What is liquid silicone rubber used for?

From HCRs and LSRs to RTVs and adhesives, we discuss how silicone has come to be used in every area of the healthcare industry by exploring the flexibility and versatility it offers device manufacturers.

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Medical technology is a broad field, encompassing many types of instruments, apparatus, implants, software, and other articles. The World Health Organization estimates there to be two million different kinds of medical devices on the market, categorised into more than 7,000 generic groups.

Many different materials are used to manufacture this array of devices &#; from metals to thermoplastics, ceramics, tissue-engineered medical products, and biologic materials. Each material has its individual advantages for specific applications, but one material stands out for another reason: versatility.

Medical-grade silicone

Silicone finds applications across most fields of medical technology since it offers excellent physical properties and resistance to chemical and thermal degradation. Perhaps most importantly, silicone is chemically inert, which is what guarantees its biocompatibility.

While the medical sector&#;s earliest use of the synthetic polymer was to coat glassware and needles, over the past 60 years silicone companies have introduced a wide range of medical-grade materials to the market, with varying properties and levels of hardness. Liquid silicone rubber is one of the more modern concepts. When introduced, it transformed production possibilities by enabling a more cost-effective method of processing called liquid injection moulding.

According to Michael Goglia, Healthcare Market Manager for Americas at Elkem Silicones, it is a combination of silicone&#;s processability and outstanding biocompatibility which have made it such a popular material in the field.

"Anytime a material is implanted into the human body it can sometimes illicit a &#;Foreign Body Reaction&#; or &#;FBR&#; silicone which produces inflammation around the implanted material, Silicones have shown over the course of historical studies to be excellent at deterring this response.,&#; Goglia explains. &#;It also has the ability to bond to other substrates, such as thermoplastics, so it can be used in combination with other materials to provide both a soft and rigid component to the device."

Another factor in silicone&#;s versatility is the range of cure mechanisms available to manufacturers, he adds, listing examples such as moisture cure at ambient temperature, thermal cure which accelerates the process through elevated temperatures, and even UVC systems that use light.

&#;In addition to that, silicones can be 3D printed today,&#; notes Goglia. &#;You can prototype with 3D printing and then convert that to actual production using traditional moulding methods.&#;

All of this has opened up a world of possibility for medical OEMs, enabling them to take advantage of silicone&#;s numerous benefits and broad processing parameter ranges. Its biocompatibility has even made it safe to use in long-term implanted devices such as stents, pacemakers, and implantable drug delivery devices.

Being soft to the touch and conformable, there are also silicones used to enhance patient comfort in pressure beds (prosthetics and orthotics), ventilation masks, and atraumatic adhesives. The material&#;s hydrophobicity makes it an effective lubricious coating for surgical tools and syringes, meanwhile this water repellence helps ensure bacteria resistance too &#; a huge benefit for the medical industry.

Silicone also has an important application in diagnostic devices that require a battery and internet connection to continuously monitor aspects of patient health in real-time. Silicone is a key material to make this combination work due to its ability to be moulded at lower temperatures than traditional plastics and adhere to multiple substrates either mechanically or through chemical bonds. 

It&#;s easy to see why silicone, in all its various forms, has become a go-to for medical devices. To explore further advantages, let&#;s take a more detailed look at the different types of silicone used by the industry.

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Types of medical-grade silicone

Liquid silicone rubber (LSR) is a popular choice. It is typically used within injection moulding machines, where it cures completely and quickly to create complex parts with fine detail, tight tolerances and low shrink rates.

&#;This has become the material of choice for medical engineers as it is scalable, cost effective, and widely recognised for its excellent biocompatible properties,&#; says Goglia. &#;Small-scale design can be done in a benchtop environment on a 3D-printed mould and scale all the way up to a fully automated multi-cavity injection environment running 24/7.&#;

High consistency rubber (HCR) has a higher viscosity and is better suited to high-strength moulding and extrusion processes. Typical applications include pharmaceutical transfer hose and gasketing, fluid handling and feeding tubes, as well as high-strength balloons that can be used in catheters. Overall, the performance characteristics of LSR and HCR can be similar and each material boasts a huge variety of medical applications. The choice between them usually comes down to required physical characteristics and manufacturing method. Elkem Silicones produces HCR-grade materials globally in the US, Europe and Asia, with various grades meeting differentiating performance criteria.

Other forms of silicone have adhesive properties, making them a great sealing solution for applications where high-strength elastic bonds between substrates are needed. These materials come in both moisture cure one-part systems and two-part addition cure systems. They are excellent at adhering silicone to silicone as well as adhering silicone to various other widely used medical substrates safely and effectively.

These same properties add another medical application to silicone&#;s long list: skin adhesion. Used across wound care, medical tape, and transdermal drug delivery patch products, silicone adhesives such as Silbione&#; Silicone Skin Adhesives provide reliable yet non-traumatic and hypoallergenic adhesion to skin. They also allow media to be removed and replaced over a period of time allowing for greater patient flexibility.

