Implantable Electrode Coating for Tissue Compatibility
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Solution Overview
Problem
Implantable stimulation electrodes face challenges in mechanical processing and electrical contacting, with existing materials like glassy carbon and titanium nitride experiencing issues with biocompatibility, tissue irritation, and impedance changes due to oxide layer formation, especially under pulsing conditions.
Innovation Solution
The development of thin, conductive coatings based on poly(pyrroles) or polythiophene polymers with specific substituents, grown on titanium nitride or related materials, which provide biocompatibility, anti-inflammatory properties, and enhanced capacitance while maintaining low impedance and stability in body fluids.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If glassy carbon is used as electrode material with activated carbon surface, then high double layer capacitance and good biocompatibility are achieved, but mechanical processing and electrical contacting become problematic
Solution Approach 1:
The patent uses a composite structure combining porous titanium nitride substrate with poly(pyrrole) coating layer. The porous titanium nitride provides high surface area and capacitance, while the poly(pyrrole) coating improves mechanical properties and facilitates electrical contacting, resolving the contradiction between achieving high capacitance and ease of manufacturing.
Solution Approach 2:
The patent employs porous titanium nitride as the substrate material, which provides high surface area for capacitance formation. The porous structure allows for effective electrical contact while maintaining the high surface area needed for double layer capacitance, addressing both capacitance requirements and manufacturability.
2Reliability
If titanium nitride layer is used as electrode coating, then high surface area and capacitance are achieved, but oxide layer formation causes impedance rise under pulsing conditions
Solution Approach 1:
The poly(pyrrole) coating acts as an intermediary layer between the titanium nitride substrate and the body tissue. This coating prevents direct contact between the titanium nitride and body fluids, thereby preventing oxide layer formation and maintaining impedance stability while preserving the high surface area benefits of the titanium nitride substrate.
Solution Approach 2:
The patent changes the chemical environment at the electrode surface by introducing the poly(pyrrole) coating, which alters the interaction between the titanium nitride and body fluids. This parameter change prevents the chemical reaction that leads to oxide formation, maintaining stable impedance characteristics.
3Object-affected harmful factors
If thin conductive coating is applied to improve biocompatibility, then tissue irritation is reduced, but charge injection capacity may be compromised
Solution Approach 1:
The patent uses porous titanium nitride as the substrate, which provides high surface area for charge injection. The porous structure maintains effective electrical contact with tissue while the poly(pyrrole) coating provides biocompatibility, thus achieving both low tissue irritation and high charge injection capacity.
Solution Approach 2:
The composite structure combines the high surface area porous titanium nitride with the biocompatible poly(pyrrole) coating. This composite material achieves both high charge injection capacity from the porous substrate and low tissue irritation from the biocompatible coating, resolving the contradiction between these two requirements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
These coatings improve tissue compatibility, reduce tissue irritation, and enhance the charge injection capacity and stability of implantable electrodes, ensuring minimal energy consumption and prolonged functionality in medical devices like pacemakers and neurostimulators.
Implementation Method 1
The coating layer or at least one of the coating layers is an electrically conductive layer of polymer having a polypyrrole polymeric backbone or polythiophene polymeric backbone
Implementation Method 2
a high double layer capacitance should form at the phase boundary of the electrode and bodily fluid
Implementation Method 3
each coating layer being an electrically conductive layer of polymer
Data Source
Figure 1
AI summary
An implantable electrode, for an implantable tissue stimulator, has an electrically conductive porous material comprising metal carbide, metal nitride, metal carbonitride, metal oxide or metal oxynitride and one or more coating layers on a surface thereof. The coating layer or at least one of the coating layers, is for contact with body tissue when the electrode is implanted. Each coating layer is an electrically conductive layer of polymer having a polypyrrole polymeric backbone or polythiophene polymeric backbone. The coating layer or layers are formed in situ by electropolymerisation. The polypyrrole or polythiophene may be substituted. The coating layer or layers can provide high charge storage capacitance and a fast discharging profile, as well as biocompatibility.