METHOD AND APPARATUS FOR INSERTION OF A SENSOR
Cross Reference to Related Applications
[0001] The present application is a continuation-in-part of U.S. Patent Application
No. 11/558,394, filed November 9, 2006, entitled "METHOD AND APPARATUS FOR
INSERTION OF A SENSOR," which claims priority to U.S. Provisional Patent
Application No. 60/735,732, filed November 11, 2005, entitled "Method and Apparatus
for Insertion of a Sensor," the entire disclosures of which are hereby incorporated by
reference in their entirety.
Technical Field
[0002] This present disclosure relates generally to devices for delivering
mechanically slender devices through skin into a body to perform various medical or
physiological functions. More specifically the present disclosure relates to a method for
transcutaneous placement of a soft cannula biosensor or flexible biosensor safely and
automatically, without the aid of a rigid and or sharp introducer device or the resultant
need for disposal of a contaminated sharp introducer device.
Background
[0003] There are several instances of medically useful devices which are
mechanically slender and flexible and are also inserted through the skin.
[0004] For example, sensors facilitate the sensing of certain conditions within a
patient. Electrochemical sensors are commonly used to monitor blood glucose levels in
the management of diabetes. In one scheme, an electrochemical sensor incorporating
an enzyme is fabricated onto a small diameter wire. A second reference electrode is
also fabricated around the wire near the sensing electrode. The sensor assembly is
inserted through the skin so that it is surrounded by interstitial fluid. A portion of the
sensor assembly exits the skin, remaining outside the body, where electrical
connections to the sensing electrode and reference electrode may be made. A suitable
electronic measuring device outside the body may be used to measure electrical current
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from the sensor for recording and display of a glucose value. These types of devices
are described, for example, in US Patent No. 5,965,380 to Heller et al. and US Patent
No.5,165,407 to Ward et al.
[0005] In addition to electrochemical glucose sensors, a number of other
electrochemical sensors have been developed to measure the chemistry of blood or
other body fluids or materials. Electrochemical sensors generally make use of one or
more electrochemical processes and electrical signals to measure a parameter. Other
types of sensors include those which use optical techniques to perform a measurement.
[0006] In other applications, a cannula and sensor combination device is inserted
through the skin to allow insulin to be introduced into the body as part of an artificial
pancreas system. In these applications, a slender (small cross-section) and flexible
device offers several advantages over a larger and more rigid device. Patient comfort is
increased, especially during long-term insertion, and trauma at the entry site is reduced.
A flexible device also is able to adjust to movement of the skin during physical activity,
increasing patient comfort. In many cases these devices will remain inserted in the
body for 5 to 7 days.
[0007] Although the slender and flexible nature of these devices increases patient
comfort, these devices are difficult to insert through the skin. Unlike a typical
hypodermic needle, these devices are too fragile and flexible to be simply pushed
through the skin surface using normal force and speed. When the tip of such a device is
forced against the skin, the device will bend and collapse with much less force than
would be required to achieve skin penetration. Although in some cases the tip of the
device may be sharpened to ease penetration, this approach is not typically adequate to
assure penetration, and some devices such as tubing-based devices are not
appropriate for sharpening. Also, the sharpening process adds to production cost and
complexity.
[0008] As will be understood by those skilled in the art, human skin possesses
biomechanical properties influenced by a relatively impenetrable outer layer, the stratum
corneum, and inner layers which are more easily penetrated. These biomechanical
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properties cause penetration of the skin surface to present the primary challenge in
introducing a relatively fragile slender, flexible device into the skin.
[0009] Current art provides several approaches for insertion of such slender
flexible devices through the skin. In one case, the device is placed coaxially inside a
hollow tube with a sharpened end, such as a hypodermic needle or trocar. The needle
is inserted through the skin with the device inside. As a second step, the needle is
withdrawn, leaving the device behind, passing through the skin into the body. See, for
example, US Patent No. 6,695,860 to Ward et al. The insertion process may be painful,
due to the large diameter needle, and a larger opening is made in the skin than required
for passing the device alone, increasing trauma and the possibility of infection.
