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Design of advanced biobased photocurable formulations: from dynamic covalent network to composite scaffold for tissue engineering
Full text linkL'abstract è presente nell'allegato / the abstract is in the attachmen
Vanillin‐Derived Thermally Reprocessable and Chemically Recyclable Schiff‐Base Epoxy Thermosets
Full text linkAbstract The paradigm shift from traditional petroleum‐based non‐recyclable thermosets to biobased repeatedly recyclable materials is required to move toward circular bioeconomy. Here, two mechanically and chemically recyclable extended vanillin‐derived epoxy thermosets are successfully fabricated by introduction of Schiff‐base/imine covalent dynamic bonds. Thermoset 1 (T1) is based on linear monomer 1 (M1) with two alcohol end groups and one imine bond, while thermoset 2 (T2) is based on branched monomer 2 (M2) with three alcohol end‐groups and three imine‐groups. Thermosets are obtained by reaction of monomer 1 (M1) and monomer 2 (M2) with trimethylolpropane triglycidyl ether. The structure of the monomers and thermosets is confirmed by nuclear magnetic resonance and Fourier transform infrared spectroscopic techniques. Both thermosets exhibit good thermal and mechanical properties and they are stable in common organic solvents. Furthermore, they can be thermally reprocessed through compression molding with good recovery of the mechanical properties. Last but not least, the fabricated thermosets can be rapidly and completely chemically recycled to water‐soluble aldehydes and amines by imine hydrolysis at room temperature in 0.1 m HCl solution. This is promising for development of future materials with multiple circularity by different routes
Sustainable Bio-Based UV-Cured Epoxy Vitrimer from Castor Oil
Full text linkVitrimers brought new properties in thermosets by allowing their reshaping, self-healing, reprocessing, and network rearrangement without changing structural integrity. In this study, epoxidized castor oil (ECO) was successfully used for the straightforward synthesis of a bio-based solvent-free vitrimer. The synthesis was based on a UV-curing process, which proceeded at low temperatures in the absence of any solvents, and within a short time. Real time Fourier-transformed infrared spectroscopy and photo-DSC were exploited to monitor the cationic photocurable process. The UV-cured polymer networks were able to efficiently undergo thermo-activated bond exchange reactions due to the presence of dibutyl phosphate as a transesterification catalyst. Mechanical properties, thermal resistance, glass transition temperature, and stress relaxation were investigated as a function of the amount of transesterification catalyst. Mechanical properties were determined by both DMTA and tensile tests. Glass transition temperature (Tg) was evaluated by DMTA. Thermal stability was assessed by thermogravimetric analysis, whilst vitrimeric properties were studied by stress relaxation experiments. Overall, the ECO-based vitrimer showed high thermal resistance (up to 200 °C) and good mechanical properties (elastic modulus of about 10 MPa) and can therefore be considered as a promising starting point for obtaining more sustainable vitrimers
Thiol-Ene Photopolymerization and 3D Printing of Non-Modified Castor Oil Containing Bio-Based Cellulosic Fillers
Full text linkThe photopolymerization process in 3D printing is considered greener once it
involves a fast reaction and low energy consumption. Various reactions for photopolymerization can be used nowadays, but a special one is the thiol-ene “click” reaction that
occurs in equimolar concentrations of thiol and alkene groups. In this sense, solventfree photopolymerizable formulations were prepared to contain non-modified castor oil,
Trimethylolpropane tris(3-mercapto propionate), and cellulosic fillers from hemp, tagua,
and walnut. All formulations presented conversions higher than 70% and fast polymerization rates. Moreover, the filled formulations presented excellent curing depths in fewer
seconds of light exposition, an important factor for their applicability in 3D printing.
