A packed Cytodex microbead array for three-dimensional cell-based biosensing

A packed Cytodex 3 microbead array was fabricated as a simple three-dimensional (3-D) cell-based biosensing format. Resting membrane potentials and voltage-gated calcium channel (VGCC) function of SH-SY5Y human neuroblastoma cells cultured on the microbead array versus collagen-coated flat (2-D) substrates were evaluated by confocal microscopy with a potentiometric dye, tetramethylrhodamine methyl ester, and a calcium fluorescent indicator, Calcium Green-1. SH-SY5Y cells, differentiated with 1 mM dibutyryl cAMP and 2.5 μM 5-bromodeoxyuridine, showed significant resting membrane potential establishment on the topographical scaffolds in a period of 13 days into differentiation, in contrast to the previously reported insignificant resting membrane potential establishment of the same cells within collagen hydrogels. On days 2, 8 and 13 into differentiation, cells on collagen-coated flat substrates developed resting membrane potentials of −6.0 ± 19.5 mV (n = 198), −30.5 ± 19.9 mV (n = 191) and −21.7 ± 18.9 mV (n = 308), in contrast to values for cells on 3-D scaffolds of −25.8 ± 14.7 mV (n = 112), −37.6 ± 13.1 mV (n = 120) and −28.7 ± 12.2 mV (n = 158), respectively. The development of VGCC function, as measured by percentage of cells responsive to 50 mM high K+ depolarization, was significantly slower for cells on 3-D scaffolds (20.0% on day 13 into differentiation) than for cells on 2-D substrates (30.7% on day 8 into differentiation). The exaggerated 2-D cell calcium dynamics, in comparison with those of 3-D cells, is consistent with previous 2-D/3-D comparative studies. This study established the rationale and feasibility of the microbead array format for 3-D cell-based biosensing.