[0010] In a variation of this approach, the functions of the device are incorporated
into a thin needle which must stay inserted into the skin. The needle provides additional
mechanical strength and a sharpened point to assist in piercing the skin. However, due
to its larger size and rigidity, this approach also contributes to patient discomfort for the
duration of the insertion. See, for example, US Patent No. 6,501,976.
[0011] In addition, the presence of a rigid needle places mechanical constraints
on the size and shape of the device housing that is attached to the surface of the skin
where the device exits the skin. The needle also must be treated asa biohazard
"sharp" since it is capable of transmitting disease if it should accidentally puncture the
skin of another individual after being used in device insertion.
Brief Description of the Drawings
[0012] Embodiments of the present disclosure will be readily understood by the
following detailed description in conjunction with the accompanying drawings. To
facilitate this description, like reference numerals designate like structural elements.
Embodiments of the disclosure are illustrated by way of example and not by way of
limitation in the figures of the accompanying drawings.
[0013] Figure 1 illustrates a block diagram of an insertion device according to an
embodiment of the present disclosure;
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[0014] Figure 2A illustrates an embodiment of an electrochemical glucose sensor
that has been fabricated onto a length of thin, flexible wire in accordance with
embodiments of the present disclosure;
[0015] Figure 28 shows a cross-section of how an electrochemical sensor
appears when inserted into skin in accordance with an embodiment of the present
disclosure;
[0016] Figure 3A shows an insertion device according to embodiments of the
disclosure in which a plunger and spring combination is utilized to insert an
electrochemical sensor;
[0017] Figure 38 shows an insertion device according to embodiments of the
disclosure in which a sensor is initially retracted from the skin and initially in contact with
a plunger;
[0018] Figure 4 shows an embodiment of the disclosure with a reduced guide and
support structure;
[0019] Figure 5A shows an embodiment of the disclosure in which the insertion
device includes a transmitter top and a sensor base;
[0020] Figure 58 shows an embodiment of the disclosure prior to the attachment
of a transmitter top and a sensor base;
[0021] Figure 6A shows an embodiment of the disclosure in which the
components of a sensor base are exposed to view;
[0022] Figure 68 shows an embodiment of the disclosure in which only some of
the components of a sensor base are exposed to view;
[0023] Figure 6C shows a cross sectional view of a sensor base in accordance
with an embodiment of the disclosure;
[0024] Figure 7A shows a guidance concept in accordance with an embodiment
of the present disclosure in which a sensor is guided using three plastic guides;
[0025] Figure 78 shows a guidance concept in accordance with an embodiment
of the present disclosure in which the sensor has attached two metallic guides that
double as conductors;
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[0026] Figure 7C shows a guidance concept in which spring contacts are mated
to metallic guides that double as conductors;
[0027] Figure 8 shows an embodiment of the disclosure in which energy stored in
a curved sensor is utilized to provide motive force to the sensor;
[0028] Figure 9A shows an embodiment of the disclosure in which a linear
solenoid is utilized to provide motive force to a sensor;
[0029] Figure 98 shows an embodiment of the disclosure in which a rotary
solenoid is utilized to provide motive force to a sensor;
[0030] Figure 10 shows an embodiment of the disclosure in which a CO2
cartridge is utilized to provide motive force to a sensor;
[0031] Figure 11 shows an embodiment of the disclosure in which an air pump
and piston are utilized to provide a motive force to a sensor;
[0032] Figure 12 shows an embodiment of the disclosure in which a mechanical
spring is utilized to provide a motive force to a sensor and the activation is controlled by
a separate bowed spring;
[0033] Figure 13A shows an embodiment of the disclosure in which a mechanical
spring and slider combination is utilized to provide a motive force to a sensor;
[0034] Figure 138 shows a cross sectional view of an embodiment of the
disclosure in which a mechanical spring and slider combination is utilized to provide a
motive force to a sensor;
[0035] Figure 14 shows an embodiment of the disclosure in which a series of
mechanical springs and a shear member are used to control and provide a motive force
to a sensor;
[0036] Figure 15 shows an embodiment of the disclosure in which electrical
connection is made to a sensor via wires insert molded and soldered onto the
conductive regions of the sensor;
[0037] Figure 16A shows an exploded view of an embodiment of the disclosure
that utilizes a canted coil spring probe termination to make electrical contact to the
sensor;
