Biosensor device and method

Abstract

A wearable biosensor system 1 comprises a wearable sensor device 10 and a patch 50. The sensor device has a housing 20 with an electrode 30 on a skin facing surface 22. The patch 50 includes a self ad

Description

Field of Invention The present invention relates to methods and apparatus for wearable biosensor devices. In particular, the invention relates to a wearable biosensor for neuromonitoring and may for example comprise an electroencephalogram device. Background Biosensor devices have many applications, and it is often desirable to provide biosensors as a wearable device to enable monitoring over extended periods of time. Such devices may allow access to real-time biosignals information or allow data to be accumulated over a selected monitoring period. One area of application for biosensors is neuromonitoring (which may also be referred to as electrophysiologic monitoring) in which electrical signals produced by the brain are used to help diagnose and / or monitor conditions which can impact brain function. For example neuromonitoring may be useful for injuries ortrauma, seizures caused by conditions such as epilepsy, or memory problems caused by conditions such as dementia. Neuromonitoring devices may include electroencephalogram (EEG) devices. A traditional biosensor device may use sensor pads, such as electrodes, which are connected via leads to the main device such that they can be placed in use in the suitable locations for the required type of monitoring. Such devices, however, typically require a skilled user to set up the device and accurately place the sensors. As such, it is commonly necessary for a patient to attend a medical facility for either the whole monitoring period or at least for the initial configuration of the device. It would be advantageous to provide a device which can be readily self-applied so that a user can be monitored in their normal environment / activities; for example it would be beneficial if a user could receive a wearable biosensor device by mail and selfinitiate monitoring. An example of a self-contained wearable EEG patch has been disclosed in US Patent Application US2017 / 0215759. Such a device may provide improved ease of use by assembling the EEG monitoring device in a single unitary package. A disadvantage of such a device is that the location of the EEG electrodes are fixed and may not, therefore be suitable for all types of monitoring or even all types of user. Embodiments of the invention seek to provide methods and apparatus for providing a wearable biosensor with improved useability and which may, for example, help an untrained user initiate monitoring. In particular, embodiments may seek to provide a device which can be easily configured by an untrained / unskilled user (including selfapplication). Embodiments may for example be intended to be easily and readily usable outside of a clinical environment (for example in the users own home). Summary of Invention According to a first aspect of the invention, there is provided a wearable biosensor system comprising a wearable sensor device and a patch for adhering the sensor device to the skin. The wearable sensor device comprising a housing enclosing a power source and a controller. The housing has an exterior surface which is externally facing in use and a skin facing surface which is proximal to the wearer in use. The skin facing surface comprises at least one electrode. The system further comprises a patch positioned between the skin facing surface and the user in use. The patch comprises a first layer for attachment to the device housing and a skin bonding layer (which may be a self-adhesive skin bonding layer). The patch comprises at least one opening for receiving the at least one electrode such that the laminated patch surrounds the electrode. The patch may comprise a and a compliant cushioning layer between the first layer and the skin bonding layer. The wearable biosensor system may be a neuromonitoring system. The wearable biosensor system may be configured for attachment to the head, including for example the scalp. The wearable biosensor system of embodiments may comprise an electroencephalogram device. The housing may insulate the power source and a controller and may define a sealed enclosure. For ease of use and reliable operation the housing may be generally considered permanently sealed and / or tamper proof since the end user will not need to access the power source or controller. The housing may provide an enclosure which is sealed against ingress for example the housing may be water-resistant, waterproof and / or dust proof. The patch may be a laminated patch. The first layer of the patch may be an adhesive layer which bonds to the skin facing surface of the housing. In some embodiments the patch could be supplied pre-bonded to the housing but (as will be apparent from the further details below) it may be advantageous to provide the patch with a self-adhesive layerfor bonding to the housing such that it may be applied by the user when setting up the device. The self-adhesive skin bonding layer may include a removable film. A compliant cushioning layer may comprise a foam. As the skin facing surface comprises at least one electrode it will be appreciated that the wearable sensor device of embodiments may be considered to have at least one embedded electrode. In some embodiments, the (or each) opening in the patch may be a through aperture (i.e. an aperture which extends through the full thickness of the patch and is open in use to the user's skin). Such an aperture(s) may provide the at least one electrode with unimpeded access to the skin through the patch. In some embodiments the opening(s) may be a recess which