From observations of colloidal tracer particles in fibrin undergoing gelation, we introduce an analytical framework that allows the determination of the probability density function for a stochastic process beyond fractional Brownian motion. Using passive microrheology via videomicroscopy, mean square displacements of tracer particles suspended in fibrin at different ageing times are obtained. The anomalous diffusion is then described by a damped white noise process with memory, with analytical results closely matching experimental plots of mean square displacements and probability density function. We further show that the white noise functional stochastic approach applied to passive microrheology reveals the existence of a gelation parameter μ which elucidates the dynamics of constrained tracer particles embedded in a time-dependent soft material. In addition, we found that microstructural heterogeneity of particle environments decreases as the ageing time increases. This study offers experimental insights on the ageing of fibrin gels while presenting a white noise functional stochastic approach that could be applied to other systems exhibiting non-Markovian diffusive behavior.
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