Nanomechanical probing of soft matter through hydrophobic AFM tips fabricated by two-photon polymerization.

Atomic force microscopy (AFM) nanoindentation of soft materials is a powerful tool for probing mechanical properties of biomaterials. Though many results have been reported in this field over the last decade, adhesion forces between the tip and the sample hinder the elastic modulus measurement when hydrophilic soft samples are investigated. Here, two-photon polymerization (2PP) technology was used to fabricate hydrophobic perfluoropolyether-based AFM tips. The hydrophobic 2PP tips allowed us to overcome the limitations of commercial and functionalized tips as well as to successfully measure the elastic modulus of medically relevant soft materials in air. Our results obtained in the characterization of poly(dimethyl siloxane) and polyethylene glycol hydrogels showed lower adhesion forces over a larger measurement range when compared to measurements performed with commercial tips. The elastic moduli measured by means of hydrophobic 2PP AFM tips were also found to be comparable to those obtained using conventional techniques for macroscopic samples. We successfully showed that the hydrophobic AFM tips developed by this highly versatile technology enable the study of mechanical properties of soft matter, benefiting from reduced sample-tip interactions, and a custom-made shape and dimension of the tips.

Thermally Conductive and Electrically Insulating Polymer-Based Composites Heat Sinks Fabricated by Fusion Deposition Modeling.

This study explores the potential of novel boron nitride (BN) microplatelet composites with combined thermal conduction and electrical insulation properties. These composites are manufactured through Fusion Deposition Modeling (FDM), and their application for thermal management in electronic devices is demonstrated. The primary focus of this work is, therefore, the investigation of the thermoplastic composite properties to show the 3D printing of lightweight polymeric heat sinks with remarkable thermal performance. By comparing various microfillers, including BN and MgO particles, their effects on material properties and alignment within the polymer matrix during filament fabrication and FDM processing are analyzed. The characterization includes the evaluation of morphology, thermal conductivity, and mechanical and electrical properties. Particularly, a composite with 32 wt% of BN microplatelets shows an in-plane thermal conductivity of 1.97 W m-1 K-1, offering electrical insulation and excellent printability. To assess practical applications, lightweight pin fin heat sinks using these composites are designed and 3D printed. Their thermal performance is evaluated via thermography under different heating conditions. The findings are very promising for an efficient and cost-effective fabrication of thermal devices, which can be obtained through extrusion-based Additive Manufacturing (AM), such as FDM, and exploited as enhanced thermal management solutions in electronic devices.

Crosslinked Polyesters as Fully Biobased Coatings with Cutin Monomer from Tomato Peel Wastes.

Cutin, one of the main structural components of tomato peels, is a waxy biopolymer rich in hydroxylated fatty acids. In this study, 10,16-dihydroxyhexadecanoic acid (10,16-diHHDA) was extracted and isolated from tomato peels and exploited to develop fully crosslinked polyesters as potential candidates for replacing fossil-based metal protective coatings. A preliminary screening was conducted to select the base formulation, and then a design of experiments (DoE) was used as a methodology to identify the optimal composition to develop a suitable coating material. Different formulations containing 10,16-diHHDA and other biorefinery monomers, including 2,5-furandicarboxylic acid, were considered. To this end, all polyesters were characterized through differential scanning calorimetry (DSC) and gel content measurements to determine their Tg value and crosslinking efficiency. Compositions exhibiting the best trade-off between Tg value, chemical resistance, and sufficiently high 10,16-diHHDA content between 39 and 48 wt.% were used to prepare model coatings that were characterized for assessing their wettability, scratch hardness, chemical resistance, and adhesion to metal substrates. These polyester coatings showed a Tg in the range of 45-55 °C, a hydrophobic behavior with a water contact angle of around 100°, a good solvent resistance (>100 MEK double rubs), and an adhesion strength to steel higher than 2 MPa. The results obtained confirmed the potential of cutin-based resins as coatings for metal protection, meeting the requirements for ensuring physicochemical properties of the final product, as well as for optimizing the valorization of such an abundant agri-food waste as tomato peels.

Unveiling the Hidden Properties of Tomato Peels: Cutin Ester Derivatives as Bio-Based Plasticizers for Polylactic Acid.

