Self-organized vortex phases and hydrodynamic interactions in Bos taurus sperm cells.

Flocking behavior is observed in biological systems from the cellular to superorganismal length scales, and the mechanisms and purposes of this behavior are objects of intense interest. In this paper, we study the collective dynamics of bovine sperm cells in a viscoelastic fluid. These cells appear not to spontaneously flock, but transition into a long-lived flocking phase after being exposed to a transient ordering pulse of fluid flow.

Hybrid motility mechanism of sperm at viscoelastic-solid interface.

To fertilize eggs, sperm must pass through narrow, complex channels filled with viscoelastic fluids in the female reproductive tract. While it is known that the topography of the surfaces plays a role in guiding sperm movement, sperm have been thought of as swimmers, i.e.

Biological benefits of collective swimming of sperm in a viscoelastic fluid.

Collective swimming is evident in the sperm of several mammalian species. In bull () sperm, high viscoelasticity of the surrounding fluid induces the sperm to form dynamic clusters. Sperm within the clusters swim closely together and align in the same direction, yet the clusters are dynamic because individual sperm swim into and out of them over time.

Co-Adaptation of Physical Attributes of the Mammalian Female Reproductive Tract and Sperm to Facilitate Fertilization.

The functions of the female reproductive tract not only encompass sperm migration, storage, and fertilization, but also support the transport and development of the fertilized egg through to the birth of offspring. Further, because the tract is open to the external environment, it must also provide protection against invasive pathogens. In biophysics, sperm are considered "pusher microswimmers", because they are propelled by pushing fluid behind them.

Computer-assisted beat-pattern analysis and the flagellar waveforms of bovine spermatozoa.

Obstructed by hurdles in information extraction, handling and processing, computer-assisted sperm analysis systems have typically not considered in detail the complex flagellar waveforms of spermatozoa, despite their defining role in cell motility. Recent developments in imaging techniques and data processing have produced significantly improved methods of waveform digitization. Here, we use these improvements to demonstrate that near-complete flagellar capture is realizable on the scale of hundreds of cells, and, further, that meaningful statistical comparisons of flagellar waveforms may be readily performed with widely available tools.

Fluid viscoelasticity promotes collective swimming of sperm.

From flocking birds to swarming insects, interactions of organisms large and small lead to the emergence of collective dynamics. Here, we report striking collective swimming of bovine sperm in dynamic clusters, enabled by the viscoelasticity of the fluid. Sperm oriented in the same direction within each cluster, and cluster size and cell-cell alignment strength increased with viscoelasticity of the fluid.

Dynamics of Bovine Sperm Interaction with Epithelium Differ Between Oviductal Isthmus and Ampulla.

In mammals, many sperm that reach the oviduct are held in a reservoir by binding to epithelium. To leave the reservoir, sperm detach from the epithelium; however, they may bind and detach again as they ascend into the ampulla toward oocytes. In order to elucidate the nature of binding interactions along the oviduct, we compared the effects of bursts of strong fluid flow (as would be caused by oviductal contractions), heparin, and hyperactivation on detachment of bovine sperm bound in vitro to epithelium on intact folds of isthmic and ampullar mucosa.

Dynamic self-organization of microwell-aggregated cellular mixtures.

Cells with different cohesive properties self-assemble in a spatiotemporal and context-dependent manner. Previous studies on cell self-organization mainly focused on the spontaneous structural development within a short period of time during which the cell numbers remained constant. However the effect of cell proliferation over time on the self-organization of cells is largely unexplored.

An array microhabitat system for high throughput studies of microalgal growth under controlled nutrient gradients.

Microalgae have been increasingly recognized in the fields of environmental and biomedical engineering because of its use as base materials for biofuels or biomedical products, and also the urgent needs to control harmful algal blooms protecting water resources worldwide. Central to the theme is the growth rate of microalgae under the influences of various environmental cues including nutrients, pH, oxygen tension and light intensity. Current microalgal culture systems, e.

Interstitial flows promote amoeboid over mesenchymal motility of breast cancer cells revealed by a three dimensional microfluidic model.

Malignant tumors are often associated with an elevated fluid pressure due to the abnormal growth of vascular vessels, and thus an increased interstitial flow out of the tumors. Recent in vitro works revealed that interstitial flows critically regulated tumor cell migration within a three dimensional biomatrix, and breast cancer cell migration behavior depended sensitively on the cell seeding density, chemokine availability and flow rates. In this paper, we focus on the role of interstitial flows in modulating the heterogeneity of cancer cell motility phenotype within a three dimensional biomatrix.

Microgrooves and fluid flows provide preferential passageways for sperm over pathogen Tritrichomonas foetus.

Successful mammalian reproduction requires that sperm migrate through a long and convoluted female reproductive tract before reaching oocytes. For many years, fertility studies have focused on biochemical and physiological requirements of sperm. Here we show that the biophysical environment of the female reproductive tract critically guides sperm migration, while at the same time preventing the invasion of sexually transmitted pathogens.

Emergence of upstream swimming via a hydrodynamic transition.

We demonstrate that upstream swimming of sperm emerges via an orientation disorder-order transition. The order parameter, the average orientation of the sperm head against the flow, follows a 0.5 power law with the deviation from the critical flow shear rate (γ-γ_{c}).

Cooperative roles of biological flow and surface topography in guiding sperm migration revealed by a microfluidic model.

