Shape Memory Bone Anchor for Pull-Out Resistance
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Solution Overview
Problem
Current bone fixation screws lack sufficient resistance against pull-out or back-out, especially in osteoporotic bone, leading to instability and lower bone fusion rates in spinal surgeries, due to their dependence on cortical and cancellous bone composition and thread-based fixation mechanisms.
Innovation Solution
A bone fastener or anchor with a temperature-sensitive composition and a flexible mesh section made of shape memory wires or polymers, which expands after insertion to prevent pull-out, featuring a conical penetrating edge and rigid sections for enhanced stability and attachment to bone.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional bone fixation screws are used, then the fixation mechanism is simple, but the resistance against pull-out or back-out is insufficient, especially in osteoporotic bone
Solution Approach 1:
The anchor shaft is divided into three distinct sections: a first rigid section, a flexible mesh intermediate section, and a second rigid section. This segmentation allows each section to perform its specific function - the rigid sections provide structural support while the flexible mesh section provides expansion capability to prevent pull-out, thereby resolving the contradiction between strength and complexity.
Solution Approach 2:
The intermediate section is designed with shape memory material that allows it to dynamically change its cross-sectional breadth. Before insertion, the breadth is small to facilitate passage through the opening. After insertion, the shape memory material causes expansion to at least twice the size of the opening, dynamically adapting to provide maximum pull-out resistance while maintaining structural integrity.
2Strength
If the anchor is designed with a flexible mesh section that expands after insertion, then the pullout strength increases significantly, but the insertion process becomes more complex
Solution Approach 1:
The shape memory material in the intermediate section changes its physical parameters (cross-sectional breadth) in response to temperature changes. Before insertion, the material is in a martensitic phase with small breadth. After insertion into the body, body temperature triggers transformation to austenitic phase, causing expansion to at least twice the opening size, thereby achieving high pullout strength while maintaining ease of insertion.
Solution Approach 2:
The conical penetrating edge is designed to facilitate preliminary action by enabling easy penetration and insertion through the surgically created opening in the bone. This preliminary insertion action is simplified by the conical geometry, which guides the anchor through the opening before the flexible mesh section expands to provide pullout resistance.
3Ease of operation
If the anchor uses a threadless solid design with conical penetrating edge, then the insertion through small incisions is easier, but the fixation stability may be compromised
Solution Approach 1:
The flexible mesh intermediate section provides dynamic adaptation after insertion. The shape memory material causes the section to expand from a compact insertion configuration to an expanded fixation configuration with breadth at least twice the opening size, thereby achieving both easy insertion through small incisions and reliable fixation stability through the expanded anchor body.
Solution Approach 2:
The anchor combines rigid materials for the first and second sections with shape memory materials for the intermediate section. This composite construction provides the rigid sections for structural support and connection while the shape memory intermediate section provides dynamic expansion capability, resolving the contradiction between ease of insertion and fixation stability.
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 anchor provides greater resistance against pull-out or back-out, improving implant stability and bone fusion rates, and can be inserted through small incisions, with a potential 60 to 300 times increase in pullout strength compared to traditional screws, and better postoperative clinical outcomes.
Implementation Method 1
a plurality of interwoven shape memory wires or polymer fibers or a combination thereof connected between the first circumference and the second circumference
Implementation Method 2
sections or segments that include a temperature sensitive composition. the transition temperature ranges for the change from a first distinct shape to a second distinct shape of the composition can range from about −20 degrees Celsius to about +110 degrees Celsius
Data Source
AI summary
An anchor including shape memory metals, shape memory polymers or a combination thereof. The anchor has surgical and nonsurgical uses.