Trabecular scaffolds created using micro CT guided fused deposition modeling

Free form fabrication and high resolution imaging techniques enable the creation of biomimetic tissue engineering scaffolds. A 3D CAD model of canine trabecular bone was produced via micro CT and exported to a fused deposition modeler, to produce polybutylene terephthalate (PBT) trabeculated scaffolds and four other scaffold groups of varying pore structures. The five scaffold groups were divided into subgroups (n=6) and compression tested at two load rates (49 N/s and 294 N/s). Two groups were soaked in a 25 °C saline solution for 7 days before compression testing. Micro CT was used to compare porosity, connectivity density, and trabecular separation of each scaffold type to a canine trabecular bone sample. At 49 N/s the dry trabecular scaffolds had a compressive stiffness of 4.94±1.19 MPa, similar to the simple linear small pore scaffolds and significantly more stiff (p<0.05) than either of the complex interconnected pore scaffolds. At 294 N/s, the compressive stiffness values for all five groups roughly doubled. Soaking in saline had an insignificant effect on stiffness. The trabecular scaffolds matched bone samples in porosity; however, achieving physiologic connectivity density and trabecular separation will require further refining of scaffold processing.     

Trabecular scaffolds created using micro CT guided fused deposition modeling

Free form fabrication and high resolution imaging techniques enable the creation of biomimetic tissue engineering scaffolds. A 3D CAD model of canine trabecular bone was produced via micro CT and exported to a fused deposition modeler, to produce polybutylene terephthalate (PBT) trabeculated scaffolds and four other scaffold groups of varying pore structures. The five scaffold groups were divided into subgroups (n = 6) and compression tested at two load rates (49 N/s and 294 N/s). Two groups were soaked in a 25 °C saline solution for 7 days before compression testing. Micro CT was used to compare porosity, connectivity density, and trabecular separation of each scaffold type to a canine trabecular bone sample. At 49 N/s the dry trabecular scaffolds had a compressive stiffness of 4.94 ± 1.19 MPa, similar to the simple linear small pore scaffolds and significantly more stiff (p < 0.05) than either of the complex interconnected pore scaffolds. At 294 N/s, the compressive stiffness values for all five groups roughly doubled. Soaking in saline had an insignificant effect on stiffness. The trabecular scaffolds matched bone samples in porosity; however, achieving physiologic connectivity density and trabecular separation will require further refining of scaffold processing.     

Compressive behaviour of Neovius Triply Periodic Minimal Surface cellular structure manufactured by fused deposition modelling

ABSTRACT

Compressive behaviour of Triply Periodic Minimal Surface type Neovius structure is investigated. The structure was manufactured by Fused Deposition Modelling (FDM) Additive Manufacturing technology in ABS material. The Neovius cellular structures with four different unit cell sizes of 8, 10, 12 and 14?mm with the volume fractions of 15%, 20% and 25% were investigated. Morphology of the samples was analysed through optical microscopy, and the pore and strut sizes were compared for the designed model and FDM samples. During the compression test, the Neovius structure showed the oscillating behaviour of the stress–strain curve with the larger unit cell size showing fracture across multiple layers in different orientations. Optical analysis of the struts after the compression tests showed that struts are the weakest link with the highest stressed area and the fracture was seen initiated at the struts. Both compressive modulus and strength increased with the increase in volume fraction.     

Fabrication of modeling platform for fused deposition modeling using vacuum casting

This study presents a cost‐effective approach for rapid fabricating modeling platforms utilized in fused deposition modeling three‐dimensional printing system. A small‐batch production of modeling platforms about 20 pieces can be obtained economically through silicone rubber mold using vacuum casting without applying the plastic injection molding. The air venting systems is crucial for fabricating modeling platform using vacuum casting. Modeling platforms fabricated can be used for building rapid prototyping model after sandblasting. This study offers industrial value because it has both time‐effectiveness and cost‐effectiveness.     

