*3.2.1 Natural polymers*

1.Collagen is extracted from animal (bovine and porcine skin or bone) and marine sources. However, animal derived collagen poses risk to public health and safety [22]. Collagen is the main organic component of dentin matrix and presents a good alternative for dental implantations [41].

Adhesion of calcium salts to a suspension of collagen and glycosaminoglycan in phosphorous acid results in precipitation of brushite form of calcium phosphate into the collagen network, which upon subsequent lyophilization form porous foam. A portion of calcium and phosphate ions from these mineralized scaffolds are released and accelerate osteogenesis. As craniofacial bones rely on intramembranous ossification, these mineralized collagen scaffolds

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

are shown to promote osteogenesis in rabbit calvaria and sub-critical sized porcine mandible [43].

2.Silk fibroin is a natural, low-cost, biodegradable and biocompatible polymer obtained from cocoons of *Bombyx mori*, *Antheraea pernyi* (tussah), *Antheraea mylitta* (tasar) and *Philosamia ricini* (eri). Being a natural polymer, it offers good permeation for oxygen and water but has a low compressive strength [44].

Silk can be manipulated into various forms for fabrication of scaffolds for craniomaxillofacial tissue engineering applications. Addition of methacrylate groups to amine-containing side groups of silk gives rise to silk methacrylate (SilMA) scaffolds, whereas combing methacrylate groups with amine-containing side groups of gelatin results in gelatin methacrylate (GelMA), that becomes photocross linkable in the presence of photoinitiator [9].

3.Chitosan is a deacetylated form of chitin and is the second largest natural polysaccharide after cellulose. It is extracted from crustacean shells and marine sponges. It exhibits fungicidal and anti-microbial activities [24, 41]. Its biodegradability, biocompatibility and excellent cell adhesive properties make it a popular choice for implant material [41]. But its weak mechanical strength and high rate of biodegradability requires crosslinking with other natural or synthetic polymers (e.g. blends) for orthopedic or periodontal applications [24]. For example, chitosan is crosslinked with polyethylene glycol diacrylate (PEGDA) to produce photocrosslinkable blends [9].
