Albright provides solutions to our customers’ most challenging prototyping and production projects by working with a wide range of raw silicone material suppliers and leveraging our experience. We have molded complex geometries out of a wide range of silicone materials ranging from high durometer (> 80 Shore A) to very low durometer (< 1 durometer). Silicone exhibits excellent properties for many medical devices due to its thermosetting nature, which gives it more stable and repeatable performance. Silicone has found use as replacements in many rubber applications. Silicone in general demonstrates relatively stable properties across a wide range of temperatures allowing them to be autoclaved. Some formulations of silicone are relatively bio-inert and have very low levels of volatiles that may be extracted from the material. Some of these favorable silicone properties include:
- High elongation, greater than 1200% in some materials, allowing features with significant undercuts that can be molded without side actions or collapsing cores.
- Surface finish detail down to the micron level.
- Thin profiles and part features are possible well into the 0.005in/0.127mm range.
- Dimensionally stable
- Electrically and thermally insulating, although this can be modified.
- Wide temperature ranges for use, -40 to 200°C (-40 to 392°F).
Medical Grade Silicones refers to silicone materials that have passed or are capable of passing a set of standardized biocompatible tests. One of the most common grades is USP Class VI in silicone and thermoplastic. This means they have passed three biological reactivity tests including a system injection test, intracutaneous test, and an implantation test. Medical silicone materials are defined by the suppliers by range of use limitations such as:
- Skin contact only
- Short term implantable, which is typically up to 29 days.
- Long term implantable, which is greater than 29 days.
The combination of the properties and biocompatibility lead to the use of silicone in medical device applications. Silicone meets the needs of applications such as those that require a soft feel, high flexibility, biocompatability, high cyclic life, and stable behavior across a wide temperature range like:
- Seals and gaskets
- Valves / Septum
- Encapsulation of electronics
- Implant components
- Syringe pistons
- Menstrual cups
- Respiratory masks
Silicone materials have improved in performance and cost since the 1940s. Silicone materials are based on a silicon-oxygen polymer backbone giving it flexibility. Silica fillers, chemical structure, and catalysts are designed to drastically improve manufacturing efficiency and performance in medical devices. Most of the materials we prefer to work with are platinum cure materials, which is an addition cure reaction. We prototype and production mold with peroxide, but for medical applications these are becoming less common. Medical silicone like most silicones fall into three categories based on the chemistry, curing, and flow behavior.
Liquid Silicone Rubber (LSR) is the primary silicone type used. Also, it is sometimes called LIM (Liquid Injection Molding). LSR is injection molding friendly, although we can also mold parts in compression or transfer as well. The raw material viscosity ranges between warm syrup and cold molasses. The material properties are very broad due to the large number of materials. Materials generally range from 10 to 80 Shore A hardness. These materials are used in medical silicone prototyping and production.
High Consistency Rubber (HCR) or Hard Silicone Rubber (HSR) refers to a high viscosity material. The viscosity feels more like formable clay. These materials tend to be of higher durometer, starting around 30 Shore A or greater. We can transfer or compression mold parts for prototyping and production but requires more handling to mix and mold materials. These materials are not as injection friendly as LSR.
Room Temperature Vulcanizing (RTV) refers to a low viscosity material that can typically be poured like warm maple syrup in some cases. These materials are often curable at room temperature as the name implies. Some may be accelerated with process heat. They commonly have lower durometer and are often used in encapsulation of temperature sensitive electronics or in rapid prototyping. These materials are limited to compression molding and casting due to the very low viscosity, high cure rate, and occasionally off ratio mixture rates required.
We work with all kinds of irregular and complex projects that may require some very specialty materials and approaches. Do you need a custom formulation? The answer depends on your application, but the answer for most projects is no. The challenge in medical devices is the need to prove safety and efficacy so an off the shelf solution may be a better option. Custom formulations are often an extra variable in your project. However, for some projects, custom combinations create properties that lead to performance. If you have a custom formulation that you want to mold, give our team a call, and we can work with you to find a process for your material. Here are a few common specialty applications:
- Bonding to substrates such as plastics and metals requires special formulations, surface treatments, mechanical interlock, and/or medical grade primers to achieve the best bond possible.
- Radio opacity (for showing up in X-rays). This may be an additive or a material kit with predetermined radio opacity. These materials are commonly used for placement as well as visualizing function or locating within the body.
- Color may be added to most silicone materials. There are implantable colors available for those projects that need color such as identification and color coding. Many medical devices do not have color to avoid testing the additional material and introducing additional variables.
- Self-lubricating materials exude an oil (typically silicone oil) to create a lubricous surface. These are often a special class of medical materials supplied as a kit or additives which may be added to a base silicone and fall into custom formulations.
Albright offers molding and assembly in a controlled environment room. We have taken deliberate action to minimize contamination risks through filtered air handling, rigorous cleaning and maintenance, special handling, and inspection processes. We can deliver clean, high quality products to our customers.
Albright does not offer sterilization services. Most silicone materials are resistant to autoclaving, ETO (Ethylene Oxide), and GAMMA irradiation. Please note that irradiation sterilization methods tend to drive up crosslinking, potentially causing materials to become harder and have lower elongation. We can easily work with you and your preferred sterilization supplier to find a solution to your needs.
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