does not extend through the full thickness of the patch. In such an embodiment the patch may include at least one conductive portion to provide an interface between the skin and the (or each) electrode. The wearable sensor device may comprise a plurality of electrodes. The patch may have a corresponding plurality of openings. The size and spacing of the openings may match the size and spacing of the electrodes. The wearable sensor device may comprise a pair of electrodes. The skin facing surface may comprise a pair of spaced apart electrodes. The least one least one opening may comprises a pair of corresponding spaced apart openings configured to match the configuration of the pair of spaced apart electrodes. In embodiments the system may comprise a plurality of types of patches for use with a common wearable sensor device. Some of the plurality of types of patches may be configured to interface with the at least one (embedded) electrode of the wearable sensor device and temporarily modify the electrode configuration. For example the patch may modify the relative size and / or position of the electrode (for example different patch types may have define different pre-determined spacings between a pair of spaced apart electrodes). Some of the plurality of types may be configured to allow the at least one (embedded) electrode of the wearable sensor device to be used with an unmodified electrode configuration. Advantageously, embodiments enable the provision of a modular system in which a single common wearable sensor device may be usable in a plurality of different electrode configurations. In embodiments, the system may comprise a plurality of patches each defining a different electrode configuration. In contrast to prior art devices using, for example, flexible leads the provision of preconfigured patches of different types may enable an unskilled user to quickly and easily apply the device with an appropriate required electrode placement on the body. Modification of the spacing between the electrodes may for example be useful to allow a range of different monitoring activities to be carried out by a single type of device or to allow a single type of device to be adaptable for different users (for example for use by both adults and infants) In embodiments, each patch may comprise a machine-readable identifier. The wearable device may further comprise a reader for the machine-readable identifier. The controller of the wearable sensor device may be configured to use the reader to identify the attached patch and apply at least one associated device setting. As such, embodiments may enable the system to automatically reconfigure when a selected one of a plurality of types of connector is in use. It will be appreciated that such automatic configuration of the device is a further usability advantage when the device is intended to be self-applied or applied by an unskilled / untrained user. The reader may, for example, be configured to automatically read the identifier when the patch is attached to the housing of the device (for example as a result of the identifier coming into proximity with the reader). The machine-readable identifier and reader may for example be an optical arrangement (such as a barcode or QR code). The machine-readable identifier and reader may for example be an electro-magnetic arrangement (for example a magnetic or hall effect arrangement). The machine-readable identifier and reader may for example be RFID. In some embodiments the identifier and reader may be an electrical connection formed when the patch is attached to the housing. In embodiments the patch may further comprise an embedded conductive element. The patch may include a plurality of conductive elements, for example a separate conductive element may be provided for each electrode on the device. For example the (or each) embedded conductive element may be a flexible conductive layer, for example a conductive tape or a flexible PCB. The (or each) conductive element may extend from a terminal portion on a device facing side to a sensor portion on the skin facing side. The terminal portion may be positioned and configured to connect to the at least one electrode. As such, the conductive element may provide an electrical path in use between the at least one electrode and the skin. Thus, it may be appreciated that, when the patch is connected to the device, the sensor portion(s) of the (or each) conductive element may become the effective position of the (or each) electrode. The conductive element may be at least partially embedded within the patch (for example between layers of a laminated patch). Embedded portions of the conductive element may provide insulated conductive paths for signal isolation. In embodiments the conductive element (or elements) modifies the electrode configuration of the wearable biosensor system. For example, the conductive element may change the relative position of the skin interfacing portion of the or each electrode. In embodiments the wearable biosensor system may further comprise an assembly guide. The assembly guide may be configured to assist the correct configuration of the wearable sensor device and patch to ready the system for use. The assembly guide may comprise a body having a mount with a size and shape matching the configuration of the patch and at least one alignment feature for positioning the wearable sensor device housing relative to the mount (and therefore the patch). The mount may for example be a recess or depression which receives the patch. The internal shape and dimensions of the mount may match the external shape and dimensions of the patch. In embodiment with a plurality of types of patches, an assembly guide may comprise a plurality of mounts