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.
Millimeter-scale calcium alginate aqueous core capsules (mm-CaSA-Caps) are suitable for embedding of temperature and chemical sensitive substances because of its excellent biocompatibility and biodegradability. In this study, mm-CaSA-Caps were coated with multiwalled carbon nanotubes (MWNTs) via in situ self-polymerization of dopamine (DA) under mild conditions. During the modification process, mm-CaSA-Caps transferred quickly from colorless and transparent capsules to dark and opaque “pearls” in 15 min. The obtained MWNTs-polydopamine- (PDA-) modified mm-CaSA-Caps (mm-MWNTs-PDA@CaSA-Caps) retained the spherical appearance of mm-CaSA-Caps with uniform coating of MWNTs-PDA. Obviously, the MWNTs were easily coated on the mm-PDA@CaSA-Caps due to the strong adhesive property of PDA. As the MWNTs content increased, the stacking density of MWNTs on surface of the mm-MWNTs-PDA@CaSA-Caps raised. The water loss ratio of mm-MWNTs-PDA@CaSA-Caps was enhanced ascribed to increasing the path length of water by raising stacking density of MWNTs. This study provided a new path for enhancement of the barrier property of hydrogel capsules.
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