Silicone, a highly versatile synthetic polymer, seems to show up everywhere from cooking utensils and adhesives to sealants and cosmetics. Its unique properties have contributed to silicone’s traditional appeal in more complex fields as well; for decades, the material has been an integral ingredient in medical technology. Valued by original equipment manufacturers (OEMs) and product designers for its adaptability, silicone lends itself to intense applications in implantable medical devices, reusable and single-use components, and other health care technologies involving hospital equipment and surgical tools that demand reliability and trustworthy performance. (See Figure 1)
Until recently, few materials filled the same requirements as silicone for these applications, making it the default choice in many instances. Medical-grade silicone is one of the most common materials in jackets and coatings for wire and cable assemblies utilized for medical devices, largely due to a lack of adequate alternatives. Although silicone offers advantages in biocompatibility and versatility, there are still challenges in integrating the ingredient into medical cable components. Lack of availability of supply, long lead times, and multiple curing processes often result in high initial investments with hidden long-term costs. Silicone products also tend to be vulnerable to abrasion damage, extensive sterilization, and repetitive motion, decreasing their overall life span.
To combat these difficulties without sacrificing biocompatibility or utility, medical device designers and manufacturers have developed field-proven silicone substitutes. Innovative silicone alternatives build on the foundation and history of silicone’s successes in medical applications while paving the way forward for improved performance.
The History of Silicone in Medical Applications
Chemists first discovered silicon, the naturally occurring element that forms the basis for silicone, in the early 1800s. Just over a century later, in the 1940s, silicone materials became commercialized and companies such as Dow Corning and General Electric were discovering the full extent of their properties. Resistance to temperature extremes, environmental factors, and electricity were noted, and silicone materials quickly gained acceptance and adoption.
A key factor in silicone’s rise to popularity was its ability to adapt and succeed in a highly diverse range of applications. Silicone has been used in life sciences, aerospace/defense, electrical, and industrial applications since the 1960s. In medical manufacturing, the material is suitable for use in a broad variety of components, from valves and tubing to long- and short-term implantable devices, and far beyond. It is often used as the external jacketing on medical wire and cable for hospital equipment, surgical tools, patient monitoring systems, imaging and diagnostic instruments, and other medical devices.
Although additional processing and potential costly reapplication of parylene is required for silicone to meet stringent FDA and biocompatibility requirements, the core ingredients are abundant and easy to manipulate. This accessibility, combined with silicone’s adaptability, makes it an obvious choice for use in medical manufacturing. When the material is processed to medical-grade standards, it results in silicone cable products that are biocompatible, hypoallergenic, flexible, and durable—all necessary characteristics for use in health care environments.
Advantages of Silicone-Jacketed Medical Cable
Silicone has proven its worth in medical manufacturing over the past several decades by achieving reliable high performance across a number of complex requirements. For siliconejacketed cable assemblies, these include biocompatibility and tolerance to sterilization, flexibility and durability, and userfriendly appearance and feel.
Biocompatibility is critical for components that interact with, or are implanted into, the human body. Medical-grade silicone can adhere to meticulous and comprehensive biocompatibility standards, such as USP Class VI, the most demanding standard in its category, and ISO 10993, often considered even more intensive than USP Class VI. To further enhance its safety to patients, silicone jacketing satisfactorily tolerates severe hospital sterilization in autoclaves and other forms of sterilization. This allows silicone-coated cable to operate in both single-use and reusable applications.
Beyond sterilization, silicone cables stand up to day-to-day wear that typically occurs in hospital environments. From resistance to common cleaning solutions to exceptional stability in temperature extremes, durability is often listed as a top advantage of silicone materials. Similarly, silicone-jacketed cable products afford a high level of flexibility and elongation, particularly useful in medical device cable involving cameras, power tools, robotic surgery, and other electrosurgical instruments.
In addition to excelling in these prominent requirements for life science cable components, silicone allows for a look and feel that is supportive of both patients and medical professionals. Silicone-jacketed cables are soft and supple to prevent irritation or tearing of skin or tissue and make it easier for medical staff to apply wound dressings.
These advantages have limitations, however. Silicone jacketing tolerates autoclaves and other forms of sterilization to a point, but will break down after several hundred cycles at best. The material is very sturdy and stable when faced with temperature extremes, but its durability is greatly decreased with abrasion and tear—and silicone is especially vulnerable to this type of external damage. In a fast-paced hospital or clinic, repetitive motion and heavy rolling equipment create ample opportunity for silicone cables to be damaged in this way. (See Figure 2)
Durability can be improved by thickening the cable jacket, but this compromises flexibility. Silicone-coated cable is soft and supple, but generally requires an additional coating to support these features. With this coating, it does not catch on patients, but measures must be taken to ensure that it does not catch on itself or become irreparably tangled when subjected to continuous motion or torque.
The procurement of medical-grade silicone for wire and cable applications also presents significant hurdles.
Silicone is a thermoset material, requiring a curing process to support biocompatibility and application-based specifications. Once cured, it cannot be changed. The curing process requires a careful balance of temperature, pressure, and time, as well as additional equipment and various curing catalysts. As a result, leading OEMs for silicone brands typically offer lead times of at least 8 to 12 weeks in the United States. The curing process can also involve substantial added expenses, and there are typically opportunity costs related to the lengthy development time.
Looking Ahead to Future Innovation
With today’s life science technology evolving and changing at one of the most rapid paces in history, source materials used in medical devices and critical system components must progress as well. Product designers, engineers, and research and development teams have risen to this call by developing effective and original substitutes to silicone-based cable assemblies. Many of these inventive solutions have successfully retained the comprehensive biocompatibility silicone enjoys and improved on the traditional material’s strength, resilience, flexibility, and versatility. Moreover, these materials can often be made without additional curing or coating processes, supporting faster paths to market and saving manufacturers money.
In laboratory tests, innovative silicone cable alternatives surpassed conventional components in a number of trials. In one example, a silicone cable assembly was subjected to rollover cycles by a 200-pound hospital gurney. The silicone assembly failed in fewer than 10,000 cycles, whereas the alternative product exceeded 186,000 cycles.
A similar test examined autoclave sterilization. In this situation, the silicone alternative also outperformed traditional silicone, retaining full tensile strength, elongation, and color clarity in more than 500 steam autoclave cycles. Other areas where alternatives overtook traditional materials included continuous motion and flex, retractability, fungal resistance, and chemical resistance. (See Figure 3)
To ensure quality and the long life span of these original silicone alternatives, interested buyers should be sure to conduct thorough research into the supplier, their quality management systems, and manufacturing processes. Unlike silicone, whose history affords it a well-defined process, the emerging market of silicone substitutes represents an assortment of different approaches. When conducting supplier evaluation, be sure to ask:
- What is the manufacturing methodology?
- What standards of biocompatibility does the material meet?
- Does it adhere to FDA regulations, USP Class VI, RoHS2, and ISO-10993?
- What are the supplier’s certified quality management systems?
- Has the material been fully tested in a third-party laboratory?
- Has the material been tested for resistance to sterilization, cut, tear, abrasion, and chemical interaction? If so, what were the results of these tests?
- What are typical lead times and cost investments for the material?
When produced in accordance with a robust quality management system, silicone alternatives can deliver impressive advantages in life span performance as well as short and long-term costs.
Silicone has been the traditional choice in medical cable jacketing and other life science manufacturing applications. While the material will almost certainly continue in popularity for the next several years, groundbreaking technology is surfacing that would allow for game-changing silicone alternatives that preserve silicone’s biocompatibility and improve upon sterilization tolerance, resistance to damage and environmental factors, flexibility, and life span.
Medical device manufacturers who consult silicone alternative suppliers are likely to find that, on top of performance enhancements, these materials also come with savings in cost and time. In a world as fast-paced and demanding as medical manufacturing, more product designers and engineers than ever see the need to leverage these pioneering solutions to produce the next generation of life science technology.
This article was written by Kevin DePratter, PMP®, Director of R&D at Northwire, Inc., Osceola, WI. For more information, Click Here .