Biomechanics of soft tissue-device interactions-an investigation into skin and arterial tissue

This thesis adopts a multidisciplinary approach, integrating mathematical modelling, experimental testing, and numerical simulations, to investigate the complex interactions between soft tissues and medical devices. The work focuses on two main areas: characterising the contact behaviour of skin and mouse arterial tissue during indentation, and analysing artery–stent interactions using finite element simulations. In Chapter 3, a novel method is developed to determine the Ogden hyperelastic parameters of soft tissues using indentation experiments on artificial skin. By incrementally applying Hayes’ model under the assumption that soft tissues behave approximately linearly at strain increments ≤1%, an equivalent shear modulus is calculated for each increment. Principal stresses are derived using Hooke’s law, and combined with principal strains to obtain compound stress–strain curves. The Ogden parameters are then extracted via curve fitting. Total contact force is computed by summing incremental Hayes forces. Chapter 4 applies this methodology to mouse arterial tissue and introduces an approach to determine the equivalent thickness for Hayes’ model. The optimal thickness is defined as the one that minimises the variance of the calculated equivalent shear moduli. Based on 26 indentation tests from five mouse artery samples, the estimated thickness ranges from 0.05 to 0.5 mm, with an average shear modulus of 1.22 kPa. Chapter 5 employs finite element simulations to study artery–stent interactions. The arterial model includes intima, media, adventitia, and a lipid pool, each assigned anisotropic hyperelastic properties. Contact is defined using hard contact with friction coefficients from 0.01 to 0.1. Simulations investigate different stent surface geometries. Results show stress and strain concentration in three critical areas: the contact interface, the cap’s right shoulder, and around the lipid pool. Larger friction and high-amplitude stent surfaces increase stresses, while small-amplitude convex surfaces reduce average shear stress, suggesting their potential to reduce arterial injury during stenting.