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Parametric design, fabrication and validation of one-way polymeric valves for artificial sphincters

TL;DR: In this article, the parametric design of polymeric valves, by taking inspiration from commercially exploited solutions used in the food industry and performing appropriate scaling in order to make them suitable for artificial organs and components, is discussed.
Abstract: The design of artificial sphincters requires an accurate dimensioning of dedicated valves, normally made of polymeric materials. This effort is also interesting for developing fluid and pressure regulating solutions related to other biomedical and non-biomedical fields. In this article we focused on the parametric design of polymeric valves, by taking inspiration from commercially exploited solutions used in the food industry and performing appropriate scaling in order to make them suitable for artificial organs and components. In addition, different materials with diverse mechanical properties were considered, focusing on a low-cost fabrication approach. Finite element model analyses were conducted to simulate the behavior of different valve profiles and to predict the valve opening pressure. Simulation results were validated by comparing them with experimental results, obtained by fabricating and testing different valve types. This polymeric valve parametric analysis may be exploited for the design of artificial sphincters, having the potential to tackle urinary incontinence, a disease that affects about 350 million people worldwide.

Summary (3 min read)

1. Introduction

  • Approximately 350 million individuals worldwide experienced urinary incontinence (UI) in 2008 and this number is expected to increase up to 423 million by 2018 [1].
  • All the above-mentioned mechatronic solutions are rather invasive and their long-term safety and efficacy still have to be demonstrated.
  • They are not usable as components for artificial urinary sphincters, due to the high pressure range (12 kPa–120 kPa) and to the small flow rates [18].

2.1. Valve profile and its parameterization

  • To select the valve profile, the authors took inspiration from the food industry, especially from the valves integrated in many water bottles.
  • Normally, they are used to guarantee hermetic sealing up to a certain pressure, a feature that makes it easier to drink liquids during sport activities, for example.
  • Another important aspect of the analysis concerned how valve performance changed in function of the other eight parameters, once a certain valve size was selected.

2.2. Finite Element Model (FEM) simulations

  • Matlab® R2013a and Abaqus 6.13 (Dassault Systemes) were used to manage data and to perform FEM simulations, respectively.
  • Once the simulation was completed, the extreme points of the valve strip reached during the simulation were stored in a file, from which Matlab® was able to indentify the valve OP.
  • The second valve element was obtained from the complete revolution (360◦) around the valve axis of the area delimited by sections A1A2, A2A9, A9A10 and A10A11.
  • The third element (valve strip) was meshed with 81 cells.
  • The mentioned mesh size value was identified as a good compromise between adherence of the predicted OP values to the real ones and the time needed to complete each simulation.

2.3. Polymer synthesis and mechanical testing

  • The material selected for valve fabrication was PDMS (Sylgard 184, Dow Corning).
  • This material is particularly suitable for biomedical applications, due to its high biocompatibility, its tunable mechanical properties, and its good thermal and chemical stability.
  • Furthermore, PDMS surface can be activated by oxy- performing traction tests.
  • Data were recorded at a frequency of 100 Hz, the stress was calculated as the load divided by the cross-section area of tensile specimens, while the strain was calculated as the ratio between the extension and the initial length of tensile specimens.
  • Mechanical tests were repeated on three different samples, for each sample type.

2.4. Valve fabrication

  • In order to validate the simulation results, polymeric valves were fabricated by exploiting dedicated molds.
  • The molds were composed of two parts, provided with through holes, needed for aligning the parts and closing the mold (using M3 screws and nuts).
  • A thin teflon film (LOCTITE 8192) was deposited by spraying it on the mold surface, to facilitate subsequent PDMS removal from the mold, also known as (2) Mold surface treatment.
  • After PDMS casting, the mold was closed and thermally treated at 90 ◦C for 3 h, to allow full valve polymerization, also known as (4) Polymerization.
  • It was then subjected to die cutting by the dedicated frame and custom blade.

2.5. Valve testing

  • To test the polymeric valve functionality, a dedicated experimental set-up was developed (Fig. 2).
  • The horizontal stroke kept constant the height of the water column downstream of the valve during the tests, which was needed to detect the valve OP.
  • Speed control was compiled into a development board (STM32F407, ST) exploiting Simulink environment with a sampling frequency of 1 kHz.
  • The testing set-up allowed a syringe (5 ml) and its plunger, connected with the piston pusher, to be mounted.
  • Once the twenty-four polymeric valves had been fabricated, they were tested in order to measure their OP (detected using the dedicated sensor to measure pressure drop).

3.1. PDMS mechanical properties

  • The stress–strain curves experimentally obtained for the PDMS samples with different mechanical properties as shown in Fig.
  • These curves were imported in the Abaqus environment, in order to properly simulate material mechanical behavior.
  • Young’s moduli of the PDMS samples tested, for different monomer/curing agent ratios.
  • Three samples were tested, for each sample type.

3.2. Simulation results

  • Fig. 4 shows some frames captured from valve FEM simulations, in which progressive valve vault compression and opening phases are reported.
  • In each dataset, the 5 parameter values of Table 1 were combined with 6 material stiffness values, thus generating 30 simulation results.
  • By focusing on the obtained coefficient values, especially with regard to the exponential coefficient c, an immediate comparison between parameters (P1 and P9) is possible.
  • Therefore, it can be useful to select a design protocol aiming at reducing the overall simulation effort.
  • Fig. 6 shows the valve performances when valve thickness (P3) varied.

