mohammad nikkhoo

In this study, the biomechanical behavior of individuals before and after laminoplasty surgery has been compared with the aim of measuring the ability of finite element modeling in facilitating technologies for diagnosis, treatment and prevention of cervical spine injuries and also determine its role in improving the standardization of surgery and reducing complications in patients. The main goal of this research is to extract the personalized parametric finite element model of patients so that it can be used to predict the biomechanics of the cervical spine of patients after laminoplasty. In this sense, first, a personalized geometric parametric model is created based on 16 anatomical parameters that are extracted from the patient's radiographic images. In this research, Mimics 2012 software was used to gather 2D CT images and convert them into point clouds and make initial corrections of point clouds. The software used for modification, leveling and finally creating 3D models was Geomagic Studio 2012. After modeling all the tissues of the neck, the model was entered into the Abaqus 2012 finite element software, and in this software, the process of simulation and analysis of the cervical spine took place. Therefore, in the current research, an attempt was made to create a geometric model in the modeling of volumetric tissues as well as in the modeling of ligaments and muscles with very high accuracy, in order to create a suitable platform for future studies on the properties of materials and the behavior of tissues, away from the fear of geometric model problems.

The biomechanical impacts of Conventional Open Surgery (COS) versus Minimally Invasive Surgery (MIS) fusion techniques on adjacent segments and their potential role in developing Adjacent Segment Disease (ASD) remain uncertain for spondylolisthesis. This study aimed to investigate the impact of MIS and COS fusion surgeries on adjacent spinal segments for spondylolisthesis, through on muscle injury and developing ASD. This prospective and non-randomized controls study used a validated musculoskeletal model to compare the biomechanical effects of COS and MIS L4/L5 fusion surgery on patients with spondylolisthesis. The model incorporated kinematic data from 30 patients who underwent each surgery. A sitting task was simulated to model post-operative muscle atrophy, and the analysis focused on changes in biomechanics of adjacent spinal segments. Lumbar flexion was significantly greater (201%) in MIS vs. COS, despite similar pelvic tilt. Consequently, Lumbopelvic Rhythm (LPR) also increased in MIS (133%). Both techniques altered inter-segmental moments. While inter-joint load was higher in COS, only the lower joint’s compressive load was significantly greater (67%). Additionally, MIS required lower overall muscle force with reduced loads and passive moment on spinal joints compared to COS.  This study demonstrates that MIS fusion preserves physiological LPR better than COS. MIS maintains normal spinal curvature and maintains lumbar lordosis. While open surgery can lead to abnormal curvature and increased muscle forces to compensate for spinal stability. The study emphasizes the importance of paraspinal muscles in influencing spinal load distribution during MIS compare to COS.

The design of efficient membranes for desalination in order to help alleviate the water shortage crisis has been the subject of various studies. In this study, WS2 nanosheets were first prepared and the surface of thin film composite (TFC) membranes was modified by them. After that, a new nanocomposite consisting of CuAl LDH and WS2 nanosheets was synthesized by hydrothermal method and a new type of thin film nanocomposite (TFN) membranes were made using them. Then the performance of all prepared membranes in the forward osmosis (FO) process was studied. The effects of the prepared compounds on the morphology, chemical structure, hydrophilicity and topology of the polyamide (PA) active layer were investigated using FE-SEM, FT-IR, EDX, XRD, AFM and water contact angle analyses. Finally, by comparing the results for both types of modified membranes the membrane containing 0.025% by weight of the nanocomposite modifier showed the highest water flux (29.30 LMH) and selectivity (0.38 g/L), which is the optimal membrane. Selected.

Cervical spine injuries often cause disability and adversely affect the overall performance and life quality of people. Therefore, recognition of the damage and dysfunction of the cervical spine and biomechanical response to external stimuli is of paramount importance. Accordingly, finite element (FE) modeling can help researchers to access the internal stresses and strains in the bones, ligaments and soft tissues. The present study aimed to compare the biomechanical behavior of the cervical spine before and after trauma.

