Electrolytic Wire as an Alternative Bio Interface:

A Case Study in Plant Tissue

Ernane José Xavier Costa, Luciana Vieira Piza and Ana Carolina de Sousa Silva

Computational and Applied Physics Lab – Basic Science Department – FZEA, University of São Paulo,

Rua Duque de Caxias Norte, Pirassununga, Brazil

Keywords: Bio-electrode, Bioelectricity, Aqueous Junction.

Abstract: One of challenge in physiological research is how to reconnect bioelectricity or turn on the transduction of

signals in biological systems such as nerves and other tissues after some injuries or degenerative process. The

electrical interactions in biological system can be understood by looking into the extracellular space between

cells. In such spaces, contain ions and several charged organic molecules. Despite the fact that the common

way to artificially link biological systems reported in the literature is by using metallic wires or bio-potentials

electrodes, this paper present the hypothesis that an electrolytic conductor is more efficient to transmit

information between biological systems when compared to the transmission carried out using electronic

conductors. To test this hypothesis an experiment was conducted using two leaves of ornamental plant (Agave

atenuata) connected by means of electronic and electrolytic wire and stimulated with electrical square waves

with 1V of amplitude at 20Hz. The quality of signal transmitted using electronic conductor was compared to

the signal transmitted using electrolytic conductor by measuring the distortion of the signal transmitted. The

results shown that the transmission of stimuli using electrolytic wire is less disturbed than by using electronic

wire.

1 INTRODUCTION

In this century, many technological approaches have

been tested to develop systems that link biological

system with electronic systems (Navarro et al., 2005)

or others biological interfaces (Agnew et al., 1989;

Hwang et al.,2016) to improve or to restore sensory

functions in several kinds of diseases. A number of

scientific approaches have been presented in order to

the establishment of state-of-art in the biological and

bionic interfaces (Lauer et al.,2000).

Each interaction among biological system involve

bioelectrical information generated, transmitted, and

broadcasted through organics pathways that link the

bio-processors, biosensors and bio-actuators

embedded throughout the organic systems (Enderle,

2011). The development of an interfacing method to

artificially place information into the biological

system, or to monitoring the information from it,

would improve the way one can make the biological

systems interacts each other and with the artificial

systems.

Bioelectrical signals like EEG, EKG and EMG are

detected by means of skin contact with electrodes

connected to signal amplifiers (Enderle, 2011). The

electrical contacts are performed by using

biocompatible conductive hydrogels applied between

skin and electrode. This process create an interface

that influences the quality of signal and depending of

this interface the signal quality is improved due the

presence of conductive hydrogel (Pedrosa et

al.,2017). The use of such electrolytic gels provides

an effective contact but the information acquired from

the biological system mediated by ionic interaction

must be transduced in to electronic information in the

metal electrode side (Clement et al.,2011). Despite

this electrode provide excellent signal quality there

are several difficulties related to it is use and to

overcome such difﬁculties, some alternative

electrodes that would be acceptable in physiological

research were tested, for example dry electrodes

(Mesiane et al.,2013). Even the most efficient

electrodes still present an interface between an

electronic conductor and the biological medium.

So far, an evaluation of electrodes technology

applied to link biological system is little understood,

this paper present an investigation on conductive

hydrogels capability to be used like an electrolyte

Costa, E., Piza, L. and Silva, A.

Electrolytic Wire as an Alternative Bio Interface: A Case Study in Plant Tissue.

DOI: 10.5220/0006549101330138

In Proceedings of the 11th International Joint Conference on Biomedical Engineering Systems and Technologies (BIOSTEC 2018) - Volume 4: BIOSIGNALS, pages 133-138

ISBN: 978-989-758-279-0

133

wire to conduct bioelectrical signal in plant tissue and

then we suggest that this kind of wire could be

considered as a future solution to bio-electronic

interface.

