Stepped Cannula Design for CNS Material Delivery
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Solution Overview
Problem
Current cannula designs for delivering materials into the central nervous system face issues with reflux and material loss due to exposure to stainless steel surfaces, which is exacerbated when small volumes are delivered, leading to inefficiency and waste, especially for expensive or difficult-to-obtain biologically active agents.
Innovation Solution
The development of stepped cannulas with a decreasing diameter in a stepwise fashion and the use of non-stainless steel surfaces, such as fused silica, to minimize reflux and material loss, combined with a system that includes a reservoir and pump for precise delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If a conventional cannula design with uniform diameter is used, then the structure is simple and easy to manufacture, but material loss due to exposure to stainless steel surfaces is substantial
Solution Approach 1:
The cannula is divided into multiple segments with different diameters, creating a stepped configuration. The distal segment has a smaller diameter to reduce surface area contact with the material, while proximal segments have progressively larger diameters. This segmentation reduces material loss to stainless steel surfaces while maintaining structural integrity.
Solution Approach 2:
Different portions of the cannula have different diameters optimized for their specific functions. The distal end has a small diameter to minimize material exposure and loss, while the proximal end has a larger diameter for structural stability and ease of insertion. This local differentiation of geometric properties addresses the material loss problem without compromising overall cannula performance.
2Productivity
If small volumes of material are delivered, then the efficiency and cost-effectiveness improve, but reflux along the injection track becomes more problematic
Solution Approach 1:
The stepped configuration creates distinct segments that help control material flow. The gradual change in diameter along the cannula length helps prevent sudden reflux while maintaining the ability to deliver small volumes efficiently. The geometry guides the material flow directionally toward the target site.
Solution Approach 2:
The cannula design incorporates a dimensional change along its length, transitioning from larger diameter at the proximal end to smaller diameter at the distal end. This dimensional variation creates a gradient that prevents reflux while enabling small volume delivery, addressing both contradictions simultaneously.
3Loss of substance
If the cannula interior surface is made of stainless steel, then the manufacturing is simple and cost-effective, but substantial loss of biologically active agents occurs due to exposure
Solution Approach 1:
A coating layer is applied to the cannula interior surface to act as an intermediary between the stainless steel substrate and the biologically active material. This coating prevents direct contact between the material and stainless steel, reducing adsorption and loss of agents while maintaining the structural benefits of stainless steel manufacturing.
Solution Approach 2:
The cannula combines stainless steel with a coating material to create a composite structure. The stainless steel provides structural integrity and ease of manufacture, while the coating material prevents agent loss through reduced surface interaction. This composite approach resolves the contradiction between manufacturing simplicity and material preservation.
Data Source
AI summary
Described herein are cannulas having a stepped exterior. Also described are methods of making and using these cannulas, for example to deliver one or more materials to the central nervous system of an animal.