Ajay Kottapalli Photo by Reyer Boxem

The smart sensors of Kottapalli

By touch

Ajay Kottapalli Photo by Reyer Boxem
Ajay Kottapalli loves engineering. But he also wants his work to benefit other people. Now, he is making tiny sensors that not only help Parkinson’s patients to walk but can even mimic human skin.
8 December om 9:06 uur.
Laatst gewijzigd op 21 December 2021
om 14:24 uur.
December 8 at 9:06 AM.
Last modified on December 21, 2021
at 14:24 PM.
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Door Christien Boomsma

8 December om 9:06 uur.
Laatst gewijzigd op 21 December 2021
om 14:24 uur.
Avatar photo

By Christien Boomsma

December 8 at 9:06 AM.
Last modified on December 21, 2021
at 14:24 PM.
Avatar photo

Christien Boomsma

Achtergrondcoördinator en wetenschapsredacteur Volledig bio »
Background coordinator and science editor Full bio »

This story starts with a fish.

It’s a fish that has been living in deep underwater caves for so long, that its eyes have degenerated up to a point that it’s completely blind. However, Astyanax fasciatus can swim at high speeds, it never ever collides with rocks or other objects in the water and has a perfect sense of where it is. Better even, it seems, than fish that do have eyes. 

How does it do that? And what can we learn from it? That is what Ajay Kottapalli asked himself when he was working on his PhD project, trying to make a navigation system for vehicles in the water.

Turns out the animal has rows of tiny biological sensors on its body. It uses them to detect the pressure of the water as it flows around its body and create a 3D map of its environment. Better than cameras that often can’t see well under water. Better than sonar, too, because that can be harmful to other animals. 

‘We made these flow sensors that are extremely sensitive to pressure’, Kottapalli explains, ‘and then we put those on a robot. And it worked! We were actually able to test them in the sea.’


That was way back, when the was still working in Singapore and at MIT as a postdoc. But his work set the stage for what he is doing right now at the Engineering and Technology institute Groningen (ENTEG). 

Because even though he loved engineering on an extremely tiny scale, he wanted to do something that would actually mean something in the world. ‘I wanted to do something that directly benefits lives’, he says. ‘I didn’t want to develop a solution that has to go looking for a problem.’

I didn’t want to develop a solution that has to go looking for a problem

What he had was lots of know-how in the field of tiny, flexible sensors that gather all that information on movement. Wouldn’t it be cool if he were able to use that in healthcare? Or sports? What if he could create wearable electronics that gather information on heartbeat, steps or breathing of an athlete, or can monitor the distorted movements of someone suffering from MS or Parkinson’s?


The UG offered him the opportunity to do just that. He came to Groningen to set up a lab here and seek out other scientists to work with. ‘People are really open to collaborate in the Netherlands’, he says. ‘I can write an email to a big professor and most of the time they respond, saying: Yes! Let’s meet and have a chat.’

Turns out people were very interested in what he had to offer. And now he collaborates with – among others – the medical centre UMCG, and a rehabilitation centre for Parkinson’s patients in the Groningen neighbourhood of Helpman. 

It did take him years of research to get where he is now, though. For his sensors to be applicable they had to be piezoresistive, which means that they produce a tiny flow of electrical energy when they are stretched, when – for example – you put your foot down when walking or bend your knee. 


But piezoresistive sensors are usually made from silicone, which is in no way flexible enough to be used in clothing or shoes as he wanted them to. ‘It had to be polymers’, Kottapalli says. ‘Because polymers have both the stretchability we need and are possibly biocompatible.’

But how was he going to make a polymer piezoresistive?

But then, his PhD student Debarun Sengupta came up with an idea. Why not use polyacrylonitrile, or PAN-fibres? By putting those in a polymer solution, electrospinning them – charging the material with electrical currents – and then heating them up, he was able to create piezoresistive fibres that could be used in textiles. 

However, these fibres were still too fragile, and they would break under pressure. ‘We then finally embedded them into polymers, so they can be easily handled and are stretchable.’


That finally did the trick. Now, Kottapalli is looking on all the different ways that he can actually use his sensors.  An overview of all the applications he is working on right now was published recently in an article in the Nature partnership journal Flexible Electronics.

The good thing is that we are able to produce them at extremely low cost: under three euros

‘One thing we did is develop a sensor that we put in the sole of the shoes of Parkinson’s patients’, Kottapalli explains. ‘If we measure pressure, we get a good idea of how a person is walking and whether he’s about to fall.’

This vital information is transferred to a receptor strapped to the person’s leg and then wirelessly sent to a computer. The system then warns the patients about the danger they are in, so they can adjust their gait or posture. ‘But it also gives us information about the progression of the disease, the influence of their medication, and how long it takes before their medication wears off.’


He and a team led by his postdoc Amar Kamat have been testing his sensors in the Helpman rehabilitation centre for two years. Patients, he says, are really enthusiastic about them. ‘And the good thing is that we are able to produce them at extremely low cost: under three euros.’ At this point he’s even trying to 3D print a complete shoe, with the sensors already included. 

The Parkinson’s project has been the most practical of his endeavours. But it is in no way the only one. His PhD candidate Sengupta is working on creating a glove that might – in the future – replace the information you skin gives you. 

‘By placing sensors on it, we can get information about the hardness of an object, about the texture or form. You could use a glove like that on an artificial limb’, he says, ‘so that a patient gets the right information to pick something up or be able to sense what it is.’

Big strides

He realises that a glove can never be as agile as human hands. ‘But what we are trying to do is establish how many shapes you can recognise, how much pressure should I apply in terms of grabbing a soft cup versus a hard cup? These are big strides.’

We don’t know yet, so all of this is quite futuristic to us as well

Of course, up until now it’s the computer that gets the information, not the patient themselves. But that might change, as Kottapalli is applying for a grant working with other researchers from all over the Netherlands. ‘There are people from neuromorphic computing and people from exoskeletons too’, he says. 

‘I am working on the sensors, but they focus on questions like: how does this amputated limb connect to the muscles? Can we use smart implants? We don’t know yet, so all of this is quite futuristic to us as well.’


Finally, he is also working on sensors that can be used in the clothes of athletes, so they won’t even need to wear that smartwatch anymore to measure our heartbeat while running. 

However, for that he still needs to establish one thing: make absolutely sure that his sensors are washable. ‘We believe them to be’, he smiles, ‘as they are embedded in polymer and those are waterproof.’

But it needs to be tested first. Will a washing machine be installed in his lab? He smiles. ‘Well, we do need one. Or we’ll just take the clothing home.’