Knotless Closure and How Barbed Sutures Anchor

Knotless closure is soft-tissue approximation using a barbed suture, in which anchorage comes from barbs cut into the surface of a monofilament engaging the tissue along the strand's length rather than from a tied knot at either end.

By Dolphin Sutures Reviewed by Dolphin Sutures Last reviewed July 19, 2026

Why it matters

A tied knot concentrates the holding function at two points. A barbed strand distributes it along the whole length that has passed through tissue, which is a different mechanical arrangement rather than a refinement of the same one. Understanding that the barbs are cut into the strand — subtracted from a monofilament, not added onto it — is what explains why barb geometry, strand diameter and termination are discussed together.

Anchorage without a tie

In a conventional closure the holding function sits at two points: the knot at the start and the knot at the end. Everything between them is a smooth strand passing through tissue and carrying load between those two anchors.

A barbed strand rearranges that. The barbs engage tissue along the whole length that has passed through it, so the holding function is distributed rather than concentrated. This is why “knotless” describes an arrangement rather than an improvement: the anchorage has moved, not disappeared.

The barbs are cut, not added

The single most common misunderstanding about barbed suture is that something has been attached to the thread. It has not. The barbs are cut into the surface of a monofilament, raising a projection out of the strand’s own material — which means the manufacturing process removes material rather than adding it.

That has a direct consequence: the diameter left after cutting is not the diameter of the uncut strand. Core diameter and gauge are separate specifications for that reason, and both belong to the product rather than to the technique.

Cut angle, depth and how the barbs are distributed around the circumference are manufacturing parameters, fixed when the strand is made.

Why direction decides the ending

If every barb rakes the same way, nothing along the strand opposes them, and the far end has to be anchored somehow. That is what the loop at the end of a unidirectional strand is for — the needle end passes through it and the run begins from a fixed point.

A bidirectional strand solves the same problem differently. Its barbs rake away from a midpoint in both directions, so the two halves pull against one another and the strand anchors against itself. It needs no loop, and the reason is structural rather than a matter of preference.

The smooth band at the centre of a bidirectional strand is where that reversal happens. No barb can sit exactly at the point where the rake changes direction, so the transition zone is left uncut.

Key terminology

Barb: A cut made into the surface of a monofilament, raising a projection that yields in one direction and engages in the other. It is subtracted from the strand, not attached to it.
Unidirectional: A strand whose barbs are all raked the same way. Because nothing opposes them, the far end must be anchored — commonly by a loop through which the needle end is passed.
Bidirectional: A strand whose barbs rake away from a midpoint in both directions, so the two halves oppose one another and the strand anchors against itself.
Transition zone: The smooth central band on a bidirectional strand where the rake reverses and no barb can sit.
Loop: A closed loop formed at one end of a unidirectional strand, used as the anchor point at the start of a run.
Core diameter: The diameter of the strand remaining after the barbs are cut. Cutting into a monofilament necessarily removes material, so core diameter and the uncut gauge are not the same figure.

Technical characteristics

Construction: Monofilament with barbs cut into the surface
Anchorage: Distributed along the barbed length rather than at a tied knot
Unidirectional form: Barbs raked one way; terminated with a loop at the far end
Bidirectional form: Barbs raked away from a central transition zone in both directions; no loop
Barb geometry: Cut angle, depth and spiral spacing are manufacturing parameters, product-specific
Material: Barbed sutures are made from absorbable and non-absorbable monofilament polymers depending on the product
Strength retention and absorption: Stated in the instructions for use supplied with the product — product-specific and not reproduced here.
Indications: Stated in the instructions for use. Approved indications vary by product and market.

How it compares

Construction and termination. These describe how each form is built and finished, not how either performs.
Form	Barb direction	How it anchors	Termination
Unidirectional barbed	All barbs raked the same way	Against tissue along one direction of travel	Loop at the far end
Bidirectional barbed	Raked away from a central transition zone	The two halves oppose one another	No loop; each half anchors the other
Smooth monofilament	Not applicable	At the tied knot	Knot
Coated braid	Not applicable	At the tied knot	Knot

What clinicians weigh when selecting

Where the holding function sits

The relevant difference is between anchorage concentrated at two knots and anchorage distributed along the barbed length. That is a change in arrangement, and what it means for a given closure is a judgement about the closure.

Barb direction and termination

A unidirectional strand has nothing opposing its barbs, which is why it carries a loop. A bidirectional strand opposes itself and does not. The two are terminated differently because they anchor differently.

Cutting into the strand

Barbs are cut, so material is removed. Core diameter and the uncut gauge are different figures, and both are product specifications rather than properties of the technique.

Handling is not the same as knotting

A knotless strand removes the tie-down step and introduces others. Whether that suits a given procedure is a technique judgement for the operator.

Barb geometry is a manufacturing parameter

Cut angle, depth and how the barbs are distributed around the circumference are set in manufacture and stated per product. They are not adjustable at the point of use.

The instructions for use govern

Approved indications, warnings and any handling guidance are stated in the product's instructions for use, and they vary by market.

Frequently asked questions

Are the barbs attached to the suture?

No. They are cut into the surface of a monofilament, so the projection is raised from the strand's own material. Nothing is added to the outside of the thread.

Why do unidirectional barbed sutures have a loop?

Because every barb is raked the same way, nothing opposes them along the strand, so the far end needs an anchor point. The loop provides it. A bidirectional strand does not need one because its two halves oppose each other.

What is the smooth band in the middle of a bidirectional suture?

The transition zone, where the rake of the barbs reverses. No barb can sit at the point of reversal, so that band is left smooth.

Does a barbed suture still need a knot?

The construction is designed to anchor without one, which is what "knotless" describes. How a given product is intended to be started and finished is stated in its instructions for use.

Are barbed sutures absorbable?

Both absorbable and non-absorbable barbed monofilaments exist. Which a given product is, and its strength-retention and absorption profile, is stated in its instructions for use.

Is knotless closure faster?

We do not publish comparative speed or performance claims. The construction removes the tie-down step and changes how the strand is run; what that means in practice is a matter for the operator and the case.

The product Polypropylene Barbed Sutures (Polybarb) Polybarb is a non-absorbable polypropylene barbed suture from Dolphin Sutures — a knotless wound closure device whose barbs spiral along the whole strand, supplied as a unidirectional loop with one swaged needle. See the product → The range Specialty Sutures Feature sutures beyond standard materials — triclosan-coated antibacterial sutures and barbed knotless sutures — that add an antibacterial coating or a self-anchoring barbed design to established suture polymers. View the range →

Instructions for use

The instructions for use supplied with the product is the controlled document for indications, contraindications, strength-retention and absorption data, warnings, precautions and handling. Where this article and the instructions for use differ, the instructions for use govern. Approved indications vary by market. Surgical technique remains a matter for the operating surgeon.

Medical & regulatory notice

This article is general reference information for healthcare professionals about how a suture construction anchors. It is not medical advice, not surgical instruction, not a recommendation for any technique, procedure or patient, and not a substitute for the instructions for use supplied with the product or for clinical judgement. Product availability and approved indications vary by market. Dolphin Sutures manufactures surgical sutures; nothing here should be read as a claim of clinical benefit or of superiority over another material or technique.

References

Written by Dolphin Sutures Medical content, reviewed before publication

Reviewed by Dolphin Sutures In-house regulatory and quality review

Last reviewed July 19, 2026 Reviewed on a scheduled cycle