Freeform Fabrication System Research Articles

Design and experimental study on the freeform fabrication with polymer melt droplet deposition

Purpose3D printing based on additive manufacturing has advantages in manufacturing products with high geometrical complexity. However, there are many limitations to print plastic products with the existing commercial 3D printers. The polymer materials processing industry needs new devices which can satisfy the trend of processing individual units and small batch sizes of plastic parts.Design/methodology/approachIn this study, a freeform fabrication system with the method of polymer melt droplet deposition is proposed. The performance of this system under different conditions was studied by changing the operating parameters. Furthermore, the dimensional uniformity of droplets and their deposition process are analyzed, and a plastic sample was fabricated with this system as an example.FindingsThe results show a clear correlation between the processing parameters and the droplet diameter. In the experiment for examining the dimensional uniformity of the droplet, the droplets become spindles, and there appears a melt filament between the droplets. The variation of the droplet’s diameters is within 5 per cent. Furthermore, a successfully processed rectangular plastic sample verified the feasibility of this technology for the printing of plastic products.Originality/valueA freeform fabrication system with polymer melt droplet deposition is proposed, which can process a wide variety of materials in the form of standard granulates like injection molding or extrusion. Based on the principle of droplet deposition, multi-component or colorful materials can be printed.

Fabrication of mesoporous calcium silicate/calcium phosphate cement scaffolds with high mechanical strength by freeform fabrication system with micro-droplet jetting

In this study, we explored the feasibility of fabrication bioactive mesoporous calcium silicate/calcium phosphate cements (MCS/CPC) scaffolds with high mechanical strength by Freeform Fabrication System with Micro-Droplet Jetting. After preparation of ordered mesoporous calcium silicate (MCS) powder, ready-to-use MCS/CPC paste was formed by mixing calcium phosphate cement (CPC) powder and MCS powder with the binder polyvinyl alcohol (PVA) aqueous solution at a certain ratio of powder to liquid. MCS/CPC scaffolds with various architectures, pore sizes, and interconnectivity were then directly printed at room temperature using MCS/CPC paste. The mechanical strength, apatite formation, degradation rate, and cytocompatibility of the composite scaffolds were systematically investigated. The results showed that MCS/CPC paste exhibited outstanding printability to form MCS/CPC scaffolds. The hybrid MCS/CPC scaffolds with predefined pore size of 350 μm showed fast degradation rate, high mechanical strength, and good cytocompatibility. It was indicated that the hybrid MCS/CPC scaffolds might be a promising candidate for critical bone defect repair.

Fabrication of an osteochondral graft with using a solid freeform fabrication system

Current approaches for the engineering of osteochondral grafts are associated with poor tissue formation and compromised integration at the interface between the cartilage and bone layers. Many researchers have attempted to provide osteochondral grafts of combined cartilage and bone for osteochondral repair to help overcome the limitations of standard procedures. Solid freeform fabrication is recognized as a promising tool for creating tissue engineering scaffolds due to advantages such as superior interconnectivity and a highly porous structure. This study aimed to develop a three-dimensional plotting system to enable the manufacturing of a biphasic graft consisting cartilage and subchondral bone for application to osteochondral defects. The material advantages of both synthetic (poly L lactide-co-polyglycolide) and natural (alginate) polymers were combined for a supporting frame and cell printing. Specifically, in order to promote the maturity of the osteochondral graft in our study, cartilage-derived ECM (cECM) or hydroxyapatate (HA) substances blended with alginate was plotted together with human fetal cartilage-derived progenitor cells in the cartilage or subchondral bone layer under a multi-nozzle deposition system. Notably, a plotted biphasic graft shows good integration between cartilage and subchondral bone layers without structural separation. Furthermore, the non-toxicity of the cECM and HA substances were proved from a live/dead assay of plotted cell-laden alginate. A fabricated osteochondral graft with cECM and HA substances showed dominant cartilage and bone tissue formation in a differentiation assay. Future studies should be done to modify the alginate physical properties for long-lasting structural stability.

