Microrheology and microstructure of Fmoc-derivative hydrogels

Area of Science:

• Materials Science
• Polymer Chemistry
• Rheology

Background:

• Hydrogels are crucial in various applications, but their dynamic properties during formation require detailed study.
• Understanding the gelation process of low-molecular-weight hydrogelators like Fmoc-tyrosine is key to controlling material properties.

Purpose of the Study:

• To probe the viscoelasticity of Fmoc-tyrosine hydrogel networks during gelation.
• To characterize the dynamic properties and network structure using particle-tracking microrheology.

Main Methods:

• Particle-tracking microrheology to monitor mean square displacement (MSD) of probe particles.
• Analysis of MSD versus lag time to identify percolation transition and self-similar network formation.
• Application of generalized Stokes-Einstein relation to determine viscoelastic moduli.
• Cryogenic scanning electron microscopy (Cryo-SEM) for network visualization.

Main Results:

• Superimposable MSD plots indicate a self-similar hydrogel network formed via percolation.
• Determined gel time (t(gel) = 43.4 ± 0.05 min) and critical relaxation exponent (n(c) = 0.782 ± 0.007), close to theoretical values for semiflexible polymers.
• Viscoelastic moduli analysis reveals a structurally and rheologically fragile critical gel.
• High-frequency scaling (G'/G″ as ω(~3/4)) and Cryo-SEM images support semiflexible behavior with a long fibrillar persistence length.

Conclusions:

• Fmoc-tyrosine hydrogels exhibit semiflexible polymer network characteristics.
• The study demonstrates the utility of particle-tracking microrheology for characterizing dynamic gelation processes.
• This system offers a platform for further rheological investigations of Fmoc derivatives.