Polylactic acid (PLA) is one of the most important biopolymers employed on the market due to its good mechanical strength and barrier properties. On the other hand, this material presents a rather low flexibility, limiting its employment. The valorization of bio-based agro-food waste for the modification of bioplastics is a highly appealing approach for the replacement of petrol-based materials. The aim of this work is to employ cutin fatty acids derived from a biopolymer (i.e., cutin), present in waste tomato peels and its bio-based derivatives as new plasticizers to enhance PLA flexibility. In particular, pure 10,16-dihydroxy hexadecanoic acid was extracted and isolated from tomato peels and then functionalized to give the desired compounds. All the molecules developed in this study were characterized by NMR and ESI-MS. Blends at different concentrations (10, 20, 30, and 40% w/w) the flexibility (Tg measurements with differential scanning calorimetry-DSC) of the final material. Furthermore, the physical behavior of two blends obtained by mechanical mixing of PLA and 16-methoxy,16-oxohexadecane-1,7-diyl diacetate was investigated through thermal and tensile tests. The data collected by DSC show a lowering in the Tg of all the blends of PLA with functionalized fatty acids, in comparison with pure PLA. Lastly, the tensile tests highlighted how PLA blended with 16-methoxy,16-oxohexadecane-1,7-diyl diacetate (20% w/w) can efficiently enhance its flexibility.

Metallization of Recycled Glass Fiber-Reinforced Polymers Processed by UV-Assisted 3D Printing.

An ever-growing amount of composite waste will be generated in the upcoming years. New circular strategies based on 3D printing technologies are emerging as potential solutions although 3D-printed products made of recycled composites may require post-processing. Metallization represents a viable way to foster their exploitation for new applications. This paper shows the use of physical vapor deposition sputtering for the metallization of recycled glass fiber-reinforced polymers processed by UV-assisted 3D printing. Different batches of 3D-printed samples were produced, post-processed, and coated with a chromium metallization layer to compare the results before and after the metallization process and to evaluate the quality of the finishing from a qualitative and quantitative point of view. The analysis was conducted by measuring the surface gloss and roughness, analyzing the coating morphology and thickness through the Scanning Electron Microscopy (SEM) micrographs of the cross-sections, and assessing its adhesion with cross-cut tests. The metallization was successfully performed on the different 3D-printed samples, achieving a good homogeneity of the coating surface. Despite the influence of the staircase effect, these results may foster the investigation of new fields of application, as well as the use of different polymer-based composites from end-of-life products, i.e., carbon fiber-reinforced polymers.

Inkjet Printing of a Benzocyclobutene-Based Polymer as a Low-k Material for Electronic Applications.

Polymeric materials with a low dielectric constant are widely used in the electronic industry due to their properties. In particular, polymer adhesives can be used in many applications such as wafer bonding and three-dimensional integration. Benzocyclobutene (BCB) is a very interesting material thanks to its excellent bonding behavior and dielectric properties. Usually, BCB is applied by spin-coating, although this technology does not allow the fabrication of complex patterns. To obtain complex patterns, it is necessary to use a printing technology, such as inkjet printing. However, inkjet printing of BCB-based inks has not yet been investigated. Here, we show the feasibility of printing complex patterns with a BCB-based ink, reaching a resolution of 130 µm. We demonstrate that with a proper dilution, BCB-based inks enter the printability window and drop ejection is achieved without the formation of satellite drops. In addition, we present the conditions in which there is an appearance of the coffee ring effect. Inks that feature a too high interaction with the substrate are more likely to show the coffee ring effect, deteriorating the printing quality. We also observe that it is possible to achieve a better film uniformity by increasing the number of printed layers, due to redissolution of the BCB-based polymer that helps to level possible inhomogeneities. Our work represents the starting point for an in-depth study of BCB-based polymer fabrication using jet printing technologies, as a comparison of the bonding quality obtained with different materials and different technologies could give more information and broaden the perspective regarding this field.

UV-Assisted 3D Printing of Polymer Composites from Thermally and Mechanically Recycled Carbon Fibers.

Despite the growing global interest in 3D printed carbon fiber reinforced polymers, most of the applications are still limited to high-performance sectors due to the low effectiveness-cost ratio of virgin carbon fibers. However, the use of recycled carbon fibers in 3D printing is almost unexplored, especially for thermoset-based composites. This paper aims to demonstrate the feasibility of recycled carbon fibers 3D printing via UV-assisted direct ink writing. Pyrolyzed recycled carbon fibers with a sizing treatment were firstly shredded to be used as a reinforcement of a thermally and photo-curable acrylic resin. UV-differential scanning calorimetry analyses were then performed to define the material crosslinking of the 3D printable ink. Because of the poor UV reactivity of the resin loaded with carbon fibers, a rheology modifier was added to guarantee shape retention after 3D printing. Thanks to a customized 3D printer based on a commercial apparatus, a batch of specimens was successfully 3D printed. According to the tensile tests and Scanning Electron Microscopy analysis, the material shows good mechanical properties and the absence of layer marks related to the 3D printing. These results will, therefore, pave the way for the use of 3D printed recycled carbon fiber reinforced polymers in new fields of application.

Additive Re-Manufacturing of Mechanically Recycled End-of-Life Glass Fiber-Reinforced Polymers for Value-Added Circular Design.

