Orientated Polymeric Devices for Bone Fixation
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Solution Overview
Problem
Shape memory polymer sleeves used for fixating medical devices to bone often experience inefficient heating and incomplete expansion due to uneven radial stress distribution, leading to insufficient fixation.
Innovation Solution
The development of shape memory polymer materials with tailored stress patterns, where specific regions have different amounts of stored stress in perpendicular directions, allowing for controlled radial and axial deformation upon energy application, ensuring consistent expansion and contraction to enhance fixation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a heat source is placed within the through hole of the sleeve, then the sleeve can be heated to trigger shape memory effect, but the through hole expands away from the heat source causing inefficient heating and incomplete expansion
Solution Approach 1:
The patent applies local quality by creating non-uniform stress distribution within the sleeve material. Specifically, the sleeve is designed with higher stored stress in the radial direction at certain regions compared to other regions, allowing different parts of the sleeve to expand at different rates and directions. This localized stress differentiation enables the sleeve to maintain the through hole diameter while expanding radially outward, solving the heating efficiency problem without compromising fixation reliability.
2Strength
If the sleeve expands radially to engage the bone, then fixation strength is improved, but the through hole expands away from the device causing inefficient heating
Solution Approach 1:
The patent utilizes parameter changes by modifying the stored stress parameters within the sleeve material during manufacturing. The sleeve is processed to achieve specific stress states in different directions and regions, particularly creating higher radial stress in targeted areas. This parameter control allows the sleeve to expand predictably and uniformly when heated, ensuring complete expansion and proper engagement with both the device and bone, thereby improving energy utilization efficiency while maintaining fixation strength.
3Manufacturing precision
If the sleeve material is heated uniformly, then complete expansion is achieved, but the through hole still relaxes away from the heat source causing uneven expansion
Solution Approach 1:
The patent applies asymmetry by intentionally creating an asymmetric stress distribution pattern within the sleeve material. Rather than uniform stress throughout, the sleeve is designed with specific regions having higher stored stress in the radial direction. This asymmetric stress pattern compensates for the thermal gradient caused by the heat source position, ensuring that the through hole remains stable while the outer surface expands uniformly to engage the bone, achieving both through hole stability and expansion uniformity.
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
This approach ensures efficient and uniform expansion of the sleeve, improving the fixation of medical devices to bone by maintaining the inner diameter unchanged while increasing the outer diameter, thereby reducing device failure and enhancing bone engagement.
Implementation Method 1
sleeves of shape memory polymer material may be used in fixating medical devices to bone... energy is then provided to the sleeve causing the sleeve to shrink axially and expand radially
Implementation Method 2
the device is inserted into a bone and energy is then provided to the sleeve causing the sleeve to shrink axially and expand radially
Data Source
AI summary
The present disclosure relates to a shape memory polymer material containing at least one two dimensional region having a first amount of stored stress in a first direction and a second amount of stored stress higher than the first amount of stored stress in a second direction, wherein the two dimensional region is capable of changing shape in only one of the first or second directions.