•High-pressure compatible microfluidic (μLC) devices were micro-machined from titanium.•Straight and serpentine μLC columns with nominal i.d.’s of 0.15, 0.3 and 0.5 mm were packed with 1.8 μm C18 ...sorbent and evaluated under isocratic and gradient conditions.•Devices with curved (serpentine) channels exhibited a significant loss in LC performance, especially for those with 0.5 mm i.d. channels.•Experimental gradient peak capacity is impaired to a far smaller degree by turns in the channels than the measured isocratic efficiency.
We prepared a series of planar titanium microfluidic (μLC) columns, each 100 mm long, with 0.15, 0.3 and 0.5 mm i.d.’s. The microfluidic columns were packed with 1.8 μm C18 sorbent and tested under isocratic and gradient conditions. The efficiency and peak capacity of these devices were monitored using a micro LC instrument with minimal extra column dispersion. Columns with serpentine channels were shown to perform worse than those with straight channels. The loss of efficiency and peak capacity was more prominent for wider i.d. columns, presumably due to on-column band broadening imparted by the so-called “race-track” effect. The loss of chromatographic performance was partially mitigated by tapering the turns (reduction in i.d. through the curved region). While good performance was obtained for 0.15 mm i.d. devices even without turn tapering, the performance of 0.3 mm i.d. columns could be brought on par with capillary LC devices by tapering down to 2/3 of the nominal channel width in the turn regions. The loss of performance was not fully compensated for in 0.5 mm devices even when tapering was employed; 30% loss in efficiency and 10% loss in peak capacity was observed. The experimental data for various devices were compared using the expected theoretical relationship between peak capacity Pc and efficiency N; (Pc−1) = N0.5 × const. While straight μLC columns showed the expected behavior, the devices with serpentine channels did not adhere to the plot. The results suggest that the loss of efficiency due to the turns is more pronounced than the corresponding loss of peak capacity.
This paper describes a simple method for the effective and rapid separation of hydrophobic molecules on polydimethylsiloxane (PDMS) microfluidic devices using Micellar Electrokinetic Chromatography ...(MEKC). For these separations the addition of sodium dodecyl sulfate (SDS) served two critical roles - it provided a dynamic coating on the channel wall surfaces and formed a pseudo-stationary chromatographic phase. The SDS coating generated an EOF of 7.1 x 10(-4) cm(2) V(-1) s(-1) (1.6% relative standard deviation (RSD), n = 5), and eliminated the absorption of Rhodamine B into the bulk PDMS. High efficiency separations of Rhodamine B, TAMRA (6-carboxytetramethylrhodamine, succinimidyl ester) labeled amino acids (AA), BODIPY FL CASE (N-(4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene-3-propionyl)cysteic acid, succinimidyl ester) labeled AA's, and AlexaFluor 488 labeled Escherichia coli bacterial homogenates on PDMS chips were performed using this method. Separations of Rhodamine B and TAMRA labeled AA's using 25 mM SDS, 20% acetonitrile, and 10 mM sodium tetraborate generated efficiencies > 100,000 plates (N) or 3.3 x 10(6) N m(-1) in <25 s with run-to-run migration time reproducibilities <1% RSD over 3 h. Microchips with 30 cm long serpentine separation channels were used to separate 17 BODIPY FL CASE labeled AA's yielding efficiencies of up to 837,000 plates or 3.0 x 10(6) N m(-1). Homogenates of E. coli yielded approximately 30 resolved peaks with separation efficiencies of up to 600,000 plates or 2.4 x 10(6) N m(-1) and run-to-run migration time reproducibilities of <1% RSD over 3 h.
