Injection Spring Design for Aged Prefilled Syringe
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Solution Overview
Problem
Traditional injection time simulations for prefilled syringes fail to account for changes over time, leading to increased resistive forces that can slow down the injection process, causing discomfort and potential incomplete delivery of therapeutic fluids.
Innovation Solution
An auto injector with an injection spring designed to accommodate higher extrusion forces by determining suitable spring parameters through accelerated aging simulations, ensuring the spring can move the stopper within the desired time frame while preventing stalling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional injection time simulations are used based on initial prefilled syringe parameters, then the injection time can be initially calculated, but the simulation fails to account for increased resistive forces that develop over time leading to injection delays
Solution Approach 1:
The patent applies preliminary action by performing accelerated aging simulations before final injection time calculations. The method ages the prefilled syringe components (stopper, barrel, lubricant) to simulate long-term storage conditions, thereby predicting future friction characteristics and resistive forces before actual clinical use. This allows the injection time simulation to account for time-dependent changes in the system.
Solution Approach 2:
The patent changes physical parameters of the prefilled syringe components through controlled aging processes. Specifically, the lubricant viscosity increases over time due to aging, and the friction forces between the stopper and barrel increase. These parameter changes are measured and incorporated into the injection time simulation to reflect real-world degradation.
2Force
If the injection spring is designed based on initial friction forces, then the spring force can be initially determined, but the spring may be insufficient to overcome increased resistive forces in aged syringes
Solution Approach 1:
The injection spring force is determined after performing preliminary aging simulations on the prefilled syringe. The aging process reveals the maximum resistive forces that will develop during the product shelf life. The spring force is then calculated to ensure it exceeds these aged friction forces, guaranteeing reliable injection completion even after extended storage.
3Reliability
If accelerated aging simulations are performed to determine suitable spring parameters, then the spring can accommodate higher extrusion forces, but the device complexity increases
Solution Approach 1:
The patent replaces complex physical aging tests with computational simulations. Instead of physically storing prefilled syringes for extended periods and testing them, the method uses computer-based models to simulate the aging process and predict friction force changes. This substitution maintains reliability while reducing the complexity and time required for spring parameter determination.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution ensures consistent and complete delivery of therapeutic fluids by overcoming increased resistive forces associated with artificially aged prefilled syringes, maintaining injection efficiency and patient comfort.
Implementation Method 1
an injection spring configured to apply a dispensing force to the stopper by driving a piston rod toward the stopper upon actuation of the auto injector, the dispensing force being at least a portion of the spring force
Implementation Method 2
Friction forces during delivery are generally approximated using step-wise functions to simulate a constant break loose force in a start of injection period and a constant gliding force in the rest of injection period
Implementation Method 3
These parameters enable simulation of the hydrodynamic forces that the fluid applies against the stopper. The Hagen-Poiseuille equation is an example of a formula that models hydrodynamic forces
Data Source
AI summary
An auto injector apparatus includes a syringe and an auto injector. The syringe includes a barrel holding a therapeutic fluid including an anti-calcitonin gene-related peptide (anti-CGRP) antibody. The syringe also includes a stopper disposed within the barrel and the stopper moves axially within the barrel between a first position and a second position to expel at least some of the therapeutic fluid from the syringe. The auto injector includes a rod that abuts the stopper and an injection spring that drives the rod to apply a dispensing force through the rod to the stopper. The dispensing force includes a first dispensing force of between 20 N and 40 N and a second dispensing force of between 12 N and 20 N. The injection spring initially applies the first dispensing force and then applies the second dispensing force to move the stopper to the second position.