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The Glass Bone Matrix

Glass, it seems at first glance, is almost endlessly versatile. We use glass to repair our eyesight, to adorn skyscrapers and to create artistic treasures. We employ it to reflect, refract and transmit light, and to exchange unthinkable quantities of information in slices of seconds. But all this is just the surface, says Himanshu Jain. Someday, if we can learn to tailor its chemical and mechanical properties, glass may be used to mimic and even restore the miracles of nature.

A glass scaffold with interconnected nano- and macropores shows promise in stimulating damaged and diseased bone to regenerate
Jain, director of NSF's International Materials Institute (IMI) for New Functionality in Glasses at Lehigh University, has spent three decades exploring the myriad uses of glass.

He accepted a new challenge during the 2004 U.S.-Africa Materials Workshop in Cairo, when he took a break to visit the University of Alexandria on Egypt's Mediterranean coast.

Mona Marei, head of the tissue-engineering lab at the university's Faculty of Dentistry, had asked Jain for help with a growing medical problem – the deterioration of people's teeth and jawbones. Osteoporosis, she told Jain, was causing the bone around people's teeth to weaken, making it difficult for doctors to replace loosening or diseased teeth with prosthetics or implants and, in severe cases, causing fractures that required removal of bone and teeth.

Marei was experimenting with biocompatible glass bone transplants to replace damaged teeth and bone, but was not satisfied with her results.

Biocompatible materials can be placed inside the body without triggering a systemic reaction or an infection. But Jain suspected something more than biocompatibility was required of the glasses that Marei was testing.

The ideal treatment for diseased or damaged bone is to coax the body's natural bone tissue to regrow. Doctors have succeeded in taking a bone graft from one part of a person's body and using it as a "scaffold" to stimulate bone tissue elsewhere to regrow. But although biocompatible glasses have been used as bone transplants, no one has yet succeeded in using glass as a bone scaffold.

Until now.

Today, working with researchers in four countries on three continents, Jain and his collaborators have modified a biocompatible glass belonging to the calcium-phosphate-silicate family into a scaffold that promises to stimulate bone regeneration. They have successfully tested the glass in in vitro experiments at Lehigh's IMI. Marei and her group are preparing to run in vivo tests at the University of Alexandria.

An overseas assist with dual porosity
In seeking an effective scaffold for bone regeneration, Jain and Marei sought to develop a glass that would promote transport of nutrients and blood while allowing new cells to "in-grow" and adhere to the scaffold.

Like the spongy interior of bone, the new material would need interconnected pores to facilitate the production of red blood cells and the flow of blood to other areas of the bone.

A glass scaffold might emulate the mechanical properties of bone, Jain believed, if it could be made porous at both the nano and macro scales.

Nanopores measuring several nanometers in diameter (1 nm equals one one-billionth of a meter) would allow cell adhesion and crystallization of bone's structural components.

Macropores measuring in the tens of microns or larger, roughly 10,000 times the size of nanopores, would allow bone cells to grow inside the scaffold and to vascularize, or form new blood vessels and tissue.

To achieve "dual porosity" in a biocompatible glass, Jain turned to two researchers he knew from the Instituto Superior Técnico in Lisbon, Portugal – Rui Almeida, professor of materials science and engineering, and Ana Marques, a research scientist who has studied pore formation while preparing wave guides for optical amplifiers.

During a recent stay at Lehigh's IMI, Marques used common lab equipment, including a ventilated hood and a hot plate, to develop glass with dual porosity. She employed standard experimental techniques – nitrogen adsorption and porosimetry to measure material surface areas and pore-size distributions and high-resolution scanning electron microscopy (SEM) to detect pores.

Marques also employed the sol-gel process, a wet-chemistry technique that uses relatively low temperatures to prepare glass. After mixing a solution, she allowed it to gelate and then heat-treated the gel until it formed a glass.

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An international group led by Himanshu Jain is preparing glass for a major new medical role
"This is the next generation of biomedical applications. It will be helpful for all bones, ranging from teeth to arms and legs. It can be used for breaks, tumors and other defects." —Ana Marques

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