McGowan Institute for Regenerative Medicine faculty members Freddie Fu, MD, David Silver Professor of Orthopedic Surgery and Chairman of the Department of Orthopedic Surgery, and Constance Chu, MD, Assistant Professor in the Departments of Bioengineering and Orthopedic Surgery and Director in the Cartilage Restoration Program, both at the University of Pittsburgh School of Medicine and University of Pittsburgh Medical Center, recently assessed new research results on enhanced cartilage regeneration involving carbon nanotubes. Nanotubes are molecular-scale types of graphitic carbon that are among the stiffest and strongest fibers known and are great conductors of electrons. They are being studied intensively worldwide for a range of commercial, industrial, and medical uses.
Scientists have long wrestled with how to aid those who suffer cartilage damage and loss. One popular way is to inject an artificial gel that can imitate cartilage’s natural ability to act as the body’s shock absorber. The gel pads do not always adhere well to the remaining cartilage in the joint, which means that many patients require follow-up injections. “A concern,” Dr. Fu says, “is that even if the gel sticks it may not last long.”
Now a Brown University nanotechnology specialist and his team have found a way to regenerate cartilage naturally by creating a synthetic surface that attracts cartilage-forming cells. These cells are then coaxed to multiply through electrical pulses.
"The use of nanotechnology in scaffolds to assist with regenerating cartilage is novel," says Dr. Chu, "and would be of high interest if it can eventually improve the functional properties of the regenerated cartilage."
The Brown team found that the tubes, due to their unique surface properties, work well for stimulating cartilage-forming cells, known scientifically as chondrocytes. The nanotube’s surface is rough; microscopically, it looks like a bumpy landscape. Yet that uneven surface closely resembles the contours of natural tissue, so cartilage cells see it as a natural environment to colonize.
The Brown researchers also learned they could prod the cartilage cells to grow more densely by applying electrical pulses. Scientists don’t completely understand why electricity seems to trigger cartilage growth, but they think it helps calcium ions enter a cell, and calcium is known to play an integral role in growing cartilage.
Orthopedic surgeons commend the team’s research, but say it is too early to tell whether the approach will be successful. “Although the idea of creating stronger, better-adhering cartilage sounds good, placing permanent particles such as carbon nanotubes inside the joint may introduce other problems,” says Dr. Fu. His major concern: carbon nanotubes may not be biologically compatible with existing cartilage tissue in the joint.
Illustration: Carbon nanotube reinforced cartilage: A cartilage-forming cell (known as a chondrocyte) interacts with carbon nanotube fibers in this image. The researchers' goal is to grow carbon nanotube-reinforced cartilage in the body that is stronger than the torn or worn cartilage it is replacing. --Courtesy of Brown University.
Brown University Media Relations (06/03/08)
Scientific American (06/16/08)
Dr. Fu biography
Dr. Chu biography