Influence of the Degree of Cure in the Bulk Properties of Graphite Nanoplatelets Nanocomposites Printed via Stereolithography

In this work, we report on the fabrication via stereolithography (SLA) of acrylic-based nanocomposites using graphite nanoplatelets (GNPs) as an additive. GNPs are able to absorb UV-Vis radiation, thus blocking partial or totally the light path of the SLA laser. Based on this, we identified a range of GNP concentrations below 2.5 wt %, where nanocomposites can be successfully printed. We show that, even though GNP is well-dispersed along the polymeric matrix, nanocomposites presented lower degrees of cure and therefore worse mechanical properties when compared with pristine resin. However, a post-processing at 60 degrees C with UV light for 1 h eliminates this difference in the degree of cure, reaching values above 90% in all cases. In these conditions, the tensile strength is enhanced for 0.5 wt % GNP nanocomposites, while the stiffness is increased for 0.5-1.0 wt % GNP nanocomposites. Finally, we also demonstrate that 2.5 wt % GNP nanocomposites possess characteristic properties of semiconductors, which allows them to be used as electrostatic dispersion materials

Printable Graphene Oxide Nanocomposites as Versatile Platforms for Immobilization of Functional Biomolecules

A series of novel nanocomposites containing graphene oxide (GO) suitable for stereolithography is presented. Different loads of GO are tested, identifying that these materials can be printed with concentrations up to 2.5 wt% GO, presenting improved mechanical properties for concentrations below 1.0 wt% GO. In this range, the nanocomposites exhibit higher strength and toughness when compared to the pristine resin. Microscopic analyses of the material demonstrate that this can be correlated with the good compatibility of GO with the resin, which favors its homogeneous dispersion in the form of flexible nanoplates. After manufacturing, the availability of GO to participate in surface modification reactions with chitosan (CHI) and an alkaline phosphatase (ALP) is evaluated. CHI and ALP are well-known to act as biological cues in biorecognition processes, evidencing that these nanocomposites are suitable as platforms for selective immobilization of functional biomolecules.This work was funded by the Ministry of Science, Innovation and Universities (TEC2017-86102-C2-2-R), the 2014-2020 ERDF Operational Programme and the Department of Economy, Knowledge, Business and University of the Regional Government of Andalusia (FEDER-UCA18-106586). Co-funding from UE and the research group INNANOMAT (ref. TEP-946) is also acknowledged. A.S.d.L. and M.d.l.M. acknowledge Ministry of Science, Innovation and Universities for their Juan de la Cierva Incorporacion postdoctoral fellowships (IJC2019-041128-I, IJCI-2017-31507). SEM and TEM measurements were carried out at the DME-SC-ICyT-ELECMI-UCA

Influence of Network Topology on the Viscoelastic Properties of Dynamically Crosslinked Hydrogels

Biological materials combine stress relaxation and self-healing with non-linear stress-strain responses. These characteristic features are a direct result of hierarchical self-assembly, which often results in fiber-like architectures. Even though structural knowledge is rapidly increasing, it has remained a challenge to establish relationships between microscopic and macroscopic structure and function. Here, we focus on understanding how network topology determines the viscoelastic properties, i.e., stress relaxation, of biomimetic hydrogels. We have dynamically crosslinked two different synthetic polymers with one and the same crosslink. The first polymer, a polyisocyanopeptide (PIC), self-assembles into semi-flexible, fiber-like bundles, and thus displays stress-stiffening, similar to many biopolymer networks. The second polymer, 4-arm poly(ethylene glycol) (starPEG), serves as a reference network with well-characterized structural and viscoelastic properties. Using one and the same coiled coil crosslink allows us to decouple the effects of crosslink kinetics and network topology on the stress relaxation behavior of the resulting hydrogel networks. We show that the fiber-containing PIC network displays a relaxation time approximately two orders of magnitude slower than the starPEG network. This reveals that crosslink kinetics is not the only determinant for stress relaxation. Instead, we propose that the different network topologies determine the ability of elastically active network chains to relax stress. In the starPEG network, each elastically active chain contains exactly one crosslink. In the absence of entanglements, crosslink dissociation thus relaxes the entire chain. In contrast, each polymer is crosslinked to the fiber bundle in multiple positions in the PIC hydrogel. The dissociation of a single crosslink is thus not sufficient for chain relaxation. This suggests that tuning the number of crosslinks per elastically active chain in combination with crosslink kinetics is a powerful design principle for tuning stress relaxation in polymeric materials. The presence of a higher number of crosslinks per elastically active chain thus yields materials with a slow macroscopic relaxation time but fast dynamics at the microscopic level. Using this principle for the design of synthetic cell culture matrices will yield materials with excellent long-term stability combined with the ability to locally reorganize, thus facilitating cell motility, spreading, and growth

Self-Assembly of CsPbBr3Perovskites in Micropatterned Polymeric Surfaces: Toward Luminescent Materials with Self-Cleaning Properties

