The synthesis of polymeric materials as living and self-healing systems.

Sharp, Elliot Bryce (2022) The synthesis of polymeric materials as living and self-healing systems. Doctoral thesis, Northumbria University.

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Abstract

Advancements in smarter materials will play a major role in reducing materials, energy use, pollution, and carbon emissions. This creates a need for research to devise new composite materials incorporating the latest technologies in fields such as whole-cell catalysts and self-healing methods to create biocomposite materials. Functional biocomposite materials can be produced by depositing immobilised microorganisms onto a surface of a substrate material in a flexible, non-porous polymer which can sustain living cells. Ideally these biocoatings should be easy to apply using manual draw down techniques or by ink-jet printing for well-defined patterns and show activity rates at least comparable with free-floating cells.

The focus of this thesis was to create a method for the development of multichannel 3D substrates, embedding immobilised cells within a polymer matrix to create a multifunctional bioactive coating. To achieve this, a latex polymer coating was synthesised using styrene, butyl acrylate and acrylic acid. This composition was adjusted to create several latex polymer samples with varying physical properties. Increases in styrene content correlated directly to increasing glass transition temperature and hardness. Latex polymers were subject to coalescing agents to enhance film formation and reported small changes in coating properties. Several feasible substrates were coated and analysed for adhesion and surface coverage, the highest performing were implemented into biocatalysis reaction assays. Assays when compared to equivalent cell suspension systems reported reaction rates up to five times that of suspended yeast cells.

Distribution of cells were analysed using fluorescent E. coli under confocal and scanning electron microscopes. The development of these techniques enabled the analysis of BL21 (DE3) competent E. coli cells containing a pOPINF plasmid to be immobilised into the co-polymer coating and cell survival measured through expression of a green fluorescent protein.

Latex polymer composites were used to immobilise two strains of cyanobacteria. S. elongatus PCC 7942 and CCAP 1479/1A were tested on loofah substrates for toxicity, adhesion, net CO2 fixation rates and biological responses. CO2 uptake was found to increase by 19 - 22 and 4 - 7-fold for CCAP 1479/1A and PCC 7942 for the best performing biocomposites relative to their suspension controls. While immobilized, CCAP biocomposites survived in excess of 12 weeks, however PCC 7942 biocomposites experienced cell leaching after 4 weeks.

A complex and high-resolution piezoelectric ink-jet printer was used to deposit small (<50 μm) latex-cell droplets onto a 3D laser-cut scaffold of a polyacrylic material which created a channeled network reactor. A continuous flow circuit was created and tested using a standard cell assay.
In parallel, a suite of self-healing polyurethane samples were synthesised and the optimal composition of alcohols and diisocyanate monomers investigated. To measure self-healing capabilities polyurethane samples were cut and rejoined after 1 and 24 hours. Samples were analysed using tensile strength testing and compared to identical uncut samples. The polymer was found to retain between of 63 - 98 % (after 24 h) and 33 - 61 % (after 1 h) of its uncut strength.

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