Patent Publication Number: US-11638776-B1

Title: Medical devices and methods for forming medical devices having a porous structure

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a non-provisional of, and claims the benefit of the filing date of, U.S. provisional patent application No. 62/911,690, filed Oct. 7, 2019, entitled “Medical Devices and Methods for Forming Medical Devices Having a Porous Structure,” the entirety of which application is incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The present disclosure generally relates to medical devices, and more particularly, but not exclusively, to medical devices, such as implants, and methods of coating a surface of the implants to produce an enhanced porous coating morphology. 
     BACKGROUND 
     Certain medical devices, such as orthopedic implants, have a surface coating designed to enhance osseointegration. Orthopedic implants include, but are not limited to, bone plates, intermedullary nails, hip implants, knee implants, shoulder implants, spinal implants, etc. Surface coatings may be textured or porous to more closely resemble trabecular bone. Porous surface coatings have interconnecting networks of pores, which are similar to those of trabecular bone, and may serve to promote bone ingrowth into the porous coating and provide better long-term implant fixation. Adhesion between the implant and bone depends, in part, on the thickness and porosity of the coating. For example, powder size of the coating may be varied to manipulate pore size and/or porosity. However, when the powder size is increased, attachment strength between the porous coating and the implant typically decreases. Decreasing powder size aids with adhesion, but decreases the porosity of the coating. Therefore, a compromise takes place, and porosity typically stays at the lower end to maintain attachment strength. 
     A similar compromise can be seen for coating thickness. As layers of coating are added to increase thickness, attachment strength between the porous coating and the implant typically declines. With larger powder size, whether symmetric or asymmetric, attachment points are reduced per volume, resulting in reduced attachment strength. 
     Spray coating metallic implants can be particularly problematic. For example, porous plasma spraying titanium onto a metallic surface produce reduced porosity percentages and/or attachment strength. 
     For a number of reasons, it would be beneficial to utilize methods for coating medical devices, such as implants, with a porous coating that produces enhanced coating morphology (e.g., increased pore sizes and/or porosity). In particular, it would be beneficial to improve methods for spray coating metallic implants with a porous plasma sprayed titanium coating. As such, a need remains for further improvements in this technological field. The present disclosure addresses this need. 
     SUMMARY 
     The Summary is provided to introduce a selection of concepts in a simplified form, the concepts further described below in the Detailed Description. The Summary is not intended to identify key features or essential features of the claimed subject matter, nor is the Summary intended as an aid in determining the scope of the claimed subject matter. 
     Approaches for forming medical devices, such as implants, having a porous coating, are disclosed. In one embodiment, a medical device may include a plurality of texture features extending from a base surface and a porous coating formed over the plurality of texture features and the base surface. The porous coating may include a plurality of coating structures, wherein a first coating structure group of the plurality of coating structures has a first size, wherein one or more coating structures of the first coating structure group is in direct contact with the plurality of texture features or the base surface, wherein a second coating structure group of the plurality of coating structures has a second size, and wherein the first size is less than the second size. 
     In another embodiment, a method of forming a medical implant may include patterning a plurality of texture features from a substrate, and forming a porous coating over the substrate. The porous coating may include a plurality of coating structures, wherein a first coating structure group of the plurality of coating structures has a first size, wherein one or more coating structures of the first coating structure group is in direct contact with the plurality of texture features or the base surface, wherein a second coating structure group of the plurality of coating structures has a second size, and wherein the first size is less than the second size. 
     In yet another embodiment, an implant may include a plurality of texture features extending from a base surface, and a porous coating formed over the plurality of texture features and the base surface. The porous coating may include a plurality of coating structures, wherein a first coating structure group of the plurality of coating structures has a first size, a first porosity, and a first pore size, wherein a second coating structure group of the plurality of coating structures has a second size, a second porosity, and a second pore size, wherein the first size is less than the second size, wherein the first porosity is less than the second porosity or the first pore size is less than the second pore size, and wherein one or more coating structures of the first coating structure group is in direct contact with the plurality of texture features or the base surface. 
     In these and other embodiments, the implant surface is treated prior to receiving the porous coating in order to enhance porous coating morphology. The implant surface preparation can be achieved through texturization via, for example, chemical etching, mechanical etching/grooving, laser etching, or other texturing mechanisms. The texture can be symmetric or asymmetric, 2-D or 3-D. Increased spacing and depth of the etched implant surface allows a reduction in coating layers, while still achieving a desired pore morphology. In one embodiment, the porous coating is a porous plasma sprayed titanium coating applied to a metallic implant. In one embodiment, the thickness of the porous plasma sprayed titanium coating is approximately equal to the height of the texturization (e.g., textured surface), or slightly larger than the height of the textured surface. 
