Hernia mesh has been utilized in surgical operations since the 1960s. Over the years there have been many different design variations and materials used in the manufacturing of these implants. The three main material groups are polypropylene (PP), polytetrafluorethylene (PTFE) and Polyester (POL). PP is a hydrophobic polymer of carbon atoms with alternating methyl moieties. It is a flexible but strong material that is easily cut and integrates with surrounding tissue while remaining resistant to infection. PTFE is a chemically inert synthetic fluoropolymer that does not incorporate into human tissue and becomes encapsulated, which increases the chances of hernia recurrence. It is also micro porous which allows bacteria passage. These problems led to the expansion of PTFE to become a uniform, fibrous and a micro porous structure with improved strength that is known as ePTFE. POL is a carbon polymer of terepthalic acid and can be fashioned into strong fibers suitable to be woven into a prosthetic mesh.
An ideal synthetic mesh is biocompatible, strong, resistant to infection, non-immunogenic and results in minimal bioreactivity. Tissue incorporation is the goal and depends on factors such as material, density, construction, filament type, pore size and compliance. For instance, mesh implants with larger pores allow for tissue ingrowth and are more flexible because they avoid granuloma bridging. Granulomas can form around individual mesh fibers when there is a foreign body reaction. They typically occur when the pore size is small and can cause a stiff scar plate and reduced flexibility of the mesh. The weight of the mesh is another characteristic that affects its performance. Heavyweight meshes use thick polymers, have small pore size and high tensile strength. As where lightweight meshes are composed of thinner filaments and have larger pores. Typically, lightweight meshes contain less material which initiates less of a foreign body reaction and are more elastic. Contraction occurs with all mesh products and can be problematic if there is too much contraction and becomes restrictive. There is a direct correlation between the degree of inflammatory response and contraction. Thus, lightweight tissue that causes a lesser degree of inflamation will have less contraction.
Elasticity and mesh strength is also an important factor that determines the performance of the mesh implant. If the mesh is too flexible and weak it will increase the risk of hernia reoccurrence. However, the mesh must be flexible enough so that the natural flexibility of the abdominal wall is preserved. If the mesh is too restrictive it will resist abdominal distension which can be painful and could result in the mesh breaking. The strength of the mesh depends on the filament type (multi-or mono-), woven or knitted, and the polymer type. Knitted meshes have greater flexibility and larger pores but are not as strong as woven meshes. Knitted meshes can be stretched in any direction as where woven meshes only stretch in one direction.
The latest mesh designs are composite meshes which are made from more than one material. The advantages of these meshes is that they can be used in the intraperitoneal space with minimal adhesion formation. However, in most instances, the safety and efficacy of these combined materials have not been sufficiently tested. These meshes have distinct sides; a visceral side and non-visceral side. The visceral side has a micro porous surface to prevent visceral adhesions and the non-visceral side is often macro porous to allow tissue ingrowth. All of these typically use either PP, POL or ePTFE combined with an additional material such as titanium, omega 3, monocryl, polyvinylidene fluoride or hyaluronate. There are two categories, either absorbable or permanent. Typically, barrier coatings in absorbable composite meshes require hydration prior to use and cannot be cut. Parietex composite mesh was the first to offer a resorbable collagen barrier on one side to limit visceral attachment and a polyester knit structure on the other side to promote tissue ingrowth. These coatings can cause bacteria entrapment that leads to bad infections. Other problems that have been associated with some of these implants has been mesh migration, folding over or balling up. Several manufacturers such as Ethicon, Bard/Davol, Atrium, and Covidien have composite meshes,
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