2 ELECTROLYTIC CONDUCTOR

The electrical interactions in biological system can be

understood by looking into the extracellular space

between cells. In such spaces, with no more than 150

Å wide, contain ions and several charged organic

molecules that are not only sensitive to electric fields

but also generate their own fields and these electrical

interactions flow to neighbouring disturbing it. For

the sake of simplicity, it is inferred that this space is

filled by an electrolytic solution.

Before the application of an external field in an

electrolytic solution, it is behaviour can be

understood by having a time-averaged electro

neutrality in the electrolyte i.e. the net charge in any

macroscopic volume of solution is zero because the

total charge due to the positive ions is equal to the

total charge due to the negative ions. If an electric

field arise in an electrolytic solution, the opposite

occur. The effect of this ionic drift on the state of

charge of an electrolytic solution is to send positive

ions near the positively charged area and the negative

ions near the negatively one producing a spatial

separation of charge. Because of this gross charge

separation, the electro neutrality tends to be disturbed.

Additionally, the separated charge tends generate its

own field, which would be contrary to the externally

applied field but equal in magnitude and then the

resultant field in the solution will vanish. This not

imply that an electrolytic solution would sustain only

a transient migration of ions because in practice, an

electrolytic solution can conduct electricity i.e., keep

a continuous flow of ions. It can be understand by

comparing electrolytic solution with a metallic

conductor (Horno et al.,1992).

There is a lattice of positive ions that hold their

equilibrium positions during the conduction process

in a metallic conductor and, there are free conduction

electrons, which transport charge. In the electrolytic

conductor, however, if an electrical contact to and

from the electrolyte is mediated by an interface

electricity in the interface side and ions carry the

charge in the electrolytic solution and if a change of

charge carrier at the interface exist then a steady flow

of charge in the entire circuit will be maintained. This

electron transfers phenomenal between ions and the

interface result in chemical changes.

The occurrence of a reaction at interface side is

equivalent to the removal of equal amounts of

positive and negative charge from the solution. In

other words, when electronic disturbance reactions

occur in the interface side, the ionic drift does not lead

to the charges separation and no opposite field is

created and then the flow of charge can continue i.e.,

the solution conducts, it is an electrolytic conductor.

In view of the above, the hypothesis that an

electrolytic conductor is more efficient to transmit

information between biological systems when

compared to the transmission carried out using

electronic conductors is postulated. To test this

hypothesis an experimental setup using plant tissue is

presented.

3 PLANT BIOELETRICITY

Literature studies shown that bioelectrical signals

play central role in both cell-cell and long-distance

communication in plants (Van Bel et al.,2014). There

are four types of bioelectrical signals generated by

plants: oscillatory potentials – OP, action potentials –

AP, variations potentials – VP and system potentials

–SP. Although AP, SP and VP is generated by

distinct molecular dynamic, OP arise from complex

mixing of bioelectric activities (AP, SP,VP) by means

of a complex web of systemic interaction at short a

long range level (Cabral et al.,2011; From et al.,

2013; Choi et al., 2016). Plant Bio-potentials has lot

of important information related with plant behavior

and then can be used for test several aspects of

bioelectricity.

4 MATERIAL AND METHODS

This experiment was carried out in Applied Physics

and Computational Laboratory (LAFAC) at the

Faculty of Animal Science and Food Engineering,

University of São Paulo (USP), Brazil.

Leaves of ornamental plants Agave atenuata

were collected in pairs and packaged in a beaker

containing water. One leave was designed to be

stimulate (Ls) and another leave (Lr) was designed to

receive the stimuli transmitted by Ls. Each

experimental section took place over 1 hour after

leaves preparation. The experiment were conducted

in the Faraday cage with controlled light incidence,

and the temperature and relative humidity in the cage

did not change significantly during the experience. To

monitor the bioelectricity transmission between Ls

BIOSIGNALS 2018 - 11th International Conference on Bio-inspired Systems and Signal Processing

134

and Lr, they were connected each other in two

experimental arrangement. The first using normal

wire needle electrode connecting the leaves and the

second using electrolytic wire conductor. The

schematic diagram of experimental setup concept is

illustrated in diagram of Figure 1 and experimental

arrangement is illustrated in Figure 2.

