A unique technology for profiled sapphire crystal growth has been developed by the scientists from the Institute of Solid Physics, Russian Academy of Sciences (Chernogolovka). The profiled crystals means the ones of assigned profile, i.e., of any shape and of almost any size, at any case, from superfine hollow capillaries through massive crystals, which are almost ten centimeters thick. This is extremely important to oncologists and to physicians in general, because sapphire capillaries and optical fiber enable to make laser therapy and diagnostics much more efficient and less traumatic than it is now with employment of quartz and polymer optical fiber. The technology developed and being patented by the authors enables to grow from the melt ideally straight solid sapphire tubules (capillaries), which are up to 30 centimeters long. The interior diameter of such a capillary is less than 1 millimeter, and exterior diameter is 1.2 millimeters. These are exactly the ones needed to physicians.
Thus, to begin with, here comes a briefing for those who fortunately have never heard about laser application to tumor diagnostics and therapy. The main point is that the optical fiber (thin light guiding fiber) is brought to the tumor located not on the surface but in the depth of the body. Laser of a certain wavelength generates irradiation, which is forwarded to the tumor via the optical fiber. Then the tumor should be looked at, i.e., it is necessary to capture the light reflected from the tumor, which would come back via the same optical fiber, or more or less powerful irradiation should be fed. Irradiation will either kill or burn out the tumorous tissue, or it will affect the substance preliminary injected into the tumor, which is able to decompose under the influence of irradiation accompanied by heat release (the so-called photodynamic therapy).
Now, quartz is the most popular material for optical fiber (polymer light guides are also being used but they fall out quickly). However, it is not deprived of drawbacks either, the main one being the ability to interact with biological tissues and blood. As a result, it is possible that healthy tissue would burn and irradiation parameters would change. This is no good – as the light intensity and wavelength should be strictly controlled under photodynamic therapy.
The light guide per se is a superfine and very fragile fiber (its diameter making 500 to 600 microns), therefore, to avoid its breaking when piercing the skin it has to be placed into the syringe needle, which serves a casing for the light guide.
So, the authors have suggested that the light guide casing or cover should be made of sapphire – in the form of a capillary, provided at the end with a solid “lance” sharpened at a required angle or, vice versa, with a spherical nozzle. Sapphire light guides are suggested because the properties of this crystal fully comply with the needed requirements. Sapphire is a very hard, durable and chemically inert material, and it transmits light very well in a very wide spectral range.
The technology developed by the researchers is based on the old method of crystal growth from the melt. The fuse of a required shape is put into the melting-pot containing the melt and is stretched out very slowly. This is done slowly so that the atoms had enough time to line up in a “correct” order, and the cooled article became a crystal but of a reassigned shape. However, it is very difficult to obtain at the output the tubules with superfine even walls along the full length and an ideally smooth surface. If the temperature is a bit higher or if a minor failure occurs in the speed – the capillary would “stick together”. Nevertheless, a group of researchers under the guidance of Vladimir Kurlov, Doctor of Science (Engineering), have succeeded. The technology developed by them and enriched by a lot of original “inventions” enables to solve the problem as well as many others. For example, to stretch out several dozens of capillaries at once during a single process.
In principle, physicians did like the concept of such sapphire casing as it allows to make multi-purpose interstitial irradiators, which almost do not traumatize the patient. The only thing that disturbed them was fragility of a capillary, which is, of course, not as durable as a suture needle. “A problem was posed for us to solve – to test the capillary on a piece of lard with skin, says Vladimir Kurlov. We were to try to pierce through the lard at least at the depth of 2 centimeters and to bend it so that to check at what angle of bending the capillary would break. The outcome was a pleasant surprise: the capillary easily penetrated the sample and broke only when it was bent at a 40-degrees angle. So, physicians are pleased with mechanical properties of the capillaries. There are no doubts that such quartz light guides in sapphire casing would not yield to traditional light guides in terms of efficiency.”