Abstract:
The present invention relates to a device for penetrating human nails as a part of treatment for Onychomycosis, commonly known as fungal nail. The device comprises a reusable electromechanical system and a single use cutting component. The electromechanical system incorporates an electrical motor and drive train to advance the cutting component through the nail. The electromechanical system also incorporates sensors for measuring the cutting resistance for the purpose of preventing the cutting device from overrunning into the nail bed. The device can be used to penetrate the nail in a controlled manner which will create a portal through the nail without penetrating the nail bed below the nail.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     None. 
     BACKGROUND TO THE PRESENT INVENTION 
     The present invention relates to a device for controlled penetration of the nail found on the hands and feet of a patient, and more particularly a device for the controlled penetration of the nail to aid in the treatment of infection of the nail such as for example the treatment for Onychomycosis commonly known as fungal nail. The device will penetrate the nail using a cutter advanced by a control system that will prevent the cutter from overrunning and entering the nail bed below. 
     Onychomycosis is an example of a fungal nail infection that is most common in the feet of the elderly affecting as many as 60% in the United States. It causes the nail to change shape, thicken and becoming brittle. Over the counter creams and ointments have a very low level of efficacy (of between 5-12%). Oral treatments are much more effective, however they must be taken for 2-3 months and can affect the liver making them contraindicated for some patients. An alternative means of treatment is the use of lasers to treat the infection, however the cost of the equipment and treatment is very high making it unavailable to many patients. 
     If untreated the nail can be permanently deformed and can have a significant impact upon the patient&#39;s quality of life due to the unsightly appearance of the nail and pain when wearing shoes. 
     To increase the local efficacy of topically applied treatment it is advantageous to deliver the treatment to areas within and below the nail. This greatly increases concentration levels that can be achieved in the nail bed and consequently improves efficacy of the treatment. The matrix is the tissue upon which the nail rests, the part of the nail bed that extends beneath the nail root and contains nerves, lymph and blood vessels. The matrix is responsible for the production of the cells that become the nail plate. The nail plate or body of nail is like hair and skin, made of translucent keratin protein made of amino acids. In the nail it forms a strong flexible material made of several layers of dead, flattened cells. If the nail is perforated then it allows antifungal treatment to be applied directly to the nail bed below the nail, where the infection resides. The challenge with drilling through the nail is to penetrate the nail without piercing the nail bed below. The nail bed is very sensitive and piercing it can cause the patient a lot of pain. 
     US patent application number 2006/0225757 A1 describes a drill for making a hole in the fingernail or toenail, however there is no provision for preventing the drill from overrunning into the nail bed, other than the skill of the user. 
     U.S. Pat. No. 6,264,628 B1 describes a device for cutting a notch in the nail. In order to prevent damage to the nail bed, the depth to which the notch is cut is predetermined prior to use. There is no method described for detecting the point at which the cutter breaks through the nail. 
     US patent application number 2011/0046626 A1 describes a method for drilling through the nail without drilling far into the nail bed. The author describes a method for detecting the point at which the drill breaks through the nail and into the nail bed below by measuring the electrical impedance of the tissue being drilled. The electrical impedance of the material being drilled is measured by using the drill as one electrode and having a second electrode placed on the skin of the patient. A change in impedance between the two electrodes may be used to detect the point at which the drill breaks through the nail and into the nail bed below. At this point however the drill may have progressed further into the nail bed than is desirable. 
     US patent application number 2010/0145373 A1 describes apparatus for drilling a hole in a nail of a subject. The Author describes a drill control unit configured to 2-60 back and forth motions per second. The apparatus is fed into the nail by the user and is dependent upon the user to ensure that it is not pressed too deeply into the nail bed. The Author describes a control unit configured to stop drilling in response to the force exceeding a threshold force, however the force will fluctuate according to the amount applied by the user. 
     SUMMARY OF THE PRESENT INVENTION 
     The present invention provides a device for automatically controlling the drilling through a nail of a human or other animal and also provides a device for automatically controlling the drilling through a tissue of a human or other animal. Optional features of both of these devices are also described. 
