Computational modeling and uncertainty prediction of hyperelastic constitutive responses of damaged brain tissue under different temperature and strain rates.

The effect of strain rate and temperature on the hyperelastic material stress-strain characteristics of the damaged porcine brain tissue is evaluated in this present work. The desired constitutive responses are obtained using the commercially available finite element (FE) tool ABAQUS, utilizing 8-noded brick elements. The model's accuracy has been verified by comparing the results from the previously published literature. Further, the stress-strain behavior of the brain tissue is evaluated by varying the damages at various strain rates and temperatures (13, 20, 27, and 37°C) under compression test. Additionally, the sensitivity analysis of the model is computed to check the effect of input parameters, that is, the temperature, strain rate, and damages on the material properties (shear modulus). The modeling and discussion sections enumerate the inclusive features and model capabilities.

Study on rock fracture mechanism and hydraulic fracturing propagation law of heterogeneous tight sandstone reservoir.

Hydraulic fracturing technology is an effective way to develop tight sandstone reservoirs with low porosity and permeability. The tight sandstone reservoir is heterogeneous and the heterogeneity characteristics has an important influence on fracture propagation. To investigate hydraulic fracture performance in heterogeneous tight reservoir, the X-ray diffraction experiments are carried out, the Weibull distribution method and finite element method are applied to establish the uniaxial compression model and the hydraulic fracture propagation model of heterogeneous tight sandstone. Meanwhile, the sensitivity of different heterogeneity characterization factors and the multi-fracture propagation mechanism during hydraulic fracture propagation is analyzed. The results indicate that the pressure transfer in the heterogeneous reservoir is non-uniform, showing a multi-point initiation fracture mode. For different heterogeneity characterization factors, the heterogeneity characteristics based on elastic modulus are the most sensitive. The multi-fracture propagation of heterogeneous tight sandstone reservoir is different from that of homogeneous reservoir, the fracture propagation morphology is more complex. With the increase of stress difference, the fracture propagation length increases. With the increase of injection rate, the fracture propagation length increases. With the increase of cluster spacing, the propagation length of multiple fractures tends to propagate evenly. This study clarifies the influence of heterogeneity on fracture propagation and provides some guidance for fracturing optimization of tight sandstone reservoirs.

Implant Design and Cervical Spinal Biomechanics and Neurorehabilitation: A Finite Element Investigation.

INTRODUCTION: The cervical spine, pivotal for mobility and overall body function, can be affected by cervical spondylosis, a major contributor to neural disorders. Prevalent in both general and military populations, especially among pilots, cervical spondylosis induces pain and limits spinal capabilities. Anterior Cervical Discectomy and Fusion (ACDF) surgery, proposed by Cloward in the 1950s, is a promising solution for restoring natural cervical curvature. The study objective was to investigate the impacts of ACDF implant design on postsurgical cervical biomechanics and neurorehabilitation outcomes by utilizing a biofield head-neck finite element (FE) platform that can facilitate scenario-specific perturbations of neck muscle activations. This study addresses the critical need to enhance computational models, specifically FE modeling, for ACDF implant design. MATERIALS AND METHODS: We utilized a validated head-neck FE model to investigate spine-implant biomechanical interactions. An S-shaped dynamic cage incorporating titanium (Ti) and polyetheretherketone (PEEK) materials was modeled at the C4/C5 level. The loading conditions were carefully designed to mimic helmet-to-helmet impact in American football, providing a realistic and challenging scenario. The analysis included intervertebral joint motion, disk pressure, and implant von Mises stress. RESULTS: The PEEK implant demonstrated an increased motion in flexion and lateral bending at the contiguous spinal (C4/C5) level. In flexion, the Ti implant showed a modest 5% difference under 0% activation conditions, while PEEK exhibited a more substantial 14% difference. In bending, PEEK showed a 24% difference under 0% activation conditions, contrasting with Ti's 17%. The inclusion of the head resulted in an average increase of 18% in neck angle and 14% in C4/C5 angle. Disk pressure was influenced by implant material, muscle activation level, and the presence of the head. Polyetheretherketone exhibited lower stress values at all intervertebral disc levels, with a significant effect at the C6/C7 levels. Muscle activation level significantly influenced disk stress at all levels, with higher activation yielding higher stress. Titanium implant consistently showed higher disk stress values than PEEK, with an orders-of-magnitude difference in von Mises stress. Excluding the head significantly affected disk and implant stress, emphasizing its importance in accurate implant performance simulation. CONCLUSIONS: This study emphasized the use of a biofidelic head-neck model to assess ACDF implant designs. Our results indicated that including neck muscles and head structures improves biomechanical outcome measures. Furthermore, unlike Ti implants, our findings showed that PEEK implants maintain neck motion at the affected level and reduce disk stresses. Practitioners can use this information to enhance postsurgery outcomes and reduce the likelihood of secondary surgeries. Therefore, this study makes an important contribution to computational biomechanics and implant design domains by advancing computational modeling and theoretical knowledge on ACDF-spine interaction dynamics.