3.3. Fabrication and validation

  • Fig. 8 shows a polymeric valve obtained by using the dedicated mold and cutting frame.
  • The piston advanced with a constant speed of 5 mm/s and the pressure detected by the pressure sensor increased until the opening pressure was reached.
  • The actual performances of the fabricated valves are reported in Fig. 9.
  • This further demonstrates the suitability of this technological solution for the development of an AS, as well as for other applications.
  • The valve profile has been described by univocally defining the correspondent parameters (these details, in many articles, are partial, omitted, or described in a non parametric manner) [9,10,16,18,19].

4. Conclusion

  • This paper aims at describing the steps needed to design a polymeric valve suitable for application in artificial sphincter systems employed for tackling urinary incontinence diseases.
  • By analyzing the commercial valve cross section, nine parameters were extracted, which defined the valve design.
  • This approach allowed us to define a design strategy aimed at minimizing design efforts.
  • After setting the valve diameter, the most influential parameters were valve stiffness and thickness.

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Sensors
and
Actuators
A
233
(2015)
184–194
Contents
lists
available
at
ScienceDirect
Sensors
and
Actuators
A:
Physical
j
ourna
l
ho
me
page:
www.elsevier.com/locate/sna
Parametric
design,
fabrication
and
validation
of
one-way
polymeric
valves
for
artificial
sphincters
Tommaso
Mazzocchi
a,
,
Leonardo
Ricotti
a
,
Novello
Pinzi
b
,
Arianna
Menciassi
a
a
The
BioRobotics
Institute,
Scuola
Superiore
Sant’Anna,
Viale
R.
Piaggio,
34,
56025,
Pontedera,
PI,
Italy
b
Dipartimento
di
Urologia,
Università
degli
Studi
di
Siena,
Via
Banchi
di
Sotto,
55,
53100
Siena,
SI,
Italy
a
r
t
i
c
l
e
i
n
f
o
Article
history:
Received
5
January
2015
Received
in
revised
form
22
June
2015
Accepted
7
July
2015
Available
online
15
July
2015
a
b
s
t
r
a
c
t
The
design
of
artificial
sphincters
requires
an
accurate
dimensioning
of
dedicated
valves,
normally
made
of
polymeric
materials.
This
effort
is
also
interesting
for
developing
fluid
and
pressure
regulating
solutions
related
to
other
biomedical
and
non-biomedical
fields.
In
this
article
we
focused
on
the
parametric
design
of
polymeric
valves,
by
taking
inspiration
from
commercially
exploited
solutions
used
in
the
food
industry
and
performing
appropriate
scaling
in
order
to
make
them
suitable
for
artificial
organs
and
components.
In
addition,
different
materials
with
diverse
mechanical
properties
were
considered,
focusing
on
a
low-
cost
fabrication
approach.
Finite
element
model
analyses
were
conducted
to
simulate
the
behavior
of
different
valve
profiles
and
to
predict
the
valve
opening
pressure.
Simulation
results
were
validated
by
comparing
them
with
experimental
results,
obtained
by
fabricating
and
testing
different
valve
types.
This
polymeric
valve
parametric
analysis
may
be
exploited
for
the
design
of
artificial
sphincters,
having
the
potential
to
tackle
urinary
incontinence,
a
disease
that
affects
about
350
million
people
worldwide.
©
2015
Elsevier
B.V.
All
rights
reserved.
1.
Introduction
Approximately
350
million
individuals
worldwide
experienced
urinary
incontinence
(UI)
in
2008
and
this
number
is
expected
to
increase
up
to
423
million
by
2018
[1].
UI
is
a
disorder
that
produces
an
involuntary
urine
loss
caused
by
an
uncontrolled
overactive
bladder
or
a
pelviperineal
muscle
deficit
that
can
arise
as
a
surgery
complication
in
male
subjects
(e.g.
after
prostate
surgery),
while
in
female
subjects
it
may
occur
after
child-
birth
or
after
urogenital
organs
surgery.
In
hospitals,
UI
diseases
are
normally
managed
by
using
absorbent
materials
or
urethral
catheters
provided
with
a
bag
(tied
to
the
patient’s
leg).
Extra-
luminal
sphincters
(ES)
are
devices
able
to
control
fluid
flow
through
an
elastic
duct,
by
modulating
the
compression
of
the
elastic
duct
wall
itself.
They
need
to
be
implanted
via.
surgi-
cal
procedures,
so
they
are
rather
invasive.
The
most
common
ES
that
are
commercially
available
to
tackle
UI
are
the
ProAct
system
(Uromedica,
MN,
USA)
and
the
AMS
800
(American
Med-
ical
Systems,
Minnetonka,
MN,
USA).
These
solutions
require
a
surgical
procedure
for
their
installation
and
they
are
only
avail-
able
for
males
[2,3].
ProAct
and
AMS
800
are
expensive
and
can
lead
to
complications
such
as
erosion,
infection
and
mechani-
Corresponding
author.
Fax:
+39
50
883101.
E-mail
address:
t.mazzocchi@sssup.it
(T.
Mazzocchi).
cal
failure.
Therefore,
periodic
revisions
(rather
complicated
to
be
performed)
are
mandatory.
In
addition,
if
replacement
is
needed,
a
second
invasive
surgical
procedure
needs
to
be
per-
formed.
On
the
other
hand,
intraluminal
sphincters
(IS)
do
not
require
a
surgery
procedure
to
be
implanted:
they
are
usually
installed
by
using
the
duct
orifice
and
brought
to
the
site
of
interest
through
a
pushing
catheter.
At
present,
few
commercial
IS
are
available,
such
as
the
FemSoft
(Rochester
Medical
Corporation,
MN,
USA)
or
the
InFlow
device
(Vesiflo,
Inc,
WA,
USA)
[4].
IS
are
not
com-
pletely
internal
devices:
a
small
portion
of
the
system
is
inevitably
visible,
thus
raising
psychological
discomfort
in
certain
situa-
tions.
Recently,
advanced
and
rather
complex
mechatronic
solutions
have
been
proposed
to
tackle
UI.
Lamraoui
et
al.
reported
the
design,
development
and
in
vivo
testing
on
goats
of
a
60
cm
3
artificial
sphincter
(AS)
prototype
composed
of
standard
mechanical
and
electrical
components
[5].
More
recently,
a
retro-compatible
device
was
proposed
by
Hached
and
colleagues.
The
system
was
based
on
a
hydraulic
module
and
a
control
unit
and
showed
good
effi-
cacy
in
both
bench
tests
and
ex
vivo
tests
[6].
The
same
authors
also
recently
developed
a
wirelessly
controlled
and
adaptive
AS,
capable
of
postoperative
occlusive
cuff
pressure
modification
[7].
All
the
above-mentioned
mechatronic
solutions
are
rather
invasive
and
their
long-term
safety
and
efficacy
still
have
to
be
demon-
strated.
http://dx.doi.org/10.1016/j.sna.2015.07.005
0924-4247/©
2015
Elsevier
B.V.
All
rights
reserved.

