Research & Reviews: Journal of Material Sciences acids, binding strongly with negatively charged biomolecules, and useful for gene therapy [22][23][24][25] . Plus, as a cationic polymer, Ch can be combined with anionic polymers.Poly(γ-glutamic acid (γ-PGA) is one of the most promisor anionic PEs, highly due to its non-immunogenic behavior [26][27][28] and biodegradability into glutamic acid residues [29,30] . Glutamate is mostly known as major excitatory neurotransmitter in the central nervous system, acting as a synaptic transmitter, and influencing neuronal excitability, synaptic structure and function, neuronal migration during development, and neuronal viability [31][32][33][34][35] . It is also present in other tissues and organs, specifically in non-neuronal tissues like bone, pancreas, skin and cartilage [31,[33][34][35][36] , and having significant roles in their normal function, although yet not fully understood. γ-PGA, being a poly(amino acid) built by glutamic acid monomers [29,30,37,38] , may participate in similar processes.Ch/γ-PGA PECs appear to be promisor with an increasing number of references in the literature, but there is a lack of systematized information. Therefore, this review aims to overview the process of PEC formation within different architectures, as well as the current status of the Ch/γ-PGA PECs and their applications in the fields of drug delivery and regenerative medicine. Within this scope, we expect to identify the main challenges of Ch/γ-PGA PECs application for tissue regeneration.
CHITOSAN (Ch) AND POLY(γ-GLUTAMIC ACID (γ-PGA) AS POLYELECTROLYTES (PEs)Polyelectrolyte (PE) is the term used to classify polymeric macromolecules with charged or chargeable groups when dissolved in polar solvents (predominantly water) [39,40] . When a PE dissociates, it gives rise to a macroion and counterions in aqueous solution [39] . The macroion can be named polycation (positively charged PE) or polyanion (negatively charged PE) [40] . Table 1 highlights some of the most studied PEs, either from natural or synthetic origin.