Related Experiment Video
Updated: Mar 3, 2026
08:54
Chronic Implantation of Multiple Flexible Polymer Electrode Arrays
Published on: October 4, 2019
11.4K
Histological evaluation of flexible neural implants; flexibility limit for reducing the tissue response?
Heui Chang Lee1,2, Fredrik Ejserholm3,4, Janak Gaire5
1Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN, United States of America.
Journal of Neural Engineering
|May 5, 2017
Summary
Soft polymer neural probes significantly reduce foreign body response (FBR) compared to stiff silicon probes. However, further increasing probe flexibility beyond a certain threshold did not yield additional FBR reduction, suggesting mechanical mismatch is not the sole factor limiting implant longevity.
Area of Science:
- Biomaterials Science
- Neuroscience
- Medical Device Engineering
Background:
- Flexible neural probes aim to minimize chronic foreign body response (FBR) by reducing mechanical strain caused by brain micromotion.
- A significant Young's modulus mismatch persists between current flexible probes and brain tissue, questioning the necessity of bridging this gap.
Purpose of the Study:
- To quantitatively evaluate the foreign body response (FBR) to neural probes of varying mechanical compliance.
- To determine if increasing neural probe flexibility proportionally reduces FBR and investigate the impact of mechanical mismatch on implant performance.
Main Methods:
- Utilized novel off-stoichiometry thiol-enes-epoxy (OSTE+) polymer probes with distinct stiffnesses (6 MPa to 300 MPa), alongside silicon (~150 GPa) and polyimide (1.5 GPa) probes.
- Assessed FBR by quantifying fluorescence intensity of microglial/macrophage activation and blood-brain barrier (BBB) leakage markers at 4 and 8 weeks post-implantation.
Main Results:
- A significant reduction in FBR biomarkers was observed for three soft polymer probes (OSTE+ and polyimide) compared to stiff silicon probes.
- No consistent differences in FBR biomarkers were found among the different soft polymer probes, indicating a potential threshold effect.
- Blood-brain barrier (BBB) leakiness was also reduced around the softer probes.
Conclusions:
- Neural probe mechanical compliance can modulate FBR, but this effect plateaus after a certain softness threshold.
- Addressing only the mechanical mismatch between probes and brain tissue may have limited impact on improving the long-term performance and lifespan of neural implants.
- Further research should explore other factors beyond mechanical properties that influence the foreign body response to neural implants.
