Integrated carbon fiber electrodes within hollow polymer microneedles for transdermal electrochemical sensing

Abstract

In this study, carbon fiber electrodes were incorporated within a hollow microneedle array, which was fabricated using a digital micromirror device-based stereolithography instrument. Cell proliferation on the acrylate-based polymer used in microneedle fabrication was examined with human dermal fibroblasts and neonatal human epidermal keratinocytes. Studies involving full-thickness cadaveric porcine skin and trypan blue dye demonstrated that the hollow microneedles remained intact after puncturing the outermost layer of cadaveric porcine skin. The carbon fibers underwent chemical modification in order to enable detection of hydrogen peroxide and ascorbic acid; electrochemical measurements were demonstrated using integrated electrode-hollow microneedle devices.

Figure 1

Computer-aided design drawing of the microneedle array that was fabricated using the digital micromirror device-based stereolithography instrument.

Figure 2

Schematic showing steps used for assembly of the microneedle device.

Figure 3

Optical images of (a) an array of carbon fiber electrodes (scale bar=1 mm) and (b) a single carbon fiber electrode (scale bar=100 μm).

Figure 4

MTT viability data for cells grown on e-Shell 200 acrylate-based polymer and glass cover slip. (a) MTT viability of human epidermal keratinocytes grown on e-Shell 200 acrylate-based polymer compared to glass cover slip. A and B denote statistical differences (p<0.05) between the polymer and the control. (b) MTT viability of human dermal fibroblasts grown on e-Shell 200 acrylate-based polymer compared to glass coverslip. A and B denote statistical differences (p<0.05) between the polymer and the control.

Figure 5

Scanning electron microscopy image of hollow microneedles prior to incorporation of carbon fiber electrodes: (a) plan view of hollow microneedle array and (b) isometric view of single hollow microneedle.

Figure 6

Images of microneedle array and cadaveric porcine skin after microneedle insertion. (a) Optical micrograph showing delivery of trypan blue into microneedle-fabricated pores within cadaveric porcine skin (scale bar 1=mm). (b) Optical micrograph showing hollow microneedles before insertion into cadaveric porcine skin. (c) Optical micrograph showing hollow microneedles after insertion into cadaveric porcine skin.

Figure 7

Scanning electron microscopy images of hollow microneedles after incorporation of carbon fiber electrodes: (a) plan view of electrode-hollow microneedle array and (b) isometric view of single electrode-hollow microneedle.

Figure 8

Cyclic voltammetric scan of 5 mM ferricyanide in 1 M KCl vs Ag∕AgCl and Pt reference counterelectrodes, respectively, at a scan rate of 100 mV∕s.

Figure 9

Cyclic voltammetric scans of 0, 50, 100, 300, and 500 μM hydrogen peroxide (pink, black, green, blue, and red curves) vs Ag/AgCl and Pt reference counterelectrodes, respectively, at a scan rate of 100 mV/s.

Figure 10

Linear sweep voltammograms of 0 mM (black) and 1 mM (red) ascorbic acid in 100 mM phosphate buffer (pH=7) vs Ag/AgCl and Pt reference counterelectrodes, respectively, at a scan rate of 100 mV/s.