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Penetrating Microindentation of Hyper-soft, Conductive Silicone Neural Interfaces in Vivo Reveals Significantly Lower Mechanical Stresses

Published online by Cambridge University Press:  17 September 2019

Arati Sridharan Open the ORCID record for Arati Sridharan [Opens in a new window] ,
Vikram Kodibagkar Open the ORCID record for Vikram Kodibagkar [Opens in a new window]  and
Jit Muthuswamy
Arati Sridharan
Affiliation:
Neural Microsystems Laboratory, School of Biological & Health Systems Engineering, 501 E Tyler Mall, Arizona State University, Tempe, AZ, USA, 85287
Vikram Kodibagkar
Affiliation:
Prognostic BioEngineering (ProBE) laboratory, School of Biological & Health Systems Engineering, 501 E Tyler Mall, Arizona State University, Tempe,AZ, USA, 85287
Jit Muthuswamy*
Affiliation:
Neural Microsystems Laboratory, School of Biological & Health Systems Engineering, 501 E Tyler Mall, Arizona State University, Tempe, AZ, USA, 85287
*
*(Email: jit@asu.edu)
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Abstract

There is growing evidence that minimizing the mechanical mismatch between neural implants and brain tissue mitigates inflammatory, biological responses at the interface under long-term implant conditions. The goal of this study is to develop a brain-like soft, conductive neural interface and use an improvised, penetrating microindentation technique reported by us earlier to quantitatively assess the (a) elastic modulus of the neural interface after implantation, (b) mechanical stresses during penetration of the probe, and (c) periodic stresses at steady-state due to tissue micromotion around the probe. We fabricated poly- dimethylsiloxane (PDMS) matrices with multi-walled carbon nanotubes (MWCNTs) using two distinct but carefully calibrated cross-linking ratios, resulting in hard (elastic modulus∼484 kPa) or soft, brain-like (elastic modulus∼5.7 kPa) matrices, the latter being at least 2 orders of magnitude softer than soft neural interfaces reported so far. Subsequent loading of the hard and soft silicone based matrices with (100% w/w) low-molecular weight PDMS siloxanes resulted in further decrease in the elastic modulus of both matrices. Carbon probes with soft PDMS coating show significantly less maximum axial forces (-587 ± 51.5 µN) imposed on the brain than hard PDMS coated probes (-1,253 ± 252 µN) during and after insertion. Steady-state, physiological micromotion related stresses were also significantly less for soft- PDMS coated probes (55.5 ± 17.4 Pa) compared to hard-PDMS coated probes (141.0 ± 21.7 Pa). The penetrating microindentation technique is valuable to quantitatively assess the mechanical properties of neural interfaces in both acute and chronic conditions.

Keywords

biomaterialmicroscaleviscoelasticityelastic propertiestissue
Type
Articles
Information
MRS Advances , Volume 4 , Issue 46-47: Soft Materials and Biomaterials , 2019 , pp. 2551 - 2558
Copyright
Copyright © Materials Research Society 2019 

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