Biosynthesis of highly pure poly-γ-glutamic acid for biomedical applications

The remarkable properties of poly-aminoacids, mainly their biocompatibility and biodegradability, have prompted an increasing interest in these polymers for biomedical applications. Poly-gamma-glutamic acid (gamma-PGA) is one of the most interesting poly-aminoacids with potential applications as a biomaterial. Here we describe the production and characterization of gamma-PGA by Bacillus subtilis natto. The gamma-PGA was produced with low molecular weight (10-50 kDa), high purity grade (> 99 %) and a d-/l-glutamate ratio of 50-60/50-40 %. To evaluate the feasibility of using this gamma-PGA as a biomaterial, chitosan (Ch)/gamma-PGA nanoparticles were prepared by the coacervation method at pH ranging from 3.0 to 5.0, with dimensions in the interval 214-221 nm with a poly-dispersion index of ca. 0.2. The high purity of gamma-PGA produced by this method, which is firstly described here, renders this biopolymer suitable for biomedical applications. Moreover, the Ch/gamma-PGA nanocomplexes developed in this investigation can be combined with biologically active substances for their delivery in the organism. The fact that the assembly between Ch and gamma-PGA relies on electrostatic interactions enables addition of other molecules that can be released into the medium through changes from acidic to physiological pH, without loss in biological activity.