Optical Sensing of Tissue Freezing Depth by Sapphire Cryo-Applicator and Steady-State Diffuse Reflectance Analysis.

This work describes a sapphire cryo-applicator with the ability to sense tissue freezing depth during cryosurgery by illumination of tissue and analyzing diffuse optical signals in a steady-state regime. The applicator was manufactured by the crystal growth technique and has several spatially resolved internal channels for accommodating optical fibers. The method of reconstructing freezing depth proposed in this work requires one illumination and two detection channels. The analysis of the detected intensities yields the estimation of the time evolution of the effective attenuation coefficient, which is compared with the theoretically calculated values obtained for a number of combinations of tissue parameters. The experimental test of the proposed applicator and approach for freezing depth reconstruction was performed using gelatin-based tissue phantom and rat liver tissue in vivo. It revealed the ability to estimate depth up to 8 mm. The in vivo study confirmed the feasibility of the applicator to sense the freezing depth of living tissues despite the possible diversity of their optical parameters. The results justify the potential of the described design of a sapphire instrument for cryosurgery.

Porcine heart valve, aorta and trachea cryopreservation and thawing using polydimethylsiloxane.

The most common cryopreservation protocols of biological tissues suitable for their further implantation has some disadvantages and limited to one sample per procedure with no possible repeated freezing in case of clinical needs. This study is aimed to improve a biological tissues cryopreservation by adding a new heat transfer fluid - polydimethylsiloxane (PDMS). To evaluate its efficiency the porcine biological tissues (heart valves, aortic and trachea fragments) were cryopreserved and thawed in low-viscous PDMS. According to the computer simulation, the midsection cooling rate was up to 490 °C/min and the midsection thawing rate was up to 1140 °C/min with admissible temperature uniformity. Cryoprotectants and liquid nitrogen were not used. The quality of tissue cryopreservation was evaluated using a number of histological and immunohistochemical methods (Orcein, H&E, Anti-CD34, Anti-Vimentin, Anti-Actin staining). Cryopreserved tissues showed no significant morphological difference in comparison with control group both in case of immediate thawing, and after 2 months of low temperature storage. Computer simulation of heat transfer showed the thermal limitations of used approach for larger specimens. The use of PDMS is proposed for preservation of vascular tissue in order to implant it in the form of homotransplants or biobanking with the possible additional use of an internal hydrophilic coating to prevent hydrophobization.