Rosa María Quispe-Siccha

Los avances recientes en la preparación de hidrogeles han impulsado el diseño de fantomas biomédicos capaces de simular tejidos blandos y facilitar el estudio de propiedades biológicas, en particular la densidad aparente y efectiva. Estos avances permiten la calibración de equipos de imagenología, la validación de dispositivos médicos y el entrenamiento de personal clínico. La presente revisión bibliográfica de alcance, basada en el análisis sistemático de la literatura publicada entre 2020 y 2026 en las bases de datos Scopus, Web of Science, PubMed y Google Scholar, identifica y compara tres métodos de fabricación de fantomas ampliamente utilizados por su versatilidad operacional: métodos químicos de reticulación basados en procesos sol-gel, técnicas de impresión 3D y procesos de electrohilado. Cada método presenta ventajas específicas. Los métodos químicos destacan por su sencillez y estabilidad; la impresión 3D aporta control geométrico y reproducibilidad, posibilitando la creación de arquitecturas complejas que influyen directamente en la densidad volumétrica; mientras que el electrohilado permite crear micro y nanoestructuras fibrosas que imitan la matriz extracelular y ofrece un control preciso de la densidad a través del diámetro, la orientación y la fracción de vacíos entre las fibras. La evidencia disponible indica que la convergencia de los métodos de impresión 3D y electrohilado en enfoques híbridos representa una frontera tecnológica prometedora para superar las limitaciones individuales de cada técnica, lo que permite la fabricación de fantomas con fidelidad anatómica a escala macroscópica y mimetismo estructural a escala nanométrica. Los hidrogeles constituyen uno de los materiales más ampliamente utilizados en la fabricación de fantomas debido a su reproducibilidad, su simplicidad y su capacidad de incorporar partículas que mejoran la simulación de tejidos biológicos. Polímeros naturales como el quitosano, el alginato y el alcohol polivinílico permiten ajustar la densidad mediante la concentración polimérica, el grado de reticulación y la incorporación de agentes de relleno. La medición de la densidad en los hidrogeles es esencial para evaluar su interacción con fluidos biológicos y optimizar su rendimiento en aplicaciones como la terapia celular. Se examinan los materiales empleados, las propiedades ajustables, los métodos de caracterización y las aplicaciones clínicas de estos sistemas. Técnicas no invasivas, como la bioimpedancia eléctrica, la tomografía por ultrasonido y el ultrasonido inducido por láser, emplean hidrogeles para calibrar densidades tisulares, lo que mejora la calidad de las imágenes y amplía sus aplicaciones clínicas. En conjunto, estos avances consolidan a los hidrogeles como herramientas clave para el desarrollo de fantomas biomédicos más realistas y para su futura aplicación clínica. Como principal contribución, el trabajo propone un marco comparativo que orienta la selección de la tecnología según la aplicación biomédica, destacando la convergencia de la impresión 3D y el electrohilado como un enfoque híbrido prometedor. Adicionalmente, se identifican los principales desafíos en materia de estandarización, resolución multiescala y multifuncionalidad, y se delinean las perspectivas futuras en el desarrollo de materiales inteligentes y estrategias de fabricación híbrida.

The photoacoustic (PA) effect is an emerging technique for characterizing the structural and compositional features of materials by combining light absorption with the generation of pressure waves. In practice, it is only possible to measure the pressure wave at the sample surface using an ultrasound transducer, namely a PA signal. However, reconstructing the initial pressure is an inverse problem with a non-trivial solution. This work introduces a dynamic state estimator (DSE) that virtually measures wave propagation to compute the initial pressure profile from boundary measurements. The proposal is based on a dynamical model that describes the spatiotemporal evolution of a PA signal, where the states represent the pressure waves within the sample. Through the DSE, the method provides a smooth reconstruction of the initial pressure in a straightforward yet robust manner. The state estimator is tested in both numerical and real experiments, outperforming traditional model-based algorithms and yielding results comparable to the well-known time-reversal algorithm in signal-to-noise ratio, contrast, and computational speed. The results suggest that the state estimator represents a technological advancement in overcoming the inherent ill-posedness of the PA inverse problem in a wide range of applications.

Photoacoustic tomography (PAT) is a promising imaging technique that combines the high spatial resolution of ultrasound with the high contrast of optical imaging. One of the challenges in PAT is the ill-posed nature of the inverse problem, where limited measurement data and noise often lead to inaccurate reconstructions. This work introduces a kernel-based regularization (KBR) approach for model-based reconstruction algorithms in photoacoustic (PA) imaging. The proposed method leverages kernel-induced feature space to enforce smoothness and spatial coherence in the reconstructed images, thereby improving the robustness to noise and data sparsity. By incorporating prior knowledge of the signal dynamics for solving the PA inverse problem, KBR enhances the reconstruction fidelity, especially in regions with low signal-to-noise ratio. Numerical experiments and phantom studies demonstrate that the proposed algorithm outperforms traditional regularization techniques, such as Tikhonov and total variation regularization, regarding reconstruction accuracy and computation speed. The results suggest KBR provides a powerful tool for addressing the inherent challenges in PA image reconstruction, offering potential improvements in several applications.

