This invention describes an adhesive used for bonding dental and medical biomaterials to hard tissues via a molecular bridge formed from calcium-reactive amines and acrylic or methacrylic ester monomers to hard tissues such as enamel, dentin, and bone. This formulation consists of an acid-stable polymerizable compound with multi-functional acrylate cross-linkers. This formula provides good self-adherence without prior preparation of the hard tissue substrates. The formulation can contain chemical- and/or light-activated free-radical initiators.