Patent Publication Number: US-2020297479-A1

Title: Soft filled prosthesis shell with discrete fixation surfaces

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 15/923,932, filed on Mar. 16, 2018, which is continuation of U.S. patent application Ser. No. 15/212,601, filed on Jul. 18, 2016, now U.S. Pat. No. 9,918,829, issued Mar. 20, 2018, which is a continuation of U.S. patent application Ser. No. 14/273,292, filed on May 8, 2014, now U.S. Pat. No. 9,393,106, issued Jul. 19, 2016, which is a continuation of U.S. patent application Ser. No. 13/953,379, filed on Jul. 29, 2013, now U.S. Pat. No. 9,138,311, issued Sep. 22, 2015, which is a continuation of U.S. patent application Ser. No. 12/540,317, filed Aug. 12, 2009, now U.S. Pat. No. 8,506,627, issued Aug. 13, 2013, which claims the benefit of U.S. Provisional Patent Application Ser. No. 61/088,418, filed on Aug. 13, 2008, the entire disclosures of which are incorporated herein by this specific reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to soft prosthetic implants and, more particularly, to textured exterior surfaces of such implants, for instance, breast implants. 
     BACKGROUND OF THE INVENTION 
     Implantable prostheses are commonly used to replace or augment body tissue. In the case of breast cancer, it is sometimes necessary to remove some or all of the mammary gland and surrounding tissue, which creates a void that can be filled with an implantable prosthesis. The implant serves to support surrounding tissue and to maintain the appearance of the body. The restoration of the normal appearance of the body has an extremely beneficial psychological effect on post-operative patients, eliminating much of the shock and depression that often follows extensive surgical procedures. Implantable prostheses are also used more generally for restoring the normal appearance of soft tissue in various areas of the body, such as the buttocks, chin, calf, etc. 
     Soft implantable prostheses typically include a relatively thin and flexible envelope or shell made of vulcanized (cured) silicone elastomer. The shell is filled either with a silicone gel or with a normal saline solution. The filling of the shell takes place before or after the shell is inserted through an incision in the patient. 
     In the United States, women can choose between two different types of breast implant shell surfaces: a smooth surface and a textured surface. The surgeon generally recommends the type of surface based on his or her technique and the shape of the breast implant chosen to best fit the needs of each patient. 
     Breast implants are not without complications, one of which is termed capsular contracture. This is a complication that occurs upon contraction of a fibrous outer capsule that forms around the implant, which tends to render the implant spherical and stiff and aesthetically undesirable. According to the United States Food and Drug Administration&#39;s (FDA) Breast Implant Consumer Handbook (2004), the literature shows that textured surface breast implants may decrease the capsular contracture rate. 
     Texturing may be provided in a number of ways. Silicone gel breast implants covered with a thin layer of textured polyurethane foam enjoyed considerable popularity in the 1980s because of their remarkable resistance to the early development of fibrous capsular contracture. For example, U.S. Pat. No. 3,293,663 describes a soft gel-filled prosthesis with a porous polyester fabric on the back side for tissue ingrowth and anchoring to the chest wall. Although these devices are no longer available in the U.S. because of regulatory constraint, their medical and commercial success stimulated interest in surface texturization of silicone implants. 
     Despite many advances in the development of safe and comfortable prosthetic implants, there remains room for improvement. 
     SUMMARY OF THE INVENTION 
     The present invention provides a prosthesis suitable for implantation in a human being, for example, a breast implant suitable for use in reconstruction or augmentation of the human breast. The prosthesis generally comprises an implantable member, for example, an elastomeric shell that is filled or is fillable with a liquid or gel. The implantable member has an exterior surface including one or more fixation regions defined thereon and configured, positioned or structured to provide enhanced or controlled tissue ingrowth or adhesion. 
     In accordance with one aspect of the invention, the fixation surfaces are discrete, generally elongated surface portions extending across an anterior face or a posterior face of the implant. These fixation surfaces, sometimes herein referred to as “fixation regions”, are generally defined by a texture, roughness or sheen that is different from a texture, roughness or sheen of adjacent surface portions of the implant. 