T.
Mazzocchi
et
al.
/
Sensors
and
Actuators
A
233
(2015)
184–194
185
Fig.
1.
Commercial
valve
used
in
many
water
bottles.
The
whole
structure
and
a
section,
are
reported
(A),
together
with
its
parameterization
(B).
The
valve
axis
and
the
load
distribution
are
shown
in
C
and
D,
respectively.
The
authors
also
recently
highlighted
a
possible
new
design
for
IS,
based
on
magnetically
responsive
mechanisms
able
to
engage
a
unidirectional
valve
and
thus
modulate
its
stiffness
[8].
At
present,
a
UI
solution
suitable
for
both
sexes
featuring
high
stability
and
low
invasiveness
(without
altering
the
body
scheme)
is
not
available.
Passive
unidirectional
polymeric
valves
are
a
key
component
of
devices
designed
to
tackle
UI
diseases.
They
are
useful
to
control
the
liquid
pressure
between
two
compartments,
thus
ensuring
a
unidirectional
flow
when
a
certain
pressure
threshold
is
overcome.
Biocompatible
polymers
are
obviously
needed
and
independence
from
energy
sources
would
reduce
the
intrinsic
hazards
related
to
the
use
of
such
systems.
The
achievement
of
an
artificial
IS
suitable
for
both
sexes
requires
an
accurate
dimensioning
of
ad
hoc
one-way
passive
valves.
To
this
purpose,
the
analysis
of
available
solutions
for
other
biomedical
or
non-biomedical
fields
can
provide
some
interest-
ing
hints.
Many
literature
studies
have
focused
on
the
correlation
between
geometry
and
valve
performance,
highlighting
the
impor-
tance
of
numerical
simulations
such
as
non-linear
finite
element
models
(FEM)
in
order
to
optimize
the
design
and
the
sizing
of
valve
profiles.
In
the
biomedical
field,
this
approach
has
been
exten-
sively
used
to
design
heart
valves.
Different
valve
profiles
have
been
reviewed
by
Mohammadi
and
Mequanint
[9],
in
terms
of
both
modelling
and
design
strategies.
Recently,
Burriesci
and
col-
leagues
focused
on
a
novel
design
strategy
for
polymeric
heart
valves
(supported
by
numerical
simulations),
in
order
to
increase
valve
performances
and
reduce
stress
levels
[10].
Another
inter-
esting
study
was
carried
out
by
Labrosse
et
al.,
which
developed
a
geometric
model
of
an
aortic
trileaflet
valve,
for
the
purpose
of
eval-
uating
how
much
the
dimensions
of
the
aortic
valve
components
could
be
varied,
while
still
maintaining
proper
target
performances
[11].
More
recent
studies
focused
on
applying
FEM
analyses
to
properly
design
leaflet
materials
and
to
predict
the
hydrodynamic
behavior
of
nanocomposite-based
polymeric
aortic
valves
[12,13].
However,
the
aforementioned
studies
cannot
be
easily
generalized
and
applied
to
the
design
of
a
urinary
system
valve.
This
is
mainly
due
to
the
rather
complicated
design
and
manufacturing
processes,
needed
to
build
heart
valves
which
require
several
steps
in
order
to
combine
a
metallic
stent
with
the
polymeric
leaflets.
A
different
approach
must
be
adopted
when
facing
scalable
manufacturing
in
the
presence
of
high
pressure
ranges
and
small
flow
rates
(l/min).
Although
these
conditions
are
not
typical
of
the
urinary
system,
this
approach
has
been
widely
adopted
for
the
design
of
micro-valves
to
be
used
in
microfluidic
systems.
The
geo-
metrical
parameters
of
the
valve,
including
shape,
fluid
channel
width
and
membrane
thickness
are
usually
examined.
Snakenborg
et
al.
designed
a
polydimethylsiloxane
(PDMS)
membrane
pro-
vided
with
an
incision
in
order
to
fabricate
a
check
valve
able
to
control
the
flow
rate
[14].
Mohan
et
al.
reported
interesting
consid-
erations
concerning
the
design
and
the
application
of
elastomeric
microvalves,
focusing
on
actuation
pressure
minimization,
reliable
operation
and
convenient
integration
into
complex
microfluidic
devices
[15].
Jahanshahi
et
al.
focused
on
the
design
of
a
micro-valve
characterized
by
a
high
pressure
range
and
a
relatively
high
seal-
ing
capability
(no
flow
up
to
0.6
MPa
reverse
pressure)
[16].
Hilbert
and
colleagues
introduced
an
innovative
micro-valve
manufactur-
ing
technique
by
using
PDMS
loaded
with
neodymium
particles,
to
adjust
the
switching
point
of
each
single
valve
[17].
Hickerson
and
colleagues
developed
a
valve
design
strategy
suitable
for
scalable
manufacturing,
and
based
on
standard
tech-

