BIOPRINTING BIPHASIC JAMMED BIOINKS USING MULTI-NOZZLE PRINTHEADS ON PHYSIOLOGICAL SURFACES AND IN REDUCED GRAVITY

Most tissues of the human body are designed along curvilinear surfaces.Biofabrication approaches intended to mimic their structure are therefore required to adapt to allow for the rapid, gravity-independent delivery of bioinks onto physiologically curved surfaces.Examples include limbs with concave and convex topologies at the elbow and knee joints.The small curvature radii of fingers and toes allow for individual bending and flexing, facilitating a multitude of tasks such as grasping.The face is the most intricate and complex topology of the human body [1], is characterized by a multitude of locally varying curvature radii that include the convex shape of the forehead, the concave or planar cheeks, as well as the convex contours of the nose and chin with their small curvature radii.In situ bioprinting approaches enable the formation of architected biomaterial and tissue structures.To achieve clinical relevance in the wound healing context, bioink must be rapidly delivered independent of substrate.Here, we introduce the rapid delivery of granular biphasic bioinks through a soft-robot actuated multinozzle printhead.This elastomeric printhead is actively deformed by a curvature actuator that conforms to a physiological topology with convex curvature, ensuring precise control over the bioink deposition process (Figure 1).The bioink, derived from gelatin microgels with tailored size and volume fraction, exhibits desirable shear-thinning rheological behavior (Figure 1F).This approach allows for conformal, in situ delivery of millimeter-thick bioink layers onto surfaces with various orientation angles and curvature radii.Additionally, we demonstrate for the first time that these granular bioinks can be deposited in microgravity environments (Figure 2), extending the applicability of this method to deep space missions.Skin defines the external boundary of the human body to its environment, and it is therefore at high risk of being injured during long-duration spaceflight [2].Burns secondary to fire, skin abrasions and skin lacerations are among the 100 medical conditions listed in NASA's Integrated Medical Model, an evidence-based list of medical conditions at higher risk of occurring during a space mission [3].Next, human dermal fibroblasts were dispersed within the biphasic bioink.Results indicate viability exceeding 85% at day 1 and 3 post-bioprinting (Figure 3A andB) suggesting favorable cytocompatibility of our bioprinting approach.We characterized the effect of fibrinogen concentration, CF, on cell proliferation using EdU staining.Cells staining for both EdU+ and DAPI (nuclei) are proliferating.Interestingly, we observe a weak correlation of cell proliferation for the evaluated CF range (Figure 3C andD).As a proof of concept, we demonstrate in situ bioprinting on different parts of the human face.A human head phantom was 3D-scanned and then 3D printed, selecting three areas with varying radii of curvature (not shown here).The average mean and Gaussian curvatures of the areas are similar to a previous study [2] on human facial features showing the relevance.This work represents a significant advancement in the utilization of in situ bioprinting technologies for human wound healing applications.