Developing a novel biocomposite on selective laser sintering for tissue engineering

Selective Laser Sintering (SLS) is used to fabricate tissue engineering scaffold due to its versatility in processing various polymeric materials and good stability of its products. Propriety SLS materials are non-biocompatible as they were conventionally invented for production of industrial parts. Suitable biomaterial powders that can be processed in SLS without allowing damages on the material properties need to be identified. A theoretical study based on heat transfer phenomena during SLS process was carried out to identify the significant biomaterial and laser beam properties that influence the sintering result. Poly(vinyl alcohol) (PVA) and hydroxyapatite (HA) were identified as elements for the biocomposite. The most prominent sintering results were obtained by mechanical mixing of as-received PVA and HA powder, which yielded homogenous biocomposite powders with good repeatability. Characterization studies found that chemical composition of PVA as the scaffold matrix was not affected during the sintering process. PVA/HA (5 vol.% HA) scaffolds gave compression stress and compression modulus up to 2.26 MPa and 8.30 MPa, respectively, which is suitable for application in the craniomaxillofacial skeleton area. Cell culture study using osteoblast-like Saos-2 cells found that cell proliferation was favourable on the SLS fabricated scaffold.DOCTOR OF PHILOSOPHY (MAE

Selective laser melting of titanium alloy with 50 wt% tantalum : microstructure and mechanical properties

In this study, selective laser melting (SLM) was used to fabricate samples of titanium-tantalum (TiTa) alloy comprising 50 wt% of each element. Based on observation from scanning electron microscopy, as-fabricated samples comprised of randomly dispersed pure tantalum particles in a TiTa matrix. The microstructure exhibited equiaxed grains of β titanium and tantalum in random orientations, determined by combination of field emission scanning electron microscopy, electron back scatter diffraction and X-ray diffraction. The resulting samples have ultimate tensile strength of 924.64 ± 9.06 MPa and elastic modulus of 75.77 ± 4.04 GPa. The TiTa alloy produced can be a potential material for biomedical applications due to its high strength to modulus ratio, as compared to Ti6Al4V and commercially pure titanium.Accepted versio

Characterisation of micro-lattices fabricated by selective laser melting

β-titanium alloys have been touted as the new titanium alloys in biomedical applications due to its lower elastic modulus as compared to the titanium alloys of other phases. In particular, titanium-tantalum has been explored for such applications due to the high biocompatibility of both titanium and tantalum. The alloying and fabrication of titanium-tantalum using selective laser melting have been proven in previous study. In this study, the effect of SLM processing parameters on the porosity and compression behaviour of titanium-tantalum microlattice structures is investigated. The as-fabricated micro-lattices have elastic constants ranging from 1.36 ± 0.11 GPa to 6.82 ± 0.15 GPa and yield strength of between 31.93 ± 3.79 MPa and 426.84 ± 19.62 MPa. The range of mechanical properties exhibited by the lattice structures shows the versatility of SLM in producing titanium-tantalum lattice structures for orthopaedic applications.Published versio

Selective laser melting of lattice structures: a statistical approach to manufacturability and mechanical behavior

This paper investigates the effect of processing parameters on the dimensional accuracy and mechanical properties of cellular lattice structures fabricated by additive manufacturing, also known as 3D printing. The samples are fabricated by selective laser melting (SLM) using novel titanium-tantalum alloy. The titanium-tantalum alloy has the potential to replace commercially pure titanium and Ti6Al4V as biomedical material. In this study, the unit cell used is specially designed to carry out the analysis using regression method and analysis of variance (ANOVA). Due to the effect of the SLM process parameters, the elastic constant of the cellular lattice structures ranged from 1.36 ± 0.11 to 6.82 ± 0.15 GPa using the same unit cell design. The elastic constant range, while showing the versatility of titanium-tantalum as biomedical material, is rather wide despite using the same lattice structure designed. This shows that there is a need to carefully control the processing parameters during the lattice structures fabrication so as to obtain the desired mechanical properties. Based on the statistical analysis, it is found that the dimensional accuracy and mechanical properties such as elastic constant and yield strength of the cellular lattice structures are most sensitive to laser power as compared to other parameters such as laser scanning speed and powder layer thickness

Selective Laser Melting of Novel Titanium-Tantalum Alloy as Orthopedic Biomaterial

