Sutter Characterization

Sutures, whose primary purpose is to provide temporary mechanical support to tissue, are used to hold tissues together following surgical procedures or injuries that result in bodily incisions. Sutures are characterized by their tensile strength, dimensions, filament structure, surface texture, degradation properties, and the materials from which they are made.

Tensile Strength

The strength value of sutures that hold opposing wound regions together until the tissue regains its own strength is importance. Sutures must be selected with tensile strength appropriate to the tissue into which they are implanted. If the tensile strength of a suture chosen for a wound is too low, it will not provide adequate tissue support for healing; if it is too strong, it may cut through the tissue. Therefore, for suture selection, both linear and knot tensile force important are key parameters. A knotted suture has approximately one-third the tensile strength of the same material in an unknotted state.

Tensile strength is defined by the United States Pharmacopeia (USP) as the weight required to break a suture divided by its cross-sectional area. The standard for determining tensile strength in sutures is based on the zero count in suture size codes. As the cross-sectional diameter decreases, the zero count in the size designation increases. In this system, a 4-0 suture has a larger diameter and greater strength than a 6-0 nylon suture.

Sutures made from polyglactin 910 (Vicryl), polyester (Velosorb), polyglyconate (Maxon), polydioxanone (PDS, PDO), and poliglecaprone 25 (Monocryl) like synthetic exhibit high tensile strength. Natural sutures such as silk, catgut, and chromic catgut have low tensile strength. Generally, synthetic materials are stronger than natural ones.

Suture Size

Two standard systems are used to designate suture diameter. The more widely adopted system is the United States Pharmacopeia (USP) classification, while the other is the European Pharmacopeia (EP). In both systems, suture sizes are expressed using size codes. In the commonly used USP classification, sizes such as 3/0 and 4/0 are used, where an increase in the number before the zero indicates a decrease in suture diameter. In the EP standard, size codes range from 0.1 to 10. In this system, dividing the assigned code number by 10 gives the minimum diameter of the suture.

Filament Structure

Sutures are classified into two types based on filament structure: monofilament and multifilament. Multifilament sutures may be braided or twisted. Although these sutures offer greater ease of handling, flexibility, and knot security compared to monofilament sutures, their higher inflammatory response and capillary action increase the risk of infection. The disadvantage of multifilament sutures having a rough surface is often mitigated by applying a surface coating.

Surface Design

Suture surfaces can be either smooth (standard) or barbed. Barbed sutures have sharp projections along their surface that anchor the suture into the tissue. In standard sutures, this anchoring is achieved through knots, which secure the stitch. Barbed sutures eliminate the need for knot placement and offer significant advantages in deep surgical areas where minimal manipulation is required.

Degradation Properties

Based on degradation properties, sutures are classified as absorbable or non-absorbable. Absorbable sutures lose their tensile strength within 60 day and are absorbed by the body. Sutures that do not meet these criteria are classified as non-absorbable. The properties of absorbable sutures are evaluated based on two parameters: the rate of mass loss due to tissue dissolution and the duration for which tensile strength is maintained.

Material Composition

Sutures can be either natural or synthetic, depending on their material composition. Common natural sutures include absorbable silk and non-absorbable chromic catgut. Natural sutures have disadvantages compared to synthetic sutures, such as a higher inflammatory response and uneven power distribution along the suture. Natural sutures are composed of proteins that degrade via proteolysis, while synthetic sutures are copolymers that degrade via hydrolysis.