water and salt solutions has been studied. The swelling of hydrogels loaded with metal cations (Cu2+, Zn2+) was also investigated. The swelling process was monitored by the increase in the weight of hydrogel as a function of time. The absorption properties of metal ions were studied by using the hydrogel, and different concentrations of copper and zinc solutions (prepared from sulphate salts). The influence of pH on the absorption process was studied. For the absorption of metal ions, the amount of ions absorbed within the hydrogel can be calculated from the initial and equilibrium concentrations of the metal ions in aqueous phase, the weight of the hydrogel, and the volume of solution used. Metal absorption increased when pH, salt concentration in external solution and itaconic acid content is levelled. The swelling isotherms which consisted of an initial fast increase levelled off asymptotically to the equilibrium swelling limit. The experimental data clearly suggest that our hydrogels follow a second-order kinetics for both cases (unload and metal loaded). The kinetics rate constant and the equilibrium water content, K, have been calculated for every monomer ratio from the experimental data according to the kinetics equation. Both magnitudes decreased as the itaconic acid content decreases in the xerogels. [ABSTRACT FROM AUTHOR]

The mechanical and thermodynamic properties of poly(acrylic acid-co-methyl methacrylate) hydrogels with varying ratios of AA/MMA are reported. Swelling capacity increases but elasticity decreases as the content of AA in the hydrogels increases. Thermodynamic analysis indicates that swelling is an unfavorable and endothermic process. Both thermodynamic quantities increase with increasing hydrophobic nature of the hydrogel. The amount of freezing and non-freezing water in the hydrogels was determined by DSC. The ratio of non freezing to total water content increases with the increasing hydrophobic nature of the hydrogels. [ABSTRACT FROM AUTHOR]

Highlights: [•] New gels based on PEG and PVA of different degrees of hydrolysis were synthesized. [•] PVA degree of hydrolysis and PEG content of the network control the swelling capacity. [•] The pH influences the degree of swelling and the rate of hydrolysis of the hydrogel. [•] The degree of hydration decreases with temperature because their entropy is negative. [Copyright &y& Elsevier]

Abstract: Networks of β-cyclodextrin have been prepared by reaction with acylated poly(ethylene glycol) with a molar mass of 600g/mol. Samples with different β-cyclodextrin/poly(ethylene glycol) ratios: 1/4, 1/6, 1/8 and 1/10 have been prepared. Both components are bonded by ester groups, resulting in a network that can be degraded by hydrolysis in basic and acidic media. The maximum stability of the hydrogels is reached at pH 4. The hydrogel percentage water content depends on β-cyclodextrin content ranging from 82 to 98, and the swelling data obtained for these hydrogels fit well with a second order kinetics. The sorption behavior of these hydrogels has been tested by employing 1-naphthol as model molecule. The sorption capacity is close to other cyclodextrin networks previously reported and depends on the hydrogel composition and the concentration of 1-naphthol. [Copyright &y& Elsevier]