Medical Design Briefs - September 2021 - 13

medications over fixed or variable periods
of time. The evolution of this product
has included the following five
components:
1. Adhesive Patch. This component represents
a unique design challenge for
device manufacturers. Adhesives are
not a component found in many previous
drug-delivery devices, requiring
manufacturers to acquire a new set of
skills and expertise. The adhesive
properties need to be optimized for
patient comfort during use and re -
moval of the product, and the adhesive
patch also needs to be designed
in a way that ensures proper orientation
and skin contact are maintained
during the delivery process.
2. Device Body. The device body houses
all internal mechanical and electrical
subcomponents of the system. The
main purpose of the mechanical components
is to dispense the drug to the
body at either a set or variable flow
rate. Certain devices have controllers
that can define the flow rate, either
through physical means on the device
or through a paired application. The
flow rate can either be a user preference
based on comfort, or a physician
requirement. The electronic subcomponents
typically allow for communication
with external devices to assist
the patient with tracking their pro -
gress over time. It is also common to
have a viewing window and audio/
visual feedback to alert the patient
when the delivery is complete.
3. Drug Cartridge. The cartridge is
where the required drug volume or
bolus is held. This generally consists
of a glass container, a rubber stopper,
a rubber seal, and an aluminum
crimped cap. The break-loose and
glide force for the stopper needs to be
evaluated to properly design the actuation
mechanism.
4. Activation Button. The device will
generally have a clearly marked button
for starting the injection. There
are many factors that need to be considered
in the button design, including
tactical feedback, activation force,
and design features to prevent accidental
actuation.
5. Needle/Soft Cannula. While a stainlesssteel
needle is most commonly used, a
soft cannula can instead be used in
cases where the delivery time may be
longer than 20 minutes and patient
comfort is a concern. The needle and
soft cannula require similar evaluations
Medical Design Briefs, September 2021
Intro
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Vmax
10
Vmin
8
tmin
6
tmax
4
2
5
10
Time (min)
Fig. 1 - This chart shows an example of a drug-delivery dose profile. Dotted lines help visualize the
bounds for maximum and minimum delivery dose and time.
determining the insertion depth and
lockout confirmation. As in all drugdelivery
systems, sharps protection is
critical, requiring a passive mechanism
to hide the needle after injection.
Wearable Device Benefits
Wearable injection devices come with
a wide array of benefits to the user and
drug manufacturer beyond the simplicity
of the device. The device's functionality
provides increased opportunities for
delivering both larger doses and higher
viscosities, and in some cases both. This
is accomplished while mitigating discomfort
to the patient associated with
larger doses, and in many cases reducing
the total number of injections required.
In situations where drugs are delivered
intravenously over long periods of time,
as is often found in the treatment of cancer
or auto-immune diseases, these
products can allow for delivery in the
patient's home rather than a clinical setting.
Limiting unnecessary time in hospital
or clinical settings also reduces the
risk of hospital acquired
infections (HAIs).
Wearable devices also
introduce increased opportunity
for connectivity
between digital health
platforms and the devices.
The design of these products can
allow for additional electronics to be
built in, offering an unparalleled
level of digital control and oversight.
Through connected applications, the
patient can adjust the deliverable volume
or flow rate depending on their
www.medicaldesignbriefs.com
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A
µ
15
20
25
The Instron 6800
universal testing system
is performing a
90° peel test to determine
the adhesive
strength of the material.
This test provides a
uniform way to evaluate
adhesive strength
after conducting a
range of simulated conditions
to fully characterize
the material.
13
Volume (mL)
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Medical Design Briefs - September 2021

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