**4.1 Electrospinning**

Electrospinning was first applied in 1934 by Anton Formhals and represents a combination of electrospray and spinning of fibers [51]. A typical electrospinning apparatus includes a capillary tube with a spinneret, a high voltage power supply and a collector (**Figure 2**). During electrospinning, polymer droplets are generated by extruding polymer solution from the electrically conductive spinneret. A high voltage is applied between the spinneret and the grounded collector. The polymer solution ejects from the spinneret when the potential between the solution breaks through the surface tension of the droplets, resulting in fibrous polymer scaffold (diameter ranging from 100 nm to several micrometers)

[52]. Introduction of a liquid bath collector in an electrospinning setup results in production of fluffy morphologies such as yarn or spongiform fabric. For example, the collector may contain ethanol and water-ethanol (non-solvents), for spinning of polysaccharides such as cellulose/heparin (blend) and cellulose/ multiwall carbon nanotubes (core/sheath) [20]. In addition, antibiotics can also be incorporated into the electrospun scaffold to prevent bacterial colonization after implantation [53].

The electrospun scaffold is physically like a tissue paper with easy handling and therefore is well adapted for critical bone defects in craniomaxillofacial region [54]. On the basis of initial state of polymer electrospinning can be categorized as solution electrospinning, emulsion electrospinning and melt electrospinning writing [18, 55].


*Advances in Tissue Engineering Approaches for Craniomaxillofacial Bone Reconstruction DOI: http://dx.doi.org/10.5772/intechopen.94340*

geometries, that are individualized for attachment of osteoblast on one side and keratinocytes and fibroblast on the other side [19].

Ceramic, metallic, glass-based fibers can be produced by electrospinning, by injecting the polymers to a simple syringe with metallic tip of different diameters [47]. PCL and nano-HA composite scaffolds fabricated using similar technique holds potential for repairing of critical bone in craniomaxillofacial region [54]. These scaffolds not only have superior mechanical properties but also possess ability to carry growth factors and drugs [56]. It was demonstrated that trigeminal ganglion when added to ε-PCL membranes synthesized by electrospinning and functionalized with nerve growth factor nanoreservoirs, were able to regenerate peripheral axons in the pulp cavity, two weeks after implantation [57].

Melt spinning and wet spinning: Melt spinning involves melting of the polymer followed by its extrusion through small holes resulting in formation of solidified fibers after cooling. The resulting fibers are collected by a take-up wheel to form continuous fiber strands. Wet spinning involves dissolution of polymer in appropriate solvent followed by extrusion of polymer solution through a spinneret into a coagulation bath containing a non-solvent [22].

### **4.2 Electron beam melting (EBM)**

EBM was developed and patented by Swedish Arcam Company. The equipment is mainly composed of an electron beam gun compartment and a specimenfabrication compartment, both kept in high vacuum. The technology employs high energy electron beam to melt the metal powder. The electron beam preheats the powder bed to reach a slight-sintering state by scanning the powder layer quickly before EBM. This step is followed by selective scanning of powder layer by electron beam based on the 3D hierarchical data, causing the preheated powder to melt and solidify together. The high beam-material coupling efficiency makes it a method of choice for processing of metals with extremely high melting points. One of the case studies demonstrated fabrication of 3D titanium scaffold with EBM for reconstruction of whole mandible defect [52].

#### **4.3 Gas foaming**

The principle of gas foaming is to generate pores in a polymeric matrix through a nucleation-growth mechanism of gas bubbles that results in formation of microporous material after venting out of the bubbles. This process is compatible with both hydrophobic and hydrophilic polymeric matrices and is usually performed under mild temperatures [11]. This solvent free technique consists of 3 steps


Supercritical CO2 (scCO2) foaming and compressed CO2 foaming are two of the green technology processes that utilize the valorization [11] and plasticizing effect of CO2 under super critical conditions (temperature and pressure above the critical point of CO2, 31.1°C and 72.8 bar) for reducing the apparent glass transition (Tg) and the melting temperature of the polymers. When the pressure is reduced, CO2 dissolved in the polymer matrix gets super saturated resulting in formation of pores from growing nucleation sites. This method employs mild conditions and avoids the use of organic solvents, thus retaining the activity of thermally sensitive compounds such as growth factors [46].
