Keywords

Nanoelectrodes, electrical stimulation, stem cells

Introduction

Adipose-derived stem cells (ADSCs) have gained increasing attention in the recent times, for regenerative medicine and tissue engineering applications due to their high proliferative capacity, multi-lineage potential and ease in harvesting compared to other stem cells [1]. Similarly, penetrating nanoelectrodes that can interface or assess the interior of the cell, without causing cell damage are increasingly being used as biosensors and for cell interrogation studies [2, 3]. In this work, for the first time, we show that (a) silicon nanopillars/nanoelectrodes of optimized size and shape can penetrate ADSCs without any loss of cellular function and (b) electrical stimulus can be applied through the penetrating electrodes to differentiate ADSCs into neuronal lineages. ADSCs are generally differentiated into neurons by using growth factors, genetic manipulators, cytokines and/or other chemical reagents [4]. However, there are many issues associated with the use of chemical reagents, including problems in translational studies, cell toxicity and induced cell stress [5]. On the other hand, endogenous electrical stimulus, which plays many important roles in physiological processes, can modulate or control biological processes including cell migration, orientation, and differentiation [6].

Materials and Methods

Nanopillars design and fabrication

The nanoelectrodes (nanopillars/nanofins) were designed to overcome the trade-offs between electrode impedance and electrode size. Compared to conventional 3 x 3 array of 150nm diameter nanowire electrodes [2. 3], the current nanoelectrodes were designed to reduce electrode impedance by a factor of 20 due to a large capacitance and small charge transfer resistance, while maintaining minimal cell damage. The fabrication of nanoelectrodes or nanopillars starts on single crystal silicon wafer followed by a series of lithographic patterning, deposition and etching steps, as shown in Fig. 1. The dimensions of the nanopillars were tuned to give desired height, width, and thickness at the tip. The density of the nanopillars was varied between 4.8x103 and 8.3x103 pillars/cm2, and the tip dimension ranged from 100nm x 100nm to 100nm x 7.5µm. The height of the nanopillars was maintained at a constant height.