Medical implants like stents, catheters and tubing introduce risk for blood clotting and infection – a perpetual problem for many patients.
Colorado State University engineers offer a potential solution: A specially grown, “superhemophobic” titanium surface that’s extremely repellent to blood. The material could form the basis for surgical implants with lower risk of rejection by the body.
Biomedical, materials approaches
It’s an outside-the-box innovation achieved at the intersection of two disciplines: biomedical engineering and materials science. The work, recently published in Advanced Healthcare Materials, is a collaboration between the labs of Arun Kota, assistant professor of mechanical engineering and biomedical engineering; and Ketul Popat, associate professor in the same departments.
Kota, an expert in novel, “superomniphobic” materials that repel virtually any liquid, joined forces with Popat, an innovator in tissue engineering and bio-compatible materials. Starting with sheets of titanium, commonly used for medical devices, their labs grew chemically altered surfaces that act as perfect barriers between the titanium and blood. Their teams conducted experiments showing very low levels of platelet adhesion, a biological process that leads to blood clotting and eventual rejection of a foreign material.
A material “phobic” (repellent) to blood might seem counterintuitive, the researchers say, as often biomedical scientists use materials “philic” (with affinity) to blood to make them biologically compatible. “What we are doing is the exact opposite,” Kota said. “We are taking a material that blood hates to come in contact with, in order to make it compatible with blood.” The key innovation is that the surface is so repellent, that blood is tricked into believing there’s virtually no foreign material there at all.
The undesirable interaction of blood with foreign materials is an ongoing problem in medical research, Popat said. Over time, stents can form clots, obstructions, and lead to heart attacks or embolisms. Often patients need blood-thinning medications for the rest of their lives – and the drugs aren’t foolproof.
“The reason blood clots is because it finds cells in the blood to go to and attach,” Popat said. “Normally, blood flows in vessels. If we can design materials where blood barely contacts the surface, there is virtually no chance of clotting, which is a coordinated set of events. Here, we’re targeting the prevention of the first set of events.”
The researchers analyzed variations of titanium surfaces, including different textures and chemistries, and they compared the extent of platelet adhesion and activation. Fluorinated nanotubes offered the best protection against clotting, and they plan to conduct follow-up experiments.
Growing a surface and testing it in the lab is only the beginning, the researchers say. They want to continue examining other clotting factors, and eventually, to test real medical devices.
First real-life study to provide data on the potential of powering medical implants with solar cells
The notion of using solar cells placed under the skin to continuously recharge implanted electronic medical devices is a viable one. Swiss researchers have done the math, and found that a 3.6 square centimeter solar cell is all that is needed to generate enough power during winter and summer to power a typical pacemaker.
The study is the first to provide real-life data about the potential of using solar cells to power devices such as pacemakers and deep brain stimulators. According to lead author Lukas Bereuter of Bern University Hospital and the University of Bern in Switzerland, wearing power-generating solar cells under the skin will one day save patients the discomfort of having to continuously undergo procedures to change the batteries of such life-saving devices. The findings are set out in Springer’s journal Annals of Biomedical Engineering.
Most electronic implants are currently battery powered, and their size is governed by the battery volume required for an extended lifespan. When the power in such batteries runs out, these must either be recharged or changed. In most cases this means that patients have to undergo implant replacement procedures, which is not only costly and stressful but also holds the risk of medical complications. Having to use primary batteries also influences the size of a device.
Various research groups have recently put forward prototypes of small electronic solar cells that can be carried under the skin and can be used to recharge medical devices. The solar cells convert the light from the sun that penetrates the skin surface into energy.
To investigate the real-life feasibility of such rechargeable energy generators, Bereuter and his colleagues developed specially designed solar measurement devices that can measure the output power being generated. The cells were only 3.6 square centimeters in size, making them small enough to be implanted if needed. For the test, each of the ten devices was covered by optical filters to simulate how properties of the skin would influence how well the sun penetrates the skin. These were worn on the arm of 32 volunteers in Switzerland for one week during summer, autumn and winter.
No matter what season, the tiny cells were always found to generate much more than the 5 to 10 microwatts of power that a typical cardiac pacemaker uses. The participant with the lowest power output still obtained 12 microwatts on average.
“The overall mean power obtained is enough to completely power for example a pacemaker or at least extend the lifespan of any other active implant,” notes Bereuter. “By using energy-harvesting devices such as solar cells to power an implant, device replacements may be avoided and the device size may be reduced dramatically.”
Bereuter believes that the results of this study can be scaled up and applied to any other mobile, solar powered application on humans. Aspects such as the catchment area of a solar cell, its efficiency and the thickness of a patient’s skin must be considered.
Learn more: The beating heart of solar energy
Tune In, Turn On, Power Up
Human beings don’t come with power sockets, but a growing numbers of us have medical implants that run off electricity. To keep our bionic body parts from powering down, a group of Arizona researchers is developing a safe, noninvasive, and efficient means of wireless power transmission through body tissue. The team presents their findings at the 166th meeting of the Acoustical Society of America, held Dec. 2 – 6 in San Francisco, Calif.
Medical implants treat a variety of conditions such as chronic pain, Parkinson’s disease, deep brain tremors, heart rhythm disturbances, and nerve and muscle disorders. If the batteries in the devices lose their charge, minor surgery is needed to replace them, causing discomfort, introducing the risk of infection, and increasing the cost of treatment.
This is a scenario the Arizona researchers are aiming to change.
Their novel wireless power approach is based on piezoelectric generation of ultrasound. The Greek root, “piezo”, means “squeeze.” In piezoelectrical systems, materials are squeezed or stressed to produce a voltage. In turn, applied voltages can cause compression or extension. Piezoelectric materials have specific crystalline structures. The team’s piezoelectric system has been tested in animal tissue with encouraging results.