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Page 2 of 13 Lesch et al. Mini-invasive Surg 2023;7:25 https://dx.doi.org/10.20517/2574-1225.2023.31

influences acting on the abdominal wall compound. Considering the biomechanical reality is important for open
and minimally invasive abdominal wall reconstruction.

Keywords: Incisional hernia, biomechanical repair, abdominal wall reconstruction, multiaxial tissue assessment,
low cyclic fatigue (LCF) testing

INTRODUCTION
A durable repair of the abdominal wall must be assessed in a lifelike setting. The human abdominal wall gets
[1]
stressed by repetitive intraabdominal pressure peaks every day . The tissue and the repair materials get
loaded in unison . Our assessments follow modern biomechanics. We must consider all components of a
[2]
repaired abdominal wall as a coherent compound. For this purpose, we developed a test bench [Figure 1]. It
allows the study of such a compound under cyclic, repetitive loads . Repetitive high peak pressures occur
[3,4]
during daily activities, such as coughing or sports (DIS = dynamic intermittent strain). Pressures of more
[2,5]
than 200 mmHg can develop for less than 1 s . These inevitable loads increase the risk of a failed
reconstruction .
[6]
The repaired abdominal wall can be considered as a layered polymer. It consists of the tissue with a textile
mesh and fixation. Pulse loads repeatedly transmit energy to the abdominal wall. The amount of transmitted
energy is related to the pressure peak, the impact area, and the duration of the cyclic pulse, which may differ
during activities such as coughing, weight-lifting, or similar movements. The dissipation of this energy
within the compound depends on the temperature and material properties of a component. The load
transmission happens at the component interfaces. Currently, there is no unifying theory considering the
shakedown of Elastoplast polymers. However, recent experiments have verified the validity of the stability
limit analysis model of a multilayer structure .
[7]
A cyclic load bench test can factorize the influences named above independently. Based on the mesh-defect
area ratio, it is possible to relate the clinical and experimental results to a mathematical formula . A stable
[3,8]
repair needs to reach a critical resistance toward impacts related to pressure (CRIP) . Any repair gains
[9]
resistance toward impacts related to pressure (GRIP). Once the acquired GRIP surpasses the necessary
CRIP, the repair seems durable . The design of a repair has to consider the area of the unstable abdominal
[10]
wall and its distention. The GRIP/CRIP concept is applicable to open and minimally invasive/robotic
abdominal wall repair. We gain deeper insights into these topics through technology. Segmentation and AI
analysis can process data from CT scans. We use abdominal scans at rest and during the Valsalva maneuver
[9]
[Figure 2] .
Suture failure begins early after closure [11,12] . The interplay of the biomechanical properties determines the
long-term durability of a repair. These properties include the dynamic stiction of the materials, the closure
technique, the tissue behavior of the individual, and, importantly, the type of loads applied [9,13] . The size of
an incisional hernia increases over time and with the intensity of the loading . A larger hernia requires
[14]
higher GRIP. The neglect of the biomechanical reality results in a more comple × repair and raised costs to
society . The US spends over $ 7 billion every year on repeated incisional hernia repair, sick leave, and
[15]
early retirement . In Germany, the costs amount to at least € 1.8 billion. Using the GRIP concept, more
[16]
than 99 % of the patients are pain-free and have no recurrence after one year [3,10] .

This article describes the state-of-the-art of cyclic load bench test design and requirements for the future. It
illustrates the complexity and the broad range of influencing factors when considering cyclic impact loads.