Staying Connected - June 2011

End-of-Life Design Considerations for Medical Cables
and Connectors



All cables will eventually
reach their end-of-life

The Life Cycle

All products have a life cycle.  At the end of that life cycle, the product is no either no longer usable or there is no use for the product.  For medical cables, the end of the products life cycle is typically when it ceases to function as intended.

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.

Service Life

Service life, also known as wear-out-life, is the length of time a product functions properly, and as intended, before reaching its end-of-life.  Establishing 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.


Gold plated pins are longer lasting than
nickel plated pins, but are also more costly

Component Specifications

The selection of raw materials and components plays a very large part 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 of 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

Medical cable assemblies are comprised of one or more conductors and are virtually all stranded.  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 many fine strands offers greater flexibility and durability than using conductors with fewer and thicker strands.  The trade-off is that finer stranding is more costly than standard stranding.

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, common copper conductors heat up and can become “work hardened.”  That is the more they 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 commonly 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 an synthetic fiber adds tensile strength.



Cable jacket material plays
a large role in determining the
service-life of a 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.

The following table offers guidelines as to the suitability of common cable materials based on various cleaning, disinfection and sterilization methods.  These materials are commonly used for both cable jackets and molded assemblies.

Cleaning and Disinfection

Material Sodium Hypochlorite (bleach 10%) Isopropyl
Alcohol
Glutaral-dehyde (Cidex)
PVC Good Good Fair
TPE/TPR Excellent Excellent Excellent
TPU Poor Poor Good
Silicone Good Excellent Good

Sterilization

Material Autoclave Gamma Ethylene oxide (ETO) VHP1
(Sterrad)
Paracetic Acid (Steris)
PVC Poor Excellent Excellent Good Good
TPE/TPR Fair/Good Excellent Excellent Good Good/ Excellent
TPU Poor Excellent Excellent Good Good
Silicone Excellent Excellent Good Excellent Good/ Excellent

1 Vaporized Hydrogen Peroxide

Materials Selection for Rigid Molded Components


Affinity engineer Matt Pathmajeyan
discusses durability of rigid plastics

Virtually all medical cable assemblies and connectors contain plastic injection molded parts.  There is a wide variety of plastics available 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 plastics, Affinity engineer 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. Not always do these attributes exist in the same polymer.”



Examples of injection molded parts
used in medical cables and connectors

“As an example, ABS is stronger than Styrene when speaking in terms of impact strength, but ABS will not withstand as many autoclave cycles as 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 by clinicians and how long it is expected to last should be considered when choosing rigid polymer materials.

Protecting Terminations Increases Service-Life


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

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 point 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 some measure of protection, it is less than that of an overmolded strain relief.

Depending upon the degree of durability and service 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 of a low cost material may be a reasonable choice.  For longer life a two-shot overmold – inner and outer – may be called for.  When even greater service-life is required, choosing overmold materials that will bond to the cable jacket with improve performance even more.

Design for Environment


Design for Environment (DFE) can be applied to medical cables and connectors as device manufactures require products to meet global RoHS and REACH requirements. 
Three such materials that have been commonly used in medical cable assemblies are lead –as in lead solder – PVC and cadmium.  At Affinity, the switch to lead free solder was completed several years ago.  The only exceptions are where the OEM device manufacturer specifically requires the use of leaded solder.

PVC is commonly used in lower cost medical cables and leadwires but many localities are restricting the use or disposal of PVC.  Cadmium has been used in alloys to increase the flex life and tensile strength of copper conductors, but may not meet RoHS requirements.  Knowing that all medical cables will eventually be discarded, reducing or eliminating potential hazardous materials should be addressed in the design stage.

Most of the components used in the manufacture of medical cable assemblies and connectors are recyclable and the metallic components may be valuable.  Because these devices may have become biologically contaminated in use, decontamination may be necessary before disposal or recycling.

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 likely unnecessary to design and manufacture it to last ten years.