Fabrication and characterization of toughness-enhanced scaffolds comprising β-TCP/POC using the freeform fabrication system with micro-droplet jetting

A novel elastomeric material, poly(1,8-octanediol-co-citrate) (POC), has demonstrated tremendous versatility because of its advantageous toughness, tunable degradation properties, and efficient drug release capability. In this study, POC was used to improve the mechanical performance of β-tricalcium phosphate (β-Ca3(PO4)2, β-TCP). (3D) β-TCP/POC composite scaffolds were fabricated by a 3D printing technique based on the freeform fabrication system with micro-droplet jetting (FFS-MDJ). The physiochemical properties, compressive modulus, drug release behavior, and cell response of β-TCP/POC composite scaffolds were systematically investigated. The results showed that β-TCP/POC scaffolds had uniform macropores of 300–400 μm, porosity of approximately 45%, biodegradability in phosphate-buffered saline, and high compressive modulus of 50–75 MPa. With the incorporation of POC into β-TCP, the toughness of the composite scaffolds was improved significantly. Moreover, β-TCP/POC scaffolds exhibited sustained drug (ibuprofen (IBU)) release capability. Additionally, β-TCP/POC scaffolds facilitated C2C12 cell attachment and proliferation. It was indicated that the 3D-printed porous β-TCP/POC scaffolds with high compressive modulus and good drug delivery performance might be a promising candidate for bone defect repair.

Vector optimization of laser solid freeform fabrication system using a hierarchical mutable smart bee-fuzzy inference system and hybrid NSGA-II/self-organizing map

The purpose of current investigation is to develop a robust intelligent framework to achieve efficient and reliable operating process parameters for laser solid freeform fabrication (LSFF) process as a recent and ongoing topic of investigation. Firstly, based on mutable smart bee algorithm (MSBA) and fuzzy inference system (FIS) two models are developed to identify the clad hight (deposited layer thickness) and the melt pool depth as functions of scanning speed, laser power and mass powder. Using the obtained model, the well-known multiobjective evolutionary algorithm called non-dominated sorting genetic algorithm (NSGA-II) is used for multi-criterion optimization of LSFF process. According to the available reported information and also the author's experiments, it is observed that the obtained Pareto front is not justifiable since it fails to cover the entire Pareto hyper-volume due to the lack of intensified exploration. To tackle this deficiency, authors execute a post optimization process through utilizing a competitive unsupervised machine learning approach known as self-organizing map (SOM) with cubic spatial topology. Achieved results indicate that this grid based network is capable of enhancing the intensification of Pareto solutions since its synaptic weights successfully imitate the characteristics of non-dominated solutions (optimal values of mass powder, laser power and scanning speed). For extracting the corresponding objective functions of these non-dominated synaptic weights, MSBA---FIS is used again to map the operating parameters to objective functions space. After the termination of abovementioned procedures, a valuable archive, containing a set of non-dominated solutions, is obtained which lets the authors to make a deliberate engineering trade-off. Simulation experiments reveal that the proposed intelligent framework is highly capable to cope with complex engineering systems. Besides, it is observed that MSBA is more efficient in evolving the structure of hierarchical fuzzy inference system in comparison with classic hierarchical GA-FIS model. This rises from the simple structure of MSBA that turns it into a fast and robust algorithm for handling constraint distributed systems (i.e. hierarchical FIS in current investigation). The obtained results also indicate that the introduced intelligent framework is applicable for optimal design of complex engineering systems where there exists no analytical formulation that describes the phenomenon as well as information of optimal operating parameters.

Optimal design of laser solid freeform fabrication system and real-time prediction of melt pool geometry using intelligent evolutionary algorithms