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[0038] Figure 16B depicts an assembled view of an embodiment of the disclosure
that utilizes a canted coil spring probe termination to make electrical contact to the
sensor;
[0039] Figure 17A shows an embodiment of the disclosure in which a paper
guidance structure is utilized both to secure a sensor prior to insertion and to guide the
sensor during insertion;
[0040] Figure 17B shows a view of an embodiment of the disclosure after sensor
insertion in which a paper guidance structure has been utilized to guide the sensor
during insertion;
[0041] Figure 18 shows a cross-sectional view of a sensor disposed in a coaxial
guidance structure and placed on skin in accordance with an embodiment;
[0042] Figure 19 shows a cross-sectional view of another embodiment in which a
sensor is disposed in a coaxial guidance structure and placed on skin;
[0043] Figure 20A shows a cross-sectional view of a sensor disposed in a
guidance structure during insertion with the skin untensioned in accordance with an
embodiment;
[0044] Figure 20B shows a cross-sectional view of a sensor disposed in a
guidance structure during insertion with the skin tensioned in accordance with an
embodiment;
[0045] Figure 21 shows a cross-sectional view of a sensor during insertion into
skin at an angle in accordance with an embodiment;
[0046] Figure 22A shows a graph of the absolute value of pusher velocity versus
displacement in accordance with an embodiment;
[0047] Figure 22B shows a graph of the absolute value of pusher velocity versus
time in accordance with an embodiment;
[0048] Figure 23A shows a cross-sectional view of a sensor inserted into skin in
accordance with an embodiment; and
[0049] Figure 23B shows a cross-sectional view of a sensor inserted into skin at
an angle in accordance with an embodiment.
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Detailed Description of Disclosed Embodiments
[0050] In the following detailed description, reference is made to the
accompanying drawings which form a part hereof, and in which are shown by way of
illustration embodiments that may be practiced. It is to be understood that other
embodiments may be utilized and structural or logical changes may be made without
departing from the scope. Therefore, the following detailed description is not to be
taken in a limiting sense, and the scope of embodiments is defined by the appended
claims and their equivalents.
[0051] Various operations may be described as multiple discrete operations in
turn, in a manner that may be helpful in understanding embodiments; however, the
order of description should not be construed to imply that these operations are order
dependent.
[0052] The description may use perspective-based descriptions such as
up/down, back/front, and top/bottom. Such descriptions are merely used to facilitate the
discussion and are not intended to restrict the application of disclosed embodiments.
[0053] The terms "coupled" and "connected," along with their derivatives, may be
used. It should be understood that these terms are not intended as synonyms for each
other. Rather, in particular embodiments, "connected" may be used to indicate that two
or more elements are in direct physical or electrical contact with each other. "Coupled"
may mean that two or more elements are in direct physical or electrical contact.
However, "coupled" may also mean that two or more elements are not in direct contact
with each other, but yet still cooperate or interact with each other.
[0054] For the purposes of the description, a phrase in the form "AlB" or in the
form "A and/or B" means (A), (B), or (A and B). For the purposes of the description, a
phrase in the form "at least one of A, B, and C" means (A), (B), (C), (A and B), (A and
C), (B and C), or (A, B and C). For the purposes of the description, a phrase in the form
"(A)B" means (B) or (AB) that is, A is an optional element.
[0055] The description may use the terms "embodimenf or "embodiments,"
which may each refer to one or more of the same or different embodiments.
Furthermore, the terms "comprising," "including," "having," and the like, as used with
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respect to embodiments, are synonymous, and are generally intended as "open" terms
(e.g., the term "including" should be interpreted as "including but not limited to," the term
"having" should be interpreted as "having at least," the term "includes" should be
interpreted as "includes but is not limited to," etc.).
[0056] With respect to the use of any plural and/or singular terms herein, those
having skill in the art can translate from the plural to the singular and/or from the
singular to the plural as is appropriate to the context and/or application. The various
singular/plural permutations may be expressly set forth herein for sake of clarity.
[0057] Various embodiments herein provide an insertion device configured to
insert an analyte sensor into skin without the aid of a sharpened introducer. An analyte
sensor is also configured to be inserted into skin without a sharpened introducer.
