1. Biofabrication in Microfluidics: 
According to the journal Biofabrication launched in 2009 by IOP, biofabrication uses cells or biologics as the basic building blocks to manufacture biological models, systems, devices and products.  Biofabrication is considered as a convergent fabrication paradigm that bridges biotechnology and microfabrication.  Fundamentally, transfer of signals in biology is via ions and small molecules, while in microfabricated devices the transmitting components are electrons and photons.  Microfabrication uses top-down methods to pattern surfaces with permanent features.  Biological components are labile and the construction starts with bottom-up genetic information to code amino acid sequence and protein folding.  As such, the use of biological components and mechanisms for construction represents an enabling strategy to interface microfabrication with biology. 

Biofabrication in microfluidics is a perfect representation of integrating microfabricated devices with biology.  By consuming less fluidic volume and offering faster and parallel process control, advances in microfluidic technology are revolutionizing integrated platforms with applications in biology, biochemistry, medicine and biotechnology studies.  Biofabrication in microfluidics encompasses the benefits of microfluidic technology to construct biological systems that offers unprecedented capabilities. 

Our research group exploits device-imposed electrical signals (a & b), flow-driven chemical gradients (c & d) and air-bubble initiated electrostatic interactions (e) to guide the assembly of polysaccharides including chitosan, alginate and collagen in microfluidics.  The signal-guided assembly of biopolymers in microfluidic networks is spatially and temporally programmable.  Electrodeposited chitosan and alginate scaffolds have enabled the conjugation of nucleic acids, proteins, metabolic enzymes and cells in microfluidics.  Biofabricated chitosan membrane and polyelectrolyte complex membranes (PECM) allow selective penetration of small molecules while prohibiting macrobiomolecues such as antibodies diffusing through the freestanding membranes.  We envisioned that biofabrication in microfluidics can be implemented to a wide spectrum applications from biological and biochemical analysis to biomedical engineering studies.

a. Electroaddressing of Chitosan & Biomolecules
b. Electroaddressing of Alginate & Cells
c. Flow Assembly of Chitosan Membranes

 d. Flow Assembly of Alginate & Cells
e. Air Bubble-initiated Assembly of Polyelectrolyte Complex Membrane (PECM)

Representative publications:

  1. X. Luo, T. Vo, F. Jambi, P. Pham and J. Choy, “Microfluidic partition with in situ biofabricated semipermeable biopolymer membranes for static gradient generation”, Lab on a Chip, 2016,2016, 3815-3823. [link]
  2. X. L. Luo, H. C. Wu, J. Betz, W. E. Bentley and G. W. Rubloff, “Air bubble-initiated biofabrication of freestanding, semi-permeable biopolymer membranes in PDMS microfluidics”, Biochemical Engineering Journal, 2014, 89, 2-9. [link]
  3. J. F. Betz, Y. Cheng, C. Y. Tsao, A. Zargar, H. C. Wu, X. L. Luo, G. F. Payne, W. E. Bentley and G. W. Rubloff, “Optically clear alginate hydrogels for spatially controlled cell entrapment and culture at microfluidic electrode surfaces”, Lab on a Chip, 2013, 10, 1854-1858. [link]
  4. T. Gordonov, B. Liba, J. L. Terrell, Y. Cheng, X. L. Luo, G. F. Payne and W. E. Bentley, “Bridging the Bio-Electronic Interface with Biofabrication”,  Journal of Visualized Experiments, 2012, 64, e4231, DOI: 10.3791/4231. [link]
  5. X. L. Luo, “Biofabrication in microfluidics: a converging fabrication paradigm to exploit biology in microsystems”, Journal of Bioengineering & Biomedical Science, 2012, 2:e104. [link]
  6. Y. Cheng, X. L. Luo, G. F. Payne and G. W. Rubloff, “Biofabrication: Programmable Assembly of Hydrogels in Microfluidics as Scaffolds for Biology”, Journal of Materials Chemistry, 2012, 22, 7659-7666. [link]
  7. X. L. Luo, S. B. Buckhout-White, W. E. Bentley and G. W. Rubloff, “Biofabrication of chitosan-silver composite SERS substrates enabling quantification of adenine by spectroscopic shift”, Biofabrication, 2011, 3, 034108. [link]
  8. Y. Cheng, X. L. Luo, J. Betz, G. F. Payne, W. Bentley and G. W. Rubloff, “Mechanism of anodic electrodeposition of calcium alginate”, Soft Matter, 2011, 7, 5677-5684. [link]
  9. S. T. Koev, P. H. Dykstra, X. L. Luo, G. W. Rubloff, W. E. Bentley, G. F. Payne and R. Ghodssi, “Chitosan: an integrative biomaterial for lab-on-a-chip devices”, Lab on a chip, 2010, 10, 3026-3042.  [link]
  10. Y. Cheng, X. L. Luo, J. Betz, S. Buckhout-White, O. Bekdash, G. F. Payne, W. E. Bentley and G. W. Rubloff, “In situ quantitative visualization and characterization of chitosan electrodeposition with paired sidewall electrodes”, Soft Matter, 2010, 6, 3177-3183. [link]
  11. X. L. Luo, D. Larios Berlin, J. Betz, G. F. Payne, W. E. Bentley and G. W. Rubloff, “In situ generation of pH gradients in microfluidic devices for biofabrication of freestanding, semi-permeable chitosan membranes”, Lab on a Chip, 2010, 10, pp. 59-65. [link] Highlights in Chemical Technology
  12. X. L. Luo, A. T. Lewandowski, H. M. Yi, R. Ghodssi, G. F. Payne, W. E. Bentley and G. W. Rubloff, “Programmable assembly of a metabolic pathway enzyme in a pre-packaged reusable bioMEMS device”, Lab on a Chip, 2008, 8, pp. 420-430. [link]

