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

Mathematical Modeling of Oxygen Transfer in Porous Scaffolds for Stem Cell Growth: The Effects of Porosity, Cell Type, Scaffold Architecture and Cell Distribution

Oxygen plays a key role in human mesenchymal stem cell growth. Without adequate oxygen (hypoxic condition), cells are not able to survive, proliferate, and migrate. The objective of the present study is to investigate oxygen transfer through the cell-seeded scaffolds stored in static or dynamic bioreactors using a mathematical model. The effects of porosity, cell type, scaffold architecture and cell distribution as potential effective parameters on oxygen transfer kinetics were examined. The results suggest the substantial effect of porosity and cell type on the oxygen concentration within the scaffold compared to scaffold architecture (homogeneous vs. gradient). The obtained data show that the direction of oxygen transfer in deep regions with dead cells changes over time and reverse mass transfer allows the cells to nourish from both top and bottom layers. Finally, the extent of oxygen transfer in static bioreactors/cultures was compared to dynamic ones. The results show that dynamic bioreactors have a better performance and are more efficient for oxygen transfer

Fused Deposition Modeling of Polymethylmethacrylate for Use in Patient-Specific Reconstructive Surgery

facial reconstruction and as bone cement and antibiotic-impregnated spacers in orthopaedics. The polymerization of PMMA in-situ causes tissue necrosis and other complications due to the long surgical times associated with mixing and shaping the PMMA. PMMA is a thermoplastic acrylic resin suitable for extrusion in FDM thus 3D anatomical models can be fabricated prior to surgery directly from medical imaging data. The building parameters required for successful FDM fabrication with medical-grade PMMA filament (1/16”Ø) were developed using an FDM 3000. It was found that a liquefier and envelope temperature of 235ºC and 55ºC, respectively, as well as increasing the model feed rate by 60%, were necessary to properly and consistently extrude the PMMA filament. Scaffolds with different porosities and fabrication conditions (tip wipe frequency and layer orientation) were produced, and their compressive mechanical properties were examined. Results show that both the tip wipe frequency (1 wipe every layer or 1 wipe every 10 layers) and layer orientation (transverse or axial with respect to the applied compressive load) used to fabricate the scaffolds, as well as the porosity of the scaffold had an effect on the mechanical properties. The samples fabricated with the high tip frequency had a larger compressive strength and modulus (Compressive strength: 16 ± 0.97 vs. 13 ± 0.71 MPa, Modulus: 370 ± 14 vs. 313 ± 29 MPa, for samples fabricated in the transverse orientation with 1 tip wipe per layer or 1 tip wipe per 10 layers, respectively). Also, the samples fabricated in the transverse orientation had a larger compressive strength and modulus than the ones fabricated in the axial orientation (Compressive strength: 16±0.97 vs. 13±0.83 MPa, Modulus: 370±14 vs. 281±22 MPa, for samples fabricated with 1 tip wipe per layer, in the transverse and axial orientation, respectively). Overall, the compressive strain for the samples fabricated with the four different conditions ranged from 8 – 12%. In regards to the porosity of the samples, in general, the stiffness, yield strength and yield strain decreased when the porosity increased (Compressive strength: 12±0.71 – 7±0.95 MPa, Modulus: 248±10 – 165±16 MPa, Strain: 7±1.5 – 5±1% for samples with a porosity ranging from 55 – 70%). The successful FDM fabrication of patient-specific, 3D PMMA implants with varying densities, including the model of a structure to repair a cranial defect and the model of a femur, was demonstrated. This work shows that customized structures with varying porosities to achieve tailored properties can be designed and directly fabricated using FDM and PMMA.Mechanical Engineerin