[0058] One embodiment provides an insertion device that includes a guidance
structure adapted to provide axial support to a flexible analyte sensor. The insertion
device further includes an injection activation device associated with the guidance
structure. The injection activation device includes a mechanism adapted to apply a high
speed motive force to the flexible analyte sensor such that, when the high speed motive
force is applied, the flexible analyte sensor moves at least partially through the guidance
structure and at least partially passes through an exit port of the gUidance structure to
cause insertion of only the flexible analyte sensor into skin.
[0059] The high speed motive force is configured such that a velocity of the
flexible analyte sensor at a time of insertion is in the range of 5 meters per second to 15
meters per second, such as 6.4 meters per second. In one embodiment, the high
speed motive force is 11 to 53 Newtons, such as 22 Newtons.
[0060] According to one embodiment, the guidance structure is configured so that
an unsupported length of the sensor is less than a buckling length of the sensor. The
buckling length of the sensor is determined by a formula Pcr =if*k / (3*L2), wherein Pcr
is a value of the high speed motive force applied to the sensor, k is a stiffness of the
sensor, and L is the unsupported length of the sensor.
[0061] In an embodiment, the insertion device is configured to insert the analyte
sensor at an insertion angle of 10 to 40 degrees with respect to a plane of the skin. For
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example, the insertion device includes a housing having a bottom surface associated
with the guidance structure, and the guidance structure is configured so that the sensor
passes through the exit port at an angle from 10 to 40 degrees with respect to the
bottom surface of the housing.
[0062] In an embodiment, the insertion device further includes a tensioning
structure to tension the surface of the skin so that a distance from the surface of the
skin at an insertion site to the exit port is less than the buckling length of the sensor.
The tensioning structure may include a nub surrounding the exit port of the guidance
structure configured to indent the skin at an insertion site such that the sensor is
inserted into skin at an angle that is substantially perpendicular to a plane of a local skin
surface at the insertion site. According to one embodiment, the sensor is inserted with
an insertion length of 12 millimeters (mm).
[0063] Another embodiment provides an analyte sensor that includes an elongate
wire and an outer membrane surrounding the elongate wire at a distal end of the
analyte sensor. The distal end is configured to be inserted into skin by a motive force
applied to the analyte sensor without the aid of a sharpened introducer. In an
embodiment, an elongate wire has a stiffness of 1.4 to 22.6 grams-force per millimeter
of deflection for an unsupported length of 10 millimeters.
[0064] According to one embodiment, the wire has a diameter of 0.15 to 0.30
millimeters. The distal end of the sensor may be sharpened or may be substantially
blunt.
[0065] For the purposes of describing embodiments herein and the claims that
follow, the term "high speed motive force" refers to a force sufficient to drive a thin,
flexible medical device into animal skin - including the relatively impenetrable outer
layer, the stratum corneum, as well as the inner layers that are more easily penetrated without
substantial bending or substantial deflection of the sensor. In some
embodiments, the high speed motive force is about 11 to about 53 Newtons, such as
about 20 to about 22 Newtons applied to the sensor. As would be obvious to one of
ordinary skill in the art, the force necessary to drive a thin, flexible medical device into
animal skin increases if the medical device encounters resistance other than that
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provided by the surface of animal skin such as, for example, scar tissue or frictional
resistance caused by a guidance structure or tube that the medical device must pass
through. The term "high speed motive force" encompasses force necessary to drive the
thin, flexible medical device into animal skin in situations where the medical device
encounters such other resistance. Stated another way, the term "high speed motive
force" encompasses any amount of motive force necessary to be applied to a thin,
flexible medical device such that the sum of all forces acting on the medical device as
the motive force is applied is sufficient to drive it into animal skin.
[0066] The term "actuator" refers to any of various electric, hydraulic, magnetic,
pneumatic, or other means by which something is moved or controlled. The term
"solenoid actuator" refers to a variety of electromechanical devices that convert
electrical energy into linear or rotational motion. The term "trigger" indicates any of
various electric, hydraulic, magnetic, pneumatic, or other means of initiating a process
or reaction. The term "sabot" indicates a thick circular disk with a center hole.
