Fused Filament Fabrication and Computer Numerical Control Milling in Cultural Heritage Conservation.

This paper reports a comparison between the advantages and disadvantages of fused filament fabrication (FFF) and computer numerical control (CNC) milling, when applied to a specific case of conservation of cultural heritage: the reproduction of four missing columns of a 17th-century tabernacle. To make the replica prototypes, European pine wood (the original material) was used for CNC milling, while polyethylene terephthalate glycol (PETG) was used for FFF printing. Neat materials were chemically and structurally characterized (FTIR, XRD, DSC, contact angle measurement, colorimetry, and bending tests) before and after artificial aging, in order to study their durability. The comparison showed that although both materials are subject to a decrease in crystallinity (an increase in amorphous bands in XRD diffractograms) and mechanical performance with aging, these characteristics are less evident in PETG (E = 1.13 ± 0.01 GPa and σ = 60.20 ± 2.11 MPa after aging), which retains water repellent (ca = 95.96 ± 5.56°) and colorimetric (∆E = 2.6) properties. Furthermore, the increase in flexural strain (%) in pine wood, from 3.71 ± 0.03% to 4.11 ± 0.02%, makes it not suitable for purpose. Both techniques were then used to produce the same column, showing that for this specific application CNC milling is quicker than FFF, but, at the same time, it is also much more expensive and produces a huge amount of waste material compared to FFF printing. Based on these results, it was assessed that FFF is more suitable for the replication of the specific column. For this reason, only the 3D-printed PETG column was used for the subsequent conservative restoration.

From Virtual Reconstruction to Additive Manufacturing: Application of Advanced Technologies for the Integration of a 17th-Century Wooden Ciborium.

3D modelling and 3D printing techniques have become increasingly popular in different fields, including cultural heritage. In this field, there are still many challenges to overcome, such as the difficulty of faithfully reproducing complex geometries or finding materials suitable for restoration, due to the limited scientific studies. This work proposes an example of the application of advanced technologies for the reproduction of four missing columns of a 17th century polychrome wooden ciborium. The difficulties of an automatic scan due to its reflective surface (water gilding and estofado decorations) were overcome by creating a 2D manual survey and a subsequent manual 3D redrawing. The CAD model was used to print the missing elements with fused filament fabrication (FFF) in polyethylene terephthalate glycol (PETG), using the following printing parameters: nozzle 0.4 mm, infill 20%, extrusion temperature of PLA 200 °C and of PETG 220 °C, plate temperature 50 °C, printing speed 60 mm/s, layer height 0.2 mm. The conservation and restoration of the ciborium is nearing completion. This study highlights the importance of collaboration between different professionals for the correct design of a restoration, as well as the need to promote scientific research into the development of new high-performance 3D printing materials suitable for conservation.

The Role of 3D Printing in the Development of a Catalytic System for the Heterogeneous Fenton Process.

Recycling of catalysts is often performed. Additive manufacturing (AM) received increasing attention in recent years in various fields such as engineering and medicine, among others. More recently, the fabrication of three-dimensional objects used as scaffolds in heterogeneous catalysis has shown innumerable advantages, such as easier handling and waste reduction, both leading to a reduction in times and costs. In this work, the fabrication and use of 3D-printed recyclable polylactic acid (PLA) scaffolds coated with an iron oxide active catalyst for Fenton reactions applied to aromatic model molecules, is presented. These molecules are representative of a wider class of intractable organic compounds, often present in industrial wastewater. The 3D-printed PLA-coated scaffolds were also tested using an industrial wastewater, determining the chemical oxygen demand (COD). The catalyst is characterized using electron microscopy coupled to elemental analysis (SEM/EDX) and thermogravimetry, demonstrating that coating leach is very limited, and it can be easily recovered and reused many times.

Age-Related Properties of Aquaponics-Derived Tilapia Skin (Oreochromis niloticus): A Structural and Compositional Study.

