Protein Fibers: Processing Techniques, Structural Mechanics, and Emerging Opportunities

Molecular structures and versatile functions of proteins have made them valuable components in biotechnology and medicine. Adhesives, gels, coatings, cultured meat, and scaffolds for tissue engineering are a few examples of each having different requirements for protein assembly. Proteins can self-assemble into supramolecular structures, but due to their relatively weak physical interactions, they have a shorter lifetime than chemically cross-linked structures. Enhancing the stability of supramolecular structures requires developing strategies to modulate protein interaction strengths. Whether proteins exhibit a fibrous or globular shape, and the distribution of electrostatic charges and their quantity on the protein surface convolute the assembly of long-range ordered structures.

In this talk, we provide an overview of research on assembling proteins using electro-hydrodynamic jetting to create quasi-one-dimensional structures with orientational order. To create macroscopic fibers, jet stabilization is required via viscoelasticity; proteins exhibit a strong secondary or tertiary structure, so there is not enough interaction between them to ensure entanglement and a global network. (Lauricella, et al., 2020) Thus, the common approach to introduce viscoelasticity is adding another, typically synthetic, polymer to the protein solution. Alternatively, unfolding of proteins into linear-like chains can impart the solution with the required properties, albeit at the expense of introducing toxic solvents (Dror et al., 2008; Boas et al., 2019). Nonetheless, some proteins are prone to profuse intermolecular interactions upon denaturation, causing them to aggregate.

In order to process proteins without the above weaknesses, we focus on the development of a supermolecular structure by bridging proteins with oppositely charged weak polyelectrolyte macromolecules (e.g., polysaccharides). There are many factors influencing the likelihood of such bridging interactions, including the distance between the chains, the charge density, the conformation of the protein, and the ionic strength of the solution (Martin et al., 2019; Warwar Damouny, et al. 2022). A global network containing a significant amount of proteins relative to polyelectrolytes can be formed by optimizing these parameters. We demonstrate the formation of a global network and the processing of the protein-polyelectrolyte complex into nanofibers using strong electric fields. The mechanical properties of nanofibers are discussed along with their tunability under different fiber stimulations. Lastly, tissue engineering and cultured meat are discussed as possible bio-related applications.

References

Lauricella, M., Succi, S., Zussman, E., Pisignano, D., and Yarin, A.L., (2020). Models of polymer solutions in electrified jets and solution blowing. Reviews of Modern Physics, 92(3) 035004.

Dror, Y., Ziv, T., Makarov, V., Wolf, H., Admon, A., and Zussman, E. (2008). Nanofibers made of globular proteins. Biomacromolecules, 9(10), 2749–2754.

Boas, M., Vasilyev, G., Vilensky, R., Cohen, Y. and Zussman, E. (2019). Structure and Rheology of Polyelectrolyte Complexes in the Presence of a Hydrogen-Bonded Co-Solvent. Polymers, 11(6) 1053..

Martin, P., Vasilyev, G., Chu, G., Boas, M., Arinstein, A., and Zussman, E. (2019). pH‐Controlled Network Formation in a Mixture of Oppositely Charged Cellulose Nanocrystals and Poly(allylamine). J. Polym. Sci. Part B Polym. Phys., 57(22), 1527–1536.

Warwar Damouny, C., Martin, P., Vasilyev, G., Vilensky, R., Redenski, I., Srouji, S., and Zussman, E. (2022). Injectable hydrogels based on inter-polyelectrolyte interactions between hyaluronic acid, gelatin, and cationic cellulose nanocrystals”, Biomacromolecules, 23(8), 3222-3234.