[0067] For the purposes of describing embodiments herein and in the claims that
follow, the term "axial support" means the support or bracing of a relatively straight,
slender object when a motive force is applied to the object in such a way as to resist
force vectors acting perpendicular to an imaginary line drawn through the device
lengthwise; such support or bracing sufficient to prevent or reduce crimping, creasing,
folding, or bending of the straight, slender object; or such support or bracing sufficient to
enable the object to return to a relatively straight configuration after minimal bending
such that the object substantially retains its original shape with minimal crimping,
creasing, folding, or bending.
[0068] For the purposes of describing embodiments herein and in the claims that
follow, the term "associated with" indicates that an object, element, or feature is coupled
to, connected to, or in proximity to and in communication with another object, element,
or feature. For example, as depicted in Figure 1, mechanism 102 applies a high speed
motive force to analyte sensor 108 such that analyte sensor 108 moves through
guidance structure 106. Mechanism 102 is therefore both proximally near guidance
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structure 106 and in communication with guidance structure 106 and is thus "associated
with" gUidance structure 106.
[0069] In another example, shown in Figure 3A, spring 307 forces plunger 305
down toward sensor 301 to drive sensor 301 through guidance structure 303.
Therefore, plunger 305 and spring 307 are in communication with guidance structure
303 and are thus "associated with" guidance structure 303. Plunger 305 and spring 307
mayor may not make physical contact with guidance structure 303, and mayor may not
be in contact when in a static position. Also in Figure 3, spring 307 is associated with
plunger 305 in that spring 307 is connected to plunger 305.
[0070] In another example, shown in Figure 6A, slider 605 is coupled to guidance
structure 601 and insertion spring 603 forces slider 605 to move over the top of
guidance structure 601. In such a way, both insertion spring 603 and slider 605 are
"associated with" curved guidance structure 601.
[0071] In yet another example shown in Figure 10, CO2 cartridge 1001 releases
CO2 gas into manifold 1003 which allows the gas to pass through an internal valve (not
shown) and enter hollow pin 1009 forcing rod 1011 forward striking a sensor (not
shown) for insertion. Therefore C02 cartridge 1001 is in communication with a sensor
(not shown) and thus "associated with" the sensor.
[0072] For the purposes of describing embodiments herein and in the claims that
follow, the term "guide member" means a device that at least partially axially surrounds
the analyte sensor, whether at an end or along the sensor, and is adapted to fit inside
the guidance structure such that the guide member at least partially occupies at least
some part of the space between the sensor and the guidance structure either during
insertion, before insertion, and/or after insertion. A guide member may either provide
axial support, assist a sensor in moving through the guidance structure, or both.
Exemplary guide members include a sabot, a spiral of plastic, a rectangular metallic
guide, an end-cap, an open cell foam plastic cylinder, and a thin plastic disk. As will be
appreciated by one of ordinary skill in the art, a guide member may be made of many
different materials and shaped in various geometries corresponding to the geometry of
the guidance structure.
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[0073] For the purposes of describing embodiments herein and in the claims that
follow, the term "electrical network" means electronic circuitry and components in any
desired structural relationship adapted to, in part, receive an electrical signal from an
associated sensor and, optionally, to transmit a further signal, for example to an
external electronic monitoring unit that is responsive to the sensor signal. The circuitry
and other components include one or more of a printed circuit board, a tethered or wired
system, etc. Signal transmission may occur over the air with electromagnetic waves,
such as RF communication, or data may be read using inductive coupling. In other
embodiments, transmission may be over a wire or via another direct connection.
[0074] An embodiment of the present disclosure includes, as shown in Figure 1,
a mechanism 102 adapted to generate a high speed motive force coupled to a guidance
structure 106 which is adapted for insertion of an analyte sensor 108. Mechanism 102 is
controlled by a trigger 114. In various embodiments, analyte sensor 108 is driven by a
high speed motive force generated by mechanism 102 through the guidance structure
and out of guidance structure opening 112. In Figure 1, guidance structure opening 112
is shown flush with the edge of housing 110. However, in embodiments, the guidance
structure opening is placed either outside of housing 110 or nested inside a larger
opening of housing 110.
