Chemical composition of Biolox delta, a zirconia-toughened alumina with small additions of chromium oxide and strontium aluminate. Credit: Pawar, IJACT

Last July’s 4th International Congress on Ceramics was the setting for multiple presentations on the use of advanced ceramics in various industries. Among the application areas covered were biology and medicine. This post is a recap of a paper on the topic from the May/June issue of AcerS’ International Journal of Applied Ceramic Technology.

According to author Vivek Pawar, a materials researcher at Smith and Nephew Inc. (Memphis, Tenn.), seven presentations at the event focused on bioceramics for orthopedic, tissue engineering, and dentistry applications, as well as on innovative manufacturing techniques and novel ceramic materials for use as bearing surfaces.

Pawar writes that the bioceramics used in hard or soft tissue replacement can be classified as bioactive glasses made mainly from calcium oxide, sodium oxide, phosphorus pentoxide, and silica; apatite-based ceramics made from synthetic hydroxyapatite and calcium phosphates; and ceramics that are used as bearing surfaces for orthopedic applications.

Since development of the first bioactive glass by Larry Hench more than 40 years ago, few alterations have been made to the materials’ composition. Pawar reports current research in the area focuses on developing compositions that maintain or increase bioactivity after crystallization during sintering. The goal is to develop low-density, easily machinable materials with fracture toughness greater than 1 MPa m^1/2.

A new material aimed at meeting those criteria is a product called ‘Biosilicate’ from Vitrovita (São Carlos, Brazil), which is reported to have antimicrobial properties. In one study assessing the effectiveness of Biosilicate against a variety of microorganisms, the material displayed activity against all the bacteria except one, drastically reducing the number of viable cells in the first 10 minutes of contact.

Hydroxyapatite (HA) coatings are commonly used in orthopedic devices to promote bone in-growth on metallic implants. Pawar writes that current research focuses on increasing the material’s bioactivity by incorporating bioactive ions in the HA crystal structure. Researchers have investigated magnesium, strontium, silver, zinc, titanium, iron, sodium, and potassium cationic substitutions. Anionic substitutions considered include fluorine, chlorine, hydroxide, phosphate, and silicate ions. These ions perturb the HA crystal structure and change solubility. Current work is aimed at understanding how each of these ions affects bioactivity. Substitutions with silver, for example, have increased HA solubility and shown bactericidal effects.

Hip arthroplasty remains the predominant use for ceramic bearing surfaces in orthopedic implants, and materials used in this application have included alumina, yttria-stabilized zirconia, and zirconia-toughened alumina. Newer ceramic materials with higher strength and toughness than alumina and reduced risk of fracture include ‘Biolox delta‘ from CeramTec (Plochingen, Germany). A zirconia-toughened alumina with small additions of chromium oxide and strontium aluminate, the material is “being considered for challenging applications such as hip resurfacing femoral heads and knee femoral components,” Pawar writes.

Another potential bearing material is silicon nitride, which offers high strength and toughness, excellent wear resistance, imaging compatibility, affinity to bone, and an antibacterial surface. Produced by Amedica (Salt Lake City, Utah), Si₃N₄ is already being used in spinal devices.

In the article Pawar notes, “Although no significant clinical problems have been reported with these two materials, a long-term clinical followup will be required to evaluate the performance of these materials.”

Innovations in ceramic processing techniques are being driven by specific biomedical applications. For example, camphene freeze casting processes are being used to create a 3-D interconnected porous bioceramic scaffold with the aim of producing a bioactive glass scaffold with high strength and bioactivity.

Also proposed is a 3-D printing process for apatite-based ceramics using stereolithography. The method is said to enable production of customized solutions based on clinical needs. A limited clinical study of the technology for repair of large craniofacial bone defects is under way at 3DCeram (Limoges, France).

Finally, nanoceramics with particle sizes of 1 to 100 nm are the focus of considerable research. The unique properties of materials produced using nanoparticles—higher surface-to-volume ratios, no light scattering, and unique mechanical properties in composite form—have led to use in dental fillings and crowns. Bone grafting, bone cement, and bioactive ceramic applications also offer research opportunities. Pawar expects future research in this area will focus on development of methods to produce customized nanoceramics based on patient needs.

