Asymmetric Injection Needle Point for Reduced Tissue Trauma
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Solution Overview
Problem
Current medical injection needles, particularly those used in ophthalmic and cosmetic surgery, pose a risk of tissue damage and bacterial endophthalmitis due to their design, which is not sufficient to prevent these complications during procedures like intravitreal injection.
Innovation Solution
The injection needle features a needle tube with a unique edge surface formed by three ground facets, where the needle point is offset from the central plane, allowing for a distributed force application that reduces tissue damage and bacterial entry risks, with specific dimensions and angles optimizing the puncture process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a conventional injection needle with a sharp needle point on the central plane is used, then penetration force is reduced, but tissue damage and bacterial entry risk increase
Solution Approach 1:
The needle point is deliberately positioned asymmetrically, offset from the central plane of the needle tube by 0.01 to 0.05 mm. This asymmetric positioning causes the needle point to contact tissue at an angle, distributing the penetration force across a broader area rather than concentrating it at a single point, thereby reducing tissue damage while maintaining penetration effectiveness
Solution Approach 2:
The ground facets are designed with specific angular ranges (first facet: 10-45 degrees, second facet: 5-30 degrees, third facet: 5-30 degrees relative to the central axis) to create optimal force distribution characteristics. The asymmetric needle point position combined with these angled facets creates a localized force distribution pattern that minimizes tissue trauma while ensuring adequate penetration
2Length of moving object
If the needle tube outside diameter is reduced to minimize insertion depth, then tissue damage is reduced, but penetration force increases
Solution Approach 1:
The asymmetric needle point offset creates a mechanical advantage where the angled contact between the needle point and tissue generates both penetrating and spreading force components. This allows a smaller diameter needle to achieve effective penetration without requiring excessive force, as the asymmetric geometry converts part of the applied force into lateral tissue displacement that facilitates entry
Solution Approach 2:
The ground facets are designed with specific angular parameters (first facet 10-45 degrees, second and third facets 5-30 degrees) that optimize the force transformation characteristics. These angular parameters enable the needle to penetrate tissue more efficiently with reduced diameter by converting axial force into a combination of penetrating and spreading components
3Ease of manufacture
If the needle point is centered on the central plane, then manufacturing is simpler, but tissue damage increases due to concentrated force
Solution Approach 1:
The asymmetric needle point design is achieved through a practical manufacturing approach: forming an initial needle point on the central plane, then selectively removing material (grinding or etching) to offset the needle point by 0.01 to 0.05 mm from the central plane. This method maintains manufacturing simplicity while achieving the tissue-protective asymmetric geometry
Solution Approach 2:
The manufacturing process first creates a symmetric needle point on the central plane (easy to manufacture), then applies a secondary processing step to offset the needle point asymmetrically. This preliminary symmetric formation followed by asymmetric modification allows the benefits of both simple initial manufacturing and the tissue-protective asymmetric final geometry
Data Source
AI summary
An injection needle includes a needle tube having a proximal end and a distal end, and an edge surface provided at the distal end of the needle tube. The edge surface includes a first ground facet, a second ground facet, and a third ground facet. The first ground facet is located at a position proximal to the second ground facet and the third ground facet. The second ground facet and the third ground facet converge to form a needle point that is offset from a central plane that perpendicularly crosses the first ground facet and includes a central axis of the needle tube. A length of the edge surface is 0.6 to 2.2 mm. An outside diameter of the needle tube is 0.18 to 0.6 mm. A ratio of the outside diameter of the needle tube to the length of the edge surface is 0.265 to 0.325.