periodontate in order to render the tyrosine residues converted to reactive dopa residues required for strong adhesion the enzyme oxidation may serve as an oxidative agent and as a copolymer molecular oxygen can also be used to oxidize dopa to a quinone possible cross linking agents are oxygen polyvalent metal ions fe 3 and al 3 aldehydes and many types of bi polyfunctional cross linkers the addition of other macromolecules to the mefp 1 protein u2014 such as collagen casein or keratin u2014 has been recommended by companies in order to increase the adhesive properties of the individual protein mefp 1 in the form of cell tak biopolymers corp of farmington conn has been tested as a surgical adhesive between a number of different cells or tissues from a range of species for example studies testing the efficiency of cell tak biopolymers corp of farmington conn compared to other adhesives have included porcine cartilage bone and skin see chivers r a wolowacz r g the strength of adhesive bonded tissue joints international journal of adhesion and adhesives 1997 17 2 127 132 rat tissue see schmidt s p resser j r sims r l mullins d l smith d j the combined effects of glycyl l histidyl l lysine copper ii and cell tak on the healing of linear incision wounds wounds a compendium.