**2. Mesenchymal stem cells (MSCs) for tissue engineering**

MSCs are multipotent stem cells with the ability to proliferate and differentiate into a variety of mature cells, mainly osteocytes, chondrocytes, and adipocytes [5].

MSCs can be isolated from a multitude of adult and fetal tissues including but not limited to the bone marrow, adipose tissue, peripheral blood, synovial tissue, placenta, Wharton's jelly, and umbilical cord blood. Importantly, it has been shown that MSCs isolated from different tissue sources possess differential proliferation and differentiation capacity toward various lineages [6] (**Figure 1**). Since their description by Friedenstein et al. [7], MSCs have been evolved as the stem cell type with the most regenerative medicine applications and the only stem cell type used in clinic to date.

MSCs represent attractive stem cell candidates for the use in tissue engineering and regenerative medicine applications for a variety of reasons. Firstly, they have the ability to proliferate and differentiate producing tissues, which are clinically relevant for regenerative medicine purposes such as musculoskeletal and neural tissues. In addition, they offer the possibility of autologous use, which can avoid adverse immune responses to allogeneic cells while also possessing an immunomodulatory capacity being able to regulate the immune environment even when implanted in an allogeneic fashion. Finally, the use of MSCs avoids the ethical shortcomings of embryonic stem cell (ESC) use and is not associated with the formation of teratomas which is a characteristic of pluripotent stem cell implantation (ESCs and induced pluripotent stem cells—iPSCs) [8–10]. Recently, protocols for the derivation of MSCs from iPSCs have also enabled the production of unlimited MSC

**67**

*The Use of Alginate Hydrogels for the Culture of Mesenchymal Stem Cells (MSCs): In Vitro and…*

numbers by exploiting the unlimited proliferation capacity of iPSCs prior to their

The use of MSCs for tissue engineering and regenerative medicine purposes requires the robust characterization of MSCs at several levels. At the moment, the International Society for Cell and Gene Therapy (ISCT) has posed the minimal criteria that need to be fulfilled so that a cell population is characterized as MSCs. These include the adherence to plastic; the presence (≥95%) of surface markers including CD73, CD90, and CD105; and the absence (≤2%) of hematopoietic markers (CD34, CD45, CD79a or CD19, CD14 or CD11b, and HLA II). Finally, cells characterized as MSCs should possess the capacity to differentiate to osteoblasts, chondroblasts, and adipocytes in vitro [14]*.* Other surface markers have been utilized over the years for the characterization of MSCs including Stro-1, CD271, CD146, and MSCA-1, but their use has not yet been established as a routine for MSC research [15–18]. Recently, omics strategies have emerged as promising alternatives for the comprehensive evaluation of MSC quality at the undifferentiated and

**3. The use of alginate hydrogels and MSCs in tissue engineering and** 

Due to the lack of bioactive molecules on the alginate structure, alginate hydrogels used for cell-based applications require functionalization with molecules which can aid cell adhesion, increase cellular proliferation, and/or guide stem cell differentiation toward the desired cell lineages. In an attempt to increase cell adhesion on alginate hydrogels, a wide variety of extracellular matrix proteins or protein fragments have been employed. The most commonly used molecules include collagen, gelatin (product of collagen hydrolysis), and arginylglycylaspartic acid (RGD) peptide, which is the functional adhesion sequence in several extracellular matrix (ECM) proteins. Gelatin has been widely utilized for the enhancement of cell adhesion and differentiation in alginate hydrogels [24] either mixed [25] or crosslinked with alginate [26]. It has also been shown that crosslinking of alginate with gelatin reduces gelatin leak over prolonged culture while enhancing cell adhesion and vascular endothelial growth factor (VEGF) secretion compared to natural alginate

Oxidized alginate has been widely used for tissue engineering purposes. Alginate can be oxidized with the use of agents including sodium permanganate (KMnO4) and periodate, to produce two free aldehyde groups on the alginate backbone, offering enhanced in vitro and in vivo. Alginate oxidation is necessitated by the lack of natural alginate degrading enzymes in mammals, which is translated to a slower biodegradation of alginate hydrogels [28, 29]. Additionally, free aldehyde groups offer sites for possible crosslinking with amine group-containing molecules, which can be used for the robust functionalization of hydrogels used for tissue engineering [29, 30]. Similarly to natural alginate, a wide range of biomolecules have been used for the functionalization of oxidized alginate. The most commonly used are gelatin

and RGD, which have been shown promote cell adhesion and viability [31] .

Culture of MSCs in alginate hydrogels has been attempted for applications ranging from the regeneration of bone, cartilage, and tendon to the repair of damaged myocardium and trachea. Most of the initial data on the use of alginate/MSC

**3.1 In vitro paradigms of alginate/MSC constructs**

constructs have been obtained in vitro (**Table 1**).

*DOI: http://dx.doi.org/10.5772/intechopen.88020*

differentiation to MSCs [11–13].

differentiated states [11, 19–23].

and RGD-alginate [27].

**regenerative medicine applications**

**Figure 1.**

*Tissue sources and properties of mesenchymal stem cells.*

*The Use of Alginate Hydrogels for the Culture of Mesenchymal Stem Cells (MSCs): In Vitro and… DOI: http://dx.doi.org/10.5772/intechopen.88020*

numbers by exploiting the unlimited proliferation capacity of iPSCs prior to their differentiation to MSCs [11–13].

The use of MSCs for tissue engineering and regenerative medicine purposes requires the robust characterization of MSCs at several levels. At the moment, the International Society for Cell and Gene Therapy (ISCT) has posed the minimal criteria that need to be fulfilled so that a cell population is characterized as MSCs. These include the adherence to plastic; the presence (≥95%) of surface markers including CD73, CD90, and CD105; and the absence (≤2%) of hematopoietic markers (CD34, CD45, CD79a or CD19, CD14 or CD11b, and HLA II). Finally, cells characterized as MSCs should possess the capacity to differentiate to osteoblasts, chondroblasts, and adipocytes in vitro [14]*.* Other surface markers have been utilized over the years for the characterization of MSCs including Stro-1, CD271, CD146, and MSCA-1, but their use has not yet been established as a routine for MSC research [15–18]. Recently, omics strategies have emerged as promising alternatives for the comprehensive evaluation of MSC quality at the undifferentiated and differentiated states [11, 19–23].
