Abstract:
A mammary implant and method of making are provided herein. The implant includes an outer shell configured to retain fluid therein, an injection element coupled to the outer shell and adapted to receive therethrough an injection device for injecting fluid into the outer shell, and an injection marker zone made of a material having ultrasonically detectable markers incorporated therein. The markers are a plurality of microcavities that are located relative to the injection element so that, when ultrasonically detected, such detection indicates a location of the injection element.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to implantable devices, and more particularly to tissue expanders and prostheses having markers to assist in locating the implant or selected area(s) of the implant once implanted. Although the tissue expanders may be used in other areas of the body, one specific application is mammary implants such as soft tissue expanders. 
         [0002]    Tissue expanders are devices that are implanted beneath the skin or muscle and then gradually inflated to stretch the overlying tissue. Expanders are commonly used either to create a pocket for receiving a permanent prosthesis, or to generate an increased skin surface area in anticipation of the new skin being utilized for grafting or reconstruction. 
         [0003]    Conventional implantable mammary tissue expanders are formed of a silicone polymer shell. After implantation, a fluid, such as saline, is periodically injected into the expander to enlarge it over time. Between injections, the surrounding skin is permitted to stretch and grow to create the increased skin surface and the increased tissue pocket for receipt of the permanent implant. Typically, a tissue expander will be provided with an injection element through which fluid can be introduced into or withdrawn from the expander. One such injection element is an integrated injection dome comprising a septum that can be pierced with a hypodermic needle for the introduction into or withdrawal of fluid from the expander. Alternatively, the injection element may be a self-sealing area on the tissue expander which allows penetration by a hypodermic needle and self-closing after the withdrawal of the needle. 
         [0004]    It can be difficult, however, to accurately locate the injection element through the overlying tissue once the expander has been implanted. If the injection element is missed and the needle punctures the shell of the tissue expander, the expander can leak, which typically requires removal and replacement of the expander. In an effort to reduce the likelihood of inadvertent puncture, one known device provides an injection element surrounded by a self-sealing member, which provides a safety zone around the injection element. This type of arrangement is disclosed, for example, in the U.S. Pat. No. 6,743,254, the disclosure of which is hereby incorporated by reference herein. Other solutions include providing a palpation ring around the injection element. It still can be difficult, however, to identify the proper location through tissue, and a raised palpation ring may cause additional pain and discomfort to the patient. Other known expanders use a magnetic component near or around the injection dome (such as sealing ring) or behind the dome (such as a needle stop). A detection device is then utilized to locate the magnetic component through interaction with the magnetic field. Yet other known devices have used radiographic detection of the access port, such as is disclosed in U.S. Pat. Nos. 8,382,723 and 8,382,724 and U.S. Patent Publication Nos. 2006/0264898 and 2010/0198057. 
         [0005]    U.S. Patent Publication No. 2011/0275930, entitled “SYSTEMS AND METHODS FOR IDENTIFYING AND LOCATING AN IMPLANTED DEVICE”, discloses a system for identifying an attribute of an implanted medical device, such as an access port. In one embodiment, the identification system includes a marker and an external detection device with a signal source that emits an incident electromagnetic signal for impingement on the marker and a detector that detects a return signal from the marker, and a user interface for conveying information relating to the attribute based on detection of the return signal. In the case of an implantable access port, for instance, the described system enables information, such as the ability of the port to withstand power injection of fluids therethrough, to be ascertained even after the port has been subcutaneously implanted within the patient. 
         [0006]    Systems and methods of the types described above are not ideal. Magnetic field based detection systems incorporate magnets or metallic parts, which may be undesirable to some patients, and which result in difficulties in passing through airport security or undergoing MRI procedures, etc. Radiographic detection systems require additional exposure to radiation, which is undesirable. Further, these types of devices require additional parts, which add to the cost of the expander itself. Thus, there is a need to provide an implant including an improved marker for more readily locating the implant once implanted. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    The present invention provides a mammary implant including an outer shell configured to retain a fluid therein, an injection element coupled to the outer shell and adapted to receive therethrough an injection device for injecting fluid into said outer shell, and an injection marker zone made of a material having ultrasonically detectable markers incorporated therein. The markers are a plurality of microcavities that are located relative to the injection element so that, when ultrasonically detected, such detection indicates a location of the injection element. 
