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American Society for Testing and Materials

Additive manufacturing (AM) alias 3D printing translates computer-aided design (CAD) virtual 3D models into physical objects. By digital slicing of CAD, 3D scan, or tomography data, AM builds objects layer by layer without the need for molds or machining. AM enables decentralized fabrication of customized objects on demand by exploiting digital information storage and retrieval via the Internet. The ongoing transition from rapid prototyping to rapid manufacturing prompts new challenges for mechanical engineers and materials scientists alike. Because polymers are by far the most utilized class of materials for AM, this Review focuses on polymer processing and the development of polymers and advanced polymer systems specifically for AM. AM techniques covered include vat photopolymerization (stereolithography), powder bed fusion (SLS), material and binder jetting (inkjet and aerosol 3D printing), sheet lamination (LOM), extrusion (FDM, 3D dispensing, 3D fiber deposition, and 3D plotting), and 3D bioprinting....

Polymers for 3D Printing and Customized Additive Manufacturing

Additive manufacturing processes take the information from a computer-aided design (CAD) file that is later converted to a stereolithography (STL) file. In this process, the drawing made in the CAD software is approximated by triangles and sliced containing the information of each layer that is going to be printed. There is a discussion of the relevant additive manufacturing processes and their applications. The aerospace industry employs them because of the possibility of manufacturing lighter structures to reduce weight. Additive manufacturing is transforming the practice of medicine and making work easier for architects. In 2004, the Society of Manufacturing Engineers did a classification of the various technologies and there are at least four additional significant technologies in 2012. Studies are reviewed which were about the strength of products made in additive manufacturing processes. However, there is still a lot of work and research to be accomplished before additive manufacturing technologies become standard in the manufacturing industry because not every commonly used manufacturing material can be handled. The accuracy needs improvement to eliminate the necessity of a finishing process. The continuous and increasing growth experienced since the early days and the successful results up to the present time allow for optimism that additive manufacturing has a significant place in the future of manufacturing.

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A Review of Additive Manufacturing

Additive manufacturing (AM), widely known as 3D printing, is a method of manufacturing that forms parts from powder, wire or sheets in a process that proceeds layer by layer. Many techniques (using many different names) have been developed to accomplish this via melting or solid-state joining. In this review, these techniques for producing metal parts are explored, with a focus on the science of metal AM: processing defects, heat transfer, solidification, solid-state precipitation, mechanical properties and post-processing metallurgy. The various metal AM techniques are compared, with analysis of the strengths and limitations of each. Only a few alloys have been developed for commercial production, but recent efforts are presented as a path for the ongoing development of new materials for AM processes.

The metallurgy and processing science of metal additive manufacturing

3D Printing promises to produce complex biomedical devices according to computer design using patient-specific anatomical data. Since its initial use as pre-surgical visualization models and tooling molds, 3D Printing has slowly evolved to create one-of-a-kind devices, implants, scaffolds for tissue engineering, diagnostic platforms, and drug delivery systems. Fueled by the recent explosion in public interest and access to affordable printers, there is renewed interest to combine stem cells with custom 3D scaffolds for personalized regenerative medicine. Before 3D Printing can be used routinely for the regeneration of complex tissues (e.g. bone, cartilage, muscles, vessels, nerves in the craniomaxillofacial complex), and complex organs with intricate 3D microarchitecture (e.g. liver, lymphoid organs), several technological limitations must be addressed. In this review, the major materials and technology advances within the last five years for each of the common 3D Printing technologies (Three Dimensional Printing, Fused Deposition Modeling, Selective Laser Sintering, Stereolithography, and 3D Plotting/Direct-Write/Bioprinting) are described. Examples are highlighted to illustrate progress of each technology in tissue engineering, and key limitations are identified to motivate future research and advance this fascinating field of advanced manufacturing.

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Recent advances in 3D printing of biomaterials

The effect of calcium fluoride (CaF(2)) on the chemical solubility of an apatite-mullite glass-ceramic material.

