Novel poly(N-isopropylacrylamide)-clay (PNIPAM-clay) nanocomposite (NC) hydrogels with both excellent responsive bending and elastic properties are developed as temperature-controlled manipulators. The PNIPAM-clay NC structure provides the hydrogel with excellent mechanical property, and the thermoresponsive bending property of the PNIPAM-clay NC hydrogel is achieved by designing an asymmetrical distribution of nanoclays across the hydrogel thickness. The hydrogel is simply fabricated by a two-step photo polymerization. The thermoresponsive bending property of the PNIPAM-clay NC hydrogel is resulted from the unequal forces generated by the thermoinduced asynchronous shrinkage of hydrogel layers with different clay contents. The thermoresponsive bending direction and degree of the PNIPAM-clay NC hydrogel can be adjusted by controlling the thickness ratio of the hydrogel layers with different clay contents. The prepared PNIPAM-clay NC hydrogels exhibit rapid, reversible, and repeatable thermoresponsive bending/unbending characteristics upon heating and cooling. The proposed PNIPAM-clay NC hydrogels with excellent responsive bending property are demonstrated as temperature-controlled manipulators for various applications including encapsulation, capture, and transportation of targeted objects. They are highly attractive material candidates for stimuli-responsive “smart” soft robots in myriad fields such as manipulators, grippers, and cantilever sensors.

Novel multi-stimuli-responsive microcapsules with adjustable controlled-release characteristics are prepared by a microfluidic technique. The proposed microcapsules are composed of crosslinked chitosan acting as pH-responsive capsule membrane, embedded magnetic nanoparticles to realize “site-specific targeting”, and embedded temperature-responsive sub-microspheres serving as “micro-valves”. By applying an external magnetic field, the prepared smart microcapsules can achieve targeting aggregation at specific sites. Due to acid-induced swelling of the capsule membranes, the microcapsules exhibit higher release rate at specific acidic sites compared to that at normal sites with physiological pH. More importantly, through controlling the hydrodynamic size of sub-microsphere “micro-valves” by regulating the environment temperature, the release rate of drug molecules from the microcapsules can be flexibly adjusted. This kind of multi-stimuli-responsive microcapsules with site-specific targeting and adjustable controlled-release characteristics provides a new mode for designing “intelligent” controlled-release systems and is expected to realize more rational drug administration.

A novel positively K⁺-responsive membrane with functional gates driven by host-guest molecular recognition is prepared by grafting poly(N-isopropylacrylamide-co-acryloylamidobenzo-15-crown-5) (poly(NIPAM-co-AAB₁₅C₅)) copolymer chains in the pores of porous nylon-6 membranes with a two-step method combining plasma-induced pore-filling grafting polymerization and chemical modification. Due to the cooperative interaction of host-guest complexation and phase transition of the poly(NIPAM-co-AAB₁₅C₅), the grafted gates in the membrane pores could spontaneously switch from “closed” state to “open” state by recognizing K⁺ ions in the environment and vice versa; while other ions (e.g., Na⁺, Ca²⁺ or Mg²⁺) can not trigger such an ion-responsive switching function. The positively K⁺-responsive gating action of the membrane is rapid, reversible, and reproducible. The proposed K⁺-responsive gating membrane provide a new mode of behavior for ion-recognizable “smart” or “intelligent” membrane actuators, which is highly attractive for controlled release, chemical/biomedical separations, tissue engineering, sensors, etc.

Thermo-responsive composite polyethersulfone (PES) membranes blended with monodisperse poly(N-isopropylacrylamide) (PNIPAM) nanogels were prepared from blends of PES solution and PNIPAM nanogels by phase inversion. The monodisperse and spherical PNIPAM thermo-responsive nanogels were synthesized by precipitation polymerization. The blended PNIPAM nanogels did not affect the formation of the finger-like pore structure of the PES membrane but resulted in microporous structures. The water flux across the composite membrane at temperatures above the lower critical solution temperature (LCST) of PNIPAM was much higher than that below the LCST because of thermo-responsive shrinking/swelling of the PNIPAM nanogels, and the thermo-responsive permeation characteristics were affected by the content of blended PNIPAM nanogels. The thermo-responsive permeation performance of the composite membranes was reversible and reproducible.

