Conformable Electrode Array Strain Relief for Implantable Stimulators
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Solution Overview
Problem
Implantable electrical stimulation systems face challenges in precisely aligning electrodes due to tissue curvature, leading to unpredictable electrical resistance and patient discomfort, with subcutaneous implants experiencing skin erosion and lead migration, and existing encapsulation methods fail to adequately protect electronics from bodily fluids.
Innovation Solution
An implantable stimulator with a conformable substrate and electrode array, featuring a conductive elastomer encapsulation layer and mechanical braces to resist separation, along with a thin thickness of 0.5 mm or less, ensuring high conformability and protection against fluid ingress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a cylindrical lead with substantial thickness is used, then the lead has structural strength, but it causes skin erosion and lead migration due to poor conformability to curved tissues
Solution Approach 1:
The patent applies a curved/arched configuration to the substrate rather than a straight cylindrical shape. This curvature allows the lead to conform to the natural anatomical curves of the body, improving adaptability to tissue surfaces while maintaining structural integrity through the arched design that distributes mechanical stresses.
Solution Approach 2:
The patent uses a thin-film substrate (e.g., polyimide or PTFE) with thickness of 0.1-0.5mm instead of thick cylindrical insulation. This thin-film approach provides flexibility and conformability to curved surfaces while the underlying structure maintains necessary strength. The thin substrate allows the lead to bend and conform to anatomical structures without causing skin erosion.
2Adaptability or versatility
If the substrate thickness is reduced to improve conformability, then flexibility increases, but protection against fluid ingress and mechanical strength decrease
Solution Approach 1:
The patent employs a multilayer nested structure where the thin substrate is enclosed within an encapsulation layer. The substrate is positioned between the encapsulation layer and the electrode array, creating a protected sandwich structure. This nesting provides fluid ingress protection while maintaining the thin-profile flexibility of the overall device.
Solution Approach 2:
The patent combines multiple materials with complementary properties: a flexible substrate material (polyimide or PTFE) is combined with an encapsulation layer material that provides fluid barrier properties. This composite structure achieves both flexibility from the substrate and fluid protection from the encapsulation layer, resolving the contradiction between thinness and protection.
3Reliability
If an encapsulation layer is added to protect electronics, then fluid ingress resistance improves, but bonding reliability deteriorates due to delamination between encapsulant and substrate
Solution Approach 1:
The patent introduces an adhesion layer as an intermediary between the encapsulation layer and the substrate. This intermediate layer is specifically designed to bond to both materials, with one surface bonding to the substrate and the other surface bonding to the encapsulation layer. This mediator resolves the bonding incompatibility between the encapsulant and substrate, preventing delamination while maintaining fluid ingress resistance.
Solution Approach 2:
The patent creates a three-layer composite structure (substrate-adhesion layer-encapsulation layer) where each layer is selected for its bonding compatibility with adjacent layers. The adhesion layer is specifically chosen or designed to be compatible with both the substrate material (e.g., PTFE or polyimide) and the encapsulation material, ensuring stable bonding across the interface while maintaining the protective function of the encapsulation layer.
4Ease of manufacture
If conventional encapsulation materials are used, then ease of manufacture improves, but biocompatibility and moisture barrier performance deteriorate
Solution Approach 1:
The patent changes the material parameters by selecting PTFE or polyimide as the substrate material, which have inherently low moisture permeability and good biocompatibility. These materials have specific physical parameters (low water vapor transmission rate, chemical inertness) that simultaneously provide moisture barrier performance and reduced tissue reaction, while still being manufacturable using established thin-film fabrication techniques.
Solution Approach 2:
The patent uses composite material construction where the substrate itself (PTFE or polyimide) provides both structural support and moisture barrier properties, eliminating the need for separate barrier layers. The encapsulation layer is then applied over this biocompatible substrate, creating a composite structure that maintains biocompatibility while adding enhanced protection. This approach achieves low moisture permeability and good biocompatibility without sacrificing manufacturability.
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
The solution provides improved patient comfort, reduced lead migration, and enhanced protection of electronic components, maintaining reliability and longevity by minimizing electrical mismatch and fluid exposure.
Implementation Method 1
The implantable stimulator comprises at least one conductive elastomer, configured and arranged to electrically connect one or more electrical interfaces between the plurality of electrical interconnections and the pulse generator
Implementation Method 2
the at least one encapsulation layer being configured to resist separation of the conformable second portion from the first portion at the meeting of the first portion and the conformable second portion
Implementation Method 3
Bodily fluids typically contain ions that may cause electrochemical reactions, like corrosion, in the presence of an electric current. Encapsulation is thus a critical component for the design of a medical device - it acts as a barrier between these ionic fluids and critical electronic/electric interfaces
Data Source
Figure 1A~1C
Figure 2A~2C
Figure 3A~3C
AI summary
An implantable stimulator has a substrate 300, 1400 comprising a first portion 2010, 2110, 2210, 2310 with a pulse generator 500, and a conformable portion 2020, 2120, 2320 with an electrode array 200, 400, 1220. Electrical interconnections 250, 1210 are provided to the pulse generator with an electrical interface comprising an electrically conductive elastomer 2260. An encapsulation layer 1300, 1310, 1320, 2150, 2250 is provided, configured to resist separation of the conformable portion from the first portion at the meeting of the first and conformable portions. The conformable portion has a thickness equal to or less than 0.5 millimeters. Optionally, a mechanical brace 2140, 2240, 2340 is provided at the meeting of the first and conformable portions to further resist separation. By providing an encapsulant, a conductive elastomer may be used to simplify manufacturing or repair. An ACA elastomer such as ACF provides a high separation resistance to longitudinal forces.