Sharif Digital Repository

This paper presents a simplified Multi-Degree-Of-Freedom (MDOF) model through modification of fish-bone model (or generic frame). Modified Fish-Bone (MFB) model is developed through three enhancements: (i) the moment of inertia for half-beams is reduced slightly to modify the assumption of equal rotation at each story joints, (ii) a number of truss elements are inserted to the fish-bone model to simulate flexural deformation of moment frames due to axial elongation and contraction of columns, and (iii) moment-rotation relationship of representative rotational springs is supposed to be bilinear instead of trilinear in order to consider simultaneous yielding at both ends of the beam in moment... 

Controlling topographic features at all length scales is of great importance for the interaction of cells with tissue regenerative materials. We utilized an indirect three-dimensional printing method to fabricate polymeric scaffolds with pre-defined and controlled external and internal architecture that had an interconnected structure with macro- (400-500 μm) and micro- (∼25 μm) porosity. Polycaprolactone (PCL) was used as model system to study the kinetics of tissue growth within porous scaffolds. The surface of the scaffolds was decorated with TiO2 and bioactive glass (BG) nanoparticles to the better match to nanoarchitecture of extracellular matrix (ECM). Micrometric BG particles were... 

An analytical approach which is popular in micromechanical studies has been extended to the solution for the interference fit problem of the femoral stem in cementless total hip arthroplasty (THA). The multiple inhomogeneity problem of THA in transverse plane, including an elliptical stem, a cortical wall, and a cancellous layer interface, was formulated using the equivalent inclusion method (EIM) to obtain the induced interference elastic fields. Results indicated a maximum interference fit of about 210 μm before bone fracture, predicted based on the Drucker-Prager criterion for a partially reamed section. The cancellous layer had a significant effect on reducing the hoop stresses in the... 

Mechanical alloying and sintering were used to fabricate nanostructured Ti6Al4V scaffolds of highly controllable pore geometry and fully interconnected porous network. Elemental powders were milled for different periods of time (10, 20, 30, 40 and 60 h), mixed with 40-60 vol.-% of 200-400 μm cuboidal NaCl, compacted at 500-600 MPa and sintered according to single or double stage heat treatment regimes at 790 and 950°C under vacuum. After sintering, the samples were soaked in distilled water to washout the NaCl. Foamy microstructures were obtained showing well shaped biopores and fragmentary embedded micropores. The shape of initial NaCl was copied into the biopores which had highly... 

Aseptic loosening of femoral components is a significant problem affecting the life of current total knee replacements. To help reduce the problem of aseptic loosening, a new metal-ceramic poros functionally graded biomaterial (FGBM) has been designed to replace the existing metal alloy material normally used. In order to investigate the effect of using a FGBM on distal femur stresses compared to using standard material in a femoral component, a three-dimensional finite element model of the knee prosthesis has been developed. The results of the modeling and subsequent analysis indicate that by using the new FGBM compared to the existing material in a femoral component, higher levels of... 

The aim of this study was to use finite element analysis (FEA) to assess the influence of microthread design at the implant neck on stress distribution in the surrounding bone. A commercially available implant with 3.5 mm diameter and 10.5 mm length was selected and used as a model. For the purpose of designing the microthread implant model, microthreads were added to the implant neck in a computerized model. A force measuring 100 N was then applied to the entire surface of the abutment in the vertical direction. The results showed that in both models, stress was mainly concentrated at the cortical bone adjacent to the neck of the implant. Maximum stress values in the cortical bone... 

Hydroxyapatite (HA) is the most substantial mineral constituent of a bone which has been extensively used in medicine as implantable materials, owing to its good biocompatibility, bioactivity high osteoconductive, and/or osteoinductive properties. Nevertheless, its mechanical property is not utmost appropriate for a bone substitution. Therefore, a composite consist of HA and a biodegradable polymer is usually prepared to generate an apt bone scaffold. In the present work polycaprolactone (PCL), a newly remarkable biocompatible and biodegradable polymer, was employed as a matrix and hydroxyapatite nanoparticles were used as a reinforcement element of the composite. HA/PCL nanocomposites were... 

Hydroxyapatite (HA) is the most substantial mineral constituent of a bone which displays splendid biocompatibility and bioactivity properties. Nevertheless, its mechanical property is not utmost appropriate for a bone substitution. Therefore, a composite consist of HA and a biodegradable polymer is usually prepared to generate an apt bone scaffold. In the present work polycaprolactone (PCL) was employed as a matrix and hydroxyapatite nanorods were used as a reinforcement element of the composite. HA/PCL nanocomposites were synthesized by a new in-situ sol-gel process using low cost chemicals. Chemical and physical characteristics of the nanocomposite were studied by X-ray diffraction (XRD),... 

In this research, bioactive glass (BG) of the type CaO-P2O 5-SiO2 and nanocrystalline forsterite (NF) bioceramic were successfully synthesized via sol-gel processing method. Heat-treatment process was done to obtain phase-pure nanopowders. After characterization of each sample, the nanocomposite samples were prepared by cold pressing method and sintered at 1000°C. The samples were fully characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR) analyses. The average nanocrystallite size was determined using the Debye-Scherrer's formula 19.6 nm. The bioactivity was examined in vitro... 

