A stretchable hardness sensor for systemic sclerosis diagnosis

Systemic sclerosis (SSc) is a multi-organ desmosis exhibiting the symptom of skin sclerosis. Due to the complexity of human skin, the assessment of skin sclerosis was traditionally implemented through palpation by a clinician, which has numerous limitations. Wearable flexible sensor is expected to open up new approaches for SSc diagnosis. Herein, a thin hardness sensor comprising a strain sensor and a pressure sensor was developed to assess the hardness of skin quantitatively. The strain sensor exhibited a gauge factor of 1.45 while the pressure sensor exhibited a considerable force sensitivity of 0.46 N-1. The above two sensors were stretchable and bonded to yield the hardness sensor, which can be easily attached on touched material and deform with the touched material under external force. Results showed that the sensor was able to distinguish touched materials with different Young's modulus. A harder material can be identified by a larger sensor output. Furthermore, the sensor was mounted on the skin to compare and assess the hardness of a healthy person as well as a patient. Obvious hardening was found to occur on some locations of the patient’s skin by the sensor, which was also verified by a commercial durometer. The reliable performance enables our hardness sensor highly promising in the diagnosis of SSc and meritorious to the design of wearable sensors.