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Journal of Biomedical Materials... May 2024Stress shielding is one of the major concerns for total ankle replacement implants nowadays, because it is responsible for implant-induced bone resorption. The bone...
A numerical investigation for the development of functionally graded Ti/HA tibial implant for total ankle replacement: Influence of material gradation law and volume fraction index.
Stress shielding is one of the major concerns for total ankle replacement implants nowadays, because it is responsible for implant-induced bone resorption. The bone resorption contributes to the aseptic loosening and failure of ankle implants in later stages. To reduce the stress shielding, improvements can be made in the implant material by decreasing the elastic mismatch between the implant and the tibia bone. This study proposes a new functionally graded material (FGM) based tibial implant for minimizing the problem of stress shielding. Three-dimensional finite element (FE) models of the intact tibia and the implanted tibiae were created to study the influence of material gradation law and volume fraction index on stress shielding and implant-bone micromotion. Different implant materials were considered that is, cobalt-chromium, titanium (Ti), and FGM with Ti at the bottom and hydroxyapatite (HA) at the top. The FE models of FGM implants were generated by using different volume fractions and the rule of mixtures. The rule of mixtures was used to calculate the FGM properties based on the local volume fraction. The volume fraction was defined by using exponential, power, and sigmoid laws. For the power and sigmoid law varying volume fraction indices (0.1, 0.2, 0.5, 1, 2, and 5) were considered. The geometry resembling STAR® ankle system tibial implant was considered for the present study. The results indicate that FGMs lower stress shielding but also marginally increase implant-bone micromotion; however, the values were within the acceptable limit for bone ingrowth. It is observed that the material gradation law and volume fraction index influence the performance of FGM tibial implants. The tibial implant composed of FGM using power law with a volume fraction index of 0.1 was the preferred option because it showed the least stress shielding.
Topics: Titanium; Tibia; Arthroplasty, Replacement, Ankle; Humans; Finite Element Analysis; Durapatite; Prosthesis Design; Stress, Mechanical; Materials Testing
PubMed: 38742468
DOI: 10.1002/jbm.b.35417 -
Soft Matter Oct 2023Examples of self-assembled multiple emulsion droplets on the nanometre scale are very rare. In this work, we use coarse-grained (CG) molecular dynamics simulations to...
Examples of self-assembled multiple emulsion droplets on the nanometre scale are very rare. In this work, we use coarse-grained (CG) molecular dynamics simulations to study the self-assembly of ternary mixtures consisting of water, -heptane, and nonionic surfactant tetraethylene glycol monododecyl ether (C12E4). The water volume fractions studied are 1%, 3%, and 5%, respectively. Various nanoscale emulsions are obtained in a spontaneous process. When the water/surfactant volume ratio = 1.0/1.0, the obtained emulsion droplets are identified as oil-in-water-in-oil (O/W/O) double types, consisting of an oil core, an inner surfactant layer, a water layer, and an outer surfactant layer. The water molecules are distributed around the hydrophilic ends of the surfactants, while the hydrophobic ends of the surfactants wrap the oil cores and penetrate into the oil bulk. Hydrogen-bond interactions among water and the hydrophilic ends of the surfactants form cross-links that stabilize the double emulsion droplets. The sizes of all the oil cores inside the droplets are <6 nm in diameter, even with the highest water volume fraction of 5%. Both the concentration of free water molecules on the order of 10 mol/cm and the favourable energy change during emulsion formation indicate that the emulsion droplets are thermodynamically stable. In contrast, for = 1.0/5.5, no double emulsion but a simple water-in-oil emulsion was observed, with morphologies evolving from oblate to bicontinuous phases with an increase in the water volume fraction from 1% to 5%. Our coarse-grained molecular dynamics simulations provide valuable insight for the preparation of nanoscale double emulsions and the characterization of their structures.
