Deposition of collagenous matrices by tendon fibroblasts in vitro: a comparison of fibroblast behavior in pellet cultures and a novel three-dimensional long-term scaffoldless culture system.

Tendons transmit tensile loads from muscle to bone. They consist primarily of parallel collagen fibers between longitudinally oriented rows of tendon fibroblasts. In this study, we describe a novel scaffoldless dialysis-roller culture system that allows tendon cells to form large, organized, tendon-like structures. We compare cell and collagen orientation and synthesis in these cultures with that of monolayer and high-density pellet cultures. Monolayers are unable to deposit a substantial matrix, losing most of their secreted collagen to the medium. High-density pellet cultures deposit more matrix, lose less to the medium, and become organized at their periphery but show signs of nutritional compromise in the center core. In the novel system, cells formed highly organized structures resembling embryonic tendons, synthesized much more collagen, and incorporated around 70% of the secreted collagen into the tendon-like extracellular matrix. The three-dimensional cultures appear to allow substantial cell-cell interactions and may mimic important aspects of the early development of tendons, including the formation of membrane-bound extracellular spaces to contain and organize the secreted collagen.