IUD String Knot Constraint Structure to Prevent Retraction

Solution Overview

Problem

Existing intrauterine devices (IUDs) suffer from the issue of knotted strings curling up and retracting into the cervical canal, leading to potential expulsion and difficulty in verification and removal.

Innovation Solution

The IUD design incorporates a spherical bulge and a defined trajectory for the string, restricting the knot's pivoting and lateral movement, ensuring the string remains projected and accessible.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If the string is knotted and left free to move, then the knot can pivot and lateral shift, but the string curls up and retracts into the cervical canal

Engineering Contradiction:

Improvestring accessibility for verificationVSAvoidstring position stability

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The patent applies local quality by creating a specific geometric constraint (the spherical bulge with through-hole) at the precise location where the string knot forms. This localized structure provides the necessary restriction on knot movement without affecting the overall string length or other parts of the IUD. The spherical bulge with its specific through-hole configuration creates a unique constraint zone that prevents curling while maintaining string accessibility.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent introduces a spatial dimensionality change by forming a spherical bulge structure that constrains the knot in three-dimensional space. The through-hole in the spherical bulge creates a specific geometric pathway that limits the knot's pivoting motion and lateral shift, thereby preventing the string from curling up into the cervical canal while still allowing the string to remain accessible for verification.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Reliability

If the string is restricted from pivoting and lateral movement, then curling and retraction are prevented, but the knot movement is completely constrained

Engineering Contradiction:

Improvestring position stabilityVSAvoidknot movement restriction mechanism

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent applies local quality by creating a specific geometric constraint (the spherical bulge with through-hole) at the precise location where the string knot forms. This localized structure provides the necessary restriction on knot movement without affecting the overall string length or other parts of the IUD. The spherical bulge with its specific through-hole configuration creates a unique constraint zone that prevents curling while maintaining string accessibility.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent utilizes spheroidality by forming a spherical bulge structure that naturally constrains the knot through its curved geometry. The spherical shape with its through-hole creates a specific spatial constraint that limits the knot's movement in pivoting and lateral directions, thereby preventing string curling and retraction without requiring complex mechanical restriction mechanisms.

Inventive Principle:

Principle #14Spheroidality (Curvature)

3Ease of manufacture

If a through-hole is provided in the spherical bulge for string passage, then the string can be attached to the IUD, but the knot may pivot and lateral shift causing curling

Engineering Contradiction:

Improvestring attachment simplicityVSAvoidstring position stability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent applies local quality by creating a specific geometric constraint (the spherical bulge with through-hole) at the precise location where the string knot forms. This localized structure provides the necessary restriction on knot movement without affecting the overall string length or other parts of the IUD. The spherical bulge with its specific through-hole configuration creates a unique constraint zone that prevents curling while maintaining string accessibility.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent introduces a spatial dimensionality change by forming a spherical bulge structure that constrains the knot in three-dimensional space. The through-hole in the spherical bulge creates a specific geometric pathway that limits the knot's pivoting motion and lateral shift, thereby preventing the string from curling up into the cervical canal while still allowing the string to remain accessible for verification.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Data Source

PatentEP3206637B1An intrauterine device with a restricted movement of a string knot

Publication Date: 2026.01.28 PREGNA INT

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Figure 1C

AI summary

An intrauterine device (20) with a restricted movement of a knot (5) of the string (4) due to a region (3) having such differed shape and size at a distal end (12) of central vertical stem (1) and due to a trajectory for string (4) in the region (3) that the length of the string (S) is shorter than the distance (r) of the region (3); and the loop (15) of the string and therefore the knot (5) is unable to pivot around the axis (14). The lateral shift of the knot (5) is also prevented. Consequent to restricted pivoting and restricted lateral shift of the knot (5), the hanging portion (9) of the string (4) continue to project downwards and do NOT develop tendency to get retracted and thus do not curl up in the uterus (16) through the cervix (17).