Optically based-indentation technique for acute rat brain tissue slices and thin biomaterials

Area of Science:

• Biomaterials Science
• Mechanical Engineering
• Neuroscience

Background:

• Micro-indentation of soft biological materials is hindered by instrumental drift, limiting long-term mechanical property measurements like equilibrium modulus.
• A lack of reliable methods exists for determining the equilibrium modulus of delicate biological tissues.

Purpose of the Study:

• To develop and validate a novel indentation technique combined with optical coherence tomography (OCT) for precise, long-time scale mechanical testing of soft biological materials.
• To measure the equilibrium modulus of agarose hydrogels and acute rat brain tissue slices.

Main Methods:

• Utilized indentation coupled with OCT to measure surface deformation profiles of submerged samples after applying spherical beads.
• Tested low-concentration agarose hydrogels (0.3-0.6% w/v) and acute rat brain tissue slices over 30 minutes.
• Assessed cell viability using Fluor-Jade C (FJC) staining to determine safe testing durations.

Main Results:

• Successfully measured large equilibrium deformations, enabling prediction of the equilibrium modulus (μ(∞)) through finite element analysis.
• Obtained μ(∞) values for hydrogels between 0.07–1.8 kPa.
• Determined μ(∞) for rat brain tissue: 0.13 ± 0.04 kPa (cortex) and 0.09 ± 0.015 kPa (hippocampus).

Conclusions:

• The combined indentation-OCT technique provides a localized, real-time, high-resolution method for long-time scale mechanical characterization of soft materials.
• This method can be adapted for viscoelasticity studies, diverse tissue/biomaterial testing, and analysis of internal structural changes under load.
• Ensured cell viability during testing through FJC staining, validating the method's applicability to biological samples.