Novel Concept for a Mechanical Intraurethral

Artificial Urinary Sphincter

Alexander Preis

, Johannes Treviranus

, Elisabeth Benke

, Sebastian Reitelshöfer

and Jörg Franke

Institute for Factory Automation and Production Systems, Friedrich-Alexander-Universität Erlangen-Nürnberg,

Egerlandstraße 7, Erlangen, Germany

Keywords: Implant, Urinary Incontinence, Stress Incontinence, Artificial Urinary Sphincter, Intraurethral.

Abstract: Stress urinary incontinence is a common pathologic condition in society and an increasing socio-economic

challenge. Current artificial urinary sphincters for severe cases have high failure rates, cannot be applied sex-

independent and their handling is not intuitive. To address these issues, a novel intraurethral closure system

was developed. It works without an external energy supply and consists of an inflatable balloon that presses

against the inner contour of a surrounding cylindrical structure implanted in the urethra. Regulation of the

closure system is achieved by the interaction of the three main components: the closure balloon, the throttle

and the compensating reservoir. The developed closing mechanism seals the bladder at rest and during short

peak loads and opens only when the bladder pressure is increased by pressing with the abdominals for a longer

period of time for micturition.

1 INTRODUCTION

1.1 Urinary Incontinence

Urinary incontinence is a common pathologic

condition in society, which is defined as the

“involuntary leakage of urine” (Schmelz et al. 2014).

It is estimated that five to eight million people in

Germany and 50 to 200 million people worldwide

suffer from some form of urinary incontinence. An

exact number of those affected cannot be determined

since the tabooing of the subject is leading to an

avoidance of consultation, and thus a lack of acquired

data. (Sebsthilfeverband Inkontinenz e.V. 2013;

Niederstadt et al. 2007) Along with the physical

pathology, those affected experience a high level of

psychosocial stress and the costs for the national

health care systems are high (Milsom and Gyhagen

2019). This leads to socio-economic challenges in

addition to the medical ones (Yoo et al. 2020).

Urinary incontinence can be divided into stress,

https://orcid.org/0000-0003-3469-5982

https://orcid.org/0000-0002-3925-5356

https://orcid.org/0000-0002-6610-4430

https://orcid.org/0000-0002-4472-0208

https://orcid.org/0000-0003-0700-2028

mixed and urge incontinence. This publication’s

focus is on stress incontinence, which can be

distinguished from the other forms of urinary

incontinence both in its occurrence and in its causes

and treatment. It is defined by the involuntary leakage

of urine during load and without bladder contraction,

caused by an insufficient closure system.

(Sebsthilfeverband Inkontinenz e.V. 2013;

Niederstadt et al. 2007).

The main risk factor for the development of stress

incontinence is age. The connective tissue loses

tension in the later years of life and thus favors a

change in position of the bladder and urethra, so that

its closure is no longer guaranteed. In men, there is an

age-related increase in the size of the prostate, which

often necessitates surgery and can lead to the

postoperative occurrence of stress incontinence. In

the context of demographic change, an increase in the

number of people with stress incontinence is to be

expected, since the older part of the population is

growing steadily. Other causes are stresses on the

pelvic floor, such as those occurring during

170

Preis, A., Treviranus, J., Benke, E., Reitelshöfer, S. and Franke, J.

Novel Concept for a Mechanical Intraurethral Artiﬁcial Urinary Sphincter.

DOI: 10.5220/0010885700003123

In Proceedings of the 15th International Joint Conference on Biomedical Engineering Systems and Technologies (BIOSTEC 2022) - Volume 1: BIODEVICES, pages 170-176

ISBN: 978-989-758-552-4; ISSN: 2184-4305

pregnancy and childbirth, but also as a result of

obesity. Due to the increasing number of obese people

in the population, a higher number of people suffering

from stress incontinence is also to be expected.

(Niederstadt et al. 2007; Bundeszentrale für politische

Bildung 2020; Radtke 2017; Gasser 2019)

1.2 State of the Art of Surgical

Therapy

The therapy of stress incontinence depends on the

severity. For mild forms, conservative and drug

therapy methods are used, while for more severe

degrees, surgical procedures are standard. The goal of

these procedures is mostly to reposition the urethra

and support the sphincter muscle. (Hamann et al.

2014; Manski 2020) Depending on the method, these

have very high efficacy rates, but at the same time

entail a risk of complications during the procedure

and during use. In women, the former standard is

colposuspension according to Burch, where the

success rate is around 90% after one year and 70%

after 10 years. Perioperative complications such as

bladder injury, hematoma, and wound healing

problems occur in 5-10% of treatments.

