Staying Connected - October 2012

Service Life of a Medical Cable

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



Gold plated contacts are typically used
where a large number of mate/un-mate
cycles are required, but are also more
costly than nickel plated contacts

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.

Component Specifications

The selection of raw materials and components 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 specified.  On the other hand if the product must function properly for years or in a critical application, more careful evaluation and selection of materials and components is necessary.

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

Design element Less durable Durable More durable
Conductor material Copper Copper alloy Tinsel conductors with strength member
Contact plating Nickel plating Gold plating Heavy gold plating
Cable jacket material ruggedness PVC TPR/TPE (e.g. Santoprene®) Polyurethane
Cable jacket autoclave withstand PVC TPR/TPE (e.g. Santoprene®) Silicone
Rigid plastic components Polystyrene ABS Polycarbonate
Conductor Stranding Common stranding, e.g. 28 gauge with 7 ea. 36 gauge strands (7/36) Fine stranding, e.g. 28 gauge conductor with 19 ea. 40 gauge strands (19/40) Very fine stranding, e.g. 28 gauge conductor with 40 ea, 44 gauge strands (40/44)
Cable strain relief construction OEM supplied slip-on boot Single shot overmold Double shot overmold, inner and outer

Conductor Stranding and Materials Effect on Service life


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


Medical cable assemblies are 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.  Finer stranded wire is more costly than wire cabled with fewer strands.

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 conductors are flexed, the less flexible the conductor becomes, eventually failing.  Copper alloys can offer much greater flexibility and service life because these materials resist work hardening.  Copper alloys are more expensive than standard copper 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 characteristics and strength member made of a synthetic fiber adds tensile strength.



Cable jacket material plays a large role
in determining the durability and service
life of a medical cable assembly
.

Cable Jacket Material

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.  A cable jacket offers mechanical, chemical and environmental protection to the conductors within the jacket.

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

How a wire or cable will be cleaned, including what it will be cleaned with is a very important consideration in establishing service life.  A detailed explanation of Cleaning and Sterilization of Medical Cables and Connectors is the focus of the September issue of “Staying Connected” and will not be repeated here.

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 different ways 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 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 mold materials.



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 less than that of an overmolded strain relief.

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 called for.  When even greater service life is required, choosing mold materials that will bond to the wire or cable jacket with improve performance even more.

Technology Cycle

The technology cycle is another aspect 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-life.  With new models of medical devices being introduced at a faster rate than in the past, it is reasonable to consider the anticipated technology cycle as well as the expected service life.  If a cable assembly will become obsolete in five years, it is unnecessary to design and manufacture it to last ten years.

Summary

The service life of a medical cable assembly, connector or other interconnect device should be established early in the product design process.  The selection of materials, coupled with design for service life and appropriate manufacturing techniques will produce a device meeting the service life objective.

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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Molex Acquires Affinity Medical

Molex Incorporated acquired Affinity Medical Technologies on October 10, 2012!
 
“After more than fifteen years it was time to sell Affinity so the company that Bob Frank and I founded could continue to grow and reach its full potential,” said former President and CEO Mary Phillipp.  “A number of companies expressed interest in buying Affinity, but I was not going to sell to just anyone.  One of the most important considerations in choosing who to sell the company to was understanding their commitment to grow Affinity with the current team in its present location.  Equally as important as that was the culture of the company.  Molex has a culture very similar to ours at Affinity and one that I thought our team would feel comfortable with.”



Mary Phillipp and Bob Frank,
founders of Affinity Medical

With Mary resigning her role as President and CEO, Bob Frank was chosen to lead the company as General Manager.  “I’ve worked with Mary virtually my entire career.  And, while I am truly excited about my new position, it is hard to imagine Affinity without Mary.  I am thankful that she has agreed to continue on for a period as a consultant.  It will be a challenge for me to fill her role,” said Bob.

“Most of us at Affinity are here because of an acquisition,” said Hank Mancini, Affinity Business Development Manager.  “My experience with mergers and acquisitions is that customers are the biggest losers.  The message to all is that it is business as usual here at Affinity.  Molex has a high regard for how we have managed our business and wants us to continue with the same focus on quality and service.”


