Plunger Rod Assembly with Dual Locking Mechanisms

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Solution Overview

Problem

Syringe-based medical devices are prone to use-related errors, such as inadvertent activation before reconstitution, inaccurate activation, and inadvertent removal of the plunger rod, leading to missed doses, partial doses, and user frustration.

Innovation Solution

A plunger rod assembly with two locking mechanisms that control the movement of the plunger rod relative to a finger rest, preventing inadvertent activation and removal, and ensuring accurate activation by limiting movement to axial and radial directions based on specific positions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If a plunger rod assembly allows free movement for ease of operation, then the user can easily administer the drug, but use errors such as inadvertent activation and inaccurate dosing increase

Engineering Contradiction:

Improveease of drug administrationVSAvoidaccuracy of activation and dosing

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The plunger rod assembly employs dynamic locking mechanisms that adapt to different operational phases. The first locking mechanism engages during reconstitution to prevent inadvertent activation, then disengages to allow rotation for activation. The second locking mechanism engages after activation to prevent over-pushing. This dynamic behavior enables the system to be restrictive when needed and free when appropriate, resolving the contradiction between ease of operation and reliability.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The locking control is segmented into distinct mechanisms for different operational phases: first locking mechanism for reconstitution phase, second locking mechanism for post-activation phase. Each mechanism operates independently at specific positions, allowing the system to provide appropriate constraints for each stage while maintaining overall ease of use. This segmentation enables precise control without compromising operational simplicity.

Inventive Principle:

Principle #1Segmentation

2Reliability

If the plunger rod is constrained to prevent use errors, then reliability improves, but device complexity increases

Engineering Contradiction:

Improvereduction of use errorsVSAvoidnumber of locking mechanisms

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The first and second locking mechanisms are merged into a single integrated plunger rod assembly that shares common structural elements with the barrel and finger rest. The locking features are incorporated into the existing components rather than adding separate independent mechanisms, thereby reducing overall complexity while maintaining the dual-locking functionality needed for reliability.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The locking mechanisms are designed to engage and disengage automatically based on the plunger rod's position and movement phase, without requiring user intervention or complex control systems. The first locking mechanism self-engages during reconstitution and self-disengages when rotation begins; the second locking mechanism self-engages after activation. This self-service behavior reduces complexity by eliminating the need for external control mechanisms.

Inventive Principle:

Principle #25Self-service

3Adaptability or versatility

If the plunger rod allows rotation for activation, then the activation function is achieved, but inadvertent removal of the plunger rod may occur

Engineering Contradiction:

Improveactivation capabilityVSAvoidretention of plunger rod

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The locking control operates in periodic phases corresponding to the operational sequence: the first locking mechanism is active during reconstitution, then becomes inactive to permit rotation for activation, and finally the second locking mechanism becomes active to prevent removal. This periodic engagement and disengagement of locking mechanisms enables the plunger rod to rotate when needed while preventing inadvertent removal at other times, resolving the contradiction between adaptability and reliability.

Inventive Principle:

Principle #19Periodic action

Data Source

PatentUS20250186703A1Plunger rod assembly configured to reduce use error associated with operation of a medical device including the plunger rod assembly

Publication Date: 2025.06.12 NOVO NORDISK US HOLDINGS INC

AI summary

A plunger rod assembly for use with a medical device. The plunger rod assembly includes a finger rest adapted to be coupled to a barrel of the medical device, and a plunger rod coupled to the finger rest. The finger rest includes an interface that selectively engages the plunger rod to control movement of the plunger rod relative to the finger rest. The plunger rod includes a first locking mechanism and a second locking mechanism. When the plunger rod is in a first position, the first locking mechanism engages a first portion of the interface such that the plunger rod is only movable relative to the finger rest by moving the plunger rod in an axial direction until the plunger rod reaches a second position. When the plunger rod is in the second position, the second locking mechanism engages a second portion of the interface such that the plunger rod is only movable relative to the finger rest by rotating the plunger rod in a first radial direction until the plunger rod reaches a third position. When the plunger rod is in the third position, the second locking mechanism engages the first portion of the interface such that the plunger rod is only movable relative to the finger rest by moving the plunger rod in the axial direction until the plunger rod reaches an activated position.