Staying Connected - February 2014

Medical Cable Service-Life



Extremely durable medical cable
assembly due to design, materials,
construction and workmanship

All medical devices, including medical cable assemblies will eventually reach the end of their service-life and fail.  How long a cable or connector functions before it reaches its end-of-life is largely determined by the design, including selection of materials, construction and workmanship.

Product Service-life

Service-life is the length of time a product functions properly, and as intended, before reaching its end-of-life.  Establishing and documenting the expected service-life is an important part of designing a medical connector or cable assembly because it will affect all aspects of the design.

The Role of Components in Service-Life

The selection of components and raw materials plays a significant role in determining what the service-life of a medical cable assembly or connector will be.  If the device is being designed for a single use or limited use, less durable and less costly materials may be used.  On the other hand, if the product must function properly for years or in a critical application, a more careful evaluation and selection of materials and components is essential to achieve the desired service-life.

The following chart is an example of various design elements and a comparison of durability of various materials and constructions.



Flex testing of production
cables confirms that the
design requirements are met


Conductor Material and Stranding
Effect Service-life

Medical cable is comprised of one or more stranded conductors.  And, except for the infrequent use of non-metallic carbon filaments, conductors are copper based.

When the cable assembly or lead wire needs to withstand a high number flex cycles without failing, using conductors that have a high number of fine strands offers greater flexibility and durability than using conductors with fewer, thicker strands.  The higher the number of strands, the more flexible the conductor will be, but finer stranded wire is more costly than wire cabled with fewer strands.


Tinsel conductors wrapped around a
strength-member enhances flexibility,
tensile strength and service-life


Besides stranding, the composition of the copper conductor can play a large role in determining flex life and service-life.  As a cable or leadwire flexes, conductors heat up and can become “work hardened.”  The more the conductors are flexed, the less flexible the conductors become, eventually failing.  Copper alloys offer greater flexibility and service-life because these materials resist work hardening, remaining more flexible than pure copper conductors.  Copper alloys are more costly than standard copper conductors and are therefore used where greater flex life and higher reliability is required.

When even greater flex life and service-life is required and where only low voltage signals are carried, tinsel conductors wrapped axially around a strength member is a logical design choice.  Tinsel conductors offer excellent flex-life characteristics and a strength member made of a synthetic fiber such as Kevlar adds a great deal of tensile strength.



Cable jacket material, thickness and
durometer play a large role in
determining the durability and service
life of a medical cable assembly


The Cable Jacket’s Role in Service-Life

When designing a medical cable assembly or leadwire, one of the considerations is the jacket material.  The jacket material is not only the part of the cable or wire that is most visible; it plays a large role in the performance and service-life of the finished cable assembly.  Because the cable jacket offers mechanical, chemical and environmental protection to the conductors within the jacket it can have a significant effect on service-life.

The wall thickness of the jacket plays a role in determining the durability and service-life of a cable assembly.  Comparing the same material with similar hardness, the greater the jacket wall thickness, the more durable the jacket will be.

Because the cable or wire jacket is exposed, the conditions the cable will be used under and how it will be cleaned, disinfected or sterilized should be addressed early in the design stage.

Properties of Resins Used to Mold Rigid Parts

Virtually all medical cable assemblies and connectors contain injection molded parts.  There is a wide variety of resins available for injection molding and determining the material with the properties most suitable for the end product can be an engineering challenge.

When asked about the durability of various resins, Affinity Engineering Manager, Matt Pathmajeyan commented: “Durability can be defined differently depending on the intended use. There are materials that are more durable for applications requiring impact strength vs. higher heat deflection vs. the ability to withstand solvents. These various attributes do not always exist in the same polymer.”


Resin specification plays a key role in
determining the service-life of molded
components such as this enclosure
which is part of a cable assembly





“As an example, ABS is stronger than Styrene when speaking in terms of impact strength, but ABS will not withstand as many autoclave cycles compared to materials like Ultem® (amorphous thermoplastic polyetherimide) or a liquid crystal polymer (LCP).  Polymers like Ultem® and LCP have higher resistance to chemicals and solvents than ABS does.  On the other hand, Ultem® and LCP require special processing and are more costly as a result.  Styrene is inexpensive and easy to mold but is less shatter resistant. Polypropylene and polyethylene are difficult to shatter but are not very resistant to abrasion or heat.”

Understanding the performance requirements and how the cable assembly or connector will be used, including how it may be cleaned and how long it is expected to last should be considered when choosing resins for molded parts.



The use of a clamp or ferrule can add
extra strength and durability to a cable
assembly particularly when captured
within an overmold


Protecting Terminations Increases Service-life

Besides materials, the way a medical cable assembly or connector is designed and manufactured can play a large role in determining service-life.  The most common point of failure for cable assemblies is at the point where conductors are terminated either by soldering or crimping.  Designing and manufacturing a cable or connector so that no stress is transferred to the termination points will increase service-life.

Preventing stress from being transferred from the body of a cable assembly to a termination point is commonly achieved by the use of a strain or bend relief.  Most off-the-shelf connectors are available with slip-on boots or strain reliefs.  While a slip-on boot provides a measure of protection, it is typically less than that of an overmolded strain relief that bonds to the cable and connector.

