Non-contact method for accelerating wound healing using an electromagnetic coil to induce an electric field transverse to an axis of the wound

Abstract

A method for accelerating the migration of cells by applying a time-varying magnetic field to induce eddy currents that promote electrotaxis (galvanotaxis) of cells. The method of the present invention accelerates the healing of wounds by electrotaxis of cells.

Claims

1. A method for controlling cell migration comprising the steps of: providing an electromagnetic coil having a first end and a second end; connecting the electromagnetic coil to a function generator; applying a time-varying voltage waveform to the electromagnetic coil; inducing a time-varying electric field around the electromagnetic coil; placing the electromagnetic coil adjacent to the location of a wound, the wound comprised of wound cells; orientating the placement of the electromagnetic coil to control the direction of the induced electric field; directing the induced electric field in a direction transverse to an axis of the wound; wherein the time-varying voltage waveform has a sharp drop at the trailing edge of the waveform and wherein the induced electric field is produced by a rapidly time-varying magnetic field; and controlling the migration of the wound cells using the induced electric field.

2. A method according to claim 1 further comprising the step of: inducing eddy currents near the location of the wound.

3. A method according to claim 1 further comprising the step of: accelerating the healing of the wound by accelerating the migration of the wound cells using the induced electric field.

4. A method according to claim 1, wherein the time-varying waveform is a sawtooth waveform.

5. A method according to claim 1, wherein the time-varying waveform is a 20 volts peak to peak, 100 Khz sawtooth waveform with a 50 ns drop off at its trailing edge.

6. A method according to claim 1, further comprising the step of: beaming an EM field from a remote source to the location of the wound.

7. A method according to claim 1, further comprising the steps of: placing a culture plate on top or on the sides of the electromagnetic coil; placing keratinocytes in the culture plate with a region between the keratinocytes devoid of keratinocytes.

8. A method according to claim 7 further comprising the steps of: taking an image of the wound after the step of inducing a time-varying electric field; and quantifying the healing potential of the induced electric field.

9. A method according to claim 1, further comprising the steps of: inducing an electric field in the direction of the surface of the wound; from below the surface of the wound; and controlling migration of cells of different types to the surface of the wound.

10. A method according to claim 1, further comprising the step of: inducing a rotating electric field in the wound.

11. A method according to claim 1, further comprising the step of: inducing a inhomogeneous electric field in the wound.

12. A method for controlling cell migration comprising the steps of: providing an electromagnetic coil having a first end and a second end; connecting the electromagnetic coil to a function generator; applying a time-varying voltage waveform to the electromagnetic coil; inducing a time-varying electric field around the electromagnetic coil; placing the electromagnetic coil adjacent to the location of a wound, the wound comprised of wound cells; orientating the placement of the electromagnetic coil to control the direction of the induced electric field; directing the induced electric field in a direction transverse to an axis of the wound; controlling the migration of the wound cells using the induced electric field; inducing an electric field in the direction of the surface of the wound; from below the surface of the wound; and controlling migration of cells of different types to the surface of the wound.

13. A method according to claim 12 further comprising the step of: inducing eddy currents near the location of the wound.

14. A method according to claim 12 further comprising the step of: accelerating the healing of the wound by accelerating the migration of the wound cells using the induced electric field.

15. A method according to claim 12, wherein the time-varying waveform is a sawtooth waveform.

16. A method according to claim 12, wherein the time-varying waveform is a 20 volts peak to peak, 100 Khz sawtooth waveform with a 50 ns drop off at its trailing edge.

17. A method according to claim 16, wherein the sawtooth waveform has a sharp drop and wherein the induced electric field is a rapidly time-varying magnetic field.

18. A method according to claim 12, further comprising the steps of: varying the characteristics of the waveform to control the migration of the wound cells.

19. A method according to claim 12, further comprising the steps of: placing a culture plate on top of the electromagnetic coil; placing keratinocytes in the culture plate with a region between the keratinocytes devoid of keratinocytes.

