bioprosthetic devices include an exterior biological tissue member which at least partly defines a cavity , and a proteinaceous biopolymer which fills the cavity , and intercalates and is chemically bound to the tissue of the surrounding biological tissue member . in preferred forms , the bioprosthetic device is a bioprosthetic vertebral disc having a fibrillar outer annulus which surrounds and defines an interior cavity and is formed by removal of at least a substantial portion of the natural gelatinous core therefrom . the cavity defined by the fibrillar outer annulus may then be filled with a flowable proteinaceous biopolymer . preferably , the proteinaceous biopolymer is a liquid mixture comprised of human or animal - derived protein material and a di - or polyaldehyde , which are allowed to react in situ to form a cross - linked biopolymer within the cavity . the liquid mixture may be formed in advance of being introduced into the cavity , or may be formed simultaneously during introduction into the cavity .