Freeform Fabrication Method Research Articles

A Structure Property Processing Comparison of Cold rolled PM Copper and Cold Gas Dynamically Sprayed Copper

Cold gas dynamic spray processing (cold spray) is a solid-state material deposition process used for coating and repair processes in many alloy systems. Cold spray has long been proposed as a potential method for freeform fabrication. The cold spray process imparts great deformation to the impacting particles, affecting the final properties of the deposit through work hardening, grain refinement and inter-particle bonding. For the purpose of demonstrating the feasibility of cold spray as a viable freeform fabrication method, the microstructure and hardness of bulk cold sprayed samples were characterized in as received and annealed condition, then compared to cold rolled material, which was previously vacuum hot pressed from the same powder stock used in spraying. Microstructure was analyzed via scanning electron microscopy and electron channeling contrast imaging to assess grain refinement and thermal annealing response in the cold sprayed and cold rolled materials. Vickers micro hardness was measured to assess the effects of cold spray impact on the properties of bulk, as-sprayed copper relative to cold rolled copper. In postannealed materials, greater hardness is achieved with the cold spray process through the suspected mechanism of grain refinement unachievable in the rolling process.

Tissue engineering bone-ligament complexes using fiber-guiding scaffolds

Regeneration of bone-ligament complexes destroyed due to disease or injury is a clinical challenge due to complex topologies and tissue integration required for functional restoration. Attempts to reconstruct soft-hard tissue interfaces have met with limited clinical success. In this investigation, we manufactured biomimetic fiber-guiding scaffolds using solid free-form fabrication methods that custom fit complex anatomical defects to guide functionally-oriented ligamentous fibers in vivo. Compared to traditional, amorphous or random-porous polymeric scaffolds, the use of perpendicularly oriented micro-channels provides better guidance for cellular processes anchoring ligaments between two distinct mineralized structures. These structures withstood biomechanical loading to restore large osseous defects. Cell transplantation using hybrid scaffolding constructs with guidance channels resulted in predictable oriented fiber architecture, greater control of tissue infiltration, and better organization of ligament interface than random scaffold architectures. These findings demonstrate that fiber-guiding scaffolds drive neogenesis of triphasic bone-ligament integration for a variety of clinical scenarios.

Evaluation of the effect of computed tomography scan protocols and freeform fabrication methods on bone biomodel accuracy

To assess the effect of computed tomography (CT) scan protocols (radiation amounts) and fabrication methods on biomodel accuracy and variability. Cadaveric femur of a Basset Hound. Retroreconstructions (n = 158) were performed of 16 original scans and were visually inspected to select 17 scans to be used for biomodel fabrication. Biomodels of the 17 scans were made in triplicate by use of 3 freeform fabrication processes (stereolithography, fused deposition modeling, and 3-D printing) for 153 models. The biomodels and original bone were measured by use of a coordinate measurement machine. Differences among fabrication methods accounted for 2% to 29% of the total observed variation in inaccuracy and differences among method-specific radiation configurations accounted for 4% to 44%. Biomodels underestimated bone length and width and femoral head diameter and overestimated cortical thickness. There was no evidence of a linear association between thresholding adjustments and biomodel accuracy. Higher measured radiation dose led to a decrease in absolute relative error for biomodel diameter and for 4 of 8 cortical thickness measurements. The outside dimensions of biomodels have a clinically acceptable accuracy. The cortical thickness of biomodels may overestimate cortical thickness. Variability among biomodels was caused by model fabrication reproducibility and, to a lesser extent, by the radiation settings of the CT scan and differences among fabrication methods.

