Micro-finite element models of bone tissue-engineering scaffolds

Tissue engineering is an emerging area in bioengineering at the frontiers between biomaterials, biology and biomechanics. The basic knowledge of the interactions between mechanical stimuli, cells and biomaterials is growing but the quantitative effect of mechanical stimuli on cells attached to biomaterials is still unknown. The objective of this study was to develop finite element models of various bone scaffolds based on calcium phosphate in order to calculate the load transfer from the biomaterial structure to the biological entities. Samples of porous calcium phosphate bone cement and biodegradable glass were scanned using micro-CT to determine the overall macroporosity, architecture and to develop finite element models of such materials. Compressive loads were applied on the models to simulate the in vitro environment of a bioreactor and stress and strain distributions were calculated. It was found that the effective Young's modulus was linearly related to the sample macroporosity. Results suggest that a 0.5% overall compressive strain can produce internal strain of the same order of magnitude as found in previous in vitro mechanically cell-strained studies or in mechanoregulation studies. Stress and strain concentrations due to the porous structures are possible candidate for favouring cell differentiation. Although strain distributions were similar between bone cement and porous glass, the stress distribution is clearly different. Future in vitro results could correlate the results obtained with such finite element study to explain the influence of mechanical stimuli on cell behaviour.