It Was an Accident, I Swear! The Scientific Discovery of Conductive Polymers

Published by on November 3, 2023

Some of the most revolutionary scientific discoveries have occurred accidentally; luck is sometimes the most important factor leading to new discoveries (Donald, 2013). Conductive polymers were an accidental finding by scientists Shirakawa, MacDiarmid and Heeger in 1977 (Guo and Facchetti, 2020). These organic polymers were found to have high conductive properties typically associated with metals. They possess other characteristics that can advance the field of biomedical engineering for the development of biosensors and drug-delivery systems. Recent studies have proven conductive polymers to be advantageous in tissue engineering (Guo and Ma, 2018), as well as in the absorption of environmental pollutants (Khan, et al., 2021). 

Figure 1 – The chemical structures of the most-used conductive polymers for tissue engineering, as well as for pollutant absorption (Namsheer and Rout, 2020)

These polymers are synthesized as nanomaterials through various methods, including chemical and electrochemical synthesis. Their unique ability to conduct electricity occurs due to the jumping of electrons to different atoms within each molecule (Balint, Cassidy and Cartmell, 2014). Their structure consists of alternating single and double bonds, facilitating the delocalization of electrons (Balint, Cassidy and Cartmell, 2014). Conductive polymers allow for a stimulus response without any external source of power. They are controlled through stimulation from pH, temperature, light, and electrical changes (Balint, Cassidy and Cartmell, 2014).  

Figure 2 – The electrical properties of conductive polymers occur due to the delocalization of electrons as they jump from alternating single and double bonds of the molecule (Balint, Cassidy and Cartmell, 2014). 

Scaffolds of these polymers are built so they can be applied to various tissues. In bone tissue, these scaffolds are able to facilitate the adhesion of osteoblast cells, which are responsible for secreting the matrix for bone formation. Using these scaffolds also leads to an increase in the filling of bone matrix, and thus enhances bone strength. As the concentration of conductive polymers increases, so does cell adhesion and viability (Guo and Ma, 2018).   

Skeletal tissue engineering has similarly benefitted from the application of conductive polymers. Even as one of the most regenerative types of tissue, following episodes of stress or trauma, skeletal tissue loses the ability to replenish (Guo and Ma, 2018). Conductive polymer scaffolds have been shown to increase the number of cells containing myosin (Guo and Ma, 2018), which is a fibrous protein forming the filaments of muscle cells and allowing them to contract (Craig and Woodhead, 2006). Conductive polymers contribute to myogenesis (Guo and Ma, 2018), which is the process where myoblasts (the precursor cells) are merged into fibres called myotubes (Bryson-Richardson and Currie, 2008). Besides bone and skeletal tissue engineering, other body tissues able to benefit from these polymers include nerve, cardiac, and skin tissue (Guo and Ma, 2018). 

Conductive polymers’ range of applications are not limited to the medical field, but are also effective in the absorption of environmental spills. These include inorganic pollutants such as heavy metal ions, or organic pollutants such as dyes (Khan, et al., 2021). For instance, polyaniline has been used to remove tannic acid from wastewater (Sun, et al., 2017). The effectiveness of conductive polymers is due to their redox properties (Khan, et al., 2021). The π–π and hydrogen bonds, in addition to hydrophobic, electrostatic, and acid-base interactions with organic dyes have shown improvements in absorption rates (Khan, et al., 2021).

As complex as science is, the most significant discoveries do not always arise from complicated experiments. Beyond their applications in tissue engineering and pollutant absorption, conductive polymers must be further researched to seize their full potential.

References

Balint, R., Cassidy, N., Cartmell, S., 2014. Conductive polymers: Towards a smart biomaterial for tissue engineering. Acta Biomaterialia. 10(6): 2341-2353. https://doi.org/10.1016/j.actbio.2014.02.015. 

Bryson-Richardson, R., Currie, P., 2008. The genetics of vertebrate myogenesis. Nature Reviews Genetics. 9: 632–646. https://doi.org/10.1038/nrg2369. 

Craig R., Woodhead, J., 2006. Structure and function of myosin filaments. Current Opinion in Structural Biology. 16(2): 204-212. https://doi.org/10.1016/j.sbi.2006.03.006. 

Donald, G., 2013. The Accidental Scientist: The Role of Chance and Luck in Scientific Discovery. London: Michael O’Mara Books.

Guo, B., Ma, P., 2018. Conducting Polymers for Tissue Engineering. Biomacromolecules. 19(6): 1764-1782. https://doi.org/10.1021/acs.biomac.8b00276. 

Guo, X., Facchetti, A., 2020. The journey of conducting polymers from discovery to application. Nature Materials. 19: 922–928 (2020). https://doi.org/10.1038/s41563-020-0778-5. 

Khan, M., Almesfer, M., Elkhaleefa, A., Shigidi, I., Shamim, M., Ali, I., and Rehan, M., 2021. Conductive Polymers and Their Nanocomposites as Adsorbents in Environmental Applications. Polymers. 13(21): 3810. https://doi.org/10.3390/polym13213810. 

Namsheer, K., Rout, C., 2020. Conducting polymers: a comprehensive review on recent advances in synthesis, properties and applications. RSC Advances. 11: 5659-5697. doi: https://doi.org/10.1039/D0RA07800J.

Sun, C., Xiong, B., Pan, Y. and Cui, H., 2017. Adsorption removal of tannic acid from aqueous solution by polyaniline: Analysis of operating parameters and mechanism. Journal of Colloid and Interface Science, 487, pp.175–181. https://doi.org/10.1016/j.jcis.2016.10.035.