A comparative study of the physical and mechanical properties of porous hydroxyapatite scaffolds fabricated by solid freeform fabrication and polymer replication method

A novel porous scaffold designed for application as a bone substitute, with a structure containing three-dimensional (3D) pore channels in a hydroxyapatite (HA) scaffold, was fabricated using a combination of a solid freeform fabrication (SFF) and cast in a mold using freezing casting method. This study was performed to evaluate the physical and biomechanical properties of the HA scaffolds fabricated by SFF and using polymer replication method (PRM), one of the conventional methods. Although the phase composition and porosity of these two scaffolds are similar, their external shape and mechanical property were different. All of the fabricated scaffolds showed similar patterns through X-ray diffraction. The difference between porosities of two HA scaffolds were not statistically significant (P>0.05). However, the average compressive strength of the scaffold fabricated by SFF was 14.6 MPa, and that of the scaffold fabricated using polymer replication was 3.56MPa (P<0.05). It was confirmed that SFF fabrication could have a relatively higher mechanical property than PRM fabrication at the same porosity.

Pore Independent Crack Propagation of Glass-Alumina Functionally Graded Materials

Abstract Crack propagation of glass-alumina functionally graded materials prepared by a novel freeform fabrication method was investigated. Pores were intentionally introduced by partial decomposition of poly vinyl alcohol gel. Preferential distribution of pores adjacent the alumina particles is confirmed due to the integrated liquid-phase sintering process, especially the migration of the activated alumina interfaces towards the equilibrium state. Crack propagation and distribution were directly observed by scanning electron microscopy. Cracks propagate through the weakly bonded interfaces which finally cause the glass matrix to fracture. However, pores have little effect on the crack propagation.

Free form fabricated features on CoCr implants with and without hydroxyapatite coating in vivo: a comparative study of bone contact and bone growth induction

The current study evaluates the in vivo response to free form fabricated cobalt chromium (CoCr) implants with and without hydroxyapatite (HA) plasma sprayed coatings. The free form fabrication method allowed for integration of complicated pyramidal surface structures on the cylindrical implant. Implants were press fit into the tibial metaphysis of nine New Zealand white rabbits. Animals were sacrificed and implants were removed and embedded. Histological analysis, histomorphometry and electron microscopy studies were performed. Focused ion beam was used to prepare thin sections for high-resolution transmission electron microscopy examination. The fabricated features allowed for effective bone in-growth and firm fixation after 6 weeks. Transmission electron microscopy investigations revealed intimate bone-implant integration at the nanometre scale for the HA coated samples. In addition, histomorphometry revealed a significantly higher bone contact on HA coated implants compared to native CoCr implants. It is concluded that free form fabrication in combination with HA coating improves the early fixation in bone under experimental conditions.

Influence of Liquid Phase Migration on Intermittent Extrusion of Aqueous Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Paste

Extrusion Freeform Fabrication Process (EFF) is an environmentally friendly solid freeform fabrication method that uses aqueous pastes to fabricate ceramic-based components. The Liquid Phase Migration (LPM) causes variation in liquid content and consequently problems in the paste extrusion. To get uniform ceramics parts with desired composition, the LPM should be avoided in extrusion process. This paper investigated the influence of LPM on extrusion process for aqueous alumina paste in EFF process. It shows that the liquid phase migration occurs in Freeform Extrusion Fabrication process and has a strong impact on extrusion pressure. The LPM can be characterized by the extrusion pressure-ram displacement profiles. The liquid phase migration becomes more serious in intermittent extrusion at low ram velocity.

Effect of processing parameters and microstructural defects on fatigue properties of direct metal laser sintered bronzeâ nickel parts

Production of bronze–nickel parts was undertaken by solid freeform fabrication method involving direct metal laser sintering (DMLS). Sintering speed, scan spacing and hatch pattern were considered as effective process variables governing the quality of parts manufactured. Two values were chosen for each of these process variables and tests for studying their effect on fatigue cycles failure using Taguchi technique. To understand the, generally, observed scatter in mechanical properties of DMLS parts, specimens produced under different processing conditions were also subjected to microstructural examination by optical microscopy and scanning electron microscopy. Microstructural defects include regions containing micro- as well as macrosegregation of bronze which cause the observed scatter in mechanical properties of DMLS parts. The likely physical reasons for the occurrence of these microstructural defects have been explained. From the analysis of results of fatigue test, it has been concluded by contribution of different processing parameters.

