The electrohydrodynamic stabilization of direct-written fluid jets is explored to design and manufacture tissue engineering scaffolds based on their desired fiber dimensions. It is demonstrated that melt electrowriting can fabricate a full spectrum of various fibers with discrete diameters (2-50 µm) using a single nozzle. This change in fiber diameter is digitally controlled by combining the mass flow rate to the nozzle with collector speed variations without changing the applied voltage. The greatest spectrum of fiber diameters was achieved by the simultaneous alteration of those parameters during printing. The highest placement accuracy could be achieved when maintaining the collector speed slightly above the critical translation speed. This permits the fabrication of medical-grade poly(ε-caprolactone) into complex multimodal and multiphasic scaffolds, using a single nozzle in a single print. This ability to control fiber diameter during printing opens new design opportunities for accurate scaffold fabrication for biomedical applications.
Additive manufacturing with electrohydrodynamic direct writing is a promising approach for the production of polymeric microscale objects. In this study we investigate the stability of one such process, melt electrospinning writing, to maintain accurate placement of the deposited fibre throughout the entire print. The influence of acceleration voltage and feeding pressure on the deposited poly(ε-caprolactone) fibre homogeneity is described, and how this affects the variable lag of the jet drawn by the collector movement. Three classes of diameter instabilities were observed that led to poor printing quality: (1) temporary pulsing, (2) continuous pulsing, and (3) regular long bead defects. No breakup of the electrified jet was observed for any of the experiments. A simple approach is presented for the melt electrospinning user to evaluate fibre writing integrity, and adjust the processing parameters accordingly to achieve reproducible and constant diameter fibres.
Melt processing is routinely used to fabricate medical polymeric devices/implants for clinical reconstruction and can be incorporated into quality systems procedures for medical device manufacture. As additive manufacturing (AM) becomes increasingly used for biomaterials and biofabrication, the translation of new, customizable, medical devices to the clinic becomes paramount. Melt processing is therefore a distinguishable group within AM that provides an avenue to manufacture scaffolds/implants with a clinical end-point. Three key melt processing AM technologies are highlighted in this review: melt micro-extrusion, selective laser sintering and melt electrospinning writing. The in vivo (including clinical) outcomes of medical devices and scaffolds made with these processes are reviewed. Together, they encompass the melt AM of scaffold architectures with feature sizes and resolutions ranging from 800 nm up to 700 μm.
Melt electrowriting (MEW) is an additive manufacturing (AM) technique using thermoplastic polymers to produce microscale structures, including scaffolds for tissue engineering. MEW scaffolds have, in general, high porosities and can be designed with different fiber diameters, spacings, and laydown patterns. The need for a reliable method for scaffold characterization is essential for quality assurance and research purposes. In this study, we describe the use of submicrometer X-ray tomography for the generation of local thickness maps of volume porosity of 16 different scaffold groups, comprising 2 diameter groups, 2 fiber spacing groups, and 4 different laydown patters (0/90°, 0/60/120°, 0/45/90/135°, and 0/30/60/90/120/150°), all made using a custom-built MEW printer with medical-grade poly(ɛ-caprolactone). The results showed a porosity range between 77.7% and 90.7% for all the scaffolds. Moreover, the influence of the scaffold regularity and flatness in the more regular pore shapes (0/90°, 0/60/120°) lead to the shift of the local thickness graph to one side, and thus the prevalence of one pore size. This nondestructive method for MEW scaffold characterization overcomes the limitations of microscopic methods of pore shape and size estimation. Impact Statement Melt electrowriting is an AM technology that bridges the gap between solution electrospinning and melt microextrusion technologies. It can be applied to biomaterials and tissue engineering by making a spectrum of scaffolds with various laydown patterns at dimensions not previously studied. Using submicrometer X-ray tomography, a “fingerprint” of porosity for such scaffolds can be obtained and used as an important measure for quality control, to ensure that the scaffold fabricated is the one designed and allows the selection of specific scaffolds based on desired porosities.
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