Embryoid body
[14] Additionally, although EBs largely exhibit heterogeneous patterns of differentiated cell types, ESCs are capable of responding to similar cues that direct embryonic development.
Such microtissues are promising to directly[15] or indirectly[17][18] repair damaged or diseased tissue in regenerative medicine applications, as well as for in vitro testing in the pharmaceutical industry and as a model of embryonic development.
As hESC undergo apoptosis when cultured as single cells, EB formation often necessitates the use of inhibitors of the rho associated kinase (ROCK) pathway, including the small molecules Y-27632[25] and 2,4 disubstituted thiazole (Thiazovivin/Tzv).
As an alternative, the hydrodynamic forces imparted in mixed culture platforms increase the homogeneity of EB sizes when ESCs are inoculated within bulk suspensions.
[28] In addition, technologies have also been developed to physically separate cells by forced aggregation of ESCs within individual wells or confined on adhesive substrates,[29][30][31][32] which enables increased throughput, controlled formation of EBs.
[35][36] The cells at the exterior then deposit extracellular matrix (ECM), containing collagen IV and laminin,[37][38] similar to the composition and structure of basement membrane.
[42] However, alternative media compositions, including the use of fetal bovine serum as well as defined growth factor additives, have been developed to promote the differentiation toward mesoderm and endoderm lineages.
[48] Tissue-like structures are often exhibited within EBs, including the appearance of blood islands reminiscent of early blood vessel structures in the developing embryo, as well as the patterning of neurite extensions (indicative of neuron organization) and spontaneous contractile activity (indicative of cardiomyocyte differentiation) when EBs are plated onto adhesive substrates such as gelatin.
[49] Much of the research central to embryonic stem cell differentiation and morphogenesis is derived from studies in developmental biology and mammalian embryogenesis.
Therefore, the delivery of morphogens to EBs results in increased heterogeneity and decreased efficiency of differentiated cell populations compared to monolayer cultures.
