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Four-dimensional printing refers to a process through which a 3D printed object transforms from one structure into another through the influence of an external energy input. Self-folding structures have been extensively studied to advance 3D printing technology into 4D using stimuli-responsive polymers. Designing and applying self-folding structures requires an understanding of the material properties so that the structural designs can be tailored to the targeted applications. Poly(N-iso-propylacrylamide) (PNIPAM) was used as the thermo-responsive material in this study to 3D print hydrogel samples that can bend or fold with temperature changes. A double-layer printed structure, with PNIPAM as the self-folding layer and polyethylene glycol (PEG) as the supporting layer, provided the mechanical robustness and overall flexibility to accommodate geometric changes. The mechanical properties of the multi-material 3D printing were tested to confirm the contribution of the PEG support to the double-layer system. The desired folding of the structures, as a response to temperature changes, was obtained by adding kirigami-inspired cuts to the design. An excellent shape-shifting capability was obtained by tuning the design. The experimental observations were supported by COMSOL Multiphysics ® software simulations, predicting the control over the folding of the double-layer systems.

Fullerene adducts have attracted attention in a variety of applications including organic optoelectronic devices. In this regard, we have designed a covalently linked donor-acceptor dyad comprising a fluorobenzothiadiazole-thiophene (BTF 2 -Th) unit with the electron acceptor fullerene in an Acceptor-Donor-Acceptor (A-D-A) molecular arrangement. We synthesized and characterized two new covalently bonded benzothiadiazole-based fullerene molecules, mono-adduct, 7 (benzothiadiazole : PC 61 BM = 1 : 1, anchored terminally via esterification reaction) and multi-adduct, 10-I (benzothiadiazole : PC 61 BM = n  : 1, where n ≥ 1, attached directly to the fullerene core via the Prato reaction) using different synthetic strategies. A broadening of the UV-visible spectra of the modified fullerene derivative with strong absorption from 350 to 500 nm and at low wavelengths is observed as compared to PC 61 BM. A suitable bandgap, good electronic conductivity, and appreciable solubility in solvents suggest their utility in optoelectronic devices. The mono-adduct 7 showed two-order higher electron mobility as compared to bis-adduct 10-I due to retention of extended conjugation in fullerene, as in the case of PC 61 BM. Experimentally determined optical properties and energy levels of the fullerene adducts were found to be in good agreement and supported by theoretical calculations. The presence of BTF 2 affects the ground state dipole moments as well as the absorption strengths, most noticeable in the case of two attached BTF 2 moieties. The HOMO and LUMO levels are found to be localized on the fullerene cage with the extension of the HOMO to the BTF 2 unit more and the same is noticed in ground state dipole moment in the side-chain functionalized structure. Such structural arrangement provides easy charge transfer between acceptor and donor units to allow a concomitant effect of favorable optoelectronic properties, energy levels of the frontier orbitals, effective exciton dissociation, and charge transport which may reduce processing complexity to advance single material-based future optoelectronic devices., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

3D printing involves the use of photopolymerizable resins, which are toxic and typically have incompatible properties with materials such as polystyrene (PS), which present limitations for biomedical applications. We present a method to dramatically improve the poor adhesion between the PS insulative layer on 3D printed Microelectrode Array (MEA) substrates by functionalizing the resin surface with polydopamine (PDA), a mussel-inspired surface chemistry derivative. A commercial 3D printing prepolymer resin, FormLabs Clear (FLC), was printed using a digital light processing (DLP) printer and then surface functionalized with PDA by alkali-induced aqueous immersion deposition and self-polymerization. It was observed that the adhesion of the PS to FLC was improved due to the precision emanating from the DLP method and further improved after the functionalization of DLP printed substrates with PDA at 1, 12, and 24 h time intervals. The adhesion of PS was evaluated through scotch tape peel testing and instron measurements of planar substrates and incubation testing with qualitative analysis of printed culture wells. The composition and topology of the samples were studied to understand how the properties of the surface change after PDA functionalization and how this contributes to the overall improvement in PS adhesion. Furthermore, the surface energies at each PDA deposition time were calculated from contact angle studies as it related to adhesion. Finally, biocompatibility assays of the newly modified surfaces were performed using mouse cardiac cells (HL-1) to demonstrate the biocompatibility of the PDA functionalization process. PDA surface functionalization of 3D DLP printed FLC resin resulted in a dramatic improvement of thin film PS adhesion and proved to be a biocompatible solution for improving additive manufacturing processes to realize biosensors such as in vitro MEAs., Competing Interests: Prof. Rajaraman is a co-founder and major equity holder at Primordia Biosystems that may have some interests in licensing parts of the technologies described. All other authors have no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

