Molecular dynamics simulations of the interaction between Fe3O4 and biocompatible polymer

• We built the interface models between biocompatible polymers and Fe3O4.
• The polymer with hydrogen bond donor has a strong interaction with Fe3O4.
• The high flexibility polymer chain might form a dense polymer layer on Fe3O4.

Molecular dynamics simulation was employed to investigate the interaction mechanism between several kinds of biocompatible polymers and Fe3O4 (1 1 1) surface at the atomic level. The interaction energies between Fe3O4 (1 1 1) surface and different biocompatible polymers implied that the interactions between polysaccharides (chitosan and dextran) and Fe3O4 (1 1 1) surface were stronger than that of polyesters (PLGA and PLA), PEI and PEG. The existence of the hydrogen bonds between the functional groups of polysaccharides and the oxygen atoms of Fe3O4 (1 1 1) surface have been proved by the radial distribution function analysis, which might be the reason of forming strong interaction. By contrast, the weak interactions between the polymers else and Fe3O4 (1 1 1) surface have formed because of the intermolecular force between oxygen or nitrogen atoms on polymers and the iron atoms on Fe3O4 (1 1 1) surface. It could be seen from concentration profiles, only the distance between the innermost layer polymer and Fe3O4 (1 1 1) surface have influenced by the interfacial interactions. The flexibility of polymer chain was proved to be the most important factor for affecting the morphology of polymer on Fe3O4 (1 1 1) surface by analyzing the mean squared displacement. From the simulation snapshot, it could be seen that the distribution of PEG, which had the weakest interaction with Fe3O4 (1 1 1) surface and the highest flexibility, was compact on the Fe3O4 (1 1 1) surface. This study revealed that the stable interface would form easily between the polymer with hydrogen bond donor and Fe3O4 (1 1 1) surface and the high flexibility of polymer chain might be propitious to the formation of the dense polymer layer on Fe3O4 (1 1 1) surface.

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