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.
BackgroundThe spectrum of indications for the use of membranes and scaffolds in the field of oral and maxillofacial surgery includes, amongst others, guided bone regeneration (GBR). Currently available membrane systems face certain disadvantages such as difficult clinical handling, inconsistent degradation, undirected cell growth and a lack of stability that often complicate their application. Therefore, new membranes which can overcome these issues are of great interest in this field.MethodsIn this pilot study, we investigated polycaprolactone (PCL) scaffolds intended to enhance oral wound healing by means of melt electrospinning writing (MEW), which allowed for three-dimensional (3D) printing of micron scale fibers and very exact fiber placement. A singular set of box-shaped scaffolds of different sizes consisting of medical-grade PCL was examined and the scaffolds’ morphology was evaluated via scanning electron microscopy (SEM). Each prototype sample with box sizes of 225 μm, 300 μm, 375 μm, 450 μm and 500 μm was assessed for cytotoxicity and cell growth by seeding each scaffold with human osteoblast-like cell line MG63.ResultsAll scaffolds demonstrated good cytocompatibility according to cell viability, protein concentration, and cell number. SEM analysis revealed an exact fiber placement of the MEW scaffolds and the growth of viable MG63 cells on them. For the examined box-shaped scaffolds with pore sizes between 225 μm and 500 μm, a preferred box size for initial osteoblast attachment could not be found.ConclusionsThese well-defined 3D scaffolds consisting of medical-grade materials optimized for cell attachment and cell growth hold the key to a promising new approach in GBR in oral and maxillofacial surgery.
Mechanotransduction is important for mesenchymal regeneration and differentiation. Exaggerated high or very low impact yields pathological outcome resulting in fracture or tissue atrophy. Pathological strain in animal models was described but tools to dissect the respective stimuli and downstream pathways are limited. We expand the analytical tools to describe DNA strain response elements in a reporter gene approach. Deletion constructs of the human cysteine-rich protein 61 (CYR61) promoter were cloned into luciferase vectors and stably transfected into human telomerase-immortalised mesenchymal stem cells (hMSC-TERT). Cells were mechanically stimulated with variable frequencies, amplitudes and durations. Promoter activity was determined as well as CYR61 mRNA and protein expression. In silico promoter analysis identified putative transcription factor binding sites, one of which was a cAMP response element, verified by electrophoretic mobility shift assay. We demonstrate for the first time that the activity of promoter regions is inhibited in low, but stimulated in high frequency stimulations. We conclude that by varying conditions of mechanical strain it is possible to characterize stimulatory versus inhibitory strain on cellular levels. Our work may be helpful in future studies to dissect the molecular pathways of physiological versus pathological strain and may have implications for clinical exercise based treatment strategies.
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