Permeability of three-dimensional fibrin constructs corresponds to fibrinogen and thrombin concentrations

Research in the last few years have focused on the use of three-dimensional (3D) fibrin construct to deliver growth factors and cells. Three-dimensional construct permeability and porosity are important aspects for proper nutrient uptake, gas exchange, and waste removal-factors that are critical for cell growth and survival. We have previously reported that the mechanical strength (stiffness) of 3D fibrin constructs is dependent on the fibrinogen and thrombin concentration. In this study, we established two new in vitro models to examine how fibrin composition affects the final 3D fibrin construct permeability and pore size; thereby, influencing the diffusivity of macromolecules throughout the network of fibrin fibrils. Flow measurements of both liquid and fluoresceinated-dextran microparticles are conducted to calculate the permeability and pore size of 3D fibrin constructs of different fibrinogen and thrombin concentrations. Similarly, the diffusivity of liquid and fluoresceinated-dextran microparticles through these 3D fibrin constructs are determined through diffusion models. Data from these studies show that the structural permeability and pore size of 3D fibrin constructs directly correlate to fibrinogen and thrombin concentration in the final 3D fibrin construct. More specifically, at a constant thrombin concentration of 2 or 5 μ/mL, pore size of the 3D fibrin constructs is dependent on fibrinogen if the concentration is 5 mg/mL and to a lesser extent if the concentration is 10-15 mg/mL. These findings suggest that fibrin's diffusive property can be manipulated to fabricate 3D constructs that are optimized for cellular growth, protein transport, and for the controlled delivery of bioactive molecules such as growth factors.