The Best Rubber For Medical Devices:
Silicone vs. Latex

According to the United States Department of Commerce, the domestic medical device market — the largest in the world — has a market size of $110 billion. The forecast points to an increase to $133 billion by 2016. In 2012, 6,500 medical device companies garnered a 38 percent share of the global marketplace for medical products and devices. The medical device industry consists of a broad range of products and technologies, including appliances, materials, apparatuses, and other items. These products function as standalone products or in combination with other parts and products for diagnosis, monitoring, mitigation, treatment, compensation, and prevention of diseases and other conditions.

These products can also be used to alter structures and functions in patients as determined by domestic and international governmental agencies, such as the following:

  • Food and Drug Administration (FDA)
  • Center for Devices and Radiation Health (CDRH)
  • FDA Center for Devices and Radiologic Health
  • European Commission Medical Device Directive

These devices are categorized, regulated and accredited based on factors such as complexity, degree of invasiveness, duration of contact and body systems risk.

The primary materials used in manufacturing medical devices include latex and silicone.

Both products are in the thermoset category, signifying that each material goes through a chemical reaction that permanently sets the product’s shape. However, each product has distinctive performance characteristics and application usage.

One of the most important characteristics of any material used to manufacture medical devices has to do with its biocompatibility, which is the device’s ability to perform its intended function without causing undesirable side effects. Generally, biocompatibility entails a number of factors, including:

  1. Physical attributes of the device, such as rigidity and surface smoothness.
  2. Chemical nature (allergenic or toxic).
  3. The body’s reaction to and effect on the product’s function.

When evaluating the attributes of latex vs. silicone for your medical device, you must weigh a variety of factors in order to arrive at the best decision for you organization.

Silicone for Medical Devices

silicone for medical devices latex alternative

The use of silicone for medical devices began in 1946, when pioneers added silicone to the glassware used to discourage blood clotting. Around the same time, surgeon F. Lahey implanted a silicone elastomeric tube for duct repair in biliary surgery. The qualities that make silicone an attractive latex alternative for medical devices include the following attributes:

  • Biocompatibility. Odorless and tasteless, liquid silicone rubber (LSR) has proven to be extremely compatible with human tissue and body fluids. It also hinders bacteria growth, and it does not stain or cause other materials to erode. Medical grade silicone meets the FDA, ISO, and Tripartite biocompatibility guidelines for medical products.
  • Chemical Resistance. Silicone has a resistance to water, ammonia, oxidizing chemicals and some acids.
  • Insulation/Electrical Properties. Silicones have strong insulation properties and are suitable for a variety of electrical applications. The inherent nonconductive characteristic of silicone, and its ability to maintain dielectric strength in extreme thermal environments, surpasses the performance of latex and other materials.
  • Mechanical Properties. LSR has tensile strength and excellent elongation. In addition, silicone offers superior flexibility, low compression set and a durometer range (hardness) of 5 to 80 Shore A.
  • Thermal Resistance. Compared to other elastomers, silicone remains stable within a temperature range of -75° to 500°F. Customers can use a variety of methods for sterilization, such as EtO gas, gamma or E-beam irradiation and steam autoclaving.

Experienced manufacturers can mold simple and complex shapes with different walls of thickness within the same element, which promotes ultimate usability. Silicone is transparent, it will not stain and it resists the effects of ultraviolet light.

Significant progress in material science provides medical device designers, inventors and engineers with a number of silicone material options. There are many silicone-based materials on the market, including High Consistency Silicone Rubber (HCR), Fluorosilicone Rubber (FSR) Compounds, and Liquid Silicone Rubber (LSR).

For applications that require seals, gaskets, casings, valves and other critical components, an increasing number of medical device manufacturers are choosing LSR because of its resistance to stress, fatigue and tearing.

Combining these characteristics with high purity and chemical inertness make for truly cutting-edge materials that vendors can use to create devices that goes beyond skin contact. They’re ready for insertion inside the human body for both short- and long-term applications.

Introduced in the 1970s, LSR has become the most common material used in the manufacturing of medical devices, including:

  • Gaskets and o-rings
  • Syringe stoppers
  • Infusion pumps
  • Dialysis filters
  • Diaphragms
  • Pull rings

Not only is LSR suitable for an array of implantable and non-implantable medical devices, but the material can also be overmolded. This process simultaneously combines LSR with other materials like plastic or metal, and then produces soft-touch surfaces for medical electronic products.

Silicone manufacturers have prepared special medical grade silicone that meets or exceeds the demands and performance requirements of health agencies. Utilizing an internal certification process for bio-contact applications, manufacturers employ a series of tests produced by the United States Pharmacopeia (USP). Each test certifies the level of biocompatibility for a particular silicone material and determines the suitability for use in medical devices, as well as food and pharmaceutical applications.

six usp tests

Liquid Injection Molding

Manufacturers used three main processes to mold silicone:

  • Transfer molding
  • Compression molding
  • Liquid injection molding (LIM)

Transfer and compression molding requires equipment that operates at pressures of 250 to 2,000 psi and temperature range of 245°F to 485°F. Considered legacy methods, both transfer and compression molding methods require separate premixing of the rubber on a two-roll mill and are more labor intensive. Transfer and compression molding have longer molding cycles because of the lower operating temperature.

The LIM process has operation pressures that range from 2,000 to 8,000 psi and temperatures of 200°F to 370°F. Many industry analysts consider it the future of LSR molding because of factors like cleanliness and speed.

