Papers by Morad Karimpour
Biomed Research International, 2024
Purpose: Dental reconstruction for patients diagnosed with severe mandibular bone atrophy using c... more Purpose: Dental reconstruction for patients diagnosed with severe mandibular bone atrophy using common dental implants is a challenging process. In such cases, surgeons may encounter challenges such as insufficient available bone, soft tissue, damage to the inferior alveolar nerve, and even the risk of bone fracture. In this study, a new design concept of mandibular patient-specific implants for severely atrophic ridges followed by finite element evaluation was presented to investigate the mechanical functionality of the concept. Method: The implant is comprised of two modular parts including an inferior border cover and a horseshoe-shaped structure. This horseshoe segment fits into the cover and is then screwed to it using two screws on each side. A 1 mm deflection was applied to a reference point located between the two anterior posts to extract the resulting Von Mises stress distribution in each part and the reaction force on the reference point which corresponds to the chewing force that the patient must apply to deform the horseshoe. This 1 mm gap is a design consideration and critical distance that horseshoe contacts the gingiva and disturbs the alveolar nerve. Results: The results revealed that load was transmitted from the horseshoe to the cover, and there were no stress contours on the body of the mandible. However, stress concentration was observed in screw locations in the mandible, the amount of which was decreased by increasing the number of used screws. In horseshoe, stress concentration values were around 350 MPa, and the measured reaction force on the reference point was just under 200 N. Conclusion: The finite element analysis results showed that this concept would be functional as the minimum load would be transmitted to the mandibular ridge, and since the patients diagnosed with atrophic ridge are not able to apply load to an amount near 200 N, the horseshoe would not contact the gingiva. Also, it is concluded that increasing the number of bone screw fixations would decrease the risk of long-term screw loosening.
Journal of Orthopaedics, Jun 1, 2024
Journal of craniomaxillofacial research, Apr 7, 2024
Background: Musculoskeletal modeling has paved the way of measuring kinematic and kinetic variabl... more Background: Musculoskeletal modeling has paved the way of measuring kinematic and kinetic variables during motions. Nonetheless, since the commonly-used generic models are created based on averaged data; thus, they cannot accurately mimic subjects with skeletal deformities. To overcome this obstacle, one can build personalized models based on subjects MRI or CT scan data, which is both time and money consuming. The other promising way is to manipulate generic models and create semi-personalized models to match with the individuals skeletal system at the joint of interest. Research Question: Can a semi-personalized model reduce marker error in gait analysis? How a semi-personalized model differentiates the ROM of the lower limb joints and muscle activation pattern while having varus deformity? Method: We developed the varus-valgus tool (freely available on: https://simtk.org/projects/var-val-tool) in MATLAB using OpenSim Application Programming Interface (API) to incorporate varus-va...
Trauma Case Reports
The use of customized 3D-printed structures has been gaining popularity in non-union management, ... more The use of customized 3D-printed structures has been gaining popularity in non-union management, as it allows for bypassing the defect while promoting osseointegration. Additionally, porous titanium implants minimize stress shielding due to their stiffness and elastic modulus being closer to that of bone. The interconnected channels increase the surface area and provide space for cell adhesion and proliferation. This study presents the case of a 62-year-old female patient with concomitant knee osteoarthritis recalcitrant aseptic atrophic nonunion in the tibial proximal metaphysis. Due to the small distance between the nonunion site and the joint line, nonunion treatment had to be included in the treatment plan, as it would result in a lack of mechanical stability of the tibial component, and techniques such as plating were not an option. A customized 3D-printed porous titanium cone was used to bypass the fracture site and support the stem used with the CCK prosthesis, allowing for simultaneous nonunion and osteoarthritis management.
PubMed, Aug 1, 2022
Background: The opening wedge high tibial osteotomy (HTO) fixation using the Tomofix system is at... more Background: The opening wedge high tibial osteotomy (HTO) fixation using the Tomofix system is at the risk of mechanical failure due to unstable fixation, lateral hinge fracture, and hardware breakage. This study aimed to investigate the effect of the level of anatomical fit (LOF) of the plate on the failure mechanisms of fixation. Methods: A finite element model of the HTO with a correction angle of 12 degrees was developed. The LOF of the TomoFix plate was changed parametrically by altering the curvature of the plate in the sagittal plane. The effect of the LOF on the fixation performance was studied in terms of the factor of safety (FOS) against failure mechanisms. The FOSs were found by 1) dividing the actual stiffness of the plate-bone construct by the minimum allowable one for unstable fixation, 2) dividing the compressive strength of the cortical bone by the actual maximum pressure at the lateral hinge for the lateral hinge fracture, and 3) the Soderberg criterion for fatigue fracture of the plate and screws. Results: The increase of the LOF by applying a larger bent to the plate changed the fixation stiffness slightly. However, it reduced the lateral hinge pressure substantially (from 182 MPa to 71 MPa) and increased the maximum equivalent stresses in screws considerably (from 187 MPa to 258 MPa). Based on the FOS-LOF diagram, a gap smaller than 2.3 mm was safe, with the highest biomechanical performance associated with a 0.5 mm gap size. Conclusion: Although a high LOF is necessary for the Tomofix plate fixation to avoid mechanical failure, a gap size of 0.5mm is favored biomechanically over complete anatomical fit.
