Patent Application
20160193475
The invention relates to apparatus for treating biological tissue using a low-pressure plasma according to the preamble to claim 1. The invention further relates to a method for treating biological tissue using a low-pressure plasma.
It is known that plasmas have antimicrobial properties. The causes of the antibacterial effect of a plasma lie in heat, dehydration, shear stress, UV radiation, free radicals and charges. In the case of low-pressure plasmas, which are also called cold plasmas, heat plays a subordinate role, since these plasmas are operated at room temperature. In such low-pressure plasmas particularly reactive particles are produced, such as for example different oxygen or nitrogen species, which have a sufficiently long service life to damage organic compounds with indirect exposure. These particles include inter alia atomic oxygen, superoxide radicals, ozone, hydroxyl radicals, nitrogen monoxide and nitrogen dioxide. These particles exhibit a destructive effect on the most varied cell components.
If cell walls of bacteria, germs, viruses, fungi or other comparable microorganisms are directly exposed to the plasma, they become negatively charged by the bombardment with electrons present in the plasma. Due to the electrostatic repulsion this leads to mechanical stresses to the extent of exceeding the tensile strength and destruction of the cell wall. However, the cell walls can be destroyed not only by mechanical stresses due to the charge, but also by the disruption of the charge balance of the cell wall by different, further electrostatic interactions and by electrolysis, for example due to changing of the permeability of the cell walls. A mechanism for inactivation of microorganisms is also produced by the very high-energy ions, which may have more than 100 eV in capacitively coupled systems. Bombardment with such species can alter or destroy the structural integrity of the cells; however, an apparatus for generating such ion beams is complex and only suitable for treating living biological tissue, in particular human or animal tissues, with very high expenditure on apparatus.
Low-pressure plasmas are therefore particularly well suited for treatment of human or animal tissue, in particular skin surfaces, open wounds, the gums, the oral cavity or the like, in order to achieve disinfection of the tissue, in particular killing bacteria, germs, viruses, fungi or other comparable microorganisms which are located in or on the tissue.
An apparatus and a method for treating biological tissue with ozone is known from DE 10 2005 000 950 B3. This apparatus consists substantially of a transformer which can be adjusted in voltage and/or current intensity by means of a control device for generation of special directed voltage or current pulses having the most varied characteristic with or without a d.c. voltage component. In this case the d.c. voltage component is built up by additional electrodes on the biological tissue to be treated with the aid of an external voltage source or circuit. The primary coil of the transformer is the coil of a damped oscillating circuit through which high-frequency alternating current flows. Together with the capacitor to be charged, the secondary coil forms a resonant circuit of which the frequency corresponds to that of the transformer. A resonant transformer often serves as current source. Thus the treatment of different tissue types is possible, such as for example gums for treatments in the oral cavity or skin tissue for dermatological treatments with ozone. The setting of the power of the pulse generator takes place by means of operating elements which are disposed on the control device. By means of a rotary knob the power is set within a power range by the user or the attending doctor with reference to a numerical scale.
However, in the known apparatus it is possible that, depending upon the specific treatment situation, the power or current consumption of the tissue to be treated is different, so that on the one hand the functioning of the apparatus can be negatively influenced. On the other hand the patient to be treated may also be harmed by an increased power or current consumption.
Therefore the object of the invention is to modify an apparatus for treating biological tissue using a low-pressure plasma with the features of the preamble to claim 1 in such a way that when the power or current output by the apparatus is changed, in particular increased, the current supply is interrupted. On the other hand it is an object of the invention to provide an information device for such an apparatus, which informs the user about the distance between the probe and the tissue to be treated as well as the treatment time.
In terms of apparatus this object is achieved by an apparatus with all the features of claim 1.
In terms of method this object is achieved by a method with all the features of claim 9.
Advantageous embodiments of the invention are set out in the claims which are dependent upon the independent claims 1 and 9.
The apparatus according to the invention for treating biological tissue using a low-pressure plasma essentially comprises
Due to this special configuration of the apparatus according to the invention, on the one hand in spite of an increased power or current output into the tissue to be treated is immediately interrupted, so that damage to the apparatus according to the invention and harm to the patient to be treated due to an excessively high current is avoided. On the other hand the treatment period is indicated to the user optically and/or acoustically, and for this purpose the apparatus has corresponding optical display means and loudspeakers. Furthermore these optical display means and loudspeakers can be used in in order to inform the user about the distance of the treatment surface of the probe from the tissue to be treated. If the distance changes from an optimal distance for treatment, which may be fixed by the person skilled in the art, this is indicated to the user on an optically display arrangement or signalled acoustically by a loudspeaker, wherein with the aid of an acoustic warning signal it can also be ascertained whether the distance is too small or too great.
