Patent Publication Number: US-2020289106-A1

Title: Retraction devices and methods of its use and manufacture

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This continuation application claims priority to and the benefit of U.S. patent application Ser. No. 15/993,771, filed May 31, 2018, and titled RETRACTION DEVICES AND METHODS OF ITS USE AND MANUFACTURE, which claims priority to and the benefit of U.S. patent application Ser. No. 14/604,686 (now U.S. Pat. No. 9,999,414, which issued on Jun. 19, 2018), filed Jan. 24, 2015, and titled RETRACTION DEVICES AND METHODS OF ITS USE AND MANUFACTURE, which claims priority to and the benefit of U.S. Provisional Patent Application No. 61/931,218, filed Jan. 24, 2014 and titled RIB RETRACTOR; the disclosure of which are incorporated herein by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     The presently disclosed subject matter relates to medical device systems and methods of making and using the systems. Particularly, the present subject matter relates to retraction devices for separating ribs for thoracic surgeries, as well as methods of making and using the retraction devices. 
     BACKGROUND 
     For treating a medical condition, such as a diseased tissue present in an esophageal or spinal tumor, a failing heart valve, or cancerous lungs, surgeons may need to gain direct access to a thoracic cavity of a patient to perform surgery. Typically, surgeons gain access by performing open-chest procedures where the patient&#39;s sternum is split and separated for organ exposure. While this technique has provided surgeons with sufficient visualization of target organs in the thorax, it is extremely invasive and can cause the patient to suffer through a painful and prolonged post-surgical recovery. 
     There exist some minimally invasive techniques for thoracic access that are less disruptive to a patient&#39;s body. Thoracotomy procedure is one of the minimally invasive techniques that is widely performed on hundreds of thousands of people each year worldwide. In a thoracotomy procedure, the surgeon gains access to the inner thoracic cavity by physically separating the patient&#39;s ribs to create an opening into the thorax through which tools and video scopes can be passed through during the surgery. To perform the thoracotomy procedure, the surgeon may make a lateral skin incision on the patient&#39;s torso to expose the underlying chest wall. Subsequently, the surgeon may laterally cut the intercostal muscle or remove it from one of the ribs to create a space between the ribs that can be opened physically with a thoracic retraction device. Once the retraction device is installed in the incision, the surgeon can manually open the space using the hand-operated retraction device. The most common opening mechanism includes a Finochietto rack-and-pinion gear system that retracts the blades a fixed incremental distance per handle turn. 
     These retractors, which are also used for sternotomies have been successful in creating visual access for the surgeons but have always been the primary source for significant pain and complications that nearly half of all thoracotomy patients experience for months after their procedures. A neurovascular bundle in humans and large mammals runs along the bottom edge of each rib. Disturbance and damage to the intercostal nerve is nearly inevitable in every thoracotomy procedure and physical compression of the intercostal nerve by retractors is the leading cause of patients to experience painful breathing for a significant period of time after the surgery. 
     The tissue engaging structures, referred to as blades, for typical thoracic retraction devices (or retractors) are typically constructed of surgical grade stainless steel. The blades of these retractor usually have a flat planar surface, which can be continuous or fenestrated. When the flat blades press against the intercostal tissue during retraction, high concentrations of mechanical stress occur at the distal ends of the metal blade. At these distal ends of the blade, the tissue pivots and bends over the middle surface of the blade. The concentration of stress at the distal ends of the blades can be so great that not only does the intercostal nerve get crushed at these local points, but the patient may experience one or more rib fracturing at these same points. The negative consequences of this problem are not only felt by the patients. The significant nerve damage and rib fractures that the patients experience can be detrimental to the cost-saving interests of the hospitals during the acute phase of the cycle of care for the patients. 
     In view of the foregoing, there is a need for improved retraction devices and methods. 
     SUMMARY 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. 
     Disclosed herein are the embodiments of a retraction device that may include retractor blades. The retraction device may be designed to engage patient tissue with a flexible material that may minimize maximum forces exerted on the patients&#39; tissues and bones by increasing the contact surface area between the retractor blades and tissue, independent of the patient&#39;s unique anatomical intercostal features. The minimization of local stresses applied to the patient&#39;s tissues during thoracic retraction in turn may reduce surgical damage to the patient&#39;s intercostal and inter-sternal tissue. A flexible blade may be pressed against intercostal tissue and the blade may change shape to match a radius of curvature of the tissue that is being displaced. The retraction device may further be designed with an area moment of inertia and modulus of elasticity in mind to account for the engagement of more than one type of tissue in a single instance. 
     An embodiment of the present disclosure provides a retraction device having a first frame portion and a second frame portion. The second frame portion may be attached to the first frame portion. The second frame portion may mechanically move between a first position and a second position with respect to the first frame portion. The retraction device may also include a first blade being pivotally attached to the first frame portion and may include a flexible material. The retraction device may also include a second blade being pivotally attached to the second frame portion and may include a flexible material. 
     Another embodiment of the present disclosure provides a retraction device including a first frame portion including a proximal end and a distal end. The first frame portion may define a number of teeth extending between the proximal end and the distal end. The retraction device may also include a second frame portion being attached to and mechanically movable between a first position and a second position with respect to the first frame portion. The retraction device may also include a first blade pivotally attached to the first frame portion. The first blade may include a flexible material. The retraction device may further include a second blade pivotally attached to the second frame portion. The second blade may include a flexible material. The retraction device may further include a lever and gear mechanism attached to the second frame portion. The lever and gear mechanism may be configured to engage the teeth for moving the second frame portion between the first position and the second position. The retraction device may also include a multiple drive system operably engaged with the lever and gear mechanism. The multiple drive system may be configured to control the lever and gear mechanism in at least two different speeds for displacement rates per full rotation of the lever. 
     A further embodiment of the present disclosure provides a retraction device including a first frame portion and a second frame portion being attached to the first frame portion. The second frame portion is mechanically movable between a first position and a second position with respect to the first frame portion. The retraction device may also include a first blade being pivotally attached to the first frame portion and defining a surface having a locking structure. The retraction device may also include a second blade being pivotally attached to the second frame portion and defining a surface having a locking structure. The surfaces of the first and second blade may face each other. The locking structures can interlock with one another to prevent pivoting of the first blade and second blade when the surfaces are brought into proximity with one another. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following drawings. In the drawings, like reference numerals refer to like parts throughout the various figures unless otherwise specified. 
