The adsorption of DNA by cationic core-shell diblock copolymer polystyrene-block-poly(N-methyl 4-vinylpyridine iodide) micelles

Abstract

The diblock copolymer polystyrene-block-poly(N-methyl 4-vinylpyridine iodide) (PS-b-P4VPQ) with the molecular weight of PS 3.5 × 10³ g/mol and P4VPQ 11.6 × 10³ g/mol forms core-shell polymer micelles in aqueous solution. The cationic brush shell of the polymer micelle can be used to accommodate hydrophilic drugs and biomolecules, such as DNA, for biomedical applications. It is essential to understand how biomolecules are adsorbed within the brush layer. Here we investigated the interaction of the cationic brush of the polymer micelle with DNA by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). It is found when adding only relatively small amounts of on average 30 base pairs (bp) DNA, at 19.6 and 39.2 μM for 0.1 mM PS-b-P4VPQ, most of the polymer micelle/DNA complexes remain well dispersed. The brush layer of the polymer micelles are slightly swelled due to the adsorption of DNA within the brush layer. When the DNA concentration is increased to 58.8 μM or higher, the polymer micelle/DNA complexes form closely packed agglomerates. At high DNA concentrations, some adsorbed DNA will start to build up at the edge or surface of the brush layer which could induce aggregation of the polymer micelle/DNA complexes. This means that it is possible to prepare mostly dispersed polymer/DNA complexes by keeping the DNA concentration below the aggregation concentration. The well dispersed polymer micelle/DNA complexes are advantageous for many DNA related biomedical applications.

Keywords: Cationic polymer brush; Core-shell diblock copolymer micelle; DNA adsorption; Small-angle X-ray scattering.