Elastic particle deformation in rectangular channel flow as a measure of particle stiffness.

In this study, we experimentally observed and characterized soft elastic particle deformation in confined flow in a microchannel with a rectangular cross-section. Hydrogel microparticles of pNIPAM were produced using two different concentrations of crosslinker. This resulted in particles with two different shear moduli of 13.3 ± 5.5 Pa and 32.5 ± 15.7 Pa and compressive moduli of 66 ± 10 Pa and 79 ± 15 Pa, respectively, as measured by capillary micromechanics. Under flow, the particle shapes transitioned from circular to egg, triangular, arrowhead, and ultimately parachute shaped with increasing shear rate. The shape changes were reversible, and deformed particles relaxed back to circular/spherical in the absence of flow. The thresholds for each shape transition were quantified using a non-dimensional radius of curvature at the tip, particle deformation, circularity, and the depth of the concave dimple at the trailing edge. Several of the observed shapes were distinct from those previously reported in the literature for vesicles and capsules; the elastic particles had a narrower leading tip and a lower circularity. Due to variations in the shear moduli between particles within a batch of particles, each flow rate corresponded to a small but finite range of capillary number (Ca) and resulted in a series of shapes. By arranging the images on a plot of Ca versus circularity, a direct correlation was developed between shape and Ca and thus between particle deformation and shear modulus. As the shape was very sensitive to differences in shear modulus, particle deformation in confined flow may allow for better differentiation of microparticle shear modulus than other methods.

Generation and characterization of monodisperse deformable alginate and pNIPAM microparticles with a wide range of shear moduli.

Monodisperse particles of varying size, shape, and deformability were produced using two microfluidic strategies. For both strategies, monodisperse emulsion droplets of a crosslinkable solution were generated via flow-focusing. Subsequently, droplets were crosslinked either on chip or in an external bath. On-chip gelation resulted in spherical particles; varying the degree of crosslinking varied the deformability systematically. The optimized flow-focusing device design separated the production of monodisperse aqueous alginate droplets and the on-chip introduction of crosslinking ions. Two features were then adapted to target softer particles: the dispersed phase design and the polymer choice. The alternative design used a sheathed dispersed phase, with the polymer solution surrounding an unreactive viscous core, which generated alginate particles with a softer core. Poly(N-isopropylacrylamide) (pNIPAM) allowed access to a broad range of moduli. The resulting spherical particles were characterized using capillary micromechanics to determine the shear (G) and compressive (K) moduli. Particles with G = 0.013 kPa to 26 kPa and K = 0.221 kPa to 34.9 kPa were obtained; the softest particles are an order of magnitude softer than those previously reported. The second approach, based on earlier work by Hu et al., produced axisymmetric, non-spherical particles with fore-aft asymmetry. Alginate drops were again formed in a flow-focusing device but were crosslinked off-chip in an external gelation bath. By changing the bath viscosity, crosslinker concentration, and outlet height, the falling droplets deformed differently during gelation, resulting in a variety of shapes, such as teardrop, mushroom, and bowl shapes.

Retention models and interaction mechanisms of acetone and other carbonyl-containing molecules with amylose tris[(S)-α-methylbenzylcarbamate] sorbent.

