  This paper presents a synthesis approach in a density-based topology
optimization setting to design large deformation compliant mechanisms for
inducing desired strains in biological tissues. The modelling is based on
geometrical nonlinearity together with a suitably chosen hypereleastic material
model, wherein the mechanical equilibrium equations are solved using the total
Lagrangian finite element formulation. An objective based on least-square error
with respect to target strains is formulated and minimized with the given set
of constraints and the appropriate surroundings of the tissues. To circumvent
numerical instabilities arising due to large deformation in low stiffness
design regions during topology optimization, a strain-energy based
interpolation scheme is employed. The approach uses an extended robust
formulation i.e. the eroded, intermediate and dilated projections for the
design description as well as variation in tissue stiffness. Efficacy of the
synthesis approach is demonstrated by designing various compliant mechanisms
for providing different target strains in biological tissue constructs.
Optimized compliant mechanisms are 3D-printed and their performances are
recorded in a simplified experiment and compared with simulation results
obtained by a commercial software.
