The authors' goal is to develop a neural interface system that enables connection of the human nervous system with external devices and allows transmission of information in both directions. One way to connect interface to neurons is a regenerative electrode, where the electrode is placed between the two cut ends of a nerve. The cut nerve fiber can regenerate through channels in a metallic electrode on a two-dimensional (2D) plane of the regenerative electrode. As this type of electrode enables both the recording of signals from a single nerve fiber and the stimulation of a single nerve fiber, attempts have been made to develop it using traditional 2D microfabrication techniques. However, it is difficult to process such electrodes with these 2D microfabrication techniques, particularly the high-density integrated structure of the electrical wiring. The authors previously designed a neural interface system-a type of regenerative electrode consisting of an electrode segment and many carbon microtubes for guiding the regenerating axons of the neuronal cells-that can be made through three-dimensional processing. In the current study, the authors have fabricated a prototype of the guiding segment of the electrode (which was previously reported) and evaluated the biocompatibility of diamondlike carbon (DLC) made by focused-ion-beam chemical vapor deposition (FIB-CVD) and carbon microtubes in vitro. The microtubes were fabricated using FIB-CVD. DLC was deposited with a scanning 30 keV Ga+ ion beam in an atmosphere containing phenanthrene (C14H10). The scanning patterns were determined by a computer-aided-design system before the fabrication. The beam was scanned over a Au-coated glass capillary or polycarbonate membrane to deposit DLC and form the carbon microtubes. For observation of the axon growth through the microtubes, the authors fabricated bifurcated carbon microtubes with an inner diameter of 3-6 mu m on the glass capillary and straight microtubes on the polycarbonate membrane. The fabricated microtubes were immersed in a culture medium containing nerve growth factor and PC 12 cells were cultured inside the capillary and on the membrane to evaluate whether they could extend axons through the microtubes. Here, the authors show that cultured rat phaeochromocytomas adhered to and survived for days on a DLC surface while preserving their morphology provided that the adhesion molecule poly-D-lysine was used as an organic substance to anchor the cells to the DLC surface. As a result, cells spread and neurites projected on the DLC area, suggesting that the DLC had little cytotoxic effect. (c) 2006 American Vacuum Society.