An interdisciplinary collaboration bringing together specialists in orthopaedic surgery, sports science and veterinary medicine have recently demonstrated knee tissue regeneration using carefully engineered, 3D-printed sheep menisci.
The meniscus is a crescent-shaped structure in the knee that provides us with crucial functions such as correct weight distribution and reduced friction in the joints. The cartilage found in the meniscus can absorb compressions, tensions and friction in a baffling way – it can handle forces of up to six times the body weight. However, it does not exhibit the same self-healing capacity as that of our bones. For this reason, damage to meniscus tissue poses serious challenges.
Currently, a common strategy for meniscus injuries is the removal (partial or complete) of the compromised structure, sometimes followed by substitution with a graft. However, this is a rather crude solution: giving up the precious cartilage increases risks of osteoarthritis, while grafts can expose patients to immune rejection.
Researchers at Columbia University aimed at addressing these issues by inducing the very cells of the injured patient to play a central role in the regeneration of a damaged meniscus – with a little help from a 3D-printed implant.
First, the team obtained a 3D image of a healthy meniscus that would be used to make an accurate scaffold rendition of the original. The 3D printer then follows the computer-prescribed recipe, building an anatomically-correct scaffold composed of layers of molten polyester fibres that reproduce the desired internal structure. The arrangement of strands and channels in the scaffold defines its mechanical properties and, in turn, those of the regenerated meniscus.
Crucially, the 3D-printed scaffold contains two distinct proteins that promote the production of new tissue by in-house cells, therefore reconstructing the assorted, cellular components of a healthy meniscus. These proteins must be released from the implant according to a specific sequence of events, which scientists optimised through preliminary testing.
Successful treatment of meniscus injuries must ensure correct tissue regeneration and restored biomechanics of the knee joints. To this end, the researchers tested their scaffolds on a small sheep herd. One group of sheep received implants loaded with the two proteins, whereas the control group was treated with empty scaffolds.
Twelve weeks after surgery, the fully integrated menisci of the animals in the treatment group mapped the characteristics of healthy tissues and showed mechanical properties similar to those of intact knee joints; this was not the case in the control group.
These results are encouraging not only because of the observed correct tissue regeneration in a large animal; they suggest a tailored, off-the-shelf approach to meniscus damage. If the strategy proposed by these researchers proves to be successful over longer time scales, one day we may be able to request freshly printed scaffolds for our injured knees.