1,2-Bis{(3,5-dimethylpyrazol-1-yl)methyl}benzene (L) reacts with [Cu(OAc) 2 ] and C 6 H 5 COOH, 4-OH-C 6 H 4 COOH, 2-Cl-C 6 H 4 COOH and (3,5-NO 2 ) 2 -C 6 H 3 COOH to afford the copper complexes [Cu 2 (C 6 H 5 COO) 4 (L) 2 ] (1), [Cu 2 (4-OH-C 6 H 4 COO) 4 (L) 2 ] (2), [Cu 2 (2-Cl-C 6 H 4 COO) 4 (L) 2 ] n (3) and [Cu{(3,5-NO 2 ) 2 -C 6 H 3 COO} 2 L] n (4) which are characterised by IR, mass spectrometry, elemental analyses, and X-ray crystallography. The structural data revealed two geometries that are adopted by the complexes: (i) paddle wheel in 1, 2·7H 2 O, 3 and (ii) regular chains in 3 and 4. Magnetic studies show strong antiferromagnetic couplings in the paddle wheel complexes and a weak antiferromagnetic coupling in the monometallic chain one. Catalysis studies performed with these complexes (1-4) showed that they initiate ring opening polymerization (ROP) of ε-caprolactone (ε-CL) under solvent-free conditions and d,l-lactide in toluene at elevated temperatures. Polycaprolactone (PCL) and poly(d,l-lactide) (PLA) obtained from the polymerization reactions are of low molecular weights (858 for PCL and 602 Da for PLA for initiator 1) and polydispersity indices (typically 2.16 for PCL and 1.64 for PLA with 1 as the initiator). End group analysis of the polymers, determined by MALDI-ToF MS, indicates that the polymers have benzoate, hydroxyl, methoxy and cyclic end groups., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Olefin bonds participate in co-reaction with the benzoxazine functionality of the monomer and are one of the strategies used to affect the crosslink density of a polybenzoxazine network. In general, the double bond incorporation in starting material is usually catalyzed by expensive, rare earth metals affecting the sustainability of the reaction. The natural abundance of feedstocks with inherent double bonds may be a powerful platform for the development of novel greener structures, with potential applications in polymers. Here, we report the design, synthesis, and characterization of a biobased non-halogen flame retardant, consisting of naturally occurring phenols, eugenol (E), and cardanol (C). The presence of a covalently linked phosphazene (P) core allowed the synthesis of hexa-functional flame retardant molecules, abbreviated as EP and CP. The chemical structures of the synthesized EP and CP were confirmed by Fourier transform infrared (FTIR), nuclear magnetic resonance ( 1 H, 13 C, 31 P NMR), and single crystal XRD (only in the case of EP). Their polymerization with cardanol sourced tri-oxazine benzoxazine monomer, C-trisapm, was followed by FTIR, NMR, and DSC studies. The thermal stability and flame retardant properties of the hybrid phosphazene-benzoxazine copolymers was determined by thermogravimetry analysis (TGA), limiting oxygen index (LOI), vertical burning, and smoke density analyses. SEM images of the char residues of the polymers with or without the addition of reactive phosphazene molecules confirmed the intumescent flame retarding mechanism. Current work highlights the utility of sustainable origin non-halogen flame retardant (FR) molecules and their utility in polybenzoxazine chemistry., (Copyright © 2020 Appavoo, Amarnath and Lochab.)

Stimulus-responsive polymers have been used in improving the efficacy of medical diagnostics through different approaches including enhancing the contrast in imaging techniques and promoting the molecular recognition in diagnostic assays. This review overviews the mechanisms of stimulus-responsive polymers in response to external stimuli including temperature, pH, ion, light, etc. The applications of responsive polymers in magnetic resonance imaging, capture and purification of biomolecules through protein-ligand recognition and lab-on-a-chip technology are discussed.

The hydrogen-bonded arene ruthenium metalla-rectangle, [(p-cymene)2Ru2(OO∩OO)(UPy)2]2(4+), obtained from 1-(4-oxo-6-undecyl-1,4-dihydropyrimidin-2-yl)-3-(pyridin-4-ylmethyl)urea (UPy) and the dinuclear arene ruthenium clip (p-cymene)2Ru2(OO∩OO)Cl2 (OO∩OO = 2,5-dioxido-1,4-benzoquinonato), is investigated by means of solution-phase NMR spectroscopy. Rotating frame nuclear Overhauser effect measurements are used to probe the H-bond network that drives the UPy self-assembly as well as the full rectangular supramolecular system. An effective distance that takes into account both intra- and intermolecular polarization-transfer pathways is utilised for data analysis. The experimental findings are corroborated by DFT calculations of NMR parameters and internuclear distances, thus confirming the formation of a very stable tetranuclear metalla-assembly.