Production and physicochemical characterization of bacterial poly gamma- (glutamic acid) to investigate its performance on enhanced oil recovery.

Bacillus licheniformis LMG 7559, which is capable of producing extracellular poly gamma- (glutamic acid) (PGA), was provided for the biopolymer synthesis. Using a modified PGA medium for PGA production, the isolated biopolymer, undergone dialysis process mainly for desalination and removal of other impurities. The bacteria produced high molecular weight biopolymers with a weight average molecular weight (M̅n) of 1.6 × 105 g/mole identified by gel permeation chromatography (GPC). Furthermore, GPC analysis was utilized to determine the poly-dispersity of PGA as well as molecular weight variation by cultivation time. The heavy weight fraction of 1.85 × 105 g/mole with poly-dispersity index of 7.42 was distinguished. For the extracted and dialyzed biopolymer, thermal properties were studied using DSC/TGA by which a mass loss of 36 percent was observed. Eventually, the biopolymer solution was injected into the oil saturated heterogeneous porous medium to evaluate the recovery factor enhancement by PGA flooding. It was found that 31.45% of oil in place was recovered by biopolymer flooding, whereas only 16.6% of oil in place was obtained by water flooding.

Material properties and cell compatibility of poly(γ-glutamic acid)-keratin hydrogels.

Given the great demand for biopolymer and protein-based products from renewable resources, synthesis of a keratin-based hydrogel is presented herein. In this work, a novel hydrogel of poly(γ-glutamic acid) (γ-PGA) and keratin was synthesized through facile EDC·HCl/HOBt chemistry. Since keratin main chain is rich in amino side groups, carboxyl groups in γ-PGA were crosslinked with multi terminated amine groups in keratin. In the following, the hydrogel characteristics, including swelling ratio (2010% at molar ratio of HOBt/EDC = 0.105), in vitro degradation and mass loss (about 20% at day 21 for the aforementioned sample), chemical decomposition and the rheological properties were investigated. The chemical activator agents, enhanced the elastic modulus of swollen hydrogel from around 1000 to 4000 Pa by increasing the crosslinking degree. Despite good biocompatibility for cell growth, some kind of self-assembled keratin hydrogels are not suitable for microscopic observation while the γ-PGA-Keratin hydrogel in our study is transparent. The γ-PGA-Keratin hydrogels possess significant features of rapid hydrogel formation in seconds, maximum swelling ratio of about 2500% maximum elastic modulus (stiffness) of about 4.5 kPa (for the swollen sample) with controllable matrix pore size. For further application, the biocompatibility of the γ-PGA-Keratin hydrogel was assessed by live/dead assay. Recent studies have demonstrated the effect of hydrogel porosity, water absorbing and stiffness on cell spreading, proliferation and differentiation of mesenchymal stem cells. Bone marrow mesenchymal stem cells could be differentiated into various cell fates depending on the elastic modulus of materials they are cultured on. We carried out a statistical study (to skip the cell work labor) to predetermine the proper working span in which we can gain a hydrogel to cover all features needed to be applied for some application like cartilage repair.