Today, vacuum technology is used extensively in many facets of the medical industry. From the manufacture of prosthetics and the coating of medical devices to magnetic resonance imaging and proton therapy, vacuum equipment has helped revolutionize modern medicine. And as the medical field grows more high tech every day, the use of vacuum equipment will undoubtedly become even more widespread. Here are five medical applications in which vacuum technology currently plays a prominent role.
Due to several unique factors, titanium is the ideal metal for the medical industry. Titanium’s light weight, strength, corrosion resistance, biocompatibility, and ability to join with human bone make it perfect for producing prosthetic body parts, such as orthopedic pins, rods, plates, and joints.
In terms of strength, titanium is as strong as steel, yet it weighs only 60 percent as much. Titanium is also highly durable, and prosthetics made from it can last nearly 20 years. Further, titanium is non-ferromagnetic, which allows patients with artificial body parts to be safely scanned by MRIs and NMRIs. Most notably, titanium is one of the only metals that will effectively bond with human bone and tissue. This property, known as osseointegration, makes it the obvious choice for making prosthetic body parts.
Vacuum equipment is used in two different parts of the titanium manufacturing method known as the “Kroll Process.” In one part of the process, liquid titanium is mixed with molten magnesium, and this mixture is vacuum distilled until an elemental form of titanium, known as sponge, is produced. The next step that involves vacuum is when the sponge is refined into ingot form. To do this, the sponge is crushed and put into a vacuum arc re-melting furnace (VAR). This melts the sponge, and the resulting liquid solidifies inside the vacuum, creating a titanium ingot. These ingots are cylindrical in shape and can weigh more than 15 tons each.
Currently, millions of baby boomers are hitting their elder years while maintaining highly active and mobile lifestyles. Given this, it’s quite likely that we’ll see even more innovative applications for titanium in the medical field over the next few decades.
Magnetic Resonance Imaging
While X-rays are mainly used to examine bones, magnetic resonance imaging (MRI) is used to look at soft tissues, such as organs, ligaments, the circulatory system, and the spinal cord. MRI scans help doctors diagnose numerous conditions, such as brain tumors, cancer, strokes, multiple sclerosis, and ligament damage.
Most MRI scanners employ large superconducting magnets that are made from coils of special conductive wire containing rare-earth materials through which electrical current is run. The unique properties of these rare-earth materials result in zero resistance when cooled to cryogenic temperatures. The magnets work in tandem with radiofrequency coils to generate electrical signals from the hydrogen atoms in the patient’s body. A computer in the MRI control room digitizes these signals to create the image of the patient’s tissue.
The cryogenic fluid (liquid helium in this case) is used to cool the magnet to near absolute zero whereby the magnet coils become “superconducting”. Once in the superconducting state (i.e. zero resistance), current can flow through the magnet coils indefinitely and no continuous electrical power source is needed. The magnet is housed in a cryostat, which is a vessel built inside another vessel. The inner vessel houses the magnet and liquid helium bath. Between the inner and outer vessel is where vacuum plays a critical part. A vacuum environment is used to help insulate the cryogenic fluid inside the magnet cryostat. This vacuum insulation prevents too much heat from entering the cryogenic fluid causing it to “boil off” or worse, resulting in damage to the expensive superconducting magnet (referred to as a magnet “quench”).
Proton therapy is the most advanced form of radiation therapy today. While traditional radiation therapy uses photons and X-rays to irradiate diseased tissue, proton therapy uses a beam of protons. Proton therapy is most often used to treat cancer, and unlike traditional radiation therapy, it directly treats the cancerous tissue, without harming surrounding healthy tissue and organs. This makes proton therapy far less invasive and allows patients to maintain their quality of life and return to normal activities more quickly.
Proton therapy’s precise delivery of radiation is due to the way in which protons release their energy as they travel through the body. When protons enter the body, they slow down as they interact with electrons. As they travel slower, they eventually release a burst of energy known as the “Bragg Peak.” By regulating the velocity of the protons, doctors can tailor the proton treatment so this burst occurs at the precise site of the cancer, minimizing damage to healthy tissue.
