Biomedical subjects

Francis Lin

Publications and source records attributed to Francis Lin.

8 recordsLinked to original sources

PubMed2006

T cell chemotaxis in a simple microfluidic device.

This paper describes the use of a simple microfluidic device for studying T cell chemotaxis. The microfluidic device is fabricated in poly(dimethylsiloxane) (PDMS) using soft-lithography and consists of a "Y" type fluidic channel. Solutions are infused into the device by syringe pumps and generate a concentration gradient in the channel by diffusion. We show that the experimentally measured gradient profiles agree nicely with theoretical predictions and the gradient is stable in the observation region for cell migration. Using this device, we demonstrate robust chemotaxis of human T cells in response to single and competing gradients of chemokine CCL19 and CXCL12. Because of the simplicity of the device, it can flexibly control gradient generation in space and time, and would allow generation of multiple gradient conditions in a single chip for highly parallel chemotaxis experimentation. Visualization of T cell chemotaxis has previously been limited to studies in 3D matrices or under agarose assays, which do not allow precise control or variation in conditions. Acknowledging the importance of lymphocyte homing in the adaptive immune response, the ability to study T cell chemotaxis in microfluidic devices offers a new approach for investigating lymphocyte migration and chemotaxis in vitro.

Cells, Cultured↗

PubMed2006

A microfluidic multi-injector for gradient generation.

This paper describes a microfluidic multi-injector (MMI) that can generate temporal and spatial concentration gradients of soluble molecules. Compared to conventional glass micropipette-based methods that generate a single gradient, the MMI exploits microfluidic integration and actuation of multiple pulsatile injectors to generate arbitrary overlapping gradients that have not previously been possible. The MMI device is fabricated in poly(dimethylsiloxane) (PDMS) using multi-layer soft lithography and consists of fluidic channels and control channels with pneumatically actuated on-chip barrier valves. Repetitive actuation of on-chip valves control pulsatile release of solution that establishes microscopic chemical gradients around the orifice. The volume of solution released per actuation cycle ranged from 30 picolitres to several hundred picolitres and increased linearly with the duration of valve opening. The shape of the measured gradient profile agreed closely with the simulated diffusion profile from a point source. Steady state gradient profiles could be attained within 10 minutes, or less with an optimized pulse sequence. Overlapping gradients from 2 injectors were generated and characterized to highlight the advantages of MMI over conventional micropipette assays. The MMI platform should be useful for a wide range of basic and applied studies on chemotaxis and axon guidance.

Dimethylpolysiloxanes↗

PubMed2006

A parallel-gradient microfluidic chamber for quantitative analysis of breast cancer cell chemotaxis.

Growth factor-induced chemotaxis of cancer cells is believed to play a critical role in metastasis, directing the spread of cancer from the primary tumor to secondary sites in the body. Understanding the mechanistic and quantitative behavior of cancer cell migration in growth factor gradients would greatly help in future treatment of metastatic cancers. Using a novel microfluidic chemotaxis chamber capable of simultaneously generating multiple growth factor gradients, we examined the migration of the human metastatic breast cancer cell line MDA-MB-231 in various conditions. First, we quantified and compared the migration in two gradients of epidermal growth factor (EGF) spanning different concentrations: 0-50 ng/ml and 0.1-6 ng/ml. Cells showed a stronger response in the 0-50 ng/ml gradient. However, the fact that even a shallow gradient of EGF can induce chemotaxis, and that EGF can direct migration over a large dynamic range of gradients, confirms the potency of EGF as a chemoattractant. Second, we investigated the effect of antibody against the EGF receptor (EGFR) on MDA-MB-231 chemotaxis. Quantitative analysis indicated that anti-EGFR antibody impaired both motility and directional orientation (CI = 0.03, speed = 0.71 microm/min), indicating that cell motility was induced by the activation of EGFR. The ability to compare, in terms of quantitative parameters, the effects of different pharmaceutical inhibitors, as well as subtle differences in experimental conditions, will aid in our understanding of mechanisms that drive metastasis. The microfluidic chamber described in this work will provide a platform for cell-based assays that can be used to compare the effectiveness of different pharmaceutical compounds targeting cell migration and metastasis.

Breast Neoplasms↗

PubMed2005

Neutrophil migration in opposing chemoattractant gradients using microfluidic chemotaxis devices.

