Autoinjector Plunger Damping for High-Viscosity Drug Delivery
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Solution Overview
Problem
Existing autoinjectors and on-body injectors experience excessive mechanical shocks due to high spring forces, leading to discomfort, potential drug product damage, and breakage, especially when delivering high viscosity drugs.
Innovation Solution
Incorporation of a damping mechanism, such as a dashpot, to reduce the velocity of the plunger before it impacts the stopper, using viscous friction to absorb energy and minimize shock, while maintaining the intended force for drug delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If higher spring forces are used to deliver higher viscosity drugs, then the drug delivery capability is improved, but the mechanical shock and kinetic energy applied to the drug and container increase excessively
Solution Approach 1:
A damping mechanism is introduced between the spring-driven plunger and the stopper to provide beforehand cushioning. The damping mechanism absorbs and dissipates the excessive kinetic energy and mechanical shock that would otherwise be transmitted to the drug and container during the injection process, while still allowing the spring force to effectively drive the plunger forward for drug delivery.
Solution Approach 2:
The damping mechanism serves as an intermediary element between the high-force spring system and the drug container. It mediates the force transmission by allowing the spring to exert its full force on the plunger while simultaneously filtering out the harmful high-velocity impact components before they reach the stopper and drug product.
2Speed
If spring driven plunger impacts the stopper with high velocity, then the injection speed is improved, but the patient feels excessive physical bump and discomfort
Solution Approach 1:
The damping mechanism provides beforehand cushioning by being positioned in the force transmission path between the plunger and stopper. It reduces the velocity of the plunger just before impact with the stopper, thereby cushioning the physical bump that would otherwise be felt by the patient, while still maintaining sufficient injection speed for effective drug delivery.
3Power
If high force springs are used, then the energy for drug delivery is improved, but the shear rate applied to the drug product increases excessively
Solution Approach 1:
The damping mechanism acts as an intermediary that decouples the high-force spring system from the drug product. It allows the spring to generate the necessary power and force for driving the plunger through the high-viscosity drug, while simultaneously reducing the shear rate transmitted to the drug by dampening the high-velocity impact components.
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 damping mechanism reduces the kinetic energy applied to the drug and container, preventing discomfort to the user, minimizing drug product damage, and allowing for safer delivery of high viscosity drugs.
Implementation Method 1
a damping mechanism for reducing the velocity of the plunger prior to acting on the stopper, the damping mechanism comprising a housing, a piston assembly movable in the housing and acted upon by the plunger, and a working fluid displaceable by the piston assembly for resisting movement of the plunger
Data Source
Figure 1
Figure 2~3C
Figure 4A~4C
AI summary
An injection device, method, and system for drug delivery includes a primary container for storing a drug, the container having a stopper movably disposed in the container for expelling the drug, an injection drive mechanism comprising a plunger for acting on the stopper and an energy source for exerting a force on the plunger to cause the plunger to act on the stopper to expel the drug, the force causing the plunger to accelerate to a velocity prior to acting on the stopper, and a damping mechanism for reducing the velocity of the plunger prior to acting on the stopper. The damping mechanism can include a dashpot or an energy absorbing material associated with the plunger. Alternatively or additionally, the damping mechanisms can include absorbing material disposed between support members of an outer casing of the injection device and the primary container.