SOP_BioPrint – Protocols for standardized bioprinting

Reproducibility through standardization

When it comes to the transition to industrial applications, criteria such as accuracy of shape and reproducibility of products generated by additive manufacturing are of crucial importance. The considerable diversity of the printer systems available on the market and the current low level of standardization of available biomaterials for manufacturing bio-inks lead to a “data jungle,” where it is difficult to establish any universal criteria for materials and processes that would allow 3D bioprinting to be carried out in a targeted and results-based way.

Round robin test for a standard operating procedure (SOP)

To solve these challenges, the Karlsruhe Institute of Technology (KIT) invited 13 renowned partners, selected on the basis of their published expertise in this field, to participate in a round robin test as part of the SOP_BioPrint project. These trials are normally used for quality assurance or to validate measuring and testing procedures. Standard operating procedures (SOPs) give precise descriptions of manufacturing or testing procedures to ensure that the results are always reproducible, and therefore comparable, regardless of the manufacturer or test laboratory that carries them out.

The SOP_BioPrint project therefore investigated the extent to which it is possible to print reproducible and comparable structures with standardized bio-inks in different locations and on different devices, but with the same parameters. To get around the variances that arise from preparing inks at the locations with different 3D bioprinters, partners supplied two bio-inks in addition to one commercially available bio-ink.

Fraunhofer IGB not only participated in this round robin test, but also supplied a gelatin-based crosslinkable bio-ink for all the partners involved. This meant that the IGB bio-ink was one of the three bio-inks investigated in the round robin test. As well as the material (modified gelatins, radical starter, buffer), we also supplied the round robin partners with an SOP for the modification and formulation of the bio-inks. This SOP allowed all those taking part to produce and use bio-inks with identical chemical and physical properties.

Methacrylated gelatin according to standardized modification process

This involvement in the round robin test led to the creation of the first standardized manufacturing procedure for a gelatin-based bio-ink developed at Fraunhofer IGB. Here, the now standardized modification of gelatin with methacrylic anhydride stands out as a simple and cost-effective strategy for integrating photopolymerizable groups into the biopolymer.

The resulting methacrylated gelatin derivatives can crosslink covalently through photo-induced radical polymerization. In this way, they form a versatile matrix that can be used to produce tissue analogs ranging from blood vessels, cartilage, ligaments, tendons and bones to fatty tissue and heart tissue [1].

As well as the biological advantages, another important feature is the ability to use chemically crosslinkable gelatin-based hydrogels in bioprinting to establish mechanical stiffness. Methacrylation also allows the rheological behavior of the gelatin to be controlled so that it becomes fluid at room temperature. This provides a high degree of control over the hydrogel design in 3D bioprinting.