The incidence of peripheral nerve injuries is on the rise and the current gold standard for treatment of such injuries is nerve autografting. Given the severe limitations of nerve autografts which ...include donor site morbidity and limited supply, neural guide conduits (NGCs) are considered as an effective alternative treatment. Conductivity is a desired property of an ideal NGC. Reduced graphene oxide (rGO) possesses several advantages in addition to its conductive nature such as high surface area to volume ratio due to its nanostructure and has been explored for its use in tissue engineering. However, most of the works reported are on traditional 2D culture with a layer of rGO coating, while the native tissue microenvironment is three‐dimensional. In this study, PCL/rGO scaffolds are fabricated using electrohydrodynamic jet (EHD‐jet) 3D printing method as a proof of concept study. Mechanical and material characterization of the printed PCL/rGO scaffolds and PCL scaffolds was done. The addition of rGO results in softer scaffolds which is favorable for neural differentiation. In vitro neural differentiation studies using PC12 cells were also performed. Cell proliferation was higher in the PCL/rGO scaffolds than the PCL scaffolds. Reverse transcription polymerase chain reaction and immunocytochemistry results reveal that PCL/rGO scaffolds support neural differentiation of PC12 cells.
As a promising additive manufacturing method, direct energy deposition has been widely used to fabricate complex thin-walled parts. However, some defects such as uneven layer surface and excessive ...build-ups always occur in this process. In this study, a high-fidelity model adopting a novel laser/powder source is developed to simulate the detailed multi-layer deposition process. With layer surfaces being tracked in real-time, laser source model incorporates local incidence angle and defocusing amount to adjust absorbed energy and beam radius on the track surfaces. The powder catchment efficiency varies with the defocusing amount timely. The simulations demonstrate that build-ups are mainly induced by unstable linear powder feed rate and worsen due to laser/powder defocusing and accumulated heat. The layer surface unevenness results from powder positive defocusing, while molten pool dynamics, laser positive defocusing and accumulated heat plays a supplementary role. Eliminating methods are proposed based on the simulations and validated by experiments.
Bone defects and diseases are devastating, and can lead to severe functional deficits or even permanent disability. Nevertheless, orthopedic implants and scaffolds can facilitate the growth of ...incipient bone and help us to treat bone defects and diseases. Currently, a wide range of biomaterials with distinct biocompatibility, biodegradability, porosity, and mechanical strength is used in bone‐related research. However, most orthopedic implants and scaffolds have certain limitations and diverse complications, such as limited corrosion resistance, low cell proliferation, and bacterial adhesion. With recent advancements in materials science and nanotechnology, metallic and metallic oxide nanoparticles have become the subject of significant interest as they offer an ample variety of options to resolve the existing problems in the orthopedic industry. More importantly, these nanoparticles possess unique physicochemical and mechanical properties not found in conventional materials, and can be incorporated into orthopedic implants and scaffolds to enhance their antimicrobial ability, bioactive molecular delivery, mechanical strength, osteointegration, and cell labeling and imaging. However, many metallic and metallic oxide nanoparticles can also be toxic to nearby cells and tissues. This review article will discuss the applications and functions of metallic and metallic oxide nanoparticles in orthopedic implants and bone tissue engineering.
Tissue engineering has showed promising results in restoring diseased tendon tissue functions. Herein, a hybrid three-dimensional (3D) porous scaffold comprising an outer portion rolled from an ...electrohydrodynamic jet printed poly(ɛ-caprolactone) (PCL) fiber mesh, and an inner portion fabricated from uniaxial stretching of a heat-sealed PCL tube, was developed for tendon tissue engineering (TE) application. The outer portion included three layers of micrometer-scale fibrous bundles (fiber diameter: ~25 µm), with an interconnected spacing and geometric anisotropy along the scaffold length. The inner portion showed orientated micro-ridges/grooves in a parallel direction to that of the outer portion. Owning to the addition of the inner portion, the as-fabricated scaffold exhibited comparable mechanical properties to those of the human patellar tendon in terms of Young’s modulus (~227 MPa) and ultimate tensile stress (~50 MPa). Compared to the rolled electrospun fibers, human tenocytes cultured in the tendon scaffolds showed increased cellular metabolism. Furthermore, the 3D tendon scaffold resulted in up-regulated cell alignment, cell elongation and formation of collagen type I. These results demonstrated the potential of mechanically-enhanced 3D fibrous scaffold for applications in tendon TE, with desired cell alignment and functional differentiation.
