Anomalous Subsurface Thermal Behavior in Tissue Mimics Upon Near Infrared Irradiation Mediated Photothermal Therapy

Photothermal therapy using (Near Infrared) NIR region of EM spectrum is a fast emerging technology for cancer therapy. Different types of nanoparticles may be used for enhancing the treatment. Though the treatment protocols are developed based on experience driven estimated temperature increase in the tissue, it is not really known what spatiotemporal thermal behavior in the tissue is. In this work, this thermal behavior of tissue models is investigated with and without using nanoparticles. An increased temperature inside tissue compared to surface is observed which is counter intuitive from the present state of knowledge. It is shown from fiber level microstructure that this increased temperature leads to enhanced damage at the deeper parts of biomaterials. Nanoparticles can be utilized to control this temperature increase spatially. A multiple scattering based physical model is proposed to explain this counterintuitive temperature rise inside tissue. The results show promising future for better understanding and standardizing the protocols for photothermal therapy.