(150d) Controlled Drug Delivery From PEG Hydrogel Encapsulated Eosin Functionalized Hydrophobic Aerogels

A novel method for the sequential formation of silica aerogel and PEG hydrogel composite, and its potential as a drug delivery system are investigated. The composite was synthesized by encapsulation of hydrophobic aerogels within PEG hydrogel via photoinitiated polymerization. Disks of aerogels were synthesized by the two step sol-gel method using tetraethylortosilicate (TEOS) as the silica precursor. After the gels were aged in ethanol, the alcogels were then contacted with a solution of eosin-Y, a photoinitiator, dissolved in ethanol. Eosin-Y incorporated alcogels were subsequently dried by supercritical CO₂ at 313 K and 10.3 MPa. The surface of eosin functionalized silica aerogels was rendered hydrophobic using hexamethyldisilazane (HMDS) as the surface modification agent, and scCO₂ as solvent at 20.68 MPa and 333.2 K. Hydrophobicity of aerogel was tuned by changing HMDS amount dissolved in ScCO₂ phase which changes the contact angle between 0-130^o. The hydrophobic aerogels were then dipped into a PEG diacrylate prepolymer solution, and photopolymerization was carried out using visible light (514 nm). The hydrogel coating around the hydrophobic aerogel was only restricted to the external surface of the monolithic disks, since the water based prepolymer solution did not penetrate into the hydrophobic aerogel structure. BET surface area and pore size distribution measurements were done for both non-coated and coated aerogel. The data show data that both hydrogel encapsulation and eosin-Y loading did not affect the pore structure of the aerogel. The potential of this novel composite as a drug delivery vehicle was tested by as a model drug Ketoprofen due to its solubility in the scCO₂. The results demonstrate that both drug loading capacity and drug release profiles could be tuned by changing hydrophobicity of aerogels, and that drug loading capacity increases with decreased aerogel hydrophobicity while slower release rates are achieved with increased hydrophobicity from eosin functionalized aerogels. The drug release was complete during the first 10 hours for the hydrophilic aerogels, while it took about 6 days for the hydrophobic aerogel to completely release the drug. PEG hydrogel encapsulation of hydrophobic aerogels may allow for extended release time scales for the model drug. Furthermore, it may be possible obtain subsequent release profiles for drugs or proteins with various hydrophobicities from this aerogel-hydrogel composite through loading of additional drug or protein into the PEG hydrogel structure.