Consider this: Every year, nearly one million bone replacement procedures are performed in the United States – a number that is expected to rise with an aging population. Though the procedures will, in most cases, restore mobility and relieve pain, the average lifespan for metal implants is about 10 years, primarily because metal is not easily incorporated into the body.
To develop a good bone imitation with the same physical, mechanical, and biological properties as real bones is the goal of Dr. Susmita Bose and her colleague/husband Dr. Amit Bandopadhyay at Washington State University in Pullman. Their goal is to develop bone and dental implants to match the strength and stiffness of natural bone while making them acceptable to the human body. With this in mind, Bose is developing nano-structured calcium phosphate based ceramics for repair and reconstruction of bone defects. But after seven years of pioneering research Bose admits, “It’s not very easy to remake nature."
All along Bose’s idea is simple, but the potential is tremendous. Since our original bones are made from extremely tiny ultrafine particles, why not make replacement bones out of a similar substance?
Bone is a natural calcium phosphate based ceramic consisting of nanometer size grains. However, one of the determining factors in the success of bone implants is what happens at the interface between the tissue and the implant material. An implant that isn’t bonded well to its surrounding tissue fails easily. But by constructing powder particles in nanometer size, the surface-to-volume ratio of the material is increased, creating a greater surface area to which particles or grains can bond with tissue efficiently. The increased number of smaller particles also causes the surface to be rougher, which creates an additional opportunity for bonding.
Already the Bose group has synthesized nano-powders of calcium phosphates at WSU with particle size in the range of 30 to 50 nanometers, or 2000 times smaller than the width of a human hair. These nano-powders improve densification and inherent strength of ceramics.
Nano-powders are currently being used to develop porous ceramic implants for spinal fusion, small-scale bone defects, and dental applications. What is really needed for these applications are high strength porous biocompatible structures that will initiate tissue in-growth and provide structural support during the healing process.
To simulate the properties of real bones, Bose and her group are synthesizing calcium phosphate based powders using novel processing methods that will lead to better bonding between the particles.
So far, the researchers have brought the particle size down to 50 nanometers, or 2000 times smaller than the width of a human hair. The densification of these nanometer size powder particles have already been found to be significantly higher compared to commercially available calcium phosphates. They are also working to add to their recipe other mineral ions that are typically found in human body system. It is anticipated that adding minute amounts of these metal ions such as magnesium, or sodium will strengthen these synthetic implants.
Bose hopes the nanoscale ceramic will be more familiar than metal to body tissue and will therefore bond better with surrounding tissue. Because of its better bonding capability at the nanoscale, the ultra-fine material could also be used to develop stronger imitation bone implants than are currently available.
But there are many intricacies of bones that Bose and her colleagues have not yet been able to replicate, such as the complex polymers in human bones. Bose and her team work to add tiny amounts of metal ions to the bone implants, strengthening them more.
Because they are building the calcium phosphate up from the most basic level, researchers can synthesize these ceramic bone materials into any type of bone a patient requires.
“By making materials from the atomic or molecular level, there’s so much flexibility to make them the way you want them with tailored properties,’’ Bose said. “The nanoscale technologies have a lot to offer for biomedical research, tissue engineering and bioengineering applications in the 21st century.’’
A novel surfactant assembly technique she is using involves trapping tiny particles within the core of a synthetic soap molecular assembly. The nanoscale material also has advantages over materials with larger particles because natural bone also is constructed of nanoscale constituents and body cells are accustomed to interacting with the nanostructured surfaces of natural bone.
Bose, an assistant professor at the School of Mechanical and Materials Engineering, received her B.Sc. in chemistry from Kalyani University (1990), M.S. in chemistry from IIT Kanpur (1992), and Ph.D. in physical organic chemistry from Rutgers (1998). Dr. Bose joined WSU as a tenure track faculty member in fall 2001. She received the CAREER award from the NSF in 2002 and the 2004 Presidential early career award for her “innovative and multidisciplinary research on bioactive bone implants.”
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