The use of acetone to enhance the infiltration of HA nanoparticles into a demineralized dentin collagen matrix

Hydroxyapatite (HA) has been used in orthopedic, dental, and maxillofacial surgery as a bone substitute. The aim of this investigation was to study the effect of surface topography produced by the presence of microporosity on cell response, evaluating: cell attachment, cell morphology, cell proliferation, total protein content, and alkaline phosphatase (ALP) activity. HA discs with different percentages of microporosity (< 5%, 15%, and 30%) were confected by means of the combination of uniaxial powder pressing and different sintering conditions. ROS17/2.8 cells were cultured on HA discs. For the evaluation of attachment, cells were cultured for two hours. Cell morphology was evaluated after seven days. After seven and fourteen days, cell proliferation, total protein content, and ALP activity were measured. Data were compared by means of ANOVA and Duncans multiple range test, when appropriate. Cell attachment (p = 0.11) and total protein content (p = 0.31) were not affected by surface topography. Proliferation after 7 and 14 days (p = 0.0007 and p = 0.003, respectively), and ALP activity (p = 0.0007) were both significantly decreased by the most irregular surface (HA30). These results suggest that initial cell events were not affected by surface topography, while surfaces with more regular topography, as those present in HA with 15% or less of microporosity, favored intermediary and final events such as cell proliferation and ALP activity.

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Surface topography of hydroxyapatite affects ROS17/2.8 cells response

Objectives: 3D colour printing, a method of additive manufacturing, has been developed and utilised to produce facial soft tissue prostheses. This was achieved by layered fabrication of a biocompatible powder held together by an aqueous binder containing a resin and coloured inks, followed by infiltration with a medical grade silicone polymer. The aim of this study was to investigate the elastomer infiltration depths within the 3D printed models. Methods: Three sets of 30 cubes – 20x20x20 mm – were used to investigate the infiltration depth of Sil-25 maxillofacial silicone polymer (an MSP) under atmospheric pressure, 2 bar and 3 bar pressure for 5, 10, 15, 20 and 25 min. The investigation was also repeated with two other MSPs – Promax-10 and M-3428 – under 3 bar pressure. Following infiltration, the cubes were bisected, the internal aspects stained with dye, and the infiltration depth measured using a travelling microscope. Infiltration quality was also assessed using scanning electron microscopy (SEM). Results: At standard atmospheric pressure, the maximum infiltration depth of Sil-25 was 1.45 mm after 25 min. However, after 25 min at 2 and 3 bars pressure, the infiltration depth increased to 3.9 mm and 8.7 mm, respectively. At 3 bars the infiltration depth of Promax-10 and M-3428 was 2.4 mm and 7.5 mm, respectively. In all samples SEM revealed a disorganised distribution of starch particles within the MSP infiltrate. Significance: Pressure significantly increased the infiltration rate and depth of the MSPs within 3D printed constructs. The infiltration depth obtained is sufficient for prostheses that are less than 16 mm thick.

Investigation of Elastomer Infiltration into 3D Printed Facial Soft Tissue

Potassium fluorrichterite (KNaCaMg5Si8O22F2) glass–ceramics were modified by either increasing the concentration of calcium (GC5) or by the addition of P2O5 (GP2). Rods (2 × 4 mm) of stoichiometric fluorrichterite (GST), modified compositions (GC5 and GP2) and 45S5 bioglass, which was used as the reference material, were prepared using a conventional lost-wax technique. Osteoconductivity was investigated by implantation into healing defects in the midshaft of rabbit femora. Specimens were harvested at 4 and 12 weeks following implantation and tissue response was investigated using computed microtomography (μCT) and histological analyses. The results showed greatest bone to implant contact in the 45S5 bioglass reference material at 4 and 12 weeks following implantation, however, GST, GC5 and GP2 all showed direct bone tissue contact with evidence of new bone formation and cell proliferation along the implant surface into the medullary space. There was no evidence of bone necrosis or fibrous tissue encapsulation around the test specimens. Of the modified potassium fluorrichterite compositions, GP2 showed the greatest promise as a bone substitute material due to its osteoconductive potential and superior mechanical properties.

Richard van Noort

Papers

The effect of calcium fluoride (CaF(2)) on the chemical solubility of an apatite-mullite glass-ceramic material.

The use of acetone to enhance the infiltration of HA nanoparticles into a demineralized dentin collagen matrix

Surface topography of hydroxyapatite affects ROS17/2.8 cells response

Investigation of Elastomer Infiltration into 3D Printed Facial Soft Tissue

Determination of relative in vivo osteoconductivity of modified potassium fluorrichterite glass–ceramics compared with 45S5 bioglass