Nuno A. T. C. Fernandes

This study presents a multi-scale computational framework to quantify how externally applied acoustic waves propagate through the knee joint and induce mechanotransductive strain at the level of the chondrocyte nucleus. Patient-specific knee geometries ( n = 8) were used to simulate acoustic wave transmission through layered tissues, while a representative volume element modelled the coupled solid–shell–acoustic behaviour of the chondrocyte, pericellular matrix, and extracellular matrix. Modal and frequency–response analyses identified the spheroidal s ₃ mode as the dominant contributor to nuclear deformation. Strain amplification was found to occur within defined frequency bands rather than at a single frequency, with healthy patients exhibiting a broader mid-frequency amplification region (50–170 kHz) and diseased patients showing a shifted low-frequency (30–85 kHz) dominance due to hypertrophy and altered stiffness. Macro-to-micro coupling demonstrated that, despite anatomical variability, consistent transmissibility trends were preserved across patients, with ideal frequencies for healthy and OA patients. Time-explicit simulations comparing linear and nonlinear acoustic formulations revealed negligible harmonic generation at the applied pressure levels, indicating that linear acoustics adequately describe propagation within the mechanotransductive strain range considered. Overall, the results demonstrate that cartilage stimulation is frequency-band dependent and disease-sensitive, and they provide a mechanistically grounded basis for optimizing ultrasound excitation parameters based on cellular-scale mechanics rather than empirical frequency selection.

Purpose: Accurate measurement of ultrasound acoustic fields in biological tissues is essential for the characterization and calibration of therapeutic ultrasound devices, particularly in transcranial applications where high spatial resolution, broadband sensitivity, and controlled directivity are required. This paper presents a physically grounded framework for the design and validation of an acoustic horn needle attachment compatible with existing commercial ultrasound transducers, avoiding the need to develop fully custom hydrophone systems. Methods: Numerical simulations were performed in COMSOL Multiphysics to investigate guided longitudinal wave propagation within the horn needle and to optimize key geometric parameters, including needle length and base transition geometry, using frequency-domain parametric studies over the 1–5 MHz range. Cylindrical, conical, and exponential horn geometries were evaluated in terms of geometry optimization, directivity and sensitivity. Experimental validation was carried out by mechanically coupling the optimized horn needle toa commercial piezoelectric transducer (Mitech, 1 MHz, 24 mm diameter) using epoxy adhesive bonding. Results: The assembled system was characterized experimentally in water and in a cranial medical phantom. Measured receiver sensitivity ranged from − 53.34 to − 33.6 dB re 1 V/μPa over a bandwidth from 0.1 to 9 MHz. Sound transmission loss values between 63.4 and139.2 dB were obtained in the 0.5–5 MHz range at a depth of 15 mm within the brain-mimicking region, in agreement with values reported in the literature. Conclusion: Overall, the results demonstrate that wavelength-scaled horn needle attachments can achieve performance comparable to custom hydrophones, providing a reproducible and versatile solution for broadband ultrasound field characterization.

Sustainable mobility has been an emerging topic in recent years, and in this regard, investing heavily in public transport seems to be the best solution. For people to embrace this form of mobility, services must meet expectations, and one of the parameters to be considered is the comfort offered by vehicles. This is directly affected by the vibrations that affect vehicles. This work was developed to create a proof of concept for a support structure for bus seats that mitigates the vibrations felt by passengers, making these vehicles more comfortable and appealing to use. Current systems are expensive and complex, and the proposed solution presented here is based on the field of metamaterials. This study investigated vehicle dynamic loads and comfort standards from ISO 2631 to design a metamaterial-based seat support with optimized stiffness and damping. Using MATLAB (R2024b), ideal parameters were defined (k = 13,422.66 N/m, c = 534.07 Ns/m), with stiffness provided by the cell geometry and damping provided by a viscoelastic material. Parametric modeling and simulations in ANSYS (2025 R2) assessed stiffness, damping, and strength, followed by prototype fabrication and testing. The best structure showed 2.23 m/s² at 4.5 Hz, achieving the target transmissibility above 8 Hz. While most designs effectively attenuate vibrations beyond 5 Hz, resonance peaks remain high, suggesting future work should focus on improved resonance reduction strategies.

