Suture Materials

Introduction

There are several different ways of categorising suture material, which can seem confusing. They can be categorised into absorbable/non absorbable or braided/monofilaments

Absorbable sutures

Absorbable materials (E.G. catgut) are designed to be fully absorbed, and they begin to loose their tensile strength from the first day that they are used in surgery. The material is absorbed through phagocytosis or hydrolysis. Clearly it is important that the strength reduces at the same rate that the wound gains strength. Absorbable sutures commonly used for tissue closure prior to the closure of the skin layer. Some absorbable suture materials have antibacterial properties to aid with asepsis.

Absorbable materials include:

• Catgut; made from sheep intestinal submucosa or cattle intestinal serosa, catgut is highly antigenic and can cause a profound tissue reaction which make the rate of absorption unpredictable. Catgut is available coated with chromic salts which lessens this effect.
• Polyglactin 910 (‘Vicryl’) is commonly used in as a synthetic alternative to catgut, as it is far less antigenic. It looses 45% of its tensile strength by day 14 post operatively, and 90% at 28 days. Polyglactin 910 is coated to reduce tissue drag and to improve the material's knotting characteristics.
• ‘Vicryl Rapide’ is a modified polyglactin 910 that has 70% less tensile strength than ‘Vicryl’ and is used mostly when an absorbable suture is required for skin closure.
• Polyglcolic Acid (‘Dexon’) is a coated synthetic absorbable material which looses its strength by 33% in 7 days It has high tissue drag despite being a coated material and poor knot security
• Polydioxanone (‘PDS’) has a slow rate of hydrolysis, which makes it ideal for extended tissue support. It looses 25% of its tensile strength after 14 days. The material has low tissue drag, which minimises tissue trauma, and is often used to suture tendons and fascia. Polyglyconate (‘Maxon’) is a similar material to ‘PDS’.
• Poliglecaprone 25 (‘Monocryl’) has a high tensile strength initially when compared to other absorbable materials, but it looses this strength rapidly; 40% in 7 days. It is commonly used for intradermal and subcutaneous wound closures.

Non absorbable sutures

• Silk (e.g. ‘Mersilk’) is a natural fibre that does degrade and is absorbed, but this occurs so slowly that the material is classified as non absorbable. It does induce considerable tissue reaction, and has significant capillary action, so can never be used in the presence contamination or established infection. It is mainly used for ligatures, and is available in a coated form to reduce the capillary action of the fibre. Knot security can be a problem with this material.
• Nylon (‘Ethilon’) is used predominantly for skin sutures as it has a high tensile strength, but the material's ‘memory’ – where the suture reverts back to the packaging shape – makes it hard to handle and knot security is poor.
• Polypropylene (‘Prolene’) is similar to nylon, but the material flattens when knotted which improves knot security. It induces little reaction once placed and is used for vascular surgery or when placing meshes in large uncontaminated wounds.
• Stainless steel is mainly used in haemostatic clips or skin staples to facilitate rapid wound closure. It is strong but fatigues easily. Stainless steel is available as a flexible suture material but it is difficult to use - it is indicated when a protracted time for tissue healing is required such as cases of significant wound breakdown in vital structures such as the linea alba.
• Tissue adhesives (‘Vetbond’, ‘Vetseal’) are indicated for the repair of small partial thickness wounds and some 'small furry' surgeries. The glue should be applied to a dry wound with adequate haemostasis as it polymerises quickly on contact with moisture. Adhesives are contra-indicated in the eye area because of the risk of accidental application into the eye.

Monofilament sutures

Suture material can also be classified as monofilament of braided: a monofilament material is a single strand of material which gives it the advantage of less tissue drag and no internal spaces to harbour bacterial growth when compared to braided filaments. Monofilament materials, however weaken if they are roughly handled during placement and have reduced ease of handling and knot security when compared to braided filaments.

Braided sutures

Multifilament or braided suture materials are comprised of several strands of material twisted together and coated to give them greater handling characteristics with good knot security and reduced tissue drag. They are contra-indicated in contaminated or infected tissues as bacteria can easily become established within the braided material where they remain undetected by the immune system.

A summary of the various materials available and the categories of suture material is as follows:

	Monofilment	Braided (Multifilament)
Absorbable	Catgut Polydioxanone (‘PDS’) Polyglyconate (‘Maxon’) Poliglecaprone 25 (‘Monocryl’)	Polyglycolic Acid (‘Dexon’) Polyglactin 910 (‘Vicryl’)
Non-absorbable	Nylon (’Ethilon’) Polypropylene (‘Prolene’) Stainless Steel (suture material)	Silk Stainless Steel (staples)

Suture Material sizes

Suture materials come in a variety of sizes and strengths. Use the smallest diameter that will adequately hold the tissue to minimise tissue trauma and reduce knot size whilst matching the strength of the suture material to the tissue.

There are several systems of sizing suture material; the metric system which indicates the diameter of the material, and the USP (United States Pharmacopeia) system which is more commonly used. With synthetic materials and catgut the USP system sizes these two classes of material differently; for example, 3-0 ‘Vicryl’ is the equivalent to 4-0 catgut in terms of the actual diameter of the suture material.