Types of Sutures

Absorbable and non-absorbable

The first classification is whether the body breaks the strand down. An absorbable suture is degraded in tissue over time; a non-absorbable suture is not, and is either removed once a surface wound has closed or left in place. Because a strand lying on the outside of the body can be taken out without reopening anything, non-absorbable materials are the ones that can be used where removal is practical — which is a fact about access, not about the material.

Within the absorbable group the more informative question is the mechanism. Synthetic absorbables — polyglycolic acid, polyglactin 910, poliglecaprone 25, polydioxanone — are cleaved by hydrolysis: water reaches the polymer backbone and breaks it, and the strand loses tensile strength before it loses mass. Catgut is purified collagen and is broken down by proteolytic enzymes instead, which couples its behaviour to the patient’s inflammatory response. Those two timelines — loss of strength, then loss of mass — are why strength retention and absorption period appear as separate figures in the instructions for use, and why neither is reproduced here.

Monofilament, multifilament and barbed

The second axis is construction. A monofilament is extruded as a single filament. A multifilament is many fine filaments braided or twisted into one strand, which gives the strand interstices between the filaments — the origin of capillarity, and the reason coating is a braid’s companion rather than an optional extra.

Barbed sutures are a third form: monofilaments with projections formed on the surface that engage tissue along the strand’s length, so the strand’s position is held by the barbs rather than by a knot. They are made in polydioxanone, poliglecaprone and polypropylene.

Monofilaments in general use include polypropylene, nylon, PVDF, PTFE, stainless steel, poliglecaprone and polydioxanone. Braided multifilaments include PGA, polyglactin 910, silk, polyester and UHMWPE; catgut is twisted rather than braided. See the suture materials chart for a side-by-side view.

Natural and synthetic

The third axis is the origin of the raw material. Natural fibres are derived from a living organism — catgut from purified collagen, silk from the silkworm fibre. Synthetic fibres are polymers produced by chemical synthesis, and they make up most of the materials in current use. The axis matters mainly because it tracks the absorption mechanism: the collagen-based material is the enzymatically degraded one.

Coated and uncoated

The fourth axis is the surface. A coating is a thin layer applied over the strand as manufactured, by dipping, brushing, spraying, roll, spin or flow coating. Coating is normally applied to braided rather than monofilament strands, because a braid has the surface texture that a coating addresses and takes a coating more readily.

Coating materials in use include polycaprolactone, calcium stearate, silicone, wax, PTFE and chromium salts. Coatings such as chlorhexidine, triclosan or silver ion may be applied to a suture as a surface coating in addition to the regular coating materials.

Coated materials include PGA, chromic catgut, polyglactin 910, silk, polyester, poliglecaprone and polydioxanone. Uncoated materials include polypropylene, nylon, PVDF, UHMWPE, stainless steel and PTFE.

Size and application

Sutures are also grouped by gauge and by intended application. Gauge is designated on the USP scale with a parallel metric figure; the USP fixes both the diameter range and the tensile-strength requirement at each size, and the European Pharmacopoeia sets an equivalent standard. The suture sizes chart sets out the ranges for collagen and synthetic materials.

Application groupings — general, cardiovascular, orthopaedic, dental, gynaecological, veterinary, cosmetic, ophthalmic — are the loosest of the classifications, because a given material may appear across many of them. What usually changes with the application is not the polymer but the size, the strand length and the needle profile.