Comparative analysis of antimicrobial agents and testing methods for polymer coatings

Abstract Antimicrobial polymer coatings (AMPCs) represent a leading innovation in suppressing surface-associated microorganisms, with reported bactericidal performance ranging from ~ 2 to > 5 log₁₀ reductions depending on agent chemistry and test conditions. To combat microbial contamination, these coatings are applied across diverse industries, including healthcare, textiles, and infrastructure. They function by combining antimicrobial agents into polymer matrices, thereby inhibiting microbial growth, biofilm formation, and adhesion, with standardized assays (e.g., ISO 22196, 24 h) have reported reductions of ~ 3–6 log₁₀ on non-porous polymeric substrates for several agent classes. However, because AMPCs are relatively new and involve a wide variety of agents and testing methods, comparing their effectiveness remains a significant challenge. This review addresses this gap by evaluating the most studied antimicrobial agents—silver nanoparticles, copper, zinc oxide, quaternary ammonium compounds, chitosan, polyethyleneimine, poly-ε-lysine, and zwitterionic polymers—across widely used testing protocols (ISO 22196, ASTM E2149, ASTM E2180, zone of inhibition (ZOI) assays, and biofilm-based methods). Information was compiled from various peer-reviewed studies to examine performance trends, assess agent–method compatibility, and highlight advantages and limitations under both static and dynamic conditions. The analysis indicates that silver nanoparticle– and QAC-based coatings typically perform well under standardized surface-contact testing, achieving ~ 4.5–5.7 log₁₀ reductions in ISO 22196 assays at 24 h, while zinc oxide and poly-ε-lysine exhibit comparable mid-to-high range efficacy (~ 3.5–4.8 log₁₀). In contrast, copper, chitosan, and polyethyleneimine show more moderate activity (~ 2.5–3.6 log₁₀) that is highly substrate- and assay-dependent. In long-term biofilm studies, zwitterionic polymers consistently demonstrate superior antifouling behavior, commonly reducing biofilm viability or coverage by ~ 90–92%, but display weaker direct bactericidal activity in planktonic or short-contact assays (~ 1–3 log₁₀). This work underscores the urgent need for a standardized testing and reporting framework, supported by a comprehensive database, to enable meaningful quantitative comparisons of AMPC performance. Although this review provides an initial evidence-based foundation, further harmonization of methodologies and long-term studies are required to fully realize the potential of antimicrobial polymer coatings. Graphical Abstract