     In some embodiments, the fixation regions have an increased or enhanced texture relative to the balance of the anterior face or posterior face of the implant. In other words, the balance of the exterior surface may be relatively less textured than the fixation regions. In some embodiments, the fixation regions are textured and adjacent surfaces, for example, the surface or surfaces that are not defined by the fixation regions, are substantially less textured, or are relatively smooth. 
     The prosthesis may be structured to encourage enhanced tissue ingrowth or adhesion at the fixation regions, relative to an otherwise identical surface without such texture, roughness or sheen. 
     In one aspect of the invention, the fixation regions are positioned and/or configured such that the prosthesis, after implantation in the body, moves more naturally with the human body, for example, in relative unity with the muscles of the body. It is contemplated that because the implant moves more naturally with the human body, the implant may be less prone to wear resulting from material stresses relative to conventional implants, for example, implants without such fixation regions. Furthermore, it is contemplated that the present implants will be more comfortable to the patient in that they will move more naturally with the body. 
     In a more specific aspect of the invention, the fixation regions may be located at specific regions on an anterior face of the shell, that is, a face of the shell which faces the front of the human body when the implant has been appropriately implanted in the human body. Alternatively or additionally, one or more discrete fixation surface may be provided on a periphery of the shell (e.g. circumferentially) and/or on the posterior face of the shell, that is, the face of the shell that faces the back of the human body when the implant has been implanted in the human body. 
     In an even more specific aspect of the invention, the fixation regions comprise at least one elongated region located on the anterior face of the shell. The at least one elongated region may be, for example, a band-shaped region or alternatively, a plurality of band shaped regions having enhanced texture, roughness or sheen. 
     The elongated fixation regions may be positioned to align with one of the pectoralis major muscle groups or pectoralis minor muscle groups of the human body when the implant is implanted in the body. For example, in one embodiment of the invention, the at least one elongated region comprises a diagonally positioned band shaped region intended to align with the pectoralis major muscle group when the implant has been implanted in the body. In another embodiment, the at least one fixation region comprises a plurality of elongated regions in a radiating configuration generally copying the positioning of the pectoralis minor muscle group wherein the implant has been implanted in the body. 
     In another broad aspect of the invention, the prosthesis comprises a breast implant having a shell including a fixation region having a first texture and a balance of the shell surface having a second texture that is different from the first texture. In other words, in some embodiments of the invention, the entire, or substantially entire, exterior of the breast implant shell is a textured surface with specific regions thereof having a greater degree of texturing relative to the remaining portions of the textured surface. 
     It is contemplated that such different texturing will stimulate or encourage different degrees of tissue ingrowth or adhesion at the different fixation regions. For example, in one embodiment, the first fixation region is located on a posterior face of the implant and the second fixation region is located on an anterior face of the implant. The first fixation region may be defined by a texture that is more conducive to tissue interaction and adhesion whereas the second fixation region may be defined by a texture that is relatively less conducive to tissue interaction and adhesion. 
     In yet another aspect of the invention, the prosthesis comprises a shell having an exterior structured to contact tissue, the shell including a first fixation surface having a first open cell structure, and a second fixation surface having a second open cell structure different than said first open cell structure. In addition, the first fixation surface and the second fixation surface are positioned to encourage respectively different degrees of tissue ingrowth or tissue adhesion by the body at a body-shell interface. 
     For example, the first open cell structure comprises relatively large open cells and the second open cell structure comprises relatively smaller open cells. Alternatively or additionally, the first open cell structure may comprise a first distribution of cells and the second open cell structure comprises a second distribution of cells wherein the first distribution of cells is relatively more dense than the second distribution of cells. 
     In yet another specific aspect of the invention, the first open cell structure comprises relatively large rounded open cells and the second open cell structure comprises relatively small rounded open cells. Alternatively, the first open cell structure comprises relatively rounded open cells and the second open cell structure comprises relatively angular open cells. 
     Advantageously, in accordance with certain embodiments, the first and second fixation surfaces are positioned and structured to be at least somewhat effective to disrupt or disorient capsular tissue formation about the prosthesis after the prosthesis has been implanted in the body. 