[0075] In an embodiment, a guidance structure is a hollow tube with a circular
cross-section. A guidance structure may be linear, or curved to allow motive force to be
applied to a sensor in a direction other than perpendicular to the skin in which the
sensor is to be inserted. A guidance structure may be a curved hollow tube with a
circular cross-section.
[0076] In various embodiments, the edge of housing 110 where opening 112 is
situated is flush against skin prior to insertion. Placing the edge of housing 110 flush
against the skin generates tension on the skin surface assisting in inserting the sensor
without buckling or deflection of the sensor. In an embodiment in which guidance
structure 112 extends beyond the surface of housing 110, the pressure of guidance
structure 112 against the skin provides tension to the skin.
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[0077] Figure 2A shows an analyte sensor 200 that may be inserted according to
various embodiments. In Figure 2A, analyte sensor 200 is an electrochemical glucose
sensor that has been fabricated onto a length of thin, flexible wire. A reference or
ground electrode 205 and a sensing electrode 207 are incorporated into analyte sensor
200. Small diameter end 201 (proximal end) of sensor 200 may be inserted through the
skin. In an embodiment, this diameter is approximately 0.25 mm or less. In an
embodiment, on the larger diameter end (distal end) of sensor 200, its diameter has
been increased by adding a sleeve of steel tubing 203 which increases its rigidity and
facilitate electrical connections. In some embodiments, the diameter of the larger
section is, for example, approximately 0.5 mm. In an embodiment, the larger diameter
portion of the sensor remains outside of the body upon insertion. Figure 28 shows a
cross-section of the sensor when inserted into the skin. In some embodiments, a 10-20
mm, for example approximately 15 mm, length of sensor 200 is implanted beneath the
skin.
[0078] In embodiments, a sensor may be rigid or flexible. The term "flexibility" is
defined as the "amount of deflection of an elastic body for a given applied force."
Flexibility is generally the reciprocal of stiffness. In some embodiments, a flexible
sensor is one that can be flexed repeatedly, such as the type of flexion experienced by
a subcutaneously implanted sensor in a human during normal movement, over a period
of time (such as 3-7 days or more) without fracture. In an embodiment, a flexible sensor
can be flexed hundreds or thousands of times without fracture.
[0079] Figure 3A shows an insertion device in accordance with an embodiment.
Sensor 301 is placed into guidance structure 303 within insertion device 300. In an
embodiment, guidance structure 303 allows free passage of larger diameter end 302 of
sensor 301 while providing axial support. Guidance structure 303 also provides some
axial support to the smaller diameter end 304 of sensor 301, although there may be
more clearance between the inside of guidance structure 303 and sensor 301 at small
diameter end 304. In an embodiment, guidance structure 303 provides axial support to
the sensor in order to successfully drive sensor 301 into the skin.
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[0080] Insertion device 300 also contains plunger 305, compression spring 307
and a release mechanism including spring 311 and pin 313. In preparation for sensor
insertion, plunger 305 is withdrawn against spring 307 using handle 309 creating
tension in spring 307. The release mechanism holds plunger 305 in position. To implant
sensor 301, pin 313 is forced into the body of plunger 305 through slot 315, thus
compressing spring 311 and freeing plunger 305 and allowing spring 307 to force
plunger 305 down barrel 321 of insertion device 300 to strike large diameter end 302 of
sensor 301. Plunger 305 drives sensor 301 into position in skin 317. Upon insertion,
insertion device 300 is withdrawn over the end of sensor 301 without disturbing its
location in skin 317.
[0081] In an embodiment, appropriate electrical connections can be made after
insertion device 300 is withdrawn. In an alternative embodiment, insertion device 300
can be integrated with a sensing device or an associated housing that has various
electrical components, including electrical connections to sensor 301. In such an
embodiment, the electrical components are connected to sensor 301 prior to insertion,
and upon insertion, insertion device 300 is withdrawn by manipulation through a slot
present in guidance structure 303 and/or in insertion device 300. In other words,
guidance structure 303 and/or insertion device 300 is/are configured with a slot (straight
or curved) to allow removal of either device from association with sensor 301 even while
sensor 301 is electrically connected at its distal end (large diameter end) to additional
electrical components.
