Medical Design Briefs - July 2022 - 24

TECHNOLOGY LEADERS Motors/Motion Control
A motor that can meet a force range
of 50-80 N is typically sufficient. These
devices are battery driven, so efficiency is
important to the pump design. Coreless
brush DC motors with precious metal
commutators are well suited to meet
these higher battery life requirements,
providing high power density and reliability.
A spur compound gearbox or
custom gearhead are ideal for limiteduse
biologic applications.
Reusable biologic pumps. Robust, ruglong-lasting
ged,
and
reusable
drugdelivery
pumps can handle drugs of various
viscosities for a broad range of
therapies. This type of delivery device
presents particularly demanding motion
requirements, however; the higherviscosity
biologics make a high axial
force output up to and higher than 100
N necessary.
Limited-use devices have both a disposable drug unit and a separate, reusable pump unit. (Credit: Portescap)
When supporting various biologics
as a platform, the pump must be able
to deliver the highest viscosity drug
while also accurately delivering the
lower viscosity ranges. Reusable pumps
are portable, so their size and weight
are important criteria. Outside diameters
for a premium biologic device motor
typically range from 10 to 12 mm
(see Table 1).
Reusable pumps can handle drugs of various viscosities for a broad range of therapies. (Credit: Portescap)
The duty cycle for disposable applications
is limited, ranging from a few seconds
to a few hours. Based on the application
requirements, a reliable, cost- optimized,
motor-driven system serves these devices
well.
Limited-use biologic devices. A motorized
device can accept multiple biologic
drug cartridges over the course of a therapy.
Limited-use devices offer the advan24
tage
of having both a disposable drug
unit and a separate, reusable pump unit.
They also provide flexible performance
as well as a lifetime that is relative to the
pump price. Limited-use devices are
generally designed for use with a single
biologic drug or limited drug offerings,
so the force and size requirements for
the motors may be different than those
of reusable devices.
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A reusable pump must also be robust
and reliable. Product warranties can range
from two to five years, so the motors and
drives have to be properly sized to deliver
the same accuracy from day one to the end
of the pump's life. For a motor-driven system,
the designer confirms a confidence
factor of greater than 90 percent to ensure
that it lasts the required lifetime.
Feedback, repeatability, and storage
conditions are additional factors in drive
system selection. An encoder confirms
that the motor has provided the needed
drug delivery, ensuring that the therapy
is successful. It also ensures that every
delivery increment is met each time. If
the biologic requires cold storage, a motor
and gearhead that can withstand lower
temperatures and humidity over periods
of time are necessary.
Overall, brushless DC motors (BLDC)
or coreless brush DC motors with precious
metal commutators are best suited
for reusable biologic pump devices.
A spur gearhead or a custom-designed
gearhead can provide a great torque-toMedical
Design Briefs, July 2022

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Medical Design Briefs - July 2022

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