Implantable Bone Distraction Device Using Wedge Clutches
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Solution Overview
Problem
Existing implantable devices for bone extension treatments face challenges in converting short reciprocating motion into unidirectional long movement with sufficient power generation, particularly due to limitations in materials like magnetostrictive, MSM, and piezoelectric actuators, which require additional electronics or mechanical transmission, and struggle with high forces and limited space.
Innovation Solution
The use of a wedging effect providing means with line contact, such as rolls or sprags, to lock the return movement, allowing multiple successive clutches to reduce clearance and withstand high forces, utilizing biocompatible materials and designs like barrel-shaped rolls or wedges with separate slanted surfaces for efficient power transmission and locking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If magnetostrictive material is used to generate reciprocating motion, then sufficient power is provided for bone extension treatment, but the length of reciprocating motion is too short (about 0.15 mm) to achieve the required distraction movement
Solution Approach 1:
The device segments the motion conversion process into multiple stages using a series of clutches (first clutch, second clutch, third clutch) arranged in sequence. Each clutch converts a portion of the short reciprocating motion into unidirectional movement, accumulating the total displacement over multiple cycles to achieve the required distraction distance.
Solution Approach 2:
A rod serves as an intermediary element that transmits the reciprocating motion from the magnetostrictive material through multiple clutches. The rod converts the short back-and-forth motion into progressive unidirectional movement by engaging with successive clutches, each locked by wedging effect providing means.
2Length of moving object
If the means allowing unidirectional movement is designed to convert short reciprocating motion into unidirectional long movement, then the required distraction is achieved, but the clearances of the device must be smaller than the change in length effected by the magnetostrictive material
Solution Approach 1:
The device divides the unidirectional movement into multiple smaller steps using successive clutches. Each clutch handles a portion of the total displacement, allowing the clearances to be larger than the magnetostrictive material's length change while still achieving the required total distraction through cumulative effect of multiple clutch engagements.
Solution Approach 2:
The clutches are designed with dynamic locking and unlocking mechanisms using wedging effect providing means (rolls, sprags, or bars). These elements dynamically engage to lock the clutch in the forward direction while allowing reverse movement, enabling the device to accommodate clearances larger than the actuator's stroke while maintaining precise controlled movement.
3Reliability
If barbs are used for locking (as in US 5415660), then locking is achieved, but the device cannot withstand the high forces and dynamic mechanical stress transmitted from the limb
Solution Approach 1:
The invention uses rolls (cylindrical elements) instead of barbs for the wedging effect providing means. The curved surface of the rolls distributes the mechanical stress over a larger area and provides more favorable stress distribution, enabling the device to withstand the high forces and dynamic loading from the limb while maintaining reliable locking function.
Solution Approach 2:
The device employs composite construction with a medullary nail made of biocompatible material and the clutch mechanism incorporating multiple elements (rolls, springs, locking surfaces) that work together to distribute and manage the high mechanical stresses, achieving both locking reliability and force resistance.
4Power
If the device is designed to transmit power for bone distraction, then the required extension force is provided, but the device must fit inside the medullary nail with limited space
Solution Approach 1:
The clutch mechanism is nested within the medullary nail structure. The rod with successive clutches is positioned inside the nail, and the entire assembly fits within the limited space of the medullary cavity. The nested arrangement allows the device to transmit high extension forces while maintaining a compact footprint that fits inside the medullary nail.
5Reliability
If multiple successive clutches are used to reduce clearance, then the locking reliability is improved, but the device complexity increases
Solution Approach 1:
The device combines multiple clutches into a single integrated rod structure. The first, second, and third clutches are arranged in sequence along the rod, sharing common elements and space, which reduces the overall complexity compared to having separate clutch assemblies. This merged design maintains high locking reliability while fitting within the constrained medullary nail space.
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 solution enables controlled, step-wise movement with reduced clearance, effectively transmitting power and locking mechanisms that withstand static and dynamic mechanical stress, suitable for high-force applications within limited spaces, ensuring reliable bone extension treatment.
Implementation Method 1
Magnetostrictive material is advantageous because it provides sufficient power, for example, in bone extension treatment. The small length of the reciprocating motion generated is, however, a problem
Implementation Method 2
The invention is characterized by the features defined in the characterizing part of the independent claim 1. According to the invention, the wedging effect providing means making line contact is used for locking the return movement of a unidirectional means
Data Source
Figure 1
Figure 2
Figure 3A~3D
AI summary
The invention relates to an implantable device fixed or interlinked to bone, which generates unidirectional movement by a member generating reciprocating motion in the same direction using means allowing unidirectional movement. In the device, the means allowing unidirectional movement comprise means based on friction which make line contact.