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The effects of mechanical stress on cells and their extracellular matrix, especially in gliding sections of tendon, are still poorly understood. This study sought to compare the effects of uniaxial stretching on both gliding and traction areas in the same tendon. Flexor digitorum longus muscle tendons explanted from rats were subjected to stretching in a bioreactor for 6, 24, or 48 h, respectively, at 1 Hz and an amplitude of 2.5%. After stimulation, marker expression was quantified by histological and immunohistochemical staining in both gliding and traction areas. We observed a heightened intensity of scleraxis after 6 and 24 h of stimulation in both tendon types, though it had declined again 48 h after stimulation. We observed induced matrix metalloproteinase-1 and -13 protein expression in both tendon types. The bioreactor produced an increase in the mechanical structural strength of the tendon during the first half of the loading time and a decrease during the latter half. Uniaxial stretching of flexor tendon in our set-up can serve as an overloading model. A combination of mechanical and histological data allows us to improve the conditions for cultivating tendon tissues.

In biomedical applications bioreactors are used, which are able to apply mechanical loadings under cultivation conditions on biological tissues. However, complex mechanobiological evolutions, such as the dependency between mechanical properties and cell activity, depend strongly on the applied loading conditions. This requires correct physiological movements and loadings in bioreactors. The aim of the present study is to develop bioreactors, in which native and artificial biological tissues can be cultivated under physiological conditions in knee joints and spinal motion segments. However, in such complex systems, where motions with different degrees of freedom are applied to whole body parts, it is necessary to investigate elements of joints and spinal parts separately. Consequently, two further bioreactors for investigating tendons and cartilage specimens are proposed additionally. The study is complemented by experimental and numerical examples with emphasis on medical and engineering applications, such as biomechanical properties of cartilage replacement materials, injured tendons, and intervertebral discs., (Copyright © 2016 IPEM. Published by Elsevier Ltd. All rights reserved.)