Nature's smart cutting system could transform surgery and reduce patient harm

Scientists at Heriot-Watt University have unlocked the secret behind how female sawflies make such specific cuts - a discovery that could revolutionise surgical instruments and dramatically reduce the cutting of healthy tissue during operations. The breakthrough research reveals how these tiny insects use a completely passive cutting system that automatically knows which materials to slice through and which to leave untouched, all without any sensors or computerised controls.

The study, published in peer-reviewed journal Bioinspiration & Biomimetics, demonstrates how the sawfly's egg-laying organ – called an ovipositor – acts like a biological reciprocating saw that instinctively knows when to cut and when to push material aside.

How nature’s smart cutting system works

Female sawflies must cut into plants to lay eggs without killing the plant host which provides food for the developing larvae. The two toothed blades slide against each other but only cut materials below a certain strength threshold. This natural selectivity prevents damage to the vital plant structures whilst allowing the insect to create precise incisions for egg laying.

Dr Martí Verdaguer Mallorquí has been leading the study at Heriot-Watt University in partnership with experts from National Museums Scotland and Senckenberg German Entomological Institute in Müncheberg. The team also used facilities from the Faculty of Biology at the University of Freiburg in Germany under the leadership of Professor Thomas Speck, Head of the Plant Biomechanics institute.

Dr Verdaguer Mallorquí said: "We've discovered something remarkable – a cutting mechanism that essentially thinks for itself. The sawfly's egg-laying organ can cut through soft plant tissue but automatically avoids the plant's tough internal "plumbing" including the tubes that carry water and nutrients. This ensures the plant survives and serves as a food supply for the larvae coming from the eggs. This selective cutting happens purely through the tooth geometry and composition interacting with different material properties of the plant. There are no sensors or computers but rather elegant engineering refined by millions of years of evolution."

Scaling up and testing the technique

The research team, led by Professor Marc Desmulliez from the School of Engineering & Physical Sciences at Heriot-Watt University, scaled up the sawfly's cutting mechanism 400 times and tested it on laboratory substrates that mimic human tissue properties. They found the system operates on an ultimate stress threshold – below this threshold, materials are cut cleanly, but above it, they are harmlessly displaced out of the cutting zone.

Professor Desmulliez explains: "This discovery has profound potential implications for surgical practice. Current surgical tools often struggle in complex operations. Surgeons frequently work in blood-flooded environments where visibility is poor and the risk of accidentally cutting vital structures is high. A surgical instrument based on this natural mechanism could instinctively avoid critical tissues whilst cutting precisely where it is needed – essentially giving surgeons a tool that helps prevent mistakes. Further input is now needed from surgeons but this newly discovered mechanism has tantalising prospects."

The team studied two sawfly species called Rhogogaster scalaris and Hoplocampa brevis, using advanced electron microscopy and 3D imaging to decode the precise geometry of their cutting teeth. They discovered that small serrations work in concert with larger protrusions to create the selective cutting action, with different tooth designs optimised for cutting different plant tissue layers.

Solving surgery challenges

When the researchers interviewed and surveyed surgeons about current surgical tool limitations, 86% reported that blood accumulation impairs visibility and increases mistake likelihood. Nearly 80% expressed concerns about accidental tissue damage, whilst 57% called for better tool designs that could differentiate between target tissues and surrounding structures.

The passive nature of the sawfly's cutting mechanism is particularly valuable for surgical applications. Unlike complex robotic systems that require sensors and computational control, this bio-inspired approach achieves selectivity through pure mechanical design. The research suggests surgical saws and scalpels based on this principle could combine the precision of scissors with the safety benefits of electrosurgical tools, but without the thermal damage risks.

Thousands more species to explore

The study examined only two species out of over 8,000 sawfly species, representing an enormous reservoir of potential engineering solutions. Different species have evolved distinct tooth geometries optimised for their specific plant hosts, suggesting multiple surgical applications could benefit from this approach.

Dr Vladimir Blagoderov, principal curator of invertebrates at National Museums Scotland ensured the research team had access to the museum’s extensive entomology collections as well as providing expert training. He said: “As a museum taxonomist, I find it immensely gratifying to see that the natural history collections are not just dusty curiosity cabinets but can directly benefit society by inspiring new technologies and materials. Nature’s engineering, honed over millions of years, still has much to teach us.”

The Heriot-Watt team also partnered with Andrew Liston, a specialist on sawflies from Senckenberg German Entomological Institute in Müncheberg.  He supported the team by helping to select suitable species of sawfly for study, specimen support and literature review. He said: "As a taxonomist who has worked on sawflies for many years, examining and comparing their saws has become a routine. Since my involvement in this research project, I have started to think much more about the possible function of the huge variety of structural adaptations found across different species".

Dr Verdaguer Mallorquí added: "What's particularly exciting is that this mechanism seems to work across multiple sawfly species, each adapted to different plant types. This suggests we could develop a range of surgical tools, each optimised for different tissue types or surgical procedures, all based on these natural cutting systems that have been perfected over millions of years."

What’s next?

The team has developed an analytical model of the selective cutting mechanism. The model explains how the natural tools achieve such remarkable selectivity through passive discrimination based on mechanical properties rather than active sensing. By understanding how structural features like compliant bands allow the cutting angle to adjust automatically when encountering different materials, the research team has created a framework that could inform the design of next-generation surgical instruments and industrial cutting tools.

The research team is now looking for further funding to translate these findings into prototype surgical instruments. The technology could be particularly valuable in neurosurgery, where precision is critical, and in procedures where surgeons work in challenging visibility conditions.

This work represents a significant advance in biomimetics, the field that develops new technologies by studying natural systems. As surgical procedures become increasingly complex and patients demand better outcomes with minimal complications, nature's own solutions may provide the key to next-generation medical devices.

ENDS

About Heriot-Watt University

Heriot-Watt University is a global research-led university based in the UK, with five campuses in Edinburgh, the Scottish Borders, Orkney, Dubai and Malaysia.

Around 27,000 students from 154 countries are currently studying with us. We have more than 173,000 alumni in 190 countries.

We are specialists in business, engineering, design and the physical, social, sports, environmental and life sciences subjects which make a real impact on the world and society.

Heriot-Watt was founded in Edinburgh in 1821 as the world’s first mechanics institute. In 1966, it became a university by Royal Charter. The university is named after 18^th century Scottish engineer and inventor James Watt and 16^th century Scottish philanthropist and goldsmith George Heriot.

86.8% of Heriot-Watt's research is classed as world-leading and internationally excellent in the Research Excellence Framework 2021 – the UK’s system for assessing the excellence of research in UK higher education providers.

The university runs 113 undergraduate programmes and 170 postgraduate programmes across six academic schools and Edinburgh Business School.

Our six academic schools are:

·         Energy, Geoscience, Infrastructure and Society

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·         Mathematical and Computer Sciences

·         Social Sciences

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Edinburgh Business School is one of the world's largest providers of postgraduate business education, with 49,000 alumni across 158 countries.

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