Anne Hahn

Metal ion release kinetics from nanoparticle silicone composites.

Metal ion release kinetics from silver and copper nanoparticle silicone composites generated by laser ablation in liquids are investigated. The metal ion transport mechanism is studied by using different model equations and their fit to experimental data. Results indicate that during the first 30 days of immersion, Fickian diffusion is the dominant transport mechanism. After this time period, the oxidation and dissolution of nanoparticles from the bulk determine the ion release. This second mechanism is very slow since the dissolution of the nanoparticle is found to be anisotropic. Silver ion release profile is best described by pseudo-first order exponential equation. Copper ion release profile is best described by a second order exponential equation. For practical purposes, the in vitro release characteristics of the bioactive metal ions are evaluated as a function of nanoparticle loading density, the chemistry and the texture of the silicone. Based on the proposed two-step release model, a prediction of the release characteristics over a time course of 84 days is possible and a long-term ion release could be demonstrated.

Development of a specially tailored local drug delivery system for the prevention of fibrosis after insertion of cochlear implants into the inner ear

A cochlear implant (CI)-associated local drug delivery system based on dexamethasone (DMS) was developed with the purpose to inhibit the growth of fibrotic tissue which influences the signal transmission from the CI to the neurons of the inner ear. For the realization of a targeted DMS delivery the following concepts were combined: modification of the silicone-based electrode carrier by incorporation of DMS and a DMS-containing polymeric coating chemically attached on the surface of the electrode carrier. It was demonstrated that the coated CI showed a high coating stability in a simulated implantation procedure. The in vitro drug release studies in a quasi-stationary model revealed a faster DMS release in the initial phase originating from the DMS-containing coatings and then a lower and sustained DMS release originating from the DMS-loaded silicone carrier. The performed in vitro biocompatibility study confirmed that the released DMS was non-toxic for cultured spiral ganglion cells.

Electrochemistry-controlled metal ion release from silicone elastomer nanocomposites through combination of different metal nanoparticles

Electrochemistry-controlled metal ion release is achieved using nanoparticle mixtures embedded into a silicone matrix. Synergistic metal ion release from silicone matrix filled with silver and copper nanoparticles as well as silver and gold nanoparticles embedded into silicone is investigated in terms of qualitative and quantitative influences. Results are compared to nanoparticle composites with only one metal. The mechanism enhancing the release of the less noble metal nanoparticle is based on the ion-mediated electrochemistry rather than on contact corrosion of both elements. A retardation as well as an enhancement of metal ion release is observed allowing a time- and rate-controlled design of bioactive nanocomposites.

Nanoparticles as potential risk during femtosecond laser ablation

During femtosecond (fs) laser ablation, fumes with remarkably low emission mass rates compared to conventional laser processes are generated. In this case the size of particles released in the workplace is relatively small, in the range of 10 nm–1 μm. The high amount of inhalable particles generated during femtosecond laser ablation has to be considered as a potential health risk, demanding quantification. In order to provide safety-related statements on nonbeam hazards during laser materials processing, the particle size distribution during femtosecond laser ablation is studied. Possible effects on this distribution like the laser parameters, materials, and the process atmosphere are examined. The mass flow rate and aerodynamic particle size distribution during femtosecond laser ablation were studied for metals (Ti, Co, Ag, Au, Mg), ceramic (ZrO2), and organic (polycarbonate, paper, graphite) materials. In addition, the influence of laser and process parameters (fluence, pulse overlap, gas atmosphere) on...

Adding functionality to metal nanoparticles during femtosecond laser ablation in liquids

