Auxetic mechanical metamaterials are engineered systems that exhibit the unusual macroscopic property of a negative Poisson's ratio due to sub-unit structure rather than chemical composition. Although their unique behaviour makes them superior to conventional materials in many practical applications, they are limited in availability. Here, we propose a new class of hierarchical auxetics based on the rotating rigid units mechanism. These systems retain the enhanced properties from having a negative Poisson's ratio with the added benefits of being a hierarchical system. Using simulations on typical hierarchical multi-level rotating squares, we show that, through design, one can control the extent of auxeticity, degree of aperture and size of the different pores in the system. This makes the system more versatile than similar non-hierarchical ones, making them promising candidates for industrial and biomedical applications, such as stents and skin grafts.

The use of umbilical cord blood as an alternative to bone marrow as a source of haematopoietic stem cells for the treatment of certain diseases has been on an increase since the first transplantation of umbilical cord-derived stem cells in 1988. In this paper, 6 of the latest case studies about the use of such stem cells have been discussed and are used as evidence to confirm the potential use of the umbilical cord as a source of haematopoietic stem cells for transplantation as treatment to various diseases. The debate over whether umbilical cord blood should be stored and why public banking facilities are preferred over those that are private have also been discussed in this paper.

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