     Embodiments of the present disclosure provide numerous advantages. For example, the embodiments provide, inter alia, enhance porous coating morphology (e.g., increased pore size and/or porosity), and improved adhesion of the porous coating to the implant. In addition, in one embodiment, the embodiments facilitate porous plasma sprayed titanium to be applied to metallic implants with enhanced pore morphology and increased adhesion strength. 
     Further features and advantages of at least some of the embodiments of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings illustrate exemplary approaches of the disclosure, including the practical application of the principles thereof, as follows: 
         FIG.  1    illustrates a side, cross-sectional view of a surface of a medical implant, in accordance with one feature of the present disclosure; 
         FIG.  2    illustrates a side, cross-sectional view of the surface of the medical implant of  FIG.  1    with a porous coating formed thereon, in accordance with one feature of the present disclosure; 
         FIG.  3    illustrates a side, cross-sectional view of the porous coating of  FIG.  2    engaged with a bone, in accordance with one feature of the present disclosure; and 
         FIG.  4    a flowchart illustrating a method for forming a medical device in accordance with one feature of the present disclosure. 
     
    
    
     The drawings are not necessarily to scale. The drawings are merely representations, not intended to portray specific parameters of the disclosure. The drawings are intended to depict example embodiments of the disclosure, and therefore are not be considered as limiting in scope. In the drawings, like numbering represents like elements. 
     Furthermore, certain elements in some of the figures may be omitted, or illustrated not-to-scale, for illustrative clarity. The cross-sectional views may be in the form of “slices”, or “near-sighted” cross-sectional views, omitting certain background lines otherwise visible in a “true” cross-sectional view, for illustrative clarity. Furthermore, for clarity, some reference numbers may be omitted in certain drawings. 
     DESCRIPTION 
     For the purposes of promoting an understanding of the principles of the present disclosure, reference will now be made to example embodiments. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended. Any alterations and further modifications in the described embodiments, and any further applications of the principles of the present disclosure as described herein are contemplated as would normally occur to one skilled in the art to which the disclosure relates. 
     The present disclosure is directed to systems and methods of coating a medical device with a porous coating surface. In one embodiment, one or more surfaces of the medical device is textured, etched, and/or otherwise prepared prior to coating in order to enhance the resulting porous coating morphology. More specifically, the surface of the medical device is initially treated in a manner arranged and configured to produce increased pore size and/or pore spacing in the subsequently applied porous coating. In addition, the treatment may be arranged and configured to produce increased tensile attachment strength between the porous coating and the implant. 
     Referring to  FIG.  1   , a surface  102  of a medical device  100  or a medical implant according to one example embodiment will be described. As shown, medical device (hereinafter “device”)  100  may be a solid structure having a plurality of texture features  104  separated by a plurality of grooves, valleys, or indentations  106  formed therein. As used herein, the device  100  may be any suitable implant or medical device now known or hereafter developed. For example, in some embodiments, the device  100  may be a bone plate, a hip implant, a knee implant, etc. Embodiments of the present disclosure are not limited in this context. 
     The device  100  may be formed by any variety of processes. Furthermore, the device  100  may be made from any suitable material such as, for example, titanium, commercially pure titanium, titanium alloy, cobalt-chromium, stainless steel, zirconium, oxidized zirconium, etc. The texture features  104  and the indentations  106  may be formed in the surface  102  of the device  100  via any suitable mechanism now known or hereafter developed such as, for example, mechanical etching/grooving (e.g., machining, shaping, scribing, knurling, etc.), laser etching/texturing, chemical etching, or other texturing mechanisms. In some embodiments, the texture etching can be symmetric and/or asymmetric, 2-D or 3-D, with a purpose of attaining improved porosity (e.g., pore size/spacing) and a desired thickness for a subsequent porous coating application. 
     In various embodiments, the texture features  104  and the indentations  106  may be formed by sharp grooves, curved grooves, undercut features, etc. Although the texture features  104  are shown as being generally rectangular-shaped, it will be appreciated that the texture features  104  and the indentations  106  may take on different shapes in other embodiments 
     The textured coating surface provides more surface area and, in some areas, more than one point of contact between the substrate and a same coating structure of a porous coating. As a result, the number of coating structures in direct contact with the substrate versus those coating structures in direct contact with only other coating structures, may be increased, thus providing greater adhesion between the porous coating and the surface of the substrate. It will be appreciated that greater or lesser points of contact may exist depending on the type/shape of porous coating and/or the type/shape of the texture features  104  and the indentations  106 . 
