###### Abstract  
Evaluation of the mechanical properties of biological tissues has always been an important issue in the field of biomedicine. The traditional method for mechanical properties measurement is to perform in vitro tissue deformation experiments. With the fast development of optical and image processing techniques, more and more non-invasive and non-contact optical methods have been applied to the analysis of tissue mechanical features. In this study, we use Mueller matrix polarimetry to quantitatively obtain the mechanical properties of bovine tendon tissues. Firstly, to study the structural information and the changes in the optical characteristics of the tendon tissue under different stretching states, 3 \(\times\) 3 Mueller matrix images of bovine tendon tissue samples are acquired by backscattering measurement setups based on a polarized camera. Then, we extract the frequency distribution histograms (FDHs) of the Mueller matrix elements to reveal the structural changes of the tendon tissue more clearly during the stretching process. Last, we calculate the Mueller matrix transformation (MMT) parameters, the total anisotropy \(t_{1}\) and the anisotropy direction \(\alpha_{1}\) of the tendon tissue samples under different stretching processes to quantitatively characterize their structural changes under different mechanical states. The central moments of the MMT parameters can be used to distinguish the different stretching states of the tendon tissue. For better discrimination based on the MMT parameters, we design a multilayer neural network that takes the first-order moments of the MMT parameters as the input features. After training, a high-precision classification model of the stretching states of tendon tissue samples is finally obtained, and the total classification accuracy achieves 98%. The experimental results show that the Mueller matrix polarimetry can be a potential non-contact tool for tissue mechanical properties evaluation. m 2022 2022 2022 2022 2022 2022 2022 2022 2022 2022 202  
mechanical parameters such as displacement and strain [6], which is a method of obtaining object performance parameters based on the natural or artificial spotting field of the surface before and after deformation. Optical coherence elastography (OCE) can measure tissue deformation due to excitation and accurately obtain tissue elastic information [7]. Ultrasound elastography and MRI [8] can obtain tissue strain and strain rate, but with limited resolution. With the fast development of optical and image processing techniques, more and more non-invasive and non-contact optical methods have been applied to the analysis of tissue mechanical features. In the past decade, Mueller matrix polarimetry is gaining more and more attention in biomedical studies and applications [9]. Compared with non-polarized optical methods, Mueller matrix polarimetry is sensitive to microstructures and can additionally provide information on the optical anisotropy of tissues, including birefringence and linear dichroism (LD), noninvasively [9; 10]. At present, the commonly used Mueller matrix measurement method is based on the dual-rotating retarders method proposed by [PERSON] [11], which can eliminate the image deformation induced by the rotation of the polarizers. Moreover, there are also Mueller matrix measurement methods based on polarization cameras to improve the measurement efficiency for dynamic biomedical samples [12]. In this work, we use Mueller matrix polarimetry to quantitatively detect and evaluate the mechanical properties of tendon tissues stretched by different external forces. Firstly, we measure the 3 \(\times\) 3 Mueller matrix images of bovine tendon tissue samples with different stretching states using the backscattering measurement setups based on a polarization camera. Then, we extract the frequency distribution histograms (FDHs) of the Mueller matrix elements to reveal the structural changes of the tendon tissue during the stretching process.