Abstract:
The present invention relates generally to a vascular access device having a septum positioned within a lumen of the device, the device further having a pusher for providing a fluid pathway through the septum. In particular, the present invention relates to systems and methods for improving flow of a fluid through the access device, while minimizing stagnation of fluids within the device. These systems and methods include various modified fluid pathways and interactions between the vascular access device body, the septum and the pusher.

Description:
RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 12/703,406, titled SYSTEMS AND METHODS FOR PROVIDNG A FLOW CONTROL VALVE FOR A MEDICAL DEVICE which was filed Feb. 10, 2010 and has now issued as U.S. Pat. No. 8,361,038, which claims the benefit of U.S. Provisional Patent Application Ser. No. 61/151,773 titled CATHETER VALVE ASSEMBLY, filed on Feb. 11, 2009. Both applications are incorporated herein in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     The present disclosure relates to fluid flow in extravascular systems used to provide infusion or other therapy to patients. Infusion therapy is one of the most common health care procedures. Hospitalized and home care patients receive fluids, pharmaceuticals, and blood products via a vascular access device inserted into the vascular system. Infusion therapy may be used to treat an infection, provide anesthesia or analgesia, provide nutritional support, treat cancerous growths, maintain blood pressure and heart rhythm, or many other clinically significant uses. 
     Infusion therapy is facilitated by vascular access devices located outside the vascular system of a patient. An extravascular system includes at least one vascular access device and/or other medical device that may access a patient&#39;s peripheral or central vasculature, either directly or indirectly. Vascular access devices include closed access devices, such as the BD Q-SYTETM closed Luer access device of Becton, Dickinson and Company; syringes; split access devices; catheters; and intravenous (IV) fluid chambers. An extravascular system may access a patient&#39;s vascular system for a short term (days), a moderate term (weeks), or a long term (months to years), and may be used for continuous infusion therapy or for intermittent therapy. 
     A common vascular access device is a plastic catheter that is inserted into a patient&#39;s vein. The catheter length may vary from a few centimeters for peripheral access to many centimeters for central access. The catheter may be inserted transcutaneously or may be surgically implanted beneath the patient&#39;s skin. The catheter, or any other vascular access device attached thereto, may have a single lumen or multiple lumens for infusion of many fluids simultaneously. 
     Although several techniques for placing such catheters are practiced in the art, many generally include the step of inserting at least a portion of the needle into the target vessel and then sliding the catheter over the needle into place. The medical worker attempts to verify proper placement of the catheter within the blood vessel. Catheter and introducer needle assemblies have been provided that include means for verifying proper placement of the catheter in a blood vessel such as a flashback chamber in the catheter hub or a notch in the introducer needle. 
     Once placement of the needle has been confirmed by the observation of flash, the user may temporarily occlude flow in the blood vessel at the catheter tip, remove the needle, leaving the catheter in place, and attach a device to the catheter for fluid removal, input, or to seal the catheter. This process has been somewhat difficult in practice since many placement sites simply do not allow easy occlusion of the target vessel. Additionally, even when such occlusion is achieved, it may be imperfect, thus resulting in blood leaking from the catheter, endangering the medical personnel employing it. 
     Catheter and introducer needle assemblies have thus been provided in the art that provide a variety of seals or valve mechanisms for preventing outflow of fluid during and following removal of the introducer needle. These structures are generally elastomeric plates designed to closely conform to the shape of a needle during storage and use to prevent leaking, then to seal upon removal of the needle. In an ideal vascular access device, the septum would continuously seal the patient&#39;s vascular system, which may include external vascular equipment intentionally coupled to the patient&#39;s internal vascular system by a medical practitioner, from the external environment. 
     Complications associated with infusion therapy include significant morbidity and even mortality. Such complications may be caused by regions of stagnant fluid flow within the vascular access device or nearby areas of the extravascular system. These are regions in which the flow of fluid is limited or non-existent due to the conformation of the septum or valve mechanism in the extravascular system or the fluid dynamics within that area of the extravascular system. Blood, air bubbles or infused medications may become trapped within these regions of stagnant flow as a result of the limited or non-existent fluid flow. When blood is trapped within the extravascular system bacteria can breed which can lead to infections. When a different medication is infused into the extravascular system, or the extravascular system is exposed to physical trauma, the extravascular system&#39;s fluid flow may become altered, releasing trapped air bubbles or residual medications back into the active fluid path of the extravascular system. This release of air bubbles and residual medication into the active fluid path extravascular system may result in significant complications. 