With the rapid growth of laser applications and the introduction of high efficiency lasers (e.g. fiber lasers), laser material processing has gained increasing importance in a variety of industries. Among the applications of laser technology, laser cladding has received significant attention due to its high potential for material processing such as metallic coating, high value component repair, prototyping, and even low-volume manufacturing. In this paper, two optimization methods have been applied to obtain optimal operating parameters of Laser Solid Freeform Fabrication Process (LSFF) as a real world engineering problem. First, Particle Swarm Optimization (PSO) algorithm was implemented for real-time prediction of melt pool geometry. Then, a hybrid evolutionary algorithm called Self-organizing Pareto based Evolutionary Algorithm (SOPEA) was proposed to find the optimal process parameters. For further assurance on the performance of the proposed optimization technique, it was compared to some well-known vector optimization algorithms such as Non-dominated Sorting Genetic Algorithm (NSGA-II) and Strength Pareto Evolutionary Algorithm (SPEA 2). Thereafter, it was applied for simultaneous optimization of clad height and melt pool depth in LSFF process. Since there is no exact mathematical model for the clad height (deposited layer thickness) and the melt pool depth, the authors developed two Adaptive Neuro-Fuzzy Inference Systems (ANFIS) to estimate these two process parameters. Optimization procedure being done, the archived non-dominated solutions were surveyed to find the appropriate ranges of process parameters with acceptable dilutions. Finally, the selected optimal ranges were used to find a case with the minimum rapid prototyping time. The results indicate the acceptable potential of evolutionary strategies for controlling and optimization of LSFF process as a complicated engineering problem.

Biocompatibility and biodegradation studies of PCL/β-TCP bone tissue scaffold fabricated by structural porogen method

Three-dimensional printer (3DP) (Z-Corp) is a solid freeform fabrication system capable of generating sub-millimeter physical features required for tissue engineering scaffolds. By using plaster composite materials, 3DP can fabricate a universal porogen which can be injected with a wide range of high melting temperature biomaterials. Here we report results toward the manufacture of either pure polycaprolactone (PCL) or homogeneous composites of 90/10 or 80/20 (w/w) PCL/beta-tricalcium phosphate (β-TCP) by injection molding into plaster composite porogens fabricated by 3DP. The resolution of printed plaster porogens and produced scaffolds was studied by scanning electron microscopy. Cytotoxicity test on scaffold extracts and biocompatibility test on the scaffolds as a matrix supporting murine osteoblast (7F2) and endothelial hybridoma (EAhy 926) cells growth for up to 4 days showed that the porogens removal process had only negligible effects on cell proliferation. The biodegradation tests of pure PCL and PCL/β-TCP composites were performed in DMEM with 10 % (v/v) FBS for up to 6 weeks. The PCL/β-TCP composites show faster degradation rate than that of pure PCL due to the addition of β-TCP, and the strength of 80/20 PCL/β-TCP composite is still suitable for human cancellous bone healing support after 6 weeks degradation. Combining precisely controlled porogen fabrication structure, good biocompatibility, and suitable mechanical properties after biodegradation, PCL/β-TCP scaffolds fabricated by 3DP porogen method provide essential capability for bone tissue engineering.

Identifying the behaviour of laser solid freeform fabrication system using aggregated neural network and the great salmon run optimisation algorithm

Bio inspiration is a branch of artificial simulation science that shows pervasive contributions to variety of engineering fields such as automated pattern recognition, systematic fault detection, machine learning and applied optimisation. In this paper, a new bio-inspired optimisation algorithm which is the simulation of 'the great salmon run' (TGSR) is developed. Thereafter, it has been used to predict the efficient structure of an aggregated artificial neural network (AANN) to identify the behaviour of laser solid freeform fabrication (LSFF) system. Our experiments show that the combination of AANN and an appropriate supervised method is best suit for modelling cited engineering process. To prove the superiority of TGSR in both robustness and quality, it has been compared with most of the state-of-the-art optimisation techniques such as fast simulated annealing (FSA), parallel migrating genetic algorithm (PMGA), differential evolutionary with parent centric crossover (DEPCX), unified particle swarm optimisation (UPSO), shuffle frog leaping algorithm (SFLA), artificial bee colony (ABC), firefly algorithm (FA) and cuckoo search (CS). The obtained results confirm the acceptable potential of the proposed method to be applied on complex engineering systems.

Research on Microwave Sintering Process for High Strength HA Porous Scaffold

This paper investigated solid freeform fabrication(SFF) and microwave sintering processes of high strength HA porous scaffold. A newly developed SFF method called motor assisted micro-syringe freeform fabrication system was introduced to construct HA scaffolds. Sintering conditions that influenced the phases, microstructure and mechanical strength of scaffolds were discussed. Study of microstructure images and strength test results showed that densification and grain size were found to play an important role in determining the mechanical properties of sintered porous scaffolds, and microwave sintering process could get a sintered scaffold with small grain size and uniform structure more rapidly at lower sintering temperature than that of the conventional sintering. The fabricated HA scaffolds with controlled architecture (interconnected macro pore of 200-400μm, micro pore of 1-10μm within the rods) and improved mechanical properties (45.2MPa, 56.2% porosity ) may find potential applications in bone tissue engineering.