From design of bio-based biocomposite electrospun scaffolds to osteogenic differentiation of human mesenchymal stromal cells

Electrospinning coupled with electrospraying provides a straightforward and robust route toward promising electrospun biocomposite scaffolds for bone tissue engineering. In this comparative investigation, four types of poly(3-hydroxybutyrate) (PHB)-based nanofibrous scaffolds were produced by electrospinning a PHB solution, a PHB/gelatin (GEL) mixture or a PHB/GEL/nHAs (hydroxyapatite nanoparticles) mixed solution, and by electrospinning a PHB/GEL solution and electrospraying a nHA dispersion simultaneously. SEM and TEM analyses demonstrated that the electrospun nHA-blended framework contained a majority of nHAs trapped within the constitutive fibers, whereas the electrospinning-electrospraying combination afforded fibers with a rough surface largely covered by the bioceramic. Structural and morphological characterizations were completed by FTIR, mercury intrusion porosimetry, and contact angle measurements. Furthermore, an in vitro investigation of human mesenchymal stromal cell (hMSC) adhesion and proliferation properties showed a faster cell development on gelatin-containing scaffolds. More interestingly, a long-term investigation of hMSC osteoblastic differentiation over 21 days indicate that hMSCs seeded onto the nHA-sprayed scaffold developed a significantly higher level of alkaline phosphatase activity, as well as a higher matrix biomineralization rate through the staining of the generated calcium deposits: the fiber surface deposition of nHAs by electrospraying enabled their direct exposure to hMSCs for an efficient transmission of the bioceramic osteoinductive and osteoconductive properties, producing a suitable biocomposite scaffold for bone tissue regeneration.     

Osteogenic differentiation and mineralization in fibre-reinforced tubular scaffolds: theoretical study and experimental evidences

The development of composite scaffolds with well-organized architecture and multi-scale properties (i.e. porosity, degradation) represents a valid approach for achieving a tissue-engineered construct capable of reproducing the medium- and long-term in vitro behaviour of hierarchically complex tissues such as spongy bone. To date, the implementation of scaffold design strategies able to summarize optimal scaffold architecture as well as intrinsic mechanical, chemical and fluid transport properties still remains a challenging issue. In this study, poly ɛ-caprolactone/polylactid acid (PCL/PLA) tubular devices (fibres of PLA in a PCL matrix) obtained by phase inversion/salt leaching and filament winding techniques were proposed as cell instructive scaffold for bone osteogenesis. Continuous fibres embedded in the polymeric matrix drastically improved the mechanical response as confirmed by compression elastic moduli, which vary from 0.214 ± 0.065 to 1.174 ± 0.143 MPa depending on the relative fibre/matrix and polymer/solvent ratios. Moreover, computational fluid dynamic simulations demonstrated the ability of composite structure to transfer hydrodynamic forces during in vitro culture, thus indicating the optimal flow rate conditions that, case by case, enables specific cellular events—i.e. osteoblast differentiation from human mesenchymal stem cells (hMSCs), mineralization, etc. Hence, we demonstrate that the hMSC differentiation preferentially occurs in the case of higher perfusion rates—over 0.05 ml min^–1—as confirmed by the expression of alkaline phosphate and osteocalcin markers. In particular, the highest osteopontin values and a massive mineral phase precipitation of bone-like phases detected in the case of intermediate flow rates (i.e. 0.05 ml min^–1) allows us to identify the best condition to stimulate the bone extracellular matrix in-growth, in agreement with the hydrodynamic model prediction. All these results concur to prove the succesful use of tubular composite as temporary device for long bone treatment.     

Anisotropy in tensile properties and fracture behaviour of 316L stainless steel parts manufactured by fused deposition modelling and sintering

Fused deposition modelling and sintering (FDMS) is a potential metal additive manufacturing technology due to its low cost and high efficiency. The mixture of metal powder and binder goes through heating, extrusion, debinding and sintering processes to produce the compact finished part. However, it is generally believed that parts produced by FDMS possess poor and anisotropic tensile properties, which always attributes to the weak interlayer combination. The current work aimed to enhance tensile properties and better understand the anisotropic fracture behavior of the 316L stainless steel prepared by FDMS. By process optimization, the yield strength and ultimate tensile strength obtained in this work are increased by 26.1% and 15.2%, based on the highest performance reported in previous studies. According to the ultimate tensile strength, the performance difference between the horizontal and vertical directions has been reduced to 27%. Furthermore, the experimental results indicated that the clustered irregular shape holes evolved from primitive voids prefer to distribute in the build direction, resulting in anisotropic tensile performance. It is suggested that the mechanical properties could be improved by applying a smaller extrusion diameter and rolling-assisted printing. In addition, the current FDMS parts show qualified performance for producing the customized and small batch components.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-022-00402-4     

Mechanical property characterization and simulation of fused deposition modeling Polycarbonate parts

