Researchers here demonstrate the use of magnetic fields and fluids to produce a more natural cell density gradient in engineered cartilage tissue. The result is bioartificial cartilage with better structural and mechanical properties than would otherwise be obtained. The approach is quite interesting, and illustrative of a broader area of research into the best way to engineer tissues that must contain variations in cell types, cell density, signal molecules, or supporting structure in order to delivery the desired end result.

Using a magnetic field and hydrogels, a team of researchers have demonstrated a new possible way to rebuild complex body tissues. “We found that we were able to arrange objects, such as cells, in ways that could generate new, complex tissues without having to alter the cells themselves. Others have had to add magnetic particles to the cells so that they respond to a magnetic field, but that approach can have unwanted long-term effects on cell health. Instead, we manipulated the magnetic character of the environment surrounding the cells, allowing us to arrange the objects with magnets.”

In humans, tissues like cartilage can often break down, causing joint instability or pain. Often, the breakdown isn’t in total, but covers an area, forming a hole. Current fixes are to fill those holes in with synthetic or biologic materials, which can work but often wear away because they are not the same exact material as what was there before. What complicates fixing cartilage or other similar tissues is that their make-up is complex. “There is a natural gradient from the top of cartilage to the bottom, where it contacts the bone. Superficially, or at the surface, cartilage has a high cellularity, meaning there is a higher number of cells. But where cartilage attaches to the bone, deeper inside, its cellularity is low.”

With that in mind, the research team found that if they added a magnetic liquid to a three-dimensional hydrogel solution, cells, and other non-magnetic objects including drug delivery microcapsules, could be arranged into specific patterns that mimicked natural tissue through the use of an external magnetic field. After brief contact with the magnetic field, the hydrogel solution (and the objects in it) was exposed to ultraviolet light in a process called “photo crosslinking” to lock everything in place, and the magnetic solution subsequently was diffused out. After this, the engineered tissues maintained the necessary cellular gradient. With this magneto-patterning technique, the team was able to recreate articular cartilage, the tissue that covers the ends of bones.

“These magneto-patterned engineered tissues better resemble the native tissue, in terms of their cell disposition and mechanical properties, compared to standard uniform synthetic materials or biologics that have been produced. By locking cells and other drug delivering agents in place via magneto-patterning, we are able to start tissues on the appropriate trajectory to produce better implants for cartilage repair.” While the technique was restricted to in vitro studies, it’s the first step toward potential longer-lasting, more efficient fixes in living subjects.