Numerical investigation of nanoparticle-assisted laser-induced interstitial thermotherapy toward tumor and cancer treatments

Present and future of metal nanoparticles in tumor ablation therapy

Cancer is an important factor affecting the quality of human life as well as causing death. Tumor ablation therapy is a minimally invasive local treatment modality with unique advantages in treating tumors that are difficult to remove surgically. However, due to its physical and chemical characteristics and the limitation of equipment technology, ablation therapy cannot completely kill all tumor tissues and cells at one time; moreover, it inevitably damages some normal tissues in the surrounding area during the ablation process. Therefore, this technology cannot be the first-line treatment for tumors at present. Metal nanoparticles themselves have good thermal and electrical conductivity and unique optical and magnetic properties. The combination of metal nanoparticles with tumor ablation technology, on the one hand, can enhance the killing and inhibiting effect of ablation technology on tumors by expanding the ablation range; on the other hand, the ablation technology changes the physicochemical microenvironment such as temperature, electric field, optics, oxygen content and pH in tumor tissues. It helps to stimulate the degree of local drug release of nanoparticles and increase the local content of anti-tumor drugs, thus forming a synergistic therapeutic effect with tumor ablation. Recent studies have found that some specific ablation methods will stimulate the body's immune response while physically killing tumor tissues, generating a large number of immune cells to cause secondary killing of tumor tissues and cells, and with the assistance of metal nanoparticles loaded with immune drugs, the effect of this anti-tumor immunotherapy can be further enhanced. Therefore, the combination of metal nanoparticles and ablative therapy has broad research potential. This review covers common metallic nanoparticles used for ablative therapy and discusses in detail their characteristics, mechanisms of action, potential challenges, and prospects in the field of ablation.

Nanoparticle-assisted, image-guided laser interstitial thermal therapy for cancer treatment

Laser interstitial thermal therapy (LITT) guided by magnetic resonance imaging (MRI) is a new treatment option for patients with brain and non-central nervous system (non-CNS) tumors. MRI guidance allows for precise placement of optical fiber in the tumor, while MR thermometry provides real-time monitoring and assessment of thermal doses during the procedure. Despite promising clinical results, LITT complications relating to brain tumor procedures, such as hemorrhage, edema, seizures, and thermal injury to nearby healthy tissues, remain a significant concern. To address these complications, nanoparticles offer unique prospects for precise interstitial hyperthermia applications that increase heat transport within the tumor while reducing thermal impacts on neighboring healthy tissues. Furthermore, nanoparticles permit the co-delivery of therapeutic compounds that not only synergize with LITT, but can also improve overall effectiveness and safety. In addition, efficient heat-generating nanoparticles with unique optical properties can enhance LITT treatments through improved real-time imaging and thermal sensing. This review will focus on (1) types of inorganic and organic nanoparticles for LITT; (2) in vitro, in silico, and ex vivo studies that investigate nanoparticles' effect on light-tissue interactions; and (3) the role of nanoparticle formulations in advancing clinically relevant image-guided technologies for LITT. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Neurological Disease Implantable Materials and Surgical Technologies > Nanoscale Tools and Techniques in Surgery.

Multiphysics Modeling of Plasmonic Photothermal Heating Effects in Gold Nanoparticles and Nanoparticle Arrays

Induced hyperthermia has been demonstrated as an effective oncological treatment due to the reduced heat tolerance of most malignant tissues; however, most techniques for heat generation within a target volume are insufficiently selective, inducing heating and unintended damage to surrounding healthy tissues. Plasmonic photothermal therapy (PPTT) utilizes light in the near-infrared (NIR) region to induce highly localized heating in gold nanoparticles, acting as exogenous chromophores, while minimizing heat generation in nearby tissues. However, optimization of treatment parameters requires extensive in vitro and in vivo studies for each new type of pathology and tissue targeted for treatment, a process that can be substantially reduced by implementing computational modeling. Herein, we describe the development of an innovative model based on the finite element method (FEM) that unites photothermal heating physics at the nanoscale with the micron scale to predict the heat generation of both single and arrays of gold nanoparticles. Plasmonic heating from laser illumination is computed for gold nanoparticles with three different morphologies: nanobipyramids, nanorods, and nanospheres. Model predictions based on laser illumination of nanorods at a visible wavelength (655 nm) are validated through experiments, which demonstrate a temperature increase of 5 °C in the viscinity of the nanorod array when illuminated by a 150 mW red laser. We also present a predictive model of the heating effect induced at 810 nm, wherein the heating efficiencies of the various morphologies sharing this excitation peak are compared. Our model shows that the nanorod is the most effective at heat generation in the isolated scenario, and arrays of 91 nm long nanorods reached hyperthermic levels (an increase of at least 5 °C) within a volume of over 20 μm³.

