Fig. 5: pH-responsive sustained release of ACA-coated PSMs.

a Schematic representation of ACA-coated microswimmer sustained release drug/nanoparticles by ion exchange. b The formation mechanism of ACA membrane. Drug is wrapped by Alginate-Ca layers structure which is due to Na-alginate has ionic interaction and gelling abilities with divalent cations (Ca²⁺), each Ca²⁺ ion can bond with two carboxylic acid moieties of guluronic acid (G). Then, the positively charged amino groups (NH³⁺) of chitosan can with the negatively charged carboxyl groups (COO⁻)of alginate and form a 3D cross-linking polyelectrolyte membrane. c The ACA membrane consists of three layers includes Alginate-Ca, Chitosan and Alginate. The SEM image shows ACA membrane when chitosan reaction during 9 min. d Relationship between the polyelectrolyte complexation reaction period and the ACA membrane thickness. The thickness of the ACA membrane increases with the increase of reaction time. Error bars indicate the standard deviation for n = 7 measurements at each data point. e The cumulative release of ACA coated microswimmers with different thickness ACA membrane. Error bars indicate the standard deviation for n = 3 measurements at each data point. f The release of FITC- dextran from the ACA coated microswimmers and uncoated microswimmer in different pH environment. Error bars indicate the standard deviation for n = 3 measurements at each data point. g Under in extreme alkali environment, the fluorescence image comparison between ACA coated microswimmers and uncoated microswimmer. h The curves of the fluorescence intensity between ACA coated microswimmers and uncoated microswimmer in extreme alkali environment. Scale bar is 20 μm.