Selective laser melting (SLM) is an additive manufacturing (AM) technique that is capable of fabricating complex functional three-dimensional (3D) metal parts directly from the complete melting and fusion of powders. As a powder bed fusion technology, SLM has the potential to expand its material library by forming alloys that were previously difficult to achieve by using metal powder mixtures that can be customized according to the application requirements. Titanium-tantalum (TiTa) is a material that has potential uses in biomedical applications due to its high strength-to-modulus ratio. However, it is still not widely used because it is difficult to obtain. SLM is chosen as the method to form this alloy due to its versatility in processing metallic materials and good results obtained from commercially pure titanium (cpTi). Preliminary studies using cpTi lattice structures designed for biomedical applications were carried out. This research aims to develop TiTa as a material to be potentially used in biomedical field by investigating its processing window, resulting microstructure, and mechanical properties.Mechanical Engineerin

Fabrication of samaria doped ceria thin film on porous substrate by slurry spin coating

Samaria doped cena (SDC) with fluorite structure has higher ionic conductivity than Yttria stabilized zirconia (YSZ) for low temperature solid oxide fùel cells (LT-SOFCs). SDC powder with cubic fluorite structure was synthesized by co-precipitation method at calcined temperature of 600 °C. The average crystallite size of the calcined SDC powder is around 15 nm determined from XRD data. The thickness of SDC thin film deposited on porous silver substrate is nearly proportional to the coating layers tìich are controllable by repeating the spin coating process. The spin-coated SDC thin film on porous silver substrate showed partially dense and uneven microstructure after sintered at 800 oc fbr 10 hours. Moreover, the microstructures were changed to notably porous structure at sintering temperature of 900 and 1000 °C for 10 hours. The SDC thin film spin-coated on Si substrate showed identical surface morphologies and more even microstructures with on porous silver substrates at the corresponding sintering temperature. The fully dense SDC thin film was obtained on the Si substrate at sintening temperature of 1300 oc for 10 hours. The result indicates that the sintering temperature is not enough for fully sintering the SDC powder into dense film and the porous substrate would make the uneven microstructure.Published versio

Selective laser melting of titanium alloy with 50 wt% tantalum : effect of laser process parameters on part quality

Selective laser melting (SLM) is a powder bed fusion additive manufacturing (AM) technique that produces three-dimensional (3D) parts by fusing metallic powders with a high-energy laser. SLM involves numerous process parameters that may influence the properties of the final parts. Hence, establishing the effect of the SLM processing parameters is important for producing parts of high quality. In this study, titanium-tantalum alloy was fabricated by SLM using a customized powder blend to achieve in situ alloying. The influence of processing parameters on the microstructure and properties such as relative density, microhardness and surface roughness was investigated. The results show that fully dense titanium-tantalum parts can be obtained from SLM. With laser power of 360 W, scan speed of 400 mm/s, powder layer thickness of 0.05 mm and hatch spacing of 0.125 mm, the titanium-tantalum alloy produced by SLM has relative density of 99.85 ± 0.18%. Despite the variation in process parameters, titanium-tantalum shows laminar β grains in random directions in both xy and yz-plane from optical microscope (OM) analysis in all the parts produced. This observation is further confirmed using x-ray diffraction (XRD).Accepted versio

Characterization of Titanium Lattice Structures Fabricated by Selective Laser Melting Using an Adapted Compressive Test Method

This paper investigates the effect of designs and process parameters on the dimensional accuracy and compressive behavior of cellular lattice structures fabricated using selective laser melting (SLM). Two unit cell types, square pyramid and truncated cube & octahedron from the Computer Aided System for Tissue Scaffolds (CASTS), an in-house developed library system were used. Powder adhesions occur on the struts of the lattice structures. The thickness of powder adhesion on the struts decreases with an increase in laser power or laser scan speed. The elastic constant in compression of the lattice structures increases with an increase in relative density, and ranged from 7.93 ± 2.73 MPa to 7.36 ± 0.26 GPa. Analysis of Variance (ANOVA) is also carried out to determine the significance of various process and design parameters on the dimensional accuracy and compressive strength of the lattice structures. The processing parameters, such as laser power and laser scan speed have no significant effect on the elastic constant but have a significant effect on the powder adhesion on the struts, which in turn, affects the dimensional accuracy. However, geometrical design parameters such as unit cell type and strut diameter have significant effects on the elastic constant but not dimensional accuracy of the lattice structures