Use of irradiated PET plastic waste for partially replacing cement in concrete?

Portland cement used in the manufacture of concrete is responsible for an estimated 5-8% of the global CO2 emissions. Recently published work (Schaefer et al., 2018) claims that γ-irradiated PET waste powder can be used as a partial replacement of cement in concrete for reducing its CO2 footprint. More specifically, exposure of PET to γ-irradiation at a dosage of 100 kGy alters its crystal structure and chemical composition, which in turn leads to a smaller reduction in concrete strength compared to non-irradiated PET waste. Hence, making it possible for irradiated PET waste to be used as a raw ingredient in the manufacture of concrete while at the same time diverting significant quantities of PET waste from landfills. The aim of this research was to independently assess and verify the above claims. For this purpose, the effect of different low irradiation dosages (0, 10 and 100 kGy) and different replacement levels (2.5 %, 5 % and 10 % by volume) of cement by PET waste on the consistency and mechanical strength of pastes and mortars was determined in a laboratory investigation. XRD, TGA and DSC were also used to study the effect of irradiation on the microstructure of raw PET waste and the microstructure of paste and mortar samples containing irradiated PET waste powder. Our results indicate that use of γ-irradiated PET waste (exposed to an irradiation dosage of up to 100 kGy) for partially replacing cement does not lead to a significant recovery of mechanical strength lost when non-irradiated PET waste is used.

Porous silicon-cyclodextrin based polymer composites for drug delivery applications.

One of the main applications of porous silicon (PSi) in biomedicine is drug release, either as a single material or as a part of a composite. PSi composites are attractive candidates for drug delivery systems because they can display new chemical and physical characteristics, which are not exhibited by the individual constituents alone. Since cyclodextrin-based polymers have been proven efficient materials for drug delivery, in this work ß-cyclodextrin-citric acid in-situ polymerization was used to functionalize two kinds of PSi (nanoporous and macroporous). The synthesized composites were characterized by microscopy techniques (SEM and AFM), physicochemical methods (ATR-FTIR, XPS, water contact angle, TGA and TBO titration) and a preliminary biological assay was performed. Both systems were tested as drug delivery platforms with two different model drugs, namely, ciprofloxacin (an antibiotic) and prednisolone (an anti-inflammatory), in two different media: pure water and PBS solution. Results show that both kinds of PSi/ß-cyclodextrin-citric acid polymer composites, nano- and macro-, provide enhanced release control for drug delivery applications than non-functionalized PSi samples.

Poly(N-isopropylacrylamide) grafted on plasma-activated poly(ethylene oxide): thermal response and interaction with proteins.

Thermoresponsive polymer layers offer the possibility of preparing smart surfaces with properties that are switchable through a phase transition, usually close to the lower critical solution temperature of the polymer. In particular, poly( N-isopropylacrylamide) (pNIPAM) has gained a great deal of attention because it has such a phase transition in a physiologically interesting temperature range. We have prepared ultrathin thermoresponsive coatings by grafting pNIPAM on a plasma-CVD-deposited, poly(ethylene oxide)-like polymer substrate that was activated in an Ar plasma discharge to initiate the grafting. The presence and integrity of pNIPAM was verified by XPS and ToF-SIMS, and a dramatic change in the wettability during the phase transition was identified by temperature-dependent contact angle measurements. The transition from the hydrated to the collapsed conformation was analyzed by temperature-dependent QCM measurements and by AFM. An unusual, reversible behavior of the viscoelastic properties was seen directly at the phase transition from the swollen to the collapsed state. The phase transition leads to a switching from protein repulsion to a state that allows the adsorption of proteins.

Use of nanopatterned surfaces to enhance immunoreaction efficiency.

In this work, we compare the immunoreaction efficiency between uniformly functionalized surface and chemically nanopatterned surfaces when applied as platforms for antigen/antibody interactions with and without the use of protein A as orienting protein. On the nanopatterned platform, the immunoreaction efficiency is higher than all the other cases with no protein A pretreatment of the surface, providing evidence of the capability of the adhesive/antiadhesive nanopatterned surface to immobilize the molecules in a reactive state, increasing their possibility to form complexes.