Advantageously the transformer comprises a transformer housing having a coupling which lies opposite the coupling for the probe for electrical/electronic connection of the control device, wherein the transformer housing is preferably constructed as a handle and is correspondingly ergonomically formed. This measure relates to a compact construction of the entire apparatus according to the invention, since both the transformer itself and also the control unit can be disposed inside the transformer housing. Only the probe for treatment of the biological tissue and, where appropriate, an external power source for supplying power to the apparatus according to the invention are not disposed inside the transformer housing. The ergonomic configuration of the transformer housing as a handle, which in its basic form is cylindrical, also enables pleasant and reliable handling of the apparatus according to the invention by the user.
Therefore for the reasons just given of compact construction and the simple, reliable and pleasant handling of the apparatus according to the invention, according to an advantageous idea of the invention the control device is disposed in the transformer housing.
However, for certain applications it may be sensible to dispose the control device outside the transformer housing. In particular when very delicate treatments have to be carried out, in which additional weight within the transformer housing designed as a handle is obstructive in the handling of the apparatus according to the invention.
The control device can be connected to an electrical power source so that the apparatus according to the invention can be supplied with the electrical power necessary for operation. In this case, in particular in the case of a control device disposed inside the transformer housing designed as a handle, a power source in the form of batteries or accumulators which is likewise accommodated in the transformer housing can, however, also be disposed outside the transformer housing. This is sensible in particular since the entire apparatus according to the invention can be operated independently of a stationary power source and in particular independently of a public or non-public electrical network. However, it is of course also conceivable to provide a stationary power source or a public or non-public electrical network as a power source to which the control unit can be connected.
The probe by which the actual treatment is carried out is preferably constructed as a glass probe, since the necessary low-frequency plasma for application to the tissue to be treated is generated by the probe. Such glass probes are simple to handle and are physiologically harmless for application to or in biological tissue.
In this case it has proved worthwhile to fill the glass probe under partial vacuum underpressure, or with respect to atmospheric pressure preferably under underpressure, or atmospheric pressure, with respect to atmospheric pressure from 500 Pa to a maximum of 3000 Pa, with a conductive gas, preferably with a noble gas or noble gas mixture. With such conductive gases, in particular noble gases and noble gas mixtures, preferably of argon and/or neon, the production of low-frequency plasmas and thus the entire apparatus according to the invention is particularly efficient. The glass probe is closed at one end by a metal contact, by which the high-frequency high voltage supplied by the transformer is conducted into the interior of the glass probe. Within the glass probe the gas is exposed to the high-frequency electromagnetic field and thus generates a glow discharge. In this case the output of the transformer can be adjusted by the control device in such a way that voltages in the range between 1800 V and 35000 V can be set, which are transmitted to the treatment surface of the glass probe by means of the conductive gas inside the glass probe. If the treatment surface of the glass probe is located immediately above the biological tissue to be treated, this voltage is set between them, optionally as a function of the electrical resistance of the surface of the biological tissue to be treated and the resistance the gases, in particular the air, between the treatment surface of the glass probe and the surface of the biological tissue to be treated.
In order that the high-frequency high voltage provided by the transformer can also be used efficiently by the probe, a good and reliable electrical contact between the transformer and the probe is indispensable. According to an independent idea of the invention this is achieved in that the probe can be coupled electrically/electronically to the transformer by means of a contact spring. In this case it is conceivable that the contact spring is disposed on the transformer or the transformer housing. On the other hand the contact spring can also be disposed on the probe. In both cases the contact spring ensures the electrical contact between the probe and the transformer, even if an undesirable play occurs within the coupling between the probe and the transformer.
The method according to the invention for treating biological tissue using a low-pressure plasma with a previously described apparatus essentially contains the following method steps:
In this connection it is pointed out that in applications in the dental field, for example in the treatment of the gums in the oral cavity, the current intensity on the side of the secondary coil is chosen to be between 0.1 μA and 100 μA, whereas in applications to other tissue surfaces, in particular dermatological treatments of the rest of the skin or of the patient to be treated or gynaecological applications, the current intensity on the side of the secondary coil is chosen to be between 0.1 μA and 300 μA.
