**3. Evolvement of the polypropylene mesh as a material**

The concept of using a prosthetic material to reinforce a fascial defect was first developed to treat hernias. Theodore Billroth (1829–1894) stated that "If we could artificially produce tissues of the density and toughness of fascia and tendon the secret of the radical cure of hernia would be discovered" Czerny [23]. The first mesh material was made of metal. In 1902 silver filigrees were used to treat difficult to treat hernias [24]. The silver wires and other metals (tantalum and stainless steel) were used until recently [25] with reasonable success rates to treat large hernia defects however they were eventually abandoned due to their association with excessive abdominal stiffness, sinus tract formation, metal failure (corrosion and fragmentation) and patient discomfort.

Following the plastics revolution in 20th century and the advancements in polymer science many diagnostic and therapeutic medical and surgical instruments made of plastic became available. Plastics had obvious advantages over metals in soft tissue reconstruction with their ductility, lightweight and handleability [26]. Among the plastics used, polypropylene (PPL) possessed favorable physical properties such as high tensile strength with easy handleability. It could be made into a monofilament, have a high softening temperature (260°F), non wettable and resistant to chemicals. Usher first manufactured and experimentally tested first plastic mesh made of polypropylene [27]. The initial experimental data in dogs with knitted PPL confirmed that it allowed tissue ingrowth in between its fibers, it was strong with excellent tensile properties and it was resistant to infections when compared to other plastics.

heavy and light-weight mesh materials implanted for inguinal hernia repairs demonstrated less pain and less sensation of a foreign material with lighter meshes [36]. Thus the polypropylene mesh evolved over the years from a heavy weight, small pore sized mesh to a light-

Synthetic Materials Used in the Surgical Treatment of Pelvic Organ Prolapse: Problems…

http://dx.doi.org/10.5772/intechopen.76671

39

Efforts to make further improvements to the current surgical mesh are still ongoing. One strategy to modify the geometry/knitting pattern of PPL to make it mechanically more compliant with the pelvic floor [37]. Another strategy is enhancing the biocompatibility of PPL by coating it with more biocompatible materials to obtain a more favorable tissue response. An extracellular matrix coated PPL when implanted in rats demonstrated an inflammatory response that is more reflective of a tissue remodeling type rather than a fibrotic one [38]. There has also been research on degradable and hybrid degradable/nondegradable mesh materials. The main idea behind a degradable mesh was that it would be absorbed after a period of time by which time the patients' own tissues would have recovered and this would avoid the long term complications of permanent mesh like infection and fistula formation. Nevertheless polypropylene is still the most widely used polymer in mesh products used

**4. Modifications to the surgical technique to improve outcomes of** 

In parallel to improvements made to the material, modifications to the surgical technique were also made to reduce side effects and recurrences. Advances in both inguinal and abdominal hernia repair techniques can be observed mainly led by Usher and Rives [39]. Usher has also made contributions to developing the technique of hernia repair, mainly he introduced the concept of buttressing a sutured repair instead of bridging the gap with a mesh. On other words the mesh would not only just fit in the hole but be 2–3 cm larger to underlap with the underlying tissues. We will only review the improvements made to the surgical approach to incisional hernia repair in the abdominal wall, where we feel it is relevant to the pelvic floor repair. The abdominal hernia repair technique evolved from an 'inlay technique' where the mesh is placed inbetween the edges of the fascia defect to an 'onlay technique' where the mesh was placed on top of the repaired fascia defect in a tension-free manner. To further reduce the complications of mesh augmented repairs, a 'sublay (retrorectus) technique' was introduced where the mesh was placed underneath a well vascularized, thick muscle tissue (the rectus abdominis muscle) in-between two fascial layers (**Figure 1**). Proximity to a well vascularized wound bed is arguably a key factor in the success of this technique [40]. Additionally in the sublay technique, as opposed to inlay and onlay, mesh had less contact with subcutaneous tissues that prevented transmission of the infection from subcutaneous tissues to the mesh as it lies quite deep in the abdominal wall [41]. Abdominal hernias are heterogeneous with regards to why they occur and how extensive they are. No single technique is suitable or feasible for all types of hernias and different methods of repair may be indicated for specific defects and locations. Nevertheless the sublay technique appears to be superior to other techniques particularly in difficult to treat wound beds (for example poorly vascularized or repeatedly operated wounds) [42, 43].

weight, and large pore sized mesh material.

clinically at the time of writing.

**mesh-augmented hernia repairs**

The use of synthetic mesh has revolutionized hernia repair surgeries reducing the recurrence rates by 2–3 fold compared to traditional suture repairs [28]. However looking retrospectively it appears that PPL was far from being complication-free when first introduced into abdominal hernia repairs. Over the years, both the surgical implantation site and the material properties of the PPL have been modified to reduce the complication rates of mesh augmented abdominal hernia repair surgeries. A brief revision of the improvements made to the surgical technique and material characteristics over many years can provide a better understanding of the current clinical problem related to vaginal mesh products.

