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Biocompatibility of Polyimide Based Neural Devices for Chronic amrel.bioe.uic.edu/NSFREU2007/presentations/  · PDF file 2015. 7. 28. · Biocompatibility of Polyimide Based Neural

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  • Biocompatibility of Biocompatibility of Polyimide Based Neural Polyimide Based Neural

    Devices for Chronic Devices for Chronic Implant Applications Implant Applications

    Samantha WatkinsSamantha Watkins Advisor: Dr. Patrick J. Advisor: Dr. Patrick J. RouscheRousche

    Neural Engineering & Applications LabNeural Engineering & Applications Lab

    Gandhi, D 2006 Assessing Chronic Functionality of Photo-Definable Polyimide Based Flexible Neural Interface for the Central Nervous System Preliminary Thesis PhD. Defense Summary.

  • Neural Device Neural Device ApplicationsApplications

    Gandhi, D 2006 Assessing Chronic Functionality of Photo-Definable Polyimide Based Flexible Neural Interface for the Central Nervous System Preliminary Thesis PhD. Defense Summary. & http://bryanbrandenburg.blog.com/Biomedical/

    NeuroNeuro Prosthesis Prosthesis –– Restore functionality in Restore functionality in

    central nervous system central nervous system tissuetissue

    –– Information exchange Information exchange Delivering and recording Delivering and recording electrical signals to and from electrical signals to and from neuronal cellsneuronal cells

    Assess the physiological Assess the physiological environment at a cellular environment at a cellular levellevel

  • LongLong--Term Term BiocompatibilityBiocompatibility

    Minimize foreign body response and immune reactionMinimize foreign body response and immune reaction Decrease the risk of scar tissue formationDecrease the risk of scar tissue formation –– Preventing device isolation from surrounding neural tissue Preventing device isolation from surrounding neural tissue

    ((gliosisgliosis))

    The interface should also reduce mechanical The interface should also reduce mechanical micromotionmicromotion strain which further reduces strain which further reduces gliosisgliosis

    Stimulation & Recording Functionality

    Brain Tissue Acceptance

    Gandhi, D 2006 Assessing Chronic Functionality of Photo-Definable Polyimide Based Flexible Neural Interface for the Central Nervous System Preliminary Thesis PhD. Defense Summary.

  • Mechanical ComplianceMechanical Compliance

    Mechanical mismatch between materialsMechanical mismatch between materials –– Polyimide has a YoungPolyimide has a Young’’s Modulus 25s Modulus 25--100 times lower than other 100 times lower than other

    materialsmaterials Polyimide flexibility causes buckling during insertionPolyimide flexibility causes buckling during insertion Enhance device strength by with Enhance device strength by with polyglycolicpolyglycolic acid (PGA)acid (PGA)

    Mechanical RigidityMechanical Rigidity

    MaterialMaterial YoungYoung’’s Moduluss Modulus Tungsten Tungsten MicrowireMicrowire 400 400 GPaGPa

    SiliconSilicon 120120--140 140 GPaGPa

    PolyimidePolyimide 4 4 GPaGPa

    Brain TissueBrain Tissue 0.067 0.067 GPaGPa

  • PGA MaterialPGA Material

    Mechanical rigidityMechanical rigidity –– YoungYoung’’s Modulus s Modulus --> 7GPa> 7GPa

    FDA approved and biodegradable suture materialFDA approved and biodegradable suture material Glass transition temperature Glass transition temperature --> 35> 3500CC –– Stable at room temperatures Stable at room temperatures

    and degrades once implantedand degrades once implanted

    MeltMelt--coating polyimide coating polyimide devices for implant devices for implant applicationsapplications

    –– OneOne--sided coatingsided coating

  • Polymer Material Polymer Material CharacterizationCharacterization

    Utilize polymerUtilize polymer--based devices to assess based devices to assess biocompatibility of neural implants in biocompatibility of neural implants in chronic applicationschronic applications –– Uncoated polyimide devicesUncoated polyimide devices –– PGA coated polyimide devicesPGA coated polyimide devices