     Released air bubbles may block fluid flow through the extravascular system and prevent its proper functioning. More seriously, released air bubbles may enter the vascular system of the patient and block blood flow, causing tissue damage and even stroke. In addition, residual medications may interact with presently infused medications to cause precipitates within the extravascular system and prevent its proper functioning. Furthermore, residual medications may enter the vascular system of the patient and cause unintended and/or undesired effects. 
     Therefore the need exists for valve mechanisms in vascular access devices that eliminate, prevent, or limit regions of stagnant flow vascular access devices and extravascular systems to provide better flush properties. 
     SUMMARY OF THE INVENTION 
     The various embodiments of the present invention provide a number of flow control valve mechanisms which eliminate or reduce areas of low or no fluid flow occurring within a vascular access device. 
     According to one aspect, a vascular access device comprises a body including a first lumen extending therethrough and a flow control valve, including a septum, and a pusher having a distal end, a proximal end, an outer surface, a second lumen therethrough, and at least one flow channel. 
     According to another aspect, a vascular access device comprises a body including a first lumen extending therethrough and a flow control valve, including a septum, a pusher having a distal end, a proximal end, an outer surface, a second lumen therethrough, and at least one rib. 
     These and other features and advantages of the present disclosure may be incorporated into vascular access devices and will become more fully apparent from the following description and appended claims, or may be learned by the practice and implementation of the present disclosure. As described above, the present disclosure does not require that all of the features described herein be incorporated into every embodiment nor is it required that certain features be used exclusive of other features. Vascular access devices within the scope of the present disclosure may include one or more combinations of the features described herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross section view of an indwelling catheter having a prior art flow control valve mechanism. 
         FIG. 2  is a cross section view of the indwelling catheter having a prior art flow control valve mechanism of  FIG. 1  with a needle removed. 
         FIG. 3  is a cross section view of the indwelling catheter having a prior art flow control valve mechanism of  FIG. 2  with a connector from a vascular access device connected thereto. 
         FIG. 4  is a perspective view of a pusher, according to an embodiment of the invention. 
         FIG. 5  is a cross section view of a catheter body having the flow control valve mechanism according to the embodiment shown in  FIG. 4 , with the pusher in the proximal position. 
         FIG. 6  is a cross section view of a catheter body having a flow control valve mechanism according to the embodiment shown in  FIG. 4 , with the pusher in the distal position. 
         FIG. 7  is a perspective view of a pusher, according to an embodiment of the invention. 
         FIG. 8  is a perspective view of a catheter body having a flow control valve mechanism according to the embodiment shown in  FIG. 7 , with the pusher in the distal position. 
         FIG. 9  is a cross section view of a catheter body having a flow control valve mechanism according to the embodiment shown in  FIG. 7 , with the pusher in the distal position. 
         FIG. 10  is a cross section view of a catheter body having a flow control valve mechanism according to an embodiment of the invention, with the pusher in the proximal position. 
         FIG. 11  is a cross section view of a catheter body having a flow control valve mechanism according to an embodiment of the invention. 
         FIG. 12  is a perspective view of a pusher, according to an embodiment of the invention. 
         FIG. 13  is a perspective view of a catheter body having a flow control valve mechanism according to the embodiment shown in  FIG. 12 , with the pusher in the distal position. 
         FIG. 14  is a perspective view of a septum, according to an embodiment of the invention. 
         FIG. 15  is a cross section view of a septum, according to the embodiment shown in  FIG. 14 . 
         FIG. 16  is a perspective view of a pusher, according to an embodiment of the invention. 
         FIG. 17  is a perspective view of a catheter body having a flow control valve mechanism according to the embodiment shown in  FIG. 16 , with the pusher in the proximal position. 
         FIG. 18  is a perspective view of a catheter body having a flow control valve mechanism according to the embodiment shown in  FIG. 16 , with the pusher in the distal position. 
