Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine最新文献

Bone microstructure governs microcrack propagation complexity. Current research, relying on linear elastic fracture mechanics, inadequately considers authentic multi-level structures, like cement lines and osteons, impacting stress intensity at cracks. This study, by constructing models encompassing single or multiple osteons, delves into the influence of factors like crack length, osteon radius, and modulus ratio on the stress intensity factor at the crack tip. Employing a fracture mechanics phase-field approach to simulate crack propagation paths, it particularly explores the role of cement lines as weak interfaces in crack extension. The aim is to comprehensively and systematically elucidate the critical factors of bone microstructure in the context of crack propagation.

Aseptic loosening is the primary cause of failure following posterior-stabilized total knee arthroplasty. It is unclear whether tibial post loading of posterior-stabilized prosthesis increases the risk of aseptic loosening of the tibial prosthesis. The purpose of this study is to investigate the biomechanical effects of tibial post loading on the tibial prosthesis fixation interface during level walking, squatting, stair descent, and standing up-sitting down activities. In this paper, finite element models with and without post were established to compare the effects of tibial post loading on the von Mises stress of the proximal tibia, shear stress of the cement, and the bone-prosthesis interface micromotion during four physiological activities. The tibial post loading had an insignificant influence on tibial biomechanics and bone-prosthesis interface micromotion during leveling walking activity. However, compared to the insert without post condition, tibial post loading significantly increased the maximum tibial von Mises stress, the maximum shear stress in the medial of cement, and the bone-prosthesis interface peak micromotion by 912.84%, 612.77%, and 921.09%, respectively, at the moment of the maximum flexion angle for the stair descent activity, and 637.92%, 351.43%, and 519.13%, respectively, at the moment of the maximum flexion angle for the standing up-sitting down activity. Tibial post loading increased the risk of postoperative aseptic loosening of tibial prosthesis in patients with posterior-stabilized total knee arthroplasty, and it was recommended that the post-cam contact mechanism of posterior-stabilized prosthesis should be optimized to reduce the biomechanical impact of tibial post loading on tibial prosthesis fixation.

A biologically-inspired actuation system, including muscles, spinal reflexes, and vestibular feedback, may be capable of achieving more natural gait mechanics in powered prostheses or exoskeletons. In this study, we developed a Virtual Muscle Reflex (VMR) system to control ankle torque and tuned it using data from human responses to anteroposterior mechanical perturbations at three walking speeds. The system consists of three Hill-Type muscles, simulated in real time, and uses feedback from ground reaction force and from stretch sensors on the virtual muscle fibers. Controller gains, muscle properties, and reflex/vestibular time delays were optimized using Covariance Matrix Adaptation (CMA) to minimize the difference between the VMR torque output and the torque measured from the experiment. We repeated the procedure using a conventional finite-state impedance controller. For both controllers, the coefficient of determination ($R^2$) and root-mean-square error (RMSE) was calculated as a function of time within the gait cycle. The VMR had lower RMSE than the impedance controller in 70%, and in 60% of the trials, the $R^2$ of the VMR controller was higher than for the impedance controller. We concluded that the VMR system can better reproduce the human responses to perturbations than the impedance controller.

The conical stem tibial design of total ankle replacement (TAR) has high implant-bone micromotion. This may lead to aseptic loosening which can be avoided by improving the tibial design. The objective was to propose the best stem design parameters to reduce implant-bone micromotion along with minimizing stress shielding using an integrated Finite Element-Multi Criteria Decision Making (FE-MCDM) approach. FE models of implanted tibia bones were prepared by changing the height of the stem, the diameter of the stem, and the slant of the stem. Weighted Aggregated Sum Product Assessment (WASPAS), Technique for Order of Preference by Similarities to Ideal Solution (TOPSIS), Evaluation based on Distance from Average Solution (EDAS), and VIseKriterijumska Optimizacija I Kompromisno Resenje (VIKOR) MCDM techniques with equal weights for micromotion and stress shielding were considered. The micromotion and stress shielding were greater when the height of the stem was increased. Whereas, the increase in diameter and slant affected them marginally. The best-performing design was the Model with stem height 6 mm (diameter 6.4 mm and slant 4°) and after that was the Model with stem height 8 mm (diameter 6.4 mm and slant 4°), and then the Model with stem height 10 mm (diameter 6.4 mm and slant 4°). The height of the stem is the most important stem design parameter. Shorter height, moderate thickness, and moderate slanting stem designs are recommended.

