3. Hybrid Nanoparticles Based on Electrostatic Interactions Between Proteins/Peptides and Synthetic Polyelectrolytes
The combination of proteins and synthetic polymers via macromolecular assembly is a very attractive approach to the fabrication of new nanomaterials avoiding elaborate synthetic procedures. The diverse family of synthetic polymers affords wide spectrum of combinations and supramolecular structures. The assembling process is directed by versatile in nature interactions including electrostatic, hydrogen bonding, van der Waals forces, or hydrophobic interactions. The investigations of protein–polymer-interacting behavior generate new knowledge about those hybrid supramolecular constructs which aids their application as novel biohybrid materials.
Synthetic polyelectrolytes are appropriate partners since proteins are charged species. The charges on the proteins originate from the ionogenic side groups in the lysine, arginine, and histidine units (generating positive charges) and in the aspartic acid, glutamic acid, and tyrosine residues (providing negative charges) of the polypeptide chains. The net charge of the proteins can be tuned by change of the pH of the solution which provides possibility for control over the interactions with the synthetic polyelectrolytes, i.e., the delivery system with a programmed response to pH changes in the biological environment can be designed. This smart behavior can include release of drug, release of shell, or (dis)assemble of the complex structure.
The electrostatic interactions are a very convenient approach for protein–polymer assembly in aqueous media under mild conditions. They are used for obtaining hybrid particles in solution and for surface modification as well. The first approach includes mixing of the synthetic polyelectrolyte with the protein at appropriate pH of the medium which results in the formation of hybrid complex aggregates (Coué and Engbersen, 2011 and Kurinomaru et al., 2012). The second approach refers to the binding of protein or polypeptide species to the oppositely charged surface of prior formed nanoparticles. The multiple deposition of oppositely charged protein and synthetic polymer in alternating fashion yields a hybrid layered surfaces applicable as biodegradable coatings and drug-releasing layers (Li, Wang, & Sun, 2012).