How Is Rheology Involved in 3D Printing of Phase-Separated PVC-Acrylate Copolymers Obtained by Free Radical Polymerization

New auto-plasticised copolymers of poly(vinyl chloride)-r-(acrylate) and polyvinylchloride, obtained by radical polymerization, are investigated to analyse their capacity to be processed by 3D printing. The specific microstructure of the copolymers gives rise to a phase-separated morphology constituted by poly(vinyl chloride) (PVC) domains dispersed in a continuous phase of acrylate-vinyl chloride copolymer. The analysis of the rheological results allows the suitability of these copolymers to be assessed for use in a screw-driven 3D printer, but not by the fused filament fabrication method. This is due to the high melt elasticity of the copolymers, caused by interfacial tension between phases. A relationship between the relaxation modulus of the copolymers and the interlayer adhesion is established. Under adequate 3D-printing conditions, flexible and ductile samples with good dimensional stability and cohesion are obtained, as is proven by scanning electron microscopy (SEM) and tensile stress-strain tests

How Is Rheology Involved in 3D Printing of Phase-Separated PVC-Acrylate Copolymers Obtained by Free Radical Polymerization

New auto-plasticised copolymers of poly(vinyl chloride)-r-(acrylate) and polyvinylchloride, obtained by radical polymerization, are investigated to analyse their capacity to be processed by 3D printing. The specific microstructure of the copolymers gives rise to a phase-separated morphology constituted by poly(vinyl chloride) (PVC) domains dispersed in a continuous phase of acrylate-vinyl chloride copolymer. The analysis of the rheological results allows the suitability of these copolymers to be assessed for use in a screw-driven 3D printer, but not by the fused filament fabrication method. This is due to the high melt elasticity of the copolymers, caused by interfacial tension between phases. A relationship between the relaxation modulus of the copolymers and the interlayer adhesion is established. Under adequate 3D-printing conditions, flexible and ductile samples with good dimensional stability and cohesion are obtained, as is proven by scanning electron microscopy (SEM) and tensile stress-strain tests

Influence of chain topology on gel formation and direct ink printing of model linear and star block copolymers with poly(ethylene oxide) and poly(ε-caprolactone) semi-crystalline blocks

In this work, a set of well-defined linear triblock copolymers and star block copolymers (3 and 4-arms) with semi crystalline blocks consisting of poly(ethylene oxide) (PEO) and poly(epsilon-caprolactone) (PCL), synthesized by combining ring-opening polymerization and organic catalyst switch strategy, were studied as thermosensitive gel-forming biomaterials for applications in 3D extrusion printing. The hydrogels derived from linear copolymers underwent a temperature-dependent sol-gel-sol transition, behaving as a flowing sol at room temperature and transforming into a non-flowing gel upon heating. On the other hand, the hydrogels derived from 4-arm star block copolymers experienced a gel-sol transition and did not flow at room temperature. This behavior allowed them to be used as 3D printing inks at room temperature. 3D printing results revealed that the semi-crystalline hydrogels of the 4-arm star block copolymers could not only be extruded and printed with high shape fidelity, but they also exhibited a favorable dissolution profile for their use as sacrificial biomaterial inks. Additionally, we thoroughly investigated the crystalline organization of the PCL and the PEO blocks within the hydrogels through comparison with the results obtained in bulk. The results demonstrated evident structural ordering in the hydrogels associated with the crystallization of the PCL blocks. Unexpectedly, DSC results combined with SAXS experiments revealed the presence of PEO block crystals within the 30 % w/v hydrogels from 4-arm star block copolymers, in addition to the PCL block crystals. Hence, remarkable double crystalline hydrogels have been obtained for the first time.This research was financially supported by the projects PID2020-113045GB-C21 and PID2020-113045GB-C22 funded by MCIN/ AEI /10.13039/501100011033 and by the Basque Government through grant IT1503-22. M.I.P. acknowledges funding through an FPI contract (PRE2018-086104) to develop a PhD thesis. The support of the ALBA (2022086944 and 2022086957 proposals) synchrotron facility is gratefully acknowledged. R.H. is a member of the CSIC Interdisciplinary Thematic Platform (PTI+) Interdisciplinary Platform for Sustainable Plastics towards a Circular Economy+ (PTI-SusPlast+) and the PTI CSIC FAB3D. The authors would also like to thank Alejandro Hernandez-Sosa for assistance regarding 3D printing experiments. P.Z., V.L., and N.H. gratefully acknowledge the support of the King Abdullah University of Science and Technology (KAUST)

Salt-induced Fmoc-tripeptide supramolecular hydrogels: a combined experimental and computational study of the self-assembly

