Experimental and Computational Analysis of High-Intensity Focused Ultrasound Thermal Ablation in Breast Cancer Cells: Monolayers vs. Spheroids

High-intensity focused ultrasound (HIFU) is a non-invasive therapeutic modality that uses precise acoustic energy to ablate cancerous tissues through coagulative necrosis. In this context, we investigate the efficacy of HIFU ablation in two distinct cellular configurations, namely 2D monolayers and 3D spheroids of epithelial breast cancer cell lines (MDA-MB 231 and MCF7). The primary objective is to compare the response of these two in vitro models to HIFU while measuring their ablation percentages and temperature elevation levels. HIFU was systematically applied to the cell cultures, varying ultrasound intensity and duty cycle during different sonication sessions. The results indicate that the degree of ablation is highly influenced by the duty cycle, with higher duty cycles resulting in greater ablation percentages, while sonication duration has a minimal impact. Numerical simulations validate experimental observations, highlighting a significant disparity in the response of 2D monolayers and 3D spheroids to HIFU treatment. Specifically, tumor spheroids require lower temperature elevations for effective ablation, and their ablation percentage significantly increases with elevated duty cycles. This study contributes to a comprehensive understanding of acoustic energy conversion within the biological system during HIFU treatment for 2D versus 3D ablation targets, holding potential implications for refining and personalizing breast cancer therapeutic strategies.

Electrospun Metal-Organic Framework-Fabric Nanocomposites as Efficient Bactericides

In this work, we utilized electrospinning to develop advanced composite membranes of polyvinyl chloride (PVC) loaded with postmetalated metal-organic frameworks (MOFs), specifically UiO-66(COOH)₂-Ag and ZIF-8-Ag. This innovative technique led to the creation of highly stable PVC/MOFs-Ag membrane composites, which were thoroughly characterized using various analytical techniques, including scanning electron microscopy, powder X-ray diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, porosity analysis, and water contact angle measurement. The results verified the successful integration of MOF crystals within the nanofibrous PVC membranes. The obtained composites exhibited larger fiber diameters for 5 and 10% MOF loadings and a smaller diameter for 20% loading. Additionally, they displayed greater average pore sizes than traditional PVC membranes across most MOF loading percentages. Furthermore, we examined the antibacterial properties of the fabricated membranes at different MOFs-Ag loadings. The findings revealed that the membranes demonstrated significant antibacterial activity up to 95% against both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria as the MOFs-Ag loading increased, even when maintaining a constant silver concentration. This indicates a contact-based inhibition mechanism. The outcomes of this study have crucial implications for the development of novel, stable, and highly effective antibacterial materials, which could serve as superior alternatives for face masks and be integrated into materials requiring regular decontamination, as well as potential water filtration systems.

Ten questions concerning the paradox of minimizing airborne transmission of infectious aerosols in densely occupied spaces via sustainable ventilation and other strategies in hot and humid climates

Airborne disease transmission in indoor spaces and resulting cross-contamination has been a topic of broad concern for years - especially recently with the outbreak of COVID-19. Global recommendations on this matter consist of increasing the outdoor air supply in the aim of diluting the indoor air. Nonetheless, a paradoxical relationship has risen between increasing amount of outdoor air and its impact on increased energy consumption - especially densely occupied spaces. The paradox is more critical in hot and humid climates, where large amounts of energy are required for the conditioning of the outdoor air. Therefore, many literature studies investigated new strategies for the mitigation of cross-contamination with little-to-no additional cost of energy. These strategies mainly consist of the dilution and/or the capture and removal of contaminants at the levels of macroenvironment room air and occupant-adjacent microenvironment. On the macroenvironment level, the dilution occurs by the supply of large amounts of outdoor air in a sustainable way using passive cooling systems, and the removal of contaminants happens via filtering. Similarly, the microenvironment of the occupant can be diluted using localized ventilation techniques, and contaminants can be captured and removed by direct exhaust near the source of contamination. Thus, this work answers ten questions that explore the most prevailing technologies from the above-mentioned fronts that are used to mitigate cross-contamination in densely occupied spaces located in hot and humid climates at minimal energy consumption. The paper establishes a basis for future work and insights for new research directives for macro and microenvironment approaches.