Neutrophils migrating in tissue respond to complex overlapping signals generated by a variety of chemotactic factors (CFs). Previous studies suggested a hierarchy between bacteria-derived CFs and host-derived CFs but could not differentiate neutrophil response to potentially equal host-derived CFs (IL-8 and LTB4). This paper reports neutrophil migration in conflicting gradients of IL-8 and LTB4 using a microfluidic chemotaxis device that can generate stable and well-defined gradients. We quantitatively characterized the movement of cells from time-lapse images. Neutrophils migrate more efficiently toward single IL-8 gradients than single LTB4 gradients as measured by the effective chemotactic index (ECI). In opposing gradients of IL-8 and LTB4, neutrophils show obvious chemotaxis toward a distant gradient, consistent with previous reports. When an opposing gradient of LTB4 is present, neutrophils show less effective chemotaxis toward IL-8 than when they are in a gradient of IL-8 alone. In contrast, the chemotactic response of neutrophils to LTB4 is not reduced in opposing gradients as compared to that in a single LTB4 gradient. These results indicate that the presence of one host-derived CF modifies the response of neutrophils to a second CF suggesting a subtle hierarchy between them.

Cell Culture Techniques↗

PubMed2004

Differential effects of EGF gradient profiles on MDA-MB-231 breast cancer cell chemotaxis.

Chemotaxis, directed cell migration in a gradient of chemoattractant, is an important biological phenomenon that plays pivotal roles in cancer metastasis. Newly developed microfluidic chemotaxis chambers (MCC) were used to study chemotaxis of metastatic breast cancer cells, MDA-MB-231, in EGF gradients of well-defined profiles. Migration behaviors of MDA-MB-231 cells in uniform concentrations of EGF (0, 25, 50, and 100 ng/ml) and EGF (0-25, 0-50, and 0-100 ng/ml) with linear and nonlinear polynomial profiles were investigated. MDA-MB-231 cells exhibited increased speed and directionality upon stimulation with uniform concentrations of EGF. The cells were viable and motile for over 24 h, confirming the compatibility of MCC with cancer cells. Linear concentration gradients of different ranges were not effective in inducing chemotactic movement as compared to nonlinear gradients. MDA-MB-231 cells migrating in EGF gradient of 0-50 ng/ml nonlinear polynomial profile exhibited marked directional movement toward higher EGF concentration. This result suggests that MDA-MB-231 cancer cell chemotaxis depends on the shape of gradient profile as well as on the range of EGF concentrations.

Breast Neoplasms↗

PubMed2004

Intracellular actin-based transport: how far you go depends on how often you switch.

Intracellular molecular motor-driven transport is essential for such diverse processes as mitosis, neuronal function, and mitochondrial transport. Whereas there have been in vitro studies of how motors function at the single-molecule level, and in vivo studies of the structure of filamentary networks, studies of how the motors effectively use the networks for transportation have been lacking. We investigate how the combined system of myosin-V motors plus actin filaments is used to transport pigment granules in Xenopus melanophores. Experimentally, we characterize both the actin filament network, and how this transport is altered in response to external signals. We then develop a theoretical formalism to explain these changes. We show that cells regulate transport by controlling how often granules switch from one filament to another, rather than by altering individual motor activity at the single-molecule level, or by relying on structural changes in the network.

Actins↗

PubMed2004

Effective neutrophil chemotaxis is strongly influenced by mean IL-8 concentration.

Neutrophils need to correctly interpret gradients of chemotactic factors (CFs) such as interleukin 8 (IL-8) to migrate to the site of infection and perform immune functions. Because diffusion-based chemotaxis assays used in previous studies suffer from temporally changing gradients, it is difficult to distinguish the influence of CF gradient steepness from mean CF concentration on chemotaxis. To better understand the roles of mean CF concentration and CF gradient steepness, we developed a microfluidic device that can maintain stable IL-8 gradients. We report that the random motility of neutrophils is a biphasic function of IL-8 concentration and its magnitude plays a decisive role in effective chemotaxis, a quantitative measure of migration. We show that the concentrations for the optimum chemotaxis in linear IL-8 gradients and for the maximum random motility in uniform IL-8 coincide. In contrast, we find that the steepness of IL-8 gradients has no significant effect on effective chemotaxis.

Chemotaxis, Leukocyte↗

PubMed2004

Generation of dynamic temporal and spatial concentration gradients using microfluidic devices.

This paper describes a microfluidic approach to generate dynamic temporal and spatial concentration gradients using a single microfluidic device. Compared to a previously described method that produced a single fixed gradient shape for each device, this approach combines a simple "mixer module" with gradient generating network to control and manipulate a number of different gradient shapes. The gradient profile is determined by the configuration of fluidic inputs as well as the design of microchannel network. By controlling the relative flow rates of the fluidic inputs using separate syringe pumps, the resulting composition of the inlets that feed the gradient generator can be dynamically controlled to generate temporal and spatial gradients. To demonstrate the concept and illustrate this approach, examples of devices that generate (1) temporal gradients of homogeneous concentrations, (2) linear gradients with dynamically controlled slope, baseline, and direction, and (3) nonlinear gradients with controlled nonlinearity are shown and their limitations are described.

Equipment Design↗