[0082] It will be appreciated to those skilled in the art that numerous alternatives
are possible for the guide and support structures, spring, plunger and release
mechanism which fulfill the various purposes of embodiments for supporting the sensor
and for providing a controlled impact and driving force.
[0083] It will also be appreciated that while a wire-based electrochemical glucose
sensor can be used, similarly-shaped devices, such as other sensors or drug delivery
•
devices such as small tubing used to dispense insulin or another medication can be
substituted for the glucose sensor in embodiments of the present disclosure.
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[0084] In an embodiment, an insertion mechanism is used only once as part of a
disposable assembly. In such an embodiment, there is no need to provide a manual
means to withdraw the plunger and set the release mechanism by the user, as the
device is assembled with the plunger already withdrawn and the release mechanism set
and ready for insertion.
[0085] To puncture the skin without damaging the sensor, a high initial impact of
the sensor tip against the skin is utilized followed by a controlled driving force to
complete the insertion through the softer inner skin layers. Note that an embodiment of
the insertion device shown in Figure 3A provides for a space or distance between the
withdrawn plunger and the end of the sensor that will be driven.
[0086] In embodiments such as shown in Figure 3A, the force of the spring
causes the plunger to accelerate through this distance before striking the end of the
sensor. The velocity of the plunger provides additional initial impact to the sensor that
assists in driving it through the tough outer layer of skin quickly. In an embodiment, the
force of the spring alone is sufficient to complete the insertion.
[0087] In other embodiments, the high initial impact of the sensor tip against the
skin can be achieved in other ways. For example, in another embodiment, shown in
Figure 38, sensor 301 is initially retracted from the skin and initially in contact with
plunger 310. In this embodiment, sensor 301 is accelerated along with plunger 310
before impacting the skin.
[0088] In yet other embodiments, the sensor alone is accelerated by a motive
force to achieve momentum causing an impact sufficient to penetrate the skin.
[0089] It will be understood by one of ordinary skill in the art that in other
embodiments, means other than a spring can be utilized to provide a high speed motive
force. Some examples include an electric solenoid, a shape memory alloy spring which
provides an electrically initiated driving force, an associated C02 cartridge, a
compressed air pump, etc.
[0090] Figure 4 shows an embodiment of insertion device 400 with a reduced and
curved guide and support means. In an embodiment, prior to insertion, sensor 401 is
supported at its larger end 402. Thin distal end 404 of sensor 401 follows a curved path
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during insertion. However, in this case, guidance structure 409 consists primarily of a
partially open region with a curved section 403 which gUides and supports the sensor
on only one side of sensor 401 that lies outside the radius of the arc formed by sensor
401 during insertion. It will be understood by those skilled in the art that while insertion
force is applied, sensor 401 exerts a radial outward force against the supporting wall of
guidance structure 409 of insertion device 400 along curved section 403. This radial
force tends to support and stabilize sensor 401 without the need for a completely
surrounding gUidance structure.
[0091] Another feature of the embodiment in Figure 4 is that the open region at
the skin contact side of guidance structure 409 allows the sensor to be easily and
completely freed from insertion device 400 when insertion is complete. In addition, in
an embodiment, the open region is large enough that additional electrical connections
and/or components associated with sensor 401 may be accommodated before, during,
and/or after insertion.
[0092] Figure 5A depicts an embodiment wherein the assembled insertion device
includes a transmitter 502, a sensor base 504, which may, in an embodiment, be
disposable, and a probe trigger 506. In this embodiment, a sensor and a means for
supplying a high speed motive force to the sensor (not shown) are contained within
sensor base 504. In an embodiment, the sensor is inserted by placing the bottom of the
sensor base 504 onto the skin and pressing on the top of transmitter 502 (in a press fit,
snap fit, or other type of arrangement) causing probe trigger 506 to move or otherwise
be triggered causing the means for supplying a high speed motive force inside sensor
base 504 to strike the sensor thereby inserting it into the skin.
[0093] The embodiment depicted in Figure 5A includes disposable and/or
reusable portions such as sensor base 504 and/or transmitter 502. Thus, in an
embodiment, a resposable device is provided comprising a reusable transmitter
component 502 and a disposable sensor base 504. In embodiments, other electrical
components (battery, processing components, etc.) may be provided in either
transmitter component 502 and/or sensor base 504.