In this study, we developed a healthy model along with two different traumatic injuries of the cervical spine modeled by the FE method. The results of the models were compared under static loading. 

We estimated and evaluated three parameters of intervertebral rotation, facet joint force and intra-disc pressure by considering follower load. The results of the mentioned parameters were evaluated in the two traumatic injury models and the healthy model in flexion, extension, side bending and axial rotation movements at all levels.

According to the results, trauma modeling caused changes in the biomechanical behavior of the model, including decreased range of motion in the traumatic injury models, reduced intra-disc pressure and increased facet joint force. This structural disruption in this complex system caused abnormal behavior in various movements. According to the results, the lack of improvement of the biomechanical behavior of the model would cause spinal instability and could increase the probability of injuries in different segments of the lower cervical spine in the long term.

The design and manufacturing cubic porous scaffolds are a considerable notion in tissue engineering (TE). From Additive manufacturing (AM) perspective, it has attained high appeal in the string of TE during the past decade. In the view of TE, the feasibility of manufacturing intricate porous scaffolds with high accuracy contrast to prominent producing methods has caused AM the outstanding option for manufacturing scaffold. From design perspective, porous scaffold structures play a crucial task in TE as scaffold design with an adequate geometries provide a route to required strength and porosity. The target of this paper is achieve of best geometry to become an optimum mechanical strength and porosity of TE scaffolds. Hence, the cubic geometry has been chosen for scaffold and Cube, Cylinder and Hexagonal prism geometries have been selected for pore of structures. In addition, for noticing the porosity effects, pore size has been chosen in three size, and a whole of nine scaffolds have been designed. Designed scaffolds were generated using Fused Deposition Modeling (FDM) 3D Printer and dimensional specifications of scaffolds were evaluated by comparing the designed scaffolds with Scanning Electron Microscope (SEM). The samples were subjected to mechanical compression test and the results were verified with the Finite Element Analysis (FEA). The results showed that firstly, as the porosity increases, the compressive strength and modulus of elasticity obviously decreased in all geometry pore scaffolds. Secondly, as the geometry changes in similar porosity, cubic pore scaffold achieved higher compressive strength and modulus of elasticity than cylinder and hexagonal prime. Experimental and FEM validated results proposed a privileged feasible pore geometry of cubic scaffold to be used in design and manufacturing of TE scaffolds.

Wound dressing materials allocate a great portion of skin and draught maintenance in the global medical market.  In previous times the conventional dressing materials as natural and synthesized bondage, Cotton and gas were used for caring of skin wounds. Nowadays the production of modern wound dressing of higher restorative capabilities has attracted the attentions. These modern wound dressing can precipitate the re-epithelization, collagen synthesis and angiogenesis. These modern wound dressing materials can reduce the PH and perform as a barrier to bacterial penetration. There are several methods available for production of fibers and nanofibers. Between these methods electrospinning has attracted much interests. By this procedure it is possible to produce composite fibers and porous mats. The cells can penetrate to these pores and grow appropriately. The manufactured fibers usually have proper uniformity and the dimensions can vary from several nanometers to micrometers. These fibers can be used in different applications such as the filters, the fortifiers, the scaffolds and the wound dressing materials. The biocompatible materials are among the best choices for fabrication of the wound dressing, They can provide the necessary condition for growth of derma and epidermal layers. The multi-polymers Mat fibers have been used for tissue engineering applications, as they have the capability of the simulation of the extracellular Matrix. Drug addition to these scaffolds can enhance the function of this system and improve the restoration capabilities.  The electrospun wound dressing materials facilitate the tissue growth. The electrospun nano-fibers have similar structures to that of the skin and have higher compatibility with blood. They make the wound and tissue restoration possible. In this research the production of two layers wound dressing materials has been conducted by the electrospinning Method. The downward layers of these wound dressing materials have been manufactured from polyvinyl alcohol. Polyvinyl alcohol is a synthetic polymer which has proper electrospinning properties, and therefore it can be used for nanofibers production. The fibers have high tensile strength and an appropriate flexibility. This material is one of the oldest and most common materials that have been utilized for drug delivery systems, wound dressing and wound maintenance, contact lens and artificial limbs. This polymer is biocompatible, and due to the hydroxyl groups, it has reasonable water absorption. Also for infection inhibition vancomycin drug has been loaded in this layer.

