Abstract
One of the mechanisms which controls bone growth, repair remodeling and absorption is mechanical loading. There exists no long-term in vitro model to study bone cells together with their matrix, nor a model that can apply quantitative mechanical forces of physiological amplitudes and frequencies. The analysis of the mechanical properties of bone (Young’s modulus and visco-elastic moduli) on small pieces of bone is also difficult with present devices. We have built a device that can maintain full viability and physiological response of bone for a period of several weeks and integrates all three functions.
10mm diameter bone cores 5 mm thick were obtained from the trabecular bone of the distal ulna of a 24 months old cow by precision cutting with diamond saws and keyhole cutters (our pattern) in sterile 7–10°C phosphate buffered saline (PBS) and cultured in a variation of DMEM containing fructose HI GEM.
Results: The results of these studies have shown that perfusion of trabecular bone can maintain all cells and maintain bone structure for at least 72 days. In conventional methods for bone organ cultures, small bones, such as rat calvaria, quickly start to resorb bone and degenerate. In our perfusion system we see no evidence of change.. Initial experiments have indicated that there are 2 visco-elastic moduli of bone with different time constants, that the elastic modulus of trabecular bone varies is site dependant and that loading to 0.4% compression raises prostaglandin E2 and insulin-like growth factor 1 within a few hours. Mechanical stiffness of bone is increased by 35% when loaded for 20 days at 4,000μ, and decreases by 25% when not loaded. PTH at 10-10M increases stiffness over the load effect and 10-6M PTH decreases stiffness even in the presence of loading. Active osteoclasts are seen during the whole culture period indicating that the stem cells are present and functional.
We gratefully acknowledge support by the German Arthrose Foundation (DAH) and the AO in Davos, CH.