Building end-use functional parts with additive manufacturing (AM) technologies is a challenging task. Several factors influence their surface finish, dimensional accuracy, mechanical properties and cost. Their orientation inside the building chamber is one of the most significant factors in AM processes. When using Fused Deposition Modeling (FDM) to build such parts, additional factors must be considered.This paper aims to accomplish two purposes: finding a good model to simulate FDM parts and correlating a finite element analysis (FEA) simulation with physical testing.The first objective was achieved by experimental tensile test of specimens to determine the nine mechanical constants that defines the stiffness matrix of an orthotropic material. Three Young’s modulus, three Poisson’s ratio and three shear modulus were experimentally obtained as well as yield tensile and ultimate strength of each specimen.A simple part was designed and manufactured in different orientations to be physically tested and simulated to achieve the second objective. Polycarbonate (PC) was used as part material. Combined loading including bending and torsion was used. Differences on mechanical response were observed during the physical test of the parts depending on the building direction. Conclusions comment results and the convenience of using a different constitutive model depending on the design and use specifications.     

Additive manufacturing of carbon fiber reinforced thermoplastic composites using fused deposition modeling

Additive manufacturing (AM) technologies have been successfully applied in various applications. Fused deposition modeling (FDM), one of the most popular AM techniques, is the most widely used method for fabricating thermoplastic parts those are mainly used as rapid prototypes for functional testing with advantages of low cost, minimal wastage, and ease of material change. Due to the intrinsically limited mechanical properties of pure thermoplastic materials, there is a critical need to improve mechanical properties for FDM-fabricated pure thermoplastic parts. One of the possible methods is adding reinforced materials (such as carbon fibers) into plastic materials to form thermoplastic matrix carbon fiber reinforced plastic (CFRP) composites those could be directly used in the actual application areas, such as aerospace, automotive, and wind energy. This paper is going to present FDM of thermoplastic matrix CFRP composites and test if adding carbon fiber (different content and length) can improve the mechanical properties of FDM-fabricated parts. The CFRP feedstock filaments were fabricated from plastic pellets and carbon fiber powders for FDM process. After FDM fabrication, effects on the tensile properties (including tensile strength, Young's modulus, toughness, yield strength, and ductility) and flexural properties (including flexural stress, flexural modulus, flexural toughness, and flexural yield strength) of specimens were experimentally investigated. In order to explore the parts fracture reasons during tensile and flexural tests, fracture interface of CFRP composite specimens after tensile testing and flexural testing was observed and analyzed using SEM micrograph.     

Osteogenic potential of cryopreserved human bone marrow-derived mesenchymal cells after thawing in culture

Cryopreserved human bone marrow-derived mesenchymal cells (hBMCs) were thawed and replated in culture dishes. Viability of the cells immediately after thawing was 98%. When the cells were cultured in the presence or absence of dexamethasone, the cells proliferated to reach confluency at culture day 7. The cells treated with dexamethasone formed abundant mineralized nodules at their extracellular regions after about culture day 14, while the cultures without dexamethasone did not exhibit bone formation. The calcein uptake into the extracellular matrix layer was detected in the dexamethasone-treated cells with the increase in fluorescent intensity with culture periods but not in the nontreated cells. These results suggest that human bone marrow-derived mesenchymal cells retain bone-forming capability even after cryopreservation/thawing.     

Cell proliferation,viability, and in vitro differentiation of equine mesenchymal stem cells seeded on bacterial cellulose hydrogel scaffolds

The culture of multipotent mesenchymal stem cells on natural biopolymers holds great promise for treatments of connective tissue disorders such as osteoarthritis. The safety and performance of such therapies relies on the systematic in vitro evaluation of the developed stem cell-biomaterial constructs prior to in vivo implantation. This study evaluates bacterial cellulose (BC), a biocompatible natural polymer, as a scaffold for equine-derived bone marrow mesenchymal stem cells (EqMSCs) for application in bone and cartilage tissue engineering. An equine model was chosen due to similarities in size, load and types of joint injuries suffered by horses and humans. Lyophilized and critical point dried BC hydrogel scaffolds were characterized using scanning electron microscopy (SEM) to confirm nanostructure morphology which demonstrated that critical point drying induces fibre bundling unlike lyophilisation. EqMSCs positively expressed the undifferentiated pluripotent mesenchymal stem cell surface markers CD44 and CD90. The BC scaffolds were shown to be cytocompatible, supporting cellular adhesion and proliferation, and allowed for osteogenic and chondrogenic differentiation of EqMSCs. The cells seeded on the BC hydrogel were shown to be viable and metabolically active. These findings demonstrate that the combination of a BC hydrogel and EqMSCs are promising constructs for musculoskeletal tissue engineering applications.     

