Khurshid Alam

Bio: Khurshid Alam is an academic researcher from Sultan Qaboos University. The author has contributed to research in topics: Cortical bone & Drilling. The author has an hindex of 14, co-authored 56 publications receiving 873 citations. Previous affiliations of Khurshid Alam include National University of Sciences and Technology & University of the Sciences.

Analysis of anisotropic viscoelastoplastic properties of cortical bone tissues.

Abstract: Bone fractures affect the health of many people and have a significant social and economic effect. Often, bones fracture due to impacts, sudden falls or trauma. In order to numerically model the fracture of a cortical bone tissue caused by an impact it is important to know parameters characterising its viscoelastoplastic behaviour. These parameters should be measured for various orientations in a bone tissue to assess bone’s anisotropy linked to its microstructure. So, the first part of this study was focused on quantification of elastic–plastic behaviour of cortical bone using specimens cut along different directions with regard to the bone axis—longitudinal (axial) and transverse. Due to pronounced non-linearity of the elastic–plastic behaviour of the tissue, cyclic loading–unloading uniaxial tension tests were performed to obtain the magnitudes of elastic moduli not only from the initial loading part of the cycle but also from its unloading part. Additional tests were performed with different deformation rates to study the bone’s strain-rate sensitivity. The second part of this study covered creep and relaxation properties of cortical bone for two directions and four different anatomical positions–anterior, posterior, medial and lateral–to study the variability of bone’s properties. Since viscoelastoplasticity of cortical bone affects its damping properties due to energy dissipation, the Dynamic Mechanical Analysis (DMA) technique was used in the last part of our study to obtain magnitudes of storage and loss moduli for various frequencies. Based on analysis of elastic–plastic behaviour of the bovine cortical bone tissue, it was found that magnitudes of the longitudinal Young’s modulus for four cortical positions were in the range of 15–24 GPa, while the transversal modulus was lower — between 10 and 15 GPa. Axial strength for various anatomical positions was also higher than transversal strength with significant differences in magnitudes for those positions. Quantitative data obtained in creep and relaxation tests exhibited no significant position-specific differences. DMA results demonstrated relatively low energy-loss capability due to viscosity of bovine cortical bone that has a loss factor in the range of 0.035–0.1.

Measurements of Surface Roughness in Conventional and Ultrasonically Assisted Bone Drilling

Abstract: Bone fracture due to an accident, aging or diseases is a feature of everyday life. One of the principal methods of repair and reconstruction of such a fracture is based on drilling the bone and fixing its separate parts together using screws, wires and plates. Morphology of the drilled hole surface and fixative components such as screws, pins and hooks influences strength of the bonds between them. Modern measurement methods provide researchers with a high-precision data on the main parameters of surface roughness. This study is concerned with measurements of surface roughness of holes drilled in a cortical bone using two drilling techniques. Hole’s surface roughness produced with conventional drilling (CD) and ultrasonically assisted drilling (UAD) was measured with, and compared for, various contact and non-contact methods. The difference in surface roughness for both drilling techniques was explained based on high-speed filming of the bone drilling processes.

Thermal analysis of orthogonal cutting of cortical bone using finite element simulations

Abstract: Bone cutting is widely used in orthopaedic, dental and neuro surgeries and is a technically demanding surgical procedure. One of the major concerns in current research is thermal damage of the bone tissue caused by high-speed power tools, which occurs when temperature rises above a certain threshold value for the tissue known as bone necrosis. Hence, optimisation of cutting parameters is necessary to avoid thermal necrosis and improve current orthopaedic surgical procedures. In this study a thermo-mechanical finite element model of bone cutting is presented that idealises cortical bone as an equivalent homogeneous isotropic material. The maximum temperature in the bone was found in the region where the thin bone layer (chip) was separated from the bone sample that was adjacent to the tool rake (i.e., front face of the tool). Temperature values were calculated with the model and compared for cutting conditions with and without a coolant (irrigation). The influence of bone's thermal properties on the depth of thermal necrosis is discussed. The simulated cutting temperatures were compared with experimental results obtained in bone drilling tests. Simulations of the cutting processes identified critical variables and cutting parameters affecting thermo-mechanics of bone cutting.

Effects of extracellular matrix viscoelasticity on cellular behaviour.

Abstract: Substantial research over the past two decades has established that extracellular matrix (ECM) elasticity, or stiffness, affects fundamental cellular processes, including spreading, growth, proliferation, migration, differentiation and organoid formation. Linearly elastic polyacrylamide hydrogels and polydimethylsiloxane (PDMS) elastomers coated with ECM proteins are widely used to assess the role of stiffness, and results from such experiments are often assumed to reproduce the effect of the mechanical environment experienced by cells in vivo. However, tissues and ECMs are not linearly elastic materials-they exhibit far more complex mechanical behaviours, including viscoelasticity (a time-dependent response to loading or deformation), as well as mechanical plasticity and nonlinear elasticity. Here we review the complex mechanical behaviours of tissues and ECMs, discuss the effect of ECM viscoelasticity on cells, and describe the potential use of viscoelastic biomaterials in regenerative medicine. Recent work has revealed that matrix viscoelasticity regulates these same fundamental cell processes, and can promote behaviours that are not observed with elastic hydrogels in both two- and three-dimensional culture microenvironments. These findings have provided insights into cell-matrix interactions and how these interactions differentially modulate mechano-sensitive molecular pathways in cells. Moreover, these results suggest design guidelines for the next generation of biomaterials, with the goal of matching tissue and ECM mechanics for in vitro tissue models and applications in regenerative medicine.

Drilling of bone: A comprehensive review.

Abstract: Background Bone fracture treatment usually involves restoring of the fractured parts to their initial position and immobilizing them until the healing takes place. Drilling of bone is common to produce hole for screw insertion to fix the fractured parts for immobilization. Orthopaedic drilling during surgical process causes increase in the bone temperature and forces which can cause osteonecrosis reducing the stability and strength of the fixation. Methods A comprehensive review of all the relevant investigations carried on bone drilling is conducted. The experimental method used, results obtained and the conclusions made by the various researchers are described and compared. Result Review suggests that the further improvement in the area of bone drilling is possible. The systematic review identified several consequential factors (drilling parameters and drill specifications) affecting bone drilling on which there no general agreement among investigators or are not adequately evaluated. These factors are highlighted and use of more advanced methods of drilling is accentuated. The use of more precise experimental set up which resembles the actual situation and the development of automated bone drilling system to minimize human error is addressed. Conclusion In this review, an attempt has been made to systematically organize the research investigations conducted on bone drilling. Methods of treatment of bone fracture, studies on the determination of the threshold for thermal osteonecrosis, studies on the parameters influencing bone drilling and methods of the temperature measurement used are reviewed and the future work for the further improvement of bone drilling process is highlighted.

Part strength evolution with bonding between filaments in fused deposition modelling

Abstract: The present work investigates, by both mathematical modelling and experiment, the contribution of bonding between the filaments to the strength of the parts manufactured by fused deposition modelling (FDM). A mathematical model for neck growth between cylindrical filaments is derived based on viscous sintering for cylindrical filaments. Theoretical ultimate tensile load is determined from the layer thickness information and predicted average final neck size between filaments. The experimental ultimate tensile load is obtained by conducting a simple tension test with two different build directions. Agreement between theoretical and experimental ultimate tensile load and scanning electron microscope (SEM) photomicrographs of the fracture surface indicate that the strength of the FDM part is primarily due to intra-layer bonding, inter-layer bonding and neck growth between filaments. It also indicates that the total time and heat available to the filaments are just sufficient to grow necks but not enough to f...