     As shown, the texture features  104  may define a vertical height ‘H’ measured from a base surface  112  of the indentations  106  to a top  114  of the texture features  104 . Furthermore, the texture features  104  may define a pitch ‘P’ between adjacent texture features  104 . In some embodiments, the height and/or pitch are substantially uniform across the device  100  for each of the texture features  104  and indentations  106 . In other embodiments, the height and/or pitch of the texture features  104  can vary. Embodiments herein are not limited in this context. 
     In  FIG.  2   , a porous coating  120  may be formed over, built on, applied, sprayed, or the like, to the device  100 . As shown, the porous coating  120  may include a plurality of coating structures (e.g., beads)  122  disposed within the indentations  106  and over the texture features  104 . Although non-limiting, the coating structures  122  may be spherically shaped and made from one or more polymers, one or more metals, sand, or other material(s). For example, the coating structures  122  may be cobalt chrome, titanium, zirconium, stainless steel, or other implantable materials (e.g. ceramic, PEEK) in a form of symmetric or asymmetric beads and/or particles, plasma sprayed, vapor deposition, and/or other means of application-specific forms. The coating structures  122  may each have a width dimension, such as a diameter ‘D’. In some embodiments, the plurality of coating structures  122  may include first and second groups of coating structures. In one embodiment, the first and second groups may have different widths or diameters. For example, the plurality of coating structures  122  may include a larger diameter group of coating structures and a smaller diameter group of coating structures. That is, as illustrated, in one embodiment, a larger diameter group  122 A of the plurality of coating structures  122  has a first size (e.g., diameter), and a smaller diameter group  122 B of the plurality of coating structures  122  has a second size (e.g., diameter), wherein the first size is different (i.e., greater) than the second size. Furthermore, in some embodiments, one or more of the plurality of coating structures  122  may have a different shape. For example, coating structure  122 C may generally have an oval shape. Embodiments herein are not limited in this context, however. 
     Although non-limiting, the porous coating  120  has a thickness ‘T’, relative to a plane defined by the base surface  112 . In some embodiments, the thickness of the porous coating  120  is greater, lesser than, or equal to the height of the texture features  104 . Although not shown, the porous coating  120  may have a generally planer upper surface after application. In some embodiments, the thickness T of the porous coating  120  is approximately equal to the height H of the textured surface, or slightly larger than the height H of the textured surface. In one embodiment, a coating mean thickness measured from the base surface  112  may be between 500-1500 micrometers. The texturized surface may have a height of between 200-1500 micrometers. In one embodiment, the textured surface may have a height between 500-1500 micrometers. In one embodiment, the thickness T of the porous coating may be larger (e.g., taller) than the height H of the texturized surface so that the texturized surface is shorter than the height of the porous coating with the porous coating extending above the texturized surface. For example, in one embodiment, the thickness T of the porous coating may be approximately 500 urn min, while the height H of the texturized surface may be approximately 200-300 urn min. Alternatively, in one embodiment, the thickness T of the porous coating is approximately 1000 micrometers, while the height H of the texturized surface is approximately 500 micrometers. However, the thickness/height of the porous coating  120  and the textured surface may vary as desired, e.g., based on pore morphology, attachment strength, coating type/shape, texturing type/shape, etc. Embodiments herein are not limited in this context. 
     As shown, spaces between each of the plurality of coating structures  122  represent pores  125  of the porous coating  120 . By varying the dimensions and shapes of the plurality of coating structures  122 , pore size can be modified. In some embodiments, it may be desirable to increase or decrease the size of the pores  125 , either uniformly across the thickness of the porous coating  120 , or just in targeted areas of the porous coating  120 . For example, smaller diameter coating structures  122 B may be first applied atop the base surface  112  between the indentations  106 , followed by the relatively larger diameter coating structures  122 A. As a result, the size of the pores  125  closer to the base surface  112  may be smaller than those pores  125  closer to the top  114  of the texture features  104 . Thus arranged, the smaller diameter coating structures  122 B initially provide increased tensile attachment strength. Thereafter, the subsequently applied, larger diameter coating structures  122 A facilitate creation of enhanced pore morphology (e.g., increased porosity and/or pore size). In other embodiments, a substantially equal amount of larger and smaller diameter coating structures  122 A,  122 B may be deposited atop the device  100  to provide a more uniform porosity throughout the porous coating  120 . In one embodiment, the smaller diameter coating structures  122 B may have a size between 10-20 μm. The larger diameter coating structures  122 A may have a size between 40-350 μm. 
