MEMS Bellows Actuator Electrolysis Fluid Dispensing
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Solution Overview
Problem
Existing microfluidic drug delivery systems face issues with diaphragm performance, scalability, power efficiency, and fluid control due to limitations in actuator design and electrolysis processes, leading to uncontrolled fluid release and challenges in refilling or sampling.
Innovation Solution
An implantable fluid delivery system utilizing a Parylene C bellows actuator with optimized electrode design and fabrication, achieving high deflection efficiency and separating electrochemical actuation from the drug reservoir to prevent pH changes and fluid mixing, with a method involving stacking stencil sheets and using PEG as a filler material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If electrolysis is used to expand the diaphragm for fluid expulsion, then fluid can be dispensed from the reservoir, but the diaphragm yields poor performance including large dead volume, large stress/strain anchor points, limited expansion, and durability issues
Solution Approach 1:
The patent replaces the traditional diaphragm with a bellows structure made of flexible thin film material. The bellows is formed by depositing a thin film layer (such as parylene, silicon nitride, or silicon oxide) over a patterned substrate with recesses, creating an accordion-like structure that can expand and contract. This flexible thin film bellows eliminates the performance limitations of solid diaphragms while maintaining the fluid expulsion function through electrolysis-driven expansion.
Solution Approach 2:
The invention transitions from a two-dimensional diaphragm surface to a three-dimensional bellows structure with multiple convolutions. The bellows comprises a series of repeating convex and concave portions that create vertical stacking of convolutions, enabling greater expansion volume and more efficient use of the available space within the device footprint. This dimensional transformation allows for larger expansion ratios without increasing the overall device footprint.
2Productivity
If interdigitated electrodes are used for electrolysis, then fluid can be pumped, but the power efficiency is less than 50% and performance is unreliable and highly dependent on design and fabrication process
Solution Approach 1:
The patent optimizes the electrode geometry parameters including the width, spacing, and pattern of the interdigitated electrodes. By carefully controlling these geometric parameters during fabrication, the design achieves more efficient current distribution and reduced ohmic losses. The electrode dimensions and spacing are specifically tuned to maximize the electrochemical reaction efficiency while minimizing the power required for a given fluid pumping rate.
Solution Approach 2:
The invention replaces the mechanically complex diaphragm expansion system with a more efficient electrochemical system. Instead of using large mechanical forces on a solid diaphragm, the system uses electrochemical gas generation at the electrode-bellows interface to create controlled pressure expansion. This substitution of mechanical expansion with electrochemical actuation improves both power efficiency and reliability.
3Loss of energy
If the device is turned off and no electrolysis is taking place, then energy is conserved, but there is uncontrolled release of fluid from the dispensing orifice
Solution Approach 1:
The patent introduces a check valve as an intermediary component between the fluid reservoir and the dispensing orifice. This one-way valve allows fluid to flow outward during active pumping but prevents backward flow or uncontrolled leakage when the device is inactive. The check valve maintains fluid control precision without interfering with the energy conservation benefit of turning the device off, as it passively regulates flow based on pressure differential alone.
4Productivity
If gases are generated during electrolysis to expand the diaphragm, then fluid can be expelled, but the gases may recombine to reverse the pressure gradient and create suction pulling in fluid that had just been dispensed
Solution Approach 1:
The patent extracts the gas generation and recombination process from the fluid dispensing pathway by using a sealed bellows structure. The bellows is formed as a closed chamber with the electrolyte and electrodes contained within recesses that are sealed from the fluid reservoir. Gas bubbles generated during electrolysis remain confined to the bellows interior, expanding it to push fluid outward, while any recombination of gases occurs within the sealed bellows without creating suction that could draw fluid back into the dispensing orifice. This separation of the electrochemical chamber from the fluid pathway eliminates the harmful suction effect.
5Duration of action of moving object
If the fluid reservoir volume decreases as fluid is dispensed, then the device can deliver drug over time, but it becomes difficult to calculate the actual fluid dispensing rate and to refill or extract samples
Solution Approach 1:
The patent incorporates a refill port and sampling port that allow for preliminary actions of refilling and sample extraction without requiring device removal or complex procedures. These ports enable the user to monitor fluid levels, extract samples for analysis, and refill the reservoir as needed, maintaining accurate knowledge of the remaining fluid volume and dispensing rate throughout the device lifecycle.
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 system achieves efficient fluid dispensing with improved scalability, power efficiency, and controlled fluid management, allowing for precise drug delivery and sampling, with a deflection of over 1.5 mm and efficiency approaching 80%, suitable for ocular and other applications.
Implementation Method 1
Electrodes may be configured to come in electrical contact with an electrolyte within the bellows and to cause electricity to run through the electrolyte, thereby causing the electrolyte to break down into a gas
Implementation Method 2
The bellows may have folds with surfaces which run substantially perpendicular to the direction of expansion in a collapsed state and which define a stacked set of convolutions
Data Source
AI summary
An implantable fluid delivery system may include a fluid reservoir configured to hold a supply of fluid, dispense that fluid under the control of an actuator, and be implanted within the body of a living host. The actuator may include a bellows configured to expand in a direction when inflated. The bellows may have folds with surfaces which run substantially perpendicular to the direction of expansion in a collapsed state and which define a stacked set of convolutions. Each convolution may have a collapsed height of no more than 1 mm and a width perpendicular to the direction of expansion of no more than 8 mm. Electrodes may be configured to come in electrical contact with an electrolyte within the bellows and to cause electricity to run through the electrolyte, thereby causing the electrolyte to break down into a gas and, in turn, to cause the bellows to expand.