Study Of Ordered Mesoporous Materials For Lipase Immobilization And Drug Controlled Release

Ordered mesoporous SBA-15 was prepared using triblock copolymer P123 as template and tetraethoxysilane (TEOS) as silica source by hydrothermal process under acidic condition. The ordered mesoporous SBA-15 was functionalized with (3-aminopropyl)triethoxysilane (APTES) by post-synthesis-grafting method and the sample was designated as NH-SBA-15. The obtained materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive spectrometer (EDS), small-angle X-ray powder diffraction (SAXRD), N₂ adsorption-desorption and Fourier transform infrared spectroscopy (FT-IR). The results indicated that SBA-15 had a 2-dimensional hexagonal p6mm mesoscopic structure, and the mesoscopic structure was remained after the functionalization procedure. The activities of porcine pancreatic lipase (PPL) immobilized in SBA-15 and immobilized in NH-SBA-15 were studied by hydrolysis of triacetin. The results demonstrated that immobilized PPL had an excellent adaptability in a wider pH region and better thermal stability, as well as a high level of reusability, compared with free PPL. In addition, immobilized lipase NH-SBA-15-PPL showed higher loading amount and greater catalytic activity comparing with SBA-15-PPL, and NH-SBA-15-PPL also showed better reusability than SBA-15-PPL, the relative activity of NH-SBA-15-PPL maintained at level exceeding 49.13% of its original activity while the numerical value was 41.96% for SBA-15-PPL after 5 reuses.Functionalized mesoporous NH-5/SBA-15, NH-10/SBA-15 and NH-15/SBA-15 were prepared by co-condensation of TEOS with APTES in a range of molar ratios (5 mol%, 10 mol% and 15 mol%) of APTES/TEOS via hydrothermal process. SAXRD, SEM, TEM, N₂ adsorption-desorption and FT-IR were used to monitor the effect of functionalization on the structural and textural features of the SBA-15. The results suggested that the structural ordering of functionalized SBA-15, as well as pore diameters, pore volumes and surface areas, were decreased with increasing the APTES molar ratio. Candida rugosa lipase (CRL) was used as a model enzyme for studying the effects of amino functionalization in loading amount and enzymatic activity. The effects of pH and temperature on catalytic hydrolysis of tributyrin by immobilized CRL were investigated. The results showed that immobilized CRL had a well adaptability in a wide pH and temperature region, and functionalized SBA-15 immobilized CRL exhibited much higher enzymatic activity than free CRL, especially, NH-5/SBA-15 immobilized CRL displayed the highest activity. However, NH-15/SBA-15 immobilized CRL showed the greatest hydrothermal stability, it still retained 87.50% of its initial activity for incubating 160 min at 60 oC, and NH-15/SBA-15 immobilized CRL exhibited the best reproducibility and reusability, its relative activity was maintained at level of 67.13% to the initial value after recycled for 6 times.The ordered mesoporous SBA-15 and functionalized mesoporous NH-5/SBA-15, NH-10/SBA-15 and NH-15/SBA-15 were employed for the controlled release of water-insolube drug emodin. The results of N₂ adsorption-desorption showed that emodin was successfully loaded into the mesoporous supports and the loading amount was decreased following the order of SBA-15, NH-5/SBA-15, NH-10/SBA-15 and NH-15/SBA-15. The controlled release profiles of emodin loaded samples were studied in phosphate buffered saline (PBS, pH = 7.4). The results showed a"burst release"phenomenon of all samples at first, but the release rate decreased after 3 h. Emodin loaded on functionalized mesoporous supports exhibited lower release rate than that of loaded on pure SBA-15, and emodin loaded on NH-10/SBA-15 showed the lowest release amount which was 71.74 wt% after stirring in PBS for 60 h, suggesting the functionalized mesoporous SBA-15 was a promising carrier to achieve prolonged release time period.