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ispartof: pages:335-340 ispartof: Procedia CIRP vol:113 pages:335-340 ispartof: 21st CIRP CONFERENCE ON ELECTRO PHYSICAL AND CHEMICAL MACHINING, ISEM XXI location:Zurich, Switzerland date:14 Jun - 17 Jun 2022 status: Published online

Aerosol Jet® Printing (AJ®P) is a relatively novel additive manufacturing technique, of the type direct writing, principally applied for printed electronics. Particularly, AJ®P has the ability to print various functional inks (conductive, dielectrics, biological solutions) at micro-scale resolution and on free-from substrates. This work investigates AJ®P to fabricate conductive patterns on stereolithography (SLA) samples towards the development of an innovative bioelectrical device for in-vitro dual bioreactor sensing. Silver nanoparticle (AgNPs) and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) inks were both tested. Preliminary results show a low metal-polymer AgNPs-SLA interaction, revealing the presence of pores and cracks along with the printed pattern after thermal sintering, with no electrical resistance (R) detected. In contrast, the PEDOT:PSS ink reveals a good covering of the SLA samples, with R decreasing with the number of printed layers (from ~700 KΩ to ~60 Ω for 15 and 40 layers, respectively, on lines 1 cm long). However, using the PEDOT:PSS ink, the total printing time was ~45 minutes, hence not ideal for an industry-oriented vision. Therefore, a study on the optimization of the AgNPs-SLA sample interaction was carried out. SLA samples were coated with Parylene-C (ParC), and further treated with a low pressure plasma. The final results show excellent conductivity (R~2.40 Ω), with a printing time of ~5.5 minutes (7 layers), demonstrating the possibility to obtain a functional circuit. Eventually, the circuit was encapsulated with polydimethylsiloxane (PDMS) in order to avoid a release of Ag+ ions, potentially toxic in the medium culture. ispartof: pages:174-179 ispartof: Procedia CIRP vol:110 pages:174-179 ispartof: V Cirp Biomanufacturing location:Calabria, Italy date:22 Jun - 24 Jun 2022 status: Published online

ispartof: pages:180-185 ispartof: Procedia CIRP vol:110 pages:180-185 ispartof: CIRP Conference on Biomanufacturing location:Calabria date:22 Jun - 24 Jun 2022 status: Published online

This article analyzes temperature fields and their variations in fused filament fabrication (FFF) from the filament entering the hot-end to the printed parts, aiming at a deeper understanding of the thermal process of this additive manufacturing technology. A standard E3D print head assembly was mounted on a robot arm for printing. A stable filament feeding region was determined with an upper limit in the volume flow rate at different nozzle temperatures. Within the limit, the steady-state temperature fields inside the hot-end were studied by a computational fluid dynamics model. Simulations indicated that the temperature became less homogeneous at higher flow rates, leading to a lower extrudate temperature at the nozzle outlet. These outlet temperatures were analyzed, validated, and used as input to simulate temperature variations in printed parts with a self-developed open-access numerical model. An interlayer time similarity rule was found in printing single-walled geometries, which specifies temperature similarities at the same interlayer time. The findings provide new insights into FFF processes, pointing out opportunities for improved production efficiency and scalability to large-scale manufacturing. ispartof: 3D Printing And Additive Manufacturing vol:9 issue:2 pages:132-142 ispartof: location:United States status: published

Temperature fields and their variations in printed parts are the basis for understanding the physical process of fused filament fabrication (FFF). However, reliable temperature data are still rather limited to date. This article presents a three-dimensional transient-state model to simulate the temporal and spatial temperature variations in FFF printed parts. Model variables range from geometry dimensions and (dynamic) material properties to process parameters, covering all important physical phenomena, including conduction anisotropy and radiant heat transfer. The validation of the model is performed against six sets of experimental temperature data obtained with different geometries, machines, materials, processes, temperature measuring methods, etc. Insights in the thermal process are also reported. For example, the heat penetration depth in printing with poly(lactic acid) is limited to 3 mm, and the Biot number intimately characterises the reheating peaks in temporal profiles. This model shows the potential to become a standardised tool to study the thermal characteristics of FFF printed parts. It is made openly available on website https://iiw.kuleuven.be/onderzoek/aml/technologyoffer. Graphic abstract