On July 24th, 2010, several explosions and fires devastated a hydrocarbon processing plant in Kharg Island, Iran. Four workers were killed and many others were severely injured. The plant became out of service for 80 days. The way the accident happened and its sequence was representing as a domino accident. In this paper, events leading up to the disaster have been analyzed in details. Graphic presentation techniques such as Fish Bone Analysis and Event Sequence Diagram (ESD) have been utilized to enhance the understanding of the accident mechanism. Finally major lessons learnt from this domino accident have been addressed  

A computational framework was developed to simulate the bone remodelling process as a structural topology optimisation problem. The mathematical formulation of the Level Set technique was extended and then implemented into a coronal plane model of the proximal femur to simulate the remodelling of internal structure and external geometry of bone into the optimal state. Results indicated that the proposed approach could reasonably mimic the major geometrical and material features of the natural bone. Simulation of the internal bone remodelling on the typical gross shape of the proximal femur, resulted in a density distribution pattern with good consistency with that of the natural bone. When... 

The low erosion resistance of titanium and its alloys has prevented their widespread application as joint implants. In addition, one essential requirement for the implants to bond with the living bone is the formation of a bone-like apatite on their surfaces in the host body. To enhance the erosion resistance of the surface, a diffused layer of TiB2 was formed at 1000uC on the commercial pure titanium. Hydroxyapatite was then coated on the boronised titanium by means of dip coating in a sol-gel solution. In order to confirm the biocompatibility of the specimens, they were soaked in a simulated body fluid for several days. The surface morphology of the specimens after exposure was studied by... 

Purpose - The purpose of this paper is to present an improved methodology for design of custom-made hip prostheses, through integration of advanced image processing, computer aided design (CAD) and additive manufacturing (AM) technologies. Design/methodology/approach - The proposed methodology for design of custom-made hip prostheses is based on an independent design criterion for each of the intra-medullary and extra-medullary portions of the prosthesis. The intra-medullar part of the prosthesis is designed using a more accurate and detailed description of the 3D geometry of the femoral intra-medullary cavity, including the septum calcar ridge, so that an improved fill and fit performance... 

Porous NiTi shape memory alloy (SMA) was fabricated by sintering of compressed constituent elements pre-mixed with NaCl or urea spacer holders. Effect of spacer to metal volume-ratio (r S) on shape, size, distribution and openness of the voids was probed by optical metallography, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Differential scanning calorimetry (DSC) was used to determine the SMA transformation temperatures. Controllable void geometry helping osteoblast proliferation and bone cell growth was gained by addition of the spacers. At r S = 0.7, percentage of the open pores reached 52% while at r S = 1.43, interconnected pores with 200 to 500 μm diameter were... 

In this study, Porous NiTi shape memory alloy has been produced by mechanical alloying of the elemental Ni and Ti powders. The compacting process was done at two temperatures (warm and cold press) and then sintering at 980 and 1050°C was performed on the specimens. Microstructure and mechanical prop-erties of the samples were investigated by optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction. Moreover, shear punch test (SPT) employed to investigate the effect of compaction pressure and sintering temperature on the mechanical properties of the fabricated samples. It was revealed that warm compaction/sintering resulted in 15% yield stress improvement and 20% ultimate... 

Bone Tissue Engineering (BTE) composed of three main parts: scaffold, cells and signaling factors. Several materials and composites are suggested as a scaffold for BTE. Biocompatibility is one of the most important property of a BTE scaffold. In this work synthesis of a novel nanocomposite including layered double hydroxides (LDH) and gelatin is carried out and its biological properties were studied. The co-precipitation (pH=11) method was used to prepare the LDH powder, using calcium nitrate, Magesium nitrate and aluminum nitrate salts as starting materials. The resulted precipitates were dried. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron... 

Osseointegrated dental implants are deficient in natural periodontal ligaments. It may therefore, disrupts the natural function of implant and leads to excessive stress and strain in jaw bone. Our new proposed implant has the nonlinear internal component which imitates periodontal ligaments function. A nonlinear finite element analysis developed to investigate the efficiency of utilizing this nonlinear internal layer for three conditions of bone implant interface conditions under vertical and horizontal loading conditions. Our results so far indicate that the use of a class of material exhibiting incompressible hyperelastic behaviour as a internal layer can reduce the peak stress deduced... 

This review covers the most recent developments of inorganic and organic-inorganic composite coatings for orthopedic implants, providing the interface with living tissue and with potential for drug delivery to combat infections. Conventional systemic delivery of drugs is an inefficient procedure that may cause toxicity and may require a patient's hospitalization for monitoring. Local delivery of antibiotics and other bioactive molecules maximizes their effect where they are required, reduces potential systemic toxicity and increases timeliness and cost efficiency. In addition, local delivery has broad applications in combating infection-related diseases. Polymeric coatings may present some... 

In this study, superparamagnetic iron oxide nanoparticles (SPION) embedded by folic acid (SPION-folate) were prepared by a modified co-precipitation method. The structure, size, morphology, magnetic property and relaxivity of the SPION-folate were characterized systematically by means of XRD, VSM, HRSEM and TEM and the interaction between folate and iron oxide (Fe3O 4) was characterized by FT-IR. The particle size was shown to be ≈5-10 nm. To ensure biocompatibility, the interaction of these SPION with mouse connective tissue cells (adhesive) was investigated using an MTT assay. Consequently, gallium-67 labeled nanoparticles ([67Ga]-SPION-folate) were prepared using 67Ga with a high labeling... 

Abstract: In this study, chitosan–Laponite nanocomposite coatings with bone regenerative potential and controlled drug-release capacity are prepared by electrophoretic deposition technique. The controlled release of a glycopeptide drug, i.e. vancomycin, is attained by the intercalation of the polymer and drug macromolecules into silicate galleries. Fourier-transform infrared spectrometry reveals electrostatic interactions between the charged structure of clay and the amine and hydroxyl groups of chitosan and vancomycin, leading to a complex positively-charged system with high electrophoretic mobility. By applying electric field the charged particles are deposited on the surface of titanium...