Three-dimensional cell culture is a technique allowing new and innovative possibilities for research. In the best scenario a 3D tissue model could potentially replace the use of animal models in certain areas. Furthermore, these types of techniques can truly open the doors deeper into personalized medicine and tissue engineering. The fast development of new and innovative bioprinters is lowering the boundaries we are facing when trying to create complex, native-tissue-like structures.
Bioprinting and its benefits
In bioprinting cells are combined with bioink i.e. a support material or hydrogel, to form three dimensional shapes for the cells to grow, divide and migrate in. The cells and the bioink are combined in sterile syringe and pushed out through a narrow nozzle or needle according to instructions given by a blueprint or a code (e.g. a .stl or .gcode-file). The code directs the bioprinter movements in X, Y and Z axis and thus determines the 3D form of the construct. The model does not need to be complex to study interactions between different cell types or migration of cells towards certain cues. The simplest models can, for example, be droplets.
Fig 1. HepG2 in an alginate bioink bioprinted in a 5×5 millimeter square on a 24-well plate. Brightfield images taken on the seventh day of the experiment show that the bioprinted construct had high viability. The HepG2 cells proliferated, forming rounded and tunnel-like clusters. Furthermore, typical hepatocyte characteristics including the bile canaliculi can be identified. Immunomarker ABCC2 (MRP2) was used to visualize these structures (green = ABCC2 and blue = nuclei). The optical transparency of CELLINK’s alginate bioink enables immunostaining and visualization of the entire bioprinted construct. (Images from here)
Bioprinted cells typically show natural morphology (see Fig. 1) and more native gene expression profiles than cells in 2D cultures. This is probably because they can grow, migrate and interact in all dimensions and, in the case of extracellular matrix (ECM) containing bioinks, interact with molecules present in the ECM. The technique allows researchers to design their own unique models, perform 3D culture screens for drug candidates and print out organoids, tumoroids etc. in a consistent way.
How to get started with Bioprinting?
Traditional 3D printers are not suitable for bioprinting as they are made for much harder materials and cannot support the sterility requirements needed for printing living cells. You may start by ordering commercial bioinks and testing how your cells grow on those substrates. Cells typically tolerate bioprinting very well, so if your cells are happy to grow in the chosen bioink you can proceed with bioprinting.
The most recent generation of bioprinters are user-friendly with inbuilt computer, touch screen, ready programs and good IT support from the manufacturer. Collective support is also available through web portals where users can ask questions, share codes or publications (THE 3D BIOPRINTING COMMUNITY). Bioprinter models (codes) can be created by using standard free 3D modeling softwares such as Tinkercad etc. and the models can be shared freely with other researchers.
The running costs for bioprinting are comparable to standard 3D cell cultures. All you need is plastic syringes, plastic nozzles or needles, hydrogel (bioink), culture plates/petri dishes or slides and cells.
How to choose the bio ink?
In principle you can print any hydrogel that your cells “like to grow in”, if you can extrude it through a narrow nozzle. However, printability is affected by the chemical properties of your ink, printing pressure, temperature, nozzle size etc. Therefore, it is often easier to start with commercially available inks with proven printability and protocols for printing, read more about bioinks. There are many options for different cell types and applications such as: skin, tumor engineering, vascular structures, bone, liver, neurons, intestine etc.
What about vascularized structures?
Larger bioprinted constructs will need vascularization for constant nutrient flow and gas exchange as well as for removal of metabolic waste. Sacrificial bioinks together with suitable normal bioinks can be used to create simple vascular structures. Sacrificial inks may be removed e.g. by cooling down the printed construct as this turns the sacrificial material into liquid that can be evacuated thus leaving a hollow vascular structure inside the construct. This is a very easy way to make perfusion compatible vascularized structures.
Interested? Contact us for more information or book a hands-on demo with BIO-X to prove it to yourself.