Abstract
Tendons attach muscles to bone and thereby transmit tensile forces during joint movement. However, a detailed understanding of the mechanisms that establish the mechanical properties of tendon has remained elusive because of the practical difficulties of studying tissue mechanics in vivo. Here we have performed a study of tendon-like constructs made by culturing embryonic tendon cells in fixed-length fibrin gels. The constructs display mechanical properties (toe–linear–fail stress–strain curve, stiffness, ultimate tensile strength, and failure strain) as well as collagen fibril volume fraction and extracellular matrix (ECM)/cell ratio that are statistically similar to those of embryonic chick metatarsal tendons. The development of mechanical properties during time in culture was abolished when the constructs were treated separately with Triton X-100 (to solubilise membranes), cytochalasin (to disassemble the actin cytoskeleton) and blebbistatin (a small molecule inhibitor of non-muscle myosin II). Importantly, these treatments had no effect on the mechanical properties of the constructs that existed prior to treatment. Live-cell imaging and 14C-proline metabolic labeling showed that blebbistatin inhibited the contraction of the constructs without affecting cell viability, procollagen synthesis, or conversion of procollagen to collagen. In conclusion, the mechanical properties per se of the tendon constructs are attributable to the ECM generated by the cells but the improvement of mechanical properties during time in culture was dependent on non-muscle myosin II-derived forces.
Highlights
The ability of tendons to transmit tensile forces is acquired during embryonic development in preparation for ambulatory movement at birth, especially in birds, reptiles and some mammals
A motivation for our Abbreviations: CVF, cell volume fraction, the fraction of the construct occupied by cells; ECM, extracellular matrix; ECMT, embryonic chick metatarsal tendon; EM, electron microscopy; FACS, fluorescence activated cell sorting; FVF, fibril volume fraction, the fraction of the construct occupied by collagen fibrils; NMMII, non-muscle myosin II; PBS, phosphate buffered saline
The results presented here show that the tendon constructs assembled a fibrous matrix with mechanical properties similar to native embryonic tendons
Summary
The ability of tendons to transmit tensile forces is acquired during embryonic development in preparation for ambulatory movement at birth, especially in birds, reptiles and some mammals. The mechanisms that establish the mechanical properties of tendon during embryogenesis have been difficult to determine because of impracticalities of studying cell biomechanics in vivo. In a previous study we showed that day 13 embryonic chick metatarsal tendon (ECMT) cells synthesize a tendon-like construct when cultured in fixed-length fibrin gels (Kapacee et al, 2008). A motivation for our Abbreviations: CVF, cell volume fraction, the fraction of the construct occupied by cells; ECM, extracellular matrix; ECMT, embryonic chick metatarsal tendon; EM, electron microscopy; FACS, fluorescence activated cell sorting; FVF, fibril volume fraction, the fraction of the construct occupied by collagen fibrils; NMMII, non-muscle myosin II; PBS, phosphate buffered saline
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