Papers by Keyword: Poly(N-isopropylacrylamide)

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Authors: Xin Cai Xiao
Abstract: In this article, a novel structure poly(N-isopropylacrylamide) (PNIPAM) hydrogel, which is featured with both ends of linear PNIPAM chains being grafted onto semicircular and cross-linked PNIPAM chains, has been successfully prepared in a three-step process by a method of sequential synthesis for the first time. The proposed hydrogel displays faster and hydration/dehydration dynamic response to temperature cycling owing to linear PNIPAM chains to form big-hole structure. This work may be highly attractive for targeting drug delivery systems, polymeric machinery, and sensors and so on.
Authors: Yun Suk Jo, Do-Kyung Kim, Young Keun Jeong, Kyung Ja Kim, Mamoun Muhammed
Abstract: A novel approach to load a hydrophilic bovine serum albumin (BSA) into the drug carriers was proposed in terms of thermosensitive dual-shell structures which were fabricated with poly(N-isopropylacrylamide), poly(lactide) and Au nanoparticles. Spherically well-defined dualshell structures were constructed by a modified-double-emulsion method (MDEM). The lower critical solubility temperature of the structures was shifted to 36.4 °C which was confirmed by UVVis spectroscopy.
Authors: Qun Feng Liu, Bo Yuan, Xiao Feng Chen
Abstract: A kind of poly(N-isopropylacrylamide) (PNIPAM) gel was synthesized by radical polymerization of N-isopropylacrylamide monomer in the present of crosslinker N,N-Methylenebisacylamide using short reaction time. This kind of PNIPAM gel exhibits higher swelling ratio at low temperature and much faster deswelling rate than conventional gel, which could be attributed to the presence of loops, dangling chains and other incomplete structure in the gel caused by short reaction time.
Authors: Xiao Xia Qiu, Jie Sun, Shu Jie Tong, Shi Jia Wang, Li Yuan Wu, Fang Yuan Cheng, Hai Ning Lv
Abstract: N-isopropylacrylamide was synthesized in a mixture of DMF and THF ( 7:3 in volume ratio) and characterized by FT-IR. The behavior of poly(N-isopropylacrylamide) chain was studied by spectrometer in mixtures of water with DMF and THF. Cononsolvency phenomena were found to be temperature-dependent, as demixing occurred upon increasing temperature. A significant shrinkage of polymer chains and deswelling of polymer gels, followed by phase separation, were observed for high water fractions.
Authors: A.A. Naddaf, H.J. Bart, I. Tsibranska
Abstract: A two-dimensional diffusion mathematical model with moving boundary conditions was developed to evaluate the diffusion kinetics of bovine serum albumin (BSA) through the network of poly(N-isopropylacrylamide) hydrogel (poly(NIPAAm)). These thermosensitive hydrogels were experimentally tested for their response to BSA by exposing the hydrogel disc-shaped geometry to different temperatures and varied protein concentration. The BSA release, which is coupled with hydrogel shrinking when reaching the low critical solution temperature (LCST) of poly(NIPAAm), could be satisfactory described by the model. During the early course of hydrogel shrinking, the hydrogel outermost surface layer collapses to form a dense layer in comparison to the interior bulk matrix. Due to the hydrophobic interaction between polymer chains and polymer protein, the formed layer is thick and dense enough to restrict the outward permeation of entrapped BSA molecules from the hydrogel interior, which greatly slows down the release rate. A good agreement between experimental and calculated data was achieved.
Authors: Qiao Feng, Ling Zhi Du, Qing Zhi Yan, Chang Chun Ge
Abstract: The synthesis of thermo-responsive hydrogels poly(N-isopropylacrylamide )(PNIPAm) by frontal polymerization (FP) was carried out in four mixed solvents, i.e. dimethylsulfoxide (DMSO) mixing with water, ethanol, tetrahydrofuran (THF) and acetone, respectively. The influences of mixed solvent on frontal parameters, pore morphologies, swelling behavior of PNIPAm hydrogels were investigated. The pore of PNIPAm hydrogel synthesized in THF/DMSO was observed a big honeycomb cells, others were channel-like cells. Furthermore, the sample obtained in THF/DMSO had higher swelling ratio as compared to others, and the one synthesized in Water/DMSO showed the lowest. Above results indicated that fine-tuned poly(N-isopropylacrylamide) hydrogels can be prepared in short time and with easy protocol by adjusting mixed solvents in frontal polymerization process.