Is Posterior Cervical Foraminotomy Better Than Fusion for Warfighters?: A Biomechanical Study.

INTRODUCTION: Cervical spondylosis in the warfighter is a common musculoskeletal problem and can be career-ending especially if it requires fusion. Head-mounted equipment and increased biomechanical forces on the cervical spine have resulted in accelerated cervical spine degeneration. Current surgical gold standard is anterior cervical discectomy and fusion (ACDF). Posterior cervical foraminotomy (PCF) is a nonfusion surgical alternative, and this can be effective in alleviating radiculopathy from foraminal stenosis caused by disc-osteophyte complex. Biomechanical studies have not been done to analyze motion associated with military aircrew personnel following PCF. The aim of this study was to compare the biomechanical responses of the effects of ACDF and PCF with different grades of facet resection under simulated military aircrew conditions using range of motion, disc pressure, and facet loads at the index and adjacent levels. MATERIALS AND METHODS: A validated 3D finite element model of the human cervical spinal column was used to simulate various graded PCF and ACDF. All surgical simulations were performed at the most commonly operated level (C5-C6) in warfighters. Pure moment loading under flexion, extension, and lateral bending, and in vivo follower force of 75 N were applied to the intact spine. Hybrid loading protocol was used to achieve 134 degrees of combined flexion-extension and 83 degrees of lateral bending in intact and surgical models to reflect military loading conditions. Segmental motions, disc pressure, and facet load were obtained and normalized with respect to the intact model to quantify the biomechanical effect. RESULTS: Anterior cervical discectomy and fusion decreased range of motion at the index and increased motion at the adjacent levels, while all graded PCF responses had an opposite trend: increased motion at the index and decreased motion at adjacent levels. The magnitude of changes depended on the level of resection, spinal level, and loading mode. Disc pressure increased at the index level and decreased at the adjacent levels after PCF. These changes were exaggerated with increasing extent of facet resection. Facet load increased at the index level after PCF especially with extension and right (contralateral) lateral bending. Complete facetectomy led to facet load increases greater than ACDF at the adjacent levels in both flexion and extension. CONCLUSIONS: Posterior cervical foraminotomy is a motion-preserving implant-free surgical alternative to ACDF for warfighters with cervical radiculopathy after failure of conservative management. The treating surgeon must pay close attention to the extent of facet resection to avoid potential spinal instability and future disc and facet degeneration after PCF. Posterior cervical foraminotomy can be more advantageous than ACDF in terms of adjacent segment degeneration, motion preservation, reoperation rate, surgical cost, and retention of warfighters.

3D Computational Modeling of Blast Wave Transmission in Human Ear From External Ear to Cochlear Hair Cells: A Preliminary Study.

