Yu-Jui Chiu

Universally applicable three-dimensional hydrodynamic microfluidic flow focusing

We have demonstrated a microfluidic device that can not only achieve three-dimensional flow focusing but also confine particles to the center stream along the channel. The device has a sample channel of smaller height and two sheath flow channels of greater height, merged into the downstream main channel where 3D focusing effects occur. We have demonstrated that both beads and cells in our device display significantly lower CVs in velocity and position distributions as well as reduced probability of coincidental events than they do in conventional 2D-confined microfluidic channels. The improved particle confinement in the microfluidic channel is highly desirable for microfluidic flow cytometers and in fluorescence-activated cell sorting (FACS). We have also reported a novel method to measure the velocity of each individual particle in the microfluidic channel. The method is compatible with the flow cytometer setup and requires no sophisticated visualization equipment. The principles and methods of device design and characterization can be applicable to many types of microfluidic systems.

In vivo engineering of bone tissues with hematopoietic functions and mixed chimerism

Significance Current bone marrow (BM) or hematopoietic stem cell (HSC) transplantations require recipient conditioning that is accompanied by significant adverse effects in patients. Here, we report engineering of bone tissues with a functional BM compartment in vivo by modular assembly of mineralized and nonmineralized macroporous structures. These engineered bone tissues support maintenance of donor hematopoietic cells, respond to an HSC mobilization agent, and yield higher mixed chimerism in circulation of nonirradiated recipient mice compared with that of intravenous transplantation. Such engineered bone tissues could potentially be used as ectopic BM surrogates to treat various nonmalignant BM diseases and as a tool to study hematopoiesis, donor–host cell dynamics, tumor tropism, and hematopoietic cell transplantation. Synthetic biomimetic matrices with osteoconductivity and osteoinductivity have been developed to regenerate bone tissues. However, whether such systems harbor donor marrow in vivo and support mixed chimerism remains unknown. We devised a strategy to engineer bone tissues with a functional bone marrow (BM) compartment in vivo by using a synthetic biomaterial with spatially differing cues. Specifically, we have developed a synthetic matrix recapitulating the dual-compartment structures by modular assembly of mineralized and nonmineralized macroporous structures. Our results show that these matrices incorporated with BM cells or BM flush transplanted into recipient mice matured into functional bone displaying the cardinal features of both skeletal and hematopoietic compartments similar to native bone tissue. The hematopoietic function of bone tissues was demonstrated by its support for a higher percentage of mixed chimerism compared with i.v. injection and donor hematopoietic cell mobilization in the circulation of nonirradiated recipients. Furthermore, hematopoietic cells sorted from the engineered bone tissues reconstituted the hematopoietic system when transplanted into lethally irradiated secondary recipients. Such engineered bone tissues could potentially be used as ectopic BM surrogates for treatment of nonmalignant BM diseases and as a tool to study hematopoiesis, donor–host cell dynamics, tumor tropism, and hematopoietic cell transplantation.

A Single-Cell Assay for Time Lapse Studies of Exosome Secretion and Cell Behaviors

To understand the inhomogeneity of cells in biological systems, there is a growing demand on the capability of characterizing the properties of individual single cells. Since single-cell studies require continuous monitoring of the cell behaviors, an effective single-cell assay that can support time lapsed studies in a high throughput manner is desired. Most currently available single-cell technologies cannot provide proper environments to sustain cell growth and, proliferation of single cells and convenient, noninvasive tests of single-cell behaviors from molecular markers. Here, a highly versatile single-cell assay is presented that can accommodate different cellular types, enable easy and efficient single-cell loading and culturing, and be suitable for the study of effects of in vitro environmental factors in combination with drug screening. One salient feature of the assay is the noninvasive collection and surveying of single-cell secretions at different time points, producing unprecedented insight of single-cell behaviors based on the biomarker signals from individual cells under given perturbations. Above all, the acquired information is quantitative, for example, measured by the number of exosomes each single-cell secretes for a given time period. Therefore, our single-cell assay provides a convenient, low-cost, and enabling tool for quantitative, time lapsed studies of single-cell properties.