Delving into the mechanism behind the molecular interactions at the atomic level of short-sequence peptides plays a key role in the development of nanomaterials with specific structure–property–function relationships from a bottom-up perspective. Due to their poor water solubility, the self-assembly of Fmoc-bearing peptides is usually induced by dissolution in an organic solvent, followed by a dilution step in water, pH changes, and/or a heating–cooling process. Herein, we report a straightforward methodology for the gelation of Fmoc-FFpY (F: phenylalanine; Y: tyrosine; and p: PO42−), a negatively charged tripeptide, in NaCl solution. The electrostatic interactions between Fmoc-FFpY and Na+ ions give rise to different nanofibrillar hydrogels with rheological properties and nanofiber sizes modulated by the NaCl concentration in pure aqueous media. Initiated by the electrostatic interactions between the peptide phosphate groups and the Na+ ions, the peptide self-assembly is stabilized thanks to hydrogen bonds between the peptide backbones and the π–π stacking of aromatic Fmoc and phenyl units. The hydrogels showed self-healing and thermo-responsive properties for potential biomedical applications. Molecular dynamics simulations from systems devoid of prior training not only confirm the aggregation of peptides at a critical salt concentration and the different interactions involved, but also corroborate the secondary structure of the hydrogels at the microsecond timescale. It is worth highlighting the remarkable achievement of reproducing the morphological behavior of the hydrogels using atomistic simulations. To our knowledge, this study is the first to report such a correspondence.Financial support from the Spanish Research Council (CSIC) and the French Research Council (CNRS) for the International Emerging Actions 2018 HYDROPRINT project is gratefully acknowledged. The authors also acknowledge the funding from the projects MAT2017-83014-C2-2-P and PID2020-113045GB-C22 by MCIN/AEI/10.13039/501100011033 and the ALBA Synchrotron (Proposal number 2021095380). R. H. is a member of the SUSPLAST+ platform of CSIC. The authors thank Dr Rafael Nuñez from CIB-CSIC for TEM and Cryo-TEM measurements and the technical and human support provided by SGIker (UPV/EHU/ERDF, EU). SAXS experiments were performed at the BL 11 NCD-SWEET beamline at ALBA Synchrotron with the collaboration of ALBA staff. ANR (Agence Nationale de la Recherche) and CGI (Commissariat à l'Investissement d'Avenir) are gratefully acknowledged for their financial support of this work through Labex SEAM (Science and Engineering for Advanced Materials and Devices) ANR 11 LABX 086, and ANR 11 IDEX 05 02. This work benefited from the access to the supercomputing facilities of the GENCI (Grand Equipement National pour le Calcul Informatique) and the access to the ITODYS P3MB facility (Université Paris Cité, CNRS UMR 7086, Paris, France)

Crystallization-induced self-assembly of poly(ethylene glycol) side chains in dithiol–yne-based comb polymers: side chain spacing and molecular weight effects

The chain architecture and topology of macromolecules impact their physical properties and final performance, including their crystallization process. In this work, comb polymers constituted by poly(ethylene glycol), PEG, side chains, and a dithiol–yne-based ring polymer backbone have been studied, focusing on the micro- and nanostructures of the system, thermal behavior, and crystallization kinetics. The designed comb system allows us to investigate the role of a ring backbone, the impact of varying the distance between two neighboring side chains, and the effect of the molecular weight of the side chain. The results reflect that the governing factor in the crystalline properties is the molar mass of the side chains and that the tethering of PEG chains to the ring backbone brings important constraints to the crystallization process, reducing the crystallinity degree and slowing down the crystallization kinetics in comparison to analogue PEG homopolymers. We demonstrate that the effect of spatial hindrance in the comb-like PEG polymers drives the morphology toward highly ordered, self-assembled, semicrystalline superstructures with either extended interdigitated chain crystals or novel (for comb polymers) interdigitated folded chain lamellar crystals. These structures depend on PEG molecular weight, the distance between neighboring tethered PEG chains, and the crystallization conditions (nonisothermal versus isothermal). This work sheds light on the role of chain architecture and topology in the structure of comb-like semicrystalline polymers.This work was funded by the Basque Government through grant IT1503-22. L.S. acknowledges Margarita Salas fellowship granted by the University of the Basque Country (UPV/EHU) and funded by the European Union-Next Generation EU and the Spanish Government. M.K. acknowledges the provision of facilities and technical support by Aalto University at OtaNano-Nanomicroscopy Center (Aalto-NMC). S.M.G. acknowledges the Boyer professorship and B.J.C. acknowledges the Louisiana Board of Regents fellowship. L.P.F. thanks the ADAGIO: Advanced Manufacturing Research Fellowship Program in the Basque New Aquitaine Region