Furthermore, the hemp filler formulation presented the highest crosslinking density as
determined by the DMTA, and was selected for printing two complex structures (pyramid
and honeycomb shape). The rheology analysis showed that the formulations had adequate
viscosities for the printer. Lastly, all polymers presented at least 97% bio-based contents,
with gel contents superior to 96%
Cationic UV-curing of bio-based epoxidized castor oil vitrimers with electrically conductive properties
Full text linkThe growing appeal of carbon nanotube composites in the contemporary market derives from their exceptional thermal and chemical stability, coupled with electrical conductivity. In this study, we combined these salient features with a biobased epoxy matrix having vitrimeric properties, hence being reprocessable and resheapable, to obtain a biobased conductive coating. Epoxidised castor oil (ECO) was chosen as a monomer precursor for the straightforward synthesis. The synthesis relied on a cationic UV-curing process, embedding the conductive carbon nanotubes in the matrix. Photo DSC and transmission FTIR analysis were conducted to determine the final conversion of the epoxy rings in the cationic photocuring process. Thermo-mechanical properties were evaluated by tensile tests, and DMTA. Thermal stability was assessed by TGA. Dielectric spectroscopy confirmed increased electrical conductivity in the presence of increasing CNT content, reaching a percolation threshold at 0.5 phr of CNTs. Vitrimeric properties were proved by stress relaxation experiments, and the UV-cured composite underwent a thermo-activated transesterification reaction starting from 70 °C, catalysed by dibutyl phosphate. Overall, the ECO-CNT composite showed high thermal resistance (up to 400 °C) electrical conductivity with 0.5 phr CNT concentration, and vitrimeric properties. The study can be, therefore, considered a promising starting point to obtain sustainable biobased and electrically conductive vitrimers
3D-Printed Biobased Porous Polymer Scaffolds Reinforced with Bioactive Glasses by High Internal Phase Emulsion Polymerization
No full textSilanized and Cu-doped bioactive glass as filler for biobased photocurable 3D printed scaffolds
Full text linkThis research explores and characterizes a photo-curable, biobased resin reinforced with bioactive glass (BGs) to produce scaffolds 3D-printed for tissue engineering applications. Through a sol-gel were synthesized two types of BGs, standard and copper-doped. The BGs were silanized to enhance resin compatibility. Transmission FTIR, photoDSC and photoreology fully characterized the UV-curing behaviour of the resin formulation. 3D-printed scaffolds’ mechanical properties were evaluated through tensile tests and dynamic mechanical thermal analysis (DMTA). At the same time, morphology and dispersion of the BGs inside the polymer matrix were assessed utilizing Scanning Electron Microscopy (SEM). Bioactivity was evaluated by immersing the scaffolds in a simulated body fluid (SBF) to evaluate hydroxyapatite (HAp) formation. Antibacterial activity tests following the
ISO 22196 protocol demonstrated 57 % fewer viable Staphylococcus aureus cells adhered to the surfaces of A7I3-sil and A7I3–Cu-sil compared to the control. SEM and 3D-reconstructed images showed reduced bacterial aggregations (from 13-14 % to 8–9%) and Z-maximum (from 4.5 μm to 2.5 μm). On the treated samples most bacterial cells appeared as single and sporadic cells, making them more easily removable with mild antibiotics. This work aims to enhance bone scaffold design that combines mechanical strength with bioactivity using sustainable and biobased materials. The findings provide a foundation for future developments in tissue engineering
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
UV-Cured Bio-Based Acrylated Soybean Oil Scaffold Reinforced with Bioactive Glasses
Full text linkIn this study, a bio-based acrylate resin derived from soybean oil was used in combination with a reactive diluent, isobornyl acrylate, to synthetize a composite scaffold reinforced with bioactive glass particles. The formulation contained acrylated epoxidized soybean oil (AESO), isobornyl acrylate (IBOA), a photo-initiator (Irgacure 819) and a bioactive glass particle. The resin showed high reactivity towards radical photopolymerisation, and the presence of the bioactive glass did not significantly affect the photocuring process. The 3D-printed samples showed different properties from the mould-polymerised samples. The glass transition temperature Tg showed an increase of 3D samples with increasing bioactive glass content, attributed to the layer-by-layer curing process that resulted in improved interaction between the bioactive glass and the polymer matrix. Scanning electron microscope analysis revealed an optimal distribution on bioactive glass within the samples. Compression tests indicated that the 3D-printed sample exhibited higher modulus compared to mould-synthetized samples, proving the enhanced mechanical behaviour of 3D-printed scaffolds. The cytocompatibility and biocompatibility of the samples were evaluated using human bone marrow mesenchymal stem cells (bMSCs). The metabolic activity and attachment of cells on the samples’ surfaces were analysed, and the results demonstrated higher metabolic activity and increased cell attachment on the surfaces containing higher bioactive glass content. The viability of the cells was further confirmed through live/dead staining and reseeding experiments. Overall, this study presents a novel approach for fabricating bioactive glass reinforced scaffolds using 3D printing technology, offering potential applications in tissue engineering
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