*2.3.4 Freeze drying/emulsification*

The principle of freeze-drying is actually the sublimation process and a promising technique for preparing scaffolds, in which the frozen water is directly

#### **Figure 5.**

*Schematic diagram of set up of electrospinning apparatus (a) typical vertical set up and (b) horizontal set up of electrospinning apparatus and (bottom column) SEM micrographs of representative electrospinning fibrous materials [ 42, 43].*

transformed from solid to gas without liquefaction. Thus, obtained highly porous interconnected polymer structure is used as a scaffold for tissue engineering [49]. The obtained scaffold usually has a high porosity, but it can be further adjusted as needed by varying the freezing method, the amount of water, the polymer concentration, the size of the ice (solvent) crystals, and the pH value of the solution as needed. Freeze drying is widely used to prepare nanocomposite scaffolds, but some of the limitations associated with this process include long preparation time, high-energy consumption, and the possible formation of closed cells by gas foaming. The obtained scaffold usually has a high porosity, but it can be further adjusted as needed by varying changing the freezing method, the amount of water, the polymer concentration, the size of the ice (solvent) crystals, and the pH value of the solution as needed. Freeze drying is widely used to prepare nanocomposite scaffolds, but some of the limitations associated with this process include long time, high-energy consumption, the use of cytotoxic solvents, and the formation of closed cells by gas foaming (**Figure 6**) [51].

*Nanocomposite Biomaterials for Tissue Engineering and Regenerative Medicine Applications DOI: http://dx.doi.org/10.5772/intechopen.102417*

**Figure 6.** *Schematic representation of freeze-drying process [50].*

The freeze-drying technique has been successfully used in many studies related to tissue engineering, such as chitin-chitosan/zirconium oxide (ZrO2) and chitosan/gelatin/nanosilicon dioxide (nSiO2)) composite material [52]. In one such study, freezedrying methods were used to produce a chitosan 3D scaffold. The results obtained by dispersing nHA and fucoidan in a chitosan matrix were found to be suitable for cell growth and nutritional supplementation. *In vitro* results show that mesenchymal stem cells (PMSCs) derived from periosteum grow well in nanocomposites, which implies the potential for tissue engineering.
