Young A. Han

THE PHYSICAL PROPERTIES OF POLY(2-HYDROXYETHYL METHACRYLATE) COPOLYMER HYDROGELS USED AS INTRAVAGINAL RINGS

Poly(2-hydroxyethyl methacrylate) (PHEMA) and poly(2-hydroxyethyl methacrylate-co-sodium methacrylate) [P(HEMA-co-SMA)] hydrogels with different compositions were prepared to be used as intravaginal rings, and their gelation time, water content, mechanical properties and morphology were investigated. The water content of PHEMA and P(HEMA-co-SMA) hydrogels decreased as the concentration of the monomer and the degree of crosslinking increased, while the water content significantly increased as the content of SMA, the hydrophilic monomer, increased. The increasing of the concentration of the crosslinking agent affected the tensile and flexural properties highly. The presence of a proper small amount of SMA also led the tensile and flexural modulus to move to a higher level. The results showed that P(HEMA-co-SMA) hydrogel with high drug load and good mechanical properties at optimum preparation conditions can be prepared for intravaginal rings to deliver nonhormonal contraceptives. These results may be applied to prepare better intravaginal drug delivery devices.

Temperature control of multizone heated rollers

Heated press rollers are used to give tactility and gloss to papers, fabrics, nonwoven fabrics, films and so on. The surface temperature of the heated roller and its uniformity are especially important. Existing heated rollers have surface temperature profiles up to 10degC deviations, causing listing in fabrics. In order to suppress the surface temperature deviation to 1degC, we propose a heated roller system having multizone electric heaters and heating oil within the steel roller. The heated roller temperature control system is ill-conditioned. Because the controller performance is very sensitive on uncertainties in the model and disturbances, very accurate identification and elaborate controller design are required. For this, recent sequential relay feedback autotuning methods are applied for identification and controller design. Experimental results are given.

Biocompatibility of Phema and P(Hema-Co-Sma) Hydrogels

To replace a poly(2-hydroxyethyl methacrylate) (PHEMA) sponge, which has limited applications as an implant material, PHEMA and poly(2-hydroxyethyl methacrylate-co-sodium methacrylate) (P(HEMA-co-SMA)) hydrogels with enhanced biocompatibility were prepared based on the copolymerization of 2-hydroxyethyl methacrylate (HEMA) and sodium methacrylate (SMA) at a high monomer concentration. When the cytotoxicity, cell adhesion, and in vivo tissue reaction of the resulting hydrogels were investigated, the results suggest that hydrogels prepared by the copolymerization of HEMA and SMA at a high monomer concentration have great potential as implant materials with an excellent biocompatibility.

Relationship between the volume phase transition and the surface area of poly (N-isopropylacrylamide) and poly (N-isopropylacrylamide-co-sodium methacrylate) hydrogels

The volume phase transition of poly(N-isopropylacrylamide) (PNIPAAm) and poly(N-isopropylacrylamide-co-sodium methacrylate) (P(NIPAAm-co-SMA)) hydrogels was investigated with consideration of the pore characteristics. The volume phase transition temperature of the hydrogel increased by incorporating sodium methacrylate (SMA). Based on the BET equation, the surface area was evaluated by a gas adsorption method. The surface area of PNIPAAm and P(NIPAAm-co-SMA) hydrogels decreased with increasing temperature, resulting from the fact that the depth and the size of pores decreased significantly in the course of the volume phase transition. Hence, it is suggested that the change of surface area has a close relationship with the volume phase transition of PNIPAAm and P(NIPAAm-co-SMA) hydrogels.

Controlled Release of Growth Factor Using Poly(N-Isopropyl Acrylamide)Copolymer Hydrogels with Different Volume Phase Transition Temperatures

The release behavior of the basic fibroblast growth factor (bFGF) from copolymer hydrogels of N-isopropyl acrylamide (NIPAAm) and sodium methacrylate (SMA) was investigated in relation to the volume phase transition temperatures, which was increased by the incorporation of SMA. In the case of the copolymer hydrogels, a higher volume phase transition temperature was obtained when poly(ethylene glycol) diacrylate (PEGDA) was used as the crosslinking agent, suggesting that the chain length of the crosslinking agent has a significant affect on the volume phase transition temperature of a P(NIPAAm-co-SMA) hydrogel. The concentration of bFGF released from the hydrogels with PEGDA increased relative to the water content, thereby showing a dependence on the volume phase transition temperature. Hence, the release behavior of bFGF from the PNIPAAm and P(NIPAAm-co-SMA) hydrogels was found to be affected by the volume phase transition temperature, which can be easily controlled by changing the comonomer, monomer feed ratio, and crosslinking agent.