Influences of Phosphates on the Adhesion of a Catechol-Containing Polymer

Bioadhesives are popular characterization targets for informing the design of synthetic materials. Many naturally occurring adhesive proteins are phosphorylated, yet we do not know why phosphorylation might be so prevalent in nature. Here, phosphate-containing biomimetic polymers were made using the chemistry of catechol, or 3,4-dihydroxyphenylalanine, for adhesion. Structure–function studies were carried out with this family of poly(catechol-phosphate) polymers to determine how phosphate groups influence bulk adhesion. Bonding was studied both dry and underwater. Under some conditions, polymers containing phosphate groups exhibited extreme levels of surface wetting on steel substrates. Dry adhesion increased moderately with greater phosphate content in the polymers. Underwater bonding was weaker than dry and achieved, only to a limited degree, when the polymer phosphate content was high. These results indicate that phosphates may provide an aid to the more impactful adhesive properties of catechols. Such insights may also help to explain the existence of phosphates in bioadhesives as well as inform the future design of high-performance materials.