Tissue-mimicking phantoms that accurately replicate human tissue are crucial for validating and optimizing elastography systems and developing new treatment methods. The use of waste-based fibrous structures has the dual benefits of waste reduction and economic viability, mitigating the environmental consequences associated with the textile industry and, thus, posing a particularly interesting avenue of research in today’s ever-more environmentally conscious society. This work explores the development of elastography phantoms through the use of textile waste for sustainable valorization. Two cotton-short fiber-based and two polyester-nonwoven-based phantoms were produced by impregnating these textile structures with animal-origin gelatin. These materials were characterized by scanning electron microscopy (SEM), revealing that the diameter of the waste-based fibers (15.28 ± 6.18–22.40 ± 5.78 μm) falls within the typical size range of scatterers used in acoustic phantoms. It was observed that these fibers provided phantoms with intrinsic acoustic scattering properties, resulting in ultrasound images similar to those obtained in biological tissues. Shear wave elastography (SWE) was used to assess the stiffness of the phantoms, which produced realistic ultrasound images with shear wave speed (SWS) values ranging from 1.87 m s⁻¹ to 8.39 m s⁻¹, closely resembling those in different anatomical structures. This research presents an innovative methodology for producing low-cost and sustainable tissue-mimicking materials, underscoring the potential of textile industry waste for phantom production.

Transcranial focused ultrasound is a promising noninvasive technique for neuromodulation in neurological and psychiatric disorders, but accurate prediction of acoustic transmission through the skull remains a major challenge. In this study, we present a five-layer numerical human head model that integrates frequency-dependent acoustic parameters with nonlinear time-explicit dynamics to realistically capture ultrasound propagation. The model explicitly represents skin, trabecular bone, cortical bone, and brain, each assigned experimentally derived acoustic properties across a clinically relevant frequency range (0.5–5 MHz). Numerical simulations were performed in the frequency domain and time-explicit to quantify sound transmission loss and focal depth under high-intensity and high-frequency stimulation. The results show the effect of frequency, radius of curvature, and skull thickness on maximum pressure ratio, focal depth, and focus zone inside the brain tissue. Findings indicate that skull geometry, particularly radius of curvature and thickness, strongly influences the focal zone, with thinner skull regions allowing deeper penetration and reduced transmission loss. Comparison of the frequency-domain model with the time-explicit model demonstrated broadly similar trends; however, the frequency-domain approach consistently underestimated transmission loss and was unable to capture nonlinear effects such as frequency harmonics. These findings highlight the importance of nonlinear, time-explicit modeling for accurate transcranial ultrasound planning and suggest that the proposed framework provides a robust tool for optimizing stimulation parameters and identifying ideal target zones, supporting the development of safer and more effective neuromodulation strategies.

With 23.4 billion pairs made and 22 billion discarded in 2023, post-consumer footwear waste is a major environmental challenge, demanding a shift toward circular economy practices. In this work, post-consumer footwear waste is repurposed into thermal/acoustic insulation materials for building construction, producing four needle-punched nonwovens (two of them compressed) composed of a post-consumer leather (30%) and footwear waste mixture (40%) with recycled polyester fibers. Nonwovens exhibited higher strain values (95.9 and 77.1% for leather residue and footwear mixture residue, respectively) but lower tensile strength (1694 and 104.9 kPa) and Young’s modulus (1767.8 and 136.10 kPa). The compressed nonwovens demonstrated higher tensile strength (7360 and 3559 kPa) and Young’s modulus values (12992 and 4020.4 kPa) and reduced strain (56.6 and 96.9%). The thermal conductivity results revealed that the nonwovens exhibited lower values (0.040 and 0.046 W/(m·K)), indicating better insulation performance when compared with their compressed counterparts (0.060 and 0.058 W/(m·K)). The nonwovens demonstrated high sound absorption at higher frequencies, reaching peak absorption coefficients of 0.917 and 0.995, ideal for acoustic insulation. The compressed nonwovens exhibited improved absorption at lower and mid-frequencies, with maximum values of 0.510 and 0.519. Given the current lack of applications for recycled materials derived from post-consumer footwear, the findings offer a novel approach to address their recycling.