(Insert image: “Inner.jpg” Caption: “The longest service-life may be achieved by using a two-step molding process consisting of a hard inner mold and a softer, user-friendly outer mold”)
(Insert image: “Outer.jpg” Caption: [center above caption below both images])

   
The longest service-life may be achieved by using a two-step molding process consisting of a hard inner mold and a softer, user-friendly outer mold

Depending upon the degree of durability and service-life required, there are design decisions when considering an overmolded strain relief.  For a cable, leadwire or connector that is designed for single or limited life, a single overmold using a low cost material may be a reasonable choice.  For longer service-life a two-shot overmold – inner and outer – may be beneficial.  When even greater service-life is required, choosing mold materials that will bond to the wire or cable jacket with improve performance even more.

Life Cycle vs. Technology Cycle

The technology cycle is a significant characteristic of a products life-cycle.  It is becoming more common for a product to become obsolete by technology before it has reached its end of service-life.  With new medical devices being introduced at a more-rapid rate than in the past, it is recommended to consider the anticipated technology cycle as well as the expected service-life.  If a cable assembly is expected to become obsolete in five years, it is not necessary to design it and manufacture it to last ten years.

Summary

The expected service-life of a medical cable assembly, connector or other interconnect device should be established early in the product design process.  The specification of materials, coupled with designing-for-service-life and appropriate manufacturing techniques is likely to produce a device meeting the service-life objective.

We invite you to take advantage of Affinity’s experience and expertise in designing rugged, reliable and long-life cable systems, contact us at +1 949-477-9495 or via email to customercare2@affinitymedical.com.

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Meet Cindy Witkowski – Customer Care Coordinator



Cindy Witkowski, Affinity’s newest
Customer Care Coordinator


Cynthia (Cindy) Witkowski joined Affinity as the newest member of the Customer Care team in January.  She brings with her over 20 years’ experience in customer service.

“As our business continues to expand, we need to make sure that we have sufficient Customer Care resources,” said Marketing Manager, Hank Mancini.  “We interviewed a lot of candidates over the past three months and we’re really happy that we found Cindy.  She is energetic and brings a lot of experience to the job.  I think customers will really enjoy working with her.”

Cindy reports to Customer Care Supervisor, Candy Golding.  Her first few weeks on the job have been largely taken up with training, with Candy, and with other department managers and supervisors.  In addition to one-on-one training, Cindy is training on Affinity’s Quality Procedures that are applicable to her job.

(Insert photo: “AtDesk.jpg” Caption: “One of Cindy’s responsibilities is Contract Review of customer orders”)


One of Cindy’s responsibilities is
Contract Review of customer orders


Asked about her first impressions of Affinity, Cindy replied, “I am really happy to have joined the Affinity family.  Everyone is friendly and I enjoy being back in the medical business.”  Discussing the challenges of her new position, Cindy continued, “This is my first position where I have worked at the manufacturing plant.  It is exciting to see our products manufactured a few feet from where I work, but also a little intimidating.  I have a lot to learn, but that excites me.

Describing herself, Cindy says she is “very organized and a stickler for details,” both traits that will be beneficial to her Affinity customers.

Cindy is a native of California and has lived in Orange county most of her life.  She and her husband Jim live in nearby Huntington Beach, California.  They have been married 25 years and have two sons, both attending California State University Long Beach.

When not working Cindy says, “I love to travel and Hawaii is our favorite spot to visit.  I love the ocean there and the weather is great.”  Cindy also plays tennis and is a real “movie buff!”

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Announcements, Information and Trivia


MD&M West in Anaheim

Once again, Affinity Medical will be exhibiting MD&M West, country’s largest medical device show.  Affinity capabilities will be featured in the Molex booth, #1746 along with Molex capabilities.

We welcome you to visit Affinity and Molex at MD&M West in Anaheim,
February 11th – 13th.



Cross-country skiing
and shooting are
combined into one event


Skeleton is a head-first
sled race in Winter Olympics

Winter Olympic Trivia 2

Biathlon – In the Winter Olympics, the Biathlon competition consists of cross-country skiing and rifle shooting.  The competition consists of a race on a cross-country trail which is broken up by shooting rounds.  This event has also been known as Military Patrol in previous games.

Quadrennial – Happening once every four years – as both the Summer and Winter Olympics do.

Skeleton – This single-person sled race was added back to Winter Olympic events in 2002 after being absent since 1948.  Skeleton riders lie on their stomach and race head-first

$51 billion dollars – it is estimated that the cost of the Winter Olympics in Sochi will cost more than the cost of the past three games, Vancouver in 2010, Turin Italy in 2006 and Salt Lake City, Utah in 2002.



Curling as an event in the
winter games began in 1924

Curling – Curling was included in the first Winter Olympics in 1924.  The event was added to the official program at the 1998 Winter Olympics in Nagano, but results of the competition were not officially recognized until the Turin games in 2006.

First Televised Games – The 1956 Winter Olympics held in Cortina d’Ampezzo in the Italian Alps were the first televised winter games.

2018 Winter Olympics – will be held in Pyeongchang, South Korea