Currently, implanting a stent to open a passageway in the body involves inflating, with a balloon, a rigid steel or titanium structure. Problems arise when the conduit shifts or flexes, and the inelastic stent cannot properly adapt. Out of the many who have searched for a material with the durability of steel and the flexibility of plastic, Dr. Jan Schroers, Associate Professor of Mechanical Engineering, may have found the “golden ticket” – a biomaterial called bulk metallic glass.
Schroers has been working with the promising substance for over a decade. From carving out the face of our president to redesigning perfume
bottles, Schroers has consistently shown that bulk metallic glass (BMG) allows one to “fabricate geometries that were previously unachievable with any metal processing technique.”
Bulk metallic glass is an amorphous metal, a substance that never reaches the crystallization point of a normal metal. The atoms are closely packed but as mobile as though they are in the liquid phase. Due to this lack of crystallization, the grain size for BMG is extremely small. As Schroer postulated, “The grain size may be as small as one atom.”
In the world of nanotechnology, the process of nanoimprint lithography (NIL) is essential. Imprinting allows one to mold a substance on the nano scale. The conventional NIL technique involves imprinting with expensive silicon molds. However, silicon becomes brittle after only a few imprintings, making the process very costly. Schroer’s laboratory is revolutionizing nanoimprinting by using BMG molds. These improved molds retain elasticity and cost less due to increased repeatability. As a material with three times the hardness and five times the elasticity of steel, BMG looks to replace commonly used metals and plastics. The implantation realm of biomedical engineering stands to gain incredible advancement from work with BMG.
When asked about specific biomedical applications, bone replacement and soft tissue implants topped Schroers’ list. “Stents, especially, would improve because BMG is more designable,” Schroers explained. As a result of its elasticity, a stent made from BMG would not require a balloon to inflate it. It would also be able to shift and flex with changes to any biological passageway over time.
Teaming up with Dr. Themis Kyriakides, Associate Professor of Pathology, Schroers combined his knowledge of BMG with Kyriakides’s medical expertise.
The team tested cell growth when in contact with the new material. Schroers was able to prepare and mold the BMG before using the substance in in vitro trials. Petri dishes of several different cell types were put in contact with BMG, and cell growth and adhesion were observed.
In vivo trials were also carried out using implants in mice. Small BMG fragments were inserted subcutaneously for four weeks. A moderate response of “middle ground” inflammation resulted, similar to that of silicon, a known biocompatible material.
Other in vivo trials consisted of inserting BMG implants into the brains of mice. The purpose of these trials was to model the potential for BMG electrodes. BMG trials produced less of an inflammatory reaction when compared to other common electrode materials such as gold, silicon, and other crystallized metals.
Currently, the neurosurgery department is in collaborations to design a functioning BMG electrode in order to test not only the body’s response to the material, but also the functionality of the substance.
When asked about potential problems with BMG, Kyriakides mentioned a few unknowns when working with the relatively new material in a biocompatible setting. For instance, the stability in a long-term living environment has yet to be assessed.
Certain biomedical applications, such as neural electrodes, would need to be built to last a lifetime. As biocompatible testing of BMG is in the early stages, these advancements are still far off. “We are in the animal stage now,” Kyriakides explained. “Two major time requirements are still ahead: product development, and of course, more testing.”
That said, Kyriakides puts the time scale at five to ten more years until the first BMG products arrive on the market. Until then, Schroers continues to think of endless physical applications for his specialty material. To get a taste of hisintentions, the upcoming Chanel 5 perfume bottle aims to redefine aesthetic limits. Its compositional makeup: bulk metallic glass.