Fabrication and Characterization of Conducting Polymer Microcups Produced via Electrospinning and Electrochemical Polymerization for Neural Microelectrodes

Open Access
Author:
Khorrami, Milad
Graduate Program:
Materials Science and Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
December 09, 2015
Committee Members:
  • Mohammad Reza Abidian, Thesis Advisor
Keywords:
  • Conducting polymer
  • microcups
  • electrochemical polymerization
  • electrospinning
Abstract:
Innovation in the fabrication of implantable micro-scale bioelectronics has been challenging owing to high impedance and low charge storage capacity that result in both low signal-to-noise ratio and low charge injection electrode-tissue interfaces. Additionally, such devices without anti-inflammatory compounds are less likely to maintain their efficacy due to fibrous encapsulation associated with tissue reaction reducing the effective transfer of signals. Thus, there is considerable incentive to fabricate devices capable of delivering therapeutic compounds while maintaining electrical performance. Polypyrrole (PPy) has gained significant interest for biomedical applications owing to its excellent biocompatibility, electrical properties, and mechanical actuation. Poly (lactic-co-glycolic) acid (PLGA) is biodegradable and highly biocompatible, making it an ideal matrix for drug encapsulation. In this research, we have produced hollow PPy cups from template PLGA microspheres on Au electrodes, which were fabricated on Si wafers (two circles with diameters 1.5 and 5.0mm connected with a rectangle 1.0x10mm). Briefly, 4/2wt% PLGA/benzyltriethylammonium chloride was dissolved in chloroform and electrosprayed on the Si electrodes using an applied electrical field of 100kVm-1. PLGA was then coated with PPy/poly (styrenesulfonate) using electrochemical deposition (current density 0.5mA/cm2) for 5 different time durations. The spherical PLGA coated with PPY was then dissolved in chloroform to create hollow PPy cups. These microspherical cups are relatively uniform in size, having average diameters of 3.45±0.31µm, indicating a CV of 9%. Furthermore, Impedance spectroscopy and cyclic voltammetry were performed on all 5 samples and a gold reference to investigate the impedance and charge storage capacity. The size and shape of PPy cups were characterized using Field-Emission SEM. The hollow PPy cups decreased the impedance from 445 ± 63 Ω for bare gold to 354 ± 39 Ω for 8 min PPy-coated electrode, a difference of 20% at 1kHz. The additional surface area obtained by removal of the PLGA cores significantly increased the effective surface area of electrode, thus lowering the impedance. The PPy cups also significantly enhanced the charge storage capacity from 2.5 to 47.5mC/cm2; nearly 95%. In conclusion, we successfully demonstrated: (1) electrochemical deposition of PPy around the electrosprayed PLGA microspheres, (2) removal of PLGA microspheres to fabricate hollow PPy cups, and (3) improvement of electrical properties of Au electrodes by decreasing impedance and increasing charge storage capacity. This study demonstrates the potential of our conductive microstructures for neural interfacing and neural regeneration while retaining functionality for drug delivery.