Study of pH/temperature dual stimuli‐responsive nanogels with interpenetrating polymer network structure

Nanogels with interpenetrating polymer network (IPN) structure based on poly(N‐isopropylacrylamide) (PNIPAM) and poly(acrylic acid) (PAA) were synthesized by in situ polymerization of acrylic acid and N, N′‐methylenebisacrylamide within the PNIPAM nanogels. Their IPN structure was confirmed using transmission electron microscopy after staining by uranyl acetate. The temperature‐ or pH‐dependent hydrodynamic diameters measured using dynamic laser light scattering show that the IPN nanogels have pH and temperature dual stimuli‐responsive properties. As compared to previously reported pH/temperature dual stimuli‐responsive nanogels, these IPN nanogels have the advantage of less mutual interference between the temperature‐responsive and pH‐responsive components, which is beneficial for their applications in controlled drug release and sensors. The temperature‐ and pH‐triggered volume phase transition mechanisms of the IPN nanogels were tested by probing the microenvironment change of their PNIPAM and PAA chains upon phase transition using infrared (IR) absorption spectra measured at different pH values and IR difference spectra obtained by subtracting the IR spectrum obtained before temperature‐induced phase transition from that obtained after phase transition. Copyright © 2012 Society of Chemical Industry     

Development of pH‐sensitive nanogels for cancer treatment using crosslinked poly(aspartic acid‐graft‐imidazole)‐block‐poly(ethylene glycol)

pH‐sensitive nanogels (NGs) based on poly(aspartic acid‐graft‐imidazole)‐poly(ethylene glycol) were developed using linear PEG with different molecular weights (2000 and 4000 Da) as crosslinkers. The pH‐sensitive NGs showed reversible size changes during continuously alternating pH changes. The anticancer treatment potential of pH‐sensitive NGs was studied using a model drug, irinotecan (IRI). IRI‐loaded NGs (ILNs) showed different drug release kinetics in acidic versus neutral pH, in addition to pH‐dependent cytotoxicity. Due to its longer crosslinker, ILN 4 (crosslinked with PEG 4000) showed faster IRI release and a greater magnitude of IRI release than ILN 2 (crosslinked with PEG 2000), resulting in greater cytotoxicity against HCT 116 colorectal cancer cells. These pH‐sensitive NGs could potentially be used in cancer treatment by mediating the accumulation and release of IRI from ILNs in the acidic tumor environment and by reducing systemic toxicity due to reversible swelling–shrinkage. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46268.     

Synthesis and in vitro biological evaluation as antitumour drug carriers of folate‐targeted N‐isopropylacrylamide‐based nanohydrogels

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     

Preparation of pH‐sensitive poly(vinyl alcohol‐g‐methacrylic acid) and poly(vinyl alcohol‐g‐acrylic acid) hydrogels by gamma ray irradiation and their insulin release behavior

A series of pH‐responsive hydrogels were studied as potential drug carriers for the protection of insulin from the acidic environment of the stomach before releasing in the small intestine. Hydrogels based on poly(vinyl alcohol) networks grafted with acrylic acid or methacrylic acid were prepared by a two‐step process. Poly(vinyl alcohol) hydrogels were prepared by gamma ray irradiation (50 kGy) and then followed by grafting either acrylic acid or methacrylic acid onto these poly(vinyl alcohol) hydrogels with subsequent irradiation (5–20 kGy). These graft hydrogels showed pH‐sensitive swelling behavior and were used as carriers for the controlled release of insulin. The in vitro release of insulin was observed for the insulin‐loaded hydrogels in a simulated intestinal fluid (pH 6.8) but not in a simulated gastric fluid (pH 1.2). The release behavior of insulin in vivo in a rat model confirmed the effectiveness of the oral delivery of insulin to control the level of glucose. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 636–643, 2004     

Thermo‐ and glucose‐sensitive microgels with improved salt tolerance for controlled insulin release in a physiological environment

