Precise and tunable time-controlled drug release system using layer-by-layer films as erodible coatings.

Unlike conventional drug carriers, time-controlled release systems do not release drug immediately, but start to release drug after a predetermined lag time. Coating a drug-loaded core with an erodible barrier is a valid way to defer drug release, however, the complicated erosion behavior of the erodible coatings makes it difficult to predict and tune the lag time. Herein we proposed that dynamic layer-by-layer films, using hydrogen-bonded poly(ethylene glycol)/tannic acid (PEG/TA) film as an example, are ideal erodible coatings, because their erosion mechanism is clear and simple, and they disintegrate at constant rate. As a proof, we demonstrated that the release of bovine serum albumin (BSA) from BMS spheres can be deferred by PEG/TA coating. More importantly, the lag time can be simply tuned by the thickness of the coating. By mixing bimodal mesoporous silica (BMS) spheres coated with different thickness PEG/TA films, multiple pulse release was achieved. Similar release patterns were also successfully achieved in vivo.