PubMed: 37789812
DOI: 10.1039/d3sm00656e -
BMC Anesthesiology Aug 2023There is the ongoing debate over the effect of inspired oxygen fraction (FiO) during mechanical ventilation on postoperative atelectasis. We aimed to compare the effects... (Randomized Controlled Trial)
Randomized Controlled Trial
BACKGROUND
There is the ongoing debate over the effect of inspired oxygen fraction (FiO) during mechanical ventilation on postoperative atelectasis. We aimed to compare the effects of low (30%) and moderate (60%) FiO on postoperative atelectasis. The hypothesis of the study was that 30% FiO during mechanical ventilation could reduce postoperative atelectasis volume compared with 60% FiO.
METHODS
We performed a randomized controlled trial with 120 patients. Subjects were randomly assigned to receive 30% or 60% FiO during mechanical ventilation in a 1:1 ratio. The primary outcome was the percentage of postoperative atelectasis volume in the total lung measured using chest CT within 30 min after extubation. The secondary outcomes included different aeration region volumes, incidence of clinically significant atelectasis, and oxygenation index.
RESULTS
In total, 113 subjects completed the trial, including 55 and 58 subjects in the 30% and 60% FiO groups, respectively. The percentage of the postoperative atelectasis volume in the 30% FiO group did not differ from that in the 60% FiO group. Furthermore, there was no significant difference in the atelectasis volume between the two groups after the missing data were imputed by multiple imputation. Additionally, there were no significant differences in the volumes of the over-aeration, normal-aeration, and poor-aeration regions between the groups. No significant differences in the incidence of clinically significant atelectasis or oxygenation index at the end of surgery were observed between the groups.
CONCLUSIONS
Compared with 60% FiO, the use of 30% FiO during mechanical ventilation does not reduce the postoperative atelectasis volume.
TRIAL REGISTRATION
Chinese Clinical Trial Registry ( http://www.chictr.org.cn ). Identifier: ChiCTR1900021635. Date: 2 March 2019. Principal invetigator: Weidong Gu.
Topics: Humans; Respiration, Artificial; Oxygen; Pulmonary Atelectasis; Lung; Postoperative Complications
PubMed: 37550648
DOI: 10.1186/s12871-023-02226-6 -
Soft Matter Apr 2024Bacteria in biofilms form complex structures and can collectively migrate within mobile aggregates, which is referred to as swarming. This behavior is influenced by a...
Bacteria in biofilms form complex structures and can collectively migrate within mobile aggregates, which is referred to as swarming. This behavior is influenced by a combination of various factors, including morphological characteristics and propulsive forces of swimmers, their volume fraction within a confined environment, and hydrodynamic and steric interactions between them. In our study, we employ the squirmer model for microswimmers and the dissipative particle dynamics method for fluid modeling to investigate the collective motion of swimmers in thin films. The film thickness permits a free orientation of non-spherical squirmers, but constraints them to form a two-layered structure at maximum. Structural and dynamic properties of squirmer suspensions confined within the slit are analyzed for different volume fractions of swimmers, motility types (, pusher, neutral squirmer, puller), and the presence of a rotlet dipolar flow field, which mimics the counter-rotating flow generated by flagellated bacteria. Different states are characterized, including a gas-like phase, swarming, and motility-induced phase separation, as a function of increasing volume fraction. Our study highlights the importance of an anisotropic swimmer shape, hydrodynamic interactions between squirmers, and their interaction with the walls for the emergence of different collective behaviors. Interestingly, the formation of collective structures may not be symmetric with respect to the two walls. Furthermore, the presence of a rotlet dipole significantly mitigates differences in the collective behavior between various swimmer types. These results contribute to a better understanding of the formation of bacterial biofilms and the emergence of collective states in confined active matter.
PubMed: 38639062
DOI: 10.1039/d4sm00075g -
The Journal of Physical Chemistry. C,... Apr 2024Concentrated and thick oil-in-water nanoemulsions have been observed to become more transparent with increasing oil volume fraction. This study demonstrates rigorously...