20. A method according to claim 19 further comprising the steps of: taking an image of the wound after the step of inducing a time-varying electric field; and quantifying the healing potential of the induced electric field.

21. A method according to claim 12, further comprising the step of: inducing a rotating electric field in the wound.

22. A method according to claim 12, further comprising the step of: inducing a inhomogeneous electric field in the wound.

23. A method according to claim 12, further comprising the step of: beaming an EM field from a remote source to the location of the wound.

24. A method according to claim 1, wherein the induced electric field has a magnitude of less than 0.7 mV/cm.

25. A method according to claim 12, wherein the induced electric field has a magnitude of less than 0.7 mV/cm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The following detailed description of the example embodiments refers to the accompanying figures that form a part thereof. The detailed description provides explanations by way of exemplary embodiments. It is to be understood that other embodiments may be used having mechanical and electrical changes that incorporate the scope of the present invention without departing from the spirit of the invention.

(2) In addition to the features mentioned above, other aspects of the present invention will be readily apparent from the following descriptions of the drawings and exemplary embodiments, wherein like reference numerals across the several views refer to identical or equivalent features, and wherein:

(3) FIG. 1A illustrates a top view of one embodiment of the apparatus of the present invention.

(4) FIG. 1B illustrates a front view of one embodiment of the apparatus of the present invention.

(5) FIG. 1C illustrates a side view of one embodiment of the apparatus of the present invention.

(6) FIG. 1D illustrates a blown up image of the simulated wound in FIG. 1A.

(7) FIGS. 2A-B illustrate the induced electric fields produced by the EM coil of FIG. 1.

(8) FIG. 3 illustrates microscopic images of a simulated wound from a control sample and another sample subject to an electric field.

(9) FIG. 4 illustrates quantitative measurements taken from FIG. 3.

(10) FIG. 5 illustrates another quantitative measurement taken based on percentage of gap closure.

(11) FIG. 6 illustrates the variation of imposed voltage and drive current in the EM coil as a result of an exemplary sawtooth waveform.

(12) FIG. 7 illustrates calculated values of the magnetic field in the vicinity of the simulated wound for one embodiment.

(13) FIG. 8 illustrates the calculated values of the induced electric field in the vicinity of the simulated healing fronts for one embodiment.

(14) FIG. 9 illustrates another view of the values of the induced electric fields in the vicinity of the simulated healing fronts for one embodiment.

(15) FIGS. 10A-B illustrates how the culture dish or coil can be moved with respect to each other to change the orientation or direction of the induced electric field on the simulated wound.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENT(S)

(16) The present invention relates to a method for inducing electric fields in a medium containing cells by applying time-varying magnetic fields. The method uses electromagnetic (EM) induction to induce electric fields and eddy currents in the medium and galvanotaxis of cells.

(17) Preliminary experiments have been conducted with human keratinocytes cultured in Dulbecco's Modified Eagle Medium (DMEM) to form a contiguous layer with a well-defined rectangular region devoid of cells so as to simulate a wound. FIG. 1 illustrates a preferred embodiment of the apparatus of the present invention. FIG. 1A is a top view, FIG. 1B is a front view, FIG. 1C is a side view and FIG. 1D illustrates a blown up image of the simulated wound in the culture plate. An EM coil 10 in a preferably cylindrical shape is placed in a holder 12. A culture plate 14 is placed on top of the EM coil (in another embodiment the culture plate can be placed to the side of the EM coil). As illustrated, in a preferred embodiment, the center line 16 of the EM coil runs in between and parallel to the gap (e.g., vacant region) that is devoid of cells (simulated wound) 18. The side view also illustrates the culture dish containing keratinocytes on top of the EM coil. The front view illustrates the culture plate on top of the EM coil as viewed from along the axis of the cylindrical coil. The top view illustrates the culture plate on top of the horizontally situated EM coil. FIG. 1D illustrates a microscope image from the top showing the region initially devoid of keratinocytes used to simulate a healing wound.

