Nature-Derived Amphiphilic Polymers Crosslinked by Calcium Ions for Microencapsulation Applications

Microcapsulation with biodegradable polymers has raised great interest in recent years since commercial products containing nonbiodegradable polymers may cause microplastic pollution that has lasting impacts on the natural environment. Here, we developed a microencapsulation approach using a nature-derived modified polysaccharide as the shell material to address this issue. This method is based on a microemulsion system involving in-situ crosslinking of a branched polymer synthesized from maltodextrin and octenyl succinic anhydride (OSA), which can be generally applied to encapsulate oil-based core materials. The connection between the maltodextrin backbone and octenylsuccinate branches is created by an esterification reaction occurring at the OSA/water interface. We synthesized a series of polymers at different reactant ratios and found the optimal ratio for the overall efficiency. With a structure combining the advantages of polyanions and amphiphilic polymers, this branched polymer is able to spontaneously stabilize the cargo oil/water microemulsion to encapsulate the oil droplets and be crosslinked by calcium ions to form a solid network. We found that the mechanism for the polymer crosslinking involves the replacement of sodium ions with calcium ions in the octenylsuccinate branches to form calcium carboxylate bonds, which act as bridges between polymer chains to create a network structure. Meanwhile, we also observed that excessive calcium ions as the crosslinking agent can unexpectedly result in a noncrosslinked polymer structure. An optimal ratio between the polymer and calcium ions was obtained to achieve the effective crosslinking. This microencapsulation method provides a nature-derived, facile approach for a wide range of applications and may be a promising solution to address the challenge of microplastic pollution caused by nonbiodegradable polymers used in existing microencapsulation techniques.