Sorkin et al recently used rat cortical cells and locust cells in order to examine how these neurons interact with carbon nanotube (CNT) island surfaces. As with other studies, they found that the CNT is a good substrate for neuronal growth and that the neurons tend to migrate to the edge of these CNT islands and encircle them.
Qualitatively, they also found that both insect and mammalian neurons either tend to intertwine with either the CNT surface, or in the case of thicker axons and dendrites against each other. The authors investigated the mechanism by which locust cells become intertwined with one another via time lapse microscopic imaging. They found three steps: 1) The growing process approaches the existing one, 2) There is molecular contact between the growing and existing process, and 3) Over the course of about two hours the intertwined processes pull on each other until they are solidly connected.
The authors speculate that a similar process occurs between the neural processes and the CNTs, which might explain why neurons adhede very well on rough surfaces lile CNTs but do not on smooth surfaces like silicon dioxide. The degree to which and geometry mimic biologically relevant surfaces correlates with how well neurons anchor onto the surface, and that is one of the reasons for how succesful CNTs have been as a substrate for neuronal growth.