Lipid-bilayer coated nanosized bimodal mesoporous carbon spheres for controlled release applications

Highly mesoporous nanosized carbon spheres (MCS) equipped with an active lipid bilayer demonstrate pronounced molecular release behavior, and excellent potential for drug delivery applications. We report a facile synthesis route for the creation of colloidal MCS with a bimodal pore size distribution, featuring a high BET surface area combined with high pore volume. Bimodal mesoporosity was achieved by a simultaneous co-assembly of a polymer resin (resol), tetraethyl orthosilicate (TEOS) and a block copolymer (Pluronic F127). The spherical geometry originates from casting the precursor mixture into a macroporous silica hard template, having a mean pore size of 60 nm, followed by thermopolymerization and final carbonization at 900 °C in nitrogen atmosphere. The final bimodal mesoporous MCS were obtained after removal of inorganic compounds by etching with hydrofluoric acid. Colloidal suspensions of MCS were prepared by oxidation with ammonium persulfate. MCS were loaded with calcein as a model drug. Efficient sealing of the MCS was achieved with a supported lipid bilayer (SLB). The SLB acts as a diffusion barrier against the uncontrolled release of encapsulated dye molecules until the release is triggered via the addition of a surface active agent. The high surface area and pore volume and the excellent release characteristics make the SLB-coated MCS a promising release-on-demand system.