Tendon refers to a band of tough, regularly arranged, and connective tissue connecting muscle and bone, transferring strength from muscle to bone, and enabling articular stability and movement. The ...limitations of natural tendon grafts motivate the scaffold‐based tissue engineering (TE) approaches, which aim to build patient‐specific biological substitutes that can repair the damaged or diseased tissues. Advances in engineering and knowledge of chemistry and biology have brought forth numerous fibre‐based technologies, including electrospinning, electrohydrodynamic jet printing, electrochemical alignment technique, and other fibre‐assembly technologies, which enable the fabrication of tendon tissue structure in 3‐dimension. Textile techniques such as knitting and braiding have also been performed based on the fibrous materials to produce more complex structure. These scaffolds showed great similarity with native tendons in architectural features, mechanical properties, and facilitate biological functionality such as cellular adhesion, ingrowth, proliferation, and differentiation towards tendon tissue. Herein, we review the techniques that have been used to assemble fibres into scaffolds for tendon TE application. The morphological structures, mechanical properties, materials, degradation characteristics, and biological activities of the induced scaffolds were compared. The existing challenges and future prospects of fibre‐based tendon TE have also been discussed.
This paper aims to improve the surface quality of 316L stainless steel parts manufactured by selective laser melting (SLM) using dry mechanical-electrochemical polishing (DMECP). DMECP is an advanced ...surface finishing method combining the advantages of both mechanical and electrochemical polishing techniques in a more environmentally friendly manner. In this paper, the SLM process-related defects causing poor surface quality are analysed first. The material removal mechanism of DMECP is investigated to continuously remove the oxide layers formed during polishing. Surface morphology and roughness evolution under different polishing conditions are characterised. The top surface roughness can be reduced by over 91% from 8.72 μm to 0.75 μm compared to side surface by over 93% from 12.10 to 0.80 μm. The material removal on the top surface is more efficient than that on the side surface under the same polishing condition. The secondary defects formed during polishing can be removed using mechanical polishing mode. The chemical element composition of the polished surface exhibits almost identical content to the initial 316L powders. Compared with the initial dark and rough surfaces, the results validate the capability of DMECP as an effective tool to improve the SLM surface quality and achieve a mirror finish.
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•Dry mechanical-electrochemical polishing (DMECP) is applied to finish selective laser melted (SLMed) surfaces.•The submicron-level surface roughness is achieved on SLMed metal parts.•Defects on SLMed 316L stainless steel are analysed and removed.•The relationship between polishing parameters and surface quality is established.•The material removal cycle and mechanism of DMECP are elucidated.
•Melted state detection by monitoring with plume and spatter signatures.•Distinctive plume and spatter signatures among different melting processes.•Plume and spatter signature variation with ...changing laser power and scanning speed.•During melting, laser power plays a more decisive role than scanning speed.
Plume-spatter signatures during Selective Laser Melting (SLM) are a good indication of their corresponding melt states. It is important to build the relationship between the signatures and defects for the SLM process monitoring. In this work, the mechanism of the plume and the spatter was investigated for the melted state detection. Single tracks were produced on the 304L stainless steel powder with monitoring by a Near-Infrared (NIR) camera. Signatures of the plume and spatter during the SLM process were collected for the analyses of the characteristics. Results provided the properties of the plume, the spatter, and the entire target region of the image as well as their relations with the melted tracks. Plume-spatter signatures had distinct behaviors among the underheating, normal, and overheating melting processes. In the melted state variation, laser power played a more decisive role than scanning speed by changing laser energy density. This work contributed to the feasibility and possibility for the SLM process monitoring by the plume and spatter signatures.
