Patent Description:
Tracking of physical disease and healing in humans often involves measuring anatomical properties of a patient's body. However, some measurements, such as those that can only be obtained internally, can be difficult to obtain. More recently, there has been an interest in sensors that can be implanted into a patient's body to track the health of the patient over time. For example, attempts have been made to use one or more strain gauges to track healing in a damaged or fractured bone. The one or more strain gauges are attached to an orthopedic implant that is in turn attached to the damaged or fractured bone. As the bone heals, the bone increasingly shares the load imparted by the patient's body on the orthopedic implant. Thus, the load imparted on the bone increases as the bone heals, while the load imparted on the orthopedic implant decreases. In principle, this change in loading can be measured over time by the one or more strain gauges to track the progress of healing in the bone. The measurement can then be communicated to a device outside of the body that can be accessed by a physician.

The present invention is defined in the appended claims and concerns an implantable sensor, which includes a substrate and protective cover that cooperate to define an enclosed sensor volume. A sealed enclosure is provided within the sensor volume, with an electronic component assembly (ECA) being located within the sealed enclosure. In some embodiments, the sealed enclosure is hermetic and/or has a near-hermetic barrier quality, such as may be provided by different types of glass, quartz, or metal. The sealed enclosure may suitably protect the ECA from any possibility of corrosion and/or may inhibit/eliminate the possibility of ingress or egress of any liquids or other ions between the subject's body and the inner enclosure volume.

A flexible circuit board assembly (FCBA) is electrically coupled with the ECA through a wall of the sealed enclosure. In some embodiments, this is accomplished through a plurality of electrical interconnects that are integrated with and extend through a wall of the enclosure. At least one transducer is provided on the FCBA in contact with the substrate, and the FCBA is held apart from the enclosure via a polymeric spacer provided therebetween. In some embodiments, the transducer is a strain gauge operative to measure an amount of elastic strain present in the substrate. When used in connection with the fixation and monitoring of bone fractures, the substrate may be a bone plate or other bone fixation member. Finally, an inert polymer fill may be provided within the sensor volume external to the enclosure as an additional means of sealing the sensor.

As used herein, the terms "a," "an," "the," "at least one," and "one or more" are used interchangeably to indicate that at least one of the item is present; a plurality of such items may be present unless the context clearly indicates otherwise. All numerical values of parameters (e.g., of quantities or conditions) in this specification, including the appended claims, are to be understood as being modified in all instances by the term "about" whether or not "about" actually appears before the numerical value. "About" indicates that the stated numerical value allows some slight imprecision (with some approach to exactness in the value; about or reasonably close to the value; nearly). In addition, disclosure of ranges includes disclosure of all values and further divided ranges within the entire range. Each value within a range and the endpoints of a range are hereby all disclosed as separate embodiment.

The present technology generally relates to an implantable sensor that maintains a high degree of biocompatibility while also enabling the use of specific monitoring transducers. This technology may be useful, for example, in creating a smart bone plate that may have integral strain sensing while being adapted for long term implantable use within a subject. The present designs utilize multiple barrier layers to create an inert and hermetically sealed sensor module that may be integrated into any implantable device.

The present device may utilize a multi-layer construction whereby an inner containment structure/enclosure is nested within a larger external protective shell. In such a design, complex circuitry and electronics may be housed within the inner enclosure, while more discrete sensing components such as strain transducers may exist outside of the inner housing, while still being protected via the sealed protective shell.

The present designs may include various levels of processing power/complexity, however in a preferred embodiment, the sensor may be devoid of any on-board electrochemical power supply/battery. Instead, in some embodiments, the sensor may be powered by way of a received alternating magnetic field.

