Thin film platinum cuff electrodes for neurostimulation: in vitro approach of safe neurostimulation parameters

Thin film technology takes more and more importance in the development of biomedical devices dedicated to functional neurostimulation. Our research about the design of implant neurostimulating electrode is oriented toward thin film cuff electrodes based on a polyimide substrate covered by a chromium/gold/Pt film. The chromium/gold sputtered film serves as adhesion layer and current collector whereas platinum acts as an electrochemical actuator. The electrode surface has been designed to obey safe stimulation criteria (i.e. chemically inert noble metal, low electrode-electrolyte impedance, high electrochemical reversibility, high corrosion stability). The electrochemical behaviour of such platinum electrodes has been assessed and compared to a foil of platinum. Extensive in vitro characterisations of the both electrode types were carried out using AFM, SEM and electrochemical techniques. The role of enhanced surface roughness enabling high double layer capacitances to be achieved was clearly highlighted. The obtained results are discussed, with particular reference to thin film electrodes stability under in vitro electrical stimulation in NaCl 0.9% (physiological serum). Therefore, these thin film devices showed reversible PtOH formation and decomposition making them potentially attractive for the fabrication of implant stimulation cuff electrodes.     

Synthesis of indaphyrins: meso-tetraarylsecochlorin-based porphyrinoids containing direct o-phenyl-to-beta-linkages

The synthesis of indaphyrins, novel meso-tetraarylsecochlorin-derived chromophores incorporating o-phenyl-to-beta-linkages, is described. Oxidative diol cleavage of meso-tetraaryl-2,3-dihydroxy-2,3-chlorins results in the formation of a secochlorin bisaldehyde. Depending on the reaction conditions during the ring cleavage reaction, one or two of the aldehyde groups react with the adjacent o-phenyl positions, leading to an intramolecular electrophilic aromatic substitution of the o-phenyl proton, and the establishment of a direct o-phenyl-to-beta-linkage. The initially formed carbinol is spontaneously oxidized to the corresponding ketone. This modification forces the aryl groups into co-planarity with the macrocycle, allowing for interactions between the pi-electrons of the aryl groups, the ketone linkage, and those of the chromophore, resulting in a significant electronic modulation of the porphyrinic pi-system. The UV-vis spectroscopic properties of the free base, CuII, NiII, and ZnII indaphyrins are discussed.