In this work, we present a series of porous, honeycomb-patterned polymer films containing CsPbBr3 perovskite nanocrystals as light emitters prepared by the breath figure approach. Microscopy analysis of the topography and composition of the material evidence that the CsPbBr3 nanocrystals are homogeneously distributed within the polymer matrix but preferably confined inside the pores due to the fabrication process. The optical properties of the CsPbBr3 nanocrystals remain unaltered after the film formation, proving that they are stable inside the polystyrene matrix, which protects them from degradation by environmental factors. Moreover, these surfaces present highly hydrophobic behavior due to their high porosity and defined micropatterning, which is in agreement with the Cassie-Baxter model. This is evidenced by performing a proof-of-concept coating on top of 3D-printed LED lenses, conferring the material with self-cleaning properties, while the CsPbBr3 nanocrystals embedded inside the polymeric matrix maintain their luminescent behavior.This work was funded by the Ministry of Science, Innovation and Universities (project TEC2017-86102-C2-2-R) and Junta de Andalucía (Research group INNANOMAT, ref. TEP-946) and co-financed by the 2014-2020 ERDF Operational Programme and by the Department of Economy, Knowledge, Business and University of the Regional Government of Andalusia (ref: FEDER-UCA18-106586). Co-funding from UE is also acknowledged. A.S.d.L. acknowledges the Ministry of Science, Innovation and Universities for his Juan de la Cierva Incorporación postdoctoral fellowship (IJC2019-041128-I). R.A. also acknowledges the support of the Spanish MINECO through projects: Retos-Colaboración 2016 Project Safetag (no. RTC-2016-5197-2) and Retos de la Sociedad Project Nirvana (no. PID2020-119628RB-C31) by MCIN/AEI/10.13039/ 501100011033 and the “Agencia Valenciana de la Innovació” for the Valorització 2018 Project Hidronio (no. INNVAL10/ 18/032) and Valorització 2021 Project CATIOX (no. INNVA1/2021/56). R.A. also thanks the Spanish MINECO for their Ramón y Cajal Fellowship (no. RYC-2015-18349). SEM and TEM measurements were carried out at the DME-SCICyT- ELECMI-UCA

Polymer Composites with Cork Particles Functionalized by Surface Polymerization for Fused Deposition Modeling

Cork powder received as a byproduct from local industries is valorized through the development of composite materials suitable for fused deposition modeling (FDM). For this purpose, a polymeric matrix of acrylonitrile-styrene-butyl acrylate (ASA) is used due to its good mechanical resistance and weather resistance properties. Prior to the manufacturing of the composites, the cork particles are characterized and modified by surface polymerization, creating a layer of poly(butyl acrylate) (PBA). Then, filaments for FDM are prepared by solvent casting and extrusion from ASA and composites with unmodified cork (ASA + C) and PBA-modified cork (ASA + C-m). PBA is one of the polymers present in the structure of ASA, which increases the compatibility between the cork particles and the polymer matrix. This is evidenced by evaluating the mechanical properties of the composites and examining their fracture surface by scanning electron microscopy. The analysis of the thermal properties shows that the developed composites also present enhanced insulating properties.This work was funded by the ADICORK project through a collaboration agreement between Junta de Andalucia (Ministry of Agriculture, Livestock, Fisheries and Sustainable Develop-ment) and the University of Cadiz (research group INNANOMAT, ref . TEP-946) . This agreement has been funded by UE Integrated Territorial Investment (ITI) . A.S.d.L. acknowledges the Ministry of Science, Innovation and Universities for his Juan de la Cierva Incorporacion postdoctoral fellowship (IJC2019-041128-I) . N.F.-D. also acknowledges co-founding by European Social Fund and Ministry of Economic Transformation, Industry, Knowledge and Universities of the Junta de Andalucia. The authors would like to thank Corchos del Estrecho for supplying the cork powder used in this research. SEM measurements were carried out at the DME-SC-ICyT-ELECMI-UCA

Itaconic-Acid-Based Sustainable Poly(ester amide) Resin for Stereolithography

Material science is recognized as a frontrunner in achieving a sustainable future, owing to its primary reliance upon petroleum-based chemical raw materials. Several efforts are made to implement common renewable feedstocks as an alternative to common fossil resources. For this purpose, additive manufacturing (AM) represents promising and effective know-how for the replacement of high energy- and resource-demanding processes with more environmentally friendly practices. This work presents a novel biobased ink for stereolithography, which has been formulated by mixing a photocurable poly(ester amide) (PEA) obtained from renewable resources with citrate and itaconate cross-linkers and appropriate photopolymerization initiators, terminators, and dyes. The mechanical features and the relative biocompatibility of 3D-printed objects have been carefully studied to evaluate the possible resin implementation in the field of the textile fashion industry.9 página

Basalt Fiber Composites with Reduced Thermal Expansion for Additive Manufacturing