         FIG. 19  is a cross section view of a pusher, according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     It will be readily understood that the components of the present disclosure, as generally described and illustrated in the figures herein, could be arranged and designed in a wide variety of different configurations. Although the embodiments of this invention are described herein in connection with an IV catheter, it is to be understood that this invention is applicable to other catheters. For example, this invention is applicable to standard peripheral IV catheters, extended dwelling catheters requiring the needle to be connected to the needle hub by a stylet as well as other medical devices where it is desirable to include a septum to regulate the flow of fluid into or out of a space. Thus, the following more detailed description, as represented in the figures, is not intended to limit the scope of the disclosure, but is merely a representative of exemplary combinations of the components. 
     The term “proximal” is used to denote a portion of a device which, during normal use, is nearest the user and furthest from the patient. The term “distal” is used to denote a portion of a device which, during normal use, is farthest from the user wielding the device and closest to the patient. The term “activation” of a valve mechanism is used to denote the action of opening or closing of such a valve. 
     An example of a prior art extravascular system is disclosed in U.S. Pat. No. 7,008,404 and shown in  FIGS. 1 to 3 . An indwelling catheter has, as shown in  FIG. 1 , a hollow catheter body  1 , a catheter  2  fitted into a holder  1   b  provided at a distal end of the catheter body  1 , a septum  3  fitted inside the catheter body  1 , and a hollow pusher  4  slidably fitted inside the catheter body  1 . The catheter tube  2 , septum  3 , and the pusher  4  are coaxially aligned in this order. 
     The catheter body  1  has a tubular shape. The inner surface  1   a  of the catheter body lumen is tapered toward the distal end, with a gradually reduced diameter. The catheter body  1  is preferably of a transparent or semi-transparent material so as to show the interior, enabling checking of movement inside. Suitable materials for catheter body  1  include, but are not limited to, thermoplastic polymeric resins such as polycarbonate, polystyrene, polypropylene and the like. 
     The catheter  2  is press-fitted into the tube holder  1   b  which communicates at its proximal end with the inside of the catheter body  1 . It is preferred that a lubricating coating is provided to the entirety or part of the catheter  2  so as to reduce resistance caused by insertion through skin or into a blood vessel. Suitable materials for catheter  2  include, but are not limited to, thermoplastic resins such as fluorinated ethylene propylene (FEP), polytetrafluoroethylene (PTFE), polyurethane and the like. Preferably, catheter  2  is formed from a thermoplastic hydrophilic polyurethane that softens with exposure to physiological conditions present in the patient&#39;s body. 
     The septum  3  is of a generally tubular shape having a proximal end  8  and a membrane section  9  having a planar flat surface located at the distal end  11 . Typically, septum  3  further includes a single needle slit  3   a  or valve aperture located about the centre of membrane section  9 , extending through membrane section  9 , to facilitate penetration of septum  3  by introducer needle  5  having a needle tip  5   a . The opposing slit surfaces of the needle slit  3   a  are designed to closely conform to the shape of introducer needle  5  during storage and prevent an outflow of fluid during and following removal of the introducer needle  5 , then to seal upon removal of the introducer needle  5 . With the pusher  4  inserted therethrough, slit  3   a  expands forward in the distal direction and opens, providing fluid communication between the catheter  2  and the rear of the catheter body  1 . An annular protrusion  3   b  is provided on the inner surface of a rear opening of the septum  3 , to engage shoulder  4   c  at the distal end of the pusher  4  so as to limit the movement of pusher  4  in the proximal direction and prevent the dislocation of the pusher  4  from septum  3 . A plurality of gaps  3   c  are defined between an outer periphery of the septum  3  and the inner surface  1   a  of the catheter body  1 . Distal and proximal spaces divided by the septum  3  communicate with each other through the gaps  3   c . Thus the septum  3  slides smoothly with air passing through the gaps  3   c.    