     The present invention further provides a breast prosthesis shell for implantation in a human being, the shell manufactured by the steps of providing a shell precursor; applying a layer of silicone elastomer to the shell precursor, applying solid particles of a first configuration to a portion of the layer of silicone elastomer and applying solid particles of a second configuration to another portion of the layer of silicone elastomer before the layer is fully cured. After the layer including the solid particles embedded therein is cured, the solid particles are then dissolved, for example, by means of a solvent that does not dissolve the silicone elastomer to any appreciable extent. The resulting elastomer shell includes a first open cell texture region formed by said application of the solid particles of the first configuration, and a second open cell texture region formed by said application of the solid particles of the second configuration. 
     In yet another aspect of the invention, a method of augmenting or reconstructing a breast of a human being is provided. The method generally comprises providing an implantable member including at least one elongated fixation region as described elsewhere herein and implanting the implantable member into a breast of a human being such that the fixation region generally aligns with one of the pectoralis major muscle group and the pectoralis minor muscle group. The method may further comprise filling the implantable member with a liquid or gel prior to or after the implanting step. 
     A further understanding of the nature and advantages of the present invention are set forth in the following description and claims, particularly when considered in conjunction with the accompanying drawings in which like parts bear like reference numerals. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features and advantages of the present invention will become appreciated as the same become better understood with reference to the specification, claims, and appended drawings wherein: 
         FIGS. 1A and 1B  are a front view and a side elevational view, respectively, of an exemplary round breast implant of the present invention; 
         FIGS. 2A and 2B  are a front view and side elevational view, respectively, of an exemplary shaped breast implant of the present invention; 
         FIGS. 3A and 3B  are schematic views of a woman&#39;s upper torso showing, alignment of the pectoralis major muscle group and the pectoralis minor muscle group, respectively; 
         FIGS. 4A and 4B  are vertical sectional views through a woman&#39;s breast and adjacent chest anatomy showing, respectively, subglandular and submuscular placement of a breast implant; 
         FIGS. 5A and 5B  are front and side elevational views of an exemplary round breast implant of the present invention having a generally elongated or band-shaped fixation surface; 
         FIGS. 6A and 6B  are front and side elevational views of an exemplary shaped breast implant of the present invention having a generally elongated or band-shaped fixation surface; 
         FIG. 7  is a front elevational view of another breast implant in accordance with the invention including a first fixation region having a first texture and a second fixation region having a second texture different from the first texture; 
         FIGS. 8A and 8B  are front and rear elevational views of an exemplary round breast implant of the present invention having a front texture and a rear texture that are different from one another. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention provides a saline- or gel-filled soft implant shell, preferably a silicone elastomer shell, with a fixation surface over an exterior portion. The primary application for such soft implants is to reconstruct or augment the female breast. Other potential applications are implants for the buttocks, testes, or calf, among other areas. 
     The terms “fixation surface” or “fixation region”, as used herein, generally refer to a region or portion of an exterior surface of an implant which is positioned, structured or adapted to encourage tissue ingrowth or adhesion at a body/implant interface. For example, a fixation region may be a texture, roughness or sheen that is distinct from, for example, more pronounced than, adjacent surfaces of the implant which do not encourage tissue ingrowth of adhesion to the same degree as the fixation region. For example, other regions or surfaces of the implant exterior may be relatively smooth or less textured relative to the fixation regions. 
     Such a fixation region may be formed by any suitable means, for example, but not limited to, a salt removal process such as described in U.S. Pat. No. 5,007,929, with appropriate changes being made. Alternatively, the fixation surfaces may be formed by separate textured elements such as textured patches or films adhered to the outside of an otherwise “smooth” or less textured implant. Still, another method for forming the discrete fixation regions may be by using a relatively roughened surface portion of a mold used to form the implant. Another method for forming the present fixation regions includes texturing the exterior of the implant after formation. The present invention should not be considered limited to any particular type of texturing or fixation surface, though there might be certain advantages with one or more of these techniques. 