(18) FIG. 2 illustrates the induced electric fields 20 produced by the EM coil. FIG. 2A illustrates the electric fields from a front view and FIG. 2B illustrates the electric fields from a side view. As illustrated from FIG. 2A, in the preferred embodiment, the electric field is directed transverse to the axis of the gap or wound (or along the axis of propagation of the healing front).

(19) Normally, the initially vacant region is filled in as the cells grow inward to close the simulated wound (in about 6 to 8 hours) when placed in an incubator (at 37° C. with 5% CO.sub.2). In one embodiment, the culture dish with the simulated wound is placed on an electromagnetic (EM) coil (R˜22Ω, L=10 mH) situated within a fixture as shown in FIG. 1. As a control sample, a similar culture dish with the same cells and region devoid of cells (but not exposed to the EM coil) is also placed in the incubator. Both of these setups can be imaged at regular intervals over a period of 8 hours. In one embodiment, this experiment is repeated twice for a total of three runs.

(20) In one embodiment, the EM coil is driven using a function generator using a 5 Vpp, 1 Hz sawtooth wave with a sharp ˜50 ns drop to generate a rapidly time-varying magnetic field with components B.sub.r and B.sub.z. In another embodiment, a 19 Vpp, 100 kHz, sawtooth wave with a sharp ˜50 ns drop is used. By Faraday's law these temporally varying magnetic fields from the EM coil induce an electric field E.sub.θ in the medium containing the cells due to the small but non-zero electrical conductivity of the medium. This component of the induced electric field E.sub.θ has its largest component directed transverse to the axis of the simulated wound and along the axis of propagation of the healing front. At the driving frequency of 1 Hz, E.sub.θ switches direction back and forth (left and right) along the axis of the advancing healing fronts. The magnitude of E.sub.θ in one direction is larger than in the other because of the asymmetric sawtooth waveform imposed on the EM coil. In one embodiment, the cells are exposed to the electric field for 50 ns per second. The duration of this field remains 50 ns because of the characteristic of the sawtooth waveform but the overall duration can be increased by increasing the duty cycle (frequency on the function generator) from 1 Hz to 100 kHz.

(21) FIG. 3 shows microscope images of the simulated wound in the control sample 22 as well as the sample subjected to the EM field 24 (images shown for 0-8 hours (h)). As illustrated, the time-varying magnetic field resulted in induced electric fields which in this geometry inhibited the advance (hence healing) of the simulated wound as can be seen in FIGS. 3-5. In contrast, the control cases (with no applied electric field) resulted in the typically observed advance of the healing fronts. Quantitative measurements from the microscope images are shown in FIG. 4 and are consistent with the qualitative information that can be gleaned from the observations shown in FIG. 3 (the data shown is for n=3 and p<0.005). Although inhibition of healing is undesirable, what is of significance is that there is a noticeable and dramatic effect because of the application of the EM field. By selecting a different set of characteristics for the driving waveform (e.g. waveform type, peak to peak, voltage, and frequency) and direction of the induced electric field (e.g. rotating E.sub.θ in the plane of the wound) it is possible to accelerate healing (i.e. advancement of the healing fronts) shown in FIG. 3.