     The pusher  4  is typically made from a rigid thermoplastic material or a like material, and has a lumen  7  extending therethrough. The pusher  4  has a tubular portion  4   a , a conical flange  4   b  connected to the rear proximal end of the tubular portion  4   a , and a shoulder  4   c  protruding from an outer periphery of the tubular portion  4   a . Thus, an annular shaped interstitial space is created between tubular portion  4   a  and the inner surface  1   a  of the catheter body  1 . The distal front end of the tubular portion  4   a  is chamfered to facilitate its penetration into slit  3   a  of the septum  3 , and is slidably supported by the annular protrusion  3   b  of the septum  3 . The conical flange  4   b  has a conical inner surface so as to facilitate insertion of the needle  5  thereinto. The peripheral surface of the flange  4   b  contacts the inner surface  1   a  of the catheter body  1  and serves to provide stability to the pusher  4  and maintain the coaxial position with respect to the catheter  2 . However the peripheral surface of the flange  4   b  does not form a fluid seal with inner surface  1   a.    
     The indwelling catheter is prepared for use in such a state as shown in  FIG. 1  with the front end of the needle  5  protruding from the front end of the catheter  2 . In this state, the needle  5  penetrates through the septum  3 , providing water-tight connection therebetween, and thereby prevents blood leakage. 
     The indwelling catheter in this state is inserted into the body of a patient. Then, as shown in  FIG. 2 , the needle  5  is removed with the tube  2  retained in the body of the patient. Septum  3  maintains a fluid seal upon removal of needle  5 , being retained by an annular protrusion  1   e  and a cavity edge  1   d . Pusher  4  is retained in a proximal position by the interaction of annular protrusion  3   b  and shoulder  4   c.    
     A connector  6  (e.g. a luer connector) of a vascular access device is then inserted from the proximal end of the catheter body  1 . When pressed into the catheter body  1 , the connector  6  pushes at its distal end the pusher  4 . The pusher  4  thus slides forward in distal direction to press the slit  3   a  of the septum  3  open, thereby activating the flow control valve to the open position. Septum  3  is then pressed against the inner surface of a tapered cavity  1   c  of the catheter body  1  which stops the forward movement of the pusher  4  at a distal position as shown in  FIG. 3 , thus providing communication between the catheter  2  and the vascular access device via the lumen  7  of the pusher  4 . The tapered inner surface  1   a  of the catheter body  1  allows for smooth insertion of the connector  6  and tight contact between an outer surface  6   a  of the connector  6  and the inner surface  1   a  through press fitting in order to prevent fluid leaking out of the proximal end of catheter body  1 . 
     However, it should be noted that this valve mechanism has problems in regard to fluid flow and flush properties. First, fluid flow will follow the path of least resistance and in the valve mechanism shown in  FIGS. 1 to 3  the majority of the fluid flow occurs through lumen  7  of pusher  4  as this is the largest opening. This results in a stable laminar fluid flow (with minimal fluid turbulence) through the valve mechanism which causes the highest degree of flow to occur at the center of lumen  7  and the center of the lumen in the catheter body  1  and the lowest degree of fluid flow to occur at the periphery of the lumen of catheter body  1 . Thus areas of low or no fluid flow can occur for example at the inner surface of tapered cavity  1   c  of the catheter body  1  near the distal face of septum  3 , which makes it difficult to subsequently flush out any blood, medicament or air bubbles which may flow into this area during use of the catheter. Second, the valve mechanism of  FIGS. 1 to 3  has small interstitial spaces/areas within the catheter body  1  into which fluids can flow during use, which give rise to areas of low or no fluid flow. For example, in use fluid can flow between the peripheral surface of the flange  4   b  and the inner surface  1   a  of catheter body  1  and into interstitial space  98  between the outer periphery of tubular portion  4   a  and the inner surface  1   a . Third, fluid can flow into interstitial space  99  which is gap  3   c  between the outer periphery of septum  3  and the inner surface  1   a  of the catheter body  1 . Any fluid present in spaces/areas  98  and  99  is essentially trapped (by septum  3 ) as there is no easy flow path out of these areas for the fluid to rejoin the main fluid flow. This makes it very difficult to subsequently flush out any blood, medicament or air bubbles which may flow into these areas  98  and  99  during use of the catheter. 
     A number of valves mechanisms in accordance with various embodiments of the subject invention which improve the flush properties and eliminate or reduce areas of low or no fluid flow occurring within a vascular access device containing a valve mechanism are illustrated in  FIGS. 4 to 19 . 
       FIGS. 4 to 6  show an embodiment of a balanced flow pusher  44  is used to equalize fluid flow evenly both through and around the proximal end of pusher  44 . This provides a balanced fluid flow path and better fluid turbulence thus reducing low or no flow fluid areas in order to remove any residual blood from the flashback, aspiration, blood draws. 
