**2.4 Bone regeneration**

*Alginates - Recent Uses of This Natural Polymer*

is present in these dressings. In situ-forming wound dressing hydrogel can be produced by oxidized alginate and gelatin in low borax concentration as shown by Balakrishnan and Jayakrishnan [28]. The homeostatic gelatin effect is present in the mixed matrix and wound healing property of alginate, and the antiseptic borax property makes alginate the appropriate wound dressing material. Tissueengineered cartilage requirement is immense and has a huge clinical importance. The main causes of disability of the articular cartilage are degenerative and traumatic lesions [29]. Nearly 100 million Chinese people suffer from osteoarthritis. Because of this reason, regeneration and repair of the cartilage have huge impact. The pros of the cartilage repair injectable therapies are that implant within the defect is not only maintained, but it also allows quick bearing of weight because of strength and stiffness which is attained quickly [30, 31]. For bringing close the mechanical properties of the native tissues with the scaffolds, the alginate physical properties are matched with the articular cartilage. Ge and solid alginate injectable hydrogel microspheres are used for cartilage regeneration. Many researchers have studied the growth factor in tissue engineering by using alginate hydrogels and alginate-based microsphere combinations [32, 33]. In one study the demonstration of immobilization of the positive effect of RGD to an alginate porous scaffold for endorsing TGF-β-induced human MSC differentiation is shown [34]. Bian et al. studied the co-encapsulation of the TGF-β including the microsphere of the alginate with the human MSCs in the hyaluronic acid (HA) hydrogels with respect to the design of the constructs implantable for the cartilage repair [35]. The immobilized RGD peptide facilitated the cell-matrix interaction which is proven to be an important feature for the microenvironment of the cells, allowing good cell availability for the chondrogenic-inducing molecule TGF-β. TGF-β-laden alginate microspheres in combination with alginate hydrogels forms a compound carrier which may retain TGF-β bioactivity in the construct and encourages hondrogenesis of MSCs when inserted. The animal experiment displayed that chondrocytes planted into the microsphere scaffold lived habitually in SCID mice and cartilage-like constructions

In the past years, drug delivery carriers draw huge interest because of large biomacromolecules like genes and proteins as well as low-molecule weight drugs

**114**

**Figure 3.**

*Alginate with cell cross-linking process.*

**2.3 Drug delivery**

were created after 4 weeks of imbedding.

For the reconstructive surgery, bone regeneration is an important challenge. It occurs due to tumor removal and trauma. To repair the bone, a good initiative is to induce osteogenesis in situ. To complete this process, one method is by using stem cell differentiation to form bone tissue and then seeding them in an injectable scaffold [44, 45]. As of now there are numerous investigations and studies on alginate-based injectable scaffolds for the bone regeneration. By using MSCs and alginate scaffolds, satisfactory bone tissue formation was noticed [46, 47]. For this reason the application of alginate for gel tissue generation is commonly used which displays angiogenic and osteogenic properties. Many researchers showed bone regeneration by means of injectable constructs by joining microspheres or alginatebased hydrogels that were combined with interchangeable ASCs or MSCs [48]. These studies demonstrated the potential of bone morphogenetic protein (BMP) and TGF-β delivery to induce osteogenic differentiation to mature osteocytes from MSCs and ASCs. Kolambkar et al. presented a growth factor hybrid system of delivery that comprises of a nanofiber mesh tube *which is electrospun* for directing regeneration of bone along with alginate hydrogel peptide modified in the tube for fixed recombination BMP-2 (rhBMP-2) release [49]. The discharge of fixed transport of rhBMP-2 through alginate hydrogel was important for significant regeneration to

take place. The mixed technology can be used clinically for the regeneration of bone in cases as huge bone defect and nonunion fractures.
