Mesh implants: An overview of crucial mesh parameters

Table 1 Definitions of the knit, warp-knit, nonwoven and woven textile structures

Textile structure	Definition
Knitted fabric	Knitted fabric consists of a number of consecutive rows of loops, called stitches. Knitted structures are manufactures from single yarn systems. Thus, knitted structures can be ribbed off. Trimming of knitted structures often leads to a complete falling apart
Warp-knitted fabric	Warp-knitted fabric consists of a number of consecutive courses of loops, called stitches. Warp-knitted structures are manufactures from multi yarn systems whereby the number of separate strands of yarn equals the number of stitches in a row. In contrast to knitted structures warp-knitted structures can be trimmed and sewed
Nonwoven fabric	Nonwoven fabric consists of non orientated or to a certain degree orientated staple or endless fibers. After the nonwoven formation the structure needs to be bonded which either is realised by mechanical, thermal or chemical bonding
Woven fabric	Woven structures consist of two distinct sets of yarns or threads which are interlaced at right angles to form a fabric

Table 2 Essential properties of the knit, warp-knit, nonwoven and woven textile structures

Textile structure	Porosity (macropores)	Elasticity	Mechanical behaviour	Trim-ability
Knitted fabric	++	++	Anisotropic	--
Warp-knitted fabric	++	++	Isotropic, anisotropic	++
Nonwoven fabric	-	-	Isotropic	++
Woven fabric	-	--	Isotropic	++

Table 3 Definitions of mechanical mesh properties based on the definitions given by the American Society for Testing and Materials[44]

Property	Definition
Tensile strength	Tensile strength is the maximum force that can be applied to a mesh without tearing or breaking of the mesh. The tensile strength is measured in Newton (N) and is usually given in relation to the clamping width as Newton per centimeter (N/cm)
Burst strength	The burst strength is the maximum uniformly distributed pressure applied at right angle to its surface that a material will withstand under standardized conditions. The burst strength is given in pressure per unit area (Pa/cm²)
Elasticity (elastic elongation)	Elasticity (elastic elongation) is the property of a material whereby it changes its shape and size under the action of opposing forces (%), but recovers its original configuration when the forces are removed. In contrast, to the elastic elongation the plastic elongation indicates the elongation ratio which does not recover after unloading the structure
Stiffness	Stiffness can be expressed as ratio of steadily increasing or decreasing force acting on a deformable elastic material to the resulting displacement or deformation. Stiffness is a crucial aspect that reflects the drapablity of a textile structure, means the ability of a textile structure to be adapted to a 3-dimensional geometry

Table 4 Essential properties of hernia meshes used for groin and abdominal wall hernia repair

Property	Recommendation
Tensile strength (abdominal wall)	22 N/cm (cranial/caudal )
	32 N/cm (lateral)
Tensile strength (groin)	16 N/cm
Elongation	20%-40%
Orientation	No specific orientation for meshes with isotropic properties
	For meshes with anisotropic properties: orientation in the appropriate direction to match the physiological stretchability
Pore size	Depending on the used raw material and the foreign body reaction, respectively. To achieve a high effective porosity: for PP meshes a pore size ≥ 1000 µm should be used; for PVDF meshes a pore size ≥ 600 µm should be used

PP: Polypropylene; PVDF: Polyvinylidenefluoride.