Titanium Dioxide Stops Germs
by April Gocha, PhD
Washing your hands is one of the best things you can do to prevent the spread of disease. But no matter how many times you scrub and sanitize, there are always more germs. Two new inventions, however, are using the power of ceramic materials to help prevent the spread of germs.
NanoTouch® Materials (www.nanotouchmaterials.com) out of Forest, Virginia, manufactures germ-neutralizing surfaces that can be applied directly to door handles and other commonly touched surfaces to kill off germs.
Standing sink water with sludge, aged clay, and dirty throwing water can all contain harmful mold and microbes, which can, in turn, be transferred from hands to door knobs, faucets, phones, and everything else we touch.
The company was recently awarded a $2 million Tobacco Commission grant to further research and develop its germ-killing products, which currently include mats, stickers, tissue box covers, and hotel channel guides. NanoTouch’s® stickers, called TouchPoints, can be applied to most frequently touched surfaces, such as doors and door handles. Those products incorporate the company’s innovative NanoSeptic® surface. NanoTouch’s® website says, “The materials science we deploy, molecularly bonded on a nanoscale, provides a non-leaching, self-cleaning surface using a light-powered catalytic oxidation process. Nothing is released from the surface, no toxins, no heavy metals, and no poisons.”
The one component we do know is present in NanoTouch’s surfaces is titanium dioxide, whose microorganism-busting capabilities (also found in some sunscreens and tattoo ink) are well known.
Titanium dioxide is a photocatalyst—upon exposure to UV light, it generates free radicals, which are particularly deadly to microorganisms. Because titanium dioxide catalyzes the reaction, it is not consumed in the process. So the surface retains its germ-busting power touch after touch. And—added bonus—it is self-cleaning.
Germs that land on a titanium dioxide-laden and UV-exposed surface not only die, but the energy of the reaction decomposes them all the way down to their constituent parts.
The company says that NanoSeptic® surfaces are very durable and will still work as long as the surfaces don’t show signs of wear. “While most surfaces will last 6–12 months, high-traffic touch points or those in critical healthcare settings might benefit from replacement every 30–90 days.”
One problem with NanoTouch’s surfaces, however, is that the titanium dioxide requires UV activation. Indoor fluorescent lighting does emit UV light, but much lower levels than surfaces exposed to direct sunlight.
Ceramics Repairing Tissue
by April Gocha, PhD
Bone is fascinating—skeletons provide our bodies with support, and yet they are not simply frameworks—they’re alive. They grow, replace, remodel, and are anything but static, making repairing them incredibly tricky.
Current strategies to repair broken or damaged skeletal tissues often focus on providing the body with scaffolds to repair itself, rather than more historic approaches of trying to replace parts with stronger foreign materials. Especially tricky is repairing joints—they combine bone with cartilage to provide structure yet flexibility and mobility. While modern repair strategies can mitigate damaged joints, they rarely achieve full functionality. Part of the problem is that while we can develop man-made materials and spare parts that are stronger than the original, these foreign materials often have trouble integrating with the existing tissues.
Parts that are incompatible with the body’s immune system are rejected. And those that aren’t rejected often don’t fully fuse with the existing skeleton. Weak interfaces then lead to prolonged complications and issues with stability.
With that in mind, researchers at Tufts University and the University of Sydney have developed a novel type of biodegradable scaffold that combines silk and ceramic to help broken bodies jointly rebuild the cartilage and bone that compose joints.
“It’s a challenging problem to tackle,” Rosemarie Hunziker, Director for the Program for Tissue Engineering at the US National Institute for Biomedical Imaging and Bioengineering (NIBIB), says in a NIBIB news story about the research. “One of the big problems in cartilage tissue engineering is that the cartilage does not integrate well with host tissue after implantation, so the graft doesn’t take. In this new approach there is a greater chance of success because the materials have architectures and physical properties that more closely resemble the native tissue.”
SEM image of the biphasic scaffold, showing (A) complete scaffold, astructural features at higher magnifications. Reproduced with permission from The Royal Society of Chemistry.
To match the two-part nature of joints’ osteochondral tissue—osteo meaning bone, and chondral meaning cartilage—the researchers developed a biphasic (having two phases) material that is flexible and strong, enabling joint movement while providing structural support.