Effect of Phase Change Material Cooling Vests on Body Thermoregulation and Thermal Comfort of Patients With Paraplegia: A Human Subject Experimental Study

STUDY DESIGN

Randomized experimental study.

OBJECTIVE

Compared to able-bodied people, patients with paraplegia due to thoracic spinal cord injury (SCI) are at an increased risk of heat illnesses during exercise due to impaired thermoregulatory responses. To overcome this limitation, we investigated the performance of three phase change material (PCM) cooling vests of different melting temperatures (Eijsvogels, #49) and coverage area of the trunk.

METHODS

Sixteen participants were divided into three groups according to their injury level. All were tested for V20 full vest (20°C Tm, 75% coverage). Mid-thoracic and high-thoracic groups were tested for V14 vest (14°C Tm, 75% coverage). The mid-thoracic group was tested for V20 half vest (20°C Tm, 50% coverage). The participants performed a 30-min arm-crank exercise followed by a recovery period inside a controlled hot climatic chamber. The heart rate, segmental skin (Tskin), and core temperature (Tcore) values were recorded, and subjective questionnaires were taken.

RESULTS

Compared to no vest (NV) test, all the vests showed an effective decrease in Tskin values of the trunk. However, the decrease in Tskin was not enough to induce a significant decrease in Tcore in all three groups. Mid-thoracic and low-thoracic groups showed a reduction in the increasing Tcore by the end of the exercise and recovery period. Finally, the level of thermal comfort was enhanced for the three groups.

CONCLUSION

The effectiveness of cooling vests for persons with paraplegia is dependent on injury level and thus the ratio of sensate to insensate skin. Future studies necessitate the investigation of the cooling effects of PCM vests at a lower Tm with a larger sample size.

Experimental study on the effectiveness of the PCM cooling vest in persons with paraplegia of varying levels

Persons with paraplegia (PA) from thoracic spinal cord injury (T1-T12) are prone to thermal stress during exercise due to impaired thermoregulation. This study evaluates the effectiveness of phase change material (PCM) cooling vests on persons with PA of different levels of injury during exercise in hot exposure. Sixteen participants were recruited and divided to three groups based on injury level; high-thoracic T1-T3, mid-thoracic T4-T8, and low thoracic T9-T12 to perform a 30-min arm-crank exercise at a 30 °C room condition. Two types of PCM vests at melting temperature of 20 °C were tested: i) V1 with PCM covering the trunk of 3.4 kg overall vest mass and ii) V2 with PCM covering chest and upper back of 2.17 kg overall vest mass. High thoracic and low-thoracic groups performed NV and V1 tests; whereas, mid-thoracic group performed NV, V1, and V2 tests. Heart rate, core, and skin temperatures were monitored during 15-min preconditioning, 30-min exercise, and 15-min recovery. In addition, thermal comfort, sensation, skin wettedness, and perceived exertion were recorded during exercise only. The main findings were that the effectiveness of the cooling vest was dependent on injury level and portion of sensate skin of trunk covered by the PCM packets. Rise in core temperature (ΔT_cr) was reduced significantly for the low-thoracic group during exercise and recovery (ΔT_cr=0.41°C, 0.26°C for NV and V1; respectively, p<0.05). For the mid-thoracic group, both V1 (p = 0.001) and V2 (p = 0.008) were effective in reducing ΔT_cr compared to the NV test at the end of the recovery period (0.74°C,0.42°C,0.56°C, for NV, V1 and V2; respectively). For the high-thoracic group, V1 was not effective in reducing core temperature (p>0.05). For the mid-thoracic group, V2 at 36% lower mass significantly improved thermal comfort (p = 0.0004) compared to the NV test and was as effective compared to V1 in reducing core temperature.

