MDTmag.com 20 / April 2014
Implantable Pump Seal
Improves Service Life and Cuts
Implantable devices can significantly impact the quality of care offered to a patient. Since they function with-
in the human body, they must be able to exist in that hostile environment without fail. As such, ensuring the
proper sealing of a device – maintaining a barrier between critical components and potentially hazardous
fluids – is essential for success.
By Steve Twork, Global Market Manager,
Medical Devices, Bal Seal Engineering Inc.
With a goal of improving the quality of life for patients with ascites, engineers at a Swiss
medical device company designed an implantable low-flow pump that dramatically
changed the standard of treatment (Sidebar:
Understanding Ascites). Doing so, however, required protecting their pump’s inner
workings from exposure to bodily fluids, and
that proved to be a major challenge prior to
testing and launch.
Device designers at Sequana Medical
reasoned that if they could move fluid from
the peritoneal cavity into the bladder by
employing a battery-powered, low-flow
pump and a set of two catheters, they could
eliminate the need for paracentesis, reduce
much of the discomfort associated with asci-
tes, and help patients reclaim their mobility.
With the implanted pump, fluid transferred
to the bladder could be expelled during
normal urination, so the patient’s quality of
life would be greatly improved as well.
The task seemed simple enough – build
on a pump prototype (originally conceived
by a physician with years of experience in
the treatment of ascites) and make a few improvements to ensure that performance and
battery life expectations could be consistently met. However, it soon became apparent
that the device motor would require an added level of protection against malfunction
caused by the potential ingress of moisture,
fibrins, large proteins, blood clots, and other
With clinical trials for the newly developed Automated Low-Flow Ascites Pump
(or alfapump system) in its sights, Sequana
Medical began looking for a solution that
combined the required FDA USP Class VI
compatibility with low friction and good
sealing performance to help maximize
device performance inside the body. The
company’s search led to several important
design changes and, ultimately, to the use of
a Bal Seal spring-energized rotary seal in the
Starting at the Heart
Before they even considered a final sealing
solution, engineers at Sequana Medical took
a step back and examined their pump’s most
crucial component – its motor.
Earlier designs employed a brushed
DC motor, but tests had proven this was
too susceptible to humidity, which could
significantly impede or even prohibit pump
performance. In addition, abrasions from the
brushes could lead to particulate generation
In order to address these issues, designers
incorporated a brushless DC motor, which
proved to be far more humidity-tolerant.
Even with this fundamental change,
however, Sequana Medical knew it needed
to be absolutely sure the motor could
perform for extended periods in a critical
implantable environment. That meant
The alphapump, which eliminates the need for
paracentesis, reduces much of the discomfort
associated with ascites and helps patients
reclaim their mobility.
The addition of the spring-energized seal to the alfapump
design reduces device power consumption by 40% and
increased battery life by 20%.