Alginate Hydrogels: A Tool for 3D Cell Encapsulation, Tissue Engineering, and Biofabrication.

A wide variety of hydrogels have been proposed for tissue engineering applications, cell encapsulation, and bioinks for bioprinting applications. Cell-laden hydrogel constructs rely on natural hydrogels such as alginate, agarose, chitosan, collagen, gelatin, fibroin, and hyaluronic acid (HA), as well as on synthetic hydrogels such as poloxamers (Pluronics®) and polyethylene glycol (PEG). Alginate has become more and more important in the last years, thanks to the possibility to prepare alginate hydrogels suitable for cell encapsulation mainly because of the mild and reversible cross-linking conditions. In this paper alginate will be described in detail with respect to its chemistry, cross-linking behavior, biocompatibility, manufacturing capacity, and possible modifications.

Effect of Cryopreservation on Cell-Laden Hydrogels: Comparison of Different Cryoprotectants.

Cell encapsulation in hydrogels is a technique that offers a variety of applications, ranging from drug delivery to biofabrication of three-dimensional scaffolds. The assembly of cell-laden hydrogel building blocks aims to generate complex biological constructs by manipulating microscale units. An important issue for the clinical implementation of this technique is the long-term storage of a large stock of cell/hydrogel building blocks. In this work, the impact of cryopreservation on the viability and functionality of cells encapsulated in alginate matrices is presented comparing different cryoprotective agents (CPAs). Human osteosarcoma MG63 cells were encapsulated in sodium alginate fiber constructs with wetspinning method and exposed to different formulations of cryopreservation media, containing dimethyl sulfoxide (DMSO), glycerol, and trehalose. The cell-laden fibers were subsequently slow-cooled down to -80°C and stored in liquid nitrogen. After thawing, viability and death pathway of encapsulated cells were investigated, and metabolic activity and proliferative capacity of cells released from the alginate matrix were evaluated. The viability of MG63 cells encapsulated in alginate matrix ranged from 71% ± 4% to 85% ± 2%, depending on the cryoprotective media formulation with no protracted harmful effects from the CPAs. On the other side, cells cryopreserved in encapsulated conditions and released from the hydrogel showed larger metabolic activity and proliferative capacity in tissue culture plate compared to cells cryopreserved in suspension, in particular when DMSO and glycerol were used as CPAs. Results have been correlated with the viscoelastic properties and water content changes of the alginate constructs loaded with the different CPAs.