Effects of intracorneal ring segments on the biomechanical response of the ectatic cornea to air-puff: A patient-specific numerical analysis

The assessment of the underlying factors that influence the biomechanics and dynamics of the cornea is essential for preserving the safety and efficacy of refractive surgeries. In the present work, the operated cornea with intracorneal ring segments (ICRSs) in a patient-specific finite-element model (FEM) was subjected to the air-puff. Then, the dynamic deformation parameters predicted by the FEM were obtained and compared with the corresponding values in clinical measurements. In this study, the effects of ICRS design, position, and implementation procedure in six different surgical scenarios were examined on the induced corneal stresses, deformation behavior, and shape regularization. While surgical scenarios with arc lengths of 160° (single and double segment), 355° implemented with the tunnel incision method provided similar maximum apical displacement (MAD) and highest concavity radius of curvature HCR), they induced significantly different flattening effects. The surgical scenarios with the segment of 160° arc-length implemented in nasal–temporal direction showed an approximately 15% higher reduction in mean corneal power ([Formula: see text]) value than the superior–inferior direction. From a solid-mechanics perspective, the study of ICRS mechanics in the cornea also confirmed the importance of the implementation position to achieve satisfactory flattening outcomes. Comparison of the two types of ICRS implementation procedures showed that, although the pocket method demonstrated a 10.23% higher MAD, it induced a higher reduction in the HCR of 21.65% compared with tunnel incision. The developed numerical model demonstrated the direct correlation of the ICRS insertion site with induced contact stresses and ICRS position stability. The study hypothesizes the significant influence of ICRS implementation position and procedure on the corneal biomechanical and dynamical behaviors. The proposed approach can be assessed as a robust and novel framework for planning optimized corneal refractive surgeries.

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Validate Mandible Finite Element Model under Removable Partial Denture (RPD) with In Vivo Pressure Measurement

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.553.322 ◽

2014 ◽

Vol 553 ◽

pp. 322-326 ◽

Cited By ~ 3

Author(s):

Hanako Suenaga ◽

Jun Ning Chen ◽

Wei Li ◽

Keiichiro Yamaguchi ◽

Keiichi Sasaki ◽

...

Keyword(s):

Finite Element ◽

Element Model ◽

Patient Specific ◽

Fe Model ◽

Removable Partial Denture ◽

Partial Denture ◽

Element Simulation ◽

Clinical Measurements

This study aims to analyze the functional contact pressure induced by Removable Partial Denture (RPD) by using a 3D finite element (FE) model constructed based on patient specific CT scans. This model was validated against the in vivo test results. The outcomes demonstrate that the finite element simulation has the capability of quantifying localized stress distribution in a complicated denture-mucosa contact problem, with a reasonable matching to clinical measurements of occlusal force and pressure distribution. The methodology is of considerable clinical implication to improve the long term outcomes of the denture treatment.

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Effects of intracorneal ring segments implementation technique and design on corneal biomechanics and keratometry in a personalized computational analysis

Scientific Reports ◽

10.1038/s41598-021-93821-5 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Niksa Mohammadi Bagheri ◽

Mahmoud Kadkhodaei ◽

Shiva Pirhadi ◽

Peiman Mosaddegh

Keyword(s):