     The present invention also provides a method of automatically controlling the drilling through a nail of a human or other animal. It will be appreciated that the optional features described in relation to the device may be used as optional features of the method of the present invention. The method of the present invention may also be used to drill through tissues other than nails. 
     The present invention also provides a method of treating a nail infection in a human or other animal. 
     The devices and methods according to the present invention do not require the user to advance the cutter (i.e. drill bit), but instead utilise a control system that controls the rate at which the cutter is advanced and the force that is applied by the cutter. The control system advances the cutter through the nail whilst monitoring the position of the cutter and automatically stops the cutter from advancing once it breaks through the nail in order to ensure that is does not overrun and enter into the nail bed. 
     The devices and methods according to the present invention may be used to detectably predict the point at which the drill bit or cutter will break out of the nail and then control it so as to prevent it from entering the nail bed and causing the patient pain. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying drawings in which: 
         FIG. 1  is a schematic illustration of the nail penetration device and a possible method of holding the device against the nail during use. 
         FIG. 2  is a schematic illustration showing that the device consists of two primary components; 1) a reusable hand-piece non-sterile and 2) detachable single use sterile cutting element. 
         FIG. 3  is a schematic illustration showing how the device may be used to produce an elongated slot shaped aperture in the nail. 
         FIG. 4  is a schematic illustration showing a simplified drive mechanism that may be used to advance the cutter in the axial plane during operation (more detail is provided in  FIG. 5 ). 
         FIG. 5  is a schematic illustration showing an embodiment of the drive mechanism and control system that may be used to advance the cutter in the axial plane and prevent it from overrunning into the nail bed during operation. A numbered components are as follows:
     1. A cross-section of the nail   2. The cutter that may take the form of a twist drill, slot cutter, end mill or other appropriate design; possibly including helical or spiral features.   3. Spring used to ensure that the nail is pressed against the nail with sufficient force to ensure reliable operation of the device.   4. A switch or sensor to detect that the spring  3  has been sufficiently compressed.   5. The motor for rotating the cutter possibly also including an integral or separate tachometer for measuring the rotational speed during operation.   6. A component that transfers force between the drive screw for advancing the motor  5  and preventing it from being rotated by the reaction from the cutter  2 . A more detailed description is provided in  FIG. 7 .   7. At least one strain gauge that may be arranged in a Wheatstone Bridge configuration in order to measure axial forces.   8. At least one strain gauge that may be arranged in a Wheatstone Bridge configuration in order to torque or rotational forces.   9. A resistor placed in series for detecting the current flow through the motor  11  used to power the drive mechanism for advancing and retracting the cutter in the axial direction.   10. A resistor placed in series with the motor for detecting the current flow through the motor  5  used to rotate the cutter  2 .   11. The motor  11  used to power the drive mechanism for advancing and retracting the cutter in the axial direction.   12. A torque sensor or component used to measure the torque applied to the motor  11  used to power the drive mechanism for advancing and retracting the cutter in the axial direction.   13. The PCB control system used to automate the system and ensure that the cutter does not overrun the nail and enter the nail bed below.   

         FIG. 6  is a schematic illustration of the nail contacting part of the single use component that will ensure that the device is pressed against the nail with sufficient force to prevent undesirable movement during operation. This also shows the cutter  2  not in contact with the nail  1  at this point. 
         FIG. 7  is a schematic illustration of an embodiment of a component  6  that may be used for one of the proposed methods for measuring the axial force and the torque produced during the cutting process, by using strain gauges  7  and  8  to measure elastic deformation of a component connecting the motor and the drive mechanism shown in  FIG. 5 . 
         FIG. 8  is a schematic illustration showing the cutter positioned on a toenail and three distinct stages of operation during use when the cutter is; 1) coming into contact with the nail, 2) passing through the nail, 3) breaking through the nail. 
         FIG. 9  is a set of illustration of graphs showing the force profiles likely to be seen whilst drilling through a solid material with special reference to features that may be seen during stages 1, 2, and 3 shown in  FIG. 8 ; a) Reaction force on the cutter  2  or motor  5 , b) Reaction torque on the cutter  2  or motor  5 , c) Power consumed by motor  5 , and d) Rotational velocity of the cutter  2 . 