In the last two decades, fisheries and fish industries by-products have started to be recovered for the extraction of type I collagen because of issues related to the extraction of traditional mammalian tissues. In this work, special attention has been paid to by-products from fish bred in aquaponic plants. The valorization of aquaponic fish wastes as sources of biopolymers would make the derived materials eco-friendlier and attractive in terms of profitability and cost effectiveness. Among fish species, Nile Tilapia is the second-most farmed species in the world and its skin is commonly chosen as a collagen extraction source. However, to the best of our knowledge, no studies have been carried out to investigate, in depth, the age-related differences in fish skin with the final aim of selecting the most advantageous fish size for collagen extraction. In this work, the impact of age on the structural and compositional properties of Tilapia skin was evaluated with the aim of selecting the condition that best lends itself to the extraction of type I collagen for biomedical applications, based on the known fact that the properties of the original tissue have a significant impact on those of the final product. Performed analysis showed statistically significant age-related differences. In particular, an increase in skin thickness (+110 µm) and of wavy-like collagen fiber bundle diameter (+3 µm) besides their organization variation was observed with age. Additionally, a preferred collagen molecule orientation along two specific directions was revealed, with a higher fiber orientation degree according to age. Thermal analysis registered a shift of the endothermic peak (+1.7 °C) and an increase in the enthalpy (+3.3 J/g), while mechanical properties were found to be anisotropic, with an age-dependent brittle behavior. Water (+13%) and ash (+0.6%) contents were found to be directly proportional with age, as opposed to protein (-8%) and lipid (-10%) contents. The amino acid composition revealed a decrease in the valine, leucine, isoleucine, and threonine content and an increase in proline and hydroxyproline. Lastly, fatty acids C14:0, C15:0, C16:1, C18:2n6c, C18:3n6, C18:0, C20:3n3, and C23:0 were revealed to be upregulated, while C18:1n9c was downregulated with age.

Does Size Matter? The Case of Piezoresistive Properties of Carbon Nanotubes/Elastomer Nanocomposite Synthesized through Mechanochemistry.

The growing interest in piezoresistive sensors has favored the development of numerous approaches and materials for their fabrication. Within this framework, carbon nanotubes (CNTs) are often employed. However, CNTs are a heterogeneous material with different morphological characteristics in terms of length and diameter, and, so far, experimental studies have not usually considered the effect of these parameters on the final sensor performances. Here, we observe how, by simply changing the CNTs length in a solvent-free mechanochemistry fabrication method, different porous 3D elastomeric nanocomposites with different electrical and mechanical properties can be obtained. In particular, the use of longer carbon nanotubes allows the synthesis of porous nanocomposites with better mechanical stability and conductivity, and with a nine-times-lower limit of detection (namely 0.2 Pa) when used as a piezoresistive sensor. Moreover, the material prepared with longer carbon nanotubes evidenced a faster recovery of its shape and electrical properties during press/release cycles, thus allowing faster response at different pressures. These results provide evidence as to how CNTs length can be a key aspect in obtaining piezoresistive sensors with better properties.

Sustainable Polymer Composites Manufacturing through 3D Printing Technologies by Using Recycled Polymer and Filler.

In the last years, the excessive use of plastic and other synthetic materials, that are generally difficult to dispose of, has caused growing ecological worries. These are contributing to redirecting the world's attention to sustainable materials and a circular economy (CE) approach using recycling routes. In this work, bio-filaments for the Fused Filament Fabrication (FFF) 3D printing technique were produced from recycled polylactic acid (PLA) and artisanal ceramic waste by an extrusion process and fully characterized from a physical, thermal, and mechanical point of view. The data showed different morphological, thermal, rheological, and mechanical properties of the two produced filaments. Furthermore, the 3D objects produced from the 100% recycled PLA filament showed lower mechanical performance. However, the results have demonstrated that all the produced filaments can be used in a low-cost FFF commercial printer that has been modified with simple hand-made operations in order to produce 3D-printed models. The main objective of this work is to propose an example of easy and low-cost application of 3D printing that involves operations such as the reprocessing and the recyclability of materials, that are also not perfectly mechanically performing but can still provide environmental and economic benefits.

Nanoarchitectonics of highly sensitive and with large working range 3D piezoresistive microporous foam based on carbon nanotubes and elastomer.