A novel sucrose porogen‐based solid freeform fabrication system for bone scaffold manufacturing

PurposeMusculoskeletal conditions are a major health concern in the USA because of a large aging population and increased occurrence of sport‐related injuries. Bone tissue engineering may offer a less painful alternative to traditional bone grafts with lower risk of infection. The purpose of this paper is to present a novel porogen‐based fabrication system for tissue engineering scaffolds using sucrose (C12H22O11) as the porogen building material.Design/methodology/approachA new solid freeform fabrication system has been developed and tested, which uses pressurized extrusion to print highly biocompatible and water soluble sucrose bone scaffold porogens (or negtives). Polycaprolactone (PCL) scaffolds are manufactured by injecting molten polymer into the porogens, and the porogens are subsequently dissolved with water. The resultant scaffolds demonstrate the defined porous structure designed into the sucrose porogen manufacturing computer‐aided design model.FindingsTo optimize the porogen manufacturing process, the viscosity of sucrose mixtures is measured. Design of experiments is used to plan and analyze the relationships between the porogen characteristics and the process parameters. Reservoir pressure and print head speed are identified as the dominant factors affecting sucrose flow rate and porogen strut diameter, respectively. The biocompatibility of the new system is assessed by in vitro cell culture testing. Endothelial hybridoma cells (EAhy 926) and osteoblasts (7F2) seeded on the fabricated PCL scaffolds adhered to the scaffold and proliferated over four to six days. Epifluorescence and scanning electron microscopy images reveal cell spreading and multiple layers of cells on the scaffold surface. The results demonstrated the potential of the structured sucrose porogen‐based fabrication method in manufacturing bone tissue scaffolds.Originality/valueThis paper describes the first time use of biomaterials‐sucrose to make scaffold porogens and how an injection molded biopolymer scaffold can then be received.

Novel scan path generation method based on area division for SFFS

A solid freeform fabrication (SFF) system using selective laser sintering (SLS) is currently recognized as a leading process of fabrication using variable materials, and SLS extends the application to machinery and automobiles. Due to the time delay in the sintering process, shrinkage and warping often occur. Curling also occurs due to laser and scan delays. These problems affect not only the accuracy of the fabricated product but also the total system efficiency. These deficiencies can be overcome by reducing the total processing time of the SFF system. To accomplish this, the laser scanning time, from mark (laser on) to jump (laser off), must be reduced as it contributes the major part of the total processing time. This can be done by employing area division scan path generation, which promotes digital efficiency. A simulation and an experiment was carried out in this study to evaluate the developed scan path method.

Fabrication of parts and their evaluation using a dual laser in the solid freeform fabrication system

A solid freeform fabrication (SFF) system using selective laser sintering (SLS) is currently recognized as a leading process for SLS extended application to machinery and automobiles, whose production involves the use of various materials. For the fabrication of a large surface using the SFF system, the dual-laser approach has been introduced in this paper. Since the building room is divided into two regions, each scan path for the dual-laser system is generated based on a single-laser scan path. The scan paths for both lasers have to be synchronized, and the mechanical strength of the large surface must be considered to prevent fracture at the interface region. This paper addresses the generation of a single-laser scan path for special cases such as those involving unnecessary scan points, and the generation of a dual-laser scan path according to various divided regions so to enhance the mechanical strength of the large surface. Moreover, the tensile strength of the specimen manufactured through single-laser scan path system has been compared with the specimen manufacture through dual-laser scan path and the effect of overlapping region with respect to tensile strength is also highlighted.