(22) Real chronic wounds are three dimensional (generally round) and not two-dimensional (or rectangular) as in the case of the assay shown in FIG. 3. Therefore, the other components of E.sub.θ, i.e., those that are not parallel to the direction of the healing front, can be used to entice different cell types (fibroblasts, immune cells, etc.) to be brought to the surface of a wound from below. Rotating the coil or inducing a rotating E.sub.θ, thereby varying the direction of the induced electric field in the plane of the wound, can also be used to accelerate rather than inhibit the healing fronts. Designing the holder and changing the position of the coil relative to the simulated wound can be used to produce an inhomogeneous E.sub.θ so that its effects are felt only on one side of the healing front or one of the healing fronts. It should be noted this result is of significance for cancer treatment where inhibition of metastasis in tumors may have beneficial effects. FIG. 6 shows the variation of imposed voltage and driven current in the EM coil as a result of the imposed sawtooth waveform. As can be seen in the figure, the asymmetric (in time) nature of the sawtooth generates a rapidly time-varying magnetic field as the imposed voltage falls within a time span of ˜50 ns. Consequently, the magnitude of the induced electric field E.sub.θ is smaller during the rising portion (˜1 s for 1 Hz excitation) and much larger for the falling portion (˜50 ns). FIG. 7 shows the calculated values of the magnetic field in the vicinity of the simulated wound. As illustrated, the maximum B field is on the order of 30 μT. FIGS. 8 and 9 show the calculated values of the induced electric field E.sub.θ in the vicinity of the simulated healing fronts. As illustrated, the maximum E.sub.θ is on the order of 0.7 mV/cm, three orders of magnitude smaller than what is reported in traditional electrotaxis or galvanotaxis experiments. This is of significance since it demonstrates the potential for improvement in the effects discussed here by increasing the magnitude of the induced electric field by increasing the current in the EM coil.

(23) In summary, a time-varying magnetic field from an electromagnetic (EM) coil has been used to induce electric fields in a medium containing human keratinocytes and simulating a wound. In vitro measurements on a simulated wound in a contiguous layer of keratinocytes have shown that closing of the initially introduced gap can be inhibited (i.e. healing is retarded) significantly compared to control experiments where no EM field is applied. It is appreciated that directional effects due to the induced electric field causes asymmetric advancement of the wound front. By varying the characteristics of the excitation of the EM coil, and positioning of the coil relative to the wound, it is possible to accelerate wound healing. The cells remain in a contiguous layer (i.e., cells or groups of cells do not move into the gap). For example, FIGS. 10A-B illustrate how the culture dish or coil can be moved with respect to each other to change the orientation or direction of the induced electric field on the simulated wound. In other words, rotating the orientation of the culture dish or coil effectively rotates the direction of E.sub.θ.

(24) It is possible to introduce a D.C. offset to the voltage imposed on the EM coil. However, it can be shown below that while this offset can increase the steady D.C. current in the EM coil, it does not increase E.sub.θ (because by Faraday's law, a time-varying magnetic field is necessary). For example, an offset voltage of V.sub.0 is imposed on a sinusoidally varying voltage imposed on the coil: V.sub.p=V.sub.0+V.sub.1 sin(ωt). Then, the resulting current flowing through the coil can be calculated to be (for long times):

(25) $I_p\left(t\right)=\frac{V_0}{R_p}+\frac{R_p{V}_1\sin \left(\omega t\right)-\omega V_1{L}_p\cos \left(\omega t\right)}{\left({\omega }^2{L}_p^2+R_p^2\right)}$
The induced electric field which drives eddy currents can then be approximately determined as:

(26) $E_{\mathrm{induced}}\frac{{\mu }_0}{4\pi }\frac{{\mathrm{dI}}_p}{\mathrm{dt}}=-\frac{{\mu }_0}{4\pi }\left[\frac{R_p{V}_1\mathrm{\omega cos}\left(\omega t\right)+{\omega }^2{V}_1{L}_p\sin \left(\omega t\right)}{\left({\omega }^2{L}_p^2+R_p^2\right)}\right]$
It can be seen that the offset V.sub.0 disappears. It is appreciated from the above expression for the induced electric field, that the asymmetric (in time) AC excitation of the coil should produce a time varying induced electric field and drive eddy currents that are largest in one direction.

(27) In another embodiment of the invention, a remotely placed EM source is configured to beam an EM field to induce an electric field at the wound site (e.g., remote induction scheme). In one example, a transmitting power source placed on the ceiling or wall of a hospital room beams an EM wave to a receiving coil placed in the vicinity of a wound. Alternatively it may be possible to transmit an EM wave focused on the wound such that electric fields are induced in the desired directions.

(28) While certain embodiments of the present invention are described in detail above, the scope of the invention is not to be considered limited by such disclosure, and modifications are possible without departing from the spirit of the invention as evidenced by the following claims: