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 . 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 . 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 . referring first to fig1 a - 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 . 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 fig1 a 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 . fig1 c 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 . fig2 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 . fig3 is a cross - sectional view of the exemplary injection dome 14 of fig2 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 . 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 . 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 . referring now to fig4 a , 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 . fig4 b 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 . fig4 c 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 . 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 fig5 a 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 . 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 fig6 a or an overall rectangular form as shown in fig6 b . 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 fig7 a and 7b . the markers 100 of the present invention will now be described in more detail with reference to fig8 - 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 . 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 . fig8 a 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 fig8 a , or aligned as shown in fig8 b . advantageously , the configuration shown in fig8 a provides for higher density of microcavities which can be positioned as shown , arranged throughout the thickness of the material , or in a multilayer arrangement . 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 . 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 . 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 . 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 . 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 . one method of forming a suspension of microbubbles in the liquid polymer is schematically illustrated in fig1 , 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 . 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 fig1 a - 11b , wherein fig1 a 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 fig1 a . 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 fig1 b , forming the injection marker zone . 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 fig1 c in a cross - sectional view and in fig1 d 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 . fig1 e is schematic top view of shell 612 of fig1 d after removal of the mask , showing injection maker zone 1420 . 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 . as indicated , subsequent layers of silicone without microbubbles can then be applied as desired . according to one illustrative embodiment shown in fig9 , 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 . 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 . as indicated above , the microcavities are readily detectable using available ultrasonic instruments . for illustrative purposes , fig1 a 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 . referring now to fig1 b , 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 . 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 . 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 fig1 , 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 fig1 and also referring to fig4 a , 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 . 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 .
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 .