Cholesterol-mediated anchoring of enzyme-loaded liposomes within disulfide-stabilized polymer carrier capsules

Polymer capsules containing multiple liposomes, termed capsosomes, are a promising new concept toward the design of artificial cells. Herein, we report on the fundamental aspects underpinning the assembly of capsosomes. A stable and high loading of intact liposomal cargo into a polymer film was achieved by non-covalently sandwiching the liposomes between a tailor-made cholesterol-modified poly(l-lysine) (PLL_c) precursor layer and a poly(methacrylic acid)-co-(cholesteryl methacrylate) (PMA_c) capping layer. The film assembly, optimized on planar surfaces, was successfully transferred onto colloidal substrates, and a polymer membrane was subsequently assembled by the alternating adsorption of poly(N-vinyl pyrrolidone) (PVP) and thiol-modified poly(methacrylic acid) (PMA_SH) onto the pre-adsorbed layer of liposomes. Upon removal of the silica template, stable capsosomes encapsulating the enzyme luciferase or β-lactamase within their liposomal sub-compartments were obtained at both assembly (pH 4) and physiological conditions (pH 7.4). Excellent retention of the liposomes and the enzymatic cargo within the polymer carrier capsules was observed for up to 14 days. These engineered capsosomes are particularly attractive as autonomous microreactors, which can be utilized to repetitively add smaller reactants to cause successive distinct reactions within the capsosomes and simultaneously release the products to the surrounding environment, bringing these systems one step closer toward constructing artificial cells.