Bundling of axons through a capillary alginate gel enhances the detection of axonal action potentials using microelectrode arrays.

Microelectrode arrays (MEAs) have become important tools in high throughput assessment of neuronal activity. However, geometric and electrical constraints largely limit their ability to detect action potentials to the neuronal soma. Enhancing the resolution of these systems to detect axonal action potentials has proved both challenging and complex. In this study, we have bundled sensory axons from dorsal root ganglia through a capillary alginate gel (Capgel™) interfaced with an MEA and observed an enhanced ability to detect spontaneous axonal activity compared with two-dimensional cultures. Moreover, this arrangement facilitated the long-term monitoring of spontaneous activity from the same bundle of axons at a single electrode. Finally, using waveform analysis for cultures treated with the nociceptor agonist capsaicin, we were able to dissect action potentials from multiple axons on an individual electrode, suggesting that this model can reproduce the functional complexity associated with sensory fascicles in vivo. This novel three-dimensional functional model of the peripheral nerve can be used to study the functional complexities of peripheral neuropathies and nerve regeneration as well as being utilized in the development of novel therapeutics.

Use of a capillary alginate gel (Capgel™) to study the three-dimensional development of sensory nerves reveals the formation of a rudimentary perineurium.

BACKGROUND: Peripheral neuropathies affect approximately 20 million people in the United States and often stem from other chronic conditions, such as diabetes. In vitro methodologies to facilitate the understanding and treatment of these disorders often lack the cellular and functional complexity required to accurately model peripheral neuropathies. In particular, they are often 2D and fail to faithfully reproduce the 3D in vivo microenvironment. NEW METHOD: Embryonic dorsal root ganglion (DRG) explants were inserted into laminin derivatized capillary alginate gel (Capgel™), a bioabsorbable, self-assembling biomaterial, possessing parallel microchannel architecture, and cultured to mimic normal nerve development, including Schwann cell myelination. RESULTS: Laminin derivatization of the microchannels improved nerve growth through the gel. Axon bundles containing myelinating Schwann cells migrated through the gel and were ensheathed by rudimentary perineurium up to 1 mm from the DRG explant site. COMPARISON WITH EXISTING METHODS: Other nerve models are two-dimensional in nature and/or fail to conserve the complicated architecture and cellular milieu observed in vivo. Our nerve model shows the simple culture technique of cells grown in 3D, which allows for a more advanced structural organization that more accurately mimics the in vivo nerve fascicle. CONCLUSIONS: When embryonic DRG explants are cultured in this system, they show a striking resemblance to in vivo peripheral nerve fascicles, including myelinated axons and the formation of a rudimentary perineurium, suggesting that both neuronal and non-neuronal cells within the DRG explant are capable of recreating the 3D structure of a developing sensory fascicle within the microchannel architecture.