Sterilization of LSR Parts for Medical Applications

Liquid Silicone Rubber (LSR) is a versatile material with countless applications across a wide variety of industries. LSR is commonly used for sealing applications and for long-term use. It’s especially valuable for its constant properties over a wide range of temperatures and low compression set, which allows it to return to its original shape when compressed repeatedly. This quality is great for pumping and pressure sensing applications.

LSR is also a preferred material choice for many medical, health care, and baby care applications due to its biocompatibility and soft-feeling attributes that make it ideal for skin-contact applications. Because it is inert, LSR is also commonly specified for products subjected to cleaning solutions, chemicals, and for hygienic products that require sterilization.

If your medical device will require sterilization, there are a variety of sterilization options and materials to consider.


Why Does Sterilization of Medical Parts Matter?

Sterilization is an essential factor for many medical devices. Because of the critical nature of medical devices and their interaction with biological matter, the medical industry has strict regulations and stringent guidelines, such as ISO 10993 and USO Class VI. Medical devices that have contact with body tissues or fluids are considered critical items. These devices should be sterile when used because any microbial contamination could result in disease transmission. 

Normally, the sterilization process is performed at temperatures between 110 degrees C and 190 degrees C, in a dry or steam environment, and sometimes with pressure. Determining if sterilization is required and the best sterilization method are important factors that must be considered when choosing the material best suited for your medical parts.

Most other materials like thermoplastic elastomers (TPE) and other elastomeric materials will fail and age when exposed to extreme temperatures and chemicals used in sterilization. LSR is inert and can withstand a wide range of temperatures, from -50 degrees to 200 degrees C, allowing it to be sterilized for compliance with health regulations.

How Does Sterilization Affect the Material and Parts?

Products used in medical applications should be sterilized repeatedly and regularly by chemical vapor or high-level energy to remove bacterial surface contamination. These treatments can impact a material’s molecular structure. 

Fortunately, LSR can withstand temps and chemicals used for sterilization. Other elastomers fail to do the same. These elastomers are sensitive to heat and can lose their structural integrity while being exposed to high temperatures. As such, consideration should be given to the sterilization methods and materials that will work best for your company’s medical devices.

Sterilization Methods for Medical Applications

There are a variety of methods that can be used for sterilizing parts in medical applications. In addition to the traditional autoclaving technique using heat, LSR parts can also be disinfected using radiation, chemicals, or alcohol.

1. Heat (Autoclaving)

The autoclave sterilizer has been around for decades and gave doctors a sterilization method that was more reliable than open flaming.

What Is an Autoclave?

An autoclave is a strong, heated container that can be used for chemical reactions involving high temperatures and pressures. You can use autoclaving to sterilize pharmaceutical items, laboratory instruments, and surgical equipment. Steam sterilization is nontoxic and a more economical solution that works quickly to heat and penetrate. 

Autoclaves come in various shapes and sizes and serve different functions. Although universally used, autoclave sterilization is not suited for all applications. One limiting factor is its size, which makes it difficult for use in small spaces.

What Are the Impacts on the Material?

Autoclaving can impact LSR by causing the combustion of lubricants and a reduced ability to transmit light.

Autoclaving can also be problematic for plastics. The combination of steam and temperatures of 121 degrees C or 134 degrees C can cause material degradation.

2. Disinfected Using a Gaseous Chemical (ETO)

Another sterilization method is to disinfect medical devices using a gaseous chemical, also known as ethylene oxide (ETO) sterilization.

What Is ETO?

ETO refers to a colorless chemical gas that is both explosive and flammable. Four essential parameters of ETO include gaseous concentration, temperature, relative humidity, and exposure time. These factors work together to build the effectiveness of ETO sterilization. 

ETO is effective at removing bacteria but has the potential to promote toxicological issues if the gas is absorbed and released into tissue. ETO is also phasing out of the industry due to environmental considerations.

What Are the Impacts on the Material?

ETO can sterilize moisture or heat-sensitive medical devices and equipment without any detriment to the material’s function. Using gases may create changes in the plasticization level and crystallinity, and LSR has been shown to lead to an improvement in tensile strength and elongation of LSR.

