A novel thermoresponsive hydrogel with ion-recognition property through supramolecular host-guest complexation

A novel thermoresponsive hydrogel with ion-recognition property was prepared via free-radical cross-linking copolymerization of N-isopropylacrylamide (NIPAM) with benzo-18-crown-6-acrylamide (BCAm) as host receptor. Both chemical structures and stimuli-sensitive properties of the prepared poly(N-isopropylacrylamide-co-benzo-18-crown-6-acrylamide) P(NIPAM-co-BCAm) hydrogel were characterized. The smart hydrogel could respond to both temperature and ion stimuli. When the crown ether units captured Ba2+ and formed stable BCAm/Ba2+ host-guest complexes, the lower critical solution temperature (LCST) of the hydrogel increased due to the repulsion among charged BCAm/Ba2+ complex groups and osmotic pressure within the hydrogel. Whereas crown ethers captured Cs+, the LCST shifted to a lower temperature because of the formation of 2:1 sandwich complexes. Unexpectedly, the LCST of the cross-linked P(NIPAM-co-BCAm) hydrogel in K+ solution did not shift to a higher temperature, which was definitely different from the previously reported linear P(NIPAM-co-BCAm) copolymer in K+ solution. The results of this work provide valuable information for development of dual thermo- and ion-responsive hydrogels which have potential applications in drug controlled-release systems or biomedical fields.     

Modelling of the pore size distribution of ultrafiltration membranes

A dilute aqueous solution of polydisperse neutral dextrans was used to determine the sieving properties (flux and rejection) of porous polyacrylonitrile membranes. Gel ermeation chromatography was used to measure the solute mole and concentration in the permeate. From these data, rejection coefficients were calculated as a function of solute molecular size. A mathematical model was then developed to relate the flux and solute rejection to pore size distribution and the total number of pores, based upon the assumption that solute rejection was the result of purely geometric considerations. As a first approximation, a solute molecule was considered either too large to enter a membrane pore, or if it entered, its concentration in the permeate from that pore, as well as the solvent flux through the pore, were not affected. This model also considered the effects of steric hindrance and hydrodynamic lag on the convection of solute through a membrane. The shape and sharpness of pore size distributions were found to be useful in comparisons of ultrafiltration membranes.     

Poly(N-isopropylacrylamide) grafted into nanopores: Thermo-responsive behaviour in the presence of different salts

Surface initiated polymerization of N(isopropylacrylamide) (NIPAM) was performed by controlled radical polymerization on PET track-etched membranes presenting two different pore diameters (narrow pores: ∼80 nm and large pores: ∼330 nm). The opening and closing characteristics of the resulting PNIPAM-g-PET membranes were investigated by conductometric measurements carried out at different temperatures below and above the LCST of PNIPAM and in the presence of different salts. Depending on the membrane pore size, two types of permeation control mechanisms are observed. In large pore membranes, expanded PNIPAM chains conformations result in reduced effective pore size and therefore lower permeabilities relative to collapsed macromolecules chain conformations. In contrast, in narrow pore membranes, the expanded PNIPAM brush presents greater degrees of hydration in the surface layer and therefore gives rise to higher permeabilities than the collapsed conformation. In this situation, the overall permeability is thus comparable to that of a hydrogel membrane.     

Development of a regenerable cell culture system that senses and releases dead cells

We developed a rapidly regenerable cell culture system in which the cell culture substrate detects cell death and selectively releases the dead cells. This culture material was achieved by combining a detector that responds to the signal from the dead cells and an actuator to release the dead cells. Benzo-18-crown-6-acrylamide (BCAm) with a pendant crown ether receptor was used as the sensor to recognize cellular signals and N-isopropylacrylamide (NIPAM) was used as the actuator. This copolymer of NIPAM and BCAm can respond to potassium ions and change its nature from hydrophobic to hydrophilic at the culture temperature of 37 degrees C. Living cells concentrate potassium ion internally; when cells die, potassium ions are released. The polymer surface recognizes the potassium ions released from the dead cells, the NIPAM hydrates, and the dead cells are selectively detached. This in vitro culture system is a novel one in which artificial culture materials work cooperatively with cellular metabolism by responding to this signal from the cells, thereby realizing in vitro tissue regeneration partly mimicking the mechanisms of in vivo homeostasis.     

