Unobtrusive printed piezoelectric sensors for non-invasive biosignal monitoring

Project Information

UNOPIEZO

Grant agreement ID: 101022433

DOI

10.3030/101022433

Project closed

EC signature date 6 April 2021

Start date 1 October 2021

End date 13 March 2024

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 198 631,68

EU contribution

€ 198 631,68

Coordinated by

TAMPEREEN KORKEAKOULUSAATIO SR
Finland

Periodic Reporting for period 2 - UNOPIEZO (Unobtrusive printed piezoelectric sensors for non-invasive biosignal monitoring)

Reporting period: 2023-01-01 to 2023-12-31

Summary of the context and overall objectives of the project

Continuous, large-scale health monitoring of cardiovascular disease (CVD) risk population carries significant benefits to the society (e.g. decreased mortality and treatment costs due to early disease detection), but is currently not possible because of the lack of unobtrusive, affordable and accurate bio-signal sensors. This MSCA project proposes to solve these issues through development of ultra-thin (< 10 µm thick) sensors which attach conformably to the skin and improve the mechanical coupling between the skin-sensor interface thereby resulting in highly unobtrusive user experience and accurate signal reproduction. Furthermore, cost-effective additive fabrication technologies are employed to make the devices affordable and to enable their mass-scale fabrication required for large-scale screening of the whole risk population.

The overall research objectives of the project are:

RO1: Determination of material parameters for modelling and application for ethical permission
RO2: Development of engineering design rules for printed ultra-thin piezoelectric sensors
RO3: Development of printing processes to fabricate the designed structures
RO4: Demonstration of device performance in bio-signal measurement

The expected outcomes of the ROs are:

RO1: Determination of mechanical, electrical and piezoelectric material parameters required for modelling in RO2. Start of application procedure for ethical permission for human studies.
RO2: Fundamental understanding how to maximize the sensitivity through material choices (e.g. substrate elastic moduli, plain strain bending modulus), manipulation of the device dimensions (e.g. piezoelectric material thickness, substrate vs. piezoelectric thickness ratio), and device architecture (e.g. charge collector layout). Understanding how to improve mechanical coupling between sensor and skin. Implemented through a finite element model (FEM). Design and fabrication of ultra-thin battery free data transmission unit (DTU).
RO3: Printed unobtrusive, affordable and accurate ultra-thin piezoelectric sensors
RO4: Clinically accurate pulse wave signal measured from the carotid/radial artery. Verification done using simultaneous measurement with state-of-the art devices used currently in hospitals.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

RO1: 1) Material parameters for FE-modelling were determined from the literature and 2) ethical permission for clinical study was submitted to Tampere University Hospital (Tampereen Yliopistollinen Sairaala, TAYS) ethical review committee.
RO2: 1) Engineering design rules were implemented for an ultra-thin piezoelectric sensors using finite element modelling. Specificially a FE-model was generated for an interdigitated electrode based ultra-thin piezoelectric sensor and it was used to optimize the sensor geometry and poling condition; the study was accepted for publication in IOP Flexible and Printed Electronics 2) Modification and optimization of an existing data transmission unit (DTU) for the piezoelectric sensor. More specifically, regarding 1) We studied the optimization of the geometry and poling condition of an interdigitated electrode based pulse wave sensor so as to maximize its sensitivity. Specifically, we developed an FE-model for ultra-thin piezoelectric poly(vinylidene-trifluoroethylene) (PVDF-TrFE) sensor with interdigitated electrodes (IDE) which included the effect of a non-homogenous poling field determined via combination of experimental and numerical methods. The study was published in IOP Flexible and Printed Electronics journal (DOI: 10.1088/2058-8585/acb36b). Regarding 2), we modified an existing data transmission unit (DTU) to be used together with a ultra-thin piezoelectric sensor. The main modification was the addition a charge amplifier to the existing DTU. This included the optimization of the amplifier bandwidth with an artificial heart test setup (AHTS). Specifically, the AHTS was used to generate a pulse wave which was measured simultaneously with an internal reference sensor of the ATHS and a printed ultra-thin P(VDF-TrFE) based piezoelectric sensor. A comparison of the pulse wave shape showed that the best correspondence between the printed and reference sensor was achieved by reducing the low cutoff frequency of the charge amplifier to ~50 mHz.
RO3: We optimized the printing and integration process of the ultra-thin piezoelectric sensor such that it could be integrated to the soft and stretchable DTU reliably. The developed printing process utilized inkjet printing for cross-linked PEDOT:PSS top and bottom electrodes, inkjet printing for stretchable PEDOT:PSS horseshoe interconnects; a motorized film applicator for printing the piezoelectric P(VDF-TrFE) layer. As for the integration of the ultra-thin sensor to the DTU, the sensor and DTU were pre-treated to improve the adhesion and a soft interconnect between the DTU and the ultra-thin sensor was developed.
RO4: We used the DTU with integrated ultra-thin piezoelectric sensor to measure the pulse wave from the distal antebrachum of the researcher. In the measurement setup, the DTU + ultra-thin sensor was clamped against the artery and the measured pulse wave signal was transmitted and recorded wirelessly on an iPad. A pulse wave signal analysis script was then developed for matlab. Alltogether 108 individual pulses were obtained from the pulse wave signal, an average pulse wave signal was calculated based on these and clinically relevant indices were calculated based on fiducial points extracted from the average pulse wave signal. The indices were then compared to literature values.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

1. Beyond state of the art status has been achieved regarding the first goal. Specifically, this has been achieved through the completion of the study related to optimization of the geometry and poling condition of an interdigitated electrode based pulse wave sensor (see more detailed explanation in previous section and technical report). This study should pave the way towards easier FE-model based optimization strategy of the piezoelectric sensors thereby providing an important step towards realizing high sensitivity ultra-thin piezoelectric devices.
2. Regarding the second goal, although the print process and resulting sensor element were ultra-thin, and thereby highly unobtrusive, the reliable operation of the wireless data transmission unit required the use of conventional electronics. A soft elastomer encapsulated flexi-PCB with conventional electronics was developed for this purpose and the ultra-thin sensor was integrated thereto. In other words, the unobtrusiveness is achieved by other means than the ultra-thin form factor.
3. Beyond state of the art status has been achieved regarding also the third goal. A print process was developed to enable affordable fabrication of the ultra-thin piezoelectric sensor such that the sensor could be integrated to the DTU.
4. Regarding the fourth goal, beyond state of the art status has not been achieved. Initial pulse wave measurement demonstration was conducted using the DTU + sensor, but large scale clinical study required for validating fthe system for large scale and continuous screening of entire CVD risk population is needed.

Development of the DTU