Fabrication and characterization of plasma processed surfaces with tuned wettability.

Engineered surfaces with controlled hydrophilic/ hydrophobic character have been fabricated by tailoring the substrate topography and chemistry. In this method, the substrate to be treated was first coated by a photoresist, which was then surface-roughened using SF6 plasma etching. The resulting rough texture was then transferred to the underlying silicon surface by over-etching of the photoresist. At this point, the topographically modified surface was modified chemically by controlled deposition of a thin polymer layer using plasma processing. In this way, both the surface texture and the surface chemistry could be varied independently, producing surfaces with variable wetting character, including super-hydrophilicity and super-hydrophobicity, depending on the choice of plasma polymer deposited. Chemical characterization demonstrates a correlation between the surface chemistry and the wettability of the samples after etching. The surface elementary composition contained more C-F groups as the measured contact angle increased, indicating that the change of wettability is due to both the roughness and the surface energy of the deposited photoresist. In the case of materials deposited on the plasma-treated rough surfaces, the strengthening of the wetting character is only due to the created surface roughness, as XPS analyses showed no significant chemical difference as compared to the flat polymer.

Micro-spot, UV and wetting patterning pathways for applications of biofunctional aminosilane-titanate coatings.

The micropatterning of functional films for biomedical applications is a key part of the process leading to a precise application. In the present work we present three different methodologies to micro-design biofunctional aminosilane-titanate coatings. The chemical functionality of the surface immobilized amino groups was initially tested by surface characterization techniques. X-ray photoelectron spectroscopy was used to analyze the films before and after derivatization with Trifluoromethylbenzaldehyde while atomic force microscopy was used to study the adsorption kinetics onto these hybrid films. The three micropatterning pathways were selected for three different kinds of applications: (1) 300 microm spots were satisfactorily used for oligonucleotide immobilization, (2) Masked regions protected from UV irradiation were intensively coated by colloidal gold nanoparticles creating a drastic contrast with respect to the UV exposed areas, and (3) radial micro stripes, used afterwards for culturing cells, were created onto Si substrates by wetting from modified precursor solutions. The results are a clear indication of the versatility of hybrid aminosilane-titanate coatings for biomedical applications requiring micropatterned biofunctional surfaces.

Cleaning and hydrophilization of atomic force microscopy silicon probes.

The silicon surface of commercial atomic force microscopy (AFM) probes loses its hydrophilicity by adsorption of airborne and package-released hydrophobic organic contaminants. Cleaning of the probes by acid piranha solution or discharge plasma removes the contaminants and renders very hydrophilic probe surfaces. Time-of-flight secondary-ion mass spectroscopy and X-ray photoelectron spectroscopy investigations showed that the native silicon oxide films on the AFM probe surfaces are completely covered by organic contaminants for the as-received AFM probes, while the cleaning methods effectively remove much of the hydrocarbons and silicon oils to reveal the underlying oxidized silicon of the probes. Cleaning procedures drastically affect the results of adhesive force measurements in water and air. Thus, cleaning of silicon surfaces of the AFM probe and sample cancelled the adhesive force in deionized water. The significant adhesive force values observed before cleaning can be attributed to formation of a bridge of hydrophobic material at the AFM tip-sample contact in water. On the other hand, cleaning of the AFM tip and sample surfaces results in a significant increase of the adhesive force in air. The presence of water soluble contaminants at the tip-sample contact lowers the capillary pressure in the water bridge formed by capillary condensation at the AFM tip-sample contact, and this consequently lowers the adhesive force.

Tailoring surface properties of biomedical polymers by implantation of Ar and He ions.

