Nau P ,Kanney J, Higgins R, Sherwinter D, Duke M, Auyang E, Poulose B, Goldblatt M, Blatnik J, Witkowski E, Sandler B, Miller H, Milone L, Szoka N, Higgins R, Lak K, Perez A, Chung A, Lee L, Pierce R, Dapri G, Saad W, Renton D.
The purpose of this project is to inform surgeons who use mesh as to the properties of the different products on the market. We will begin with an introduction which will define what these properties are, including materials, pore size, weight, and different testing parameters used in evaluating mesh. Following this will be pictograms which will contain information about each mesh available in an easy to understand and comparable format. We encourage printing of these and making them available to your surgical staff, as this will increase the knowledge of each mesh product, and increase proper selection for each hernia repair. Informed decision making is crucial in surgical care, and this tool was created to assist surgeons in their patient care.
Materials Used for Synthetic Meshes
Prosthetic materials have been used to reinforce the abdominal wall with successful improvement of patient quality of life and reduction in recurrence rates for years. These prosthetic devices, when combined with the correct technique applied to the correct patient, can offer a lifetime of benefit for hernia patients. Despite these advances, much remains unknown about the tissue-device interaction over long periods of time after initial surgical placement. In addition, the chance of low-rate potentially catastrophic complications associated with hernia repair and mesh use remains largely unknown.
Desirable characteristics of synthetic meshes include a long shelf life, easy handling during implantation, and resistance to infection. Meshes used in abdominal core surgery should ideally be biocompatible allowing enough mobility of tissues to minimize chronic pain while supporting a durable repair. Balancing these characteristics while maintaining a cost effective prosthetic remains a challenge to this day. The manufacture of synthetic meshes usually involves processing monomeric components into polymers with the desirable characteristics familiar to surgeons. It is worth noting that in the production of these products for clinical use, multiple chemicals and catalysts are used to create stable polymerization that contributes to the final product. Variations in these processes create differing properties of the final material-properties that can affect handling and likely long-term performance.
Permanent Synthetic Meshes
Permanent synthetic meshes remain the mainstay of prosthetic devices used during abdominal core surgery, including hernia repair. Nearly all products clinically available today are derived from petrochemical precursors. The most common materials used include polypropylene (PP), polyester (PE), and expanded polytetrafluoroethylene (ePTFE). The final characteristics of the mesh depend on both the underlying polymer and the weave of the mesh (affecting porosity and weight). Current data suggest that there are no measurable clinical differences between products based on these materials/ [1,2] These studies should be interpreted with caution as no evaluation has systematically evaluated long term outcomes of different materials while adequately capturing long-term catastrophic complications. The overall best estimate of cumulative 5 year mesh-related complications requiring surgical intervention is 5% in the Danish population. Surgeons are increasingly gaining experience with the use of permanent synthetic meshes in contaminated situations. Lower weight, large-pore macroporous PP is the most well studied with short term outcomes comparable to use in clean operations when placed in the retromuscular position.[4,5] Great care should be undertaken when using these products in contaminated conditions considering surgeon experience, patient comorbidities, and surgical technique.
Absorbable Synthetic Meshes
The concept of an absorbable synthetic mesh offers the theoretical advantage of no residual mesh after initial implantation. In addition to the ideal characteristics outlined above for permanent synthetic meshes, absorbable synthetic meshes have the additional characteristic of time to complete resorption. The two most popular materials used for absorbable synthetic meshes include polyglycolic acid (PGA) based products and those based on poly(4-hydroxybutyrate) (P4HB). PGA meshes have been in clinical use for several years and resorb between 2-6 months after implantation. This characteristic makes them particularly useful in difficult contaminated situations where a staged approach to abdominal wall management is warranted. P4HB is a naturally occurring molecule found in mammals; with resorption occurring over 18 months after implantation.[6,7] Initial results in terms of recurrence are promising compared to historical rates of permanent synthetic mesh use. The long-term durability, quality of life characteristics, and infection profile of absorbable synthetic meshes remain to be determined.
