Solid Freeform Fabrication Method Research Articles

Magnetic resonance imaging-three-dimensional printing technology fabricates customized scaffolds for brain tissue engineering.

Conventional fabrication methods lack the ability to control both macro- and micro-structures of generated scaffolds. Three-dimensional printing is a solid free-form fabrication method that provides novel ways to create customized scaffolds with high precision and accuracy. In this study, an electrically controlled cortical impactor was used to induce randomized brain tissue defects. The overall shape of scaffolds was designed using rat-specific anatomical data obtained from magnetic resonance imaging, and the internal structure was created by computer-aided design. As the result of limitations arising from insufficient resolution of the manufacturing process, we magnified the size of the cavity model prototype five-fold to successfully fabricate customized collagen-chitosan scaffolds using three-dimensional printing. Results demonstrated that scaffolds have three-dimensional porous structures, high porosity, highly specific surface areas, pore connectivity and good internal characteristics. Neural stem cells co-cultured with scaffolds showed good viability, indicating good biocompatibility and biodegradability. This technique may be a promising new strategy for regenerating complex damaged brain tissues, and helps pave the way toward personalized medicine.

Investigating Laser Additive Manufacturing of Functionally Graded Ni-Cr-B-Si and SS 316L

Laser additive manufacturing (LAM) is a laser based solid freeform fabrication method used for “feature based design and manufacturing”. One of the interesting applications of LAM is the fabrication of functionally graded materials (FGM) for joining materials with different thermophysical properties. In the present work, a 2 kW fiber based LAM system is deployed for the fabrication of functionally graded Ni-Cr-B-Si alloy on SS 316L. Functional grading is achieved by varying the composition of NiCr-B-Si alloy and SS 316L. Trial experiments are performed to optimize the process parameters for LAM of Ni-Cr-B-Si layers on preheated substrate of SS 316L with qualification criteria of uniform regular crack free deposit. The microstructure and the mechanical properties are investigated using optical microscopy, microhardness and ball indentation testing. The optical microscopic examination revealed that a uniform regular crack free deposition could be made at optimum process parameters. The microstructural examination revealed the presence of dendritic microstructure at the top most layers. Subsequently, a gradual transition from dendritic to cellular microstructure is observed in lower layers. Vickers microhardness testing showed a gradual decline in the hardness of the sample from Ni-Cr-B-Si to SS 316L. The average hardness of 430.63 HV0.2 of 100% Ni-Cr-BSi is reduced to 185.5 HV0.2 at the substrate. Variation of hardness and energy stored by the material can be clearly observed from Ni-Cr-B-Si to other graded composition through ball indentation studies.

Viability of Bioprinted Cellular Constructs Using a Three Dispenser Cartesian Printer.

Tissue engineering has centralized its focus on the construction of replacements for non-functional or damaged tissue. The utilization of three-dimensional bioprinting in tissue engineering has generated new methods for the printing of cells and matrix to fabricate biomimetic tissue constructs. The solid freeform fabrication (SFF) method developed for three-dimensional bioprinting uses an additive manufacturing approach by depositing droplets of cells and hydrogels in a layer-by-layer fashion. Bioprinting fabrication is dependent on the specific placement of biological materials into three-dimensional architectures, and the printed constructs should closely mimic the complex organization of cells and extracellular matrices in native tissue. This paper highlights the use of the Palmetto Printer, a Cartesian bioprinter, as well as the process of producing spatially organized, viable constructs while simultaneously allowing control of environmental factors. This methodology utilizes computer-aided design and computer-aided manufacturing to produce these specific and complex geometries. Finally, this approach allows for the reproducible production of fabricated constructs optimized by controllable printing parameters.

Mechanical Study of Polycaprolactone-hydroxyapatite Porous Scaffolds Created by Porogen-based Solid Freeform Fabrication Method

Polycaprolactone (PCL) and polycaprolactone-hydroxyapatite (PCL-HA) scaffolds with 600-µm pore size were fabricated by drop-on-demand printing (DDP) structured porogen method followed with injection molding. Specimens with special dimensions of 4.2×4.2×5.4 mm3 and 6.6×6.6×13.8 mm3 were designed and fabricated for compression and tensile tests, respectively. The mechanical study was performed on both solid and porous PCL and PCL-HA samples. The effect on mechanical properties of the HA content ratio in PCL-HA composites was investigated. Porous scaffold made of 80/20 PCL-HA composite had an ultimate compressive strength of 3.7±0.2 MPa and compression modulus of 61.4±3.4 MPa, which is in the range of reported trabecular bone's compressive strength. Increasing the concentration of HA in the composites raised compressive properties and stiffness significantly (P<0.05), which demonstrates that PCL-HA composites have the potential for application in bone regeneration. Tensile test of solid PCL and PCL-HA composites showed that the ultimate tensile strength and tensile modulus increased with increases of the concentration of HA in the composites. The tensile test was also conducted on PCL porous scaffold; the result indicated that the scaffold was slightly softer and weaker in tension compared with compression. Combining compression and tensile test results, our study may guide the possible application of these biomaterials in bone tissue engineering and support further development of microstructure-based models of scaffold mechanical properties.

