Automated Suture Swaging with Segmented Compression
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Solution Overview
Problem
Existing methods for manufacturing armed surgical needles face challenges in achieving high reliability and low failure rates due to material stress and attachment issues, particularly with harder alloys like 4310 SS, nickel-titanium SS, and 420 SS, which lead to cracking and loss of attachment over time.
Innovation Solution
An automated method using a Flexible Automatic Swage (FAS) system that secures a surgical suture to a needle with controlled tension levels, employing programmable electric actuators and grippers to swage and test the attachment, ensuring consistent and reliable suture-needle bonding while minimizing material stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple hit swaging is used to achieve reliable suture attachment, then attachment strength is improved, but material stress accumulates causing cracking and failure
Solution Approach 1:
The swaging process is divided into multiple sequential compression strokes rather than multiple rotational hits. Each stroke compresses a different radial portion of the needle barrel (top, bottom, sides) against the suture, distributing stress evenly throughout the material without accumulating localized stress that causes cracking.
Solution Approach 2:
The swaging process uses periodic compression strokes with repositioning between each stroke. The needle barrel is restrained and repositioned between strokes to ensure even stress distribution, preventing the cumulative stress damage that occurs with continuous rotational hitting.
2Reliability
If needle barrel is compressed repeatedly to ensure attachment, then suture attachment strength is improved, but residual stress causes relaxation and loss of attachment over time
Solution Approach 1:
The compression is segmented into multiple strokes affecting different portions of the needle barrel rather than repeated compression of the same area. This segmentation prevents residual stress concentration that would cause relaxation and loss of attachment over time.
Solution Approach 2:
The swaging process changes the compression parameters between strokes by restraining different radial portions of the needle barrel in sequence. This parameter variation ensures uniform stress distribution and prevents the development of residual stresses that lead to attachment degradation over time.
3Strength
If harder alloys are used to improve needle strength, then needle durability is improved, but susceptibility to cracking during swaging increases
Solution Approach 1:
The use of harder alloys is made compatible with the swaging process through periodic compression strokes with repositioning. This periodic action allows harder, more durable materials to be swaged without cracking by distributing stress evenly and preventing stress concentration that would cause fracture in brittle materials.
Solution Approach 2:
The swaging parameters are changed to accommodate harder alloys by using multiple compression strokes with restraint and repositioning. This modifies the stress application pattern to be compatible with harder materials that have lower ductility and are more susceptible to cracking under conventional swaging conditions.
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 FAS system effectively produces armed surgical needles with high reliability and low failure rates by maintaining precise tension control during swaging and testing, reducing material stress and ensuring durable suture-needle attachments.
Implementation Method 1
a swage die impinges upon the outer surface of the needle barrel, thereby compressing a portion of the bore onto the suture
Implementation Method 2
The compressed portion of the axial bore grasps the suture by mechanical interference and by surface friction
Implementation Method 3
needle materials have some elasticity, such that the relief of residual stress causes the needle barrel to relax over time
Implementation Method 4
The needle and suture materials have some degree of malleability, but when the limit of malleability is reached, the materials will fail
Data Source
AI summary
A method of attaching a surgical suture to a needle and testing the attachment includes dispensing a length of suture from a spool by using a first suture gripper, and using a surgical needle gripper for holding a surgical needle stationary. A leading end of the suture is inserted into and attached to a receiving end of the surgical needle. A second suture gripper is located between the first suture gripper and the spool. After the second suture gripper is closed for gripping the suture, the second suture gripper is advanced downstream toward the surgical needle to reduce the tension on the suture. The tension on the suture is reduced by moving the second suture gripper a pre-determined distance. The first suture gripper is opened for releasing the suture and the first suture gripper is moved toward the suture spool for re-grasping the suture at a location between the second gripper and the suture spool. The suture between the downstream side of the re-positioned first suture gripper and upstream side of the second suture gripper is cut. After the suture is cut, the second suture gripper is displaced toward the spool using a tension control system to increase the tension level between the needle and the second suture gripper.