The ‘AbdoMAN’: an artificial abdominal wall simulator for biomechanical studies on laparotomy closure techniques
The 'AbdoMAN': an artificial abdominal wall simulator for biomechanical studies on laparotomy closure techniques
L. F. Kroese 0 1 2 3 4
J. J. Harlaar 0 1 2 3 4
C. Ordrenneau 0 1 2 3 4
J. Verhelst 0 1 2 3 4
G. Gue´rin 0 1 2 3 4
F. Turquier 0 1 2 3 4
R. H. M. Goossens 0 1 2 3 4
G.-J. Kleinrensink 0 1 2 3 4
J. Jeekel 0 1 2 3 4
J. F. Lange 0 1 2 3 4
Biomechanics Incisional 0 1 2 3 4
0 Department of Surgery, VU University Medical Center , Amsterdam , The Netherlands
1 Department of Surgery, Erasmus University Medical Center , Rotterdam , The Netherlands
2 Department of Neuroscience, Erasmus University Medical Center , Rotterdam , The Netherlands
3 Department Industrial Design Engineering, University of Technology , Delft , The Netherlands
4 Medtronic , Tre ́voux , France
Purpose Incisional hernia remains a frequent complication after abdominal surgery associated with significant morbidity and high costs. Animal and clinical studies have exhibited some limitations. The purpose of this study was to develop an artificial human abdominal wall (AW) simulator in order to enable investigations on closure modalities. We hypothesized that a physical model of the human AW would give new insight into commonly used suture techniques representing a substantial complement or alternative to clinical and animal studies. Methods The 'AbdoMAN' was developed to simulate human AW biomechanics. The 'AbdoMAN' capacities include measurement and regulation of intra-abdominal pressure (IAP), generation of IAP peaks as a result of muscle contraction and measurements of AW strain patterns analyzed with 3D image stereo correlation software. Intact synthetic samples were used to test repeatability. A laparotomy closure was then performed on five samples to analyze strain patterns. Results The 'AbdoMAN' was capable of simulating physiological conditions. AbdoMAN lateral muscles contract at 660 N, leading the IAP to increase up to 74.9 mmHg (range 65.3-88.3). Two strain criteria were used to assess test repeatability. A test with laparotomy closure demonstrated closure testing repeatability. Conclusions The 'AbdoMAN' reveals as a promising enabling tool for investigating AW surgery-related biomechanics and could become an alternative to animal and clinical studies. 3D image correlation analysis should bring new insights on laparotomy closure research. The next step will consist in evaluating different closure modalities on synthetic, porcine and human AW.
Abdominal wall hernia; Laparotomy closure
Incisional hernia is a common complication after
abdominal surgery, especially after open surgery with a median
laparotomy. Incidences of incisional hernia and burst
abdomen after midline laparotomy range from 11 to 20%
and 1 to 3%, respectively, and involve frequent reoperation
[1, 2]. These complications occur even more often in
highrisk populations, like patients with comorbidities such as
obesity, smoking or diabetes [1–3] and are associated with
discomfort or pain, which result in a lower quality of life
. In the USA, over 300,000 hernia operations are
performed annually, with estimated associated costs of $3.2
billion . Mesh-based and suture-based repair of
incisional hernia exhibits recurrence rate from 0.8 to 24% and
from 12 to 67%, respectively [6–8]. Because most studies
provide only short-term follow-up, these recurrence rates
may be underestimated.
To prevent incisional hernia, laparotomy closure
techniques have frequently been investigated in both
experimental and clinical studies. Some of these showed that
incisional hernia is an early complication after closure .
Several decades of research led to recommend continuous
suture technique with small suture bites of 5 mm from the
wound edge and an inter-stitch distance of 5 mm with
slowly absorbable suture material as the most efficient
closure technique compared to the commonly used large
bites [2, 10–15]. The small bites suture technique still
exhibits 13% incidence incisional hernia at 1 year .