       For a better understanding of the present invention, reference will be made to the following Detailed Description, which is to be read in association with the accompanying drawings, wherein: 
         FIG. 1A  is a perspective view of an exemplary retraction device according to an embodiment of the present disclosure; 
         FIG. 1B  is a schematic side view of the exemplary retraction device of  FIG. 1  according to an embodiment of the present disclosure; 
         FIG. 2A  is a schematic view of a portion of a first blade of the retraction device of  FIGS. 1A-1B  according to an embodiment of the present disclosure; 
         FIG. 2B  is a schematic view of a portion of a second blade of the retraction device of  FIGS. 1A-1B  according to an embodiment of the present disclosure; 
         FIG. 3A  is a schematic zoomed view of the first blade of the retraction device of  FIGS. 1A-1B  according to an embodiment of the present disclosure; 
         FIG. 3B  is a schematic zoomed view of the second blade of the retraction device according to an embodiment of the present disclosure; 
         FIG. 4  is a schematic zoomed view of the first blade and the second blade of the retraction device in an interlocked configuration according to an embodiment of the present disclosure; 
         FIG. 5A  is a schematic side view of the second blade according to an embodiment of the present disclosure; 
         FIG. 5B  is a schematic side view of the first blade and the second blade of the retraction device of  FIGS. 1A-1B  in the interlocked configuration according to an embodiment of the present disclosure; 
         FIG. 6  is a perspective view of an exemplary blade of a retraction device according to an embodiment of the present disclosure; 
         FIG. 7  is a perspective view of another exemplary blade according to another embodiment of the present disclosure; 
         FIG. 8  is a perspective view of another exemplary blade according to another embodiment of the present disclosure; 
         FIG. 9  is a schematic view illustrating a use of a retraction device for performing a medical procedure according to an embodiment of the present disclosure; 
         FIG. 10  is a perspective view of an exemplary lever and gear mechanism (or multiple drive opening mechanism) including at least two circular gears of a retraction device according to an embodiment of the present disclosure; 
         FIG. 11  is a zoomed cross-sectional view of an exemplary worm gear mechanism of an exemplary multiple drive opening mechanism of a retraction device according to an embodiment of the present disclosure; 
         FIG. 12  is a perspective view of an exemplary retraction device containing a multiple drive worm gear mechanism and the retractor frame extension attachment (or a third frame portion) according to an embodiment of the present disclosure; 
         FIG. 13  is a graph depicting the distribution of retraction forces collected along a pig&#39;s rib using the recording instrumentation previously described at a 40.00 mm thoracotomy retraction distance using the Finochietto retractor; and 
         FIG. 14  shows the retraction force distribution during a thoracotomy performed on a pig with the prototyped retractor blade, such as blades according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The presently disclosed subject matter is described with specificity to meet statutory requirements. However, the description itself is not intended to limit the scope of this patent. Rather, the inventors have contemplated that the claimed subject matter might also be embodied in other ways, to include different steps or elements similar to the ones described in this document, in conjunction with other present or future technologies. Moreover, although the term “step” may be used herein to connote different aspects of methods employed, the term should not be interpreted as implying any particular order among or between various steps herein disclosed unless and except when the order of individual steps is explicitly described. 
     Reference throughout this specification to “a select embodiment,” “one embodiment,” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosed subject matter. Thus, appearances of the phrases “a select embodiment,” “in one embodiment,” or “in an embodiment” in various places throughout this specification are not necessarily referring to the same embodiment. 
     Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, to provide a thorough understanding of embodiments of the disclosed subject matter. One skilled in the relevant art will recognize, however, that the disclosed subject matter can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the disclosed subject matter. 
     All numeric values are herein assumed to be modified by the term “about,” whether or not explicitly indicated. The term “about” generally refers to a range of numbers that one of skill in the art would consider equivalent to the recited value (i.e., having the same or substantially the same function or result). In many instances, the terms “about” may include numbers that are rounded to the nearest significant figure. 
     The recitation of numerical ranges by endpoints includes all numbers within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5). 
     As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include or otherwise refer to singular as well as plural referents, unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed to include “and/or,” unless the content clearly dictates otherwise. 
     The following detailed description should be read with reference to the drawings, in which similar elements in different drawings are identified with the same reference numbers. The drawings, which are not necessarily to scale, depict illustrative embodiments and are not intended to limit the scope of the disclosure. 
     Embodiments of the present disclosure provides a rib retraction device or rib retractor that may be designed to engage patient&#39;s tissue in a way that minimizes maximum pressure exerted on the patients&#39; tissues and bones by increasing a contact surface area between retractor blades and the tissue. The minimization of maximum pressure applied to the patient&#39;s tissues during thoracic retraction may in turn reduce surgical damage to the patient&#39;s intercostal and intrasternal tissue. Damage to the intercostal nerve bundle and rib fractures are major contributors to post-surgical chronic pain that many patients experience after thoracotomies. Many of the rib fractures that occur are due to application of highly concentrated pressure points on the distal edges of the currently used stainless steel retractor blades. 
     The minimization of maximum forces exerted on the patient&#39;s tissue may be achieved by distributing the applied force to the patient&#39;s body in the lateral direction by increasing the contact surface area between the retractor blade and tissue. The distribution of the applied forces between the patient&#39;s tissue and the retractor blade contact surfaces prevents highly concentrated forces from being applied to the patient&#39;s body. 
       FIG. 1A  is a perspective view  100 A of an exemplary retraction device  102  according to an embodiment of the present disclosure. The retraction device  102  may include a first frame portion  104  and a second frame portion  106 . The first frame portion  104  may also include a proximal end  124  and a distal end  126 . The first frame portion  104  may define multiple teeth  122  extending between the proximal end  124  and the distal end  126 . Further, the second frame portion  106  may be attached to the first frame portion  104 . The second frame portion  106  may be configured to move between a first position and a second position with respect to the first frame portion  104 .  FIG. 1A  shows the retraction device  102  where the second frame portion is in the first position. Further, the first frame portion  104  and the second frame portion  106  may be formed using a rigid material such as, but not limited to, medical grade stainless steels, biocompatible polymer plastics, rigid fiber composites, and the like. In some embodiments, the first frame portion  104  and the second frame portion  106  includes sterilizable material. 