INTRODUCTION: Auditory disabilities like tinnitus and hearing loss caused by exposure to blast overpressures are prevalent among military service members and veterans. The high-pressure fluctuations of blast waves induce hearing loss by injuring the tympanic membrane, ossicular chain, or sensory hair cells in the cochlea. The basilar membrane (BM) and organ of Corti (OC) behavior inside the cochlea during blast remain understudied. A computational finite element (FE) model of the full human ear was used by Bradshaw et al. (2023) to predict the motion of middle and inner ear tissues during blast exposure using a 3-chambered cochlea with Reissner's membrane and the BM. The inclusion of the OC in a blast transmission model would improve the model's anatomy and provide valuable insight into the inner ear response to blast exposure. MATERIALS AND METHODS: This study developed a microscale FE model of the OC, including the OC sensory hair cells, membranes, and structural cells, connected to a macroscale model of the ear to form a comprehensive multiscale model of the human peripheral auditory system. There are 5 rows of hair cells in the model, each row containing 3 outer hair cells (OHCs) and the corresponding Deiters' cells and stereociliary hair bundles. BM displacement 16.75 mm from the base induced by a 31 kPa blast overpressure waveform was derived from the macroscale human ear model reported by Bradshaw et al. (2023) and applied as input to the center of the BM in the OC. The simulation was run for 2 ms as a structural analysis in ANSYS Mechanical. RESULTS: The FE model results reported the displacement and principal strain of the OHCs, reticular lamina, and stereociliary hair bundles during blast transmission. The movement of the BM caused the rest of the OC to deform significantly. The reticular lamina displacement and strain amplitudes were highest where it connected to the OHCs, indicating that injury to this part of the OC may be likely due to blast exposure. CONCLUSIONS: This microscale model is the first FE model of the OC to be connected to a macroscale model of the ear, forming a full multiscale ear model, and used to predict the OC's behavior under blast. Future work with this model will incorporate cochlear endolymphatic fluid, increase the number of OHC rows to 19 in total, and use the results of the model to reliably predict the sensorineural hearing loss resulting from blast exposure.

Influence of the biomechanical evaluation of rupture using two shapes of same intramedullary implant after proximal interphalangeal joint arthrodesis to correct the claw/hammer pathology: A finite element study.

We used finite element analysis to study the mechanical stress distribution of a new intramedullary implant used for proximal interphalangeal joint (PIPJ) arthrodesis (PIPJA) to surgically correct the claw-hammer toe deformity that affects 20% of the population. After geometric reconstruction of the foot skeleton from claw toe images of a 36-year-old male patient, two implants were positioned, in the virtual model, one neutral implant (NI) and another one 10° angled (10°AI) within the PIPJ of the second through fourth HT during the toe-off phase of gait and results were compared to those derived for the non-surgical foot (NSF). A PIPJA was performed on the second toe using a NI reduced tensile stress at the proximal phalanx (PP) (45.83 MPa) compared to the NSF (59.44 MPa; p < 0.001). When using the 10°AI, the tensile stress was much higher at PP and middle phalanges (MP) of the same toe, measuring 147.58 and 160.58 MPa, respectively, versus 59.44 and 74.95 MPa at corresponding joints in the NSF (all p < 0.001). Similar results were found for compressive stresses. The NI reduced compressive stress at the second PP (-65.12 MPa) compared to the NSF (-113.23 MPa) and the 10°AI (-142 MPa) (all p < 0.001). The von Mises stresses within the implant were also significantly lower when using NI versus 10°AI (p < 0.001). Therefore, we do not recommend performing a PIPJA using the 10°AI due to the increase in stress concentration primarily at the second PP and MP, which could promote implant breakage.

A forecasting model for suitable dental implantation in canine mandibular premolar region based on finite element analysis.

In recent years, dental implants have become a trend in the treatment of human patients with missing teeth, which may also be an acceptable method for companion animal dentistry. However, there is a gap challenge in determining appropriate implant sizes for different dog breeds and human. In this study, we utilized skull computed tomography data to create three-dimensional models of the mandibles of dogs in different sizes. Subsequently, implants of various sizes were designed and subjected to biomechanical finite element analysis to determine the optimal implant size. Regression models were developed, exploring the relationship between the average weight of dogs and the size of premolar implants. Our results illustrated that the regression equations for mean body weight (x, kg) and second premolar (PM2), third premolar (PM3), and fourth premolar (PM4) implant length (y, mm) in dogs were: y = 0.2785x + 7.8209, y = 0.2544x + 8.9285, and y = 0.2668x + 10.652, respectively; the premolar implant diameter (mm) y = 0.0454x + 3.3506, which may provide a reference for determine suitable clinical implant sizes for dogs.

Choosing the right electrode representation for modeling real bioelectronic interfaces: a comprehensive guide.