corresponding to each patch type. The plurality of mounts may be formed in a single body or alternatively in a plurality of separate bodies. The at least one alignment feature may temporarily retain the wearable sensor device relative to the assembly guide (and specifically the mount of the assembly guide). The alignment feature(s) could for example be a resilient engagement such as a snap fit retention. The alignment feature may comprise at least one magnetic element for engaging the wearable sensor device. A magnetic alignment could be provided by any complementary magnetic components on the device and assembly guide (for example dedicated magnets). However, conveniently a magnet may be provided which aligns and engages the at least one electrode to position the housing of the wearable sensor device. Typically a pair of magnets may be provided corresponding to a pair of electrodes on the wearable sensor device. It may be appreciated that, advantageously, magnets can provide an automatic alignment once the wearable sensor device is brought into sufficiently close proximity to the assembly guide. A further advantage of using a magnetic alignment is that such an arrangement can provide a tactile and / or audible feedback to the user when the device snaps into position. In embodiments the system comprises packaging for containing and / or protecting the wearable sensor device and patch when not in use (particularly prior to first use, when the device may for example be posted to a user). In embodiments the assembly guide may be formed integrally within the packaging. For example the assembly guide may be integrated into a protective layer of packaging with the mount being formed in a layer of the packaging (for example cut or formed into a layer of foam, cardboard or other physical protection layer). In some embodiments the system may further comprise an applicator for assisting the correct application of the device to the user's skin. The applicator may comprise a removably connected collar extending outwardly from a periphery of the patch. The collar may be used to aid alignment of the device relative to the user's body. For example the applicator may help ensure that the device is positioned with a predetermined position and / or spacing between the device and a specific body portion or feature. The collar may extend beyond the periphery of the patch and may be removed from the device after application. Such an arrangement may for example enable the size of the device and / or patch to be reduced so that, after the removal of the applicator, the device can be more conveniently worn for the required period of use. The applicator may be generally planar such that it can be easily placed against the surface of the user's skin during application of the device. The plane of the applicator may be substantially coplanar with the plane of the patch (which may locally conform to the plane of the lower face of the device housing). The applicator may provide an effective extension of the patch and may define a generally continuous skin facing surface during application of the device. The applicator may be formed from a semi-rigid sheet material. In this context it may be appreciated that a semi-rigid sheet may be considered to be a sheet which is sufficiently flexible to conform to the surface of the user's body but which will not readily crease or fold (such that it maintains its intended overall shape and size). In other words, the applicator may be a stiff but compliant sheet material. The applicator may for example be formed from a thin plastic sheet. The applicator may typically have a greater stiffness than the patch of wearable biosensor system. This is an advantage of using a removable applicator since it will not impact user comfort but can provide more accurate alignment than the patch itself (which is limited by needing to be sufficiently flexible to securely bond to the skin and be worn for an extended period of time without discomfort). The applicator may be formed from transparent material. The use of a transparent applicator may assist the user in locating the device correctly on the body. The applicator may include additional printed information or sections with reduced or non-transparency to help with positioning and / or alignment. The power source of the wearable sensor device may comprise a battery. In some embodiments a pre-charged battery may be sufficient. In other embodiments, the device further comprise a charging connection for the battery. To aid ease of use, the charging connection may comprise a connector which can engage a corresponding connector at a plurality of mutual orientations, and in some embodiments the connector may be configured to engage at any mutual angular orientation (i.e. a 360-degree connector). For example the connector may comprise one or more annular connectors on an outer surface of the device housing. The charging connector may be provided on the skin facing surface of the wearable sensor device (which advantageously may position the connector in a covered location during use). In such embodiments, the at least one electrode may project from the surface and the charging connector may be recessed relative to the face of the electrode. For example the electrode(s) may extend out from the housing to an end face forward of the skin facing surface and the charging connector may not extend beyond the plane of the skin facing surface (for example the charging connector may be recessed or flush to the surface). Such an arrangement may ensure that during use the charging connector is spaced apart from the skin (since it is above the lower plane of the electrodes). The housing of the wearable sensor device has an elongate profile when viewed from