3. Isopropyl Alcohol (IPA) Rinsing

IPA rinsing is the easiest sterilization method for medical devices.

What Is IPA Rinsing?

IPA stands for isopropyl alcohol and is a highly effective cleaning solvent. This sterilization method penetrates an organism’s cell walls and coagulates its proteins, killing the organism. IPA is commonly used in hospitals, pharmaceuticals, electronics, and clean rooms for disinfecting medical devices. Different concentrations, solutions, and purity grades yield differing results.

What Are the Impacts on the Material?

IPA rinsing does not alter properties, and it dries off without leaving residue. IPA rinsing offers a dual benefit, in addition to sterilizing the parts it also cleans the part surface. Any debris or residue remaining from secondary processes like trimming or cutting if applicable, is washed off during the IPA rinsing.

4. Radiation (Gamma or E-Beam)

Another commonly used sterilization method is radiation. 

What Is Radiation Sterilization?

Gamma and E-beam sterilization are the traditional favorites among radiation methods. Ease of use is one reason, as radiation sterilization can be performed when the components are already packaged in their final form. Because toxic materials are not used with gamma and E-beam radiation sterilization, it has become the most preferred method. 

Other benefits of radiation sterilization include its high penetration power, reliability, and accuracy. Since it kills bacteria by breaking down bacterial DNA, it can prevent division and multiplication. Using this form of sterilization does not lead to contaminations or leave any toxic residual.


What Are the Impacts on the Material?

When using LSRs, radiation sterilization can cause scission of the silicone rubber molecules, which can lead to crosslinking and a change in the mechanical properties. It may impact color, solubility, and texture. It can also reduce the tensile elongation and tear strength, increase molecular weight, and decrease elasticity. An increase in gamma radiation results in a directly proportional increase in the hardness and modulus of silicone rubber.

Radiation sterilization reacts similarly with other plastics and TPEs.For example butyl, nitrile, fluoro, and polyacrylic polymers may experience significant damage when exposed to radiation sterilization, whereas LSRs are more resilient. 

SIMTEC’s access to material information, test data, and other technical findings are valuable resources utilized to help customers understand the effects of the various sterilization options available. 

TPE vs. LSR and LSR 2k Materials

The differences between LSR and TPE are valuable to understand when choosing the right materials for your medical application:

  • LSR: LSR is best for implantable device applications due to its heat resistance and high chemical properties, along with fewer diverse reactions during skin contact.
  • TPE: Thermoplastic elastomers are a blend of polymers that, when heated, form and melt into plastic. TPE is great for permeability related applications and offers high fatigue resistance, abrasion resistance, low compression set, and high elasticity. 

LSRs are outperforming TPEs in both high and low temperatures and in other areas important to medical and healthcare device manufacturers. Many medical and healthcare devices require a durable material with excellent chemical resistance that can withstand sterilization, as well as tolerant with biocompatible attributes for skin contact applications. LSRs ability to offer these benefits and meet the challenges associated with micro molding for tiny critical components have resulted in its widespread use and preference.

For some sterilization methods, higher stabilized grades may be required.

SIMTEC Medical Device Specialists

At SIMTEC Silicone Parts, we are focused on providing the LSR and LSR Multi-Shot solutions that will best meet our customer’s product-specific needs. That’s why we work closely with our customers from the onset to obtain a thorough understanding of the product and how it’s used. When you choose SIMTEC, you’ll enjoy the following benefits:

  • Advanced molding technology: Our automated molds and molding technology provide hands-free, lights-out capable production with precision accuracy.
  • Class 8 clean room molding: SIMTEC offers a smart-design class 8 clean room for hygienic LSR and LSR 2-shot parts production and secondary processes in an ISO-certified clean environment.
  • Unparalleled quality parts and service: We deliver your products that will meet or exceed your quality specifications and your delivery requirements. At SIMTEC, we ensure you receive total support from start to finish

To discuss your project needs with one of our team members or get more information on our LSR injection molding capabilities, contact our office at SIMTEC today.