Describing the possible in vivo activity of carbon nanotubes based on in vitro analysis

Lovat et al (2005) attempted to characterize carbon nanotubes (CNTs) as a functional substrate for neuron cells in vitro.

In order to do so, they compared the effects of multiwalled carbon nanotubes (MWNTs) functionalized with azomethine ylides versus simple glass coverslips as substrates for the integration of seeded hippocampal neurons. Scanning electron microscopy after 10 days confirmed that the neuron growth did not differ in form between the MWNTs substrate and the control.

But functionally the results were astounding. Using single-patch-clamp recordings, the researchers analyzed the amount of spontaneous post-synaptic currents (PSCs) in both types of culture. The neurons on the MWNT substrate exhibited a six-fold increase in the frequency of PSCs, and there were no major differences in type: MWNT substrate neurons did not display significantly larger events, nor did was their percentage of excitatory versus inhibitory currents altered.

The authors suggest that the results may have been due to the high electrical conductivity of the CNT material, leading to a reinforcement of direct electrical coupling between neurons. Whatever the explanation, it seems quite clear that CNT material leads to a greater degree of network efficacy than a glass coverslip control.

Gheith et al (2006) attempted to show that layer-by-layer single carbon walled nanotubes (SWNTs) could be used to stimulate the neurophysiological activity of neuroblastoma/glioma hybrid cells (NG108-15). They used a voltage/patch clamp technique in order to connect the metal electrode to the internal volume of the cell.

After assembling the nanotube films, these researchers first noted that the input resistance for cells grown on the SWNT substrate was 122 +/- 55 mV, which is not significantly different from those grown on glass (140 +/- 67 mV). This confirms Lovat et al’s finding that the CNT substrate does not affect the cellular health or type of physiological activity.

They then showed that the layer-by-layer SWNT substrate can be used to stimulate electrical ion conductance in the neuron cells. They suggested that the cells were stimulated via an influx of cations, which is the typical method of stimulation under natural conditions. This electrical coupling between CNT material and neuron cells could potentially play a crucial role in future extracellular implants.

Reference

Lovat V, Pantarotto D, Lagostena L, Cacciari B, Grandolfo M, Righi M, Spalluto G, Prato M, Ballerini L. 2005 Carbon nanotube substrate boosts neuronal electrical signalling. Nano Letters 5: 1107-1110. doi: 10.1021/nl050637m.

Gheith MK, Pappas TC, Liopo AV, Sinani VA, Shim BS, Motamedi M, Wicksted JP, Kotov NA. 2006 Stimulation of neural cells by lateral currents in conductive layer-by-layer films of single-walled carbon nanotubes. Advanced Materials 18: 2975-2979. doi: 10.1002/adma.200600878.