HYPOTHESIS: Nanocarbon/polymeric 3D porous composites have been widely developed as piezoresistive sensors due to their improved performances. Functionalized nanocarbon is usually used to allow its adsorption on the surface of porous polymeric material. However, both the functionalization and the surface localized distribution of the nanomaterial can limit the nanocarbon effect on conductivity and mechanical stability of the material thus affecting piezoresistive performances. EXPERIMENTS: A novel nanoarchitectonics strategy to prepare an elastomeric/carbon nanotubes (CNTs) 3D porous piezoresistive nanocomposite is developed. The fabrication route does not require complex apparatus and CNTs chemical functionalization. Moreover, foams of any shape and dimensions can be produced with neither complex machinery and procedures nor wastes production. FINDINGS: The obtained material is characterized by the presence of well dispersed pristine CNTs on both surface and bulk of the polymeric matrix. The foam exhibited improved piezoresistive properties with excellent compressive stress (>150 kPa), sensitivity at low displacement (29 kPa-1) and limit of detection for both pressure (2 Pa) and extension (130 nm). These excellent features could allow the use of the as prepared nanocomposite in different applications ranging from wearable devices to robotic or infrastructure monitoring with outstanding flexibility.

3D Printing of Polymer Waste for Improving People's Awareness about Marine Litter.

This work is aimed at proposing demonstrative actions devoted to show reprocessing and recyclability of PET originating from bottles collected from the seaside, in order to increase the consumer awareness on the importance of recycling plastics. To this purpose, collected bottles were washed, cut, grinded, extruded in the form of a thin wire adopting different cooling rates, which leads to a modulation of the crystallinity content. Once having optimized the processing parameters, the extruded wire was used to produce 3D printed samples through the fused deposition modelling (FDM). The changes in the crystalline structure due to the different processing conditions were assessed by DSC and XRD analyses, while rheological tests were performed in order to evaluate any modification in the viscosity of PET after repeated processing cycles. The reduction in thermal stability was confirmed by TGA analysis, which showed a progressive decrease in the degradation temperature as processing cycles increased. Finally, tensile tests highlighted the difference in the mechanical response due to the predominance of the crystalline or amorphous phase in the tested sample. In particular, a good mechanical behavior was found for the 3D-printed samples.

Out-Of-Plane Permeability Evaluation of Carbon Fiber Preforms by Ultrasonic Wave Propagation.

Out-of-plane permeability of reinforcement preforms is of crucial importance in the infusion of large and thick composite panels, but so far, there are no standard experimental methods for its determination. In this work, an experimental set-up for the measurement of unsaturated through thickness permeability based on the ultrasonic wave propagation in pulse echo mode is presented. A single ultrasonic transducer, working both as emitter and receiver of ultrasonic waves, was used to monitor the through thickness flow front during a vacuum assisted resin infusion experiment. The set-up was tested on three thick carbon fiber preforms, obtained by stacking thermal bonding of balanced or unidirectional plies either by automated fiber placement either by hand lay-up of unidirectional plies. The ultrasonic data were used to calculate unsaturated out-of-plane permeability using Darcy's law. The permeability results were compared with saturated out-of-plane permeability, determined by a traditional gravimetric method, and validated by some analytical models. The results demonstrated the feasibility and potential of the proposed set-up for permeability measurements thanks to its noninvasive character and the one-side access.

A Feasibility Study of Processing Polydimethylsiloxane⁻Sodium Carboxymethylcellulose Composites by a Low-Cost Fused Deposition Modeling 3D Printer.

Additive manufacturing (AM) techniques allow the construction of complex physical models reproducing the content of a specific CAD file, and, among them, Fused Deposition Molding (FDM) stands out for its many advantages. The aim of the present work is to perform a feasibility study of 3D printing of a model of human heart to be used to simulate surgical operations or for training through a two-step method based on extrusion and FDM processes. To this purpose, typical extrusion instrumentation and a simple and low-cost FDM printer are employed, in combination with a thermoplastic polydimethylsiloxane (PDMS), chosen for its transparency, flexibility, and high resistance to multiple agents and aging. To improve its tactile properties and mimic the slimy effect of living organs, sodium carboxymethylcellulose (Na⁻CMC) fibrils are added to it. The starting materials, the neat PDMS filament and the composite one, are deeply characterized in terms of structural, thermal, and rheological properties in order to fix the most suitable extrusion and FDM parameters. The composite filaments show larger diameter and roughness, which cause undesirable effects during 3D printing, such as episodic nozzle obstruction, and exhibit a faster degradation, making the FDM step difficult. Nevertheless, the major issues are related to the low crystallinity degree of the employed polymer. The feasibility study carried out leads to the printing of composite layers, even though far from the desired final target. Possible solutions to print the fully characterized Na⁻CMC/PDMS composite are addressed in the conclusion of this work.