Many different wound dressing fabrication methods have been used for many years. Among these techniques, electrospinning has attracted a lot of attention. This simple and cost-effective method produces nano and micro fibers substrates which simulate extracellular matrixes and provide a suitable porous structure for cell adhesion and proliferation. In this study, electrospinning was used for the fabrication of two-layer wound dressing, consisted from chitosan and poly (lactide-co-glycolide) acid (PLGA) as the first layer and polyvinyl alcohol (PVA) and vancomycin as the second layer. For the first layer electrospinning, the solution of chitosan, poly-lactic co-glycolic acid has been provided and transmitted to 5 ml syringe and located in the place.  the syringe tip attached to the electrical current source and the electrospun fibers were collected it on a aluminum foil covered collector. The ejection action was performed by the flow rate of 2 ml per hour and the electrospun fibers were manufactured on a 50 mm diameter collector.  In this research, the distance between the nozzle and the collector was 120mm and the rotating speed of the collector was 16 RPM. The device voltage was set at 15 kilovolts. For electrospinning of the second layer the solution of polyvinyl alcohol and vancomycin was provided and transmitted into 5ml syringe, just like previous steps.  The injection process was performed by the volume rate of 1 ml per hour and electrospun fibers were gathered on the 15 mm diameter collector.  In this level, the distance between the nozzle and the Collector was 200mm, the rotating speed was 10 RPM and the device voltage was set at 15 kilovolts. For cross-linking, the samples were located on the vapor of glutaraldehyde and HCL by the molar ratio of 1:10 for 12 hours.

Electrospun two layer wound dressing microstructure was evaluated by scanning electron microscopy (SEM). It was observed that both layers have homogenous bead free interconnected porous structures. Image measurement software revealed that fiber diameters ranged from 0.2 to 1.2 micrometer, which can provide a proper substrate for cell proliferation. Functional groups of raw materials and chemical bonding between layers were assessed by FTIR analysis. In order to evaluate layers absorption capacity, they were soaked in PBS solution for 24 hours. They showed about 112.4±10.2 % PBS absorption after 24 hours. So they can absorb wound secretions and keep the wound environment dry. Biodegradation tests showed that 32.7 % of these two layer wound dressing was degraded after 3-weeks immersion in PBS solution. Drug release tests demonstrated a burst release of vancomycin in the first hours which followed by decreasing releasing rates. These releasing manner lowered infection appearance in the wound site. Antibacterial activity is an important factor in wound dressing and the co-existence of chitosan and vancomycin provided approximately 98.72 % bacterial reduction in the antibacterial assay. Although the antibacterial test showed a significant reduction in bacterial growth, the MTT test showed that these scaffolds are biocompatible and provide a favorable environment for cell attachment and proliferation.

The images of the microstructure electrospun substrates depicted that electrospun two-layer polyvinyl alcohol vancomycin and poly lactic co-glycolic acid chitosan substrate has a porous fiber structure, in a way that these pores are interconnected.  The fibers of two layers have no beads and they have relatively homogeneous distribution. The water absorption of these scaffolds showed suitable inflation strength in 24-hours of submerge in phosphate buffer saline.  Also the degradation capability of the samples demonstrated the approximately 32% degradation of the structure in 3-weeks.  It illustrated convenient degradation time of wound dressing and it is in good correspondence with previous researchers. Drug delivery assessment of vancomycin from these samples was relatively explosive in the initial hours.  But it reached an equilibrium state in some hours.  The initial explosive delivery can lead to eradication of the initial bacteria and it is a key factor in wound dressing applications. The antibacterial assessment of their structure demonstrated high antibacterial capabilities due to the existence of chitosan and vancomycin in these scaffolds. About 98% of the batteries at the dose of 10 mg/lit were perished.  Also the cellular viability investigation for these scaffolds proved non-toxicity and biocompatibility. The cultured cells on the scaffolds had normal morphology. According to acquired results in this study, it seems that these two layer electrospinning substrates can be useful for wound healing.