The response to temperature and glucose, high salt tolerance and self‐regulated drug delivery are simultaneously probable by applying a multifunctional microgel in a rational design by a colloid chemistry method. Such smart microgels were fabricated with thermoresponsive N‐isopropylacrylamide, glucose‐sensitive (2‐phenylboronic esters‐1,3‐dioxane‐5‐ethyl)methyl acrylate (PBDEMA) and water‐soluble crosslinker poly(ethylene glycol) diacrylate through a precipitation emulsion method. These colloidal nanoparticles exhibited PBDEMA‐composition‐dependent responsive behavior with changing temperature and ionic strength. Amongst them, the microgel with 20.7 mol% PBDEMA with a narrow size distribution is suitable for diabetes treatment because it can adapt to the surrounding medium of different glucose concentrations over a clinically relevant range (0–2.0 mg mL^?1), control the release of preloaded insulin and is highly stable under normal physiological conditions. Preliminary experiments suggest these highly stable microgels have the potential to be used for self‐regulated therapy and monitoring the response to treatment. © 2018 Society of Chemical Industry     

Synthesis and characterization of novel core‐shell magnetic nanogels based on 2‐acrylamido‐2‐methylpropane sulfonic acid in aqueous media

Ultrafine well‐dispersed Fe₃O₄ magnetic nanoparticles were directly prepared in aqueous solution using controlled coprecipitation method. The synthesis of Fe₃O₄/poly (2‐acrylamido‐2‐methylpropane sulfonic acid) (PAMPS), Fe₃O₄/poly (acrylamide‐co‐2‐acrylamido‐2‐methylpropane sulfonic acid) poly(AM‐co‐AMPS) and Fe₃O₄/poly (acrylic acid‐co‐2‐acrylamido‐2‐methylpropane sulfonic acid) poly(AA‐co‐AMPS) ‐core/shell nanogels are reported. The nanogels were prepared via crosslinking copolymerization of 2‐acrylamido‐2‐methylpropane sulfonic acid, acrylamide and acrylic acid monomers in the presence of Fe₃O₄ nanoparticles, N,N′‐methylenebisacrylamide (MBA) as a crosslinker, N,N,N′,N′‐tetramethylethylenediamine (TEMED) and potassium peroxydisulfate (KPS) as redox initiator system. The results of FTIR and ¹H‐NMR spectra indicated that the compositions of the prepared nanogels are consistent with the designed structure. X‐ray powder diffraction (XRD) and transmission electron microscope (TEM) measurements were used to determine the size of both magnetite and stabilized polymer coated magnetite nanoparticles. The data showed that the mean particle size of synthesized magnetite (Fe₃O₄) nanoparticles was about 10 nm. The diameter of the stabilized polymer coated Fe₃O₄ nanogels ranged from 50 to 250 nm based on polymer type. TEM micrographs proved that nanogels possess the spherical morphology before and after swelling. These nanogels exhibited pH‐induced phase transition due to protonation of AMPS copolymer chains. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation of glucose‐sensitive and fluorescence micelles via a combination of photoinitiated polymerization and chemoenzymatic transesterification for the controlled release of insulin

Glucose‐sensitive and fluorescence copolymer micelles were designed and prepared via a combination of photoinitiated polymerization and enzymatic transesterification. The water‐soluble photoinitiator and emulsifier 2‐oxooctanoic acid self‐polymerized dimer molecules under UV irradiation were characterized by mass spectrometry. The fluorescence dye (9‐anthracene alcohol) and biocompatible hydrophilic chains [poly(ethylene glycol)] were introduced to the polymer chains during the photopolymerization and enzymatic transesterification processes. The as‐prepared copolymers were confirmed by ¹H‐NMR spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, and dynamic light scattering. The resulting copolymers exhibited excellent glucose sensitivity and stability against protein. The optical fluorescence properties of the copolymer micelles were investigated with fluorescence spectrophotometry, fluorescence microscopy, and confocal laser scanning microscopy. Because of the amphiphilic feature, the micelles could be self‐assembled and used to load insulin. The controlled release of insulin was evaluated and was triggered by glucose in vitro. This study provided a new strategy for fabricating functional carriers as self‐regulated insulin‐release systems. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43026.     

