Bimodal mesoporous silicas functionalized with different level and species of the amino groups for adsorption and controlled release of aspirin.

The synthesis of modified bimodal mesoporous materials (BMMs) with a small pore size of around 2.9 nm and a large pore size of about 20 nm has been performed via post-grafting methods. To study the application of functionalized BMMs in drug delivery, loading and releasing profiles using aspirin as model drug were carried out. XRD, SEM, TEM, N2 adsorption, FT-IR, 29Si-NMR, TG and UV-Vis spectroscopy were used to characterize the related samples. The post-grafting modification was performed through the weak chemical interaction or hydrogen bonding in between OH groups of the mesopore surface and 3-aminopropyltriethoxysilane (N-TES) or 3-(2-aminoethylamino) propyItrimethoxysilane (NN-TES). The results showed that N-TES groups with different amount and NN-TES groups were successfully incorporated onto the mesopore surface. Subsequently, the controlled aspirin delivery properties from the resulting modified BMMs were investigated in detail. The aspirin adsorption experiments indicated that the adsorption capacities of modified BMMs were improved with the increasing amount of N-TES groups, while the NN-TES functionalized samples showed higher adsorption capacity than N-TES modified samples with the same ratio of modification. The most reason is that the interaction between the NN-TES groups and aspirin molecules is stronger than that between the N-TES groups and aspirin molecules. The in vitro tests exhibited that aspirin release behaviors mainly depended on the variation of the amount and species of the functional groups in mesoporous carries. According to the Korsmeyer-Peppas model, it is found that the kinetic release constant k reduced with the increase amount of the amino groups on the mesopore surface of modified BMMs, suggesting that the aspirin release rate from the pores of BMMs was influenced directly by organic groups on the surface. The release exponent n of all the situations were above 0.5, indicating the drug release mechanism followed a non-Fickian model that was diffusion based. Therefore, this type of materials described in this paper is of strong potential for the controlled drug release applications.