Experimental approaches for mechanical investigation of soft biological tissues as meniscal cartilage.

INTRODUCTION The main difficulty in the complete evaluation of the behaviour of a biological tissue as the meniscal cartilage when submitted to a load is connected with the extreme structural complexity of the natural tissue, which corresponds to highly differentiated mechanical properties: poroelastic, viscoelastic and hyperelastic behaviours. For these reasons, in this work a novel approach to investigate meniscus properties, less invasive for the inner structure of the tissue, was designed. This experimental approach is suitable and applicable also at others types of soft biological tissues. EXPERIMENTAL AND RESULTS The mechanical analysis is based on indentation of intact meniscus. All the tests were performed at 37 °C after immersion of the sample in physiological solution (0,9% NaCl) for 1 hour, in order to reach the maximum swelling condition. The experimental setup consisting in positioning of the meniscus, incorporated within orthodontic gypsum support, upon a rigid and tilting plate used to assure the perpendicularity of the indenter on the sample surface. The storage modulus (E’) for intact meniscus displays lower values in correspondence of the regions with higher vascularization (red zone). This differences are moreover evident considering the loss factor Q-1 = E”/E’, that, in the peripheral region, is about three time higher than the one measured in the internal zone without blood vessels (white zone). CONCLUSION The particularity of this work has been to setup a new method for mapping the mechanical properties of meniscus and, in general, complex soft biological tissues. The indentation test is less invasive for the inner structure of the tissue and allows to reduce the problems of morphological complexity of the meniscus.