Self-assembly meets additive manufacturing: Bridging the gap between nanoscale arrangement of matter and macroscale fabrication

New methods are emerging to combine the self-assembly of matter and additive manufacturing, so that new devices and constructs can simultaneously harness the unique molecular and nanostructural features afforded by self-assembly and the macroscale design freedom of additive manufacturing. The aim of this review is to analyse the body of literature and explore the crossover area where boundaries dissolve and self-assembly meets additive manufacturing (SAMAM). As a preliminary framework for this new area of research, the different experimental approaches to SAMAM can be grouped in three main categories, whereby SAMAM can be based on local interactions between molecules or nanoparticles, on 3D-printing induced forces, or on externally applied force fields. SAMAM offers numerous opportunities, such as the design of new printable materials, the ability to surpass conventional trade-offs in materials properties, the control of structural features across different length scales, process intensification and improved eco-sustainability. However, most research so far has been focused on polymer-based materials, and additional effort is needed to understand how SAMAM can be leveraged in metal- and ceramic-based additive manufacturing. On account of the weak inter-layer bonding often reported along the growth direction, it would also be interesting to explore whether SAMAM could effectively remediate undesidered anisotropic effects in additively manufactured parts

Nano-scale reservoir computing

This work describes preliminary steps towards nano-scale reservoir computing using quantum dots. Our research has focused on the development of an accumulator-based sensing system that reacts to changes in the environment, as well as the development of a software simulation. The investigated systems generate nonlinear responses to inputs that make them suitable for a physical implementation of a neural network. This development will enable miniaturisation of the neurons to the molecular level, leading to a range of applications including monitoring of changes in materials or structures. The system is based around the optical properties of quantum dots. The paper will report on experimental work on systems using Cadmium Selenide (CdSe) quantum dots and on the various methods to render the systems sensitive to pH, redox potential or specific ion concentration. Once the quantum dot-based systems are rendered sensitive to these triggers they can provide a distributed array that can monitor and transmit information on changes within the material.Comment: 8 pages, 9 figures, accepted for publication in Nano Communication Networks, http://www.journals.elsevier.com/nano-communication-networks/. An earlier version was presented at the 3rd IEEE International Workshop on Molecular and Nanoscale Communications (IEEE MoNaCom 2013

Biodegradable PLA-ZnO nanocomposite biomaterials with antibacterial properties, tissue engineering viability, and enhanced biocompatibility

Polylactic acid (PLA) is a well-known biomaterial on account of its biocompatibility and biodegradability. Zinc oxide (ZnO) nanofillers may endow PLA with advantageous antibacterial and tissue regenerative properties, but may also compromise the biocompatibility of PLA. Several strategies have been developed to improve the biomedical practicality of such composites. The importance of surface properties on amplifying the therapeutic properties and safety of a material enables two potential strategies: (i) surface modification of ZnO nanoparticles, and (ii) surface engineering of the PLA/ZnO composites. Moreover, the controllable biodegradation of PLA allows a third possible strategy: (iii) biodegradation-controlled release of ZnO. The first part of this review introduces the controllable degradation of PLA and the mechanisms of therapeutic properties and cytotoxicity of ZnO. Following this, the paper highlights current research trends regarding the biomedical application of PLA-based ZnO nanocomposites. The final section of this review discusses the potential use of ZnO in tuning the degradation rate of PLA, and the possibility of manipulating the surface properties of ZnO nanoparticles and PLA/ZnO composites in order to optimize the therapeutic properties and safe usage of PLA/ZnO composites in the biomedical field

Core-shell quantum dots: properties and applications

Fluorescent quantum dots (QDs) are semiconducting nanocrystals (NCs) that find numerous applications in areas, such as bio labelling, sensors, lasers, light emitting diodes and medicine. Core-shell quantum dots were developed to improve the photoluminescence efficiency of single quantum dots. Capping their surface with organic ligands as well as their extraction into aqueous media enables their use in sensing applications. The current review highlights the importance and applications of core shell quantum dots as well as their surface modifications and applications in the field of medicine and as sensors for chemical and biochemical analysis

Open challenges in tensile testing of additively manufactured polymers: A literature survey and a case study in fused filament fabrication

Additive manufacturing (AM, also commonly termed 3D printing) is progressing from being a rapid prototyping tool to serving as pillar of the Industry 4.0 revolution. Thanks to their low density and ease of printing, polymers are receiving increasing interest for the fabrication of structural and lightweight parts. Nonetheless, the lack of appropriate standards, specifically conceived to consistently verify the tensile properties of polymer parts and benchmark them against conventional products, is a major obstacle to the wider uptake of polymer AM in industry. After reviewing the standardisation needs in AM with a focus on mechanical testing, the paper closely examines the hurdles that are encountered when existing standards are applied to measure the tensile properties of polymer parts fabricated by fused filament fabrication (FFF, aka fused deposition modeling, FDM), which is presently the most popular material extrusion AM technique. Existing standards are unable to account for the numerous printing parameters that govern the mechanical response of FFF parts. Moreover, the literature suggests that the raster- and layer-induced anisotropic behaviour and the complicated interplay between structural features at different length scales (micro/meso/macro-structure) undermine pre-existing concepts regarding the specimen geometry and classical theories regarding the size effect, and ultimately jeopardise the transferability of conventional tensile test standards to FFF parts. Finally, the statistical analysis of the tensile properties of poly(lactic acid) (PLA) FFF specimens printed according to different standards (ASTM D638 type I and ASTM D3039) and in different sizes provides experimental evidence to confirm the literature-based argumentation. Ultimately, the literature survey, supported by the experimental results, demonstrates that, until dedicated standards become available, existing standards for tensile testing should be applied to FFF with prudence. Whilst not specified in conventional standards, set-up and printing parameters should be fully reported to ensure the repeatability of the results, rectangular geometries should be preferred to dumbbell-like ones in order to avoid premature failure at the fillets, and the size of the specimens should not be changed arbitrarily