186
T.
Mazzocchi
et
al.
/
Sensors
and
Actuators
A
233
(2015)
184–194
niques
that
allow
the
development
of
low-cost
disposable
systems.
The
reported
results
may
be
exploited
for
many
applications
that
require
specific
valve
performance.
However,
they
are
not
usable
as
components
for
artificial
urinary
sphincters,
due
to
the
high
pres-
sure
range
(12
kPa–120
kPa)
and
to
the
small
flow
rates
[18].
Uohashi
and
colleagues
took
into
account
different
one-way
valve
profiles,
achievable
by
exploiting
standard
molding
pro-
cesses.
They
ensured
high
flow
rates
(ml/min).
Interesting
results,
concerning
the
influence
of
material
stiffness
on
valve
perfor-
mance,
were
reported.
However,
an
accurate
relationship
between
valve
geometrical
parameters
and
performance
was
not
high-
lighted
[19].
In
this
article,
we
discuss
the
parametric
design,
fabrication
and
validation
of
a
one-way
polymeric
valve
as
component
of
AS,
tak-
ing
as
a
model
a
common
valve
profile
available
in
water
bottles.
Low-cost
fabrication
techniques
and
a
biocompatible
and
stiffness-
tunable
material
were
considered
for
valve
design
and
fabrication.
Simulation
results
evidenced
the
most
suitable
profiles
in
corre-
spondence
to
certain
desired
opening
pressures.
For
application
in
the
urinary
system,
hermetic
closure
should
be
assured:
sudden
coughs
and
involuntary
abdominal
muscle
contractions
can
gener-
ate
pressures
up
to
12
kPa.
However,
this
physiological
parameter
depends
on
the
patient’s
anatomical
features,
therefore
a
tunable
opening
pressure
(OP)
is
desirable
[20–22].
As
highlighted
below,
this
can
be
achieved
by
making
small
changes
to
the
valve
profile
geometry
or
by
slightly
changing
material
stiffness.
2.
Experimental
2.1.
Valve
profile
and
its
parameterization
To
select
the
valve
profile,
we
took
inspiration
from
the
food
industry,
especially
from
the
valves
integrated
in
many
water
bot-
tles.
Normally,
they
are
used
to
guarantee
hermetic
sealing
up
to
a
certain
pressure,
a
feature
that
makes
it
easier
to
drink
liquids
during
sport
activities,
for
example.
We
considered
a
commercial
valve
that
had
a
vault
shape
and
a
surface
featuring
a
six-pointed
star
die
cut.
The
notches
allow
the
valve
to
open
when
the
pressure
applied
on
the
top
surface
is
above
a
certain
threshold.
We
analyzed
the
valve
profile
and
extracted
9
parameters
able
to
describe
it,
as
shown
in
Fig.
1.
The
nine
parameters
that
allow
reproduction
of
the
com-
mercial
valve
were:
P1
c
=
3.7
mm,
P2
c
=
50
,
P3
c
=
0.20
mm,
P4
c
=
83
,
P5
c
=
1.28
mm,
P6
c
=
0.37
mm,
P7
c
=
97
,
P8
c
=
1.00
mm
and
P9
c
=
1.70
mm
(where
C
=
commercial).
We
aimed
at
fabricating
one-way
valves
with
a
specific
OP,
by
taking
into
account
the
fabrication
constraints.
The
analysis
of
the
nine
parameters
led
to
a
redundant
problem.
However,
all
parameters
were
varied,
in
order
to
highlight
how
their
different
values
influenced
overall
valve
performance.
For
each
parameter,
five
equidistant
values
were
identified
(Table
1).
Moreover,
they
were
combined
with
six
different
types
of
material
stiffness.
The
first
analysis
aimed
at
assessing
how
valve
performance
changed
when
applying
an
isotropic
scaling
(increasing
or
decreas-
ing
valve
size
by
a
scale
factor
that
was
the
same
in
all
directions).
To
this
aim,
P1
was
considered
because
it
is
related
to
the
radius
of
the
vault
valve.
A
valve
radius
suitable
for
urological
applications
must
be
smaller
than
6
mm
[23].
The
scaling
factors
(SF)
analyzed
in
this
work
were
0.35,
0.67,
1.00,
1.32
and
1.64.
They
corresponded
to
P1
values
of
1.3,
2.5,
3.7,
4.9
and
6.1
mm,
respectively.
Differently
scaled
valves
may
find
applications
in
different
fields.
Another
important
aspect
of
the
analysis
concerned
how
valve
performance
changed
in
function
of
the
other
eight
parameters,
once
a
certain
valve
size
was
selected.
This
allowed
us
to
identify