         [0008]    In one embodiment, the microcavities each have a size less than or equal to zoo microns. The microcavities may be filled with gas, and in alternate embodiments the gas may be air, nitrogen, carbon dioxide, or argon. 
         [0009]    In yet another embodiment, the microcavities are substantially uniformly distributed within the material, and/or may have a density of at least 1000 microcavities per cm 2 . 
         [0010]    The injection marker zone may be configured to substantially surround the injection element, may have a substantially circular outer shape, or may have a substantially rectangular outer shape. 
         [0011]    In yet another alternate embodiment, the injection marker zone overlays at least a portion of said injection element. Alternatively, it may form part of the outer shell, with the plurality of microcavities incorporated within the shell. Further, the shell may be made of silicone. 
         [0012]    In yet another embodiment, the injection marker zone forms part of the injection element, and the microcavities are embedded within a material forming at least a part of the injection element. 
         [0013]    The present invention also provides an inflatable implant including an outer shell configured to retain fluid therein, an injection element coupled to the outer shell and adapted to receive therethrough an injection device for injecting fluid into the outer shell, and an injection marker zone positioned relative to the injection element so as to identify a location of the injection element. The injection marker zone is made of a material having incorporated therein a plurality of gas filled microcavities each having a size less than or equal to zoo microns. 
         [0014]    Also provided herein is a method of making an implant having an ultrasonically detectable injection marker zone. The method includes the steps of forming an outer shell of the implant that is made of a flexible material, coupling to the flexible outer shell an injection element adapted to receive therethrough an injection device for injecting fluid into the outer shell, preparing a liquid material having a plurality of microcavities suspended therein, wherein the microcavities are gas filled and have a size less than or equal to zoo microns, and applying the liquid material having the plurality of microcavities suspended therein to the implant at a predetermined location to form an injection marker zone, wherein the injection marker zone identifies a relative location of the injection element when ultrasonically detected. 
         [0015]    In one embodiment, the preparing step further includes injecting a gas into the liquid material through an injector or sparger having a plurality of orifices having size less than or equal to zoo microns. 
         [0016]    In yet another embodiment, the preparing step further includes using a high speed agitator to agitate the liquid material in the presence of gas. In yet another alternate embodiment, the preparing step further includes dispersing preformed gas filled microcapsules into the liquid material. 
         [0017]    In yet another embodiment, the outer shell and injection marker zone are made of silicone. 
         [0018]    These and other objects, features and advantages of the present invention will be apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIGS. 1A-1B  are perspective and top views respectively of an exemplary mammary tissue expander according to the present invention; 
           [0020]      FIG. 1C  is a top view of an alternate embodiment of a mammary tissue expander according to the present invention; 
           [0021]      FIG. 2  is a cross-sectional, side view of the tissue expander of  FIG. 1 ; 
           [0022]      FIG. 3  is a cross-sectional, side view of an exemplary injection dome that may be used in conjunction with the present invention; 
           [0023]      FIG. 4A  is a top view of an alternative embodiment of a mammary tissue expander according to the present invention; 
           [0024]      FIG. 4B-4C  are cross-sectional views of various exemplary embodiments of an injection dome having markers incorporated therein; 
           [0025]      FIG. 5A  is a cross-sectional, side view of yet another embodiment of a mammary tissue expander according to the present invention; 
           [0026]      FIG. 5B  is an alternative embodiment of a self-sealing structure having markers according to the present invention; 
           [0027]      FIGS. 6A-6B  and  7 A- 7 B illustrate various configurations and locations for injection marker zones; 
           [0028]      FIGS. 8A-8B  illustrate various arrangements for injection marker zones according to the present invention; 
           [0029]      FIG. 9  illustrates one embodiment of a layered structure having markers embedded therein; 
           [0030]      FIG. 10  illustrates one exemplary means by which to form a suspension of microbubbles or microcavities in a liquid; 
           [0031]      FIGS. 11A-11E  illustrate various aspects of various exemplary means by which to incorporate liquid having a suspension of microcavities or microbubbles therein into or onto a mammary tissue expander; and 
           [0032]      FIGS. 12A-12B  and  FIG. 13  illustrate exemplary uses of an implant according to the present invention in conjunction with a detection device. 
       
    
    
     DETAILED DESCRIPTION 
       [0033]    In the following are described various embodiments of a mammary implant, such as a mammary tissue expander, with markers according to the present invention. Where like elements have been depicted in multiple embodiments, identical or similar reference numerals have been used for ease of understanding. 
         [0034]    As indicated, the present invention relates to implants having markers for more readily detecting the location of the implant, or portions thereof, once implanted within a patient. Exemplary implants having such markers will first be generally described below, followed by a more detailed description of the markers themselves and various methods for integrating such markers into implants, and methods for their use. 
         [0035]    The invention described below leverages the general, well known concept that the difference between solid or liquid vs. gas can be detected by ultrasound. It is further known that small air bubbles on a gelatin surface can be detected by ultrasound within limits. See “Reflection from Bound Microbubbles at High Ultrasound Frequencies”, by Olivier Couture, et al., published in IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, Vol. 56, Issue 3, pp. 536-545 (2009). The present invention provides a novel and inventive medical device that utilizes microbubbles or microcavities to readily locate an injection port or injection zone in a mammary expander, that is simple and cost effective to manufacture, that does not require additional devices or parts, and that does not adversely affect the structural integrity of the device itself. 
         [0036]    Referring first to  FIGS. 1A-1C , an exemplary mammary tissue expander  10  is shown having an outer shell  12 , preferably made of a cross-linked silicone elastomer, and an injection element  14  such as an injection dome through which an injection device, such as a syringe (not shown), is used to add or remove fluid from the outer shell  12  to adjust the shell&#39;s volume in a manner well known in the art. 
         [0037]    An injection marker zone  16  helps identify the injection dome  14  through the tissue by providing a plurality of markers  100  which will be described in more detail below. In the embodiment shown in  FIGS. 1A and 1B , the markers  100  are arranged immediately around injection dome  14  so that the injection marker zone has an overall shape of a ring. Injection dome  14  can be readily located in the center by detecting the injection marker zone  16 , as will also be described more fully below. The width w of injection marker zone  16  is selected for easy detection, and preferably is from 10% to 100% of the diameter of dome  14 , and more preferably from 20% to 40% of the diameter dome  14 . In one embodiment, the injection marker zone is from 3 mm to 20 mm wide, and more preferably 10 mm wide.  FIG. 1C  depicts an embodiment of tissue expander  10  with the injection marker zone  16   a  having generally rectangular outer shape. Although particular configurations of the injection marker zone are shown and described herein, it is to be understood that any suitable shape and configuration may be used in accordance with the present invention so long as the injection marker zone may be readily detected, and the injection element located based on such detection. 
         [0038]      FIG. 2  is a cross-sectional, side view of an exemplary mammary tissue expander  10  including an outer shell  12  with an injection dome  14 . Injection marker zone  16  is shown with markers  100  incorporated directly into the shell  12  in the area around the injection dome  14 . Also shown is an optional reinforcing area or optional self-sealing safety patch area  50  formed around the exemplary injection dome  14 .  FIG. 3  is a cross-sectional view of the exemplary injection dome  14  of  FIG. 2  showing additional details thereof. As indicated, the function of the injection dome  14  is to allow controlled introduction and/or removal of fluid from the tissue expander  10 . Generally, this is accomplished through use of a hypodermic needle or syringe (not shown) that pierces a selected region of the injection dome  14 , such as septum region  18  which may be formed of elastomeric material. 
