Adsorption of Porphyrin in Orthogonally Stacked Mesoporous Silica Films: Implications for Surface Modification of Biomedical Polyimide

An oriented cylindrical mesoporous silica (MPS) filmhas been synthesizedon rubbing-treated (rubbed) polyimide (PI), which has the potentialto be used as a surface-modified technology for biomedical catheters.However, the oriented cylindrical MPS film lacked isotropic mechanicalproperties because the cylindrical mesostructures were uniaxiallyoriented. Thus, it is possible to improve the isotropic propertiesof cylindrical MPS films by cross-laminating their cylindrical mesostructure.In this study, an orthogonally stacked and cylindrically orientedMPS film with two layers (2-L-MPS) was successfully synthesizedthrough the following processes: (i) The 1st-layer-oriented MPS filmwas synthesized on the 1st-layer-rubbed PI film. (ii) The 2nd-layer-rubbedPI film was coated on the 1st-layer-oriented MPS film where the rubbingdirection was perpendicular to that of the 1st-layer-rubbed PI film.(iii) The 2nd-layer-oriented MPS film was synthesized on the 2nd-layer-rubbedPI film. As for the 2-L-MPS film, it was proved thatthe orthogonally stacked and cylindrically oriented MPS film with2-layer from the & phi;-scan XRD patterns, and the pore diametersof the 1st- and 2nd-layer-oriented MPS films were 3.7 and 4.8 nm fromthe Barrett-Joyner-Halenda (BJH) pore size distributions.The isotropic mechanical property of the 2-L-MPS filmis thought to be enhanced by orthogonal stacking. Subsequently, the 2-L-MPS films were immersed into & alpha;,& beta;,& gamma;,& delta;-tetrakis(1-methylpyridinium-4-yl)porphyrin p-toluenesulfonate (TMPyP) solutions with different concentrations,and the structures of the immersed 2-L-MPS films wereevaluated and the adsorption states of TMPyP were investigated. Themesostructures of the 2-L-MPS films were still maintainedafter being immersed in the TMPyP solutions. Moreover, 2-L-MPS showed the different molecular adsorption states of TMPyPat the 1st- and 2nd-layer-oriented mesopores because of the differencein the pore size between each MPS layer. In the future, it is expectedto be applied as a surface modification technology to endue biomedicalmaterials such as PI catheters with excellent mechanical propertiesand oriented cell adhesion properties. Moreover, it has the potentialto be used as a coating material that loads two drug molecules withdifferent molecular diameters and releases them in a sustained mannerby utilizing the difference in the pore size between the 1st- and2nd-layer-oriented mesopores.