From telecomm to bone scaffolds, a new role for glass

	(from left to right) Doctors Ana Marquez from Portugal and Hassan Moawad from Egypt, along with Mohamed Ammar, a dentist from Egypt, prepare porous glass materials at Lehigh.

The increasingly high-tech world in which we live never ceases to amaze.
Most people are by now aware that glass, as a key ingredient in optical fibers, plays an important role in advanced telecommunications. But they might be surprised to find out that one type of glass is being tested for its ability to help human beings regenerate injured bones.
Ana Marques has become a leader in this new investigation—after making a 180-degree change in her approach to glass research.
Marques received her Ph.D. in optical materials in December from the Instituto Superior Técnico in Portugal, and was then invited to conduct a three-month study at Lehigh’s International Materials Institute (IMI) for New Functionality in Glasses.
Her goal at Lehigh was to learn to prepare bioactive, or biocompatible, glasses that have “controlled porosity.” Glasses that are porous at both the nanoscale and macroscale, she explains, possess enhanced bone-restoration capabilities.
Nanoporosity promotes cell adhesion and the rapid crystallization of hydroxyapatite, which is the chief structural component of bone.
Macroporosity allows bone cells to “in-grow” and to vascularize, or form blood vessels and tissue.
“Glass bone scaffolds” with this dual porosity, says Marques, must be bioactive and must possess mechanical properties matching those of bone. Scientists hope that when these scaffolds are inserted into the body at the site of an injury or defect they will act as a 3-D template for bone growth and thus help the body’s bone tissue to regenerate.
The next generation of applications
“Regeneration will occur,” says Marques, “because cells are prompted [by the scaffold] to repair their own tissues. The cells proliferate inside the scaffolding material and form tissues, thus facilitating the delivery of nutrients to regenerating tissue. The scaffold is eventually absorbed by the body.
“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.”
The Lehigh IMI research team in which Marques works is seeking a patent on the new technique for preparing nano- and macroporous bioactive glass. The team, headed by Himanshu Jain, the Diamond Chair Professor of materials science and engineering at Lehigh, collaborates with Princeton University and with scientists in Egypt and Senegal. Another member of the team is Rui Almeida, professor of materials science and engineering at the Instituto Superior Técnico and Marques’s Ph.D. adviser.
Marques’s efforts to develop dually porous glass ran counter to her research goals at the Instituto Superior Técnico. There, she sought to prevent the formation of pores while preparing optical planar wave guides that are used in optical amplifiers.
In her project at Lehigh, Marques 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 into a gel, and then heat-treated it until it formed a glass.
The sol-gel process inherently promotes nanoporosity, says Marques. To achieve the additional desired property of interconnected macroporosity, Marques added a polymer to the sol-gel solution and promoted a polymerization-induced phase separation that occurred parallel to the sol-to-gel transition.
The final result is heat-treated glass with pore sizes of about 20 nanometers (1 nm is one one-billionth of a meter) and about 100 microns (1 micron equals one one-millionth of a meter).
“The aim of our project was to create nano- and macroporosity in a bioactive material while achieving mechanical properties that match those of bone,” says Marques. “We believe our material will be stronger than material made with spherical voids, such as one that is prepared by foaming a sol-gel solution.”
Marques used relatively common equipment and lab techniques to develop dually porous glass. These included a ventilated hood, a hot plate, nitrogen adsorption and porosimetry to measure material surface areas and pore-size distributions, and high-resolution scanning electron microscopy to detect pores.
The next step for the researchers, says Marques, will be to measure the mechanical properties and bioactivity of the new material, as well as the responses of cells that interact with the material.
The IMI for New Functionality in Glasses was established in 2004 with a five-year, $3.25-million grant from the National Science Foundation (NSF).
The Lehigh IMI is one of six established by NSF since 2003. It represents an outgrowth of Himanshu Jain’s 25 years of glass-related research and his work with researchers in Germany, Greece, India, the United Kingdom and the Czech Republic.
--Kurt Pfitzer