MEMS-Enabled Artificial Lung
In a pioneering approach to artificial organ development, engineers at Draper Laboratory in Cambridge, Mass., are applying semiconductor manufacturing technology to the development of artificial organs such as lungs and kidneys.
Intricate internal structures produced via micro-electromechanical systems (MEMS) are being tested as vascular systems that could oxygenate a person's blood during surgery. They also could function down the road as part of an implantable device.
"This is important because oxygenators currently used during heart surgery use a significant amount of anticoagulants," says Dr. Jeffrey Borenstein, principal investigator in the tissue engineering research being conducted at Draper.
Most artificial lung devices used today consist of hollow, porous fiber bundles inside a hard-shelled jacket. Oxygen is introduced through the fibers and diffused into blood flowing around the fibers. This process often damages the blood for maximum membrane exposure.
Adverse interactions between the blood and device materials such as polyethersulfone may cause clotting. Preventing this requires a high level of anticoagulants, which can cause excessive bleeding and other problems for the patient.
Doctors at leading Boston teaching hospitals approached Borenstein and asked if Draper could research technologies to replace current oxygenating devices. The doctors were part of CIMIT, the Center for Integration of Medicine and Innovative Technology.
The idea was that microfabrication technology developed at Draper for sensors used in defense, aerospace, and commercial products such as digital cameras and the Nintendo Wii game controller might help create an artificial lung with microchannels that mimic the blood vessels in human organs.
The blood-side passages in current hollow fiber lung devices are 200-300 microns in diameter, compared with the 5-10 microns for a capillary. MEMS technology allows the creation of channels that are closer in size to the blood vessels found naturally in organs.
The result of Draper's work is a 1/100 scale prototype device that functions like a human lung. Blood enters and is infiltrated with oxygen in a microvascular network before exiting.
The basic techniques borrowed from semiconductor manufacturing are deposition of material layers, patterning by photolithography, and etching to produce the required shapes. "That's basically a planar process. The two big challenges we had were transferring from two-dimensional to three-dimensional and from inorganic silicon to medical-grade polymers," Borenstein says.
His team is using structures made of silicone rubber in the current prototype. They provide the mechanical strength and flexibility required for the device.
To become implantable, the device would need bioresorbable materials. Those materials would be engineered into a tissue scaffold, which would be seeded with a person's own stem cells and grown into a kidney, a lung, or some other organ. The bioresorbable polymer would disappear after the structure was formed.
Borenstein's work is important in the field of tissue engineering because larger organs such as kidneys and livers require intensive internal vascular structures. But that stage is well down the road.
"Our work has been funded by the National Institutes of Health, and for the next phase of development [a device used outside the human body], we are looking for commercial partners," he says. Completion of that phase is very feasible within the next several years, in Borenstein's view.
Other research groups around the world are focusing on other aspects of developing artificial lungs. For example, researchers in Cleveland have developed a prototype artificial lung that functions with air, just like human lungs.
Charles Stark Draper, an aeronautics professor at the Massachusetts Institute of Technology, formed a lab in the late 1930s to develop instruments to measure aircraft motion. The lab was later named after Draper, and its work advanced to include missile guidance systems, space exploration, advance robotic technologies, and tissue engineering. The lab was spun out of MIT in 1973.
http://www.designnews.com/document.asp?doc_id=232240&f_src=designnews_gnews
click to see a short video amd more info on this approach for a artificial lung
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