Medical-grade room temperature vulcanising (RTV) silicones comprise a two-part system that can be easily mixed and cured into soft yet durable elastomers. Ideal for prosthetic liners, orthotic inserts, bandages, and shoe insoles, RTVs provide comfort and biocompatibility in the manufacturing of soft parts in contact with a patient&#;s skin.

Silicones are also available in gels and fluids. Gels are very soft elastomers used in devices like cushions and breast forms. Silicone fluids are made from polydimethylsiloxanes fluids, emulsions and RTV lubricants, and are used to coat and lubricate parenteral packaging components such as vials and syringes, as well as surgical tools.

Since silicone comes in so many different forms and has a list of advantages to offer, it is common for medical device designers to make use of various types of silicone within a single device. Taking a wearable device as an example, Philipp Schattling, Elkem&#;s project leader for diagnostics and long-term medical implants, explains: &#;Wearable devices consist of many different components and many different building blocks, and every building block may require different properties and performance characteristics.

&#;This can be a challenge because usually with just one technology you cannot address each and every requirement. The benefit of silicones is that they cover a broad range of different technologies. We have the glue, the sealant, the adhesive, the LSR for the housing, and the HCR for the tubing.&#;

For a full selection of medical-grade silicone technologies, medical device OEMs can explore Elkem Silicones&#; Silbione&#; range of LSR, HCR, silicone adhesive, silicone skin adhesive, RTV, silicone gel, and silicone fluid products. The materials offer exceptional physical properties to help customers differentiate their products and ensure precise final performance. They are also designed with ease of processing in mind, ensuring improved productivity and enhanced competitiveness for customers.

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Since the s, liquid silicone rubber (LSR) has been the material of choice in manufacturing silicone products and parts. It has many uses across multiple industries, including LSR for automotive, medical and life sciences, baby products, and consumer products sectors. LSR&#;s unique chemical makeup and characteristics make it a common choice in those fields.

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Learn more about LSR&#;s properties and the reasons why it may be the best choice for your products.

3 Reasons to Choose Liquid Silicone Rubber (LSR)

When choosing materials to manufacture critical, durable components, consider Liquid Silicone Rubber (LSR). SIMTEC is a pioneer in LSR injection molding and ever since our founding in , LSR has been the primary material we process in our LSR, LSR two-shot, LSR multi-shot and LSR overmolding injection molding cells. With SIMTEC&#;s decades of experience and team of experts, there&#;s no better partner for your silicone rubber component requirements, and no one more experienced in providing customized value-added solutions to meet customers&#; specific requirements.

LSR&#;s characteristics and chemical properties make it an ideal material for applications spanning a wide range of industries. Keep reading to learn more about liquid silicone rubber and its advantages, or contact SIMTEC directly to find out how our team of experts can offer you value-added solutions.

1. Chemical Composition of Silicone Rubber

The unique physical properties of silicone rubber are a result of its chemical structure. Silicone rubber is an elastomer consisting primarily of a chain of molecules known as a siloxane bond (-Si-O-Si-). This chain is effectively silicone rubber&#;s &#;backbone,&#; to which a variety of organic chemical groups can be added, altering its mechanical and material characteristics.

Silicone rubber is distinguished from other elastomers by the strength of the siloxane bond. Whereas carbon bonds have a binding energy of 355 kJ/mol, the strength of the siloxane bond is 433 kJ/mol. This contributes to its greater heat resistance, chemical stability, and electrical insulation.

At the same time, silicone bonds also feature low intermolecular forces, which means that other chemical groups attached to them can rotate freely. As a result, liquid silicone rubber has a high degree of elasticity and compressibility, resilience and weatherability.

2. Mechanical Properties of LSR

Various grades of silicone rubber have different material properties. This versatility is one reason why LSR is used in so many diverse applications. Whether you have medical products for drug delivery or pumping applications that require strength, flexibility and repeatability, or automotive components that must withstand excessive heat and vibration, liquid silicone&#;s mechanical properties make it an excellent material choice.

Key material properties of silicone rubber include its fast curing and low compression set, its resistance to tearing, heat, water and oil, its transparency and electrical insulation, and its overall strength and long life. You can use LSR at temperatures between -40°C to 200°C (-40°F &#; 392°F), expose it to wind, rain and UV light for extended periods of time, or immerse it in water, oil or solvents. The various grades of LSR possess material properties that can stand up to even the most demanding applications.

3. LSR Provides Creative Solutions for Engineering Challenges

LSR is water-resistant and doesn&#;t break down when exposed to solvents. It&#;s also available in several hardness levels and a range of colors, making it a versatile option for a wide variety of products. LSR is also a low-vicosity material, meaning it flows very easily during the molding process meaning it is well suited for high cavitation molds used for high output requirements. Products with intricate design features such as undercuts, thin features, small micro-parts, and complex part geometries can be more easily achieved with LSR, allowing product designers added flexibilty and latitude.

How Is Liquid Silicone Rubber Used?

