Versatile surface modification of millimeter‐scale “aqueous pearls” with nanoparticles via self‐polymerization of dopamine

Abstract

The millimeter‐scale calcium alginate aqueous core capsules (mm‐CaSA‐Caps), which own high entrapment efficiency and excellent biocompatibility, have broad applications in food additives and drug delivery. However, due to pH sensitivity and thermal instability of Ca‐alginate, many chemical modifications with intense conditions are hardly conducted on the mm‐CaSA‐Caps. In this work, layer‐by‐layer assembly coating on the surface of the mm‐CaSA‐Caps was proceeded with in situ self‐polymerization of dopamine (DA) and nanoparticles under mild conditions. The colorless and transparent mm‐CaSA‐Caps became beautiful dark “pearls” of polydopamine (PDA) modified mm‐CaSA‐Caps (mm‐PDA@CaSA‐Caps), which had uniform coating of PDA. Obviously, deposition of PDA on mm‐CaSA‐Caps accelerated with higher concentration of DA, weak alkali condition of pH = 8.5, and oxidant of sodium periodate. Water retention ratio of mm‐PDA@CaSA‐Caps also increased because of the PDA coating. The nanoparticles were easily coated on the mm‐PDA@CaSA‐Caps due to the strong adhesive property of PDA. Two‐dimensional laminar montmorillonites were adhered to mm‐PDA@CaSA‐Caps, which lead to better barrier property of capsules than that of the one‐dimensional linear multiwalled carbon nanotubes modified capsules. It was ascribed to increasing of the path length of water by sheet‐like morphology of montmorillonites. This work provided a versatile path for enhancement of barrier property of millimeter‐scale hydrogel capsules.