         [0039]    In the illustrated embodiment, the injection dome  14  is fitted into an opening in the outer shell  12 , for example at a location intended to face the skin of the patient to be expanded. The casing  20  of the injection dome is typically formed of an elastomeric material. The septum region  18  of the casing  20  is preferably located at the central region of the upper surface of the casing. The septum region  18  is self-sealing, preventing the leaking of fluid from the implant  10  after removal of the hypodermic needle from the injection dome. A flange  22  extends around the upper edge of the dome casing  20 , and overhangs the shell  12 , which is partially sandwiched between the flange and the optional self-sealing safety patch  50 . As the flange  22  rests against the outer surface of the shell  12 , it provides a surface for securely attaching the assembled injection dome  14  to the shell. In order to prevent accidental puncture of the shell  12  through the injection dome  14  itself, the injection dome is equipped with an optional needle guard  24  which functions as a backstop for the needle. The rim portion  28  of the needle guard is fitted into an annular slot  30  in the underside of the dome casing  20 . When the needle guard  24  is inserted into the slot  30  in the injection dome  14 , compressive force is exerted on the elastomeric material of the septum region  18  of the injection dome  14 . As a result of these forces, the septum region  18  of the injection dome  14  is self-sealing. Openings  32  in the rim portion  28  of the needle guard  24  allow fluid to pass to the interior of the shell  12 . A needle damper  34 , preferably formed of a resilient material, e.g., polysulfone, is positioned on top of the base  26  of the needle guard  24  to prevent damage to the hypodermic needle tip should the needle be inserted so far as to actually strike the needle guard. It is prudent to reduce the risk of damage to the hypodermic needle because a bent tip could tear a non-repairable hole that compromises the self-sealing capability in the septum region  18  upon withdrawal of the needle from the injection dome  14 . The needle damper  34  is preferably adhesively fastened to the needle guard  24 . The outer shell  12  of the tissue expander can have any desired shape and any thickness that is suitable for the purpose of the particular expander. The shell is commonly formed of a biocompatible elastomer such as silicone. 
         [0040]    Dip molding using an appropriately sized and shaped mandrel can be used to form the outer shell  12 , although other suitable means such as injection molding or spraying may also be used. With dip molding, the mandrel is dipped into silicone dispersion and then removed to allow for partial cure and solvent evaporation. The process is generally repeated several times. Once the outer shell  12  has been formed it is removed from the mandrel. This dip molding process results in the formation of a partial shell that has an opening, e.g., a circular hole (patch hole), on the posterior side. The injection dome  14  is installed and the patch hole is subsequently covered with a patch that seals the hole, thus forming a complete, fluid impervious shell. The patch is attached to the partial shell using silicone rubber or other similar biocompatible adhesive. The completed shell can either be non-filled or partially prefilled. After implantation, the expander  10  is intraoperatively filled through the septum region  18  with saline, gel, foam, or combinations of these materials or other suitable materials known in the art to gradually expand the tissue expander to the desired dimensions. This typically takes place over the course of multiple office visits. 
         [0041]    Referring now to  FIG. 4A , an alternate embodiment of tissue expander  10  is shown with markers  100  incorporated directly into the body of injection dome  14  itself, and preferably into septum region  18 . Markers  100  can be embedded throughout septum region  18  or form any geometric shape within the septum region  18  which enables a surgeon to identify it postoperatively.  FIG. 4B  shows a schematic cross-sectional view of one embodiment of an injection dome  14  and outer shell  12  in the vicinity of injection dome  14 , with markers  100  embedded into the septum region  18 .  FIG. 4C  illustrates various alternate areas where markers  100  can be embedded, such as throughout septum region  18 , into needle damper  34 , into outer shell  12  around injection dome  14 , into optional reinforcing area or optional self-sealing safety patch area  50 , at the interface between optional reinforcing area or optional self-sealing safety patch area  50  and outer shell  12 , or into flange  22 . In certain embodiments, markers in the same tissue expander are embedded into more than one area. It is to be understood that the markers described more fully below can be embedded in any suitable area and in any suitable configuration so long as sufficient to enable identification of the location of the injection element. 