     The retraction device  102  may further include a first blade  108 A attached to the first frame portion  104 . The first blade  108 A may include a flexible material, which may allow flexible movement of the first blade  108 A. The retraction device  102  may also include a second blade  108 B pivotally attached to the second frame portion  106 . The second blade  108 B may include a flexible material, which may allow flexible movement of the second blade  108 B. In some embodiments, the rigid material of the first frame portion  104  and the second frame portion  106  may have a flexural stiffness that resists deformation under normal retraction forces. The frame portions  104  and  106  may be made of stainless steel or another material with having a modulus of elasticity of about 190 GPa. Further, the first blade  108 A and the second blade  108 B may be configured to apply spreading forces on the ribs or one or more tissues of a patient. In some embodiments, the first blade  108 A and the second blade  108 B are configured to apply spreading forces between a range of 0 and 300 pounds. 
     In further embodiments, each of the first blade  108 A and the second blade  108 B may include a flexible component. The flexible component of the first blade  108 A may be pivotally attached to the first frame portion  104 . Similarly, the flexible component of the second blade  108 B may be pivotally attached to the second frame portion  106 . The flexible component of the first blade  108 A may have a first surface  110 A and a second surface  112 A. Similarly, the flexible component of the second blade  108 B may have a first surface  110 B and a second surface  112 B. The first surfaces  110 A- 110 B may substantially oppose the second surfaces  112 A- 112 B, respectively. The first surface  110 A of the first flexible component of the first blade  108 A may face the first surface  110 B of the second flexible component of the second blade  108 B. Further, each of the first surfaces  110 A- 110 B may include a locking structure. The locking structures may interlock with one another to prevent pivoting of the first blade  108 A and the second blade  108 B when the first surfaces  110 A- 110 B are brought into proximity with one another. The locking structures may be in the form of a pin or tab, which can be manually toggled or actuated to permit rotational movement. In some embodiments, the locking structure can be provided on one or both of the blades  108 A- 108 B. 
     Further, the first blade  108 A may include a padding material  114 A attached to the second surface  112 A of the first blade  108 A. Similarly, the second blade  108 B may include a padding material  114 B attached to the second surface  112 B of the second blade  108 B. 
     In some embodiments, the first blade  108 A is removably attached to the first frame portion  104 , and the second blade  108 B is removably attached to the second frame portion  106 . In an example, the thickness of the blade may be between just over 0 mm and 10 mm, or between about 2 mm and about 4 mm. In an example, the length of a blade may be between about 55 mm and about 65 mm and the width of the blade may be between 25 mm and 35 mm. 
     Each of the first blade  108 A and the second blade  108 B may define at least one edge  116 A- 116 B, respectively. Each of the edges  116 A- 116 B may include ridges, such as ridges  118  on the edge  116 B, for gripping the one or more tissues. The ridges (such as ridges  118 ) are segmented along a length of the at least one edge  116 A- 116 B for allowing flexure of the respective first blade  108 A or the second blade  108 B. In some embodiments, the first blade  108 A and the second blade  108 B are rotatable. 
     The padding materials  114 A- 114 B of blades  108 A- 108 B can allow for conforming to small irregularities in the rib bone. The edges  116 A- 116 B may be curved edges. Each of the edges  116 A- 116 B may include a silicone lip curvature to help to stabilize the retraction device  102  in the patient&#39;s body along the z-axis. This may help the first and second blades  108 A- 108 B to stay in position between the ribs or sternum. 
     As shown, the retraction device  102  may also include a lever and gear mechanism  120  (or a gear device  120 ) attached to the second frame portion  106 . The lever and gear mechanism  120  may be configured to engage the teeth  122  for moving the second frame portion  106  between the first position and the second position. 
     In some embodiments, a multiple gear mechanism is provided described in detail with reference to  FIGS. 10-11 . For example, the retraction device  102  can include a variable number of gears per unit length of the frame portions  104 - 106  to generate a more gradual opening of the chest per turn of the opening mechanism. This can be accomplished by having smaller gaps between the teeth  122  as the first frame portion  104  moves along the length of the retraction device  102 . The multiple gear mechanism may be able to provide retraction speeds from 0 to 20 mm per handle rotation. Other example speeds are about 7.5 mm and about 15 mm per handle rotation. 
     In the embodiment, the handle  128  is provided on the retraction device  102  for allowing the surgeon to adjust down the rate at which the tissue is separated by pushing or pulling the handle and changing the diameter of the gear that moves down the frame portions  104 - 106 . This can be accomplished by having a first conical gear structure, connected to a second conical gear structure by a fixed belt. When the handle  128  is pushed, the first conical gear structure slides on a shaft, thus changing the gear ratio through the belt to the second conical gear element. By increasing or decreasing the number of gears per unit length of the retractor frame or the gear ratio, the surgeon can slowly or quickly open up the thorax and avoid fracturing ribs. 
     Further adjustability can be provided by the replaceable or detachable blades as detailed in  FIGS. 6-8 . Depending upon the specific physiology of the patient, the surgeon may desire a blade that is either wider or narrower. Because the blades  602  can be removed and replaced, the surgeon can select a blade that fits the specific needs. 
     In some embodiments, the retraction device  102  includes a third frame portion (not shown) that may be detachably connected to the first frame portion  104 . Moreover, should the particular use require an increased distance between the frame portions  104 - 106  and the blade  108 A- 108 B, a post extension i.e. the third frame portion can be used to be inserted into the frame portions  104 - 106 , to increase a length of the frame portions  104 - 106 . When one or more clips of the first blade  108 A (or  108 B) are inserted into the post extension, the increased distance may be achieved. 
     The third frame portion may define a number of teeth that may extend along a length of the third frame portion. The teeth of the first frame portion  104  and the second frame portion  106  may align when the first frame portion  104  and the third frame portion are attached. Further, in some embodiments, the lever and gear mechanism  120  may be configured to engage the teeth of the first frame portion  104  and the third frame portion for moving the second frame portion along the first frame portion  104  and the third frame portion. An operator can extend the frame portions  104 - 106  using the third frame portions. Detachable third frame portions can be installed or removed based on the size of the opening that is needed for a particular surgery. The detachable third frame portions may allow surgeons to open up large spaces (up to 30 cm or more) when needed for some procedures. Otherwise, the surgeons can remove the third frame portion to perform procedures where the tissue opening needs to be smaller. 