In this study, the advantages of porous implants compared to conventional implants in order to apply a specific type of porosity to the implant most were investigated. The use of Triply Periodic Minimal Surface (TPMS) in porous implant design due to its curvature has a high potential in designing variable structures both morphologically and in relative density with respect to its implicit structural equations. The equations of Triply periodic minimal surface are solved using the Grasshopper plugin, and finally the surface of a unit cell is obtained to design porous structure. One common dental implant and two porous dental implants with 54% and 65% porosity are modeled on Straumann's catalog according to ITI standard. In static and dynamic loading, forces were inserted into the implant in three different directions according to biomechanical principles. The results showed that after implantation of dental implants, the maximum amount of stress increased in the porous implants compared to the conventional implants so that it increased from 31.82 to 98.93 MPa in the fifth second. And in porous implants, stress distribution in the cancellous bone is increased compared to the conventional implant. Stress Shielding can be counteracted by porosity of dental implants. In this phenomenon, the implant, due to its much greater strength than the bone, prevents the transfer of stress to the bone, which results in weakening of the bone around the implant. By applying porosity and applying the TPMS to the implant. Stress distribution increase in the cancellous bone.

In recent years, spinal fusion surgery has become one of the most common treatments for spinal cord injuries, while the interbody cages, which replace the damaged interbody discs in the surgeries, have undergone extensive changes in design and material. These changes are quite visible, ranging from plain titanium cages made using the conventional manufacturing methods to customized porous titanium cages, which are made using additive manufacturing technology, or titanium-coated polymer cages. Among all the materials used in manufacturing the interbody cages, PolyEther Ether Ketone (PEEK) and titanium are the most common ones. Each of these two has its own advantages and disadvantages. Several studies have compared these two materials, mostly based on the two characteristics of subsidence and fusion rates. The present study performed a comprehensive review of the published clinical studies comparing the titanium and PEEK cages in order to make a comprehensive evaluation of these two. According to the reviewed studies, both materials had relatively similar results in subsidence rate, with no significant difference. However, it was shown that the titanium cages had a better fusion rate and subsequently were more likely to be successful in the clinical settings than the PEEK cages.

In this paper, an attempt has been made to provide a numerical method for investigating the mechanical properties of multilayer scaffolding. These scaffolds can be used as implants in bone fractures. For this purpose two numerical simulation methods are introduced to predict the elastic properties of multilayer cell scaffolds. These simulations are based on two models: a 3D model with a volumetric element, and a 1D model with a linear element. To compare the results of these models, three types of two- and three-layer titanium alloy scaffolds have been simulated by the two methods. Also, Young's modulus of the scaffolds has been compared with the experimental conclusions of earlier studies. The results confirm that simulations with 1D models are more cost-effective compared to 3D ones. Additionally, because of the more reliable agreement of Young's modulus results of numerical modeling with the linear element (1.8 to 5 times) compared to the volumetric element (11 to 23 times) compared to the experimental findings, the numerical method with the linear elements can be a reliable tool for studying multilayer scaffoldings.

