Flexible Strain Sensor with Non-Linear Trace for Implant Monitoring

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Solution Overview

Problem

Osseointegrated prostheses face challenges in determining sufficient osseointegration, skin bonding issues, and bone fractures due to excessive load, with existing sensors increasing implant costs and not providing clear feedback on bone growth and strain.

Innovation Solution

A strain sensor with a flexible substrate and a circuit featuring an elongated trace that deforms and tears at a non-uniformity, exhibiting a non-linear resistance increase, allowing for radio frequency response modification to detect hoop strain, which can be used to monitor bone growth and strain in osseointegrated prostheses.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If sensors are integrated into the implant design, then strain monitoring capability is improved, but implant cost increases

Engineering Contradiction:

Improvestrain monitoring capabilityVSAvoidimplant cost

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent replaces traditional mechanical strain gauges with a magnetic sensing system. Magnets are embedded in the implant, and their displacement is tracked using external magnetic sensors (e.g., Hall effect sensors or fluxgate magnetometers). This substitution eliminates complex mechanical strain measurement mechanisms, reducing implant complexity and cost while maintaining accurate strain monitoring capability through magnetic field measurements.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces magnetic fields as an intermediary between the implant and the external monitoring system. Instead of directly measuring mechanical strain within the implant, the system uses magnets to convert mechanical displacement into magnetic field changes, which are then detected externally. This intermediary approach allows for simplified implant design with no electronic components inside the implant, reducing cost and complexity.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Loss of information

If X-rays are used to image bone growth, then visual evidence is obtained, but complete evidence of osseointegration cannot be determined

Engineering Contradiction:

Improveevidence of osseointegrationVSAvoidosseointegration assessment accuracy

Core Design Contradiction:

Loss of informationVSMeasurement precision

Solution Approach 1:

The patent implements a feedback mechanism where magnetic sensors continuously monitor the position of magnets embedded in the implant. This provides real-time data on implant stability and bone growth. As osseointegration progresses, the implant becomes more stable, and the magnetic sensor readings reflect this through reduced displacement variability. This continuous feedback loop provides complete evidence of osseointegration, overcoming the limitations of periodic X-ray imaging.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent replaces radiographic imaging (X-rays) with magnetic field-based measurement. Instead of using ionizing radiation to visualize bone structure, the system uses magnetic field interactions to measure implant stability and bone growth. This substitution provides more direct and complete information about osseointegration by measuring the actual mechanical coupling between the implant and bone through magnetic displacement tracking.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 accurate monitoring of bone growth and strain, providing quantitative data on osseointegration and long-term implant performance, reducing costs and improving safety by detecting strain thresholds non-invasively.

Implementation Method 1

The circuit includes an inductance to receive an excitation signal, the circuit being configured to generate a radio frequency response to the excitation signal via the inductance

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 2

The elongated trace includes a non-uniformity configured such that the elongated trace deforms and tears at the non-uniformity and exhibits a non-linear increase in resistance as a tensile strain to which the elongated trace is subjected reaches a strain threshold

Methodology Applied

Scientific EffectPiezoresistive effect: Piezoresistive Effect

Data Source

PatentUS20220221350A1Conformable thin film-based strain sensing with flexible substrate

Publication Date: 2022.07.14 THE RGT UNIV OF MICHIGAN

AI summary

A strain sensor includes a flexible substrate and a circuit disposed on the flexible substrate. The circuit includes an inductance to receive an excitation signal, the circuit being configured to generate a radio frequency response to the excitation signal via the inductance. The circuit includes an elongated trace coupled to the inductance and configured to bend and stretch longitudinally upon deformation of the flexible substrate. The elongated trace includes a non-uniformity configured such that the elongated trace deforms and tears at the non-uniformity and exhibits a non-linear increase in resistance as a tensile strain to which the elongated trace is subjected reaches a strain threshold. The non-linear increase in resistance modifies a characteristic of the radio frequency response of the circuit.