Implantable drug eluting devices: Key applications for silicone

Drug eluting implant devices control the release of active pharmaceutical ingredients (API) into surrounding tissue. Biomedical grade silicone is a key material for these devices. As the material cures, it forms a permeable matrix structure, creating apertures for APIs to reside in and then permeate through in a consistent manner, allowing sustained release over time.

Sean McPherson is Senior Business Development Manager at leading supplier of medical-grade silicone materials, Elkem Silicones. Compared to other methods of drug delivery, McPherson says that one of the key benefits of drug eluting devices is the ease of use for the patient. Some drugs can be difficult to administer yourself, or just become unpleasant if you have to take them over an extended time span.

“Some patients may have difficulty remembering to take their drugs,” McPherson explains. “Patient compliance is generally looked at as the number one issue with oral medication, or even injectables. Nobody enjoys being stuck with a needle. And if you must go someplace and have a professional administer that, then that’s more effort, more drain on your day, it breaks up your schedule.

“If you can put a device in place that delivers the drug at a very steady, consistent rate, then that’s going to eliminate that patient compliance obstacle for some length of time. That’s a huge benefit to patients and to their health in general.”

Targeted drug delivery

Another important benefit is how the drugs are targeted. For injections or oral medication, the active pharmaceutical is usually ‘overloaded’ for it to try to reach the right area of the body at the optimal strength. This can potentially lead to toxicity issues, and many drugs have strong side effects. It can also limit the effectiveness of the therapy.

“If you’re not targeting the right amount to that area and the body filters out a little bit too much, it could be less effective, and therefore you have to adjust dosage amounts to try to get the right amount, which can be difficult,” says McPherson. “When you have an implanted drug delivery device, you can typically put it in the right spot. You can use less of that API, because you’re not trying to overload the system in order to get the right amount to come through. That’s going to lower side effects and it’s going to lower the overall systemic toxicity.”

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Why is silicone a suitable material for implantable drug releasing devices?

There are three main reasons, explains McPherson. Firstly, silicones have been used in implantable devices for over 60 years, and so are proven, safe biomaterials.

The second is the structure of silicones, which are permeable in a predictable and consistent way. “No matter which cure mechanism you use, and there’s several choices out there, you end up with a material that due to outgassing during its curing process, creates this permeable structure, and you typically see a very consistent elution rate over time,” reveals McPherson. “You’re not going to have fluids migrating in or out quickly.”

Third, is the range of silicones on offer. “It’s just the multiple choices within silicones that can enable your device or your delivery technique,” says McPherson. “For instance, you have Higher Consistency Rubbers (HCR). You have Liquid Silicone Rubbers (LSR), and then even adhesive materials. And there’s an array of different cure systems, so if you need a lower temperature cure because the API is very sensitive to temperature, that can be done.”

An evolving market

The market for drug eluting devices is increasing at around a CAGR of 7-9% due to a consistent exploration in new and diverse types of drugs, including developments in gene therapy and peptide treatments. As the market has evolved, devices designed to do something already specific within a patient can now have an additional level of functionality. An example is a drug eluting stent, where the addition of certain APIs can help prevent plaque build-up and relieve pain.

Additionally, there are some areas of therapy that are very difficult to address, such as the eye. “Delivering drugs to the eye is very challenging,” points out McPherson. “Crossing the blood-brain barrier is always a challenge.” Drug eluting devices could be a great way to deliver therapies to those areas.

Silicone’s drug eluting properties have put the material at the forefront of innovation in this field for many years. Here are its key applications:

Stents: Cardiac stents are typically made from resorbable biomaterials, which dissolve in the body after six months to a year. For longer term applications such as airway stents, silicone is a popular choice and can be paired with a range of APIs for slow-release medication.

Women’s health: The vaginal area is well-supplied with blood, making it a great delivery point for APIs for contraception, HIV prevention, or hormone replacement therapy. The insertion is minimally invasive yet provides long-term benefits. Silicone is available in an array of soft and comfortable materials, making it perfect for this application.

Ophthalmology: It could be as simple as a punctal plug that sits in the tear duct and elutes an API to assist with dry eye. Other devices can be fixed to the back of the eye, where they elute drugs over time to address longer-term conditions such as glaucoma.

Cardiac: Adding infection-reduction compounds to components like pacemaker leads is quite a common application. Any type of catheter could in theory use an infection-reduction collar or additive.

Oncological: Because cancer typically involves long-term treatment using some of the most toxic drugs on the market, targeting therapies directly to the source of the tumour is an exciting area of development for drug eluting devices.

Medical-grade drug eluting silicones

Silicone technologies have an excellent level of biocompatibility, making them safe for use in surgical applications. Medical-grade silicones certified ISO 10993 are one of the few materials that meet the strict standards for long-term implants.

In addition to a comprehensive series of Silbione™ Biomedical M series Liquid Silicone Rubbers (LSR) and High Consistency Rubbers (HCR), which support long-term implantable device applications, Elkem also offers the Silbione™ Biomedical LSR D series to support drug delivery applications.

These materials have undergone additional testing for filtration, explains McPherson. “The ‘D’ classification indicates this material has a special level of filtration and is processed in a certain environment. It will ultimately have a drug master file associated with it too.”

Looking forward, McPherson predicts drug eluting silicones have a long-term future with implants. “For implantable devices, some of these treatments are a really good fit. Long-term conditions, six months to a year at a time, where they may also need support from a device structure – these are interesting areas to keep our eyes on, and continually try to develop new forms or new ways to change the silicone to meet some of these new demands.”