Elasticity in Physically Cross-Linked Amyloid Fibril Networks

Area of Science:

• Biophysics
• Materials Science
• Colloid Science

Background:

• Amyloid fibrils form complex networks with mechanical properties crucial for biological function and disease.
• Understanding the elasticity of these networks is challenging due to factors like fibril flexibility and inter-fibril interactions.

Purpose of the Study:

• To develop a constitutive model for semiflexible and rigid amyloid fibril networks.
• To investigate the influence of concentration and ionic strength on network elasticity.
• To elucidate the role of electrostatic interactions in governing amyloid network mechanics.

Main Methods:

• Combined the affine thermal model of network elasticity with Derjaguin-Landau-Vervey-Overbeek (DLVO) theory.
• Validated the model against rheological experimental data for beta-lactoglobulin and lysozyme amyloid networks.

Main Results:

• The model accurately predicts the power-law scaling of elasticity (G) with concentration (c) for both semiflexible (G∼c^{2.2}) and rigid (G∼c^{2.5}) fibrils.
• The model correctly describes the scaling of elasticity with ionic strength (I) (G∼I^{4.4} for β-lactoglobulin, G∼I^{3.8} for lysozyme), independent of fibril flexibility.
• Demonstrated that screening salt reduces electrostatic repulsion, converting transient entanglements into stable cross-links.

Conclusions:

• The developed model provides a robust framework for understanding amyloid fibril network mechanics.
• Electrostatic interactions, as described by DLVO theory, are critical in determining the mechanical properties of amyloid networks.
• The salt-dependent elasticity of amyloid networks exhibits unique power-law behavior distinct from other polymer systems.