A robust uniaxial force sensor for minimally invasive surgery.

This paper presents a novel miniature uniaxial force sensor for use within a beating heart during mitral valve annuloplasty. The sensor measures 5.5 mm in diameter and 12 mm in length and provides a hollow core to pass instrumentation. A soft elastomer flexure design maintains a waterproof seal. Fiber optic transduction eliminates electrical circuitry within the heart, and acetal components minimize ultrasound-imaging artifacts. Calibration uses a nonlinear viscoelastic method, and in vitro tests demonstrate a 0-4-N force range with rms errors of 0.13 N (< 3.2%). In vivo tests provide the first endocardial measurements of tissue-minimally invasive surgery instrument interaction forces in a beating heart.