Over the past few years, the rise of miniaturised medical devices has helped reshape the industry. Driven by rising healthcare costs and the shift to home-based outpatient care, hospitals, medical practitioners and patients are demanding products that are smaller, lighter and more portable than ever before.

While the finished products – from implantable defibrillators to wearable health monitors – tend to grab the headlines, for devices to decrease in size and increase in efficiency, it is the components inside them that must fundamentally change.

For component manufacturers, miniaturising a medical device can be achieved in several different ways. But one of the most important is through micropumps – scaled down versions of a normal macroscopic pump that play an essential role in managing and dispensing gas and fluids.

“When we look at the growing trend in the medical device sector towards getting devices into the hands of end users, homecare – and hence, portability – are critical,” Abelardo Gonzalez, adjunct professor at Saint Xavier University, said in a recent article for MD+DI. “This trend has led to device miniaturisation and the proliferation of micropumps.”

All shapes and sizes

As well as their size, small pumps are associated with lower production costs, fewer leaks, decreased power consumption and increased accuracy owing to the controlled flow of fluids and delivery of drug dosage into the body. “Because of their reduced dimensions, micropumps weigh less and use less space than their macroscopic counterparts,” says an online resource from the Southwest Center for Microsystems Education.

“They have the ability to handle extremely small volumes of liquid very efficiently,” the resource adds. “The medical industry is taking advantage of these characteristics. A small drop of blood (rather than a vial of blood) can be extracted from a patient and distributed on a chip for analysis by using a micropump. Micropumps are being developed that can be used in vivo or internal to the pump.”

The first microelectromechanicalbased micropump was introduced in the 1980s by Jan Smits for use in insulin delivery systems, which control the blood sugar level of diabetic people.

Since then, micropumps have been developed in a variety of medical applications including transdermal insulin delivery, blood transportation through artificial hearts, injection of glucose and drugs, hormone treatment, and pain and wound-care management. Many consider the devices to be the ‘beating heart’ of the microfluidics industry, where microminiaturised devices are developed with chambers and tunnels through which fluids can flow.

According to a September report by Market Research Future, the global micropump market is anticipated to expand at a compound annual growth rate of about 19.4% during its forecast period of 2018–27. the US dominates the micropump market, the report adds, owing to increasing investment in healthcare, and micropump manufacturers significantly upgrading their factories and manufacturing capabilities.

While micropumps come with different shapes, flow-rate capacities, pressure and vacuum ratings, most models fall into two broad categories: mechanical micropumps, which have moving parts that create a higher pressure in the fluid inside the pump, and non-mechanical micropumps, which cause movement of fluids through other means, such as electric fields, heat and magnets.

“Different micropumps are effective and suitable for different applications, which can be determined by analysing various performance parameters such as flow rate, pressure generated, operating voltage and size,” said Partha Kumar Das, a lecturer at the Bangladesh University of Engineering and Technology, in a recent academic paper.

Disc Pump cycles in 20,000 per second, which is one or two orders of magnitude faster than traditional pumps, and above the limit of human hearing.
– Tom Harrison, TTP Ventus

This year’s model

One popular mechanical model is the peristaltic pump, which works when rollers or shoes within the pump rotate and compress the tube or hose.

This creates a vacuum that then draws fluid through the tube. Some manufacturers specialise in producing the pumps, which can be used for irrigation, waste removal and other medical applications.

Peristaltic pump technology is suited to the aforesaid applications beacause users can easily dispose of the tubing afteran individual procedure. This ensures that no cross-contamination occurs, which can prove fatal if untreated.

Another common mechanical model is the diaphragm micropump, which is usually comprised of a pumping chamber that is connected to the inlet and outlet valves necessary for flow rectification.

“As the diaphragm deflects during the expansion stroke, the pumping chamber expands resulting in a corresponding decrease in chamber pressure,” explains an article written by several academics in the journal Microfluidics and Nanofluidics.

“When the inlet pressure is higher than the chamber pressure, the inlet valve opens and liquid fills the expanding chamber,” the article adds. “During the compression stroke, the volume of the chamber decreases with the moving diaphragm, causing the internal pressure to increase whereby liquid is discharged through the outlet valve.”

