**4. Fabrication techniques**

Tissue engineering is a multidisciplinary field that imbibes the principles, knowledge and methods of chemistry, physics, engineering and biology. It involves three fundamental elements: cells, scaffold and cell signaling [7].

The fabrication of scaffolds requires pre-treatment of the graft material with various solvents, which facilitates the dissolution of the biomaterial. It is a general observation that processing and storage of scaffolds in the presence of solvent, hampers the control of spatial distribution of the bioactive agent in the porous structure of the scaffold. The final processing involves removal of these toxic organic solvents or any other residual porogen species by leaching or solvent extraction methods. This results in loss of the medically important bioactive agents. However, the methods employed for processing of scaffolds should also be evaluated from an environmental point of view. Therefore, E-factors (the actual amount of waste product produced in the process per gram of product) and low carbon footprint methods are the two parameters that deserve attention. Thus, processing technologies such as melt molding (compression, injection and extrusion molding); 3D printing; fused deposition modeling; sintering of solid particles (heat, compressed CO2 and selective laser sintering); gas foaming and compressed or supercritical CO2 foaming, operating in the absence of solvent during assembly of 3D scaffolds, present ideal strategies for development of medicated scaffolds [11].

The use of natural fiber composites over synthetic fibers also needs substantial attention from green synthesis point of view. Glass or carbon fiber-reinforced composites, belonging to the category of synthetic composites have been well researched for last 20 years. However, due to environmental and economic considerations the focus of research has diverted to natural fiber-reinforced composites. The advent of 3D and 4D printing provides huge opportunity for development of natural biocomposites, for the first time on the same time scale as their synthetic counterparts [50].

In the sections below, we will be discussing various techniques employed for fabrication of biomaterial implants for craniomaxillofacial bone reconstruction/ regeneration.