ispartof: Jom vol:74 issue:3 pages:1-9 status: Published online

In neural tissue engineering (NTE), topographical, electrical, mechanical and/or biochemical stimulations are established methods to regulate neural cell activities in in vitro cultures. Aerosol Jet® Printing is here proposed as enabling technology to develop NTE integrated devices for electrically combined stimulations. The printability of a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT: PSS) commercial ink onto a reference substrate was firstly investigated and the effect of the process parameters on the quality of printed lines was analyzed. The study was then extended for printing thick electrodes and interconnects; the print strategy was finally transferred to a silicon-based wafer with patterned microchannels of proven cellular adhesion and topographical guidance. The results showed values of electrical resistance equal to ~16 Ω for printed electrodes which are ~33 μm thick and ~2 mm wide. The electrical impedance of the final circuit in saline solution was detected in the range of 1 - 2 kΩ at 1 kHz, which is in line with the expectations for bioelectronic neural interfaces. However, cells viability assays on the commercial PEDOT: PSS ink demonstrated a dose dependent cytotoxic behavior. The potential cause is associated with the presence of a cytotoxic co-solvent in the ink's formulation, which is released in the medium culture, even after a post-sintering process on the printed electrodes. This work is a first step to develop innovative in vitro NTE devices via a printed electronic approach. It also sheds new insights the transfer of AJ® print strategies across different substrates, and biocompatibility of commercial PEDOT: PSS inks. ispartof: International Journal of Bioprinting vol:8 issue:1 pages:50-65 ispartof: location:Singapore status: published

In this work, three promising Additive Manufacturing (AM)/3D-printing technologies, able to realize conductive elements, are adopted in the realization of antennas. The selected techniques are Fused Filament Fabrication (FFF), Aerosol Jet® Printing (AJ®P), and Laser-Induced Graphene (LIG), which have been compared by measuring the performance of an ultrahigh (UHF) radiofrequency identification (RFID) tag, specifically designed, and realized for the scope. Results have also been analyzed against to data obtained by a reference sample realized in Aluminum. The FFF tag has been manufactured by extruding the Electrifi conductive filament over an ABS printed substrate, used also for the AJ®P-made antenna. Conversely, the LIG tag has been produced by laser-burning a Kapton® polyimide sheet. All the tested technologies, each one with its pros and cons, allowed to realize working prototypes, even if, as expected, with performance lower than the comparison sample. An electroplating process has been also adopted to increase conductivity, with improvements in the FFF prototype. The obtained results are quite satisfactory. Those related to LIG technology do not yet guarantee performance comparable to the other techniques. Nevertheless, the prospect of creating “green” and cost-effective antennas pushes towards further studies, already underway, which include the study of antenna shapes more suitable for the specific technique as well as process optimizations to increase conductivity. ispartof: IEEE Journal of Radio Frequency Identification vol:6 status: Published online

ispartof: pages:99-104 ispartof: V CIRP CONFERENCE ON BIOMANUFACTURING vol:110 pages:99-104 ispartof: 5th CIRP Conference on BioManufacturing (BioM) location:ITALY, Calabria date:22 Jun - 24 Jun 2022 status: published

Ageing population and new diseases are requiring the development of novel therapeutical strategies. 3D bioprinting an novel application domain of additive manufacturing emerged as a potential transformative strategy for tissue engineering and regenerative medicine. This paper introduces the concept of 3D bioprinting, discussing in detail key requirements of bio-inks and main materials used to encapsulate cells. Recent advances related to the use of smart materials and the concept of 4D printing is also discussed. Main 3D bioprinting techniques are described in detail and key limitations highlighted. Successful cases, demonstrating the relevance of 3D bioprinting are also presented. Finally, the paper addresses the main research challenges and future perspectives in the field of 3D bioprinting. Published version