the
most
relevant
parameters
for
valve
performance.
2.2.
Finite
Element
Model
(FEM)
simulations
Matlab
®
R2013a
(MathWorks)
and
Abaqus
6.13
(Dassault
Sys-
temes)
were
used
to
manage
data
and
to
perform
FEM
simulations,
respectively.
Matlab
®
environment
was
used
to
manage
the
different
param-
eters.
Once
the
desired
valve
profile
was
generated,
Matlab
®
generated
an
appropriate
file,
readable
by
Abaqus,
which
loaded
the
desired
valve
geometry,
for
detecting
the
OP
of
the
respective
profile.
This
allowed
us
to
handle
a
large
number
of
simulations
in
a
simple
manner.
The
valve
model
was
implemented
using
Python
language.
When
Abaqus
had
processed
the
simulation,
it
generated
a
file
in
which
all
the
results
were
reported.
An
algorithm
was
devel-
oped
to
compare
each
simulation
and
to
identify
the
valve
OP.
The
algorithm
tracked
all
the
extreme
points
(A8
and
A7
in
Fig.
1)
for
each
valve
strip:
when
the
distance
between
such
extreme
points
was
double
than
the
valve
thickness
(P3),
the
valve
was
considered
open.
Once
the
simulation
was
completed,
the
extreme
points
of
the
valve
strip
reached
during
the
simulation
were
stored
in
a
file,
from
which
Matlab
®
was
able
to
indentify
the
valve
OP.
After
creating
the
valve
in
the
Abaqus
environment,
experimen-
tal
data
(stress-strain
curves)
of
the
material
used
were
imported
by
exploiting
the
Hyperplastic
module
supported
by
the
program.
In
the
Abaqus
Step
module,
an
explicit
dynamic
behavior
was
defined,
by
imposing
a
mass
scaling
equal
to
100.
Appropriate
tie
constraints
between
the
described
elements
were
implemented,
thus
repro-
ducing
the
commercial
valve
of
Fig.
1A.
The
valve
model
was
provided
with
a
fixed
constraint
as
bound-
ary
condition,
applied
on
the
surface
obtained
from
the
segment
(A5A6)
revolution
around
the
valve
(A7A8)
axis.
The
top
surface
of
the
valve
was
loaded
with
a
pressure
(normal
to
the
valve
surface)
which
linearly
increased,
until
reaching
the
cracking
pressure.
The
valve
design
was
composed
of
three
elements.
The
first
one
represented
the
valve
basement,
obtained
from
the
revolu-
tion
(360
)
around
the
valve
axis
of
the
area
delimited
by
segments
A6A5,
A5A4,
A4A2,
A2A1,
A1A3
and
A3A6
(Fig.
1B).
The
second
valve
element
was
obtained
from
the
complete
revolution
(360
)
around
the
valve
axis
of
the
area
delimited
by
sections
A1A2,
A2A9,
A9A10
and
A10A11.
The
third
element
referred
to
the
valve
strips
obtained
when
the
die
cut
was
applied
on
the
top
surface
of
the
polymeric
valve.
A
single
strip
was
obtained
from
a
revolution
of
60
around
the
valve
axis
of
the
area
delimited
by
sections
A10A8,
A8A7,
A7A11
and
A11A10.
The
first
element
(valve
basement)
was
meshed
with
2160
cells,
the
second
(valve
head)
was
meshed
with
1224
cells.
The
third
ele-
ment
(valve
strip)
was
meshed
with
81
cells.
A
structured
Hex
mesh
was
used
for
the
three
bodies.
To
demonstrate
that
the
mesh
was
suitable
for
the
target
application,
we
carried
out
mesh
refinement
tests
(Supplementary
materials,
Table
S1).
The
mentioned
mesh
size
value
was
identified
as
a
good
compromise
between
adherence
of
the
predicted
OP
values
to
the
real
ones
and
the
time
needed
to
complete
each
simulation.
Once
the
mesh
grid
of
the
valve
model
was
defined,
a
set
of
nodes
was
generated
in
order
to
store
the
segment
(A8A7)
displacement
values
for
each
valve
strip,
during
the
entire
simulation.
Therefore,
12
mesh
nodes
were
selected
to
detect
valve
opening.
Von
Mises
stresses
were
also
recorded
for
each
simulation.
2.3.
Polymer
synthesis
and
mechanical
testing
The
material
selected
for
valve
fabrication
was
PDMS
(Syl-
gard
184,
Dow
Corning).
This
material
is
particularly
suitable
for
biomedical
applications,
due
to
its
high
biocompatibility,
its
tun-
able
mechanical
properties,
and
its
good
thermal
and
chemical
stability.
Furthermore,
PDMS
surface
can
be
activated
by
oxy-

