pH-Controlled Drug Release by Diffusion through Silica Nanochannel Membranes

We report in this work the fabrication of a flow-through silica nanochannel membrane (SNM) for controlled drug release applications. The ultrathin SNM consists of parallel nanochannels with a uniform diameter of ∼2.3 nm and a density of 4 × 1012 cm-2, which provide simultaneously high permeability and size selectivity toward small molecules. The track-etched porous polyethylene terephthalate film premodified with silane on its surface was used to support the ultrathin SNM via irreversible covalent bond formation, thus offering mechanical strength, flexibility, and stability to the ultrathin SNM for continuous and long-term use. Alkylamines were subsequently grafted onto the SNM surface to modulate the "on" and "off" state of nanochannels by medium pH for controlled drug release. Thiamphenicol glycinate hydrochloride (TPG), an intestinal drug, was studied as a model to permeate through an ultrathin SNM in both simulated gastric fluid (pH = 1.2) and simulated intestinal fluid (pH = 7.5). The release in the latter case was 178 times faster than that in the former. Moreover, a nearly zero-order constant release of TPG via single-file diffusion was achieved up to 24 h, demonstrating the feasibility of sustained and continuous release of small-molecule drugs in a pH-controlled manner.