## 3 Literature Review
### Additive Manufacturing and Green Manufacturing  
AM can be used to manufacture products using biodegradable materials that are environmentally friendly and can be disposed of at the end of life [44]. [PERSON] and [PERSON] [43] presented an overview of the literature on the usage of bio-degradable products in the medical industry. Typical bio-degradable polymers used in AM include polylactic acid (PLA), polyvinyl alcohol (PVA), polyhydroxyalkanoates (PHA), hot isostatic pressing (HIP), and polyethy  
Figure 2: Classification of AM processes [40]. lene terephthalhalate (PET) [44]. Polymeric materials find applications in various biomedical areas, such as scaffolds for bone regeneration, processing of digital medical images, 3D anatomical models and surgical training, surgical equipment, prosthetics and implants, tissue engineering, in vitro tissue modelling, and drug discovery, amongst others [33; 43]. Some of the requirements of the AM materials used for biomedical applications include biocompatibility, as well as structural and functional requirements tailored to specific applications. For instance, biomedical devices interfacing with cells and used in regenerative processes should provide biochemical activities that can influence the behaviors of the cells. AM has an advantage over other processing techniques in biomedical applications due to its potential to control the major compositional, structural, and functional parameters of the polymeric system [44]. [PERSON] et al. [45] designed a novel AM machine for making a bio-degradable stent. The AM machine uses the fused filament fabrication method as well as polycaprolactone (PCL), a biodegradable polyester, as the material. The performance evaluation of the AM machine was conducted by studying the effect of fluid flow, nozzle temperature, and printing speed on the accuracy of the developed product. The results obtained show that temperature and flow rate strongly influence the accuracy of the developed product over the printing precision. [PERSON] et al. [33] reported on the use of biopolymer and calcium phosphate composites of carbon apatite in polylactic acid (with a PLA/cHA ratio of 95:5 and 80:20 m/m as scaffolds for bone regeneration. The printing was performed using the following process parameters: print speed (20 mm/s), layer thickness (0.3 mm) and deposition angle (0-90\({}^{\circ}\)). The results obtained indicated that the apparent porosity of the 5% and 20% of cHA scaffolds gave a percentage porosity of about 62% and 41%, respectively. This shows that it is possible to produce 95/5 PLA/cHA composite scaffolds via AM technology. [PERSON] et al. [46] studied the production of scaffolds using bio-degradable iron-based reinforced polymers for bone regeneration. The PLA composite scaffolds were produced using AM technology, specifically the fused filament fabrication (FFF) process using two different types of iron-based powders, namely stainless steel 316L and pure iron. The outcome of the study shows that the scaffolds were manufactured with a precise pore dimension of 0.80 \(\pm\) 0.08 mm, having a homogenous distribution of iron-based powders in the PLA matrix. Furthermore, the results also indicate that the PLA/Iron scaffold has high in vitro degradation resistance, high hydrophilic wetting behavior and cytocompatibility, thereby demonstrating its feasibility for application in bone or tissue engineering. Another emerging area of research involves the additive manufacturing of natural fibers. [PERSON] et al. [47] conducted an experimental study on using natural fiber to produce structures for biomedical applications. The authors investigated the mechanical properties and bacterial characteristics of chemically treated waste natural fiber (such as silk fiber and sheep wool fibers) and inserted three-dimensional structures (NFi3 DS) produced using PLA as the matrix and fused filament deposition (FFD) as the AM method. The outcome of this study indicates the suitability of embedded structures for scaffold-based biomedical applications.