Haydar A. S. Aljaafari

Thermal shock is a promising new approach to eliminating biofilm infections on medical implants without surgically replacing the device. Most studies determining the minimum necessary thermal shock used immersion in hot media to provide precise, rapid, uniform temperature control. In vivo, however, this shock must be focused directly on the implant surface, raising the concern that bacteria may partially evade the shock by momentarily dispersing into the cooler surroundings. This study tests that hypothesis using remote induction heating, in which Pseudomonas aeruginosa biofilms were thermally shocked by an external alternating magnetic field heating the substrate directly. It also assessed the impact of tobramycin on the minimum thermal shock required. Susceptibility to tobramycin alone, thermal shock alone, and their combination was characterized over temperatures ranging from 50 to 80 °C and duration of 1 to 30 min with biofilms of two distinctly different architectures and population densities. Remote heating was then evaluated on biofilms in a flow cell where media was continuously replaced to keep its temperature below the biofilm’s. Comparison with immersion heating showed that, despite losing 90% of the biofilm to dispersion into the flushed media, biofilms thermally shocked in the flow cell had significantly higher populations than biofilms comparably shocked by immersion, though biofilms could still be completely eliminated via remote heating. Tobramycin alone did not eliminate biofilm even at clinically infeasible concentrations but, when combined with thermal shock, achieved complete elimination at milder thermal shocks, indicating a complex synergy also observed with antibiotics of another class. Remote heating successfully eliminated biofilms while delivering heat in a clinically implementable manner. As an in vitro, these findings did not directly assess thermal damage to surrounding tissue, which requires further investigation in future treatment design.

Bacterial biofilms on medical implants are a major problem, typically requiring explantation and replacement of the biofilm‐colonized implant. Thermal mitigation of these biofilms in situ has shown great promise in the laboratory, where the thermal shock can be most precisely delivered by immersion in hot media. Clinical implementation requires delivering the shock from the implant surface, however, leaving the surroundings at a cooler temperature. This study hypothesized that bacteria may rapidly, reversibly disperse into the cooler surroundings to partially evade the shock and tested this hypothesis by thermally shocking Pseudomonas aeruginosa biofilms on thermoelectric devices under media with different heat sink conditions. The time scale and equilibrium constant of this dispersion were investigated in ambient temperature immersion studies, and the effect of thermal shock on bacterial dispersion rate was investigated in a flow cell using biofilms grown on thermoelectric devices. The results showed that biofilms equilibrate with surrounding media in seconds, that a small fraction of bacteria in the biofilm are much less prone to dispersion, that thermal shock triggers an immediate increase in dispersion, and that shocking biofilms via their substrate in cooler surrounding decreases shock efficacy compared to shocks where the surrounding's temperature approaches that of the substrate.

The increasing threat of antimicrobial resistance has heightened the search for alternative therapeutic approaches that are both effective and environmentally sustainable. This study introduces a green synthesis approach for silver nanoparticles (AgNPs) from Ocimum sanctum (Tulsi) leaf extract, leveraging its rich phytochemical composition for nanoparticle formation and stabilization. Prepared AgNPs were characterized using UV–Vis spectroscopy, FTIR, FE-SEM, EDX, and XRD. These analyses verified the formation of spherical, crystalline particles averaging approximately 39.60 nm in diameter. To evaluate their antimicrobial potential, we tested Tulsi extract, AgNPs, and their combinations with conventional antimicrobial agents against Bacillus cereus and Candida albicans . The finding revealed that the AgNPs showed significantly enhanced antimicrobial activity compared to the Tulsi extract alone. Notably, the most effective outcomes were observed when the AgNPs was combined with antimicrobial agents, suggesting a synergistic interaction. These results highlight the potential of plant-mediated AgNPs to significantly enhance existing therapies, offering a novel and eco-friendly approach to combat multidrug-resistant pathogens.

Spouted bed reactors (SBRs) are highly valued for their effectiveness in chemical and biochemical processes due to their mixing and heat transfer capabilities. Understanding the heat transfer mechanisms in these reactors is necessary. This research delves into the heat transfer behavior of SBRs, which plays a role in enhancing their performance under operational conditions. The study conducted experiments to measure the heat transfer coefficient (HTC) at varying gas velocities (ranging from 0.32 to 0.74 m/s) at radial positions (r/R = 0, ±0.28, ±0.56, and ±0.85) and axial levels (H/D = 0.8, 2.1, and 3.5) within the spouted bed (SB) column using a technique, for the assessment of local heat transfer coefficients (LHTCs). The results we obtained revealed the velocity of the gas, its radial position in the reactor, and its axial height. For instance, higher gas speeds led to heat transfer efficiency and variations in radial positions highlighted how the reactor’s shape influences heat transfer dynamics. It’s worth noting that increasing the gas speed from the lowest to the level tested resulted in a 25% increase in heat transfer coefficients. These discoveries provide insights for improving the design and performance of SBRs with ranging applications in industries that rely on effective heat transfer processes.

