Another strategy to improve the viscosity and printability of GelMA-based bioinks is to introduce materials that enhance their rheological properties. Some examples of rheological modifiers used are methylcellulose, alginate, hyaluronic acid, collagen, nanosilicate, gelatin, and gellan gum. Despite the improvement of the printability with the inclusion of these modifiers, in most cases, it is necessary to use a high concentration of at least one of the components of the ink (modifier or GelMA), which leads to a high total solids content in the bioink, which can affect normal cell growth (Figure ). Furthermore, printing of GelMA using rheological modifiers is not usually done at a physiological temperature (37 ºC), making the printing process more challenging and potentially impacting the cells (Figure ). Laponite and gellan gum are notable because low concentrations of these modifiers result in suitable viscosity for extrusion -printed constructs were reported from inks containing 0.5% gellan gum and 3% GelMA at 21 ºC. Another approach reported to decrease the GelMA content in the bioink is using gelatin as an additive and taking advantage of its thermal-crosslinking. Using this strategy, a bioink containing 5% GelMA and 8% gelatin exhibited good printability, and the unmodified gelatin could be removed post-printing by dissolving through a gradual increase of the temperature. Although these approaches have reported some success, developing bioinks that contain low concentrations of GelMA and rheology modifier, and achieve high printability and cell viability at 37 ºC is still an outstanding challenge.