Effects of Micro-Milling and Laser Engraving on Processing Quality and Implantation Mechanics of PEG-Dexamethasone Coate

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Effects of Micro-Milling and Laser Engraving on Processing Quality and Implantation Mechanics of Polyethyleneglycol-Dexamethasone Coated Neural Probe ZHOU Xuhui (),

ZHANG Wenguang ∗ (),

XIE Jie (

)

(State Key Laboratory of Mechanical System and Vibration, School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China)

© Shanghai Jiao Tong University and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Abstract: Compared with stiff silicon-based probes, flexible neural probes can alleviate biological inflammation and tissue rejection. A polyethyleneglycol (PEG) coating can facilitate the insertion of flexible probes, and the fabrication methods have a significant impact on the dimensional accuracy and structural strength of the coating. In this study, a novel melting injection moulding method is used to process a PEG-dexamethasone (DEX) coating with high structural strength for a type of mesh-shaped photosensitive polyimide (PSPI) based neural probe. Combined with the digital image correlation (DIC) method, an in vitro test system with high accuracy is developed to evaluate the effects of the elastic modulus of the PEG component and two fabrication methods, i.e., computer-numerical-control (CNC) micro-milling and laser engraving, on the processing quality and implantation mechanics of a PEG-DEX coated probe. The results show that compared with laser engraving, CNC micro-milling can ensure high dimensional accuracy and sharpness for the composite coating, thus leading to small damage from implantation, whereas the elastic modulus of the composite coating has a limited effect on the implantation mechanics of the PEG-DEX coated probe. Key words: flexible neural probe, composite coating, digital image correlation (DIC), polyethyleneglycol (PEG), dexamethasone (DEX), insertion force, implantation injury CLC number: R 318.01 Document code: A

0 Introduction Implantable neural probes record the electrophysiological activities of neural systems and stimulate specific brain areas, which can have the significant potential for treating Parkinson’s disease, Alzheimer’s syndrome, and other neurological diseases[1] . Currently, implantable silicon-based neural probes have been widely used in clinical treatment. However, researchers have found that silicon-based neural probes suffer from unreliable long-term stability and can easily trigger intracranial inflammation after implantation[2] . In addition, during and after implantation, chronic tissue damage induced by a mechanical mismatch between the hard silicon substrate and soft brain tissue can lead to a reduced service life of the implants[3] . Over the past few years, the use of flexible and biocompatible polymers as thin substrate materials has spread, reducing the mechanical mismatch and longReceived: 2020-04-27 Accepted: 2020-05-27 Foundation item: the National Natural Science Foundation of China (No. 51675330) ∗E-mail: [email protected]

term damage after implantation. SU-8[4] , parylene[5] , and polymide[6] have become common choices for l