Choose the Right Drive System for Your Biologic Injection Device

Thanks to advances in biotechnology, new and innovative biologic drugs are gaining popularity. That’s good news for patients, but biologics present drug delivery challenges.

Recently developed biologics are complex drugs whose molecular weight can reach as much as 150,000 daltons (Da). As a result, biologic drugs tend to have high viscosities — much higher than those of synthesized drugs. These high viscosities make the injection profile crucial for the proper delivery of the drug, so the system that drives the delivery mechanism is key to the biologic delivery device’s effectiveness, manufacturability and cost. Design engineers must choose from a wide variety of motors and gearheads. To help simplify your selection, here are the key performance elements for drug delivery devices along with a review of the different technologies that can address them:

A comparison of key performance characteristics for different motion technologies

• Torque/power. All technologies offer the ability to produce torque, but their internal designs present different output capabilities. BLDC slotted designs deliver higher output torque than BLDC slotless, based on the higher amount of copper and magnets in the motor. When considering stepper motors, hybrids provide the highest torque.
• Speed. The drug will dictate the duration and flow for the therapy, so the device speed will be set. You can meet higher speed requirements with brushless DC and disc magnet stepper motors. Brush DC motors can satisfy medium speed requirements, while steppers can handle lower speed requirements. To increase output torque, you can add a gearbox and thereby increase the speed requirements on the motor by the corresponding ratio.
• Efficiency. Biologic drug delivery devices rely on battery power, so an efficient system will keep the battery size low. Brush DC coreless and brushless DC slotless motors have a rotor-based design, making them the best choices for an efficient system.
• Reliability. The device will have a specific life requirement based on the number of therapies to be delivered to the patient. Motor life will be determined by the commutation and bearing systems. Brush DC motors have a mechanical commutation, meaning that the motor life is dictated by brush wear. Brushless DC and stepper motors have electrical commutation, which provides a potentially longer motor life. Bearings also affect motor life, with ball bearings providing longer life than sleeve bearings. Motor technologies offer both bearing versions, with some providing them as standard and others requiring customization.
• Weight. Because these devices are portable, weight is important to patient comfort. Brush DC coreless motors offer the best option with regard to weight.
• Cost. Each technology has a cost profile based on its design. The device and accompanying therapy will mandate a cost profile for market acceptance, so be sure to understand the cost drivers for each technology.

Partner Early With Your Motor System Supplier

As biologic drug treatments continue to expand in the market, each application will present its own challenge according to biologic therapy requirements. We recommend connecting with a motor supplier early in the development process to help determine the best motor technology and accessories that will create an optimal drug delivery device.