Thermal field and tissue damage analysis of moving laser in cancer thermal therapy

In this paper, a closed-form analytical solution of hyperbolic Pennes bioheat equation is obtained for spatial evolution of temperature distributions during moving laser thermotherapy of the skin and kidney tissues. The three-dimensional cubic homogeneous perfused biological tissue is adopted as a media and the Gaussian distributed function in surface and exponentially distributed in depth is used for modeling of laser moving heat source. The solution procedure is Eigen value method which leads to a closed form solution. The effect of moving velocity, perfusion rate, laser intensity, absorption and scattering coefficients, and thermal relaxation time on temperature profiles and tissue thermal damage are investigated. Results are illustrated that the moving velocity and the perfusion rate of the tissues are the main important parameters in produced temperatures under moving heat source. The higher perfusion rate of kidney compared with skin may lead to lower induced temperature amplitude in moving path of laser due to the convective role of the perfusion term. Furthermore, the analytical solution can be a powerful tool for analysis and optimization of practical treatment in the clinical setting and laser procedure therapeutic applications and can be used for verification of other numerical heating models.

Modeling of cancer photothermal therapy using near-infrared radiation and functionalized graphene nanosheets

Photothermal therapy using near-infrared radiation and local heating agents can induce selective tumor ablation with limited harm to the surrounding normal tissue. Graphene sheets are promising local heating agents because of their strong absorbance of near-infrared radiation. Experimental studies have been conducted to study the heating effect of graphene in photothermal therapy, yet few efforts have been devoted to the quantitative understanding of energy conversion and transport in such systems. Herein, a computational study of cancer photothermal therapy using near-infrared radiation and graphene is presented using a Monte Carlo approach. A three-dimensional model was built with a cancer cell inside a cube of healthy tissue. Functionalized graphene nanosheets were randomly distributed on the surface of the cancer cell. The effects of the concentration and morphology of the graphene nanosheets on the thermal behavior of the system were quantitatively investigated. The interfacial thermal resistance around the graphene sheets, which affects the transfer of heat in the nanoscale, was also varied to probe its effect on the temperature increase of the cancer cell and the healthy tissue. The results of this study could guide researchers to optimize photothermal therapy with graphene, while the modeling approach has the potential to be applied for investigating alternative treatment plans.

Theoretical analysis of nanoshell-assisted thermal treatment for subcutaneous tumor

The hyperthermia is an efficient technique for tumor treatment, in which the tumor is subjected to a heating source, such as laser, supersonic or electromagnetic field. In order to improve the therapeutic efficiency and to protect the surrounding healthy tissues, gold nanoshells are embedded in the tumor as the additive to make it absorb more thermal energy than the healthy tissues. In the present study, a one-dimensional three-layered model is established to investigate the thermal response of the bio-tissue in the hyperthermia treatment for subcutaneous tumor. The governing equations are solved analytically by using the Green's function method and the Henriques' model is employed to evaluate the degree of thermal damage in the target tissue. The influences of the volumetric density of gold nanoshells on the temperature distribution and thermal damage are discussed in detail. When the gold nanoshells are embedded with a proper density, it can improve the efficiency of tumor killing and protecting the subcutaneous tissue from being burnt. The closed-form solution for the governing equations in multilayered tissues can be a theoretical guideline to selection of appropriate parameters of the gold nanoshells.

Potentials and pitfalls of gold-silica nanoshell as the exogenous contrast agent for optical diagnosis of cancers: a numerical parametric study

