Joy Rizki Pangestu Djuansjah

Sandwiched polymer fibre in fibrin matrices for the dictation of endothelial cells undergoing angiogenesis

We present here a three-dimensional (3D) sandwich system made by poly(ethylene terephthalate) (PET) fibre and fibrin extracellular matrix (ECM) for endothelial cell dictation and angiogenesis guidance. In this three-dimensional system, Human Umbilical Vein Endothelial cells (HUVECs) were firstly cultured for 2 (two) days to cover the PET fibre before sandwiched in two layer fibrin gel containing HUVECs. After 4 (four) days of culture, cel-to-cel connection, tube-like structure and multi-cellular lumen formation were then assessed and validated. Phase contrast and fluorescence imaging using an inverted microscope were used to determine cell-to-cell and cell-ECM interactions. Laser scanning confocal microscopy and histological techniques were used to confirm the development of tube-like structure and multi-cellular lumen formation. This study shows that polymer fibres sandwiched in fibrin gel can be used to dictate endothelial cells undergoing angiogenesis with potential application in cancer and cardiovascular study and tissue engineering vascularisation.

Linear Elastic Analysis of Bovine Cortical Bone under Compression Loading

Linear elastic response of the bovine cortical bone has been examined under compression load. Experimental and computational methods were used to observe and predict the response of cortical bone. In computational method, two mechanical behaviors of isotropic and orthotropic were considered to simulate the cortical bone deformation. In experimental process, the specimens were designed to show maximum stiffness and strength by specifying osteon direction along loading axis during tests. The tests were controlled by displacement rate of 0.5 mm/minute and the overall stiffness responses of the structures were recorded to extract mechanical properties and also for validation aims. Finite Element Method (FEM) was used to model the linear response of the structure by using ABAQUS6.9EF. The FE results using orthotropic definition shows a good correlation with experimental data. A discussion was given based on overall stiffness and effective stress variation for both mechanical behaviors. In order to design the optimal implant structure, the presented study was proposed for prediction of bone structure deformation that attached to the orthopedic implants.

Assessment of compressive failure process of cortical bone materials using damage-based model

The main failure factors of cortical bone are aging or osteoporosis, accident and high energy trauma or physiological activities. However, the mechanism of damage evolution coupled with yield criterion is considered as one of the unclear subjects in failure analysis of cortical bone materials. Therefore, this study attempts to assess the structural response and progressive failure process of cortical bone using a brittle damaged plasticity model. For this reason, several compressive tests are performed on cortical bone specimens made of bovine femur, in order to obtain the structural response and mechanical properties of the material. Complementary finite element (FE) model of the sample and test is prepared to simulate the elastic-to-damage behavior of the cortical bone using the brittle damaged plasticity model. The FE model is validated in a comparative method using the predicted and measured structural response as load-compressive displacement through simulation and experiment. FE results indicated that the compressive damage initiated and propagated at central region where maximum equivalent plastic strain is computed, which coincided with the degradation of structural compressive stiffness followed by a vast amount of strain energy dissipation. The parameter of compressive damage rate, which is a function dependent on damage parameter and the plastic strain is examined for different rates. Results show that considering a similar rate to the initial slope of the damage parameter in the experiment would give a better sense for prediction of compressive failure.

Characterisation of Al65Cu20Fe15 Quasicrystal Alloy Synthesised via In-situ Casting under Standard Room Ambient and Argon Enriched Atmosphere

Characterisation on a series of bulk Al65Cu20Fe15 quasicrystal alloy synthesised via in-situ induction casting under argon (Ar) enriched atmosphere and standard room ambient is the focal point of this research. The significance of atmospheric inertness in the course of induction casting process as well as the impacts of subsequent heat treatment at 650°C under 5 hours dwelling duration on the metallography of Al65Cu20Fe15 quasicrystal alloy were investigated through VPSEM coupled with EDX as well as XRD. The Al65Cu20Fe15 quasicrystal alloy specimens produced by induction casting under critically controlled inert environment and standard room ambient as well as subjected to posterior heat treatment process were inspected via vickers hardness test in accordance to ISO 6507-1:1997. Research findings inferred that inert atmospheric condition during induction casting is critical for the formation of icosahedral, i phase and served as oxidation retardant to the Al-Cu-Fe ternary system alloy, while the subsequent heat treatment at 650°C promoted the grain growth of Al65Cu20Fe15 icosahedral quasicrystalline compound.