2. Cell-Cell Signaling

Signaling between cells guides biological phenotype.  Communications between individual cells, clusters of cells and populations exist in complex networks that, in sum, guide behavior. There are few experimental approaches that enable high content interrogation of individual and multicellular behaviors at length and time scales commensurate with the signal molecules and cells themselves.  We exploit “biofabrication” in microfluidics as one approach that enables in-situ organization of living cells in microenvironments with spatiotemporal control and programmability. We construct bacterial biofilm mimics that offer  detailed understanding and subsequent control of population-based quorum sensing (QS) behaviors in a manner decoupled from cell number. Our approach reveals signaling patterns among bacterial cells within a single biofilm as well as behaviors that are coordinated between two communicating biofilms.  We envision versatile use of this biofabrication strategy for cell-cell interaction studies and small molecule drug discovery.

Representative publications:

  1. X. L. Luo, C. Y. Tsao, H. C. Wu, D. N. Quan, G. F. Payne, G. W. Rubloff and W. E. Bentley, “Distal modulation of cell-cell signaling in a synthetic ecosystem in partitioned microfluidics”, Lab on a Chip, 2015, 8, 1842-51.
  2. X. L. Luo, H. C. Wu, C. Y. Tsao, Y. Cheng, J. Betz, G. F. Payne, G. W. Rubloff and W. E. Bentley, “Biofabrication of stratified biofilm mimics for observation and control of bacterial signaling”, Biomaterials, 2012, 33, 5136-5143. [link]
  3. Y. Cheng, C. Y. Tsao, H. C. Wu, X. L. Luo, J. L. Terrell, J. Betz, G. F. Payne, W. Bentley and G. W. Rubloff, “Electroaddressing functionalized polysaccharides as model biofilms for interrogating cell signaling”, Advanced Functional Materials, 2012, 22, 519-528. [link]
  4. R. Fernandes, X. L. Luo (co-first authors), C. Y. Tsao, G. F. Payne, R. Ghodssi, G. W. Rubloff and W. E. Bentley, “Biological nanofactories facilitate spatially selective capture and manipulation of quorum sensing bacteria in a bioMEMS device”, Lab on a Chip, 2010, 10, pp. 1128-1134. [link]  Highlights in Chemical Technology; Journal inside cover image

3. Bacterial Chemotaxis

Bacterial cell signaling is a complex system communication between bacteria and their microenvironment. This signaling regulates individual bacterium behavior as well as the coordinated behaviors of a group of cells via the perception and a response to external signaling molecules.  Biofabrication in microfluidics provide microenvironments with precision in positioning cells and accuracy in providing chemical signals.  We are developing novel microfluidic platforms to answer some important unresolved issues in bacterial chemotaxis.

Representative publications:

  1. C. J. Wolfram, G. W. Rubloff and X. Luo, “Perspectives in Flow-Based Microfluidic Gradient Generators for Characterizing Bacterial Chemotaxis”, Biomicrofluidics, In press.

4. Artificial Cell Membranes

Engineering appropriate models of cellular structures and processes is essential in elucidating fundamental cellular mechanisms and in identifying useful targets for pharmaceutical drugs.  Model lipid bilayers (LBs) have been long used to study membrane-associated proteins that are involved in ion channel transport, membrane fusion, and in regulation of signaling pathways.  Conventionally, LBs are either manually painted or constructed with self-assembled monolayers across small apertures, followed by incorporation of membrane proteins.  Although a wide range of biological studies have been performed using these techniques over the past half century, model LBs often collapse within hours.  There is no stable LB system that can be monitored electrically, optically and allowing for rapid membrane bathing solution exchange at the same time.  We aim to develop artificial cell membranes that address these challenges.

5. Pressure and Viscosity Measurement in microfluidics

Pressure change in microfluidic devices is an important factor to control fluid flow and to provide guidelines when integrating pumps and valves in these devices. Among many technologies developed to measure pressure in microfluidics, an interesting strategy implements the principle of the ideal gas law to relate the change of compressed air to the change of pressure inside microchannels. The air compression approach is simple and efficient. However, the requirement of sealed air volume in microchannels is not applicable to the widely use, gas permeable polydimethylsiloxane (PDMS) microfluidic systems.  We are developing simple strategy to apply the ideal gas law principle to measure pressure change inside gas-permeable PDMS microchannels. The same idea can be further explored to figure out the viscosity of unknown sample fluids in a microchannel or capillary tube, therefore allowing the development of a simple viscometer based on the ideal gas law.

6. Yeast Aging Studies

For a long time in biology, budding yeast and other fungal organisms have been the models for aging research because the organismic aging in yeast is closely relevant to the aging processes occurring in the human body.  When yeast cells replicate, only the mother cell ages while the daughter cell resets the clock to zero, which represents a good model for the aging of stem cell populations in humans.  A big challenge in yeast aging studies is that as yeast cells proliferate, the mother cells are covered by daughter cells.  It is laborious to remove the daughter cells in order to keep track of the mother cells.  We are developing novel microfluidic platforms to address this and other issues to assist yeast aging studies.

Representative publications:

  1. X. Luo, T. Vo, F. Jambi, P. Pham and J. Choy, “Microfluidic partition with in situ biofabricated semipermeable biopolymer membranes for static gradient generation”, Lab on a Chip, 2016,2016, 3815-3823. [link]