Synthesis of topologically-ordered open-cell porous magnesium

The interest in porous light metals has grown rapidly in recent years with the widespread development of synthesis methods for porous aluminium and titanium. However, methods for preparing porous magnesium (Mg) have received the least attention, especially with topologically-ordered architectures. The aim of this letter is to report on an indirect solid free-form fabrication method for the processing of open-cell porous Mg with controllable macroscopic architectures. Preliminary investigations into the accuracy and limitations of the process are reported. It is found that the method is capable of replicating highly accurate porous structures (~ 5–12% error) with macroscopic features as fine as 0.8 mm.

In vitro biocompatibility of titanium alloy discs made using direct metal fabrication

Custom orthopedic implants may be generated using free-form fabrication methods (FFF) such as electron beam melting (EBM). EBM FFF may be used to make solid metal implants whose surface is often polished using CNC machining and porous scaffolds that are usually left unpolished. We assessed the in vitro biocompatibility of EBM titanium–6 aluminum–4 vanadium (Ti6Al4V) structures by comparing the cellular response to solid polished, solid unpolished, and porous EBM discs to the cellular response to discs made of commercially produced Ti6Al4V. The discs were seeded with 20,000 human adipose-derived adult stem cells (hASCs) and assessed for cell viability, proliferation, and release of the proinflammatory cytokines interleukin-6 (IL-6) and interleukin-8 (IL-8). Cell viability was assessed with Live/Dead staining 8 days after seeding. Cell proliferation was assessed using alamarBlue assays at days 0, 1, 2, 3, and 7. The hASCs were alive on all discs after 8 days. Cellular proliferation on porous EBM discs was increased at days 2, 3, and 7 compared to discs made of commercial Ti6Al4V. Cellular proliferation on porous EBM discs was also increased compared to solid polished and unpolished EBM discs. IL-6 and IL-8 releases at day 7 were lower for porous EBM discs than for other discs. Solid polished, unpolished, and porous EBM Ti6Al4V discs exhibited an acceptable biocompatibility profile compared to solid Ti6Al4V discs from a commercial source. EBM FFF may be considered as an option for the fabrication of custom orthopedic implants.

An experimental analysis of the influence of the ink properties on the drop formation for direct thermal inkjet printing of high solid content aqueous 3Y-TZP suspensions

Direct inkjet printing (DIP) of ceramics as a novel solid freeform fabrication (SFF) method has been subjected to extensive research in the recent years. The studies have focused either on the simulation of the drop ejection or the production of demonstration objects. The aim of this study was to close the gap between the simulation results and product oriented studies. 3Y-TZP inks of 24 vol.% solid content were prepared and characterized in terms of physical properties as well as dimensionless quantities ( Re, We, Ca, and Oh). The drop volume and velocity were estimated by considering a constant ejection pressure but varying physical properties of the ejected inks. A thermal inkjet printer was used to eject arrays of single drops as well as three-dimensional 3Y-TZP demonstration objects. The drop arrays were analyzed to determine the relation between the ink properties and the drop formation. The demonstration object was sintered close to the full density.

Tailoring the mechanical properties of 3D‐designed poly(glycerol sebacate) scaffolds for cartilage applications

Matching tissue engineering scaffold modulus to that of native tissue is highly desirable. Effective scaffold modulus can be altered through changes in base material modulus and/or scaffold pore architecture. Because the latter may be restricted by tissue in-growth requirements, it is advantageous to be able to alter the base material modulus of a chosen scaffold material. Here, we show that the bulk modulus of poly(glycerol sebacate) (PGS) can be changed by varying molar ratios during prepolymer synthesis and by varying curing time. We go on to show that PGS can be used to create 3D designed scaffolds via solid freeform fabrication methods with modulus values that fall within the ranges of native articular cartilage equilibrium modulus. Furthermore, using base material modulus inputs, homogenization finite element analysis can effectively predict the tangent modulus of PGS scaffold designs, which provides a significant advantage for designing new cartilage regeneration scaffolds. Lastly, we demonstrate that this relatively new biomedical material supports cartilaginous matrix production by chondrocytes in vitro. (c) 2010 Wiley Periodicals, Inc. J Biomed Mater Res, 2010.