Colposuspension has mostly been replaced by

tension-free suburethral band surgery, for example

tension-free vaginal tape (TVT) surgery, which has a

90% success rate even 11 years after surgery.

Complications with this method are much less

frequent, mainly basal perforations (2-5%) and

retropubic bleeding and hematoma (0.5-1%) occur.

Implantation of the sling via the transobturator access

route (TOT), has slightly lower success rates (84%)

and muscular discomfort is more common, but there

are less complications regarding bladder voiding

dysfunction or bleeding. Sphincteric prostheses are

used only in cases of complete loss of sphincteric

function with subjective recovery rates of 59-88%.

However, this contrasts with revision surgery in 42%

of cases within 10 years and the risks of perioperative

complications such as injury to the urethra, bladder,

and rectum. (Hamann et al. 2014; Reisenauer et al.

2013)

In contrast to the surgical therapeutic methods for

women, the use of artificial sphincters is the gold

standard for male patients with a success rate of 80-

85%. However, a prerequisite is sufficient manual

dexterity of the patient. Revision rates of 30% occur

due to mechanical problems and complications such

as arrosion, infection, or urethral atrophy are present

in 7-17% of patients. Male sling systems have success

rates as high as 70% with complications including

local wound infections, urinary tract infections,

perineal discomfort, and bladder voiding dysfunction

(up to 21%). Success rates are not higher with

adjustable slings, but readjustment is necessary in

one-third of patients. Complications with adjustable

systems include perineal pain, wound infection, and

bladder injury. (Hamann et al. 2014; Bauer et al.

2014)

1.3 Advantages of a Mechanical

Intraurethral AUS

The development of a purely mechanical,

intraurethral closing mechanism is intended to

circumvent the first-mentioned disadvantages. The

closing mechanism can be controlled by bladder

pressure alone and thus be self-sufficient from

external energy sources. A rechargeable battery

mechanism, as well as a charging mechanism, which

draws energy internally or externally, occupies a

certain amount of space, which, however, is

anatomically limited. In addition, a mechanical

implant is expected to be less expensive than a

mechatronic variant, due to its lower complexity. The

intraurethral placement of the artificial sphincter also

results in a number of other advantages. For example,

the complex multi-cavity surgical procedure of the

current gold standard can be avoided and a simple

ambulatory implantation can be performed, resulting

in a reduced cost, time and risk of complications and

infection. In addition, the significantly smaller

installation space required allows a sex-independent

use, and control by bladder pressure enables the

intuitive and unobtrusive usage of the system.

2 MATERIALS AND METHODS

The relevant parameters include the pressures at the

various sites in the lower urinary tract and the

different phases of the micturition process. According

to the definition of the International Continence

Society (ICS), these are given in the unit cmH

Measurement ranges of the pressures present are

mostly between 0-250 cmH

O. It should be noted that

the pressure is always measured against a zero value,

which corresponds to the ambient pressure, and that

the measurement height has a direct influence on the

measured value. Measured values such as filling

volume, bladder pressure and urethral pressure can be

recorded directly. Other values, such as the pressure

introduced from detrusor contraction, are determined

indirectly. (Schmelz et al. 2014; Schultz-Lampel et al.

2012) Thus, the detrusor pressure (p_det) is

calculated from the measured values of the abdominal

Novel Concept for a Mechanical Intraurethral Artiﬁcial Urinary Sphincter

171

pressure (p_abd) and the bladder pressure (p_ves) as

follows:

𝑝



= 𝑝



−𝑝



(1)

As the main function of an artificial urinary

sphincter is the sealing of the urethra at a certain

bladder pressure and for certain times, the following

criteria for the implant can be derived from the

urodynamic conditions:

• The flow of urine has to be interrupted at a

sustained 𝑝



below 50 cmH

• If a 𝑝



above 50 cmH

O is lasting longer than

5 seconds, urine flow should be allowed.

• If a 𝑝



above 100 cmH

O occurs, urine flow

should be blocked for at least 1-2 seconds.

This means, that the implant should be

continuously closed up to a certain pressure and also

should stay closed for pressure peaks with a short

duration, which are for example caused by physical

events like coughing.

2.1 Design of the AUS

The novel concept (figure 1) presented in this paper

is based on a balloon sealing the urethra. Therefore, a

cylindrical, tubular casing is inserted into the urethra,

which does not allow urine to flow past it laterally.