Proton therapy is a relatively new modality and requires a large investment, so currently there are only 30 such therapy facilities in the world. However, many more hospitals and cancer centers across the globe are looking to invest in this highly advanced treatment, so proton therapy is likely to see a significant uptick in demand over the next few years. Because the equipment used to deliver proton therapy incorporates vacuum, the increased popularity of the treatment is likely to positively affect the vacuum industry as well.
To create the necessary energy and velocity for treatment, protons are sent through a vacuum tube into a super high-speed accelerator known as a cyclotron. The cyclotron consists of a ring of magnets that speed up the protons such that they circumnavigate the ring at roughly 10 million revolutions per second. After exiting the cyclotron, the protons continue in the vacuum tube through a series of magnets that steer and focus the beam as it’s guided to the treatment room to be delivered to the patient. At its maximum, the proton beam travels 125,000 miles per second, about two-thirds the speed of light. From its starting point until it reaches the patient, the protons travel approximately 313,000 miles!
Similar to MRI, many of the cyclotron magnets are superconducting magnets housed in a cryostat, and the same principles of cooling with liquid helium and insulating with vacuum are required.
Medical Device Coatings
Many medical devices placed inside the human body are surrounded with special film coatings to protect both the device and the patient. Medical devices with such coatings include pacemakers, stents, epidural probes, and defibrillators. One of the most widely used materials to coat these devices is Parylene, and it’s deposited on the medical devices through a vacuum deposition process.
Parylene provides an ultrathin, pinhole-free barrier around the medical device. This coating serves two purposes: it protects the body from the leaching of metals or plastics and protects the device from being attacked by body fluids and moisture. Moreover, some of the latest Parylene coatings also have antimicrobial properties to fight infection.
Parylene coatings are applied to medical devices inside a vacuum chamber using vapor-deposition polymerization (VDP). The Parylene is deposited on the device at the molecular level, with the coating building up one molecule at a time. Such a process allows the Parylene to uniformly coat the entire device, penetrating even the smallest cracks and crevices and literally encapsulating the device. VDP takes place at room temperature and requires no solvents, catalysts, or plasticizers. With a high level of lubricity, Parylene is also applied to medical devices made from silicone and rubber, such as catheters. The coating reduces the friction of these materials, while also eliminating surface tackiness and preventing the entrapment of contaminants.
The latest development in coating technology provides Parylene with antimicrobial properties to eliminate harmful microorganisms on medical devices. This new coating is aimed at reducing hospital-borne infections, such as staphylococcus aureus (MRSA).
A centrifuge is used to separate components suspended in a liquid, so they can be analyzed or reused. By placing the liquid into a container and rotating it at high speeds around a fixed axis within a centrifuge, the centrifugal force causes the denser materials in suspension to move away from the lighter ones, thereby separating them. In medical labs, centrifuges are frequently used to separate plasma from blood and solids from liquids, but they can do much more than that.
Ultracentrifuges are super-powered centrifuges that rotate at speeds faster that 20,000 rpm and can separate out extremely tiny particles in solution. In medicine, ultracentrifuges can be used to isolate and study microscopic particles, such as proteins, viruses, nucleic acids, RNA, and plasmid DNA. These devices are especially useful in pharmacology.
Because ultracentrifuges spin so fast, the gaseous friction on the spinning rotors increases to the point where the rotors reach extremely high temperatures. These high temperatures cause convection currents that can disrupt the separation of the particles in the liquid. To avoid the heat buildup caused by air resistance, rotors in ultracentrifuges are housed within a vacuum. The elimination of air resistance not only allows for the rotors to be spun at very high speeds, but it also decreases the amount of power input needed to operate the device, making the vacuum environment a critical part of the process.
In summary, vacuum plays a critical role in medical applications and processes. As new, advanced products are developed, it is likely that vacuum will continue to play a central part—directly or indirectly—in the development and/or manufacture of next-generation medical devices.