Using injectable hollow, biodegradable nanofiber spheres as cell carriers is likely to repair knee cartilage more effectively than current methods, said US researchers in a paper published online in Nature Materials this week.
Lead author Peter Ma, a professor at the University of Michigan (U-M) School of Dentistry, told the press they hope their method will bring hope to people with certain types of cartilage injuries that can’t be helped with current treatments.
In their paper, Ma and U-M colleagues Xiaohua Liu, Xiaobing Jin, describe how they used the hollow microspheres, formed by the self-assembly of star-shaped biodegradable polymers, to carry cells and boost cartilage regeneration in live rabbits, and showed that compared to control groups using other methods, it achieved a smoother integration of regenerated and healthy surrounding tissue.
A normal knee needs a smooth gliding, slippery surface of cartilage on the ends of the bones that meet in the joint. This stops the bones damaging each other and helps distribute forces inflicted on them during pounding, repetitive motion, such as running and jumping.
Injury to knee cartilage can severely impair quality of life. Swollen knees that lock and flare up with pain can reduce or stop ability to work, enjoy physical pursuits and the normal tasks of daily life.
The damage usually starts as a hole in the slippery surface, and if left untreated, gradually leads to deterioration of the joint surface. Also, cartilage is not good at repairing itself, which means people need to seek treatment if they are to resume normal activity.
One such treatment is ACI (autologous chondrocyte implantation), where the patient’s own cells are injected into the wound to start the process of cartilage regeneration.
But Ma, who also has a position in U-M’s College of Engineering, said ACI’s success is limited because the cells are injected loosely. He suggests the method he and his colleagues have developed using nanospheres to carry the cells, is better because the spheres provide a structure that simulates the natural tissue environment, giving the cells a head start to regeneration, and then the spheres bio-degrade, leaving the cells in a good position to carry on forming new tissue.
Ma and the colleagues in his lab have been working to find an injectable cell carrier that will help repair tissue damage that has odd or complex shapes. Their aim is to find a carrier that will ensure an accurate fit and avoid too much surgery.
They developed the biodegradable nanofiber microspheres according to what they call a biomimetic strategy: a system that copies biology and supports the cells in a matrix as they grow.
Ma said the hollow microspheres are ideal transporters because they are highly porous, so nutrients can enter easily and feed the cells, they mimic the cellular matrix in the already living host tissue, and when they biodegrade they do not leave many harmful byproducts.
In their study, Ma and colleagues treated rabbits with a “critical-size” cartilage damage with their “nanofibrous hollow microspheres/chondrocytes” procedure and a control procedure that simulated the clinically based ACI method.
They wrote that their procedure, achieved “substantially better cartilage repair” than the ACI-based one. The nanofiber group grew as much as three to four times more tissue than the controls, said Ma.
The team now wants to find out how the nanospheres perform in cartilage repair in larger animals before they plan tests in humans and other tissue types.
“Nanofibrous hollow microspheres self-assembled from star-shaped polymers as injectable cell carriers for knee repair.”
Xiaohua Liu, Xiaobing Jin & Peter X. Ma
DOI:10.1038/nmat2999
Additional source: University of Michigan (press release 17 Apr 2011).
Written by: Catharine Paddock, PhD