Incisional hernias remain a clinical challenge. Both
biological and biomechanical mechanisms that result in the
occurrence of an incisional hernia remain globally
Therefore, further research should be conducted to
develop and systematically investigate closure techniques
and materials. Clinical studies will give the highest level of
evidence, but are expensive and in most cases not
suitable to investigate new concepts. Preclinical experiments
with cadaveric or animal specimens face several problems:
the availability of human cadaveric tissue is limited and
animal experiments tend to be more and more debated from
an ethical standpoint. Moreover, the anatomy and
physiology of animals are considerably different from the human
ones. For example, the linea alba of a rat is relatively
narrow and relatively much shorter compared to the human
linea alba . The pig abdominal wall (AW) is more
comparable to the human AW, but still exhibits numerous
Previous research has focused on linear tensile strength
testing of sutured porcine AW . Although this
research provided important conclusions for further
clinical investigation , linear testing does not take into
account the intra-abdominal pressure acting as well on the
Moreover, linear testing features a flat and not a curved
AW and therefore does not mimic the real physiology.
There is a strong need for a standardized way to
compare different closure techniques and materials under
physiological conditions. This device could be used to
investigate pathophysiology and treatment of AW
incisional hernia. A standardized artificial AW simulator could
also be used as a training device for mechanical evaluation.
The recent study published by Deerenberg et al. 
clearly shows the impact of mechanical conditions of
midline laparotomy closure on clinical outcomes.
The aim of this study was to develop a physical
simulator to investigate the mechanical behavior of the AW
under physiological conditions using 3D image stereo
correlation and to demonstrate the possibility to describe
the biomechanics of the AW after laparotomy closure.
These experiments will provide a proof of concept of the
To simulate human AW biomechanics, the ‘AbdoMAN’
(Fig. 1) was developed. The ‘AbdoMAN’ consists of
several components which simulate the AW biomechanics.
Two main factors had to be taken into account: the
intraabdominal pressure and the effect of AW muscle
Basal resting intra-abdominal pressure (IAP) varies
between 2 and 17 mmHg under normal physiological
circumstances [17–19], but can increase up to 20 mmHg in
patients suffering from ileus . To simulate the
abdominal contents, a 3.5-L air-filled Vacufix collecting
bag (B. Braun, Melsungen, Germany) was used. This
pillow was placed on a 3D-printed part, shaped like the AW
geometry. A laparoscopic insufflator (Karl Storz,
Schaffhausen, Switzerland) was used to regulate the basal
pressure level in the pillow.
IAP was measured and recorded in the air pillow using a
0.35 bar pressure sensor (Measurement specialties,
Hampton, VA, USA). As in the physiological human
situation, the IAP was achieved by the combination of a basal
IAP and IAP peaks caused by muscles contractions.
Abdominal wall muscle simulation
The external, internal oblique and transverse abdominal
muscles are situated laterally to the rectus abdominal
muscle and their fascias surround the rectus abdominal
muscle joining together in the linea alba. These lateral
muscles contribute in generating perpendicular force on the
linea alba. Those forces can be summated into one force
vector. This force can be split in a perpendicular force to
the linea alba and a force in craniocaudal direction .
Pneumatic actuators (type DMSP, Festo Technology
Group, Hauppauge, NY, USA) were used to simulate the
muscle contraction. These actuators have the capacity to
mimic the contraction of antagonistic muscles.
Highstrength fibers provided a relation between raising the
internal pressure which resulted in expansion in peripheral
direction and decreasing its size in longitudinal direction.
Three identical pneumatic actuators, activated
synchronously, were placed on both lateral sides, contracting
simultaneously (Fig. 1b).
Fig. 1 ‘AbdoMAN’ device. a Schematic overview showing all
different components. b Side view showing three lateral muscle
actuators connected to the mounted sample and the cranial/caudal
jaws used to mount the sample. c Top view showing an intact sample
mounted on the ‘AbdoMAN’ using jaws on all four sides
The AW was fixed on the cranial and caudal sites to
mimic the fixation of the rectus abdominis muscle to the rib
cage and pubic bone (Fig. 1c).
In the physiological situation, lateral muscles
contraction causes a rise in IAP. During activities such as
coughing or vomiting, IAP can increase up to 37–81 and
82 mmHg (with peaks of 255 mmHg), respectively
Fig. 2 Abdominal wall samples. a Shape of a sample prior to
mounting. b A mounted sample on the ‘AbdoMAN’ device with
fixation in four directions
[18, 19]. These rises were simulated with the pneumatic
actuators and recorded using the pressure sensor connected
to the air pillow. To create relevant IAP peaks, the
physiological value of the contraction needs to be applied on a
sample with material properties close to active human AW.
