We consider a polymerization (fragmentation) model with size-dependent parameters involved in prion proliferation. Using power laws for the different rates of this model, we recover the shape of the polymerization rate using experimental data. The technique used is inspired from [30], where the fragmentation dependence on prion strains is investigated. Our improvement is to use power laws for the rates, whereas [30] used a constant polymerization coefficient and linear fragmentation. Keywords Aggregation-fragmentation equations, self-similarity, eigenproblem, size repartition, polymerization process, data fitting, inverse problem. AMS Class. No. 35F50, 35Q92, 35R30, 45C05, 45K05, 45M99, 45Q05, 65D10, 92D25