Natural fiber exoskeletons of insects and arthropods. In shells and exoskeletons, the chitin fibers contribute to their hierarchical structure. In nature, pure chitin (100% acetylation) does not exist. It instead exists as a copolymer with chitin's deacetylated derivative, chitosan. When the acetylized composition of the copolymer is over 50% acetylated it is chitin. This copolymer of chitin and chitosan is a random or block copolymer. Chitosan is a deacetylated derivative of chitin. When the acetylized composition of the copolymer is below 50% it is chitosan. Chitosan is a semicrystalline “polymer of β-(1-4)-2-amino-2-deoxy-D-glucose”. One difference between chitin and chitosan is that chitosan is
Epiblast-derived stem cell Epiblast-derived stem cell After the blastocyst stage, once an embryo implanted in endometrium (in case of rodent), the inner cell mass (ICM) of a fertilized embryo segregates into two layers: hypoblast and epiblast. The epiblast cells are the functional progenetors of soma and germ cells which later differentiate into three layers: definitive endoderm, mesoderm and ectoderm. Stem cells derived from epiblast are pluripotent. These cells are called epiblast-derived stem cells (EpiSC) and have several different cellular and molecular characteristics with Embryonic Stem Cells (ESC). Pluripotency in EpiSC is essentially different from that of embryonic stem cells. The pluripotency of EpiSC