A novel ion-imprinted strategy is developed for synthesizing responsive hydrogels with rapid response to potassium ions. With potassium ions as templates, ion-imprinted poly(N-isopropylacrylamide-co-benzo-15-crown-5-acrylamide) (P(NIPAM-co-B15C5Am)) hydrogels are synthesized with 15-crown-5 crown ethers mounted on the polymer networks in pairs; therefore, it is very easy and fast for the crown ethers to capture potassium ions again by their Venus flytrap action and form stable 2:1 “host–guest” complexes with potassium ions in the ion-recognition process. As a result, the response rate of the ion-imprinted hydrogels to potassium ions is significantly faster than that of normal P(NIPAM-co-B15C5Am) hydrogels in which 15-crown-5 crown ethers are randomly pendent on the polymeric networks. Copyright © 2010 John Wiley & Sons, Ltd.

Thermo-responsive porous membranes with grafted linear and crosslinked poly(N-isopropylacrylamide) (PNIPAM) gates are successfully prepared at temperatures above and below the lower critical solution temperature (LCST) of PNIPAM by using a plasma-induced grafting polymerization method, and the effects of operation pressure and grafting temperature on the thermo-responsive gating characteristics of the prepared membranes are investigated systematically. The fluxes of water through the grafted membranes increase simply with increasing the operation pressure no matter whether the environmental temperature is 40 °C or 25 °C. Under high operation pressure (e.g., higher than 0.14 MPa), the grafted linear PNIPAM gates deform to a certain extent, whereas the grafted crosslinked PNIPAM gates do not deform. For both membranes with grafted linear and crosslinked PNIPAM gates, the membranes prepared at 25 °C (below the LCST of PNIPAM) show larger thermo-responsive gating coefficients than those prepared at 40 °C (above the LCST of PNIPAM), which results from different distributions of grafted PNIPAM gates in the membrane pores. When the PNIPAM gates are grafted at 25 °C, the grafted layer near the membrane surface is much thicker than that inside the membrane pores; on the other hand, when the PNIPAM gates are grafted at 40 °C, the grafted layer is homogeneously formed throughout the whole pore length. Both linear and crosslinked grafted PNIPAM gates in the membrane pores exhibit stable and repeatable thermo-responsive “open-close” switch performances under the operation pressure of 0.26 MPa. The results in this study provide valuable guidance for designing, fabricating, and operating thermo-responsive gating membranes with desirable performances.

BACKGROUND: Thermo-responsive copolymers with racemate or single enantiomer groups are attracting increasing attention due to their fascinating functional properties and potential applications. However, there is a lack of systematic information about the lower critical solution temperature (LCST) of poly(N-isopropylacrylamide)-based thermo-responsive chiral recognition systems. In this study, a series of thermo-responsive chiral recognition copolymers, poly[(N-isopropylacrylamide)-co-(N-(S)-sec-butylacrylamide)] (PN-S-B) and poly[(N-isopropylacrylamide)-co-(N-(R,S)-sec-butylacrylamide)] (PN-R,S-B), with different molar compositions, were prepared. The effects of heating and cooling processes, optical activity and amount of chiral recognition groups in the copolymers on the LCSTs of the prepared copolymers were systematically studied.

RESULTS: LCST hysteresis phenomena are found in the phase transition processes of PN-S-B and PN-R,S-B copolymers in a heating and cooling cycle. The LCSTs of PN-S-B and PN-R,S-B during the heating process are higher than those during the cooling process. With similar molar ratios of N-isopropylacrylamide groups in the copolymers, the LCST of the copolymer containing a single enantiomer (PN-S-B) is lower than that of the copolymer containing racemate (PN-R,S-B) due to the steric structural difference. The LCSTs of PN-R,S-B copolymers are in inverse proportion to the molar contents of the hydrophobic R,S-B moieties in these copolymers.

