For interactive assistance with choosing a bioink best suited for your application, please visit our bioink selection guide.
There are several characteristics to keep in mind when choosing a bioink for your application. Of course, bioinks must possess the ability to maintain cell viability before, during and after the bioprinting process. However, your application may require a bioink that has shear thinning properties, a certain viscosity or that provides structure once printed. These properties depend on the base of the bioink. Currently, bioinks range in base composition from alginate, gelatin, collagen, synthetic networks like PEG or other engineered matrices. Bioink thickners will also play role in the characteristics and can include nanocellulose, xanthan or clays. These thickners can allow previously non-printable base components to be printable.
Roughly, bioinks can be divided up into several classes based on their ultimate role in a printed structure:
|Structural bioink||Functional bioink||Sacrificial bioink||Non-sacrificial bioink|
Structural bioinks will provide the most rigid structure once printed. These inks are typically gelatin based.
Functional bioinks will provide some form of nutrient or compound that helps mimic the native environment of your particular cells. For example, for bone cells you may choose an ink with hydroxy apetite, for skin cells you may choose a bioink with collagen and so on.
Sacrificial bioinks are particularly helpful when printing more complex structures. They will help support your structure before it is crosslinked, after crosslinking you can typically wash this material away.
Non-sacrificial bioinks are typically use to provide structure but are not mixed with cells. These are often thermoplastics, silicons, and crosslinkable PEG hydrogels.
For more information about these classes of bioinks, visit the Overview of CELLINK bioinks knowledge article.
Once you know what class of bioink your application requires, you must consider the printability of the materials you need. For a bioink to have good printability, we look at four properties:
- Forms a continuous filament during extrusion
- Maintains a stable structure prior to crosslinking
- Exhibits long-term stability after crosslinking
- Supports cell viability before, during and after the bioprinting process
There are a few ways in which we improve the printability of our inks:
- Modulating the molecular weight of the biomaterial
- Changing the concentration of the biomaterials in the bioink
- Adding thickening agents or other types of biomaterials
Utilizing these changes can impact shear thinning properties, speed of gelation, self-assembly kinetics, and viscosity. Adjusting these parameters for your application can require a lot of optimization. Implementing our bioinks can reduce the time needed for optimization so you can start printing right away.
Besides adjusting the composition of your bioink, you can also optimize for printability on your bioprinter. You can improve printability using these methods:
- Using a temperature controlled printhead to maintain the temperature of the bioink during printing for optimal extrusion. This is especially useful for gelatin and collagen based bioinks.
- Using a temperature controlled printbed to control temperature after deposition. Once again, this is very useful for gelatin and collagen based bioinks.
- Using the most appropriate printhead for your ink. For example, low vicosity materials are printed most easily with the electromagnetic droplet printhead.
- Using crosslinking mechanisms such as a light source to photocrosslink the bioink and improve stability.
Other tips for improving your bioprinting experience include:
- Conical nozzles are better for extrusion of high viscosity bioinks
- Straight needles are better for extrusion of low viscosity bioinks
- Metal conical nozzles, metal needles, and nozzle sheaths are better for temperature-sensitive bioinks
- If printing thermoplastics, metal nozzles result in better extrusion
- Co-axial needles can be utilized to crosslink bioinks during extrusion
- Larger diameter nozzles can be utilized to reduce the extrusion pressure and will increase cell viability
The extrusion orifice plays a large role in the printability of your ink. In general, larger diameter nozzles will require lower pressures and have a lower chance of causing cell death due to shear stress. The size of your cells must also be taken into account. Some cell types tend to clump and will clog the needle or nozzle. In this case, you may need to consider a larger diameter orifice.
There are a lot of properties and options to consider when choosing the perfect bioink for your application. These notes should serve as a good intoduction into the world of bioinks, however if you have any concerns regarding your specific application please reach out to firstname.lastname@example.org.