Three-Dimensional Printing

Solid freeform fabrication (SFF) technology creates a 3D structure in laminated fashion by numerical models [255]. 3D printing also uses a layer-by-layer deposition technique. The molten polymers or ceramics are extruded through a small jet head, which is combined with the material on the previous layer. In fact, 3DP employs ink jet printing technique to eject a printing liquid binder from a jet head, which moved to the polymer powder bed of the porogen and polymer particles based on the CAD cross-sectional data [256, 257], as shown in Fig. 2.13 [258]. The mechanical manipulation of the x-y position of the jet head controls the pattern for each layer according to the computer parameters, which can be different or arbitrary for each deposited layer [259]. The solvent will dissolve the polymer and evaporate, and the polymer will re-precipitate to form a solid structure. The final porosity is achieved after particulate leaching and solvent removal.

Schematic of a 3D positioning system incorporating a print head and printing bed system. [258] (This article is available under the terms of the Creative Commons Attribution License)

Fig. 2.13 Schematic of a 3D positioning system incorporating a print head and printing bed system. [258] (This article is available under the terms of the Creative Commons Attribution License)

As one of the advanced technologies in tissue engineering, 3DP technology has been successfully applied for the fabrication of complex reinforced 3D scaffolds by using both direct and indirect techniques. Bakarich et al. [260] combined digital modeling and 3D printing to prepare fiber reinforced hydrogels in a single-step process. Suwanprateeb et al. [261] designed a double infiltration technique combined with 3DP technology to increase the mechanical properties of natural polymers. Christ et al. [257] also introduced the process of 3DP in detail for preparing fiber reinforcements.

The main advantage of this technique is to fabricate 3D complex scaffolds with large pore sizes and fine features that can better simulate the native tissue structure as a template for cell growth and ECM formation. 3DP also has the potential to fabricate zero-order release formulations with complex geometries. However, the drawback of the 3DP is that it is difficult to remove the organic solvent and the support powder from complex architectural features deep within the scaffold. The solvent-based process of 3DP technology results in a significant increase in manufacturing time and poor mechanical properties. Synthetic thermoplastic polymers are the only type of materials that can be processed by this method, excluding many natural biomaterials or thermosetting synthetic polymers.

 
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