     The third frame portion may be provided with two posts, which can be inserted into complimentary post recesses in the first and second frame portions  104 - 106 . Further, a screw may be used to secure the third frame portions to the existing frame portions  104 - 106  by being inserted into a threaded recess in the frame portions  104 - 106 . If an even further extension is desired, the third frame portion can be provided with additional post recesses (not shown) and the screw can have its own threaded recess (not shown), allowing for additional frame portions to be attached thereto, each with its own posts and screw(s). This assembly may permit functionally unlimited cavity sizes. This may be particularly useful when used in a veterinary setting, where the same retraction device can be used on animals of very different sizes, for example, both cats and horses. 
       FIG. 1B  is a schematic side view  100 B of the exemplary retraction device  102  shown in  FIG. 1A .  FIG. 1B  shows the second frame portion  106  in the second configuration. The lever and gear mechanism  120  may engage the teeth  122  of the first frame portion  104  for moving the second frame portion  106  from the first position to the second position. The retraction device  102  may also include a multiple drive system (not shown) operably engaged with the lever and gear mechanism  120 . The multiple drive system may control the lever and the gear mechanism  120  in at least two different speeds for displacement rates per full rotation of the lever  120 . In some embodiments, the lever and gear mechanism  120  further includes an operator-driven, moveable-gear element, connected to a worm gear element through a second movable gear element. Further, the lever and gear mechanism  120  may include a moveable, conical gear element, connected to a fixed conical gear element (not shown) through a belt (not shown). The multiple drive system may also include a handle  128  for moving the movable, conical gear element to adjust the position of the belt. Furthermore, the lever and gear mechanism  120  may include a second drive gear for the handle  128  configured to move the movable, conical gear element to adjust the position of the belt. 
       FIG. 2A  is a schematic view of a portion  200 A of the first blade  108 A of the retraction device of  FIGS. 1A-1B  according to an embodiment of the present disclosure. As shown, the first blade  108 A may include a flexible component  202 . As discussed with reference to  FIG. 1A , the flexible component  202  of the first blade  108 A may be pivotally attached to the first frame portion  104 . Further, as shown, the flexible component  202  of the first blade  108 A may have the first surface  110 A. The first surface  110 A may include a locking structure  204  that may interlock with a locking structure of the second blade  108 B. The locking structure  204  may be in the form of a pin or tab, which can be manually toggled or actuated to permit rotational movement. The locking structure  204  may be provided on one or both of the blades  108 A- 108 B. 
       FIG. 2B  is a schematic view of a portion  200 B of the second blade  108 B of the retraction device  102  of  FIGS. 1A-1B  according to an embodiment of the present disclosure. The second blade  108 B may include a flexible component  206  pivotally attached to the second frame portion  106 . The flexible component  206  of the second blade  108 B may include the first surface  110 B and the second surface  112 B. The first surface  110 B may substantially oppose the second surface  112 B, respectively. 
     Turning now to  FIG. 2B , the first surface  110 A of the flexible component  202  of the first blade  108 A may face the first surface  110 B of the flexible component  206  of the second blade  108 B. Further, the first surface  110 B of the flexible component  206  may include a locking structure  208  in accordance with the locking structure  204  of the first blade  108 A. The locking structures  208  and  204  may interlock with one another to prevent pivoting of the first blade  108 A and the second blade  108 B when the first surfaces  110 A- 110 B are brought into proximity with one another. 
       FIG. 3A  is a schematic zoomed view  300 A of the first blade  108 A of the retraction device  102  of  FIGS. 1A-1B  according to an embodiment of the present disclosure. As shown, the first blade  108 A includes the first surface  110 A and the second surface  112 A. The first surface  110 A of the first blade  108 A may include a locking structure  302 . 
       FIG. 3B  is a schematic zoomed view  300 B of the second blade  108 B of the retraction device  102  of  FIGS. 1A-1B  according to an embodiment of the present disclosure. As shown, the second blade  108 B includes the first surface  110 B and the second surface  112 B. The first surface  110 B of the second blade  108 B may include a locking structure  304 . 
     Referring again to  FIG. 3A , the locking structures  302  and  304  may interlock with one another to prevent pivoting of the first blade  108 A and the second blade  108 B when the first surfaces  110 A- 110 B are brought into proximity with one another or contact one another. 
       FIG. 4  is a schematic zoomed view  400  of the first blade  108 A and the second blade  108 B of the retraction device  102  in an interlocked configuration according to an embodiment of the present disclosure. As discussed with reference to  FIGS. 3A-3B , the locking structure  302  of the first blade  108 A and the locking structure  304  of the second blade  108 B may interlock with each other to prevent pivoting of the first blade  108 A and the second blade  108 B when the first surfaces  110 A- 110 B are brought into proximity with one another. 
       FIG. 5A  is a schematic side view  500 A of the second frame portion  106  according to an embodiment of the present disclosure.  FIG. 5B  illustrates a schematic side view  500 B of the first frame portion  104  and the second frame portion  106  of the retraction device  102  in the interlocked configuration according to an embodiment of the present disclosure. 
       FIG. 6  is a perspective view  600  of an exemplary blade  602  of a retraction device (for example, retraction device  102 ) according to an embodiment of the present disclosure. The blade  602  may be attached to a frame portion such as, the frame portion  104  as discussed with reference to  FIG. 1A . The blade  602  is removable from the frame portion such as the frame portion  104 . The blade  602  may include a first surface  604 A and a second surface  604 B opposing each other. The second surface  604 B may come in direct contact with one or more tissues of a patient when an operator performs a surgery using the retraction device including the blade  602 . The second surface  604 B may include a padding material  608 . The padding material  608  may include any suitable material such as silicon polymer, PDMS, and so forth. Further, the padding material  608  may have a constant modulus of elasticity between 0.5 Mega Pascal (MPa) and 15 MPa. 
     The padding material  608  may include a curved edge  606  for gripping tissue. The curved edge  606  may include including one or more rigids  610  segmented along a length of the edge  606  for gripping a tissue. The rigids  610  may allow flexure of the blade  602 . The blade  602  may be formed using a sterilizable material. The padding material  608  can also have counter bored holes or T-slots  616  for the ridges  610 . 
