Polymers for Better Injection Devices
Injector Pen Materials Help Make Treating Diabetes Easier
Pharmaceutical companies took the promise of simple, pen-like insulin injectors for treating diabetes to new levels in devices using DuPont™ Delrin® acetal and Zytel® nylon resin as the injector pen materials.
While the devices, and challenges, are quite different, the results in these cases are clear: better devices and better treatment options.
Autopen® 2: Giving Patients More Control
For UK-based Owen Mumford company, DuPont TM Delrin® provided low friction and strength for the Autopen® 2, which improved patient comfort and provided more control over insulin dosing.
While compact insulin injectors provided convenience and simplicity, some had a significant user issue. Once a dose had been set by the user, it could not be reduced by winding the knob in the reverse direction. Instead, the user had to expel the set dose and redial. That led to wasted medications, risk of misdosing, and frustrated users.
The Owen Mumford company of Oxfordshire, England, sought to improve patient control with a patented mechanism for its Autopen® 2 insulin injector that would let users correct a misdialed dose.
The design of the Autopen® 2 lets users select a dose and press a trigger to inject the insulin. If too large a dose is selected, the button on the top of the dose selector allows the dose to be sequentially reduced to the correct level, prior to injection. But what is simple and clear for users is actually the result of sophisticated design, production and high-performance plastics.
For instance, the Autopen® 2 locking bushing, which prevents the rotational movement of the leadscrew during delivery of the medication, is molded from a toughened grade of Delrin®. This allows it to withstand high torsional forces, particularly during dose setting.
As another example, the dose knob is molded in a laser-markable grade of Delrin® for incorporation of insulin measurements. However it must also provide a robust surface for two sets of gear teeth within the part, which works with the rewind button to allow the spring to unwind as part of the dose correction procedure.
A further five parts are molded from Delrin®, including the drive gear, rewind button, dose knob cover, ratchet drive shaft and cartridge compression cup. Rigorous and comprehensive testing confirmed the compliance of Autopen® 2 with the international standard ISO 11608 for pen-injectors.
Durability is key for the Autopen® 2. It can dispense up to 72 units of insulin per injection, and is designed to be refilled with a new insulin cartridge and used again and again. The Autopen® 2 includes intricate, geometrically advanced parts that move against each other, and Delrin® offers a range of properties to support performance, including:
- Strength and stiffness
- Dimensional stability
- Fatigue resistance
- Low coefficient of friction and resistance to wear
“Of all the plastic parts used within the Autopen® 2, seven are molded from Delrin®, and they represent all of the mechanical and robust components fundamental to its operation,” confirms Mark Eaton.
“We would not have been able to produce the Autopen® 2 without DuPont materials.”
The Delrin® products were supplied to Owen Mumford by Distrupol, DuPont’s authorized distributor of its performance polymers in the UK. Both Distrupol and DuPont provided additional technical assistance with regard to reducing friction within the dose setting and delivery mechanism.
Autopen® is a registered trademark of Owen Mumford Ltd.
An Insulin Pen Designed to Reach More People
For Indian pharmaceutical firm Wockhardt, Delrin®, Zytel® and Crastin® are key plastic materials in the manufacture of simple, safe and durable, insulin pens which are making diabetes treatment available to many more people.
In India, there was gap in bringing convenient diabetes care to patients who could benefit from it. Doctors needed affordable, simple, durable insulin pens made to high safety standards and reliably available. In response, the Indian pharmaceutical company, Wockhardt, contracted Industrial Design Consultancy Ltd. (IDC) of Datchet, UK, to design a completely new insulin pen.
The final insulin pen design created by IDC is made entirely from plastic, making it light, strong, affordable – and about the size of a marker pen.
Key moving parts are manufactured from Delrin® and Zytel® polymers. The two polymers are used in the clutch tube and locking sleeve (both Delrin®) and the drive shaft, inner housing, thumb pad and piston rod cap (all Zytel®).They provide strength, as well as natural lubricity necessary in the intricate system of ratchets and gears used within the pen’s delivery mechanism.
The pen’s dose dial and clip are made from another DuPont material, Crastin® PBT. This material provided excellent dimensional stability as well as visual appeal and suitability for printing..
For medical device polymer applications, Delrin® provides:
- Dimensional stability
In medical dispenser applications, Zytel® provides:
- Low-friction against POM
- Impact strength
- Elastic modulus
The benefits of Crastin® include:
- Visual appeal
UnoPen™: Making Patient’s Lives Easier
Ypsomed AG, an independent drug injection systems developer and manufacturer located in Burgdorf, Switzerland, found DuPont™ Delrin® to be the optimal material for key components of its UnoPen™ disposable injector pen. With the help of Delrin® SC699,which provided ultra-low-friction properties, Ypsomed AG is able to deliver to patients a product that is easy to use.
Developing an injector pen that provides ‘ease-of-use’ characteristics requires innovative design and the proper materials. Low friction is one of the key resin attributes that contributes to the usability of an injector pen. Ypsomed AG was in need of a material for use in the dose dial sleeve of the state-of-the-art UnoPen™. Located between the housing and the piston rod, the dial sleeve is used by the patient to set the required insulin (or other drug therapies) amount. This part interacts mechanically with the piston rod and together they help dispense the proper medical dosage. Low friction between these two parts is critical to the functionality of the injector pen. With less friction, the patient can apply less force when using the medical device.
Following the testing of many polymers on the market, Ypsomed AG found that DuPont ™ Delrin® (Special Control) SC699 acetal resin fulfilled the requirements more successfully than competitors. Delrin® SC699 provided the necessary low-friction qualities to the part that needed it the most. Stefan Burren, manager of product development at Ypsomed explained, “The friction properties of Delrin® SC699 used for the dose dial sleeve are fundamental to the pen’s ease of use.” Delrin® SC699 also delivers a part that exhibits the required strength and stiffness to ensure both reliable and durable mechanical performance. Using a masterbatch, Delrin® SC699 is compatible with laser marking for indication of the dose settings. In addition, it provides EU and FDA food-contact compliance and provides compliance with USP Class VI and ISO 10993-5 and -11 testing requirements.
The UnoPen™ allows patients to use less force when selecting the required medicine dosage. The lubricity of Delrin® SC699 assisted in making this possible. The Delrin® family offers resins that are strong and have excellent stiffness which creates dependable parts for medical devices. Its suitability to be manufactured at high volumes can help to create cost savings, while not losing the ability to be used for parts that require high precision. Ypsomed AG took advantage of all these benefits that Delrin® SC699 provides to developers and manufacturers.