Medical Design Briefs - July 2022 - 23

TECHNOLOGY LEADERS Motors/Motion Control
How to Select Motors to Address Biologic
Drug-Delivery Challenges
B
iologic drugs change the way
the human immune system responds
to numerous diseases
and conditions. These drugs
have revolutionized disease treatments
and offer hope to many patients who
previously had no effective remedies
for their illnesses. That's good news for
patients, but biologics present drugdelivery
challenges for device designers.
Recently developed biologics are characterized
by high molecular weights -
as much as 150,000 daltons (Da). For
designers of biologic drug-delivery devices,
such weights create different challenges
than conventional synthesized
drugs. The higher molecular weights
also means that biologics have high viscosities,
which influence the injection
profile of the drug-delivery device and,
ultimately,
the
device's
effectiveness.
These challenges make the motor system
a significant element in biologic delivery
device development.
Biologic Drug Administration Methods
Of the three methods for administering
a drug into a patient's body (see Figure 1),
biologics use subcutaneous and intramuscular
delivery methods, including:
* Intravenous. This technique, often abbreviated
as IV therapy, delivers the
medication directly
into a patient's
vein.
* Subcutaneous. Drugs intended for slow
absorption are often injected into the
subcutaneous tissue between the fat
layer just under the skin and over the
top of the muscles.
* Intramuscular. Because muscles have
larger and more numerous blood vessels
than subcutaneous tissue, intramuscular
injections are preferable for
faster drug absorption.
Technical
Considerations
Drug-Delivery Devices
Three main types of devices are used
to deliver biologic drug injections: disposable,
limited-use, and reusable biologic
pumps. How these devices are used
Medical Design Briefs, July 2022
for Biologic
Epidermis
Dermis
Subcutaneous tissue
Muscle tissue
Fig. 1 - Drug molecules for biologics (left) and traditional drugs (right).
Intravenous
Subcutaneous
* Milti-drug delvery
* Large flow rate ranges
* Long term treatment
* Medium viscosity drugs
* Low flow rates
* 1 day to 3 years treatment
Intramuscular
* High-med. viscosity drug delivery
* Flow rates fixed
* One time use
Fig. 2 - Methods and devices for injecting biologics.
- along with their technical considerations
and the motors or motion components
available to address them -
include the following:
Disposable biologic devices. Singleuse
devices are designed to costeffectively
deliver a specific drug, with
delivery time ranging from a few seconds
to a few days. Examples include
mechanical injectors and disposable
patch pumps that are worn directly on
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the body and have a reservoir, pumping
mechanism, and infusion set inside
a small case.
Various motors and drives can be a
good fit for this application. The most
suitable motor technologies are can stack
stepper and brush DC. Both motor types
offer a mature technology with advantages
over some alternative actuators that,
although they may also be appropriate,
require complex drive electronics.
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Medical Design Briefs - July 2022

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