Natural hydrogels are widely used for 3D-bioprinting of scaffolds that emulate the extracellular matrix of different human tissues; Alginate based gels are among the most broadly used. Crosslinking by Ca2+ ions is a key issue for achieving the proper mechanical response; the dynamics of this process has been reported for alginate and alginate-gelatine systems [1,2] however, 3D modelling of scaffolds of any shape, with calculated diffusion parameters is not already implemented.

The aim of this work was study the kinetics of the gelling front and the diffusion of Calcium ions within the matrix of the Alginate-Gelatine-Hyaluronic acid (Alg-Gel-HA) tripartite ink (4.5% w/v of each polymer in PBS1X) using a simple and low-cost method (video record and image analysis by ImageJ®). Experimental data could be well fitted by a numerical model (Python script) that predicts the time for maximum cross-linking, according to the dimension and shape of the scaffolds.