Bioimpedance Sensor Array for Long-Term Monitoring of Wound Healing from Beneath the Primary Dressings and Controlled Formation of H2O2 Using Low-Intensity Direct Current

Abstract

Chronic wounds impose a significant financial burden for the healthcare system. Currently, assessment and monitoring of hard-to-heal wounds are often based on visual means and measuring the size of the wound. The primary wound dressings must be removed before assessment can be done. We have developed a quasi-monopolar bioimpedance-measurement-based method and a measurement system to determine the status of wound healing. The objective of this study was to demonstrate that with an appropriate setup, long-term monitoring of wound healing from beneath the primary dressings is feasible. The developed multielectrode sensor array was applied on the wound area and left under the primary dressings for 142 h. The impedance of the wounds and the surrounding intact skin area was measured regularly during the study at 150 Hz, 300 Hz, 1 kHz, and 5 kHz frequencies. At the end of the follow-up period, the wound impedance had reached the impedance of the intact skin at the higher frequencies and increased significantly at the lowest frequencies. The measurement frequency affected the measurement sensitivity in wound monitoring. The skin impedance remained stable over the measurement period. The sensor array also enabled the administration of periodical low-intensity direct current (LIDC) stimulation in order to create an antimicrobial environment across the wound area via the controlled formation of hydrogen peroxide (H₂O₂).

Keywords: beneath the dressings; bioimpedance; hydrogen peroxide; long-term monitoring; low-intensity direct current; multielectrode; quasi-monopolar; sensor array; wound dressing; wound monitoring; wound stimulation.

Figure 1

(a) The layout of the multielectrode sensor array prototype. (b) A photograph of the sensor array. The dashed white square marks the electrodes which participated in the measurements. The electrodes k1, a4, b1, b2, c2, c3, and d2 are marked on the figure. The electrodes a4, b1, and b2 were on the wound in the first experiment and the electrodes c2, c3, and d2 in the second experiment. The remaining electrodes in the array and on the left and the right side of the array were on the intact skin. The sensor array was based on the design presented by Kekonen et al. (2018) [24].

Figure 2

(a) The materials needed for preparing the multielectrode sensor array before placement on the skin. (b,c) The placement of the sensor array on the left shin. (d) A foam dressing applied on top of the sensor array. (e) Compression bandage folded on the shin; only the connector end was outside of the bandage.

Figure 3

The impedance measurement results of the first experiment (left column) and the second experiment (right column) for 150 Hz, 300 Hz, 1 kHz, and 5 kHz frequencies. In both experiments, the impedance was measured from beneath the primary dressings for 142 h. A total of 17 electrode pairs were used in the measurements. In the first experiment, a wound was induced under the electrodes a4, b1, and b2 after 24 h of measuring skin impedance. In the second experiment, a wound was induced under the electrodes c2, c3, and d2 after 24 h of measuring skin impedance. The remaining 14 electrode pairs measured skin impedance over the 142 h follow-up period. The electrode pair k1–k2 consisted of electrodes which had a larger surface area. (a) 150 Hz; (b) 300 Hz; (c) 1 kHz; (d) 5 kHz.

Figure 3

The impedance measurement results of the first experiment (left column) and the second experiment (right column) for 150 Hz, 300 Hz, 1 kHz, and 5 kHz frequencies. In both experiments, the impedance was measured from beneath the primary dressings for 142 h. A total of 17 electrode pairs were used in the measurements. In the first experiment, a wound was induced under the electrodes a4, b1, and b2 after 24 h of measuring skin impedance. In the second experiment, a wound was induced under the electrodes c2, c3, and d2 after 24 h of measuring skin impedance. The remaining 14 electrode pairs measured skin impedance over the 142 h follow-up period. The electrode pair k1–k2 consisted of electrodes which had a larger surface area. (a) 150 Hz; (b) 300 Hz; (c) 1 kHz; (d) 5 kHz.

Figure 4

The condition of the skin and the wounds after 142 h of bioimpedance follow-up. The location of the wound electrodes is marked in the photos. (a) The first experiment. (b) The second experiment.