The photoplethysmographic (PPG) signal of the finger is being used to create embedded devices that estimate physiological variables. This project outlines an innovative method for developing a synthetic PPG generator that produces both actual reference digital signals and their equivalent analog signals using open-source technology. A series of PPG profiles is synthesized using three variant Gaussian functions. A low-frequency trend induced by respiratory frequency and background noise are then added. To generate a diverse range of continuously variable PPG profiles within specified boundaries and customizable levels of interference, all parameters undergo random fluctuations on a cycle-by-cycle basis, as per user-defined constraints. The generated signal is then converted into its equivalent analog form through the use of an RC filter that low-frequency filters a Pulse-Width Modulation square wave that is modulated directly by the generated signal. The software returns different PPG profiles and allows the signal comparison before vs after the addition of different-intensity modulated respiratory trends and background noise. The digital signal is faithfully converted into an equivalent analog voltage signal capable of reproducing not only the waveform profile but also the respiratory trend and various levels of noise.

The selection of internal fixation as the primary fixation modality for the patient is one of the challenges for the surgeon treating the patient in question. A model of the lateral tibial plateau fracture was established. Three different configurations of internal fixators namely L bone plate, T bone plate, and screw-washer were analyzed. Three stages after surgery were simulated to assess the displacement of bone plates, screws, washers, and the stress shielding ratio in the fracture area.At three stages after surgery, the T bone plate showed better stability for patients during rehabilitation compared with the remaining two schemes, and the screw-washer scheme was the least stable due to the larger internal fixation displacement and stress shielding ratio in the fracture area. In contrast, the L bone plate scheme showed better stability in the early stages after surgery but was second only to the screw-washer scheme in the middle and late stages after surgery. The T bone plate showed better stability and became a new selection for surgeons to treat related patients. At three stages after surgery, the T bone plate has better biomechanical stability compared to the L bone plate and screw-washer schemes.

The objective of this study was to synthesize and characterize porous Cellulose Acetate (CA) scaffolds using the electrospinning technique and functionalize the surface of the scaffolds obtained through the dip-coating method with a Hydroxyapatite (HA) nanocomposite and varying concentrations of graphene oxide (GO) for application in tissue engineering regeneration techniques. The scaffolds were divided into four distinct groups based on their composition: 1) CA scaffolds; 2) CAHAC scaffolds; 3) CAHAGOC 1.0% scaffolds; 4) CAHAGOC 1.5% scaffolds. Scaffold analyses were conducted using X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Raman Spectroscopy, Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM/EDS), and in vitro cell viability assays (WST). For the biological test analysis, Variance (two-way) was used, followed by Tukey's post-test (α = 0.05). The XRD results revealed the predominant presence of CaP phases in the CAHAC, CAHAGOC 1.0%, and CAHAGOC 1.5% groups, emphasizing the presence of HA in the scaffolds. FTIR demonstrated characteristics of cellulose and PO4 bands in the groups containing HA, confirming the presence of CaP in the synthesized materials, as also indicated by XRD. Raman spectroscopy showed the presence of D and G bands, consistent with GO, confirming the successful incorporation of the HAGO nanocomposite into the scaffolds. The micrographs displayed overlapping electrospun fibers, forming the three-dimensional structure in the produced scaffolds. It was possible to observe hydroxyapatite crystals filling some of these pores, creating a suitable structure for cell adhesion, proliferation, and nutrition, as corroborated by the results of in vitro tests. All scaffolds exhibited high cell viability, with significant cell proliferation. Even after 48 h, there was a slight reduction in the number of cells, but a noteworthy increase in cell proliferation was evident in the CAHAGOC 1.5% group after 48 h (p < 0.05). In conclusion, it can be affirmed that the produced scaffolds demonstrated physical and biological characteristics and properties capable of promoting cell adhesion and proliferation. Therefore, they represent significant potential for application in tissue engineering, offering a new perspective regarding techniques and biomaterials applied in regenerative therapies.

