Non-planar Micro-Needle Arrays for Neural Interfaces
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Solution Overview
Problem
Existing neural interface devices, such as the Utah Electrode Array, face challenges with long-term implantation due to flat planar needle tips that do not conform to curved surfaces, leading to gaps and connective tissue formation that reduce the quality of electrical connection and cause tissue damage.
Innovation Solution
The development of needle arrays with micro-needles having non-planar tip surfaces, such as concave or convex shapes, fabricated using wafer-scale techniques, which include dynamic and static etching to create sharp tips and optimize electrode height for better tissue interface, and the use of conductive coatings for stable electrical connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If planar needle tips are used, then manufacturing is simple, but contact with curved neural tissues is poor leading to gaps and connective tissue formation
Solution Approach 1:
The patent applies curvature by forming needle tips with spherical or domed surfaces instead of flat planar surfaces. This is achieved through processes like reflowing photoresist material or using spherical masking techniques during fabrication. The curved tip surfaces enable better conformal contact with curved neural tissues such as the retina or brain cortex, eliminating gaps that would otherwise form between planar needles and curved tissue surfaces, thereby improving electrical connection quality and reducing connective tissue formation.
2Reliability
If non-planar tip surfaces are used, then contact with curved neural tissues improves, but manufacturing complexity increases
Solution Approach 1:
The patent employs parameter changes by modifying the physical state and shape of materials during fabrication. Specifically, photoresist material is heated above its glass transition temperature to become viscous and reflow into spherical caps, or materials are deposited in controlled layers to build curved surfaces. These parameter changes (temperature, viscosity, deposition rate) enable the formation of complex non-planar tip surfaces using standard semiconductor fabrication equipment, thereby managing manufacturing complexity while achieving the desired curved geometries.
Solution Approach 2:
The patent uses copying techniques where a master pattern or mask with the desired curved surface geometry is created first, then used to replicate the curved tip shapes across multiple needles in the array. Spherical masks or reflowed photoresist patterns serve as templates that are copied onto each needle tip through photolithography or material deposition processes, enabling consistent curved surface fabrication without requiring complex individual shaping of each needle.
3Device complexity
If planar arrangement is used, then device structure is simple, but tissue damage occurs due to poor conformality
Solution Approach 1:
The patent applies curvature by forming needle tips with spherical or domed surfaces instead of flat planar surfaces. This is achieved through processes like reflowing photoresist material or using spherical masking techniques during fabrication. The curved tip surfaces enable better conformal contact with curved neural tissues such as the retina or brain cortex, eliminating gaps that would otherwise form between planar needles and curved tissue surfaces, thereby improving electrical connection quality and reducing connective tissue formation.
Data Source
AI summary
A micro-needle array having tips disposed along a non-planar surface is formed by shaping the wafer surface into a non-planar surface to define the tips of the micro-needles. A plurality of trenches are cut into the wafer to form a plurality of columns having tops corresponding to the non-planar surface. The columns are rounded and sharpened by etching to form the micro-needles.