This paper presents a fiber-shaped flexible capacitive strain sensor (FSFCSS) fabricated using direct ink writing (DIW) technology. The sensor consists of parallel helical Ag electrodes printed onto a TPU tube fiber and encapsulated with BTO@Ecoflex. This design enables dual-mode strain sensing: axial tensile strain and radial expansion strain. The FSFCSS demonstrates a wide detection range (178%), high sensitivity (0.924 for axial strain, 0.00086 mmHg⁻¹ for radial strain), low detection limit (0.6%), and low hysteresis (1.44%). Applications in wearable and implantable health monitoring, including blood pressure and heart rate measurement, are demonstrated.

Chi Zhang, Wenyu Ouyang, Lei Zhang, Dachao Li