Terry W. J. Steele

Toxicants inhibiting anaerobic digestion: a review.

Anaerobic digestion is increasingly being used to treat wastes from many sources because of its manifold advantages over aerobic treatment, e.g. low sludge production and low energy requirements. However, anaerobic digestion is sensitive to toxicants, and a wide range of compounds can inhibit the process and cause upset or failure. Substantial research has been carried out over the years to identify specific inhibitors/toxicants, and their mechanism of toxicity in anaerobic digestion. In this review we present a detailed and critical summary of research on the inhibition of anaerobic processes by specific organic toxicants (e.g., chlorophenols, halogenated aliphatics and long chain fatty acids), inorganic toxicants (e.g., ammonia, sulfide and heavy metals) and in particular, nanomaterials, focusing on the mechanism of their inhibition/toxicity. A better understanding of the fundamental mechanisms behind inhibition/toxicity will enhance the wider application of anaerobic digestion.

Recent advances in aptasensors based on graphene and graphene-like nanomaterials

Graphene and graphene-like two-dimensional nanomaterials have aroused tremendous research interest in recent years due to their unique electronic, optical, and mechanical properties associated with their planar structure. Aptamers have exhibited many advantages as molecular recognition elements for sensing devices compared to traditional antibodies. The marriage of two-dimensional nanomaterials and aptamers has emerged many ingenious aptasensing strategies for applications in the fields of clinical diagnosis and food safety. This review highlights current advances in the development and application of two-dimensional nanomaterials-based aptasensors with the focus on two main signal-transducing mechanisms, i.e. electrochemical and optical. A special attention is paid to graphene, a one-atom thick layer of graphite with exceptional properties, representing a fastgrowing field of research. In view of the unique properties of two-dimensional nanostructures and their inherent advantages of synthetic aptamers, we expect that high-performance two-dimensional nanomaterials-based aptasensing devices will find extensive applications in environmental monitoring, biomedical diagnostics, and food safety.

The effect of polyethylene glycol structure on paclitaxel drug release and mechanical properties of PLGA thin films.

Thin films of poly(lactic acid-co-glycolic acid) (PLGA) incorporating paclitaxel typically have slow release rates of paclitaxel of the order of 1 μg day(-1) cm(-2). For implementation as medical devices a range of zero order release rates (i.e. 1-15 μg day(-1) cm(-2)) is desirable for different tissues and pathologies. Eight and 35 kDa molecular weight polyethylene glycol (PEG) was incorporated at 15%, 25% and 50% weight ratios into PLGA containing 10 wt.% paclitaxel. The mechanical properties were assessed for potential use as medical implants and the rates of release of paclitaxel were quantified as per cent release and the more clinically useful rate of release in μg day(-1) cm(-2). Paclitaxel quantitation was correlated with the release of PEG from PLGA, to further understand its role in paclitaxel/PLGA release modulation. PEG release was found to correlate with paclitaxel release and the level of crystallinity of the PEG in the PLGA film, as measured by Raman spectrometry. This supports the concept of using a phase separating, partitioning compound to increase the release rates of hydrophobic drugs such as paclitaxel from PLGA films, where paclitaxel is normally homogeneously distributed/dissolved. Two formulations are promising for medical device thin films, when optimized for tensile strength, elongation, and drug release. For slow rates of paclitaxel release an average of 3.8 μg day(-1) cm(-2) using 15% 35k PEG for >30 days was achieved, while a high rate of drug release of 12 μg day(-1) cm(-2) was maintained using 25% 8 kDa PEG for up to 12 days.

High-throughput screening of PLGA thin films utilizing hydrophobic fluorescent dyes for hydrophobic drug compounds

Hydrophobic, antirestenotic drugs such as paclitaxel (PCTX) and rapamycin are often incorporated into thin film coatings for local delivery using implantable medical devices and polymers such as drug-eluting stents and balloons. Selecting the optimum coating formulation through screening the release profile of these drugs in thin films is time consuming and labor intensive. We describe here a high-throughput assay utilizing three model hydrophobic fluorescent compounds: fluorescein diacetate (FDAc), coumarin-6, and rhodamine 6G that were incorporated into poly(d,l-lactide-co-glycolide) (PLGA) and PLGA-polyethylene glycol films. Raman microscopy determined the hydrophobic fluorescent dye distribution within the PLGA thin films in comparison with that of PCTX. Their subsequent release was screened in a high-throughput assay and directly compared with HPLC quantification of PCTX release. It was observed that PCTX controlled-release kinetics could be mimicked by a hydrophobic dye that had similar octanol-water partition coefficient values and homogeneous dissolution in a PLGA matrix as the drug. In particular, FDAc was found to be the optimal hydrophobic dye at modeling the burst release as well as the total amount of PCTX released over a period of 30 days.

