The mitotic spindle must function in cell types that vary greatly in size, and its dimensions scale with the rapid, reductive cell divisions that accompany early stages of development. The mechanism responsible for this scaling is unclear, because uncoupling cell size from a developmental or cellular context has proven experimentally challenging. Here we combined microfluidic technology with Xenopus egg extracts to characterize spindle assembly within discrete, geometrically defined volumes of cytoplasm. Reductions in cytoplasmic volume, rather than developmental cues or changes in cell shape, were sufficient to recapitulate spindle scaling observed in Xenopus embryos. Thus, mechanisms extrinsic to the spindle, specifically a limiting pool of cytoplasmic component(s), play a major role in determining spindle size.

A low-pressure Carbon Filter Process (patent pending) is proposed to capture carbon dioxide (CO 2 ) from flue gas. This filter is filled with a low-cost carbonaceous sorbent, such as activated carbon or charcoal, which has a high affinity (and, hence, high capacity) to CO 2 but not to nitrogen (N 2 ). This, in turn, leads to a high CO 2 /N 2 selectivity, especially at low pressures. The Carbon Filter Process proposed in this work can recover at least 90% of flue-gas CO 2 of 90%+ purity at a fraction of the cost normally associated with the conventional amine absorption process. The Carbon Filter Process requires neither expensive materials nor flue-gas compression or refrigeration, and it is easy to heat integrate with an existing or grassroots power plant without affecting the cost of the produced electricity too much. An abundant supply of low-cost CO 2 from electricity producers is good news for enhanced oil recovery (EOR) and enhanced coal-bed methane recovery (ECBMR) operators, because it will lead to higher oil and gas recovery rates in an environmentally sensitive manner. A CO 2 -rich mixture that contains some nitrogen is much less expensive to separate from flue-gas than pure CO 2 ; therefore, mixed CO 2 /N 2 -EOR and CO 2 /N 2 -ECBMR methods are proposed to maximize the overall carbon capture and utilization efficiency.

PEG-based hydrogels have become widely used as drug delivery and tissue scaffolding materials. Common among PEG hydrogel-forming polymers are photopolymerizable acrylates such as polyethylene glycol diacrylate (PEGDA). Microfluidics and microfabrication technologies have recently enabled the miniaturization of PEGDA structures, thus enabling many possible applications for nano- and micro- structured hydrogels. The presence of oxygen, however, dramatically inhibits the photopolymerization of PEGDA, which in turn frustrates hydrogel formation in environments of persistently high oxygen concentration. Using PEGDA that has been emulsified in fluorocarbon oil via microfluidic flow focusing within polydimethylsiloxane (PDMS) devices, we show that polymerization is completely inhibited below critical droplet diameters. By developing an integrated model incorporating reaction kinetics and oxygen diffusion, we demonstrate that the critical droplet diameter is largely determined by the oxygen transport rate, which is dictated by the oxygen saturation concentration of the continuous oil phase. To overcome this fundamental limitation, we present a nitrogen micro-jacketed microfluidic device to reduce oxygen within the droplet, enabling the continuous on-chip photopolymerization of microscale PEGDA particles.

Encapsulating cells within biocompatible materials is a widely used strategy for cell delivery and tissue engineering. While cells are commonly suspended within bulk hydrogel-forming solutions during gelation, substantial interest in the microfluidic fabrication of miniaturized cell encapsulation vehicles has more recently emerged. Here, we utilize multiphase microfluidics to encapsulate cells within photopolymerized picoliter-volume water-in-oil droplets at high production rates. The photoinitiated polymerization of polyethylene glycol diacrylate (PEGDA) is used to continuously produce solid particles from aqueous liquid drops containing cells and hydrogel forming solution. It is well understood that this photoinitiated addition reaction is inhibited by oxygen. In contrast to bulk polymerization in which ambient oxygen is rapidly and harmlessly consumed, allowing the polymerization reaction to proceed, photopolymerization within air permeable polydimethylsiloxane (PDMS) microfluidic devices allows oxygen to be replenished by diffusion as it is depleted. This sustained presence of oxygen and the consequential accumulation of peroxy radicals produce a dramatic effect upon both droplet polymerization and post-encapsulation cell viability. In this work we employ a nitrogen microjacketed microfluidic device to purge oxygen from flowing fluids during photopolymerization. By increasing the purging nitrogen pressure, oxygen concentration was attenuated, and increased post-encapsulation cell viability was achieved. A reaction-diffusion model was used to predict the cumulative intradroplet concentration of peroxy radicals, which corresponded directly to post-encapsulation cell viability. The nitrogen-jacketed microfluidic device presented here allows the droplet oxygen concentration to be finely tuned during cell encapsulation, leading to high post-encapsulation cell viability.

A carbon filter that selectively captures CO 2 from flue gas on porous carbonaceous sorbents is demonstrated in field tests. A new sorbent regeneration process, referred to as steam-aided vacuum swing adsorption (SA-VSA), uses steam under vacuum to displace CO 2 from the carbon. Steam aids vacuum by reducing the partial pressure of CO 2 without the need to reduce the total pressure to deep vacuum, which is a challenge for vacuum swing adsorption (VSA). In turn, vacuum prevents the bulk condensation of steam on the sorbent, which is a challenge for CO 2 recovery using direct steam. Over 100 sorption−desorption cycles on flue gas produced in the lab and at two coal-fired power plants demonstrate that the SA-VSA-equipped carbon filter process can produce a nearly pure CO 2 product (at least 98%) while achieving high recovery (at least 98%). While stable, flexible, and robust in achieving the very high recovery and purity targets, this technology offers ample room for improvement through process optimization and, especially, sorbent optimization. For one of the reasonable but arbitrarily selected and inexpensive sorbents, a preliminary cost estimate example suggests an energy penalty of 31%, which should be less or much less for better sorbents.