Coatings and Barriers
The general recommendation is that bare synthetic meshes be placed outside the peritoneal cavity to minimize interaction with abdominal viscera. A notable exception are bare PGA based meshes which are routinely used in the intraperitoneal position given their relative resistance to infection and fast absorption profile. To facilitate placement in the peritoneal cavity, several coatings and barriers have been developed. In general, the goal of these subsstances is to provide a posterior separation layer between the mesh material and the underlying viscera to minimize adhesion formation. Ingrowth is promoted on the anterior, bare surface of the mesh. Substances used include polyurethane, PGA, hydrogel, collagen/polyethylene glycol and glycerol, absorbable omega-3 fatty acids, sodium hyaluronate and carboxymethylcellulose, poliglecaprone, and absorbable cellulose. ePTFE can be placed in the intra-peritoneal space alone or in conjunction with a PP mesh. No in vitro or clinical differences have been observed between these products in limited available comparative data.[8,9]
Considerations for the Future
Given the current wide use of products in many clinical situations by surgeons with differing expertise, it is critical that surgeons follow patients over time to determine the outcome of interventions. The implantation of a device with the intent of lifelong placement carries with it a responsibility to ensure safety and efficacy of the product over the long-term. This is especially true in the off-label use of these products. By combining the rich clinical data obtained through well-designed registries with administrative data linkages and patient reported outcomes, we can help ensure that innovations in our field ultimately benefit our patients while minimizing harm.
With the acknowledgement of utility of synthetic mesh in decreasing hernia recurrence there has been an enormous increase in the different types of mesh from which the surgeon must chose. One of the components of mesh that differs vastly between different implants is the pore size. The porosity of the mesh is the space between fibers that allow for ingrowth and, ultimately, incorporation of the mesh into the abdominal wall . There are two distinct issues for which the consideration of pore size is critical. The size of the interstices of each mesh influences the ability of bacterial to grow and proliferate with smaller pores being ideally suited for bacterial growth. Perhaps more importantly, due to the relatively larger size of the cells of the immune system, the pore size is critical in the ability of the host to mount an appropriate and effective response. Larger, macroporous meshes allow for neovascularization and passage of macrophages through the interstices of the graft, rendering the mesh more resistant to infection. Smaller, microporous implants may be more prone to infection due to the inability of the body’s immune system to access and destroy the bacterial which can readily move within smaller pores. Additionally, microporous meshes allow for more rapid bridging of the mesh with scar tissue. This is more likely to be associated with poor integration of the mesh and a state of chronic inflammation. The most commonly accepted cut off to consider a mesh macroporous is 75-100 μm whereas microporous mesh are those with pore sizes less than 10 μm.
Another critical characteristic with which the surgeon must be familiar is the weight of the mesh. This characteristic is dependent on both the type of the material being used as well as the amount utilized to create the mesh. There are several issues that make this a relevant characteristic when considering post-operative outcomes both at a structural level as well as for the patient’s subjective impression of the repair. The weight is important in how it influences the body’s inflammatory response. There is a more intense foreign body reaction to a heavier weight mesh. This increased response to the mesh leads to a more dense scar. With a more robust scar there is decreased flexibility of the repair, decreased incorporation of the mesh and a greater degree of mesh contraction.[13, 14] This inflammation can result in shrinkage by as much as 50% and can even provoke a recurrence as the mesh pulls away from the rest of the repair. From a patient perspective, the use of a heavyweight mesh has many notable sequelae. A heavyweight mesh will often have smaller interstices which places the patient at a higher risk of mesh contamination. As stated earlier, a more microporous mesh is less likely to be salvaged in the setting of contamination due to the inability of macrophages to access the smaller pores. Further, due to the robust inflammatory reaction, patients will report a greater incidence of pain during physical activities with a concomitant slower return to normal activities. While not as concerning as persistent pain, lightweight mesh is also less likely to have persistent sensations of a foreign body than its heavyweight counterpart due to decreased compliance of the prosthesis. Certainly, there is a concern of mesh failure as weight of the implant decreases. With that said, there is good evidence that all but the very lightest mesh have a burst strength that is greater than the highest predicted intra-abdominal pressure that would be achieved during forceful coughing or jumping. This has lead some to postulate that mesh failures are unrelated to the weight, but rather the location of the stitches to the edge of the prosthesis. [15,16]
Definitions of weight are somewhat vague due to several reasons. One issue is that weight is defined by the company producing the mesh which is necessarily based on internal definitions.
