Surgical mesh is a medical device used to repair weakened tissue, most commonly in the treatment of a hernia, which occurs when an organ or fatty tissue pushes through a weak spot in the surrounding muscle or fascia. The introduction of mesh marked a significant shift from older techniques that relied only on suturing the patient’s native tissue. These older methods often resulted in high recurrence rates due to the tension placed on the weakened tissue.
The mesh acts as a permanent scaffold, reinforcing the defect and allowing the patient’s own tissue to grow into its structure for long-term support. The vast majority of modern hernia procedures utilize a mesh implant to achieve a “tension-free” repair, which has significantly reduced the likelihood of the hernia returning. The types of mesh available vary widely in their material composition, physical structure, and biological properties to match the specific needs of the patient and the hernia location.
Primary Synthetic Materials
The foundation of most hernia mesh products is a synthetic polymer, chosen for its strength and durability. The most prevalent is polypropylene (PP), a non-absorbable material that forms a flexible, durable monofilament fiber. Polypropylene is the standard material for many hernia repairs because it is chemically stable and encourages a moderate inflammatory response necessary for tissue ingrowth and permanent incorporation.
Another commonly used polymer is expanded polytetrafluoroethylene (ePTFE), known for its highly inert nature and chemical stability within the body. Unlike polypropylene, ePTFE is a microporous material that resists significant tissue integration, often leading to fibrous encapsulation instead of ingrowth. This material is typically used when minimal tissue adhesion is desired, though it can undergo distortion or shrinkage over time.
Polyester (PET) is the third primary synthetic material, often processed into a multifilament or braided fabric. Polyester is more hydrophilic than the other two materials, meaning it attracts water, but it is also susceptible to hydrolysis, a breakdown reaction with water. Because of its susceptibility to degradation, polyester is primarily utilized in composite mesh designs where its structural properties can be balanced by other components.
Structural Classification of Mesh
Beyond the chemical composition, synthetic meshes are categorized based on their physical structure, specifically their weight and the size of the pores woven into the material. The pore size is a major factor influencing the body’s response, determining whether immune cells can penetrate the material to clear potential bacteria. The European Hernia Society (EHS) classification system categorizes these structures by pore size and material density.
Heavyweight mesh is characterized by a material density greater than 70 grams per square meter (g/m\(^2\)) and typically has smaller pores, often less than 1.0 millimeters (mm). This denser structure provides substantial mechanical strength but stimulates a pronounced foreign body reaction, leading to more scar tissue formation and a stiffer repair. The increased inflammatory response associated with heavyweight mesh may also contribute to a higher degree of mesh shrinkage after implantation.
In contrast, lightweight mesh utilizes less material, with a density below 60 g/m\(^2\), and features much larger pores, often exceeding 2.0 mm. This macroporous design allows for better tissue ingrowth, greater flexibility, and a lower overall foreign body reaction. The elasticity of lightweight mesh better matches the natural movement of the abdominal wall, which may contribute to less discomfort for the patient.
Specialty and Biological Meshes
To address specific surgical challenges, manufacturers have developed specialized meshes that combine materials or use biological sources. Composite meshes represent a multi-layered design, typically featuring a durable synthetic base, such as polypropylene, paired with a specialized coating. This coating is applied to the side facing the internal organs to prevent the formation of adhesions.
Common anti-adhesive coatings include absorbable materials like oxidized cellulose, hyaluronic acid, or Omega-3 fatty acids, which provide a temporary protective barrier. The synthetic side of the composite mesh is directed toward the abdominal wall, allowing for tissue integration and permanent reinforcement. This structure makes composite meshes suitable for ventral hernia repairs where the mesh must be placed directly against the viscera.
Biological meshes are derived from natural sources, such as porcine (pig) or bovine (cow) dermis or pericardium. These materials are processed to remove all cellular components, leaving behind only the natural collagen and extracellular matrix that acts as a scaffold. Biological meshes are typically reserved for complex repairs, especially those involving contamination or infection, where permanent synthetic mesh carries a high risk of failure and removal.
These biological scaffolds are eventually broken down and absorbed by the body, allowing the host’s own cells to rebuild a natural tissue layer. This temporary nature means they may have a higher recurrence rate than permanent synthetic meshes. However, their ability to avoid infection-related complications in compromised surgical fields makes them an invaluable tool, similar to biosynthetic meshes made from absorbable synthetic polymers.
Factors Influencing Mesh Selection
The selection of the appropriate mesh is a complex decision guided by clinical and patient-specific factors. The surgeon must first consider the type and location of the hernia, such as an inguinal hernia versus a larger ventral or incisional hernia. The location influences whether the mesh will be placed against the abdominal viscera, necessitating a composite or coated material.
The patient’s overall health status and risk factors are also important determinants of mesh choice. For instance, patients with a high risk of surgical site infection, such as those with obesity or diabetes, may benefit from a biological or biosynthetic mesh to avoid the long-term complication risk of a permanent synthetic material. The anticipated tension on the repair and the size of the defect also guide the choice between a lightweight, high-flexibility mesh and a heavyweight, high-strength mesh.
Finally, the surgical approach, whether an open procedure or a minimally invasive laparoscopic technique, can influence the mesh size, shape, and fixation method. Surgeons use these variables to tailor the mesh selection, aiming for the best balance between long-term durability, minimizing foreign body reaction, and mitigating the risk of complications like chronic pain and adhesion formation.