The shoulder's dynamic function is largely influenced by scapulohumeral rhythm (SHR), a coordinated movement of the scapula and humerus that facilitates a safe range of motion. While SHR has been described and quantified in terms of shoulder kinematics, its specific contribution to glenohumeral joint stability. This study aims to estimate the impact of SHR on glenohumeral stability using a biomechanical model. A five-segment musculoskeletal model based on the work of Wu et al. (2016) was implemented in OpenSim. Three SHR patterns and two loading scenarios were evaluated: a fixed scapula, a humeral-to-scapular motion ratio, and an experimentally measured SHR with free abduction or abduction while holding a 2 kg weight in the hand. Muscle forces and glenohumeral stability ratios were calculated using static optimization, and the model predictions were compared to electromyography and in vivo joint force data. While glenohumeral contact forces showed minimal variation across different SHR conditions, the stability ratio analysis revealed that the absence of SHR significantly increased the risk of joint instability. In scenarios without SHR, even small shoulder elevations resulted in overloading of the superior glenoid. The addition of weight further destabilized the joint, while substantially increasing glenohumeral force. SHR does not reduce the overall glenohumeral load but plays a critical role in maintaining glenohumeral stability, particularly during early phases of shoulder elevation and when holding additional weight. These findings highlight the importance of scapular kinematics in shoulder joint function and may have implications for managing shoulder pathologies such as rotator cuff tears and impingement, where scapular motion is often compromised.

Atomic Force Microscopy (AFM) is a powerful tool for quantifying the mechanical properties of soft biomaterials like giant unilamellar vesicles (GUVs). However, the accuracy of derived parameters such as Young’s modulus (E) and stiffness (k) is critically dependent on the precise identification of the contact point (CP). This study systematically investigates and quantifies the errors introduced by different automated CP determination strategies. We performed AFM nanoindentation on GUVs and compared a model-independent CP method, based on cantilever thermal fluctuations, against several common model-fitting approaches (e.g., linear, quadratic, Hertz). Our results demonstrate that model-based methods introduce significant and predictable biases. For instance, linear models consistently identified the contact point after the true contact, while quadratic models placed it before. This misplacement error propagates non-linearly into the final parameters, with its effect being most pronounced at shallow indentation depths, where deviations in Young’s modulus can exceed 80

The mechanical properties of liposomes are critical for their efficacy as drug delivery vehicles. A liposome's stiffness is a composite property of its membrane and encapsulated core, but deconvolving these contributions is a significant challenge, as current methods rely on model-dependent assumptions. This study introduces a novel, experimental method to isolate the core's mechanical contribution. We fabricated giant unilamellar vesicles (GUVs) with either a simple buffer or a viscoelastic hyaluronic acid (HA) core and characterized them using atomic force microscopy (AFM). The core's contribution was isolated by subtracting the force response of buffer-filled liposomes from that of HA-filled ones. The contact point was identified from the change in data fluctuations. Our results demonstrate that the HA core dramatically increases the liposome's resistance to deformation. While the membrane stiffness is dominant in small deformations (up to 25 nm), the viscous core becomes dominant at larger deformations, bearing over 80% of the total load for deformations larger than 150 nm. This direct, model-independent approach provides a tool for understanding the biomechanics of filled liposomes and enables the rational engineering of liposomal drug carriers with mechanical properties precisely tuned for enhanced therapeutic performance.

This work investigates the NiTi shape memory alloys fabricated via laser powder-directed energy deposition (LP-DED). The properties of NiTi alloys produced by powder metallurgy or additive manufacturing routes are strongly influenced by the type of feedstock material employed. Two powder feedstocks were used for DED fabrication: a blended mixture of elemental nickel and titanium powders with a nominal chemical composition of Ni56Ti44 (wt.%) and a pre-alloyed NiTi powder containing 55.75 wt.% Ni. Samples fabricated from both types of powders were subjected to microstructural characterization, phase composition analysis, and mechanical and corrosion testing. It was found that DED processing on a non-preheated CP-Ti substrate is prone to warping and that samples deposited from the elemental Ni and Ti powder mixture exhibited pronounced inhomogeneity of microstructure and mechanical properties along the build direction, accompanied by the formation of the Ti2Ni secondary phase. The absence of a superelastic plateau was observed in the corresponding stress–strain response. On the contrary, the samples deposited from the pre-alloyed NiTi powder exhibited a microstructure composed of B2 and B19′ phases and already demonstrated a clear superelastic response in the as-built condition during tensile loading. Based on the tensile test results, this NiTi material was used only for superelasticity testing. The superelastic behavior was further enhanced by post-deposition heat treatment, which significantly increased the recovery rate from 53% to 89%.

