Permanent prosthetic mesh implants are made of material that do not degrade over time. On the other hand absorbable meshes are degraded by hydrolitic enzymatic activity. Biological meshes are made from collagen rich porcine, bovine or human tissues from which all antigenic cellular tissues have been removed.
Types of prostheses:
The prosthetic material used in hernia repair is one of two basic categoties:
Synthetic
Biological
Synthetic Prosthesis:
a) Metal prosthetic graft material
Silver filigree mesh: used in the early 20th century, became brittle over time and fractured finally extruding causing multiple sinuses and fistulas.
Tolinox (Stainless steel): set up chemical reactions due to changes in its constituent composition.
(These prostheses are long out of favour due to high rate of complications and poor patient acceptability)
b) Non-Metal (polymeric) synthetic prosthesis
Nylon: Initially used for sutures but later woven into patches for hernia repair. First used in 1944 replacing rubber, metal and animal products. Disintegrates in vivo in six months.
Polythene mesh (trade name Marlex): first used in 1958; resistant to chemicals and sterilizable but unravelled after cutting.
Polypropylene mesh (trade name Marlex, Prolene, Surgipro etc): Originally modified from polythene in 1962. Widely used for last 20 years on account of strength, stability and ease of handling. Not all are equal in density weave and porosity. Growing evidence suggests that low density and larger pore size may lead to decreased inflammatory response and less contracture as it forms a thinner scar "net" and not a thick scar "plate". Available as a flat mesh as well as 3-dimensional devices. (Altex, Hermesh3, PerFix plug, Prolene Hernia System)
Polyester mesh (trade name Mersilene): First used in 1984; is hydrophilic with less scar tissue contracture than heavy weight polypropylene. As compared to prolene it is softer, more pliable and sticks to tissue less.
Polytetrafluoroethylene: Typically solid but can be woven. Tissue response to PTFE is characteristic of mesothelialization along with a less chronic inflammatory response than polypropylene. Must be removed if infections occurs.
Polyglycolic acid(Dexon) and Polyglactin (Vicryl) mesh: Absorbable meshes (8-12 weeks). Not to be used as sole mesh in repair of abdominal and groin hernias.
Biological Prostheses:
These are used in cases with increased risk of infection, contaminated operations or in exposed wounds to prevent evisceration. These are derived from human and non-human (porcine and bovine) sources including hand harvested human dermis or dermal collagen, porcine small intestinal submucosa, bovine pericardium or fetal bovine dermis. However there is no data to indicate that these products are strong enough to bridge large defects in the long term thus limiting their use in routine abdominal wall hernia repair. They provide a good initial performance in contaminated environments but relatively poor results in terms of long term hernia recurrence compared with retromuscular placement of synthetic prostheses.
Composite meshes:
Exposure of mesh
Composite meshes are 2 types:
Absorbable barrier:
Where the prosthesis remains long enough for the body to cover the mesh with a mesothelial layer.
Sepramesh: Consisting of macroporous polypropylene on one side and bioabsorbable non-immunogenic membrane of N-hyaluronate and carboxy-methyl cellulose on the other.
Parietex: Composed of multifilament polyester mesh with a purified, oxidised bovine atelocollagen Type 1 coating covered by an absorbable anti adhesion film of polyethylene glycol and glycerol.
Parientene:
Proceed:
2. Non-Absorbable barrier:
Bard mesh:
Gore-Tex dual mesh:
Composite meshes without barrier: These consist of thin filaments of Vicryl and Prolene or Monocryl and Prolene twisted and knitted to form a mesh which is partially absorbable as they have 40% Monocryl or Vicryl. These provide enough strength to the tissues and optimum mobility to he abdominal wall.