The demand for silicones in the medical market continues to grow owing to megatrends such as the aging population as well as increasing recognition of the benefits that silicone brings to patients and manufacturing operations. One type of silicone – liquid silicone rubber (LSR) – is expected to see particularly strong growth on account of its gradual replacement of high consistency rubber (HCR) in various applications. Both types are non-allergenic, passing purity and biocompatibility tests. However, LSR has the advantage of a more regular network of crosslinks, contributing to greater elasticity and absence of molecular byproducts. It is also easy to handle and ideal for cost-effectively and efficiently manufacturing complex geometries via injection moulding processes.
With further formulations including adhesives and gels, the versatility of silicones has made them important materials across a wide range of applications and device categories. Since they are biocompatible and safe for implantation for greater than 29 days, many of these include Class III medical device categories such as pacemakers and implanted prosthetics.
But what are implantable-grade silicones, chemically speaking, and how are they made? We spoke to Elkem Silicones, the medical device industry’s only vertically integrated supplier of silicone materials, to find out.
From quartz to silicon to silicone
“Silicones are considered a highly versatile family of synthetic polymers,” says Michael Goglia, Healthcare Market Manager for North America at Elkem Silicones. “Their basic structure is made up of polyorganosiloxanes, where silicon atoms are linked to oxygen to create the siloxane bond.”
The production process starts in an open pit quartz mine, where silica is obtained. Quartz is comprised of the two most abundant chemical elements on earth, with major mining locations found across the globe. One of the largest quartz mines is located at the top of Europe on the north coast of Norway. With annual output of approximately 850,000 million tonnes, this mine has been owned by Elkem since 1983.
Once quartz has been mined, manufacturers like Elkem will heat it to temperatures as high as 1,800°C. The result is pure, isolated silicon, which can then be ground to a fine powder. At this point, much of the silicon powder is supplied for the production of electronics, solar cells, industrial alloys, commodity chemicals, and other important applications, while the rest is combined with methyl chloride and heated again in order to activate a reaction.
This reaction forms methyl chlorosilanes which are then transformed through various stages of synthesis and distillation into siloxanes. After distillation, the final steps include polymerisation, resulting in a range of polymers such as polydimethyldiloxane (PDMS), methyl vinyl silicone (MVS), and flouorosilicone (FVMQ), followed by the addition of additives such as pigments and fillers and the use of multiple cure systems to achieve different properties. After careful tuning, silicone manufacturers like Elkem arrive at a range of highly customisable final products such as pastes, emulsions, gels, adhesives, and elastomers.
What makes a silicone safe for implants?
With a strong foundation in R&D, Elkem is an expert when it comes to finetuning the properties of silicones to the needs of various products, including implants. Produced and packaged within Class 7 cleanrooms or white spaces, the majority of its Silbione™ and Silbione™ Bio medical-grade materials are manufactured in an ISO-13485-compliant facility in York, South Carolina, with further ISO-13485 facilities in Caronno, Italy and Shanghai, China, ensuring a robust, global footprint.
As part of the requirements of an ISO 13485 quality management system, FTIR scans are taken to characterise each batch of raw material, enabling the detection of any impurities before production. After manufacturing, additional testing is performed according to ISO 10993, examining intracutaneous reactivity, acute systemic toxicity, cytotoxicity, mutagenicity, and skin sensitization. For a long-term implantable silicone within Elkem’s Silbione™ Biomedical line, additional testing is performed for hemolysis, pyrogenicity, and tissue irritation. These tests are performed on every single Silbione™ Biomedical batch.
In addition, certain products in the Silbione™ Biomedical line have undergone further purification to control D4, D5 and D6 levels – a precaution which may be required depending on the application and processing. Finally, Silbione™ Biomedical products also come with the submission of Master Access Files (MAF) or Drug Master Files (DMF) to support the customer’s regulatory submissions to the FDA.
Why Elkem
Elkem’s position as the only implantable-grade silicone producer that controls its raw materials all the way back to quartz has become a key benefit for its customers, particularly when it comes to change control and security of supply.
“Because we own our raw materials, we can ensure our biocompatible material production is not impacted and the supply chain is robust,” says Goglia. “If there is a material shortage, which has occurred over the years, we can always prioritise our healthcare-grade materials. With three different ISO 13485-certified sites around the world, we also have a diversified footprint in manufacturing, meaning we could produce our biomedical-grade silicones in many different subsidiaries.”
Vertical integration also enables the Norwegian company to control CO2 emissions in line with its ambitious climate targets – something that is of increasing importance to its healthcare customers looking to reduce Scope 3 emissions. With 82% of its energy coming from renewable sources in 2023, Elkem already produces silicon and silicones with a significantly lower CO2-footprint than the industry average, but its goal is to continue reducing this further. The company’s main strategy involves replacing fossil coal with biocarbon in smelting operations. It currently employs 25% biocarbon in production, with a target to reach a 50% biocarbon share at its smelters by 2031. It is also exploring carbon capture, utilisation and storage (CCUS) technology, completing the world’s first CCUS pilot on a smelter, with good results and capture rates.
Overall, a combination of its high-quality Silbione™ products, strong sustainability commitments, and security of supply make Elkem Silicones the medical device industry’s ideal provider of medical-grade and implantable-grade silicones. To learn more about implants and the role of silicones in improving device performance, patient comfort, and the efficiency of manufacturing operations, please download the whitepaper below.