Controlled release of model drugs through a molecular recognition ion gating membrane in response to a specific ion signal

A controlled-release device that responds to a specific molecular signal is an ideal goal in drug delivery and tissue engineering. A molecular recognition ion gating membrane, in which a copolymer of N-isopropylacrylamide and benzo[18]-crown-6-acrylamide was grafted onto the surface of the porous polyethylene film, was used to control the permeability of vitamin B12 and lysozyme in response to a specific ion signal. The observed response depended on the amount of grafted copolymer. When the grafting ratio was below 15%, the membrane pores opened by Ca2+ and closed by Ba2+. The permeability of model drugs became higher by opening of the pores. On the other hand, when the grafting ratio was above 15%, the properties of the membrane changed. The permeability of model drugs became lower by Ca2+ due to dehydration of the grafted copolymer. The opposite responses were observed at different grafting ratios.     

Release property of temperature-sensitive alginate beads containing poly(N-isopropylacrylamide)

The graft copolymer (APN) of alginate and poly(N-isopropylacrylamide) (PNIPAM) were synthesized and APN beads were prepared by dropping the aqueous solution of the copolymer into an aqueous solution of Ca(2+) solution. Alginate chains were employed to play a role in forming beads by electrostatic interactions with a multivalent ion, Ca(2+). Grafted PNIPAM segments were adopted to act as a valve for the pores of the beads, since they exhibit the properties of thermal contraction and expansion. The percent of release of blue dextran from APN beads was higher at 40 degrees C than at 25 degrees C. The difference in the release between two temperatures became more distinguishable when the content of PNIPAM in APN beads is higher. Below lower critical solution temperature (LCST), the expanded PNIPAM would close the pores of the beads, resulting in a lower release rate. Above LCST, the thermally contracted polymer would open the pores, resulting in a higher release rate. The percent of release from APN beads were investigated when the temperature of the release medium is altered. The release rate was relatively low at 25 degrees C. The temperature, however, changed up to 40 degrees C, a marked increase in the release rate was observed. These trends were found to be reproducible when the temperature was repeatedly altered between 25 and 40 degrees C. As a result, a stepwise response to the temperature alteration was obtained.     

Osmotic pressure control in response to a specific ion signal at physiological temperature using a molecular recognition ion gating membrane

A molecular recognition gating ion membrane was prepared by graft copolymerization of N-isopropylacrylamide and benzo[18]crown-6-acrylamide onto the pore surface of porous polyethylene film. This membrane captured Ba2+ with its crown ether receptors and generated osmotic pressure in response to Ba2+ autonomously and reversibly. However, the membrane never generated osmotic pressure in response to Ca2+. In addition, the concentration gradient of both the ion and other solute such as dextran could be used as the driving force; using a dextran concentration gradient, we can control the critical concentration and the duration time of the osmosis response.     

The effect of solute—membrane affinity on cyclic hydrocarbon—water transport in pressure-driven membrane separation processes

Experimental results for the pressure-driven membrane separation of cyclic hydrocarbons (1,3-cyclohexadiene, cyclohexene, and cyclohexane) from dilute binary aqueous solution using asymmetric cellulose acetate membranes are reported here. In these experiments, total solution fluxes are significantly lower than pure water fluxes at the same applied pressure; this flux reduction is attributed to strong solute—membrane affinity rather than to the osmotic pressure of either the bulk retentate or the boundary layer. An empirical parameter, Z, is used to describe flux reduction. A theoretically based friction parameter, B, is derived assuming the membrane can be represented as an ideal, finely porous membrane; this parameter indicates the influence of solute—membrane affinity on flow through the pores of the membrane. Both the empirical parameter Z and the theoretically based parameter B relate flux reduction to concentrations in the system. Both Z and B increase as solute—membrane affinity increases and decrease as membrane pore size increases. It is concluded that both the empirical flux reduction parameter, Z, and the theoretically based friction parameter, B, indicate the same system properties: solute—membrane affinity and membrane pore size.     

Microcalorimetric Investigation on the lower critical solution temperature behavior of N-isopropycrylamide-co-acrylic acid copolymer in aqueous solution

The lower critical solution temperature (LCST) behaviors of random and segmented copolymers of N-isopropylacrylamide (NIPAM) and acrylic acid (AA) prepared in dioxane and water have been investigated by using ultrasensitive microcalorimetry (US-DSC). The introduction of AA increases the LCST of the former but slightly affects that of the latter. When the molar fraction of AA is low (approximately 2 mol %), the LCST of the segmented copolymer shifts to a higher temperature with increasing pH, while the LCST of the corresponding random copolymer slightly changes. Below the boiling point of water, the random copolymer and segmented copolymer with the molar fraction of AA about 15 mol % no longer exhibit an LCST at pH > 5. The addition of calcium ions leads the LCST of both the segmented copolymer and random copolymer to decrease. Our results suggest that the LCST behavior of the copolymers is determined by the clustering of poly(N-isopropylacrylamide) segments.     