         [0042]    The markers of the present invention can also be used in tissue expanders that do not have an injection dome, but instead have a self-sealing zone  15  formed of a self-sealing material or self-sealing structure  60 , as known in the art. Referring now to  FIGS. 5A and 56 , the self-sealing structure  60  may be attached to outer shell  12  from the inside as illustrated. Injections are performed through self-sealing zone  15 , which is localized by markers  100  of the present invention. These markers may alternatively be embedded into outer shell  12  around the self-sealing structure  60  ( 100   a ), into outer shell  12  in the area overlaying the self-sealing structure, or at the interface between outer shell  12  and self-sealing structure  60 . In certain embodiments, markers in the same tissue expander  10  are embedded into more than one area. 
         [0043]    The markers  100  may be embedded into the self-sealing structure  60  in any suitable configuration such as an overall oval form as shown in  FIG. 6A  or an overall rectangular form as shown in  FIG. 6B . Alternatively, the markers  100  may be embedded into outer shell  12  around the self-sealing zone  15   c ,  15   d  in any suitable configuration or shape, for example as shown in  FIGS. 7A and 7B . 
         [0044]    The markers  100  of the present invention will now be described in more detail with reference to  FIGS. 8-11 . The markers are a plurality of microcavities embedded directly into specific areas of the implant such as those areas described above. The microcavities are defined herein as any small compartments formed directly within a material of the applicable implant, including gas or vacuum filled microbubbles, micropockets, microvoids. In each instance the microcavities are readily detectable by ultrasound, and are sized (maximum dimension or in the case of spherical microbubbles, outer diameter) within the range of about 0.1 micron to about 500 microns, and more preferably 0.5 micron to zoo microns, even more preferably 1 micron to 100 microns, and most preferably 1 micron to 25 microns. According to certain embodiments of the present invention, there are at least 100 microcavities per cm 2 , more preferably at least 1000 microcavities per cm 2 , most preferably at least 10000 microcavities per cm 2 . Typically the microbubbles are spherical, but they can also be ellipsoidal. 
         [0045]    Advantageously, these microcavities are readily formed directly in the structures of the implant, with no additional separate structures needed to enable detection as is the case with known mammary tissue expanders. Also, due to the small size of the microcavities, the strength of the material is not compromised and the self-sealing property of the material, if any, is not compromised. 
         [0046]      FIGS. 8A and 8B  show embodiments of any suitable material (i.e., such as a silicone based polymeric material for mammary tissue expanders) with multiple microcavities zoo embedded therein. The microcavities may be in any suitable configuration, such as the somewhat random pattern shown in  FIG. 8A , or aligned as shown in  FIG. 8B . Advantageously, the configuration shown in  FIG. 8A  provides for higher density of microcavities which can be positioned as shown, arranged throughout the thickness of the material, or in a multilayer arrangement. 
         [0047]    According to one embodiment, microcavities zoo are formed in the material  300  from microbubbles of gas which are suspended in a liquid or semi-liquid polymer which is a precursor to solid material  300 . This can be accomplished by injecting a gas into the liquid polymer through an injector or sparger having one or more fine orifices, thus forming a suspension of fine microbubbles in the liquid polymer. Alternatively, a high speed impeller can be used to agitate liquid polymer in the presence of gas, such as air or nitrogen, forming a dispersion of fine microbubbles within the liquid polymer. 
         [0048]    Other means include applying a vacuum treatment to a liquid polymer having dissolved gas therein, or applying a high pressure gas atmosphere to a liquid polymer for a period of time that allows the gas to partially dissolve in the liquid polymer, where after the pressure is removed, excess dissolved gas will form a dispersion of fine microbubbles within the liquid polymer. 
         [0049]    Still another method of forming a suspension of microbubbles in a liquid or semi-liquid polymer is by dispersing gas-filled microcapsules in the liquid or semi-liquid polymer, for instance by adding a quantity of polymer-shell gas-filled microcapsules to the liquid or semi-liquid polymer and mixing the microcapsules into the bulk of the liquid. Alternatively, polymer-shell microcapsules can be added on top of a still liquid layer of polymer being cast in a suitable form while the polymer is being cured, resulting in a uniform layer of microcavities zoo formed by gas-filled microcapsules. 