Referring to the figures, <FIG> schematically illustrates a smart bone plate <NUM> according to some embodiments of the present disclosure. The smart bone plate <NUM> includes a substantially rigid main body <NUM> that is operative to be secured to a bone <NUM> of a subject <NUM> for the purpose of locally fixating a fracture <NUM> or joint while the fracture heals/ossifies. The main body <NUM> can be formed from any suitable implantable material such as, without limitation, a metal (e.g., a titanium alloy) or a polymer such as polyether ether ketone (PEEK). The bone plate <NUM> may include a plurality of apertures <NUM> that extend through a thickness <NUM> of the main body <NUM>, where each aperture <NUM> may be operative to receive a threaded fastener <NUM> (e.g., a bone screw). The threaded fasteners <NUM> may be secured or anchored into the bone <NUM> of the subject <NUM> to locally attach the main body <NUM> to the bone <NUM> on opposing sides of the fracture. The smart bone plate <NUM> may further include one or more sensor modules <NUM> that are each operative to sense one or more mechanical parameters of the attached bone plate <NUM> and communicate these sensed parameters to an external processing device <NUM>.

While the present disclosure generally discusses the sensor design in connection with a bone plate <NUM>, it should be appreciated that the main body <NUM> of the bone plate <NUM> is simply an example of a substrate upon which the sensor module <NUM> may be mounted. Other substrates may similarly be used, including other bone fixation hardware such as pins, rods, intervertebral spacers or cages, or other implantable medical devices where monitoring a mechanical parameter of the device may be beneficial.

<FIG> provides a schematic cross-sectional view <NUM> of one of the sensors <NUM> shown in <FIG>. As illustrated, the sensor <NUM> generally includes an electronic component assembly <NUM> (ECA <NUM>) that is in electrical communication with one or more transducers <NUM> provided on a flexible circuit board assembly <NUM> (FCBA <NUM>). In general, the ECA <NUM> may form the primary "intelligence" of the sensor <NUM>, while also being primarily responsible for all input/output to/from the sensor <NUM>. As such, to protect the integrity of the electronics, the ECA <NUM> may be provided within a sealed enclosure <NUM>, where all electrical communication between the ECA <NUM> and the transducers <NUM>/FCBA <NUM> must pass through a wall of the enclosure <NUM>.

In general, the ECA <NUM> may include any combination of one or more active or passive electrical components or integrated circuit packages that are mounted on one or more printed circuit boards/dielectric substrates, or that are mounted directly on a wall of the sealed enclosure <NUM>. Functionally speaking, and as schematically shown in <FIG>, the ECA <NUM> may include power circuitry <NUM>, data communication circuitry <NUM>, signal conditioning circuitry <NUM>, and in many embodiments, may further include an antenna <NUM>.

The power circuitry <NUM> may generally be operative to provide a usable source of electrical power to the transducers <NUM> and other electrical components within the ECA <NUM>. In at least some examples, the power circuitry <NUM> can include an energy harvesting device configured to capture energy from a suitable energy source that is separate from the bone plate <NUM>. For example, the energy source can be magnetic fields or radio waves communicated from the external processing device <NUM> (and/or an antenna associated therewith). Alternatively, the power circuitry <NUM> can capture energy from the patient's body itself or from another external source such as a source external to the patient's body. More broadly speaking, the energy source can include (without limitation) sensed kinetic energy, electric fields, magnetic fields, and so on. In a preferred embodiment, however, the power circuitry <NUM> does not include a typical electrochemical battery.

In one particular configuration, instead of relying on an internal store of power, such as an electrochemical battery, the sensor module <NUM> may be inductively powered by a received magnetic flux/electromagnetic field <NUM> that may induce a current <NUM> in the antenna <NUM>. The power circuitry <NUM> may receive this current from the antenna <NUM>, may rectify and/or regulate it, and may make it available for use by other components within the sensor <NUM>.

The signal conditioning circuitry <NUM>, if included, may comprise one or more signal filters, including a high pass, low pass, and/or band pass filter, one or more digital filters implemented in the frequency domain, or any other required buffering and/or amplifying electronics to make use of the output from the one or more transducers. The signal conditioning circuitry <NUM> may comprise, for example, one or more RC circuit elements, one or more operational amplifiers, and/or one or more integrated circuit packages.