Modeling of separation of aqueous solutions of FeCl3 and AlCl3 by zeolite-clay composite membranes using a space-charge model

In our earlier work, we reported the separation of FeCl3 from its aqueous solution and AlCl3 from its aqueous solution by analcime zeolite (Z1) membrane and its nitrated (Z2 membrane) and aminated (Z3 membrane) forms. Experimental data on the separation of aqueous solutions of FeCl3 and AlCl3 by zeolite-clay composite membranes has been simulated using the two-dimensional space-charge model. The computational requirement of the model has been considerably reduced by first obtaining a series solution of the nonlinear Poisson-Boltzmann equation. The effective pore radius of the membrane is taken as the one that gives the best fit to the experimental data, while the pore length is determined from the SEM photograph of the cross-sectional view of the membrane. The effective pore radii of the Z1, Z2, and Z3 membranes for FeCl3 solute are found to be 8.0, 7.0, and 5.0 nm, respectively, while for AlCl3 they are 4.5, 2.5, and 2.5 nm, respectively. These values are much less than the average of the pore size range values determined independently in an earlier work using the bubble point method and indicate partial blocking of the pores by these salts. The effective pore radius is larger for FeCl3 as compared to AlCl3 and decreases on modification. The intrinsic rejection is also found to decrease on modification. The permeate flux calculated from the model matches very well with the experimental values.     

包覆NIPAM-ODA双亲共聚物的脂质体的温控释放行为

为了研究对温度敏感的双亲性共聚物包覆的脂质体的温控释放行为,合成了N-异丙基丙烯酰胺(NIPAM)和丙烯酸十八酯(ODA)的共聚物。利用荧光探针法研究了共聚物水溶液随温度升高时出现的LCST(lower critical solution temperature)现象,表明该高分子在温度升高到30℃以上时存在着明显的相分离行为。5(6)-羧基荧光素(5(6)-CF)为标记物,研究了高分子包覆的小单层脂质体(small unilamelar vesicles)的释放行为。发现在温度低于30℃时,5(6)-CF的释放百分率比未包覆高分子的脂质体要低;而当温度升高到30℃以上时,其释放百分率明显提高。这种温控释放行为和包覆在脂质体上的高分子在其LCST时存在的相分离行为有关。进一步利用荧光偏振法研究了脂质体膜在包覆高分子后的流动性变化,发现:在温度低于30℃时,其流动性随温度升高而增大;而在温度高于30℃时,脂质体膜流动性随温度升高而降低,进一步证实了高分子在其LCST以上时对脂质体膜的破坏作用。     

N-异丙基丙烯酰胺/丙烯酸十八酯共聚物水溶液胶束及相分离行为研究

合成了N异丙基丙烯酰胺(NIPAM)和丙烯酸十八酯(ODA)的共聚物.利用荧光探针和滴重法研究了NIPAMODA共聚物在水溶液中的胶束形成过程.同时还利用荧光探针法研究了共聚物水溶液在温度升高时出现的LCST(LowerCriticalSolutionTemperature)现象,表明该高分子在温度升高时存在着相分离现象.利用LB技术测量共聚物不溶单分子膜的PA曲线,发现随着温度升高共聚物的单分子膜越来越凝聚的反常现象,这从另一个侧面证实了共聚物NIPAMODA的相分离行为,并对此现象作了讨论.     

Temperature‐induced aggregation of the copolymers of N‐isopropylacrylamide and sodium 2‐acrylamido‐2‐methyl‐1‐propanesulphonate in aqueous solutions