In vitro and in vivo evaluation of bone formation using solid freeform fabrication-based bone morphogenic protein-2 releasing PCL/PLGA scaffolds

The aim of this study was to develop novel polycaprolactone/poly(lactic-co-glycolic acid) (PCL/PLGA) scaffolds with a heparin–dopamine (Hep–DOPA) conjugate for controlled release of bone morphogenic protein-2 (BMP-2) to enhance osteoblast activity in vitro and also bone formation in vivo. PCL/PLGA scaffolds were prepared by a solid freeform fabrication method. The PCL/PLGA scaffolds were functionalized with Hep–DOPA and then BMP-2 was sequentially coated onto the Hep–DOPA/PCL/PLGA scaffolds. The characterization and surface elemental composition of all scaffolds were evaluated by scanning electron microscope and x-ray photoelectron spectroscopy. The osteoblast activities on all scaffolds were assessed by cell proliferation, alkaline phosphatase (ALP) activity and calcium deposition in vitro. To demonstrate bone formation in vivo, plain radiograph, micro-computed tomography (micro-CT) evaluation and histological studies were performed after the implantation of all scaffolds on a rat femur defect. Hep–DOPA/PCL/PLGA had more controlled release of BMP-2, which was quantified by enzyme-linked immunosorbent assay, compared with Hep/PCL/PLGA. The in vitro results showed that osteoblast-like cells (MG-63 cells) grown on BMP-2/Hep–DOPA/PCL/PLGA had significantly enhanced ALP activity and calcium deposition compared with those on BMP-2/Hep/PCL/PLGA and PCL/PLGA. In addition, the plain radiograph, micro-CT evaluation and histological studies demonstrated that the implanted BMP-2/Hep–DOPA/PCL/PLGA on rat femur had more bone formation than BMP-2/Hep/PCL/PLGA and PCL/PLGA in vivo.

Hybrid hierarchical fabrication of three-dimensional scaffolds

Three-dimensional (3D) porous structures facilitating cell attachment, growth, and proliferation is critical to tissue engineering applications. Traditional solid freeform fabrication (SFF) methods have limited capabilities in the fabrication of high resolution micro-scale features to implement advanced biomedical functions. In this work, we present a hybrid scaffold fabrication approach by integrating electrohydrodynamic (EHD) printing technology with extrusion deposition together to fabricate hierarchical 3D scaffolds with well controlled structures at both macro and micro scale. We developed a hybrid fabrication platform and a robust fabrication process to achieve 3D hierarchical structures. The melting extrusion by pneumatic pressure was used to fabricate 3D scaffolds with filaments dimension of hundreds of microns using thermoplastic biopolymer polycaprolactone (PCL). An electrohydrodynamic (EHD) melt jet plotting process was developed to fabricate micro-scale features on the scaffolds with sub-10μm resolution, which has great potential in advanced biomedical applications, such as cell alignment and cell guidance.

Volume-Stable Adipose Tissue Formation by Implantation of Human Adipose-Derived Stromal Cells Using Solid Free-Form Fabrication-Based Polymer Scaffolds

Regeneration of volume-stable adipose tissue is required for treatment of soft-tissue loss due to cancer, trauma, burns and for correctional cosmetic surgery. In this study, we hypothesized that transplantation of human adipose-derived stromal cells (hADSCs) using polycaprolactone (PCL) scaffolds fabricated with a solid free-form fabrication method would better maintain the volume of regenerated adipose tissues, as compared with the use of fibrin gel. Six weeks after implantation into the dorsal subcutaneous pockets of athymic mice, the volumes and adipose tissue areas of hADSC-PCL scaffold implants were significantly larger than those of hADSC-fibrin implants. In addition, the mRNA expression of adipogenic genes was more extensive in the hADSC-PCL scaffold implants.

Biological Properties of Solid Free Form Designed Ceramic Scaffolds with BMP-2: In Vitro and In Vivo Evaluation

Porous ceramic scaffolds are widely studied in the tissue engineering field due to their potential in medical applications as bone substitutes or as bone-filling materials. Solid free form (SFF) fabrication methods allow fabrication of ceramic scaffolds with fully controlled pore architecture, which opens new perspectives in bone tissue regeneration materials. However, little experimentation has been performed about real biological properties and possible applications of SFF designed 3D ceramic scaffolds. Thus, here the biological properties of a specific SFF scaffold are evaluated first, both in vitro and in vivo, and later scaffolds are also implanted in pig maxillary defect, which is a model for a possible application in maxillofacial surgery. In vitro results show good biocompatibility of the scaffolds, promoting cell ingrowth. In vivo results indicate that material on its own conducts surrounding tissue and allow cell ingrowth, thanks to the designed pore size. Additional osteoinductive properties were obtained with BMP-2, which was loaded on scaffolds, and optimal bone formation was observed in pig implantation model. Collectively, data show that SFF scaffolds have real application possibilities for bone tissue engineering purposes, with the main advantage of being fully customizable 3D structures.

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.

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.

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.

Fabrication of three-dimensional collagen scaffold using an inverse mould-leaching process

Natural biopolymers, such as collagen or chitosan, are considered ideal for biomedical scaffolds. However, low processability of the materials has hindered the fabrication of designed pore structures controlled by various solid freeform-fabrication methods. A new technique to fabricate a biomedical three-dimensional collagen scaffold, supplemented with a sacrificial poly(ethylene oxide) mould is proposed. The fabricated collagen scaffold shows a highly porous surface and a three-dimensional structure with high porosity as well as mechanically stable structure. To show its feasibility for biomedical applications, fibroblasts/keratinocytes were co-cultured on the scaffold, and the cell proliferation and cell migration of the scaffold was more favorable than that obtained with a spongy-type collagen scaffold.

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.

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.