In medical dramas, surgeries end with a shot of tying off the suture. It is not as simple as thinking the biggest hurdles are cleared after removing the lesion and reconnecting blood vessels or nerves. Pull the knot too tight and blood flow is cut off; make it too loose and the wound edges separate and fester.
A surgeon and a mechanical engineer joined forces to develop a knot that helps even novice doctors achieve a perfect closure. When you pull the suture until the pre-tied knot releases, the incision edges come together perfectly. It effectively adds a kind of brake so the tension applied to the suture is neither excessive nor insufficient.
Surgery professor Cai Xiujun and aerospace engineering professor Li Tiefeng at Zhejiang University School of Medicine said they developed a way to program a surgical suture knot to release when pulled with a specific force by precisely controlling the knot's geometric structure and friction, according to a paper published in Nature on the 27th.
Surgeons judge how hard to pull a suture by eye and feel, a skill that takes years to master. The "slipknot" developed by the team helps anyone suture as well as an experienced physician.
The knot is a loop that releases when one end of the thread is pulled. When tying off at the suture site, you simply pull until the slipknot on another part of the suture releases. In rat experiments, the team said colon surgery using the slipknot restored blood flow faster and caused fewer leaks and scars compared with conventional suturing.
Li said, "The slipknot looks simple, but its internal mechanics are complex," adding, "As the knot releases, the thread bends, twists or slips and generates friction, and the knot's geometry changes very rapidly." Using physics, the team designed the slipknot to apply proper tension to the suture.
First, they experimentally identified the factors that cause knots made from different threads to release. Based on those results, they derived equations describing the relationship between the force required to release the knot and characteristics such as the tightness of the knot and the thread's surface roughness. The team said surgeons could either use thread pre-tied with a slipknot or employ a device that creates a slipknot as needed.
The team said the technique will be especially useful in laparoscopic and robotic surgeries, where doctors do not rely on tactile feedback. If the surgeon commands the robot arm to pull the suture until the slipknot releases, the incision can be closed with appropriate force. With artificial intelligence (AI), a robot could learn to pull the thread only until the slipknot releases.
Garnette Roy Sutherland, a neurosurgeon and robotics developer at the University of Calgary's medical school, told Nature the same day, "Sutures have seen no substantive change for decades," adding, "If sutures like those proposed by the authors are applied in the clinic, it would be a significant advance beyond current surgical techniques."
References
Nature (2025), DOI: https://doi.org/10.1038/s41586-025-09673-w