02 cartilage scaffold1 Cryopreservation of stem cells suspended in a 3D matrix

Injured cartilage can be repaired through tissue engineering. Cryopreservation may make this technology more widely available.

While repairing cartilage through tissue engineering is currently still being explored experimentally1, cell scaffolds designed for cryopreservation will be important if the procedure is to become widely available.  The goal is to treat people with injured or diseased articular cartilage using stem cells suspended in a 3D matrix, cultured under the right conditions to differentiate the cells, and then implanted at the site of injury.  The stem cells repopulate lost chondrocytes, the cartilage-producing bone cells.  As the cells grow and secrete their own extracellular matrix, the surrounding scaffold gradually dissolves, leaving behind new cartilage.  For this to be a routine procedure, the stem cells and scaffolds will need to be mass-produced and relatively ready-to-go.  One challenge is finding a way to preserve the bioengineered constructs.  Cryopreservation is routinely used to preserve stem cells.  Can it preserve the scaffolds that contain them, too?

Cryopreservation of hydrogels

There have been bumps in the road to developing a scaffold that can withstand cryopreservation, including issues with ice formation in the cells and changes to the scaffold itself.  Hydrogels, which are already widely used in biomedicine, may be one solution to the problem.  A new study shows that hydrogels stand up to slow-freezing cryopreservation, as do their encapsulated cells2.  The cells even get a little extra cryoprotection from the surrounding hydrogel.  After the thaw, the cells in hydrogel look and act like chondrocytes, expressing proteins associated with the cartilage extracellular matrix.  The hydrogel itself is only minimally damaged through cryopreservation: it’s a little less able to absorb impact compared to never-frozen hydrogels, but not to the extent that it would affect normal human movement.  Slow-freezing hydrogels laden with stem cells is one way that tissue tissue engineering can be brought to a broad patient population.

References for cartilage tissue engineering

1Unlike bone, cartilage regeneration remains elusive.  Huey DJ, Hu JC, Athanasiou KA. Science 2012 Nov 16;338(6109):917-21. doi: 10.1126/science.1222454

2Cryopreservation of cell laden natural origin hydrogels for cartilage regeneration strategies. Elena G. Popa ,  Márcia T. Rodrigues ,  Daniela F. Coutinho ,  Mariana B. Oliveira ,  João F. Mano ,  Rui L. Reis and Manuela E. Gomes.  Soft Mater.  Epub 16 Nov 2012. DOI: 10.1039/C2SM26846A