Selective Modification and Application for Controlled Release of TiO_2/SiO_2 Composite Hollow Spheres

The composite TiO2/SiO2 hollow spheres(CHSs) were successfully prepared via sol-gel process using carboxyl-functionalized polystyrene spheres as templates.Then the titania layer was selectively modified with stearic acid and phosphate,forming hydrophobic and hydrophilic interior,respectively.Their hollow and porous structures were confirmed by scanning electron microscope(SEM) and N2 sorption analysis.Fourier transform infrared(FT-IR) spectra indicate that the interaction between the modifiers and the surface of titania is not physical adsorption but chemical combination.Using ibuprofen(IBU) as a model drug,the investigation of drug loading amounts and release rates shows that they can be regulated by suitable modification.Compare with the unmodified system,the stearic acid modified CHSs exhibit higher drug loading amount and lower release rate due to the hydrophobic effect.The IBU loading amount reaches 189.8mg/g and only about 55% of IBU is released within 53h.However,the phosphate modified CHSs exhibit relatively low drug loading amount(153.0mg/g) and high release rate,probably associated to the hydrophilic shells and charge repulsion.Its release percentage reaches nearly 80% within 10h.Therefore,the produced CHSs have potential application in the sustained drug delivery.