Finally, the data communications circuitry <NUM> may serve to receive the output from the transducers <NUM> and/or signal conditioning circuitry <NUM> (or a signal representative thereof), and communicate the underlying signal content to the external processing device <NUM> via an electromagnetic/radio frequency signal <NUM> that is broadcast from the antenna <NUM>. The communication circuitry <NUM> may include any/all electronic components that may be required to achieve this functionality as is understood in the art. For example, the communication circuitry <NUM> can include a wireless transmitter or transponder that receives the measurement value and prepares the measurement value for wireless transmission. The communication circuitry <NUM> can also include processing components such as (without limitation) one or more of (i) memory configured to store the measurement value, (ii) a digital-to-analog converter configured to convert the measurement value to analog format, (iii) a radio-frequency (RF) modulator configured to modulate the measurement value, (iv) an error-correction encoder configured to encode the measurement value, and other processing consistent with the wireless technology employed by the system.

In one particular configuration, the power circuitry <NUM> and communication circuitry <NUM> may be integrated into a single device or package, such as a passive or active RFiD component. In such an embodiment, the power circuitry <NUM> and communication circuitry <NUM> may work in tandem to receive the ambient electromagnetic field <NUM> and output a corresponding electromagnetic signal <NUM> having a parameter that varies with changes in the output of the one or more transducers <NUM> (e.g., the transmitted signal <NUM> may simply be a phase shifted version of the received field <NUM>, with the phase shift being proportional to the output of the transducer <NUM>). In other embodiments, however, there may be greater independence between the power circuitry <NUM> and communications circuitry <NUM>, where the power circuitry <NUM> simply acts as a generic power supply to the communication circuitry.

Referring again to <FIG>, and as noted above, the ECA <NUM> may be provided within a sealed enclosure <NUM> that may serve as an environmental barrier and may protect the electronics from corrosion or degradation. In a preferred embodiment, the sealed enclosure <NUM> may surround the ECA <NUM> and may be formed from one or more materials that have low or no permeability to liquid and low or no gas or ion diffusion rates and may further have low or no electrical conductivity. Suitable materials may include crystalline materials such as glass, quartz, ceramics, various epoxies, liquid crystal polymer, and the like, or may include metallic materials that have been treated/anodized to reduced surface electrical conductivity. In one particular example, the material used to form the sealed enclosure may comprise a borosilicate glass with a boric oxide concentration of between <NUM>% and <NUM>% by mass. In still other embodiments, the enclosure may comprise a laminate material that includes at least one barrier layer formed from a material with low or no permeability to liquid and low or no gas or ion diffusion rates. For example, the enclosure may be formed from a biocompatible material, such as polyether ether ketone (PEEK), with an inner, outer, or intermediate layer formed from metallic or other barrier-type material using a technique such as atomic layer deposition or the like.

As generally shown in <FIG> and <FIG>, in one configuration, the sealed enclosure <NUM> may be formed from a plurality of walls <NUM>, each having a corresponding inner surface <NUM>, outer surface <NUM>, and thickness <NUM> defined between the inner and outer surfaces <NUM>, <NUM>. In one embodiment, the wall thickness <NUM> may be between about <NUM> and about <NUM>, or between about <NUM> and about <NUM>, or about <NUM>. The inner surfaces <NUM> of each of the plurality of walls <NUM> may collectively define an inner enclosure volume <NUM>, within which the ECA <NUM> may be located. In one configuration, the sealed enclosure <NUM> may include a base <NUM>, a plurality of side-walls <NUM>, and a cap <NUM>. Each of the base <NUM>, sidewalls <NUM>, and cap <NUM> may be formed from a similar material, and may be integrally formed with each other and/or may be fused/welded through a suitable manufacturing process.