    Monitor tissue response with histology Monitor tissue response with histology techniquestechniques

    4 0 0 μm 1 4 6 -1 5 6 μm

    1 0 0 0 0 μm 4 0 0 0 μm

    4 0 0 μm 1 4 6 -1 5 6 μm

    1 0 0 0 0 μm 4 0 0 0 μm

    1 0 0 0 0 μm 4 0 0 0 μm

    1 0 0 0 0 μm 4 0 0 0 μm4 0 0 0 μm

    Gandhi, D 2006 Assessing Chronic Functionality of Photo-Definable Polyimide Based Flexible Neural Interface for the Central Nervous System Preliminary Thesis PhD. Defense Summary.

  • Histology MethodsHistology Methods

    Device implantDevice implant-- 15 days15 days Formalin fixationFormalin fixation Paraffin embeddingParaffin embedding 88μμm sectionsm sections H&E stainingH&E staining –– Cell DistributionCell Distribution

    Immunochemistry stainingImmunochemistry staining –– GlialGlial fibrillaryfibrillary acidic protein (GFAP), acidic protein (GFAP),

    astrocyteastrocyte--specific marker specific marker –– GlialGlial scar formationscar formation

    BrightfieldBrightfield microscopy imagingmicroscopy imaging 2 Shaft Polyimide Device

    500 um

  • H&E Results H&E Results –– Uncoated Polyimide DevicesUncoated Polyimide Devices

    Sections of four implants Sections of four implants at varying depthsat varying depths Normal cell interactionNormal cell interaction

    100 um

    100 um 100 um100 um

  • H&E Results H&E Results –– PGA Coated DevicesPGA Coated Devices

    Sections of three implants Sections of three implants at varying depthsat varying depths Normal cell behaviorNormal cell behavior –– OneOne--sided responsesided response

    100 um 100 um100 um

    100 um

  • GFAP Immunochemistry GFAP Immunochemistry Results Results –– Uncoated Polyimide Uncoated Polyimide DevicesDevices

    Sections of two implants at Sections of two implants at varying depthsvarying depths Minimal Minimal glialglial scar scar formation formation

    100 um

    100 um

    100 um 100 um

  • GFAP ImmunochemistryGFAP Immunochemistry Results Results —— PGA Coated DevicesPGA Coated Devices

    Sections of three implants Sections of three implants at varying depthsat varying depths Minimal Minimal glialglial scar scar formation formation –– OneOne--sided responsesided response

    100 um 100 um 100 um

    100 um

  • ConclusionConclusion

    Polyimide material provides mechanical flexibility to Polyimide material provides mechanical flexibility to reduce reduce micromotionmicromotion strainstrain PGA material provides temporary mechanical PGA material provides temporary mechanical rigidity for insertionrigidity for insertion –– In vitro studies in our lab suggest PGA degrades within In vitro studies in our lab suggest PGA degrades within

    three daysthree days

    Histology results show successful biocompatibility of Histology results show successful biocompatibility of polymer materials with only a slight tissue responsepolymer materials with only a slight tissue response Polymer materials provide new design strategies for Polymer materials provide new design strategies for

    neural devices used in longneural devices used in long--term implantsterm implants

  • AcknowledgementsAcknowledgements

    Grant NSF EEC 0453432Grant NSF EEC 0453432 –– National Science Foundation REU National Science Foundation REU

    Program Program –– Department of Defense ASSURE ProgramDepartment of Defense ASSURE Program Dr. Dr. Rousche'sRousche's Research TeamResearch Team –– DevangDevang GandhiGandhi –– Peter Peter TekTek

    Biocompatibility of Polyimide Based Neural Devices for Chronic Implant Applications Neural Device Applications Long-Term Biocompatibility Mechanical Compliance PGA Material Polymer Material Characterization Histology Methods H&E Results – �Uncoated Polyimide Devices H&E Results – �PGA Coated Devices GFAP Immunochemistry �Results – Uncoated Polyimide Devices GFAP Immunochemistry�Results — PGA Coated Devices Conclusion Acknowledgements