Anupam Bera

Microbial synthesis of polyhydroxyalkanoate using seaweed-derived crude levulinic acid as co-nutrient.

Production of polyhydroxyalkanoates (PHAs) from Jatropha biodiesel residues, namely crude glycerol and oil cake hydrolysate, has been reported previously. Halomonas hydrothermalis (MTCC accession no. 5445; NCBI Genbank accession no. GU938192), a wild marine strain, was used in the bio-synthesis. The present study was initiated to vary the properties of the polymer. Seaweed-derived crude levulinic acid (SDCLA), containing formic acid, residual sugars and dissolved minerals additionally, was proposed as co-feed along with the biodiesel residues. Experiments were conducted at 100mL scale in batch process. Whereas the PHA yield was only 0.40 ± 0.01 g when only biodiesel residues were employed, it rose to 1.07 ± 0.02 g in presence of 0.35% (w/v) of SDCLA. The corresponding carbon utilisation efficiencies were 29.3% and 57.5%, respectively. 3-Hydroxy valerate incorporation in the PHA was pronounced in presence of SDCLA, with associated changes in polymer properties. The microbial synthesis fared poorly when SDCLA was substituted with pure levulinic acid. Thus, Halomonas hydrothermalis had a poor response to levulinic acid, as such, and other constituents present in SDCLA appear to have played a vital role in bacterial cell division and accumulation of PHA. Biodegradability tests in moist soil were also conducted as part of the study. Marine microalgal cultivation for biodiesel and seaweed cultivation for fuels may help generate biodiesel residues and crude levulinic acid in proximity, which would open up the possibility of large scale PHA manufacture in efficient and practical manner in the future through the methodology of the present study.

Degradable/cytocompatible and pH responsive amphiphilic conetwork gels based on agarose-graft copolymers and polycaprolactone

Amphiphilic conetwork (APCN) gels have emerged as an important class of biomaterials due to their diverse applications. APCN gels based on biocompatible/biodegradable polymers are useful for controlled release and tissue engineering applications. Herein, we report a facile synthesis of APCN gel films by click type sequential nucleophilic substitution reaction between pendent tertiary amine groups of agarose-g-poly(methyl methacrylate)-b(co)-poly(2-dimethylamino)ethyl methacrylate [Agr-g-PMMA-b(co)-PDMA] copolymers and activated benzyl chloride groups of polychloromethyl styrene or benzyl methyl chloride terminated polycaprolactone. A linear triblock copolymer (PDMA-b-PMMA-b-PDMA) containing a central PMMA block and end PDMA blocks was also employed for the synthesis of APCN gels for comparison purposes. These APCN gels exhibit co-continuous nanophase morphology, pH responsive water swelling and pH triggered release of hydrophobic and hydrophilic drugs. These gels are biodegradable/cytocompatible as confirmed by MTT assay and hemolysis experiment. The degraded species undergo micellization in aqueous environment and display a low critical micelle concentration. Milled APCN gel particles are injectable through a hypodermic syringe. This synthesis approach is extremely useful for the preparation of a library of APCN gels of diverse architectures and compositions for biomedical applications.

Tailoring polyamide thin film composite nanofiltration membranes by polyethyleneimine and its conjugates for the enhancement of selectivity and antifouling property

Herein, we report a suitable surface modification process for a state-of-art poly(piperazineamide) thin film composite (TFC) nanofiltration (NF) membrane by polyethyleneimine (PEI) and its conjugates (PEI–polyethylene glycol and PEI–dextran) for the enhancement of monovalent ion to divalent ion selectivity and antifouling properties. The nascent TFC NF membrane was treated with PEI and its conjugates for the purpose of modification. The modified membranes exhibited high rejection of divalent cations (88–91%), high rejection of divalent anions (85–92%) and low rejection of NaCl (30–50%). The membranes modified under optimized conditions exhibited considerably enhanced antifouling/anti-scaling properties, similar permeate flux, similar Na+ to SO42− selectivity and much better Na+ to Mg2+ selectivity compared to that of the pristine membrane during the desalination of water containing a mixture of salts and real seawater. The adjustment in permeation property and improvement in antifouling behaviour are attributed to the adjustment of surface charge and pore size by the incorporation of multi-amine containing antifouling polyethylene glycol or dextran on the membrane surface via the post modification process.

