## 3 Results
The models printed directly on a glass plate could also be cured by using Carbopol to achieve their quicker solidification. To this end, the prints were covered with Carbopol, then placed in an electric oven at 70 \({}^{\circ}\)C, allowing the extraction of the hardened models within 15 to 30 min. However, it was observed that models cured in Carbopol on a glass slide may have a rougher surface as compared to models cured for longer in the tissue culture incubator. Next, we also sought to impart porosity to the 3D printed models, given the subsequent intended in vitro colonization with osteogenic cells, which would benefit from the presence within the implants of a hydrogel containing growth factors. Moreover, the implementation in the construct of a microvascular network within pre-designed channels could be essential for the long-term in vivo success of these implants [20]. To this end, we developed a porous incus model based on the halved incus design (Figure 5A) containing large pores derived from an infilling design with more distantly spaced CPC lines (Figure 5B). The printed model exhibited visible porosity (Figure 5C), but the constructs expectedly lacked mechanical robustness: in fact, the porous prints that we attempted to remove from the glass support lost some of the surface details because of fracture (Figures S1A and S2A). Figure 3: **Half-printing and assembling of compact ceramic ossicle models by two curing methods. ****(A)** Incus model printed in two halves: top (**right**) and bottom (**left**). (**B**) Malleus model printed in two halves: top (**upper**) and bottom (**lower**). (**C**) Two incus halves assembled by the use of superglue into a whole incus model. (**D**) Two malleus halves assembled by the use of superglue into a whole malleus model. All these prints were cured without Carbopol. Bars, 2 mm. To prevent this brittle fracture, alginate was directly applied over the model after curing before removing it from the glass plate, and the gel was subsequently crosslinked. Although this is not intended to be done in actual in vivo situations, it allowed for the removal without fracture of the model from the glass plate, as well as for the construct manipulation. Excess alginate gel was then removed with a blade, cutting around the porous structure, to retrieve a final porous ceramic gel model (Figure 5D). This hybrid structure has the potential to act as a scaffold for cells that may be loaded into the alginate hydrogel. The porous models were inspected under 4\(\times\) magnification, which revealed an accurate grid pattern achieved by the REGENHU biopprinter (Figure S1B,C). Alternative porosification options were explored by including in the two-halve incus model several manually designed macroscopic pores (Figure S1D,E). Figure 4: **Embedded printing of ceramic ossicle models in a hydrogel support. ** (**A**) Replicates of whole malleus (**upper row**) and incus (**lower row**) printed within the wells of a 12-well plate containing a Carbopol support gel. (**B**) Incus model printed in the support gel placed directly on a glass slide. (**C**) Incus model after solidification and separation from the supporting gel. Bars: (**A**) 5 mm; (**B,C**) 2 mm. Figure 5: **Printing and gel loading of a porous incus model. ** (**A**) Solid BIOCAD model for the top (**left**) and bottom (**right**) halves of the incus model (**B**) Print path preview for the top (**left**) and bottom (**right**) halves of the porous incus model. (**C**) Printed porous top (**left**) and bottom (**right**) halves of the incus model. (**D**) Porous incus model soaked in alginate crosslinked with CaCl\({}_{2}\). Of note, some of the thinner details (“spikes”) detached during gel embedding. Bars, 2 mm. Additionally, the pore size distribution of a porous model was analyzed by measuring 12 distinct pores of a coronal cross section reconstruction (Figure S2B,C). Using ImageJ, the average edge of the rectangular pores was estimated to be 0.259 \(\pm\) 0.040 mm (Table S2).