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    Covalent immobilisation of invertase onto a reactive film composed of 2-hydroxyethyl methacrylate and glycidyl methacrylate: properties and application in a continuous flow system
    (Elsevier Science Sa, 2003) Bayramoglu, G; Akgol, S; Bulut, A; Denizli, A; Arica, MY
    Invertase was covalently immobilised on the poly(hydroxyethyl methacrylate-co-glycidyl methacrylate) (poly(HEMA-GMA)) film. The invertase immobilisation capacity of the films was increased as the GMA ratio increased in the film structure. The immobilised invertase on the poly(HEMA-GMA-3) composition exhibited an activity of 32.7 U cm(-2) film. The optimum temperature of the immobilised invertase increased by 5 degreesC, and the optimal pH values for the free and the immobilised enzymes were determined as 5.0. The retained activity of the immobilised invertase was between 53 and 85%. Kinetic parameters were determined for immobilised invertase as well as for the free enzyme. The values of the Michael's constant K-m of invertase were significantly larger, ca. 2.7 times upon immobilisation, indicating decreased affinity by the enzyme for its substrate, whereas V-max was smaller for immobilised invertase. Activity of the immobilised invertase was quite stable with respect to free counterpart. After 168 h reaction, only 8% of immobilised invertase activity was lost. The operational inactivation rate constant (k(opi)) of the immobilised invertase at 35 degreesC with 200 mM sucrose was 8.23 x 10(-6) min(-1). (C) 2002 Elsevier Science B.V. All rights reserved.
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    Fluoride release from microporous poly(2-hydroxyethyl methacrylate) membranes
    (Elsevier Science Bv, 2003) Yildirmaz, G; Akgol, S; Arica, MY; Sonmez, H; Denizli, A
    Fluoride ion is commonly used in the preventive treatment of tooth decay and when provided with extra fluoride, children living in regions that lack fluoride benefit from it. In the present study, the clinical properties of an intraoral controlled release fluoride delivery system were considered. Poly (2-hydroxyethyl methacrylate) (PHEMA) was examined as a fluoride carrier. Membranes were prepared by photopolymerization and then characterised. Contact angles and swelling ratios of fluoride-loaded membranes were determined. The surface morphology of the membranes were examined by using scanning electron microscopy. In vitro fluoride release studies were carried out in an artificial saliva medium. The concentration of fluoride was measured with a fluoride-specific electrode. The amount of released fluoride was determined and the effects of fluoride loading, medium pH and temperature on fluoride release were investigated. The swelling ratio of the PHEMA membrane was 58.5%, that of the fluoride-loaded PHEMA membrane was 17.8%. Increasing in the fluoride loading amount in the PHEMA membrane accelerated the fluoride release. The fluoride release ratio was increased with increasing pH and temperature. (C) 2003 Elsevier B.V. All rights reserved.
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    Polyhydroxyethylmethacrylate/polyhydroxybutyrate composite membranes for fluoride release
    (Wiley, 2003) Yildirmaz, G; Akgol, S; Arica, MY; Sonmez, H; Denizli, A
    Controlled release technology is a recent technology which has considerable potential in the fields of medicine, pharmacy, and agriculture. Fluoride ion is commonly used in the preventive treatment of decay, and when provided with extra fluoride, children living in regions that lack fluoride benefit from it. For the present study, clinical properties of an intraoral controlled release fluoride delivery system were considered. The preparation of a controlled release membrane system is described. Polyhydroxyethylmethacrylate/polyhydroxybutyrate composite systems were examined as fluoride carriers. Polymeric membranes were prepared by photopolymerization and then character-ized. Contact angles and swelling ratios of fluoride-loaded membranes were determined. The surface morphology of the microporous membranes were examined by using scanning electron microscopy (SEM). In vitro fluoride release studies were carried out in an artificial saliva medium. The amount of released fluoride was determined and the effect of medium pH and temperature on fluoride release was investigated. (C) 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 976-981,2003.