Multifunctionalization of Poly(vinylidene fluoride)/Reactive Copolymer Blend Membranes for Broad Spectrum Applications

Simultaneous immobilization and cross-linking of antifouling/low toxic polymers, e.g., poly(ethylenimine) (PEI), dextran (Dex), agarose (Agr), poly(ethylene glycol) (PEG), PEI-Dex, and PEI-PEG conjugates, and stimuli-responsive copolymers on a porous membrane surface in mild reaction conditions is desirable for the enhancement of hydrophilicity, antifouling character, cytocompatibility, and inducing stimuli-responsive behavior. Grafting to technique is required since the precursors of most of these macromolecules are not amenable to surface-initiated polymerization. In this work, we report a versatile process for the simultaneous immobilization and cross-linking of a library of macromolecules on and into the blend membrane (PVDF-blend) of poly(vinylidene fluoride) and poly(methyl methacrylate)-co-poly(chloromethylstyrene). Sequential nucleophilic substitution reaction between activated halide moieties of the copolymer and amine groups of different macromolecules readily provided series of modified membranes. These membranes exhibited antifouling property superior to that of the unmodified membrane. The effectiveness of this technique has been demonstrated by the immobilization of pH or both pH- and temperature-responsive copolymer on PVDF-blend membrane for responsive separation of poly(ethylene oxide) and bovine serum albumin. Silver nanoparticles were also anchored on the select modified membranes surfaces for the enhancement of antibiofouling property. Our approach is useful to obtain verities of functional membranes and selection of membrane for a particular application.

Anti-organic fouling and anti-biofouling poly(piperazineamide) thin film nanocomposite membranes for low pressure removal of heavy metal ions

Propensity towards anti-organic fouling, anti-biofouling property and low rejection of multivalent cation (monovalent counter ion) restricts the application of the state-of-art poly(piperazineamide) [poly(PIP)] thin film composite (TFC) nanofiltration (NF) membrane for the treatment of water containing toxic heavy metal ions, organic fouling agents and microbes. Herein, we report the preparation of thin film nanocomposite (TFNC) NF membranes with improved heavy metal ions rejection efficacy, anti-biofouling property, and anti-organic fouling properties compared to that of poly(PIP) TFC NF membrane. The TFNC NF membranes were prepared by the interfacial polymerization (IP) between PIP and trimesoyl chloride followed by post-treatment with polyethyleneimine (PEI) or PEI-polyethylene glycol conjugate and then immobilization of Ag NP. The IP was conducted on a polyethersulfone/poly(methyl methacrylate)-co-poly(vinyl pyrollidone)/silver nanoparticle (Ag NP) blend ultrafiltration membrane support. The TFNC membranes exhibited >99% rejection of Pb2+, 91-97% rejection of Cd2+, 90-96% rejection of Co2+ and 95-99% rejection of Cu2+ with permeate flux ∼40Lm-2h-1 at applied pressure 0.5MPa. The improved heavy metal ions rejection efficacy of the modified NF membranes is attributed to the development of positive surface charge as well as lowering of surface pore size compared to that of unmodified poly(PIP) TFC NF membrane.

The effect of phenol functionality on the characteristic features and performance of fully aromatic polyester thin film composite nanofiltration membranes

Fully aromatic polyester thin film composite (TFC) nanofiltration (NF) membranes were successfully prepared on polysulfone support through interfacial polymerization (IP) of trimesoyl chloride (TMC) with bi-functional resorcinol (Res), tri-functional phloroglucinol (Phg) and their mixtures. The functionality of phenol greatly influenced the properties and performances of the membranes. Most notably, the active layer thickness (estimated from cross-sectional SEM images) and pore radius (from Hagen–Poiseuille pore flow model) decreased with an increasing amount of Phg. The best salt rejection and permeate flux were obtained with the membranes prepared from 2 : 1 (w/w) Phg : Res (TFC5) or pure Phg (TFC6). The membranes were negatively charged under operating pH conditions, as a result of which divalent anions were efficiently rejected whereas divalent cation rejection was considerably lower. TFC5 and TFC6 membranes showed promise for arsenic removal, giving 70–90% rejection of Na2HAsO4 depending on the ionic strength and pH of the feed water.