Effects of surface coating on the controlled release of vitamin B₁ from mesoporous silica tablets

The controlled release of vitamin B₁ (VB₁, thiamine hydrochloride) from mesoporous silica tablets coated with a series of sol-gel coatings was investigated. Tetraethoxysilane (TEOS), n-propyltriethoxysilane (PTES), n-octyltriethoxysilane (OTES), bis(trimethoxysilyl)hexane (TSH), bis(triethoxysilyl)octane (TSO), bis (trimethoxysilylpropyl)amine (TSPA), and bis[(3-trimethoxysilyl)propyl]ethylenediamine (TSPED) were used as precursors for the coatings. The effects of organosilane type and concentration, the number of coatings, drying temperature, and release media on VB₁ release from the coated mesoporous silica tablets were comprehensively examined. The TSH, TSO, TSPA, and TSPED coatings were found to be more effective in suppression of release than the other coatings. VB₁ release decreases with the increase in the number of coatings and drying temperature. It was found that there is an optimal coating solution concentration for the controlled release. In general, more VB₁ is released in 0.01 M HCl solution than in 0.05 M phosphate buffer solution at pH 7.4 because of the electrostatic repulsions between the protonated VB₁ cations and the positively charged mesoporous silica carrier/coatings. The experimental results show that drug release can be easily controlled by changing the organosilane type and the number of coating. The method used in this study is an effective and flexible way for controlled release due to the high drug loading and the easy control of release rate.