Zinc Coordinated Cationic Polymers Break Up the Paradox between Low Molecular Weight and High Transfection Efficacy.

Cationic polymers have emerged as appealing nonviral gene vectors for decades, which, however, suffer from the paradox between low molecular weight and high transfection efficacy. Low molecular weight cationic polymers (LCPs) are well cell tolerated but are perplexed by orders-of-magnitude less efficacy compared to their macromolecular counterparts. The deficiency mainly lies in weak DNA binding of polymers and difficulty in endosomal escape of formulated polyplexes. Herein, we demonstrate that, through zinc (Zn) coordinated modification of LCPs, the high transfection efficiency and low molecular weight (thus low cytotoxicity) can be achieved simultaneously. The Zn coordinated ligand shows a high affinity to phosphate components and therefore will largely benefit the DNA packaging and endosomal membrane destabilization, addressing the defects of LCPs in gene delivery. Zn coordinative functionalization of LCPs breaks up the "efficacy-toxicity" paradox and provides great promise for the development of clinically efficient and safe nonviral gene vectors.

Performance of an anaerobic membrane bioreactor in which granular sludge and dynamic filtration are integrated.

To alleviate the fouling of a filter, simple substrates, dynamic filtration, and granular sludge were applied in an anaerobic membrane bioreactor (AnMBR). The results showed that under a transmembrane pressure < 20 kPa, the filter flux ranged between 15 and 20 l (m-2 h)-1 for a period of 30 days. The flux was higher than the typical flux of AnMBRs with conventional membranes and most current dynamic filters. In addition, the low cost of the filter avoided the need for a higher flux. Moreover, a stable granular sludge bed, which consumed all volatile fatty acids, was maintained. A compact fouling/filtration layer formed on the filter, which contributed to low effluent chemical oxygen demand concentrations and turbidity. In addition, substrate scarcity in the filtration zone resulted in the evolution of diverse bacteria on the filter.

Pulse shear stress for anaerobic membrane bioreactor fouling control.

Increase of shear stress at membrane surfaces is a generally applied strategy to minimize membrane fouling. It has been reported that a two-phase flow, better known as slug flow, is an effective way to increase shear stress. Hence, slug flow was introduced into an anaerobic membrane bioreactor for membrane fouling control. Anaerobic suspended sludge was cultured in an anaerobic membrane bioreactor (AMBR) operated with a side stream inside-out tubular membrane unit applying sustainable flux flow regimes. The averaged particle diameter decreased from 20 to 5 microm during operation of the AMBR. However, the COD removal efficiency did not show any significant deterioration, whereas the specific methanogenic activity (SMA) increased from 0.16 to 0.41 gCOD/g VSS/day. Nevertheless, the imposed gas slug appeared to be insufficient for adequate fouling control, resulting in rapidly increasing trans membrane pressures (TMP) operating at a flux exceeding 16 L/m2/h. Addition of powdered activated carbon (PAC) enhanced the effect of slug flow on membrane fouling. However, the combined effect was still considered as not being significant. The tubular membrane was subsequently equipped with inert inserts for creating a locally increased shear stress for enhanced fouling control. Results show an increase in the membrane flux from 16 L/m2/h to 34 L/m2/h after the inserts were mounted in the membrane tube.

Graphene enhanced transformation of lignin in laccase-ABTS system by accelerating electron transfer.

The degradation of lignin has attracted much attention since it represents approximately 30% of all non-fossil carbon sources and constitutes a sustainable bio-resource for fuels and aromatic derivatives. Here we investigated the degradation of lignin by laccase-catalysed reactions using 2,2'-Azino-bis(3-ethybenzothiazoline-6-sulfonic acid) (ABTS) as a mediator coupled with the carbon material graphene. Results indicated that there was a significant, two-fold, increase in the catalytic activity of lignin degradation in laccase-ABTS systems in the presence of graphene. Analysis suggested that the enhancement of lignin degradation could be attributed to graphene acting as an electron transfer conductor, thereby accelerating electron transfer, which facilitated the formation of intermediate oxidation states of ABTS and rendered the reactions between lignin and ABTS intermediates more efficient. This study could promote the development of novel enzymatic lignin degradation systems coupled with the carbon-based material graphene.

N,N,N-trimethylchitosan modified with well defined multifunctional polymer modules used as pDNA delivery vector.

A novel non-viral gene carrier based on N,N,N-trimethylchitosan (TMC) has been fabricated. First, well-defined copolymer P(PEGMA-co-DMAEMA) was synthesized through reversible addition fragmentation chain transfer (RAFT) polymerization of poly(ethylene glycol) methyl ether methacrylate (PEGMA) and N,N-(2-dimethylamino)ethyl methacrylamide (DMAEMA). Then allyl group grafting N,N,N-trimethylchitosan (Allyl-TMC) was synthesized via the reaction between allyl bromide and hydroxyl of TMC. Finally, P(PEGMA-co-DMAEMA) and folate were ordinally grafted onto Allyl-TMC to obtain TMC-g-P(PEGMA-co-DMAEMA)-FA. In comparison with pristine chitosan, TMC-g-P(PEGMA-co-DMAEMA)-FA has achieved both better water solubility and stronger pDNA packaging ability, which can contribute to improving gene transfection. Gene delivery efficiency of a series of TMC based functional polymers with different chitosan molecular weights has been tested. The results show that 20k-TMC-g-P(PEGMA-co-DMAEMA)-FA/pDNA complex at the weight ratio of 20 achieve the highest transfection efficiency in 293 T cells. This work presents a new strategy to modify chitosan efficiently as gene carrier material.

