Right now, remedies for chronic back pains are almost exclusively rather drastic ones, says Bart van Dijk. “For early back pains, a doctor may recommend physical therapy and pain killers, but if things haven’t changed after a year, there’s really no other choice but surgery.” Surgery either involves the removal of an invertebral disk and connecting adjoining vertebrae, or replacing the cartilage with a plastic implant. Still, that’s no guarantee for a life without back problems. “Both operations know a sixty to eighty percent success rate. And fixing the vertebrae will limit a person’s agility.”

You’d think all this is reason enough for finding better cures for lower back pain. Therapies aimed at stimulating cells to produce new, healthy tissue on their own could offer a solution. However, Van Dijk says there’s still fairly little money available for research into new treatments. “It probably has to do with the fact back pain isn’t life-threatening, as opposed to cardiovascular diseases and cancer. Our research field is therefore a small world with a limited budget.”

An additional complication is that most lab animals aren’t really suitable as ‘animal models’. Lower back pains are usually the result of worn invertebral disks, which are composed of a jelly-like core surrounded by a ring of fibrocartilage (the annulus). Just like all cartilaginous tissue, the invertebral disks can’t recover from wear. ‘Notochordal cells’ might play a role here. These cells are remains of the notochord, the embryonic predecessor of the spine, and disappear from people’s bodies at a young age. The invertebral disks of lab animals such as mice, rats, rabbits, and pigs do keep these cells. For that reason, using (tissue of) these animals for researching lower back pain doesn’t make a lot of sense.

There are other animals that go without notochordal cells in their invertebral disks as well, including cows and certain dog breeds like dachshunds and beagles. “Those breeds are more prone to back pain than other dogs, which is why it seems likely the problems are related to the disappearance of these cells.” Apart from the ethical objections and the costs of larger lab animals, the in vitro experiments – in a bioreactor –with damaged tissue of human donors has Van Dijk’s preference.

“Man is the best animal model”, says the biomedical engineer. “The challenge is to keep the human tissue alive in an artificial environment. And for that, you have to be able to imitate the natural conditions as accurately as possible.” The high concentration of negatively charged proteins in the tissue of invertebral disks is one of the most challenging aspects, because they cause a high osmotic pressure: nature automatically wants to balance the concentration of dissolved substances, and so the tissue attracts water.

“If you don’t try to stop that from happening, the tissue in the reactor could swell up to three times its original size. This affects the tissue structure and causes certain proteins to seep out.” Tissue that’s swollen because of osmotic pressure in a reactor differs from natural tissue in so many ways that it’s no longer suitable for research purposes.