Skeletal stem cell isolation: A review on the state-of-the-art microfluidic label-free sorting techniques

Abstract

Skeletal stem cells (SSC) are a sub-population of bone marrow stromal cells that reside in postnatal bone marrow with osteogenic, chondrogenic and adipogenic differentiation potential. SSCs reside only in the bone marrow and have organisational and regulatory functions in the bone marrow microenvironment and give rise to the haematopoiesis-supportive stroma. Their differentiation capacity is restricted to skeletal lineages and therefore the term SSC should be clearly distinguished from mesenchymal stem cells which are reported to exist in extra-skeletal tissues and, critically, do not contribute to skeletal development.SSCs are responsible for the unique regeneration capacity of bone and offer unlimited potential for application in bone regenerative therapies. A current unmet challenge is the isolation of homogeneous populations of SSCs, in vitro, with homogeneous regeneration and differentiation capacities. Challenges that limit SSC isolation include a) the scarcity of SSCs in bone marrow aspirates, estimated at between 1 in 10-100,000 mononuclear cells; b) the absence of specific markers and thus the phenotypic ambiguity of the SSC and c) the complexity of bone marrow tissue.Microfluidics provides innovative approaches for cell separation based on bio-physical features of single cells. Here we review the physical principles underlying label-free microfluidic sorting techniques and review their capacity for stem cell selection/sorting from complex (heterogeneous) samples.

Emerging Trends in Microfluidics Based Devices

“…[ 56 ] To study a microenvironment, MFDs can either be used for screening a varied range of conditions for high throughput or to reconstruct the physiological environment. [ 57 ] Several MF methods based on adhesion, surface receptor expression, size, and electrical characteristics have been reported to separate stem cells. [ 58 ] However, MFs techniques for stem cell sorting are at an early stage because of the low throughput manufacturing processes.…”

New advances in microfluidic flow cytometry

“…In a conventional flow cytometer, the sample sorting is achieved by deflecting the charged droplets under an electric field. For the microfluidic flow cytometry, many different microchip sorting systems have been described . Generally, it can be divided into active and passive methods.…”

Image‐based sorting and negative dielectrophoresis for high purity cell and particle separation

“…Skeletal stem cells can be obtained from bone marrow but are a minority subpopulation that comprises typically 0.01-0.001% of mononuclear cells [12]. For example, mesenchymal or skeletal stem cells, which exist postnatally, are multipotent and can give rise to the stromal lineages (bone, cartilage, fat, and myelosupportive stroma).…”

“…Label-free detection and sorting is an attractive alternative, not least because cells remain in an unaltered and unperturbed state [12]. Particle sorting requires inputs upon which to base decisions, for particle identification and/or differentiation.…”