Simultaneous diamagnetic and magnetic particle trapping in ferrofluid microflows via a single permanent magnet.

Trapping and preconcentrating particles and cells for enhanced detection and analysis are often essential in many chemical and biological applications. Existing methods for diamagnetic particle trapping require the placement of one or multiple pairs of magnets nearby the particle flowing channel. The strong attractive or repulsive force between the magnets makes it difficult to align and place them close enough to the channel, which not only complicates the device fabrication but also restricts the particle trapping performance. This work demonstrates for the first time the use of a single permanent magnet to simultaneously trap diamagnetic and magnetic particles in ferrofluid flows through a T-shaped microchannel. The two types of particles are preconcentrated to distinct locations of the T-junction due to the induced negative and positive magnetophoretic motions, respectively. Moreover, they can be sequentially released from their respective trapping spots by simply increasing the ferrofluid flow rate. In addition, a three-dimensional numerical model is developed, which predicts with a reasonable agreement the trajectories of diamagnetic and magnetic particles as well as the buildup of ferrofluid nanoparticles.

Viscoelastic effects on electrokinetic particle focusing in a constricted microchannel.

Focusing suspended particles in a fluid into a single file is often necessary prior to continuous-flow detection, analysis, and separation. Electrokinetic particle focusing has been demonstrated in constricted microchannels by the use of the constriction-induced dielectrophoresis. However, previous studies on this subject have been limited to Newtonian fluids only. We report in this paper an experimental investigation of the viscoelastic effects on electrokinetic particle focusing in non-Newtonian polyethylene oxide solutions through a constricted microchannel. The width of the focused particle stream is found NOT to decrease with the increase in DC electric field, which is different from that in Newtonian fluids. Moreover, particle aggregations are observed at relatively high electric fields to first form inside the constriction. They can then either move forward and exit the constriction in an explosive mode or roll back to the constriction entrance for further accumulations. These unexpected phenomena are distinct from the findings in our earlier paper [Lu et al., Biomicrofluidics 8, 021802 (2014)], where particles are observed to oscillate inside the constriction and not to pass through until a chain of sufficient length is formed. They are speculated to be a consequence of the fluid viscoelasticity effects.

Microfluidic electrical sorting of particles based on shape in a spiral microchannel.

Shape is an intrinsic marker of cell cycle, an important factor for identifying a bioparticle, and also a useful indicator of cell state for disease diagnostics. Therefore, shape can be a specific marker in label-free particle and cell separation for various chemical and biological applications. We demonstrate in this work a continuous-flow electrical sorting of spherical and peanut-shaped particles of similar volumes in an asymmetric double-spiral microchannel. It exploits curvature-induced dielectrophoresis to focus particles to a tight stream in the first spiral without any sheath flow and subsequently displace them to shape-dependent flow paths in the second spiral without any external force. We also develop a numerical model to simulate and understand this shape-based particle sorting in spiral microchannels. The predicted particle trajectories agree qualitatively with the experimental observation.

Thoracic endografting in a patient with hereditary hemorrhagic telangiectasia presenting with a descending thoracic aneurysm.

A 53-year-old woman with no classic risk factors for aneurysm disease presented with the sudden onset of chest pain and dyspnea. A large descending thoracic aortic aneurysm with focal type B dissection was identified and excluded by emergency thoracic endografting. Further postoperative evaluation revealed a history of epistaxis, perioral telangiectasias, hepatic hypervascularity, and a mutation in the gene expressing activin receptor-like kinase 1 (ALK1), leading to a diagnosis of hereditary hemorrhagic telangiectasia. Aortic aneurysms associated with hereditary hemorrhagic telangiectasia are extremely rare, and to our knowledge, this is the first report of thoracic endografting in this patient population.

Controlled release of tethered molecules via engineered hydrogel degradation: model development and validation.

A statistical-co-kinetic model has been developed to predict effects of hydrolytic or enzymatic degradation on the macroscopic properties of hydrogels formed through Michael-type addition reactions. Important parameters accounted for by the theoretical calculations are bond cleavage kinetics, microstructural network characteristics such as macromer functionality and crosslinking efficiency, and detailed analysis of degradation products. Previous work indicated the validity of this modeling approach for predicting swelling behavior of hydrolytically degradable gels during early stages of degradation and the quantitative dependence of gel degradation on kinetic and structural parameters. The theoretical methodology is extended in the current work to predict release of covalently bound proteins from the network via labile bonds. Release studies of a network-bound fluoroscopic probe allow validation of model degradation parameters and indicate that macromer functionalization and network crosslinking efficiency can be appropriately tailored to achieve desired swelling profiles and protein release rates over the lifetime of the degradable gel. The effects of these network parameters on the timing of gel dissolution and the protein release that occurs during this phase of degradation are also identified, highlighting the utility of the developed model as a comprehensive tool for optimizing degradable hydrogels as matrices for drug delivery and tissue regeneration.