Structure of fibrin gels studied by elastic light scattering techniques: Dependence of fractal dimension, gel crossover length, fiber diameter, and fiber density on monomer concentration

The concentration dependence of the structure of fibrin gels, formed following fibrinogen activation by thrombin at a constant molar ratio, was investigated by means of elastic light scattering techniques. The scattered intensity distributions were measured in absolute units over a wave-vector range q of about three decades $(\sim 3\times {10}^2–3\times {10}^5{\mathrm{cm}}^{-1}).\mathrm{}$ A set of gel-characterizing parameters were recovered by accurately fitting the data with a single function recently developed by us [F. Ferri et al., Phys. Rev. E 63, 031401 (2001)], based on a simple structural model. Accordingly, the gels can be described as random networks of fibers of average diameter d and density ρ, entangled together to form densely packed and spatially correlated blobs of mass fractal dimension $D_m$ and average size (or crossover length) ξ. As previously done for d, we show here that the recovered ξ is also a good approximation of a weight average, namely, $d\sim \sqrt{〈d^2{〉}_w}$ and $\xi \sim 〈\xi {〉}_w.$ By varying the fibrinogen concentration $c_F$ between 0.034–0.81 mg/ml, gels with $100>~\xi >~10\mu \mathrm{m},$ $100<~d<~200\mathrm{nm},$ $1.2<~D_m<~1.4,$ and constant $\rho \sim 0.4\mathrm{mg}/\mathrm{ml}$ were obtained. The power-law $c_F$ dependencies that we found for both ξ and d are consistent with the model, provided that the blobs are allowed to partially overlap by a factor η likewise scaling with $c_F$ $(2\mathrm{}>~\eta >~1).$ Recasting the whole dataset on a single master curve provided further evidence of the similarity between the structures of all the gels, and confirmed the self-consistency of the model.