Modelling and estimation of tensile behaviour of polylactic acid parts manufactured by fused deposition modelling using finite element analysis and knowledge-based library

With the rise of the Fused Deposition Modelling (FDM) industry, a better understanding of the relationship between FDM process parameters and mechanical behaviour —especially tensile behaviour —of designed parts is needed to enable development of industry specifications. To optimise and control the deposition process, modelling and predicting the mechanical behaviour of a manufactured part under various process parameters is required. Existing numerical modelling approaches either require input of extensive experimental data or lack cross-validation. In this paper, the mechanical behaviour of polylactic acid manufactured parts under tensile conditions was studied both experimentally and numerically, and the effects of printing pattern and infill density on ultimate tensile strength (UTS)-weight ratio and the modulus of elasticity were evaluated. The experimental results revealed that minimising air gaps and using a triangular infill pattern are beneficial for obtaining a good UTS/weight ratio. Of all the specimens considered, the 20% triangular pattern had the highest UTS/weight ratio. The numerical investigation revealed that the meso-structure approach described in this paper can be used to predict the modulus of elasticity and the breaking point, and does not require input from the unidirectional specimen stress-strain curves. Finally, the meso-structure numerical model and artificial neural network were used to construct a knowledge-based library that can predict the modulus of elasticity of FDM manufactured polylactic acid with three infill patterns and any infill density with an average prediction error of 14.80%.     

高分子基功能复合材料的熔融沉积成型研究进展

3D打印又称增材制造技术,是基于材料、机械控制、计算机软件等多学科交叉的先进制造技术,可得到传统加工不能制备的形状复杂制件.熔融沉积成型(FDM)是目前最通用的3D打印技术之一,具有设备简单、成本低、操作便捷等特点,广泛应用于航空航天、医疗、汽车工业等领域.本文介绍了国内外3D打印技术的整体布局、发展和规划,总结了常见...     

铁镍合金/聚乳酸复合材料的熔融沉积成形制备及其电磁吸收性能和力学性能

在制备铁镍合金(FeNi50)/聚乳酸(PLA)复合线材的基础上,利用熔融沉积成形(FDM)制备出FeNi50/PLA复合材料.采用SEM、振动样品磁强计、矢量网络分析仪和万能试验机研究了FeNi50对复合材料微观形貌、磁性、电磁性能和力学性能的影响,并讨论了其反射损耗.研究发现,复合材料的饱和磁化强度和电磁性能随着F...     

Metabolic and histological analysis of mesenchymal stem cells grown in 3-D hyaluronan-based scaffolds

Sheep mesenchymal stem cells (MSCs) were isolated and expanded using the principle of plastic adherence. Their identity as progenitor cells was confirmed by induction along the osteoblastic lineage using osteogenic supplements and observation of calcific deposits by von Kossa staining. MSCs were seeded onto two types of hyaluronan-based cylindrical scaffolds in high concentrations and cultured for varying time points up to three weeks. Culture medium was supplied using the following conditions: statically, on a shaker, by stirring with a magnetic stirrer or by perfusion in a tubular flow circuit. Total cell metabolism was assessed by MTT assay and the quality of cell coverage and matrix formation observed by SEM and histological analysis of thin sections of the constructs. Perfusion culture was established as the most appropriate culturing conditions, with cell metabolism increasing by approximately 300% over three weeks. The coverage of the scaffold surface was very good and the deposition of collagenous matrix was superior in these conditions compared to the, static and other dynamic culture conditions.     

Optimization of fused deposition modeling process parameters:a review of current research and future prospects

Fused deposition modeling(FDM) is one of the most popular additive manufacturing technologies for various engineering applications.FDM process has been introduced commercially in early 1990 s by Stratasys Inc.,USA.The quality of FDM processed parts mainly depends on careful selection of process variables.Thus,identification of the FDM process parameters that significantly affect the quality of FDM processed parts is important.In recent years,researchers have explored a number of ways to improve the mechanical properties and part quality using various experimental design techniques and concepts.This article aims to review the research carried out so far in determining and optimizing the process parameters of the FDM process.Several statistical designs of experiments and optimization techniques used for the determination of optimum process parameters have been examined.The trends for future FDM research in this area are described.     

