## 1 Introduction  
Magnesium silicate hydrate (M-S-H) cements have recently been explored as 3D printable inks for creating crystalline bioceramics suitable for use as cancellous bone scaffolds [1]. The increasing demand for bone substitutes has driven the development of materials that possess biological and physical properties akin to human bone [2]. In this context, various materials, including hydroxyapatite [3], calcium and magnesium phosphate materials [4, 5], silicates [6], and bioactive glasses [7] have been developed. Despite the widespread use of calcium phosphate and hydroxyapatite, their slow resorption rates [8, 9] have prompted interest in silicate bioceramics like clinician (MgSiO3) and forsterite (Mg2 SiO4) due to their favorable degradation rates, mechanical properties, biocompatibility, and osteesttimulation [10]. In particular, magnesium silicate ceramics, namely clinoenstatite (MgSiO3) and forsterite (Mg2 SiO4), were recently demonstrated as one of the most promising materials for bone tissue regeneration, thanks to their good resorption rate, mechanical properties, biocompatibility, and osteetimulation [11, 12, 13, 14, 15, 16]. Biocative ions such as Mg and Si within these bioceramics have been reported to enhance the adhesion, proliferation, differentiation, and mineralization of mesenchymal stem cells, facilitating the osseointegration of the porous scaffolds [12], which in turn would favor the osseointegration of the porous scaffold. Typically, MgSiO3 and Mg2 SiO4 are synthesized via a precipitation method to produce an amorphous gel phase (M-S-H, MgO)\({}_{\times}\)(SiO2)\({}_{\gamma}\)-(H2O)\({}_{\alpha}\)) that requires high-temperature treatment to achieve the desired crystalline bioceramic phases [14, 16, 17, 18, 19]. M-S-H also serves as the main binder in a recently developed eco-sustainable cement [20; 21; 22; 23; 24], and some of the authors recently demonstrated that clinoenstatite and forsterite can be prepared starting from MgO/SiO\({}_{2}\) pastes [1]. This research builds on the capability of such cements to be 3D printed [1; 25; 26], offering significant advantages [27] in both building and biomedical applications by enabling the direct creation of personalized bioceramics upon calcination. However, despite the potential and growing interest in using M-S-H for diverse applications, the preparation of complex structures via 3D printing has only recently been explored, with many cementitious materials previously printed over the past two decades, including calcium and magnesium phosphate cements [28; 29; 30; 31], sulphoaluminate cement [32], and calcium silicate hydrate cements [33; 34; 35; 36; 37; 38; 39]. Recent studies have highlighted the need for additives like superplasticizers and suspension aids to achieve extrudable M-S-H formulations [1; 25; 26]. These additives are crucial for maintaining the fluidity and plasticity required for printing, yet their effects on the properties of the resulting inks have not been fully explored. To extrudre magnesium-based cements, [PERSON] et al. reported the use of a superplasticizer (sodium hexamethaphosphate) [25], while [PERSON] et al. incorporated in the paste various additives: a plasticizer (polycarboxylate ether), a suspension-aid additive (hydroxyethyl-cellulose), a hydration agent (magnesium acetate), and a defoamer (a non-ionic surfactant) [26]. Nevertheless, even though these additives are essential for the production of extrudable 3D printable ink, their effect has been left unexplored so far. Moreover, achieving the delicate balance between fluidity for easy extrusion and sufficient stiffness to prevent deformation is a critical challenge in 3D printing cements. It is worth noting that the 3D printing of setting cements faces two conflicting requirements: the paste must be fluid enough to ensure homogeneous mixing and easy extrusion throughout the printing process, while the extruded paste must be stiff enough to prevent shape variations and bleeding.