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Antifoulants are the most vital substances in antifouling coatings to prevent marine organisms from colonizing the undersea substrate surfaces. In addition to antibacterial performance, inhibition of biofilm formation is an important criterion for antifouling coatings. In this study, we synthesized pH-responsive matrine@chitosan-D-proline (Mat@CS-Pro) nanocapsules of about 280 nm with antibacterial properties and biofilm dispersibility. The prepared Mat@CS-Pro nanocapsules exhibited high-level antibacterial properties, reaching about 93, 88, and 96% for E. coli, S. aureus, and P. aeruginosa, respectively. Such nanocapsules can cause irreversible damage to bacteria and cause them to lose their intact cell structures. Moreover, Mat@CS-Pro nanocapsules also possessed outstanding dispersal biofilm performances, in which the biofilm thickness of E. coli, S. aureus, and P. aeruginosa was decreased by 33, 74, and 42%, respectively, after 3 days of incubation. Besides, the Mat@CS-Pro nanocapsules had remarkable pH-responsive properties. As the environmental pH became acidic, the nanocapsules swelled to about 475 nm and the released concentration could reach 28.5 ppm after immersion for 10 h but maintained a low releasing rate in pH 8 conditions.

In this work, we report the design of pH-controlled releasing behaviors of polydopamine/tannic acid-allicin@chitosan (PDA/TA-ALL@CS) multilayer coatings to realize antibacterial and antifouling effects. The pH-responsive ALL@CS capsules were prepared using the microemulsion method with about 262–452 nm diameter. The bacteriostasis of ALL@CS microcapsules against E. coli, S. aureus, and P. aeruginosa all exceeded 94% as evaluated using the colony counting method. Because of the protonation in acid environments and deprotonation in alkaline environments for the amino groups of CS, ALL as biocides can be released from the nanocapsules and exert outstanding antibacterial properties. Confirmed by the plate colony counts, the ALL@CS capsules possessed an outstanding antibacterial effect for E. coli in acid solutions but were less effective in alkaline solutions. The PDA/TA-ALL@CS-7 coatings showed durable pH-responsive antibacterial activities with an efficiency of ∼87% after immersion in pH 8 solutions for seven days. The PDA/TA-ALL@CS coating with controlled release performance and antibacterial properties may provide a new solution for developing antifouling coating applications in the marine environment.