Cold rotary-swaging was applied to the metastable β-phase Ti-12Mo-6Zr-2Fe (TMZF) alloy to achieve material with high strength parameters without compromising its low elastic modulus. The process also introduced significant location-dependent property gradient, resulting in difference in the hardness of the outer region by 28.7% compared to the interior region. The increased hardness values at the surface result from a combined contribution of dominant dislocation accumulation, enhanced crystallographic texture, and pronounced subgrain boundaries. The enhanced plastic deformation at the surface together with residual strain accumulation in the interior leads to a beneficial gradient core-shell structure, where the harder shell constrains the softer core. The interplay between the unique characteristics of the TMZF alloy and the deformation mechanisms during cold rotary-swaging demonstrates a practical pathway to tailor desirable spatially distributed mechanical properties for superior fatigue resistance in other advanced alloy systems. Specifically, this work provides quantitative microstructure distribution subjected to rotary swaging.

Characterizing local mechanical properties in additively manufactured (AM) components is critical for design and qualification, yet challenging due to process-induced heterogeneity. A significant gap exists in robust methodologies for local bending assessment, a dominant loading mode in common AM structures like lattices. This study introduces and validates a novel Miniature Bending Test (MBT) utilizing sub-millimeter, C-shaped specimens fabricated from Ti6Al4V via Laser Powder Bed Fusion (LPBF). As-built specimens (mean radius r approximate to 0.60 mm, thickness t approximate to 0.20 mm) were subjected to an opening load using a custom fixture. The method demonstrated excellent repeatability, yielding a highly linear force-displacement response and a compliance corrected experimental stiffness of 23.13 +/- 0.64 N/mm. This result showed poor agreement with an analytical model based on design dimensions (12.75 N/mm) but agreed well with predictions using measured as built dimensions from analytical model based on bending (28.39 +/- 0.63 N/mm), bending, tension and shear (25.83 +/- 0.58 N/mm) and a Finite Element Analysis (24.54 N/mm). The findings underscore the critical impact of manufacturing deviations on mechanical performance at this scale. The MBT has potential to become a robust and sensitive methodology for qualifying local elastic properties, providing a vital tool for the certification of complex AM components.

Proper orientation of the acetabular cup in total hip arthroplasty (THA) is essential to reduce dislocation risk, improve range of motion, and enhance implant longevity. Misalignment can lead to complications such as impingement, wear, and aseptic loosening. Patient positioning on the operating table is a critical yet often overlooked factor influencing pelvic tilt and cup placement accuracy during THA. This study aimed to evaluate the impact of preoperative patient positioning on acetabular component placement and explore whether surgeon experience affects cup placement precision. In this prospective case series, 135 patients undergoing non-navigated THA in the supine position at a single tertiary center were included. Preoperative photographs captured pelvic inclination, which was compared to postoperative cup orientation measured on radiographs. Patients were divided into three groups based on surgeon experience (< 5 years, 5-15 years, > 15 years). Statistical analyses assessed relationships among patient positioning, cup orientation, leg length discrepancy, and surgeon experience. Greater pelvic inclination measured before sterile draping was significantly associated with a smaller acetabular cup angle (Pearson's R = -0.72, p < 0.001). Surgeons with > 15 years of experience demonstrated less variability in cup orientation and leg length discrepancy than those with fewer years of experience (p < 0.001). Despite variations in pelvic positioning, the overall postoperative cup angle was consistent across groups. Preoperative patient positioning significantly impacts acetabular cup orientation, with more experienced surgeons better able to compensate for these deviations. Positioning protocols and surgeon training on pelvic orientation may enhance THA outcomes, particularly for early-career surgeons.

The anodic oxidation process was successful in fabricating consistently ordered, well-bounded and high-density TiO2 nanotube arrays on the Ti-13Nb-13Zr alloy using an ethylene glycol electrolyte containing 0.3 wt.

