How Is Liquid Silicone Rubber (LSR) Biocompatible for Medical-Grade Parts?

how is LSR biocompatible for medical-grade parts

Medical-grade parts must show their biocompatibility. The same is true when using LSR in the design of those parts. Using this material in medical equipment requires adherence to regulations and careful design.

What Is Biocompatibility?

what is biocompatibility

For medical devices to be biocompatible, they must not cause any adverse responses in the surrounding tissues. Irritation, swelling, and redness caused by a device would make that part not biocompatible.

For American-made products, the FDA governs whether companies may use specific materials for medical-grade parts. This government organization recognizes the latest international standard: the ISO 10993-1-2018, updated in August 2018. The previously published FDA guidelines from 2016 included parameters that closely align with the newest ISO update.

The standards for medical-grade parts examine several factors of biocompatibility and types of objects. The ISO and FDA guidelines cover four types of devices — active, implantable, non-implantable, and non-active. We supply our customers with all of these components, with the exception of implantable.

Categories of devices depend on their length of contact with either the patient or the medical professional, which means these guidelines cover everything from implanted devices to gloves. Contact levels include direct, indirect, noncontact, and transient.

  • Direct: Touching any bodily tissues means a device comes into direct contact with the patient. The length of contact determines the categories such devices must show a lack of risk factors in. Items with direct contact fall into three categories — limited, prolonged, and permanent. Limited contact happens for less than 24 hours. Prolonged is more than 24 hours but less than 30 days, while permanent devices touch the body for more than 30 days.
  • Indirect: Devices that hold gases or fluids that go into a human body have indirect contact with a person. Blood bags and medicine containers indirectly contact patients.
  • Transient: If a device contacts a patient’s skin for less than a minute, it has a temporary connection. Hypodermic syringes are one example of this type of device.
  • Noncontact: Anything that has no chance of contacting a patient is noncontact. Items such as computers or software only need to show they will not touch patients. These devices do not require biocompatible testing.

According to the FDA, biocompatibility standards include the effects the device will have in multiple categories, depending on the use of the material.

  • Cytotoxicity: For all uses, the material cannot have any toxic effects on cells.
  • Sensitization or irritation: The material cannot create any sensitivity or irritation or all uses.
  • Acute system toxicity: Systemic, short-term toxicity cannot occur as a result of using a medical device.
  • Material-mediated pyrogenicity: This category was not in the previous edition of the ISO guidelines, but the 2018 version added it. The FDA has included it, along with carcinogenicity, degradation, chronic toxicity, and reproductive toxicity, since the 2016 recommendations. This category requires a material to not cause fever in a patient.
  • Hemocompatibility: The device must not cause adverse reactions with the patient’s blood.
  • Genotoxicity: Anything that could impact the genes of a person has genotoxicity. Medical devices and materials cannot have this effect, especially when used long-term in or on a patient.
  • Carcinogenicity: The capability of something to cause cancer, carcinogenicity, prevents its use in devices for long-term use.
  • Chronic toxicity: Chronic toxicity may not appear for a long time. However, for implanted or long-term use devices, this metric is critical for determining safety.
  • Degradation: For materials or devices that should degrade when in contact with tissue, the producer must submit information about the degradation for evaluation to determine biocompatibility.
  • Reproductive or developmental toxicity: Not all devices require proof they are safe for use in pregnant women and for developing fetuses, but products used with pregnant women or for reproductive organs need to show their safety in separate tests.

With people living longer than ever with implants in their bodies, doctors must know the long-term effects and risks the devices have for the patients. While tests prove safety, manufacturers now must consider the potential dangers their devices have when used long-term. Several new categories portray risks — carcinogenicity, material-mediated pyrogenicity, reproductive toxicity, chronic toxicity, and degradation. These areas were not present in older ISO guidelines, but the most recent ISO and FDA parameters include these.

To ensure biocompatibility, scientists must prove that materials perform safely and well in these areas and can withstand sterilization and cleaning, depending on their use. While many elements qualify, one that has seen a growth in the application for medical devices since its introduction in the latter half of the 20th century is LSR.

How Is LSR Biocompatible?

LSR has several attributes that make it a preferable material for use in medical devices for several manufacturers.

  • Thermal stability: Even temperatures as low as -150 degrees Fahrenheit and as high as 450 degrees Fahrenheit cannot affect the stability of LSR. This wide range of temperatures this material can tolerate also contributes to another of LSR’s assets.
  • Sterilization capability: For any products used in or around the human body, the materials must withstand the sterilization process. Medical facilities can sterilize devices with LSR components using gamma radiation, autoclave, E-beam, and EtO — ethylene oxide. Many sterilization processes, such as autoclaving, happen under temperatures ranging from 110 to 190 degrees Celsius. LSR can withstand these temperatures. However, other sterilization methods may damage the silicone. To maintain the silicone biocompatibility, avoid hydrogen peroxide, gamma radiation, or ClO2 for sterilization. These processes may change the structure of the silicone.
  • Texture: Topical devices that do not feel tacky are essential for the patient to stay compliant with using the part. LSR has a dry, nonstick surface.
  • Biologically inert: The inert qualities of LSR mean it will not react with anything in the human body, a requirement for any biocompatible material used internally.
  • Hypoallergenic: LSR does not cause allergic reactions in patients, even those with other sensitivities. This quality satisfies the need for biocompatible materials to not cause irritation or sensitization.

Just having these properties alone, however, will not prove the biocompatibility of a material. The FDA requires a three-step process that includes test results.