Photoresponsive nanogels synthesized using spiropyrane‐modified pullulan as potential drug carriers

Reversible light‐responsive nanogels were constructed from an amphiphilic spiropyrane‐modified pullulan (SpP). The polymer was synthesized by modifying a biodegradable pullulan with carboxyl‐containing spiropyrane (Sp) molecules. The SpP structure was confirmed by the appearance of a carbonyl signal in the FT‐IR and ¹H NMR spectra. The nanogels can be controlled by photostimulation, which results in the reversible structural transformation of the hydrophobic Sp to the hydrophilic merocyanine. The physical properties of the nanogels were confirmed to change dramatically after being irradiated with different wavelengths of light. Drug delivery tests showed that the model drug pyrene was completely captured by the nanogels and then released from the SpP nanogels in a light‐dependent manner. This study provides an alternative approach to constructing light‐responsive nanocarriers with excellent biocompatibility for drug uptake and release. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40288.     

Nanogels of poly(acrylic acid): Uptake and release behavior with fluorescent oligothiophene‐labeled bovine serum albumin

Nanometer‐sized poly(acrylic acid) (PAA) hydrogels were synthesized by emulsion polymerization of methyl acrylate and subsequent acidic hydrolysis. The nanohydrogel was characterized by spectroscopic methods (FTIR and ¹H‐NMR) and scanning probe techniques, and their pH‐dependent swelling behavior was studied by dynamic light scattering. To determine the suitability of PAA nanogels as pH‐sensitive carriers for biomedical applications, uptake and release of an oligothiophene fluorophore and its albumin conjugated from PAA nanogels were investigated as a function of pH by absorption and photoluminescence measurements. It was observed that uptake and release processes of both the oligothiophene and its conjugate could be controlled by changing the pH of the external solution. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Self‐organized nanogels from pullulan‐g‐poly(L‐lactide) synthesized by one‐pot method: Physicochemical characterization and in vitro doxorubicin release

Water‐insoluble pullulan‐g‐poly(L ‐lactide) (PUPL) was successfully synthesized via a one‐pot method in the presence of triethylamine in dimethyl sulfoxide, in an effort to design a novel anticancer agent carrier. Three samples (designated as PUPL 1, 2, and 3) were obtained, which differed in the moles of lactides grafted to the pullulan. The degrees of grafted lactide per 1 glucose unit in pullulan were 0.68, 0.60, and 0.45 for PUPL 1, 2, and 3, respectively. These copolymers were dissolved in several organic solvents, including dimethyl sulfoxide, acetone, and ethanol, but were insoluble in water. The self‐organized nanogels were then prepared from the polymers via dialysis. To study the organizing behavior of the polymers, their critical association concentrations were measured. Their values were 5.0, 15.9, and 52.9 mg/L for PUPL 1, 2, and 3, respectively. The results showed that lactide in the polymers could function as a hydrophobic moiety for the formation of self‐organized nanogels. To estimate the potential of PUPL 1 as an anticancer drug carrier, we used doxorubicin (DOX) as a model drug. The DOX loading efficiencies of PUPL 1 were more than 52%, which differed with differing initial DOX concentrations. High loading resulted in slower DOX release as the result of increases in hydrophobic interaction. In conclusion, PUPL nanogels may prove useful as anticancer drug carriers because of their low critical association concentrations and the controlled DOX release rate © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and characterization of a porous poly(hydroxyethylmethacrylate‐co‐ethylene glycol dimethacrylate)‐based hydrogel device for the implantable delivery of insulin

Poly(hydroxyethylmethacrylate‐co‐ethylene glycol dimethacrylate) [poly(HEMA‐co‐EGDMA)]‐based hydrogel devices were synthesized by a free‐radical polymerization reaction with 2‐hydroxyethylmethacrylate as the monomer, different concentrations of ethylene glycol dimethacrylate (EGDMA) as the crosslinking agent, and ammonium persulfate/N,N,N′,N′‐tetra‐methyl ethylenediamine as the free‐radical initiator. The porosity of the poly(HEMA‐co‐EGDMA) hydrogels was controlled with water as the porogen. The Fourier transform infrared spectrum of poly(HEMA‐co‐EGDMA) showed absorption bands associated with ? C?O stretching at 1714 cm^?1, C? O? C stretching vibrations at 1152 cm^?1, and a broad band at 3500–3800 cm^?1 corresponding to ? OH stretching. Atomic force microscopy studies showed that the hydrogel containing 67% water had pores in the range of 3500–9000 nm, whereas the hydrogel containing 7% water did not show measurable pores. The hydrogel synthesized with 1% EGDMA showed 50% thallium‐201 release within the first 30 min and about 80% release within 60 min. In vitro insulin‐release studies suggested that the hydrogel with 27% water showed sustained release up to 120 min, whereas the hydrogels with 47 and 67% water showed that nearly all of the insulin was released within 60 min. Hydrogel devices synthesized with 27% water and filled with insulin particles showed sustained release for up to 8 days, whereas the hydrogels synthesized with 47 and 67% water released insulin completely within 3 days of administration. Animal studies suggested that the hydrogel devices synthesized with 27% water and filled with insulin‐loaded particles (120 IU) were able to control blood glucose levels for up to 5 days after implantation. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Photo/pH dual‐responsive biocompatible poly(methacrylic acid)‐based particles for triggered drug delivery