       FIG. 4  shows a pusher  44  having a distal end  45  and a proximal end  46  with a lumen  47  extending therebetween. Flow ports  48  are located at the proximal end  46  of pusher  44 , with ribs  49  extending longitudinally along and evenly spaced around the outer surface  54  of pusher  44  to form flow channels  50 . Inlet ports  51  are located at the distal end of the flow channels  50  and extend through the side wall of pusher  44 .  FIG. 5  shows septum  43 , which forms a fluid seal in the lumen  42  of catheter body  41  after removal of the needle, with pusher  44  in the proximal position.  FIG. 6  shows pusher  44  in the distal position, in which a fluid flowing in distal direction from the proximal end of catheter body  41  can be diverted by four flow ports  48  between the periphery  52  of the proximal end  46  of pusher  44  and the inner surface  53  of lumen  42 , along the flow channels  50  and returns to the lumen  47  via four inlet ports  51  equally distributed around the circumference of lumen  47 . Septum  43  has a taper  55  on the inner surface to help provide a clear fluid flow path around the outer surface  54  of pusher  44  into the inlet ports  51 . Thus, a fluid flow approaching the proximal end  46  of pusher  44  in the distal direction is equally divided, such that a fluid has an equal likelihood of entering the proximal end  46  of lumen  47  of pusher  44  or flowing around the outer surface  54  of pusher  44  before rejoining lumen  47  via inlet ports  51 . Thus, the flush properties of this valve mechanism are superior to that of the valve mechanism shown in  FIGS. 1 to 3  as there is high fluid flow in the interstitial space  56  between the outer surface  54  of pusher  44  and the inner surface  53  of lumen  42 . Additionally, turbulent flow is created within lumen  47  at the confluence of the fluid streams from inlet ports  51 . 
       FIGS. 7 to 9  show another embodiment of the invention having valve mechanism similar to that shown in  FIGS. 4 to 6  which differs by the use of helical flow paths around the outside of the pusher to facilitate a complete flush.  FIG. 7  shows a pusher  74  having a distal end  75  and a proximal end  76  with a lumen  77  extending therebetween. Ribs  79  begin at the proximal end  76  of pusher  74 , extending helically along and evenly spaced around the outer surface  54  of pusher  74  to form helical flow channels  80 . Inlet ports  81  are located at the distal end of the helical flow channels  80  and extend through the side wall of pusher  74 .  FIGS. 7 to 9  show pusher  74  in the distal position in which fluid can flow either via the lumen  77  of pusher  74  or through the helical channels  80  in the outer surface  54  of pusher  44 . Fluid flowing in distal direction from the proximal end of catheter body  41  enters the helical flow channels at the proximal end  76  of pusher  74  and flows along the flow channels  80  and returns to the lumen  77  by four inlet ports  81  equally distributed around the circumference of lumen  77 . Septum  73  can also have a taper  85  on the inner surface to mate with a corresponding taper  87  around the outer surface  54  of pusher  74  in order to keep interstitial spaces to a minimum. The use of helical flow channels causes a faster flow rate and a more turbulent flow when compared to a pusher of the same design with straight longitudinal flow channels. 
       FIG. 10  shows another embodiment of a valve mechanism with helical flow channels  80   a  on the outer surface  84   a  of pusher  74   a  similar to the embodiment shown in  FIGS. 7 to 9 . However on removal of the introducer needle a hinged flow deflector  88  is deployed at the proximal end  76   a  of pusher  74   a  to restrict or prevent fluid flow through the lumen  77   a  and divert the majority of fluid flow through the helical flow channels  80   a . In addition, there are two inlet ports  81   a  each of which is approximately quarter of the circumference of the lumen  77   a  located at the distal end of the helical flow channels  80   a . Furthermore septum  73   a  has a flared face  85   a  on the inner proximal surface to help direct fluid flow into the inlet ports  81   a.    