J0207-2-3 電気分解法による気孔率分布を有する自家骨置換性人工骨の立体造形の試み([J0207-2]医療・福祉工学のための3次元造形)

Autologous-bone-replaceable artificial bones made of bioresorbable materials (e.g., β-tricalcium phosphate (β-TCP)) are degraded and resorbed, i.e., replaced with autologous bone, when placed inside the human body. Although such autologous-bone replaceability requires high porosity to promote the ingression of blood vessels and cells, the high porosity reduces the mechanical strength. Artificial bone with a porosity distribution may be one way of solving this problem. In this paper, the authors propose a solid freeform fabrication method using electrolysis for controlling the foaming. The authors created three samples with different porosity and a sample with porosity distribution using the method and confirm the efficacy and potential of the proposed approach.

Predictive Modeling and Experimental Verification of Temperature and Concentration in Rapid Freeze Prototyping With Support Material

Rapid freeze prototyping is a solid freeform fabrication method that uses water freezing into ice as the build material. Each layer of geometry is deposited and allowed to freeze before the next layer is added in order to additively create a three-dimensional ice part. A sacrificial support material is needed for the fabrication of complex ice parts. Identifying a suitable support material and understanding the interaction between the build and support materials is the motivation behind this study. A temperature prediction model and a concentration prediction model are presented. Experimental results have been obtained to validate these models.

Cell adhesion and proliferation evaluation of SFF-based biodegradable scaffolds fabricated using a multi-head deposition system

Scaffolds composed of biodegradable polymers and biocompatible ceramics are being used as substitutes for tissue engineering. In the development of such techniques, scaffolds with a controllable pore size and porosity were manufactured using solid free-form fabrication (SFF) methods to investigate the effects of cell interactions such as cell proliferation and differentiation. In this study, we describe the adhesion of human bone marrow stromal cells (hBMSCs) and proliferation characteristics of various scaffolds, which consist of biodegradable materials, fabricated using a multi-head deposition system (MHDS) that we developed. The MHDS uses novel technology that enables the production of three-dimensional (3D) microstructures. Fabrication of 3D tissue engineering scaffolds using the MHDS requires the combination of several technologies, such as motion control, thermal control, pneumatic control and computer-aided design/computer-assisted manufacturing software. The effects of a polymer and ceramic on a tissue scaffold were evaluated through mechanical testing and cell interaction analysis of various kinds of scaffolds fabricated using polycaprolactone, poly-lactic-co-glycolic acid and tri-calcium phosphate for bone regeneration applications. Based on these results, the feasibility of application to the tissue engineering of SFF-based 3D scaffolds fabricated by the MHDS was demonstrated.

In vitro evaluation of a custom cutting jig and custom plate for canine tibial plateau leveling

To design and manufacture custom titanium bone plates and a custom cutting and drill guide by use of free-form fabrication methods and to compare variables and mechanical properties of 2 canine tibial plateau leveling methods with each other and with historical control values. 10 canine tibial replicas created by rapid prototyping methods. Application time, accuracy of correction of the tibial plateau slope (TPS), presence and magnitude of rotational and angular deformation, and replica axial stiffness for 2 chevron wedge osteotomy (CWO) methods were assessed. One involved use of freehand CWO (FHCWO) and screw hole drilling, whereas the other used jig-guided CWO (JGCWO) and screw hole drilling. Replicas used for FHCWO and JGCWO methods had similar stiffness. Although JGCWO and FHCWO did not weaken the replicas, mean axial stiffness of replicas after JGCWO was higher than after FHCWO. The JGCWO method was faster than the FHCWO method. Mean +/- SD TPS after osteotomy was lower for FHCWO (4.4 +/- 1.1 degrees ) than for JGCWO (9.5 +/- 0.4 degrees ), and JGCWO was more accurate (target TPS, 8.9 degrees ). Slight varus was evident after FHCWO but not after JGCWO. Mean postoperative rotation after JGCWO and FHCWO did not differ from the target value or between methods. The JGCWO method was more accurate and more rapid and resulted in more stability than the FHCWO method. Use of custom drill guides could enhance the speed, accuracy, and stability of corrective osteotomies in dogs.

