Clinical products that are used to treat patients must be manufactured under a set of standards known as “Good Manufacturing Practice” or GMP. Drugs, catheters, stents, implants, pacemakers and so on must all be manufactured in a facility that strictly adheres to GMP standards and produces products that are consistently safe for patient use. Products made to GMP standards are free of contaminating microorganisms, free of molecules that cause robust rejection by the immune system, and known to be safe for use in a human patient.
Producing stem cells for regenerative medicine represent a tough case for several reasons. Most of the laboratory products sold off the shelf for tissue culture have some animal products in them, which disqualifies them for clinical use, since culture media with animal products can contain animal viruses or animal antigens that will cause patient’s immune systems to reject them. Growing stem cells under animal-free conditions is tedious, expensive, and the results are not always consistently reproducible. While some laboratories have made remarkable strides in growing cells under animal-free conditions, doing so in a manner that meets GMP standards is even more exacting.
New work by Kristina Lachman and Michael Thomas and their colleagues from the Fraunhofer Institute for Surface Engineering and Thin Films in Braunschweig, Germany, has shown that plastic bags coated with a plasma can provide excellent vessels for stem cell culture and can be manufactured in a manner that meets GMP standards.
The term “plasma” in physics refers to the state of a gas when a strong enough electric current is passed through it so that the gas mainly consists of ions. In such a state, the gas is no longer a gas and has properties unlike a solid, liquid or gas, but is considered a distinct state of matter. When a plasma is used to coat the inside surface of a plastic bag, it modifies the surface of the internal surface of the bag so that different types of cells can grow on it. The plasma also acts as a disinfectant while it transforms the surface of the bag so that cells are able to grow on it and even want to grow on it.
“Our goal was to realize a closed system in which cells grow undisturbed and without the risk of contamination. Coating the bags with plasma enables us to use them as a GMP laboratory,” said Henk Garritsen from Braunschweig Municipal Hospital.
To date, stem cells cultured from the patient’s own body have been grown in plastic culture dishes, spinner bottles, and bioreactors. However, systems like these, though initially sterile, must be opened in order to refill the culture medium or extract the cells. Every time the culture is opened there is a risk of contamination and the cells are rendered unusable.
Enter Werner Lindenmaier and Kurt Dittmar from the Helmholtz Center for Infection and Research who were already working on bags for stem cell cultivation. By collaborating with the experts at Fraunhofer who knew how to coat plastics with plasma, these scientists embarked on a very fruitful venture that culminated in experiments that showed that stem cells could robustly grow on plasma-coated films. Then a joint venture sponsored by the German Federal Ministry of Economics and Technology investigated the feasibility of plastic bags coated with plasma as a closed system for stem cells cultivation and growth.
To coat the bags with plasma, they are first filled with a non-reactive gas and then hit with low-voltage electrical currents. This generates a plasma in the bag and this plasma is a “luminous, ionized gas that chemically alters and at the same time disinfects the surface of the plastic,” said Lachmann.
The bags were coated in a pilot plant at Fraunhofer IST and then tested at the Helmholtz Center and the Braunschweig Municipal Hospital to test the diverse types of coatings used on the bags for their ability to support the growth of stem cells. Dittmat noted that, “We work with stem cells for bones, cartilage, fat, and nerves – the coating can be optimized for each of these cell types.”
The pilot plant at Fraunhofer IST has designed an automated system for making these stem cell culture bags. This automated system can make bags that are wholly reproducible in their composition and properties.
“We use medically approved bags for the coating,” said Thomas. “Nevertheless, the plasma treatment must be demonstrated to be innocuous before being approved for clinical use.”