       FIG. 11  shows a further embodiment of a valve mechanism with helical or spiral flow channels. This is a one-piece valve mechanism which only includes a septum and does not use a pusher. The only fluid path in this valve mechanism would be the helical flow channels  104  on the outer surface  105  of the septum  103  which would allow air to escape, minimal blood to escape and then allow for infusion to take place. Slit  109  extends through the septum to facilitate insertion of the introducer needle but forms a fluid seal after the removal of the introducer needle. Septum  103  is retained in position by the combination of taper  106  and annular protrusion  107  of the catheter body lumen  102 . It should be noted that the total cross-sectional area of helical flow channels  104  must substantially equal the combined cross-sectional areas of lumen  77  and helical flow channels  80  as shown in the embodiment of  FIGS. 7 to 9  as the total fluid flow cross-sectional area must be large enough to prevent a significant flow restriction or pressure build up. 
       FIGS. 12 and 13  show an embodiment of a valve mechanism in which the presence of ribs  29  on the outer surface  34  of pusher  24  allows a parallel coaxial fluid flow to occur both through lumen  27  and between the outer surface  34  of pusher  24  and septum  23 .  FIG. 13  shows the pusher  24  of  FIG. 12  having a distal end  25  and a proximal end  26  with a lumen  27  extending therebetween. Ribs  29  emanate from the distal end  25  of pusher  24 , extending along and evenly spaced around the outer surface  34  of pusher  24  to form flow channels  30 , and continue past proximal end  26  to provide contact points for a luer connector  39  to act on. Septum  23  is deflected by ribs  29  at the distal end  25  of pusher  24 , on reaching distal position. Ribs  29  therefore prevent a radial seal from forming between the outer surface  34  of pusher  24  and septum  23 , thus fluid can flow past the septum  23  along flow channels  30  as well as through lumen  27  of pusher  24 . 
       FIGS. 14 and 15  show an alternate embodiment to valve mechanism show in  FIGS. 11 to 13  in which ribs  29   a  are on the proximal face of membrane section  31  of septum  23   a  instead of the outer surface of pusher. 
       FIGS. 16 to 18  show an embodiment of a valve mechanism which gives high flushability due to the openness of the pusher design, and the reversal of the septum orientation. Pusher  114  includes ribs  132  that act as a spacer between a luer connector  119  and lumen  117  to provide sufficient axial length for the fluid flow to spread out from the tip of the luer connector  119  and direct a large portion of the flow through space  126  between pusher  114  and the inner wall  123  of catheter body  111 . Fenestrations or longitudinal slots  121  through the sidewall  130  of the pusher  114  allow flushing fluid to reenter the lumen  117  of the pusher  114  while bypassing the septum  113  when pusher  114  is in the distal position (as shown in  FIG. 18 ), then also allow some flow to circulate back out of the pusher  114  to clean the downstream distal side of the septum  113 . Ribs  132  interact with undercut  131  in the inner wall  113  of catheter body  111  to retain pusher  114  in the proximal position and with septum  113  to retain pusher  114  in the distal position. The septum  113  is of a generally tubular shape and has the sealing membrane section  119  located at the proximal end  134  instead of the distal end  133  as in a typical septum. This reversed orientation of the membrane section provides a less restrictive flow path as the septum  113  does not enclose the distal end  135  of pusher  114 . 
       FIG. 19  show a further embodiment of a valve mechanism which incorporates an elastomeric stopper  141  to the distal end of pusher  114   a  to provide a flow restriction to lumen  117   a  after the needle is removed and force a portion of the flushing fluid to pass along the outside of the pusher  114   a , cleaning out any blood or infusant. The balance of the relative flow rate inside lumen  117   a  and outside of pusher  114   a  can be controlled by addition and size of a hole  142  in stopper  141  or degree of occlusion of lumen  117   a  by stopper  141 . 
     Any septum described herein may have a hole present in the center of membrane section sized to produce a specified blood leakage rate if so desired and may be made of a variety of suitable materials and through a variety of suitable manufacturing methods. For example, the septum may be formed from liquid silicone rubber through suitable molding procedures, such as insert molding, injection molding, other molding techniques, or a combination of molding techniques. The septum  103 , or any septum described herein, may also include a coating of antimicrobial substance on any of its surfaces, especially those surfaces which have contact with fluid. 
     Although illustrative embodiments of the present invention have been described herein with reference to the examples, it is to be understood that the invention is not limited to those precise embodiments, and that various other changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention.