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Why Silicone Injection Molding is a Great Choice for Medical Manufacturing

When it comes to medical manufacturing, companies have a variety of methods to choose from ranging from molding to machining to 3D printing.  The following explains why silicone injection molding is a great choice for medical manufacturing – and why it may be the best option for your next project.

Why Medical Manufacturing Prefers Silicones

Silicones have long been a popular material for medical devices due to their durability, wide temperature range, chemical inertness, high tensile strength, vast range of available durometers, low toxicity, and compatibility with many sterilization methods. Furthermore, silicone has a unique molecular structure, namely its silicon-oxygen backbone, that results in several excellent properties that are desirable for medical manufacturing such as:

• Superior Biocompatibility: medical products often come in contact with the human body – either externally on a patient’s skin or internally as an implant that contacts tissue and fluids. Silicones are compatible with human tissue and body fluids, have a very low tissue response when implanted, and do not support bacteria growth. Additionally, medical-grade silicones, such as Liquid Silicone Rubber (LSR), have undergone stringent purity and biocompatibility testing that make them suitable for short and long-term usage. Simply put, silicones are unmatched in their biocompatibility, making them an excellent option for medical manufacturing.
• Withstands Sterilization: medical grade material must be able to withstand sterilization in order to minimize contaminants and the risk of infections. Devices and products made of medical grade silicone are easily sterilized and resist bacteria growth. In fact, medical grade silicones are often processed in special facilities called cleanrooms that reduce the potential for contamination. For example, all of ProMed’s manufacturing facilities are equipped with certified class 10,000 / ISO Class 7 cleanrooms, demonstrating a strong commitment to quality.
• Superb Stability: silicone is known for its resistance to UV, weather, and other environmental conditions that tend to age materials, leading to a high level of stability and long-life span for silicone products. These characteristics are critical for a number of medical devices such as implantables.
• Broad Temperature Range: compared to other materials, LSR and other silicones have excellent thermal stability. LSR blends are able to withstand high temperatures without deforming or melting. As for low temperatures, LSR maintains its flexibility and does not become brittle and vulnerable to breaking like thermoplastic elastomers.
• Low Viscosity: the low viscosity of LSR makes it a great material for making medical devices via silicone injection molding, since the LSR can easily flow into and completely fill molds with relatively low injection pressures, even those with small, complex, or high-tolerance features. A lower viscosity also makes it easier for manufacturers to mix in additives including colorants, desiccants, barium, and pharmaceuticals such as hormones or steroids. For these reasons, LSR is a great option for medical devices such as combination products.
• Quick Cure Rate: one of the benefits of silicones, like LSR, is that it cures faster than most other rubber materials – in some cases in only seconds. Additionally, due to the highly automated nature of silicone injection molding and the potential for 24/7 manufacturing, high volumes of medical products can be produced in a short period of time – adding to its popularity.

Looking for a reliable and proven partner for your next medical manufacturing project?
Contact ProMed to learn about the range of solutions and materials we offer as well as our decades of silicone injection molding experience.

Advantages of Silicone Injection Molding in Medical Manufacturing

For companies seeking high-quality and cost-effective products for the medical sector, silicone injection molding is an ideal solution.  Silicone injection molding has several benefits compared to other molding processes, and the following is why this method is a great choice for medical manufacturing. To learn more about ProMed’s medical injection molding and our commitment to quality, watch our short video.

• High Quality & Very Reproducible: silicone injection molding produces products that are virtually identical from part to part which provides excellent brand consistency and part reliability during high volume runs – this is especially crucial for devices used in the medical industry. High reproducibility also allows for production to be scaled up to very large volumes, resulting in low costs per unit once the upfront equipment set-up costs are paid.
• Excellent Versatility: silicone injection molding is able to manufacture a wide range of part sizes, materials, and colors. Additionally, this form of molding allows for the use of multiple materials simultaneously, allowing for a high degree of customization.
• Able to Produce Complex Parts: silicone injection molding is typically performed at high pressure which forces the silicone into small crevices in the mold (that other molding processes are unable to reach), enabling the production of intricate and complex parts.
• Efficient Production & Low Cost Per Unit: silicone injection molding is a very fast process that quickly generates high volumes compared to other molding methods, making injection molding a more efficient and cost-effective solution. Additionally, silicone injection molding is highly automated via the use of machines and robotics, requiring less oversight by operations personnel. Automation reduces labor costs which further decreases the manufacturing costs per unit, especially for high volume production.
• Low Waste Generation: silicone injection molding manufactures smooth products that have minimal finishing requirements after removal from the mold – resulting in less waste generation compared to other medical manufacturing techniques. In some cases, silicone injection molding waste is able to be reused, resulting in a more environmentally-friendly and lower cost process.

ProMed – Your Silicone Injection Molding Partner

ProMed was founded in 1989 to address an industry need for cleanroom manufacturing of silicone components, specifically those having a medical application. We have garnered a reputation as the world benchmark of implantable silicone components and assemblies – and are one of few companies in the world to provide contract manufacturing of drug-eluting products.

ProMed has expertise in working with the full spectrum of silicones covering a wide range of properties and characteristics. We will assist in your material selection to help ensure all design requirements are met. Our manufacturing facilities and equipment are designed for a single purpose—to mold medical and implantable silicone, combination components, and bio-material grade plastics with uncompromising quality and service. We currently have four divisions that are located within two manufacturing sites. All are certified class 10,000 / ISO Class 7 cleanrooms.

We can identify the right medical manufacturing solution for any project. We have extensive experience in a wide range of silicone injection molding techniques including:

• Automated Injection Molding
• Multi-cavity tooling
• Micro molds and micro molding
• Servo-controlled de-molding capabilities
• Insert molds, overmolds, and automation integration
• Transfer molding
• Compression molding

Click here to see why ProMed is your silicone injection molding partner. Contact ProMed today at 763-331-3800 to discuss your next medical manufacturing project.

Micro-Injection Molding 101

Medical products continue to shrink in size but grow in capability as the demand increases for more portable and functional devices such as implantables, wearable devices, hearing aids, and surgical instruments. Medical manufacturers must keep up with these advancements and be able to manufacture smaller, more complex devices without sacrificing quality.

The trend toward miniaturization of medical devices has resulted in an increase in micro-injection molding, a form of manufacturing that creates tiny and often complex parts. Below is more information on this form of injection molding and why it is gaining popularity across the healthcare sector. When it comes to selecting a micro-injection molding partner, OEMs must choose wisely as this form of manufacturing requires specialized equipment and skills that many injection molding companies do not possess. The team at ProMed have the know-how and state-of-the-art equipment to successfully perform a broad range of molding methods including micro-injection molding. Our team is focused on meeting the challenges that product miniaturization often present and we are positioned to assist with all of your injection molding needs

What is Micro-Injection Molding?

Micro-injection molding is a tight tolerance method of manufacturing that produces miniscule parts – often weighing significantly less than 1 gram with dimensions measured in millimeters. Many industries benefit from these tiny products including the medical market which has numerous applications for these devices. Healthcare providers as well as patients have pushed for less invasive procedures, thus, medical devices are meeting these demands by becoming smaller with more complex features.

While there are some variations between micro-injection molding methods, the main equipment and process are generally the same. The process begins when silicone is fed into a heated barrel. In the case of Liquid Silicone Rubber (LSR), manufacturing, the two liquid LSR components are stored in separate containers and then fed simultaneously into the barrel. Next, a screw is used to mix, heat, and transport the silicone toward to the mold. The melted material is then injected through a nozzle into the mold and travels via a gate and runner system into the tiny mold cavities; the proper design of the gate and runner system is essential to ensuring the mold is filled properly. As the silicone enters the mold, excess air can be released via vents. The pressure and temperature of the mold are maintained to allow the silicone to conform to the desired shape and harden quickly. Once the part is adequately cooled, the mold opens and the part is ejected, sometimes with the help of ejector pins. The mold is then ready to receive the next shot of silicone.

Micro-injection molding is one of the latest innovations within injection molding. Due to their size, these miniature products weigh significantly less than prior versions of medical devices. This is a significant advancement for medical manufacturing as weight has historically been a challenge for the healthcare sector. Smaller and lighter parts lead to less material usage and lower cost per part – a huge win for medical manufacturing, giving OEMs a competitive advantage.
Benefits of Using LSR for Micro-Injection Moldin

Silicones have long been a popular material for medical devices and medical device components due to their durability, ease of molding by many methods, wide temperature range, chemical inertness, high tensile strength, vast range of available durometers, low toxicity, and compatibility with many sterilization methods. Furthermore, silicone is compatible with human tissue and body fluids, has a very low tissue response when implanted, and does not support bacteria growth – making it a perfect option for implants. Additionally, medical-grade silicones, such as LSR, have undergone stringent purity and biocompatibility testing that make them suitable for short and long-term usage.

LSR has a lower viscosity than many other medical-grade silicones, meaning LSR is less viscous and more readily flows. Due to its lower viscosity, LSR is a good fit for micro-injection molding as it is able to fill the tiny micro spaces in the mold. Additionally, LSR’s desirable handling properties and lower shrink rate make it an excellent choice for manufacturing complex geometries and intricate micro-sized products. Due to the automated nature of injection molding, LSR can produce high volumes of components in a short period of time.

Looking for a reliable and proven partner for your next medical manufacturing project?
Contact ProMed to learn about the range of solutions and materials we offer as well as our decades of silicone injection molding experience.

Challenges of Micro-Injection Molding

While the micro-injection molding process is relatively similar to standard injection molding, there are some challenges that exist due to the scale of micro parts.

Micro-injection molding demands unparalleled precision. The weight and dimensional accuracy required in micro tooling and throughout the molding process is incredible – often measured in millimeters or milligrams. Tooling required for micro-injection molding is specialized and requires extreme attention to detail to ensure consistent alignment throughout the life cycle of the mold – which is often millions of micro parts.

Material dosing is more challenging when working with micro amounts. LSR is a 2-part liquid that cures into a solid form when mixed, which are often referred to as the A and B components. For micro-injection molding, feeding the precise dosage and ratio of A and B components of LSR is crucial to ensure the desired product quality and properties. Additionally, if additives, such as a color, are added the dosage must remain precise in order to achieve consistency from batch to batch.

Micro-injection molding requires a small shot of silicone material. Due to the small volume of material, operating conditions such as pressure and temperature throughout the molding process must be uniform and balanced to ensure proper filling and distribution of the material.

Due to their tiny size and weight, micro parts must be handled more carefully than standard injection molded products. Micro parts are often more fragile and susceptible to damage during handling and assembly. LSR parts are often tacky, further complicating the automated as well as manual handling process for micro parts. In addition, ensuring a thorough and comprehensive inspection of the miniature parts is often a challenge for micro molders.

In order to have a successful project, OEMs must partner with a micro-molder, like ProMed, that has the requisite experience with the equipment, materials, and potential pitfalls of micro-injection molding. Even the slightest deviation during micro-molding will result in parts that are unusable. OEMs must leverage the experience of their micro partner, especially during the part design and prototyping stages where many key decisions are made that will significantly impact the success of the final product.

What OEMs Should Look for in a Micro-Injection Molding Partner?

It is imperative that OEMs understand that not all injection molding companies are equipped for micro-injection molding. OEMs must look for certain characteristics when selecting a micro-molding partner such as quality control, state-of-the-art equipment, and tooling experience. At ProMed, we offer customers a broad range of silicone material and equipment offerings, including micro-injection molding, which enables us to provide support as your business grows over time.

Manufacturers that perform micro-injection molding must have ample experience and expertise with micro-molding equipment. Equipment that is able to manufacture small parts via injection molding is not necessarily able to create micro parts. As noted above, micro-molding operates at very tight tolerances and very small masses – requiring exacting and repeatability that is often not feasible with standard injection molding equipment. OEMs need a manufacturer, like ProMed, that has the necessary know-how and state-of-the-art tooling and equipment to successfully manufacture micro parts.