Objective.Producing realistic numerical models of neurostimulation electrodes in contact with the electrolyte and tissue, for use in time-domain finite element method simulations while maintaining a reasonable computational burden remains a challenge. We aim to provide a straightforward experimental-theoretical hybrid approach for common electrode materials (Ti, TiN, ITO, Au, Pt, IrOx) that are relevant to the research field of bioelectronics, along with all the information necessary to replicate our approach in arbitrary geometry for real-life experimental applications.Approach.We used electrochemical impedance spectroscopy (EIS) to extract the electrode parameters in the AC regime under different DC biases. The pulsed electrode response was obtained by fast amperometry (FA) to optimize and verify the previously obtained electrode parameters in a COMSOL Multiphysics model. For optimization of the electrode parameters a constant phase element (CPE) needed to be implemented in time-domain.Main results.We find that the parameters obtained by EIS can be used to accurately simulate pulsed response only close to the electrode open circuit potential, while at other potentials we give corrections to the obtained parameters, based on FA measurements. We also find that for many electrodes (Au, TiN, Pt, and IrOx), it is important to implement a distributed CPE rather than an ideal capacitor for estimating the electrode double-layer capacitance. We outline and provide examples for the novel time-domain implementation of the CPE for finite element method simulations in COMSOL Multiphysics.Significance.An overview of electrode parameters for some common electrode materials can be a valuable and useful tool in numerical bioelectronics models. A provided FEM implementation model can be readily adapted to arbitrary electrode geometries and used for various applications. Finally, the presented methodology for parametrization of electrode materials can be used for any materials of interest which were not covered by this work.

A multiscale modeling to determine in vitro mechanical responses of different cells at the cell-substrate interface under fluid perfusion.

Investigating the influence of different cellular mechanical and physical properties on cells in vitro is important for assessing cellular activities like differentiation, proliferation, and migration. Evaluating the mechanical response of the cells lodged on a scaffold due to variations in substrate roughness, substrate elasticity, fluid flow, and the shapes of the cells is the main goal of the study. In this comprehensive analysis, a combination of the fluid structure interaction method and the submodeled finite element technique was employed to anticipate the mechanical responses across various cells at the interface between cells and the substrate. Fluid inlet velocity, substrate roughness, and substrate material were varied in this analysis. Different cell shapes were considered along with various components such as cell membrane, cytoplasm, nucleus, and cytoskeletons. This analysis shows the effect of these individual parameters on the elastic strain and strain energy density of cells at the cell-substrate interface. The results highlight that substrate roughness has a more significant impact on the mechanical response of cells at the interface than substrate elasticity. However, effect of the substrate elasticity becomes crucial for extremely soft substrate materials. The results of this research can be applied to identify the optimal parameters for fluid flow and create a suitable condition for cell culture.

CutFEM-based MEG forward modeling improves source separability and sensitivity to quasi-radial sources: A somatosensory group study.

Source analysis of magnetoencephalography (MEG) data requires the computation of the magnetic fields induced by current sources in the brain. This so-called MEG forward problem includes an accurate estimation of the volume conduction effects in the human head. Here, we introduce the Cut finite element method (CutFEM) for the MEG forward problem. CutFEM's meshing process imposes fewer restrictions on tissue anatomy than tetrahedral meshes while being able to mesh curved geometries contrary to hexahedral meshing. To evaluate the new approach, we compare CutFEM with a boundary element method (BEM) that distinguishes three tissue compartments and a 6-compartment hexahedral FEM in an n = 19 group study of somatosensory evoked fields (SEF). The neural generators of the 20 ms post-stimulus SEF components (M20) are reconstructed using both an unregularized and a regularized inversion approach. Changing the forward model resulted in reconstruction differences of about 1 centimeter in location and considerable differences in orientation. The tested 6-compartment FEM approaches significantly increase the goodness of fit to the measured data compared with the 3-compartment BEM. They also demonstrate higher quasi-radial contributions for sources below the gyral crowns. Furthermore, CutFEM improves source separability compared with both other approaches. We conclude that head models with 6 compartments rather than 3 and the new CutFEM approach are valuable additions to MEG source reconstruction, in particular for sources that are predominantly radial.

Curving expectations: The minimal impact of structural curvature in biological puncture mechanics.

Living organisms have evolved various biological puncture tools, such as fangs, stingers, and claws, for prey capture, defense, and other critical biological functions. These tools exhibit diverse morphologies, including a wide range of structural curvatures, from straight cactus spines to crescent-shaped talons found in raptors. While the influence of such curvature on the strength of the tool has been explored, its biomechanical role in puncture performance remains untested. Here, we investigate the effect of curvature on puncture mechanics by integrating experiments with finite element simulations. Our findings reveal that within a wide biologically relevant range, structural curvature has a minimal impact on key metrics of damage initiation or the energies required for deep penetration in isotropic and homogeneous target materials. This unexpected result improves our understanding of the biomechanical pressures driving the morphological diversity of curved puncture tools and provides fundamental insights into the crucial roles of curvature in the biomechanical functions of living puncture systems.