         [0050]    Another method of forming a suspension of microbubbles in the liquid or semi-liquid polymer, is directional application of high energy ultrasound, or sonication, whereby due to cavitation processes and/or due to changes in gas solubility, formation of microbubbles can be induced within the liquid or semi-liquid polymer. 
         [0051]    Yet another method of forming a suspension of microbubbles in the liquid or semi-liquid polymer, is directional application of high energy laser energy, whereby due to thermal effects, formation of microbubbles can be induced within the liquid or semi-liquid polymer. 
         [0052]    One method of forming a suspension of microbubbles in the liquid polymer is schematically illustrated in  FIG. 10 , which shows in a cross-sectional view, a container  500  containing liquid polymer  510  and an optional agitator, such as a stirrer, impeller or the like  520 . Pressurized gas is supplied via gas line  530  and is injected into liquid polymer  510  through a microporous sparger  540 , such as a sintered glass, polymer, or metal frit, having pores of the order of 0.5 microns to about 20 microns, such as 1 micron or 2 microns. Injection of the gas into the liquid polymer  510  forms microbubbles  550  suspended or dispersed within the liquid polymer. 
         [0053]    After a suspension of microbubbles is formed in the liquid polymer, a number of techniques can be used to incorporate the material (or liquid precursor to material) with embedded microcavities into a tissue expander or inflatable breast implant. As indicated previously, many breast implants and mammary expanders are formed of silicone using well known dip molding techniques. Following any curing step, the shell may be selectively dipped into a different vat of liquid silicone that contains microbubbles or microcavities as described above. The mandrel may be selectively dipped so that only a desired location (i.e., one that will identify the relative location of the injection element) is dipped. The shell may then be processed as usual, with additional dipping steps if desired using the original liquid silicone, to form the final implant or expander shell. This exemplary method is illustrated in  FIGS. 11A-11B , wherein  FIG. 11A  shows mandrel  600  mounted on handle  610 , with at least one or more layers of polymer already formed on the mandrel  600  and constituting the silicone shell  612 . Mandrel  600  is subsequently partially dipped into a vat or container  500  containing liquid polymer  510  with microcavities  550  dispersed therein, so that only area  614  representing a portion of shell  612  is immersed into liquid polymer  510 . Area  614  corresponds to the area where markers  100  of the present invention are desired to be placed (i.e., in the injection marker zone). The presence of microcavities or microbubbles  550  in polymer  510  is schematically illustrated by pattern coloring of polymer  510  in  FIG. 11A . 
         [0054]    After the mandrel  600  is withdrawn from the vat or container  500  and cured, the shell  612  now includes an additional layer  616  made of polymer with gas microbubbles dispersed therein as shown in  FIG. 11B , forming the injection marker zone. 
         [0055]    As an alternative to selective dipping of only a portion of the shell, well known masking techniques can be used to “mask off” locations other than the target location for the liquid silicon having microbubbles. An exemplary mask  1404  surrounding target location  1405  and having open area  1410  is shown in  FIG. 11C  in a cross-sectional view and in  FIG. 11D  in a top view. After application of the liquid silicon having microbubbles to shell  612 , the area  1410  not covered by mask  1404  will form a coating of silicon having microbubbles dispersed therein.  FIG. 11E  is schematic top view of shell  612  of  FIG. 11D  after removal of the mask, showing injection maker zone  1420 . 
         [0056]    Alternate means for applying the liquid silicone with microcavities or microbubbles in the correct location include targeted spraying of the liquid with or without masking, or targeted application of the liquid by dropping or spreading the liquid on an already cured layer. The dispensing can be performed by using a micro-dispenser, pipette-like dispenser, liquid material printer, brush, ink-jet like spray deposition and the like, resulting in the formation of a layer made of polymer with gas microbubbles dispersed therein, thus forming an injection marker zone. 
