Medical Design Briefs - February 2025 - 21

Design Briefs
Additive Manufacturing for Platinum Alloys
By Andy Michalow, C.Hafner, Pforzheim, Germany
he use of platinum-iridium (PtIr) alloys
for pins and electrodes in medical
devices is growing substantially
in applications such as cardio and neuromodulation
devices. In this article, pens are
defined as those used in feedthroughs for
ceramic implants, generally straight wire
with specific cutoff features on the ends,
and electrodes are defined as those providing
direct electrostimulation to tissues, which
are essentially wires that have additional
features machined into them. The benefits
and features discussed herein, using additive
manufacturing (AM), also apply to
other types of PtIr components, where the
end pieces can be fabricated from different
preforms besides wires. The ongoing miniaturization
of implantable and insertable devices
is magnifying the need for controlling
the bulk metal material consistency. Cost is
always an important issue as well.
Recent developments in creating PtIr
powders by atomization have opened up
possibilities to produce PtIr components
using AM techniques. The overall production
steps with AM are generally shorter
compared to conventional techniques,
with a specifically smaller equipment effort
and material-efficient production cycles.
Analogous benefits in using AM for
PtIr alloys apply to gold-based alloys. This
article focuses on PtIr applications.
T
Powder Technology
Two keys to success with any AM process
include consistent particle size distribution
and uniform spherical particle shape.
Where the 3D structure is built by fusing
the powder layer by layer, aka, 3D printing,
a particle size distribution of between
9 and 52 µm was found to be optimal.
Too narrow a range could impede
flow with the potential for the particles
to clump together.
Additional uses for the powder include
metal injection molding, brazing
powders, and other applications. Size
distribution for these processes typically
require a maximum particle size of 25
µm. A particle size distribution of 5-25
µm can be maintained for such applications.
Any particles that are outside the
specified size range could easily be transferred
back to the furnace, where reatomization
could be done in subsequent
production. No refining is required as
the alloy does not change during atomization.
One key benefit of powder-based
technologies is the direct reuse of excess
powder without new energy-intensive
melting processes.
Background
PtIr alloys are used in medical applications
for the following reasons: biocompatibility,
electrical conductivity,
high density, ductility, chemical inertness,
mechanical robustness, resistance
to corrosion, and radiopacity. The mechanical
and thermal properties, as well
as corrosion resistance, increase with
increased Ir content. While the PtIr alConventional
Process
Platinum and iridium are melted together
in a high-temperature vacuum
furnace at the specified weight ratio to
create a uniform mixture, where the
molten material is cast into ingots and
then cooled for further processing. The
casting process must be tightly controlled
to develop a consistent grain miloy
composition can be customized to a
particular need, in medical applications,
it is easiest to use those that meet
approved ASTM specifications, which
include platinum/iridium ratios of
95/5, 90/10, and 80/20.
Grade 90/10 is the most widely used,
due to its balance of cost, mechanical
properties, and processability. Grade
80/20 is used where the mechanical
strength and/or corrosion resistance are
the most critical. For the small pins and
electrodes, most of the cost is not the raw
material but the combination of processing
and fabrication. Grade 80/20 has the
highest processing costs and is the most
difficult to work with, from alloy casting
to forming to final part fabrication.
The following sections provide a comparison
between conventional and AM
processing. For both process scenarios, after
alloy melting, the material is typically
made into a preform, such as a bar, sheet,
tube, wire, or similar shape of specified dimensions,
which is then to be fabricated
into the final configuration.
The hollowed interior features produced by SLM shown in the example photos can reduce overall weight and cost of a PtIr component.
Medical Design Briefs, February 2025
www.medicaldesignbriefs.com
21

http://www.medicaldesignbriefs.com

Medical Design Briefs - February 2025

Table of Contents for the Digital Edition of Medical Design Briefs - February 2025