A biofuel cell incorporating a bienzymatic trehalaselglucose oxidase trehalose anode and a bilirubin oxidase dioxygen cathode using Os complexes grafted to a polymeric backbone as electron relays was designed and constructed. The specific power densities of the biofuel cell implanted in a female Blaberus discoidalis through incisions into its abdomen yielded maximum values of ca. 55 mu W/cm(2) at 0.2 V that decreased by only ca. 5% after ca. 2.5 h of operation.