Timothy Steckler, Ph.D., applications technology manager and Benny David, Ph.D., director, global business development at NuSil explore how silicone materials are expanding the formulator's toolbox.
NuSil
The objective of many controlled-release delivery systems is to approximate zero-order kinetics, a steady release profile that maintains therapeutic drug concentrations over extended periods. Material selection, device design, and formulation all play critical roles in achieving this performance.
Across therapeutic areas, drug and medical device developers are looking beyond traditional active pharmaceutical ingredients (API) delivery methods to improve patient outcomes through smarter formulation strategies. Long-acting implants, vaginal rings, intrauterine devices (IUDs), and other localised drug delivery platforms are transforming how therapies are administered, reducing dosing frequency while improving adherence and patient convenience. As these technologies become more sophisticated, the materials used to develop and manufacture medical devices to deliver drugs have become just as important as the drugs themselves.
For many design engineers, silicones may be best known as materials used in medical devices. Yet advances in silicone chemistry are making them increasingly valuable as controlled-release drug delivery platforms, providing formulators with new ways to precisely engineer how therapies are delivered over weeks, months, or even years.
Designing drug release, not just the drug
Whether developing a hormone-releasing implant, a localised pain therapy, or a long-acting anti-infective, formulation scientists must carefully control how quickly a drug leaves the device, how consistently it is delivered, and how that release profile changes over time.
Silicone materials offer an unusual level of control because their chemistry can be tailored in multiple ways. Variables including crosslink density, cure chemistry, backbone chemistry, fillers, and additives can all influence how an API dissolves and then diffuses through the polymer matrix. Rather than serving as a passive carrier, silicone becomes an integral part of the formulation strategy, allowing developers to tune release kinetics to meet specific therapeutic goals.
In other words, silicone gives formulators more options than many conventional polymer systems. Instead of relying on only a handful of material properties, developers can optimise multiple parameters to create the desired release profile.
Engineering consistent release
Creating a successful long-acting therapy requires balancing material science with device design. Developers begin by evaluating whether the API is compatible with the silicone matrix and whether it will dissolve sufficiently to support controlled diffusion. Drug loading, particle size, cure chemistry, and device geometry all influence performance.
Typically, the ultimate objective is to achieve zero-order kinetics, a release profile in which the drug is delivered at a nearly constant rate throughout the life of the device. Unlike systems that release large amounts of drug initially before tapering off, zero-order release helps maintain consistent therapeutic levels, improving efficacy while reducing fluctuations in drug exposure. While achieving perfect zero-order kinetics is challenging, careful engineering of both the material and the device can closely approximate this ideal.
Many sustained-release devices use a reservoir, or core-shell, design to accomplish this. A drug-loaded core continuously replenishes dissolved API, while an outer silicone membrane regulates diffusion into surrounding tissue due to a concentration gradient from the core to the implant=tissue interface. As molecules leave the device, additional drug dissolves within the reservoir, helping maintain a controlled and predictable release profile over time. Surface area, membrane thickness, crosslink density, and device geometry all contribute to fine-tuning release kinetics. Although many devices experience an initial "burst release," thoughtful design can minimise this effect and produce the steady-state release profile that regulators and developers seek.
The result is a delivery system engineered to provide predictable therapy over weeks, months, or even years, supporting both therapeutic performance and patient adherence.
Expanding formulation options
Silicones also offer practical manufacturing advantages. Many competing drug delivery materials, including thermoplastics such as ethylene vinyl acetate (EVA) and polyurethanes, require elevated processing temperatures during moulding or extrusion. That can present challenges when working with temperature-sensitive APIs.
Silicone formulations, in contrast, can often be processed at significantly lower temperatures, even at room temperature, allowing developers to incorporate heat-sensitive compounds without exposing them to conditions that could compromise stability. For pharmaceutical developers working with increasingly complex molecules, processing flexibility can be just as valuable as the release characteristics themselves.
Why localised delivery matters
The growing interest in silicone-based delivery systems also reflects broader changes in therapeutic development. Rather than delivering drugs systemically through oral tablets or injectables, many new therapies seek to deliver medicine directly where it is needed. Localised delivery can reduce the amount of drug required while maintaining therapeutic effectiveness and minimising systemic exposure.
Equally important is patient adherence. Long-acting implants and sustained-release devices reduce dependence on daily dosing schedules, helping ensure patients receive therapy as intended. Improved adherence can translate into better clinical outcomes while lowering healthcare costs associated with missed or inconsistent treatment.
A platform for innovation
These benefits have helped establish silicone-based systems across women's health applications, including hormone-releasing IUDs and vaginal rings, where long-term, localised delivery has demonstrated clear clinical value.
The evolution of the dapivirine vaginal ring illustrates how continued advances in materials science can improve existing therapies.
NuSil has worked with the Population Council and its predecessor organisation for nearly two decades to supply high-purity implant-grade silicones for controlled-release HIV prevention implants. Building on the success of the approved one-month vaginal ring, a three-month version designed to reduce the number of devices needed each year while maintaining consistent drug release is now in development.
While the application is specific, the underlying principles are broadly relevant. Optimising material selection and release kinetics can improve convenience, increase adherence, reduce costs, and expand access to treatment, objectives shared across many therapeutic areas.
Although silicone-based drug delivery has been established for decades in women's health, its future may extend much further. Drug developers are exploring opportunities in ophthalmic therapies, localised pain management, and other applications where sustained delivery of small-molecule drugs could improve therapeutic outcomes. As pharmaceutical companies continue developing combination products and longer-acting therapies, demand for materials that can be precisely engineered to control drug release is likely to grow.
For formulation scientists, that represents an important shift in perspective. The next breakthrough in drug delivery may not come solely from discovering a new molecule. It may come from designing a smarter delivery system, one in which materials science plays as significant a role as pharmacology. As controlled-release therapies continue to evolve, silicone is proving to be far more than a structural material. It is becoming a sophisticated formulation tool that gives developers greater control over how therapies perform, opening new possibilities for safer, more effective, and more patient-friendly medicines.