Elastomeric Infusion Pump Symmetrical Expansion
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Solution Overview
Problem
Elastomeric pumps in healthcare settings often face limitations in delivering fluids with consistent flow rates due to asymmetrical bladder expansion and pressure distribution, leading to initial flow spikes and variability in delivery profiles.
Innovation Solution
A portable infusion pump design featuring a pair of rigid surface elements with a hinge assembly that allows constrained separation, enabling symmetrical radial and axial expansion of a holding reservoir, coupled with a cylindrical support member and a sleeve that restricts light transmission, ensuring uniform pressure and consistent fluid delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the bladder is allowed to expand freely, then the fluid storage capacity increases, but the expansion becomes asymmetrical causing non-uniform pressure distribution and flow rate variability
Solution Approach 1:
The patent employs a flexible bladder made of elastomeric material that can expand to store fluid while maintaining structural integrity. The bladder is designed with specific geometric features including a rounded bottom and tapered neck that guide symmetrical expansion. When fluid is injected, the bladder expands uniformly in all directions, ensuring even pressure distribution throughout the fluid volume, thus resolving the contradiction between storage capacity and pressure uniformity.
Solution Approach 2:
The bladder is designed with a spheroidal or rounded geometry rather than flat or angular shapes. This curved configuration promotes uniform stress distribution during expansion, preventing localized stress concentrations that would cause asymmetrical deformation. The rounded bottom and curved walls ensure that when the bladder expands, the pressure is distributed evenly across the fluid, maintaining flow rate consistency while maximizing storage volume.
2Stability of the object's composition
If a rigid outer cover is used to constrain bladder expansion, then symmetrical expansion is achieved, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The bladder is designed to be self-constraining through its own geometric features and material properties. The rounded bottom, tapered neck, and specific wall thickness distribution create inherent geometric constraints that guide symmetrical expansion without requiring external rigid structures. The elastomeric material itself provides the necessary constraints through its elasticity and memory, allowing the bladder to return to its original shape and maintain symmetry throughout the expansion and contraction cycles.
Solution Approach 2:
The patent utilizes changes in material parameters and geometric parameters of the bladder to achieve symmetrical expansion. By carefully selecting elastomeric materials with specific durometer values and designing the bladder with optimized wall thickness variations, the system achieves self-constraint. The geometric parameters such as the radius of curvature at the bottom, the taper angle of the neck, and the overall aspect ratio are tuned to ensure symmetrical expansion behavior without additional constraining structures.
3Productivity
If the flow rate is increased to improve delivery speed, then the initial flow spike increases, but the flow rate consistency deteriorates
Solution Approach 1:
The system is pre-filled with fluid and the bladder is pre-expanded to a controlled volume before use. The initial conditions are carefully set so that when fluid delivery begins, the pressure gradient is optimized for consistent flow. The bladder geometry and pre-fill volume are designed to ensure that the initial flow rate matches the desired steady-state flow rate, eliminating the typical initial spike that occurs when elastomeric pumps are first activated.
Solution Approach 2:
The system incorporates a flow sensor that continuously monitors the fluid delivery rate and provides feedback to a control system. When the sensor detects deviations from the target flow rate, the control system adjusts the pump operation in real-time to maintain consistency. This closed-loop feedback mechanism ensures that flow rate variability is minimized even at higher delivery speeds, resolving the contradiction between productivity and reliability.
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 infusion pump achieves a constant flow rate with reduced initial spikes and minimal temperature dependence, suitable for various administration methods, and is manufactured from hypoallergenic materials compatible with a wide range of drugs, ensuring consistent performance and safety.
Implementation Method 1
a bladder made of silicon or another rubber polymer... When filled, the bladder expands and the increased surface area of the bladder stores energy that exerts pressure on the fluid, driving the fluid out of the bladder
Implementation Method 2
a pair of substantially rigid surface elements for defining a volume that is variable according to constrained separation of the pair of surface elements... The constrained separation of the pair of surface elements is defined by a hinge assembly
Data Source
AI summary
An apparatus for delivering fluid at a substantially constant flow rate includes a pair of substantially rigid surface elements for defining a volume that is variable according to constrained separation of the pair of surface elements. The apparatus further includes a support member disposed within the volume defined by the pair of surface elements; and a holding reservoir disposed within the volume defined by the pair of surface elements. The holding reservoir is attachably fastened at a first end to the support member and attachably coupled at a second end to the pair of surface elements.