A METHOD OF 3D FREEFORM FABRICATION USING A CURING OF PHOTOPOLYMER RESIN

Recently, Study of 3D freeform fabrication method was working in the various applications. For example, in the powder base, it's laminated using a binding method or laser sintering method. However, the demerits of these methods are to take long time for post process and not enough to keep high strength of manufacturing part. The binding method needs the post process and the time for post process needs longer time than a manufacturing time. The sintering method has huge size of system with module of the laser. In this paper, we introduce a method of 3D freeform fabrication using a curing of photopolymer resin. A photopolymer curing method has simply fabrication process and high strength of manufacturing part. So, we are configuration the system with compact type module for the office environment and experiment a UV curing test with photopolymer resin in the 3D freeform fabrication method. In the conclusion, we fabricate the 3D freeform part, which is suitable to the office environment using a photopolymer curing method.

Fabrication of a SFF-based three-dimensional scaffold using a precision deposition system in tissue engineering

Recent developments in tissue-engineering techniques allow physicians to treat a range of previously untreatable conditions. In the development of such techniques, scaffolds with a controllable pore size and porosity have been manufactured using solid free-form fabrication methods to investigate cell interaction effects such as cell proliferation and differentiation. In this study, we describe the fabrication of scaffolds from two types of biodegradable materials using a precision deposition system that we developed. The precision deposition system uses technology that enables the manufacture of three-dimensional (3D) microstructures. The fabrication of 3D tissue-engineering scaffolds using the precision deposition system required the combination of several technologies, including motion control, thermal control, pneumatic control and CAD/CAM software. Through the fabrication and cell interaction analysis of two kinds of scaffolds using polycaprolactone and poly-lactic-co-glycolic acid, feasibility of application to the tissue engineering of the developed SFF-based precision deposition system is demonstrated.

Novel freeform fabrication method for rutile ceramic components

A novel freeform fabrication method for rutile ceramic components based on the rapid liquid–solid transformation of aqueous polyvinyl alcohol (PVA) solution induced by aqueous borax solution is proposed. Layer by layer fabrication is conducted by gelling of a TiO2 PVA suspension induced by 4 wt-% borax aqueous solution. Before each layer is gelled, computer aided cutting of the layer is performed and the cut slots filled in situ 15 wt-% PVA aqueous solution, which remains gelled during the deposition of the following layer. The final fabrication is then dried and the binder burnt out and sintered. As well as demonstrating freeform fabrication, PVA films before and after gelation were investigated by differential scanning calorimetry to investigate the debinding process in the green rutile body. A reduction of heating rate before the endothermic decomposition peak temperature and an extension of the heat preservation time around the peak temperature of the gelled PVA are essential to minimise porosity in the rutile component. No evidence of delamination and no residual traces of boron and its compounds were found. As sintered three layer rutile ceramic components showed a mean three point flexural strength of 45˙6 MPa.

Encapsulation of silver particles using co-axial jetting

An electrically charged jet of polymer solution is used to encapsulate silver particles contained in a suspension using co-axial dual needle jetting. The polymer solution flowing through the outer needle undergoes electrospinning while the silver suspension is simultaneously subjected to electrohydrodynamic atomization in the inner needle. The pattern and uniformity of encapsulation in the core is mainly determined by the speed of jetting in the inner needle. We demonstrate that this process could be utilized as a commercial freeform fabrication method of encapsulating metal particles within a polymeric sheath and this development could have numerous advanced technological applications.