As generally shown in <FIG>, and with more clarity in <FIG>, the base <NUM> may include a plurality of electrical interconnects <NUM> or vias that each extend through the thickness <NUM> of the base <NUM> from the inner surface <NUM> to the outer surface <NUM>. Each interconnect/via <NUM> may be fluidly sealed to the surrounding material of the base <NUM> and may generally include an inner solder pad <NUM> provided on the inner surface <NUM>, and outer solder pad <NUM> provided on the outer surface <NUM>, and a metallic post <NUM> extending therebetween to electrically couple the inner solder pad <NUM> with the outer solder pad <NUM>. In one particular configuration, one or more inner solder pads <NUM> may be physically offset from its corresponding metallic post <NUM> along the inner surface <NUM>. In such an embodiment, the inner solder pad <NUM> may be electrically coupled to the corresponding metallic post <NUM> via one or electrical traces <NUM> or wires provided on or below the inner surface <NUM>. Such a design may accommodate ECA packaging that may be smaller than the preferred spacing of the outer solder pads <NUM>. Similarly, in some embodiments one or more of the outer solder pads <NUM> may be physically offset from its corresponding metallic post <NUM> along the outer surface <NUM>. In such a design, the outer solder pads <NUM> may be electrically coupled to the corresponding metallic post <NUM> via one or electrical traces or wires provided on or below the outer surface <NUM>.

As further shown in <FIG>, in one configuration, the side walls <NUM> may be formed from a plurality of layers <NUM> that are arranged in a stacked assembly. In this design, each layer <NUM> may have an approximately equal layer thickness <NUM>, which also may be approximately equal to the thickness <NUM> of the cap <NUM> and/or base <NUM>. Adjacent layers may by fused through the use of, for example, an applied heat treatment or laser welding.

For the purpose of electrically interconnecting with other components, the ECA <NUM> may generally include one or more surface mount electrical pads <NUM> that when assembled may match with and may be directly soldered to the inner solder pads <NUM> of the electrical interconnects <NUM>.

As noted above, the one or more transducers <NUM> may be external to the sealed enclosure <NUM> so that they may more accurately experience and monitor the intended mechanical parameter. Furthermore, to prevent the rigid enclosure <NUM> from influencing the output of the transducers <NUM>, it may also be preferable for the transducers to not be directly mounted to the enclosure <NUM> itself. To accomplish these design goals, in one embodiment, such as shown in <FIG>, the transducers <NUM> may be mounted on a flexible membrane (the FCBA <NUM>) that is external to the enclosure <NUM> and in electrical communication with the ECA <NUM> through a wall <NUM> of the sealed enclosure <NUM>.

In a primary use, the one or more transducers <NUM> may comprise one or more strain gauges <NUM> that are operative to sense an experienced elastic strain in the main body <NUM> of the bone plate <NUM>. In response to the sensed strain, the one or more transducers <NUM>/strain gauges <NUM> may modulate an electrical parameter that is provided to the ECA <NUM>. In one configuration, each strain gauge <NUM> may have a resistance that varies in a predictable and repeatable way in response to an experienced strain. In another embodiment, each strain gauge <NUM> may be a reactive/piezoelectric material whereby experienced strain induces an electrical potential across two terminals.

In one particular configuration, the one or more strain gauges <NUM> may comprise a plurality of strain gauges <NUM> that are each provided at a different respective orientation on the FCBA <NUM>. More specifically, each strain gauge <NUM> may have a primary sensing axis and/or longitudinal centerline. The primary sensing axis for each strain gauge <NUM> may be provided at an angle on the FCBA <NUM> that is not parallel to the primary sensing axis of any other strain gauge <NUM>. In one particular configuration, each strain gauge <NUM> may have a primary sensing axis that is angularly offset from every other primary sensing axis by an angle that is an integer multiple of <NUM> or <NUM> degrees. Further disclosure of examples of sensing electronics that may be used with the present packaging designs are provided in <CIT>.