Mandibular biomechanics rehabilitated with different prosthetic restorations under normal and impact loading scenarios.

BACKGROUND: Restorative treatment options for edentulous patients range from traditional dentures to fixed restorations. The proper selection of materials greatly influences the longevity and stability of fixed restorations. Most prosthetic parts are frequently fabricated from titanium. Ceramics (e.g. zirconia) and polymers (e.g. PEEK and BIOHPP) have recently been included in these fabrications. The mandibular movement produces complex patterns of stress and strain. Mandibular fractures may result from these stresses and strains exceeding the critical limits because of the impact force from falls or accidents. Therefore, it is necessary to evaluate the biomechanical behavior of the edentulous mandible with different restorations under different loading situations. OBJECTIVE: This study analyzes the biomechanical behavior of mandibles after four prosthetic restorations for rehabilitation under normal and impact loading scenarios. MATERIAL AND METHODS: The mandibular model was constructed with a fixed restoration, which was simulated using various materials (e.g. Titanium, Zirconia & BIOHPP), under frontal bite force, maximum intercuspation, and chin impact force. From the extraction of tensile and compressive stresses and strains, as well as the total deformation of mandible segments, the biomechanical behavior and clinical situations were studied. RESULTS: Under frontal bite, the anterior body exhibited the highest tensile (60.34 MPa) and compressive (108.81 MPa) stresses using restoration 4, while the condyles and angles had the lowest tensile (7.12 MPa) and compressive (12.67 MPa) stresses using restoration 3. Under maximum intercuspation, the highest tensile (40.02 MPa) and compressive (98.87 MPa) stresses were generated on the anterior body of the cortical bone using restoration 4. Additionally, the lowest tensile (7.7 MPa) and compressive (10.08 MPa) stresses were generated on the condyles and angles, respectively, using restoration 3. Under chin impact, the highest tensile (374.57 MPa) and compressive (387.3 MPa) stresses were generated on the anterior body using restoration 4. Additionally, the lowest tensile (0.65 MPa) and compressive (0.57 MPa) stresses were generated on the coronoid processes using restoration 3. For all loading scenarios, the anterior body of the mandible had the highest stress and strain values compared with the other segments. Compared to the traditional titanium restoration.2, restoration.1(zirconia) increases the tensile and compressive stresses and strains on the mandibular segments, in contrast to restoration.3 (BIOHPP). In addition, zirconia implants exhibited higher displacements than the other implants. CONCLUSION: In the normal loading scenario, the tensile and compressive stresses and strains on the mandible were within the allowable limits when all restorations were used. Under the chin impact loading scenario, the anterior body of the mandible was damaged by restorations 1 and 4.

Motion reconstruction and finite element analysis of the temporomandibular joint during swallowing in healthy adults.

There is a close physiological connection between swallowing and the temporomandibular joint (TMJ). However, a shortage of quantitative research on the biomechanical behavior of the TMJ during swallowing exists. The purpose of this study was to reconstruct the movement of the temporomandibular joint (TMJ) based on in vivo experiment and analyze the biomechanical responses during swallowing in healthy adults to investigate the role of the TMJ in swallowing. Motion capture of swallowing, computed tomography (CT), and magnet resonance images (MRI) were performed on six healthy subjects. The movements of the TMJ during swallowing were reconstructed from the motion capture data. The three-dimensional finite element model was constructed. The dynamic finite element analysis of the swallowing process was performed based on the motion data. The range of condylar displacement was within 1 mm in all subjects. The left and right condyle movements were asymmetrical in two-thirds of the subjects. The peak stresses of the discs were relatively low, with a maximum of 0.11 MPa. During swallowing, the condylar displacement showed two trends: slow retraction and slow extension. The tendency to extend could lead to a gradual increase in stress on the disc.

Reliability analysis of the solidification cooling of solid rocket motor grain material.

The reliability of solid rocket motor grain structure during solidification cooling is analyzed. First, a three-dimensional parametric modeling of the grain is carried out by ANSYS finite element software. The dangerous point and dangerous moment can be obtained based on the transient and dynamic thermo-structure coupling under the cooling condition. Moreover, the maximum equivalent strain and temperature values are extracted. Second, a dual neural network model is established based on the probability distribution of the copula function and specific parameters. Finally, the instantaneous reliability during the solidification cooling process of the grain is calculated. Then, the dynamic reliability analysis is realized. The proposed method reduces the computational cost of dynamic reliability of grain structure, demonstrating its applicability in practical engineering problems. Furthermore, comparing the results of the proposed method with the MCS method demonstrates that the proposed method has high computational accuracy.