     As shown in  FIG.  3   , in use, the porous coating  120  may contact a patient&#39;s bone  130 . In one example embodiment, the porous coating  120  is formed by plasma-sprayed metal, such as titanium. As will be appreciated, plasma-sprayed titanium tends to be extremely dense resulting in coatings having reduced porosity and/or pore sizes, and reduced tensile attachment strength. In accordance with the principles of the present disclosure, by initially texturizing the surface of the device, plasma-sprayed titanium may be applied to the surface of the device. In one embodiment, the height H of the texturization is approximately equal to the height of the desired coating. By initially texturizing the surface of the implant, manufacturers are able to spray less material with varying grain size (e.g., initially spraying smaller bead sizes to provide initial tensile attachment strength) and subsequently increasing the bead size to provide increased pore morphology. In use, the texturized features act to move the plasma-sprayed titanium away from the surface of the device. Plasma sprayed coatings may form a three-dimensional interconnected array of pores  125 . Tissue of the live bone  130  will integrate into a portion of the pores  125 , providing enhanced implant fixation. 
     Referring now to  FIG.  4   , an example of a method  200  for forming a medical device, such as an implant, will be described in greater detail. At block  201 , the method  200  includes applying a plurality of texture features onto a surface of the medical device. In some embodiments, the plurality of texture features may be applied in a uniform or non-uniform manner. For example, the plurality of texture features may be applied in a uniform height and/or pitch. In some embodiments, the texture features and the indentations may be formed in a surface of the device via mechanical etching/grooving (e.g., machining, shaping, scribing, knurling, etc.), laser etching/texturing, chemical etching, or other texturing means. In some embodiments, the texture etching can be symmetric and/or asymmetric, 2-D or 3-D. 
     At block  203 , the method  200  may include forming a coating over the substrate, the coating comprising a plurality of coating structures, wherein a first coating structure group of the plurality of coating structures has a first size, wherein one or more coating structures of the first coating structure group is in direct contact with the plurality of texture features or the base surface, wherein a second coating structure group of the plurality of coating structures has a second size, and wherein the first size is less than the second size. In some embodiments, the first coating structure group of the plurality of coating structures has a first porosity and a first pore size, and the second coating structure group has a second porosity and a second pore size, wherein the first porosity is less than the second porosity or the first pore size is less than the second pore size. 
     In some embodiments, the porous coating is formed by plasma spraying titanium over the substrate, including over the plurality of texture features. In some embodiments, forming the porous coating includes plasma spraying cobalt chrome, titanium, zirconium, oxidized zirconium, or stainless steel over the substrate, including over the plurality of texture features. In one embodiment, the coating may have a height substantially equal to the height of the texturized surface. 
     As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. 
     The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Accordingly, the terms “including,” “comprising,” or “having” and variations thereof are open-ended expressions and can be used interchangeably herein. 
     All directional references (e.g., proximal, distal, upper, lower, upward, downward, left, right, lateral, longitudinal, front, back, top, bottom, above, below, vertical, horizontal, radial, axial, clockwise, and counterclockwise) are only used for identification purposes to aid the reader&#39;s understanding of the present disclosure, and do not create limitations, particularly as to the position, orientation, or use of this disclosure. Connection references (e.g., attached, coupled, connected, and joined) are to be construed broadly and may include intermediate members between a collection of elements and relative movement between elements unless otherwise indicated. As such, connection references do not necessarily infer that two elements are directly connected and in fixed relation to each other. 
     Furthermore, identification references (e.g., primary, secondary, first, second, third, fourth, etc.) are not intended to connote importance or priority, but are used to distinguish one feature from another. The drawings are for purposes of illustration only and the dimensions, positions, order and relative sizes reflected in the drawings attached hereto may vary. 
     Furthermore, the terms “substantial” or “substantially,” as well as the terms “approximate” or “approximately,” can be used interchangeably in some embodiments, and can be described using any relative measures acceptable by one of ordinary skill in the art. For example, these terms can serve as a comparison to a reference parameter, to indicate a deviation capable of providing the intended function. Although non-limiting, the deviation from the reference parameter can be, for example, in an amount of less than 1%, less than 3%, less than 5%, less than 10%, less than 15%, less than 20%, and so on. 
     Still furthermore, although the illustrative methods are described above as a series of acts or events, the present disclosure is not limited by the illustrated ordering of such acts or events unless specifically stated. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein, in accordance with the disclosure. In addition, not all illustrated acts or events may be required to implement a methodology in accordance with the present disclosure. Furthermore, the methods may be implemented in association with the formation and/or processing of structures illustrated and described herein as well as in association with other structures not illustrated. 
     The present disclosure is not to be limited in scope by the specific embodiments described herein. Indeed, other various embodiments of and modifications to the present disclosure, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such other embodiments and modifications are intended to fall within the scope of the present disclosure. Furthermore, the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose. Those of ordinary skill in the art will recognize the usefulness is not limited thereto and the present disclosure may be beneficially implemented in any number of environments for any number of purposes.