Determination of Cu2+ in drinking water using a hydroxyjulolidine-dihydroperimidine colorimetric sensor

A new and highly efficient colorimetric Cu2+ chemosensor HL, synthesized by condensation between 8-hydroxyjulolidine-9-carboxaldehyde and 1,8-diaminonaphthalene, has been rationally designed and thoroughly studied. In a buffered aqueous methanol mixture, interactions between HL and Cu2+ produce an intense visible band at 421 nm, considerably red-shifted (~ 100 nm) from the peak maxima of HL (320 nm). Absorbance spectrophotometry experiments pointed to an exceptional 2.3 nM limit of detection (LoD) calculated from the ratiometric response upon Cu2+ binding. Furthermore, without the aid of instrumentation an impressive 0.5 µM LoD is possible by naked-eye observations, far below the 31.5 µM (2 mg/L) guidelines for drinking water established by the World Health Organization. Spectrophotometric pH titrations allowed the determination of the equilibrium constants and speciation plots for the formation of the various chemical species of HL in the absence and presence of Cu2+, with only mononuclear complexes being found. Additional studies highlighted the selectivity of HL to Cu2+ when in the presence of other metal ions, and a 1:1 (M:L) binding stoichiometry has also been confirmed with results from Cu2+ titrations, Job’s plot and ESI-HRMS in good agreement. The Cu2+ sensing mechanism was also found to be reversible by cycling with H2Na2EDTA

Ultrasensitive colorimetric and ratiometric detection of Cu2+ : acid-base properties, complexation, and binding studies

Herein, we report the synthesis and characterization of a chemosensor, 5-(diethylamino)-2-(2,3-dihydro-1H-perimidin-2-yl)phenol (HL), synthesized from a condensation between 4-(diethylamino)salicylaldehyde and 1,8-diaminonaphthalene. Upon investigation of the sensing properties of HL, it was found that this sensor may be employed for simple yet efficient detection of Cu2+ in aqueous methanol solutions. The selective and ratiometric response to Cu2+ yielded an outstandingly low limit of detection of 3.7 nM by spectrophotometry and is also useful as a naked-eye sensor from 2.5 μM. The system was studied by spectrophotometric pH titrations to determine Cu2+ binding constants and complex speciation. Binding of Cu2+ to HL occurs in 1:1 stoichiometry, in good agreement with high-resolution electrospray ionization mass spectrometry (ESI-HRMS) results, Cu2+ titrations, and Job’s plot experiments, while the coordination geometry was tentatively assigned as square pyramidal by spectroscopic studies

Anion tuning of Zn2+ architectures using a Tris-base salicylic ligand

In this study, a hydroxyl-rich Schiff base ligand, HL, and its resulting complexes with ZnCl, Zn(CHCOO) and Zn(ClO) were explored. Interestingly, depending on the zinc salt and/or the crystallisation method, four unique structures were obtained. A synthesis with ZnCl gave 1, a mononuclear structure ((HL)Zn), while with Zn(CHCOO), a trinuclear system [(HL)Zn(CHCOO)], 2, was found. Interestingly two multinuclear architectures were observed with Zn(ClO). Firstly, diethyl ether diffusion of a methanolic reaction mixture with minimal atmospheric air volume gave 3, a hexanuclear architecture of the type [(HL)(HL)Zn](ClO), while slow evaporation of a similar mixture gave 4, a nonanuclear architecture with the formula [(HL)Zn(CO)](ClO). Compound 4 unexpectedly fixed atmospheric CO as CO, incorporating it into the architecture. As expected, a diethyl ether diffusion with a larger volume of air (∼100 mL) of a similar methanolic reaction mixture gave a mixture of 3 and 4. In addition, bulk samples of all compounds were also investigated by PXRD, and results are in good agreement with the observed single crystal data. Furthermore, complexes 1-4 were characterised using FT-IR and simultaneous thermal analysis (STA), and additionally the photophysical properties of HL and complexes 1-4 have also been explored

3D spatially controlled chemical functionalization on alumina membranes

Among the myriad microfabrication approaches, Deep X-ray Lithography (DXRL) takes advantage of the high penetration depth of hard X-rays. For the first time, this feature has been exploited for the precise control of surface chemical functionalities on a thick porous ceramic material. As a proof of concept, porous alumina membranes with controlled thickness (50 µm) have been chosen to test the potential of DXRL. The Al2O3 membranes were decorated with fluoro- and amino-silanes. These functionalized ceramic membranes were exposed to hard X-rays in a synchrotron facility, which allowed for the selective decomposition of the chemical functionalities in controlled areas. The water contact angle of hydrophobic-functionalized samples was measured to confirm the decomposition of the fluoro-silane in the exposed area, and water diffusion through the 200 nm pores of the alumina membranes was observed to occur only in the exposed area. The patterned amino-functionalized Al2O3 samples were tested with an alcoholic solution containing Au cations, where it was found that gold nanoparticles only formed in the unexposed areas, whereas the amino functionality survived the radiation damage induced by the X-rays