Clinical Data ◽

Three Dimensional ◽

Element Model ◽

Von Mises Stress ◽

Patient Specific ◽

Average Error ◽

Constant Thickness ◽

Arc Length ◽

Implementation Techniques ◽

Von Mises

AbstractThe implementation of intracorneal ring segments (ICRS) is one of the successfully applied refractive operations for the treatment of keratoconus (kc) progression. The different selection of ICRS types along with the surgical implementation techniques can significantly affect surgical outcomes. Thus, this study aimed to investigate the influence of ICRS implementation techniques and design on the postoperative biomechanical state and keratometry results. The clinical data of three patients with different stages and patterns of keratoconus were assessed to develop a three-dimensional (3D) patient-specific finite-element model (FEM) of the keratoconic cornea. For each patient, the exact surgery procedure definitions were interpreted in the step-by-step FEM. Then, seven surgical scenarios, including different ICRS designs (complete and incomplete segment), with two surgical implementation methods (tunnel incision and lamellar pocket cut), were simulated. The pre- and postoperative predicted results of FEM were validated with the corresponding clinical data. For the pre- and postoperative results, the average error of 0.4% and 3.7% for the mean keratometry value ($$\text {K}_{\text{mean}}$$ K mean ) were predicted. Furthermore, the difference in induced flattening effects was negligible for three ICRS types (KeraRing segment with arc-length of 355, 320, and two separate 160) of equal thickness. In contrast, the single and double progressive thickness of KeraRing 160 caused a significantly lower flattening effect compared to the same type with constant thickness. The observations indicated that the greater the segment thickness and arc-length, the lower the induced mean keratometry values. While the application of the tunnel incision method resulted in a lower $$\text {K}_{\text{mean}}$$ K mean value for moderate and advanced KC, the induced maximum Von Mises stress on the postoperative cornea exceeded the induced maximum stress on the cornea more than two to five times compared to the pocket incision and the preoperative state of the cornea. In particular, an asymmetric regional Von Mises stress on the corneal surface was generated with a progressive ICRS thickness. These findings could be an early biomechanical sign for a later corneal instability and ICRS migration. The developed methodology provided a platform to personalize ICRS refractive surgery with regard to the patient’s keratoconus stage in order to facilitate the efficiency and biomechanical stability of the surgery.

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Stress and Fatigue Life Modeling of Cannon Breech Closures Including Effects of Material Strength and Residual Stress

Journal of Pressure Vessel Technology ◽

10.1115/1.1320442 ◽

2000 ◽

Vol 123 (1) ◽

pp. 150-154

Author(s):

John H. Underwood ◽

Michael J. Glennon

Keyword(s):

Residual Stress ◽

Finite Element ◽

Fatigue Life ◽

Yield Strength ◽

Residual Stresses ◽

Solid Mechanics ◽

Element Model ◽

Pressure Vessels ◽

Material Strength ◽

Element Analysis

Laboratory fatigue life results are summarized from several test series of high-strength steel cannon breech closure assemblies pressurized by rapid application of hydraulic oil. The tests were performed to determine safe fatigue lives of high-pressure components at the breech end of the cannon and breech assembly. Careful reanalysis of the fatigue life tests provides data for stress and fatigue life models for breech components, over the following ranges of key parameters: 380–745 MPa cyclic internal pressure; 100–160 mm bore diameter cannon pressure vessels; 1040–1170 MPa yield strength A723 steel; no residual stress, shot peen residual stress, overload residual stress. Modeling of applied and residual stresses at the location of the fatigue failure site is performed by elastic-plastic finite element analysis using ABAQUS and by solid mechanics analysis. Shot peen and overload residual stresses are modeled by superposing typical or calculated residual stress distributions on the applied stresses. Overload residual stresses are obtained directly from the finite element model of the breech, with the breech overload applied to the model in the same way as with actual components. Modeling of the fatigue life of the components is based on the fatigue intensity factor concept of Underwood and Parker, a fracture mechanics description of life that accounts for residual stresses, material yield strength and initial defect size. The fatigue life model describes six test conditions in a stress versus life plot with an R2 correlation of 0.94, and shows significantly lower correlation when known variations in yield strength, stress concentration factor, or residual stress are not included in the model input, thus demonstrating the model sensitivity to these variables.

