Wearable Printed Sensors for Non-Invasive Penile Tumescence Monitoring

Abstract

This work presents an elastomer-based wearable fully printed sensor patch for the non-invasive measurement of axial rigidity, specifically for Erectile Dysfunction (ED) diagnostics. ED is a prevalent condition, but current assessment tools often lack objective analysis. The proposed sensor combines adaptive strain-sensing layers to enable high-resolution monitoring of tumescence behavior during Nocturnal Penile Tumescence (NPT) tests to detect ED. The patch is manufactured using a layered printing method, integrating flexible and stretchable electronic components in a multi-layered design. The strain sensors use resistive elements printed with conductive silver ink on an elastomeric Flexdym substrate, ensuring seamless conformity to the skin with high durability and stretchability. To enhance performance, strain sensors of varying thicknesses (0.5 mm and 1 mm) and form factors, enabling high sensitivity and comprehensive measurements across different deformation conditions. The measurement principle primarily relies on changes in resistance across the strain-sensing elements as they deform under axial forces. As the resistive elements elongate, their electrical resistance increases, correlating with deformation and enabling precise tracking of rigidity changes. An alternative measurement approach using capacitive elements is also employed, where changes in capacitance due to deformation provide a complementary method for tracking strain. Both principles allow for versatile and precise monitoring of rigidity. Force vs. elongation tests on different sensor samples show that the force required to achieve 100% strain ranged from 1.9 N to 6 N, demonstrating the adaptability of the sensor design for various sensitivity needs. Resistance change vs. elongation tests reveal notable differences between two types of silver ink: ink 1 exhibited a 10-fold increase in resistance at 50% stretch, while ink 2 showed a 130-fold increase at the same elongation, demonstrating the sensor's ability to measure a broad range of deformations with high sensitivity. The strain sensors record both minor and significant deformations, offering a detailed understanding of tissue behavior during controlled erection simulations. This allows for the analysis of rigidity changes and deeper insights into the physiological responses relevant to ED. The multi-dimensional sensor array captures a wide range of rigidity levels, significantly enhancing diagnostic sensitivity beyond traditional methods. Beyond ED diagnostics, the sensor's modular design allows broader applications in fields such as urology and sports medicine. Future developments will focus on improving device robustness, scalability in manufacturing, and ease of use, advancing patient-specific diagnostic and therapeutic processes through precise wearable technology.