From ambulance to operating room, recovery room to discharge at home, patients today encounter any number of medical devices that must be lightweight, small, safe, and often, portable. To maintain these safe, hygienic designs, most medical device manufacturers rely on pneumatics because they are highly customizable and compact.
As the demands for these types of components have evolved, so have the pneumatic cylinders and valves used in them. The need for smaller, lighter devices has translated into a push for valves that offer more flow at lower power (often battery power). In addition, this all means the need for lighter materials, so plastic has grown in use, said Bonnie Martens, marketing communications specialist at Kalmazoo, Mich.-based Humphrey Products.
“The need for increased flow from smaller valves at lower power is driving the change in the solenoid valve arena,” said Martens. “Additionally, the need for quiet valves is also driving these new designs.”
Rob Clippard, vice president of sales and marketing at Clippard Instrument Laboratory, Cincinnati, added that Clippard innovated the internal workings of these innovative pneumatic valve designs. “Clippard is the benchmark for valve technology used in medical devices. Our spider design or flat armature spring element provides a valve that is quiet, fast, reliable, and has exceptional life,” he said.
The need for higher flows and lower power consumption was what drove Clippard to redesign its benchmark valve design, coming up with its new DV valve, which offers flows up to 100 lpm and only consumes 1.9 W in power. Additionally, Clippard said that the company also offers power saving circuits and latching valves in applications where low power use is critical.
Adaptation is critical
Pneumatics is used heavily in oxygen concentrators, infusion pumps, ventilators, wound therapy, blood analyzers, pressure cuff devices, medical bed surfaces, breathable gas delivery systems and anesthesia devices because they all use some type of gas to control their functions.
But because pneumatic components were initially designed for industrial use, manufacturers have had to adapt their use to medical designs. “The challenge is making an industrial-grade product work in a medical device because their needs are different than industrial applications,” said Paul Gant, sales manager at AVENTICS, the newly branded company that was formerly Bosch Rexroth’s pneumatics division, based in Lexington, Ky.
However, this forced adaptation has allowed for some unique innovations because there aren’t a great deal of regulations or standards that restrict design, Gant added. Although RoHS, REACH and ISO standards are critical to design, there is no one rule to follow. “If you come up with a pretty good idea, there’s not a lot of history or regulations that tie you from using that product,” Gant said.
Clippard added that adjustments to standard products are application specific. “For example, increasing pressure on the blood pressure monitoring cuffs now would allow you to market your product as a tourniquet,” Clippard said, concluding that most medical device manufacturers are looking for partners that can help them simplify their design and manufacturing process.
In the majority of cases, the relationship between pneumatics companies and medical device manufacturers becomes an engineering partnership.
For example, Humphrey was recently recognized for its work with Stryker Medical. Stryker was honored with a 2014 Medical Design Excellence Award through the Medical Device and Diagnostic Industry for its newest hospital bed technology—the Isolibrium critical-care air support surface. The goal of the device is to serve as a tool for nurses to care for patients while the pressure redistribution system helps prevent pressure ulcers in patients. Humphrey was recognized as a “supplier to a winner” for its efforts in the design of the pneumatic controls portion of the Isolibrium Surface.
In another application, Humphrey’s custom valve assembly (pictured) enabled a respiratory care manufacturer to provide critical pressure monitoring when delivering a CO2 – O2 mixture to patients suffering from toxic gas or smoke inhalation.
Gant said AVENTICS’ key involvement is with oxygen concentrators. Meeting the low-pressure needs of portable oxygen concentrators (POCs) was a challenge, he said. These portable designs were reduced from 10 lb to about 2 or 3 lb, so adapting an industrial valve to this smaller, lighter weight design required some product redesigns. In industrial settings, pilot-operated valves operate at about 40 psi to open a larger valve. But these medical devices were operating at pressures in the range of 3 to 7 psi.
“One of our challenges was to reduce the operating pilot pressure and still use a dual-stage valve, which gives you high flow, but have it operating at less than 6 or 7 psi,” Gant said. “To accomplish this, we used polycarbonate bodies that we designed to maximize the area of the operating valve.”