Bioheat modeling of elderly and young for prediction of physiological and thermal responses in heat-stressful conditions

Exposure to hot and humid conditions results in physiological changes in metabolism, cardiac output and thermoregulation of the young adult and these changes deviate with elderly due to aging. The elderly population is more vulnerable than the healthy and young population due to age-weakened physiology and thermoregulatory functions. There are, however, limited bioheat models addressing such changes due to hot exposure in the young and the elderly. This paper develops robust bioheat models for young and elderly while incorporating the physiological changes under exposure to heat-stressful conditions for both age groups the age-related changes in physiology and thermoregulation to an elderly human. However, due to a large variability of thermoregulation among the elderly population, a sensitivity analysis revealed that the average elderly is characterized by metabolic rate and cardiac output, which are lower than those of the young by 21% and 14.4%, respectively. Moreover, the thresholds of the onset of vasodilation and sweating are delayed from those of young adults by 0.5 °C and 0.21 °C, respectively. The elderly and young bioheat models were validated with number of independent published experimental studies under hot exposures in steady and transient conditions. Model predictions of core and mean skin temperatures showed good agreement with published experimental data with a discrepancy of 0.1 °C and 0.5 °C, respectively.

Would personal cooling vest be effective for use during exercise by people with thoracic spinal cord injury?

People with thoracic spinal cord injury (SCI), named people with paraplegia (PA), are vulnerable to thermal heat stress during exercise due to disruption in their thermal physiology. Using personal cooling vests with phase change material (PCM) or ice presents a possible solution for PA to suppress the increase in core temperature and body heat storage. With the limited published experimental studies about effective cooling vest for PA, this work aims to develop an altered PA bioheat model combined with cooling vest model to study cooling vest performance during exercise. The integrated PA bioheat and vest models predict core and skin temperatures, latent and sensible heat losses and change in body heat storage for PA with and without a cooling vest. The models were validated with published experimental data on PA without the cooling vest and on PA with two cooling vests; one using PCM at melting temperature of 15 °C and the other using ice packets during exercise. It was observed that sensible heat losses at the four torso segments (abdomen, lower back, chest and upper back) increased with the vest case compared to the no-vest case; while, latent heat losses decreased compared to the no-vest case. However, insignificant change was seen in core temperatures and body heat storage as was also reported experimentally. The performance of each of the cooling vest during exercise on PA was dependent on skin coverage area and melting temperatures.

An optimal two-bout strategy with phase change material cooling vests to improve comfort in hot environment

Cooling vests incorporating phase change material (PCM) packets are used to improve comfort of workers in hot environments. This work aims to investigate by modeling and experimentation the effect of dividing the working duration into two bouts, where different PCM melting temperatures are used in each bout. An integrated bio-heat and fabric-PCM model predictions of physiological and subjective votes are validated via active human subject testing at hot conditions. A parametric study is performed to select, at two conditions (40°C and 45°C), the optimal PCM melting temperatures of the two bouts that would result with similar thermal comfort and sensation to the optimal single-bout case. The optimal case achieves most reductions in energy use for PCM regeneration, PCM carried weight and material cost. The results of the parametric study showed that heat storage is reduced in the second bout due to wearing the second vest with lower PCM melting temperature, thus thermal comfort and sensation are significantly improved. The optimal case at the 40°C environment uses a vest with 21°C PCMs in the first bout and a vest with 21°C PCMs in the second bout (V21→V21). At 45°C, the optimal case is V18→V10 with significant PCM weight reductions from the reference single bout case by a minimum of 47%. Thus, the issue of extra carried weight that affect metabolism and ease of movement when applying continuous cooling during work have been mitigated by using the two-bout strategy.