         [0057]    As indicated, subsequent layers of silicone without microbubbles can then be applied as desired. According to one illustrative embodiment shown in  FIG. 9 , a three-layer construct is cast in a form  80  with outside layers  305  and  307  being formed by a material having no microbubbles dispersed therein, with layers  305  and  307  sandwiching between them material  300  having microbubbles  201  dispersed therein. After casting and curing, a composite material with embedded microcavities is formed. Layers  305  and  307  can be made of the same material as layer  300 , or of a different polymeric material. 
         [0058]    According to the present invention, a specific gas other than air can be used to fill microcavities  200 , such as nitrogen, carbon dioxide, argon, etc. Forming of cavities can be performed under specific gas atmosphere or specific gas can be used to inject into liquid polymer. Alternatively gas can be allowed to diffuse into cavities under elevated temperature and pressure over an extended period of time. In other embodiments, microcavities zoo are vacuum-filled, i.e., there is less than atmospheric pressure of any gas inside. 
         [0059]    As indicated above, the microcavities are readily detectable using available ultrasonic instruments. For illustrative purposes,  FIGS. 12A and 12B  show a device having markers  100  according to the present invention in conjunction with such a detection device. A mammary tissue expander  10  is shown implanted into tissue  450 , and which includes a shell  12  with an injection element  75  coupled to shell  12 , with microcavities  100  embedded directly into and throughout the injection element  75 . Ultrasonic detector  400  includes both a directional source of ultrasound and a receiver of reflected ultrasound, and is operatively connected to a visualization device  410 , such as information display or monitor via cable  405 . Ultrasonic detector  400  in position P 1  which is not directly opposite the injection element  75  will detect no enhanced reflectance from microcavities  100 , as schematically shown on visualization device  410 . Ultrasonic detector  400  in position P 2 , which is directly opposite the injection element  75 , will detect enhanced ultrasound reflectance from microcavities  100 , as schematically shown on visualization device  410 . 
         [0060]    Referring now to  FIG. 12B , tissue expander  10  includes microcavities  110  embedded around the injection element  75 . In the position shown, ultrasonic detector  400  will detect enhanced reflectance from microcavities  110 , as schematically shown on visualization device  410 . Once its location is identified as described above, fluid for expanding the tissue expander  10  can be injected at the center of localized spot  401  or ring  402 . 
         [0061]    Alternatively, the ultrasonic detector may have no separate visualization display, but rather provides audible, visual, or vibratory feedback, or alternatively a combination of any two or all three of the above types of feedback, or any other additional modality of feedback or combinations of modalities of feedback. The ultrasonic detector may alternatively have a means to provide feedback, such as visual feedback from a built-in light source, such as one or more LED lamps, when detecting ultrasonic reflection from microcavities. Preferably, light output can change from one color, e.g., red, when there is no reflection; changing to a second color, such as to yellow, when reflection is stronger; and optionally changing to yet another color, such as green, when reflection is strongest. These types of devices are also well known in the art, and those skilled in the art will readily understand how to use them in conjunction with the present invention. 
         [0062]    Once detector  400  has identified the position of markers  110 , a health practitioner can optionally mark the area by using the position of detector  400 . Referring to  FIG. 13 , in one embodiment, there is an aperture  460  within ultrasonic detector  400  through which the injection syringe  480  can be then placed. Alternatively, a pen can be used to mark the tissue through the aperture, or adjacent to the detector. Advantageously, as shown in  FIG. 13  and also referring to  FIGS. 4A ,  6 A and  6 B, markers are embedded into the septum and the injection or withdrawal of fluid can be performed directly through the septum zone where markers are embedded. The microbubbles do not interfere with the injection needle piercing the septum and do not affect sealing of the septum after the withdrawal of the needle due to the small size of the microbubbles. 
         [0063]    Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. For example, although the present invention is described primarily in connection with a mammary tissue expander, it is to be understood that the inventive concept is similarly applicable to any inflatable mammary implant, such as an adjustable permanent implant, or any other expandable implant. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.