Concentrated and thick oil-in-water nanoemulsions have been observed to become more transparent with increasing oil volume fraction. This study demonstrates rigorously experimentally and numerically that such unusual behavior is due to dependent scattering including not only far-field but also near-field effects. Indeed, when the droplet concentration is sufficiently large, their interparticle distance becomes small compared to the wavelength of light and scattering by a given droplet may be affected by the proximity of others. This situation is referred to as dependent scattering. Light transfer through nanoemulsions and other colloids has previously been modeled by solving the radiative transfer equation accounting for dependent scattering using the static structure factor based on far-field approximations. Here, oil-in-water nanoemulsions were prepared with oil volume fraction ranging between 1 and 20% and a peak droplet radius of 16 nm. The spectral normal-hemispherical transmittance of the different nanoemulsions in 10 mm thick cuvettes was measured experimentally between 400 and 900 nm. Numerical predictions for nonoverlapping randomly distributed nanoscale oil droplets in water and accounting for dependent scattering including near-field effects-using the recently developed radiative transfer with reciprocal transactions (RT) method-were in excellent agreement with experimental measurements. Simulations revealed that assuming independent scattering underestimated the normal-hemispherical transmittance even for a relatively small oil volume fraction. Additionally, simulations using the dense medium radiative transfer (DMRT) and static structure factor predicted that dependent scattering prevailed for oil volume fractions slightly greater than those predicted by the RT method. Interestingly, the DMRT method predicted large increases in transmittance when the oil droplet size and volume fraction were larger than 10 nm and 10%, respectively. Finally, simulations also revealed that dependent scattering enables the design of oil-in-water nanoemulsions to backscatter or absorb light by tuning the oil droplet size and volume fraction. The results validate that the RT method could be used to characterize nanoemulsions or to investigate their formation, composition, and stability for drug delivery, food, and cosmetics applications. Future studies could extend the use of the RT method to colloidal suspensions with particles of arbitrary shapes and to radiation transfer of polarized light in turbid media.
PubMed: 38655060
DOI: 10.1021/acs.jpcc.3c08072 -
Advances in Radiation Oncology Jan 2024The response of cystic brain metastases (BMets) to radiation therapy is poorly understood, with conflicting results regarding local control, overall survival, and...
PURPOSE
The response of cystic brain metastases (BMets) to radiation therapy is poorly understood, with conflicting results regarding local control, overall survival, and treatment-related toxicity. This study aims to examine the role of Gamma Knife (GK) in managing cystic BMets.
METHODS AND MATERIALS
Volumetric analysis was conducted to measure tumor and edema volume at the time of GK and follow-up magnetic resonance imaging studies. Survival was described using the Kaplan-Meier method, and the cumulative incidence of progression was described using the Aalen-Johansen estimator. We evaluated the association of 4 variables with survival using Cox regression analysis.
RESULTS
Between 2016 and 2021, 54 patients with 83 cystic BMets were treated with GK at our institution. Lung cancer was the most common pathology (51.9%), followed by breast cancer (13.0%). The mean target volume was 2.7 cm (range, 0.1-39.0 cm), and the mean edema volume was 13.9 cm (range, 0-165.5 cm). The median prescription dose of single-fraction and fractionated GK was 20 Gy (range, 14-27.5 Gy). With a median follow-up of 8.9 months, the median survival time (MST) was 11.1 months, and the 1-year local control rate was 75.9%. Gamma Knife was associated with decreased tumor and edema volumes over time, although 68.5% of patients required steroids after GK. Patients whose tumors grew beyond baseline after GK received significantly more whole-brain radiation therapy (WBRT) before GK than those whose tumors declined after GK. Higher age at diagnosis of BMets and pre-GK systemic therapy were associated with worse survival, with an MST of 7.8 months in patients who received it compared with 23.3 months in those who did not.
CONCLUSIONS
Pre-GK WBRT may select for BMets with increased radioresistance. This study highlights the ability of GK to control cystic BMets with the cost of high posttreatment steroid use.
