Diffusive and convective transport of proteins in fibrin gels

The human body is a composite of billions of cells within three-dimensional extracellular matrices (ECM) organized into tissues and organs. Mass transport of proteins within the extracellular matrix is required to provide communication signals for growth, maintenance, and repair. These same proteins are exploited by tissue engineers to treat disease and assist wound healing. In vivo studies have demonstrated the significance of the ECM on the transport of proteins, but mass transport has not been systematically studied within tissue ECM. In this thesis, experimental methods are developed to measure protein transport rates in a model ECM and the results are compared with mathematical models to systematically study transport of proteins in biological gels.; A system utilizing fluorescence microscopy was built to measure one-dimensional concentration profiles of proteins in three dimensional fibrin gels. The profiles of insulin-like growth factor I, a protein hormone in wound healing, diffusing into fibrin were reconciled with a similarity solution to a Fick diffusion model to calculate a diffusion coefficient of 1.55*10-6+/-0.155*10 -6cm2/s. A porous membrane supporting the fibrin gel interface produced gels with stable microstructures as evident by the elimination of gel hysteresis. The Darcy permeability (hydrodynamic permeability) of the gels under physiological salt conditions was determined to be 7.49*10 -10+/-1.65*10-10cm2. The broadening of a pulse of ribonuclease, a model protein for mass transport studies, was quantified as it was convected through the fibrin gel. The pulse broadening data were analyzed using both the method of moments and a Laplace transform method to calculate dispersion coefficients and average liquid velocities inside and outside of the gel. An important result is that convection inside the gel causes a level of dispersion that is greater than predicted by molecular diffusion alone.; The methods for determining the diffusion coefficient and convective-diffusion parameters of proteins in gels that were developed could be applied in the future to more complicated matrices, for example, fibrin gels containing cells and hormone binding proteins.