Bahman Anvari

Self-Assembly Synthesis, Tumor Cell Targeting, and Photothermal Capabilities of Antibody-Coated Indocyanine Green Nanocapsules

New colloidal materials that can generate heat upon irradiation are being explored for photothermal therapy as a minimally invasive approach to cancer treatment. The near-infrared dye indocyanine green (ICG) could serve as a basis for such a material, but its encapsulation and subsequent use are difficult to carry out. We report the three-step room-temperature synthesis of approximately 120-nm capsules loaded with ICG within salt-cross-linked polyallylamine aggregates, and coated with antiepidermal growth factor receptor (anti-EGFR) antibodies for tumor cell targeting capability. We studied the synthesis conditions such as temperature and water dilution to control the capsule size and characterized the size distribution via dynamic light scattering and scanning electron microscopy. We further studied the specificity of tumor cell targeting using three carcinoma cell lines with different levels of EGFR expression and investigated the photothermal effects of ICG containing nanocapsules on EGFR-rich tumor cells. Significant thermal toxicity was observed for encapsulated ICG as compared to free ICG at 808 nm laser irradiation with radiant exposure of 6 W/cm(2). These results illustrate the ability to design a colloidal material with cell targeting and heat generating capabilities using noncovalent chemistry.

Selective cooling of biological tissues: application for thermally mediated therapeutic procedures

The ability to control the degree and spatial distribution of cooling in biological tissues during a thermally mediated therapeutic procedure would be useful for several biomedical applications of lasers. We present a theory based on the solution of the heat conduction equation that demonstrates the feasibility of selectively cooling biological tissues. Model predictions are compared with infrared thermal measurements of in vivo human skin in response to cooling by a cryogen spurt. The presence of a boundary layer, undergoing a liquid-vapour phase transition, is associated with a relatively large thermal convection coefficient (approximately 40 kW m-2 K-1), which gives rise to the observed surface temperature reductions (30-40 degrees C). The degree and the spatial-temporal distribution of cooling are shown to be directly related to the cryogen spurt duration.

A theoretical study of the thermal response of skin to cryogen spray cooling and pulsed laser irradiation: implications for treatment of port wine stain birthmarks.

The successful treatment of port wine stain (PWS) patients undergoing laser therapy is based on selective thermal coagulation of blood vessels without damaging the normal overlying epidermis. Cryogen spray cooling of skin may offer an effective method for minimizing epidermal thermal injury. Inasmuch as the density of melanosomes and depth of PWS blood vessels can vary considerably, an optimum cooling strategy is required on an individual patient basis. We present a theoretical study of the thermal response of various pigmented PWS lesions to spray cooling in conjunction with flashlamp-pumped pulsed dye laser irradiation (585 nm). Results of our model indicate that precooling of skin using tetrafluoroethane as the cryogen spray is sufficient to eliminate epidermal thermal injury when using incident fluences less than 10 J cm-2 and 8 J cm-2 on patients with intermediate and high epidermal melanin content, respectively. Cryogens that have lower boiling points than tetrafluoroethane may allow successful treatment when using fluences equal to or greater than those indicated.

Dynamic epidermal cooling in conjunction with laser-induced photothermolysis of port wine stain blood vessels

When a cryogen spurt is applied to the skin surface for an appropriately short period of time (on the order of tens of milliseconds), the spatial distribution of cooling remains localized in the normal overlying epidermis, while leaving the temperature of the deeper port wine stain (PWS) blood vessels unchanged. Furthermore, cooling continues after pulsed laser exposure as cryogen remaining on the surface evaporates and removes heat deposited by light absorption in epidermal melanin. An additional advantage of dynamic cooling is a reduction in the level of pain and discomfort associated with flashlamp‐pumped pulsed dye laser therapy of PWS. Preliminary clinical studies and supporting theoretical calculations demonstrate the feasibility of selective epidermal cooling while achieving photothermolysis of blood vessels during pulsed laser treatment of PWS.

Imaging laser heated subsurface chromophores in biological materials: determination of lateral physical dimensions

We describe a non-contact method using infrared radiometry to determine lateral physical dimensions of laser heated subsurface chromophores in biological materials. An imaging equation is derived that relates measured radiometric temperature change to the reduced two-dimensional temperature increase of laser heated chromophores. From measured images of radiometric temperature change, the lateral physical dimensions of chromophores positioned in an in vitro model of human skin are determined by deconvolution of the derived imaging equation using a non-negative constrained conjugate gradient algorithm. Conditions for optimum spatial resolution are found by analysis of a derived radiometric transfer function and correspond to superficial chromophores and/or weak infrared absorption in a laser irradiated biological material. Analysis indicates that if the infrared attenuation coefficient is sufficiently small (i.e., less than 10mm-1), infrared radiometry in combination with a deconvolution algorithm allows estimation of lateral physical dimensions of laser heated subsurface chromophores in human skin.

