Mechanical properties of fibroblast populated collagen matrices

Bio-artificial tissues, composed of cells in a collagen matrix, are being developed as replacement organs for damaged biologic tissue. A review of the current literature shows a need for more comprehensive mechanical testing of these replacement organs. Characterization of the mechanical properties is especially important in load bearing applications such as bio-artificial blood vessels.; Fibroblast populated collagen matrices (FPCMs) were used to investigate the mechanical behavior of bio-artificial tissues. Uniaxial tests on FPCM rings showed that these tissues exhibit nonlinear, viscoelastic and softening behavior. The uniaxial results were used to design protocols for biaxial testing. A pressure-diameter, force-length test system was designed and built for biaxial testing of FPCMs. For biaxial tests, the FPCM geometry was changed and the new tissues were termed FPCVs (fibroblast populated collagen vessels).; The mechanical constraints were controlled during FPCV incubation to produce tissues with two different cell orientations: axial and circumferential. FPCVs with oriented cells could be stretched to higher strains with lower stresses in the direction perpendicular to the cell orientation, than in the direction parallel to the cell orientation. Biaxial tests were also performed with added drugs to eliminate the mechanical contribution of the cells. The FPCVs were anisotropic even without the cellular contribution.; A constitutive model, based on the model presented in Zahalak et al. (2000), was developed to relate the FPCV microstructure to the mechanical properties. The FPCV stress was considered to be the sum of the contributions from linearly elastic cells with a preferred orientation and a nonlinear, pseudo-elastic, orthotropic matrix. Model parameters were fit to the biaxial test data for each FPCV, but it was difficult to determine unique parameters from the biaxial test data alone.; The test data and modeling in this dissertation are a first step toward providing material parameters and a constitutive relation to predict the behavior of bio-artificial tissues in vivo. A microstructurally based constitutive relation would allow tissues to be designed with specific mechanical properties. However, to predict the total stress from the contributions of cells and matrix, more information must be obtained about the relative stress contribution of each component.