Medical Design Briefs - August 2021 - 13

capital investment. There are also material and precious metal
requirements for the manufacturing process since most electrodes
are made from platinum group metals and their alloys.
Many of these techniques pose technological challenges in a
manufacturing environment. Difficulties include an inability to
employ serial or in-line processing approaches in production, a
need for costly time-consuming vacuum/batch processes, and
the selective masking and coating of areas of interest on the
electrode surface. Despite the favorable electrochemical properties
some of these materials and technologies offer, more
important challenges include poor adhesion of coatings and
additive layers to the underlying substrate or electrode surface,
affecting electrode function, as reported in platinum black,
IrO2 or conducting polymers.
Surface morphology of materials is a key factor in governing
various surface properties such as optical, mechanical, wetting,
chemical, biological, and electrochemical characteristics of
solid surfaces. Ultrashort pulse and femtosecond laser technology
have emerged as novel and versatile technologies for producing
a variety of micro- and nanostructured surfaces suitable
for a wide range of applications in photonics, plasmonics,
optoelectronics, biochemical sensing, micro- and nanofluidics,
optofluidics, and biomedicine, among others.
The Invention
Pulse Technologies Inc. has developed a patented technology
using ultrashort pulse lasers for hierarchical surface restructuring
(see Figure 1) of electrode materials for implantable medical
device applications (see Figure 2). Ultrashort pulse lasers
offer the unique advantage of athermal material ablation with
no induced damage such as heat affected zone, micro cracking,
surface debris, and recast layer. This technology can engineer
and tune surface texture and morphology (see Figure 3) to
increase surface roughness and available surface area to
enhance electrochemical performance of the electrodes by several
orders of magnitude.
The hierarchical surface structures induced are comprised of
varying length scales ranging from micro- to nanostructures (see
Figures 4 and 5). This surface hierarchy greatly increases available
electrochemical surface area (ESA), in turn significantly
enhancing electrochemical performance of the electrode.
Performance Benefits
Some performance benefits - including an increase in
charge storage capacity and reduction in impedance derived
from hierarchical surface restructuring of electrodes - can be
measured using electrochemical techniques. Cyclic voltammetry
(CV) was used to measure charge storage capacity, and electrochemical
impedance spectroscopy (EIS) was used to measure
impedance and specific capacitance. Both tests were performed
in a three-electrode cell (see Figure 6) comprising a
Ag/AgCl reference electrode, a coiled Pt counter-electrode
and identically sized electrodes using commercially available
phosphate-buffered saline (PBS) solution.
All potentials were recorded with respect to Ag/AgCl. All CV
tests were measured at a 50 mV/s sweep rate between potential limits
of -0.6 and 0.8 V, beginning at open-circuit potential and sweeping
in the positive direction first. Total charge storage capacity
(CSCtotal) was calculated by integrating the area under the cyclic
voltammagrams for a bare Pt10Ir electrode and a series of electrodes
restructured under varying laser restructuring conditions
(see Figure 7). The voltammagrams compare electrodes restrucMedical
Design Briefs, August 2021
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Medical Design Briefs - August 2021

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