the plane of the skin facing surface. The housing may for example have a generally rectangular shape with rounded ends (for example a stadium-shape). It may be appreciated that the size and shape of the housing may be primarily constrained by the dimensions of the power source and the electrodes. The power may comprise at least one cylindrical battery cell (for example a button battery). The electrode(s) may be generally circular. As such, to optimise the compactness the battery(s) and electrode(s) may be arranged in a stacked orientation within the device. In embodiments the device maycomprisea pair of side-by-side battery cells (for example button battery cells). Each battery cell may be aligned such that it is stacked over one of a pair of electrodes (on the skin facing surface). In order to provide a compact package, embodiments may further comprise the battery cells being sandwiched between first and second (i.e. upper and lower) PCBs. Both the PCB and power source may be enclosed within the housing. The lower PCB may interface with the electrodes. The PCBs may include the controller. The controllerof the wearable device may be configured to switch the device between active and sleep modes (for example the sleep mode may be a low power state and the active mode may be a mode in which the device is collecting data). It is advantageous for the device to automatically switch between modes (for example to improve ease of use for non-skilled / trained users). In embodiments the controller is configured to automatically activate the wearable sensor device from a sleep mode in response to a combination of sensor inputs. The use of a combination of inputs improves the reliability of mode switching and helps more accurately predict the when the device is actually intended to be in use. The combination of sensor inputs may for example be indicative of a user applying the wearable biosensor system to the skin. The combination of sensor inputs may include signals indicative of: device movement; skin impedance, skin proximity, patch connection and / or a change in ambient conditions. The controller may for example, be configured to identify at least two of these signals to automatically wake or activate the device. In some embodiments a removable film may cover the self-adhesive skin bonding layer for removal by the user prior to application of the device to the skin. The controller may be configured to detect removal of the removable film. For example, the removable film may comprise a conductive element such that the wearable sensor device can detect the removal of the adhesive film. In order to reduce the need to add additional components the conductive element of the removable sleeve may interact with the electrodes of the device. For example, prior to removal the removable film may short circuit across a pair of spaced apart electrodes. The detection of removal of the self-adhesive film may provide a particularly reliable means of auto-waking the device, particularly for example when combined with one or more secondary indicators of use of the device. This may be useful in its own right. Accordingly, a further aspect of the invention may provide a wearable biosensor system comprising a wearable sensor device and a patch positioned between a skin facing surface of the device and the user in use. The may patch comprising a self-adhesive skin bonding layer and a removable film covering the self-adhesive skin bonding layer prior to use and wherein the removable film comprises a conductive element such that the wearable sensor device can detect the removal of the adhesive film by the user in preparation for application of the device. The device may comprise a housing enclosing a power source and a controller, the housing having an exterior surface which is outwardly aligned in use and a skin facing surface which is proximal to the wearer in use and the skin facing surface comprises at least one electrode. The controller may be configured to utilise detection of removal of the film as an indicator for automatically activating the wearable sensor device from a sleep mode. The controller may also be configured to require at least one further sensor input indicative of use of the device prior to activation of the device. The further sensor input may comprise one or more signal indicative of: device movement; skin impedance, skin proximity, connection of the patch to the device and / or a change in ambient conditions around the device. 5 Whilst the invention has been described above, it extends to any inventive combination of the features set out above or in the following description or drawings. Unless otherwise stated, each of the integers described may be used in combination 10 with any other integer as would be understood by the person skilled in the art. Further, although all aspects of the invention preferably "comprise" the features described in relation to that aspect, it is specifically envisaged that they may "consist" or "consist essentially" of those features outlined in the claims. In addition, all terms, unless specifically defined herein, are intended to be given their commonly 15 understood meaning in the art. Description of the Drawings Embodiments of the invention may be performed in various ways, and embodiments thereof will now be described by way of example only, reference being made to the accompanying drawings, in which: Figure 1 shows a three dimensional view of a wearable biosensor system in accordance with an embodiment comprising a wearable sensor device and a patch for adhering the sensor device to the skin; Figure 2 shows the wearable sensor device of figure 1 with the housing removed; Figure 3 shows a wearable biosensor system in accordance with an embodiment