In neural tissue engineering (NTE), topographical, electrical, mechanical and/or biochemical stimulations are established methods to regulate neural cell activities in

Printed Electronics (PE) involves additive deposition of functional materials on a substrate via printing processes to realize electronic circuits, interconnects, electrical components or devices. This methodology is opposite to the conventional microelectronics industry which is based on subtractive manufacturing techniques (e.g. etching). Some of the advantages of PE over conventional electronics are low prototyping costs, short time to market, less processing steps, etc. One of the features is the ability to manufacture flexible and customized products and devices. The applications of Printed Electronics apply to different sectors of industry like electronics, packaging, bio-medical, automotive, communication, etc. In this work, we present Aerosol Jet® Printing (AJ®P) and Screen Printing as two techniques for the realization of flexible and mass customized PE devices. Whereas the use of AJ®P is focused on rapid prototyping, Screen Printing allows to upscale for mass production. The two technologies are here implemented to realise conductive antennas on paper substrates, potentially to integrate into a delivery parcel box for the development of “smart packaging”. This antenna design is based on the 13.56 MHz working frequency, which lies in the frequency spectrum of HF RFID/NFC applications. The print quality, electrical resistance and the basic functional characterization (working frequency) of these paper-based antennas are here investigated and reported. Acknowledgments The authors would like to express gratitude to the Agentschap ‘Innoveren & Ondernemen’. Apart from that, sincere thanks to all the partners of the project PAPERONICS especially Fetra vzw. This study is part of the CORNET project ‘PAPERONICS: Low cost multisensory paper & packaging applications’ (2019-2020). It is funded by Flanders Innovation & Entrepreneurship (VLAIO), Belgium (HBC.2018.0225) and AiF - German Federation of Industrial Research Associations, Germany. This work is also part of the TETRA 3D ElektroPrint -3D printen van vrije vorm elektrische/elektronische toepasssingen -HBC.2016.0067, also funded by VLAIO. Lastly, Jurre de Weerdt and Marc Scheirs are acknowledged for their expertise in 2.4 GHz antenna measurements.

In this study, an original and green procedure to produce water-based solutions containing nanometric recycled carbon particles is proposed. The nanometric particles are obtained starting from carbon waste ashes, produced by the wooden biomass pyro-gasification plant CMD (Costruzioni motori diesel) ECO20. The latter is an integrated system combining a downdraft gasifier, a spark-ignition internal combustion engine, an electric generator and syngas cleaning devices, and it can produce electric and thermal power up to 20 kWe and 40 kWth. The carbon-based ashes (CA) produced by the CMD ECO20 plant were, first, characterized by using differential scanning calorimetry (DSC) and microcomputed tomography (microCT). Afterward, they were reduced in powder by using a milling mortar and analyzed by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectrometry, thermogravimetric analysis (TGA), X-ray diffraction (WAXD) and Fourier-transform infrared (FTIR) spectroscopy. The optimization of an original procedure to reduce the dimensions of the ashes in an aqueous solution was then developed by using ball milling and sonication techniques, and the nanometric dimensions of the particles dispersed in water were estimated by dynamic light scattering (DLS) measurements in the order of 300 nm. Finally, possible industrial applications for the nanomaterials obtained from the waste ashes are suggested, including, for example, inks for Aerosol Jet® Printing (AJ® P). ispartof: Nanomaterials vol:11 issue:3 ispartof: location:Switzerland status: published