A novel dual‐responsive (light and pH) particle based on poly(methacrylic acid), poly(methacrylic acid)–poly[1‐(2‐nitrophenyl)ethane‐1,2‐diyl bis(2‐methylacrylate)]was prepared with the facile method of two‐step homogeneous radical polymerization with methacrylic acid as the monomer and 1‐(2‐nitrophenyl)ethane‐1,2‐diyl bis(2‐methylacrylate) as a photodegradable crosslinker. Photolytic assessments were conducted upon irradiation with a UV lamp; this led to particle disintegration caused by cleavage of the photolabile crosslinking points. The light‐dependent degradation was investigated through particle size changes, absorption spectra variations, surface morphology changes, Fourier transform infrared spectroscopy, and the release of Nile red from the particles after irradiation. The pH dependence of the particle systems induced by the protonation and deprotonation of poly(methacrylic acid) was also confirmed by fluorescence spectroscopy. The triggered release of fluorescein diacetate was investigated to demonstrate that the release behavior in cells was light dependent. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44003.     

Surface‐active amphiphilic poly[(2‐acrylamido‐2‐methylpropanesulfonic acid)‐co‐(N‐isopropylacrylamide)] nanoparticles as stabilizer in aqueous emulsion polymerization

This work reports the effect of nanogel solid particles on the surface and interfacial tension of water/air and water/styrene interfaces. Moreover, the work aimed to use nanogels as a stabilizer for miniemulsion aqueous polymerization. A series of amphiphilic crosslinked N‐isopropylacrylamide (NIPAm) and 2‐acrylamido‐2‐methylpropanesulfonic acid (AMPS) copolymer nanogels were synthesized based on an aqueous copolymerization batch method. Divinylbenzene and N,N‐methylene bisacrylamide were used as crosslinkers. The morphologies of the prepared nanogels were investigated using transmission and scanning electron microscopies. The lower critical transition temperatures were determined using differential scanning calorimetry. The surface tension of colloidal NIPAm/AMPS dispersions was measured as functions of surface age, temperature and the morphology of the NIPAm/AMPS nanogels. The NIPAm/AMPS nanogels reduced the surface tension of water to about 30.1 mN m^?1 at 298 K with a small increase at 313 K. Surface activities of these nanogels in water were determined by surface tension measurements. The NIPAm/AMPS dispersions had high surface activity and were used as a stabilizer to prepare a crosslinked poly(styrene‐co‐AMPS) microgel based on emulsion crosslinking polymerization. © 2013 Society of Chemical Industry     

pH‐ and temperature‐sensitive in vitro release of salicylic acid through poly(vinyl alcohol‐g‐acrylamide) membranes

In this study, acrylamide (AAm) was grafted onto poly(vinyl alcohol) (PVA) in solution with UV radiation, and membranes were prepared from the graft copolymer (PVA‐g‐AAm) for transdermal release of salicylic acid (SA) at in vitro conditions. Permeation studies were carried out using a Franz‐type diffusion cell. Release characteristics of SA through PVA and PVA‐g‐AAm membranes were studied using 2.0 mg/mL SA solutions. Effects of the presence of AAm in the copolymer, pH of donor and acceptor solution, and concentration of SA and temperature on the release of SA were investigated. Permeation of SA through the membranes was found to be pH‐dependent, and increase in pH generally increased the release percentage of SA, and the presence of AAm in the membrane positively affected the permeation. The effect of concentrations of SA on the permeation was also searched using saturated solution of SA, and permeated amount of SA was found to be less than in the case of unsaturated SA solution. Studies showed that the release of SA from PVA‐g‐AAm membranes was temperature‐sensitive and increase in temperature increased the permeation rate. 82.76% (w/w) SA was released at the end of 24 h at (39 ± 1)°C, and the overall activation energy for the permeation of SA through PVA‐g‐AAm membranes was found to be 19.65 kJ/mol. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Temperature‐induced volume change and glucose sensitivity of poly[(N‐isopropylacry‐ lamide)‐co‐acrylamide‐co‐(phenylboronic acid)] microgels

