Membranes with porous substrates and functional gates that are responsive to environmental stimuli are attracting increasing interest from various fields. Their permeation properties can be controlled or adjusted by the gates according to the external chemical and/or physical environment, and they may find various applications e.g. in controlled drug delivery, bioseparation, chemical separation, water treatment, tissue engineering, and as chemical sensors. The functional gates for stimuli-responsive membranes serve as chemical valves, and have been reported to act in response to changes in environmental temperature, [1-5] pH, [5-10] ionic strength, [11] glucose concentration, [12, 13] electric field, [14] light, [15] redox properties, [16] or different molecules. [17-19] There are many cases in which environmental temperature fluctuations occur naturally, and in which the temperature stimuli can be easily designed and artificially controlled; therefore much attention has recently been focused on thermoresponsive membranes. [2-1] Up to now, almost all of the thermoresponsive gating membranes have featured positively thermoresponsive characteristics, that is, the membrane permeability increases with increasing environmental temperature, because all of the thermoresponsive functional gates were constructed from poly (Nisopropylacrylamide) (PNIPAM). [1-5] In these cases, the membrane pores change from a "closed" to an "open" state when the environmental temperature increases from below the lower critical solution temperature (LCST) of PNIPAM to above the LCST, as a result of the swelling/shrinking conformational change of the polymer. In certain applications, however, an inverse mode of the thermoresponsive gating behavior of the membranes is preferred. Here we report a novel family of thermoresponsive gating membranes with negatively thermoresponsive gating characteristics, that is, "opening" of the membrane pores is induced by a decrease rather than an increase in temperature.

A glucose-sensitive microcapsule with a porous membrane and with linear-grafted polyacrylic acid (PAAC) chains and covalently bound glucose oxidase (GOD) enzymes in the membrane pores acting as functional gates was successfully prepared. Polyamide microcapsules with a porous membrane were prepared by interfacial polymerization, PAAC chains were grafted into the pores of the microcapsule membrane by plasma-graft pore-filling polymerization, and GOD enzymes were immobilized onto the PAAC-grafted microcapsules by a carbodiimide method. The release rates of model drug solutes from the fabricated microcapsules were significantly sensitive to the existence of glucose in the environmental solution. In solution, the release rate of either sodium chloride or VB12 molecules from the microcapsules was low but increased dramatically in the presence of 0.2mol/L glucose. The prepared PAAC-grafted and GOD-immobilized microcapsules showed a reversible glucose-sensitive release characteristic. The proposed microcapsules provide a new mode for injection-type self-regulated drug delivery systems having the capability of adapting the release rate of drugs such as insulin in response to changes in glucose concentration, which is highly attractive for diabetes therapy.

A novel type of polyethersulfone porous microcapsule membranes with straight pores across the whole thickness was successfully prepared with a gel-sol phase inversion method for the immobilization of microbial cells. The mean diameter of the microcapsules was about 2mm, and the microcapsule membranes were full of straight finger pores. The pore size distribution was from 3.5 to 53.6m and the median pore diameter was 13.6m. The prepared microcapsules had large total pore volume, and total pore area and porosity (as large as 91.7%). The prepared porous microcapsules were used as carriers for the immobilization of microbial cells in the anaerobic wastewater biotreatment process. Immobilized anaerobic microbial cells were found both inside the membrane pores and in the inner spaces of microcapsules. The prepared porous microcapsules were proven to be efficient for the microbial immobilization under anaerobic conditions.

Microcapsules can encapsulate various chemical substances in their inner spaces, and it is thus possible to attain a controlled permeation of chemicals by using appropriate microcapsules. Because of their characteristics such as small size, huge total surface area, large inner volume, and stable membrane, microcapsules have found many applications in various fields from drug delivery through to the textile, petroleum, and pesticide industries. As the release rate from core-shell microcapsules is generally controlled by the rate of diffusion of the permeants across the thin microcapsule membrane, a faster response of the release rate to environmental stimuli may be expected as compared to crosslinked gels and microspheres. Therefore, core-shell microcapsules are suitable for stimuli-responsive controlled-release systems. Since the 1980s, environmental stimuli-responsive microcapsules have been investigated widely. These microcapsules control the release of their contents according to environmental stimuli. They are considered to be potentially useful as controlled-release systems, and especially so for drug delivery, because the target of a controlled drug delivery system is improved drug treatment (outcome) through rate- and time-programmed and site-specific drug delivery. [1] By encapsulation inside these microcapsules, chemicals or drugs can be released at a desired rate only when and/or where the release is needed. Modern environmental stimuli-responsive microcapsules have been reported to act in response to changes in temperature, [2-9] pH, [10-16] light, [17] external electric field, [18] redox conditions, [19] Ca2-ions, [20] and other stimuli, and these ™smartº capsules continue to gather increasing attention. In order to promote the applications of environmental stimuli-responsive microcapsules, development of microcapsules responsive to other signals remains essential. Herein, we report on the development of a molecular-recognition microcapsule for environmental stimuli- responsive controlled release: The release of the solute vitamin B12 (VB12) from the prepared microcapsules was significantly sensitive to the presence of Ba2+ ions in the environmental solution. In solution, the release of VB12 from the microcapsules was fast but slowed dramatically in the presence of BaCl2. The prepared microcapsules showed satisfactorily reversible and reproducible molecular-recognition stimuli-responsive release characteristics.

Experimental investigations on the Shirasu-porous-glass (SPG)-membrane emulsification processes for preparing monodisperse core-shell microcapsules with porous membranes were carried out systematically. The results showed that, to get monodisperse oil-in-water (O/W) emulsions by SPG membrane emulsification, it was more important to choose an anionic surfactant than to consider hydrophile-lipophile balance (HLB) matching. Increasing the viscosity of either the disperse phase or the continuous phase or decreasing the solubility of the disperse phase in the continuous phase could improve both the monodispersity and the stability of emulsions.With increasing monomer concentration inside the disperse phase, the monodispersity of emulsions became slightly worse and the mean diameter of emulsions gradually became smaller. Monodisperse monomer-containing emulsions were obtained when the SPG membrane pore size was larger than 1.0