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Utilization of 3D MRI for the Evaluation of Sphincter Pharyngoplasty Insertion Site in Patients With Velopharyngeal Dysfunction

The Cleft Palate-Craniofacial Journal ◽

10.1177/10556656211044656 ◽

2021 ◽

pp. 105566562110446

Author(s):

Kazlin N. Mason ◽

John E. Riski ◽

Joseph K. Williams ◽

Richard A. Jones ◽

Jamie L. Perry

Keyword(s):

Insertion Site ◽

Patient Specific ◽

3D Mri ◽

Scar Contracture ◽

Time Points ◽

Repeated Measures Design ◽

Initial Location ◽

Tissue Changes ◽

Sphincter Pharyngoplasty ◽

Tissue Migration

Sphincter pharyngoplasty is a surgical method to treat velopharyngeal dysfunction. However, surgical failure is often noted and postoperative assessment frequently reveals low-set pharyngoplasties. Past studies have not quantified pharyngoplasty tissue changes that occur postoperatively and gaps remain related to the patient-specific variables that influence postoperative change. The purpose of this study was to utilize advanced three-dimensional imaging and volumetric magnetic resonance imaging (MRI) data to visualize and quantify pharyngoplasty insertion site and postsurgical tissue changes over time. A prospective, repeated measures design was used for the assessment of craniometric and velopharyngeal variables postsurgically. Imaging was completed across two postoperative time points. Tissue migration, pharyngoplasty dimensions, and predictors of change were analyzed across imaging time points. Significant differences were present between the initial location of pharyngoplasty tissue and the pharyngoplasty location 2 to 4 months postoperatively. The average postoperative inferior movement of pharyngoplasty tissue was 6.82 mm, although notable variability was present across participants. The pharyngoplasty volume decreased by 30%, on average. Inferior migration of the pharyngoplasty tissue was present in all patients. Gravity, scar contracture, and patient-specific variables likely interact, impacting final postoperative pharyngoplasty location. The use of advanced imaging modalities, such as 3D MRI, allows for the quantification and visualization of tissue change. There is a need for continued identification of patient-specific factors that may impact the amount of inferior tissue migration and scar contracture postoperatively.

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Biomechanical modeling of knee for specific patients with chronic anterior cruciate ligament injury

Computer Science and Information Systems ◽

10.2298/csis120531014f ◽

2013 ◽

Vol 10 (1) ◽

pp. 525-545 ◽

Cited By ~ 4

Author(s):

Nenad Filipovic ◽

Velibor Isailovic ◽

Dalibor Nikolic ◽

Aleksandar Peulic ◽

Nikola Mijailovic ◽

...

Keyword(s):

Gait Analysis ◽

Acl Reconstruction ◽

Cruciate Ligament ◽

Biomechanical Model ◽

Element Model ◽

Gait Pattern ◽

Von Mises Stress ◽

Ligament Injury ◽

Patient Specific ◽

Reconstruction Technique

In this study we modeled a patient specific 3D knee after anterior cruicate ligament (ACL) reconstruction. The purpose of the ACL reconstruction is to achieve stability in the entire range of motion of the knee and the establishment of the normal gait pattern. We present a new reconstruction technique that generates patient-specific 3D knee models from patient?s magnetic resonant images (MRIs). The motion of the ACL reconstruction patients is measured by OptiTrack system with six infrared cameras. Finite element model of bones, cartilage and meniscus is used for determination stress and strain distribution at different body postures during gait analysis. It was observed that the maximum effective von Mises stress distribution up to 8 MPa occurred during 30% of the gait cycle on the meniscus. The biomechanical model of the knee joint during gait analysis can provide insight into the underlying mechanisms of knee function after ACL reconstruction.

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Corrigendum to “Development of a Patient-Specific Finite Element Model for Predicting Implant Failure in Pelvic Ring Fracture Fixation”

Computational and Mathematical Methods in Medicine ◽

10.1155/2017/8956549 ◽

2017 ◽

Vol 2017 ◽

pp. 1-1

Author(s):

Vickie Shim ◽

Andreas Gather ◽

Andreas Höch ◽

David Schreiber ◽

Ronny Grunert ◽

...