Advances in the additive manufacturing technology have led to the production of complex microstructures with unprecedented accuracy and due todesigning an effective implant is a major scientific challenge in bone tissue regeneration and bone growth. In this research, titanium alloy cylindrical scaffolds with three-dimensional architectures have been simulated and compared for curing partial bone deficiencies. The cylindrical networks in the scaffold (outer diameter 15 and length 30 millimeters) were designed in 36 different convergent, two-layer and three-layer types with 50% and 70% porosity. In all the samples, outer layers were denser than the inner layers. Mechanical characteristics of these scaffolds have been determined by simulating uniform compression load. The stress-strain curve of the samples showed that Young’s modulus and yield stress in the scaffolds with constant porosity were related to a unit-cell and the two-layer scaffolds, without changing Young’s modulus, had higher yield stress. This advantage was more significant in high-density scaffolds.

 Pedicle screw-based spine fusion has been employed as a felicitous approach for treatment of degenerative lumbar spinal diseases.  Although the pedicle screw designs and fixation techniques have progressed, many clinical studies have reported the adjacent segment degeneration (ASD) and several other adverse effects after surgery. In the case of fixation techniques, the use of semi-rigid rods such as Polyarylether ether ketone (PEEK) rods can be an appropriate substitute for rigid fusion instrumentation. However, the biomechanical effects of using viscoelastic PEEK rods for use in clinical studies are still unclear.

 In this study, the effects of using two pedicle screw-based stabilization systems, i.e. viscoelastic PEEK rods and elastic Titanium rods, on the stress distribution in L3-L4 intervertebral disc and the surrounding osseous tissue were investigated. An L1-L5 lumbar region was modeled. Subsequently, a mild degenerative disc disease was simulated in the L3-L4 lumbar level. Next, an axial cyclic torque was applied to the model.

 The results showed that, at the end of the loading cycle, the maximum von-Mises stress in the L3-L4 intervertebral disc as well as the overall value of stress in the surrounding osseous tissue were slightly greater in the viscoelastic model as compared to the elastic one. Nonetheless, the stress distribution contours and the location of maximum stress were different in the two models.

 It can be postulated that the vulnerable areas of lumbar bone are different in two models.

About 80% of the population will experience back pain in their lifetime; however, although many patients have low back pain associated with disc degeneration, the exact course of degeneration is still unclear. The disc degeneration disorder has affected one-third of the worldchr('39')s young population. During degeneration, the disc undergoes morphological and biochemical changes, which in turn alter the tissue hydration, permeability, and ultimately the load-bearing capacity of the disc. Therefore, the finite element model, designed to study the relationship between frequent loading and disk degeneration, must be able to analyze the complex loading in the in-vivo conditions. The aim of this study was to construct and update models of finite element components with the prolastic properties so that different quasi-static loads could be investigated by presenting a personalized model in different individuals and applied in clinical studies to simulate the daily biomechanical behavior for accurate diagnosis and treatment.

This study simulated three different modes of finite element modeling, including axial symmetry method, parametric model and precision model with poroelastic mechanical properties and its results were compared with experimental in-vivo experiments.

To validate the constructed models, the results of three different quasi-static creep experiments were performed, including short-term creep, long-term creep and creep under regular daily activities, the results of which predicted changes. The results predicted height changes, axial displacement of the spine and the intradiscal pressure of the nucleus.

All the proposed results indicated that the models presented in quasi-statistic behavior predicted acceptable results and have sufficient validity to be examined in other quasi-statistic experiments. Therefore, it is possible to take a step forward in examining the results of clinical activities in determining the process of intervertebral disc degeneration.

  Low back pain is one of the most common problems that force individuals to seek medical care. Since surgery is the last treatment strategy, predicting the process of conducting surgical procedures seems beneficial and somehow crucial. In this regard, the first step is having a validated biomechanical model based on the anatomical parameters of patients’ lumbar spine. Despite the impressive progress in this field, there is still a need to designing a model that could include important anatomical parameters and be applicable in terms of clinical applications. This study aimed to develop the personalized spinal finite element model with 23 anatomical parameters. The initial data was extracted from the radiology picture of the average healthy volunteers and was designed in Catia software. Afterwards, the finite element model was analyzed in Abaqus, and results of the range of motion of motionsegments in movements of flexion, extension and left and right lateral bending were verified based on the results of experimental studies present in the literature. In order to observe the application of the patient-specific spinal parametric model, a model of a patient after spinal fusion was presented. Moreover, results of the range of motion of the motion segments and intradiscal pressure were compared to the healthy model. Since acceptable results were obtained at each step, it is possible to predict the result of spinal fusion and compare the biomechanical results in case of decreased or increased fusion level by developing a parametric parient-specific model for each patient, which can be an effective achievement for clinical fields.

