Blood component separation in straight microfluidic channels.

Separation of blood components is required in many diagnostic applications and blood processes. In laboratories, blood is usually fractionated by manual operation involving a bulk centrifugation equipment, which significantly increases logistic burden. Blood sample processing in the field and resource-limited settings cannot be readily implemented without the use of microfluidic technology. In this study, we developed a small footprint, rapid, and passive microfluidic channel device that relied on margination and inertial focusing effects for blood component separation. No blood dilution, lysis, or labeling step was needed as to preserve sample integrity. One main innovation of this work was the insertion of fluidic restrictors at outlet ports to divert the separation interface into designated outlet channels. Thus, separation efficiency was significantly improved in comparison to previous works. We demonstrated different operation modes ranging from platelet or plasma extraction from human whole blood to platelet concentration from platelet-rich plasma through the manipulation of outlet port fluidic resistance. Using straight microfluidic channels with a high aspect ratio rectangular cross section, we demonstrated 95.4% platelet purity extracted from human whole blood. In plasma extraction, 99.9% RBC removal rate was achieved. We also demonstrated 2.6× concentration of platelet-rich plasma solution to produce platelet concentrate. The extraction efficiency and throughput rate are scalable with continuous and clog-free recirculation operation, in contrast to other blood fractionation approaches using filtration membranes or affinity-based purification methods. Our microfluidic blood separation method is highly tunable and versatile, and easy to be integrated into multi-step blood processing and advanced sample preparation workflows.

Label-free enrichment of human adipose-derived stem cells using a continuous microfluidic sorting cascade.

Human adipose tissue is a rich source of mesenchymal stem cells (MSCs). Human adipose-derived stem cells (ADSCs) are first prepared by tissue digestion of lipoaspirate. The remaining constituent contains a mixture of ADSCs, other cell types and lysed fragments. We have developed a scalable microfluidic sorter cascade which enabled high-throughput and label-free enrichment of ADSCs prepared from tissue-digested human adipose samples to improve the quality of purified stem cell product. The continuous microfluidic sorter cascade was composed of spiral-shaped inertial and deterministic lateral displacement (DLD) sorters which separated cells based on size difference. The cell count characterization results showed >90% separation efficiency. We also demonstrated that the enriched ADSC sub-population by the microfluidic sorter cascade yielded 6× enhancement of expansion capacity in tissue culture. The incorporation of this microfluidic sorter cascade into ADSC preparation workflow facilitates the generation of transplantation-scale stem cell product. We anticipate our stem cell microfluidic sorter cascade will find a variety of research and clinical applications in tissue engineering and regeneration medicine.

Three dimensional modeling of biologically relevant fluid shear stress in human renal tubule cells mimics in vivo transcriptional profiles.

The kidney proximal tubule is the primary site for solute reabsorption, secretion and where kidney diseases can originate, including drug-induced toxicity. Two-dimensional cell culture systems of the human proximal tubule cells (hPTCs) are often used to study these processes. However, these systems fail to model the interplay between filtrate flow, fluid shear stress (FSS), and functionality essential for understanding renal diseases and drug toxicity. The impact of FSS exposure on gene expression and effects of FSS at differing rates on gene expression in hPTCs has not been thoroughly investigated. Here, we performed RNA-sequencing of human RPTEC/TERT1 cells in a microfluidic chip-based 3D model to determine transcriptomic changes. We measured transcriptional changes following treatment of cells in this device at three different fluidic shear stress. We observed that FSS changes the expression of PTC-specific genes and impacted genes previously associated with renal diseases in genome-wide association studies (GWAS). At a physiological FSS level, we observed cell morphology, enhanced polarization, presence of cilia, and transport functions using albumin reabsorption via endocytosis and efflux transport. Here, we present a dynamic view of hPTCs response to FSS with increasing fluidic shear stress conditions and provide insight into hPTCs cellular function under biologically relevant conditions.

Co-cultured microfluidic model of the airway optimized for microscopy and micro-optical coherence tomography imaging.

We have developed a human bronchial epithelial (HBE) cell and endothelial cell co-cultured microfluidic model to mimic the in vivo human airway. This airway-on-a-chip was designed with a central epithelial channel and two flanking endothelial channels, with a three-dimensional monolayers of cells growing along the four walls of the channel, forming central clear lumens. These cultures mimic airways and microvasculature in vivo. The central channel cells are grown at air-liquid interface and show features of airway differentiation including tight-junction formation, mucus production, and ciliated cells. Combined with novel micro-optical coherence tomography, this chip enables functional imaging of the interior of the lumen, which includes quantitation of cilia motion including beat frequency and mucociliary transport. This airway-on-a chip is a significant step forward in the development of microfluidics models for functional imaging.