Assessing the biocompatibility of oligomers and amine-functionalized polymers for use in two-phase partitioning bioreactors

Abstract

Two-phase partitioning bioreactors (TPPBs) are a bioprocessing tool that limits inhibition of cell growth by toxic compounds in bioreactors by utilizing an immiscible secondary phase to sequester compounds that inhibit microbial cell growth. Early TPPBs used organic solvents as the sequestering phase despite challenges identifying solvents that were inexpensive and biocompatible, although recent efforts have utilized polymers as the sequestering phase in TPPBs. Research on the selection of polymers for use as the sequestering phase in TPPBs has focused on predicting solute uptake by first principles in order to maximize the partitioning coefficient of a target solute. Some research has shown that low molecular weight (MW) polymers have improved partitioning coefficients, although their biocompatibility is in need of further study; this thesis investigates the effect of polymer MW on microbial biocompatibility. Trends in biocompatibility were assessed for polypropylene glycol to Saccharomyces cerevisiae and Pseudomonas putida. Given that log P has been used as an important physiochemical property for predicting biocompatibility, with higher log P values associated with improved biocompatibility, experiments were performed to determine the log P of polymers. Polymers were also water-washed to shift the log P upwards by removing low MW polymer chains. Average log P determination experiments showed that as the polymer MW increased, the measured log P also increased. Biocompatibility, as measured by the change in optical density of the cultures after 24 hours of exposure to the polymers, also improved with increasing MW and log P, and that polypropylene glycols possessing MWs of 1000 and higher were all found to be biocompatible. It was also shown that water-washing noticeably improved biocompatibility by removing low MW polymer from samples. Initial research was also undertaken to examine the use of amine-functionalized reactive polymers for extracting organic acids in TPPB in terms of their efficacy and their biocompatibility. An amine functionalized polyacrylate was synthesized which was stable under acidic conditions, and did not inhibit cell growth over 24 hour exposure. It was also shown to extract 60-85% of organic acids from aqueous solution over 2 hours with polymer concentrations of 10 g/L, and acid concentrations of 2.5 g/L.