Transmission electron microscopy characterisation of Spirulina bioplastics

Plastic pollution is impacting global ecosystem health. Bioplastics made from unprocessed biomass, including whole or fragmented tissues, are one potential solution. They are biodegradable and exhibit competitive mechanical performance. Seaweed and microalgae have gained popularity over the last decade as bioplastic feedstocks due to their abundance and ease of cultivation. To grasp the complexity of transforming biomatter into bioplastics and to optimise their performance, it is essential to develop processing-structure-property relationships. Transmission electron microscopy can be used to observe the morphology of bioplastics; however, current infiltration techniques are designed for biomaterials in their natural state, and harsh reagents can cause artefacts in bioplastic structure. This paper examines four different fixation methods for Spirulina bioplastics and investigates the impact of fixative, contrasting, dehydration, and resin embedding on Spirulina ultrastructure before and after bioplastic transformation. Our study suggests that the key to preserving bioplastic morphology is to prepare the specimen for electron microscopy by exposing it to gas-phase infiltration.