The culture of bone marrow derived mesenchymal stem cells (MSCs), as well as the control of its differentiation toward different tissue lineage, is a very important part of tissue engineering, where cells are combined with artificial scaffold to regenerate tissues. Graphene (G) and graphene oxide (GO) sheets are soft membranes with high in-plane stiffness and can potentially serve as a biocompatible, transferable, and implantable platform for stem cell culture. While the healthy proliferation of stem cells on various carbon platforms has been demonstrated, the chemical role of G and GO, if any, in guiding uncommitted stem cells toward differentiated cells is not known. Herein, we report that the strong noncovalent binding abilities of G allow it to act as a preconcentration platform for osteogenic inducers, which accelerate MSCs growing on it toward the osteogenic lineage. The molecular origin of accelerated differentation is investigated by studying the binding abilities of G and GO toward different growth agents. Interestingly, differentiation to adipocytes is greatly suppressed on G because insulin, which is a key regulator for the synthesis of fatty acids, is denatured upon π-π adsorption on G; in contrast, GO does not interfere with adipogenesis due to electrostatic binding with insulin. The different binding interactions and their subsequent influence on stem cell growth and differentiation are ascribed to different degrees of π-π stacking and electrostatic and hydrogen bonding mediated by G and GO.
The enumeration and characterization of circulating tumor cells (CTCs), found in the peripheral blood of cancer patients, provide a potentially accessible source for cancer diagnosis and prognosis. This work reports on a novel spiral microfluidic device with a trapezoidal cross-section for ultra-fast, label-free enrichment of CTCs from clinically relevant blood volumes. The technique utilizes the inherent Dean vortex flows present in curvilinear microchannels under continuous flow, along with inertial lift forces which focus larger CTCs against the inner wall. Using a trapezoidal cross-section as opposed to a traditional rectangular cross-section, the position of the Dean vortex core can be altered to achieve separation. Smaller hematologic components are trapped in the Dean vortices skewed towards the outer channel walls and eventually removed at the outer outlet, while the larger CTCs equilibrate near the inner channel wall and are collected from the inner outlet. By using a single spiral microchannel with one inlet and two outlets, we have successfully isolated and recovered more than 80% of the tested cancer cell line cells (MCF-7, T24 and MDA-MB-231) spiked in 7.5 mL of blood within 8 min with extremely high purity (400-680 WBCs mL(-1); ~4 log depletion of WBCs). Putative CTCs were detected and isolated from 100% of the patient samples (n = 10) with advanced stage metastatic breast and lung cancer using standard biomarkers (CK, CD45 and DAPI) with the frequencies ranging from 3-125 CTCs mL(-1). We expect this simple and elegant approach can surmount the shortcomings of traditional affinity-based CTC isolation techniques as well as enable fundamental studies on CTCs to guide treatment and enhance patient care.
Surface engineering of substrates offers the possibility of controlling the physiological functions of cells at the molecular level. Fluorinated graphene promotes the differentiation of MSCs towards neuronal lineages. Cell alignment using printed polydimethylsiloxane channel arrays on fluorinated graphene further enhances the neuro-induction of MSCs even in the absence of chemical inducers.
Recent advances in stem cell research and nanotechnology have significantly influenced the landscape of tissue engineering and regenerative medicine. Precise and reproducible control of the fate of stem cells and their lineage specification have, therefore, become more crucial than ever for the success of stem cell-based technologies. Extensive research has been geared towards developing materials that are capable of mimicking the physiological microenvironment of stem cells and at the same time, controlling their eventual fate. An interesting example of these materials is two-dimensional graphene and its related derivatives. A high specific surface area coupled with superior chemical stability, biocompatibility, and flexibility in functionalization render graphene-based nanomaterials one of the most exciting platforms for tissue engineering and regenerative medicine applications, especially for stem cell growth, proliferation, and differentiation. In this review, we discuss the love-hate relationship between stem cells and graphene-based nanomaterials in tissue engineering and regenerative medicine. We first discuss the role and importance of stem cells in tissue engineering and regenerative medicine. We then highlight the use of nanomaterials for stem cell control, the interaction between stem cells and graphene nanomaterials as well as their biocompatibility, biodistribution, and biodegradability considerations. We also offer our perspectives on the various challenges and opportunities facing the use of graphene and its derivatives for stem cell growth and differentiation.
Efficient synchronization and selection of cells at different stages of the cell replication cycle facilitates both fundamental research and development of cell cycle-targeted therapies. Current chemical-based synchronization methods are unfavorable as these can disrupt cell physiology and metabolism. Microfluidic systems developed for physical cell separation offer a potential alternative over conventional cell synchronization approaches. Here we introduce a spiral microfluidic device for cell cycle synchronization, using the combined effects of inertial forces and Dean drag force. By exploiting the relationship between cell diameter and cell cycle (DNA content/ploidy), we have successfully fractionated several asynchronous mammalian cell lines, as well as primary cells comprising bone marrow-derived human mesenchymal stem cells (hMSCs), into enriched subpopulations of G0/G1 (>85%), S, and G2/M phases. This level of cell cycle enrichment is comparable to existing microfluidic systems, but the throughput (∼ 15 × 10(6) cells per h) and viability (∼ 95%) of cells thus synchronized are significantly greater. Further, this platform provides rapid collection of synchronized cells or of diameter-sorted cells post-separation, to enable diverse applications in the study and manipulation of cell proliferation.
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