APPLICATION AND PERFORMANCE EVALUATION FOR THE DMS SYSTEM IN THE SLS PROCESS

A Solid Freeform Fabrication (SFF) system using Selective Laser Sintering (SLS) is currently recognized as a leading process and SLS extends the applications to machinery and automobiles due to the various materials employed. Especially, accuracy and processing time are very important factors when the desired shape is fabricated with Selective Laser Sintering (SLS), one of Solid Freeform Fabrication (SFF) system. In the convectional SLS process, laser spot size is fixed during laser exposing on the sliced figure. Therefore, it is difficult to accuracy and rapidly fabricates the desired shape. In this paper, to deal with those problems a SFF system having ability of changing spot size is developed. The system provides high accuracy and optimal processing time. Specifically, a variable beam expander is employed to adjust spot size for different figures on a sliced shape. Therefore, design and performance estimation of the SFF system employing a variable beam expander are achieved and the mechanism will be addressed to measure the real spot size generated from the variable beam expander. Also, the reduction of total processing time is an important issue in SFF system. A digital mirror system (DMS) is a system which scans the laser beam with different spot size. The spot size is selected based on the slicing section to decrease and accuracy of the process time and improve the processing efficiency. In this study, the optimal scan path generation for DMS will be addressed, and this development will improve the whole processing efficiency and accuracy through the scan efficiency by considering the existing scan path algorithm and heat energy distribution.

Electrowetting-based multi-microfluidics array printing of high resolution tissue construct with embedded cells and growth factors

To overcome limitations of current tissue fabrication methods, explore new biocompatible materials, and develop new biomimetic manufacturing process for soft tissue, we are developing a new technology, electrowetting-based microfluidics array printing, which will be used in a solid freeform fabrication (SFF) system to meet the challenges of high resolution manufacture of hydrogel scaffolds with dimension scale less than 10 µm, cell placement, growth factor delivery, and vascularization for soft tissue engineering. Preliminary work has been done on the biomaterials research, electrowetting printing, biomimetic modeling, scaffold fabrication, and system integration and control. This research is the first application of electrowetting on dielectric to tissue engineering and dispensing hydrogels.

Development and performance evaluation of solid freeform fabrication system by using dual laser sintering process

A solid freeform fabrication (SFF) system using selective laser sintering (SLS) is currently recognized as a leading process and SLS extends the application to machinery and automobiles due to the various materials employed. In order to develop a more elaborate and rapid system for fabricating large objects compared to existing SLS, this study employs a new selective dual-laser sintering process. It contains a three-axis, dynamic focusing scanner system for scanning large areas instead of the existing fθ lens used in commercial SLS. Therefore, the unique scanning path generation is necessary to eliminate the factors of quality deterioration in case of fabricating larger objects. Also, this paper will address development of a SFF system which employs the dual laser system and the unique scanning device. In the SLS, the sintering temperature, laser beam power and layer thickness have a great influence on sintering of the polymer. Experiments were performed to evaluate the effect of a scanning path and fabrication parameters on the sintering process and to fabricate the various three-dimensional objects using polymer powders.

Studies on Porous Titanium Alloy Implant Manufactured by Three Dimensional Solid Freeform Fabrication System

Titanium (Ti) alloys have emerged to become valuable biomaterials for biomedical and orthopedic applications due to their high strength to weight ratio, excellent biocompatibility and corrosion resistance. In this study, the authors utilized Solid Freeform Fabrication (SFF), also commonly known as a rapid prototyping technology to investigate a new porous three-dimensional (3D) Ti alloy implant. Elemental powders for producing a Ti-Al-Fe-Zr alloy were mechanically alloyed and blended with water soluble binder material. The blended powders were manufactured by Three Dimensional Printer (3DP), followed by debinding and sintering in an inert environment. The effects of process parameters on structural and geometrical requirements were assessed. Results from these investigations demonstrated that Ti alloys are promising biomaterials for near net shape fabrication of porous 3D implants, which retained their interconnected pore network. As an illustration, complex geometries of porous 3D Ti alloy specimens were manufactured as a demonstration of 3D SFF System.