PubMed: 38260234
DOI: 10.1016/j.adro.2023.101304 -
Annals of Clinical and Translational... Jun 2024To evaluate the intrinsic and extrinsic microstructural factors contributing to atrophy within individual thalamic subregions in multiple sclerosis using in vivo...
OBJECTIVE
To evaluate the intrinsic and extrinsic microstructural factors contributing to atrophy within individual thalamic subregions in multiple sclerosis using in vivo high-gradient diffusion MRI.
METHODS
In this cross-sectional study, 41 people with multiple sclerosis and 34 age and sex-matched healthy controls underwent 3T MRI with up to 300 mT/m gradients using a multi-shell diffusion protocol consisting of eight b-values and diffusion time of 19 ms. Each thalamus was parcellated into 25 subregions for volume determination and diffusion metric estimation. The soma and neurite density imaging model was applied to obtain estimates of intra-neurite, intra-soma, and extra-cellular signal fractions for each subregion and within structurally connected white matter trajectories and cortex.
RESULTS
Multiple sclerosis-related volume loss was more pronounced in posterior/medial subregions than anterior/ventral subregions. Intra-soma signal fraction was lower in multiple sclerosis, reflecting reduced cell body density, while the extra-cellular signal fraction was higher, reflecting greater extra-cellular space, both of which were observed more in posterior/medial subregions than anterior/ventral subregions. Lower intra-neurite signal fraction in connected normal-appearing white matter and lower intra-soma signal fraction of structurally connected cortex were associated with reduced subregional thalamic volumes. Intrinsic and extrinsic microstructural measures independently related to subregional volume with heterogeneity across atrophy-prone thalamic nuclei. Extrinsic microstructural alterations predicted left anteroventral, intrinsic microstructural alterations predicted bilateral medial pulvinar, and both intrinsic and extrinsic factors predicted lateral geniculate and medial mediodorsal volumes.
INTERPRETATION
Our results might be reflective of the involvement of anterograde and retrograde degeneration from white matter demyelination and cerebrospinal fluid-mediated damage in subregional thalamic volume loss.
Topics: Humans; Female; Male; Adult; Thalamus; Cross-Sectional Studies; Middle Aged; Multiple Sclerosis; Atrophy; White Matter; Diffusion Magnetic Resonance Imaging
PubMed: 38725151
DOI: 10.1002/acn3.52026 -
International Journal of Cardiology.... Dec 2023The aspects of right ventricular volumes and function investigated with 3D echocardiography in a large cohort of left ventricular noncompaction morphology (LVNC)...
The aspects of right ventricular volumes and function investigated with 3D echocardiography in a large cohort of left ventricular noncompaction morphology (LVNC) population remains unclear. The objective of our research was to study the left (LV) and right (RV) ventricular parameters using 3D echocardiography and analyze the clinical features of a LVNC population with preserved LV ejection fraction (EF > 50 %) in comparison with healthy controls (HC). We selected 41 LVNC subjects with preserved LV function (EF: 52.91 ± 3 %, male n = 26) and without any comorbidities and compared them with an age and sex-matched HC. Three dimensional endocardial contours were evaluated to determine the following LV and RV parameters: end-diastolic (EDV) and end-systolic (ESV) volumes, stroke volume, EF, LV global longitudinal and circumferential strain and RV septal and free wall longitudinal strain. Regarding the clinical characteristics, the family involvement had a notable proportion, accounting for 51%. The EF and strain values of the LVNC population were significantly decreased in both RV and LV compared to HC. Although the LV volumes of the LVNC group were significantly elevated, the RV volumetric parameters did not differ significantly compared to controls. We found significant correlations between LV and RV volumetric and functional parameters and linear regression models showed that LV EDV and LV ESV determined the RV volumetric values. While the alteration and relationship of the RV parameters may represent the potential of biventricular involvement, clinical characteristics of the LVNC group underlines the necessity of monitoring this population, even with preserved EF.