with an alternate patch configuration; Figure 4 shows a wearable biosensor system and an assembly guide in accordance with an embodiment; Figure 5a and 5b shows upper and lower views of a patch in accordance with embodiments; and Figure 6a, 6b and 6c show a wearable biosensor system and an applicator in accordance with embodiments. Detail Description of Embodiments The description will describe the wearable biosensor system in accordance with its general alignment in use. It will be appreciated that in use the device is intended to be attached to a test site on the skin (which may for example include, without limitation, the scalp or forehead). For convenience the skin proximal side of the device (or any components thereof) will be understood to be the lower and / or inner side or direction. Likewise any component or surface which is intended to be relatively distal to the skin in use may be referred to as an upper and / or outer surface or direction. It will, therefore, be appreciated that the use of such terms (upper and lower, inner and outer) can be considered to be generally relative to the in-use orientation of the device and not limiting to the actual device orientation. A wearable biosensor system 1 comprising a wearable sensor device 10 and a patch 50 is shown in figure 1. The biosensor 1 of the embodiment is specifically adapted for se as an electroencephalogram (EEG) device which is normally connected to the head to measure and monitor electrical signals produced by the brain. As will be explained further below, the device 10 includes a power source and a controller within a housing 20 which is typically an environmentally sealed moulded plastic case. The patch 50 provides an interface between the device 10 and the user's skin and is generally used to bond the device to a monitoring site whilst ensuring that the electrodes of the device are in electrical communication with the skin. The housing 20 defines a lower, skin-facing surface 22, an opposing upper surface 24. The upper 24 and lower 22 surfaces are substantially parallel. A side surface 26,which is generally perpendicular to the planes of the upper 24 and lower 22 surfaces, extends around the periphery of the housing. It will be appreciated that the general form of the housing may be easily adapted for aesthetic and / or ergonomic reasons but that it is generally desirable to have the device 10 in as compact a package as possible. The lower surface 22 is generally flat and intended to be substantially aligned with the surface of the skin in use. As will be explained further below (with reference to figure 2 in which the housing is excluded) it is generally desirable for the device to have minimal dimensions and, as such, embodiments may have a "lozenge" type shape / profile. A pair of electrodes 30a and 30b are positioned in a spaced apart relationship on the lower face 22 of the housing 20. The electrodes 30 are typically circular in profile and project outwardly from the plane of the lower face 22. The spacing between the electrodes 30a and 30b along the width of the lower face 22 may be defined by the electrode spacing required in use for at least one application type (and as will be explained below an advantage of the invention is that this electrode spacing can be temporarily modified). In order to maximise the space utilisation and minimise the device footprint, a power connector 40 may be provided between the two electrodes 30a, 30b. The power connector 40 consists of a plurality of generally circular (and typically annular) connector terminals which advantageously allow a charging connection to be made at any relative angular orientation of the device 10. The power connector 40 in the embodiment is formed from a printed / embossed connection on the lower face 22 of the housing 20. This ensures that the power connector 40 is generally flush with the face 22 and recessed relative to the skin facing portion of the electrodes 30. The housing 20 may further comprise one or more touch contacts 28 (which are covered during normal use) which may, for example, allow a hard reset of the device whilst removing the need to accommodate a switch or button. A first example of a patch 50 is shown alongside the device 10 in Figure 1. The patch comprises an upper layer 56 for attachment to the device housing, a lower self-adhesive skin bonding layer 52 and an optional compliant cushioning foam layer 54 therebetween. The self-adhesive layer 52 will normally be initially covered by a removable film which the user removes when ready to apply the patch to the skin. The compliant cushioning layer 54 may provide a degree of cushioning between the housing of the device 10 and the users skin for both comfort and to allow the device 10 to self-align on the skin (for example with the electrodes 10 in good contact / alignment with the skin surface). In some embodiments, the upper layer 56 could be pre-bonded to the lower face 22 of the housing 20 but typically may be a self-adhesive layer which is initially covered by a film which the user removes before attaching the patch to the housing 20 in an initial step of preparing the wearable biosensor system 1 for use. The patch 50 of the embodiment of figure 1 has a general profile which corresponds to the profile of the lower surface 22 of the housing 20 but in the present embodiment has a slightly larger profile such that the periphery of the patch in use extends beyond the sides of the device 10 (it will be appreciated that this is optional and in some embodiments the housing and patch may be the same size). The patch includes a tab region 58 which extends laterally from the main portion of the patch 50 and which may provide a graspable feature to assist the user when applying