     Turning now to the Figures,  FIGS. 1A and 1B  are front and side elevational views of an exemplary round breast implant  20  of the present invention. Generally, the implant  20  comprises an exterior surface defined by a relatively smooth anterior face  21 , a textured posterior face  22  and a textured peripheral region  24  located between the anterior face  21  and the posterior face  22 . The relatively smooth anterior face may be a relatively less textured surface (relative to texture of posterior face  22 ), such as, for example, a fine textured surface or even a matte finish. In some embodiments, the implant  20  has a relatively smooth posterior face, a textured anterior face and a textured or smooth peripheral region. The fixation surfaces  22 ,  24  themselves may have differing degrees of texturing. The diameter D and front-to-back thickness T of the implant are shown and vary depending on the patient&#39;s chest size and aesthetic considerations. 
     In the shown embodiment, the rear fixation surface  22  extends to the apex  26  or generatrix of the convex outer periphery of the implant  20 . The peripheral fixation surface  24  continues forward a short distance S onto the anterior or front surface  21 . In some embodiments, the distance S is between about 10% and about 30% of the thickness T. In some embodiments, the peripheral fixation surface  24  extends substantially entirely around the periphery of the implant  20 , such that the implant  20  is axi-symmetric. In other embodiments, the peripheral fixation surface  24  may be abbreviated so as to extend around only a portion of the periphery of the implant, such as the inferior or superior half, or the peripheral fixation surface may be broken up into spaced apart segments. In some embodiments, the peripheral fixation surface  24  comprises substantially evenly spaced segments resulting in alternating smooth and textured areas. 
       FIGS. 2A and 2B  illustrate an exemplary shaped breast implant  30  of the present invention having an inferior frontal lobe  32  simulating a natural breast. Like implant  20 , implant  30  includes a rear fixation surface  34  and a peripheral fixation surface  36 . The width W, height H, and front-to-back thickness T of the implant are shown. If the front projection is round, then W=H, otherwise W may be greater than or less than H. When provided with a natural shape, the implant  30  has a proper orientation, namely with the inferior lobe  32  at the lower center. Accordingly, the peripheral fixation surface  36  may extend completely around the periphery of the implant, or may be formed in discrete areas and be oriented relative to the natural shape of the implant. For example, the peripheral fixation surface  36  may be formed only around the inferior or lower half of the implant, or may be formed only on the sides. 
       FIG. 3A  illustrates a woman&#39;s upper torso schematically showing on one side placement and alignment of the pectoralis major muscle group, while  FIG. 3B  illustrates the placement and alignment of the pectoralis minor muscle group. These two muscle groups overlap one another and extend generally from the shoulder or collarbone region to the rib cage underneath the breast. One aspect of the present invention is to provide an implant including fixation surfaces such as described elsewhere herein, which are substantially aligned with these muscle groups when the implant is placed in the body. 
     While not wishing to be bound by any specific theory of operation, the regions or lines of contact of the implant with the primary chest muscles experience greater movement than other areas of the implant not interfacing the muscles. It is believed by the present inventors that by providing a fixation region of the implant that is substantially coincident with or in substantial alignment with one or more of these muscle groups is more likely to remain secured (i.e., they move with the muscle). In addition, it is contemplated that such discrete fixation regions may provide the benefit of disrupting capsule formation and/or reducing the potential for capsular contraction. 
       FIG. 4A  is a vertical sectional view through a woman&#39;s breast and adjacent chest anatomy showing a subglandular placement of a breast implant  40 . The implant  40  is positioned over the top of the pectoralis major muscle group  42 , which in turn overlays the pectoralis minor muscle group  44 . The chest wall  48  showing a plurality of ribs  50  is also indicated underneath the pectoralis minor muscle  44 .  FIG. 4B  is a vertical sectional view as in  FIG. 4A  but showing a submuscular placement of the implant  40 , underneath the pectoralis major muscle group  42 . Both these two implant placements are utilized primarily depending on the surgeon&#39;s clinical determination, sometimes influenced by a dialogue between patient and the surgeon and desired outcome. Depending on the implant placements, the implant  40  may be in contact with one or both muscle groups. In some embodiments of the invention, the implant includes substantially elongated fixation regions as described and shown herein, and said fixation regions being in substantial alignment with the appropriate muscle group which interface the implant when the implant is placed in the body. 