This study presents an approach to the in-situ functionalization of metal nanoparticles, established by laser ablation in solution. Additives as polyvinylpyrrolidone (PVP), thiols or alkoxysilanes, that undergo physisorption with the surface of the nanoparticles, can be added to the solution and used as functionalization agents. The concentration of the additive influences the particle size distribution, which leads to plasmon resonance shifts, measurable by UV/VIS spectroscopy. As an example, the size dispersion and stability of generated gold nanoparticles can be controlled by varying the concentration of dodecanthiol as an additive during laser ablation of gold in n-hexane. Moreover, silica shells can be generated to protect metal nanoparticles (gold and copper) against oxidation by in-situ coating and subsequent silica shell formation.In-situ functionalizations of nanoparticles during laser ablation in liquids present a promising approach to the development of nanomaterials for biomedical applications.This study presents an approach to the in-situ functionalization of metal nanoparticles, established by laser ablation in solution. Additives as polyvinylpyrrolidone (PVP), thiols or alkoxysilanes, that undergo physisorption with the surface of the nanoparticles, can be added to the solution and used as functionalization agents. The concentration of the additive influences the particle size distribution, which leads to plasmon resonance shifts, measurable by UV/VIS spectroscopy. As an example, the size dispersion and stability of generated gold nanoparticles can be controlled by varying the concentration of dodecanthiol as an additive during laser ablation of gold in n-hexane. Moreover, silica shells can be generated to protect metal nanoparticles (gold and copper) against oxidation by in-situ coating and subsequent silica shell formation.In-situ functionalizations of nanoparticles during laser ablation in liquids present a promising approach to the development of nanomaterials for biomedical applications.

Health risks of nanoparticulate emissions during femtosecond and picosecond pulsed laser machining

Nanoparticles are known to cause adverse health effects. But the generation of nanoparticles cannot be avoided during laser machining, especially ultrashort-pulsed laser ablation which releases a high share of nanoparticles. The nanoparticulate size fractions emitted during picosecond (ps) laser ablation are compared with those released during femtosecond (fs) laser ablation using steel, zirconia and brass. At the same pulse energy, fs pulses release similar share of nanoparticles (>80%) in the aerosol fraction, with fs compared to ps generating a far higher share of ultrasmall (7 nm) sized particles during machining of metals and ceramics. The frequency maximum corresponds to the particle size of 50 nm independently of the ablated material and applied pulse duration. During ps laser ablation the absolute nanoparticle emission rate is higher than during fs laser ablation, whereas the emission rate per pulse is two magnitudes lower. Finally, the nanoparticle emission rates and its nanoparticle surface equivalent for ps and fs laser micromachining of metal and ceramic are compared with inflammatory thresholds derived from toxicology studies. It would take more than 6.500 working days to exceed this theoretical threshold of inflammation during laser operation at 0.5-2W and at least 260 working days using high-power lasers.

Picosecond and Femtosecond Laser Machining May Cause Health Risks Related to Nanoparticle Emission

It is well known that nanoparticles are generated as by-products during ultrashort-pulsed laser ablation. Airborne nanoparticulate matter is well known as potential health risk for exposed workers. In order to provide safety-related statements on nanoparticles generated during laser micromachining, we studied the particle size distribution during laser ablation. Results on particle size distributions using femtosecond (fs) laser pulses have already been presented at last ILSC. In this study we present a comparison and risk assessment of picosecond (ps) versus fs generated airborne nanoparticles. At the same pulse energy, fs pulses release similar share of nanoparticles (>80%) in the aerosol fraction, while fs compared to ps pulses generate a far higher portion 7 nm sized particles during machining of metals (steel, brass) and ceramics (zirconia). These nanoparticles sampled at the workplace have the same chemical composition than the ablated material (iron-chromium-nickel alloy, yttria-doped zirconia). A quantitative risk assessment is carried out and compared with indicators of toxi-cological effects of inhaled nanoparticles. The surface equivalent of nanoparticles dispersed in the air of the workplace is not likely to exceed the surface dose which cause inflammatory response in animal lung. But within one 8 h shift an efficient fume extraction is strongly recommended for safe operation during fs and ps laser micromachining even in research laboratories.It is well known that nanoparticles are generated as by-products during ultrashort-pulsed laser ablation. Airborne nanoparticulate matter is well known as potential health risk for exposed workers. In order to provide safety-related statements on nanoparticles generated during laser micromachining, we studied the particle size distribution during laser ablation. Results on particle size distributions using femtosecond (fs) laser pulses have already been presented at last ILSC. In this study we present a comparison and risk assessment of picosecond (ps) versus fs generated airborne nanoparticles. At the same pulse energy, fs pulses release similar share of nanoparticles (>80%) in the aerosol fraction, while fs compared to ps pulses generate a far higher portion 7 nm sized particles during machining of metals (steel, brass) and ceramics (zirconia). These nanoparticles sampled at the workplace have the same chemical composition than the ablated material (iron-chromium-nickel alloy, yttria-doped zirconia). A ...