Similar to injection molding, OEMs must ensure micro-injection molding companies meet the requisite regulations and quality standards for the healthcare sector. Clean rooms are one method that medical manufacturers use to meet these requirements. At ProMed, our manufacturing facilities are equipped with certified class 10,000 / ISO Class 7 clean rooms, demonstrating our strong commitment to quality.

About ProMed

ProMed was founded in 1989 to address an industry need for cleanroom manufacturing of silicone components, specifically those having a medical application. Over time, we broadened our product offerings to include assembly, micro-molding of highly engineered plastics, and combination products. We have garnered a reputation as the world benchmark of implantable silicone components and assemblies – and are one of few companies in the world to provide contract manufacturing of drug-eluting products.

ProMed has expertise in working with the full spectrum of silicones covering a wide range of properties and characteristics. We will assist in your material selection to help ensure all design requirements are met. Our manufacturing facilities and equipment are designed for a single purpose—to mold medical and implantable silicone, combination components, and bio-material grade plastics with uncompromising quality and service. We currently have four divisions that are located within two manufacturing sites. All are certified class 10,000 / ISO Class 7 cleanrooms.

We can identify the right manufacturing solution for any project. We have extensive experience in a wide range of injection molding techniques including:

· Automated Injection Molding

· Multi-cavity tooling

· Micro molds and micro molding

· Servo-controlled de-molding capabilities

· Insert molds, overmolds, and automation integration

· Transfer molding

· Compression molding

Click here to see why ProMed is your silicone injection molding partner. Contact ProMed today at 763-331-3800 to discuss your next silicone injection molding project

Lean Manufacturing in the Medical Sector

The concept of lean manufacturing, or lean as it is sometimes called, has been around for decades and focuses on streamlining production to improve value and productivity while minimizing waste. From a lean perspective, waste is considered anything that does not add value. 

What are the Key Strategies of Lean Manufacturing?

Below is a summary of the 5 key principles of lean manufacturing. When implemented effectively, lean manufacturing results in significant efficiencies and productivity gains that lower production costs – providing the competitive edge companies are seeking. These concepts can be successfully applied to any sector including medical manufacturing.

1. Value – this principle is based on how the customer defines “value”. It is nearly impossible to streamline a manufacturing process if the value points are not clearly understood.
2. Value Stream – this step involves mapping out the processes that contribute to the value stream from beginning to end. It often starts with raw material acquisition and ends when the final product is delivered to the customer. This is a crucial aspect of lean manufacturing as the purpose is to identify potential waste areas and then work to reduce or eliminate the waste.
3. Flow – once the waste is removed, the manufacturing operations should run more smoothly and efficiently. Teams should revisit the value stream to ensure all waste has been removed where possible.
4. Pull – with the process running more smoothly, products can be manufactured and delivered “just in time”, reducing inventory requirements and costs. This also results in shorter time to market, further driving competitiveness.
5. Perfection – the final principle is about continuous improvement as lean manufacturing is intended to be an on-going assessment to avoid waste and inefficiencies from creeping back into the process. Companies with a lean culture ensure all personnel are empowered to participate in continuous improvement efforts.

Looking for an efficient and reliable partner for your medical manufacturing project?
Contact ProMed to learn about our lean manufacturing approach and the range of silicone injection molding solutions we offer.

How is Lean Manufacturing Applied to Medical Manufacturing?

Let us now discuss how lean principles can be applied to medical manufacturing. There are several types of waste that are often identified when a lean approach is used in medical manufacturing: surplus inventory, unnecessary motion (of personnel or equipment), waiting (personnel or machinery), over-processing or over-engineering a product, off-spec product or other quality issues, inefficient logistics and transportation – and various others.