T.
Mazzocchi
et
al.
/
Sensors
and
Actuators
A
233
(2015)
184–194
187
Table
1
Parameter
values
considered
during
FEM
simulations.
gen
plasma,
for
modifying
surface
properties
and
mechanical
and
chemical
performances
[24],[25].
PDMS
stiffness
can
be
modulated
by
varying
the
ratio
between
the
monomer
and
its
curing
agent.
In
this
work,
6
different
monomer/curing
agent
ratios
were
analyzed:
5:1,
10:1,
20:1,
30:1,
40:1
and
50:1
(w/w).
Sample
mechanical
properties
were
evaluated
with
an
INSTRON
4464
Mechanical
Testing
System,
by
using
a
±10
N
load
cell,
and

188
T.
Mazzocchi
et
al.
/
Sensors
and
Actuators
A
233
(2015)
184–194
performing
traction
tests.
Samples
were
cut
into
20
×
5
×
2
mm
3
slices
and
allocated
between
two
aluminium
clamps.
All
samples
were
pulled
at
the
constant
speed
of
5
mm/min,
until
reaching
sample
failure.
Data
were
recorded
at
a
frequency
of
100
Hz,
the
stress
was
calculated
as
the
load
divided
by
the
cross-section
area
of
tensile
specimens,
while
the
strain
was
calculated
as
the
ratio
between
the
extension
and
the
initial
length
of
tensile
specimens.
The
tensile
modulus
for
each
tested
sample
was
calculated
start-
ing
from
the
stress/strain
curve,
according
to
a
standard
procedure
[26].
Mechanical
tests
were
repeated
on
three
different
samples,
for
each
sample
type.
2.4.
Valve
fabrication
In
order
to
validate
the
simulation
results,
polymeric
valves
were
fabricated
by
exploiting
dedicated
molds.
The
molds
were
composed
of
two
parts,
provided
with
through
holes,
needed
for
aligning
the
parts
and
closing
the
mold
(using
M3
screws
and
nuts).
To
achieve
the
die
cut
on
the
valve
surface,
a
proper
frame
(designed
to
constrain
the
polymeric
valve)
and
a
custom
blade
were
used.
Both
cutting
frame
and
molds
were
fabricated
by
using
a
3D
printer
(HD3000,
ProJet).
The
custom
blade
was
obtained
by
mod-
ifying
the
cutting
edge
of
an
off-the-shelf
surgical
blade
(CHIMO,
size
22).
The
valve
fabrication
process
was
based
on
the
following
steps:
(1)
PDMS
preparation:
monomer
and
curing
agent
were
mixed
with
the
desired
ratio,
then
the
mixture
was
degassed
for
20
min
in
a
vacuum
chamber.
(2)
Mold
surface
treatment:
a
thin
teflon
film
(LOCTITE
8192)
was
deposited
by
spraying
it
on
the
mold
sur-
face,
to
facilitate
subsequent
PDMS
removal
from
the
mold.
(3)
PDMS
casting:
once
the
mixture
was
well
degassed,
it
was
casted
into
the
teflon-coated
mold.
(4)
Polymerization:
after
PDMS
cast-
ing,
the
mold
was
closed
and
thermally
treated
at
90
C
for
3
h,
to
allow
full
valve
polymerization.
(5)
Valve
extraction
and
cutting:
the
mold
was
opened
and
the
polymeric
valve
removed.
It
was
then
subjected
to
die
cutting
by
the
dedicated
frame
and
custom
blade.
2.5.
Valve
testing
To
test
the
polymeric
valve
functionality,
a
dedicated
experi-
mental
set-up
was
developed
(Fig.
2).
The
set-up
consisted
of
a
motorized
piston
provided
with
a
fine
control
of
both
horizontal
stroke
and
speed.
The
horizontal
stroke
kept
constant
the
height
of
the
water
column
downstream
of
the
valve
during
the
tests,
which
was
needed
to
detect
the
valve
OP.
Speed
control
was
compiled
into
a
development
board
(STM32F407,
ST)
exploiting
Simulink
(MathWorks)
environment
with
a
sampling
frequency
of
1
kHz.
To
monitor
the
OP,
the
development
board
was
connected
to
a
pressure
sensor
(HCX001D6
V,
purchased
from
Sensor
Technics)
for
wet
environments,
capable
of
measuring
pressures
up
to
100
kPa.
The
mechanical
parts
of
the
testing
set-up
included
a
Screw
Ball
(BSSC1510-300-SC10,
diameter
15
mm,
stride:
10
mm,
stroke:
300
mm)
and
appropriate
tools
for
supporting
it
(BSW12,
BUN12,
BNFB1505C-30
produced
by
MISUMI
company).
These
com-