         FIG. 10  is a schematic illustration of graphs showing the how the signals may be filtered including the first-order differential of the signals that may be used to detect the point at which the drill (or cutter  2 ) breaks through the nail:
     a) An unfiltered signal for the force profile   b) The same signal shown in a) filtered using a low-pass filter for example a Kalman filter   c) The first-order differential of an unfiltered signal for the force profile as seen in a)   d) The first-order differential for the filtered signal for the force profile as seen in b)   

         FIGS. 11 a - f    is a set of illustration profiles of various cutter design that may be used and that will change the signal profiles shown in  FIG. 9 :
     a) Conventional drill point design, where 50% of the axial force is carried on the leading chisel edge   b) Centre point design similar to a wood drilling bit   c) Circumference cutting design   d) Combination of centre point b) and circumference cutting c) designs   e) Counter bore design designed to produce a counter bore hole   f) Flat end design to help prevent damage to the nail bed when exiting the nail  1 .   
     
    
    
     SUMMARY OF PREFERRED EMBODIMENTS 
     Reference is now made to  FIGS. 1, 2, 4 and 5 , of the drawings showing schematic illustrations of an embodiment of the nail penetration device. The device may be handheld and presses against the nail during use as in  FIG. 1 . 
     The device may require a predetermined load to be applied, determined by the spring elements  3  shown in  FIG. 6 , in order to ensure that the device is stable and there is no motion that may prevent the control system from correctly determining the position of the cutter in relation to the surface of the nail. 
     The device may incorporate a pressure activated switch  4  as in  FIG. 5  in order to prevent the device from being operated when not firmly pressed against the nail, where the applied load will help to prevent accidental motion in both the axial and horizontal planes i.e. less likely to slide across the surface of the nail. 
     The component in  FIG. 6 , also seen in  FIG. 5 , helps prevent the likelihood of the device slipping across the surface of the nail. 
     The device may be either activated by the depression of a button or upon the application of the required amount of load. 
     The control system may rotate the cutter and advance it into the nail at a constant feed rate until it is halted, e.g. using the drive mechanism  6  shown in  FIG. 5  and  FIG. 4 . 
     The control system may monitor the progress of the cutter as it is advanced through the nail in order to stop the cutter from advancing as it breaks through the nail thus preventing it from entering the nail bed below. 
     Various designs of cutter may be used (see some of the possible profiles shown in  FIG. 11 ) in order to make it easier to detect the point at which the cutter breaks through the nail and also reduce the likelihood of unwanted splinters or debris at the point of break out. 
     The control system may energise the motor in  FIG. 4  which rotates the cutter at a suitable rotational speed, for example between 1000 rpm and 100000 rpm. 
     The control system may energise the lead-screw motor  11  in order to advance the cutter towards the nail  1 . 
     The control system may monitor the progress of the cutter through the nail including stages 1 to 3 depicted in  FIG. 8 . 
     The control system may monitor any combination of the following signals in order to determine the progress of the cutter while it is advanced through the nail:— 
     The axial reaction force experienced by the cutter measured by the strain gauges  7  in  FIGS. 5 and 7  or the current flow through the resistor  9  in series with the motor  11  or a drop in speed in motor  11  powering the drive mechanism to advance the cutter in the axial direction; the reaction torque experienced by the cutter measured by the strain gauges  8  in  FIGS. 5 and 7  or the current flow through the resistor  10  in series with motor  5  rotating the cutter  6  or the power required to drive the motor rotating the cutter or the change in rotational speed of the cutter and/or the motor rotating the cutter. 
     The control system may be configured to stop advancing the cutter upon detecting the point at which the cutter breaks through the nail (stage 3 in  FIG. 8 ) by detecting the axial reaction force reducing below a pre-determined threshold as in  FIG. 9   a.    
