Changing gears from chemical adhesion of cells to flat substrata toward engulfment of micro-protrusions by active mechanisms

Abstract

Microelectrode arrays increasingly serve to extracellularly record in parallel electrical activity from many excitable cells without inflicting damage to the cells by insertion of microelectrodes. Nevertheless, apart from rare cases they suffer from a low signal to noise ratio. The limiting factor for effective electrical coupling is the low seal resistance formed between the plasma membrane and the electronic device. Using transmission electron microscope analysis we recently reported that cultured Aplysia neurons engulf protruding micron size gold spines forming tight apposition which significantly improves the electrical coupling in comparison with flat electrodes (Hai et al 2009 Spine-shaped gold protrusions improve the adherence and electrical coupling of neurons with the surface of micro-electronic devices J. R. Soc. Interface 6 1153-65). However, the use of a transmission electron microscope to measure the extracellular cleft formed between the plasma membrane and the gold-spine surface may be inaccurate as chemical fixation may generate structural artifacts. Using live confocal microscope imaging we report here that cultured Aplysia neurons engulf protruding spine-shaped gold structures functionalized by an RGD-based peptide and to a significantly lesser extent by poly-l-lysine. The cytoskeletal elements actin and associated protein cortactin are shown to organize around the stalks of the engulfed gold spines in the form of rings. Neurons grown on the gold-spine matrix display varying growth patterns but maintain normal electrophysiological properties and form functioning synapses. It is concluded that the matrices of functionalized gold spines provide an improved substrate for the assembly of neuro-electronic hybrids.

Long-Term, Multisite, Parallel, In-Cell Recording and Stimulation by an Array of Extracellular Microelectrodes

“…In an earlier study, we established that culturing Aplysia neurons on a dense matrix (4,8,12, and 16 m pitch) of gold mushroomshaped protrusions for over a week does not alter the excitable membrane properties and synaptic physiology of the neurons (Hai et al 2009b). However, we did not examine the functional stability of the junctions formed between the neurons and the gME.…”

“…1). We have not studied the mechanisms underlying the generation of these critical events but noted in an earlier structural study (Hai et al 2009b) that engulfment of gMEs is much more effective when functionalized with EPP than by poly-L-lysine. We thus tentatively believe that the EPP plays a role in the induction of the engulfment and that binding events of receptors displayed on the plasma membrane and the EPP activate a highly conserved cascade leading to phagocytosis like processes (Stuart and Ezekowitz 2005).…”

“…Nevertheless the gME clearly maintains an extracellular position in respect to the neuron's plasma membrane. Live confocal microscope imaging of neurons grown on gME-based matrixes revealed that the engulfment of the gME is associated with restructuring of the actin cytoskeleton to form an actin ring around the stalk of the gME (Hai et al 2009b).…”

Flexible and stretchable micro-electrodes for in vitro and in vivo neural interfaces

“…Most of these arrays are microfabricated using MEMS technology and stiff materials including silicon, glass and metals. Dense arrays of up to 256 electrodes are used in vitro to monitor/stimulate individual neurons or acute tissue slices [14,27] and in vivo to treat or repair damaged brain tissues or peripheral nerves [16,31]. These 2D arrays interface very well with neurons' population cultured in vitro or 2D-organized neural networks in vivo such as ganglionic neurons in the retina.…”

Frequency-dependent signal transfer at the interface between electrogenic cells and nanocavity electrodes

“…Nevertheless, the simple fabrication of low-impedance and high-spatial-resolution electrodes still remains an experimental challenge. Attempts to lower the impedance, including the use of advanced interface materials [16][17][18] and patterning of metal electrodes [19][20][21][22], have led to promising results. However, they often require sophisticated techniques of production or lack mechanical stability and longevity.…”