We have developed a new method for analyte preconcentration on a microfluidic device using a porous membrane fabricated via sol-gel chemistry. These porous membranes were fabricated within the ...channels of glass microfluidic devices exploiting laminar flow to bring an alcoholic sol-gel precursor (titanium isopropoxide in 2-propanol) into contact with an alcohol-water solution at a channel cross intersection. These two streams reacted at the fluidic interface to form a porous titania membrane. The thickness of the membrane could be altered by changing the H₂O. Analyte concentration was accomplished by applying a voltage across the titania membrane. The level of analyte enrichment was monitored, and enrichment factors of above 4000 in 400 s were obtained for 2,7-dichlorofluorescein.
A poly(dimethylsiloxane)−poly(ethylene oxide) (PDMS−PEO) vinyl terminated block copolymer has been synthesized via a simple hydrosilylation reaction between hydride-terminated PDMS and PEO divinyl ...ether. This prepolymer can be subsequently cross-linked into an elastomer in a second hydrosilylation reaction involving a methylhydrosiloxane−dimethylsiloxane copolymer, forming a material suitable for the purposes of fabricating microfluidic devices. The presence of the PEO block in the prepolymer chain results in a much more hydrophilic material following cross-linking. The surface water contact angle of the PDMS−PEO material is 65° ± 3 (n = 6), as opposed to approximately 110° for native PDMS. Droplets of water straddled by air within molded channels of the PDMS−PEO are concave in shape with contact angles where the fluid meets the side walls of 32° ± 4 (n = 8), while droplets in PDMS microchannels are more convex with contact angles of 95° ± 6 (n = 6). The length of the PDMS−PEO prepolymer chain and the multifunctional hydride cross-linker chains appear to dictate the durability of the elastomeric material. Young’s modulus measurements yielded values of 0.94 ± 0.08, 2.6 ± 0.8, and 1.91 ± 0.06 MPa for a 5% vinyl excess prepolymer and 10-fold excess of cross-linker, 10% vinyl excess prepolymer and 5-fold excess of cross-linker, and 10:1 PDMS, respectively, confirming that the elasticity of the cross-linked PDMS−PEO is similar to that of PDMS (Sylgard 184:10:1 mixture of elastomeric base to elastomer curing agent). The PDMS−PEO material still possesses enough PDMS character to allow molded channel architectures to be sealed between two pieces of the block copolymer by conformal contact. As a result of the more hydrophilic nature of the material, the channels of devices fabricated from this polymer are self-filling when using aqueous buffers, making it more user-friendly than PDMS for applications calling for background electrolytes void of organic modifiers. Different compositions of PDMS−PEO devices feature different electroosmotic flow values with the 5% vinyl excess prepolymer EOF values of 2.5 ± 0.7 × 10−4 and 5.7 ± 0.8 × 10−4 cm2/(V s) at pHs 6 and 9, respectively, and 1.2 ± 0.3 × 10−4 and 2.5 ± 0.3 × 10−4 cm2/(V s) for the 10% vinyl excess prepolymer device at pHs 6 and 9, respectively.
Microfabricated fluidics technology, e.g., lab-on-a-chip devices, offers many attractive features for performing chemistry and biochemistry on space-based platforms. We have constructed a portable, ...battery-operated microfluidic platform that was tested under reduced gravity and hypergravity conditions that would be experienced in space flight and launch. This device consisted of a microchip, microchip holder, two 0−8-kV high-voltage power supplies, a high-voltage switch, a solid-state diode-pumped green laser, an optical train, a channel photomultiplier, and an inertial mass measurement unit all under the control of a laptop computer and powered by 10 D-cell alkaline batteries. The unit was tested on NASA's reduced gravity research aircraft at gravity levels that are relevant to NASA's intended use of bioreporter-based microchips for environmental monitoring of space and planetary environments on manned and unmanned spacecraft. Over the course of two flights, 834 fast electrophoretic separations of four amino acids were performed under a variety of gravitational environments including zero-g, Martian-g, lunar-g, and ∼1.8-g. All separations were performed in less than 12 s and automatically analyzed. After correction with an internal migration standard, the migration time reproducibilities were all <1% relative standard deviation.
