Current technological shortcomings limit the economic viability of capturing and utilizing small sources of methane. The development of a reactor to overcome these limitations would unlock economic opportunity and incentivize reduced methane emissions. A microfluidic bioreactor containing immobilized methanotrophs has the potential to overcome these limitations by profitably converting small quantities of methane to more valuable liquid products.The material used for immobilizing bacteria in a microfluidic bioreactor must meet four criteria: biocompatibility, mechanical stability, reactor adhesion, and economic viability. This paper describes the development of a novel blend of agar and cross-linked polyvinyl alcohol (PVA) that meets these requirements. The properties of agar PVA blend hydrogels strongly depend on the ratio and absolute concentration of the constituent polymers, and the processes by which the polymers are cross-linked. The microscopic morphology of these blend hydrogels is theorized to be two interacting and competing phases formed by agar and PVA molecules mutually interfering with cross-linking via hydrogen bonding, and separating due to spinodal decomposition. Evidence for the proposed morphology is discussed.Blend hydrogels of 2 5% agar PVA are particularly promising, combining the desirable properties of both agar (low swelling) and PVA (strength and adhesion). The 2 5% agar PVA gels exhibited little swelling in water and nitrate mineral salts-based media. They also adhered to polycarbonate and stainless steel surfaces treated with ozone or oxygen plasma. Cultures of Methylomicrobium buryatense 5GB1 (5GB1) immobilized in these gels showed a reduction of metabolic activity rates, partly due to exposure to high concentrations of sulfate and phosphate during cross-linking. Shortening cross-linker exposure time from 2 hours to 30 minutes greatly improved activity rates, and immobilized cells exhibited increased activity rates over time as fresh methane was added. Based on these results, the 2 5% agar PVA blend hydrogels are suitable for the immobilization of 5GB1 in a microfluidic bioreactor. Further improvement of activity rates may be possible.Preservation of 5GB1 by lyophilization was unsuccessful. Cultures preserved in solutions of 5% bovine serum albumin and 10% sucrose or trehalose maintained metabolic activity rates after freezing at -80°C, but showed no activity after lyophilization.
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