Stress analyses of GaN film manufactured by ECR plasma-enhanced chemical vapor deposition

The residual stress in GaN film grown on (0001) α-Al₂O₃ substrate at 450-500 °C by electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR-PECVD) is investigated. Macro deformation analysis reveals a low level of compressive stress, from −0.46 GPa to −1.03 GPa in GaN/Sapphire. Low growth temperature and high N₂:TMG flow ratio contributes to decreasing of residual stress. A blue shift for the edge peak in photoluminescence analysis (PL) is related to compressive stress. Roughness statistics and AFM morphology of GaN film show a fine smoothness and uniform surface. All results demonstrate that ECR-PECVD process is favorable for depositing GaN films at low temperature.     

Chondrogenic differentiation of mesenchymal stem cells in a leakproof collagen sponge

A three-dimensional culture of mesenchymal stem cells (MSCs) in a porous scaffold has been developed as a promising strategy for cartilage tissue engineering. The chondrogenic differentiation of MSCs derived from human bone marrow was studied by culturing the cells in a novel scaffold constructed of leakproof collagen sponge. All the surfaces of the collagen sponge except the top were wrapped with a membrane that has pores smaller than the cells to protect against cell leakage during cell seeding. The cells adhered to the collagen, distributed evenly, and proliferated to fill the spaces in the sponge. Cell seeding efficiency was greater than 95%. The MSCs cultured in the collagen sponge in the presence of TGF-β3 and BMP6 expressed a high level of genes encoding type II and type X collagen, sox9, and aggrecan. Histological examination by HE staining indicated that the differentiated cells showed a round morphology. The extracellular matrices were positively stained by safranin O and toluidine blue. Immunostaining with anti-type II collagen and anti-cartilage proteoglycan showed that type II collagen and cartilage proteoglycan were detected around the cells. These results suggest the chondrogenic differentiation of MSCs when cultured in the collagen sponge in the presence of TGF-β3 and BMP6.     

Mechanical characteristics of oil palm fiber reinforced thermoplastics as filament for fused deposition modeling (FDM)

Fibers are increasingly in demand for a wide range of polymer composite materials. This study's purpose was the development of oil palm fiber (OPF) mixed with the thermoplastic material acrylonitrile butadiene styrene (ABS) as a composite filament for fused deposition modeling (FDM). The mechanical properties of this composite filament were then analyzed. OPF is a fiber extracted from empty fruit bunches, which has proved to be an excellent raw material for biocomposites. The cellulose content of OPF is 43%-65%, and the lignin content is 13%-25%. The composite filament consists of OPF (5%, mass fraction) in the ABS matrix. The fabrication procedure included alkalinizing, drying, and crushing the OPF to develop the composite. The OPF/ABS materials were prepared and completely blended to acquire a mix of 250 g of the material for the composition. Next, the FLD25 filament extrusion machine was used to form the OPF/ABS composite into a wire. This composite filament then was used in an FDM-based 3D printer to print the specimens. Finally, the printed specimens were tested for mechanical properties such as tensile and flexural strength. The results show that the presence of OPF had increased the tensile strength and modulus elasticity by approximately 1.9% and 1.05%, respectively. However, the flexural strength of the OPF/ABS composite had decreased by 90.6% compared with the virgin ABS. Lastly, the most significant outcome of the OPF/ABS composite was its suitability for printing using the FDM method.The full text can be downloaded at https://link.springer.com/content/pdf/10.1007%2Fs40436-019-00287-w.pdf     

Coupling of gelatin to inner surfaces of pore walls in spongy alginate-based scaffolds facilitates the adhesion,growth and differentiation of human bone marrow mesenchymal stromal cells

We have developed a novel wide-pore scaffold for cell 3D culturing, based on the technology of freeze-drying of Ca-alginate and gelatin. Two different preparation methodologies were compared: (i) freeze-drying of Na-alginate + gelatin mixed solution followed by the incubation of dried polymer in saturated ethanolic solution of CaCl₂; (ii) freeze-drying of the Na-alginate solution followed by the chemical “activation” of polysaccharide core with divinylsulfone with subsequent gelatin covalent attachment to the inner surfaces of pore walls. The scaffolds produced using the first approach did not provide adhesion and proliferation of human bone marrow mesenchymal stromal cells (MSCs). Conversely, the second approach allowed to obtain scaffolds with a high adherence ability for the cells. When cultured within the latter type of scaffold, MSCs proliferated and were able to differentiate into adipogenic, osteogenic and chondrogenic cell lineages, in response to specific induction stimuli. The results indicate that Ca-alginate wide-pore scaffolds with covalently attached gelatin could be useful for stem cell-based bone, cartilage and adipose tissue engineering.