or removing the device (for example, the tab may be used for removing the protective film(s) from self-adhesive layer(s)). The patch 50 includes openings 60a and 60b which are sized and spaced to match the position of the electrodes 30a and 30b. In the embodiment of figure 1 the openings 60a and 60b are through apertures extending through the full thickness of the patch 50. The electrodes 30a and 30b can be received into the openings 60a and 60b and extend beyond the patch (beyond the compliant layer 54) to be held in contact with the skin. In other embodiments, as will be described further below with reference with figure 3, the opening may be a recess which does not extend through the full thickness of the patch. In such an embodiment the patch may include a conductive portion to provide an interface between the skin and the at electrode. When the patch 50 is appropriately aligned on the lower surface 22 of the device the patch substantially surrounds each of the electrodes 30a, 30b. This ensures that the system 1 of embodiments provides a good contact between the electrodes 30 and the skin. The patch 50 may also include an additional cut out 64 which aligns in use with the power connector 40 (so that the device 10 may still be charged when a patch 50 has been attached to the lower surface 22). Figure 2 illustrates the internal components of the device 10 without the housing 20. The internal configuration of the device 10 comprises a pair of parallel spaced apart PCBs 34a and 34b which are substantially parallel to the lower surface 22 of the device 10. It will be appreciated that the PCB's can incorporate the controller of the device 10 and interface with the electrodes 30 on the lower face. A pair of button cell batteries 32a and 32b are sandwiched between the PCB's 34a and 34b. It can be noted that the batteries 32a and 32b are respectively stacked above one of the electrodes 30a and 30b which provides improved compactness. The plan form of the PCB's 34 (and the device 20) is a stadium shaped profile - i.e. it is generally elongate rectangular type shape with curved opposing ends (for example semicircles at the opposing ends). This provides a compact shape which conforms closely to the foot print of the two spaced apart (circular) electrodes 30a, 30b. Figure 3 shows an example of how the system of embodiments can be used with an alternative patch 50' so that the same wearable sensor device 10 can be modified for different electrode configurations. For example, the patch 50 of Figure 1 (with a patch which does not alter the electrode effective position) could provide a 60mm electrode spacing for monitoring a first condition (such as Dystonia) and the patch 50' of Figure 3 could provide a 100mm electrode spacing for monitoring a second condition (for example sleep monitoring). In contrast to the patch 50 of figure 1 the openings in patch 50' for receiving the electrodes 30 are not through openings but instead are closed recesses extending through the compliant layer 54 but not through the skin facing layer 52. The recesses each define a terminal 71a and 72b which can form a connection to the electrodes. A flexible electrical element extends from each terminal 72a, 72b to a sensor portion 76a, 76b via a connector 74a, 74b. The terminal 72, connector 74 and sensor 76 are formed by an embedded flexible conductive tape which can be provided between layers of the patch to provide insulation of the conductive path and ensure signal isolation to the electrodes. The specific patch arrangement of figure 3 includes arms portions 70a and 70b which project outwardly from opposing sides of the main body portion 52 of the patch 50'. The respective connectors 74a, 74b extend along the length of the arm 70. It will be appreciated that the specific configuration of the patch can be easily modified to provide a range of different effective electrode configurations (for example with different lengths or relative alignments). To aid ease of use, the device 10 may be configured to automatically detect the type / configuration of the patch 50 / 50' which has been connected to the device. This can for example be achieved by providing sensor in the device 10 and embedding a corresponding tag into the patch 50. The tag can be any form of machine readable tag but could for example be a hall effect marker. The device 10 may automatically configure the settings after detecting the patch which has been attached, for example the device may identify from the type of patch which electrode spacing / configuration is attached and automatically configure itself to carry out the corresponding type of monitoring. This automatic configuration may include for example the type and regularity of data which is logged and / or may set the required sensitivity / accuracy level of data recorded (those skilled in the art may appreciate that the appropriate level of sensitivity may need to be set as a compromise between accuracy and power consumption and may therefore be directly connected to the type of monitoring to be carried out). Figure 4 illustrates an assembly guide 100 which may be provided with the wearable biosensor system 1 of embodiments. Whist the assembly guide 100 is shown in isolation in figure 4, it will be appreciated that it may typically be integrated into a packaging for the system. The assembly guide has a mount defined by a recess 110 which has a size and shape which matched the (or one of the) patch 50. The user can position a patch 50 on the mount 110 and remove the film of a self-adhesive upper layer. The device 10 can then be placed onto the patch 50 and is brought into correct alignment by a pair of magnetic alignment features 112a and 112b which interface with the electrodes of 30a, 