‘Play-putty’ that reads the body’s electric signals could open a new field of flexible biometric sensors

A new study by University of Massachusetts Amherst researchers demonstrates the effectiveness of homemade play putty at reading brain, heart, muscle and eye activity. Published in Device, the research outlines the conductive properties of this material, so-named “squishy circuits.”

“[Squishy circuits] are literally child’s play putty, that is also conductive,” says Dmitry Kireev, assistant professor of biomedical engineering and senior author on the paper.

The conductive squishy circuits—whether homemade or store-bought—are made of flour, water, salt, cream of tartar and vegetable oil. “Salt is what makes it conductive,” Kireev explains.

As a child’s toy, this modeling clay is a malleable way to add lights to an art project by connecting them to a power source as a way to teach kids about circuits. Now, Kireev and his team have demonstrated that the material has more potential.

“We used the squishy circuits as an interface to measure electricity or measure bioelectrical potentials from a human body,” he says.

They found that, compared to commercially available gel electrodes, these squishy circuits effectively captured various electrophysiology measurements: electroencephalogram (EEG) for brain activity, electrocardiogram (ECG) for heart recordings, electrooculogram (EOG) for tracking eye movement and electromyography (EMG) for muscle contraction.

“What makes one electrode material better than another in terms of the quality of the measurements is impedance,” he explains. Impedance is a measure that describes the quality of conductivity between two materials.

“The lower the impedance between the electrode and the tissue, the better the conductivity in between and the better your ability to measure those bioelectrical potentials.”

The study found that the impedance for the squishy circuit electrode was on par with one of the commercially available gel electrodes and twice as better as a second comparison electrode.

Kireev highlights several benefits to this material. First is cost: Even using pre-made putty, the cost per electrode was about 1 cent. Typical electrodes cost on average between $0.25 and $1.

Also, the material is resilient: it can be formed and reformed, molded to the contours of the skin, combined with more putty to make it bigger, reused and easily reconnected if it comes apart. Other comparable state-of-the-art wearable bioelectronics have been made of carbon nanotubes, graphene, silver nanowires and organic polymers. While highly conductive, these materials can be expensive, difficult to handle or make, single use or fragile.

Kireev also highlights the availability of these materials. “It’s something you can do at home or in high school laboratories, for example, if needed,” he says. “You can democratize these applications [so it’s] more widespread.”

He gives credit to his research team of undergraduate students (some of whom have since graduated and are continuing with graduate studies at UMass): Alexandra Katsoulakis, Favour Nakyazze, Max Mchugh, Sean Morris, Monil Bhavsar and Om Tank.

A new study by University of Massachusetts Amherst researchers demonstrates the effectiveness of homemade play putty at reading brain, heart, muscle and eye activity. Published in Device, the research outlines the conductive properties of this material, so-named “squishy circuits.”

“[Squishy circuits] are literally child’s play putty, that is also conductive,” says Dmitry Kireev, assistant professor of biomedical engineering and senior author on the paper.

The conductive squishy circuits—whether homemade or store-bought—are made of flour, water, salt, cream of tartar and vegetable oil. “Salt is what makes it conductive,” Kireev explains.

As a child’s toy, this modeling clay is a malleable way to add lights to an art project by connecting them to a power source as a way to teach kids about circuits. Now, Kireev and his team have demonstrated that the material has more potential.

“We used the squishy circuits as an interface to measure electricity or measure bioelectrical potentials from a human body,” he says.

They found that, compared to commercially available gel electrodes, these squishy circuits effectively captured various electrophysiology measurements: electroencephalogram (EEG) for brain activity, electrocardiogram (ECG) for heart recordings, electrooculogram (EOG) for tracking eye movement and electromyography (EMG) for muscle contraction.

“What makes one electrode material better than another in terms of the quality of the measurements is impedance,” he explains. Impedance is a measure that describes the quality of conductivity between two materials.

“The lower the impedance between the electrode and the tissue, the better the conductivity in between and the better your ability to measure those bioelectrical potentials.”

The study found that the impedance for the squishy circuit electrode was on par with one of the commercially available gel electrodes and twice as better as a second comparison electrode.

Kireev highlights several benefits to this material. First is cost: Even using pre-made putty, the cost per electrode was about 1 cent. Typical electrodes cost on average between $0.25 and $1.

Also, the material is resilient: it can be formed and reformed, molded to the contours of the skin, combined with more putty to make it bigger, reused and easily reconnected if it comes apart. Other comparable state-of-the-art wearable bioelectronics have been made of carbon nanotubes, graphene, silver nanowires and organic polymers. While highly conductive, these materials can be expensive, difficult to handle or make, single use or fragile.

Kireev also highlights the availability of these materials. “It’s something you can do at home or in high school laboratories, for example, if needed,” he says. “You can democratize these applications [so it’s] more widespread.”

He gives credit to his research team of undergraduate students (some of whom have since graduated and are continuing with graduate studies at UMass): Alexandra Katsoulakis, Favour Nakyazze, Max Mchugh, Sean Morris, Monil Bhavsar and Om Tank.