The hematopoietic stem cells (HSCs) have been unquestionably important to therapies that involve blood and immune system replacement. However, the in-vitro culture and the expansion of HSCs inhibit their application. This work aims to develop a composite biodegradable 3D scaffold that would simulate key aspects of the in-vivo microenvironment (niche) in which expansion of the hematopoietic stem cells takes place in human bone marrow. Hydroxyapatite (HA) has been chosen as a scaffold material because of its biocompatibility and the ability to create an osteogenic scaffold and thereby simulate trabecular bone that is known to be important to the HSC niche in bone marrow. It is hypothesized that the use of a Ca-rich HA scaffold will create a three dimensional, protective environment for HSCs and further promote their in-vitro expansion by releasing Ca ions into the culture medium. udThe first part of this study examined the processing of Ca-rich HA and the release of calcium ions into saline over time. The Ca-rich phase was introduced into the HA by an infiltration process and has been shown to release calcium into the culture medium over 42 days. The second part of this study examined the effect of the scaffold material on the fate of human umbilical vein endothelial cells (HUVECS), a well-known endothelial progenitor model. The results showed, for the first time, that at least some HUVEC cells have hematopoietic potential and that the scaffold promoted differentiation down the hematopoietic cell lineage. This is thought to be due to hemangioblast character in the HUVEC cells which is also shared by HSCs. Finally the effects of the scaffold on the in-vitro co-culture of an osteoblast cell line and primary human bone marrow derived HSCs was studied. The infiltrated scaffolds were shown to stimulate the HSC population to differentiate down the hematopoietic lineage and also showed greater potential to differentiate down the HSC lineage in consequent CFU assays.
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