Skin and organ transplantation can save many patients, but this technology has disadvantages such as insufficient sources and rejection reactions. 3D bioprinting is considered as a solution, so it has become a hot research direction in the current medical field. However, one of the most important problems it faces is the slow progress in the research of bioprinting materials. Usually, the inks used in 3D printing are inanimate substances such as plastic or metal powder, which are suitable for making some high-strength materials. However, biocompatible materials, such as skin grafts, have extremely high requirements for softness and toughness, and traditional inks simply don't fit the bill.
In recent years, scientists have been developing 3D printing technology. With the realization of 3D printing to manufacture human organs, there is almost nothing that cannot be printed with it. In 2017, Science Advances magazine reported a breakthrough study in which researchers developed a new 3D printing platform that can form various three-dimensional structures based on the different types of bacteria added, which is expected to be used for skin and organ transplants in the future.
Living Ink for 3D Printing
A research team from the Composites Laboratory at the Federal Institute of Technology in Zurich (ETHZ) has developed a 3D printing platform that enables the digital fabrication of free-standing cell-laden hydrogels, with full control of cells or microorganisms in complex and self-supporting 3D architectures spatial distribution and concentration. The team developed a 3D printed living ink containing different types of bacteria. Based on the characteristics of various types of bacteria, it is suitable for skin transplantation, chemical degradation and other fields.
Fig.1 Schematics of the 3D bacteria-printing platform for the creation of functional living materials (Schaffner M., et al. 2017).
This functional living ink is named "Flink", the main component of the ink is a biocompatible hydrogel composed of hyaluronic acid, long chains of sugar molecules and pyrogenic silica in which bacteria can survive. The gel was infused with living organisms, including Pseudomonas putida, which can be used to degrade waste commonly found in chemical production, and Acetobacter xylinum, which synthesizes cellulose that can be used in skin and organ transplants.
As Thick As Toothpaste
During the development of the ink, the flow properties of the hydrogel have a special challenge: the ink had to be fluid enough to pass through the pressure nozzle. The harder the ink, the harder it is for bacteria to move. However, the print must be strong enough to support the weight of subsequent layers. If they are too fluid, it is impossible to print structures that are stable enough because they will collapse under the weight. Researchers of the Composites Laboratory at the Federal Institute of Technology in Zurich (ETHZ) summed up the key to the ink, which has to be as viscous as toothpaste and have the consistency of hand cream.
Application Potential of Bacterial Inks
Members of the research team said that 3D printing using this kind of living ink will exert its huge potential in countless possible fields in the future. Most people only associate bacteria with disease, but in reality we couldn't survive without them. The researchers believe their bacterial ink is completely safe, as the bacteria used are all harmless and beneficial.
In addition to medical and biotechnological applications, researchers envision many other potential uses. For example, this substance can be used to study degradation processes or biofilm formation. One practical application could be 3D printed sensors containing bacteria to detect toxins in drinking water. Another idea is to create filters containing bacteria for use in catastrophic oil spills.
To realize these applications, we first need to overcome the challenges of slow 3D bioprinting time and poor scalability. Currently, it takes several days for Acetobacter xylinum to produce cellulose for biomedical applications. The scientists believe they can further optimize and speed up this process.
Reference
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Schaffner M.; et al. 3D printing of bacteria into functional complex materials. Science Advances. 2017, 3(12): eaao6804.
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