When lean principles are applied, these sources of waste are reduced, or even eliminated, improving operations efficiency and product quality – adding significant value for customers. With shorter production times, medical manufacturers are more nimble and able to respond to customer needs and market conditions. Additionally, lean strategies can be applied to supply chain and product development processes, leading to quicker speed to market and a significant competitive edge.  

At ProMed, the main focus of our lean manufacturing techniques is maximizing customer value while minimizing waste – and we empower every employee to make a difference. Our team achieves these objectives through the application of Lean Six Sigma methodologies. Six Sigma and lean are both process improvement programs used in medical manufacturing, each focused on the same goal: eliminate waste in order to elevate production efficiency.  

The professionals at ProMed monitor product and process performance during the development and production phases of manufacturing by incorporating Lean Six Sigma quality management principles. As part of our commitment to quality, we have certified Lean Six Sigma Black Belts on our team and we use a Lean Six Sigma Green Belt certification program to train our personnel on lean manufacturing principles. These efforts ensure we reliably deliver the highest quality products to our customers.

ProMed – Your Silicone Injection Molding Partner

ProMed was founded in 1989 to address an industry need for cleanroom manufacturing of silicone components, specifically those having a medical application. We have garnered a reputation as the world benchmark of implantable silicone components and assemblies – and are one of few companies in the world to provide contract manufacturing of drug-eluting products.

ProMed has expertise in working with the full spectrum of silicones covering a wide range of properties and characteristics. We will assist in your material selection to help ensure all design requirements are met. Our manufacturing facilities and equipment are designed for a single purpose—to mold medical and implantable silicone, combination components, and bio-material grade plastics with uncompromising quality and service. We currently have four divisions that are located within two manufacturing sites. All are certified class 10,000 / ISO Class 7 cleanrooms.

We can identify the right manufacturing solution for any project. We have extensive experience in a wide range of injection molding techniques including:

• Automated Injection Molding
• Multi-cavity tooling
• Micro molds and micro molding
• Servo-controlled de-molding capabilities
• Insert molds, overmolds, and automation integration
• Transfer molding
• Compression molding

Click here to see why ProMed is your silicone injection molding partner. Contact ProMed today at 763-331-3800 to discuss your next silicone injection molding project.

Liquid Silicone Rubber vs High Consistency Rubber for Medical Device Components

Silicone elastomers have long been a popular material for medical devices and medical device components due to their durability, ease of molding by many methods, wide temperature range, chemical inertness, high tensile strength, vast range of available durometers, low toxicity, and compatibility with many sterilization methods. Furthermore, silicone is compatible with human tissue and body fluids, has a very low tissue response when implanted, and does not support bacteria growth – making it a perfect option for implants due to its excellent biocompatibility.

Silicone elastomers are available in two commercial forms: Liquid Silicone Rubber (LSR) and High Consistency Rubber (HCR). HCR is known for its gummy consistency and mostly comes in partially vulcanized sheets. LSR is a newer technology and starts out as a 2-part liquid that cures into a solid form when mixed. LSR generally comes in buckets and has a longer shelf life than HCR.

Medical device OEMs often face a tough decision: should we use HCR or LSR for our medical device component manufacturing? LSR and HCR are both used to manufacture medical device products; however, there are some key differences. The following compares LSR and HCR to shed some light on their differences and when each should be utilized.

Viscosity Difference Leads to Different LSR and HCR Manufacturing Techniques

The performance characteristics of HCR and LSR are relatively similar; however, viscosity is a key differentiator between LSR and HCR, and has a significant impact on the equipment and processes used to manufacture each of these elastomers.

Simply put, viscosity is a measure of a material’s ability to flow. A low viscosity indicates a material is less viscous and more readily flows where a high viscosity indicates a material is more viscous and less apt to flow well. For reference, water has a relatively low viscosity and easily flows whereas molasses has a higher viscosity and is more resistant to flow.

