A multi-scale study of fibrin gels formation: from the early phases to the final network.

Fibrin gel polymerization, key element of blood coagulation, produces the network inside which platelets and other blood components are trapped, forming the hemostatic plug that stops bleeding. As fully biocompatible materials with extraordinary mechanical properties, fibrin gels are ideal substrates for many biotechnological applications. By studying the early phases of polymerization, using simultaneous Small Angle X-ray Scattering and Wide Angle Light Scattering, we defined a new polymerization model in which single-bonded "Y Ladder" polymers rapidly elongate before undergoing a delayed transition to the traditional double-stranded fibrils. Completely formed fibrin gel appears as a fractal collection of straight fibers, almost monodisperse in diameter and connected together at nodal points with a branching order 3-4. Taking into account these features, we implemented a simple iterative algorithm able to generate in silico gels. The resulting 3D network resembles real fibrin gels and can be sketched as an assembly of densely packed fractal blobs. Using this model we refined the analytical expression of the form factor which is capable of accurately fitting the Light Scattering data, giving the gels' structural parameters. By globally fitting Low Angle Elastic Light Scattering data with the refined form factor and Turbidimetry data with a function obtained by angularly integrating the scattering form factor, all the parameters characterizing the gel can be robustly recovered. Finally we have also developed a 2D method for the determination of the gel pore size that analyze thin stacks of randomly sampled thresholded 3D confocal images.