Lay-Up and Consolidation of a Composite Pipe by In Situ Ultrasonic Welding of a Thermoplastic Matrix Composite Tape.

In this work, the potential of preformed thermoplastic matrix composite tapes for the manufacturing of composite pipes by filament winding assisted by in situ ultrasonic welding was evaluated. Unidirectional tapes of E-glass-reinforcedamorphous poly (ethylene terephthalate) were laid up and consolidated in a filament winding machine that was modified with a set-up enabling ultrasonic welding. The obtained composite specimens were characterized by means of morphological and dynamic mechanical analysis as well as void content evaluation, in order to correlate welding parameters to composite properties.

Development of semi- and grafted interpenetrating polymer networks based on poly(ethylene glycol) diacrylate and collagen.

PURPOSE: The objective of this work was to develop composite hydrogels based on poly(ethylene glycol) diacrylate (PEGDA) and collagen (Coll), potentially useful for biomedical applications. METHODS: Semi-interpenetrating polymer networks (semi-IPNs) were obtained by photo-stabilizing aqueous solutions of PEGDA and acrylic acid (AA), in the presence of collagen. Further grafting of the collagen macromolecules to the PEGDA/poly(AA) network was achieved by means of a carbodiimide-mediated crosslinking reaction. The resulting hydrogels were characterized in terms of swelling capability, collagen content and mechanical properties. RESULTS AND CONCLUSIONS: The grafting procedure was found to significantly improve the mechanical stability of the IPN hydrogels, due to the establishment of covalent bonding between the PEGDA/poly(AA) and the collagen networks. The suitability of the composite hydrogels to be processed by means of stereolithography (SLA) was also investigated, toward creating biomimetic constructs with complex shapes, which might be useful either as platforms for tissue engineering applications or as tissue mimicking phantoms.

Hepatic vessel segmentation for 3D planning of liver surgery experimental evaluation of a new fully automatic algorithm.

RATIONALE AND OBJECTIVES: The aim of this study was to identify the optimal parameter configuration of a new algorithm for fully automatic segmentation of hepatic vessels, evaluating its accuracy in view of its use in a computer system for three-dimensional (3D) planning of liver surgery. MATERIALS AND METHODS: A phantom reproduction of a human liver with vessels up to the fourth subsegment order, corresponding to a minimum diameter of 0.2 mm, was realized through stereolithography, exploiting a 3D model derived from a real human computed tomographic data set. Algorithm parameter configuration was experimentally optimized, and the maximum achievable segmentation accuracy was quantified for both single two-dimensional slices and 3D reconstruction of the vessel network, through an analytic comparison of the automatic segmentation performed on contrast-enhanced computed tomographic phantom images with actual model features. RESULTS: The optimal algorithm configuration resulted in a vessel detection sensitivity of 100% for vessels > 1 mm in diameter, 50% in the range 0.5 to 1 mm, and 14% in the range 0.2 to 0.5 mm. An average area overlap of 94.9% was obtained between automatically and manually segmented vessel sections, with an average difference of 0.06 mm(2). The average values of corresponding false-positive and false-negative ratios were 7.7% and 2.3%, respectively. CONCLUSIONS: A robust and accurate algorithm for automatic extraction of the hepatic vessel tree from contrast-enhanced computed tomographic volume images was proposed and experimentally assessed on a liver model, showing unprecedented sensitivity in vessel delineation. This automatic segmentation algorithm is promising for supporting liver surgery planning and for guiding intraoperative resections.