Furthermore, many newer meshes are composite products which have an absorbable component. Over time, the weight of the mesh decreases as the absorbable components disappear to leave only the synthetic material behind. Most would agree that a light weight mesh would be less than 50 g/m2 and a heavyweight mesh > 50 g/m2.[17,18]
Hernia mesh is designed and constructed to possess specific biomechanical properties. Once a mesh is manufactured, testing is performed to quantify the mechanical properties of the material. A variety of tests have been devised and utilized by both industry and independent researchers to study and describe mesh performance. While this review does not present every available method of testing, the most commonly performed studies and their rationale are outlined below.`
The specific parameters of reported tests often conform to published industry standards, such as those from the American Society for Testing and Materials (ASTM). (https://www.astm.org/Standard/index.html) This is not always the case, however, and it is therefore important to understand the testing methodology that was used to determine mesh properties. Certain measures, such as biaxial tension testing, can only be understood in the context of the exact test parameters.
Each commercially produced mesh is manufactured to a specified porosity and weight. A single or multiple polymers or biomaterials can be knitted, woven, or laminated in many ways, followed by application of coating or barrier materials. Pore size and structure can be demonstrated and measured with various types of microscopy, as can fiber thickness and thickness of the entire mesh. Mesh weight (density) is determined by the raw weight of materials for a specific area (g/m2 or g/cm2).
Ball-burst (strength, strain)
One of the most commonly performed and reported tests, ball-burst assessment involves compressing a stainless-steel ball onto a mesh. This can assess several properties including maximum tensile strength (N/cm) and strain (%). Ball-burst testing does not account for anisotropy (directionality), but rather is a mimic of total force applied to the abdominal wall from intraabdominal pressure.
Tension testing (uniaxial or biaxial tensile strength)
Another important metric when assessing the aggregate strength of a mesh is tension testing. These studies involve measuring the maximum tension applied to a piece of mesh prior to failure, and can better address the issue of mesh anisotropy. When mesh is pulled in one direction, it is referred to as a uniaxial test. Biaxial testing pulls the mesh in two directions simultaneously. Different materials may have similar uniaxial strength, but remarkably different properties in biaxial testing. These properties can inform both the selection of an appropriate biomaterial, as well as optimal orientation when implanted.
Suture retention (pullout strength)
To simulate a suture pulling the edge of a mesh, a stainless-steel wire is passed through the mesh at a fixed distance from the edge. Force is then applied, and the maximum sustained tension prior to failure of the mesh is recorded. This can be clinically important, depending on the intended use of a prosthesis.
Mesh failure may occur when a tear propagates through the material. Tear resistance is assessed by making a controlled tear in the mesh, then determining the maximum sustained tension applied across the tear prior to propagation of the defect.
The stiffness of mesh and bending resistance has been reported less commonly than other mesh properties. This property may also be variable after mesh implantation, scar formation, and tissue remodeling. When reported, the results of these tests should be interpreted carefully within the context of the test design.
Test performance is routinely reported for mesh products as delivered (i.e. “out of the package”). After implantation, the biomechanical properties of may change, as is seen with shrinking of permanent synthetics or the degradation of absorbable, biosynthetic, and biologic materials. Tissue ingrowth and remodeling is also variable across mesh products. Many of these factors, as well as native tissue strength, contribute to the final biomechanical properties of the mesh-augmented tissue. Testing of mesh-reinforced tissue strength (e.g. in vivo abdominal wall models) is outside the scope of this review.