Keyword(s):

Finite Element ◽

Finite Element Model ◽

Fracture Fixation ◽

Pelvic Ring ◽

Element Model ◽

Implant Failure ◽

Pelvic Ring Fracture ◽

Patient Specific ◽

Ring Fracture

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A patient-specific, finite element model for noncommunicating hydrocephalus capable of large deformation

Journal of Biomechanics ◽

10.1016/j.jbiomech.2013.03.008 ◽

2013 ◽

Vol 46 (8) ◽

pp. 1447-1453 ◽

Cited By ~ 12

Author(s):

Joel A. Lefever ◽

José Jaime García ◽

Joshua H. Smith

Keyword(s):

Finite Element ◽

Finite Element Model ◽

Large Deformation ◽

Element Model ◽

Patient Specific ◽

Noncommunicating Hydrocephalus

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Predicting calvarial morphology in sagittal craniosynostosis

Scientific Reports ◽

10.1038/s41598-019-55224-5 ◽

2020 ◽

Vol 10 (1) ◽

Author(s):

Oyvind Malde ◽

Connor Cross ◽

Chien L. Lim ◽

Arsalan Marghoub ◽

Michael L. Cunningham ◽

...

Keyword(s):

Finite Element ◽

Input Parameter ◽

Surgical Techniques ◽

Element Model ◽

Specific Model ◽

Patient Specific ◽

Sagittal Craniosynostosis ◽

Sensitivity Tests ◽

Ct Data

AbstractEarly fusion of the sagittal suture is a clinical condition called, sagittal craniosynostosis. Calvarial reconstruction is the most common treatment option for this condition with a range of techniques being developed by different groups. Computer simulations have a huge potential to predict the calvarial growth and optimise the management of this condition. However, these models need to be validated. The aim of this study was to develop a validated patient-specific finite element model of a sagittal craniosynostosis. Here, the finite element method was used to predict the calvarial morphology of a patient based on its preoperative morphology and the planned surgical techniques. A series of sensitivity tests and hypothetical models were carried out and developed to understand the effect of various input parameters on the result. Sensitivity tests highlighted that the models are sensitive to the choice of input parameter. The hypothetical models highlighted the potential of the approach in testing different reconstruction techniques. The patient-specific model highlighted that a comparable pattern of calvarial morphology to the follow up CT data could be obtained. This study forms the foundation for further studies to use the approach described here to optimise the management of sagittal craniosynostosis.

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Numerical Simulation and Experimental Investigation of Laser Ablation of Al2O3 Ceramic Coating

Materials ◽

10.3390/ma13235502 ◽

2020 ◽

Vol 13 (23) ◽

pp. 5502

Author(s):

Shuang Liu ◽

Zongjun Tian ◽

Lida Shen ◽

Mingbo Qiu

Keyword(s):

Laser Ablation ◽

Solid Mechanics ◽

Ceramic Coating ◽

Element Model ◽

Laser Damage ◽

Damage Analysis ◽

Mechanism Analysis ◽

Continuous Irradiation ◽

Al2o3 Ceramic ◽

Micro Cracks

This paper presents an evaluation of the molten pool laser damage done to an Al2O3 ceramic coating. Mechanism analysis of the laser damage allowed for a 2D finite element model of laser ablation of the Al2O3 ceramic coating to be built. It consisted of heat transfer, laminar flow, and a solid mechanics module with the level set method. Results showed that the laser damage mechanisms through laser ablation were melting, gasification, spattering, and micro-cracking. The ablation depth and diameter increased with the increasing laser ablation time under continuous irradiation. The simulation profile was consistent with the experimental one. Additionally, the stress produced by the laser ablation was 3500–9000 MPa, which exceeded the tensile stress (350–500 MPa), and fracturing and micro-cracks occurred. Laser damage analysis was performed via COMSOL Multiphysics to predict laser damage morphology, and validate the 3D surface profiler and scanning electron microscope results.

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