Porous Antimicrobial Coatings for Killing Microbes within Minutes

Antimicrobial coatings can be used to reduce the transmission of infectious agents that are spread by contact. An effective coating should kill microbes in the time between users, which is sometimes minutes or less. Fast killing requires fast transport, and our proposed method of fast transport is a porous coating where the contaminated liquid imbibes (infiltrates) into the pores to achieve rapid contact with active material inside the pores. We test the hypothesis that a porous antimicrobial coating will enable faster inactivation of microorganisms than a planar coating of the same material. We use hydrophilic pores with dimensions of 5–100 μm such that liquid droplets imbibe in seconds, and from there transport distances and times are short, defined by the pore size rather than the droplet size. Our coating has two levels of structure: (A) a porous scaffold and (B) an antimicrobial coating within the pore structure containing the active ingredient. Two scaffolds are studied: stainless steel and poly(methyl methacrylate) (PMMA). The active ingredient is electrolessly deposited copper. To enhance adhesion and growth of copper, a layer of polydopamine (PDA) is deposited on the scaffold prior to deposition of the copper. This porous copper coating kills 99.84% of Pseudomonas aeruginosa within 3 min, which is equivalent to a half-life of 27 s. In contrast, the same layer of PDA/copper on a nonporous coating kills 79.65% in the same time frame, consistent with the hypothesis that the killing rate is increased by the addition of porosity. Using the porous PMMA scaffold, the porous antimicrobial coating kills >99.99% P. aeruginosa in 5 min, which is equivalent to a half-life of 21 s. The higher rate of kill on the porous antimicrobial solid is appropriate for hindering the spread of infectious agents on common-use objects.