Effect of Antimicrobial Divalent Metal Cations Onto Oxidized Surface of Polyhydroxyalkanoate Films on Biodegradability in Seawater

Poly[(R)-3-hydroxybutyrare-co-(R)-3-hydroxypivalate] (P(3HB-co-3HPi)) films, a type of polyhydroxyalkanoate (PHA), are oxidized using photoactivated chlorine dioxide radical (ClO₂•) gas to generate carboxyl groups and loaded with divalent metal cations, including Cu²⁺, Zn²⁺, and Ca²⁺ ions, via ionic interactions. The P(3HB-co-3HPi) films loaded with Cu²⁺ ions exhibit enhanced antibacterial activity against Gram-positive bacteria (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli) compared with untreated P(3HB-co-3HPi) films. In seawater, the biodegradation of these Cu²⁺ and Zn²⁺-loaded films is initially inhibited by the antimicrobial activity of the cations and occurs gradually; therefore, loading antimicrobial divalent metal cations onto the surface of PHAs inhibits biodegradation in seawater temporarily but allows biodegradation to occur with time. These results indicate that PHAs could be employed in seawater without undergoing biodegradation, such that PHAs could be used in fishing gear, including fishing lines that are repeatedly exposed to seawater for short periods.