This study aims to analyze the physical-mechanical properties and dynamic models of tissue-simulating hydrogels, specifically the photoacoustic (PA) response signals, by varying the concentrations of polyvinyl alcohol (PVA) and molecular weight (MW). A state-space model (SSM) is proposed to study the PVA hydrogels to retrieve the PA-related signal’s damping ratio and natural frequency. Nine box-shaped PVA hydrogels containing saline solution were used, with five concentrations of PVA (7, 9, 12, 15, 20%) for MW1 and four for MW2. The results indicated that the concentration of PVA and MW played an important role in the PA wave’s amplitude, arrival time, and speed of sound over the hydrogels. The SSM parameters showed that increasing PVA and MW concentrations improved the hydrogels’ ability to absorb and transfer energy under the PA effect. These parameters were also found to be correlated with density and modulus of elasticity. Additionally, the concentrations of PVA and MW affected the absorption and optical scattering coefficients. The physical-mechanical properties, including porosity, density, and modulus of elasticity, improved as the concentration of PVA and MW increased. The ultimate goal of this study is to develop hydrogels as phantoms that can be used for tissue simulation and imaging.

This study aims to analyze the physico-mechanical properties and dynamic models of tissue-simulating hydrogels, specifically the photoacoustic (PA) response signals, by varying the concentrations of polyvinyl alcohol (PVA) and molecular weight (MW). A state space model (SSM) is proposed to study the PVA hydrogels to retrieve the PA-related signal's damping ratio and nat-ural frequency. Nine box-shaped PVA hydrogels containing saline solution were used, with five concentrations of PVA (7, 9, 12, 15, 20%) for MW1 and four for MW2. The results indicated that the concentration of PVA and MW played an important role in the PA wave's amplitude, arrival time, and speed of sound over the hydrogels. The SSM parameters showed that increasing PVA and MW concentrations improved the hydrogels' ability to absorb and transfer energy under the PA effect. These parameters were also found to be correlated with density and modulus of elasticity. Addi-tionally, the concentrations of PVA and MW affected the absorption and optical scattering coeffi-cients. The physical-mechanical properties, including porosity, density, and modulus of elasticity, improved as the concentration of PVA and MW increased. The ultimate goal of this study is to develop hydrogels as phantoms that can be used for tissue simulation and imaging.

Most gait parameters decrease with age and are even more importantly reduced with frailty. However, other gait parameters exhibit different or even opposite trends for aging and frailty, and the underlying reason is unclear. Literature focuses either on aging, or on frailty, and a comprehensive understanding of how biomechanical gait regulation evolves with aging and with frailty seems to be lacking. We monitored gait dynamics in young adults (19–29 years, n = 27, 59% women), middle-aged adults (30–59 years, n = 16, 62% women), and non-frail (>60 years, n = 15, 33% women) and frail older adults (>60 years, n = 31, 71% women) during a 160 m walking test using the triaxial accelerometer of the Zephyr Bioharness 3.0 device (Zephyr Technology, Annapolis, MD, USA). Frailty was evaluated using the Frail Scale (FS) and the Clinical Frailty Scale (CFS). We found that in non-frail older adults, certain gait parameters, such as cadence, were increased, whereas other parameters, such as step length, were decreased, and gait speed is maintained. Conversely, in frail older adults, all gait parameters, including gait speed, were decreased. Our interpretation is that non-frail older adults compensate for a decreased step length with an increased cadence to maintain a functional gait speed, whereas frail older adults decompensate and consequently walk with a characteristic decreased gait speed. We quantified compensation and decompensation on a continuous scale using ratios of the compensated parameter with respect to the corresponding compensating parameter. Compensation and decompensation are general medical concepts that can be applied and quantified for many, if not all, biomechanical and physiological regulatory mechanisms of the human body. This may allow for a new research strategy to quantify both aging and frailty in a systemic and dynamic way.

The frailty syndrome is characterized by a decreased capacity to adequately respond to stressors. One of the most impaired physiological systems is the autonomous nervous system, which can be assessed through heart rate (HR) variability (HRV) analysis. In this article, we studied the chronotropic response (HR and HRV) to a walking test. We also analyzed HRV indices in rest as potential biomarkers of frailty. For this, a 160 m-walking test and two standing rest tests (before and after the walking) were performed by young (19–29 years old, n = 21, 57% women), middle-aged (30–59 years old, n = 16, 62% women), and frail older adults (>60 years old, n = 28, 40% women) and non-frail older adults (>60 years old, n = 15, 71% women), classified with the FRAIL scale and the Clinical Frailty Scale (CFS). Frequency domain parameters better allowed to distinguish between frail and non-frail older adults (low-frequency power LF, high-frequency power HF (nu), LF/HF ratio, and ECG-derived respiration rate EDR). Frail older adults showed an increased HF (nu) and EDR and a reduced LF (nu) and LF/HF compared to non-frail older adults. The increase in HF (nu) could be due to a higher breathing effort. Our results showed that a walk of 160 m is a sufficient cardiovascular stressor to exhibit an attenuated autonomic response in frail older adults. Several HRV indices showed to be potential biomarkers of frailty, being LF (nu) and the time required to reach the maximum HR the best candidates.

Today, visual classification of the degree of lipemia in blood samples is frequently performed in clinical laboratories. However, achieving standardization of this classification at low cost and with fewer resources is an objective that is still under development. In this work, a comparison is made between the visual inspection and optical measurements of blood plasma for quantifying lipemia. The plasma refractive index’s real part was measured using an Abbe refractometer and transmittance measurements were made at a 589 nm wavelength and wavelengths ranging from 320 to 1100 nm in the spectral region, respectively. Taking the slope of the transmittance spectrum at two specific wavelengths, it is possible to establish a more standardized selection criterion and implement it quickly using low-cost optical devices. Furthermore, using the proposed transmittance-spectrum-slope method, statistically significant differences (p < 0.05) were found between healthy blood samples and lipemia 1, 2, 3, and 4. However, there were no statistical differences between lipemia 1 and 2.