Further objects, advantages, features and possible applications of the present invention are apparent from the following description of embodiments with reference to the drawings. In this case all the features described and/or illustrated, considered alone or in any sensible combination, form the subject of the invention, also independently of their composition in the claims or their dependencies.
In the drawings:
In
In this embodiment the secondary coil 5 is wound around a rod core 10 which is preferably made of a ferrite, whereas the primary coil 4 is wound with a spacing around the secondary coil 5. This spacing increases continuously from the end of the coils 4 and 5 facing the coupling 9 with a spacing dl to the end of the coils 4 and 5 facing the coupling 7 up to a spacing d2, so that the primary coil is disposed conically coaxially over the secondary coil. In the present embodiment both coils 4 and 5 have the same length L, so that they form an overlap region B over their entire length. In this case the primary coil 4 also takes on the function of an electromagnetic shield, or ensures a shielding effect, by which electromagnetic interference fields cannot critically disrupt the high-frequency electromagnetic field generated by the transformer 1, so that satisfactory functioning of the apparatus according to the invention is provided. In addition sealing means can also be provided in an end section of the converter.
In this embodiment the transformer 1 constructed as a high-voltage transformer is designed in such a way that the inner secondary coil 5 is wound around a rod core 10 made of ferrite in chambers 11. In the embodiment shown here the secondary coil 5 has 500 turns per chamber 11; however, other numbers of turns are also conceivable.
On the one hand the transformer 1 takes on the task of converting the high-frequency low voltage supplied by the power source 13 and the control unit 3 into a high-frequency high voltage. On the other hand, however, it also takes on the task of conducting the generated high voltage in particular via a glass tube (not shown here) of the probe 2 constructed as a glass probe to the treatment surface thereof which is disposed on the end of the probe opposite the coupling 7.
The arrangement of the coils 4 and 5 inside the transformer 1 leads to the provision of pulses with a predetermined signal form, preferably of sinusoidal pulses and particularly preferably of exponentially damped sinusoidal pulses, such as are illustrated for example in
The probe 2 of
Furthermore the probe 2 may have a connecting device 40 in order to dispose the probe body on a support, for example on a rod-like support such as a transformer housing 8 constructed as a handle. In this case it is possible that this connecting device 40 is constructed as a stopper which is introduced into the interior of the probe body 20 and pushed into the support or the coupling 7 of the transformer housing 8.
By means of an electrical connection 50 within the connecting device 40 or the holding device the probe 2 is connected by a connecting line 25 to a power source 13 or the control device 3. A two-core cable can be used for example as a connecting line 2.
During the treatment the current circuit between the apparatus according to the invention and the patient or the tissue G to be treated in or outside the human or animal body by the probe 2. The apparatus according to the invention generates the cold plasma or the low-pressure plasma.
On the end of the transformer housing 8 having the coupling 7 for the probe 2 this housing is equipped with a contact spring 12 which is connected electronically to the transformer 1. As already mentioned briefly, the contact spring 12 produces the contact with the probe 2. The voltage pulses are transmitted to the probe 2 by the contact. In the embodiments of
At the end opposite the treatment surface the probe 2 is closed by a metal flap which together with the contact spring 12 and the coupling 7 produces the electrical plug-type connection system with the transformer 1 disposed in the transformer housing 8.
Between the treatment surface of the probe 2 and the biological tissue G to be treated, with a spacing between 1 mm and 5 mm, the supplied high-frequency a.c. voltage and the typical pulse pattern produce the formation of the cold plasma or of the low-pressure plasma by which bacteria, germs, viruses, fungi or other comparable microorganisms adhering to the tissue G can be killed.
The gas in the probe 2 constructed as a glass probe is exposed to the generated high-frequency, electromagnetic alternating field in order to generate a glow discharge (microdischarge). In this case the output of the transformer can be adjusted via the control device 3 in such a way that voltages in the range between 1.8 V and 35 V can be set, which are transmitted to the treatment surface of the probe 2 by means of the conductive gas. If the treatment surface of the probe 2 is located immediately above the tissue G to be treated, the voltage thereof is set as a function of the skin resistance of the air between the instrument probe tip and the skin surface.