PubMed: 38035261
DOI: 10.1016/j.ijcha.2023.101289 -
Materials (Basel, Switzerland) Aug 2023As a typical brittle material, the tensile strength of concrete is much lower than its compressive strength. The main failure mode of concrete buildings under explosive...
As a typical brittle material, the tensile strength of concrete is much lower than its compressive strength. The main failure mode of concrete buildings under explosive and impact loading is spalling, so it is crucial to understand the dynamic tensile performance of concrete. This paper presents an experimental study on the dynamic tensile strength of steel-fiber-reinforced self-compacting concrete (SFRSCC). Specimens of two different self-compacting concrete (SCC) mixes (C40 and C60) and four different fiber volume fractions (0.5%, 1.0%, 1.5%, and 2.0%) are fabricated. Dynamic tensile strengths of SFRSCC are obtained using a modified Hopkinson bar system. The relationships between the dynamic tensile strength of the corresponding SCC mix, the quasi-static compressive strength, and the fiber volume fraction are discussed. An empirical equation is proposed. It is shown that SFRSCC with high compressive strength has higher dynamic tensile strength than low-strength SFRSCC for the same fiber content, and the dynamic tensile strength of SFRSCC possesses an approximately linear relation with the fiber volume fraction. The mechanism underlying this fiber-reinforcement effect is investigated.
PubMed: 37629996
DOI: 10.3390/ma16165707 -
Asian Pacific Journal of Cancer... Feb 2024We aim to compare TRAK & TPS based isodose volumes in cervical cancer brachytherapy and assess the feasibility, accuracy and potential future implications of TRAK in...
OBJECTIVE
We aim to compare TRAK & TPS based isodose volumes in cervical cancer brachytherapy and assess the feasibility, accuracy and potential future implications of TRAK in this regard and as a newer emerging tool to assess treatment intensity in cervical cancer brachytherapy.
METHODS
one hundred patients with histologically proven squamous cell carcinoma of cervix uteri were assessed for brachytherapy (after completion of external radiation) and prospectively enrolled for the study. 60 Gy, 75 Gy, and 85 Gy isodose volumes were obtained from the TPS (VTPS) for 50, 25 & 25 patients with Manchester, Fletcher & interstitial implant respectively, receiving various fractionation schedules by Ir192 HDR remote after-loading system. Using the formula Vpred=4965(TRAK/dref)3/2+170(TRAK/dref)-1.5 the TRAK based isodose surface volumes (Vpred) were derived. Reference doses (dref) were calculated based on accumulated EBRT and brachytherapy doses. The two sets of volume were compared with respect to applicator type, standard, and optimised plan. Surrogate point A dose was also correlated.
RESULT
VTPS - Vpred were 5.24 ± 2.7%, all volumes being predicted within 10%. Correlation of TRAK vs VTPS60/ VTPS75/ VTPS85 showed R2 of 0.994, 0.987 and 0.971 respectively. There was no significant difference in predicted volumes with respect to applicator type. The surrogate point A showed mean volume and standard deviation of 7.44 ± 13.4%, 17.63 ± 16.38 and 3.5 ± 0.95 for Manchester optimised, Fletcher optimised and standard plans respectively. TRAK with point A (R2=0.5632), bladder (R2=0.2015) and rectal doses (R2=0.121) yielded no correlation.
CONCLUSION
Volumes calculated by TRAK correlate with TPS obtained volumes significantly and the formula predicting isodose surface volumes within 10% accuracy for ICBT applications and not for pure interstitial implants. However, TRAK fails to correlate with surrogate point A, bladder and rectal doses hence has questionable utility as a marker for biological response & treatment intensity.
Topics: Female; Humans; Radiotherapy Dosage; Brachytherapy; Uterine Cervical Neoplasms; Radiotherapy Planning, Computer-Assisted; Dose Fractionation, Radiation
PubMed: 38415545
DOI: 10.31557/APJCP.2024.25.2.587