Fig. 1
Comparison of mesh (light- and heavyweight) strength with abdominal wall pressures
Lightweight meshes were first introduced in 1998 (Vypro) and their superiority over the heavyweight meshes is now widely accepted. These meshes have large pores (normally 3–5 mm) and a small surface area. They stimulate a reduced inflammatory reaction and, therefore, have greater elasticity and flexibility [9]. They also shrink less and have been shown to decrease pain after Lichtenstein inguinal hernia repair. Unfortunately, despite these improvements, they continue to have complications such as recurrence, infection, and adhesion formation.
The maximum intra-abdominal pressures generated in healthy adults occur while coughing and jumping (Fig. 1). These are estimated to be about 170 mmHg [10]. Meshes used to repair large hernias therefore need to withstand at least 180 mmHg before bursting (tensile strength up to 32 N/cm). This is easily achieved as even the lightest meshes will withstand twice this pressure without bursting (e.g., burst pressure of Vypro = 360 mmHg [11]. This illustrates that the tensile strengths of 100 N/cm of the original meshes were vastly overestimated.
Porosity is the main determinant of tissue reaction. Pores must be more than 75 μm in order to allow infiltration by macrophages, fibroblasts, blood vessels, and collagen. Meshes with larger pores allow increased soft tissue ingrowth and are more flexible because of the avoidance of granuloma bridging. Granulomas normally form around individual mesh fibers as part of the foreign body reaction. Bridging describes the process whereby individual granulomas become confluent with each other and encapsulate the entire mesh. This leads to a stiff scar plate and reduced flexibility. It occurs in meshes with small pores of less than 800 μm.
The weight of the mesh depends on both the weight of the polymer and the amount of material used (pore size) [12].
Heavyweight meshes use thick polymers, have small pore sizes, and high tensile strength. These meshes typically weigh 100 g/m2 (1.5 g for a 10 × 15 cm mesh). The strength is derived from a large mass of material, which activates a profound tissue reaction and dense scarring.
Lightweight meshes are composed of thinner filaments and have larger pores (>1 mm). Their weight is typically 33 g/m2 (0.5 g for a 10 × 15 cm mesh). They initiate a less pronounced foreign body reaction and are more elastic. Despite a reduced tensile strength, they can still withstand pressures above the maximum abdominal pressure of 170 mmHg (minimum tensile strength 16 N/cm).
A new generation of even lighter meshes includes the titanium/propylene composite meshes. These have been shown to be associated with a more rapid recovery in a recent, randomized controlled trial (RCT) [13]. The lightest of these (Extralight TiMesh) may have insufficient tensile strength in some situations (maximum tensile strength 12 N/cm).
Numerous randomized prospective trials have evaluated lightweight versus heavyweight mesh in ventral hernia repair with equal outcomes in ventral hernia repair recurrence [14–16]. The choice between a lightweight and heavyweight mesh is multifactorial and superiority has yet to be proven.
Shrinkage occurs due to contraction of the scar tissue formed around the mesh. Scar tissue shrinks to about 60% of the former surface area of the wound [11]. The smaller pores of heavyweight meshes lead to more shrinkage due to the formation of a scar plate.
The popularization of laparoscopic intraperitoneal mesh placement has led to increasing concern regarding mesh-related adhesions. Adhesions result from the fibrin exudates that follow any kind of trauma. These exudates form temporary adhesions until the fibrinolytic system absorbs the fibrin. Absorption is delayed in the presence of ischemia, inflammation, or foreign bodies (e.g., meshes). In these situations, they mature into tissue adhesions.
All meshes produce adhesions when placed adjacent to bowel, but their extent is determined by pore size, filament structure, and surface area. Heavyweight meshes induce an intense fibrotic reaction that ensures strong adherence to the abdominal wall but also causes dense adhesions. In contrast, microporous ePTFE does not allow tissue ingrowth. It has a very low risk of adhesion formation, but is unable to adhere strongly to the abdominal wall.
These two extremes illustrate the difficulty of producing a mesh that will adhere well to the abdominal wall but not to the bowel. Composite meshes aim to do this by providing an additional surface that can be safely placed in contact with bowel while peritoneal mesothelial cells grow over the mesh. These combine more than one material and are the basis of most new mesh designs. The main advantage of the composite meshes is that they can be used in the intraperitoneal space with minimal adhesion formation. They require a specific orientation: the visceral side has a microporous surface to prevent visceral adhesions, whereas the nonvisceral side is often macroporous to allow parietal tissue ingrowth. Despite the vast selection of brands available, nearly all these meshes continue to use one or another of three basic materials; PP, POL, and ePTFE, which are used in combination with each other or with additional materials such as titanium, omega 3, monocryl, polyvinylidene fluoride (PVDF), and hyaluronate. However, all of them come with some disadvantages, contrary to the manufacturers’ literature [4, 17].
There are two categories of composite meshes: absorbable and permanent . Barrier coatings in absorbable composite meshes require hydration prior to usage, and they are not amenable to modification, so they cannot be cut. However, they allow for neoepithelialization of the mesh before visceral adhesion, which mitigates viscera–mesh-related complications, and can aid in tissue ingrowth. Parietex® composite mesh was the first to offer a resorbable collagen barrier on one side to limit visceral attachments and a three-dimensional polyester knit structure on the other to promote tissue ingrowth and ease of use. The collagen film is composed of glycerol, polyethylene glycol, and porcine collagen. This balance of material properties produces superior cellular proliferation when compared to PP mesh in vitro and works with the body’s natural systems to provide rapid fibrous ingrowth, minimal shrinkage, and strong tissue integration [18, 19].
Permanently combined meshes take advantage of the properties of both macro- and microporous meshes. A microporous mesh permits placement adjacent to viscera, whereas macroporous mesh promotes parietal tissue ingrowth. These meshes can be modified and are easily cut to fit specific applications. They have also been demonstrated in animal models to lessen visceral adhesions and complications [20]. These properties permit intraperitoneal placement (e.g., Dual Mesh®, Dulex®, and Composix®).
There are also absorbable synthetic meshes that are used in contaminated cases where primary abdominal closure is not feasible. These absorbable materials provide a lattice for new collagen formation and then become absorbed, thus they are not suitable for permanent hernia repair. The recurrence rate is >50%, but whatever recurrences develop could be repaired at a later date with a nonabsorbable mesh. Dexon® (polyglycolic acid) and Vicryl® (polyglactin 910) are examples of such meshes (Fig. 2).
Fig. 2
A list of composite meshes (for intraperitoneal use) and their characteristics
Laparoscopic and Robotic Suture Materials
Suturing and knot tying in laparoscopic and da Vinci robotic surgery constitute advanced minimally invasive surgery skills. Developing proficiency in the standard methods with needle drivers is often an arduous process because of loss of tactile feedback. In laparoscopic surgery limited tactile feedback is present but in robotic surgery tactile feedback is replaced by haptic feedback. Recent advances in laparoscopic and robotic instrumentations have presented surgeons and gynecologists with easier methods of suturing and tying. The evolution of laparoscopic and da Vinci robotic surgery has expanded to more advanced and complex general surgery, and urological and gynecological procedures. For patients to get benefit from minimal access surgery surgeons must first develop and become expert in those laparoscopic surgery skills necessary for these advanced operations. Suturing and knot tying are among these advanced minimally invasive surgery skills required for many complex procedures. Developing proficiency in the standard methods of minimal access surgical suturing and knot tying with needle drivers may often be an arduous process [21].
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