The method for direct generation of a low-pressure plasma or cold plasma corresponds to the structure of the dielectric barrier discharge illustrated in
Physical assessment of the plasma formation by dielectric barrier discharge. The dielectric barrier discharge, also called dielectrically hindered discharge or silent discharge, causes non-thermal plasma filaments P at atmospheric pressure during the ignition phase. In this assessment the dielectrically hindered discharge or silent discharge is, alongside corona discharge, a variant of the gas discharges which cause non-thermal plasma filaments P at atmospheric pressure during the ignition phase. The difference between the two forms of gas discharge lies in the extinguishing mechanism of the discharge filaments. In the case of the corona discharge it is space charge-oriented and in the case of the barrier discharge it is surface charge-oriented.
The basic structure illustrated in
The physical assessment of the plasma formation takes place according to the Paschen and Townsend method. The analysis relates to the model for the dielectric barrier discharge illustrated in
The starting point is a capacitor with a plate spacing of d=1 mm. Air is situated between the plates thereof. Let α be the probability per unit of length that an electron ionises a neutral atom or molecule, wherein impacts of ions with neutral atoms can be disregarded because of the rapidly changing field and the large mass of the ions.
If N is the number of electrons produced, then the following applies:
dN/dx=αN (1.1)
=>N(d)=Noead (1.2)
In this case N0 is the number of externally generated electrons, for example by cosmic radiation. The number of ionising impacts is proportional to the pressure p and to the probability for an ionisation impact.
Moreover for the kinetic energy of the electrons the following applies:
Eion=eEλion (1.3)
In this case λion is the acceleration path and E is the applied electrical field strength. Because of inelastic impacts only a fraction
It follows for the constant α
With the breakdown voltage Uzünd=Ed the following is obtained:
In this case y is the number of generated electrons per ion (third Townsend coefficient), with which the ignition condition
γ(ead−1)≧1 (1.6)
is produced. In this case generally y<<1 applies
Paschen curve for air (curve 1) and SF6 (curve 2).
p: pressure
s: gap size.
The Paschen curve describes the dependence of the breakdown voltage for the generation of a gas discharge upon the product of gap size and pressure.
For the present case the dependence of the breakdown voltage upon the gap widths can be estimated.
Thus the electrical breakdown occurs at a voltage of 3 kV for air at 1 bar. Since all atoms or molecules are ionised here on the entire path d, this is the upper limit for the voltage which is necessary for a stable plasma. Below this voltage, in a barrier discharge thin discharge channels (plasma filaments P) which are characteristic for a cold plasma form between the electrodes (spacing in the region of 1 mm). At atmospheric pressure, statistically distributed, a large number of transient discharge channels (microdischarges) are observed.
A necessary criterion for the existence of a plasma is that the Debye length is small by comparison with the measurements of the system. This shielding length is characterised in that on this length the potential of a local ion or electron discharge has fallen sufficiently dramatically (generally to 1/e times). This is therefore because in a plasma a positive ion is surrounded by a spherical cloud of electrons, so that the charges compensate each other to some extent, wherein the radius of these spheres is the Debye length. In the present case the movement of the ions in the alternating field relative to that of the electrons may be disregarded because of the much greater mass of the ions, The same applies to the Debye length.
For a non-isothermal plasma, in which because of their smaller mass the electrons have a higher temperature than the ions, in the case of a barrier discharge
T
e˜1−10eV (2.2) (electron temperature) and
n
e˜1020−1021m−3 (2.3) (volume number density of the electrons).
If these values are inserted into the equation (2.1), then for the Debye length of a non-isothermal plasma of a barrier discharge
λd=2.35·10−6m (2.4),
wherein this Debye length was calculated for the most unfavourable case of a number density of ne=1020 m−3 and an electron temperature of Te=10 eV=1,16·105 K.
If it is assumed for the present case that the system is of an order of magnitude in the mm range, then the Debye length is smaller by a factor of 1000, whereby the necessary criterion for the existence of a plasma is met.
A further criterion is that the average number of charged particles in the Debye sphere is greater than one. In the unfavourable situation ne=1020 m−3 approximately 5000 charged particles are situated in the Debye sphere, whereby this criterion is also met.
The parameters of the apparatus according to the invention meet the physical prerequisites for generating a cold plasma.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2012 025 080.0 | Dec 2012 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2013/003158 | 10/21/2013 | WO | 00 |
