How Elephant Trunks And Octopus Tentacles Are Transforming Modern Surgery

By Xing Ning Tan 

At first glance, elephant trunks, octopus tentacles or even human tongues don’t seem to have much in common. Look closer and you’ll find that they are all boneless biological muscles that rely on internal pressure to change their shape. These belong to a class known as muscular hydrostats. 

Unlike the arm, where your biceps and triceps are attached to a bone, muscular hydrostats consist of their own support system - individual muscles (known as fascicles) that can be activated to change the entire muscle’s overall shape. Since the force spreads evenly through the muscle, this makes its structure particularly strong and agile, capable of complex movement like twisting and bending. Interestingly, these same features are exactly what ideal surgical tools need.

Current passive catheters used for heart procedures are considered ‘minimally invasive’, but their rigid tips make it difficult to steer due to a restricted range of motion. Moreover, they may accidentally puncture blood vessels and cause internal bleeding when inserted. Additionally, without a sense of touch when using standard forceps, surgeons can risk pinching the tissue too hard when grasping it.

Studying biomimicry is one thing, but applying it into biomedical settings is the real challenge. To copy nature’s blueprint, engineers are developing different methods to mimic similar movement in robots:

1. Fluidic actuation: Pumping air/fluid into tiny chambers within the robot to make it inflate and curve.

2. Smart material actuation: Using advanced materials that respond to changes in temperature or chemicals.

3. Magnetic actuation: Steering the robot by changing external magnetic fields for movement in all directions (omnidirectional bending).

4. Structure based actuation: Folding flexible 3D origami to change structure.

5. Tendon driven actuation: Pulling internal cables that are connected to the robot to change its direction.

What makes muscular hydrostats incredibly useful for surgical tools is variable stiffness - the ability to change between flexibility and firmness. Because they lack rigid metal joints, they can elongate, shorten or bend, enabling infinite degrees of free movement. This allows surgical tools to safely navigate slippery organs, tight spaces and tortuous pathways, without injuring any tissue. Once they reach the intended spot, they can stiffen to make precise cuts. Often, these soft robots are made up of materials with a low Young’s modulus (similar to that of soft biological tissue) like elastomers or silicon.

Building a soft robotic tool is a massive engineering balancing act. Fluid-powered tools mimic natural muscle movement most similarly, but have the risk of leaking inside the body. Magnetic controls offer the best precision, but require large, expensive equipment in the operating room. Even shrinking the tools down using 'smart materials' creates a new problem: heat and electricity is introduced near delicate organs. Because no single technology is flawless on its own, the future of surgery will likely rely on a hybrid approach.

For engineers, implementing these actuation types into surgical designs also comes with its own hurdles. For instance, scaling them down to microscopic levels for instruments like bronchoscopes without sacrificing flexibility or strength can be challenging. There are additional factors that need to be considered, like managing heat produced by electrical currents and connecting the tool to an energy source. As of now, there are limited biomechanical models to simulate the interaction between human organs and soft robotic material, making it challenging to accurately predict their movement within the human body. Compounding such challenges, the flexible elastomers and silicones used in soft robotics must also be non-toxic and completely safe for human tissue.

Overcoming these obstacles would allow the next generation of soft robotic surgical tools to be developed even further, likely incorporating smart features such as AI path-following algorithms and non-Newtonian fluids, improving human-robot interaction. To solve the problem with forceps, future soft robots could rely on electrostatic adhesion, which is a technology that uses electric charge to attract neutrally charged tissue, offering an extremely gentle but firm grip that minimises tissue damage. Most importantly, embedding sensors within the robot would enable shape sensing, real time force feedback and spatial tracking, easing surgeon control and paving the way for gentler, safer surgeries in the future.

Fig 1: Fluidically actuated soft robot with internal ridges and channels for air flow (photograph by author)

Fig 2: Soft robots are made of flexible materials like silicon (photograph by author)

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Summary of article:

By mimicking how boneless animal muscles move, scientists are creating soft, flexible robotic tools that can safely navigate the human body during surgery. While fluidic movement is most similar to natural muscle movement, future surgical tools will likely combine different methods to achieve both flexibility and precision.