The sample has to be placed on a relevant surrogate of the
Synthetic abdominal wall
To standardize testing, a custom-made 5-mm-thick
synthetic AW, especially made for this study, was used
(Fig. 2a). This synthetic material is made of a polyurethane
matrix with two layers of elastane fibers (The Chamberlain
Group, Great Barrington, USA). A small piece of each
synthetic sheet was placed in a tensile testing machine
(Instron, High Wycombe, England) to determine the
stiffness in two directions [directions 1 (D1) and (D2)]. With
Fig. 3 Synthetic abdominal wall stiffness testing. Each sample was
tested in two directions (D1 and D2)
the stiffness of these directions, the anisotropy ratio was
calculated. This material has a comparable stiffness
compared to the active human AW .
Before sample mounting, two PTFE sheets were placed
on the AbdoMAN to minimize any possible friction
between the sample and the support. AW samples were
mounted on the ‘AbdoMAN’ using clamps to attach the
pressure actuators (Fig. 2b). On the cranial and caudal
sides, samples were clamped to ensure pretension.
Fig. 4 ‘AbdoMAN’ test setup
repeatability results. a Synthetic
abdominal wall stiffness
determined by tensile machine
testing of a small piece of each
sample. b Peak intra-abdominal
pressure during cough cycle of
the samples mounted on the
‘AbdoMAN’. c Mean strain
over surface area of the samples
mounted on the ‘AbdoMAN’.
d Mean strain over transversal
line of the samples mounted on
3D image stereo correlation
To capture strain patterns in the artificial AW, 3D image
stereo correlation system (Dantec Dynamics, Skovlunde,
Denmark) was used. This system captures the 3D
displacement and establishes the strain of the tested sample using two
cameras and dedicated software. Prior to the test, a black and
white paint speckle was applied on the area of interest.
Test setup repeatability
To investigate test reliability and repeatability, pressure
and 3D image stereo correlation data were evaluated for a
series of synthetic AW samples.
To simulate the physiological conditions, a test setup
was chosen with standard IAP of 10 mmHg and to simulate
coughing, actuator inner pressure, necessary to generate the
lateral muscle force, was increased up to 3000 mmHg
during three cycles at 1 Hz frequency.
Midline closure repeatability
One of the purposes of this part of the experiment was to
investigate the repeatability and the possibilities of
visualizing the biomechanical effects of bite size and
interFig. 5 3D stereo correlation
criteria of intact samples.
a Exemplary strain image of an
intact synthetic abdominal wall
sample at peak intra-abdominal
pressure. b Schematic image of
used strain analysis areas for 3D
stereo correlation: linear strain
in the muscle force direction
and area strain of a larger
suture distance using 3D image stereo correlation. A 15 cm
median laparotomy was carried out on five synthetic AWs.
The incision was closed using PDSII 1 sutures (Ethicon,
Somerville, NJ, USA) and using a continuous 5 9 5
modality (5 mm distance between suture and incision,
5 mm distance between two sutures). The suture was
knotted five times on both ends. After suturing, the sample
was placed on the ‘AbdoMAN’ and cough tests were
performed as described above. Strain patterns and incision
distension at the moment of muscle contraction were
measured using the 3D image stereo correlation system to
test the reproducibility of sutured samples.
Video material is available as supplemental material
Test setup repeatability
The stiffness of five synthetic samples was tested in a
tensile machine in two directions (D1 and D2). A graph of
the synthetic AW stiffness in both directions is shown in
Fig. 3. The mean Young’s modulus of the stiffest direction
was 815 kPa (range 765–885 kPa; Fig. 4a) and the mean
anisotropic ratio was 1.26 (range 1.22–1.28).
After these tests, samples were mounted on the
‘AbdoMAN’. The inner pressure of 3000 mmHg in each
pneumatic actuator resulted in a muscle force of
660 Newton (N) (220 N per cylinder) on each lateral side.
The length of the sample within the lateral jaws is 28.5 cm
and his thickness is 5 mm. The force is applied on a
crosssection of 14.25 cm2, which results in a stress of 0.46 MPa.