In this study, an Arduino®-based electrospinning device was developed with which the electrospun-fibre properties can be accurately controlled by varying the process parameters; voltage, flow rate and the needle-collector distance. The performance of the machine was evaluated by spinning a biocompatible material, thermoplastic poly-urethane (TPU). N,N-dimethylformamide (DMF) was chosen as the solvent for the TPU because of its suitable electrical conductivity and ideal viscosity for the electrospinning process. In addition, tetrahydrofuran (THF) was mixed in the solution in order to control the morphology of the spun fibres. The effect of the different parameters on the fibre morphology was studied by varying both the machine and material parameters. Solutions with different concentrations of TPU (8-15 wt.%) and ratio’s DMF/THF (50/50, 60/40, 80/20) were tested at different settings for the applied voltage (9-18 kV), needle-collector distance (12-19.5 cm) and flow rate (0.6-1 ml/h). The addition of THF drastically decreased the amount of beads present in the samples, suggesting that the solvent completely evaporated. Furthermore, the samples appeared to be stronger after the addition of THF. The smallest average diameter attained was around 900 nm, this was achieved using an 8 wt.% TPU solution, 50/50 DMF/THF ratio, a voltage of 15 kV, a needle-collector distance of 17 cm and a flow rate of 0.8 ml/h, which is comparable to results found in previous research. These results confirm the ability of this machine to achieve results comparable to that of laboratory commercial machines at a fraction of the price. ispartof: pages:97-102 ispartof: Procedia CIRP pages:97-102 ispartof: 20th CIRP Conference on Electro Physical and Chemical Machining location:Zurich, Switzerland date:19 Jan - 21 Jan 2021 status: Published online

In this study, carbon based ashes were produced by the wooden biomass pyro-gasification plant CMD ECO20. CMD ECO20 is a micro-scale combined heat and power system powered with biomass, under development by the Italian company Costruzioni Motori Diesel (C.M.D) S.p.A. It is an integrated system combining a downdraft gasifier, a spark ignition internal combustion engine, an electric generator and syngas cleaning devices, and it is able to produce electric and thermal power up to 20 kWe and 40 kWth. Three different types of fillers were produced from ashes starting from innovative green waste: the first type (MA) was obtained by mortar milling, while the second (DBA) and the third (WBA) one were produced by dry and wet ball milling, respectively. MA, DBA e WBA fillers were characterized by several techniques including Scanning Electron Microscopy (SEM), Multi-angle light scattering (MALS) and Energy Dispersive X-ray (EDX) Spectrometry. Each filler was added to epoxy resin EC01 in an amount equal to 1, 3, 5 and 10 wt%. The curing agent (22phr) was added to the resin that was cured for 1 h at 60 °C and 2 h at 150 °C. Finally, the flexural properties and the glass transition temperature of the cured neat epoxy and ashes filled epoxy composites were measured. The elastic modulus of the epoxy resin containing an amount of fillers from 1 to 10 wt% is higher in comparison to that of the neat epoxy. The flexural strength of the epoxy resin containing an amount of DBA of 3 wt% is also higher than that of the neat epoxy.

In this work, two promising Additive Manufacturing (AM)/3D-printing technologies, enable to realize conductive elements, are analysed, and compared with respect to the realisation of RFID applications. The selected techniques are the Fused Filament Fabrication (FFF) and Aerosol Jet® Printing (AJ® P), which have been compared, for the first time, by measuring the performance of an UHF RFID tag, specifically designed and realized for the scope. Results have also been analysed against to data obtained by a reference sample realized using the well-known technique of shaping an aluminium adhesive foil with a cutting plotter. While the resulting FFF-made tag can be read up to maximum 3 meters, the AJ® P one can be read up to 7 meters. Despite having major differences in terms of performance, this work demonstrates that both the technologies are capable to realize functional RFID prototypes.

