Biofilms as Living Coatings: Surface Adhesion, Extracellular Matrix Formation, and Interfacial Properties

Biofilms are self-organized microbial communities embedded in a self-produced matrix of extracellular polymeric substances (EPS). Usually studied as biofouling or persistent infection, they can also be treated as self-assembling, self-repairing biological soft coatings. Previous reviews have addressed matrix biology, biofilm mechanics and engineered living materials largely separately; this review connects them through the biofilm–substrate interface. It covers the physics of attachment, from extended DLVO models to adhesins and surface-sensing circuits whose regulation differs between species; the matrix as a structural material whose assembly and turnover are increasingly well characterized; and self-repair, which in the systems studied so far has required a surviving viable layer and a nutrient supply. Cohesive, adhesive and mixed-mode failure are used as the organizing distinction. Stratified cohesion and variable failure loci are established experimentally, whereas the expectation that matrix reinforcement without matching interfacial anchoring shifts failure toward the interface is presented as a design hypothesis. Engineered living coatings are then assessed, characterization methods from force spectroscopy to interfacial electrochemistry and permeability are mapped, and a minimum reporting standard is proposed to make results comparable between laboratories.