Spherical Nitinol Cage Manufacturing via Wire Braid and Mandrel
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Solution Overview
Problem
Current methods for manufacturing Nitinol cages for AVN treatment in hip replacement surgery are limited by the inability to mass-produce spherical cages using mechanical methods, as existing approaches result in Nitinol tubes rather than spheres, and handmade cages are not feasible for widespread use.
Innovation Solution
A method involving a wire braid and spherical ball is used, where the braid and ball are placed in a mold, excess braid is trimmed, and the assembly is heat set to create a spherical Nitinol cage, leveraging Nitinol's shape-memory properties to form a spherical shape.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If mechanical methods are used to mass manufacture Nitinol cages, then productivity is improved, but the shape accuracy deteriorates (producing tubes instead of spheres)
Solution Approach 1:
A spherical mandrel is introduced as an intermediary object to form the spherical cage during manufacturing. The mandrel serves as a temporary support structure that defines the spherical geometry, allowing mechanical manufacturing processes to produce accurate spherical shapes rather than tubes. After the cage is formed, the mandrel is removed, leaving the final spherical product.
Solution Approach 2:
The wire braid is pre-formed and pre-assembled around the spherical mandrel before the final shaping process. This preliminary arrangement of the braid in the correct spherical configuration allows the subsequent heat treatment and forming processes to maintain shape accuracy while enabling mass production through consistent replication.
2Manufacturing precision
If handmade methods are used to manufacture Nitinol cages, then shape accuracy is improved (spherical shape achieved), but productivity deteriorates (not feasible for mass manufacture)
Solution Approach 1:
The spherical mandrel acts as a reusable template that guides the formation of multiple cages in sequence. Instead of hand-shaping each cage individually, the mandrel provides consistent geometric guidance for mechanical processes, enabling replication of the spherical shape across mass production while maintaining accuracy.
Solution Approach 2:
Manual shaping operations are replaced with controlled thermal and mechanical processes. The heat treatment process (solution annealing, quenching, and aging) substitutes for hand-forming operations, automatically achieving the desired spherical geometry and Nitinol material properties through standardized thermal cycles rather than manual manipulation.
3Reliability
If traditional THR procedure is used for AVN treatment, then effectiveness is improved (complete joint replacement), but invasiveness worsens (very invasive major surgery)
Solution Approach 1:
The spherical cage is extracted as a separate, standalone component that can be inserted through a minimally invasive approach rather than requiring complete joint replacement. This extracted component addresses the AVN pathology directly by reinforcing the femoral head, eliminating the need for the more invasive total hip replacement procedure.
Solution Approach 2:
Instead of replacing the entire hip joint, the treatment applies a localized solution by inserting a spherical cage only into the affected femoral head region. This local intervention addresses the specific AVN pathology while preserving the natural joint structures, reducing surgical invasiveness while maintaining treatment effectiveness for the specific condition.
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 method enables the efficient mass production of spherical Nitinol cages, addressing the challenge of creating the necessary spherical shape for AVN treatment, facilitating more accessible and effective hip replacement surgeries.
Implementation Method 1
The mold is heat set and the spherical ball and wire braid are removed from the mold
Implementation Method 2
The Nitinol cage is compressed during insertion and placed inside of the femoral head. Once inside the femoral head, the Nitinol cage then returns to its spherical shape
Data Source
AI summary
A method for manufacturing a spherical cage. The method includes providing a wire braid and inserting a spherical ball inside the wire braid. The wire braid and spherical ball are placed inside a mold. Excess wire braid is trimmed from the mold, creating trimmed ends of the braid. The mold is heat set with the spherical ball and wire braid. The spherical ball and wire braid are removed from the ball and the spherical ball is removed from the wire braid, resulting in a spherical wire cage.