MEKC of standard proteins was investigated on PDMS microfluidic devices. Standard proteins were labeled with AlexaFluor® 488 carboxylic acid tetrafluorophenyl ester and filtered through a ...size‐exclusion column to remove any small peptides and unreacted label. High‐efficiency MEKC separations of these standard proteins were performed using a buffer consisting of 10 mM sodium tetraborate, 25 mM SDS, and 20% v/v ACN. A separation of BSA using this buffer in a 3.0 cm long channel generated a peak with a plate height of 0.38 μm in <20 s. Additional fast separations of myoglobin, α‐lactalbumin, lysozyme, and cytochrome c also yielded peaks with plate heights ranging from 0.54 to 0.72 μm. All proteins migrated with respect to their individual pIs. To improve the separations, we used a PDMS serpentine chip with tapered turns and a separation distance of 25 cm. The number of plates generated increased linearly with increasing separation distance on the extended separation channel chips; however, the resolution reached an asymptotic value after about 7 cm. This limited the peak capacity of the separation technique to 10–12.
BACKGROUNDTibial plateau fractures with an ipsilateral compartment syndrome are a clinical challenge with limited guidance regarding the best time to perform open reduction and internal fixation ...(ORIF) relative to fasciotomy wound closure. This study aimed to determine if the risk of fracture-related infection (FRI) differs based on the timing of tibial plateau ORIF relative to closure of ipsilateral fasciotomy wounds. METHODSA retrospective cohort study identified patients with tibial plateau fractures and an ipsilateral compartment syndrome treated with 4-compartment fasciotomy at 22 US trauma centers from 2009 to 2019. The primary outcome measure was FRI requiring operative debridement after ORIF. The ORIF timing relative to fasciotomy closure was categorized as ORIF before, at the same time as, or after fasciotomy closure. Bayesian hierarchical regression models with a neutral prior were used to determine the association between timing of ORIF and infection. The posterior probability of treatment benefit for ORIF was also determined for the three timings of ORIF relative to fasciotomy closure. RESULTSOf the 729 patients who underwent ORIF of their tibial plateau fracture, 143 (19.6%) subsequently developed a FRI requiring operative treatment. Patients sustaining infections were: 21.0% of those with ORIF before (43 of 205), 15.9% at the same time as (37 of 232), and 21.6% after fasciotomy wound closure (63 of 292). ORIF at the same time as fasciotomy closure demonstrated a 91% probability of being superior to before closure (RR, 0.75; 95% CrI, 0.38 to 1.10). ORIF after fasciotomy closure had a lower likelihood (45%) of a superior outcome than before closure (RR, 1.02; 95% CrI; 0.64 to 1.39). CONCLUSIONData from this multicenter cohort confirms previous reports of a high FRI risk in patients with a tibial plateau fracture and ipsilateral compartment syndrome. Our results suggest that ORIF at the time of fasciotomy closure has the highest probability of treatment benefit, but that infection was common with all three timings of ORIF in this difficult clinical situation.
This paper presents progress on the design of a "smart elevator" to be used in conjunction with deep sea ROV operations. Deep sea elevators are gravity driven untethered platforms used to deliver and ...or return items from the sea floor. Elevators are used when items are too large or heavy to be handled by the ROV, or when the turn around time to recover and redeploy the ROV system for sample removal is prohibitive. Unfortunately, efficiency is complicated by the precision with which elevators can be landed at a specific location on the bottom and recovered on the surface because of currents and the inadequately known hydrodynamic effects. To improve the effectiveness of elevators we have investigated the gliding behavior of an elevator outfitted with wing foils in a variety of configurations. The foils are able to produce forward motion and turning that could be used to drive the elevator against a current or to a specific position on the seafloor. The results presented here for 1/10th and 1/2 scale models show achievable glide slopes of foward to downward velocity approaching .5 for situations representative of typical operating conditions.