Fused filament fabrication (FFF) is gaining attention as an efficient way to create parts and replacements on demand using thermoplastics. This technology requires the development of new materials with a reliable printability that satisfies the requirement of final parts. In this context, a series of composites based on acrylonitrile styrene acrylate (ASA) reinforced with basalt fiber (BF) are reported in this work. First, several surface modification treatments are applied onto the BF to increase their compatibility with the ASA matrix. Then, once the best treatment is identified, the mechanical properties, coefficient of thermal expansion (CTE) and warping distortion of the different specimens designed and prepared by FFF are studied. It was found that the silanized BF is appropriate for an adequate printing, obtaining composites with higher stiffness, tensile strength, low CTE and a significant reduction in part distortion. These composites are of potential interest in the design and manufacturing of final products by FFF, as they show much lower CTE values than pure ASA, which is essential to successfully fabricate large objects using this technique

High-Resolution 3D Fabrication of Glass Fiber-Reinforced Polymer Nanocomposite (FRPN) Objects by Two-Photon Direct Laser Writing

This paper reports on the nanofabrication of a fiber-reinforced polymer nanocomposite (FRPN) by two-photon direct laser writing (TP-DLW) using silica nanowires (SiO2 NWs) as nanofillers, since they feature a refractive index very close to that of the photoresist used as a polymeric matrix. This allows for the best resolution offered by the TP-DLW technique, even with high loads of SiO2 NWs, up to 70 wt %. The FRPN presented an increase of approximately 4 times in Young's modulus (8.23 GPa) and nanohardness (120 MPa) when compared to those of the bare photoresist, indicating how the proposed technique is well-suited for applications with higher structural requirements. Moreover, three different printing configurations can be implemented thanks to the use of silicon chips, on which the SiO2 NWs are grown, as fabrication substrates. First, they can be effectively used as an adhesive layer when the laser beam is focused at the interface with the silicon substrate. Second, they can be used as a sacrificial layer, when the laser beam is focused in a plane inside the SiO2 NW layer. Third, only the outer shell of the object is printed so that the SiO2 NW tangle acts as the internal skeleton for the structure being fabricated in the so-called shell and scaffold printing strategy

Additive Manufacturing of Gold Nanostructures Using Nonlinear Photoreduction under Controlled Ionic Diffusion

Multiphoton photoreduction of photosensitive metallic precursors via direct laser writing (DLW) is a promising technique for the synthesis of metallic structures onto solid substrates at the sub-micron scale. DLW triggered by a two photon absorption process is done using a femtosecond NIR laser (lambda = 780 nm), tetrachloroauric acid (HAuCl4) as a gold precursor, and isinglass as a natural hydrogel matrix. The presence of a polymeric, transparent matrix avoids unwanted diffusive processes acting as a network for the metallic nanoparticles. After the writing process, a bath in deionized water removes the gold precursor ions and eliminates the polymer matrix. Different aspects underlying the growth of the gold nanostructures (AuNSs) are here investigated to achieve full control on the size and density of the AuNSs. Writing parameters (laser power, exposure time, and scanning speed) are optimized to control the patterns and the AuNSs size. The influence of a second bath containing Au3+ to further control the size and density of the AuNSs is also investigated, observing that these AuNSs are composed of individual gold nanoparticles (AuNPs) that grow individually. A fine-tuning of these parameters leads to an important improvement of the created structures' quality, with a fine control on size and density of AuNSs.W.D.C. and M.G. acknowledge the support of the CNR Facility Beyond-Nano-Polo di Cosenza. W.D.C. acknowledges MIUR (Ministero dell'Istruzione, dell'Universita e della Ricerca-Italy) for her industrial PhD grant (PONa3_00362). This work was also funded by Ministry of Science, Innovation and Universities (project TEC2017-86102-C2-2-R) and Junta de Andalucia (Research group INNANOMAT, ref. TEP-946). Co-funding from UE is also acknowledged. A.S.d.L. and M.d.l.M. acknowledge Ministry of Science, Innovation and Universities for their Juan de la Cierva Incorporacion postdoctoral fellowships (IJC2019-041128-I, IJCI-2017-31507). SEM and TEM measurements were carried out at the DME-SC-ICyT-ELECMI-UCA. Documen

Synthesis and Characterisation of ASA-PEEK Composites for Fused Filament Fabrication

In this paper, a series of polymer composites made from acrylonitrile-styrene-acrylate (ASA) and poly (ether ether ketone) (PEEK) were manufactured. ASA acts as a polymer matrix while PEEK is loaded in the form of micro-particles that act as a reinforcing filler. The composites were compounded by single screw extrusion and then, different specimens were manufactured either via injection moulding (IM) or fused filament fabrication (FFF). Two different types of PEEK (commercial and reused) in different concentrations (3 and 6 wt.%) were tested and their influence in the mechanical, structural, and thermal properties were studied. It was observed that reused PEEK enhanced the stiffness and tensile strength and thermal stability of the composites both, for injected and printed specimens. This evidences the suitability of these composites as potential candidates as novel materials with enhanced properties following an approach of circular economy