Understanding the mechanism of artificial disc degeneration using animal models is useful to study the regenerative techniques in hope of finding potential therapeutic strategies. For any type of potential therapeutic techniques, first we need to have the degenerated model. Disc degeneration can be mimicked in animal studies using needle puncture. However, the detailed mechanical response of the artificial degenerated disc using needle puncture under physiological diurnal activities has not been analyzed well. Hence, reverse finite element analyses combined with in-vitro experiments were used in this study to find the mechanical properties of intact (N=8) and injured discs using needle puncture (N=8). Afterward, specimen-specific FE models for 16 discs were simulated during physiological diurnal activity. The results showed that the variation of axial displacement, intradiscal pressure, and total fluid exchange in intact discs were significantly higher than the injured ones after 24h. But the maximum axial stress within disc was significantly higher in injured group. The achieved results are correlated with previous human cadaver data for natural disc degeneration. Therefore, it is concluded that the G-16 needle puncture injury is a simple and cost-effective methodology which can be used to mimic the degeneration mechanism in animal models.

To develop the advanced technologies in medical device industry, design and manufacturing of cervical cage was performed in Iran for the first time. This research-based industrial project should be accomplished based on precise biomechanical studies and mechanical tests. Hence, this study presents the optimization and biomechanical functional investigations of the first Iranian cervical cage (Manufactured by Attila Ortopaed Co.). For this purpose the intact cervical spine (C2-C7) was developed and was validated with in-vitro experiments. Three inputs (i.e. geometrical parameters of the cage) and two outputs (i.e. deformation of the teeth in static and dynamic tests) parameters were selected for optimization procedure. Furthermore, the surgery in C5-C6 level was simulated by implanting the cervical cage. Finally, the biomechanical responses were investigated. The result confirmed that the biomechanical response of cervical cage is within the standard range and can be used well in clinics for surgical procedures.

Prediction of the relationship between different types of mechanical loading and the failure of the intervertebral disc is so important to identify the risk factors which are difficult to study in vivo and   in vitro. On the basis of finite element methods some of these issues may be overcome enabling more detailed assessment of the biomechanical behavior of the intervertebral disc. The objective of this paper is to develop a nonlinear axisymmetric poroelastic finite element model of lumbar motion segment and show its capability for studying the time-dependent response of disc. After comparison of the response of different models in quasi-static analysis, the poroelastic model of intervertebral disc is presented and the results of short-term, long-term creep tests and cyclic loading were investigated. The results of the poroelastic model are in agreement with experimental ones reported in the literature. Hence, this model can be used to study how different dynamic loading regimes are important as risk factors for initiation of intervertebral disc degeneration.

According to mechanobilogical studies as an infrastructure for tissue engineering researches, this paper presents a triphasic finite element modeling of intervertebral discs such a hydrated porous soft tissue. First, the governmental equations were derived on the basis of the laws of continuum mechanics. Then the standard Galerkin weighted residual method was used to form the finite element model. The implicit time integration schemes were applied to solve the nonlinear equations. The formulation accuracy and convergence for one dimensional case were examined with Simon's and Sun's analytical solutions and also Drost's experimental Data. It was shown that the mathematical model is in excellent agreement and has the capability to simulate the intervertebral disc response under different types of mechanical and electrochemical loading conditions. Finally, to have a short review of the capability of the model, a homogenous two dimensional version of the model was applied to simulate the response of a simple sagittal slice of the intervertebral disc.