Implantable and direct contact electronic devices for underpinning complex tissue functions as well as physiological monitoring have the opportunity to revolutionize health care in an ageing population. A major EU-consortium of 25 partners has been developing electronic devices for functional electrical stimulation, glaucoma and CNS pressure monitoring and as cochlear, retinal and urethral implants. A key need, however, is the packaging of such complex devices to enhance tissue biocompatibility, and to protect conducting elements from in vivo corrosion during extended use. Accordingly, we have investigated candidate polymeric barriers as hydration resistant and solute impermeable in interphases to mitigate the major problems of chronic implantation. Materials include silicone rubber, PVC, polyurethane, sulphonated polyetherether sulphone polyether-sulphone (SPEES-PES) and polycarbonate as underlayer and carbon like carbon (DLC), sol-gel modified oxides and Parylene C for top layers. A key strategy is polymer modification through incorporation variously of surfactant (Aliquat 336) and synthetic lipid (isopropyl myristate) to manipulate permeability to water and to low molecular weight solutes. Surface biocompatibility was assessed on the basis of protein film deposition in vitro and by cell viability studies in tissue culture. Polypyrrole deposited on gold coatings was used as a substrate for cell testing. None of the materials tested showed short-term toxicity, though there were substantial differences in hydration. Results with polypyrrole suggest that both electrical conductivity and tissue interfacing to be viable if used as coatings over active electrode components. © International Federation for Medical and Biological Engineering 2007.