Matt Pathmajeyan,
Affinity’s Engineering Manager


“The entire Affinity team will remain in place and the only changes will be the addition of new team members to support our growth,” said Bob.  “We’re adding two new project engineers, an additional quality engineer as well as new team members in production, customer care and human resources.  I am excited about our growth and want to assure our OEM partners that we will continue to provide the same high level of quality and service that they expect from Affinity.”

With Bob Frank taking on leadership of Affinity, Matt Pathmajeyan was promoted to Engineering Manager.  Matt has worked for Affinity for five years as a project engineer.

Affinity will be a part of Molex’s Integrated Products Division.  Bob will report to Mike Miskin, Vice President and General Manager of the division’s Cable Products Business Unit.

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Meet James C. Sisneroz – Production Supervisor



James C. Sisneroz
- Affinity Medical
Production Supervisor

James brought more than 30 years of manufacturing experience, including extensive lean training, with him when he joined Affinity in September 2011.  He spent 29 years with Robertshaw Controls as lead person in high-speed robotics production.  His position with Robertshaw ended when the plant was closed and manufacturing was moved to Mexico.  James spent the next three years working in various manufacturing jobs in the area, but did not find a long-term home until he joined the Affinity team.

“I applied on-line for a molding supervisor job with Affinity,” said James.  “After three interviews with fourteen different Affinity people I was offered a Production Supervisor’s position.  I love the family atmosphere and love coming to work at Affinity.  I feel like I have found a home.”


James and Kevin Kom,
Affinity Manager of Manufacturing


When asked about his first year at Affinity, James replied, “The past year has gone by so quickly.  I still have a lot to learn about our products and sometimes I get frustrated that I am not learning faster.  Affinity is cleaner and quieter than the other plants that I have worked in.  Our throughput is high, but I never feel rushed.  I like the emphasis on quality and lean manufacturing.  Because Affinity feels like home, I want to do the very best that I can.”



James at Santa
at Affinity, Dec 2011

James met his wife Jeannie while they were both working at Robertshaw controls.  They worked together for 23 years and when their children were younger, they worked opposite shifts.  James and Jeannie have been married 21 years.  They have seven children, ten grandchildren and live in nearby Long Beach.  James survived a brain aneurism in 1992.  And, while he considers himself pretty healthy, James says he is still bothered by occasional headaches.

Asked about what he likes to do when not working, James replied, “I love to fish and camp.  Our favorite location is Lake Cuyamaca in San Diego County.  We also have a ski boat which we enjoy on the Colorado River.

Last December, James dressed as Santa in order to help celebrate both the holidays and Mary Phillipp’s birthday.

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Announcements, Information and Trivia

Visit Affinity at Medica November 14th through 17th in Dusseldorf Germany.  The Affinity team, Bob, Mary, Hank, Jim, Didier and Roberto (from MPS) will be at its usual location in Hall 9, Stand C74

If you would like to schedule an appointment at Affinity’s stand or at your company’s stand, please email Jim Itkin at jitkin@affinitymedical.com.



Daylight Savings Time Ends in U.S.

U.S. readers - remember to set your clocks back an hour Sunday, November 4th!  We gain the hour that we “lost” last spring!

Halloween Trivia

Samhain – Halloween traces its origin to the Celtic holiday called Samhain, meaning “end of summer.”  Custom has it that masks were worn so that the roaming ghosts and spirits would not recognize those wearing masks.


Jack O’ Lantern – believed to have originated in Ireland where candles were placed in hollowed-out turnips to keep away ghosts and spirits.

Souling – Trick or treating dates to the 9th century when, on All Soul’s Day, when the poor would go door to door begging for food.  The common treat was called “soul cakes” and was a bread-like pastry made with currants.



Anoka Minnesota – Located in the United States, the first city-wide Halloween celebration was held in Anoka Minnesota in 1921

Commercial Success – Halloween has grown in popularity to become the second most popular holiday in the U.S. in terms of dollars spent.  Approximately two billion dollars will be spent this year on Halloween candy alone!