A series of random copolymers of N‐isopropylacrylamide (NIPAM) and sodium 2‐acrylamido‐2‐methyl‐1‐propanesulphonate (AMPS) was synthesized by free‐radical copolymerization. The content of AMPS in the copolymers ranged from 1.1 to 9.6 mol %. The lower critical‐solution temperature (LCST) of copolymers in water increased strongly with an increasing content of AMPS. The influence of polymer concentration on the LCST of the copolymers was studied. For the copolymers with a higher AMPS content, the LCST decreased faster with an increasing concentration than for copolymers with a low content of AMPS. For a copolymer containing 1.1 mol % of AMPS the LCST dropped by about 3 °C when the concentration increased from 1 to 10 g/L, whereas for a copolymer containing 9.6 mol % of AMPS the LCST dropped by about 10 °C in the concentration range from 2 to 10 g/L. It was observed that the ionic strength of the aqueous polymer solution very strongly influences the LCST. This effect was most visible for the copolymer with the highest content of AMPS (9.6 mol %) for which an increase in the ionic strength from 0.2 to 2.0 resulted in a decrease in the LCST by about 27 °C (from 55 to 28 °C), whereas for the copolymer containing 1.1 mol % of AMPS the LCST decreased only by about 6 °C (from 37 to 31 °C) when the ionic strength increased from 0.005 to 0.3. The reactivity ratios for the AMPS and NIPAM monomer pairs were determined using different methods. The values of r_AMPS and r_NIPAM obtained were 11.0–11.6 and 2.1–2.4, respectively. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2784–2792, 2001     

Molecular dynamics simulations of PNIPAM‐co‐PEGMA copolymer hydrophilic to hydrophobic transition in NaCl solution

Classical molecular dynamics simulations were carried out to investigate the hydrophilic to hydrophobic transition of PNIPAM‐co‐PEGMA close to its lower critical solution temperature (LCST) in 1 M NaCl solution. PNIPAM‐co‐PEGMA is a copolymer of poly(N‐isopropylacrylamide) (PNIPAM) and poly(ethylene glycol) methacrylate (PEGMA). The copolymer consists of 38 monomer units of NIPAM with two PEGMA chains attached to the PNIAPM backbone. The PNIPAM‐co‐PEGMA was observed to go through the hydrophilic?hydrophobic conformational change for simulations at temperature slightly above its LCST. Na⁺ ions were found to bind strongly and directly with amide O, even more strongly with the O atoms on PEGAMS chains, whereas Cl^? ions only exhibit weak interaction with the polymer. Significantly a novel caged stable metal‐organic complex involving a Na⁺ ion coordinated by six O atoms from the copolymer was observed after the PNIPAM‐co‐PEGMA copolymer went through conformational transition to form a hydrophobic folded structure. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Morphological changes of ethylene/vinyl acetate-based controlled delivery systems during release of water-soluble solutes

Thin slabs of theophylline and monomer albumin release systems were prepared by dispersing 212-300 μm and 300-25 μm particles respectively, of these bioactive agents in a methylene chloride solution of ethylene/vinyl acetate (EVAc) copolymer (40 wt% vinyl acetate), and evaporating the solvent at low temperatures according to the Langer—Folkman technique. Compositions containing 21.41 wt%, 31.04 wt% and 40.0 wt% albumin, and 19.32 wt% theophylline were prepared. Solute release experiments were performed in deionized water at 37 ± 0.1°C under perfect-sink conditions. The concentration of released solute was determined by measuring the absorbance of the UV spectra at 276 nm for albumin and 272 nm for theophylline. Both solutes could be released for long periods of time at controlled rates. The main mechanism of release was established to be solute dissolution and diffusion through the generated, waterfilled pore structure. Photomicrographs present the main features of this pore network. Mercury porosimetry was used to determine the pore volume and size of pores for freezedried slabs before, during and after the dissolution/diffusion/release process. Considerable pore collapse was observed and pore diameters of 8-650 μm were detected. In addition to solution diffusion through large pores, diffusion might occur through small constrictions between large pores or through a pore network of much smaller pores created in the matrix.     

Preparation of NOx modified PMMA-EGDM composite membrane for the recovery of chromium (VI)

A non-interpenetrating cross-linked poly (methyl methacrylate-ethylene glycol dimethacrylate) copolymer ultrafiltration membrane on a microporous ceramic support has been prepared from the monomers in two stages. The polymer membranes thus obtained have been nitrated using NO_x (a mixture of NO and NO₂) by the gas phase reaction at 80 °C. Separation experiments on the chromium (VI) salt solution have been carried out using unmodified (giving 68% rejection per pass) and nitrated membranes (giving as much as 67% rejection per pass). For nitrated membranes, the water flux and the solute flux increased with time of nitration about hundred folds because of the increase in the hydrophilicity as well as the pore size.     

