Yi-Xin Zhou

Minimally invasive probe system capable of performing both cryosurgery and hyperthermia treatment on target tumor in deep tissues

Cryosurgery is a clinical therapy aiming at the destruction of diseased target tissues through a controlled deep freezing and subsequent rewarming. It has recently been realized that freezing immediately followed by a rapid and strong heating of the target tissues would significantly improve the treatment effect. However, most of the currently available cryoprobe systems are only capable of performing a single freezing function. To accommodate to the rapid growth of the combined freezing and heating therapy of tumor treatment, we have developed a new cryoprobe system with a powerful heating feature, which can be conveniently applied to destroy the tumor in deep tissue using a minimally invasive approach. Its operation performance will be characterized through a series of experimental tests in air, water, phantom gel, in vitro tissues and rabbits under anaesthesia. This system is perhaps the first one aiming at performing both cryosurgery and hyperthermia on target tumors. Therefore, it provides the clinicians with more choices and algorithms on treating a specific diseased tissue. Further, strain sensors and thermocouples were applied to simultaneously record the transient temperature and the thermal stress fields over the tissues subjected to freezing and strong heating. It was observed that a sudden change in the transient thermal stress was often induced when phase change occurs, which may imply that an evident thermal stress occurs at the liquid‐solid interface. This modifies the commonly accepted viewpoint that no stress should exist at the liquid‐like phase change interface. Further, implementations of this new system in clinical cryosurgery or hyperthermia are discussed. In addition to the applications in tumor treatment, the present system can also be very useful in fundamental research such as revealing the thermal stress mechanisms in tissues due to quick freezing and heating, which is hard to do otherwise. One interesting result presented in this paper is the experimental discovery of shock rings induced in the biomaterials around the probe, due to alternant freezing and heating by the present system.

Freeze tweezer to manipulate mini/micro objects

In this paper, we propose a freeze tweezer using the freezing force of a small volume of nucleotide ice to manipulate mini/micro objects in an aqueous state. Several prototypes of such a device based on the Joule–Thompson throttling effect have been fabricated and there have been preliminary demonstrations of their applicability in manipulating a wide variety of objects. By regulating the freezing conditions of the cooler, an ice ball can be formed between the tweezer tip and the object it contacts and then the object can be picked up. This freezing force is strong enough to manipulate objects with any shape, electric charge, light or heavy, biological or non-living, on the condition that the contact area can be frozen. Successful manipulation of a series of specific objects presented in this paper indicates that it would be much easier for the freeze tweezer to handle objects with smaller size. Therefore, further nanoscale freeze tweezers following the same idea as above can be put forward; this is expected to have exciting applications in micro/nano engineering field. Furthermore, theoretical analysis and experiments have been performed to quantify the response time of the freeze tweezer and the mechanical force generated on the tweezer tip. This study has also raised quite a few new fundamental issues related to the fabrication and practices of the freeze tweezer.

A convective cooling enabled freeze tweezer for manipulating micro-scale objects

A freeze tweezer is a new kind of manipulation tool which employs the freezing force of a small volume of nucleotide ice for operating the micro-objects in an aqueous state. Previously, such a typical device prototype was realized based on the Joule–Thompson (J–T) throttling effect or thermoelectric cooling (TEC) principle, where the generated cooling power is conducted to the tip of the tweezer. However, fabricating a J–T or TEC-type freeze tip would encounter big challenges in extremely small scales since transferring the cooling power to the tweeze tip is rather difficult, if not impossible. In addition, the formation of frost on the tweezer surface which would invalidate the micro-dimension of the tweezer tip is generally inevitable. Aiming to resolve these deficiencies, this paper is dedicated to presenting an alternative feasible way for realizing a freeze tweezer in micro or even much smaller size. The basic idea is based on ventilating low-temperature gas to the tweezer tip and thus directly generating freezing there via convective cooling. In this way, the tweezer tip at any small size can be frozen which would then serve to manipulate the target. Through conceptual experiments, it was demonstrated that the new type of freeze tweezer can not only complete all the functions its existing type would achieve, but could also make up for the inherent shortcomings. Further, the theoretical interpretation on convective heat transfer in micro-scale regimes and the numerical simulation on three-dimensional flow and heat transfer in the manipulation space were also performed to better understand the convective cooling based freeze tweezer. Although there may still exist certain difficulties for such a tweezer to be routinely used, it was shown that the new method is expected to be highly feasible in making a freeze tweezer for a wide variety of small-size occasions.