Successful reproduction in mammals requires sperm to swim against a fluid flow and through the long and complex female reproductive tract before reaching the egg in the oviduct. Millions of them do not make it. Despite their clinical importance, the roles played in sperm migration by the diverse biophysical and biochemical microenvironments within the reproductive tract are largely unknown.

SENSING DNA WITH ALTERNATING CURRENTS USING A NANOGAP SENSOR EMBEDDED IN A NANOCHANNEL DEVICE.

We report an integrated nanochannel/nanoelectrode sensor for the detection of DNA using alternating currents. We find that DNA can be detected using platinum as the metal for the detecting electrodes, with a signal to noise ratio exceeding 10. We argue that the signal is at least in part electrochemical in nature, thus holds the promise to yield a sequence-dependent signal.

A contact line pinning based microfluidic platform for modelling physiological flows.

This work introduces a contact line pinning based microfluidic platform for the generation of interstitial and intramural flows within a three dimensional (3D) microenvironment for cellular behaviour studies. A contact line pinning method was used to confine a natively derived biomatrix, collagen, in microfluidic channels without walls. By patterning collagen in designated wall-less channels, we demonstrated and validated the intramural flows through a microfluidic channel bounded by a monolayer of endothelial cells (mimic of a vascular vessel), as well as slow interstitial flows within a cell laden collagen matrix using the same microfluidic platform.

Universal protein fluctuations in populations of microorganisms.

The copy number of any protein fluctuates among cells in a population; characterizing and understanding these fluctuations is a fundamental problem in biophysics. We show here that protein distributions measured under a broad range of biological realizations collapse to a single non-gaussian curve under scaling by the first two moments. Moreover, in all experiments the variance is found to depend quadratically on the mean, showing that a single degree of freedom determines the entire distribution.

Acceleration of emergence of bacterial antibiotic resistance in connected microenvironments.

The emergence of bacterial antibiotic resistance is a growing problem, yet the variables that influence the rate of emergence of resistance are not well understood. In a microfluidic device designed to mimic naturally occurring bacterial niches, resistance of Escherichia coli to the antibiotic ciprofloxacin developed within 10 hours. Resistance emerged with as few as 100 bacteria in the initial inoculation.

An introduction to micro-ecology patches.

Bacterial systems offer excellent tests of how well the general theoretical predictions of ecology dynamics do or do not in fact conform to reality. We believe that the basic rules that govern the cohabitation of competing species for limited resources are the same from bacteria to man, we just don't know the rules, and that fundamental studies of the games bacteria play will give fundamental insight into the vastly more complex systems we hope to attack later. In this tutorial review we discuss how simplified micro-ecologies constructed using tools of micro and nanofabrication techniques offer some idea of how physical principles and analysis can address the issue of complex ecology dynamics.

Upconverting nanophosphors for bioimaging.

Upconverting nanoparticles (UCNPs) when excited in the near-infrared (NIR) region display anti-Stokes emission whereby the emitted photon is higher in energy than the excitation energy. The material system achieves that by converting two or more infrared photons into visible photons. The use of the infrared confers benefits to bioimaging because of its deeper penetrating power in biological tissues and the lack of autofluorescence.

Complementary metal oxide semiconductor compatible fabrication and characterization of parylene-C covered nanofluidic channels with integrated nanoelectrodes.

Nanochannels offer a way to align and analyze long biopolymer molecules such as DNA with high precision at potentially single basepair resolution, especially if a means to detect biomolecules in nanochannels electronically can be developed. Integration of nanochannels with electronics will require the development of nanochannel fabrication procedures that will not damage sensitive electronics previously constructed on the device. We present here a near-room-temperature fabrication technology involving parylene-C conformal deposition that is compatible with complementary metal oxide semiconductor electronic devices and present an analysis of the initial impedance measurements of conformally parylene-C coated nanochannels with integrated gold nanoelectrodes.

Effects of different immersion media in multiphoton imaging of the epithelium and dermis of human skin.

In this work, we compared the performance of objectives with similar numerical aperture of 0.75 but different immersion media of air, water, glycerin, and oil in the imaging of human skin epithelium and dermis. In general, we found that the oil immersion objective recorded the strongest intensity at the same mechanical depth.

In vivo and scanning electron microscopy imaging of up-converting nanophosphors in Caenorhabditis elegans.

We show here that upconversion phosphors can be imaged both by infrared excitation and in a scanning electron microscope. We have synthesized and characterized for this work up-converting phosphor nanoparticles nonaggregated nanocrystals of size range 50-200 nm. We have investigated the optical properties of 50-200 nm nanoparticles and found a square dependence of the emitted visible fluorescence on the infrared excitation and verified that under electron excitation similar narrow band emission spectra can be obtained as is seen with IR upconversion.

Effects of objective numerical apertures on achievable imaging depths in multiphoton microscopy.

Multiphoton microscopy is a powerful technique for achieving three-dimensional submicron imaging in biological specimens. However, specimen optical parameters such as refractive indices and scattering coefficients can result in the loss of image resolution and decreased signal in depth. These factors are coupled to the focusing objective's numerical aperture (NA) in limiting the achievable imaging depths.

Dynamics of spiral waves under phase feedback control in a Belousov-Zhabotinsky reaction.

Feedback control of spiral waves by the phases of the spiral tip is investigated experimentally in a light-sensitive Belousov-Zhabotinsky reaction. The phases of rotation (Psi(r)) and meandering (Psi(m)) of the spiral tip are obtained in real time during experiments. It is found that, for both meandering and rigid rotating spirals, one can manipulate the spirals to move with any arbitrary paths by the feedback signals derived from Psi(r).