Selective laser sintering of bioactive glass scaffolds and their biological assessment for bone repair

Bone scaffold fabrication using powder-bed based additive manufacturing techniques, like the selective laser sintering (SLS) process, provides control over pore interconnectivity, pore geometry, and the overall shape of the scaffold, which aids in repairing different regions of the bone. The main objectives of this dissertation were to develop bioactive glass (BG) scaffolds using the SLS process and evaluate the scaffolds for their effectiveness in bone repair both in vitro and in vivo. 13-93 glass, a silicate based BG, and 13-93B3 glass, a borate based BG, are designed to accelerate the body\u27s natural ability to heal itself and are used in this research. After the initial feasibility study, the material and process parameters were optimized to improve the compressive strength from ~20 MPa to ~41 MPa, for a 13-93 BG scaffold with a porosity of ~50%. Pore geometry of the scaffold plays a crucial role as it not only affects the mechanical properties and subsequent degradation but also the bone cell proliferation. Scaffolds with a porosity of ~50% and five different pore geometries, namely, cubic, spherical, X, diamond, and gyroid, were fabricated and assessed in vitro for a possible preferential cell proliferation. The MTT labeling experiments indicated that the scaffolds with diamond and gyroid pore geometries have higher curvature-driven MLO-A5 cell proliferation. Finally, scaffolds with diamond and cubic pore geometries were evaluated in vivo using a rat calvarial defect model for 6 weeks. Though the results indicated no significant difference in the amount of new bone formation with respect to the defect region, the maturation of the fibrous tissue to bone appeared to be quicker in the scaffolds with diamond architecture --Abstract, page iv

NX 10 for Engineering Design -- Learning Edition

NX is one of the world’s most advanced and tightly integrated CAD/CAM/CAE product development solution. Spanning the entire range of product development, NX delivers immense value to enterprises of all sizes. It simplifies complex product designs, thus speeding up the process of introducing products to the market. The NX software integrates knowledge-based principles, industrial design, geometric modeling, advanced analysis, graphic simulation, and concurrent engineering. The software has powerful hybrid modeling capabilities by integrating constraint-based feature modeling and explicit geometric modeling. In addition to modeling standard geometry parts, it allows the user to design complex free-form shapes such as airfoils and manifolds. It also merges solid and surface modeling techniques into one powerful tool set. This self-guiding tutorial provides a step-by-step approach for users to learn NX 10. It is intended for those with no previous experience with NX. However, users of previous versions of NX may also find this tutorial useful for them to learn the new user interfaces and functions. The user will be guided from starting an NX 10 session to creating models and designs that have various applications. Each chapter has components explained with the help of various dialog boxes and screen images. These components are later used in the assembly modeling, machining and finite element analysis. The files of components are also available online to download and use. We first released the tutorial for Unigraphics 18 and later updated for NX 2 followed by the updates for NX 3, NX 5, NX 7 and NX 9. This write-up further updates to NX 10. Our previous efforts to prepare the NX self-guiding tutorial were funded by the National Science Foundation’s Advanced Technological Education Program and by the Partners of the Advancement of Collaborative Engineering Education (PACE) program

Selective Laser Sintering and Freeze Extrusion Fabrication of Scaffolds for Bone Repair using 13-93 Bioactive Glass: A Comparison

13-93 glass is a third-generation bioactive material which accelerates the bone’s natural ability to heal by itself through bonding with surrounding tissues. It is an important requirement for synthetic scaffolds to maintain their bioactivity and mechanical strength with a porous internal architecture comparable to that of a human bone. Additive manufacturing technologies provide a better control over design and fabrication of porous structures than conventional methods. In this paper, we discuss and compare some of the common aspects in the scaffold fabrication using two such processes, viz. selective laser sintering (SLS) and freeze extrusion fabrication (FEF). Scaffolds fabricated using each process were structurally characterized and microstructure analysis was performed to study process differences. Compressive strength higher than that of human trabecular bone was achieved using SLS process and strength almost comparable to that of human cortical bone was achieved using FEF process

Effect of Architecture and Porosity on Mechanical Properties of Borate Glass Scaffolds Made by Selective Laser Sintering