Novel gradient casting method provides high-throughput assessment of blended polyester poly(lactic-co-glycolic acid) thin films for parameter optimization

Pure polymer films cannot meet the diverse range of controlled release and material properties demanded for the fabrication of medical implants or other devices. Additives are added to modulate and optimize thin films for the desired qualities. To characterize the property trends that depend on additive concentration, an assay was designed which involved casting a single polyester poly(lactic-co-glycolic acid) (PLGA) film that blends a linear gradient of any PLGA-soluble additive desired. Four gradient PLGA films were produced by blending polyethylene glycol or the more hydrophobic polypropylene glycol. The films were made using a custom glass gradient maker in conjunction with a 180 cm film applicator. These films were characterized in terms of thickness, percent additive, total polymer (PLGA+additive), and controlled drug release using drug-like fluorescent molecules such as coumarin 6 (COU) or fluorescein diacetate (FDAc). Material properties of elongation and modulus were also accessed. Linear gradients of additives were readily generated, with phase separation being the limiting factor. Additive concentration had a Pearsons correlation factor (R) of >0.93 with respect to the per cent total release after 30 days for all gradients characterized. Release of COU had a near zero-order release over the same time period, suggesting that coumarin analogs may be suitable for use in PLGA/polyethylene glycol or PLGA/polypropylene glycol matrices, with each having unique material properties while allowing tuneable drug release. The gradient casting method described has considerable potential in offering higher throughput for optimizing film or coating material properties for medical implants or other devices.

Factors influencing polycation/siRNA colloidal stability toward aerosol lung delivery

Hexanediol diacrylate cross-linked oligoethylenimine (OEI-HD) is a non-viral polymeric vector designed to deliver siRNA. To achieve safe and effective in vivo siRNA delivery using this vector, the polyplex must have sufficient colloidal stability if administered intravenously or nebulized for delivery by the pulmonary route. In this study, polyplexes from OEI-HD and siRNA were formulated for aerosol-based lung delivery, regarding their colloidal stability, optimal particle size, and in vitro biological activity. Herein, we describe how these properties are dependent upon the polymer-to siRNA weight ratios, buffer composition they were complexed in, PEG-grafting, and the addition of commercial lung surfactants and/or non-ionic surfactants to the formulation. Lastly, the effects of nebulization of the formulation into aerosol droplets, on the polyplex particle size and transfection efficiency, were evaluated. Polyplex size was monitored for up to 2 h after polyplex formation to determine the extent of aggregation and final particle sizes when stability was achieved. Our results suggest that PEG-grafting and polyethylenimine-PEG mixing were effective in achieving colloidal stability in isotonic saline buffers. In addition, colloidal stability was achieved in isotonic glucose buffers using commercially available non-ionic surfactant Pluronic™ P68 or the lung-derived surfactant Alveofact™. The smallest particle size, 140 nm, was obtained with Pluronic™ F68. For transfection efficiency, both Alveofact™ and Pluronic™ F68 achieved equal or better transfection when added to the OEI-HD/siRNA polyplexes. For long term storage of OEI-HD/siRNA formulations, we propose a lyophilization method that created in situ polyplexes upon addition of water. Preparation of OEI-HD/siRNA polyplexes by this method allowed dry storage at room temperature for up to the 3 months. In conclusion, we have identified approaches to achieve formulation and colloidal stability of OEI-HD/siRNA complexes, a step toward successful application of polyplexes for in vivo siRNA delivery.

