Young-Ha Kim

Synthesis and photopolymerization of multifunctional methacrylates derived from Bis-GMA for dental applications

Two multimethacrylates having three methacrylate groups (BPA-3M) and four methacrylate groups (BPA-4M) have been prepared by reacting hydroxyl groups of 2,2-bis[4-(2′-hydroxy-3′-methacryloyloxypropoxy)phenyl]propane (Bis-GMA) with methacryloyl chloride. BPA-3M and BPA-4M have much lower viscosities than the starting Bis-GMA, because they have only one or no hydroxyl group. Photopolymerizations of the multifunctional methacrylates were conducted by exposure to visible light using camphorquinone and 2-(N,N-dimethylamino)ethyl methacrylate as a photoinitiating system. High conversions >50% resulted from photopolymerization of BPA-3M, whereas Bis-GMA showed lower conversions under the same condition, implying better mechanical properties for the composite resins made from BPA-3M. BPA-4M showed much lower conversions in the photopolymerization condition. Water sorption of the photocured composite of BPA-3M containing 50 wt % of inorganic fillers was found to be 0.15%, which is only one-tenth of the commercial Bis-GMA composite.

Albumin immobilized polyurethane and its blood compatibility.

Surface pretreatment with albumin on a blood contacting material inhibits platelet adhesion, activation, and subsequent thrombus formation. Although adsorbed albumin improves blood compatibility, rapid desorption occurs when this surface is exposed to circulating blood. In this study, human serum albumin was immobilized on a polyurethane (PU) surface to investigate its blood compatibility and extended effects on a blood-material interface. The PU surface was treated with hexamethylene diisocyanate (HMDI), and the PU-HMDI was further grafted with albumin to produce an albumin immobilized PU surface (PU-albumin). The PU-albumin surface was characterized by attenuated total reflection infrared electron spectroscopy for chemical analysis, scanning electron microscopy, and dynamic contact angle. Blood compatibility was evaluated by in vitro protein adsorption, platelet adhesion, and occlusion time in an ex vivo rabbit arterio-arterial shunt. Immobilization of albumin was confirmed by the disappearance of the -NCO peak observed at 2,250 cm-1 on the PU-HMDI surface by infrared spectroscopy and the existence of sulfur atomic percent by electron spectroscopy for chemical analysis. The concentration of PU-albumin was approximately 5.8 micrograms/cm2. The PU-albumin also showed a slight increase in hydrophilicity on the Wilhelmy plate method, and there was less fibrinogen adsorption than a PU control. In addition, PU-albumin had less platelet adhesion, platelet activation, and thrombogenicity. The ex vivo occlusion time of untreated PU was 50 min, that of PU-albumin was extended to 150 min, indicating that a PU-albumin surface has better blood compatibility than PU alone.

Effect of shear rates on protein adsorption in the total artificial heart.

Plasma protein adsorption is the first event in blood-material interaction and influences subsequent platelet adhesion and thrombus formation. Thromboembolic events are strongly influenced by surface characteristics of materials and fluid dynamics inside the blood pump. In vitro flow visualization, and an animal experiment with a moving actuator total artificial heart (TAH), were performed to investigate fluid dynamic effects on protein adsorption. The different levels of shear rate inside the ventricle were determined by considering the direction of opening of the four heart valves in the implanted TAH, and the visualized flow patterns as well. Each ventricle of the explanted TAH was cut into 12 segments according to the shear rate level. The adsorbed protein on each segment was quantified using an ELISA method after soaking in 2% (w/v) SDS/PBS for 2 days. Adsorbed protein layer thicknesses were measured by the immunogold method under transmission electron microscopy. Scanning electron microscopic observation showed that the right ventricle, immobilized with albumin, displayed different degrees of platelet adhesion on each segment, whereas the left ventricle, coated with polythyleneoxide-sulfonate, indicated nearly the same platelet adhesion behavior, regardless of shear rates. The surface concentrations of adsorbed proteins in the low shear rate region are higher than those in the high shear region, which was confirmed statistically.

Effect of Dopants on Characteristics of Polypyrrole as a Liquid Crystal Alignment Layer

Abstract Electrochemically polymerized polypyrrole (PPy) films with different dopants showed different surface energies. The films were used as alignment layers of liquid crystal displays (LCDs). The PPy films doped with ClO4 − (PPy/ClO4) and PF6 − (PPy/PF6) showed surface energies of 43.2 and 32.3 mJ/m2, respectively, while the pretilt angles of 4-cyano-4′-pentylbiphenyl on the films were 5.6 ± 0.3 and 14.0 ± 2.2 degrees, respectively. The electro-optic response time measured by light transmittance through the twisted nematic(TN) LCDs on switch-on was shorter for the display with PPy/PF6 than for that with PPy/ClO4. However, the turn-off response time was shorter for the display with PPy/ClO4 than for that with PPy/PF6. The total response time, which is the sum of the turn-on and turn-off response times, was 75 and 120 msec at 3.0 V pp for the displays with PPy/ClO4 and PPy/PF6, respectively.