Finger impairment is a common challenge in post-stroke patients which leads to the loss of hand f... more Finger impairment is a common challenge in post-stroke patients which leads to the loss of hand function. To regain normal movement abilities, rehab exercise is essential in the recovery process and rehab robots can play a key role to facilitate physical therapy especially for post-stroke patients. In this paper, a finger exoskeleton is developed to assist the three essential passive rehabilitation training. The desired finger joint trajectories for three rehab exercises were determined. A novel mechanism with two degrees of freedom (DOF) was then designed and fabricated for assistive training. A position control was finally implemented that satisfies the motion characteristics of the finger. The device performance was then verified experimentally. The tests were conducted on two post-stroke subjects with finger lengths of 60 and 90 mm to evaluate the kinematics and control attributes of the exoskeleton. The results indicated that the exoskeleton provides good kinematic compatibility to the human finger within a wide range of motion (ROM). Furthermore, the paths traced by the exoskeleton’s joints were in good agreement with the desired joint trajectory.
Modares Mechanical Engineering, Mar 10, 2019
Archives of Metallurgy and Materials, Jul 26, 2023
In the present paper, the effects of the subsequent extrusion after multi-pass equal-channel angu... more In the present paper, the effects of the subsequent extrusion after multi-pass equal-channel angular pressing (ECAP) process on the mechanical properties and microstructure of WE43 magnesium alloy are investigated. First, second and fourth passes ECAP followed by an extrusion process are applied on WE43 magnesium alloy to refine the microstructure and to improve the mechanical properties for biomedical applications. The results showed that among the ECAPed samples, the highest and lowest strength were obtained in the second and the first pass processed samples, respectively. The four passes processed sample showed the highest elongation to failure with moderate strength. The sample processed via first pass ECAP followed by extrusion exhibits an excellent combination of ductility and strength. The highest strength was obtained in the sample processed via the second pass ECAP followed by extrusion while the highest elongation was achieved in the sample processed via fourth pass ECAP followed by extrusion. Moreover, Vickers micro-indentation tests demonstrate that hardness is enhanced by an increase in the number of ECAP passes. Furthermore, a grain refinement process is presented for ECAP processing of WE43 alloy which shows a good agreement with microstructural investigations.
Procedia Materials Science, 2015
Abstract Laser shock peening (LSP) is one of the modern surface treatment methods in which surfac... more Abstract Laser shock peening (LSP) is one of the modern surface treatment methods in which surface of the work-piece is peened using short and intense laser pulses. In this process, favorable compressive residual stresses are induced on and near the surface of the material. This process is usually used to improve fatigue life of the component and has been applied in different industries such as aerospace, automotive, nuclear, medical, etc. Many researchers have used the finite element method (FEM) to simulate the LSP. In the majority of the conducted researches, results are in good agreement with the experimental data which shows FEM is capable of accurately simulating the LSP process. Simulations reduce the costs related to experimental measurement. Moreover with simulations, it is easier to understand, and is possible to analyze and optimize the process. To conduct a parametric study, it is first necessary to be able to simulate a single shot. After verification of the results, it is necessary to investigate the effect of multiple close impacts on the final results. Therefore, three dimensional analysis should be used. Since deformation is caused by the generated shockwave, there is a high strain rate (in the order of 10 6 s -1 ) in this process which necessitates the use of a very fine mesh. This in conjunction with a 3D simulation significantly increases the computational cost. This analysis is crucial for the design and optimization process of laser shock peening for a specific application. The present article, investigates the effect of overlapping laser pulses. Residual stress distribution on a range of overlap ratios (0 to 80% overlap) with square laser spot shape has been presented. With a laser intensity of 8GW/cm 2 , and a desirable compressive stress of 300 MPa, it was found that the optimum choice of overlap is between 0 to 20 percent.
