Preparation of rat tail tendons for biomechanical and mechanobiological studies.

Rat tail tendons (RTTs) are a common biological model used in experimental in vitro studies in the fields of tendon physiology and tendinopathy. Working with those tissues is challenging because they are very fragile, and until now there was no rigorously detailed protocol for their isolation. Faced with these challenges, we have developed methods and instruments to facilitate manipulation of RTTs and control tissue viability, sterility and integrity. This article describes the experimental procedures used to prepare RTTs for biomechanical and mechanobiological studies. Our work is divided into four main steps: extraction, cross-sectional area measurement, rinsing and loading into the bioreactor chamber. At each step, all procedures, materials and manipulations are presented in detail so that they can be easily reproduced. Moreover, the specific instruments developed are presented: a manipulation plate used to segregate RTTs, an optic micrometer to position the tissue during the cross-sectional area measurement and an anchoring system to attach the RTTs onto a bioreactor. Finally, we describe the results obtained after multiple tests to validate our methods. The viability, sterility and integrity evaluations demonstrate that our procedures are sufficiently rigorous for manipulations of fragile tissues such as rat tail tendons.

Relative contributions of mechanical degradation, enzymatic degradation, and repair of the extracellular matrix on the response of tendons when subjected to under- and over- mechanical stimulations in vitro.

Tendon response to mechanical loading results in either homeostasis, improvement, or degeneration of tissue condition. In an effort to better understand the development of tendinopathies, this study investigated the mechanical and structural responses of tendons subjected to under- and over-stimulations (1.2% and 1.8% strain respectively, 1 Hz). The objective was to examine three sub-processes of tendon response: mechanical degradation, enzymatic degradation, and repair of the extracellular matrix. We subjected rat tail tendons to a 10-day stimulation protocol with four periods of 6 h each day: 30 min of stimulation and 5 h 30 min of rest. To investigate the contribution of the three sub-processes, we controlled the contribution of the cells through variations in the nutrient and protease inhibitor content in the in vitro solutions. Using nondestructive cyclic tests, we evaluated the daily changes in the peak stress. To assess structural changes, we carried out microscopic analyses at the end of the study period. We observed that the relative contributions of the sub-processes differed according to the stimulation amplitude. With over-stimulation of tendons immersed in DMEM, we succeeded in reducing enzymatic degradation and increasing peak stress. In under-stimulation, the addition of protease inhibitors was required to obtain the same result.