Ceramic dreams31 October 2017
The use of ceramics in medical devices is changing rapidly, and the material is now being used in increasingly complex products and techniques. Lynette Eyb speaks to Dr Andy Weymann, chief medical officer at Smith & Nephew, and Eileen de Guire, of the American Ceramic Society, about some of the innovations taking place.
Mention ceramics to a person on the street and chances are they’ll assume you’re about to launch into a spiel about pottery classes or porcelain dolls. Unless, of course, they’ve had a hip replacement or dentures, or maybe even a prosthetic leg fitted. That’s because ceramics have been a mainstay in modern medical devices since debuting more than 40 years ago in total-joint arthroplasty. Ceramics – in the form of tricalcium phosphate and other compounds – have been used since the early 20th century as bone fillers. But it wasn’t until alumina emerged in the 1960s that there was a ceramic option tough enough to withstand the payload needed for hip joints. Synthetic calcium-phosphate ceramics and zirconia followed, paving the way for a new generation of the material.
Today, ceramics continue to be a go-to material in arthroplasty and orthopaedics. They’re used in everything from femoral heads and acetabular cup liners to knee femoral and tibial components. Dental technicians, meanwhile, look to ceramic – or porcelain – for dentures, crowns, veneers and bridges. Hearing aid manufacturers use ceramics for housings and microphones, while they’re also found in pacemakers, respirators, dialysis machines, and innumerable other devices and gadgets used to improve or maintain health.
Ceramics may have their origins in the ancient world – the word ‘ceramic’, after all, comes from the Greek word keramos, meaning ‘potter’ or ‘pottery’ – but the material today is as cutting edge as any other modern tool of medicine.
In a sector crowded with new and emerging technologies competing to produce better, stronger and more costeffective products, ceramics have kept pace, evolving and innovating rapidly. Industry analysts forecast the medical ceramics market will be worth as much as $16.3 billion by 2020, with this growth largely driven by an ageing population’s increasing demand for orthopaedic and dental solutions.
Dr Andy Weymann is chief medical officer at Smith & Nephew, a leading provider of products for orthopaedics, wound management and endoscopy. The company’s orthopaedics division specialises in the provision of joint replacement systems for knees, hips and shoulders.
Weymann says ceramics offer a range of advantages over other materials. “The characteristics of ceramics make them suitable for a number of medical device applications, including hip and knee replacements. Ceramics ideally need to possess low-wear properties, resulting in a longer-lasting implant,” he says.
“Firstly, ceramics are harder than metals. They have better corrosion resistance and can withstand body fluids. As they’re considered inert materials, they’re less likely to produce adverse biological responses. They also provide low-wear bearing couples when combined with polyethylene or when used as ceramic on ceramic. This all helps to reduce the risk of the implants loosening and the risk of revision.”
Eileen de Guire, of the American Ceramic Society, agrees that biocompatibility remains a key strength of ceramics in healthcare solutions. “The body’s interior is a very chemically active place, which can lead to corrosion or dissolution of metals,” she says. “Ceramic materials, such as hydroxyapatite, also known as HAp, mimic bone composition. Zirconia is used for teeth because of its toughness, impact resistance and colour. Ceramics also provide structure and highly tunable compositions.
“The evolution towards more biocompatibility and better device design is continual. Hip implants, for example, have evolved to accommodate anatomical differences between men and women; ball and socket materials are more wearresistant; bone cements adhere better and longer.”
Depending on the application, manufacturers and surgeons now consider a range of high-tech materials for use in conjunction with or alongside ceramics. For example, the combination of a titanium hip prosthesis with a ceramic head and polyethylene acetabular cup may be used. Weymann says that in some applications, alternative solutions may reduce friction and offer an increased resistance to abrasion when compared with ceramics, while also retaining the toughness of metal.
“Ceramics provide limited options in terms of design flexibility; for example, femoral head off-sets,” says Weymann. “They are also known to be less hard than other materials, so they may not be suitable for all patients. They need to be used for the right applications and used with care.”
The same case-by-case analysis should be used when determining cost savings. “In certain applications, ceramic devices provide better performance, safety and survivorship, and can reduce the overall healthcare burden and the cost to society,” says Weymann. “But the same is true of other products on the market.”
Looking to the future
De Guire says the ceramics sector has in recent years embraced diversification well beyond orthopaedics or dental applications. While hip and other joint replacement technology remains a cornerstone, the sector is evolving – and evolving fast. Ceramics and associated glass technology are now being applied to more products than before and are also servicing patients with a greater range of medical conditions.
“Most people think of implants when they hear the term ‘medical devices’– things like hip implants and fasteners,” she says. “But the field encompasses much more, as it relates to ceramic and glass technology. For example, glass spheres deliver radiation or chemotherapy payloads directly to cancers; glass fibres help the body repair open wounds where conventional wound treatments fail; ceramic nanofibres are being developed for breathalysers that can detect organic markers of disease in breath; tattoo-like sensors are being developed for diabetes monitoring; ceramic blades for surgery, and the list goes on.
“To me, the more interesting evolution relates to how materials are used to support health. In the beginning, materials like ceramics were used for replacement parts: hips, knees, teeth, fasteners to hold broken bones together. These are still very important applications, especially for the people who are suffering or injured.”
However, De Guire says, as researchers saw how materials interacted with the body and began to understand the mechanisms, they started to ask how materials could help the body rebuild, heal or defend itself. “This shift in thinking looks at materials as sojourners in the body, rather than permanent residents,” she adds.
This has, for example, led to technologies such as bone scaffolds made of HAp. The scaffold provides mechanical structure and chemical building blocks as the bone grows into it and eventually absorbs the scaffold.
“In another example, a company here in the US – Mo-Sci, in Missouri – has developed a fibrous glass that looks like cotton candy, for wound healing. People with large open wounds often have little success with existing treatment protocols – despite wound care being a $5-billion industry,” she says.
“Part of the problem is that wounds are poorly vascularised areas. That is, there is little blood flow to bring treatment from the inside of the body. With this technology, the glass fibres act like an artificial scab, with chemical constituents the body can use to heal the wound. The body’s venous structure can bring tools or materials, but not both. So the glass brings the materials from the outside, the body brings the tools from the inside and healing occurs. The glass dissolves as the body uses it to heal.”
She cites further examples of bioactive glass ceramics being used in toothpaste to remineralise teeth and repair enamel fissures, as well as in commercial bone cements. However, De Guire says, some of the most revolutionary research is looking at ways ceramics can contribute to the building of new body parts. “For example, would it be possible to 3D print a new kidney and eliminate the tethering of dialysis? What about other body parts that hugely impact quality of life, such as urethras or trachea?” she says.
Regulation and beyond
Looking beyond implants, tiny glass spheres are on the market for delivering radiation to liver cancers. They are small enough to inject and flow into the liver, where they clog up around tumours, says De Guire.
“There are also some interesting developments in diagnostics that take advantage of the unique atomic structure and defect chemistry of ceramic materials. One example is the work of Dr Pelagia- Irene Gouma, who’s now at Ohio State University,” De Guire says. “She’s been working on breathalysers that can detect organic markers for serious diseases. The device uses nanofibres of transition metal oxides, such as tungsten oxide.”
The nanofibres provide a very large surface area and the defect structure of the oxide creates voids, like tunnels or cages, that organic compounds fit into. The oxide compositions can be tuned to specific compounds that mark diseases.
De Guire says the industry faces one major hurdle in the US market as far as medical device development is concerned: regulation. Regulators need to keep pace with R&D, and ensure medical devices based on emerging and evolving technologies like ceramics can be brought to market as quickly and as efficiently as possible. She cites slow FDA approvals and says current regulatory hurdles could hold back device development, including those reliant on ceramics.
Regulation aside, as ceramics continue to improve in biocompatibility, strength and longevity, they will continue to be used in new and exciting applications. From implants and diagnostic equipment to orthopaedic devices, and delivery tools for cancers and other life-threatening illnesses, a material conceived in the ancient world is evolving for the 21st century and beyond.
What are ceramics?
Ceramics can encompass materials like glass, as well as metal oxides such as alumina; non-oxides such as silica; and nitrides like silicon nitride. Some cements are also included in what is a relatively loose definition. However, ceramics no longer need to be derived from the earth like clay-based ceramics or pottery.
Bioceramics are ceramic-based materials that are biocompatible. There are two types of bioceramics: ‘bioinert’ and ‘bioactive’. The bioinert family requires a layer of tissue to separate the bone from the ceramic, while bioactive ceramics are able to nurture a direct marriage between the body and the implant to promote healing.