Stiffening by fiber reinforcement in soft materials: a hyperelastic theory at large strains and its application.

This work defines an incompressible, hyperelastic theory of anisotropic soft materials at finite strains, which is tested by application to the experimental response of fiber-reinforced rubber materials. The experimental characterization is performed using a uniaxial testing device with optical measures of the deformation, using two different reinforcing materials on a ground rubber matrix. In order to avoid non-physical responses of the underlying structural components of the material, the kinematics of the deformation are described using a novel deformation tensor, which ensures physical consistency at large strains. A constitutive relation for incompressible fiber-reinforced materials is presented, while issues of stability and ellipticity for the hyperelastic solution are considered to impose necessary restrictions on the constitutive parameters. The theoretical predictions of the proposed model are compared with the anisotropic experimental responses, showing high fitting accuracy in determining the mechanical parameters of the model. The constitutive theory is suitable to account for the anisotropic response at large compressive strains, opening perspectives for many applications in tissue engineering and biomechanics.

Biorobotic investigation on the muscle structure of an octopus tentacle.

The present paper aims at understanding the biomechanics of an octopus tentacle as preliminary work for designing and developing a new robotic octopus tentacle. The biomechanical characterization of the biological material has been carried out on samples of Octopus vulgaris tentacles with engineering methods and tools, i.e. by biomechanical measurements of the tentacle elasticity and tension-compression stress/stretch curves. Another part of the activities has been devoted to the study of materials that can reproduce the viscoelastic behavior of the tentacle. The work presented here is part of the ongoing study and analysis on new design principles for actuation, sensing, and manipulation control, for robots with increased performance, in terms of dexterity, control, flexibility, applicability.

Modeling, design and validation of a novel microfluidic sensor for in-vitro isotonic measurement of microvessel contraction/dilation.

The paper presents an innovative fluidic microdevice for in-vitro isotonic measurements of microvessel contraction/dilation. The proposed microdevice is based on the well-known fluid dynamic principle which correlates a geometrical change of a solid body immersed in a constant flow, with the differential pressure change induced in the flow itself. Indeed, a biochemically-induced change of microvessel diameter lead to a change of its hydraulic resistance which can be in-vitro measured by a differential pressure sensor. The novel microfluidic sensor has been modeled, designed and fabricated in order to properly implement this working principle. The fluidic scheme of the sensor consists of two pressure-sensorized chambers which are connected by a calibrated channel where the microvessel is placed. Experimental tests have been performed by using three microvessel passive simulators with different inner diameter (300, 600 and 800 microm), in order to validate the expected sensor functioning characterized by two sensitivities: the pressure drop S (PL) and the overall S 2-3 ones. Their measured values (S (PL,m)=2.132 mV/V/Pa, S (2-3,m)=0.787 mV/V/(mm3/s)/mm) confirm the validity of the proposed working principle and permit to be confident in a future application of the sensor in a clinical context.