Related Experiment Video
Updated: Dec 11, 2025
Microengineering 3D Collagen Hydrogels with Long-Range Fiber Alignment
Published on: September 7, 2022
Microrheology imaging of fiber suspensions - a case study for lyophilized collagen I in HCl solutions
Johanna Hafner1, Claude Oelschlaeger1, Norbert Willenbacher1
1Department of Mechanical Engineering and Mechanics, Applied Mechanics Group, Karlsruhe Institute of Technology, Karlsruhe, Germany. johanna.roether@kit.edu.
Abstract:
In fiber suspensions with low optical contrast, the in situ characterization of structural properties with conventional microscopy methods fails. However, overlaying subsequent images of multiple particle tracking (MPT) videos including short trajectories usually discarded in MPT analysis allowed for direct visualization of individual fibers and the network structure of lyophilized collagen I (Coll) distributed in hydrochloric acid solutions. MPT yielded a broad distribution of mean square displacements (MSDs). Freely diffusing tracer particles yielded viscosities indicating that, irrespective of concentration, a constant amount of Coll is dissolved in the aqueous phase. Particles found elastically trapped within fibrous Coll structures exhibited a broad range of time-independent MSDs and we propose a structure comprising multiple fiber bundles with dense regions inaccessible to tracers and elastic regions of different stiffness in between. Bulky aggregates inaccessible to the 0.2 μm tracers exist even at low Coll concentrations, a network of slender fibers evolves above the sol-gel transition and these fibers densify with increasing Coll concentration. This novel MPT-based imaging technique possesses great potential to characterize the fiber distribution in and structural properties of a broad range of biological and technical suspensions showing low contrast when imaged with conventional techniques. Thus, MPT imaging and microrheology will help to better understand the effect of fiber distribution and network structure on the viscoelastic properties of complex suspensions.
Insights
This study visualizes fiber networks in low-contrast suspensions using particle tracking. It reveals collagen structures and their impact on fluid properties, advancing complex suspension characterization.
Area of Science:
- Biophysics
- Materials Science
- Rheology
Background:
- Conventional microscopy struggles with low-contrast fiber suspensions.
- Characterizing the structure of collagen I (Coll) in solution is challenging.
- Understanding fiber network properties is crucial for complex fluid behavior.
Purpose of the Study:
- To develop a novel method for visualizing and characterizing fiber networks in low-contrast suspensions.
- To investigate the structure of lyophilized collagen I in hydrochloric acid solutions.
- To correlate fiber network structure with viscoelastic properties.
Main Methods:
- Utilized multiple particle tracking (MPT) analysis of videos, including short trajectories.
- Analyzed mean square displacements (MSDs) of tracer particles.
- Applied microrheology to assess fluid properties.
Main Results:
- Visualized individual fibers and the network structure of collagen I.
- Identified distinct structural features: dense fiber bundles and elastic regions of varying stiffness.
- Observed bulky aggregates even at low collagen concentrations, with network densification above the sol-gel transition.
- Determined a constant amount of dissolved collagen irrespective of concentration.
Conclusions:
- The novel MPT-based imaging technique effectively visualizes fiber distribution and structural properties in low-contrast suspensions.
- The proposed structure of collagen I networks explains observed microrheological behavior.
- This approach enhances understanding of how fiber networks influence viscoelastic properties in complex fluids.