The initial plastic mesh was prepared from a monofilament 8 mils in diameter (200 μm), 42 × 40 per inch thread count by a simple taffeta weave. This mesh was then autoclaved and cut into desired patterns before implantation [33]. On the other hand, the modern surgical mesh constructed from a knitted polypropylene has smaller pores with an area density of 90–95 g/m<sup>2</sup> . These heavy-weight, first generation meshes are now known to cause a vigorous foreign body reaction and resulting dense scar tissue leading to a loss of the compliance of the abdominal wall [34].

Over the next few years heavy weight meshes were replaced by medium to light weight meshes that reduced the bulk of the foreign material leading to less inflammation, foreign body reaction, fibrosis and the associated pain sensation [34]. Also the pore sizes were made larger (macroporous). A study demonstrated that the bulk density of PPL (Prolene®) mesh could be reduced down to 25% of its original weight without significantly compromising its efficacy with reduced major and minor complications [35]. Also clinical studies comparing


**Table 1.** Milestones in the development of surgical mesh materials and their use in pelvic floor disorders.

heavy and light-weight mesh materials implanted for inguinal hernia repairs demonstrated less pain and less sensation of a foreign material with lighter meshes [36]. Thus the polypropylene mesh evolved over the years from a heavy weight, small pore sized mesh to a lightweight, and large pore sized mesh material.

possessed favorable physical properties such as high tensile strength with easy handleability. It could be made into a monofilament, have a high softening temperature (260°F), non wettable and resistant to chemicals. Usher first manufactured and experimentally tested first plastic mesh made of polypropylene [27]. The initial experimental data in dogs with knitted PPL confirmed that it allowed tissue ingrowth in between its fibers, it was strong with excellent tensile properties and it was resistant to infections when compared to other plastics.

The use of synthetic mesh has revolutionized hernia repair surgeries reducing the recurrence rates by 2–3 fold compared to traditional suture repairs [28]. However looking retrospectively it appears that PPL was far from being complication-free when first introduced into abdominal hernia repairs. Over the years, both the surgical implantation site and the material properties of the PPL have been modified to reduce the complication rates of mesh augmented abdominal hernia repair surgeries. A brief revision of the improvements made to the surgical technique and material characteristics over many years can provide a better understanding of

The initial plastic mesh was prepared from a monofilament 8 mils in diameter (200 μm), 42 × 40 per inch thread count by a simple taffeta weave. This mesh was then autoclaved and cut into desired patterns before implantation [33]. On the other hand, the modern surgical mesh constructed from a knitted polypropylene has smaller pores with an area density of 90–95 g/m<sup>2</sup>

heavy-weight, first generation meshes are now known to cause a vigorous foreign body reaction and resulting dense scar tissue leading to a loss of the compliance of the abdominal wall [34].

Over the next few years heavy weight meshes were replaced by medium to light weight meshes that reduced the bulk of the foreign material leading to less inflammation, foreign body reaction, fibrosis and the associated pain sensation [34]. Also the pore sizes were made larger (macroporous). A study demonstrated that the bulk density of PPL (Prolene®) mesh could be reduced down to 25% of its original weight without significantly compromising its efficacy with reduced major and minor complications [35]. Also clinical studies comparing

1963 Francis Usher (1908–1980) introduced first woven, plastic mesh made of polypropylene for hernia repair. 1995 [31] Ulmsten and Petros described the Integral theory of stress urinary continence and performed the first

1902 [24] First prosthetic mesh (silver filigrees) to be routinely used to treat difficult to treat hernias.

**Table 1.** Milestones in the development of surgical mesh materials and their use in pelvic floor disorders.

1948 [30] Formation of a darn using a Nylon suture for inguinal hernia repair.

2004\* First 'mesh kit' (Apogee®, Perigee®) cleared by FDA for POP.

1940 [29] Tantalum gauze fabric introduced

38 Pelvic Floor Disorders

intravaginal mesh-sling surgery 1996\* PPL (Marlex®) received FDA clearance for SUI.

1998\* First lightweight PPL mesh introduced. 2002\* First mesh product for POP (Gyneacare®).

Reviewed in Dällenbach [32].

\*

. These

the current clinical problem related to vaginal mesh products.

Efforts to make further improvements to the current surgical mesh are still ongoing. One strategy to modify the geometry/knitting pattern of PPL to make it mechanically more compliant with the pelvic floor [37]. Another strategy is enhancing the biocompatibility of PPL by coating it with more biocompatible materials to obtain a more favorable tissue response. An extracellular matrix coated PPL when implanted in rats demonstrated an inflammatory response that is more reflective of a tissue remodeling type rather than a fibrotic one [38]. There has also been research on degradable and hybrid degradable/nondegradable mesh materials. The main idea behind a degradable mesh was that it would be absorbed after a period of time by which time the patients' own tissues would have recovered and this would avoid the long term complications of permanent mesh like infection and fistula formation. Nevertheless polypropylene is still the most widely used polymer in mesh products used clinically at the time of writing.