Prior to implantation, the balloon located in the tube

body is filled with liquid and a suitable internal

pressure is set so that the balloon is pressed against

the wall of the tube. The balloon is connected via a

throttle to an elastic compensating reservoir, which

ensures that the closing pressure is maintained.

Figure 1: The concept for the artificial urinary sphincter

uses a pressurized balloon to block of urine flow.

If the bladder pressure increases, it presses against

the balloon and increases the pressure inside, so that

the liquid flows out of the balloon through the throttle

and into the compensating reservoir. This reduces the

volume of the balloon and allows urine to flow past

it. The throttle is used here to ensure that the sealing

effect only diminishes at longer pressures and that

short-term pressure peaks are not causing any

involuntary leakage.

2.2 Experimental Analysis

Following components and machines were used for

the experimental analysis of the concept:

• Balloons “Endo-Breezer” from servoprax GmbH

(Germany), as the main obstructive mechanism.

• Pressure sensors “MPX-4250DP” from NXP

Semiconductors (Netherlands), to measure the

bladder and balloon pressures.

• Inflator “Everest” from Medtronic (Ireland), to

control the fill volume of the balloons in the

submillilitre range.

• Material jetting printer “Agilista 3200W” from

Keyence (Japan), to manufacture the cylindrical

tube and auxiliary parts.

In a first experiment, the balloon properties are

recorded (figure 2 A). The expansion of the balloon

at a certain filling volume plays an important role,

since, depending on the filling volume, the balloon

material expands elastically, resulting in an additional

internal pressure. The aim of the experiment is to

determine the internal pressure of the balloon at free

expansion as a function of the filling volume. For this

purpose, the prepared balloon is connected to a

pressure sensor and to the inflator.

Figure 2: To analyze balloon behavior, two experimental

setups where used to test balloon pressure depending on fill

volume (A) and balloon pressure correlated to bladder

pressure and the systems leakage point (B).

As the bladder pressure increases, the balloons

internal pressure also increases. Since this

phenomenon is relevant for the closure system, it is

examined in more detail by the following experiment.

As an experimental setup, the balloon is placed in the

associated cylindrical tube. The balloon is connected

to a pressure sensor and the inflator. The proximal

end of the tube is connected to a second pressure

sensor and a device for applying the bladder pressure.

In the experimental procedure, the balloon pressure is

set to 100, 150, and 200 cmH

O, respectively. Now

the bladder pressure is increased in 10 cmH

O steps

up to a maximum pressure of 200 cmH

O. Each step

is held for 15 seconds to reduce measurement

deviations.

Next, for a given bladder pressure, it is

determined at which fill volume leakage of the

balloon

Compensating

reservoir

throttle

ves

cylindrical tube

balloon inflator

pressure sensor

balloon

inflator

pressure sensorpressure sensor

cylindrical tube

ves

application

BIODEVICES 2022 - 15th International Conference on Biomedical Electronics and Devices

172

closure system occurs. The previous used setup is also

adopted for this experiment (figure 2 B). The balloon

is connected to the inflator and a pressure sensor. The

cylindrical tube containing the balloon is connected

to the device for applying the bladder pressure and the

second pressure sensor. The balloon is brought to a

pressure of 100, 150 and 200 cmH

O respectively and

a constant bladder pressure of 200 cmH

O is applied.

Now the balloons volume is decreased by removing

0.055 ml of fluid from the balloon step by step. Each

step is again paused for 15 seconds to reduce the

measurement error. The volume removal is continued

until water flows out through the closure system.

Lastly, the numerical simulation software

ANSYS Fluent is used to suitably design the throttle.

Here the influences of diameter and length of the

throttle, as well as the influence of the applied

pressure difference were analyzed.

3 EXPERIMENTAL RESULTS

Figure 3 shows the balloons internal pressure in

relation to the filling volume. It can be seen that the

balloons show a very strong increase in pressure

when they are filled for the first time, in contrast to

the subsequent filling processes. At the maximum

filled volume, the pressure values no longer deviate

so much. In reference tests after a 24 h waiting period,

this strong pressure increase is not observed. For all

filling processes except the first, the values fluctuate

within a certain tolerance range, with a standard

deviation of max. ± 38 cmH

O. The strong pressure

increase during the first filling can possibly be

explained by sticking and very strong relaxation of

the material during the first use after production. As a

result, it can be stated that the balloons used exhibit a

relatively constant expansion behavior.