     The blade  602  may have a flat planar shape when not pressed against the ribs or tissues. Upon contact with the ribs/tissues, the blade  602  may take on a curved shape to adapt to the stiffness and unique shape of the patient&#39;s ribs/tissues. The padding material  608  may be chosen such that the modulus of elasticity with the area moment of inertia of the blade  602  matches the stiffness (EI) of the area being retracted. 
     In some embodiments, the blade  602  matches a radius of curvature of the tissue contacted during tissue displacement. In the case of a thoracic retractor, the blade  602  may match the radius of curvature of the patient&#39;s rib during retraction. One such example is shown in  FIG. 6 . 
     Since surgeons have different methods of separating the intercostal soft tissues during thoracotomy, it is possible that the blade  602  may come in contact with a composite of both soft (muscle) and hard tissues (ribs) during retraction. Therefore, different shape and size of the blade may be formed.  FIG. 7  and  FIG. 8  show two exemplary blades  702 - 802 , respectively, having different cross sectional area. 
     When the blade (such as  602 ) has a flexural stiffness (N*m 2 ) that matches that of the tissues contacted, the radius of curvature of the blade and tissue can match and the blade  602  may apply a uniform load across the length of the tissue. The flexural stiffness of the blade  602  (or  702 - 802 ) may be determined by the product of the blade&#39;s cross sectional area moment of inertia (I) and the modulus of elasticity (c). Intercostal tissue in humans has been found to have total flexural stiffness between 0.01 and 500 N*m 2 . The blade&#39;s inducement of a bending moment on the tissue by application of a uniform, distributed load is important because it prevents the concentration of high stress (N/m 2 ) at discrete points on the tissue during retraction. The application of high stress points to human tissue by non-conforming tissue engaging devices is the primary cause of broken ribs and crushed intercostal vasculature and nerves during thoracotomy. This embodiment of the device designed to match the composite flexural stiffness of the tissues retracted provides the most uniform load possible and can minimize post-surgical pain for the patient while allowing an appropriate visual field for the surgeon. 
     In some embodiments, the padding material  608  is inert, non-toxic and non-flammable and may be classified as having no marked harmful effects on organisms in the environment (according to Ullmann&#39;s Encyclopedia of Industrial Chemistry), such as a silicone-based organic polymer, for example PDMS. The padding material  608  may form a layer or pad having a thickness of at least 0.5 mm, such as, between approximately 1 mm to 10 mm, between approximately 3 mm to 6 mm, and approximately 4 mm. 
     As discussed with reference to  FIGS. 6-8 , the blades  602 - 802  are removable and can be removed from the frame portions (such as frame portions  104 - 106 ). In some embodiments, the frame portions and the blades  602 - 802  are provided with connecting elements. For example, each frame portion can have a tube  612  extending outward, and transversely, into which clips (not shown) may be provided on the blades  602 - 802  are inserted. Connection of this particular prototype may be accomplished through a quick connect, allowing for easy removal and replacement of the blades  602 - 802 . The tubes  612  may have a larger inner diameter proximal to the frame portions to allow the clips of the blades  602 - 802  to nest therein the retraction device  102 . 
     The tubes  612  may also have openings  614  for compressing the barbed clips for easy insertion and removal. Alternatively, there may be a narrowing inside the tube  612  such that when the blade  602  (or  702 - 802 ) is rotated about the axis 45 to 90 degrees, the clips are compressed to allow for removal. 
     In alternative embodiments, for attachment the blade  602  includes a keyed connector that either can be rotated about the pivot to release the blade  602  or compressed. This may allow for the blade  602  to rotate after insertion to allow for more accurate force distribution, thereby reducing unnecessary injury to the patient. For example, as the blade  602  separate as the first frame portion (for example, frame portion  104 ) moves down the retraction device ( 102 ), i.e., away from the second frame portion  106 , the forces exerted upon the blade  602  can similarly be parallel to the frame portions  104 - 106 . Because the blades  602  of the frame portions  104 - 106  are permitted to rotate as they are separated, the retraction device  102  may allow the blades  602  to have significantly greater surface contact with the cavity within the patient&#39;s body. The increased surface contact area results in less force being exerted on any individual area, and therefore, less injury to patient tissues. 
     Turning now to  FIG. 8 , the blade  802  are provided with a number of teeth  804  configured to limit rotational movement of the blade  602  during insertion of the retraction device  102 . The teeth  804  may be designed to mesh, such that forces tending to rotate the blade  802  can be hindered. The mesh teeth  804  may be configured to prevent the blade from sliding along the length of the ribs during rotational movement of the blade  602 . In another embodiment, the blades  802  can be provided with a locking mechanism (not shown). 
     In some embodiments, for resisting, but not prohibiting rotational movement springs and structure holders (not shown) may be provided along with the tube  612 , such that the blades  602  of the frame portions  104 - 106  are permitted to rotate, but only after overcoming a predetermined amount of force. Similarly, the blades  602  of the frame portions  104 - 106  may be maintained or biased to their not rotated condition by the holders. The amount of biasing force provided by the holders can be selected depending upon the specific uses. In other words, different retraction devices  102  can be selected (with different holders and different biasing forces) for treating different medical conditions. 
     Further, one or both of the blades  602  of the frame portions  104 - 106  may be provided with one or more tabs. The tabs may be designed to prevent the blades  602  from slipping out of the cavity with the blades  602  separate. In one embodiment, the tabs may extend perpendicularly from the blades  602  (or  108 A- 108 B), but the angle defined by the blades  602  and the tabs can be at any angle, such as, at an angle larger than 45 degrees. 
     As discussed with reference to  FIG. 7 , the blade  702  can be reinforced along the axis of rotation with inter-digitated support to minimize deflection while the cross section is maintained along the length  704  of the rib to allow flexing. 