Adhesive curing through low-voltage activation

Instant curing adhesives typically fall within three categories, being activated by either light (photocuring), heat (thermocuring) or chemical means. These curing strategies limit applications to specific substrates and can only be activated under certain conditions. Here we present the development of an instant curing adhesive through low-voltage activation. The electrocuring adhesive is synthesized by grafting carbene precursors on polyamidoamine dendrimers and dissolving in aqueous solvents to form viscous gels. The electrocuring adhesives are activated at −2 V versus Ag/AgCl, allowing tunable crosslinking within the dendrimer matrix and on both electrode surfaces. As the applied voltage discontinued, crosslinking immediately terminated. Thus, crosslinking initiation and propagation are observed to be voltage and time dependent, enabling tuning of both material properties and adhesive strength. The electrocuring adhesive has immediate implications in manufacturing and development of implantable bioadhesives.

Collagen-cellulose composite thin films that mimic soft-tissue and allow stem-cell orientation.

Mechanical properties of collagen films are less than ideal for biomaterial development towards musculoskeletal repair or cardiovascular applications. Herein, we present a collagen–cellulose composite film (CCCF) compared against swine small intestine submucosa in regards to mechanical properties, cell growth, and histological analysis. CCCF was additionally characterized by FE-SEM, NMR, mass spectrometry, and Raman Microscopy to elucidate its physical structure, collagen–cellulose composition, and structure activity relationships. Mechanical properties of the CCCF were tested in both wet and dry environments, with anisotropic stress–strain curves that mimicked soft-tissue. Mesenchymal stem cells, human umbilical vein endothelial cells, and human coronary artery smooth muscle cells were able to proliferate on the collagen films with specific cell orientation. Mesenchymal stem cells had a higher proliferation index and were able to infiltrate CCCF to a higher degree than small intestine submucosa. With the underlying biological properties, we present a collagen–cellulose composite film towards forthcoming biomaterial-related applications.Graphical Abstract

Tunable chemical release from polyester thin film by photocatalytic zinc oxide and doped LiYF4 upconverting nanoparticles.

Once manufactured or implanted, polyester release kinetics tend to be fixed with little modulation possible for optimal local chemical concentrations. Here, a typical implantable polyester was fabricated into thin films (∼50 μm thick) with additives of photocatalytic ZnO nanoparticles, lanthanide-doped LiYF4 nanoparticle upconverting nanoparticles, or a combination thereof and irradiated with either 6 mW ultraviolet (365 nm) light emitting diodes or 50 mW near-infrared (980 nm) laser diodes to induce polymer photooxidation. Irradiated polyester films with the aforementioned photoadditives had enhanced release kinetics up to 30 times more than nonirradiated, neat films with extended release times of 28 days. Near-infrared, ZnO-mediated photocatalysis had the highest light on/light off ratio release kinetics of 15.4, while doped LiYF4 upconversion nanoparticles paired with ZnO nanoparticles had the highest linear R(2) correlation of 0.98 with respect to duty cycle and release kinetics. Future applications of the technology will aim toward modulation of previously developed polymeric reagents/drugs for real-time, feedback-optimized release.

Influence of soluble PEG-OH incorporation in a 3D cell-laden PEG-fibrinogen (PF) hydrogel on smooth muscle cell morphology and growth

We have been able to control hydrogel compliance and cell spreading in a three-dimensional (3D) cell-laden system (hydrogel) using soluble PEG-OH. This was accomplished by encapsulating smooth muscle cells (SMCs) into poly(ethylene glycol)-fibrinogen (PEG-fibrinogen or PF) with poly(ethylene glycol)-diol (PEG-OH) as a macromolecular leachant. The cell-encapsulating hydrogels were prepared with three concentrations of soluble PEG-OH having a mass of 10 kDa (1, 5 and 10% w/v). Rheology was used to measure the elastic (storage) component of the complex shear modulus of these hydrogels, while quantitative morphometrics were used to characterize SMC morphology. PF hydrogel with a higher amount of PEG-OH displayed a lower storage modulus and a higher elongated cell morphology of SMCs. Structural changes of PF hydrogels mainly owing to gelation-induced phase separation imparted by the soluble PEG-OH in 3D cell-laden hydrogels dramatically affected both the properties of the hydrogel network including the modulus as well as cell spreading.