A bone marrow-on-a-chip that maintains hematopoietic regenerative capacity in vitro

Abstract

The bone marrow niche is composed of a complex set of cellular, chemical, structural and physical cues that are required to maintain viability and function of the hematopoietic system. [1-5]. The source of all differentiated blood cells, the hematopoietic stem cell (HSC), is housed within the protective confines of the bone marrow where the complex microenvironment regulates its ability to undergo self-renewal or to differentiate into all of the mature functional blood cell types that constitute the hematopoietic system [4-7]. Engineering an artificial bone marrow that reconstitutes the critical inductive cues of naturally occurring bone marrow in vivo that maintains them in vitro could lead to new models of hematopoietic diseases, as well as enable expansion of bone marrow for therapeutic transplantation and manufacturing of differentiated blood cell replacements. It has proven difficult, however, to identify or combine the correct set of biomaterials and biological signals necessary to recreate the complex bone marrow microenvironment or to maintain functional, multi-potent, self-renewing HSCs in culture [8-13]. Here, we describe a microfluidic bone marrow-on-a-chip created in vivo by combining microsystems and tissue engineering strategies to produce bone that contains a complex bone marrow niche. The hematopoietic compartment of the engineered bone marrow (eBM) has a distribution of HSCs, hematopoietic progenitor cells, and differentiated blood cell types that is virtually identical to natural marrow. Moreover, these hematopoietic populations are retained in normal proportions and the HSCs maintain their full regenerative capacity when the eBM is explanted and cultured in the microfluidic bone marrow chip in vitro. After four days of culture on-chip, hematopoietic cells isolated from the eBM engrafted a lethally-irradiated mouse, reconstituted the compromised bone marrow, and fully restored all differentiated blood cell lineages. Preliminary work with human umbilical cord blood (hCB) suggests that the bone marrow-on-a-chip platform may be extended beyond the mouse to support human HSCs and hematopoietic progenitors in vitro. This ability to engineer a complex bone marrow niche that is capable of maintaining functional HSCs offers new tools for expansion of cells for transplantation, manufacturing. differentiated blood cells, evaluation of drug efficacy and toxicities, and study of hematopoietic diseases.