Examples of two prototypes of acellular biological materials are discussed: Surgisis® and Permacol®.

Surgisis (Cook Surgical, Bloomington, Indiana, USA) was produced following studies by Hodde et al. [11] describing the development of an extracellular matrix (ECM) made from sterilized porcine small bowel mucosa with its ECM components. Related studies by Cook Surgical postulated complete new tissue regeneration, which was qualitatively similar to the surrounding tissue [12]. As yet, there have been no long-term randomized studies to prove its superior quality. Clinical results comparing Surgisis with other meshes for use in diaphragmatic hernia demonstrated a similarly high recurrence rate of 50% [13]. Our own animal studies demonstrated that 4 months after insertion Surgisis had disintegrated and had been substituted by lower-quality scar tissue, resulting in inferior mechanical quality compared with a polypropylene mesh [14–17]. No improvement of tissue tensile strength was found when comparing animals implanted with Surgisis with control animals without mesh [18]. In a rat model, animals with Surgisis had a much lower tensile strength compared with polypropylene [19].

Surgisis did not show any convincing advantage compared with synthetic materials with respect to seroma formation, adhesions, tensile strength [20], shrinkage [21], and recurrence rates following hernia repair [22].

In summary, the insufficient mechanical strength of Surgisis renders it unsuitable for any application where mechanical support is essential [23], e.g., pelvic prolapse surgery.

Permacol (acellular cross-linked porcine dermal matrix) is another type of biomaterial that is regularly inserted in different hernia locations, including parastomal hernias, and plevic prolapse surgery [24]. Within this group of crosslinked meshes, collagen molecules are covalently bound to each other following chemical processing. This protects the material to a certain degree against degradation by host tissue collagenases. In a study, Permacol showed satisfactory tensile strength over 6 months and better mechanical properties compared with other cross-linked materials [20]. Another study demonstrated a lower hernia recurrence rate with Permacol compared with polytetrafluoroethylene (PTFE) [25]; however, the follow-up time was short and patient numbers were small. In prolapse surgery, clinical short-term results were shown to be promising [26].

However, several recent studies have revealed problems with the use of biological meshes. In a long-term follow-up study using different materials for abdominal incisional hernia repair, Permacol did not show an advantage compared with synthetic meshes [25]. In a clinical study, the recurrence rate of incisional hernia at 18 months using Permacol was 15%, with a complication rate of 35% (e.g., wound infection) [27]. This is no improvement on currently used synthetic meshes. The fistula rate following the use of Permacol intra-abdominally is low, but not unheard of; equally, bowel adhesions with the need for re-intervention have been described [6].

Additionally, Permacol has shown a marked inflammatory response in rats up to 40 days postimplantation, and no ingrowth of skeletal muscle cells [28].

The cross-linked Permacol has demonstrated better mechanical qualities compared with non-cross-linked materials [20], but inferior qualities compared with synthetic meshes. Similar findings were shown in an animal study comparing Pelvicol® with Pelvisoft®, Gynemesh®, and Surgisis. The polypropylene-based Gynemesh showed the highest tensile strength and least stiffness compared with the cross-linked Pelvicol. In addition, Pelvicol showed encapsulation after 3 months insertion time, whereas Gynemesh was found to be incorporated [29]. A clinical study using Surgisis or Pelvicol for sacrocolpopexy at 2 years follow-up found the anatomical recurrence rate to be very high (70%), with a functional recurrence rate of 40% [30].

These results compare very badly with studies on prolapse surgery using synthetic meshes. On the other hand, long-term clinical follow-up results on the use of synthetic mesh for laparoscopic anterior rectopexy for rectal prolapse describe very low recurrence rates of no more than 5% [31, 32].

Additionally, the hope for superior behavior of biological materials within a contaminated area is contradicted by multiple studies. Following inoculation of meshes with bacteria, findings have indicated a possible higher tendency of infection when using biological materials [33]. Additionally, inoculation seems to weaken the tensile strength of the biological mesh [34].

In summary, biological materials have not shown convincing superiority compared with synthetic nonabsorbable meshes in hernia repair [35, 36], or in prolapse/pelvic floor surgery [37–39]. Another disadvantage with biomaterials is their inconsistent ECM composition (e.g., type and amount of collagen). Therefore, their functional outcome is not predictable, plus, this inconsistency renders them unsuitable for surface modulation.

The search for the ideal mesh is ongoing. The advantage of synthetic meshes is the possibility of modifying the surface of currently available commercial meshes (Fig. 27.1) [56–59]. It is possible to add active agents such as antibiotics, protein- repellent substances, and inflammatory response proteins. Also, one can configure a three-dimensional scaffold that allows cell inoculation according to the required needs. Ongoing in vitro research is attempting to establish a system in order to test cell interaction with different biomaterials [60–64]. Controlled release of active substances (e.g., antibiotics, cytokines, growth hormones) bound to the mesh is also easily achieved [65].