Affinity project team reviews design
prior to releasing tooling for fabrication

Summary

Establishing clear and reasonable objectives for the service-life of medical cable assemblies, connectors and interconnect devices should be considered early in the product design stage.  The selection of appropriate materials coupled with design for service-life and appropriate manufacturing techniques will produce a device meeting your design objectives.

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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MeetMeet Mary Phillipp – Affinity President and CEO



Affinity President and
CEO Mary Phillipp

Affinity founder Mary Phillipp is from Minnesota and relocated to Southern California over 20 years ago.  She graduated from Morehead State College in Minnesota with a degree in Accounting.  Mary is a C.P.A and her financial training and background has helped her keep Affinity on very sound financial footing since its founding.

Mary began her career in the medical device industry working for Tronomed which was a large medical cable manufacturer.  She started out in finance, but was soon promoted to President of the company.  While at Tronomed, she met and worked with Bob Frank who helped found Affinity in 1997 after Tronomed was acquired by a large east coast company.  “Bob and I have worked together longer than either of us has been married to our spouses,” said Mary.

Even though Affinity has grown to over 250 employees, Mary encourages a “family” atmosphere.  “Most of us spend more time at work than at home with our families.  I think that it is important to have an atmosphere where everyone is respected and feels at home,” said Mary.  Affinity Business Development Manager, Hank Mancini said of Mary, “It is a real pleasure to work for and work with someone who values our OEM partners as much as Mary does.  She understands and conveys to the entire Affinity team how important our customers are.”


Unexpected snow during a
visit to an OEM customer


Mary is not one to spend a lot of time behind her desk.  She travels both domestically and internationally visiting Affinity’s customers.  “The thing that I enjoy the most is visiting our OEM partners,” said Mary.  “I think it is important for me to personally know as many of our customers as possible.  In the rare instance where there is an unresolved issue, our OEM partners know that they can call me directly.“

 



Mary welcoming the Affinity team to
the 14th Anniversary Luncheon

Mary and her husband Dave Johnson live only a few miles from Affinity.  Mary is an avid golfer and enjoys competing in tournaments in her free time.  Mary and Dave have season tickets to the Orange County Performing Arts Center and the Anaheim Ducks, our local NHL team.  They also spend enjoy spending time during the summer months with family and friends at their cabin in Northern Minnesota.

 “The last year was very exciting for Affinity.  We topped 200 employees, moved to our new facility and shipped more product than ever before.  We are fortunate to have a great team and equally great customer partners,” said Mary.

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Announcements, Information and Trivia



Gold is the only metal
that does not rust

Trivia

Google is the name for a number with a million zeros.  It would take the average person writing non-stop nearly 12 days to write one million zeros.
 
Gold is the only metal that doesn't rust, even if it's buried in the ground for thousands of years.

Your tongue is the only muscle in your body that is attached at only one end.
 
If you stop getting thirsty, you need to drink more water.  When a human body is dehydrated, its thirst mechanism shuts off.

Zero is the only number that cannot be represented by Roman numerals.

 

Affinity Customer Care and Hours of Operation



Candy, Suzann and Cesar – the Affinity Customer
Care team - the Affinity Customer Care Team

At Affinity Medical, we don’t have a customer service department.  In place of customer service, we have Customer Care Coordinators.  While our Customer Care Coordinators perform many of the same functions that customer service representative would, we strive to offer our OEM partners more than that.  The job of our Customer Care Coordinators is to take care of our OEM customer partners.

Affinity Medical Technologies Customer Care specialists are available to assist you from 7:00 A.M. until 4:00 P.M., Monday through Friday, U.S. Pacific Time, except holidays.

 

Affinity Medical Technologies

3545 Harbor Boulevard, Suite 150
Costa Mesa, CA 92626 USA
Phone: +1 949 477 9495
Fax: +1 949 477 9499

Email: Customercare2@affinitymedical.com
Website: www.affinitymedical.com
Blog: http://blog.affinitymed.com