ponents
were
assembled
on
a
derlin-polycarbonate
frame.
A
DC-micromotor
(Series
2342
012CR,
Faulhaber)
provided
with
a
Planetary
Gearhead
to
increase
the
motor
torque
with
a
reduc-
tion
ratio
of
43:1
(Series
30/1S3,
Faulhaber),
a
high
performance,
low-cost,
three-channel
optical
incremental
encoder
(HEDS-5540,
Avago
Technologies)
and
a
full
H-Bridge
(L298,
ST)
were
mounted
on
the
system.
The
testing
set-up
allowed
a
syringe
(5
ml)
and
its
plunger,
con-
nected
with
the
piston
pusher,
to
be
mounted.
A
three-way
T-joint
Table
2
shows
the
different
PDMS
monomer/curing
agent
ratios
and
the
corresponding
Young’s
moduli,
obtained
by
way
of
linear
fitting
of
the
stress–strain
curves
in
the
initial
(linear)
region.
Monomer/curing
agent
ratio
Young’s
modulus
[MPa]
5:1
4.95
±
0.33
10:1
3.55
±
0.35
20:1
1.26
±
0.16
30:1
0.41
±
0.06
40:1
0.14
±
0.02
50:1
0.08
±
0.01
connected
the
valve
seat,
the
pressure
sensor
and
the
syringe
out-
put.
The
valve
opening
direction
was
horizontal,
to
avoid
gravity
effects.
Six
polymeric
valve
types
(four
valves
for
each
type)
were
fabricated
by
using
three
different
molds
(thus,
three
different
geometries)
and
two
different
material
types
(10:1
and
20:1
PDMS).
The
first
valve
geometry
to
be
fabricated
featured
a
P1
value
of
3.7
mm
and
a
P3
value
of
0.2
mm.
The
second
valve
geometry
fea-
tured
a
P1
value
of
2.5
mm
and
a
P3
value
of
0.25
mm.
The
third
valve
geometry
featured
a
P1
value
of
2.5
mm
and
a
P3
value
of
0.3
mm.
The
other
parameters,
common
for
the
different
valve
geometries,
were:
P2
=
50
,
P4
=
83
,
P5
=
0.86
mm,
P6
=
0.25
mm,
P7
=
97
,
P8
=
0.67
mm
and
P9
=
0.13
mm.
Once
the
twenty-four
polymeric
valves
had
been
fabricated,
they
were
tested
in
order
to
measure
their
OP
(detected
using
the
dedicated
sensor
to
measure
pressure
drop).
The
syringe
was
filled
with
air
or
distilled
water
(d-H
2
O)
and
the
piston
speed
was
set
at
5
mm/s.
Each
valve
was
tested
three
times,
and
six
cycles
of
open-
ing/closure
were
performed,
within
each
test.
Thus,
eighteen
OP
values
were
recorded
for
each
tested
valve.
An
additional
test
was
carried
out,
in
order
to
evaluate
the
tight-
ness
of
the
fabricated
valves.
During
this
test,
the
piston
speed
was
set
at
0.25
mm/s
and
it
was
stopped
before
reaching
the
valve
OP.
Different
constant
pressure
values
were
kept
for
10
s.
This
allowed
the
valve
pressure
loss
to
be
measured
when
relatively
high
pres-
sures
were
applied
and
kept
constant.
3.
Results
and
discussion
3.1.
PDMS
mechanical
properties
The
stress–strain
curves
experimentally
obtained
for
the
PDMS
samples
with
different
mechanical
properties
as
shown
in
Fig.
3.
These
curves
were
imported
in
the
Abaqus
environment,
in
order
to
properly
simulate
material
mechanical
behavior.
Table
2
Young’s
moduli
of
the
PDMS
samples
tested,
for
different
monomer/curing
agent
ratios.
Three
samples
were
tested,
for
each
sample
type.
3.2.
Simulation
results
Fig.
4
shows
some
frames
captured
from
valve
FEM
simulations,
in
which
progressive
valve
vault
compression
and
opening
phases
are
reported.
A
dynamic
simulation
of
valve
opening
and
a
compar-
ison
between
the
real
and
the
simulated
valve
are
shown
in
Video
S1
(see
Supplementary
materials).
The
analysis
of
the
9
parameters
generated
9
datasets.
In
each
dataset,
the
5
parameter
values
of
Table
1
were
combined
with
6
material
stiffness
values,
thus
generating
30
simulation
results.
A
simple
approach
that
immediately
highlights
macroscopic
dif-
ferences
between
the
obtained
datasets
is
desirable.
We
fit
the
simulation
results
and
compared
the
coefficients
obtained
from
the
fitting,
in
order
to
identify
which
parameter
was
more
relevant
for

