Embedded Sensors in Fiber-Reinforced Orthopaedic Composites
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Solution Overview
Problem
Existing orthopaedic composite devices face challenges in monitoring biomechanical forces and structural health due to the mechanical properties degradation caused by embedded sensors, high costs of fiber optic sensors, and adverse biological reactions from machining processes.
Innovation Solution
Low-cost sensors are embedded between layers of filament-wound composite structures, using copper wires or biocompatible ceramic particles, and wireless telemetry coils to monitor static and cyclic strains, allowing for real-time health monitoring and preventing catastrophic failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sensors are embedded in composite structures to monitor structural health, then measurement capability is improved, but mechanical properties of the composite material deteriorate
Solution Approach 1:
The patent applies local quality by placing sensors only at specific critical locations within the composite structure rather than uniformly throughout. Sensors are positioned at the neutral axis and at locations experiencing maximum stress or strain, allowing structural health monitoring while minimizing overall impact on mechanical properties. This selective placement ensures measurement capability is improved only where most needed.
Solution Approach 2:
The patent employs thin-film strain gauges and flexible sensor elements that can be embedded within composite layers without significantly disrupting the structural integrity. These thin-film sensors conform to the composite structure and transmit minimal stress concentration, thereby maintaining mechanical properties while enabling measurement.
2Measurement precision
If fiber optic sensors are used to monitor cure and structural health, then measurement capability is improved, but device complexity and cost increase
Solution Approach 1:
The patent employs inexpensive strain gauges and simple sensors that can be embedded during manufacturing rather than expensive fiber optic sensors requiring complex interrogation systems. These simpler sensors provide adequate measurement capability for orthopaedic applications without the need for sophisticated signal processing equipment.
Solution Approach 2:
The patent replaces complex optical sensing systems with simpler electrical strain gauges and resistance-based sensors. This substitution eliminates the need for expensive fiber optic interrogation equipment while providing sufficient measurement capability for monitoring structural health in orthopaedic implants.
3Ease of manufacture
If machining pockets in pre-preg tape after winding to embed sensors, then sensor integration is improved, but manufacturing precision deteriorates due to discontinuous fiber ends
Solution Approach 1:
The patent applies preliminary action by embedding sensors during the pre-preg tape winding process itself, rather than machining pockets afterward. Sensors are placed within the continuous fiber reinforcement as the structure is being built, ensuring fiber continuity is maintained and avoiding the creation of stress concentration points at machined interfaces.
Solution Approach 2:
The patent merges the sensor embedding process with the composite manufacturing process. Sensors are integrated into the pre-preg tape layup and wound together with the fiber reinforcement in a single continuous operation, eliminating the need for separate machining steps and preserving fiber continuity throughout the structure.
4Strength
If thin film gauges are bonded to host substrate using sputtering, then bonding strength is improved, but thermal damage occurs to polymer composite structure
Solution Approach 1:
The patent changes the temperature parameter by avoiding high-temperature sputtering processes. Instead, sensors are embedded at lower temperatures during the composite manufacturing process, or bonding is performed using low-temperature adhesives and consolidation methods compatible with polymer matrix temperatures, thereby preventing thermal damage while achieving adequate bonding strength.
Solution Approach 2:
The patent introduces an intermediary bonding layer or adhesive that enables sensor attachment without requiring high-temperature sputtering. This intermediary material provides sufficient bonding strength at lower temperatures compatible with polymer composite structures, eliminating thermal damage while maintaining attachment integrity.
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 biomechanical forces and structural integrity, reducing the risk of failures and adverse reactions, while maintaining the mechanical properties of the composite material.
Implementation Method 1
The sensing element includes a wire arranged such that loads on the orthopaedic fixation device result in a change in the electrical resistance of the wire
Data Source
Figure 1~2
Figure 3
Figure 4A~4B
AI summary
In one general aspect, an orthopaedic fixation device includes an inner core and shaft formed of a multi-layered, fiber-reinforced composite. A sensing element is embedded within the multi-layered, fiber-reinforced composite.