**7.1** *In-situ* **printing**

In-situ printing or *in-vivo* 3D bio-printing is defined as the direct printing of bioinks at the defects' site with the aim of creating or repairing damaged tissue in a clinical setting. In this procedure, the robotic arms are assembled with the bio-printing unit, and the printing is conducted in minimally invasive routes in the defect site [153]. Cohen et al. [154] used in-situ bio-printing for the treatment of osteochondral defects. The alginate and demineralized bone matrix were printed using a built-in-house extrusion-based bio-printer for this purpose. Two types of defects were created in the calf femur: a cartilage only and an osteochondral defect. The results demonstrated the high geometric precision of the in-situ printing process. In another study, Kerique et al. [155] in situ printed the Nano-hydroxyapatite in the mouse calvaria defect model using a laser printer. They suggested that the in-situ printing usage by surgeons or actual robots can reduce the used materials to pL volume and the spatial resolution increased. In another trial on the robotic *in-situ* bio-printing for large bone healing, Li et al. [156] presented a new method for optimizing robotic printing. The extrusion-based bio-printer was selected due to the easier structural and mechanical controllability and a modified 4-DOF robot with higher kinematic accuracy of 0.5 mm was used. The bio-printing was performed using a double-network hydrogel bio-ink consisting of alginate, polyethene glycol diacrylate (PEGDA), and methacrylated gelatin (GelMA). Alginate was cross-linked with calcium ions and PEGDA and GelMA created a covalently cross-linked network. The in-vivo successful results on the large tibia bone defects of pigs revealed the high potential of this method for future clinical applications of *in-situ* large bone regeneration.