Several attempts have been made to fabricate esophageal tissue engineering scaffolds. However, most of these scaffolds possess randomly oriented fibres and uncontrollable pore sizes. In order to ...mimic the native esophageal tissue structure, electro-hydrodynamic jetting (e-jetting) was used in this study to fabricate scaffolds with aligned fibres and controlled pore size. A hydrophilic additive, Pluronic F127 (F127), was blended with polycaprolactone (PCL) to improve the wettability of the scaffolds and hence the cell adhesion. PCL/F127 composite scaffolds with different weight ratios (0–12%) were fabricated. The wettability, phase composition, and the mechanical properties of the fabricated scaffolds were investigated. The results show that the e-jetted scaffolds have controllable fibres orientated in two perpendicular directions, which are similar to the human esophagus structure and suitable pore size for cell infiltration. In addition, the scaffolds with 8% F127 exhibited better wettability (contact angle of 14°) and an ultimate tensile strength (1.2 MPa) that mimics the native esophageal tissue. Furthermore, primary human esophageal fibroblasts were seeded on the e-jetted scaffolds. PCL/F127 scaffolds showed enhanced cell proliferation and expression of the vascular endothelial growth factor (VEGF) compared to pristine PCL scaffolds (1.5- and 25.8- fold increase, respectively;
P
< 0.001). An
in vitro
wound model made using the PCL/F127 scaffolds showed better cell migration than the PCL scaffolds. In summary, the PCL/F127 e-jetted scaffolds offer a promising strategy for the esophagus tissue repair.
Support structures are needed due to the complexities of induced structural, thermal and process factors in Selective Laser Melting (SLM). To date, little systematic study is found to unveil the ...support removability by a post-machining process. This paper presents an experimental study of removing 316L stainless steel cone and block supports by milling. The effect of different supports is identified by the variation in the microhardness distribution and microstructure of the workpieces. The milling performance of cone and block supports at different cutting depths is studied on the surface finish, surface roughness, milling force, and tool wear and chip formation. The cone supports are subjected to severe collapse, whilst the block supports are mainly removed by localized shearing. The milling force and specific cutting energy of cutting block supports are lower than that of cone supports, and so is the tool wear. A finite element method (FEM) model is developed to explain the removal mechanisms. The results of this study provide an essential reference and unique insight into removal of metal support structures. Moreover, the removability of supports, which is derived from the post-processing stage, should be considered as a new factor in the support design for additive manufacturing.
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•The effect of different support structures is identified by the variation in the microhardness distribution and microstructure.•A systematic study unveils the metal support removability in selective laser melting (SLM) by milling.•Milling performance between cone and block support structures is compared at different cutting depths.•A finite element method (FEM) model is developed to explain the support removal mechanisms.
This paper focuses on the influence mechanism of process parameters on the geometry morphology and microstructure characteristic of single-track and multi-track 316L/CuSn10 multiple materials ...manufactured by laser powder bed fusion (LPBF). The width of single-track increases with the increase of laser power and layer thickness, and decreases with the increase of scanning speed. Both variations in the copper content and wetting angle of the molten pool were investigated. In addition, the comparison of defect characteristics shows that the scanning speed and layer thickness have a greater influence on the formation of single cracks. The traces of Marangoni convection are observed directly in the centre of the molten pool due to the difference in microstructure between 316L and CuSn10 alloys. It is found that the copper penetration cracks appear on the steel side at the molten pool bottom. Moreover, fine grains appear in the copper-rich region, and the large-angle grain boundary distribution seems to be the reason for the concentration of dislocations. Four types of crack formation mechanisms are found in the cross section of the multi-track: crack formation inside the molten pool, passing through the track boundary, extending to the steel substrate, and copper penetration cracks.
•316L/CuSn10 single and multiple track manufactured by LPBF was investigated.•Thermal stress and liquid copper penetration are the main cause of microcracks.•Copper diffusion causes fine grains, distributed LAG boundaries and dislocations.•Four types of cracks were found in the cross section of the multiple track.
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