As he explained, the physics of fluid power is simple—the pressure to open something is based on the size of what you’re pushing. In most valves, the actual operating element is tiny compared to the valve body. “What we needed to do was make the body smaller and the operating element a larger portion of that whole percentage,” Gant concluded.
Getting into the Internet of Things
Automation and diagnostics have become a critical part of medical devices, and increasingly, pneumatic components are supporting this need for data transmission, said Gant.
“What this means for pneumatics, is that if the machine is going to get more automated, the pneumatic devices change slightly to where something that might have been a manual device—a toggle valve or something like that—now suddenly has to be electronic and guided by a PLC or motherboard,” Gant described, saying that things like pressure control must be electronic and changeable depending on what the device is.
“Theoretically, the more information they have, the more they can tailor your treatment to you. It gives you the best care, but that also means, perhaps, less procedures and less hospital care because more things can be done through the better diagnostics,” Gant concluded. “All of these things lead to better personalized healthcare.”
Clippard Instrument Laboratory
Pneumatics: the heart of the heart
As it worked to perfect its artificial heart design, SynCardia Systems, Inc. turned to Bimba Manufacturing, University Park, Ill., for a custom pneumatic cylinder that could be the main actuator of its Freedom portable driver, the wearable power unit driving the heart. As Tom Carlson, manager of service excellence at Bimba said, SynCardia chose the pneumatics company because, “Bimba is known for diving into and becoming intimately involved in special designs and that’s exactly what this one was. It required Bimba’s engineering to really plug in and connect with Syncardia’s engineering, and in this instance to work hand-and-hand and become an engineering resource or arm of their engineering department.”
It helped that the lightweight designs of Bimba’s cylinders were highly compatible with the designs that SynCardia already had in place. The 13.5-lb Freedom driver can be carried in a backpack, shoulder bag, walker or a rolling caddy. It powers the Total Artificial Heart with precisely calibrated pulses of air and a small amount of vacuum so that the diaphragm is in the proper position to accept the next filling of blood into each artificial ventricle.
Like a heart transplant, the SynCardia Total Artificial Heart is designed to eliminate the source of end-stage biventricular failure by replacing both failing ventricles and the four heart valves of a patient. The Freedom runs on lithium-ion batteries that are re-charged using a standard electrical outlet or a car charger that can be used in autos and many boats.
The good news, too, is that SynCardia just received FDA approval on June 26 for use with the SynCardia temporary Total Artificial Heart as a bridge to transplantation in cardiac transplant candidates who are clinically stable. This means instead of just a select few test patients, the device is open for use by more clinically stable patients. Until now, the Freedom driver was in a FDA Premarket Approval Study, for 106 prequalified patients.
The SynCardia Total Artificial Heart with the Freedom Drive System allowed 75% of those patients to be discharged from the hospital, while 86% of the 106 patients either were bridged to heart transplants or were alive and supported by the SynCardia Total Artificial Heart and the Freedom driver as of June 30, 2014.
Although the Bimba component is fairly simple—a custom pneumatic cylinder—it is a crucial part of the Freedom driver. “We supply the main driver, or the heart of the heart pump, if you will,” said Carlson.
Bimba’s custom actuator acts more like a pump, as it is actuated by a motor supplied by SynCardia. “That actuation is helping to pump the diaphragms that are inside a patient,” Carlson said. “Instead of using compressed air to make it move, they’re (SynCardia) using a motor to make the cylinder supply air.”
What attracted SynCardia to Bimba was its normal materials of construction. The cleanliness offered by Bimba’s thin-walled stainless-steel actuators was an added bonus to how compact and lightweight it already was.
“The Bimba actuator is probably the size of a beer mug that’s encapsulated into a 12 x 12 x 5 in. cube that the patient would put on a backpack and walk around,” Carlson said.
On the outside, Bimba’s actuator helps actuate the diaphragm inside the artificial heart’s ventricles that are surgically implanted inside the patient. Two diaphragms are positioned inside the ventricles, which are connected to the external Freedom driver. The driver is connected to the heart via two small air tubes, which are connected to Bimba’s cylinder. When actuated, the cylinder pumps the diaphragms of the artificial heart, acting much like a natural heart as it pumps blood through the body.
SynCardia Systems Inc.