Electrowetting Droplet Generation with Charge-Assisted Splitting

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Solution Overview

Problem

Existing droplet generation methods using electrowetting face limitations due to physical constraints, such as narrow plate spacing and finite electrowetting force, which hinder the production of small droplets and the manipulation of microparticles or cells, especially when counteracting surface tension.

Innovation Solution

A method involving cycles of electrowetting forces and electrostatic charge application to elongate and sever droplets, utilizing alternating electrowetting and electrostatic surface charge to counteract surface tension, allowing for the generation of smaller droplets.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Force

If electrowetting force is applied to elongate the sample region, then droplet generation is enabled, but surface tension opposes the elongation requiring progressively increasing force

Engineering Contradiction:

Improveelectrowetting forceVSAvoidplate spacing constraint

Core Design Contradiction:

ForceVSDevice complexity

Solution Approach 1:

The patent changes the physical state of the sample by electrostatically charging it, transforming it from a neutral liquid to a charged droplet. This parameter change (adding electrostatic charge) fundamentally alters the force balance, allowing electrostatic repulsion to counteract surface tension and enable elongation with limited electrowetting force.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces electrostatic charge as an intermediary force mediator between the electrowetting force and the sample. The charge accumulates on the sample surface and acts as an intermediate mechanism that amplifies the effect of limited electrowetting force, enabling droplet elongation without requiring extremely narrow plate spacing.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Force

If electrowetting force is increased to counteract surface tension, then droplet elongation improves, but dielectric breakdown and surface fouling occur

Engineering Contradiction:

Improveelectrowetting forceVSAvoiddielectric breakdown

Core Design Contradiction:

ForceVSObject-affected harmful factors

Solution Approach 1:

The patent changes the force balance by introducing electrostatic repulsion from accumulated charge. This parameter change allows the system to achieve the necessary elongation force without increasing the electrawetting force to harmful levels, thereby avoiding dielectric breakdown and surface fouling.

Inventive Principle:

Principle #35Parameter changes

3Volume of moving object

If plate spacing is minimized to enable small droplet splitting, then droplet size reduction is achieved, but manipulation of microparticles and cells becomes impossible

Engineering Contradiction:

Improvedroplet sizeVSAvoidsample manipulation capability

Core Design Contradiction:

Volume of moving objectVSAdaptability or versatility

Solution Approach 1:

The patent changes the physical state of the sample by electrostatically charging it, which fundamentally alters the force balance. This parameter change enables droplet elongation and splitting with limited electrowetting force, allowing small droplet generation without requiring extremely narrow plate spacing that would prevent microparticle and cell manipulation.

Inventive Principle:

Principle #35Parameter changes

4Productivity

If electrowetting force is applied continuously to elongate the sample, then droplet generation proceeds, but surface tension requires progressively increasing force

Engineering Contradiction:

Improvedroplet generation rateVSAvoidelectrowetting force

Core Design Contradiction:

ProductivityVSForce

Solution Approach 1:

The patent employs periodic cycles of electrowetting force application followed by electrostatic charging periods. This periodic action allows the system to accumulate charge during charging phases, which then counteracts surface tension during subsequent elongation phases, enabling sustained droplet generation without continuously increasing the electrowetting force.

Inventive Principle:

Principle #19Periodic action

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

Enables the production of droplets less than 25 microns with reduced elongation distance, facilitating the manipulation of microparticles and cells without narrowly spaced plates, and supports optical electrowetting force generation.

Implementation Method 1

applying an electrowetting force to cause a region of the sample to become elongated

Methodology Applied

Scientific EffectElectrowetting: Electrowetting

Implementation Method 2

The electrostatic charge accumulated on the surface of the droplet acts to counteract the surface tension through like-charge repulsion

Methodology Applied

Scientific EffectElectrostatic repulsion: Ion Repulsion/Attraction

Data Source

PatentUS12485421B2Droplet generator and generation method

Publication Date: 2025.12.02 LIGHTCAST DISCOVERY LTD

AI summary

A method of generating droplets from a liquid sample is described and is characterised by the steps of a) locating the sample at a first electrowetting location and applying an electrowetting force to cause a region of the sample to become elongated in a direction in which the electrowetting force is applied; b) temporarily altering the electrowetting force on the sample and accumulating electrostatic surface charge on the sample to counter surface tension forces between the bulk of the sample and the elongated sample region; c) restoring the electrowetting force; d) further elongating the charged elongated sample region using the electrowetting force and e) severing a droplet from the charged elongated sample region. A corresponding droplet generator is also described.