High-consistency rubber (HCR) offers medical device manufacturers an established biocompatibility pedigree, broad processing parameter ranges and excellent physical properties.

Brian Reilly, NuSil Technology

High-consistency rubber silicone (HCR) has long been used by the medical device industry. From tubing and balloons to sheeting and molded parts, HCRs are comprised of a high molecular-weight polymer combined with silica. The result is a versatile silicone that has a clay-like consistency in its uncured form.

Along with versatility, HCRs have a proven history of use in numerous approved implantable and non-implantable applications. These silicone elastomers were first used in the 1960s for implantable devices like hydrocephalus shunts. Since then, HCR use has expanded into a wide range of medical applications because of the material’s established biocompatibility, broad processing parameter ranges and excellent physical properties.

Curing versatility

Part of HCR’s versatility stems from its ability to use different curing systems. Options like peroxide- and platinum-catalyzed solutions offer device manufacturers different advantages depending on the application.

A key advantage of a peroxide-catalyzed system is that the curing mechanism is not activated until the HCR is exposed to heat, providing a very long work period that is ideal for a molding or extrusion process. This curing system creates unique elastomeric properties that can be useful in manufacturing balloons or similar applications where “tension set” is important.

For platinum-catalyzed HCRs, the cure chemistry is designed to accommodate faster cure times and increased throughput without corrosive byproducts. Platinum-catalyzed, addition-cured HCRs typically yield much higher physical properties than traditional peroxide-catalyzed HCRs, also making them ideal for applications that use molded or extruded components.

Processing versatility

HCRs offer broad processing parameters, so manufacturers considering a silicone should be aware that different end-use applications require different fabrication methods. For example, extrusion is the most efficient production method for silicone tubing that will be incorporated into a medical device. Once the processing method is established, consider additional requirements, such as: What properties should the tube have? Does it need to be stiff and rigid or soft and flexible? These and other factors can help determine whether it requires a peroxide-cure or platinum-cure system. An experienced HCR supplier can guide manufacturers through the process of choosing the most appropriate silicone and fabrication method.

Three considerations for using HCRs

The versatility of these silicone elastomers makes them well-suited for a variety of medical device applications. Here are three factors to consider when choosing an HCR:

• • Integration/interaction with other materials: One of HCR’s advantages is the ability to incorporate additives, such as colorants or active pharmaceutical ingredients (APIs), into the pre-cured formulation. Manufacturers using additives or other materials within the device should consider how they will interact with the silicone and the molding process. Additives may be temperature-sensitive and can also adversely interact with formulary components, resulting in an incomplete cure. Consider partnering with a silicone supplier that can customize solutions to address these challenges before they arise.
  • Avoiding cross-contamination: Be mindful of other chemicals that are used in the manufacturing process. Some chemicals may negatively affect platinum-cured HCRs in their uncured state, causing a partial or incomplete cure. Manufacturers can prevent contamination by implementing clean manufacturing practices, such as using dedicated instruments such as spatulas for subdividing HCR and cleaning all surfaces between uses.
  • Flexibility in HCRs: Medical devices and fabrication processes vary widely, so it’s essential to work with a silicone partner that uses innovative solutions that provide greater manufacturing process flexibility. For example, a provider using an optimization system can help device engineers optimize process requirements, such as work time and cure profile.

Final considerations for HCR selection

Silicone suppliers with deep expertise in providing HCRs for medical devices offer significant advantages to manufacturers. For example, suppliers who already have established relationships with regulatory bodies can more efficiently and more effectively help meet essential guidelines.

Another key consideration is whether the supplier has a robust quality system, including ISO 9001 certification, knowledge of ISO 13485 requirements for medical devices and experience with FDA master file submissions. A silicone supplier with this expertise can provide support throughout the design and regulatory submission process to help medical device manufacturers save time and money as well as move devices to market faster.

Brian Reilly is business development director of biomaterials for NuSil Technology, part of Avantor. He holds a B.S. in Biological Sciences from California Polytechnic State University-San Luis Obispo.

The opinions expressed in this blog post are the author’s only and do not necessarily reflect those of Medical Design and Outsourcing or its employees.