With reference to <FIG>, <FIG>, in one configuration, the FCBA <NUM> may generally comprise a sensor portion <NUM> and one or more connector portions <NUM>. The plurality of transducers <NUM> may be mounted on the sensor portion <NUM>, while the one or more connector portions <NUM> may electrically couple the transducers <NUM> with the electrical interconnects <NUM> provided on the enclosure <NUM>. As noted above, to maintain some degree of mechanical isolation from the enclosure, the sensor portion <NUM> may be maintained some minimum distance <NUM> away from the enclosure <NUM>. As further shown in <FIG>, the sensor portion <NUM> and the connector portion <NUM> may both be formed from the same flexible sheet, where the geometry of the connector portion <NUM> may facilitate a transverse separation of the sensor portion <NUM> from the enclosure <NUM>. For example, in one configuration, the connector portion <NUM> may have a geometry similar to that of a ribbon cable which may roll backward <NUM> degrees over the edge of the sensor portion <NUM>. Alternatively, as shown in <FIG>, the connector portion <NUM> may have a geometry similar to that of a staircase which may double back on itself to minimize the slope of the bend.

The minimum distance <NUM> between the sensor portion <NUM> of the FCBA <NUM> and the outer surface <NUM> of the sealed enclosure may be maintained, for example, through the use of a flexible spacer <NUM>. In one configuration, the spacer <NUM> may be formed from a compliant polymer, such as silicone, and may have a transverse thickness, measured between the FCBA <NUM> and the outer surface <NUM> of the base <NUM> of the enclosure <NUM>, of between about <NUM> and about <NUM> or between <NUM> and about <NUM>, or between <NUM> and about <NUM>. The material used to form the spacer <NUM> may have a hardness, measured on the Shore A scale, of between about 35A and about 65A, or between about 45A and about 55A, or about 50A, and in one embodiment may comprise an injection molded silicone, such as sold under the name NuSil MED-<NUM>, commercialized by Avantor, Inc. In one configuration, the flexible spacer <NUM> may have a hollow central portion and/or a concave recess on the side in contact with the sensor portion <NUM> of the FCBA <NUM>. Such a design may aid in maintaining adequate separation between the sealed enclosure <NUM> and the sensor portion <NUM> of the FCBA <NUM>/transducers <NUM>, while further reducing any influence that the spacer <NUM>, itself, may have on the sensor readings.

To further the biocompatibility of the present device, in some configurations, the flexible membrane of the FCBA <NUM> may be formed from a polyimide or liquid crystal polymer material. For example, as generally illustrated in <FIG>, a plurality of electrically conductive, traces/conductors <NUM> may be provided on a first sheet <NUM> of LCP, whereafter a second sheet <NUM> of LCP may be overlaid on top of the traces <NUM> (thus sandwiching the traces <NUM> between the two layers <NUM>, <NUM>). Following this, the adjacent layers <NUM>, <NUM> of LCP may be thermally fused together and/or heated to a point where the polymer may reflow and solidify as a single thickness of material. While an FCBA <NUM> with only two layers is shown in <FIG>, more than two layers of LCP may be used with traces <NUM> included between any or all adjacent layers.

As generally illustrated in <FIG>, the FCBA <NUM> may be electrically coupled to the outer solder pads <NUM> of the sealed enclosure via one or more solder joints <NUM>. While solder provides excellent electrical connectivity, lead-free solder formulations have especially poor mechanical strength. As such, to insulate and protect the solder joints <NUM>, made between the FCBA <NUM> and the outer solder pads <NUM> on the sealed enclosure <NUM>, each solder joint <NUM> may be covered with a biocompatible epoxy <NUM>. This may provide both a mechanical resiliency to the joint <NUM>, and may provide a further environmental barrier around the material of the joint itself.