Nanoparticles - Potential risk during pulsed laser ablation

Nanoparticles are generated as by-products during laser ablation with an amount of 50 – 90% of the overall particulate emissions. The quantity and size of particulate emission depends strongly on the laser type, feed rate and process gas. Laser ablation using ultrashort laser pulses leads to the highest relative release of nanoparticles. In order to provide safety-related statements on nanoparticles generated during laser materials processing, the particle size distribution during laser ablation of ten materials (metal, ceramic, polymer) is studied. The number frequency of nanoparticles may increase up to over 99% if nitrogen is used as process gas. Based on data of the concentration and particle size distribution, a risk assessment is carried out. The number concentration and the particle surface area of nanoparticles in the workplace area are compared with indicators of toxicological effects available in the literature. The number concentration after an 8 hour shift is up to 100 times higher than the background condition. Although the assessment shows that the nanoparticle concentrations are negligible compared to toxicological thresholds, sufficient capturement during laser ablation processes is strongly recommended.Nanoparticles are generated as by-products during laser ablation with an amount of 50 – 90% of the overall particulate emissions. The quantity and size of particulate emission depends strongly on the laser type, feed rate and process gas. Laser ablation using ultrashort laser pulses leads to the highest relative release of nanoparticles. In order to provide safety-related statements on nanoparticles generated during laser materials processing, the particle size distribution during laser ablation of ten materials (metal, ceramic, polymer) is studied. The number frequency of nanoparticles may increase up to over 99% if nitrogen is used as process gas. Based on data of the concentration and particle size distribution, a risk assessment is carried out. The number concentration and the particle surface area of nanoparticles in the workplace area are compared with indicators of toxicological effects available in the literature. The number concentration after an 8 hour shift is up to 100 times higher than the ba...

A polymer based local drug delivery system on plasma activated silicon implant surfaces

Medical implants which include a local drug delivery system are a growing area in implant development. For many implant applications silicone is used as material because of its chemical inertness and good biological performance. However the choice of silicone as material brings up some challenges when a local drug delivery system should be applied. To enhance adhesion of a drug containing polymeric coating silicone was activated by aid of plasma chemistry. This treatment leads to reactive groups which can be used for further modification. After an additional treatment with 3-Aminopropyl-triethoxysilane (APTS) polymers activated by 1-[3-Dimethylamino)propyl]-3-ethylcarbo-diimide hydrochloride (EDC) were coupled to the surface to give a polymeric monolayer. Afterwards a polymer coating with Dexamethasone incorporation was applied to the silicone by a spray coating technique. Coatings on the basis of PLLA and P(4HB) show an increased mechanical stability. Investigations on the release of Dexamethasone from these coatings show as well that the conducted work is a good basis for further developments.

Non-beam hazards during laser machine

Laser material processing is gaining increasing importance in micro and macro machining. During laser processing of polymers and metals dangerous air pollutants have to be considered with regard to occupational safety. Moreover, technical measures for the handling of Laser Generated Air Contaminants (LGACs) often contribute to more than 10 % of the operating costs of laser machinery. Therefore, data are required for an adequate design and scaling of emission capturing systems. An overview on the characterization, handling, and filtration of non-beam hazards during laser processing as well as a consideration of economic aspects is given. Based on these data we introduce the Laser Micropyrolysis-GC/MS as a novel method for emission prognosis. Finally, technical precaution measures for a variety of laser machining processes are evaluated.Laser material processing is gaining increasing importance in micro and macro machining. During laser processing of polymers and metals dangerous air pollutants have to be considered with regard to occupational safety. Moreover, technical measures for the handling of Laser Generated Air Contaminants (LGACs) often contribute to more than 10 % of the operating costs of laser machinery. Therefore, data are required for an adequate design and scaling of emission capturing systems. An overview on the characterization, handling, and filtration of non-beam hazards during laser processing as well as a consideration of economic aspects is given. Based on these data we introduce the Laser Micropyrolysis-GC/MS as a novel method for emission prognosis. Finally, technical precaution measures for a variety of laser machining processes are evaluated.