Transient transport model of particles resulting from high momentum respiratory activities: Inter-personal exposure

In this work, a transient mathematical multi-region zonal transport model of particle behavior resulting from high momentum respiratory activities (HMRA) is developed focusing on the transient inter-personal exposure (IPE) in indoor spaces ventilated by displacement ventilation (DV) systems. The developed model was validated by experimentation and by published empirical data. Three stages are identified with respect to time for the variation of the IPE: a first stage dominated by the propagation and decay of the exhaled jet, a particles' redistribution stage, and a particles' removal stage. The inhaled dose is affected by the DV flow rate, cough velocity, particle diameter and distance between the occupants. The DV system with a flow rate of 100 L/s reduced significantly the inhaled dose during particle redistribution and removal stages decreasing the total inhaled dose by 83% compared to a flow rate of 50 L/s. IPE is higher when particle diameter is increased from 1 to 20 μm due to the opposition of particle removal by the upward DV. A comparison between steady and transient modeling of the IPE showed that steady modeling captures the physics affecting particle spread due to HMRA but it over-predicts the inhaled dose. It is found that for a DV flow rate of 100 L/s and a cough velocity of 22 m/s during 1 s, and 1 μm particles, the minimum required distance between the occupants for a threshold inhaled dose of 10^-5 kg is nearly 0.5 m by transient modeling while it is 2.15 m by steady state modeling.

Elderly bioheat modeling: changes in physiology, thermoregulation, and blood flow circulation

A bioheat model for the elderly was developed focusing on blood flow circulatory changes that influence their thermal response in warm and cold environments to predict skin and core temperatures for different segments of the body especially the fingers. The young adult model of Karaki et al. (Int J Therm Sci 67:41-51, 2013) was modified by incorporation of the physiological thermoregulatory and vasomotor changes based on literature observations of physiological changes in the elderly compared to young adults such as lower metabolism and vasoconstriction diminished ability, skin blood flow and its minimum and maximum values, the sweating values, skin fat thickness, as well as the change in threshold parameter related to core or skin temperatures which triggers thermoregulatory action for sweating, maximum dilatation, and maximum constriction. The developed model was validated with published experimental data for elderly exposure to transient and steady hot and cold environments. Predicted finger skin temperature, mean skin temperature, and core temperature were in agreement with published experimental data at a maximum error less than 0.5 °C in the mean skin temperature. The elderly bioheat model showed an increase in finger skin temperature and a decrease in core temperature in cold exposure while it showed a decrease in finger skin temperature and an increase in core temperature in hot exposure.

A new mathematical model to simulate AVA cold-induced vasodilation reaction to local cooling

The purpose of this work was to integrate a new mathematical model with a bioheat model, based on physiology and first principles, to predict thermoregulatory arterio-venous anastomoses (AVA) and cold-induced vasodilation (CIVD) reaction to local cooling. The transient energy balance equations of body segments constrained by thermoregulatory controls were solved numerically to predict segmental core and skin temperatures, and arterial blood flow for given metabolic rate and environmental conditions. Two similar AVA-CIVD mechanisms were incorporated. The first was activated during drop in local skin temperature (<32 °C). The second mechanism was activated at a minimum finger skin temperature, T(CIVD, min), where the AVA flow is dilated and constricted once the skin temperature reached a maximum value. The value of T(CIVD,min) was determined empirically from values reported in literature for hand immersions in cold fluid. When compared with published data, the model predicted accurately the onset time of CIVD at 25 min and T(CIVD,min) at 10 °C for hand exposure to still air at 0 °C. Good agreement was also obtained between predicted finger skin temperature and experimentally published values for repeated immersion in cold water at environmental conditions of 30, 25, and 20 °C. The CIVD thermal response was found related to core body temperature, finger skin temperature, and initial finger sensible heat loss rate upon exposure to cold fluid. The model captured central and local stimulations of the CIVD and accommodated observed variability reported in literature of onset time of CIVD reaction and T(CIVD,min).