In this paper we investigate the application of a direct writing technique for printing conductive patterns onto a biocompatible electrospun-pyrolysed carbon-fibre-based substrate. The result is a first study towards the production of bio-electrical scaffolds that could be used to enhance the promotion of efficient connections among neurons for in vitro studies in the field of neural tissue engineering. An electrospinning process is employed for production of the materials derived from the precursor polyacrylonitrile, in which the embedding of carbon nanotubes (CNTs) is also investigated. Subsequently, the methodology of research into suitable parameters for the printed electronics, using a commercial silver nanoparticle (Øavg,particle size ∼ 100 nm) ink, is described. The results show values of 2 Ω cm for the resistivity of the carbon-fibre materials and conductive printed lines of resistance ∼50 Ω on glass and less than ∼140 Ω on carbon-fibre samples. Biocompatibility results demonstrate the possibility of using electrospun-pyrolysed mats, also with embedded CNTs, as potential neural substrates for spatially localized electrical stimulation across a tissue. In addition, the data concerning the potential toxicity of silver suspensions are in accordance with the literature, showing a dose-dependent behaviour. This work is a pioneering feasibility study of the use of the flexible and versatile printed electronic approach, combined with engineered biocompatible substrates, to realize integrated bio-electrical scaffolds for in vitro neural tissue engineering applications. ispartof: BIOFABRICATION vol:12 issue:2 ispartof: location:England status: published

The aim of this work is the development and characterization of biodegradable thermoplastic recycled carbon ashes/maize starch (TPAS) composite films for agricultural applications. A proper plasticizer, that is, glycerol, was added to a commercial maize starch in an amount of 35 wt.%. Carbon-based ashes were produced by the biomass pyro-gasification plant CMD ECO 20, starting from lignocellulosic wastes. The ashes were added to glycerol and maize native starch at different amounts ranging from 7 wt. % to 21 wt.%. The composite was mixed at 130 &deg, C for 10 min and then molded. The effect of the different amounts of carbon based ashes on the thermal and physical-mechanical properties of the composite was assessed by using several techniques, such as rheology, wide- angle X-ray diffraction (WAXD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), moisture absorption, degradation and mechanical tests. The presence of the carbon waste ashes allows to improve thermal and durability performances of the thermoplastic starch (TPS) films. It reduces the water absorption of starch matrix and strongly decreases the deterioration of starch, independently from fillers amount, enhancing the lifetime of the TPS films in outdoor conditions. In addition, the waste carbon ashes/maize starch films present an advantage in comparison to those of neat starch, it can biodegrade, releasing the plant nutrients contained in the ashes into the soil. In conclusion, this approach for recycling carbon waste ashes increases the efficiency of industrial waste management, along with a reduction of its impact on the environment.

Heated build plates are common yet essential components in many additive manufacturing (AM) machines. However, their influence on the air temperature above and the subsequent impact on the AM process are barely discussed. This article proposes a simple model for the air temperature above the plate Ta(z), which exponentially decays from the plate temperature to the far environment temperature by a characteristic dimension lc in the range of 2–9 mm. The model has been empirically validated for three fused filament fabrication (FFF) machines, including open and closed systems, small and large build chambers. Temperature simulations in printed parts suggest that Ta(z) plays a critical role when printing at low layer thicknesses, such as 300 µm. Besides, adding an enclosure to FFF machines can significantly raise the far environment temperature inside the chamber, delaying the part cooling. However, its effect is noticeable for the portion above 10 mm only.

Intelligent packaging is an emerging technology, aiming to improve the standard communication function of packaging. Radio frequency identification (RFID) assisted smart packaging is of high interest, but the uptake is limited as the market needs cost-efficient and sustainable applications. The integration of screen printed antennas and RFID chips as smart labels in reusable cardboard packaging could offer a solution. Although paper is an interesting and recyclable material, printing on this substrate is challenging as the ink conductivity is highly influenced by the paper properties. In this study, the best paper/functional silver ink combinations were first selected out of 76 paper substrates based on the paper surface roughness, air permeance, sheet resistance and SEM characterization. Next, a flexible high frequency RFID chip (13.56 MHz) was connected on top of screen printed antennas with a conductive adhesive. Functional RFID labels were integrated in cardboard packaging and its potential application as reusable smart box for third party logistics was tested. In parallel, a web-based software application mimicking its functional abilities in the logistic cycle was developed. This multidisciplinary approach to developing an easy-scalable screen printed antenna and RFID-assisted smart packaging application is a good example for future implementation of hybrid electronics in sustainable smart packaging. ispartof: MATERIALS vol:14 issue:19 ispartof: location:Switzerland status: published