LSR parts are used in a range of different industries. It&#;s resistance to steam, heat and moisture and its purity make it an excellent choice for parts that must be manufactured in an environmentally controlled hygienic environment such as a ISO clean room and may also require sterilization.  Gaskets, seals and diaphragms used in gas and other consumer appliances such as dishwashers, gas furnaces and water heaters must perform in extreme temperatures and environments. Oil and heat resistance, superior sealing attributes and vibration and insulative properties are required in many automotive components and as a result LSR is used throughout a vehicle &#; under the hood, in EV battery packs, sensors and electrical connectors used throughout the vehicle.

Properties of LSR Parts

LSR&#;s specific material properties are a result of its unique chemical structure. Its backbone is formed by a series of siloxane bonds which, compared to carbon bonds, are stronger and more stable. This allows liquid silicone rubber to be:

Chemically Inert

Liquid silicone rubber has an organic backbone and is therefore inert, meaning it does not react chemically with other chemicals. LSR is also resistant to damage from water, oxidation, UV rays, ozone, and radiation, as well as a variety of alkali or acid products. For products subjected to frequent cleaning, exposed to water and moisture, used outdoors or in other harsh environments, LSR has the chemical properties to perform well in these conditions.

Hypoallergenic

Inherently hypoallergenic and non-toxic, LSR will not cause irritation or allergic reactions with contact, even in those with sensitive skin. For respiratory products such as oxygen and CPAP masks, or products like earbuds, hearing aids, or wearable monitoring devices worn for extended periods of time, LSR provides a safe and comfortable solution.

Biocompatible

LSR&#;s molecular structure also contributes to its biocompatibility. It is odorless and does not have a taste. Because it also complies with Food and Drug Administration (FDA) requirements, it is widely used in baby products and other food- and beverage- related products.

Physical Properties

LSRs physical and thermal stability properties are exceptional and the reason why LSR is the preferred choice over other elastomeric polymers. LSR maintains its physical properties in a wide range of temperatures &#; both high and low temperatures, ranging from -40 degrees Celsius to 200 degrees Celsius, depending on the grade.

Additional physical characteristics include:

• Compression set: LSR parts will retain their shape when compressed
• Surface: LSR has a naturally smooth texture
• Modulus: LSR offers flexibility and rigidity
• Seals: LSRs are widely chosen for their sealing attributes
• Responsive: Sensitive, responsive, and ideal for delicate sensing membranes
• Insulative: Naturally insulating &#; electrically and thermally
• Hardness: Available in a range of durometers, most commonly used are 10 to 80 Shore A durometers

Liquid silicone rubber molded parts are odorless and tasteless. Unique colors and visual effects can be achieved through the use of pigments and master-batches. Parts are also ozone and UV safe. Other notable features of liquid silicone rubber parts include:

• Resistance to steam and humidity
• Flame retardancy
• Low creep and compression set
• Weatherability
• Vibration absorption
• Corrosion resistance
• Resistance to mold, mildew, and bacteria growth
• UL component recognition
• And more

Many different variations of LSR are available to support potential applications in a wide range of industries. To learn more about the specific properties of different liquid silicone rubber products, contact SIMTEC to speak with one of our in-house engineers.

Liquid Silicone Rubber Applications

At this point, you may be asking what exactly silicone rubber is used for. Liquid silicone rubber is a highly versatile material, and new applications for it are discovered and tested every day. It is a mainstay in healthcare manufacturing, automotive component manufacturing, electronics and consumer products, gaskets and other hardware, and many other markets.

Typical liquid silicone rubber products manufactured for its customers by SIMTEC include:

• Valves for IVs and fluid handling equipment
• Diaphragms in pumps and regulators
• Gaskets and seals in connectors
• Hand-held surgical instrument components
• Syringe stoppers and septum
• Ear tips for hearing aids Needle-free valve sights
• Bellows and membranes
• Skin contact devices
• Soft-touch buttons/surfaces
• Steam-sterilized parts
• Seals for housing and covers
• And much more

These components are used for many purposes in various industries. In healthcare, LSR&#;s biocompatibility, hypoallergenic and hygienic qualities are particularly useful, so it is used in syringes, surgical sleeves, masks, and respirators. An appliance or vehicle manufacturer might value its resistance to heat and vibrations, using LSR for gaskets, seals, and other connections. Safety products rely on LSR&#;s longevity, and consumer product manufacturers often use it to protect sensitive electronics from moisture and vibrations, such as in blenders and toothbrushes.

The list goes on &#; LSR&#;s design flexibility makes it highly customizable. It can take on different formulations and be molded to small parts and complex geometries, which is necessary for many precise applications like automotive parts and special products. You can find LSR used in industrial settings, hospitals, cars, labs, and all over the average home. If an application calls for a responsive material that&#;s safe, durable, and customizable to specific application demands, LSR is a common choice.

Contact SIMTEC to Discuss Your Project Today

At SIMTEC, we have one of the most advanced manufacturing facilities in the country, as well as a long history of helping our customers develop innovative solutions to the challenges that cost them money and affect their productivity.

Liquid silicone rubber isn&#;t the right choice for every application, but there&#;s a good chance it has applications you haven&#;t yet considered. For specific information regarding material and application alternatives, we recommend visiting our Technical Information page or contacting us directly.

If you want to learn more, please visit our website Silikon Oil.