30b of the device. It will be appreciated that the use of magnetic features 112a and 112b may cause the device 10 to "snap" into position once the electrodes 30a and 30b are in close proximity to the assembly guide 100. This ensures an effective user experience with intuitive use and tactile feedback. The assembly guide ensures that the user quickly and easily aligns the device 10 and patch 50. The mount 100 may be formed from a resilient material such as a foam which allows the user to compress the device against the patch 50 and ensure a good bond therebetween. Figure 5a shows a patch 50 in isolation to illustrate another optional feature of embodiments. The patch 50 may include a conductive element 55 which is integrated into the removable film on the skin facing surface of the patch. The conductive element 55 extends across both openings 60a and 60b of the patch and, as such, the element may effectively short circuit across the electrodes 30. Thus, the patch 50 may be provided with a simple arrangement which allows the device 10 to detect the presence of the patch and / or the removal of the protective film as the user prepares to apply the device. An alternative configuration of the patch 50' is shown in Figure 5b. In this embodiment the conductive element 55' comprises a specifically aligned strip of conductive material ratherthan a general layer as in figure 5a. The embodiment of figure 5b may, for example, provide a connection between dedicated contacts provided on the PCB rather than interfacing with the electrodes 30. Features such as the detection of the film removal and the identification of the patch applied help ensure that the system of embodiments is easy to use with minimal user intervention required. This may also be useful in helping to ensure that the device efficiently utilises the battery by being inactive prior to the device being configured for use by the user. Maximising battery usage is particularly beneficial for devices which are intended to be self-applied by a user in providing a user-friendly and simple use experience. Embodiments may further enhance the use by using multiple inputs to detect when to switch on or wake the device in order to provide a more reliable detection and, for example, avoid false positive detection of events. The device 10 may for example include at least one accelerometer to detect movement indicative of the device being worn. The device may also detect skin impedance indicative of the electrodes being in communication with the skin. The device may also include a sensor for detecting changes in ambient conditions such as temperature which would be indicative of the device being configured for use (for example due to being attached to the body). Figure 6a, 6b and 6c show how embodiments of the invention may further comprise an applicator 200 to assist the correct application of the system onto the test site of the body by an unskilled / untrained user. The applicator 200 comprises a collar which extends outwardly from a periphery of the patch 50 and device 10. The collar is removably attached to either the patch 50 or the device 10 such that it can be removed after the device is attached to the skin and does not cause discomfort or inconvenience during the period in which the device is worn. The collar 200 extends to an outer edge 210 which is shaped to provide a guide for placement of the device, for example in the example of the figure the collar is shaped with a curve which is intended to follow the curvature of the rear of the users ear and result in an appropriate alignment and position for the device 10. The applicator 200 is formed from a semi-rigid transparent plastic sheet which is sufficiently stiff to maintain its shape and dimensions (for example it will not easily fold) but which also has a small degree of flex sufficient to enable the applicator 200 to conform to the surface form of the skin. The use of a transparent material helps to provide the user with an unimpeded view whilst positioning the device. In may be noted that the applicator can also include printed information 250-for example "LEFT EAR" and an "UP" to assist in correct application. This is particularly useful if the device is supplied as a set of devices (as in the figure) which are to each be applied in a different location. As can be seen in the instructions shown in Figure 6B, the sequence of application of an embodiment including an applicator requires the user to first remove the film from the skin adhesive layer of the patch 50 before using the applicator 200 to align the device 10 and patch 50. Once the device has been firmly pressed into place and is secure the applicator can be carefully removed. Figure 6c shows an example of an embodiment including an applicator 200' for use 5 when the device 10 is configured for use with a patch 50' which has a 100mm electrode spacing (similar to that shown in figure 3). The applicator 200' of this embodiment extends around the connector 74 and sensor 76 of the patch 50'. It can be noted that the edge 210' of the applicator 200' can be configured to be aligned across a user's forehead with the markings 250 providing guidance specifying the 10 intended position of the patch in use - for example indicating the "UP" direction and the portion of the applicator which is to "REST ON EYEBROW". Although the invention has been described above with reference to preferred embodiments, it will be appreciated that various changes or modification may be 15 made without departing from the scope of the invention as defined in the appended claims. For example, whilst the wearable device described above is in the form of a wrist worn device, other devices could be arranged for example a wearable pendant or patch.