Despite the large use of composites for industrial applications, their end-of-life management is still an open issue for manufacturing, especially in the wind energy sector. Additive manufacturing technology has been emerging as a solution, enhancing circular economy models, and using recycled composites for glass fiber-reinforced polymers is spreading as a new additive manufacturing trend. Nevertheless, their mechanical properties are still not comparable to pristine materials. The purpose of this paper is to examine the additive re-manufacturing of end-of-life glass fiber composites with mechanical performances that are comparable to virgin glass fiber-reinforced materials. Through a systematic characterization of the recyclate, requirements of the filler for the liquid deposition modeling process were identified. Printability and material surface quality of different formulations were analyzed using a low-cost modified 3D printer. Two hypothetical design concepts were also manufactured to validate the field of application. Furthermore, an understanding of the mechanical behavior was accomplished by means of tensile tests, and the results were compared with a benchmark formulation with virgin glass fibers. Mechanically recycled glass fibers show the capability to substitute pristine fillers, unlocking their use for new fields of application.

Surface behavior and molecular recognition in DNA microarrays from N,N-dimethylacrylamide terpolymers with activated esters as linking groups.

A series of terpolymers made of DMA, NAS and MAPS were synthesized by free radical copolymerization and used as functional coatings for the fabrication of glass slide DNA microarrays. The surface properties of coated glass slides were investigated through contact angle measurements, ellipsometry and atomic force microscopy. The terpolymer molecular weight showed a moderate effect on surface tension (gamma(s) = 56-62 mN x m(-1)), but no clear effect on polymeric layer thickness (5-8 nm) and roughness. Hybridization experiments with amine-functionalized oligonucleotides gave the best fluorescence intensity results for microarrays coated with intermediate-molecular-weight terpolymers. Finally, an accelerated ageing test of the microarray in a humidity chamber showed a nice relationship between decay curves of contact angle against water and fluorescence intensity.

Thermoresponsive Polymer Micropatterns Fabricated by Dip-Pen Nanolithography for a Highly Controllable Substrate with Potential Cellular Applications.

We report a novel approach for patterning thermoresponsive hydrogels based on N,N-diethylacrylamide (DEAAm) and bifunctional Jeffamine ED-600 by dip-pen nanolithography (DPN). The direct writing of micron-sized thermoresponsive polymer spots was achieved with efficient control over feature size. A Jeffamine-based ink prepared through the combination of organic polymers, such as DEAAm, in an inorganic silica network was used to print thermosensitive arrays on a thiol-silanized silicon oxide substrate. The use of a Jeffamine hydrogel, acting as a carrier matrix, allowed a reduction in the evaporation of ink molecules with high volatility, such as DEAAm, and facilitated the transfer of ink from tip to substrate. The thermoresponsive behavior of polymer arrays which swell/deswell in aqueous solution in response to a change in temperature was successfully characterized by atomic force microscopy (AFM) and Raman spectroscopy: a thermally induced change in height and hydration state was observed, respectively. Finally, we demonstrate that cells can adhere to and interact with these dynamic features and exhibit a change in behavior when cultured on the substrates above and below the transition temperature of the Jeffamine/DEAAm thermoresponsive hydrogels. This demonstrates the potential of these micropatterned hydrogels to act as a controllable surface for cell growth.

Fine tuning and measurement of mechanical properties of crosslinked hyaluronic acid hydrogels as biomimetic scaffold coating in regenerative medicine.

Chemically crosslinked hyaluronic acid hydrogels are synthesized with a homogeneous crosslinking process using divinyl sulfone (DVS) as crosslinking agent. Testing different conditions, in terms of both DVS content and curing time, we aim to keep control over the crosslinking process in order to prepare biocompatible hydrogels with mechanical properties closely approximating those of extracellular matrix (ECM) of natural stem cells niches (0.1÷50kPa). The hydrogels properties are evaluated through a reliable methodology based on three independent techniques: dynamic rheological analysis, used as benchmark method; swelling experiments following the Flory-Rehner theory and atomic force microscope (AFM) nanoindentation experiments. Our results demonstrate that controlling crosslinking parameters it is possible to design hydrogels with desired elastic moduli values. HA hydrogels can be ideal coating materials to be implemented in regenerative medicine and particularly in the engineering of ECM niches in vitro.

Surface properties of femtosecond laser ablated PMMA.

The effects of femtosecond laser ablation on the physical and chemical properties at the surface of poly methylmethacrylate (PMMA) were studied. Femtosecond laser microfabrication caused the initially wetting behavior of PMMA to become nonwetting, mainly because of the laser-induced surface porosity at the submicroscale. Static and dynamic contact angle measurements along with morphological characterization revealed that after the laser irradiation, the system lies in an intermediate regime between those theorized by Wenzel and Cassie-Baxter. Spectroscopic analysis did not evidence any significant variation in the chemical properties of the processed polymeric surfaces.