Medical researchers were shocked to discover that virtually all human embryonic stem cell lines being used in 2005 were contaminated. Animal byproducts used to line Petri dishes had left traces on the human cells. If those cells had been implanted in a human body they likely would have been rejected by the patient's immune system.
Even today, with new stem cell lines approved for use in medical research, there remains a risk that these cells will be contaminated in the same way. Most research labs still use animal-based "feeder layers" because it remains the cheapest and most reliable way to get stem cells to multiply.
Materials scientists at the University of Washington have now created an alternative. They built a three-dimensional scaffold out of a natural material that mimics the binding sites for stem cells, allowing the cells to reproduce on a clean, biodegradable structure. Results published in the journal Biomaterials show that human embryonic stem cells grow and multiply readily on the structure.
"The major challenge for stem cell therapy today is it's very difficult to make a lot of them with high purity," said lead author Miqin Zhang, a UW professor of materials science and engineering. "So far it seems like this material is very good for stem cell renewal."
Medical researchers hope to someday use stem cells to grow new tissues and organs. Key to the research is the fact that new cells maintain the property that holds medical promise - the ability to differentiate into any of the more than 220 cell types in the adult human body.
Growing the cells in three dimensions better resembles conditions in the human body. It also allows mass production, which will be needed for any clinical applications.
"Three-dimensional scaffolds are an active area of research," said Carol Ware, a UW professor of comparative medicine and expert on stem cells. "They are not commonly used yet, but will be important to transition embryonic stem cells to the clinic. To date, nobody has found a perfect matrix."
Zhang's cylindrical scaffold is made of chitosan, found in the shells of crustaceans, and alginate, a gelatinous substance found in algae. Chitosan and alginate have a structure similar to the matrix that surrounds cells in the body, to which cells can attach. Different processing techniques can make the scaffold out of interconnected pores of almost any size, Zhang said.
Researchers first seeded the scaffold with 500,000 embryonic stem cells, and after 21 days the scaffold was completely saturated. The cells infiltrated the structure, Zhang added, unlike other materials where cells often grow only on the surface.
"This scaffold mimics the extracellular matrix at the atomic level, and so the cells are able to grow in this environment," Zhang said.