Nearly monodisperse glucose‐sensitive poly[(N‐isopropylacrylamide)‐co‐acrylamide‐co‐(phenylboronic acid)] microgels were synthesized in aqueous media by the functionalization of poly[(N‐isopropylacrylamide)‐co‐acrylamide‐co‐(acrylic acid)] microgels with 3‐aminophenylboronic acid via carbodiimide coupling. The glucose‐sensitive and thermosensitive behaviour of the microgels was investigated using a dynamic light scattering technique. The introduction of the hydrophobic phenylboronic acid (PBA) group significantly decreases the temperature at which maximum volume change of the resultant microgel particles is observed. The glucose sensitivity of the PBA‐containing microgels relies on the stabilization of the charged phenylborate ions by binding with glucose, which can convert more hydrophobic PBA groups to the hydrophilic phenylborate ions. The effect of pH, ionic strength and PBA content on temperature‐induced volume change and glucose sensitivity was systemically studied. The effect of NaCl on the glucose sensitivity was also investigated at physiological pH and ionic strength. Copyright © 2011 Society of Chemical Industry     

Prolonged zero‐order BSA release from pH‐sensitive hydrogels of poly(AAc‐co‐DMAPMA) having rich nano through micro scale morphology

New variety of pH‐sensitive hydrogels, having macroporous interior with honey‐comb type architecture and continuous skin at the surface, have been developed by single step aqueous copolymerization of acrylic acid (AAc) and N‐[3‐(dimethylamino)propyl]‐methacrylamide (DMAPMA) in different feed ratios at 41 ± 1°C. Interlocked nanogels of ～ 300 nm were identified as the building blocks in all of these cylindrical poly(AAc‐co‐DMAPMA) matrices (PDMAAc). The gels showed good compressive strength even at a swelling as high as 4330% (mass) at pH 7.0. Morphology of McCoy fibroblast cell line remained unchanged in direct contact with different PDMAAc gels, and cell viability (±SD) was recorded to be in the range of 105 (±3)% to 87 (±8)% after 72 h. Bovine serum albumin (BSA) loaded gels were prepared by means of equilibrium partitioning. Loading efficiency of PDMAAc gels has been found to be in the range of 210–277 mg/g dry gel. BSA release from PDMAAc gels at 37°C has been found to follow non‐Fickian diffusion mechanism in simulated gastric juice (pH 1.2), and Case II transport in simulated intestinal juice (pH 7.4). In vitro study showed that the gels are capable of retaining >95% of the loaded BSA in gastric medium through average gastric emptying period. Again, ～ 56% BSA release was recorded in 24 h at pH 7.4, indicating prolonged BSA diffusion in intestinal condition. Constant rate of BSA diffusion was reflected from the release profiles at both the pH. Diffusion exponents also supported the same and indicated for absolute zero‐order kinetics at pH 7.4. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Poly(hexylacrylate)Core‐poly(ethyleneglycol methacrylate)Shell nanogels as fillers for poly(2‐hydroxyethyl methacrylate) nanocomposite hydrogels

The preparation of poly(hexylacrylate)_core‐poly(ethyleneglycol methacrylate)_shell (PHA‐co‐PEGMA) nanogels, to be used as fillers in nanocomposite hydrogels, is reported. Stable nanogels with particle sizes between 90–300 nm were obtained varying the conditions of synthesis. The synthesis recipe of the nanogels could be easily scaled up. Purified and dispersed nanogels in aqueous solution were used as soft fillers for poly(2‐hydroxyethyl methacrylate) (PHEMA) hydrogels, crosslinked with ethylene glycol dimethacrylate (EGDMA). The obtained nanocomposite hydrogels exhibit a larger swelling capacity and a higher thermal stability in comparison with the non‐filled PHEMA hydrogels. Young, storage, and lost moduli, increase largely, in the better case up to 72.5% in the swollen state; while in the dry state the storage modulus increase up to 4.7 fold with a very low load on nanogels (0.64 wt%); resulting in biomaterials with improved properties with potential applications in medical devices. POLYM. ENG. SCI., 59:170–181, 2019. © 2018 Society of Plastics Engineers     