The stoichiometric displacement models developed in the literature have been widely used for understanding the adsorption mechanisms of solutes in various chromatography systems. The models were used to explain the linear plots of the logarithms of the solute retention factor versus the molar concentration of a competitive modifier in an inert solvent. The slope of the linear plot was inferred to be the total number of modifier molecules displaced from the sorbent and from the solute-modifier complex upon adsorption of a solute molecule. The slopes reported in the literature were generally greater than 1. In this study, we determined the retention factors of five monovalent solutes, acetone, cyclo hexanone, benzaldehyde, phenylacetaldehyde, and hydrocinnamaldehyde, on a derivatized polysaccharide sorbent, amylose tris[(S)-α-methylbenzylcarbamate], or AS, as a function of the concentration of a polar modifier isopropanol (IPA) in n-hexane (an inert solvent). Each solute has one CO functional group, which can form an H-bond with a sorbent NH group and the OH group of IPA. The slopes, from 0.25 to 0.45, of the log-log plots are less than 1, which cannot be explained by the literature displacement models. The results of Infrared Spectroscopy and Density Functional Theory simulations show clear evidence of acetone-IPA complexation and IPA aggregation with average aggregation number n=3. A new thermodynamic retention model is developed to take into account IPA aggregation, IPA-solute complexation, and competitive adsorption. Dimensionless group analysis indicates that aggregation of IPA can lead to slopes B below 1, even at high IPA concentrations. The model parameters (IPA aggregation number and equilibrium constants) are estimated from the retention factors at different IPA concentrations. The retention model and the parameters are further validated with dynamic chromatography simulations. The results show that the aggregation leads to a significant reduction in the IPA monomer concentration, which affects the IPA-sorbent binding and the IPA-solute complexation. As a result, the slope of the log-log plot at a high IPA concentration approaches 1/n without complexation, or 2/n with complexation. The variations of B between the five achiral solutes can be due to different strengths of solute-IPA complexation. Hence, the complexation and aggregation of the polar modifier in the mobile phase must be accounted for in the retention models used in the interpretation of the retention factors and the adsorption mechanisms.

Quantitative X-ray tomography of the mouse cochlea.

Imaging with hard X-rays allows visualizing cochlear structures while maintaining intrinsic qualities of the tissue, including structure and size. With coherent X-rays, soft tissues, including membranes, can be imaged as well as cells making use of the so-called in-line phase contrast. In the present experiments, partially coherent synchrotron radiation has been used for micro-tomography. Three-dimensional reconstructions of the mouse cochlea have been created using the EM3D software and the volume has been segmented in the Amira Software Suite. The structures that have been reconstructed include scala tympani, scala media, scala vestibuli, Reissner's membrane, basilar membrane, tectorial membrane, organ of Corti, spiral limbus, spiral ganglion and cochlear nerve. Cross-sectional areas of the scalae were measured. The results provide a realistic and quantitative reconstruction of the cochlea.

Infrared neural stimulation: beam path in the guinea pig cochlea.

It has been demonstrated that INS can be utilized to stimulate spiral ganglion cells in the cochlea. Although neural stimulation can be achieved without direct contact of the radiation source and the tissue, the presence of fluids or bone between the target structure and the radiation source may lead to absorption or scattering of the radiation, which may limit the efficacy of INS. The present study demonstrates the neural structures in the radiation beam path that can be stimulated. Histological reconstructions and microCT of guinea pig cochleae stimulated with an infrared laser suggest that the orientation of the beam from the optical fiber determined the site of stimulation in the cochlea. Best frequencies of the INS-evoked neural responses obtained from the central nucleus of the inferior colliculus matched the histological sites in the spiral ganglion.

Access to urologic care for children in California: Medicaid versus private insurance.

OBJECTIVES: To compare the access to urologic care for a child with cryptorchidism insured by Medi-Cal versus one insured by private insurance. Medi-Cal (California State Medicaid) is a joint state and federal health insurance program that plays a significant role in providing healthcare coverage to low-income children. METHODS: A total of 54 randomly chosen urology offices throughout California were surveyed by telephone to determine whether the office accepted pediatric patients, accepted Medi-Cal, and when the earliest appointment date would be for a patient with Medi-Cal versus one with private insurance. RESULTS: Of the 46 practices that accepted pediatric patients, 96% offered a new patient appointment to a child with private insurance, but only 41% were willing to offer an appointment to a child with Medi-Cal (P < 0.0001). Of the offices that would not see a child with Medi-Cal, 75% were unable to recommend a urology office that might accept Medi-Cal. CONCLUSIONS: Children insured by Medi-Cal have significantly less access to necessary urologic care compared with children with private insurance.