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22 Jan 2019
TL;DR: After immersion in artificial urine formulations and continuous mechanical agitation for 4 weeks, WS2 coating resulted the most resistant to encrustations, paving the way to the adoption of WS2 coatings for developing long-lasting stable urinary devices.
Abstract: Artificial urinary devices are commonly employed to restore the lost functionalities of the urinary system, due to diseases, disfunctions or organ resections. However, the long-term operation of these devices in the urinary system is affected by encrustations. In this paper, three different nanostructured coatings, based on diamondlike carbon (DLC), molybdenum disulfide (MoS2) and Tungsten disulfide (WS2), were deposited on polydimethylsiloxane substrates, an elastomer suitable for coating different kinds of urinary devices, and tested in terms of resistance to urinary encrustations. DLC coatings were deposited using plasma enhanced-chemical vapor deposition (T < 180 °C), whereas MoS2 and WS2 coatings were achieved through self-assembly at room temperature. All coatings showed good adhesion and stability on PDMS substrate over one month, relatively small roughness, a strongly hydrophobic behavior, and low surface energy. After immersion in artificial urine formulations and continuous mechanical agitation ...

13 citations

Journal ArticleDOI
TL;DR: The fluid–structure interaction model presented in this study can simulate structural behaviour of a stented valve with flexible leaflets, providing insight into the haemodynamic performance of a polymeric aortic valve.
Abstract: This paper describes a computational method to simulate the non-linear structural deformation of a polymeric aortic valve under physiological conditions. Arbitrary Lagrangian-Eulerian method is incorporated in the fluid-structure interaction simulation, and then validated by comparing the predicted kinematics of the valve's leaflets to in vitro measurements on a custom-made polymeric aortic valve. The predicted kinematics of the valve's leaflets was in good agreement with the experimental results with a maximum error of 15% in a single cardiac cycle. The fluid-structure interaction model presented in this study can simulate structural behaviour of a stented valve with flexible leaflets, providing insight into the haemodynamic performance of a polymeric aortic valve.

10 citations

References
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"Parametric design, fabrication and ..." refers background in this paper

  • ...gen plasma, for modifying surface properties and mechanical and chemical performances [24],[25]....

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Journal ArticleDOI
TL;DR: This report focuses on the most common urodynamics examinations; uroflowmetry, pressure recording during filling cystometry, and combined pressure–flow studies.
Abstract: This is the first report of the International Continence Society (ICS) on the development of comprehensive guidelines for Good Urodynamic Practice for the measurement, quality control, and documentation of urodynamic investigations in both clinical and research environments. This report focuses on the most common urodynamics examinations; uroflowmetry, pressure recording during filling cystometry, and combined pressure-flow studies. The basic aspects of good urodynamic practice are discussed and a strategy for urodynamic measurement, equipment set-up and configuration, signal testing, plausibility controls, pattern recognition, and artifact correction are proposed. The problems of data analysis are mentioned only when they are relevant in the judgment of data quality. In general, recommendations are made for one specific technique. This does not imply that this technique is the only one possible. Rather, it means that this technique is well-established, and gives good results when used with the suggested standards of good urodynamic practice.

1,544 citations

Journal ArticleDOI
01 Oct 2011-BJUI
TL;DR: Study Type – Symptom prevalence (prospective cohort) and Cause of Death – Causes of Death and Mortality (Prospective cohort).
Abstract: Study Type – Symptom prevalence (prospective cohort) Level of Evidence 1b What’s known on the subject? and What does the study add? Few prevalence studies used current ICS LUTS symptom definitions and to our knowledge no studies exist that estimate total worldwide prevalence of reported LUTS symptoms One of the primary goals of this analysis was to estimate current and future worldwide prevalence of LUTS among adults Our estimation model suggests that LUTS are highly prevalent worldwide, with an increasing burden predicted over time OBJECTIVE • To estimate and predict worldwide and regional prevalence of lower urinary tract symptoms (LUTS), overactive bladder (OAB), urinary incontinence (UI) and LUTS suggestive of bladder outlet obstruction (LUTS/BOO) in 2008, 2013 and 2018 based on current International Continence Society symptom definitions in adults aged ≥20 years PATIENTS AND METHODS • Numbers and prevalence of individuals affected by each condition were calculated with an estimation model using gender- and age-stratified prevalence data from the EPIC study along with gender- and age-stratified worldwide and regional population estimates from the US Census Bureau International Data Base RESULTS • An estimated 452%, 107%, 82% and 215% of the 2008 worldwide population (43 billion) was affected by at least one LUTS, OAB, UI and LUTS/BOO, respectively By 2018, an estimated 23 billion individuals will be affected by at least one LUTS (184% increase), 546 million by OAB (201%), 423 million by UI (216%) and 11 billion by LUTS/BOO (185%) • The regional burden of these conditions is estimated to be greatest in Asia, with numbers of affected individuals expected to increase most in the developing regions of Africa (301–311% increase across conditions, 2008–2018), South America (205–247%) and Asia (197–244%) CONCLUSIONS • This model suggests that LUTS, OAB, UI and LUTS/BOO are highly prevalent conditions worldwide Numbers of affected individuals are projected to increase with time, with the greatest increase in burden anticipated in developing regions • There are important worldwide public-health and clinical management implications to be considered over the next decade to effectively prevent and manage these conditions

772 citations

Journal ArticleDOI
01 Oct 2011-BJUI
TL;DR: Prevalence of urinary incontinence among women and its impact on quality of life in a semirural area of Western Turkey and the prevalence of overactive bladder in Spain: a population-based study.
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258 citations

Frequently Asked Questions (1)
Q1. What have the authors contributed in "Parametric design, fabrication and validation of one-way polymeric valves for artificial sphincters" ?

In this article the authors focused on the parametric design of polymeric valves, by taking inspiration from commercially exploited solutions used in the food industry and performing appropriate scaling in order to make them suitable for artificial organs and components. This polymeric valve parametric analysis may be exploited for the design of artificial sphincters, having the potential to tackle urinary incontinence, a disease that affects about 350 million people worldwide.