Fifteen tests were performed using five identical
synthetic AWs. The mean IAP peak was 74.9 mmHg (range
65.3–88.3 mmHg; Fig. 4b).
The displacement and strain fields were calculated
after each test (Fig. 5). Two criteria were defined to
assess the repeatability of the test, the mean transversal
strain over an area centered on the sample and the mean
transversal strain over a transversal line (Fig. 5b), which
exhibited, respectively, 12.27% (range 11.38–12.75;
Fig. 4c) and 12.19% (range 11.38–12.75; Fig. 4d) of
Fig. 6 3D stereo correlation criteria of 5 9 5 mm suture modality.
a Mean maximum strain around suture points. The areas are indicated
in the white circles. b Peak-to-peak normalized strain profile through
the suture points. Maximum and minimum peaks are indicated and
connected with the green lines. c Maximum opening length of the
incision. This is indicated with the red line
Midline closure repeatability
Five incised samples were closed with a 5 9 5 mm
modality, resulting in a mean suture length to wound length
ratio of 6.02 (range 5.88–6.17). No suture breaks were
observed. Three comparison criteria between suture
modalities were defined based on the analysis of the
displacement and strain field of this configuration (Fig. 6):
Mean maximum strain around suture points. This area
surrounds the place where the suture perforates the
tissue. This area was used as an area of interest, because
maximum force is brought upon this area. These strain
areas are indicated in Fig. 6a. The testing of five
samples resulted in a mean value of 13.76% (range
11.7–15.1; Fig. 7a).
Strain profile through suture points along the incision
line.A line was drawn passing through all suture points.
The strain profile was used as a result to compare each
Peak-to-peak normalized strain profile through the
suture points. Figure 6b shows the strain on a line,
drawn along all points where the sutures perforated the
tissue. As can be seen, the strain is the highest around
the suture points and the lowest in the area between two
suture points. The peak-to-peak normalized strain takes
the mean variance between those two extremes. By
doing so, attention is not only paid to the absolute value
of the strain around the suture points, but also to the
strain in relation to its surrounding tissue. The testing of
five samples resulted in a mean value of 3.8% (range
1.3–6.7; Fig. 7b).
Maximum opening length of the incision. This was
defined as the maximum distance between the two sides
of the incision, measured during the peak of the muscle
contraction (Fig. 6c). The testing of five samples
resulted in a mean value of 0.34 mm (range 0.2–0.5;
The ‘AbdoMAN’ is the first human AW simulator that
enables dynamic testing under physiological conditions. It
combines both intra-abdominal pressure (IAP) and
abdominal muscle activity.
The stiffness of the synthetic materials (765–885 kPa) is
equivalent to an active human AW (600–1000 kPa) .
The found anisotropic rate of 1.22–1.28 is also in the same
order of magnitude as that reported of human linea alba
(1.47) . For coughing, the force applied by the pressure
actuators, 660 N, and the resulting stress applied on the
sample, 0.46 MPa, are within the range of the skeletal
muscles stress (0.089–0.801 MPa) [18, 19, 25–27]. Mean
peak IAP was 74.9 mmHg (range 65.3–88.3 mmHg;
Fig. 3b) which is entirely in the physiological range of
37–81 mmHg during coughing [18, 19].
Fig. 7 Midline closure
repeatability results. a Mean
maximum strain around suture
points as indicated in Fig. 6a.
b Peak-to-peak normalized
strain profile through the suture
points as indicated in Fig. 6b.
c Maximum opening length of
the incision as indicated in
The use of 3D image stereo correlation in combination
with a physiological biomechanical simulation model to
analyze strain patterns and displacement in AW research
was described before [23, 28, 29]. However, the
combination with a dynamic simulation device has not been
demonstrated yet, and provides insights into the
biomechanics of the sutured AW.
The midline closure part demonstrates the possibility to
visualize strain patterns around the incision and the suture
points. Using a combination of the three criteria described
previously, it might be possible to investigate different
closure modalities and to find an optimal laparotomy
closure modality from a biomechanical standpoint. The
criteria used in this part show consistent test results when
repeating test cycles with different samples. Therefore,
they can be used to compare different suture modalities
(i.e., bite sizes).