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There’s a new pen in town!

Peter Wray, retired Director of Communications, reflects on his "retirement career" at ACerS. Credit: ACerS.

For the last five years, ACerS Director of Communications Peter Wray has been the dominant voice of the engineered ceramics blogosphere. In fact, he started it. He was hired in 2008 to establish a “web presence” for the Society by then-executive director, Scott Steen. And, wow, did he ever!

Peter came to ACerS after retiring from the Ohio Civil Services Employee Association, where he directed the public relations department. “I was looking for something to do for about five years until my wife retired,” he says. “Coming to ACerS was sort of like a hobby, but with a lot of interesting challenges, interesting technology, and interesting people.”

He established the Ceramic Tech Weekly blog with weekly updates of news and trends relating to ceramic engineering and science (see an early post here). Quickly, it grew to Ceramic Tech Today with daily updates that are broadly distributed in a twice-weekly email. Peter also was editor of the ACerS Bulletin and published a number of memorable articles on topics such as concrete recycling in Haiti, wound-healing glass, and Pyrex cookware.

Long story, short—Mrs. Wray retired in January. Peter stayed true to his plan and retired in February. Well, sort of. He is still working with us part-time to produce CTT posts, videos, and some special projects.

ACerS new associate editor, Jim Destefani. Credit: ACerS.

As we bid an affectionate “adieu” to Peter, we are pleased to welcome a new member to our team. Jim Destefani joined our staff yesterday as associate editor and will be writing CTT posts, editing the ACerS Bulletin, reporting on conferences, and following the news and trends regarding our favorite materials.

Jim brings a depth of technical magazine publishing experience to ACerS, with particular expertise in the manufacturing and metalworking areas. He worked previously for the Society of Manufacturing Engineers as well as for several for-profit business-to-business publishers.

We are excited to have Jim on our staff and look forward to his contributions.

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Oxide CMC exhaust ground test demonstrator consists of a 1.60-m diameter nozzle and 1.14-m diameter × 2.34-m conical centerbody with titanium end cap inspection portal. Credit: Steyer; IJACT.

Ceramic matrix composite (CMC) materials can benefit aerospace in propulsion and exhaust, thermal protection, and hot primary structure applications, according to Todd E. Steyer of The Boeing Company (Huntington Beach, Calif.).

Reviewing aerospace-related presentations from last July’s 4^th International Congress on Ceramics in a recent paper in the ACerS International Journal of Applied Ceramic Technology, Steyer outlined several emerging aerospace opportunities for CMCs, including propulsion and exhaust, thermal protection, and hot primary structure applications.

In the propulsion area, gas turbines have long been dominated by the use of nickel-based superalloys and titanium alloys. According to Steyer, engine manufacturers are now taking a closer look at CMCs for use in engine hot sections. Silicon carbide-based composites can handle temperatures to 1200°C while reducing weight and cooling requirements, resulting in reduced fuel burn and improved performance.

According to an article in MIT Technology Review, new engines being developed by CFM, a partnership between GE and France’s Snecma, feature CMC components that will reduce fuel consumption by about 15 percent—enough to save nearly $1 million per year per airplane, assuming a fuel cost of $2.50 per gallon.

CFM’s LEAP engine uses SiC-reinforced CMC parts that don’t require cooling, enabling air that would normally be diverted to keep superalloy components from melting to be used to generate thrust. It also uses parts produced using a 3-D printing process, according to the MIT article.

The company already has orders for 4,500 of the new engines. In addition to saving money, the engines will help users comply with current and anticipated emissions regulations.

In engine exhaust systems, work is underway to produce an alumina-fiber reinforced aluminosilicate matrix composite centerbody and exhaust nozzle for commercial aircraft. Currently in ground testing, the ceramic nozzle will reduce weight and engine noise and increase component lifetime, Steyer wrote.

Ceramic materials have long been used in aerospace thermal protection applications—for 30 years, ceramic tiles with glass-based coatings provided thermal protection for the US’s now-retired space shuttle fleet. Initially composed of silica fibers with a nominal density of 0.14 g/cm³ and a glaze aimed at controlling emissivity and limiting catalysis for oxygen and nitrogen recombination from the plasma on reentry, the tiles provided effective insulation but required heavy maintenance between flights. Engineers improved durability over the shuttle’s service life using new tile substrates and coatings.

For new thermal protection applications, Steyer reported on CMCs developed and tested by NASA researchers for use at temperatures to 1700°C. Toughened Uni-piece Fibrous Reinforced Oxidation-Resistant Composite (TUFROC) materials build on the success of insulating fibrous tiles with high-emissivity/low-recombination-efficiency coatings using a refractory ceramic carbon-insulated layer for dimensional stability.

Supersonic and hypersonic flight vehicles present unique challenges for primary hot structural materials, and ultrahigh-temperature ceramics (UHTCs) have been emerging as a promising class of materials for leading edges for hypersonic vehicles. The refractory nature of this class of carbides, borides, and nitrides makes them good candidates for the highest heat flux areas as well as areas with high integrated heat load as a function of time, Steyer wrote.

Particulate, whisker, and chopped or continuous fiber reinforcements are resulting in improved mechanical properties, but the materials’ relatively high density and difficulty in large-scale processing are potential drawbacks. Steyer reported one recent example in which CMCs consisting of 0.5- to 1-mm long chopped Hi-Nicalon SiC fibers in a ZrB₂ matrix hot-pressed at 1700°C showed significantly improved chevron-beam fracture toughness at compositions containing up to 20 vol.% fiber.

Increased use of CMCs in aerospace will require microstructure optimization, a path to entry into service, and improved affordability. Steyer believes fundamental and applied research in damage accumulation mechanisms/models, life prediction methodologies and modeling, nondestructive inspection techniques, and robust field and depot-level repair methods will result in more CMCs in aerospace applications.

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James C. Phillips, who will speak at GOMD a symposium in his honor, discusses the idea of “big data” in this YouTube video, “Six Impossible Things.” Credit: YouTube.

Have you ever met a verb?

This is how I think of people who are all action. They have a great deal of energy, seem to be always in motion, and their enormous intellectual curiosity generates new ideas at a dizzying pace. Because they move so fast, their intellectual wakes cut a wide swath.

Allow me to highlight three of the “verbs” that will be at the Glass and Optical Materials Division Annual Meeting that will take place in conjunction with PACRIM 10, June 2-7. They are James Charles Phillips, Arun Varshneya, and John Mauro.

Phillips (Verb #1) will be honored in the aptly named, “James C. Phillips Honorary Symposium.” The symposium’s eight sessions span the entire five days of the conference’s technical program! Phillips, who celebrated his 80th birthday in March, is a condensed matter physicist by training, but his influence appears to be boundless.

The symposium organizer, Corning researcher John Mauro (Verb #2) says of Phillips, “Every decade since he began working, he has made huge contributions to science.”

Phillips is credited with developing semiconductor pseudopotential theory in the 1950s, which provided the basis for more than 30,000 published articles on the electronic structure of materials. In the 1960s, he dove into understanding superconductivity tunneling mechanisms. According to a Wikipedia biography, his microscopic theory of superconductive tunneling usurped the prevailing theory of the time, which had been proposed by the late Nobel-laureate, John Bardeen.

Phillips earned BS and MS degrees in mathematics and physics from the University of Chicago, and his PhD in algebraic topology. In the 1970s, the full weight of that education and research backgrounds led to the development of the topological constraint theory of glasses, in particular, as it applies to the optimization of glassy networks.

And, this is the point of intersection among the three “verbs” of this story. While Arun Varshneya (Verb #3) was a professor at Alfred University, he introduced Mauro—who was then an undergraduate student in glass science—to Phillips’ papers on topological constraint theory. The ideas resonated with Mauro, and he developed them further in his PhD work. At Corning Inc., Mauro used topological constraint theory to engineer Gorilla Glass 3, as explained in an earlier post.

“Jim works at the intersection of physics and glass,” Mauro says. “Not many of us work in both fields. He is interested not only in knowing the science of glass, but also in applying it to glass, including industrial glass.”

However, Mauro notes, “Jim’s work as a condensed matter physicist has so much influence in traditional fields and others,” as his work in the 1980s and 1990s gives witness. In the 1980s, he made significant contributions to theory of high temperature superconductors, and in the 1990s, he contributed new discoveries about disordered networks to the field.

