Self Expanding Structures for Cardiovascular Sensor Attachment

Our group is currently developing a wireless pressure sensor able to perform 24/7 measurement of arterial blood pressure: the correct design of the sensor attachment (stent) is instrumental for preventing migration and avoiding excessive strain on the artery, which may cause remodelling or function impairment. For this reason, the radial force of the stent was analysed to predict its impact: a mixed numerical-experimental approach was devised for predicting in-vivo exerted radial force from single-repetitive – element (SRE) tensile properties. The approach was tested on a simplified model (Λ-model): the mechanical response to simple tensile testing was analysed by means of finite element modelling (ANSYS mechanical with shape-memory alloy) and compared with an analytical solution achieved by means of the Castigliano theorem.  To validate the model, experimental results were gained by means of an identically shaped nitinol prototype tested on a tensile testing machine. A maximum of 3% difference in tensile stiffness was found between the three methods.

The approach was subsequently applied to a laser-cut stent and the radial force was estimated by means of the formula RF (D) = LF (δ) * 2 π / n , where RF is the radial force when the outer diameter is D, LF is the linear force exerted by the SRE when subject to a linear displacement equal to δ and n is the number of times the SRE is repeated in the final configuration (δ = ΔD/n). The results were compared with those obtained experimentally with mylar-film test and satisfactory matching was found. Future development will see finite element analysis of stent deployment inside realistic pulmonary artery structures and induced wall stresses will be linked with radial force values.