Mechanical properties of the abdominal wall and biomaterials utilized for hernia repair

Abstract

Abdominal wall hernias are one of the most common and long-standing surgical applications for biomaterials engineering. Yet, despite over 50 years of standard use of hernia repair materials, revision surgery is still required in nearly one third of patients due to hernia recurrence. To date, hernia mesh designs have focused on maximizing tensile strength to prevent structural failure of the implant. However, most recurrences occur at the biomaterial-tissue interface. There is a fundamental gap in understanding the degree to which a mechanical mismatch between hernia repair materials and host tissue contributes to failure at this interface. This review summarizes the current literature related to the anatomy and mechanics of both human and animal abdominal wall tissues, as well as the mechanical properties of many commonly-utilized hernia repair materials. The studies reviewed here reported greater compliance of the linea alba, larger strains for the intact abdominal wall, and greater stiffness for the rectus sheath and umbilical fascia when the tissues were loaded in the longitudinal direction compared to transverse. Additionally, greater stresses were observed in the linea alba when loaded in the transverse direction compared to longitudinal. Given these trends, a few recommendations can be made regarding orientation of mesh. The most compliant axis of the biomaterial should be oriented in the cranio-caudal (longitudinal) direction, and the strongest axis of the biomaterial should be oriented in the medial-lateral (transverse) direction. The human abdominal wall is also anisotropic, with anisotropy ratios as high as 8-9 reported for the human linea alba. Current biomaterial designs exhibit anisotropy ratios in the range of 1-3, and it is unclear whether an ideal ratio exists for optimal match between mesh and tissue. This is likely dependent on implantation location as the linea alba, rectus sheath, and other tissues of the abdominal wall exhibit different characteristics. Given the number of unknowns yet to be addressed by studies of the human abdominal wall, it is unlikely that any single biomaterial design currently encompasses all of the ideal features identified. More data on the mechanical properties of the abdominal wall will be needed to establish a full set of guidelines for ideal mesh mechanics including strength, compliance, anisotropy, nonlinearity and hysteresis.

Biochemical, Biophysical and Mechanical Characterization of Decellularized Dermal Implants

“…When used as filler without mechanical requirements, such as in the breast or in the face, there are few complications as long as the cellular components of the tissue are removed, the graft does not contain antibodies to viral components, the viral load, is reduced and the implant does not cause pressure on the surrounding tissue. In applications that are structural, such as in repair of herniated abdominal wall, the mechanical properties of the graft material play an important role [16]. The results of recent studies suggest that allograft failure can be due to mechanical mismatches between graft and the host tissues [16].…”

“…In applications that are structural, such as in repair of herniated abdominal wall, the mechanical properties of the graft material play an important role [16]. The results of recent studies suggest that allograft failure can be due to mechanical mismatches between graft and the host tissues [16]. It is known that intimal hyperplasia occurs with vascular grafts due to mechanical mismatch between a low modulus vessel wall and a stiff graft made of polyethylene terephthalate, Dacron [26].…”

“…Allografts and xenografts have grown appreciably in their use in applications that include: bladder regeneration [3], burns [4], breast reconstruction [5], facial cosmetic defects [6], free flap coverage [7], hernias [8], ophthalmic defects [9], oral defects [10], replacement of cardiovascular tissues [11], tendon/ligament repair [12], and vaginal repair [13]. They also have been used as replacements in the repair of rotator cuff, Achilles and quadriceps tendons, primary staged and revised breast reconstruction, hernia repair, treatment of chronic wounds such as diabetic foot ulcers and pulmonary patches [14] [15] [16].…”

“…In addition, more than one third of hernia replacements require revision surgery. Failures of these implants typically occur at the implant-tissue interface due to mechanical mismatches [16]. Therefore, the mechanical properties of allograft materials appear to be an important characteristic needed for a positive outcome at least in hernia repair.…”

Biomaterial Implants in Abdominal Wall Hernia Repair: A Review on the Importance of the Peritoneal Interface

“…The difficulty in finding the proper equilibrium between the intended clinical effect and avoidance of collateral damage has resulted in a significant evolution in the number and types of prosthetic materials available for abdominal wall reconstruction. Currently, nearly 150 options for prosthetic materials with varying composition, weight, cost, and indications for use in the surgical field are available to the general surgeon [68,69], with the ongoing development of new additional meshes [9]. An in-depth knowledge of the advantages and disadvantages of the diverse materials currently available is needed when selecting the optimal mesh according to a specific situation.…”