What’s the Best Way to Preserve Personalized Bone Grafts?

The Context: After a bone graft is created from stem cells, it will likely have to be preserved for a while before it reaches a patient. Since engineered bone grafts are an emerging approach for treating bone injury and disease, it is not yet clear how best to store bone grafts made from stem cells in a way that minimizes damage.

The Study: Hypothermic preservation (storing at a few degrees above freezing) supports cell viability in stem-cell-derived bone grafts better than cryogenic preservation, finds a new study in the Annals of the New York Academy of Sciences by NYSCF – Ralph Lauren Senior Research Investigator Dr. Giuseppe Maria de Peppo.

The Importance: This study is an important step toward establishing best practices for bringing personalized bone grafts out of the lab and into the clinic.

Bone grafts engineered from stem cells could revolutionize the way we treat bone disease and injury. These personalized grafts have the potential to easily integrate into the body’s dynamic environment, form connective tissue and vasculature, and grow and change along with patients, eliminating the need for children to frequently get their implants replaced.

But before these grafts reach the clinic, many factors need to be optimized. For example, once a graft is made, it has to be properly preserved before it can be implanted into a patient. What’s the best way to do this? A new study published in the Annals of the New York Academy of Sciences and led by NYSCF – Ralph Lauren Senior Research Investigator Giuseppe Maria de Peppo, PhD, tested the two most common methods (hypothermic vs. cryogenic preservation) to determine which is better for keeping stem-cell-derived grafts safe and healthy before they reach an operating room.

Cold vs. Really Cold

Cells are typically preserved in one of two ways: in a hypothermic environment or a cryogenic environment. Cells that undergo hypothermic preservation are kept at temperatures a few degrees above freezing (32°F), and this method is a favorite for short-term storage. Cells that are cryogenically preserved are kept at subzero temperatures (-112 to -310° F), which is generally preferred for long-term conservation.

The effects of hypothermic vs. cryogenic preservation differ across cell types, and can adversely affect their viability, but prior to this study, it was unclear how these preservation methods would affect bone grafts made from stem cells.

The Winner Is…

Dr. de Peppo’s team tested the preservation methods on bone grafts engineered from stem cells. One group of grafts was stored for 48 hours in a phosphate-buffered saline solution at 39° F (hypothermic preservation). The other was stored for the same amount of time in a substance called Synth-a-Freeze at -292° F (cryogenic preservation).

The scientists then warmed the grafts up in a water bath and examined their viability. While the cells stored cryogenically showed cell death and some structural abnormalities, those stored in a hypothermic environment were not significantly affected — crowning hypothermic preservation as the better option for short-term storage.

“This study is important because it identifies an optimal method for preserving bone grafts engineered from stem cells, and establishing best practices for storing stem-cell-derived products will be critical for bringing these grafts from the lab to the clinic,” remarked Dr. de Peppo. 

Journal Article

Hypothermic and cryogenic preservation of tissue-engineered human bone
Tam E, McGrath M, Sladkova M, AlManaie A, Alostaad A, de Peppo GM. Annals of the New York Academy of Sciences. 2019 Oct 31. doi: 10.1111/nyas.14264.