Figure 1: Schematic diagr am of experimental setup

concept.

Figure 2: Experimental arrangement.

The electrical signals from the leave Lr were

monitored using two Ag/AgCl disc electrodes

connected to the leave surface, by means of a

conductive aqueous gel as described in Cabral et al.,

(2011). The electrodes were connected with screened

cables to a high-input impedance (≈109 MΩ)

electrometer that sent the data acquired to a computer

by using wireless technology in real-time at sample

rate frequency of 200 Hz.

The electrolytic wire was built by using a flexible

non-conducting polymeric tube with the extremity

needle-shaped to be connected in the leaf tissue and

filled with a hydrophilic polymer known as hydrogels

(Farina et al., 2004). Figure 3 illustrate the

electrolytic wire developed.

Figure 3: Electrolytic wire.

The Ls was stimulated using a square wave

electrical signal with 1 V of amplitude and 20 Hz in

frequency. Square wave was chosen because it is

commonly used in experiments with stimuli (Declan

et al.,2014) and 20 Hz was chosen due the fact that

plants have oscillatory characteristics in a frequency

range from 5 to 15 Hz (Cabral et al., 2011) so 20 Hz

is out of this range. Each experimental arrangement

was repeated six times. To compare the effect of the

type of wire used to transmit the signal from Ls to Lr

the signal acquired was analysed by measuring the

signals to noise and distortion ratio (SINAD)

(Karandjeff et al.,2011, Grigoriev and Kharin, 2011)

of signal acquired in relation of a signal acquired

locally in Ls. The SINAD was used due the

oscillatory characteristic of plant response to the

stimuli. So, the signal source is the Ls leave response

to square wave and the receiver is the Lr bioelectrical

signal acquired. The bioelectrical signal from the Ls

source is converted in to a form convenient for

transmission along the communications channel

represented by connection between the leaves. During

the conversion, the initial information is distorted due

to the fact that the conversion is non ideal.

The distortion measurement was made by using

the Matlab

signal processing toolbox and the

normalized SINAD results were presented.

The hydrophilic gel have demonstrated great

potential to be used in biological systems. The

hydrophilic gel polymer is biocompatible due its high

water content. Hydrophilic gel polymer have a high

afﬁnity for water, nevertheless do not dissolve into it,

because of its chemical and physical property; water

molecules can only penetrate into the chains of the

polymer network, subsequently causing swelling and

formation of a hydrogel (Katter et al.,2017). For

convenience was used the hydrogel currently

available in local pharmaceutical market with

conductivity (σ) and constant phase element

parameters (A) measured in some papers in the

literature. The chemical compositions of hydrogel

used are listed as follows: water, disodium

ethylenediaminetetraacetic acid, lithium chloride,

Electrolytic Wire as an Alternative Bio Interface: A Case Study in Plant Tissue

135

propylene glycol, methylparaben and sodium

carbomer. Conductivity (σ) and constant phase

element (A) parameters of the hydrogel used has the

follow value: σ = 2.02 S m

−1

and A = 0.90 x 10

Ω/s

(Freire et al., 2010).

5 RESULTS AND DISCUSSION

In Figure 4 the signal acquired in Lr without any

stimulation is shown.

Figure 4: Signal acquired from leaf Lr without any

stimulation and disconnected from Ls leaf.

Figure 5 shown the results of signal transmission

from Ls connected to Lr by mean of copper wire or

electronic conductor. Ls was stimulated by a square

wave with 1 Volts of amplitude and 10 Hz of

frequency.

Figure 5: Leaves connected by electronic conductor.

Experience with electric square wave stimuli.

Figure 6 shown the results of signal transmission

from Ls connected to Lr by mean of electrolytic

conductor.

Figure 6: Leaves connected by electrolytic conductor.

Experience with electric square wave stimuli.

The signal to noise and distortion ratio calculate

for each signal acquired is shown in Table 1.

Table 1: SINAD measurement of signal acquired after

electrical stimulation of the leaf Ls. Mean of six

experimental run.