LSR has a lower viscosity than HCR. Due to the lower viscosity, LSR is most often processed via injection molding. LSR’s desirable handling properties and lower shrink rate make it an excellent choice for manufacturing highly complex geometries and intricate products. Additionally, due to the automated nature of injection molding, LSR can produce high volumes of components in a short period of time. For this reason, deciding whether HCR or LSR injection molding is the better choice for your project largely depends on the production volume required.

A lower viscosity makes it easier for manufacturers to mix additives into LSR. Additives that can readily be incorporated into a batch of LSR include colorants, desiccants, barium, and pharmaceuticals such as hormones or steroids. For these reasons, LSR is a great option for medical devices such as combination products. The low viscosity of LSR and the temperatures needed to vulcanize LSR are usually low enough that significant degradation of compounded substances, like Active Pharmaceutical Ingredients (APIs) that are used in combination products, can be avoided.

Due to its higher viscosity and more challenging handling properties, HCR is typically processed using compression and transfer molding methods, which are more labor-intensive. In some cases, HCR is used in injection molding projects.

OEMs Often Prefer LSR

For companies already using HCR to manufacture medical device components, it may make sense to continue using this elastomer especially since the initial capital equipment costs have already been made. For new product development, however, LSR is often the best choice given the lower capital costs and labor associated with processing this elastomer. Due to its lower manufacturing cost and versatility with formulations, companies often prefer LSR over HCR – but the decision is on a case-by-case basis.

ProMed’s Silicone Manufacturing Capabilities

At ProMed, we combine industry-leading medical-grade LSR and HCR expertise with the latest developments in silicone materials and technology. We have garnered a reputation as the world benchmark of implantable silicone components and assemblies. From helping OEMs incorporate the latest medical-grade silicone formulations into their designs to delivering rapid silicone prototypes, we serve as a premier silicone molding contract manufacturer for medical device OEMs.

ProMed has expertise in working with the full spectrum of silicones covering a wide range of properties and characteristics. Our wide range of materials include: Liquid Silicone Rubber (LSR) 5 to 80 Durometer, High-consistency Rubber (HCR): 20 to 80 Durometer, Room Temperature Vulcanizing silicone (RTV). We will assist in your material selection to help ensure all design requirements are met.

Our manufacturing facilities and equipment are designed for a single purpose—to mold medical and implantable silicone, combination components, and bio-material grade plastics with uncompromising quality and service. We currently have four divisions that are located within two manufacturing sites. All are certified class 10,000 / ISO Class 7 cleanrooms.

Contact ProMed today at 763-331-3800 to discuss your next medical device project.

Implantable Drug Delivery Devices – An Overview

Introduction

Implantable devices are called upon to serve a variety of functions, from vascular stents that preserve blood flow to electrostimulation devices that regulate heart rhythm or block spurious signals in the brain, to orthopedic devices that mechanically reinforce the spine or restore range of motion of hips and knees. For over a decade there has been an increasing convergence between implantable devices and drug therapies, including devices that deliver drugs as a primary of action. This article reviews some representative applications that materials and processes device designers can leverage in developing new products for these growing markets.

Why implantable devices for drug delivery?

Implantable drug delivery devices offer several advantages over conventional oral or parenteral dosage forms. First, implantable devices allow site specific drug administration where the drug is most needed. Examples include implants used in the treatment of brain tumors (Gliadel® wafer) or prostate cancer (Lupron® depot). This may also allow for significantly lower doses of drug which can minimize potential side effects. Second, implantable devices allow for sustained release of a therapeutic agent, as highlighted in the accompanying illustration (Figure 1). The last and perhaps most important advantage is patient compliance, as the treatment regimen associated with an implantable device is generally less burdensome than pills or injections.

Figure 1: Idealized comparison of tissue drug levels for injections compared with an implantable drug delivery device. Clearance of the drug after an injection may result in significant time outside of the therapeutic window.