New Cryoprobe System With Powerful Heating Features and Its Performance Tests on Biomaterials

Cryosurgery is a clinical therapy aiming at destroying the target of diseased tissues through a controlled deep freezing and subsequent rewarming [1,2]. Applications of this treatment are quite wide in skin cancers, glaucoma, lung tumor etc. [3]-[10]. In contrast to the freezing therapy, heating of tumors has also long been proved to be an effective way of selectively killing the cells of cancerous tissues [11]-[13]. Clinical tests showed that heating the tumor to above a critical minimum temperature such as 42–43 °C for an extended period could effectively destroy the target. It was recently realized that freezing immediately followed by a rapid and strong heating of the target tissues would significantly improve the treatment effect [14]-[16]. Therefore, an apparatus thus developed will be of great importance in cancer clinics. But until now, most of the currently available cryoprobe systems are only capable of performing a single freezing function, in which the treated tissue is often let to naturally re-warm by simply switching off the apparatus. The first one and only commercially available cryoprobe system aiming at both freezing and heating therapy is perhaps Endocare Corporation’s Ar-He Cryoprobe system [14]. However, the highest tissue temperature for this system to achieve is about 0–20 °C [17], which is not high enough to thermally destroy the target tissues. Presently, there is a strong lack of freezing applicators with powerful heating functions for hyperthermia purposes. Without strong enough heating, tumors may still have a chance to regenerate. This is perhaps one of the critical reasons to impede the widespread of cryosurgery in destroying pathological tissues.Copyright

Liquid metal bath as conformable soft electrodes for target tissue ablation in radio-frequency ablation therapy

Abstract Background: Radio-frequency ablation has been an important physical method for tumor hyperthermia therapy. The conventional rigid electrode boards are often uncomfortable and inconvenient for performing surgery on irregular tumors, especially for those tumors near the joints, such as ankles, knee-joints or other facets like finger joints. Material and methods: We proposed and demonstrated a highly conformable tumor ablation strategy through introducing liquid metal bath as conformable soft electrodes. Different heights of liquid metal bath electrodes were adopted to perform radio-frequency ablation on targeted tissues. Temperature and ablation area were measured to compare the ablation effect with plate metal electrodes. Results: The recorded temperature around the ablation electrode was almost twice as high as that with the plate electrode and the effective ablated area was 2–3 fold larger in all the mimicking situations of bone tumors, span-shaped or round-shaped tumors. Another unique feature of the liquid metal electrode therapy is that the incidence of heat injury was reduced, which is a severe accident that can occur during the treatment of irregular tumors with plate metal boards. Conclusions: The present method suggests a new way of using soft liquid metal bath electrodes for targeted minimally invasive tumor ablation in future clinical practice.

Numerical Evaluation on the Cooling Capability of MEMS Based Liquid Metal Cooling Device Used in Harsh Environment

The thermal management of the increasing fast chips has been a major concern in packaging of micro/nano systems [1]. These chips are squeezing into tighter and tighter spaces with no enough places for heat to dissipate. It is expected that heat flux levels in excess of 100 W/cm2 for commercial electronics and over 1000 W/cm2 for selected military high power electronics will soon become a realistic challenge to overcome. Meanwhile, high-capacity cooling options remain limited for many small-scale applications such as micro-systems, sensors and actuators, and micro/nano electronic components.Copyright