In one configuration, a similar epoxy may also be used to hold the sensor portion <NUM>, including the transducers <NUM>, in substantially rigid contact with the main body <NUM> of the bone plate <NUM>. Ideally, the epoxy selected to adhere the FCBA <NUM> to the main body <NUM> should be sufficiently rigid to ensure continuous contact while being flexible enough to not significantly affect the monitored mechanical parameter.

In some embodiments, following assembly, the FCBA <NUM> and sealed enclosure <NUM> may both be coated in an inert barrier material to provide enhanced biocompatibility and environmental protection. Such a coating may be applied, for example, using a deposition process (e.g., atomic layer deposition (ALD), plasma layer deposition (PVD), chemical layer deposition (CVD), or the like). In this process, the assembly may be coated with a barrier material such as, for example, a deposited metal oxide (e.g., AL<NUM>O<NUM>, TiO<NUM>, HfO<NUM>) and/or a barrier polymer. In some embodiments, the barrier material may comprise a laminate that alternates one or more different metallic oxide layers and/or one or more polymer layers. For example, in one particular configuration, the barrier material may comprise a laminate formed by alternating layers of hafnium oxide and aluminum oxide. In another configuration, the barrier material may comprise a laminate that alternates layers of a metal oxide laminate (e.g., HfO<NUM> - Al<NUM>O<NUM> - HfO<NUM>) with one or more layers of a polymer (e.g., Parylene). One particular embodiment of this configuration may include at least three layers of the oxide laminate, and at least two layers of the polymer in an alternating configuration. In some embodiments the barrier layer may have an average thickness of between about <NUM> and about <NUM>.

Referring again to <FIG>, as a final layer of mechanical and fluidic protection for the enclosed electronics, a protective cover <NUM> may surround the sealed enclosure <NUM> and FCBA <NUM>. The protective cover <NUM> may be coupled to the main body <NUM> of the bone plate <NUM> to define a sensor volume <NUM> therebetween. In some embodiments, any space within the sensor volume <NUM> that is not filled by the sealed enclosure <NUM> or FCBA <NUM> may be filled with a biocompatible polymer such as silicone during the assembly process. In one configuration, this polymer fill may have a hardness when cured of between about 35A and about 65A, or between about 45A and about 55A, or about 50A, and in one embodiment may comprise a low-viscosity silicone, such as sold under the name NuSil MED-<NUM>, commercialized by Avantor, Inc. In one configuration, the protective cover <NUM> may include a convex/domed upper surface <NUM> to provide improved impact resistance. Likewise, the cover <NUM> may be formed from a biocompatible material such as PEEK.

<FIG> schematically illustrates one manner of mechanically attaching the protective cover <NUM> to the main body <NUM> of the bone plate <NUM>. As shown, the main body <NUM> may include a concave recess <NUM> formed in an outer surface <NUM>. When the protective cover <NUM> is attached to the main body <NUM>, at least a portion of the cover <NUM> (i.e., a side opposite the domed upper surface <NUM>) may extend within the recess <NUM>. In one configuration, the protective cover <NUM> may include a protrusion or other mechanical engagement feature <NUM> that is configured to interlock with a mating portion of the main body <NUM> within the recess <NUM>. As shown in <FIG>, in one configuration, this protrusion may extend radially outward away from the sensor volume <NUM> and may seat within a concave indent <NUM> in the wall of the recess <NUM> to resist the cover <NUM> from being freely removed from the bone plate <NUM>.