Authors: Qiao Feng, Ya Qi Zhao, Xiang Chen
Abstract: The thermo-responsive hydrogels poly(N-isopropylacrylamide) (PNIPAm) were synthesized by frontal polymerization (FP) in dimethylsulfoxide (DMSO) and ethanol mixture. The effects of composition of synthesis-solvent on FP feature and porous morphologies as well as their response behavior of the final products were studied. PNIPAm hydrogel synthesized in mixture exhibited a porous structure, which was responsible for its higher swelling ratio. Moreover, an improvement in swelling capability of the final PNIPAm hydrogel was found when the ethanol content in mixed media was elevated. The approach, frontal polymerization in mixed solvent, reported here provides a promising option to synthesize porous intelligent hydrogels PNIPAm.
Authors: Chen Zhang, Xiao Yun Liu, Liu Sheng Zha
Abstract: The microgels with semi-interpenetrating polymer network (semi-IPN) structure based on cross-linked poly(N-isopropylacrylamide) (PNIPAM) and linear poly(acrylic acid) (PAA) were fabricated by one-step precipitation polymerization technique. The chemical composition of the microgels was determined by Fourier transformation infrared spectroscopy and elemental analysis. It was found that the PAA content inside the microgels decreased as the pH value of reaction media increased. The semi-IPN structure of the microgels was confirmed by transmission electron microscopy using uranyl acetate staining method. The pH dependent hydrodynamic diameters obtained by dynamic light scattering revealed that these microgels can reversibly shrink and swell in the pH range from 4.0 to 6.0. The semi-IPN microgels synthesized at pH 3.0 could undergo about 120 times volume change in the pH range.
Authors: Qiong Jiao Yan
Abstract: A novel graded hydrogel based on poly(N-isopropylacrylamide) (PNIPAM), which is characterized with both ends of slightly cross-linked PNIPAM chains being grafted onto cross-linked PNIPAM chains, has been successfully prepared in a three-step process by a method of sequential synthesis for the first time in this paper. In the preparation of the graded hydrogels, with decreasing the crosslinker dosage, the swelling ratio of the hydrogel increased. The graded hydrogel displays faster and hydration/dehydration dynamic response to temperature cycling owing to slightly cross-linked PNIPAM chains to form big-hole structure. The proposed hydrogel structure provide a new mode of the phase transition behavior for thermo-sensitive "smart" or "intelligent" monodisperse micro-actuators, which is highly attractive for targeting drug delivery systems, chemical separations, sensors and so on.
Authors: Chang Jing Cheng, Rui Xie, Xiao Jie Ju, Liang Yin Chu
Abstract: Submicron-sized monodisperse and spherical poly(N-isopropylacrylamide-co-glycidyl methacrylate)-β-cyclodextrin (PNG-CD) microgels with both thermo-responsive and molecular-recognition characteristics have been successfully fabricated via soap-free emulsion polymerization and subsequent chemical modification method. The thermo-responsivity of the microgels is based on the volume phase transition of poly(N-isopropylacrylamide) (PNIPAM) and the molecular-recognition property is based on the host-guest inclusion complexation of β-cyclodextrin (β-CD) units with specific guest molecules. The as-prepared microgels are characterized by Fourier transform infrared (FT-IR), scanning electron microscope (SEM), and dynamic light scattering (DLS) instrument. When β-CD is introduced onto the PNG-CD microgels, the volume phase transition temperature (VPTT) of resultant PNG-CD microgels shifts about 6 °C to a higher temperature in comparison with that of corresponding PNG microgels. When the β-CD units in PNG-CD microgels recognize 8-anilino-1-naphthal-enesulfonic acid ammonium salt (ANS) molecules in aqueous solution, the VPTT of PNG-CD microgels shifts around 3 °C negatively to a lower temperature. PNG-CD microgels present molecular-recognition induced swelling characteristics at fixed temperature. The results in this study provide valuable information for development of monodisperse and spherical dual thermo-responsive and molecular-recognition microgels which have potential applications in the fields of microscale molecular sensors and actuators and so on.
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