1 Sensors Research Laboratory, Department of Chemical Engineering, University of South Florida, Tampa, Florida 33620, USA. 2 Shriners Hospitals for Children of Tampa, 12502 Pine Drive, Tampa, Florida 33612, USA.

Background/Motivation:

Ischemic osteonecrosis of the femoral head (IOFH) is a disease that causes bone death resulting from poor blood supply being circulated to certain area of bone3. IOFH is a disease of concern because it can cause bone to collapse due to the dead areas of the bone loosing structural integrity2, and are therefore weakened. The area most affected by this disease is the hip and upper part of the thigh bone which makes up the ball-and- socket joint (the femoral head). The end result of this process is pain and osteoarthritis3. IOFH is a localized deformity2, and therefore, there is a necessity for finding different methods of transporting proteins and medicine into the affected area in order to keep the disease confined to the damaged area of bone. There is much new excitement surrounding the use of single-walled nanotubes (SWNTs) for many applications in research on the molecular level. The unique and superior electrical, mechanical, and thermal properties of carbon nanotubes are what have attracted so many people to study and conduct research with them. All of these properties make carbon nanotubes great candidates for research in the area of orthopedics. The idea being presented here is the use of SWNTs as molecular transporters of proteins and medicine into osteoblastic cells to see if they can help in bone formation, and applying the knowledge gained through experiments to new methods of treating IOFH. The primary questions that need to be answered are: do proteins adsorb non-specifically to the SWNT sidewalls, and will the SWNT/protein solution permeate the osteoblastic cells without toxicity? Once these questions are answered, the doors will be opened to new research and methods in the area of orthopedics. Previous studies have used various proteins, DNA, and RNA as biological transporters and have shown that these cargos do adsorb onto the SWNT and cellular uptake is achievable without toxicity4.

Experimental:

An experiment was conducted by taking funtionalised SWNTs suspended in a deoxygenated water solution and mixing them with fluoresently labeled bone morphogenetic protein-2 (bmp-2) in order to verify if the proteins would bond non-specifically to the sidewalls of the SWNT. Functionalised SWNTs with a concentration of .1 mg/ml were diluted to .025 mg/ml with phosphate buffer saline (PBS). The fluorescently labeled bmp-2 was diluted to 1 uM by adding 1 ul to 1 ml of the PBS solution. 20 ul of the SWNT solution and 20ul of the bmp-2 solution were then mixed and left to blend for 2 hours. 20 ul of this mixture was then place on a 1 cm^2 plasma cleaned (to increase hydrophobicity) silicon wafer, cleaned, and left to dry for an hour. The samples then waited to be observed under scanning electron microscopy (SEM). It was found that bmp-2 does absorb non-specifically to the sidewalls of SWNT (Figure 1).

Results/Discussion:

As discussed, the first question to be answered in this project was to evaluate if bmp-2 would adsorb non-specifically to the SWNT. With this answered, the next step is to evaluate if the SWNT/protein solutions will permeate the osteoblastic cells. Mouse osteoblastic MC3T3-E1 cells were cultured with a 10% FBS medium. More of the SWNT and bmp-2 solution has been prepared. Fluorescent microscopic studies to evaluate osteoblastic cell wall permeation are underway and results will be presented.

3 . 4 Kam, Jessop, Wender, and Dai, “Nanotube Molecular Transporters: Internalization of Carbon Nanotube-Protein Conjugates into Mammailian Cells,” JACS, May 2004, (31 March 2007).

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