Design of a New 3D‐printed Joint Plug

This paper introduces a kit of parts as a novel three‐dimensional (3D)–printed joint plug, in which each of the parts function cooperatively to treat cartilage damage in joints of the human body (e.g., hips, wrists, elbow, knee, and ankle). Three required and one optional parts are involved in this plug. The first part is a 3D‐printed hard scaffold (bone portion) to accommodate bone cells, and the second is a 3D‐printed soft scaffold (cartilage portion) overlying the bone portion to accommodate chondrocytes. The third part of joint plug is a permeable membrane, termed film, to cover the entire plug to provide coordinated sliding of the joint during the regeneration of the cartilage. Film is also responsible for retention of the chondrocytes while allowing nutrients to diffuse through the membrane. The plug may further include a fourth part, called barrier, which is a membrane to assist the bone portion in avoiding the loss of chondrocytes from the cartilage portion beyond the barrier. Various engagement means among the parts of the plug are assumed, which are discussed in this paper. Moreover, the detailed design criteria and selection of suitable materials for different parts are elaborated. The 3D‐printing practice allows the plug to be personalized and fabricated to fit the shape/size of the target joint and the injured section. Also discussed are the configuration options of the plug to be surgically implanted in a joint. Although the focus of this paper is on the design, a brief overview of a prototype is presented

Computer Aided Tissue Engineering For The Generation Of Unit Library Structure Of Scaffold For Human Bone (In-Vitro)

Tissue engineering scaffold is a biological substitute that aims to restore, maintain or to improve tissue functions. The scaffold for orthopedic surgeries needs to be designed very accurately for absolute benefit to the patient. In this study various unit library structure designs for scaffold are presented for improvement in scaffold characteristics and advancements in its applications. These structures are designed to achieve the specific mechanical structure and properties which are superior to the available conventional techniques of scaffold fabrication. As the requirements for a better scaffold are met adequately through better and appropriate designing techniques, the prospects of fabricating a more successful engineering scaffold also improves. In this study, Finite Element Analysis was performed to investigate the characteristic features of the unit library structure designs to evaluate and examine their mechanical properties including porosity, effective modulus, compatibility with other designs and stress distribution. DICOM images for human foot were processed and reconstructed using image processing tools and 3D reconstruction software. The validated design of unit library structure was made in the bulk form and given a shape of reconstructed bone. Fused Deposition Modelling was used to manufacture the validated design

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

Additive Manufacturing of Porous Titanium Structures for Use in Orthopaedic Implants

This dissertation explores additive manufacturing of porous titanium structures for possible use as scaffolds in orthopaedics. Such scaffolds should be tailored in terms of mechanical properties and porosity to satisfy specific physical and biological needs. In this thesis, powder metallurgy was combined with additive manufacturing to successfully fabricate porous Ti structures. This study describes physical, chemical, and mechanical characterizations of porous titanium implants made by the proposed powder bed inkjet-based additive manufacturing process to gain insight into the correlation of process parameters and final physical and mechanical properties of the porous structure. A number of processing parameters were investigated to control the mechanical properties and porosity of the structure. In addition, a model was developed based on the microstructural powder compaction to predict the porosity as a function of the developed sinter neck among the particles during the sintering process. The produced samples were characterized through several methods including porosity measurement, compression test, Scanning Electron Microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX), and shrinkage measurements. Additionally, a new method for manufacturing Ti implants includes encapsulated networks of macro-sized channels was introduced. Also, the influence of different orientations and numbers of channels within the additive-manufactured structures were investigated. The characterization test results showed a level of porosity in the samples in the range of 12-43%, which is within the range of cancellous and cortical bone porosity. The compression test results showed that the porous structure’s compressive strength is in the range of 56-1000 MPa, yield strength is in the range of 27-383 MPa, and Young’s modulus is in the range of 0.77-11.46 GPa. This technique of manufacturing porous Ti structures demonstrated a low level of shrinkage with the shrinkage percentage ranging from 1.5-12%. Also, the experimental results demonstrated excellent agreement with the developed model. Moreover, the novel method of fabricating the encapsulated channel show a reduction in the shear strength to 24-30% that is advantageous for bone implants. The results demonstrate that the channel orientation in the structure affect the shrinkage rate in the parts with vertically orientated channels, in which a relatively isotropic shrinkage in vertical and horizontal directions is achieved after sintering