In a 2011 lecture on “big data” posted on YouTube, Phillips quips, “One of the things physicists worry about is that there is nothing left to do.” Phillips is proof to the contrary. As the 21^st century unfolds, he is applying his considerable intellectual talents and experience to detecting and fighting cancer. The new research involves taking theories used to optimize glass design and applying them to protein design. Phillips will provide the details himself in his talk, “Curing cancer using engineered viruses,” on Wednesday afternoon (June 5) at 2:00 p.m.

Varshneya, now professor emeritus of glass science at Alfred University, will be teaching a short course at GOMD: “Fundamentals of Glass Science.” He traditionally teaches this course at GOMD and usually to a full-capacity crowd.

It is not possible to separate Varshneya-the-glassman from Varshneya-the-teacher. Varshneya says he knew he would be a teacher from a young age. “I loved teaching ever since I was an 8th grader back in India,” where he tutored some of his classmates in the basics of math and science. “I knew then that I wanted to be a teacher some day,” he writes in an email.

As a teacher, he says his primary objective is to motivate his students to learn more, starting with the basics. The short course is designed for professionals working in other scientific or engineering disciplines and builds on their knowledge and experience, like “dendrites attempting to develop lots of branches,” he says. This year, he says, he plans to incorporate more examples from everyday life to demonstrate glass science principles and practices.

I’ve sat in on Varshneya’s course. He is a verb.

Register here for PACRIM–GOMD and for the “Fundamentals of Glass Science” course.

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Larry Hench. Credit: ACerS.

Last Thursday Larry Hench (FACerS and Distinguished Life Member) was the guest of honor at the Michigan/Northwest Ohio Section and recipient of the Toledo Glass and Ceramics Award. The award was bestowed annually from 1956-1986, and after a 20-year hiatus, the section resurrected the award in 2006. Hench is emeritus professor of the University of Florida and of Imperial College London, and also holds positions at Florida Gulf Coast University, University of Central Florida, and Florida Institute of Technology.

The list of recipients over its 50+ year history is a “Who’s Who” of glass and ceramics leaders including such giants in the field as Alistair Pilkington, S.D. Stookey, Norbert Kreidl, Dominick Labino, Fay Tooley, Alfred Cooper, and more recently, Delbert Day, Prabhat Gupta, and Katherine Faber.

In his talk, “The story of Bioglass: From O-I to OR!,” Hench recounted the influences early in his career that led him to graduate school and to the study of glass. About 35 attended the event and many in the audience worked with Hench over the years, so the evening felt like an intimate gathering of friends.

He attributes his discovery of Bioglass to three “miracles.” The first of these was a chance encounter with an Army colonel who challenged him (as a representative of the scientific community) to “make a material that will survive exposure to the human body” that could be used to help the soldiers who were coming back from Vietnam with debilitating injuries. (At the time, Hench was researching the effects of radiation on glass.) The second “miracle” was receiving funding to study bioactive glasses from the Army’s medical funding branch. It was virtually unheard of for a principal investigator without a medical degree to get funded. The third “miracle” was his choice of the best Na₂O-CaO-P₂O₅-SiO₂ composition on the first try! Systematic testing of other compositions on the phase diagram showed that, ultimately, the ‘45S5′ Bioglass bonded to bones faster and better than any other composition.

Hench refers to these three events as miracles, but he also admits, “You can never tell where basic science studies might go as far as applications.”

To this day, 45S5 is the composition most used for bioactive applications and is marketed by GlaxoSmithKline under the tradename NovaMin. It has been used for a wide range of applications, such as to construct delicate inner ear bones and rebuild roots of teeth. A new toothpaste, Sensodyne Repair and Protect, includes 45S5 and is effective for rebuilding tooth enamel and helping to halt periodontal disease. The toothpaste is readily available in Europe, but it is unclear whether or when it will be available in the US. (See the May ACerS Bulletin for a sidebar story about this toothpaste.)

Hench was engaging, funny, and enlightening. He also was clearly delighted with the award and to have his name added to the list of distinguished awardees.

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