A Novel Bio-carrier Fabricated Using 3D Printing Technique for Wastewater Treatment.

The structure of bio-carriers is one of the key operational characteristics of a biofilm reactor. The goal of this study is to develop a series of novel fullerene-type bio-carriers using the three-dimensional printing (3DP) technique. 3DP can fabricate bio-carriers with more specialized structures compared with traditional fabrication processes. In this research, three types of fullerene-type bio-carriers were fabricated using the 3DP technique and then compared with bio-carrier K3 (from AnoxKaldnes) in the areas of physicochemical properties and biofilm growth. Images acquired by 3D profiling and SEM indicated that the surface roughness of the 3DP bio-carrier was greater than that of K3. Furthermore, contact angle data indicated that the 3DP bio-carriers were more hydrophilic than K3. The biofilm on the 3DP bio-carriers exhibited higher microbial activity and stronger adhesion ability. These findings were attributed to excellent mass transfer of the substrate (and oxygen) between the vapour-liquid-solid tri-phase system and to the surface characteristics. It is concluded that the novel 3DP fullerene-type bio-carriers are ideal carriers for biofilm adherence and growth.

Adsorption behavior of tightly bound extracellular polymeric substances on model organic surfaces under different pH and cations with surface plasmon resonance.

Tightly bound extracellular polymeric substances (TB-EPS) play a substantial role on microbial aggregates, which can promote microbial cells to aggregate and adhere onto the carrier in bioreactor. However, the attachment and adsorption of TB-EPS on different surfaces were awaited to be elucidated. In this study, four self-assembled monolayers (SAMs) carrying methyl (CH3-SAM), amino (NH2-SAM), hydroxyl (OH-SAM), and carboxyl (COOH-SAM) terminal groups were prepared to model different surfaces. TB-EPS adsorption on these surfaces under different pH conditions and additional cations were investigated using surface plasmon resonance. The adsorption of TB-EPS dramatically decreased with the decreasing pH values. CH3-SAM surface achieved the maximum adsorption at the same condition. Na(+) promoted the TB-EPS adsorbed on COOH-SAM surface. The Ca(2+)-mediated complexes were attracted by COOH-SAM and repelled by NH2-SAM, respectively. The adsorptions of TB-EPS on the four SAM surfaces were significantly increased by adding Fe(3+). These results demonstrated that the TB-EPS adsorption on the organic surfaces were dependent on the pH and cation of solution.

Composition of EPS fractions from suspended sludge and biofilm and their roles in microbial cell aggregation.

The adhesion and aggregation properties of microbial cell are closely related to extracellular polymeric substances (EPS). In this work, the composition and physicochemical characteristics of EPS in biofilm and suspended sludge (S-sludge) were determined to evaluate their roles in microbial cell aggregation. Raman spectroscopy and three-dimensional fluorescence spectra have been employed to reveal each EPS fraction in different composition. The flocculating capacity of each EPS fraction in the S-sludge shows extraordinary activity, comparing its counterpart in biofilm. Microbial cell surfaces present high hydrophobicity and increased zeta potentials upon EPS extraction. In addition, the respective contribution of EPS to cell aggregating was elucidated. The contribution of combined SEPS and LB-EPS was 23% for S-sludge sample, whereas that was negligible for biofilm sample. The contribution of LB-EPS and TB-EPS were 16% and 30% for S-sludge sample, and -6% and negligible for biofilm sample, respectively. Therefore, EPS promoted the S-sludge cells to aggregate, while in contrast, they showed a negligible or negative effect on the biofilm cells aggregating.

Analysis of mass transfer characteristics in a tubular membrane using CFD modeling.

In contrast to the large amount of research into aerobic membrane bioreactors, little work has been reported on anaerobic membrane bioreactors (AMBRs). As to the application of membrane bioreactors, membrane fouling is a key issue. Membrane fouling generally occurs more seriously in AMBRs than in aerobic membrane bioreactors. However, membrane fouling could be managed through the application of suitable shear stress that can be introduced by the application of a two-phase flow. When the two-phase flow is applied in AMBRs, little is known about the mass transfer characteristics, which is of particular importance, in tubular membranes of AMBRs. In our present work, we have employed fluid dynamic modeling to analyze the mass transfer characteristics in the tubular membrane of a side stream AMBR in which, gas-lift two-phase flow was applied. The modeling indicated that the mass transfer capacity at the membrane surface at the noses of gas bubbles was higher than the mass transfer capacity at the tails of the bubbles, which is in contrast to the results when water instead of sludge is applied. At the given mass transfer rate, the filterability of the sludge was found to have a strong influence on the transmembrane pressure at a steady flux. In addition, the model also showed that the shear stress in the internal space of the tubular membrane was mainly around 20 Pa but could be as high as about 40 Pa due to gas bubble movements. Nonetheless, at these shear stresses a stable particle size distribution was found for sludge particles.