Biomedical Engineering Online, Apr 15, 2015
Background: The management and prognosis of aortic dissection (AD) is often challenging and the u... more Background: The management and prognosis of aortic dissection (AD) is often challenging and the use of personalised computational models is being explored as a tool to improve clinical outcome. Including vessel wall motion in such simulations can provide more realistic and potentially accurate results, but requires significant additional computational resources, as well as expertise. With clinical translation as the final aim, trade-offs between complexity, speed and accuracy are inevitable. The present study explores whether modelling wall motion is worth the additional expense in the case of AD, by carrying out fluid-structure interaction (FSI) simulations based on a sample patient case. Methods: Patient-specific anatomical details were extracted from computed tomography images to provide the fluid domain, from which the vessel wall was extrapolated. Two-way fluid-structure interaction simulations were performed, with coupled Windkessel boundary conditions and hyperelastic wall properties. The blood was modelled using the Carreau-Yasuda viscosity model and turbulence was accounted for via a shear stress transport model. A simulation without wall motion (rigid wall) was carried out for comparison purposes. Results: The displacement of the vessel wall was comparable to reports from imaging studies in terms of intimal flap motion and contraction of the true lumen. Analysis of the haemodynamics around the proximal and distal false lumen in the FSI model showed complex flow structures caused by the expansion and contraction of the vessel wall. These flow patterns led to significantly different predictions of wall shear stress, particularly its oscillatory component, which were not captured by the rigid wall model. Conclusions: Through comparison with imaging data, the results of the present study indicate that the fluid-structure interaction methodology employed herein is appropriate for simulations of aortic dissection. Regions of high wall shear stress were not significantly altered by the wall motion, however, certain collocated regions of low and oscillatory wall shear stress which may be critical for disease progression were only identified in the FSI simulation. We conclude that, if patient-tailored simulations of aortic dissection are to be used as an interventional planning tool, then the additional complexity, expertise and computational expense required to model wall motion is indeed justified.
The archives of bone and joint surgery, 2018
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2022
bioRxiv (Cold Spring Harbor Laboratory), Jun 1, 2022
Walking in healthy elderly people is characterized by lower performance. Since conventional train... more Walking in healthy elderly people is characterized by lower performance. Since conventional training programs have had limited success in improving gait performance, it is essential to identify underlying causes of walking deficits in healthy elderly adults. Recent studies have qualitatively shown that the decreased relative displacement of Achilles subtendons is likely the primary contributor to lower propulsion in the elderly's walking by creating a higher dependency on their triceps-surae muscle functions. Due to the invasive nature of experimental investigations, in this study, we developed a computational model and analyzed the effects of reduced Achilles subtendons relative displacement on the total metabolic rate and muscles' force profiles during normal walking. Our musculoskeletal simulations revealed a 17% increase in the total metabolic rate in elderly adults whose Achilles subtendons were restricted to have no relative displacement. Changing the restriction level resulted in significant changes in the force distribution of the plantar flexor muscles, notably, a 40% reduction in the Medial Gastrocnemius and a 124% increase in the Soleus forces during the propulsion phase of walking. Also, we quantitatively presented the higher dependency of triceps-surae muscle functions regarding the limitation on their corresponding Achilles subtendons' relative displacement. The results of this study confirm the experimental observations and can be used as initial insight into devising novel rehabilitation training programs with the focus on improving Achilles subtendons relative displacement.
International Journal for Numerical Methods in Engineering, Jun 12, 2012
A novel scheme is presented for incorporating finite thickness cohesive interfaces in virtual gra... more A novel scheme is presented for incorporating finite thickness cohesive interfaces in virtual grain structures for crystal plasticity finite element (CPFE) analyses of intergranular crack initiation and propagation. A Voronoi tessellation model is used to define the virtual grain structure, with automatically generated nonzero thickness cohesive zones (CZs) representing the grain boundaries and multiple junctions. An efficient grain boundary offsetting algorithm is presented, and issues related to automatically partitioning multiple junctions are discussed. Two feasible junction partitioning schemes are presented, the second of which has the advantage of partitioning junctions using uniform quadrilateral elements and naturally defining their normal and tangential directions. For the second scheme, a rule-based method is presented that carries out the preliminary meshing of CZ junctions, including data representation, edge event processing, and cut and trim operations. A virtual grain structure modelling system, VGRAIN, is introduced to implement the proposed CZ junction partitioning method and directly generate meshed virtual grain structures with CZ grain boundaries for CPFE studies. To demonstrate the proposed junction partitioning and CZ representation schemes, two finite strain CPFE simulations are presented for plane strain uniaxial tension and three-point bending, demonstrating large-scale crack initiation and propagation under shear and opening modes. Copyright
Computational Materials Science, Feb 1, 2013
ABSTRACT Multilayer thin films have demonstrated enhanced behaviour relative to monolayers of equ... more ABSTRACT Multilayer thin films have demonstrated enhanced behaviour relative to monolayers of equivalent thickness (e.g. the superlattice effect). However, multilayer constituents can differ considerably in their microstructures (e.g. from interrupted growth and phase suppression), hence mechanical properties, compared to their monolayer or bulk counterparts. Although methods for extracting effective properties of multilayers are well established, identifying the mechanical properties of the individual constituents of a multilayer required for corresponding finite element models remains very difficult. This paper presents an inverse method for identifying the properties of material constituents in their multilayer states from a combination of finite element simulations and indentation data, which is extensible to multilayers containing any number of constituents. The method is demonstrated using simulations and analysis corresponding to nanoindentation experiments on CrN, TiN and NbN monolayers, and TiN/CrN, NbN/CrN and TiN/NbN multilayers. Constituent properties extracted using the method are presented, and FE models using the extracted properties are employed to assess the applicability of a simple relationship between hardness and yield stress for the constituent materials, and a rule of mixtures for the multilayers.