Types of drug delivery devices

Implantable drug pumps are used to deliver insulin in the treatment of diabetics and to administer pain medications directly to the spine (intrathecal pumps). These are typically programmable “active” devices which require regular resupply of the medication through an access port. Subcutaneous solid implants, conversely, provide long-term, “passive” release without the need for replenishment. Typically found as thin flexible rods or “matchsticks”, these delivery systems are particularly effective for the delivery of highly potent drugs such as hormones. Commercial examples include histrelin implants for the palliative treatment of prostate cancer and uterine fibroids(Vantas®), and early puberty in children(Supprelin®), levonorgestrel (Jadelle®) and etonogestrel (Implanon®) implants for family planning, and buprenorphine for the treatment of opioid addiction (pending FDA approval). Additional indications in development include subcutaneous implants for treatment of schizophrenia, breast cancer, photosensitivity, and Parkinson’s disease.

A number of promising solid implant applications can be found in ophthalmology for the treatment of macular edema and retinal vein occlusion using corticosteroids (Osurdex®), with products in development for the treatment of glaucoma (prostaglandins) and age-related macular degeneration (anti-VEGF).

Opportunities in women’s health

In addition to subcutaneous implants, novel drug delivery forms such as intrauterine devices (IUDs) and intravaginal rings (IVRs) and are finding increasing applications in the area of women’s health. For more than two decades after serious safety issues were encountered with the Dalkon shield, no IUDs were marketed in the US. In 2000 the FDA approved a levonorgestrel eluting IUD (Mirena®) providing contraception for up to 5 years of use. Later, use of the device was expanded to include an indication for severe menstrual bleeding and a smaller device (Skyla®) has been approved for women who have not had children. IVRs are commercially available for contraception (Nuvaring®), hormone replacement therapy (Estring®), and to improve the rate of in vitro fertilization (in development).

Contraceptive devices used made from silicone (IUD, left) or ethylene vinyl acetate (IVR, right)

Materials for drug delivery

As with all implantable devices, key materials considerations for use in drug delivery include biocompatibility, stability and durability (except in the case of biodegradable drug delivery systems), and the ability of the material to control release of the active pharmaceutical ingredient (API). Silicones have long been a material of choice for drug delivery given their extreme chemical inertness, range of stable mechanical properties, and ability to compound various APIs within the matrix. The rate of release is generally proportional to the loading of drug within the silicone, typically 5-50% by weight. Ethylene vinyl acetate (EVA) is also finding use in drug delivery application due to the additional ability to control release rate by varying the vinyl acetate content. Like silicone, EVA is processed at relatively low temperatures, typically 150-250oF, which helps to minimize risks associated with degradation of the API. Polyurethanes and acrylate hydrogels have also been utilized in select applications.

Another option is to use a biodegradable material such as poly(lactic-co-glycolic acid) or PLGA to controllable release the drug while essentially “dissolving away” by hydrolysis to produce lactic and glycolic acid. While clearly most developers exhibit a preference for materials with an established history of use in vivo, new materials for drug delivery remain an active field of research, including tyrosine-derived polycarbonates which have the added benefit of being inherently radiopaque.

Processing of drug delivery materials

All of the above materials lend themselves to manufacturing processes based on molding or extrusion. At ProMed, work has historically focused on molding silicone drug delivery devices using injection and compression molding techniques. Several factors must be considered in optimizing the material formulation and developing a robust molding or extrusion process. The material system (e.g. liquid silicone vs. high consistency rubber), mixing or compounding technique, API particulate size cure temperature, and pressure will all potentially affect the drug release consistency and drug content uniformity of a manufacturing lot. In some cases, co-extrusion or over molding of a thin, drug-free layer has been used to enable more uniform release of drug from the implant.

Prototype mold for production of subcutaneous implants

Site-specific, controlled release of therapeutic agents represents an attractive option for companies looking to enhance the efficacy of an existing drug product or provide additional benefit in conjunction with an implantable device. A small but well-established pallet of durable and biodegradable polymeric materials provides options for delivery of potent compounds such as hormones, opioids, antibiotics, and oncology drugs. Well-established silicone rubber and plastic forming processes can be leveraged to make commercial volumes of devices with excellent consistency and reproducibility.

This article was written by James Arps, Ph.D., Director, ProMed Pharma LLC