Evaluation of polymerization shrinkage stress and cuspal strain in natural and typodont teeth.

To evaluate the polymerization shrinkage stress and cuspal strain (CS) generated in an artificial (typodont) and in a natural tooth using different resin composites. Twenty artificial and 20 extracted natural molars were selected. Each tooth was prepared with a 4x4 mm MOD cavity. The natural and typodont teeth were divided into four experimental groups (n=10), according to the resin composite used: Filtek Z100 (3M Oral Care) and Beautifil II LS (Shofu Dental). The cavities were filled using two horizontal increments and the CS (µS) was measured by the strain gauge method. Samples were sectioned into stick-shaped specimens and the bond strength (BS) (MPa) was evaluated using a microtensile BS test. Shrinkage stress and CS were analyzed using 3D finite element analysis. No difference was found between the type of teeth for the CS as shown by the pooled averages: Natural tooth: 541.2 A; Typodont model: 591.4 A. Filtek Z100 CS values were higher than those obtained for Beautifil II LS, regardless of the type of teeth. No statistical difference was found for the BS data. Adhesive failures were more prevalent (79.9%). High shrinkage stress values were observed for Filtek Z100 resin, regardless of tooth type. The CS of typodont teeth showed a shrinkage stress effect, generated during restoration, equivalent to that of natural teeth.

Modeling the stress and forces on multi-channel TMS coil arrays in high-field MRI scanners.

Transcranial magnetic stimulation (TMS) is a non-invasive method for stimulating the cortex. Concurrent functional magnetic resonance imaging can show changes in TMS-induced activity in the whole brain, with the potential to inform brain function research and to guide the development of TMS therapy. However, the interaction of the strong current pulses in the TMS coil in the static main magnetic field of the MRI produces high Lorentz forces, which may damage the coil enclosure and compromise the patient's safety. We studied the time-dependent mechanical behavior and durability of two multi-locus TMS (mTMS) coil arrays inside a high-field MRI bore with finite element modeling. In addition, coil arrays were built and tested based on the simulation results. We found that the current pulses produce shock waves and time-dependent stress distribution in the coil plates. The intensity and location of the maximum stress depend on the current waveform, the coil combination, and the transducer orientation relative to the MRI magnetic field. We found that 30% glass-fiber-filled polyamide is the most durable material out of the six options studied. In addition, novel insights for more durable TMS coil designs were obtained. Our study contributes to a comprehensive understanding of the underlying mechanisms responsible for the structural failure of mTMS coil arrays during stimulation within high static magnetic fields. This knowledge is essential for developing mechanically stable and safe mTMS-MRI transducers.

Multi-physical field simulation calculation and analysis of simulated high-level waste liquid spray calcination.

Aiming at the independent research and development of a simulated high-level waste liquid spray calcination transformation treatment test device, a three-dimensional multi-physical field model of spray calcination was established by means of finite element analysis method. In this paper, the simulated high-level waste liquid is a mixed solution of nitrate solution and sucrose. The main chemical components of nitrate dissolution are HNO3 and NaNO3. The process of evaporation and calcination of high-level waste liquid to form oxides is also called the pretreatment of high-level waste liquid or the conversion of high-level waste liquid. In this experiment, the atomized droplets sprayed at high speed are evaporated, dried and calcined in turn in the calciner to obtain the calcined product. The distribution law of temperature flow field and chemical reaction state and results inside the test device were revealed by simulation calculation. The results show that under the condition of multi-physical field coupling, the chemical reaction temperature has an effect on the yield of the product. The temperature is positively correlated with the product concentration, and the effect of temperature on the yield of NO2 is greater than that of Na2O. At the same time, in this chemical reaction, the concentration of reactants (NaNO3 and HNO3) had a positive correlation with the concentration of main products (NO2 and Na2O). However, the rate of increase in the concentration of the main products (NO2 and Na2O) decreased with the increase of the concentration of the reactants (NaNO3 and HNO3).

Cryosurgery process applications - a mathematical review.

