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In this work, shape-customized scaffolds based on waterborne polyurethane-urea (WBPUU) were prepared via the combination of direct ink writing 3D-printing and freeze-drying techniques. To improve the printing performance of the ink and guarantee a good shape fidelity of the scaffold, cellulose nanocrystals (CNC) were added during the synthesis of the WBPUU and some of the printed constructs were immersed in CaCl2 prior to the freeze-drying process to promote ionic crosslinking between calcium ions and the polyurethane. The results showed that apart from allowing the ink to be successfully printed, obtaining scaffolds with good shape fidelity, the addition of the CNC resulted in a greater homogeneity of the porous structure as well as an increase of the swelling capacity of the scaffolds. Additionally, the CNC has a reinforcement effect in the printed systems, presenting a higher compression modulus as the CNC content increases. In the case of samples crosslinked by calcium ions, a rigid shell was observed by scanning electron microscopy, which resulted in stiffer scaffolds that presented a lower water absorption capacity as well as an enhancement of the thermal stability. These results showed the potential of this type of post-printing process to tune the mechanical properties of the scaffold, thus widening the potential of this type of material. [ABSTRACT FROM AUTHOR]

In order to continue the development of inks valid for cold extrusion 3D printing, waterborne, polyurethane–urea (WBPUU) based inks with cellulose nanofibers (CNF), as a rheological modulator, were prepared by two incorporation methods, ex situ and in situ, in which the CNF were added after and during the synthesis process, respectively. Moreover, in order to improve the affinity of the reinforcement with the matrix, modified CNF was also employed. In the ex situ preparation, interactions between CNFs and water prevail over interactions between CNFs and WBPUU nanoparticles, resulting in strong gel-like structures. On the other hand, in situ addition allows the proximity of WBPUU particles and CNF, favoring interactions between both components and allowing the formation of chemical bonds. The fewer amount of CNF/water interactions present in the in situ formulations translates into weaker gel-like structures, with poorer rheological behavior for inks for 3D printing. Stronger gel-like behavior translated into 3D-printed parts with higher precision. However, the direct interactions present between the cellulose and the polyurethane–urea molecules in the in situ preparations, and more so in materials reinforced with carboxylated CNF, result in stronger mechanical properties of the final 3D parts. [ABSTRACT FROM AUTHOR]

• TPU residues from livestock sector were mechanically recycled. • TPU waste was processed using traditional and advanced technologies. • Thermal and mechanical degradation was more severe as reprocessing cycles increased. • The filament obtained after a single processing stage was suitable for 3D printing. • Electrospun mats of continuous microfibers were directly obtained from TPU waste. In this work different ways to valorise discarded ear tags made of TPU from livestock sector were studied. This singular residue does not require separation from other plastics like other industrial and urbane wastes, which could contribute to simplify its management. Firstly, mechanical processing was carried out by several cycles of consecutive extrusion and injection processes. The material obtained in each process was characterized using different physical, chemical and mechanical characterization techniques in order to study the degradation as a consequence of processing cycles. Thereafter, suitable filaments for 3D printing were obtained and the effect of infill pattern in the mechanical properties of the printed pieces was investigated. Besides, an electrospun mat constituted by TPU waste microfibers was successfully obtained by electrospinning, and its morphology together with superficial and mechanical properties were characterized. Results showed that these applications were suitable options to valorise TPU waste consisting of discarded ear tags. [ABSTRACT FROM AUTHOR]

In this work, polycaprolactone–polyethylene glycol (PCL–PEG) based waterborne polyurethane–urea (WBPUU) inks have been developed for an extrusion-based 3D printing technology. The WBPUU, synthesized from an optimized ratio of hydrophobic polycaprolactone diol and hydrophilic polyethylene glycol (0.2:0.8) in the soft segment, is able to form a physical gel at low solid contents. WBPUU inks with different solid contents have been synthesized. The rheology of the prepared systems was studied and the WBPUUs were subsequently used in the printing of different pieces to demonstrate the relationship between their rheological properties and their printing viability, establishing an optimal window of compositions for the developed WBPUU based inks. The results showed that the increase in solid content results in more structured inks, presenting a higher storage modulus as well as lower tan δ values, allowing for the improvement of the ink's shape fidelity. However, an increase in solid content also leads to an increase in the yield point and viscosity, leading to printability limitations. From among all printable systems, the WBPUU with a solid content of 32 wt% is proposed to be the more suitable ink for a successful printing performance, presenting both adequate printability and good shape fidelity, which leads to the realization of a recognizable and accurate 3D construct and an understanding of its relationship with rheological parameters. [ABSTRACT FROM AUTHOR]

3D printing has exponentially grown in popularity due to the personalization of each printed part it offers, making it extremely beneficial for the very demanding biomedical industry. This technique has been extensively developed and optimized and the advances that now reside in the development of new materials suitable for 3D printing, which may open the door to new applications. Fused deposition modeling (FDM) is the most commonly used 3D printing technique. However, filaments suitable for FDM must meet certain criteria for a successful printing process and thus the optimization of their properties in often necessary. The aim of this work was to prepare a flexible and printable polyurethane filament parting from a biocompatible waterborne polyurethane, which shows potential for biomedical applications. In order to improve filament properties and printability, cellulose nanofibers and graphene were employed to prepare polyurethane based nanocomposites. Prepared nanocomposite filaments showed altered properties which directly impacted their printability. Graphene containing nanocomposites presented sound enough thermal and mechanical properties for a good printing process. Moreover, these filaments were employed in FDM to obtained 3D printed parts, which showed good shape fidelity. Properties exhibited by polyurethane and graphene filaments show potential to be used in biomedical applications. [ABSTRACT FROM AUTHOR]

This work explores the preparation of a bioactive ink suitable for direct ink writing (DIW) 3D printing by adding extract obtained from Salvia officinalis L. during the synthesis of a waterborne polyurethane urea (WBPUU). Additionally, to guarantee a successful printing performance, cellulose nanocrystals (CNC), a well-known rheology modulator, have been added after the synthesis process. In order to predict the behaviour of the inks in DIW, the rheological properties of the inks with and without the Salvia extract and the CNC have been studied. The results showed that the incorporation of Salvia extract into the WBPUU ink resulted in a decrease of the viscosity, yield point and storage modulus, obtaining an ink that cannot maintain the shape after being printed. On the contrary, the incorporation of the CNC into the WBPUU/ Salvia ink increased the aforementioned rheological parameters leading to the obtaining of pieces presenting a good shape fidelity without compromising their printability. Finally, scaffolds were prepared from the printed pieces by freeze-drying technique and were tested against Gram negative Escherichia coli and Gram positive Staphylococcus aureus. The scaffolds containing CNC and Salvia showed bactericide behaviour against both bacteria, which was not seen in the WBPUU matrix, confirming the bioactive capacity of this ink. [Display omitted] • A printable ink has been prepared based on a waterborne polyurethane urea, cellulose nanocrystals and Salvia extract. • Addition of cellulose nanocrystals improves the shape fidelity of the inks resulting in self-sustainable 3D printed pieces. • Incorporation of Salvia extract provides antibacterial properties against Escherichia coli and Staphylococcus aureus. [ABSTRACT FROM AUTHOR]