While the above disclosure generally refers to the sealed enclosure <NUM> as its own entirely enclosed box/container with the ECA <NUM> being entirely surrounded by the walls of this enclosure <NUM>, in another embodiment, the ECA <NUM> may form one of the walls of the enclosure and/or one of the walls of the enclosure <NUM> may be integral to the ECA <NUM>. Slightly restated, the embodiments described above generally consider the ECA <NUM> to comprise one or more electrical components or integrated circuits mounted to a printed circuit board (PCB), whereby the components and the PCB are surrounded by the enclosure <NUM> (as illustrated in the figures). In an alternate embodiment, however, the sealed enclosure <NUM> may include one or more insulated electrical traces directly on or in one or more walls <NUM>. In such a design, the electrical components of the ECA <NUM> may be mounted on the wall, thus eliminating the need for a separate PCB. In a first variation of this configuration, the wall containing the traces (e.g., the base <NUM>) may be formed from the barrier material much like every other wall. In a second variation, however, the wall containing the traces (e.g., the base <NUM>) may be formed from a first material, while the remaining side walls <NUM> and cap <NUM> may be formed from the barrier material. Such a design may require an exterior barrier coating, though may enable the PCB to serve as a wall, which may reduce manufacturing complexity.

In still another embodiment, rather than being a container that has a well-defined interior cavity/volume defined by a plurality of generally plain walls, the sealed enclosure <NUM> may instead be simply a barrier coating applied to the ECA <NUM>. In such an embodiment, the inner enclosure volume <NUM> may have an identical, or near identical size as the ECA <NUM> (i.e., by virtue of it being directly applied to the ECA <NUM>). In such an embodiment, the coating may be a barrier coating such as Al<NUM>O<NUM> or LCP, and may be applied using a suitable coating process such as dip-coating or Atomic Layer Deposition.

As noted above, in some embodiments, the sealed enclosure <NUM> may be formed from a metallic material. If this metallic material is radio opaque, then placing the antenna <NUM> within the sealed enclosure <NUM> would compromise or destroy the wireless functionality of the sensor <NUM>. In such a design, however, the antenna <NUM> may be provided external to the sealed enclosure <NUM> and coupled to the ECA <NUM> through one or more electrical interconnects <NUM> provided through a wall of the enclosure <NUM> (i.e., electrical antenna interconnects) though electrically insulated from any electrically conductive walls. In such an embodiment, the antenna <NUM> may be physically separated from the enclosure <NUM> by a distance of between about <NUM> and about <NUM>. More specifically, about <NUM> of physical separation may be required to minimize any RF distortion or interference effects caused by a metallic housing/wall. In such a design, the antenna <NUM> may be provided on an opposite side of the enclosure <NUM> from the transducers <NUM> and/or main body <NUM> of the bone plate <NUM>.

<FIG> schematically illustrates one example of a method <NUM> for assembling an implantable sensor such as described above with respect to <FIG>. The method may generally begin at <NUM> by soldering an electronic component assembly (ECA) to one or more inner solder pads on the inner surface of a base of an enclosure. In one particular embodiment, this soldering step may be performed through an automated process using, for example, a pick and place machine and a solder reflow oven. In one embodiment, a plurality of enclosure bases may be initially joined together as part of a common platter.

Sidewalls for the enclosure may be formed either by etching or otherwise forming recesses into the platter, or by stacking up one or more wall layers on top of the base and subsequently bonding or fusing all adjoining layers together, such as through a laser fusing process (shown at <NUM>, though no order relative to <NUM> should be implied unless the walls are formed through an etching process - in which case the etching likely need occur prior to the ECA being soldered to the base).

Following the creation of the sidewalls (at <NUM>) and installation of the ECA on the base (at <NUM>), a cap may be secured to the walls (at <NUM>) to fully enclose each ECA within its own inner enclosure volume. In one configuration, the cap may be similar to the base in material and thickness, and in some configurations may also be similar in material and in thickness to the walls (or to each of a plurality of stacked wall layers). The cap may be secured to the walls, for example, by a process such as laser welding.

If a plurality of enclosures are all formed on a common platter, then at <NUM>, the platter may be diced into discrete enclosures. Suitable dicing or cutting processes may be used to separate the enclosures, such as through one or more cutting tools/processes, or through the use of laser energy. In one embodiment, the cutting process may simultaneously weld each of the base, wall layers, and cap together, thus reducing the need to separately affix them.