     The control system may be configured to stop advancing the cutter upon detecting the point at which the cutter breaks through the nail (stage 3 in  FIG. 8 ) by detecting the reaction torque reducing below a pre-determined threshold as in  FIGS. 9 b    and  c.    
     The control system may be configured to stop advancing the cutter upon detecting the point at which the cutter breaks through the nail (stage 3 in  FIG. 8 ) by detecting a change in rotational speed of the cutter as in  FIG. 9   d.    
     Once the drill bit has cut to the desired depth it may be moved in a translational direction to produce a portal that is longitudinal in form such as a slot as in  FIG. 3 . 
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention relates to a fully automated device that drills through the nail in a controlled manner in order to prevent overrun of the drill  2  into the nail bed below. The device must be held in against the nail  1  (see  FIG. 1  and  FIG. 6 ) in a controlled manner in order to accurately track the progress of the cutter  2  through the nail  1  thus preventing it overrunning into the nail bed (see  FIG. 8  and  FIG. 9 ). When the device is first placed against the nail  1  the cutter  2  will not be in contact with the nail  1  (see  FIG. 6 ). Upon activation the cutter will start to rotate and will then be advanced in an axial direction towards the nail  1 . When the cutter makes contact with the nail  1  there will be a reaction force from the nail  1  in the axial direction and a reaction torque applied to the cutter. These forces can be measured using various sensors, for example; both forces could be measured by using strain gauges  7  and  8  to detect elastic deformation of a component  6  connected indirectly to the cutter as shown in  FIG. 5  and  FIG. 7 . Measuring these forces tells us about the mechanical properties of the material that the cutter  2  is in contact with. 
     The amount of energy required to rotate the cutter will depend upon the material that the cutter is passing through, i.e. significantly less energy will be required to rotate the cutter whilst it is rotating in free space, when compared to the amount of energy required to rotate the cutter as it is advanced through the nail  1 . The amount of energy required to rotate the cutter can be measured (e.g. by measuring the voltage drop across a resistor  10 ) or controlling the amount of power that is delivered to the motor  5  that drives the cutter. The same principle can also be used in order to measure the amount of energy required to advance the cutter e.g. by measuring the voltage drop across resistor  9  in series with motor  11  it is possible to determine the current drawn by motor  11  and thus determine the axial reaction force generated by the material being drilled. Possibly the simplest way to measure the mechanical properties of the material being drilled would be to measure the current drawn by the motor  5  when rotating the cutter and/or changes in the speed of rotation using a tachometer that is either separate or integral to the motor  5 . 
     As explained in the earlier paragraphs, measuring the forces required to drill through a material provides information about the mechanical properties of the material. As the nail  1  can be considered to be relatively uniform in its mechanical properties we can predict the force profiles that would be obtained by drilling through this material.  FIGS. 9 a  to  d    shows the force profiles that we would expect to see as the cutter  2  advances through the nail  1 . Drilling through a uniform material (such as the nail  1 ) may be divided into the following three distinct stages (as shown in  FIG. 8 ). As can be seen from  FIGS. 9 a  to  d    each stage can be identified by features in the force profiles. Stage  1  is when the drill (or cutter  2 ) starts to enter the material the force profiles rise sharply in line with the increased energy required to rotate the cutter. Stage  2  is while the drill (or cutter  2 ) is passing through the material and the force profile remains relatively constant. Stage  3  is the point at which the drill (or cutter  2 ) starts to break out of the material and where a sharp drop in the axial force can be seen. The same is torque also drops sharply once the cutter has broken out of the material, however this is often preceded by an initial increase in torque at the point of breakthrough (see  FIGS. 9 b, c  and  a   ). This information can be used to track the progress of the drill (or cutter  2 ) through the nail in order to stop the advancement of the drill (or cutter  2 ) at the point of breakthrough in order to prevent it entering the nail bed below. The nail bed contains lymph and blood vessels and is much softer than the nail which is constructed of primarily keratin. Consequently if the drill (or cutter  2 ) where to pass through the nail into the nail bed below the system can easily detect a change in the materials being drilled. 