This two part liquid component — a catalyst and crosslinker — are pumped into the mixer to ensure a homogenous material. The material flows into the mold cavity and undergoes high temperatures. It’s a closed process that results in a quick turnaround. There is a minimal chance of contamination, and you can expect consistent quality from part to part. Available in a fully automated system, here is a summary of the LIM benefits:

  • Superior processing performance
  • Rapid cure rate
  • Reduced cycle times
  • Lower production costs

In addition, the LSR/LIM process works well for intricate designs manufactured in large, automated quantities. The LSR/LIM process increases your production efficiency.

LSR/LIM and Other Industry Applications

Advances in material and injection molding technologies have enabled the medical/healthcare industry to improve the process of how companies manufacture medical devices. Silicone has replaced latex for a variety of products and devices, and in most cases, provides a safe latex alternative. The low cost of silicone makes it possible to efficiently and cost-effectively create gloves, gowns, syringes and many more products.

silicone for medical devices latex alternative

The processes for medical device approval include stringent regulatory requirements in the states and internationally. These processes help ensure the safety of the products for patients and healthcare workers. It’s critical to have a person on your team that understands the intricacies of material selection, as well as how to choose the right molding process.

If you want your medical device to meet the required specifications, choose a company with knowledge of the needed internal policies and procedures. This includes implementation of an audit trail designed to lessen the chances of incurring a problem and an expensive product recall.

Latex for Medical Devices

Latex has a natural, milky-white and thick colloidal suspension, which many people recognize in the form of latex rubber gloves. Skilled tappers must cut the bark at the appropriate depth in order to avoid damaging the tree; by properly cutting the tree, it will produce latex for a number of years, without causing harm to its overall health. The fluid actually flows into the damaged area on the tree directly below the surface of the bark. Most people learn that latex comes from the sap of the Hevea tree, native to Brazil.

After the removal of the latex from the trees, suppliers add ammonia-based preservatives, which inhibit microbial spoilage. Latex manufacturers use a variety of processes, such as the following:

  • Creaming
  • Centrifugation
  • Evaporation

These processes produce a concentrated form of latex material. The blending of different chemical additives along with the concentrated latex facilitates vulcanization, binds the materials and reduces degradation. The finished latex material offers the advantage of flexibility. It also has the ability to withstand bending, elongation or pulsating forces.

For decades, the medical industry has used natural latex products as tourniquets and as tubing for devices used for fluid transfer. The human immunodeficiency virus (HIV) pandemic, which occurred in the 1980s, led to a significant rise in demand for latex gloves and condoms. The increased usage of latex during this period overlaps with the rise in reports of latex allergies.

According to some reports, between 8 and 17 percent of healthcare workers have latex allergies, but such allergies are not limited to workers in the medical field. People with spinal cord problems, such as Spina Bifida patients, who have had repeated exposure to latex catheters for example, have also been impacted. Children with Spina Bifida have shown sensitivity to latex, ranging from 30 to 41 percent.

In 2014, the FDA finalized its policy recommendation for medical device manufacturers. If using natural rubber latex (NRL) proteins to affix labels to products, you should warn customers of the presence of NRL. Even if a medical product claims to be latex-free, it is not guaranteed because of the inability to verify the declaration. Instead, the FDA advises companies to use the following language: “not made with natural rubber latex.”

Over the years, many manufacturers have used latex to manufacture a wide variety of medical products and devices, which include:

  • Diaphragms
  • Stethoscope tubing
  • Endotracheal tubes
  • Surgical gloves
  • Piggyback IV ports
  • EKG straps and electrode pads
  • Band-Aids
  • Ventilator bellows
  • Anesthesia and oxygen masks
  • Adhesive tapes
  • Adhesives
  • Multiple-use mediation vials
  • Blood pressure cuffs
  • Rubberized bed sheets
  • Pads on crutches
  • Wheel chairs cushions and tires

Primary Latex Molding Method

latex products

The manufacturer uses a tool called a mandrel, which has been fabricated into the required shape and size of the product. After dipping the mandrel in a coagulant solution, such as calcium nitrate, the fabricator immerses the mandrel into a container that holds the prepared liquid latex material.

After withdrawal from the vat of latex material, the fabricator inserts the mandrel into an oven or other heating mechanism to complete the coagulation process. To increase the thickness, the fabricator simply repeats the process of dipping the mandrel into the latex. The part is then sprayed with water to get rid of coagulant and other additives.

Next, the part goes through a vulcanization process. After another wash with water, some manufacturers use a powder lubricant or perform a surface treatment such as chlorination, to prevent the part from sticking to other surfaces.

The Real Cost of Silicone Versus Latex

Silicone materials cost more than latex. However, a host of other factors must go into the decision-making process when you’re ready to select the material and process for the production of your medical device.

For example, urinary tract infections make up more than 40% of all nosocomial infections. Most nosocomial infections have a direct correlation with indwelling catheters. These infections have also caused a three-fold increase in fatalities among hospitalized patients.

As for the economic impact, patients spend an average of 2.4 days in the hospital due to acquired urinary tract infections. Studies show that catheters manufactured from silicone not only improve the patient’s comfort level, but also have a positive effect on the following factors:

  • Fewer incidents of allergic responses
  • Fewer occurrences of phlebitis
  • Lower frequency of sepsis
  • Smaller number of catheter insertions
  • Reduction in the likelihood of mineral encrustations
  • Decreased risk for potential for bacterial migration
  • Fewer occurrences of premature balloon deflation

LSR-based medical devices can reduce the potential for nosocomial infections and expensive product liability costs.

If you have any questions about latex vs silicone, LSR/LIM or liquid injection molding, or would like a quote for your LSR/LIM project, contact a SIMTEC representative today!

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