Silk Sutures

From raw filament to surgical strand

Surgical silk begins as a natural filament spun by the silkworm. As spun, it is not one substance but two: a core of the structural protein fibroin, and a surrounding gum — sericin — that coats the filament and binds filaments together. The gum is not wanted in a suture. It is removed by degumming, and what is left is the fibroin filament.

Degumming is the step that makes the rest possible. Raw silk with its gum intact cannot be braided into the compact, uniform strand a suture has to be; the processing removes the extraneous material while leaving the filament’s natural body and elasticity, and only then is the fibre braided. Everything downstream — the braid, the coating, the gauge — is working on a degummed filament.

Non-absorbable, and not unchanging

Silk is classed non-absorbable, and silk loses strength in tissue over time. Both of those statements are true, and holding them together is the most useful thing on this page.

The resolution is in what the classification asks. A non-absorbable material is one the body does not break down and metabolise the way it handles an absorbable suture — a process coupled to wound healing and measured on that timescale. Silk is not handled that way, and it is classed accordingly. But silk is a protein. Its chain is joined by peptide bonds, the same hydrolysable linkage found in the body’s own proteins and the bond that proteolytic enzymes act on. A protein sitting in living tissue is not in a chemically indifferent environment, and over long periods the strand does change.

This is a material-science observation, not a performance statement. What it means for any particular product — how much strength, over what period — is exactly the kind of figure that belongs in the instructions for use and nowhere else, and it is not reproduced here.

Polyamide makes the same point from the synthetic side: an amide bond is a hydrolysable bond, and nylon slowly hydrolyses in vivo while remaining non-absorbable. Silk and nylon are the two materials in this class that reward reading the category precisely. Polypropylene, polyester and steel do not change in this way, and the difference between the two groups is chemistry rather than classification.

The braid and the coating

Silk is braided — many fine filaments worked into a single strand. The braid is what gives it pliability and the particular way it seats a knot, and it is the property most often remarked on in the hand.

The same construction leaves interstices between the filaments and gives the strand surface texture, which is why silk is coated; wax and silicone are the usual coatings, and they alter how the strand passes through tissue and how a knot ties down. The coating is a response to the braid rather than an addition to it. Capillarity follows from the braid too, and whether it matters is a question about the surgical field rather than about the material.

Silk is commonly supplied dyed black — an identification and visibility aid with no bearing on how the material behaves. Colour and gauge availability are product-specific; the product page lists what is offered.