  1. Create a biological evaluation plan, or BEP: The BEP outlines how the producer will evaluate and test the risks and evaluate the safety of the materials and product. How the device will affect patients plays a significant role in dictating the types of testing the BEP recommends and the potential risks the part could have.
  2. Conduct tests: Testing the materials based on the categories of the ISO 10993-1-2018’s appendix A determines whether the product offers adequate biocompatibility. Researchers may conduct several types of assessments to prove safety and risk factors. These tests include chemical analysis and toxicology risk evaluation, in vivo or in vitro biological studies, and literature analysis based on clinical studies and scientific experiments.
  3. Write the biological evaluation report, or BER: The finalized report summarizes the findings of the tests and analysis. The FDA receives a copy of this report, along with all test results, to make its final decision on the biocompatibility of a device.

Doctors use devices with biocompatible silicone rubber internally and externally in their patients. The versatility of this material has led to the creation of numerous medical products, including catheters, rings, cushioning pads, gaskets, closures, stoppers, and liquid feeding bottles. While versatile, LSR still requires safety testing and risk assessment remain to determine its use in medical applications. Numerous factors, including the surface structure and chemical composition, will dictate the use of a medical device made with LSR. These other issues are why testing the final product for biocompatibility is so crucial for patients’ safety.

Why Medical Device Biocompatibility Is Important

why medical devices biocompatibility is important

Doctors take an oath to “first do no harm,” and using medical devices without knowing their risk levels increases the chances of adverse reactions in patients. In some cases, untested medical device biocompatible parts could make a patient’s condition worse. To prevent such situations, the FDA requires all medical devices that contact patients to submit biocompatibility test results. The types of tests depend on the level of contact the devices have with the patients, but even items with brief contact must prove their safety. Without such proof, patients could suffer harm from their medical treatments.

Testing biocompatibility on finished products is crucial. The creation process could introduce structures and chemicals that might affect the safety of the materials used in the device. Thorough biochemical assessment with risk analysis and testing ensures the finished part will not cause any injury or danger to the patient.

Importance of Testing Implants

Testing biocompatibility of devices could prevent serious complications, especially in patients with implants. Though the same materials used in an implant may not pose problems when applied externally, interactions with the body’s blood and tissues could lead to complications when the elements remain inside the body for an extended time. For example, in implantable electronics, the insulating materials are typically the only parts of the device that directly contact tissues. Depending on their composition, even inert insulations could cause thrombosis, fibrosis, or bacterial growth from differences in surface structure or makeup. Risk evaluation and testing could prevent doctors from using devices made of such materials.

The long-term nature of implants brings potential risks such as carcinogenicity. The FDA and ISO standards only recently added this testing category to implants, reflecting on the growing knowledge of environmental carcinogens as well as the increased longevity of newer implant devices. Even if the materials prove safe for a few months, carcinogenicity examination will determine their dangers over years of use in the body.

Importance of Testing External Devices

Biocompatible devices used outside the body must not cause sensitivity in any patient. Some patients have higher sensitivity levels, and hypoallergenic, nonreactive devices ensure all patients can benefit from the products. Creating products all patients can use allows faster application of the part to the patient without a doctor needing to test it first. Biocompatibility testing ensures patients’ safety and comfort with all devices, internal and external.

Another advantage of LSR in external use is its pleasing texture. For external use, medical professionals and patients don’t want sticky, tacky devices. A tacky feel could make a patient less compliant with treatment or a medical professional less inclined to use the part. Testing of the texture of a finished product, while not a required part of biocompatibility testing, does help ensure the comfort of those who touch the device.

Benefits of Biocompatible Parts for the Medical Industry

Benefits of biocompatible parts for the medical industry

Tests used to examine biocompatibility ensure safety for patients, but they also protect medical facilities and professionals from using harmful products. The criteria set forth by the FDA and ISO 10993-1-2018 ensure all medical devices will conform to the same exacting standards for safety.

Testing is crucial for ensuring patient safety, but when a material or device does not conform to the standards, that material may need modifications to bring it to the ISO or FDA standards for its intended use. For instance, LSR may pose problems when used in implants. However, changes to the surface make the material safer and less prone to harboring bacteria.

  • Graft polymerization: Grafting hydrogels prevents platelets from gathering on the surface of the LSR while reducing the absorption of proteins. Graft polymerization will not suffice for every medical device use, though, because the hydrogels can affect the mechanical properties of the surface.
  • Ion implantation: Ion implantation increases the LSR’s interactions with area cells while preventing bacteria growth. Implanting carbon atoms into the LSR does not affect the mechanical structure, but it does improve cytocompatibility.

Ensuring the safety of medical devices is only one benefit of testing the biocompatibility of the devices. Another advantage comes from understanding the risks for the use of the parts and taking steps to mitigate those. Long-term use of a device could result in physical or chemical changes in the body that may not seem apparent with short-term use. Biocompatibility testing now considers chronic toxicity of devices in addition to their acute effects.

Biocompatibility testing also examines how the human body could affect the operation of medical devices. By ensuring the patient’s tissues won’t react with the part, researchers can promote the safe operation of the device. Materials used in the part, while biologically inert, could affect the function of the implant. Biocompatibility includes information about the materials used in the construction of the device as part of the product’s physical and chemical makeup. Testing ensures the safety of these materials for both the patient and the device.

Biocompatible parts play vital roles in the medical industry by protecting patients and ensuring the operation of devices. Without testing, the safety and reliability of any parts that contact patients would forever be in question.

Contact SIMTEC Silicone Parts

LSR biocompatibility lends it to its use in numerous medical and dental parts. Learn more about medical-grade LSR from our site or by contacting us at SIMTEC directly. Our experts will give you the guidance you need in crafting LSR-based medical-grade parts and devices. Having made billions of LSR parts made since our founding in 2002, we have honed the manufacturing process of medical devices and many other products containing LSR. This material has been the focus of our production since the start. Our expertise, tools, and experience give us the knowledge to help you make your medical devices better.

 

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