An injection molding process for the fabrication of disposable plastic microfluidic chips with a cycle time of 2 min has been designed, developed, and implemented. Of the sixteen commercially available grades of cyclo-olefin copolymer (COC) that were screened for autofluorescence and transparency to ultraviolet (UV) light, Topas 8007 x 10 was identified as the most suitable for production. A robust solid metal mold insert defining the microfluidic channels was rapidly microfabricated using a process that significantly reduces the time required for electroplating. No wear of the insert was observed even after over 1000 cycles. The chips were bonded by thermal fusion using different bonding conditions. Each condition was tested and its suitability evaluated by burst pressure measurements. The COC microfluidic chips feature novel, integrated, reversible, standardized, ready-to-use interconnects that enable operation at pressures up to 15.6 MPa, the highest value reported to date. The suitability of these UV transparent, high pressure-resistant, disposable devices was demonstrated by in situ preparation of a high surface area porous polymer monolith within the channels.

The standard LIGA process takes advantage of the use of x-ray lithography to produce mold inserts with nearly vertical sidewall; the typical slope of patterns produced by x-ray lithography of polymethylmethacrylate is 0.1%. This lack of significant taper (draft angle) greatly increases the difficulty associated with ejecting parts during demolding. In this paper, a procedure is described to fabricate a mold insert with tapered features having a height of approximately 1 mm and lateral dimensions of approximately 300 μm. A set of six oblique exposures of a thick layer of SU-8 (an EPON epoxy based negative tone resist) is used to create hexagonal posts with a 3° draft angle. An electroforming process is used to fabricate a nickel mold insert with the tapered features. This mold insert is used to injection mold tapered polymer high aspect ratio microstructures. The dimensions of the SU-8 tapered structures (as well as the mold insert) are within 4 μm of desired/predicted values.

OMEGA is a system for cultivating microalgae using wastewater contained in floating photobioreactors (PBRs) deployed in marine environments and thereby eliminating competition with agriculture for water, fertilizer, and land. The offshore placement in protected bays near coastal cities co-locates OMEGA with wastewater outfalls and sources of CO 2-rich flue gas on shore. To evaluate the feasibility of OMEGA, microalgae were grown on secondary-treated wastewater supplemented with simulated flue gas (8.5% CO 2 V/V) in a 110-liter prototype system tested using a seawater tank. The flow-through system consisted of tubular PBRs made of transparent linear low-density polyethylene, a gas exchange and harvesting column (GEHC), two pumps, and an instrumentation and control (I&C) system. The PBRs contained regularly spaced swirl vanes to create helical flow and mixing for the circulating culture. About 5% of the culture volume was continuously diverted through the GEHC to manage dissolved oxygen concentrations, provide supplemental CO 2 , harvest microalgae from a settling chamber, and add fresh wastewater to replenish nutrients. The I&C system controlled CO 2 injection and recorded dissolved oxygen levels, totalized CO 2 flow, temperature, circulation rates, photosynthetic active radiation (PAR), and the photosynthetic efficiency as determined by fast repetition rate fluorometry. In two experimental trials, totaling 23 days in April and May 2012, microalgae productivity averaged 14.1 ± 1.3 grams of dry biomass per square meter of PBR surface area per day (n = 16), supplemental CO 2 was converted to biomass with >50% efficiency, and >90% of the ammonia-nitrogen was recovered from secondary effluent. If OMEGA can be optimized for energy efficiency and scaled up economically, it has the potential to contribute significantly to biofuels production and wastewater treatment.

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