Segmented Microneedle Design for Intradermal Injection
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Solution Overview
Problem
Microneedles of prior art do not optimally meet the desired operational characteristics such as ease of skin penetration, high injection depth to penetration ratio, low fluid impedance, minimal leakage, and mechanical robustness.
Innovation Solution
A microneedle design with symmetrical vertical side surfaces meeting at a vertical leading edge and an inclined surface, featuring a vertical bore with a cross-sectional shape that is elongated along the front-to-back axis, and a leading edge formed as a circular arc, optimizing dimensions to balance pain minimization, penetration ease, fluid flow, and mechanical strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If microneedles are made with conventional simple geometries, then manufacturing is easier, but operational characteristics such as penetration ease, injection depth ratio, fluid impedance, and mechanical robustness are not optimized
Solution Approach 1:
The microneedle is segmented into multiple functional zones along its length: a leading edge portion for penetration, a body portion with varying cross-sectional geometry, and a base portion. This segmentation allows each zone to be optimized for its specific function while maintaining manufacturability through techniques like multi-layer lamination or sequential deposition.
Solution Approach 2:
Different portions of the microneedle have different geometric properties: the leading edge has a smaller cross-section for ease of penetration, the body has optimized dimensions for structural integrity and fluid flow, and the base provides mechanical support. This local variation in geometry optimizes operational characteristics without compromising manufacturability.
2Object-affected harmful factors
If microneedles have a smaller cross-sectional area at the leading edge, then skin penetration is easier and pain is minimized, but mechanical robustness decreases
Solution Approach 1:
The microneedle design incorporates a gradual taper from the base to the leading edge, allowing stress to be distributed progressively along the structure. This preliminary geometric configuration prevents stress concentration at the narrow leading edge, reducing the risk of breakage during insertion while maintaining sharpness for easy penetration.
Solution Approach 2:
The microneedle may be constructed from composite materials or multi-layer structures where different materials provide different properties: a harder, sharper leading edge material for penetration and a more ductile base material for mechanical support, or a gradient material composition that transitions from sharp to robust.
3Length of moving object
If the bore is positioned closer to the leading edge, then injection depth to penetration ratio increases, but fluid flow impedance increases
Solution Approach 1:
The bore is positioned close to the leading edge in the longitudinal dimension to maximize injection depth, but its cross-sectional dimensions are optimized to maintain low fluid impedance. This multi-dimensional optimization allows the bore to be both short (for high depth ratio) and wide enough (for low impedance) by utilizing different spatial dimensions independently.
4Strength
If microneedles have a larger cross-sectional area, then mechanical robustness improves, but skin penetration becomes more difficult and painful
Solution Approach 1:
The microneedle is divided into segments with different cross-sectional areas: a narrow leading edge for painless penetration and a larger base for mechanical strength. This segmentation allows the structure to have both small and large dimensions in different locations, resolving the contradiction between robustness and penetration ease.
Solution Approach 2:
The microneedle incorporates curved or rounded transitions between segments rather than sharp corners, distributing stress more evenly and preventing stress concentration. This curvature allows smooth transition from the narrow penetrating tip to the broader supportive base, maintaining both penetration ease and mechanical strength.
Data Source
AI summary
A microneedle for intradermal injection or diagnostics, constructed as a protrusion above a substrate and whose shape is defined by a pair of vertical side surfaces, configured to be symmetrical about a vertical plane of symmetry and to meet along a vertical leading edge, and by an inclined surface, intersecting the side surfaces, the microneedle also including a vertical bore, located centrally between the two side surfaces and substantially near the leading edge,wherein each of the side surfaces is divided, sequentially along the front-to-back direction, into at least two contiguous planar segments, forming pairs of corresponding segments along the respective side surfaces; each pair of corresponding segments mutually form an acute angle, the angle being between 40 and 70 degrees for the pair of segments adjacent the leading edge and less than 35 degrees for the pair of segments farthest from the leading edgeand wherein the leading edge is formed so that its profile includes an arc, joined to the side surfaces.