The wonders of plasma technologies for an aging population

The world’s population is aging rapidly - according to the World Health Organization, one in six people will be aged over 60 by 2030. While older people contribute positively to their families and communities, their ability to do so depends on their continued health and wellbeing. Researchers from the University of Sydney are working toward improving the lives of older people thanks to a novel process which is making big advances.

Common conditions that prevent older people from living productive lives include osteoarthritis, osteoporosis-related bone fractures and skeletal injuries, which often require treatments such as bone implants. Every time a patient receives a bone implant, a gamble is involved: will the body accept the new arrival or reject it as an invading entity? Will it become infected requiring drastic action to save it? While most implants are successful, if rejection or infection occurs, it is the start of a potentially risky and costly ordeal for the patient.

Fortunately, researchers at the University of Sydney’s Faculty of Engineering are working on a solution to minimize the rejection and infection associated with bone implants after surgery.

The answer comes from the pioneering world of biomedical engineering where researchers take advances in technology and design and apply them to medical problems. Robotic and laser surgery, super-detailed medical imaging and advanced systems to monitor vital signs have all been shaped by biomedical engineers.

Researchers like Dr Behnam Akhavan from the School of Biomedical Engineering at the University of Sydney and the University of Sydney Nano Institute, who is, among many other things, a surface engineer, are working at the atomic scale. It’s a field that can fly under the radar, but as it creates new coatings and surfaces to reduce friction, stop corrosion and absorb or reflect sound, light and energy, surface engineering is the quiet achiever of new technologies.

Consider the benefits of a surface engineer turning their eye to medical implants and the surfaces they have where rejection and infection begin.

“Like all our projects, we started this by thinking backwards from the problem,” says Dr Akhavan. “We asked if our method could solve the problem. Turns out it could.”

The question to answer in this case was: how can the surface of an implant be changed to minimise the chance of rejection which would also reduce the possibility of infection?

Dr Behnam Akhavan in the Plasma Processing Lab at the University of Sydney.

Nitrogen plasma used for surface engineering of implantable biomedical devices in a process called plasma immersion ion implantation.

Starting out with Hydrogels

The starting point is in substances called hydrogels, which are soft and jelly-like with the ability to contain large amounts of liquid without losing their essential structure. They’re not unlike human soft tissue, so they’re often used in medical treatments. For example, a gauze dressing saturated with a hydrogel can keep the dressing from sticking to the wound surface and provide moisture and pain relief through its high-water content. They can also gently deliver infused medications.

Their jelly-like characteristics make hydrogels seem less alien to the human body which logically implied the idea that coating an implant with a hydrogel could reduce the likelihood of implant rejection. But there was a major obstacle.

“Hydrogels are inherently weak and structurally unstable, so they don’t easily attach to solids, making them difficult to use in mechanically demanding implant applications like cartilage and bone tissue engineering," says Dr Akhavan.

The plasma solution

The challenge has been engineering the surfaces of medical implants to have a more robust ability to attach to hydrogels. The solution came through plasm technology; specifically, a process called plasma immersion ion implantation, which allows bespoke surface modifications to a depth of mere atoms, with plasma being the medium that allows the process to happen.

Though plasma isn’t commonly encountered on Earth, it is by far the most abundant substance in the wider universe. A gas-like substance, it is classified as the fourth state of matter after solid, liquid and gas. You could describe it as a soup of electrons and ionised particles that were once together as atoms but were torn apart by electric fields or super-high temperatures, like those found in stars.

The sun is essentially a giant ball of plasma, but the plasma used by Dr Akhavan and his team has nitrogen gas as its starting point (an inexpensive and plentiful raw material for their purpose), which is subjected to electric fields.

The process of surface engineering that enhances the function of implants (and the other surface enhancements that Dr Akhavan has devised) starts with a vacuum chamber being filled with nitrogen gas at low pressure. An electrical field causes the nitrogen electrons to break away from their atoms putting the nitrogen gas into a plasma state, so it is ready to be used for what researchers like Dr Akhavan call ‘surface activation’.

The thing about plasma that makes it effective for surface activation is that the mix of freewheeling charged particles makes plasma hyper-active. Place, say, a piece of polymer (like PEEK, epoxy, polyester, Teflon, or silk) in the chamber and the plasma particles will collide with the polymer so powerfully that individual carbon atoms in the polymer will be dislodged, creating lone electrons in the structure of the polymer so the polymer itself becomes highly reactive.

A polymeric surface activated in this way becomes like sticky tape for various substances, including hydrogels.

The result is a hydrogel-attracting surface suitable for implants used in cartilage and bone repairs, artificial nerves and blood vessels. This break-through process also has uses in aeronautics, microelectronics, and other areas of medicine.

The good news is that research indicates the new coating could also enhance the functionality of bone producing cells which will allow an implant to bind firmly to the host bone, minimizing the risk of complications and allowing patients to return to a healthy lifestyle.

“Our latest research presents great promise for the creation of a new class of robust, bio-active surfaces for orthopaedic implants,” says Dr Akhavan.

Academics at the University of Sydney Nano Institute are transforming everyday life through multidisciplinary research in nanoscale science and technology.

An environmentally friendly outcome

An added bonus is the environmentally friendly nature of much of the work with plasma technologies.

“It’s a truly green technique,” Dr Akhavan says. “Whether your goal is activating the surface of an implantable device for attaching hydrogel or making absorbents for water purification, the one-step process happens in typically less than a few minutes, at room temperature, with no toxic acids or other chemicals and it produces literally no waste.”

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