     As shown in  FIG. 8 , the use of inter-digitated support or the teeth  804  may allow the blade  802  to take on extremely thin thickness to fit in smallest possible incision space. The teeth  804  may help the blades  802  stay paired together in contact during installation. The blades  802  can be installed into the thoracic space without being attached to the frame portions  104 - 106 . The interlocking mechanisms on the blades  802  may keep the blades  802  from sliding against each other and make it easier for the frame portions  104 - 106  to be attached to the blades  802 . It is noted that a connector can support the bottom side of each of the blades  802  for controlling the amount of blade flexure. Additional connectors may be utilized to increase rigidity. 
     As discussed with reference to  FIGS. 6-8 , the blade  602  (or  702 - 802 ) may be reinforced along the axis of rotation to minimize deflection while the cross section is maintained along the length of the rib to allow flexing. 
     The blades  602  may have a very narrow insertion edge to reduce the space needed for insertion of the retraction device  102  into a cavity in the body. This can be achieved by having the edge  606  of the blades  602  distal the clips narrow, for example, tapered or stepped, such that the edge  606  has a significantly smaller cross section than other areas of the blade  602 . In some embodiments, when the edges  606  of complimentary blades  602  are joined, as shown in  FIG. 5B , the edges  606  may together form a very small narrow tip, necessarily reducing the size of the incision to be made by the doctor. Because the thickness of the blade  602  increases from the edge  606 , inserting the blade  602  further into the cavity made by the incision can help to widen the incision without the doctor needing to cut further. In some embodiments, the padding material  608  may only present on a section of the blade  602 , such that the tip formed by the two edges  606  of the blades  602  together is typically less than approximately 10 mm, preferably between approximately 2 mm and approximately 8 mm, and most preferably between approximately 3 mm and approximately 6 mm. The thickness of the blade  602  may be dependent upon the material (EI). Therefore, EI may be about 0.01 N*m 2  plus or minus an order of magnitude. The range may cover up to at least 500 N*m 2 . 
     In some embodiments, the tubes  612  of each of the blades  602  are positioned on the frame portions  104 - 106  and the clips are positioned on the blades  602 . In alternative embodiments, an annular cavity is disposed in the blade  602 . A complimentary structure, e.g., barbed clips (not shown), could be used on the frame portions  104 - 106  to permit attachment of the blades  602  to the frame portions  104 - 106 . 
     In some embodiments, the blade  602  may include a larger area for contacting the tissue. Accordingly, the padding material  608  may be provided on a larger section of the blade  602  as the surface contacting the tissue is also larger. In some embodiments, the padding material  608  is provided on the blade  602  only where the tissue is expected to contact the blade  602 , and as a result, the padding material  608  is separated into two separate areas. 
     Further, the blade  602  may take on a variety of forms to accomplish the same goals as described above. 
     In an exemplary scenario for performing a surgery using the retraction device  102 , a space of about 1 inch side is made in the sternum, pectoralis muscles, or ribs, before the blades are inserted. The total thickness of the lip formed by the blades in paired contact may be about 25.4 mm or less to fit the size of the incision. The total thickness may be about 10 mm-15 mm, but this may depend on the strength of the elastic properties of the material selected to make the blade. The tabs are positioned below the sternum with the padding material against the bone. When a ratcheting lever is actuated, the first frame portion is moved along the length of the retraction device  102 . As a result, the first blade moves away from second blade, and the cavity is forced open. Each movement of the lever repeats this action until the cavity is open to the desired spacing. 
     As discussed with reference to  FIG. 1 , the frame portions  104 - 106  or other parts of the retraction device  102  may be manufactured from stainless steel or other autoclavable material with sufficient strength for retraction. The connection tubes (e.g.  612 ) may have a larger inner diameter proximal to the frame portions  104 - 106  to allow the clips of the blade to nest. The connection tubes also generally have two openings for compressing the barbed clips for removal (alternatively, there can be a narrowing inside the tube such that when the blade is rotated about the axis 45 to 90 degrees the clips are compressed to allow removal). Another option for attachment would be through a keyed connector that either needs to be rotated about the pivot to release blade or compressed. The reusable material may be such that it can withstand temperatures exceeding 115° C. 
     In some embodiments, the various components of the retraction device  102  are of a construction that allows for sterilization after a single use. This permits the retraction device  102  to be used multiple times without having to be replaced. However, in alternative embodiments, certain parts of the retraction device  102  may be designed to be replaced. This allow for a significantly broader class of materials to be used. 
     For example, many types of materials which are suitable to be used as the padding material on the blades, due to the correct physical properties, makes such materials incapable of withstanding the pressures and temperatures typically used in sterilization techniques. Therefore, in some embodiments, the connection between the blades and the remainder of the retraction device  102  is designed such that the blades (such as blades  108 A- 108 B) can be removed. Accordingly, if the blades cannot be sterilized after use, it is possible to replace the blades with new blades, and the old blades removed and discarded. The replacement blades can be of different construction or of different materials than the blades that are removed. Thus, after an initial use, the blades would be removed and discarded awhile the remainder of the retractor would be sterilized by conventional methods. Thereafter, new blades would be connected. 
       FIG. 9  is a schematic view  900  illustrating use of a retraction device  902  for performing a medical procedure according to an embodiment of the present disclosure. As shown, a first frame portion  906  and a second frame portion  908  may be inserted between in a cavity such that blades move between two ribs  904  of a patient. Thereafter, using a handle  910  of the retraction device  902 , an operator may actuate the movement of the blades (not shown) for enlarging the cavity and performing the medical procedure. The blades may be manually rotated by the operator, or otherwise moved by the force applied by the ribs  904 . 
       FIG. 10  is a perspective view  1000  of an exemplary lever and gear mechanism  1002  (or multiple drive opening mechanism) including at least two circular gears  1004 A and  1004 B of a retraction device  1006  according to an embodiment of the present disclosure. The retraction device  1006  may include a variable number of gears (circular gears  1004 A- 1004 B) per unit length of the frame portions  104 - 106  to generate a more gradual opening of the chest per turn of the opening lever and gear mechanism  1002 . This can be accomplished by having smaller gaps between the teeth of the frame portion of the retraction device  1006  as the first frame portion  104  moves along the length of the retraction device  102 . The two circular gears  1004 A and  1004 B may be configured to drive a single rack and pinion mechanism. Examples of the two circular gears  1004 A and  1004 B may include, but are not limited to, spur gears. The two circular gears  1004 A and  1004 B may rotate single internal pinion along teeth  1010  of a frame portion  1012  of the retraction device  1006 . Further, only one of these two circular gears  1004 A- 1004 B may remain in direct contact with the internal pinion. The internal pinion mechanism can be similar to the pinion mechanism implemented by other Finochietto style retractors known in the prior art. Additionally, the pinions size can be adjusted depending on the strength of the material that is used to make the pinion and the frame portion  1012 . Additionally, the two circular gears  1004 A and  1004 B may have different diameters to allow for at least two different retraction speeds. The circular gears  1004 A and  1004 B may be in a 2:1 gear ratio so as to allow a normal speed and a half-speed retraction. Each of these circular gears  1004 A and  1004 B may have a protruding socket element that allows installation of the detachable handle  1008 . Depending on the user&#39;s preference, the handle  1008  can be placed on either of the two circular wheels to select a retraction speed. 