     The actual signals that may be detected using the methods described in the previous paragraphs may contain noise or fluctuation creating a profile similar to that shown in  FIG. 10 a   . In order to make the system more reliable it may be necessary to filter the signal using a low-pass filter for example a Kalman filter. This will produce a smoother profile similar to the one shown in  FIG. 10   b.    
     As stages 1 and 3 are denoted by either a rapid increase or decrease in the forces measured these features may be more easily identified by measuring the first-order differential as in  FIG. 10 d   . The first-order differential may also need to be smoothed using a low pass filter (see  FIGS. 10 c  and  d   ). 
     There are a number of ways to detect the point at which the drill (or cutter  2 ) begins to break out of the material including setting a minimum threshold for the forces or the first-order differential of the forces. 
     Once the system has detected that the drill (or cutter  2 ) has broken through the material it will stop advancing the drill (or cutter  2 ) in order to prevent it from penetrating and damaging the nail bed below. At this point the cutter may either be retracted or remain at the same depth and transversely in order to produce a longitudinal slot in the nail (see  FIG. 3 ). 
     Once a suitable cutter  2  has perforated the nail to produce an access port, a suitable anti-fungal agent (for example a solution containing 1% Terbinafine) can be applied to the nail bed through the access port. The cutter may be used to apply the antifungal agent to the nail bed. If the cutter contains a spiral or helix portion (as in standard twist drill, slot or milling cutter designs) this will facilitate the removal of swarf while cutting. When rotated in the opposite direction the spiral or helix portion may be used to drive (or pump) anti-fungal agent through the nail to the nail bed. A vacuum device may also be incorporated in the device or used in conjunction with the device in order to remove debris that may cause cross-infection. 
     Reference is now made to  FIGS. 8 to 10  which are schematic representations of the stages of the cutter passing through the nail and the signals that may be used and processed in order to detect the point at which the cutter breaks through the nail in order to stop the cutter from advancing into the nail bed. 
     The axial reaction force may be measured by using strain gauges  7  to detect elastic deformation of a component applying force to advance the cutter as shown in  FIG. 5  and  FIG. 7 . 
     The axial reaction force may be measured by sensing the level of current required to advance the cutter using the motor  11  for the drive mechanism shown in  FIG. 5 . 
     The reaction torque may be measured by strain gauges to detect elastic deformation of a component  12  used to prevent the drive motor  11  for the drive mechanism from rotating as shown in  FIG. 5 . 
     The reaction torque may be measured by strain gauges  8  to detect elastic deformation of a component applying used to prevent the drive motor for the cutter from rotating as shown in  FIG. 5  and  FIG. 7 . 
     The reaction torque may be measured by sensing the level of current required drive the motor  5  that rotates the cutter  2  shown in  FIG. 5 . 
     The reaction torque may be measured by sensing the level of power required drive the motor  5  that rotates the cutter  2  shown in FIG. 
     The reaction torque may be measured by sensing the rotational speed of the motor  5  that rotates the cutter  2  or the cutter itself shown in  FIG. 5 . 
     The point at which the cutter breaks through the nail stage 3 in  FIG. 8  can be detected by the any of the cutting forces dropping below a threshold that is either pre-determined of calculated from measurements recorded during cutting as in  FIGS. 9 a    to  d.    
     The signals from the various methods of sensing the cutting forces may contain noise or erratic changes, making it difficult to detect the point at which the cutter breaks though the nail as shown in  FIGS. 10 b  and  c   . In this case a low pass filter may be used to smooth the signal and amplify the feature used to detect the point at which the cutter breaks through the nail see  FIGS. 10 a    and  d.    
     A low pass filter such as a Kalman filter may be used to smooth the signals obtained from various sensors. 
     The cutter may also cut or mill horizontally in order to produce a slot for example a slot cutter as used in a conventional vertical milling machine. Once the cutter has been advanced to the point of breaking through the nail without overrunning, the cutter can then be moved in a translational direction in order to produce a slot shaped aperture in the nail as in  FIG. 3  in order to facilitate better access to the nail bed for antifungal agents used to treat the Onychomycosis.