Self-Assembled Pico-Liter Droplet Microarray for Ultrasensitive Nucleic Acid Quantification

Nucleic acid detection and quantification technologies have made remarkable progress in recent years. Among existing platforms, hybridization-based assays have the advantages of being amplification free, low instrument cost, and high throughput, but are generally less sensitive compared to sequencing and PCR assays. To bridge this performance gap, we developed a quantitative physical model for the hybridization-based assay to guide the experimental design, which leads to a pico-liter droplet environment with drastically enhanced performance and detection limit several order above any current microarray platform. The pico-liter droplet hybridization platform is further coupled with the on-chip enrichment technique to yield ultrahigh sensitivity both in terms of target concentration and copy number. Our physical model, taking into account of molecular transport, electrostatic intermolecular interactions, reaction kinetics, suggests that reducing liquid height and optimizing target concentration will maximize the hybridization efficiency, and both conditions can be satisfied in a highly parallel, self-assembled pico-liter droplet microarray that produces a detection limit as low as 570 copies and 50 aM. The pico-liter droplet array device is realized with a micropatterned superhydrophobic black silicon surface that allows enrichment of nucleic acid samples by position-defined evaporation. With on-chip enrichment and oil encapsulated pico-liter droplet arrays, we have demonstrated a record high sensitivity, wide dynamic range (6 orders of magnitude), and marked reduction of hybridization time from >10 h to <5 min in a highly repeatable fashion, benefiting from the physics-driven design and nanofeatures of the device. The design principle and technology can contribute to biomedical sensing and point-of-care clinical applications such as pathogen detection and cancer diagnosis and prognosis.

A Self-Confined Single-Cell Loading Platform Combining PDMS Mesh and Patterned Cytop for Non-invasive Studies of Single Cell Secretions

Single cell analysis provides information of individual cells that is lost in measurements of large cell populations. There is a growing demand on the capability of characterizing the properties of individual single cells. Since transient and temporal studies of single cells require continuous monitoring of the cell behaviors, an effective single-cell assay that can support time lapsed studies in a high throughput manner is highly desirable. Currently, most single-cell technology platforms do not provide optimal in vitro micro-environments to sustain cell growth yet allow continuous studies of single cell behaviors based on the quantitative analysis of their molecular marker signals. In this study, we present a highly versatile single-cell assay to accommodate different cellular types and culturing conditions and to allow studies of single cell responses to environmental factors. Our assay is non-invasive and can collect and survey single cell secretions at different time points. It provides a convenient, low-cost, and enabling tool to investigate single cell properties in a high-throughput manner, generating accurate temporal and quantitative information unachievable in other methods.

A multi-channel clogging-resistant lab-on-a-chip cell counter and analyzer

Early signs of diseases can be revealed from cell detection in biofluids, such as detection of white blood cells (WBCs) in the peritoneal fluid for peritonitis. A lab-on-a-chip microfluidic device offers an attractive platform for such applications because of its small size, low cost, and ease of use provided the device can meet the performance requirements which many existing LoC devices fail to satisfy. We report an integrated microfluidic device capable of accurately counting low concentration of white blood cells in peritoneal fluid at 150 μl min−1 to offer an accurate (<3% error) and fast (~10 min/run) WBC count. Utilizing the self-regulating hydrodynamic properties and a unique architecture in the design, the device can achieve higher flow rate (500–1000 μl min−1), continuous running for over 5 h without clogging, as well as excellent signal quality for unambiguous WBC count and WBC classification for certain diseases. These properties make the device a promising candidate for point-of-care applications.

Rapid white blood cell detection for peritonitis diagnosis

A point-of-care and home-care lab-on-a-chip (LoC) system that integrates a microfluidic spiral device as a concentrator with an optical-coding device as a cell enumerator is demonstrated. The LoC system enumerates white blood cells from dialysis effluent of patients receiving peritoneal dialysis. The preliminary results show that the white blood cell counts from our system agree well with the results from commercial flow cytometers. The LoC system can potentially bring significant benefits to end stage renal disease (ESRD) patients that are on peritoneal dialysis (PD).