The pore size and permeability control of a glucose-responsive gating membrane with plasma-grafted poly (acrylic acid) (PAAC) gates and covalently bound glucose oxidase (GOD) enzymes were investigated systematically. The PAAC-grafted porous polyvinylidene fluoride (PVDF) membranes with a wide range of grafting yields were prepared using a plasma-graft pore-filling polymerization method, and the immobilization of GOD was carried out by a carbodiimide method. The linear grafted PAAC chains in the membrane pores acted as the pH-responsive gates or actuators. The immobilized GOD acted as the glucose sensor and catalyzer; it was sensitive to glucose and catalyzed the glucose conversion to gluconic acid. The experimental results showed that the glucose responsivity of the solute diffusional permeability through the proposed membranes was heavily dependent on the PAAC grafting yield, because the pH-responsive change of pore size governed the glucose-responsive diffusional permeability. It is very important to design a proper grafting yield for obtaining an ideal gating response. For the proposed gating membrane with a PAAC grafting yield of 1.55%, the insulin permeation coefficient after the glucose addition (0.2mol/l) was about 9.37 times that in the absence of glucose, presenting an exciting result on glucosesensitive self-regulated insulin permeation.

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.