UHMWPE Sutures

What “ultra-high-molecular-weight” names

Polyethylene is the simplest of the polyolefins — a chain of repeating ethylene units, a backbone of carbon and hydrogen and nothing else. That description fits every grade of polyethylene ever made, which is the place to start from: the grades do not differ in what the chain is made of. They differ in how long the chain is, and in how readily the chains pack against one another.

“Ultra-high-molecular-weight” is a statement about the first of those. It says the chains are very long — a high degree of polymerisation — and says nothing about a different monomer or a different linkage. A reader arriving at the term expecting an exotic chemistry finds the same ethylene unit as in any other polyethylene, at a very different chain length.

Chain length has a processing consequence. Chains that long are heavily entangled and do not flow the way shorter polyethylene grades do, so producing a filament from the material involves a route that draws and orients those long chains along the axis of the fibre. That is a fact about how a fibre is made, not about how a suture behaves in a procedure.

The strand is a blend

UHMWPE suture as supplied is not 100% UHMWPE. It is braided with polyester, so a single strand carries two different backbone chemistries at once: the carbon–carbon chain of the polyolefin, and the ester-linked aromatic chain of polyethylene terephthalate.

Both are classed as non-absorbable. The polyethylene backbone offers nothing for water or a tissue enzyme to cleave — there is no ester, no amide, no peptide bond in it — and suture-grade polyester is likewise not appreciably degraded or metabolised in tissue. The blended strand is therefore non-absorbable: it is not broken down by the body.

The blend matters for a second reason, which is how this article should be read. UHMWPE fibre turns up in a good many places outside the operating theatre, and whatever is known about it there was learned about a fibre rather than about this strand. What is on the reel is a braid of two polymers, and its properties belong to that braid.

The braid, and what follows from it

Braiding many fine filaments into one strand is what gives a multifilament its pliability and the way it seats a knot, and it is the most immediate difference between a strand like this one and a monofilament such as polypropylene.

The same construction has two further consequences. It leaves interstices between the filaments, and it gives the strand surface texture — which is why braided sutures are the ones that get coated. A coating is a response to the construction rather than an addition to it; a monofilament has no braid to smooth. Whether a particular product is supplied coated is stated on its product page and in its instructions for use.

Capillarity follows from the same source. It is the tendency of a multifilament to draw fluid along its length by wicking, it is absent from a monofilament by definition, and whether it is a relevant consideration in a given case is a question about the surgical field rather than about the spool on the shelf.

Colour, and where it sits in the class

UHMWPE suture is supplied undyed with a blue tracer — a coloured element carried within the braid, so that an otherwise undyed strand can be told from another during a procedure. Whether two distinguishable strands are useful in a given closure is a question about the operative plan.

The non-absorbable class is the least homogeneous of the suture families. It holds a metal, a natural protein fibre, and a set of synthetics whose backbones have little in common with one another. UHMWPE with polyester is unusual even there, in being a blend of two synthetics braided into one strand. Being non-absorbable is a statement about what the body does not do to the material; what a given product is approved to be used for is a separate question, and its instructions for use is where that is answered.

Dolphin Sutures manufactures UHMWPE suture under the brand name Durafibr.