Euler and Cardan angles representation in biomechanical analysis allows straightforward description of joint rotations. However, application of Euler or Cardan angles can be problematic due to a singularity called gimbal lock. Quaternions offer an alternative way to describe rotation that avoids this problem, but they are not commonly used in biomechanics as they are complex and not inherently intuitive, specifically in dynamic models actuated by muscles. This study introduces a mathematical framework for describing muscle actions in dynamic quaternion-based musculoskeletal simulations. The proposed method estimates muscle torques in a quaternion-based musculoskeletal model. Its application is shown in a three-dimensional double-pendulum system actuated by muscle elements. Furthermore, the transformation of muscle moment arms obtained from muscle paths based on Euler or Cardan angles into a quaternion-based description is presented. The proposed method is advantageous for dynamic modeling of musculoskeletal models with complex kinematics and joints with large ranges of motion like the shoulder joint.

Background: Short-stem hip replacements are designed to provide improved load distribution and to mimic natural biomechanics. The interplay between implant design, positioning, and resulting bone biomechanics in individual patients remains underexplored, and the relationship between radiographically assessed bone remodeling around short stems and biomechanical predictions has not been previously reported. Methods: This study evaluated three short-stem hip implant designs: Proxima, Collo-MIS, and Minima. Postoperative bone remodeling patterns were analyzed, categorizing remodeling as bone gain, bone loss, or no observable activity, with changes tracked over time. Patient-specific biomechanical models were generated from 6-week postoperative radiographs. Finite element simulations incorporated body weight and gluteal muscle forces to estimate stress and strain distributions within the proximal femur. Strain energy was then applied to a mechanostat-based remodeling algorithm to predict bone remodeling patterns. These biomechanical predictions were compared to observed radiographic remodeling at 2 years post-surgery. A validated biomechanical model was further used to simulate different postoperative positions of the three types of stems. Results: No differences in bone remodeling patterns were observed among the three short-stem designs. Computational modeling demonstrated a statistically significant correlation between predicted remodeling and radiographic measurements at 2 years (p < 0.001). Proxima stems showed a tendency towards increased cortical bone loading under pronounced varus or valgus position in comparison to other two stems, although this observation requires further validation. Conclusions: This exploratory study demonstrates the feasibility of using biomechanical modeling to estimate bone remodeling around short-stem hip implants based on early postoperative radiographs. While the results are promising, they should be interpreted with caution due to the limited cohort size. The proposed modeling approach may offer clinical value in evaluating implant behavior and informing patient-specific treatment strategies. However, further research with larger populations is necessary to refine and validate these predictive tools.

Cellular mechanical properties provide insights into the state and health of cells. However, accurately measuring these properties is challenging due to the small size and low stiffness of cells. In recent years, Atomic Force Microscopy (AFM) has emerged as a promising tool for assessing the mechanical characteristics of individual cells. The evaluation of AFM measurements is complicated by the nonlinear contact between the AFM tip and the cell, which induces deformations throughout the entire cell. This leads to a nonlinear cell stiffness that varies with the depth of indentation. To bridge the gap between measured indentation data and the inherent material properties of the cell, irrespective of the experimental setup, we have introduced a theoretical model for cell deformation during indentation. Our model is built upon the Laplace equation adopted for fluid membranes. It predicts the areas of contact and the corresponding indentation forces as functions of indentation depth, aligning closely with experimental observations. Furthermore, our model takes into consideration both the size of the AFM tip and the dimensions of the cell while characterizing cell material properties through an area expansion modulus. Notably, this material parameter, derived by fitting the AFM deflection curve of DPPC liposomes, falls within the range documented in existing literature. This model holds the potential for further enhancement by factoring in adhesion energy and exploring the effects of different AFM tip shapes. Such refinements could advance our understanding of cell mechanics by accurately measuring cell membrane intrinsic material properties.