Ion implantation at 25 and 100 keV has been used as a tool for the modification of the surface properties of two biomedical polymers. The modulation induced by the different energy dispersion mechanisms of Ar and He have allowed satisfactory modifications for both the activation of the surfaces of chemically functional polycaprolactone (PCL) and the stabilization of anti-fouling poly(ethylene glycol) (PEG). In both cases the implantations have been performed at doses of 10(14) cm(-2) by taking into account the effect of different current densities, which are shown to distinctly influence the fragmentation-crosslinking of the target polymers. The resultant films were characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, time of flight secondary ion mass spectroscopy and atomic force microscopy. Both shifts in zeta potential versus pH curves and the alteration of the polar components of the surface free energy (contact angle measurements) were correlated with the composition analysis. The response of the modified surfaces towards biomolecular interaction is demonstrated by the induction of preferential adsorption on irradiated PCL and the inhibited adsorption onto implanted PEG regions for selected oligopeptides and proteins.

Electrochemical release testing of nickel-titanium orthodontic wires in artificial saliva using thin layer activation.

Alloys based on Ni-Ti intermetallics generally exhibit special shape memory and pseudoelastic properties, which make them desirable for use in the dental field as orthodontic wires. The possibility of nickel release from these materials is of high concern, because the allergenicity of this element. The aim of this study was to test pseudoelastic Ni-Ti wires in simulated physiological conditions, investigating the combined effect of strain and fluoridated media: the wires were examined both under strained (5% tensile strain) and unstrained conditions, in fluoridated artificial saliva at 37 degrees C. Real time electrochemical nickel release testing was performed using a novel application of a radiotracer based method, thin layer activation (TLA). TLA was validated, in unstrained conditions, against adsorptive stripping voltammetry methodology. Control tests were also performed in non-fluoridated artificial saliva. From our research it transpired that the corrosion behaviour of Ni-Ti alloy is highly affected by the fluoride content, showing a release of 4.79+/-0.10 microg/cm2/day, but, differently from other biomaterials, it does not seem to be affected by elastic tensile strain. The application of the TLA method in the biomedical field appears a suitable technique to monitor in real time the corrosion behaviour of biomedical devices.

Surface analysis of plasma-patterned biofunctional hybrid titanate-aminosilane xerogel films.

The functionalization and patterning of biomedical materials with enhanced surface activity is a main objective for the development of high-specificity biosensors. The surfaces of sol-gel condensed aminopropyltriethoxysilane-tetraisopropyl orthotitanate hybrid materials have been studied in order to describe the mechanisms that allow the fixation of amino groups. X-ray photoelectron spectra obtained from these surfaces are compared with those coming from the surfaces of plasma-etched coatings. The results show that aminopropyl radicals remain on the surface after room-temperature condensation and that they are drastically removed after partial etching of the coating in an Ar plasma. This confirms that the functionalization is effectively a surface feature and suggests that amino groups may remain at the surface covalently bonded to the original amorphous Si-O- structure. Further evidence of the surface functionalization efficiency is illustrated with contact angle and zeta-potential measurements. It is complementarily proved by confocal microscopy that masked regions conserve their molecular activity and are not affected by the etching process. These facts suggest that these materials could play an active role when incorporated into biosensor devices.

Combination of ion beam stabilisation, plasma etching and plasma deposition for the development of tissue engineering micropatterned supports.

The performance of biomedical assays at both molecular and cellular level depends greatly on the ability to design new polymer surfaces. Patterns can be created by using materials with contrasted surface properties. In this work we describe in detail the preparation of micropatterned surfaces to be used as tissue engineering supports. Poly(ethylene glycol) (PEG) was used as the 'anti-fouling' polymer in opposition to functional regions covered by acrylic acid (AAc). Since spin-casted PEG films are unstable, ion beam stabilization (IBS) treatment was applied in order to render it insoluble. On the other hand, AAc films were deposited by low-power plasma chemical vapour deposition. Chemical properties of both polymers were monitored by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy while topographic features were followed by atomic force microscopy. Finally, a micropattern was produced by using a mask, which isolated the IBS-PEG from the AAc-deposited regions. Endothelial cells cultured on the surface were observed to follow the micropatterns. In fact, for a certain surface density it was observed that the cells present tensile or compressive stresses when forced to remain in the anti-fouling or the functionalised regions, respectively.