A method was developed to prepare thermosensitive poly (N-isopropylacrylamide) (PNIPAAm) hydrogels with an interpenetrating polymer network (IPN) structure for the purpose of improving its mechanical properties, response rate to temperature and sustained release of drugs. Although the differential scanning calorimetry data exhibited similarly lower critical solution temperature (LCST) between IPN-and non-IPN-PNIPAAm hydrogels, an increase in the glass transition temperature (Tg) ofthe IPNs relative to the normal PNIPAAm hydrogel was observed. In addition, the mechanical properties ofthe IPNs were greatly improved when compared with the normal PNIPAAm hydrogel. The interior morphology ofthe IPN-PNIPAAm hydrogels was revealed by scanning electron microscopy (SEM); the IPN hydrogels showed a fibrillar-like porous network structure that normal PNIPAAm did not have. Furthermore, by measuring the temperature dependence ofthe swelling ratio and deswelling kinetics, these IPN hydrogels also exhibited improved intelligent characteristics (e.g., controllable faster response rate) that depended on the composition ratio of the two network components. From the applications viewpoint, the effects of a shrinking-reswelling cycle around the LCST on the properties ofthe IPN hydrogels were examined to determine ifthese properties would be stable for potential applications. Bovine serum albumin was chosen as the model protein for examining its release from the IPNs at different temperatures. The release data suggested that an improved controlled release could be achieved by the IPN-PNIPAAm hydrogels without losing their intelligent properties.

We have demonstrated a new strategy for preparing poly (N-isopropylacrylamide) (PNIPAAm) gel with significantly improved properties by polymerization-crosslinking in organic solvent (dimethyl sulfoxide, DMSO) and at low temperatures (0.5 and -22℃, below the melting point of DMSO). The effects of different synthesis conditions, including monomer concentration and polymerization temperature, on the formation of the PNIPAAm gels in DMSO were investigated. The properties of the resulting cryo-PNIPAAm gels were characterized by scanning electron microscopy (SEM) to reveal their interior morphology as well as the temperature dependence of the equilibrium swelling ratio, shrinking and swelling kinetics in water and their oscillatory shrinking-swelling kinetics over 3 min temperature cycles between 26 and 37℃. The SEM micrographs reveal that the interior microstructures of the cryo-PNIPAAm gels are very different from conventional PNIPAAm gels, and are much more regular and oriented than the conventional gels. This unique interior morphology of the cryo-PNIPAAm gels is believed to be responsible for the improved swelling and deswelling kinetics and excellent dynamic response without loss of water retention upon temperature cycling.

Through copolymerization/crosslinking in dimethyl sulfoxide (DMSO) at temperature below the melting point of DMSO, we demonstrated a novel poly (N-isopropylacrylamide) (PNIPAAm) hydrogel with regularly oriented micromatrix; the superfast/stable oscillatory hydration-dehydration character of this hydrogel would find wide applications in biomedical field.

A crown ether derivative (4′-allyldibenzo-18-crown-6, CE) was covalently incorporated into the network of temperature sensitive poly (Nisopropylacrylamide) (PNIPA) hydrogels by copolymerization in a mixed solvent of water and tetrahydrofuran (H2O/THF). The poly(Nisopropylacrylamide-co-4′-allyldibenzo-18-crown-6) (poly(NIPA-co-CE)) hydrogels exhibited dramatically faster deswelling rates than normal PNIPA hydrogels at a temperature (50℃) above their lower critical solution temperatures. The effect of the solvent component ratio in the mixed solvent during the copolymerization on the swelling properties of the poly (NIPA-co-CE) hydrogel was investigated. The thermosensitive poly (NIPA-co-CE) hydrogels have potential applications in the extraction of cations and separation of chiral drugs.

Transdermal delivery is one of the most convenient drug administration routes. In this study, the cellulose acetate membranes were cast with acetone as a solvent at 22 and 40℃. Polyethylene glycol (PEG, MW 600) was used as a pore-forming agent. The in vitro release rates of scopolamine base as a model drug through the membranes were evaluated in phosphate buffer solution (PBS, pH 7.4) at 32℃. The membranes were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermal mechanical analysis (TMA) and thermogravimetric analysis (TGA). It was observed that the drug permeation through the cellulose acetate membranes was obviously affected by the incorporated PEG content and formed membrane morphology. There was no drug flux from the cellulose acetate membranes prepared without PEG. An increased PEG content resulted in a faster scopolamine release due to a more porous structure created. Both the membrane fabrication temperature and the PEG content can affect the thermal, mechanical and morphological properties of the resultant membranes. With the optimized fabrication conditions, linear in vitro release profiles of scopolamine over 3 days were achieved. The membranes developed would be useful for transdermal delivery of drugs.