Transmission

medium

SINAD of signal transmitted

measured in Lr (dB)

Electronic

14.45 ± 0.07

Electrolytic

15.12 ± 0.3

6 A PRELIMINAR MODEL

PROPOSITION

One of challenge in physiological research is how to

reconnect bioelectricity or turn on the transduction of

signals in biological systems such as nerves and other

tissues after some injuries or degenerative process

(Lauer et al.,2000). Some biological systems like in

mammals, looks like wired systems, bio-structures

like the brain send commands to others bio-structure

like muscles. However, the mechanism related to the

information transmission along such structures

remain misunderstood. In fact, the information is

related to the bioelectricity that pass among the

structures like nerves, but this bioelectricity do not

move in such structures as electrons move through a

metallic conductor, for example, the rate of passage

in bio structures is slower than that of electrons

through a wire.

Another fact is the relationship between the

bioelectricity and the electrolytic medium present in

the extracellular medium of the biological structures,

that is modelled via Nernst-type equation (Horno et

al.,1992). Thus, the theoretical approach to the

passage of bioelectricity through biological systems

is related to the electrolytic conduction.

Despite the fact that the common way to

artificially link biological systems reported in the

literature is by using metallic wires or bio potentials

electrodes (Navarro et al.,2005) the result in this

paper allow us to discuss that another way to do that

is using a electrolytic wire. The main argument to

support this idea is that if two electrolytic solution is

interfaced each other with different ions

concentration and different ions mobility then a

liquid-junction potential (Enderle, 2011) will arise

between them with the magnitude given by:









































(1)

When 



is the liquid-juction potential; 



and





represent the mobility; 



and 



are the activities

of the ions of each side of liquid-junction; R is the

universal gas constant; T represent the system’s

50 100 150 200 250 300 350 400

-0.5

-0.4

-0.3

-0.2

-0.1

0.1

0.2

0.3

0.4

samples (1/s)

Amp. (mV)

BIOSIGNALS 2018 - 11th International Conference on Bio-inspired Systems and Signal Processing

136

temperature; z represent the system’s valence and F

the system’s Faraday constant.

Based in equation (1) the transduction of signal

from junction is not necessarily linear and therefore

can be modelled as illustrated in Figure 7.

Figure 7: A simple non-linear model proposition for

bioelectricity information transmission in an aqueous

interface.

In the model of Figure (7) the ions activities will

act like a negative feedback function F() and the

coefficients 



and 



represent the mobility

responsible by the nonlinear transduction in the

interface. The signal transduction between the

interfaces can be described as:

u(t) = v(t) – Fy(t) (2)

F represent the ions activities that act like an

unilateral transference function. In this model, the

distortion of the information caused by the interface

is dependent of how the coefficients 



, 



and the

ions activities are adjusted.

The results presented in this paper, suggest that de

SINAD is related to several property of the interface,

as described in the literature. When a liquid junction,

i.e, an electrolytic wire, makes the transmission, the

model proposed in Figure 7 can give a direction to the

explanation of why the SINAD of signal transmitted

by electrolytic wire is less than the signal transmitted

by electronic wire. Future works will conducted in

order to test if the model proposed will explain the

data obtained. Overall results in this study allow the

follow scientific question: is electrolytic transmission

the alternative way to send signal in biological

structures? To answer this question more experiments

must be done with different kinds of biological

structures but this start point open a door in the area

of bioelectricity transmission.

7 CONCLUSIONS

A new method for transmission of bioelectricity using

electrolytic wire was presented. The signal distortion

of signal transmitted by electrolytic wire was less

than the signal transmitted by an electronic wire. In

addition, a non-linear model to explain the effect of

aqueous junction was proposed and could explain the

results obtained. Overall results allow to conclude

that in plant tissues the transmission of bioelectricity

is less disturbed than by means of electronic

transmission. This research open a new door in the

area of bioelectricity transmission among biological

structures.

ACKNOWLEDGEMENTS

The author would like to thanks the National Agency

for Research Support CNPq (Proc Num, 311084).

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