Interaction between fatty acid salts and elastin: kinetics, absorption equilibrium, and consequences for elasticity

Elastin from bovine ligamentum nuchae is incubated in aqueous solutions of sodium salts of fatty acids (FAS). The FAS are laurate, myristate, and palmitate. Absorption of FAS in the elastin network is studied as a function of time, FAS concentration, and ionic strength. The consequences of this uptake for the elasticity of the elastin are studied by static and dynamic stress-strain measurements. Generally, distinction must be made between the initial time-dependent stage (I) and the final equilibrium stage (II). In I the initial rate of absorption follows a second-order binding mechanism, with the rate constant increasing with decreasing length of the FAS. In this regime, the elasticity modulus remains more or less unaffected. Especially in regime II the absorption of FAS is enhanced by a reduction in the cross-link density in the elastin network. This is ascribed to an osmotic pressure primarily caused by the concomitant uptake of low molecular weight ions in the elastin. The absorption equilibrium can be described by Langmuir theory. The absorption affinity increases with increasing hydrocarbon chain length of the FAS, indicating the contribution of hydrophobic interaction. Although the elasticity is not lost, the modulus is now reduced and a concomitant viscous component is developed.