The porosity and architecture of bone scaffolds, intended for use in bone repair or replacement, are two of the most important parameters in the field of bone tissue engineering. The two parameters not only affect the mechanical properties of the scaffolds but also aid in determining the amount of bone regeneration after implantation. Scaffolds with five different architectures and four porosity levels were fabricated using borate bioactive glass (13-93B3) using the selective laser sintering (SLS) process. The pore size of the scaffolds varied from 400 to 1300 μm. The compressive strength of the scaffolds varied from 1.7 to 15.5 MPa for porosities ranging from 60 to 30%, respectively, for the different architectures. Scaffolds were soaked in a simulated body fluid (SBF) for one week to measure the variation in mechanical properties. The formation of the Hydroxyapatite and in-vitro results are provided and discussed

In Vitro Assessment of Laser Sintered Bioactive Glass Scaffolds with Different Pore Geometries

The pore geometry of bioactive glass scaffolds intended for use in bone repair or replacement is one of the most important parameters that could determine the rate of bone regeneration. The pore geometry would also affect the mechanical properties of the scaffolds and their rate of degradation. Scaffolds with five different architectures, having ~50% porosity, were fabricated with silicate (13–93) and borate (13–93B3) based bioactive glasses using a laser sintering process. An established, late-osteoblasts/early-osteocytes cell line was used to perform cell proliferation tests on the scaffolds. The results indicated that the cells proliferate significantly more on the scaffolds which mimic the trabecular bone architecture compared to traditional lattice structures

Design of Lattice Structures with Graded Density Fabricated by Additive Manufacturing

Lattice structures fabricated by Additive Manufacturing (AM) processes are promising for many applications, such as lightweight structures and energy absorbers. However, predicting and controlling of their mechanical behaviors is challenging due to the complexity of modeling and the uncertainties exist in the manufacturing process. In this paper, we explore the possibilities enabled by controlling the local densities. A set of lattice structures with different density gradients are designed using an implicit isosurface equation, and they are manufactured by Selective Laser Melting (SLM) process with 304L stainless steel. Finite element analysis and compression test are used to evaluate their mechanical properties. The results demonstrate the strong correlations between the structural gradient and the mechanical behavior. Introducing the density gradient provides more possibilities in the design phase, which can be used to further customize the design both structurally and functionally

Near-Field Electrospinning of a Polymer/Bioactive Glass Composite to Fabricate 3D Biomimetic Structures

Bioactive glasses have recently gained attention in tissue engineering and three-dimensional (3D) bioprinting because of their ability to enhance angiogenesis. Some challenges for developing biological tissues with bioactive glasses include incorporation of glass particles and achieving a 3D architecture mimicking natural tissues. In this study, we investigate the fabrication of scaffolds with a polymer/bioactive glass composite using near-field electrospinning (NFES). An overall controlled 3D scaffold with pores, containing random fibers, is created and aimed to provide superior cell proliferation. Highly angiogenic borate bioactive glass (13-93B3) in 20 wt.% is added to polycaprolactone (PCL) to fabricate scaffolds using the NFES technique. Scaffolds measuring 5 mm x 5 mm x 0.2 mm 3 in overall dimensions were seeded with human adipose-derived mesenchymal stem cells to investigate the cell viability. The cell viability on PCL and PCL+glass scaffolds fabricated using NFES technique and 3D printing is compared and discussed. The results indicated higher cell proliferation on 3D biomimetic scaffolds fabricated by NFES technique

Selective Laser Sintering and Freeze Extrusion Fabrication of Bioglass Bone Scaffolds [abstract]