     Further, the multiple gear mechanism  1002  may be configured to provide retraction speeds from 0 to 20 mm per handle rotation. Other example speeds are about 7.5 mm and about 15 mm per handle rotation. In this example, the handle  1008  is provided on the retraction device  1006  for allowing the surgeon to adjust down the rate at which the tissue is separated by pushing or pulling the handle and changing the diameter of the gear that moves down the frame portions of the retraction device  1006 . This may also be accomplished by having a first conical gear structure, connected to a second conical gear structure by a fixed belt. When the handle  1008  may be pushed, the first conical gear structure slides on a shaft, thus changing the gear ratio through the belt to the second conical gear element. By increasing or decreasing the number of gears per unit length of the retractor frame or the gear ratio, the surgeon can slowly or quickly open up the thorax and avoid fracturing ribs. 
       FIG. 11  is a zoomed cross-sectional view  1100  of an exemplary worm gear mechanism  1102  of an exemplary multiple drive opening mechanism  1104  of a retraction device  1106  according to an embodiment of the present disclosure. The retraction device  1106  may include a fixed first frame portion and a movable second frame portion. In this embodiment of the opening mechanism, a single worm gear  1108  may be contained on or within a movable first frame portion movable second frame portion of the retraction device  1106 . The first frame portion may define a number of teeth extending between a proximal end and a distal end of the first frame portion. The single worm gear  1108  may adjust the position of the movable second frame portion along the length of the first frame portion having teeth. The worm gear  1102  may be directly driving the displacement of the moveable second frame portion along the first frame portion having the teeth. The rotation of the worm gear  1102  may be driven by either of two miter or bevel gears  1110 A and  1110 B (also referred as worm driving gears) oriented at 90 degrees at both ends of the worm gear  1102 . The first gear  1110 A may drive the first end of the worm gear  1102  and may have a first diameter. The second gear  1110 B may drive the second end of the worm gear  1102  and may have a second diameter. The driving of the worm gear  1102  with either of two diameter gears  1110 A and  1110 B may allow an operator to retract at two distinct speeds per full rotation of a handle (See  1008  of  FIG. 10 ) of the gear mechanism  1104 . The handle may be detachable and may be installed into one of the two worm driving gears  1110 A and  1110 B using a socket method. 
     According to some embodiments of the worm gear mechanism  1104 , the two worm driving gears  1110 A and  1110 B of different diameters may be in contact with each other on one end of the worm gear mechanism  1104  containing a bevel or miter gear  1110 A and  1110 B at 90 degrees. This embodiment may reduce the number of gear elements on the worm gear mechanism  1104  by one. In this embodiment, the worm gear mechanism  1104  is driven on only one end and is in direct contact with only one of the driving gears  1110 A and  1110 B. The second worm driving gear  1110 B may be in direct contact with the first worm driving gear  1110 A, which is in contact with the worm gear  1110 B. This design may allow selection between two different speeds of retraction per full rotation of the detachable handle mechanism. 
       FIG. 12  is a perspective view  1200  of an exemplary retraction device  1202  containing a multiple drive worm gear mechanism  1212  and the retractor frame extension attachment  1206  (or a third frame portion) according to an embodiment of the present disclosure. The retraction device  1202  may include a first frame portion  1204 A, and a second frame portion  1204 B. Flexible blades  1208 A and  1208 B may be installed by an operator and may be secured by a connection mechanism that can allow the blades  1208 A and  1208 B to freely rotate when the opposing flexible blades  1208 A and  1208 B are not in contact with one another. 
     Further, the retraction device  1202  may include the multiple worm gear mechanism  1212  that may be actuated by the operator using a handle  1210  of the multiple worm gear mechanism  1212 . The multiple worm gear mechanism  1212  may include multiple worm gear  1214  capable of being shielded and encased within a hollow internal portion or body  1216  of the first frame portion  1204 A. Further, two gears  1218 A and  1218 B that drive the single worm gear  1214  may also be encased within the hollow portion  1216 . The encasement of the gears  1218 A and  1218 B (and  1214 ) may help to prevent entrapment of patient tissue and surgical tools in teeth  1220  of the first frame portion  1204 A. The frame extension attachment or the third frame portion  1206  may allow an opening size to be increased beyond the length of the standard frame portions (i.e.  1204 A and  104 B). The third frame portion  1206  may include one or more male pins or prongs that may insert into female sockets on the end of the first or second frame portions  1204 A and  1204 B of the retraction device  1202 . The purpose of the prong socket mechanism is to align the two connected frames so that the movable second frame portion  1204 B can move between the first frame portion  1204 A and the third frame portion  1206  seamlessly. Once the third frame portion  1206  has been connected using the socket mechanism, the frame portions  1206  and  1204 A or  1204 B may be secured together using a threaded bolt that runs through the center of the third frame portion  1206  and may screw into a threaded hole in the center of the end of the original retractor frame i.e. frame portions  1204 A and  1204 B. The unthread end of the bolt may have a socket to allow a hand tool to be installed. The operator may subsequently turn the non-thread end of the bolt, causing the two frame portions ( 1206  and  1204 A or  1204  B) to tighten and secure together. The operator may turn the bolt in the opposite direction to release the third frame portion. 