“The goal was to develop an artificial scaffold with mechanical and bioactive properties that successfully promotes healing of damaged tissue to restore a fully functional joint. Bioactive properties include having a scaffold with the correct pore sizes that allow cells to enter and populate the scaffold after implantation, and being fully degradable over time to remove barriers to tissue regeneration,” according to the NIBIB news story.
To create such a demanding bifunctional material, the team fabricated a cartilage-like scaffold from silk protein (from the silkworm Bombyx mori) joined to a bone-like ceramic scaffold of strontium–hardystonite–gahnite (Sr–Ca2ZnSi2O7).
Researchers fashioned the ceramic material—fabricated from a mixture of Sr–Ca2ZnSi2O7 powder and aluminum oxide (Al2O3) powder (15 wt%)—into a scaffold via a polymer sponge method, in which they coated the ceramic slurry onto a sacrificial polyurethane foam. Sintering the scaffold burned out the structural foam, leaving behind only the hardened ceramic scaffold.
Lead researcher Teja Guda at the University of Texas at San Antonio reported on similar material and repair research, saying, “It almost looks like a kitchen sponge. The scaffold is 85% open space. The cells grow into it, and because we give them something solid to grow into, they start to regenerate tissue.”
The Tufts–Sydney team also coated its bone scaffold with a silk protein solution “to facilitate adequate integration with the cartilage phase and allow control over size of the interface region, with the added benefit of enhancing the toughness of the ceramic scaffold by reducing the chance of crack propagation under load,” the paper states.1
The researchers report that the biphasic scaffold maintained structural integrity during stretch and compression tests, standing up “under forces that were much higher than would be encountered in the body under physiological conditions.” To test whether living cells regarded the new scaffolds as suitable homes to colonize, the team then performed in vitro experiments with cultured human mesenchymal stem cells. “The smaller pore size of the silk cartilage-like segment caused the mesenchymal cells to differentiate into cartilage cells,” NIBIB reports. “The larger pore size of the ceramic bone-like segment caused the mesenchymal cells to differentiate into bone cells.” And all without the addition of bioactive molecules to the scaffold, a fact that would make potential commercial fabrication easier.
The team validated that the differentiated bone cells expressed genes characteristic of bone cells, and that differentiated cartilage cells expressed genes characteristic of cartilage cells.
1 Published in Journal of Materials Chemistry B, is “A biphasic scaffold based on silk and bioactive ceramic with stratified properties for osteochondral tissue regeneration” (DOI: 10.1039/C5TB00353A).
Cross section showing a new generation of ceramic polymer blends used for dental implants. Photo courtesy of Investigación y Desarrollo.
Stronger and Cheaper Ceramic Teeth
by Jessica McMathis
If you’ve ever lost a tooth, you likely know how expensive a dental implant can be. Replacing a single tooth with an dental implant can cost anywhere from $1500 to $7500. Experts from the Autonomous University of Baja California (UABC) in Baja California, Mexico, are hoping to make dental implants more effective and more importantly, more affordable through the use of new materials.
Their new generation of dental implants are made from a ceramic-polymer blend—a mixture they say is not only more resistant to the impact of chewing and corrosion but also costs less than traditional titanium implants.
“By optimizing the geometry and consistency of the implants we can ensure that they remain in place longer, but with a lower cost than the titanium implant,” says collaborator Mauricio Paz González, who is responsible for the project’s industrial design.
According to a press release, the team has tested and optimized the ceramic-polymer implant’s performance by simulating the repetitive chewing and grinding we inflict on our teeth. Doing so has allowed them to “ensure that the impact of stress is absorbed by the piece and not by the bone structure.”
In an effort to lessen stress on the bone structure during placement of the implant, researchers employed mathematical simulations. Additionally, they sought the help of vitamin D. Juan Antonio Paz González, who heads the project’s manufacturing processes, says that they hope to coat the pieces with the vitamin, which would help to spur the growth of the bone tissue that surrounds the implant.
Once pilot tests have been completed, the UABC group plans to compare the lower-cost vitamin D-coated ceramic implants against more expensive traditional titanium pieces. “Additionally we seek to include vitamin D in the composition of dental implants, to achieve a better integration of the piece with the bone structure of the patient.”
These articles originally appeared on The American Ceramic Society’s Ceramic Tech Today blog. Learn more at www.ceramics.org/ctt.