Biomedical Tissue Engineering, Biomaterials, and Medical Devices Poster SessionBioactive glasses are promising materials for bone scaffolds due to their ability to assist in tissue regeneration. When implanted in vivo, bioactive glasses can convert to hydroxyapatite, the main mineral constituent of human bone and form a strong bond with the surrounding tissues, providing an advantage over polymer scaffold materials. Bone scaffold fabrication using additive manufacturing (solid freeform fabrication) methods provides control over design and fabrication of pores in the scaffold. 13-93 bioglass (manufactured by Mo-Sci Corporation), a third-generation bioactive and resorbable material designed to accelerate the body's natural ability to heal itself, was used in the research described herein to fabricate bone scaffolds using two different additive manufacturing methods - Selective Laser Sintering and Freeze Extrusion Fabrication. Selective Laser Sintering (SLS) is a process where a laser light is controlled to selectively sinter the particles in a powder bed layer-by-layer to fabricate a 3D part based on a CAD model. The SLS machine used in this research was a DTM Sinterstation 2000. 13-93 bioglass mixed with stearic acid (as the polymer binder) by ball milling was used as the powder feedstock for the SLS machine. The fabricated green scaffolds underwent binder burnout to remove the stearic acid binder and then sintered at temperatures between 6500C and 7000C. After sintering, the scaffolds were mechanically tested, achieving a maximum compressive strength of 16 MPa for scaffolds with 60% apparent porosity. Bioactivity results showed the ability of the SLS scaffolds to support the growth of osteoblastic cells. Scanning electron microsocopy analysis and MTT formazan formation measurements provided evidence that the bioglass scaffolds fabricated by the SLS process offer a surface capable of supporting robust cell growth. Freeze Extrusion Fabrication (FEF) is a process where an aqueous-based glass paste is extruded and deposited layer-by-layer to fabricate a 3D part in a sub-freezing temperature environment. The FEF system, developed at Missouri S&T, consists of a 3-axis positioning system, a ram extruder for paste extrusion, and position and force sensors for measurement and control. Bioglass slurry was prepared by ball milling 13-93 bioglass particles along with a dispersant (surfynol) and a binder (aquazol). Further, a lubricant (PEG-400) was added to the paste to aid in extrusion. The bioglass slurry was then heated to obtain bioglass paste. Scaffolds with varying pore sizes from 300μm to 800μm were successfully fabricated using the FEF process. Post processing of green scaffolds, including binder burnout and sintering, is currently being performed. Scaffolds produced by the FEF process will be evaluated and compared with the scaffolds obtained using the SLS process

Selective laser sintering of 13-93 bioactive glass

Bioactive glasses are promising materials for bone scaffolds due to their ability to assist in tissue regeneration. When implanted in vivo, bioactive glasses can convert to hydroxyapatite, the main mineral constituent of human bone and form a strong bond with the surrounding tissues, thus providing an advantage over polymer scaffold materials. Bone scaffold fabrication using additive manufacturing techniques like selective laser sintering (SLS) provide control over pore interconnectivity during the fabrication of scaffold, which helps in mimicking human trabecular bone. 13-93 glass, a third-generation bioactive material designed to accelerate the body\u27s natural ability to heal itself, was used in the research described herein to fabricate bone scaffolds using SLS process. 13-93 bioactive glass mixed with stearic acid (as the polymer binder) by ball milling was used as the powder feedstock for the SLS machine. The fabricated green scaffolds underwent binder burnout to remove the stearic acid binder and were then sintered at temperatures between 675ʻC and 700ʻC. The sintered scaffolds had pore sizes ranging from 300 µm to 800 µm with 50% apparent porosity and a maximum compressive strength of 23.6 MPa, which is the highest reported for controlled porosity scaffolds fabricated with bioactive glasses using the SLS process. The MTT labeling experiment and measurements of MTT formazan formation are evidence that the rough surface of SLS scaffolds, as seen in scanning electron microscope (SEM) images, provides a cell-friendly surface capable of supporting robust cell growth --Abstract, page iv

In Vitro Assessment of Laser Sintered Bioactive Glass Scaffolds with Different Pore Geometries

Purpose - The purpose of this paper is to utilize the selective laser sintering (SLS) process to fabricate scaffolds with complex pore shapes and investigate the effects of pore geometry in vitro. The pore geometry of scaffolds intended for use in bone repair is one of the most important parameters used to determine the rate of bone regeneration. Design/methodology/approach - Scaffolds with five different architectures, having approximately 50 per cent porosity, were fabricated with silicate (13-93) and borate (13-93B3)-based bioactive glasses using the SLS process. An established late-osteoblasts/early-osteocytes cell line was used to perform cell proliferation tests on the scaffolds. The cell-seeded scaffolds were incubated for two, four and six days followed by MTT assay to quantify the metabolically active cells. Findings - The results indicated that the cells proliferate significantly more on the scaffolds which mimic the trabecular bone architecture compared to traditional lattice structures. The surface roughness of the SLS-fabricated scaffolds drives the initial cell proliferation which is followed by curvature-driven cell proliferation. Originality/value - There have been very few studies on the effects of pore geometry on tissue growth and the existing reports do not provide clear indications. Instead of using bio-polymer or titanium-based scaffolds, we use bioactive glass scaffolds. The results obtained from this study add to the understanding of the effect of pore geometry on cell proliferation, which is based on the experimental data and analysis of the scaffolds\u27 surface curvature