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Dry Electrodes

Microneedle-based Electrodes for ECG Monitoring

The collection of electrocardiography (ECG) data requires signal recording hardware which is usually interfaced to the human body using adhesive electrodes.  Although effective for short-term measurements, these electrodes often require painful abrasion and/or shaving of the skin prior to application, which is inconvenient for patient and clinician alike.  They also suffer from issues with signal quality caused by degradation of the electrolytic gel pad that is used to ensure electrical contact between the skin and electrode, which means that these ‘wet’ electrodes are particularly unsuited to long-term ECG recording.

Our recent research has suggested that ‘dry’ electrodes based upon the use of microneedle arrays may prove a viable alternative for long-term physiological recording applications.  Microneedles are short (generally <1 mm), sharp microstructures, originally intended for use in transdermal drug and vaccine delivery.  It has been shown that electrically conductive microneedle arrays can pierce the outermost skin layer (known as the stratum corneum) and make direct contact with the moist epidermal layers directly beneath.  

This reduces the electrical impedance between skin and electrode, provides a stable interface, and eliminates the need for skin preparation and/or electrolytic gel.  Furthermore, the sub-millimetre microneedle height ensures that no pain receptors are stimulated, nor is any blood drawn.  This minimises patient discomfort and risk of infection after the electrode is removed.

Micromoulded epoxy needle wafer prior to metallisation
Micromoulded epoxy needle wafer prior to metallisation. Note the circular sections that are easily detached for assembly into electrodes.
Detail of gold coated polymeric microneedle array
Detail of gold coated polymeric microneedle array.
Prototype microneedle-based dry electrode (left) and conventional wet electrode (right).
Prototype microneedle-based dry electrode (left) and conventional wet electrode (right). Both electrodes are covered by a protective plastic lid.

 

To be commercially successful in such a competitive market, it is essential that dry electrodes are manufacturable in high volumes and at low cost.  At Tyndall, researchers have solved these issues by developing a unique replication process that can produce microneedle electrodes at a cost comparable to conventional devices.  Using our ultrasharp silicon microneedles as a master template, double-sided micromoulding technologies have been developed to accurately replicate these microstructured electrodes in medical-grade polymeric materials.  

Typical ECG signal recorded using Tyndall’s microneedle-based dry electrodes
Typical ECG signal recorded using Tyndall’s microneedle-based dry electrodes.

Qualitative comparisons of signals indicate comparable electrode performance between microneedle and commercially available wet electrodes, and tests show that specific waveforms in EEG, ECG or EMG signals could be easily distinguished when using these dry electrodes.

 

 

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