CONCLUSION: The results provide valuable guidance for designing and fabricating thermo-responsive chiral recognition systems with desired LCSTs. Copyright © 2008 Society of Chemical Industry

A novel thermoresponsive membrane for chiral resolution with high performance has been developed. The membrane exhibits chiral selectivity based on molecular recognition of beta-cyclodextrin (β-CD) and thermosensitivity based on the phase transition of poly(N-isopropylacrylamide) (PNIPAM). Linear PNIPAM chains were grafted onto porous nylon-6 membrane substrates by using a plasma-graft pore-filling polymerization method; the chains thus acted as microenvironmental adjustors for β-CD molecules. β-CD moieties were introduced into the linear PNIPAM chains by a chemical grafting polymerization method and acted as chiral selectors. The phase transition of grafted PNIPAM chains affects the microenvironment of β-CD molecules and, thus, the association between β-CD and guest molecules. The chiral selectivity of the prepared thermoresponsive membranes in chiral resolution operated at temperature below the lower critical solution temperature (LCST) of PNIPAM is higher than that of membranes with no thermosensitivity. Furthermore, the decomplexation ratio of enantiomer-loaded thermoresponsive membranes in decomplexation at temperatures above the LCST is much higher than that of membranes with no thermosensitivity. Thus, by simply changing the operation temperature, high, selective chiral resolution and efficient membrane regeneration are achieved. The proposed membrane provides a new and efficient way to solve the difficult decomplexation problem of chiral solid membranes, which is highly attractive for chiral resolution.

A new hydrocyclone was designed with a volute chamber positioned prior to the inlet. Since the volute chamber prior to the inlet has a pre-sedimentation function due to the centrifugal sedimentation effect, coarse particles are concentrated on the outer side and fine particles are concentrated on the inner side as the particles reach the entrance of the hydrocyclone. Consequently, coarse particles in the hydrocyclone are easily separated into the underflow and fine particles are easily transferred into the overflow. As a result, the separation or classification performance of the hydrocyclone was improved effectively. Compared with the traditional type of hydrocyclone, this new type of hydrocyclone with a volute chamber before the inlet was shown to possess a much higher classification efficiency for fine particles.

The effect of hydrophobic modification and regeneration of Shirasu porous glass (SPG) membranes was systematically investigated on the monodispersity of emulsions. The results showed that the hydrophobic modification and regeneration of SPG membranes had little influence on the monodispersity of emulsions, no matter how many modification and regeneration runs were operated. The emulsification runs affected the emulsification performance to a certain extent when hydrophobically-modified SPG membranes were used for preparing water-in-oil (W/O) emulsions repeatedly. However, they almost did not affect the emulsification performance when regenerated hydrophilic SPG membranes were used for preparing oil-in-water (O/W) emulsions. The SPG membranes could be used repeatedly after hydrophobic modification or regeneration with almost the same emulsification performance as fresh or freshly-modified ones. The results provided some valuable guidance for the repetitive use of SPG membranes to prepare monodisperse O/W and W/O emulsions.

A new type of glucose-responsive hydrogel with rapid response to blood glucose concentration change at physiological temperature has been successfully developed. The polymeric hydrogel contains phenylboronic acid (PBA) groups as glucose sensors and thermo-responsive poly (N-isopropylacrylamide) (PNIPAM) groups as actuators. The response rate of the hydrogel to environmental glucose concentration change was significantly enhanced by introducing grafted poly(N-isopropylacrylamide-co-3-acrylamidophenylboronic acid) [poly(NIPAM-co-AAPBA)] side chains onto crosslinked poly(NIPAM-co-AAPBA) networks for the first time. The synthesized comb-type grafted poly(NIPAM-co-AAPBA) hydrogels showed satisfactory equilibrium glucose-responsive properties, and exhibited much faster response rate to glucose concentration change than normal type crosslinked poly(NIPAM-co-AAPBA) hydrogels at physiological temperature. Such glucose-responsive hydrogels with rapid response rate are highly attractive in the fields of developing glucose-responsive sensors and self-regulated drug delivery systems. Copyright © 2008 John Wiley & Sons, Ltd.