     For example,  FIGS. 5A and 5B  are front and side elevational views of an exemplary round breast implant  60  of the present invention having a posterior face  62 , a peripheral region  64 , and an anterior face including an elongated or band-shaped fixation region  66 . The band-shaped fixation region  66  extends generally along a diagonal angle and commences at the front border of the peripheral fixation surface  64 . The illustrated embodiment, the fixation region  66  has a substantially constant width W as seen from the front in  FIG. 5A . In one embodiment, the width W is between about  1  mm to about 20 mm, for example, between about 2 mm to about 15 mm. Alternatively, although not shown, the fixation region  66  may have a configuration that is other than a constant width. 
     In one embodiment, the band-shaped fixation surface  66  is generally oriented or aligned with either the pectoralis major muscle group or pectoralis minor muscle group when the implant is implanted in the breast. For instance, if the implant  60  is destined for a submuscular placement such as in  FIG. 4B , the fixation surface  66  may be oriented to be generally aligned with the pectoralis major muscle group, as seen in  FIG. 3A . Alternatively, the angle at which the insertion surface  66  is oriented may be an approximation of the average angle of the pectoralis major and pectoralis minor muscle groups. In this way, the implant  60  has a fixation surface  66  to encourage tissue ingrowth or adhesion along the major stress lines of the implant. Preferably, the fixation surface  66  is angled between about 30-60° with respect to a vertical plane through the implant  60 . Of course, if the implant  60  is round as shown, the fixation surface  66  itself defines the orientation thereof. In one embodiment, the band-shaped fixation surface  66  is centered about the center of the implant  60 , therefore creating two symmetric orientations about 180° apart. This arrangement facilitates implant by providing two possible orientations for the surgeon. 
     The band-shaped fixation region  66  may extend substantially across the anterior face of the implant and may be defined by a texture that is different from a balance of the anterior face. The fixation region  66  may also have a different texture, for example, a more pronounced or more aggressive texture, than the rear fixation surface  62  or peripheral surface  64 . 
       FIGS. 6A and 6B  illustrate another exemplary shaped breast implant  70  of the present invention. The implant  70  again features a rear fixation surface  72 , a peripheral fixation surface  74 , and a plurality of separate band-shaped fixation surfaces  76   a,    76   b,    76   c.  These discrete fixation surfaces  76   a,    76   b,    76   c  are positioned or configured to align with one or more of the muscle groups described above. For example, the three fixation surfaces  76   a,    76   b,    76   c  may be generally oriented relative to the fan-shaped pectoralis minor muscle group. Because the shaped implant  70  is orientation-specific, proper placement of the implant orients the fixation surfaces  76   a,    76   b,    76   c  with the particular muscle group. As mentioned above, the various fixation surfaces  72 ,  74 ,  76   a,    76   b,  and  76   c  may be formed with a similar level of roughness, or some may be less textured, such as with a matte finish. For instance, the rear and peripheral fixation surfaces  72 ,  74  may have a fine, matte finish, while the frontal fixation surfaces  76   a,    76   b,    76   c  are more densely textured. The present invention contemplates all permutations of texturing choices. 
     In cross-section, the textured implant shells of the present invention may be single- or multi-layered. The overall thickness of the textured implant shell wall may be somewhat greater than a similar smooth-walled shell because of the extra layers of texture. 
     Turning now to  FIG. 7 , an anterior (front) view of another breast implant of the present invention is shown generally at  110 . The implant  110  includes a shell  112  having an exterior surface including a first fixation region  114  having a first texture  116  and a second fixation region  118  having a second texture  122  that is different from the first texture  116 . In the shown embodiment, the first texture  116  is a more “aggressive” texture than the second texture  122 . The first texture  116  is structured to encourage a greater degree of tissue interaction than the second texture  122 . 
     In lieu of the second texture  122 , it is contemplated that the second fixation region  118 , and perhaps the entire balance of the exterior of the shell  112 , may be a low sheen surface, for example, a matte finish. 