     An initial comparative study or experiment was performed in a pig cadaver model that characterized the force distribution profiles of two different retractor blades during surgery. The flat blades of a stainless steel Finochietto retractor were compared to a prototyped blade  108 A-B of the invention embodiment depicted in  FIG. 3 . The prototyped blade  108 A-B was constructed of ABSplus thermoplastic (layer thickness 0.254 mm) that was 3D printed using a Stratasys uPrint SE Plus. The prototyped blade  108 A-B had total ABSplus thickness of 4 mm. A 2×5 array of single element force sensors was placed directly on the tissue engaging face of blade  108 A-B. The five pairs of force sensors were arranged to measure the average pressure over five equally spaced segments along the length of the tissue engaging face of blades  108 A-B. Both types of blades had tissue engaging faces with dimensions 66 mm×25 mm. 
     The force sensors were connected to a custom analog signal amplification circuit which was connected to computer controlled data acquisition unit. A mechanical plate with pistons was placed on top of each force sensor pair to ensure complete transfer of force to the sensing areas of the force sensors. Then a custom molded 3 mm silicone pad (as shown in  FIG. 3 ) was placed on top of the five mechanical loading plates of the prototyped blades  108 A-B. The Finochietto retractor blades had identical force measuring setups installed, however no silicone pad was placed on top of the mechanical loading plates. The Finochietto retractor had metal in direct contact with the pig tissue. 
     Three pig cadavers weighing between 154-176 kg had lateral thoracotomies performed on both sides using the instrumented Finochietto and prototyped retractors. The lateral incision lengths were all 20.0 cm in length. All retractions on these pigs were performed until the tissue opening was 40.00 mm in height. The retraction forces recorded by the force sensor arrays for both retractors were compared when the retraction reached 40.00 mm. All retraction forces are expressed in units of Newtons (N). 
       FIG. 13  is a graph depicting the distribution of retraction forces collected along a pig&#39;s rib using the recording instrumentation previously described at a 40.00 mm thoracotomy retraction distance using the Finochietto retractor. Each bar represents the force measured by a sensor pair at a perpendicular distance (millimeters) from the rotational axis of the blades. Herein, the term rotational axis may be used to describe the central axis of both retractor blades  108 A- 108 B, however the blades of the Finochietto retractor were not permitted to rotate. The prototyped blades  108 A- 108 B may be permitted to rotate. The two measurements taken 30 mm from the rotational axis represent the forces applied by the retractor blade at its two distal ends. The data from a single trial in  FIG. 13  indicates that the distal ends of the Finochietto blade applied noticeably higher levels of force compared to the other blade locations during the trial. In this trial the center (0 mm in  FIG. 13 ) of the Finochietto blade did not maintain contact with the ribs at the 40.00 mm retraction distance as the rib bent around a fixed-shape, metal retractor blade. The results of this type of force distribution for the retractor blade can cause significant damage to the tissues; including rib fracture. 
       FIG. 14  shows the retraction force distribution during a thoracotomy performed on a pig with the prototyped retractor blade, such as blades  108 A and  108 B. Compared to the Finochietto, the blades  108 A- 108 B may apply a more uniform distribution of retraction force along the length of the blade (distances 30, 15, 0, 15, 30 mm in Fig. B). The blades  108 A and  108 B may have a flexible structure that allowed it to maintain contact with the ribs along the blade&#39;s lateral length. The maximum force applied by each of the blades  108 A and  1008 B at any single location is 25 Newtons compared to the over-30 Newton measurements seen on the distal ends of the Finochietto blade. The total force across all sensor pairs in these two retractor type trials  FIGS. 13 and 14  were approximately 85 Newtons at the same retraction distance (40.00 mm). However, their force distribution profiles were noticeably dissimilar. The use of a flexible retractor blades  108 A and  108 B may prevent unnecessary tissue damage to a patient&#39;s tissue during surgery. 
     An embodiment of the present disclosure provides a method for preventing damage of one or more tissues within a body of a patient while performing a medical procedure by an operator. The method includes selecting a pair of blades, and attaching the selected blades to the disclosed retraction device (such as the retraction device  102 ). The method also includes aligning the blades parallel to each other by interlocking the blades along the complimentary mating surfaces of the blades. The method further includes inserting the blades into a cavity in a patient&#39;s body. The method further includes separating the blades to enlarge the cavity. The method further includes rotating the blades. 
     According to an aspect of the present disclosure the retraction device may be designed to engage patient tissue with a flexible material that may minimize maximum forces exerted on the patients&#39; tissues and bones by increasing the contact surface area between the retractor blades and tissue, independent of the patient&#39;s unique anatomical intercostal features. The minimization of local stresses applied to the patient&#39;s tissues during thoracic retraction in turn may reduce surgical damage to the patient&#39;s intercostal and inter-sternal tissue. 
     Reference throughout this specification to “a select embodiment”, “one embodiment”, or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosed subject matter. Thus, appearances of the phrases “a select embodiment”, “in one embodiment”, or “in an embodiment” in various places throughout this specification are not necessarily referring to the same embodiment. 
     Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, to provide a thorough understanding of embodiments of the disclosed subject matter. One skilled in the relevant art will recognize, however, that the disclosed subject matter can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the disclosed subject matter. 
     The above specification, examples and data provide a complete description of the structure and use of exemplary embodiments of the present disclosure. Although various embodiments of the present disclosure have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of this present disclosure. In particular, it should be understood that the described technology may be employed independent of a personal computer. Other embodiments are therefore contemplated. It is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative only of particular embodiments and not limiting. Changes in detail or structure may be made without departing from the basic elements of the present disclosure as defined in the following claims. 
     It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art, which are also intended to be encompassed by the following claims. 
     The above description does not provide specific details of manufacture or design of the various components. Those of skill in the art are familiar with such details, and unless departures from those techniques are set out, techniques, known, related art or later developed designs and materials should be employed. Those in the art are capable of choosing suitable manufacturing and design details. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other systems, methods, or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure as encompassed by the following claims. 
     Features from one embodiment or aspect may be combined with features from any other embodiment or aspect in any appropriate combination. For example, any individual or collective features of method aspects or embodiments may be applied to apparatus, system, product, or component aspects of embodiments and vice versa. 
     While the embodiments have been described in connection with the various embodiments of the various figures, it is to be understood that other similar embodiments may be used or modifications and additions may be made to the described embodiment for performing the same function without deviating therefrom. Therefore, the disclosed embodiments should not be limited to any single embodiment, but rather should be construed in breadth and scope in accordance with the appended claims.