Once the sealed enclosure is created, terminals or solder pads provided on the flexible circuit board assembly (FCBA) may be soldered to corresponding outer solder pads provided on the outer surface of the sealed enclosure (at <NUM>). Each terminal or solder joint may then be covered in epoxy (at <NUM>) to serve as a barrier layer, but more importantly to provide enhanced mechanical bonding between the FCBA and the enclosure and not simply rely on the mechanical properties of the solder itself. In some embodiments, the sealed enclosure and FCBA may then be coated in barrier layer, for example, using an atomic layer deposition process (at <NUM>).

Following the attachment of the FCBA to the sealed enclosure, a flexible polymeric spacer may be inserted between the sensor portion of the FCBA and the sealed enclosure (at <NUM>). The FCBA may then be epoxied or otherwise adhered to a substrate that is desired to be monitored, such as the main body of a bone plate (at <NUM>).

An injection molded protective cover may then be filled with a low-viscosity inert polymer, such as a silicone (at <NUM>). More specifically, the protective cover may be inverted such that the open end is upward-facing, and the cover resembles a cup. The interior volume of the cover may then be filled with the low-viscosity inert polymer.

Once the cover is filled with the polymer (at <NUM>), the uncured polymer may be degassed (at <NUM>) such as by subjecting the polymer to a negative relative pressure. For example, in one embodiment, the substrate (e.g., the main body of the bone plate) and attached sealed enclosure and FCBA may be positioned, together with the polymer-filled cover, within a vacuum chamber. A vacuum pump may then draw down the ambient air pressure within the vacuum chamber to a level that is below atmospheric pressure and sufficiently low to effect a degassing of the polymer/uncured silicone. Once sufficiently degassed within the chamber (at <NUM>), the cover may be joined with the substrate (at <NUM>) such that the sealed enclosure, flexible spacer, and/or FCBA impresses into the polymer/uncured silicone. In one configuration, the cover may be joined with the substrate by bringing the two components into contact, and further by nesting the cover within a recess in the substrate and/or interlocking a protrusion on one component with a corresponding recess on the other component in a manner that resists withdrawal/removal of the cover from the substrate.

Once joined (at <NUM>), the polymer fill may be cured (at <NUM>), such as through the application of thermal energy/heat and/or by waiting a predetermined amount of time for the material to self-cure. Following the completion of the curing, any displaced/excess polymer fill may be removed (at <NUM>).

Claim 1:
An implantable device adapted for use within a living subject, the device comprising:
a substrate;
a sealed enclosure (<NUM>) having a plurality of walls defining an inner enclosure volume (<NUM>) therebetween, the sealed enclosure (<NUM>) comprising a plurality of electrical interconnects (<NUM>), each electrical interconnect (<NUM>) extending through one of the plurality of walls (<NUM>);
an electronic component assembly (ECA <NUM>) provided within the inner enclosure volume (<NUM>), the ECA (<NUM>) being electrically coupled to each of the electrical interconnects (<NUM>);
a flexible circuit board assembly (FCBA <NUM>) provided external to the sealed enclosure (<NUM>) and in contact with the substrate, the FCBA (<NUM>) being electrically coupled to each of the electrical interconnects (<NUM>) such that the FCBA (<NUM>) is in electrical communication with the ECA (<NUM>) through the sealed enclosure (<NUM>), the FCBA (<NUM>) further including:
at least one transducer (<NUM>) operative to monitor a physical characteristic of the substrate and alter an electrical parameter accessible to the ECA (<NUM>) in response to the monitored physical characteristic; and
a protective cover (<NUM>) coupled to the substrate to define an enclosed sensor volume (<NUM>) therebetween, and wherein the sealed enclosure (<NUM>) and FCBA (<NUM>) are both located within the enclosed sensor volume (<NUM>).