- Cevasco M, Itani KMF. Ventral hernia repair with synthetic, composite, and biologic mesh: characteristics, indications, and infection profile. Surg Infect (Larchmt). 2012;13:209–15.
- Totten C, Becker P, Lourd M, et al. Polyester vs polypropylene, do mesh materials matter? A meta-analysis and systematic review. Med Devices (Auckl). 2019;12:369–378.
- Kokotovic D, Bisgaard T, Helgstrand F. Long-term Recurrence and Complications Associated With Elective Incisional Hernia Repair. Jama. 2016;316:1575.
- Carbonell AM, Criss CN, Cobb WS, et al. Outcomes of synthetic mesh in contaminated ventral hernia repairs. J Am Coll Surg. 2013;217:991–998.
- Carbonell AM, Matthews BD, Dréau D, et al. The susceptibility of prosthetic biomaterials to infection. Surg Endosc Other Interv Tech. 2005;19:430–435.
- Hoefer P. Poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) 4.2. Poly(4-hydroxybutyrate) and poly(3-hydroxyoctanoate) with copolymers 4.3. Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) 5. 2010.
- Roth JS, Anthone GJ, Selzer DJ, et al. Prospective evaluation of poly-4-hydroxybutyrate mesh in CDC class I/high-risk ventral and incisional hernia repair: 18-month follow-up. Surg Endosc. 2018;32:1929–1936.
- Schreinemacher MHF, van Barneveld KWY, Dikmans REG, et al. Coated meshes for hernia repair provide comparable intraperitoneal adhesion prevention. Surg Endosc. 2013;27:4202–9.
- Gómez-Gil V, Pascual G, Bellón JM. Biomaterial implants in abdominal wall Hernia Repair: A review on the importance of the peritoneal interface. Processes.;7 . Epub ahead of print 2019. DOI: 10.3390/pr7020105.
- Shankaran V, Weber DJ, Reed RL 2nd, Luchette FA. A review of available prosthetics for ventral hernia repair. Ann Surg. 2011 Jan;253(1):16-26.
- Baylón K, Rodríguez-Camarillo P, Elías-Zúñiga A, Díaz-Elizondo JA, Gilkerson R, Lozano K. Past, Present and Future of Surgical Meshes: A Review. Membranes (Basel). 2017 Aug 22;7(3).
- Bilsel Y, Abci I. The search for ideal hernia repair; mesh materials and types. Int J Surg. 2012;10(6):317-21.
- Gonzalez R, Ramshaw BJ. Comparison of tissue integration between polyester and polypropylene prostheses in the preperitoneal space. Am Surg. 2003 Jun;69(6):471-6; discussion 476-7.
- Bellón JM, Rodríguez M, García-Honduvilla N, Gómez-Gil V, Pascual G, Buján J. Comparing the behavior of different polypropylene meshes (heavy and lightweight) in an experimental model of ventral hernia repair. J Biomed Mater Res B Appl Biomater. 2009 May;89(2):448-55.
- Brown CN, Finch JG. Which mesh for hernia repair? Ann Roy Coll Surg Eng 2010; 92: 272e8.
- Deeken CR, Melman L, Jenkins ED, Greco SC, Frisella MM, Matthews BD. Histologic and biomechanical evaluation of crosslinked and non-crosslinked biologic meshes in a porcine model of ventral incisional hernia repair. J Am Coll Surg 2011;212(5): 880–888
- Melkemichel M, Bringman S, Widhe B. Lower recurrence rate with heavyweight mesh compared to lightweight mesh in laparoscopic totally extra-peritoneal (TEP) repair of groin hernia: a nationwide population-based register study. Hernia. 2018 Dec;22(6):989-997.
- Sajid MS, Kalra L, Parampalli U, Sains PS, Baig MK. A systematic review and meta-analysis evaluating the effectiveness of lightweight mesh against heavyweight mesh in influencing the incidence of chronic groin pain following laparoscopic inguinal hernia repair. Am J Surg. 2013 Jun;205(6):726-36.