Peptide Display Directed Assembly of Biopolymer Core–Silica Shell Particles

The unique hierarchical core-shell structures of silica capsules contributing to delivery of active compounds have attracted broad interest. To overcome the limited cargo-loading capacity of silica capsules but harness the silica mediated cargo protection, Escherichia coli is engineered to efficiently assemble submicrometer-sized biopolyester particles (BPs) that densely display the positively charged RK1 peptide ((RKK)₄G₃Y), which mediates nucleation and growth of silica. The peptide-coated BPs are tested as biomimetic template and treatment with silica precursors results in formation of BP core-silica shell structures. Electron microscopy reveals changes in BP surface morphology consistent with silica shell formation further confirmed through Fourier transform infrared spectroscopy. Thermogravimetric analysis shows 0.10 g of silica shell per gram of BPs is formed, with no impact on crystallinity as assessed by X-ray diffraction. The payload of the lipophilic biopolyester core for the lipophilic model compound, curcumin, increases to an encapsulation efficiency of 23.6%. Silica coating of BPs does not cause cytotoxicity and BPs show efficient cellular uptake. This study presents an innovative and environmentally benign approach for efficiently assembling robust biopolyester core-silica shell structures. The nontoxic polymer core provides drug payload capacity, protected by a silica coating ideal for controlled drug delivery applications.