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A bone allograft being placed into position.

The University of the Basque Country (Universidad del País Vasco) reports that one of its Ph.D. students has developed a new porous, biodegradable nanocompound support for the regeneration of bone tissue. According to UPV, Beatriz Olalde, in her doctoral thesis, reported on her approach that combines polylactic acid, hydroxyapatite and carbon nanotubes to form a material that could be used instead of bone grafts. Her material interacts chemically and electrically with bone cells and adjoining tissue to speed bone replacement and recovery.

Olalde

Each of the components in Olalde’s foam-like material plays a specific role. The polylactic acid forms a basic biodegradable scaffold. Hydroxyapatite – a benign, bone-like bioceramic substance that is very compatible with tissues – is added attract cell growth and provide a source of calcium. The CNTs are added to provide strength. The CNTs also provide a material that reacts with an external electric field in a way that stimulates cell growth.

The desire for materials like Olalde’s (alloplastic grafts) stems from problems the medical profession faces when, due to events like large scale physical trauma or tumor removal, a patient loses a significant section of bone. Bone has the ability to regenerate itself to a large extent, but that requires time and support for the injured area.

Typically, bone grafts have been used either from the patient (an autograft), a living donor or a cadaver (allografts). But often a patient isn’t capable of providing the graft and donated bone raises complications due to tissue rejection issues, contamination, etc.

According to Olalde, trials involving both in vitro and in vivo experiments have shown satisfactory results. She says the foam displayed good mechanical properties and bone support. In in vivo trials, bone growth was observed after three weeks, and after 16 weeks this new bone showed mechanical, histomorphometric and densitometric properties similar to those of intact, healthy bone tissue.

Olalde has published before about polylactic acid and carbon nanotubes, and has collaborated with the University of Aberdeen, Scotland, and the Institute of Biomechanics of Valencia (IBV). She was awarded her Ph.D. and is currently working as a researcher in the Department of Biomaterials and Nanotechnologies Unit Tecnalia Health.

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ACerS Fellow Prashant Kumta has been a pioneer in the use of nanoceramic materials for bone regeneration and to bind and transport proteins and protein-like substances into cells. Kumta, who teaches at both Carnegie Mellon University and the University of Pittsburgh’s Schools of Engineering and Dental Medicine, discusses how his interest in bioglass and bioceramics coincided with the explosion of nanotechology, opening up new opportunities for biocompatible materials that could be slowly absorbed by the body.

9 minutes.

Credit: Bok Yeop Ahn and Jennifer A. Lewis.

As you can see above, ACerS Fellow Jennifer Lewis and her team at the University of Illinois at Urbana-Champaign have figured out how to make intriguing and beautifully simple (yet complex) origami structures by bending and folding planar lattices. The lattices are made by extruding “inks” of ceramic, metal or polymeric materials using a precise, direct-write method.

In general, beads of inks are laid down in a particular pattern and allowed to partially dry. They are then trimmed, folded and finally annealed to complete the structure.

Direct writing of lattice. Credit: Bok Yeop Ahn and Jennifer A. Lewis.

But this makes it sound much too easy. In fact, Lewis,  Bok Yeop Ahn, David C. Dunand and others in her team faced significant materials and technical challenges. In a University press release, Lewis says, “Most of our inks are based on aqueous formulations, so they dry quickly. They become very stiff and can crack when folded.”

She says the challenge, then, was to find a solution that would render the printed sheets pliable enough to manipulate, yet firm enough to retain their shape after folding and annealing. The answer came by combining  wet-folding origami techniques (where paper is partially wetted to enhance its foldability) with special inks containing a mixture of fast- and slow-drying solvents.

The combination yields a lattice that can can be partially dry but flexible enough to fold through multiple steps. The origami crane - requiring 15 steps – allows them to demonstrate the agile possibilities of their methods.

For Lewis, a professor of materials science and engineering and the director of the university’s Frederick Seitz Materials Research Laboratory, these structures have a serious side. “By combining these methods, you can rapidly assemble very complex structures that simply cannot be made by conventional fabrication methods,” Lewis says.

Practically speaking, this technique could provide an alternative to existing “rapid prototyping” approaches to build scaffolds for tissue engineering. There are limits to rapid prototyping, which builds 3D structures by laying down layer after layer of material, due to the sagging of lower layers or compressing under their own weight.

Lewis’ team’s method could create light, strong structures that can be bent, folded and rolled out of lattices  formed from nearly any pattern. Stents, bone-repair scaffolds, biomedical devices or even catalytic substrates are possible.

Samples of stents and other structures. Credit: Bok Yeop Ahn and Jennifer A. Lewis.

Dunand says the next step is to try larger and much smaller structures and test ink compositions that would contain other ceramic and metallic materials.

“We’ve really just begun to unleash the power of this approach,” Lewis said.

A short video providing a closer look at some of the structures is available here.

Adding . . . Advanced Materials published a paper on this work, and if you look in the comments, the editor of the magazine has kindly posted a link for a free download of the paper.

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If you have a glass-top stove, you may have wondered why the rest of the glass stays cool when you have only one burner turned on. Linda Pinckney can explain why. Pinckney, an ACerS Fellow, has worked for Corning Inc. for more than 27 years in the field of glass–ceramic materials. Glass–ceramics combine the best of both worlds by carefully controlling the growth of crystals during the reheating of glass (often seeded with nucleating additives). Glass-top stoves are one example. So is Corning Wear and other similar heat resistant nonmetallic cookware. Pinckney also discusses examples of biocompatible and bioactive glass–ceramics.

In the case of stove tops and cookware, researchers and engineers take advantage of the thermomechanical properties of glass–ceramics that provide considerable strength even while be subjected to extremes of very low and very high temperatures.

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I got a chance to interview Muhammet Toprak at the recent ICACC’10 conference. Toprak is a researcher in the Multifunctional Materials Division of the KTH – Royal Institute of Technology in Stockholm. In this video, Toprak discusses his work as part of a cross-functional team that is working to assemble and test nanoparticle systems for biomedical applications. In particular, they have been working on the synthesis, characterization and in vitro compatability (with immune-competent cells) of tunable superparamagnetic Fe₃O₄–SiO₂ core–shell nanoparticles.

In general, the systems Toprak is working on are similar to those that were discussed in last week’s video regarding drug-delivery systems. Toprak’s materials are conceived as being as being able to deliver a payload, but they are first working on using them to improve imaging of biological tissue sites. For example, he discusses how particles loaded with both magnetic materials (such as iron) and flourescent dyes could help with imaging a specific tumor, first, before treatment, to plan a surgical approach, and second, during the surgery to indicate if and where residual tumor cells need to be removed.

8 minutes.