Mechanics of Materials, Dec 1, 2012
A three-dimensional (3D) controlled Poisson Voronoi tessellation (CPVT) model has been developed ... more A three-dimensional (3D) controlled Poisson Voronoi tessellation (CPVT) model has been developed for generating 3D polycrystalline grain structures for micromechanics simulations. A virtual grain structure generated using the CPVT model has the property that its grain size distribution is statistically equivalent to the actual grain structure in term of the specified physical parameters: the mean grain size, a small grain size, a large grain size, and the percentage of grains within that range. Development of the CPVT model requires three steps: (1) Defining the regularity that specifies the uniformity of a tessellation, and deriving the control parameter based on the regularity, (2) establishing the mapping from the regularity to the distribution parameter of a one-parameter gamma distribution, (3) defining the mapping from the set of physical parameters to the distribution parameter. Relations between the regularity and distribution parameter, for a range of regularity values, are determined by a comprehensive set of statistical experiments, in which data fitting for the grain size distribution model is in each case obtained by an evolutionary optimisation algorithm. A software system (VGRAIN) has been developed for implementing the proposed three-dimensional CPVT model to generate the grain structure for crystal plasticity finite element (CPFE) analysis. To demonstrate the proposed scheme and the VGRAIN system, CPFE analyses of compression of micro-pillars are performed, and the effects of both regularity and grain size on the deformation are studied.
![Research paper thumbnail of Deformation behaviour of [001] oriented MgO using combined in-situ nano-indentation and micro-Laue diffraction](https://attachments.academia-assets.com/115574809/thumbnails/1.jpg)
Acta Materialia, Feb 1, 2018
We report a coupled in-situ micro-Laue diffraction and nano-indentation experiment, with spatial ... more We report a coupled in-situ micro-Laue diffraction and nano-indentation experiment, with spatial and time resolution, to investigate the deformation mechanisms in [001]-oriented single crystal MgO. Crystal plasticity finite element modelling was applied to aid interpretation of the experimental observations of plasticity. The Laue spots showed both rotation and streaking upon indentation that is typically indicative of both elastic lattice rotation and plastic strain gradients respectively in the material. Multiple facets of streaking of the Laue peaks suggested plastic slip occurring on almost all the {101}-type slip planes oriented 45 to the sample surface with no indication of slip on the 90 {110} planes. Crystal plasticity modelling also supported these experimental observations. Owing to asymmetric slip beneath the indenter, as predicted by modelling results and observed through Laue analysis, sub-grains were found to nucleate with distinct misorientation. With cyclic loading, the mechanical hysteresis behaviour in MgO is revealed through the changing profiles of the Laue reflections, driven by reversal of plastic strain by the stored elastic energy. Crystal plasticity simulations have also shown explicitly that in subsequent loading cycles after first, the secondary slip system unloads completely elastically while some plastic strain of the primary slip reverses. Tracking the Laue peak movement, a higher degree of lattice rotation was seen to occur in the material under the indent, which gradually decreased moving laterally away. With the progress of deformation, the full field elastic strain and rotation gradients were also constructed which showed opposite lattice rotations on either sides of the indent.
Pharmaceutics
In order to achieve the optimal level of effectiveness and safety of drugs, it is necessary to co... more In order to achieve the optimal level of effectiveness and safety of drugs, it is necessary to control the drug release rate. Therefore, it is important to discover the factors affecting release profile from a drug delivery system. Geometry is one of these effective factors for a tablet-shaped drug delivery system. In this study, an attempt has been made to answer a general question of how the geometry of a tablet can affect the drug release profile. For this purpose, the drug release process of theophylline from two hundred HPMC-based tablets, which are categorized into eight groups of common geometries in the production of oral tablets, was simulated using finite element analysis. The analysis of the results of these simulations was carried out using statistical methods including partial least squares regression and ANOVA tests. The results showed that it is possible to predict the drug release profile by knowing the geometry type and dimensions of a tablet without performing nume...
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Papers by Morad Karimpour