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MEDICAL & PHARMACEUTICAL


INDUSTRY FOCUS


motion solutions for biologics B


iopharmaceuticals have revolutionised the treatment of many illnesses. Commonly known as biologics, these drugs have the


ability to change the way the human immune system reacts, down-regulating the inflammatory response or supporting tumour-specific defence. Biologics are delivered by injection and


accuracy is critical. With the drugs typically administered at regular intervals, reliance is placed on the delivery mechanism, which is driven by a miniaturised motion solution. The type of biologic determines several factors


including the frequency and type of injection, as well as selection of the tissue type to be injected. These factors also impact the selection of the biologics injection device, and in turn, the required attributes of its motion system. Disposable devices are intended for one-


time use of a specific drug, delivered in the range of seconds to hours, and are a low-cost solution. These are mechanical injectors and disposable patch pumps, worn directly on the body with a reservoir, pump and infusion set inside a small case worn. Can-stack stepper and brush DC motors are commonly used because they are reliable and cost effective. Limited use, motorised solutions separate a


disposable drug unit from the reusable pump system and enable the infusion of multiple biologic drug cartridges over the course of the


therapy. As these may administer more than one type of biologic, each with its own viscosity and injection requirements, flexibility in injection force is advantageous. This means that a motion solution that can deliver a range between 50N and 80N is useful. Limited use devices are battery-driven, so efficiency also has to be considered in pump design. Coreless brush DC motors with precious metal commutators are suited to higher battery life requirements, offering high power density and reliability. A spur compound gearbox or custom gearhead pairing can also enhance performance. Fully reusable pump systems, which are


designed to be longer lasting and can handle various viscosities, can require a force output exceeding 100N. Worn by the patient, the motion solution has to be small and lightweight. Higher power density also means the system can accommodate drug volumes up to 50ml. A brushless DC motor or coreless brush DC


motor with precious metal commutators are the ideal selection to achieve these requirements. With efficiency and size parameters, BLDC


slotless designs are comparatively more efficient, lower vibration, and easier to manufacture for smaller frame sizes


such as 10mm, 12mm and 16mm, compared to slotted motors. The motors should


also be combined with a spur or custom-designed gearhead to optimise torque density. To ensure optimum delivery accuracy, an


absolute or incremental encoder with


a special arrangement can be combined to provide feedback and additional repeatability. As reusable pump systems could be used for


three to five years, the motion solution has to be robust. Brushless DC and stepper motors have electrical commutation, which provides longer motor life potential compared to the mechanical wear inherent to a brush DC motor. Motor life is also dependent on bearings, with ball bearings providing longer life than sleeve bearings. A tailored approach to motion system design


will most closely deliver the requirements for the specific biologics involved. This will also help the OEM deliver the most cost-effective solution.


Portescap www.portescap.com


JULY/AUGUST 2022 DESIGN SOLUTIONS 17


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