Calibration of shoulder radiographs is required for accurate preoperative planning. Current practice mostly uses an empirical fixed calibration factor of 5

The curvature of the lumbar spine plays a critical role in maintaining spinal function, stability, weight distribution, and load transfer. We have developed a mathematical model of the lumbar spine curve by introducing a novel mechanism: minimization of the elastic bending energy of the spine with respect to two biomechanical parameters: dimensionless lumbosacral spinal curvature c LS and dimensionless curvature increment along the spine CI. While most of the biomechanical studies focus on a particular segment of the spine, the distinction of the presented model is that it describes the shape of the thoracolumbar spine by considering it as a whole (non-locally) and thus includes interactions between the different spinal levels in a holistic approach. From radiographs, we have assessed standard geometrical parameters: lumbar lordosis LL, pelvic incidence PI, pelvic tilt PT, sacral slope ψ0 and sagittal balance parameter SB = sagittal vertical axis (SVA)/sacrum-bicoxofemoral distance (SFD) of 42 patients with lumbar spinal stenosis (SS) or degenerative spondylolisthesis (SL) and 21 radiologically normal subjects. SB statistically significantly correlated with model parameters c L5 (r = -0.34, p = 0.009) and -CI (r = 0.33, p = 0.012) but not with standard geometrical parameters. A statistically significant difference with sufficient statistical power between the patients and the normal groups was obtained for c LS, CI, and SB but not for standard geometrical parameters. The model provides a possibility to predict changes in the thoracolumbar spine shape in surgery planning and in assessment of different spine pathologies.

The NiTi alloy, known as Nitinol, represents one of the most investigated smart alloys, exhibiting a shape memory effect and superelasticity. These, among many other remarkable attributes, enable its utilization in various applications, encompassing the automotive industry, aviation, space exploration, and, notably, medicine. Conventionally, Nitinol is predominantly produced in the form of wire or thin sheets that allow producing many required components. However, the manufacturing of complex shapes poses challenges due to the tenacity of the NiTi alloy, and different processing routes at elevated temperatures have to be applied. Overcoming this obstacle may be facilitated by additive manufacturing methods. This article provides an overview of the employment of additive manufacturing methods, allowing the preparation of the required shapes of Nitinol products while retaining their exceptional properties and potential applications.

Cell mechanics are a biophysical indicator of cell state, such as cancer metastasis, leukocyte activation, and cell cycle progression. Atomic force microscopy (AFM) is a widely used technique to measure cell mechanics, where the Young modulus of a cell is usually derived from the Hertz contact model. However, the Hertz model assumes that the cell is an elastic, isotropic, and homogeneous material and that the indentation is small compared to the cell size. These assumptions neglect the effects of the cytoskeleton, cell size and shape, and cell environment on cell deformation. In this study, we investigated the influence of cell size on the estimated Young’s modulus using liposomes as cell models. Liposomes were prepared with different sizes and filled with phosphate buffered saline (PBS) or hyaluronic acid (HA) to mimic the cytoplasm. AFM was used to obtain the force indentation curves and fit them to the Hertz model. We found that the larger the liposome, the lower the estimated Young’s modulus for both PBS-filled and HA-filled liposomes. This suggests that the Young modulus obtained from the Hertz model is not only a property of the cell material but also depends on the cell dimensions. Therefore, when comparing or interpreting cell mechanics using the Hertz model, it is essential to account for cell size.

Background: The diagnosis of joint replacement infection is a difficult clinical challenge that often occurs when the implant cannot be salvaged. We hypothesize that the pH value of synovial fluid could be an important indicator of the inflammatory status of the joint. However, in the literature, there is a lack of data on the pH changes in hip and knee joint replacements and their relation to infection and implant failure. In this study, we aimed to measure the pH levels of synovial fluid in patients with hip and knee joint replacements. We also investigated the potential of pH measurement as a diagnostic tool for joint replacement infection. In this study, we recorded the pH values to be 7.55 and 7.46 in patients where Pseudomonas aeruginosa was identified as the cause of the prosthetic joint infection. We attribute this to the different environments created by this specific bacterium. In other cases where the pH was higher, chronic mitigated infections were diagnosed, caused by strains of Staphylococcus aureus, Streptococcus agalactiase, and coagulase negative staphylococcus. Materials and methods: In our cohort of 155 patients with implanted hip (THA; n = 85) or knee (TKA; n = 70) joint replacements, we conducted a prospective study with a pH measurement. Out of the whole cohort, 44 patients had confirmed joint replacement infection (28.4%) (44/155). In 111 patients, infection was ruled out (71.6%) (111/155). Joint replacement infection was classified according to the criteria of the Musculoskeletal Infection Society (MSIS) from 2018. Based on the measured values, we determined the cut-off level for the probability of ongoing inflammation. We also determined the sensitivity and specificity of the measurement. Results: The group of patients with infection (n = 44) had a significantly lower synovial fluid pH (pH = 6.98 ± 0.48) than the group of patients with no infection (n = 111, pH = 7.82 ± 0.29, p < 0.001). The corresponding median pH values were 7.08 for the patients with infection and 7.83 for the patients with no infection. When we determined the cut-off level of pH 7.4, the sensitivity level of infected replacements was 88.6%, and the specificity level of the measurement was 95.5%. The predictive value of a positive test was 88.6%, and the predictive value of a negative test was 95.5%. Conclusions: Our results confirm that it is appropriate to include a pH measurement in the diagnostic spectrum of hip and knee replacements. This diagnostic approach has the potential to provide continuous in vivo feedback, facilitated by specialized biosensors. The advantage of this method is the future incorporation of a pH-detecting sensor into intelligent knee and hip replacements that will assess pH levels over time. By integrating these biosensors into intelligent implants, the early detection of joint replacement infections could be achieved, enhancing proactive intervention strategies.

