Biopolymer-based functional inks for the preparation of artificial cartilage via bioprinting technology
The future vision of implants comprises the generation of artificial tissue generated from the patient's own cells. Furthermore, sophisticated complex tissue models will help to perform adequate in vitro testing and avoid animal experiments. In order to develop artificial, biomimetic structures which perform as well as natural ones, we need fabrication processes that do not set any limits to the generation of shapes, and materials that allow for tailoring of their physical, chemical, and biological properties. Thereby, biomolecules from the extracellular matrix of native tissues constitute very promising materials as they hold natural signalling motifs for the stimulations of cell adhesion, migration and function. With respect to the generation of artificial tissues by bioprinting technology, for instance articular cartilage, we develop printable and photo-crosslinkable material systems, based on bio-polymers derived from the native extracellular matrix (ECM), e.g. gelatin. Such bioinks can be used for 3D encapsulation of cells and cell printing, thereby constituting biomimetic matrices with adjustable properties for engineering of complex tissue models. In this study we present biopolymer-based biomaterials which are processable by inkjet printing and dispensing technology and can be crosslinked into hydrogels with tunable physico-chemical properties. These biomaterials are used for the biofabrication of artificial articular cartilage with biomimetic hierarchical structure. Photo-crosslinkable derivatives of the ECM biopolymers gelatin, chondroitin sulfate, and hyaluronan are prepared by their derivatization with methacrylic anhydride . These biopolymer derivatives can be converted into thermo-stable hydrogels by UV-induced radical crosslinking in the presence of a water-soluble photoinitiator . To furthermore achieve printable and dispensable bioinks, the viscous behavior of gelatin precursor solutions is adapted to the requirements of the printing technologies by additional functionalization with acetyl groups . The developed bioinks are then used for bioprinting with porcine articular chondrocytes to proof their cytocompatibility as well as the cytocompatibility of the printing process . For fabrication of zonal cartilage models bioinks with appropriate biopolymer composition for replication of the three cartilage zones (superficial, middle, deep) are determined. Criteria for evaluation are the visco-elastic properties of the resulting hydrogels, such as mechanical strength, swellability, and degradability, as well as their potential to preserve cell viability and functionality. Finally, three-dimensional, zonal cartilage models were fabricated and evaluated for their quality.