Poor integration of tissue-engineered cartilage and surrounding healthy cartilage, lateral integration, is common in failure of cartilage repair strategies. Mechanical stimuli regulate cartilage development. Altering the mechanical environment in a controlled manner will enable the determination of pivotal stimuli in cartilage lateral integration allowing for improvement in cartilage repair strategies, development of rehabilitation regimes, and study of mechanisms underlying integration. The studies in this proposal will lead to the development of a mathematical model that correlates mechanical stimuli with the integration of cartilage tissue engineered constructs and surrounding healthy cartilage, lateral integration. This will be accomplished through the completion of the following aims: 1) the effects of different clinically relevant hydrodynamic environments on lateral tissue integration will be evaluated. An existing integration model (25) will be modified for implementation in a spinner flask and cartilage lateral integration of five combinations of shear stress and osmotic loading will be compared. The combinations are as follows: 1) static, 2) hypotonic + shear, 3) isotonic + shear 4) hypertonic + shear 5) hypertonic. The chondrogenic response will be evaluated through GAG analysis;gene expression analysis through qRT-PCR of aggrecan, collagen Type I and collagen Type II;biomechanical unconfined compression testing;and computerized histomorphometry. To measure strength of integration, a push test will be conducted. 2) The hydrodynamic environments implemented in the integration culture model will be characterized. This will be accomplished through quantization of the fluid flow fields by means of a computational fluid dynamic model which will be validated through particle image velocimetry. 3) Finally, a mathematical model will be created correlating hydrodynamic environment to tissue lateral integration and cartilage development. Using the data from Aim 1 applied to a published differentiation growth model (29) which describes how the quantity of differentiated and undifferentiated progenitor cells and the amount of extracellular matrix evolve with time, rate constants will be determined. The mechanical strength of integration will be correlated with rate constants to evaluate how they change with the different hydrodynamic environments. The model will be validated using historical data from previous studies.
Approximately one in six Americans is affected by arthritis, a condition commonly caused by damage to cartilage. Since the prominent reason cartilage repair therapies fail is lack of reparative tissue integrating with healthy tissue, this proposal aims to create a mathematical model capable of predicting how cartilage will integrate based on the mechanical environment experienced by the growing repair tissue. In doing so, this model could be used as a predictive tool when developing surgical repair techniques, developing rehabilitation regimes, and studying mechanisms underlying integration of engineered tissues with healthy cartilage and ultimately reduce the number of patients that develop premature arthritis.