     Turning now to  FIGS. 8A and 8B , anterior (front) and posterior (rear) views, respectively, of another breast implant in accordance with the invention are shown generally at  210 . The implant  210  includes a shell  212  having an anterior face  212   a  and a posterior face  212   b,  and including a first fixation region  214  having a first texture  216  and a second fixation region  218  having a second texture  222  that is different from the first texture  216 . In the shown embodiment, the first texture  216  may encompass the entire, or substantially entire, anterior face  212   a  of the implant  210 . The first texture  216  is defined by a first distribution of pores, crevices or caverns that is relatively less dense than that of the second texture  222 . The second texture  222 , which may encompass the entire, or substantially entire, posterior face  221   b  of the implant  210 , may be structured to encourage a greater degree of tissue interaction and adhesion than that of the first texture  216 . 
     The shells  112  and  212  may be manufactured by a method of the invention comprising the steps of providing a shell precursor; applying a layer of silicone elastomer to the shell precursor, applying solid particles of a first configuration to a portion of the layer of silicone elastomer and applying solid particles of a second configuration to another portion of the layer of silicone elastomer before the layer is fully cured. After the layer including the solid particles embedded therein is cured, the solid particles are then dissolved, for example, by means of a solvent that does not dissolve the silicone elastomer to any appreciable extent. The resulting elastomer shell includes a first open cell texture region formed by said application of the solid particles of the first configuration, and a second open cell texture region formed by said application of the solid particles of the second configuration. 
     One process for forming flexible implant shells for implantable prostheses involve dipping a suitably shaped mandrel into a silicone elastomer dispersion. Many such dispersions are used in the field. Basically they contain a silicone elastomer and a solvent. The silicone elastomer is typically polydimethylsiloxane, polydiphenyl-siloxane or some combination of these two. Typical solvents include xylene or 1,1,1-trichloroethane. Different manufacturers vary the type and amount of the ingredients in the dispersion, the viscosity of the dispersion and the solid content of the dispersion. Nonetheless, the present invention is expected to be adaptable to have utility with a wide variety of silicone rubber dispersions. 
     The mandrel is withdrawn from the dispersion and the excess silicone elastomer dispersion is allowed to drain from the mandrel. After the excess dispersion has drained from the mandrel at least a portion of the solvent is allowed to volatilize or evaporate. Normally this is accomplished by flowing air over the coated mandrel at a controlled temperature and humidity. Different manufacturers use various quantities, velocities or directions of air flow and set the temperature and humidity of the air at different values. However, the desired result, driving off the solvent, remains the same. 
     It is also common for prostheses manufacturers to repeat this dip and volatilize procedure a number of times so that a number of layers are built up on the mandrel to reach a desired shell thickness. A layered structure like most current silicone elastomer shells can be made by sequentially dipping the mandrel in different dispersions. Alternatively, the steps may be repeated in a single dispersion so that the finished product is a single homogenous material or layer. That is, the dipping process may be done in multiple stages or steps, each step adding more material, yet the finished product exhibits no distinct layers and the entire shell wall is homogenous or uniform in composition. 
     An exemplary process for forming the fixation surfaces on either a multi-layered shell or a single-layered shell will now be described. After the mandrel is raised out of the dispersion with what is to be the final layer adhering thereto, this layer is allowed to stabilize. That is, it is held until the final coating no longer flows freely. This occurs as some of the solvent evaporates from the final coating, raising its viscosity. 
     Again, it should be understood that alternative methods are contemplated for forming the flexible shell prior to the texturing process. The dip molding process advantageously results in the flexible shell pre-mounted on a dipping mandrel, which can then be used for the texturing process. However, if the flexible shell is made by another technique, such as by rotational molding, it can subsequently be mounted on a dipping mandrel and the process continued in the same manner. 
     Once the flexible shell has been stabilized and mounted on the mandrel, any loose fibers or particles are removed from the exterior of the shell, for example, with an anti-static air gun. A tack coat layer is then applied. The tack coat layer may be sprayed on, but is desirably applied by dipping the flexible shell on the mandrel into a tack coat dispersion. The operator immerses the flexible shell into the dispersion and returns the mandrel to a rack for stabilization. The time required for stabilization typically varies between 5-20 minutes. A suitable tack coat layer is desirably made using the same material employed in the base layers. 