For nanoshell-assisted optical detection of cancers, gold shell, silica core (gold-silica) nanoshells are engineered to be the exogenous contrast agent. This work has performed systematic numerical parametric study to investigate the nonlinear dependences of the hemisphere diffuse reflectance on gold-silica nanoshells, laser irradiance, and hosting biology tissue. Planar phantom based tissue models have been constructed as platforms for study. The radiant transport equation (RTE) has been applied to mathematically describe the interactions among laser lights, hosting tissues, and hosted nanoshells. The diffuse reflectance signal under various combinations of parametric conditions has been computed and analyzed. Parametric parameters whose effects on the diffuse reflectance signal have been investigated are: (1) optical properties of a nanoshell generic, (2) nanoshell volume fraction, which is an indicator of nanoshell accumulation in the target tissue site, (3) the width of irradiating laser beam, and (4) thickness of the tissue slab. Seven nanoshell generics have been tested as the exogenous contrast agent including the R[50, 10] (radius of silica core is 50 nm and thickness of gold shell is 10 nm), R[55, 25], R[40, 15], R[40, 40], R[104, 23], R[75, 40] and R[154, 24] nanoshells. It has been found the R[55, 25] nanoshell works best as the exogenous contrast agent, the R[75, 40] and R[104, 23] nanoshells show good potentials as well while the R[50, 10] and R[40, 15] nanoshells should be avoided for diagnostic usage. The practice of neglecting the absorption characteristic of the exogenous contrast agent, which is quite common among the bio-nano community, has been proven to end up with an over-prediction of the effectiveness of the exogenous contrast agent. Such practice therefore is not well justified and should be avoided in future research. Interactions among laser lights, the tissue and nanoshells are highly nonlinear, demonstrated by that nanoshell generics with totally different optical properties might have similar effects on the diffuse reflectance signal and vice versa. Prior to any bench experiment, preliminary numerical investigation as this work has showcased is highly recommended.

Evaluation of theranostic perspective of gold-silica nanoshell for cancer nano-medicine: a numerical parametric study

Using gold-silica nanoshell as a reference nano-agent, this work has performed preliminary numerical parametric study to investigate the feasibility and if feasible the efficiency of using a single nano-agent to achieve theranostic goals. In total, seven generics of gold-silica nanoshells have been tested including the R[50,10] (radius of the silica core is 50 nm and thickness of the gold shell is 10 nm), R[40,15], R[55,25], R[40,40], R[75,40], R[104,23], and R[154,24] nanoshells. A planar tissue model has been constructed as the platform for parametric study. For mathematical modeling, radiant transport equation (RTE) has been applied to describe the interactions among laser lights, the hosting tissue, and the hosted nanoshells and Penne's bio-heat equation has been applied to describe the hyperthermia induced by such interactions. Effects of different nanoshell generics on the diffuse reflectance signal and hyperthermia temperature transition have been simulated, basing on which the potential of a certain nanoshell generic as theranostic nano-agent has been evaluated. It has been found that it is highly feasible for gold-silica nanoshells to be engineered for theranostic purpose and nanoshell generics that are preferentially scattering should be explored for good theranostic candidates. On the condition that nanoshell generic with the right optical properties has been located, a moderate nanoshell retention in the target tissue site is already sufficient to induce effective theranostic effects, which indicates that theranostic nano-medicine might not have a stringent requirement for the delivery technique. Among nanoshells that have been tested, the R[55,25] nanoshell seems to be a promising candidate as theranostic nano-agent. Further testing on it is highly recommended. Nanoshells that are preferentially absorbing such as the R[50,10] and R[40,15] nanoshells are efficient photothermal agent and could be used for therapeutic purpose only. However, it is not recommended that preferentially absorbing nanoshells being used for theranostic purpose due to possible negative effects such nanoshells might bring to the diffuse reflectance signal.

Non-Fourier thermal transport induced structural hierarchy and damage to collagen ultrastructure subjected to laser irradiation

Comprehending the mechanism of thermal transport through biological tissues is an important factor for optimal ablation of cancerous tissues and minimising collateral tissue damage. The present study reports detailed mapping of the rise in internal temperature within the tissue mimics due to NIR (1064 nm) laser irradiation, both for bare mimics and with gold nanostructures infused. Gold nanostructures such as mesoflowers and nanospheres have been synthesised and used as photothermal converters to enhance the temperature rise, resulting in achieving the desired degradation of malignant tissue in targeted region. Thermal history was observed experimentally and simulated considering non-Fourier dual phase lag (DPL) model incorporated Pennes bio-heat transfer equation using COMSOL Multiphysics software. The gross deviation in temperature i.e. rise from the classical Fourier model for bio-heat conduction suggests additional effects of temperature rise on the secondary structures and morphological and physico-chemical changes to the collagen ultrastructures building the tissue mass. The observed thermal denaturation in the collagen fibril morphologies have been explained based on the physico-chemical structure of collagen and its response to thermal radiation. The large shift in frequency of amides A and B is pronounced at a depth of maximum temperature rise compared with other positions in tissue phantom. Observations for change in band of amide I, amide II, and amide III are found to be responsible for damage to collagen ultra-structure. Variation in the concentration of gold nanostructures shows the potentiality of localised hyperthermia treatment subjected to NIR radiation through a proposed free radical mechanism.