Staphylococcus epidermidis is a major contributor to bacterial infections on medical implants, currently treated by surgical removal of the device and the surrounding infected tissue at considerable morbidity and expense. In situ hyperthermia is being investigated as a non-invasive means of mitigating these bacterial biofilm infections, but minimizing damage to the surrounding tissue requires augmenting the thermal shock with other approaches such as antibiotics and discerning the minimum shock required to eliminate the biofilm. S. epidermidis biofilms were systematically shocked at a variety of temperatures (50–80 °C) and durations (1–10 min) to characterize their thermal susceptibility and compare it to other common nosocomial pathogens such as Staphylococcus aureus and Pseudomonas aeruginosa. Biofilms were also exposed to three classes of antibiotics (ciprofloxacin, tobramycin and erythromycin) separately at concentrations ranging from 0 to 128 μg mL⁻¹ to evaluate their impact on the efficacy of thermal shock and the subsequent potential regrowth of the biofilm. S. epidermidis biofilms were shown to be more thermally susceptible to hyperthermia than other common bacterial pathogens. All three antibiotics substantially decreased the duration and/or temperature needed to eliminate the biofilms, though this augmentation did not meet the criteria of synergism immediately following thermal shock. Subsequent reincubation, however, revealed strong synergism on a longer timescale.

Due to the significant increase in heavy feedstocks being transported to refineries and the hydrocracking process, the significance of adopting an ebullated bed reactor has been reemphasized in recent years. The predictive modelling of gas hold-up in an ebullated two-phase reactor was performed using 10 machine learning methods based on support vector machine (SVM) and Gaussian process regression (GPR) in this study. In an ebullated bed reactor, the impacts of three features, namely liquid velocity, gas velocity, and recycling ratio, on the gas hold-up were examined. The liquid velocity has the most impact on the predicted gas hold-up, according to the feature significance analysis. The rotational-quadratic, squared-exponential, Matern 5/2, and exponential kernel functions integrated with the GPR models and the linear, quadratic, cubic, fine, medium, and coarse kernel functions integrated with the SVM model performed well during training and testing, with the exception of the fine SVM model, whose R² is very low. According to the R² > 0.9 and low RMSE and MAE values, the rotational-quadratic, squared-exponential, and Matern 5/2 GPR models performed the best.

Methicillin-Resistant Staphylococcus aureus (MRSA) biofilms are among the most dangerous infections on medical implants, typically requiring surgical explantation and replacement. This study investigated the thermal susceptibility of MRSA biofilms to thermal shocks from 60 to 80 °C for 1-30 min as well as the effect of various antibiotics (most notably methicillin) on thermal mitigation. Pre- and post-shock exposure to three different classes of antibiotics (ciprofloxacin, tobramycin, and methicillin) at concentrations ranging from 0.25 to 128 μg mL^-1 were investigated. MRSA biofilms exhibited thermal susceptibility comparable to other common nosocomial pathogens, such as Pseudomonas aeruginosa, though with greater variability. Exposure to antibiotics of any class significantly decreased the degree of thermal shock required for reliable mitigation, including at subclinical concentration. These combined treatments reduced biofilm population more than the sum of thermal and chemical treatments alone, demonstrating synergism, while also indicating a critical population drop of ∼4.5 log₁₀ beyond which the biofilms typically became non-viable.

Bacterial biofilm infections are a major liability of medical implants, due to their resistance to both antibiotics and host immune response. Thermal shock can kill established biofilms, and some evidence suggests antibiotics may enhance this efficacy, despite having an insufficient effect themselves. The nature of this interaction is unclear, however, complicating efforts to integrate thermal shock into implant infection treatment. This study aimed to determine whether these treatments were truly synergistic or simply orthogonal (i.e., independent). Pseudomonas aeruginosa biofilms of different architectures and stationary-phase population density were subjected to various thermal shocks, antibiotic exposures, or combinations thereof, and examined either immediately after treatment or after subsequent reincubation. Population decreases from the combination treatment matched the product of the decreases of individual treatments, indicating their orthogonality. However, reincubation showed binary behavior, where biofilms with an immediate population decrease beyond a critical factor (~10⁴) died off completely during reincubation, while biofilms with a smaller immediate decrease regrew. This critical factor was independent of the initial population density and the combination of treatments that achieved the immediate decrease. While antibiotics do not appear to enhance thermal shock directly, their contribution to achieving a critical population decrease for biofilm elimination can make the treatments appear strongly synergistic, strongly decreasing the intensity of thermal shock needed.