The present study reviews some of the prominent mathematical models that are used to simulate the cryosurgery treatment of tumor tissues, i.e., destruction of tumor tissues via controlled freezing with cryoprobes with minimizing the impact on surrounding healthy tissues. Numerical simulation of the appropriate mathematical models that reflect practical situations may help the physicians to design a planning framework for the treatment, which includes total number of cryoprobes to be used, their placement design and the duration of optimal freezing, etc. Finite element method, meshfree method, and finite volume method are some of the suitable numerical techniques for simulating bio-heat transfer process within complex tissues during treatment. Doi.org/10.54680/fr24510110112.

Finite element modeling of stress distribution and safety factors in a Ti-27Nb alloy hip implant under real-world physiological loading scenarios.

Total hip arthroplasty (THA) is one of the most successful orthopaedic interventions globally, with over 450,000 procedures annually in the U.S. alone. However, issues like aseptic loosening, dislocation, infection and stress shielding persist, necessitating complex, costly revision surgeries. This highlights the need for continued biomaterials innovation to enhance primary implant integrity and longevity. Implant materials play a pivotal role in determining long-term outcomes, with titanium alloys being the prominent choice. However, emerging evidence indicates scope for optimized materials. The nickel-free ß titanium alloy Ti-27Nb shows promise with excellent biocompatibility and mechanical properties. Using finite element analysis (FEA), this study investigated the biomechanical performance and safety factors of a hip bone implant made of nickel-free titanium alloy (Ti-27Nb) under actual loading during routine day life activities for different body weights. The FEA modelled physiological loads during walking, jogging, stair ascent/descent, knee bend, standing up, sitting down and cycling for 75 kg and 100 kg body weights. Comparative analyses were conducted between untreated versus 816-hour simulated body fluid (SBF) treated implant conditions to determine in vivo degradation effects. The FEA predicted elevated von Mises stresses in the implant neck for all activities, especially stair climbing, due to its smaller cross-section. Stresses increased substantially with a higher 100 kg body weight compared to 75 kg, implying risks for heavier patients. Safety factors were reduced by up to 58% between body weights, although remaining above the desired minimum value of 1. Negligible variations were observed between untreated and SBF-treated responses, attributed to Ti-27Nb's excellent biocorrosion resistance. This comprehensive FEA provided clinically relevant insights into the biomechanical behaviour and integrity of the Ti-27Nb hip implant under complex loading scenarios. The results can guide shape and material optimization to improve robustness against repetitive stresses over long-term use. Identifying damage accumulation and failure risks is crucial for hip implants encountering real-world variable conditions. The negligible SBF effects validate Ti-27Nb's resistance to physiological degradation. Overall, the study significantly advances understanding of Ti-27Nb's suitability for reliable, durable hip arthroplasties with low revision rates.

Evaluation of the effect of different attachment configurations on molar teeth in maxillary expansion with clear aligners - a finite element analysis.

OBJECTIVE: To evaluate the effects of different attachment configurations with and without buccal root torque on expansion movements achieved with aligners through finite element analysis (FEA). METHODS: FEA modelling was done with 0.25 mm buccal expansion force application to the maxillary molars with different attachment configurations: Eight models were tested (1) no attachment (NA), (2) horizontal attachment (HA), (3) gingivally beveled horizontal attachment (GHA), and (4) occlusally beveled horizontal attachment (OHA), as well as models with 6obuccal root torque, (5) no attachment (TNA), (6) horizontal attachment (THA), (7) gingivally beveled horizontal attachment (TGHA), and (8) occlusally beveled horizontal attachment (TOHA). RESULTS: The first and second molars exhibited buccal tipping in all models. The highest amount of buccal tipping for the molars was observed in the NA (6CMB, 0.232 mm; 6CMP, 0.246 mm; 7CMB, 0.281 mm; 7CMP, 0.312 mm) and GHA (6CMB, 0.230; 6CMP, 0.245; 7CMB, 0.279 mm; 7CMP, 0.311 mm) models, respectively, while the least tipping was observed in the TOHA model (6CMB, 0.155 mm; 6CMP, 0.168 mm; 7CMB, 0.216 mm; 7CMP, 0.240 mm). In all groups, the buccal tipping of the second molars was higher than that of the first molars. CONCLUSION: This FEA study showed that expansion with aligners tip maxillary molars buccally and the use of occlusally beveled attachments and addition of buccal root torque reduces uncontrolled buccal tipping.