Figure 3: The balloons internal pressure increases with fill

volume.

Figure 4 shows the influence of the bladder

pressure on the internal balloon pressure. It can be

seen that the balloon pressure increases differently

dependent on the initial pressure, which leads to a

decrease of pressure difference at higher bladder

pressures. From this experiment, it is evident that the

valve system is partially a self-amplifying system as

the bladder pressure is passed on to the balloons

internal pressure and thus pressing it against the outer

contour. However, the bladder pressure is not

completely transferred to the balloons internal

pressure. This is because the pressure distribution on

the proximal and distal sides is different and the

bladder pressure on the proximal side displaces

volume from the balloon to the distal side, where

there is no additional ambient pressure.

Figure 4: The balloons internal pressure increases with

bladder pressure.

The relation of balloon pressure and urine leakage

is shown in Figure 5. Here the removal volume in ml

is shown on the X-axis and the balloons internal

pressure in cmH

O on the Y-axis. The lowest value in

each test series represents the last internal balloon

pressure at which the system is still sealed at the

applied bladder pressure of 200 cmH

O. It can be seen

that a higher initial balloon pressure, which also

means a higher initial fill volume, leads to a larger

volume being able to be removed before the system is

not any longer sealed.

Figure 5: The removed volume needed to cause the leakage

of urine increases with initial internal balloon pressure.

The influence of the flow rate through the throttle

can be seen in Figure 6. As can be seen, the flow rate

increases with increasing throttle diameter and

pressure difference and decreases with increasing

throttle length. The simulation also shows, that the

throttle diameter is the most influential factor,

regarding this simple throttle, especially considering

the limited building space available.

-50

100

150

200

250

300

350

400

450

500

00.511.522.533.544.55

Internal balloon pressure in cmH2O

Fill volume in ml

First filling

100

120

140

160

180

200

220

240

260

280

300

320

0 20 40 60 80 100 120 140 160 180 200

Internal balloon pressure in cmH2O

Bladder pressure in cmH2O

100 cmH2O 150 cmH2O 200 cmH2O

Initial pressure:

Novel Concept for a Mechanical Intraurethral Artiﬁcial Urinary Sphincter

173

Figure 6: Fluid flow through the throttle increases with

diameter (A) and differential pressure (C) and decreases

with increasing throttle length (B).

4 DERIVATION OF THE SYSTEM

BEHAVIOR

Based on the previously conducted experiments, the

behavior of the overall system under three scenarios

relevant to the implants function is derived. The basic

state is the filling of the bladder over a longer period

of two hours up to a bladder pressure of 50 cmH

The sudden load is defined as the occurrence of a peak

in bladder pressure with a maximum value of 200

cmH

O over a period of two seconds. The final

scenario examined is the voluntary micturition, in

which bladder pressure increases to 100 cmH

O with

the patient pressing and is maintained until the

bladder is completely emptied. Figures 7 to 9 show

the pressure curves for these three scenarios. In each

case, the curve of bladder pressure, internal balloon

pressure, and internal pressure of the compensating

reservoir are plotted over the appropriate time axis for

the corresponding scenario. Based on bladder

pressure, the dashed line indicates the leakage point

at which the balloons internal pressure is low enough

to cause the closure system to leak. This leakage point

is calculated using the formula:

𝑝

𝑡𝑖𝑝𝑝𝑖𝑛𝑔 𝑝𝑜𝑖𝑛𝑡

= 0,849 ∗ 𝑝

𝑣𝑒𝑠

62,85

(2)

The experiments showed, that the internal balloon

pressure is influenced by the bladder pressure. An

internal pressure of 100 cmH

O in the balloon is set

as the starting pressure to close the closure system in

the basic state. The direct influence of the bladder

pressure on the balloons internal pressure is

calculated using the formula:

𝑝

𝑏𝑎𝑙𝑙𝑜𝑜𝑛

= 0,774 ∗ 𝑝

𝑣𝑒𝑠

 98,567

(3)

For the basic state, a bladder pressure of 0 cmH

at the beginning is assumed, which increases to 50

cmH

O over the duration of two hours. Accordingly,

the balloons internal pressure is set to 100 cmH

O at

the beginning and increases to 137 cmH

O. The

calculated leakage point is not undershot at any time,

which means that the sealing of the system can be

assumed. The pressure increase in the balloon causes

a pressure difference between the balloon and the

equalizing body, which is balanced by the flow of

fluid out of the balloon and into the compensating

reservoir. Due to the throttle, the pressure in the

equalizing body rises with a slight delay in relation to

the pressure inside the balloon.

