Proteomic characterization of collagen-based animal glues for restoration.

Animal glues are widely used in restoration, serving as adhesives, binders, and consolidants for organic and inorganic materials. Their variable performances are intrinsically linked to the adhesive properties of collagen, which determines the glue's chemical, physical, and mechanical properties. We have molecularly characterized the protein components of a range of homemade and commercial glues using mass spectrometry techniques. A shotgun proteomic analysis provided animal origin, even when blended, and made it allowed to distinguish between hide and bone glue on the basis of the presence of collagen type III, which is present abundant in connective skin/leather tissues and poorly synthesized absent in bones. Furthermore, chemical modifications, which arose as a consequence of the preparation protocols from the original animal tissue, where thoroughly evaluated. Deamidation, methionine oxidation and backbone cleavage have been systematically analyzed as significant collagen signatures modifications, demonstrating their variability of collagen modifications among different glues and showing that, on average, bone glues are on average less deamidated than hide glues, but more fragmented, and mixed-collagen glues are overall less deamidated than pure glues. We believe that these data may be of general analytical interest in the characterization of collagen-based materials and may properly guide help restorers in the selection of the most appropriate materials to be used in conservation treatments.