The multi-facets of sustainable nanotechnology : lessons from a nanosafety symposium

An international symposium for nanosafety was held recently at the Nanyang Technological University in Singapore. Topics relating to understanding nanomaterial properties, tools, and infrastructure required for predicting hazardous outcomes, measuring nanomaterial exposure levels, systems approach for risk assessment and public's perception of nanotechnology were covered. The need for a multidisciplinary approach, across both natural and social sciences, for developing sustainable nanotechnology solutions was heavily emphasized. This commentary highlights the major issues discussed and the commitment of the nanosafety research community in Singapore to contribute collectively to realise the vision of sustainable nanotechnology

Superhydrophilicity-assisted preparation of transparent and visible light activated N-doped titania film

A novel and environmental friendly method was developed to prepare transparent, uniform, crack-free and visible light activated nitrogen doped (N-doped) titania thin films without the use of organic Ti precursors and organic solvents. The N-doped titania films were prepared from heating aqueous peroxotitanate thin films deposited uniformly on superhydrophilic uncoated glass substrates. The pure glass substrates were superhydrophilic after being heated at 500 degrees C for 1 h. Nitrogen concentrations in the titania films were adjusted by changing the amount of ammonia solution. The optimal photocatalytic activity of the N-doped titania films was about 14 times higher than that of a commercial self-cleaning glass under the same visible light illumination. The current reported preparative technique is generally applicable for the preparation of other thin films.Nanyang Technological University [1 RG29/07

Tailoring thin films for implant-specific applications

Research and development of polyester thin film implants can be tailored for controlled drug release, mechanical properties and surface properties. The high number of parameters often makes the optimization process slow and laborious. By employing high-throughput drug release and gradient-casting techniques, we show how these properties can be rapidly optimized. The employment of these techniques has yielded methods in which drug release can be tailored without the use of additives and how the choice of certain additives can change material properties while negligibly affecting drug release. Alternatively, plasma post-treatment may allow tailoring of thin film material properties though the judicious use of plasmas such as oxygen, argon, or a combination of them

Biomimetic processing of bioactive interface on silicon substrates

To facilitate the implantation of silicon-based devices in vivo, the presence of a biocompatible and bioactive coating is noted to be an essential factor. The objective of this present work is therefore to explore a relatively simple and low cost process to induce the formation of bioactive apatite on silicon. The formation of apatite on silicon was carried out by a biomimetic approach on two orientations of silicon wafer, namely (100) and (111). The samples are functionalized by chemical etching, followed by incubation in a simulated body fluid. Scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction analysis, and X-ray photoelectron spectroscopy were carried out. It was found that the growth of apatite is dependent on the orientation of the silicon wafer. Cell culturing experiment further verified the biological performance of the apatite-coated silicon samples

A cuprous oxide–reduced graphene oxide (Cu2O–rGO) composite photocatalyst for hydrogen generation : employing rGO as an electron acceptor to enhance the photocatalytic activity and stability of Cu2O

Photocorrosion, that causes rapid deactivation of Cu2O photocatalysts, was addressed by incorporating this oxide in a composite with reduced graphene oxide which acts as an electron acceptor to extract photogenerated electrons from Cu2O. Cu2O–rGO composite engineering also allows enhancing significantly photocatalytic activities of Cu2O for H2 generation

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.NRF (Natl Research Foundation, S’pore)Accepted versio

Novel Sensor-Enabled Ex Vivo Bioreactor: A New Approach towards Physiological Parameters and Porcine Artery Viability

The aim of the present work is to design and construct an ex vivo bioreactor system to assess the real time viability of vascular tissue. Porcine carotid artery as a model tissue was used in the ex vivo bioreactor setup to monitor its viability under physiological conditions such as oxygen, pressure, temperature, and flow. The real time tissue viability was evaluated by monitoring tissue metabolism through a fluorescent indicator “resorufin.” Our ex vivo bioreactor allows real time monitoring of tissue responses along with physiological conditions. These ex vivo parameters were vital in determining the tissue viability in sensor-enabled bioreactor and our initial investigations suggest that, porcine tissue viability is considerably affected by high shear forces and low oxygen levels. Histological evaluations with hematoxylin and eosin and Masson’s trichrome staining show intact endothelium with fresh porcine tissue whereas tissues after incubation in ex vivo bioreactor studies indicate denuded endothelium supporting the viability results from real time measurements. Hence, this novel viability sensor-enabled ex vivo bioreactor acts as model to mimic in vivo system and record vascular responses to biopharmaceutical molecules and biomedical devices.Published versio

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.NRF (Natl Research Foundation, S’pore)Accepted versio

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 Pearson’s 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.Accepted versio

Modulating drug release from poly(lactic-co-glycolic acid) thin films through terminal end-groups and molecular weight

Biodegradable PLGA is commonly employed for controlled drug release on the order of weeks to months. Hydrophobic drugs distribute homogeneously in PLGA, but their strong hydrophobic interaction typically results in narrow release profiles. In this study, three molecular weights (MW) and two different terminal end-groups of biodegradable PLGA were applied to broaden the range of drug release and vary the mechanical properties without the use of additives. Films knife-casted from PLGA polymers with terminal carboxylic acid end-groups were found to 1) absorb more water, 2) have higher rates of polymer mass loss, 3) increased hydrophobic drug release as compared to films knife casted from similar MW PLGA polymers with terminal ester end-groups. The highest drug release rates were obtained from low MW PLGA that had the densest surface concentration of terminal acid groups. An intermediate drug release profile was obtained with a blend of high and low MW PLGA. The various PLGA polymers (differing in MW, terminal groups, and combinations thereof) described herein could give rise to PLGA\PLGA blends that would allow independent tuning of drug release and mechanical properties without the inclusion of non-degradable additives with respect to hydrophobic, small molecule drugs.Accepted versio