Fab@Home: the personal desktop fabricator kit

PurposeSolid freeform fabrication (SFF) has the potential to revolutionize manufacturing, even to allow individuals to invent, customize, and manufacture goods cost‐effectively in their own homes. Commercial freeform fabrication systems – while successful in industrial settings – are costly, proprietary, and work with few, expensive, and proprietary materials, limiting the growth and advancement of the technology. The open‐source Fab@Home Project has been created to promote SFF technology by placing it in the hands of hobbyists, inventors, and artists in a form which is simple, cheap, and without restrictions on experimentation. This paper aims to examine this.Design/methodology/approachA simple, low‐cost, user modifiable freeform fabrication system has been designed, called the Fab@Home Model 1, and the designs, documentation, software, and source code have been published on a user‐editable “wiki” web site under the open‐source BSD License. Six systems have been built, and three of them given away to interested users in return for feedback on the system and contributions to the web site.FindingsThe Fab@Home Model 1 can build objects comprising multiple materials, with sub‐millimeter‐scale features, and overall dimensions larger than 20 cm. In its first six months of operation, the project has received more than 13 million web site hits, and media coverage by several international news and technology magazines, web sites, and programs. Model 1s are being used in a university engineering course, a Model 1 will be included in an exhibit on the history of plastics at the Science Museum London, UK, and kits can now be purchased commercially.Research limitations/implicationsThe ease of construction and operation of the Model 1 has not been well tested. The materials cost for construction (US$2,300) has prevented some interested people from building systems of their own.Practical implicationsThe energetic public response to the Fab@Home project confirms the broad appeal of personal freeform fabrication technology. The diversity of interests and desired applications expressed by the public suggests that the open‐source approach to accelerating the expansion of SFF technology embodied in the Fab@Home project may well be successful.Originality/valueFab@Home is unique in its goal of popularizing and advancing SFF technology for its own sake. The RepRap project in the UK predates Fab@Home, but aims to build machines which can make most of their own parts. The two projects are complementary in many respects, and fruitful exchanges of ideas and designs between them are expected.

On the manufacturability of scaffold mould using a 3D printing technology

PurposeTo investigate the effect of operation parameters and printing configuration on the manufacturability of moulds in the manufacture of tissue engineering scaffolds using a 3D printing system.Design/methodology/approachThe scaffold moulds were built using proprietary biocompatible materials using a modified Solidscape T66 ink‐jet printing system. The manufacturability of biological scaffold moulds has been investigated in terms of resolution, accuracy, and minimum and maximum manufacturable features.FindingsThe results demonstrated that the 3D system used in this study is able to fabricate structures with high reproducibility and flexibility. It was found that thermal degradation of BioSupport material had an adverse effect on resolution and accuracy of moulds printed for scaffold manufacturing. The maximum features, including maximum length and height, are geometrical dimension and orientation dependent. The system could produce a longer and higher features when the mould was aligned perpendicular to the axis of the mill than that parallel to the axis of the mill. The bigger the cross‐sectional area, the longer/higher the manufacturable feature the machine can produce. The accuracy and resolution are attributed to the size of the molten droplet of BioBuild that caused local melting of the support layer and which partially diffused into the support layer.Research limitations/implicationsThe results provide a guide to the design and fabrication of precision scaffold for tissue engineering using biocompatible materials.Originality/valueThis paper describes a method and process to evaluate the manufacturability of a scaffold mould using 3D printing technique. The limits to mould design are established, it could be extended to other solid freeform fabrication systems for effective operation and precision control.

Optimization of accumulating sequence for solid freeform fabrication system

Solid freeform fabrication system has recently been used in many practical areas for fast manufacturing of a concept model. Prototype model can easily be made using a solid freeform fabrication system at the product-developing step for checking and correcting the probable design error. The system considered for this paper basically consists of laser cutting apparatus and material handling equipment. The basic principle of the process is such that 3D CAD data is sliced into thin 2D layers, each slice is cut by laser source along the profile of the 2D layer information and the slices are stacked for sintering in a furnace. Material for the process initially was raw ceramic green tape and becomes hard enough for practical use

Development of Industrial SFF System Using a New Selective Dual-Laser Sintering Process

In order to develop more elaborate and speedy system for large objects than existing selective laser sintering (SLS), this study applies a new selective dual-laser sintering process. It contains a 3-axis dynamic focusing scanner system for scanning large area instead of the existing fθ lens. As sintering parameters, the sintering temperature, the laser beam power and the layer thickness have a great influence on sintering of the polymer and metal powder. This paper will address the development of a solid freeform fabrication (SFF) system employing the dual laser system. Experiments were performed to evaluate the effect of a scanning path and to fabricate the large-sized object.