The development of commercial collagen inks for extrusion-based bioprinting has increased the amount of research on pure collagen bioprinting, i.e., collagen inks not mixed with gelatin, alginate, or other more common biomaterial inks. New printing techniques have also improved the resolution achievable with pure collagen bioprinting. However, the resultant collagen constructs still appear too weak to replicate dense collagenous tissues, such as the cornea. This work aims to demonstrate the first reported case of bioprinted recombinant collagen films with suitable optical and mechanical properties for corneal tissue engineering. The printing technology used, aerosol jet® printing (AJP), is a high-resolution printing method normally used to deposit conductive inks for electronic printing. In this work, AJP was employed to deposit recombinant human collagen type III (RHCIII) in overlapping continuous lines of 60 µm to form thin layers. Layers were repeated up to 764 times to result in a construct that was considered a few hundred microns thick when swollen. Samples were subsequently neutralised and crosslinked using EDC:NHS crosslinking. Nanoindentation and absorbance measurements were conducted, and the results show that the AJP-deposited RHCIII samples possess suitable mechanical and optical properties for corneal tissue engineering: an average effective elastic modulus of 506 ± 173 kPa and transparency ≥87% at all visible wavelengths. Circular dichroism showed that there was some loss of helicity of the collagen due to aerosolisation. SDS-PAGE and pepsin digestion were used to show that while some collagen is degraded due to aerosolisation, it remains an inaccessible substrate for pepsin cleavage. ispartof: Polymers vol:13 issue:17 ispartof: location:Switzerland status: Published online

The linear tool wear compensation method (LCM) is commonly applied in micro-EDM 3-D milling to compensate the tool length wear in order to achieve high machining accuracy. Traditional LCMs mainly rely on empirical models and off-line wear measurements, whereas the process dynamics are not taken into account. When machining complex 3D cavities, an increasing number of tool wear compensation cycles have usually to be performed in order to maintain the targeted machining accuracy. This negatively affects the duration of the overall machining cycle. To realize efficient precision micro-EDM cavity milling, without the necessity to predefine Z-axis tool feed in the NC trajectory before machining, an in-situ process control system is developed to adaptively control the tool wear compensation factor based on the discharge pulse behavior. Experiments have shown that the change of the compensation factor can be detected and also a continuous increase of the factor (over compensation) leads to the saturation of the mean effective pulse frequency. Pulse monitoring therefore provides valuable information for understanding the process dynamics and for selecting the machining parameters towards better machining efficiency. Furthermore, the information gathered in-situ can be utilized to predict the tool wear and perform in-situ tool wear prediction. To implement this on machine-level, a combined off-line and in-line adaptive control of the tool wear compensation factor is proposed and experimentally validated by milling different 3D cavities. The off-line adaptive control is only necessary when the predicted machining depth error exceeds a certain limit. In this way, more than 80% of the off-line adaptive control cycles can be eliminated, whereby a total save of cycle time up to 18% has been reached, while still maintaining the desired dimensional and form accuracy.

© 2019 CIRP Temperature management is crucial in Fused Filament Fabrication (FFF). This paper presents an infrared based set-up able to record spatial and temporal variations during printing of an FFF part, with a field of view of (21.7 × 14.9)mm 2 and at spatial resolution of 30.2 μm. The system is experimentally verified and the captured temperature profiles are compared to numerical data, obtained via an own-developed FFF numerical model. This work is a first step towards a combined experimental-numerical approach for in-process monitoring of FFF, with implications for filament developers, machine builders and (end-)users, ultimately demanding high quality (certified)parts. ispartof: CIRP ANNALS-MANUFACTURING TECHNOLOGY vol:68 issue:1 pages:213-216 status: published