Claims

1. A wearable biosensor system comprising:a wearable sensor device comprising a housing enclosing a power source and a controller, the housing having an exterior surface which is outwardly aligned in use and a skin facing surface which is proximal to the wearer in use; wherein the skin facing surface comprises at least one electrode; anda patch positioned between the skin facing surface and the user in use, the patch comprising a first layer for attachment to the device housing and a self-adhesive skin bonding layer, and wherein the patch comprises at least one opening for receiving the at least one electrode such that the laminated patch surrounds the electrode.

2. The wearable biosensor system of claim 1, wherein the patch further comprises a compliant cushioning layer between the first layer for attachment to the device housing and a self-adhesive skin bonding layer.

3. The wearable biosensor system of claim 1 or 2, wherein the skin facing surface comprises a pair of spaced apart electrodes and the at least one least one opening comprises a pair of spaced apart openings configured to match the configuration of the pair of spaced apart electrodes.

4. The wearable biosensor system of claim 1, 2 or 3, wherein a plurality of patches are provided for use with a common wearable sensor device, each of the plurality of laminated patches defining a different electrode configuration.

5. The wearable biosensor system of claim 4, wherein each patch comprises a machine-readable identifier and the wearable sensor further comprises a reader for the machine-readable identifier, and wherein the controller of thewearable sensor device is configured to use the reader to identify the attached patch and apply at least one associated device setting.

6. The wearable biosensor system of any preceding claim, wherein a patch further comprises an embedded conductive element.

7. The wearable biosensor system of claim 6, wherein the conductive element extends from a terminal portion on a device facing side to a sensor portion on the skin facing side.

8. The wearable biosensor system of claim 7, wherein the conductive element modifies the electrode configuration of the wearable biosensor system.

9. The wearable biosensor system of any preceding claim, further comprising an assembly guide comprising a body having a mount with a size and shape matching the configuration of the patch and at least one alignment feature for positioning the sensor housing relative to the recess.

10. The wearable biosensor system of claim 9, wherein the at least one alignment feature comprises at least one magnet.

11. The wearable biosensor system of claim 9 or 10, comprising packaging for containing the wearable sensor device and patch prior to use, wherein the assembly guide is formed in the packaging.

12. The wearable biosensor system of any preceding claim, further comprising an applicator, the applicator comprising a removably connected collar extending outwardly from a periphery of the laminated patch to aid alignment of the device relative to the user's body.

13. The wearable biosensor system of claim 12, wherein the applicator is a semirigid sheet material.

14. The wearable biosensor system of claim 12 or 13, wherein the applicator is transparent.

15. The wearable biosensor system of any preceding claim, wherein the power source of the wearable sensor device comprises a battery and the device further comprises a charging connection for the battery, the charging connection comprising a connector which can engage a corresponding connector at any mutual angular orientation.

16. The wearable biosensor system of claim 15, wherein the charging connector is provided on the skin facing surface of the wearable sensor device and wherein the at least one electrode projects from the surface and the charging connector is recessed relative to the face of the electrode.

17. The wearable biosensor system of any preceding claim, wherein the housing of the wearable sensor device has an elongate profile when viewed from the plane of the skin facing surface and wherein the power source comprises a pair of side-by-side button battery cells and wherein each battery cell is aligned such that it is stacked over one of a pair of electrodes on the skin facing surface.

18. The wearable biosensor system of claim 17, wherein the battery cells are sandwiched between first and second PCBs, both the PCB being enclosed within the housing.

19. The wearable biosensor system of any preceding claim wherein the controller is configured to automatically activate the wearable sensor device from a sleep mode in response to a combination of sensor inputs indicative of a user applying the wearable biosensor system to the skin.

20. The wearable biosensor system of claim 19 or 20, wherein the combination of sensor inputs includes at least two signals indicative of: device movement;skin impedance, skin proximity, patch connection ora change in ambient conditions.

21. The wearable biosensor system of any preceding claim, wherein a removable film covers the self-adhesive skin bonding layer for removal by the user prior to application of the device to the skin and wherein the removable film comprises a conductive element such that the wearable sensor device can detect the removal of the adhesive film.

22. A wearable biosensor system comprising:a wearable sensor device comprising a housing enclosing a power source and a controller, the housing having an exterior surface which is outwardly aligned in use and a skin facing surface which is proximal to the wearer in use; anda patch positioned between the skin facing surface and the user in use, the patch comprising a self-adhesive skin bonding layer and a removable film covering the self-adhesive skin bonding layer prior to use and wherein the removable film comprises a conductive element such that the wearable sensor device can detect the removal of the adhesive film by the user in preparation for application of the device.

23. The wearable biosensor system of claim 22, wherein the controller is configured to utilise detection of removal of the film as an indicator for automatically activating the wearable sensor device from a sleep mode.

24. The wearable biosensor system of claim 23, wherein the controller is configured to require at least one further sensor input indicative of use of the device prior to activation of the device.

25. The wearable biosensor system of claim 24, wherein the further sensor input comprises one or more signal indicative of: device movement; skinimpedance, skin proximity, connection of the patch to the device and / or a change in ambient conditions around the device.

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