Flux reduction of ultrafiltration membranes with different cut-off due to adsorption of a low-molecular-weight hydrophobic solute-correlation between flux decline and pore size

The flux of ultrafiltration membranes may be severely reduced when treating low-molecular-weight hydrophobic solutes even though the cut-off of the membrane is orders of magnitudes greater than the size of the solute molecules. In this investigation, the flux reduction was correlated to the membrane pore size using octanoic acid as a model substance. As a comparison, the pore size was also determined by measuring the retention of a dextran solution and by using the liquid–liquid displacement porometry method (LLDP). The membranes used were four asymmetric polysulphone and polyethersulphone membranes with nominal molecular weight cut-off (NMWCO) between 6 and 50 kDa. It is shown that the use of a low-molecular-weight hydrophobic solute may provide a rapid and simple method of characterising hydrophobic ultrafiltration membranes, both regarding their sensitivity to flux reduction due to adsorption, and their pore-size distribution.     

Super macroporous poly(N‐isopropyl acrylamide) cryogel for separation purpose

Polymers that can respond reversibly by changing their physical or chemical properties are recognized as stimuli‐responsive polymers. The renowned temperature‐sensitive polymer is poly(N‐isopropyl acrylamide) (p(NIPAM)), and here, homopolymeric supermacroporous p(NIPAM)) cryogel was synthesized via cryopolymerization technique at cryogenic condition (below melting point of solvent, −18°C). Then, the prepared p(NIPAM) cryogel was characterized via scanning electron microscopy, Fourier transform infrared radiation spectrometer, and thermogravimetric analyzer. The lower critical solution temperature (LCST) value of the prepared p(NIPAM) cryogel was determined from % swelling equilibrium swellings at various temperatures, 20, 25, 30, 35, 40, 45, and 50°C, respectively. Furthermore, the pore volume and porosity of p(NIPAM) cryogels were compared below and above the LCST values. Finally, the separation capability of p(NIPAM) cryogels for some molecules such as tannic acid, gallic acid, nicotine (N), and caffeine (C) was investigated at the below and above the LCST values.     

Synthesis,characterization, and temperature‐responsive behaviors of novel hybrid amphiphilic block copolymers containing polyhedral oligomeric silsesquioxane

Organic/inorganic hybrid amphiphilic block copolymer poly(methacrylate isobutyl POSS)‐b‐poly(N‐isopropylacrylamide‐co‐oligo(ethylene glycol) methyl ether methacrylate) (PMAPOSS‐b‐P(NIPAM‐co‐OEGMA)) was synthesized via reversible addition–fragmentation chain transfer polymerization. The self‐assembly behavior of this block copolymer in aqueous solution was investigated by dynamic light scattering (DLS) and transmission electron microscopy. The results indicate that the novel block copolymer can self‐assemble into spherical micelles with PMAPOSS segment as the hydrophobic part and P(NIPAM‐co‐OEGMA) segment as the hydrophilic part. The temperature‐responsive characteristics of the assemblies were tested by UV–Vis spectra and DLS. Some factors such as the concentration, molecular weight, and copolymer generation that may affect the cloud point were studied systematically. The results reveal that this copolymer exhibits a sharp and intensive lower critical solution temperature (LCST). The essentially predetermined LCST can be conveniently achieved by adjusting the content of NIPAM or OEGMA domain. In addition, these novel hybrid micelles can undergo an association/disassociation cycle with the heating and cooling of solution and the degree of reversibility displaying a tremendous concentration dependence, as a novel organic/inorganic hybrid material with distinctive virtues can be potentially used in biological and medical fields, especially in drug nanocarriers for targeted therapy. Copyright © 2014 John Wiley & Sons, Ltd.     

SEM研究PET核孔膜的光接枝聚合

以PET核孔膜为基材 ,二苯甲酮为引发剂 ,采用光接枝方法实现了丙烯酸和丙烯酰胺在核孔膜上的接枝 ,用扫描电镜 (SEM)直接观察了接枝前后膜的表面形貌 ,考察了不同因素对于接枝位置和接枝效果的影响 .发现膜材料本身特性和接枝反应条件对接枝位置和接枝效果有较大影响 .通过光接枝能够实现膜孔的封盖、缩小、填堵等不同的效果 .采用正侧涂布法反应 ,标准直孔 ,特别是小孔径膜 (0 4 μm) ,不利于孔内的接枝 ,接枝主要在膜的表面 ,从而产生孔封盖效应 .双锥形的非标准直孔 ,由于孔壁的受光性好 ,容易发生孔壁上的接枝从而被填充 .大孔径的膜 (5 μm) ,需要加入交联剂才能在孔壁上形成厚的接枝层 .提出了一种新的反应方法 背侧吸附法 ,反应液依靠毛细作用由膜的底部吸入膜孔 ,膜的向光侧表面不存在反应液 ,接枝只发生在膜孔内 ,从而得到很好的填孔效果 .