Diaphragm micropumps use a number of different actuation mechanisms, most notably actuators that use piezoelectric materials, actuation that uses electrostatic forces and electromagnetic actuation that uses a permanent magnet attached to a diaphragm and surrounded by a coil.

“While there are differences among them, all diaphragm pumps can be delivered in a smaller form factor than other pump types,” said Gonzalez for MDDI. “Diaphragm pumps are an excellent technology when you are trying to achieve a good trade-off between performance, size and lifespan.”

The power of three

Of course, diaphragm pumps are not the only game in town, with new models are regularly hitting the market. At last year’s American Association for Clinical Chemistry (AACC) annual meeting, TTP Ventus showcased the Disc Pump, a new ‘silent’ micropump platform based on ultrasonic resonance. The company claims that the micropump could be particularly useful in point-of-care diagnostic devices, offering less irritation to patients and disruption to healthcare workers.

“Disc Pump cycles in 20,000 per second, which is one or two orders of magnitude faster than traditional pumps, and above the limit of human hearing,” said Tom Harrison, business development manager at TTP Ventus, in an interview with Technology Networks. “This makes our pump silent, which satisfies the growing consumer appetite for quieter products – whether for home or hospital use. “A second benefit of high-frequency operation is that each pump cycle can move a smaller quantity of air than compared with a low-frequency pump, in order to deliver the same pumping output. This results in a reduction in pulsatility in the pump output, providing more stable pressure and flow. In our case, the reduction in pulsatility is so substantial that the pump is virtually pulse-free. This eliminates mechanical vibration, too.”

Whatever the model, designing and engineering a micropump is not easy. In a recent article for Medical Design and Outsourcing, Sam Ruback, product manager at Parker Hannifin Corporation summarised three of the core engineering challenges, “Valves and pumps must consume less power so batteries can be smaller and yet last longer… must better integrate into manifolds to consume less and cannot sacrifice flow rates, create thermal issues or increase costs,” he said.

In the end, every application has different performance requirements and will therefore need a unique micropump solution. Much of the responsibility for this falls on the component manufacturers, who have become increasingly powerful in recent years as OEMs outsource most of their design and engineering functions.

Industry experts say OEMs and suppliers should engage with each other as early on in the design process as possible. When choosing a suitable micropump, manufactures must gain a “clear definition from the marketing team of the criteria for a successful product release,” said Dan Schimelman, then of Hargraves Technology, in a 2009 article for World Pumps.

“Then, it is important to prioritise these capabilities and select the components and their respective performance specifications needed to best meet the ranked criteria,” Schimelman said. “Since there are usually trade-offs, this will help to ensure that major product objectives are met and that development timelines don’t suffer from subsequent changes to the project scope.”

Future developments

Micropumps are being used for new medical applications. Recently, for example, Sensile Medical announced it had developed a wearable micropump for a European pharmaceutical company that is designed to treat Parkinson’s disease. The device uses Sensile Medical’s patented SenseCore micro rotary piston pump and a personally programmable basal profile that enables patients to receive the precise dosage they need.

“In developing the micropump for Parkinson’s treatment, we have completed a highly ambitious project to exacting requirements that improves treatment for patients,” said Derek Brandt, CEO of Sensile Medical, in a news release. “The device comes with a large number of different languages already on board, enabling its use in many countries around the world.” Researchers at Pennsylvania State University working under Tony Huang, a professor of engineering science and mechanics, have demonstrated a cost-effective acoustofluidic micropump solution for lab-on-a-chip disease diagnosis.

The micropump is powered by a miniaturised piezoelectric transducer that oscillates a series of sharp-edged structures hundreds ofmicrometres long that have been constructed onto the side wall of a microfluidic channel made of PDMS, the widely used, silicon-based organic polymer.

“The field of microfluidics and lab-ona- chip technologies has the potential to revolutionise the healthcare industry with cost-effective, high-performance miniature biomedical diagnostic devices,” said Huang in a news release. “Despite its tremendous potential, the field has only delivered very limited numbers of products and tools for realworld applications. It is difficult to fabricate micropumps that are simple and inexpensive, yet effective.”

Of course, while a lot of progress has been made in micropump research, development and performance in practical applications, work must be done in designing new models and making those that exist work more efficiently, across a range of medical applications.

“There is still a need to design more versatile micropumps that can meet multiple applications with much more effectiveness,” concluded Kumar Das.