The local peri‐implant pH changes caused by sterile inflammation and bacterial and fungal infections are studied herein. Then, a sensing electrode based on polyaniline and poly(2‐methyl‐2‐oxazoline) on a titanium alloy support is developed for potentiometric detection of peri‐implant pH changes to enable early detection of the aforementioned pathologies. The infected endoprosthesis area is shown to have an average pH of 0.79 units lower than the aseptic sample. The pH measurements of the individual pathogenic bacteria or pathogenic yeast reveal that Escherichia coli decreased the pH by 1.24 units, Staphylococcus aureus decreased the pH by 1.33 units and the methicillin‐resistant Staphylococcus aureus bacteria decreased the pH from 7.2 to 5.6 during 10 h, followed by a subsequent increase to 6.4. The results are statistically significant (α = 0.01). Pseudomonas aeruginosa is not shown to change pH levels. On the other hand, the pathogenic yeast has the lowest recorded pH, which decreases from 5.8 to 4.8. This difference in pH can be used to identify the nature of the infection. The developed electrodes have a pH response between pH 5 and 8, with a Nernstian slope of −59.6/pH. The developed electrode can contribute to the next generation of biosensors.

Burr hole trepanation is a surgical procedure in which one or more small holes, or trephines, are made in the skull to allow for the drainage of fluids or to relieve pressure within the skull. Burr hole trepanation is generally considered a safe and effective treatment for conditions such as brain abscesses and subdural hematomas. However, the bone defects must be closed after the surgery with a suitable implant. Current designs are mostly based on bone plates with limited lifetime, revision access, and low esthetic. Within this study, a new type of cranial implant is proposed made using additive manufacturing (AM) techniques. The implant is anchored in the burr hole and does not penetrate the skull space or prominate the skull. Four different types of implants have been proposed on the basis of an analytical model and verified using finite element analysis (FEA). New push-in mechanical tests are introduced using artificial bone to determine the strength of the locking mechanisms and ensure the safety of implants. The burr-hole implant with an overlap on the bone surface after implantation was proven to be the safest solution. The design of the new cranial implant could improve the esthetic outcome after surgery and minimize invasiveness in reoperations.

Background: Variations observed in biomechanical studies might be attributed to errors made by operators during the construction of musculoskeletal models, rather than being solely attributed to patient-specific geometry. Research question: What is the impact of operator errors on the construction of musculoskeletal models, and how does it affect the estimation of muscle moment arms and hip joint reaction forces?Methods: Thirteen independent operators participated in defining the muscle model, while a single operator performed 13 repetitions to define the muscle model based on 3D bone geometry. For each model, the muscle moment arms relative to the hip joint center of rotation was evaluated. Additionally, the hip joint reaction force during one-legged stance was assessed using static inverse optimization.Results: The results indicated high levels of consistency, as evidenced by the intra- rater and inter-rater agreement measured by the Intraclass Correlation Coefficient (ICC), which yielded values of 0.95 and 0.99, respectively. However, the estimated muscle moment arms exhibited an error of up to 16 mm compared to the reference musculoskeletal model. It was found that muscles attached to prominent anatomical landmarks were specified with greater accuracy than those attached over larger areas. Furthermore, the variability in estimated moment arms contributed to variations of up to 12% in the hip joint reaction forces.Significance: Both moment arm and muscle force demonstrated significantly lower variability when assessed by a single operator, suggesting the preference for employing a single operator in the creation of musculoskeletal models for clinical biomechanical studies.