Photo-sensitive hollow capsules: an alternative drug delivery approach

The skin provides a natural physical barrier against particle penetration. However, skin is a widely used route to delivery local and systemic drugs. In fact, drug loaded polymeric carriers are of special interest for the treatment of skin diseases, owing to their striking dermal delivery efficiencies following topical applications. Topically applied carriers are subjected to biodegradation. However, the inclusion of a stimuli-responsive system into the carriers allow a temporal control of the drug release. This strategy besides enhancing topical bioavailability will also enable to develop a cutaneous therapy with reduced drug doses as well as low administration frequencies.

In this work is proposed the employment of Layer-by-layer (LbL) methodology to prepare hollow capsules. LbL assembly is a simple and highly versatile method to fabricate robust and highly-ordered nanostructured coatings over almost any type of substrate and with a wide range of substances.

The design of biocompatible photo-responsive multilayer systems based on a polyoxometalate (POM) ([NaP₅W₃₀O₁₁₀]^14-) and a natural origin polymer, chitosan (CHT), appeared as a possibility to promote light-stimuli responses. The photo-reduction properties of the POM allow a spatially controlled disruption of the assembled layers due to the weakening of the electrostatic interactions between layers, which promote capsule destruction and consequent content release[1].Conditions necessary for the successful construction of capsules were achieved using QCM analysis in a 2D model. The employed procedure to the production of LbL capsules will be defined according to the well-known protocols[2, 3], wherefreshly prepared CHT and POM salt solutions, coated into CaCO₃ template particles are used to produce micro-particles. The morphology of the produced carriers was accessed by SEM analysis, different particle sizes between 2-5µm may be obtained by tailoring the number of layers and the assembling conditions.  Delivery efficiency of the proposed system was studied using BSA-FITC loaded capsules, being the fluorescence of supernatant measured at different time points, the release was modulated through different radiation exposure times.

In summary, is proposed the rational design and characterization of tailored, stimuli-responsive carriers, and their subsequent stepwise screening for delivery efficiency that may find application as a top-down approach yielding the best carrier system for topical applications.