Synthesis and characterization of poly(acrylic acid‐co‐N‐[3‐(dimethylamino)propyl]‐methacrylamide) hydrogel membranes for biomedical applications

A series of new hydrogel membranes with different compositions of acrylic acid (AAc) and N‐[3‐(dimethylamino)propyl]‐methacrylamide (DMAPMA) were prepared by aqueous copolymerization, without using chemical crosslinker or radiation. Chemical structure of the membranes (PADMAs) was characterized by Fourier transform infrared spectroscopy (FTIR). Swelling experiments were carried out in simulated body fluid (SBF) at 37 ± 1°C to investigate degree of swelling, dimensional stability, and pore size of the PADMA membranes. In SBF, the variation of pore size with membrane composition was monitored by optical microscopic technique. Morphology of the membranes was characterized, before and after exposure to SBF, by scanning electron microscopy (SEM). It was observed that the membranes are composed of closely packed nanogels of ～200 nm. Macroporous network structure of the SBF‐swollen PADMA was also observed to be composed of interconnected nanogels. Blood compatibility of the PADMA membranes was evaluated in vitro, by performing hemolysis assay and thrombogenicity assay. The extent of hemolysis due to PADMA membranes was found to be <2%, which ensured that all of the membranes were highly hemocompatible. Salicylic acid (SA) was chosen as a model drug. Diffusion coefficient of SA through PADMA membranes was investigated. It was observed that membrane composition regulates both pore size and drug diffusion. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Poly[(N‐isopropylacrylamide)‐co‐(itaconic acid)] hydrogels with poly(ethylene glycol)

The aim of the work reported here was to investigate temperature‐ and pH‐sensitive hydrogels of N‐isopropylacrylamide (NIPAM) and itaconic acid (IA) and their semi‐interpenetrating polymer networks (semi‐IPNs) with varying contents of poly(ethylene glycol) (PEG). The stimuli responsiveness, swelling behaviour and mechanical properties of the hydrogels and semi‐IPNs were studied in order to investigate the effect of various amounts of PEG. Pulsed‐gradient spin‐echo NMR experiments were carried out to investigate the diffusion process. The pH sensitivity increased with an increasing amount of PEG in the semi‐IPNs, while the overall rate of water uptake was diffusion‐controlled (n < 0.5). For certain PEG contents (5 and 10 wt%), the semi‐IPNs exhibited better mechanical properties than the poly(NIPAM‐co‐IA) copolymer. The calculated values of the self‐diffusion coefficients of water indicated facilitated diffusion of water through the system with increased amounts of PEG, while the self‐diffusion coefficients of a model compound, metoprolol tartrate, showed no significant dependence on the amount of PEG. According to the results obtained and compared to results reported in the literature, the investigated semi‐IPNs may have potential applications in the controlled release of macromolecular active agents such as proteins and peptides. Copyright © 2009 Society of Chemical Industry     

Characterization of p(AA‐co‐AM)/bent/urea and its swelling and slow release behavior in a simulative soil environment

In this work, a novel slow release fertilizer contained 14.98% nitrogen was prepared via free radical polymerization of acrylic acid, acrylamide, and bentonite in the presence of cross‐linker (N,N′‐methylenebis acrylamide), initiator (potassium persulfate), and nutrient source (urea). The samples were analyzed using a Fourier transform infrared spectrometer, X‐ray diffraction, Scanning electron microscopy, Thermogravimetric analysis, and Brunauer, Emmett and Teller analysis. Results showed that the swelling and release behaviors were strongly dependent on the type and concentration of salt solution added to the medium, pH levels of the solutions, and temperature. Moreover, the experimental data indicated that the addition of Bent not only improved water absorbency and water retention capacities but also controlled the release of nutrients. The release kinetic simulation analysis findings showed that the release of urea was predominated by a Case II release mechanism with skeleton erosion. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43082.