Estimation of internal skin temperatures in response to cryogen spray cooling: implications for laser therapy of port wine stains

In many port wine stain (PWS) patients, successful clearing is not achieved even after multiple laser treatments because of inadequate heat generation within the targeted blood vessels. Use of higher radiant exposures has been suggested to improve lesion clearing, but risk of epidermal injury due to nonspecific absorption by melanin increases. It has been demonstrated that cryogen spray cooling (CSC) can protect the epidermis from nonspecific thermal injury during laser treatment of PWS. Inasmuch as epidermal melanin concentration and blood vessel depth vary among patients, evaluation of internal skin temperatures in response to CSC is essential for further development and optimization of treatment parameters on an individual patient basis. We present internal temperature measurements in an epoxy resin phantom in response to CSC and use the results in conjunction with a mathematical model to predict the temperature distribution within human skin for various cooling parameters. Measurements on the epoxy resin phantom show that cryogen film temperature is well below the cryogen boiling point, but a poor thermal contact exists at the cryogen-phantom interface. Based on phantom measurements and model predictions, internal skin temperature reduction remains confined to the upper 400 /spl mu/m for spurt durations as long as 200 ms. At the end of a 100 ms spurt, our results show a 31/spl deg/C temperature reduction at the surface, 12/spl deg/C at a depth of 100 /spl mu/m, and 4/spl deg/C at a depth of 200 /spl mu/m in human skin. Analysis of estimated temperature distributions in response to CSC and temperature profiles obtained by pulsed photothermal radiometry indicates that a significant protective effect is achieved at the surface of laser irradiated PWS skin. Protection of the epidermal basal layer, however, poses a greater challenge when high radiant exposures are used.

Spatially selective photocoagulation of biological tissues: feasibility study utilizing cryogen spray cooling

Successful laser treatment of selected dermatoses such as hemangiomas requires thermally induced damage to blood vessels while protecting the epidermis. We present and test a procedure in a rabbit liver tissue model that utilizes cryogen spray cooling during continuous Nd:YAG laser irradiation to induce deep photocoagulation necrosis while protecting superficial tissues from thermal injury. Gross and histologic observations are consistent with calculated thicknesses of protected and photocoagulated tissues and demonstrate the feasibility of inducing spatially selective photocoagulation when cryogen spray cooling is used in conjunction with laser irradiation. This procedure may be useful in the thermal treatment of some pathological conditions for which it is desired that deep photocoagulation be induced while protecting superficial tissues.

Measurement of radiometric surface temperature and integrated backscattered light intensity during feedback-controlled laser-assisted cartilage reshaping

Cartilage undergoes characteristic mechanical stress relaxation following laser irradiation below the ablation threshold. Porcine auricular cartilage (1–2 mm thickness) was irradiated with a Nd:YAG laser (λ=1.32 μm) at two power levels (W/cm2). Surface temperature (Sc(t) (°C)) (monitored using a single element HgCdTe infrared detector, 10-14 μm spectral range), and integrated back scattered light intensityI(t) were measured during laser irradiation. A HeNe laser beam (λ=632.8 nm) was incident on the back surface of the cartilage specimen and fractional integrated backscattered light intensity was measured using an integrating sphere anda silicon photodiode. Laser irradiation (5.83 W/cm2, 50 Hz pulse repetition rate (PRR)) continued until surface temperature reached approximately 70°C, during which cartilage mechanical stress relaxation was observed. Integrated back scattered light intensity reached a plateau at about 70°C). At higher laser power (39.45 W/cm2, 50 Hz PRR), a feedback-controlled cryogen spray was used to maintain surface temperature below 50°C. A similar plateau response was noted in integrated backscattered light intensity. This signal may be used to optimise the process of stress relaxation in laser cartilage reshaping. Several clinical applications involving reconstructive surgery are proposed.

Dynamic epidermal cooling in conjunction with laser treatment of port-wine stains: Theoretical and preliminary clinical evaluations

The clinical objective in laser treatment of port-wine stains (PWS) is to induce selective photothermolysis of subsurface blood vessels without damaging the overlying epidermis. This paper investigates the effectiveness of ‘dynamic’ cooling, where a cryogen is sprayed on the skin surface for an appropriately short period of time, to eliminate epidermal thermal injury during laser treatment of PWS. Comparative measurements of radiometric surface temperature from cooled and uncooled laser irradiated (585 nm) PWS sites, and theoretical predictions of temperature distributions within skin in response to dynamic cooling in conjunction with laser irradiation are presented. Rapid reduction of skin surface temperature and localization of cooling the epidermis are obtained when a cryogen is sprayed on skin prior to laser irradiation. Successful blanching of the PWS without thermal injury to the overlying epidermis is accomplished.

Laser-Induced Heating of Dextran-Coated Mesocapsules Containing Indocyanine Green

Indocyanine green (ICG) is a photosensitive reagent with clinically relevant diagnostic and therapeutic applications. Recently, ICG has been investigated for its utility as an exogenous chromophore during laser‐induced heating. However, ICGapos;s effectiveness remains hindered by its molecular instability, rapid circulation kinetics, and nonspecific systemic distribution. To overcome these limitations, we have encapsulated ICG within dextran‐coated mesocapsules (MCs). Our objective in this study was to explore the ability of MCs to induce thermal damage in response to laser irradiation. To simulate tumorous tissue targeted with MCs, cylindrical phantoms were prepared consisting of gelatin, intralipid emulsion, and various concentrations of MCs. The phantoms were embedded within fresh chicken breast tissue representing surrounding normal tissue. The tissue models were irradiated at λ = 808 nm for 10 min at constant power (P = 4.2 W). Five hypodermic thermocouples were used to record the temperature at various depths below the tissue surface and transverse distances from the laser beam central axis during irradiation. Temperature profiles were processed to remove the baseline temperature and influence of light absorption by the thermocouple and subsequently used to calculate a damage index based on the Arrhenius damage integral. Tissue models containing MCs experienced a maximum temperature change of 18.5 °C. Damage index calculations showed that the heat generation from MCs at these parameters is sufficient to induce thermal damage, while no damage was predicted in the absence of MCs. ICG maintains its heat‐generating capabilities in response to NIR laser irradiation when encapsulated within MCs. Such encapsulation provides a potentially useful methodology for laser‐induced therapeutic strategies.