     At this point, granulated solid particles (i.e., salt crystals) are applied over that portion of the exterior surface that will end up as the fixation surface. The solid particles may be applied manually by sprinkling them over the surface while the mandrel is manipulated, or a machine operating like a bead blaster or sand blaster could be used to deliver a steady stream of solid particles at an adequate velocity to the coating on the mandrel. However, a preferred method of solid particle application is to dip the mandrel/shell into a body of the solid particles or expose it to a suspension of the solid particles. It should be understood that the present invention is not intended to be restricted to any one particular method of applying particles. One possible method to apply solid particles to some but not all of the shell is to mask off areas of the shell for which particles are not to be applied and then apply the particles to the non-masked areas. 
     The tacky flexible shell may then be immersed in a fluidized (air-mixing) aqueous salt bath having regular cubic salt crystals between about 10 to about 600 microns, or round crystals between about 50-2000 microns or a combination thereof. Varying degrees of texturing may be formed with the salt removal process by using differently sized or shaped salt granules (for example, round salt crystals versus angular salt crystals, large salt crystals versus relatively small salt crystals, high density distribution of salt crystals versus relatively low density distribution of salt crystals), on different areas of the shell. The shell is rotated for even coverage, removed, and then allowed to stabilize. After a suitable period of stabilization, such as between about 5-20 minutes, the flexible shells may be dipped into an overcoat dispersion. A suitable overcoat dispersion may be made using the same material employed in the base layers. The flexible shells on the mandrels are then mounted on a rack and allowed to volatilize, such as, for example, about 15 minutes. 
     The entire silicone elastomer shell structure is vulcanized or cured in an oven at elevated temperatures. The temperature of the oven is preferably kept between about 200° F. and about 350° F. for a curing time preferably between about 20 minutes and about 1 hour, 40 minutes. Upon removal from the oven, the mandrel/shell assembly is placed in a solvent for the solid particles, and the solid particles allowed to dissolve. The solvent does not affect the structure or integrity of the silicone elastomer. When the solid particles have dissolved, the assembly is removed from the solvent and the solvent evaporated. The shell can then be stripped from the mandrel. At this point, it is preferable to place the shell in a solvent for the solid particles and gently agitate it to ensure complete dissolution of all the solid particles. When the shell is removed from the solvent, the solvent is evaporated. 
     Dissolving the solid particles leaves behind open, interconnected, cavities in the surface of the shell where the salt had been. 
     After finishing the shell according to the steps described above, the steps required to make a finished breast implant prosthesis may be similar to those known in the art. For example, an opening left by the dip molding process is patched with uncured sheeting, usually made of silicone rubber. Then, if the prosthesis is to be filled with silicone gel, this gel is added and cured, the filled prosthesis packaged, and the packaged prosthesis sterilized. If the prosthesis is to be inflated with a saline solution, a one-way valve is assembled and installed, the prosthesis is post cured if required, and the prosthesis is then cleaned, packaged and sterilized. A combination breast implant prosthesis can also be made wherein a gel-filled sac is positioned inside the shell to be surrounded by saline solution. 
     In addition to the aforementioned dipping process, the flexible shell for the prosthetic implant may be formed using a molding process. For example, a rotational molding process such as described in Schuessler, U.S. Pat. No. 6,602,452 the entire disclosure of which is incorporated herein, may be used. The process for forming texturing on the exterior surface may be done using a dipping technique after the shell is molded, but another method is to roughen the inside of the mold. For example, a mold having a generally smooth interior surface except for rough areas as described above will produce an implant shell having discrete fixation surfaces. The rotational molding process is advantageous because the entire implant shell may be formed in relatively few manufacturing steps. 
     Although the invention has been described and illustrated with a certain degree of particularity, it is understood that the present disclosure has been made only by way of example, and that numerous changes in the combination and arrangement of parts can be resorted to by those skilled in the art without departing from the scope of the invention, as hereinafter claimed.