Effect of Cold Rolling Treatment on the Formation of Titanium Oxide Layer on Ti6Al4V Alloys by Thermal-electrochemical Anodizing Processes

The present work concerns on preparing suitable titanium alloy substrate that might induce better characteristic of titanium oxide layer on the substrate. Different degree of cold rolling treatments were applied on Ti6Al4V alloy before thermal-electrochemical anodizing processes. The later processes were performed to produce titanium oxide layer which combines thermal process by heat treatment and followed with electrochemical anodizing process. After thermal heat treatment process, it was observed more homogeneous titanium oxide layer for the samples given cold rolling treatment as compared with sample without the treatment. This condition is believed due to the finer substrate surface after cold rolling treatment as observed from surface roughness measurement. Similar situation was observed after anodizing process that irregular oxidized layer was observed for sample without cold rolling treatment, whereas more homogenous layer was observed for sample with cold rolling treatment. Except for sample without cold rolling treatment, anodizing treatment tends to create finer oxidized layer. Therefore, it can be concluded that cold rolling treatment on titanium substrate before oxidizing process induces the formation of homogeneous oxide layer, whereas additional anodizing process create finer titanium oxide layer.

Development of Phase Field Simulation for the Growth of Dendrite Structure of Al-Si Cast Alloy

Micro to nano scale study of dendrite structure is important in order to have better properties control of casting product. The present study concerns on the morphological study of dendrite structure by phase-field simulation, in order to obtain the morphological growth of this structure that close its real morphology. Focus was given on the morphological growth of dendrite structure of Al-Si cast alloys, therefore thermodynamic data were taken for this type of materials. Anisotropy noise, strength of anisotropy and different undercooled conditions were applied as the variable parameters in the present works. It was observed that by introducing higher anisotropy noise, higher degree fragmentation of dendrite structure was obtained. Similar condition was obtained by introducing higher strength of anisotropy value, that higher degree of fragmentation was obtained. Both of these phenomena was also supported by the heat flux rate features of these variations that higher heat flux rate to almost all direction was obtained with the higher value of anisotropy noise and strength of anisotropy. In addition it was also observed that higher degree fragmentation of dendrite only possible to occur if sufficient undercooled condition established.

Formation of Titanium Oxide by Thermal-Electrochemical Process on the Blasted Titanium Alloys Substrate

Titanium oxide is believed as one of the key factors that influence the excellent corrosion properties as well as biocompatibility of titanium alloy. In the present research, thermal-electrochemical anodizing processes were performed in order to form thick layer of titanium oxide on titanium alloys (Ti6Al4V) surface. Oxidation temperature, blasting and anodizing voltage were selected as the evaluated parameters process at the present study. It was observed that temperature plays important role in the formation of oxide layer, where the thickness of the oxide increases significantly as temperature increases. However, for the case of oxide layer formed by thermal oxidation at temperature of 950oC, oxide layer on the non-blasted sample become easily peel off, whereas oxide layer on the blasted sample shows good adhesion properties. In addition, oxide layer on the blasted samples also have thicker layer as compared with oxide on the non-blasted sample. On the other hand, it was observed that further oxidation by anodizing at 43V and 63V create finer oxide layer by the filled up of porosity on the existing oxide layer. However decreasing of oxide layer thickness was also observed after anodizing, which is predicted due to the breaking up the outer oxide layer during anodizing process.