Figure 7: The model shows, that the closure system stays

sealed during the filling phase of the bladder.

During the sudden load, the bladder pressure

increases abruptly from 20 to 200 cmH

O for the

duration of two seconds and then drops again to 20

cmH

O. Both, internal balloon pressure and leakage

point can be calculated using the formulas 2 and 3

presented before. When the bladder pressure

increases to 200 cmH

O, the balloons internal

pressure also increases from 114 to 253 cmH

O. Due

to the throttle, the system is quasi blocked at first, so

that there is a pressure difference of 253 cmH

O in

the balloon to 114 cmH

O in the compensating

reservoir occurring, which leads to a fluid flow from

the balloon into it. Derived from the previous

experiments, in order to reach the leakage point, of

233 cmH

O, a volume of 0.22 ml has to flow into the

compensating reservoir. The simulation shows that a

throttle with a diameter of 0.3 mm and a length of 5

mm is sufficient to prevent the balloons internal

BIODEVICES 2022 - 15th International Conference on Biomedical Electronics and Devices

174

pressure from dropping below the leakage point for

about two seconds, thus ensuring the sealing of the

closure system. Following the load, the system

returns to its initial state.

Figure 8: It is shown, that the closure system stays sealed

for at least two seconds, when high sudden loads occur.

During micturition, the bladder pressure is

increased from 50 to 100 cmH

O by active abdominal

pressing of the patient. The balloons internal pressure

thus increases to 175 cmH

O, which, with a leakage

point of 148 cmH

O, results in a volume of about 0.4

ml needed to flow into the compensating reservoir. At

a flow rate of 0.06 ml/s through the throttle described

above, this corresponds to a duration of about 7

seconds. After a sufficient drop in internal balloon

pressure, micturition occurs, at the end of which the

bladder pressure drops again to 0 cmH

O. The

pressure gradient between the balloon and the

compensating body is reversed, so that fluid flows

back into the balloon and the initial state with an

internal balloon pressure of 100 cmH

O is re-

established.

Figure 9: Through active pressing for at least seven

seconds, the closure system can be opened and the

micturition can be conducted.

5 SUMMARY AND OUTLOOK

The aim of this work was to develop a concept for a

closing mechanism that functions autonomously

without external energy generation or supply. For this

purpose, the relevant requirements for the mechanical

closing mechanism were analyzed. Based on the

conducted experiments and derived models an

advanced functional concept for the closing

mechanism was developed, shown in Figure 10. The

closure system consists of an inflatable balloon that

presses against the inner contour of an outer cylinder.

Regulation is achieved by the interaction of the three

main components, the closure balloon, the throttle

and the compensating reservoir. The presented

closing mechanism fulfills the requirements placed

on the implant, sealing the bladder at rest and during

short peak loads and opening only when the bladder

pressure is increased by pressing with the abdominals

for a longer period of time for micturition.

Particularly advantageous for this mechanism is the

simple design and the low number of components,

which means that a high reliability can be expected

due to the limited interfaces between the different

components. In addition, the low number of

components has an advantageous effect on the

expected manufacturing costs.

Figure 10: Resulting prototype of the artificial urinary

sphincter based on the data acquired and models derived

from the presented experiments.

In the case of the individual functional elements,

there is potential for optimization and a number of

properties that require further investigation. For the

balloons, a better sealing effect can be produced by

changing the basic geometry. The shape and material

thickness can be used to control the behavior of the

balloon more precisely. Here especially the

investigation of different fabrication strategies for the

balloons should be conducted, since the currently

applied method does not provide consistent results. In

addition, it is necessary to investigate how the

balloons behave over a longer period of time. In the

case of the outer cylinder, which is also part of the

closing system, different geometries need to be

investigated. Additionally, the installation space for

Novel Concept for a Mechanical Intraurethral Artiﬁcial Urinary Sphincter

175

the throttle can be reduced by using different throttle

shapes, e.g. with inserted flow obstacles or by

introducing a low-viscosity fluid instead of water,

thus changing the flow properties. For the

compensating reservoir, the pressure-volume

characteristic needs to be optimized to allow a better

control of the system behavior. In addition, further

investigations into the behavior of the overall system

are necessary, as the long-term stability of the implant

in contact with urine has not yet been investigated and

the question of whether complete voiding of the

bladder is possible with this concept has not yet been

clarified.

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