Effective thermal transport properties in multiphase biological systems containing carbon nanomaterials

Here we report computational results from an off-lattice Monte Carlo investigation of the effective thermal transport properties in multiphase biological systems containing carbon nanomaterials.

Mesoscopic modeling of cancer photothermal therapy using single-walled carbon nanotubes and near infrared radiation: insights through an off-lattice Monte Carlo approach

Single-walled carbon nanotubes (SWNTs) are promising heating agents in cancer photothermal therapy when under near infrared radiation, yet few efforts have been focused on the quantitative understanding of the photothermal energy conversion in biological systems. In this article, a mesoscopic study that takes into account SWNT morphologies (diameter and aspect ratio) and dispersions (orientation and concentration), as well as thermal boundary resistance, is performed by means of an off-lattice Monte Carlo simulation. Results indicate that SWNTs with orientation perpendicular to the laser, smaller diameter and better dispersion have higher heating efficiency in cancer photothermal therapy. Thermal boundary resistances greatly inhibit thermal energy transfer away from SWNTs, thereby affecting their heating efficiency. Through appropriate interfacial modification around SWNTs, compared to the surrounding healthy tissue, a higher temperature of the cancer cell can be achieved, resulting in more effective cancer photothermal therapy. These findings promise to bridge the gap between macroscopic and microscopic computational studies of cancer photothermal therapy.

Investigation on nanoparticle distribution for thermal ablation of a tumour subjected to nanoparticle assisted thermal therapy

This study investigates the effect of the distribution of nanoparticles delivered to a skin tumour for the thermal ablation conditions attained during thermal therapy. Ultimate aim is to define a distribution of nanoparticles as well as a combination of other therapeutic parameters to attain thermal ablation temperatures (50-60 °C) within whole of the tumour region. Three different cases of nanoparticle distributions are analysed under controlled conditions for all other parameters viz. irradiation intensity and duration, and volume fraction of nanoparticles. Results show that distribution of nanoparticles into only the periphery of tumour resulted in desired thermal ablation temperature in whole of tumour. For the tumour size considered in this study, an irradiation intensity of 1.25 W/cm(2) for duration of 300 s and a nanoparticle volume fraction of 0.001% was optimal to attain a temperature of ≥53 °C within the whole tumour region. It is concluded that distribution of nanoparticles in peripheral region of tumour, along with a controlled combination of other parameters, seems favourable and provides a promising pathway for thermal ablation of a tumour subjected to nanoparticle assisted thermal therapy.

Role of optical coefficients and healthy tissue-sparing characteristics in gold nanorod-assisted thermal therapy

PURPOSE

This study seeks to define parameters for gold nanorod assisted thermal therapy, to achieve the thermal ablation temperature (50-60°C) in the tumour region and spare healthy tissue surrounding the tumour. Also, a criterion for size selection of gold nanorods is described based on the role of optical coefficients.

THEORY AND METHODS

In this study a tissue domain (comprising a 3 mm tumour and 7 mm of surrounding healthy tissue) embedded with gold nanorods is irradiated with electromagnetic radiation within the therapeutic wavelength band. Optical interaction is captured using light scattering theory (Mie-electrostatic approach). The resulting temperature field is evaluated using Penne's bioheat model. The effect of key parameters, namely irradiation intensity, irradiation duration and volume fraction, on tissue temperature is also modelled numerically.

RESULTS

With increasing nanorod diameter - from 5 nm to 15 nm - the scattering coefficient increases ∼76 times as compared to a 1.7-fold increase in absorption coefficient. Scattering is considerably minimised by having smaller gold nanorods of 5 nm diameter. For this study, gold nanorods of 5 nm diameter and volume fraction 0.001%, irradiated with 50 W/m(2)-nm for 250 s ablated the tumour as well as spare healthy tissue 2 mm beyond the tumour region.

CONCLUSION

Overall it may be concluded that tumour ablation as well as surrounding healthy tissue-sparing (within millimetres immediately adjacent to the tumour) can be achieved through a combination of specified parameters, namely diameter and volume fraction of gold nanorods, irradiation intensity and duration.