The next step in this research field will be the systematic
testing of different midline closure modalities using both
the ‘AbdoMAN’ and the 3D image stereo correlation
system. In the future, human cadaveric AW or porcine AW
could also be used with the ‘AbdoMAN’ device. For this
purpose, additional experiments will be needed to check if
the criteria used to compare modalities on synthetic AW
will still be relevant using biological tissue.
When this next step has been completed, the
‘AbdoMAN’ can be used in experiments in which (cough)
cycles are being repeated numerous times. This will reflect
the physiological situation in which incisional hernias
develop over time after a longer period of repeated,
When more will be known about strain and
displacement data interpretation, the ‘AbdoMAN’ may be used for
future research on finding new, ideal suture modalities.
Moreover, different suture materials (such as elastic or
barbed sutures) or mesh augmentation could be
investigated using the ‘AbdoMAN’. Even more challenging and
interesting would be the creation and closure (with or
without mesh) of AW defects to investigate different
Finally, the ‘AbdoMAN’ could provide an easily
accessible tool for training of laparotomy closure and
hernia repair. For example, the effect of a suboptimal
closure technique performed by a trainee could be directly
To our opinion, the complete test setup can be
reproduced at other sites, enabling standardized, simultaneous
experiments or teaching settings throughout one (or more)
The ‘AbdoMAN’ has limitations. It is not possible to
simulate tissue healing, as it is a mechanical simulator.
One other limitation is the fact that in this setup,
although the stiffness of the synthetic materials was set up
to mimic active tissue, the AW does not reproduce the
material properties changes driven by the contraction. This
might result in different phenomena.
Also, the synthetic AW consists of two components to
provide both the strength and flexibility needed to simulate
the human AW features. This may react differently than the
human linea alba, consisting only of connective tissue. The
dimensions of the sample, comparable to a human AW, but
five times thicker than a fascia , the friction between
the sample and the artificial abdominal cavity could as well
Some variance was found in IAP and strain data, which
might be explained by slight stiffness differences observed
between synthetic abdominal walls.
The ‘AbdoMAN’ could become a promising alternative to
or complement for animal and clinical studies on AW
closure techniques. The device showed reliable and
repeatable results. A first experiment to analyze laparotomy
closure demonstrated the possible application of the
‘AbdoMAN’ device. Future research will evaluate different
closure modalities on both synthetic and human or porcine
AW to find out more about the underlying mechanisms that
drive the biomechanics of laparotomy closure and
incisional hernia repair.
Acknowledgements This study was partially funded by Medtronic,
Tre´voux, France and part of it was conducted in collaboration with
Medtronic, Tre´voux, France.
Author contributions LK designed the study, performed
experiments, collected, analyzed and interpreted data and wrote the report.
JH designed the study, performed device development, interpreted
data and wrote the report. CO performed experiments, collected,
analyzed and interpreted data and wrote the report. JV designed the
study, interpreted data and wrote the report. GG performed
experiments, collected, analyzed and interpreted data and wrote the report.
FT analyzed and interpreted data and wrote the report. RG performed
device development, interpreted data and wrote the report. JJ
designed the study, interpreted data and wrote the report. GK
designed the study, interpreted data and wrote the report. JL designed
the study, interpreted data and wrote the report.
Compliance with ethical standards
Conflict of interest LK declares no conflict of interest directly
related to the submitted work. JH declares no conflict of interest
directly related to the submitted work. CO declares conflict of interest
not directly related to the submitted work (Medtronic employment).
JV declares no conflict of interest directly related to the submitted
work. GG declares conflict of interest not directly related to the
submitted work (Medtronic employment). FT declares conflict of
interest not directly related to the submitted work (Medtronic
employment). RG declares no conflict of interest directly related to
the submitted work. JJ declares no conflict of interest directly related
to the submitted work. GK declares no conflict of interest directly
related to the submitted work. JL declares no conflict of interest
directly related to the submitted work.
Human and animal rights This article does not contain any studies
with human participants or animals performed by any of the authors.
Funding Supported by Medtronic, Tre´voux, France.
Open Access This article is distributed under the terms of the
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license, and indicate if changes were made.
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