Conductive plastic lets nerve cells send signals

In her doctoral thesis Maria Bolin, has connected organic electronics with biological cells. A nerve cell readily develops on a ball of conductive plastic threads. If a voltage is applied, the nerve cell also sends out a signal – a nerve impulse.

Artificial nerve impulses can be of use in many different fields, for example creating sensation in a prosthesis. So far the research has not reached the application stage, however Bolin has constructed a porous, tissue-friendly surface of conductive plastic and managed to stimulate nerve cells to grow into it.

When a voltage is applied to the conductive plastic, the nerve cell emits a signal; in this case it emits calcium.

“There are voltage-sensitive ion channels in the cell membrane, and the cells react normally by emitting calcium or sodium ions,” Bolin says.

This means that an electric signal could be used to control a biological signal – in this case, a nerve impulse.

It all started when the Swerea research institute wondered whether Professor Magnus Berggren and his team of researchers in organic electronics had any use for leftover thin PET plastic fibres. Bolin became interested and slowly arrived at a method for creating an even, thin surface around the entire fibre made of the electrically conductive plastic Pedot – poly (3,4-ethylenedioxythiophene).

“It took a little time, but we found a method that covers each fibre entirely, and even deep into piles of fibres. The method – vapour phase polymerization – vaporizes the plastic but doesn’t make the threads stick together. It also works for many other substrates and geometries,” Bolin says.

Now they have also developed a porous surface, a ball of nanometre-thin fibres, where each fibre has a core of PET covered by Pedot plastic – and which is therefore electrically conductive.

Pedot is what’s known as a ‘conjugated polymer’ consisting of long chains of molecules with alternating double and single bonds, and where electrons can move along the chain or hop between different chains. Pedot plastic is stable, translucent, has good conductive qualities, and is also biocompatible.

“This is a substrate that nerve cells like being on,” Bolin states.

She knew that nerve cells grew into the plastic ball, but how the whole thing functions over time remains to be discovered.

In her thesis, she also produces different surfaces to find out where cells thrive best, in an oxidized or reduced environment. This part of the thesis deals with basic cell biology, certainly important for understanding how the border between human cells and organic electronics appears.

“We’ve produced what’s called a Redox gradient, where we can see where cells thrive best. The next step should be studying multi-cell systems to get more knowledge on what requirements the cells have in their microenvironment. A number of cell types thrive on the reduced side, and others on the oxidized side; these are processes we have in our bodies all the time.”

But she’ll gladly leave this research to others; Bolin now wants to cooperate with industrial sectors and is diligently looking for a job.

“I would really like to continue with research, but I don’t feel the need to do the lab work myself any longer. I’ve done this for years now; it would be nice to work in project management or sales, for example,” she says.

She had six job interviews last week, so industry’s interest is clearly there.

Doctoral thesis
Conjugated Polymer Surface Switches for Active Cell Control, Maria Helene Bolin, Department of Science and Technology, Linköping University. Campus Norrköping, 2011.

Monica Westman Svenselius 2011-11-10