Medical Design Briefs - October 2022 - 18

Orthopedic Implants
A cobot can be added to a universal testing system, allowing an operator to simply load a specimen rack and the
cobot will automatically load and unload the entire batch for testing. (Credit: Instron)
date. The responsibility is on the manufacturer
to provide ample evidence to
regulatory bodies that the product is the
same or better than what is produced using
existing technologies, and mechanical
testing is a crucial piece of measuring
process performance.
Mechanical Testing Considerations
Traditionally produced implants require
extensive mechanical testing including
quantification of raw material
properties, measurement of device responses
to anatomically representative
stresses, and determination of implant
fatigue performance, among other
things. The use of AM creates a need for
extensive qualification testing related
to the variable parameters mentioned
in the previous section. By creating test
coupons, a range of static tests can be
performed on the material, including
tensile, compressive, flexural, and torsional
testing. A universal testing system
is optimal for performing this kind of
qualification, along with the necessary
Preprocessing
Parameters
Build Volume
Placement
Support Material
Locations
Slice Thickness
Build Paths
Printing Process
Parameters
Build Speed
Nozzle Diameter
fixturing for each test type. Partnering
with mechanical testing experts is
important to ensure compliance with
relevant ASTM or ISO material standards
such as ASTM D638, ASTM D695,
ASTM D790, and ISO 6892. Generally,
the properties in question will be the
material's stiffness [elastic modulus],
yield strength, ultimate strength, and
ultimate elongation. System accuracy
related to force and displacement is crucial
when attempting to determine the
cause of variations in material properties
between slight modifications of AM process.
Ensuring that a supplier can provide
materials testing systems with high
accuracy load cells and extenso meter
options is invaluable for determining
material properties with the necessary
resolution for parameter optimization.
The use of coupons is not solely limited
to the qualification process. Many
manufacturers will make the decision
to incorporate coupon testing as an inprocess
control, placing coupons on the
print tray between parts or in specific
Material Reuse
Filtration Process
Percent Reused
Material
Delivery System Energy Material Changes
-
-
Table 1. AM processes introduce numerous variables to manufacturing.
18
Postprocessing
Parameters
Cleaning Protocols
Heat Treatments
Sterilization
-
locations of the tray for each build. The
coupon placement can be purposefully
done to capture the " worst case " scenario
for the system, based on the orientation
or the location within the build
volume. Additional mechanical testing
will need to be performed to prove the
coupon is representative of the finished
part but doing so will make the subsequent
in-process testing simpler and
more repeatable.
To address the sheer volume of testing
that will need to be performed for validation,
automation solutions such as a
cobot could be beneficial, removing the
need for dedicated system operators. The
cobot is designed primarily for flexibility
and can be quickly taught to pick and
place specimens from any arrangement.
This flexibility also extends to the various
test types, meaning a cobot solution can
perform tensile, compressive, or flexural
tests with minimal modifications to the
software aside from the necessary test
method changes. Improving test throughput
will be a significant factor in reducing
the time to market for the product.
AM has the potential to completely
revolutionize the landscape of orthopedic
implant production, improving
patient outcomes while circumventing
many supply chain challenges. Designing
and printing implantable prostheses
customized to the patient ensures an optimal
fit, with as little unnecessary augmentation
to the existing skeletal structures
as possible. AM techniques can
allow implants to be provided at or directly
near the point of care, increasing
responsiveness to patient demands and
easing supply chain burdens. Manufacturers
pursuing this technology will need
a flexible and adaptable mechanical testing
program, ideally partnering with a
supplier that is familiar with the unique
testing challenges that come along with
AM processes.
References
1. Murr, L. (2018). Additive Manufacturing of Biomedical
Devices: An Overview. Materials Technology,
57-70.
2. Shan, L. B. (2014). Total Hip Replacement: A
Systematic Review and Meta-Analysis on Midterm
Quality of Life. Osteoarthritis and Cartilage,
389-406.
This article was written by Landon
Goldfarb, Biomedical Market Manager at
Instron, Norwood, MA. Contact: landon_
goldfarb@instron.com. For more information,
visit www.instron.com.
www.medicaldesignbriefs.com
Medical Design Briefs, October 2022

http://www.instron.com http://www.medicaldesignbriefs.com

Medical Design Briefs - October 2022

Table of Contents for the Digital Edition of Medical Design Briefs - October 2022