Speaker
Description
"Introduction: Bioprinting is a booming and promising technology to create tissue models, with numerous applications in tissue engineering and regenerative medicine. However, the biomaterials commonly used for bioprinting involve non-physiological stimuli (e.g., sudden changes in temperature, pH, ionic forces) and lack tunability post-printing. These biomaterials are therefore still far from recapitulating the physicochemical and biological characteristics required to create relevant in vitro tissue models. To date, a biologically relevant, ultra-tunable, fast- and easy-to-use bioink platform remains to be invented.
Methodology: We envisioned to create a novel bioink platform with tunable composition and mechanical properties post-printing. To succeed, we hypothesized that a dynamic covalent hydrogel, which can flow, can be modified with a reactive moiety so that mechanical and biochemical properties can be adjusted after printing upon the simple addition of a complementary reactive molecule to the culture medium. Using hyaluronic acid (HA) as a natural polymer of interest, boronate ester crosslinking was investigated for the design of the platform dynamic covalent bioink. Regarding the secondary chemical reaction, we used a « click » reaction, namely the strain-promoted azide-alkyne cycloaddition (SPAAC), able to meet rigorous criteria (i.e., physiological conditions of pH and temperature, no byproducts, no purification, bioorthogonality) and allow post-printing modifications in the presence of cells. By combining these two chemical tools, we successfully created what we called « clickable dynamic bioinks ». We then investigated the feasibility of various post-printing modifications (e.g., stiffening, peptide addition) to drive cell fate and build biologically relevant tissue models.
Results: We demonstrated for the first time that boronate ester crosslinking can be used for the design of printable hydrogels, with non-swelling/non-shrinking, shear-thinning and self-healing properties, tunable viscoelasticity (G’ of 200 to 2500 Pa, at 1 Hz), and in vitro stability over months. We showed that these hydrogels are cytocompatible (>90% viable cells) with various primary human cell types (e.g., MSCs, chondrocytes), and that they can prevent cell sedimentation in a cartridge, circumventing what is a common issue in bioprinting. These new bioinks allowed us to design constructs of various shapes and volumes (tested up to 10 layers). The 3D bioprinted constructs immersed in culture medium can be tuned by simply adding to the medium the SPAAC-modified molecule of interest, which diffuses in the constructs and react with the dynamic network. We showed that the composition of a bioprinted construct can be tuned by adding chondroitin sulfate, low molecular weight HA, gelatin or an adhesive peptide (RGD). This technique also allowed us to increase the rigidity of a construct (G’ increased from 200 to 1200 Pa) or control cell adhesion. Of major value, we demonstrated that these post-printing modifications can be controlled in time and space.
Conclusions: We showed that clickable dynamic bioinks constitute a simple and versatile platform for bioprinting. It carries the hope of easy, fast and cost-effective access to any kind of tissue with adaptable composition and architecture, paving the way to biologically relevant 4D bioprinting, with virtually unlimited tissue engineering applications."
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