Steady-state visually evoked potential is one of the active explorations in the brain-computer interface research. Electroencephalogram based brain computer interface studies have been widely applied to perceive solutions for real-world problems in the healthcare domain. The classification of externally bestowed visual stimuli of different frequencies on a human was experimented to identify the need of paralytic people. Although many classifiers are at the fingertip of machine learning technology, recent research has proven that ensemble learning is more efficacious than individual classifiers. Despite its efficiency, ensemble learning technology exhibits certain drawbacks like taking more time on selecting the optimal classifier subset. This research article utilizes the Harris Hawk Optimization algorithm to select the best classifier subset from the given set of classifiers. The objective of the research is to develop an efficient multi-classifier model for electroencephalogram signal classification. The proposed model utilizes the Boruta Feature Selection algorithm to select the prominent features for classification. Thus selected prominent features are fed into the multi-classifier subset which has been generated by the Harris Hawk Optimization algorithm. The results of the multi-classifier ensemble model are aggregated using Stacking, Bagging, Boosting, and Voting. The proposed model is evaluated against the acquired dataset and produces a promising accuracy of 96.1%, 98.7%, 91.91%, and 99.01% with the ensemble techniques respectively. The proposed model is also validated with other performance metrics such as sensitivity, specificity, and F1-Score. The experimental results show that the proposed model proves its supremacy in segregating the multi-class classification problem with high accuracy.

The aim of this study was to evaluate the effect of rotation frequency (rpm) of different polishing discs on the surface roughness of a nanohybrid resin composite material. 126 specimens were prepared in metal molds of 10 mm diameter and 2 mm depth using a nanohybrid resin composite material. The prepared specimens were kept in distilled water for 24 hours. Polishing treatments at 5k, 10k, 15k, and 20k rpm were applied to the nanohybrid resin composite material by grouping different brand polishing discs: Sof-Lex Contouring and Polishing Discs (3M Espe, USA) (3M Group), Optidisc (Kerr Corporation, USA) (Kerr Group), Super-Snap Rainbow Technique Kit (Shofu Dental, Japan) (Shofu Group), Finishing Disc (Bisco Dental, USA) (Bisco Group). The surface roughness was evaluated at three different points by atomic force microscopy for all specimens and scanning electron microscopy was used for visual assessment. Data were evaluated by Two Way ANOVA and Tukey's HSD Test. The mean surface roughness (Ra, μm) of all prepared samples showed significant differences (α = 0.05). According to Two-Way ANOVA, there is a statistically significant relationship between the rpm values and the discs. The 3M group showed the highest roughness value at all rpm speeds. Shofu group at 15k, 20k rpm, Bisco group at 10k, 15k, 20k rpm, the Kerr group at 15k, 20k rpm showed the lowest roughness value and had roughness close to the surfaces finished with a mylar strip. The smoothest surfaces were obtained at 15k rpm, even though polishing discs from different brands were used. It was also observed that 5k and 20k rpm polishing speeds can increase the surface roughness of the nanohybrid resin composite material.

The objectives of this study were to compare the chondrogenic potential of cells derived from different layers of Mandibular condyle cartilage and to gain further understanding of the impact of chondrogenic cues when embedded into a novel hydrogel scaffold (PGH, a polymer blend of poly (ethylene glycol), gelatin, and heparin) compared to a gelatin hydrogel scaffold (GEL). Cartilage layer cells (CLCs) and fibroblastic superficial layer cells (SLCs) were harvested from the mandibular condyle of boer goats obtained from a local abattoir. After expansion, cells were seeded into PGH and GEL hydrogels and cultured in chondrogenic media for 3 weeks. Scaffolds were harvested at 0, 1, and 3 week(s) and processed for gross appearance, histochemical, biochemical, and mechanical assays. In terms of chondrogenesis, major differences were observed between scaffold materials, but not cell types. Glycosaminoglycan (GAG) staining showed GEL scaffolds deposited GAG during the 3 week period, which was also confirmed with the biochemical testing. Moreover, GEL scaffolds had significantly higher compressive modulus and peak stress than PGH scaffolds at all time points with the largest difference seen in week 3. It can be concluded that GEL outperformed PGH in chondrogenesis. It can also be concluded that materials play a more important role in the process of chondrogenesis than the tested cell populations. Fibroblastic SLCs were shown to have similar chondrogenic potential as CLCs cells, suggesting a rich pool of progenitor cells in the superficial fibroblastic layer capable of undergoing chondrogenesis given appropriate physical and chemical cues.