17
Attorney Docket No. 112455-158826
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[0094] The transmitter component can contain circuitry which may include an
electrical network adapted to receive an electrical signal from an associated sensor and
to transmit a further signal, for example to an external electronic monitoring unit that is
responsive to the sensor signal. In embodiments, an electrical network can comprise a
variety of components in any desired structural relationship, whether or not the network
has a printed circuit board, a tethered or wired system, etc. In an embodiment, signal
transmission occurs over the air with electromagnetic waves, such as RF
communication, or data can be read using inductive coupling. In other embodiments,
transmission is over a wire or via another direct connection.
[0095] In an embodiment, shown disassembled in Figure 58, sensing device
500 is assembled by sliding transmitter 502 into grooves 506 on sensor base 504.
Grooves 506 on sensor base 504 align and secure sensor base 504 and transmitter 502
together. In an embodiment, locking latch 508 secures to locking edge 510 to provide
additional securing.
[0096] In an embodiment, a transmitter may be reused while the sensor base
may be adapted to be used once and discarded. In other embodiments, the sensor
base and transmitter may both be reused. In still other embodiments, both may be
adapted to be discarded.
[0097] In embodiments, a handtool is used to assemble the transmitter and
sensor base together. The handtool is used by first placing the transmitter upside down
on the handtool. The sensor base is provided with tape strip and a backing card situated
along the bottom of the sensor base in place and with a protective bubble cap over the
opposite face. The bubble cap may be removed from the sensor base and the sensor
base may then be placed on to a sliding member of the handtool. The backing card is
used to align the sensor within the handtool. Next, the sliding member may be pushed
over the transmitter snapping the transmitter and sensor base together. In an
alternative embodiment, the handtool has two components that hinge together rather
than a sliding member. After assembly, the backing card is removed and the tool is
used to position the device on a patient's body. In embodiments, by pushing on the
tool, the trigger moves, activating an injection activation device and the sensor is
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Attorney Docket No. 112455-158826
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Date of Transmission: March 8, 2012
inserted in the patient. The handtool is released by squeezing on release tabs. It will
be apparent to one of ordinary skill in the art that many different embodiments of a
handtool could be utilized, or, in embodiments, no handtool may be used.
[0098] In some embodiments, the means for supplying a high speed motive force
is attached to the sensor base. In other embodiments, the means for supplying a high
speed motive force is attached to the transmitter. In embodiments, the means for
supplying a high speed motive force is in a separate handle not part of either the sensor
base or the transmitter. In embodiments, such a handle is removed after insertion.
Details about such a handle can be found in US Patent Application No. 11/468,673,
which describes a device that uses a handle to provide motive force to insert a sensor
also employing a trocar. Although the present disclosure primarily involves a method
and apparatus to insert a sensor without using a trocar or related device, details from
US Patent Application No. 11/468,673 - including the handle - can be extended to
various embodiments of the present disclosure.
[0099] Figure 6A shows components of sensor base 600 in accordance with an
embodiment. Curved guidance structure 601 is coupled to insertion spring 603 via
slider 605 which houses the upper end of a curved probe (not shown). Leads 607 and
609 are soldered to the sensor to make electrical contact. Thus, slider 605 provides a
housing for insert-molding thereby sealing the terminations and providing protection for
the otherwise exposed probe.
[00100] Insertion spring 603 is attached during manufacturing and pulled back
over the outermost end of slider 605. Slider 605 is kept from moving forward by two
beams 611 (only one shown) which protrude from slider 605 and engage the edges of
rectangular holes 613 in base surface 615 of sensor base 600. In this manner, insertion
spring 603 holds potential energy and slider 605 remains stationary.
[00101] Battery leads 617 and 619 are, for example, spot welded to battery 621
and battery 621 is secured in place using a potting compound (not shown) and/or other
suitable securing compound or mechanical means. All four leads 607,609,617, and
619 are attached to small wire springs 623 that are insert-molded into connector
assembly 625. A soft rubber gasket 627 is attached to the periphery of connector
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Attorney Docket No. 112455-158826
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Date of Transmission: March 8, 2012
assembly 625 for sealing with a corresponding contact pad on the transmitter (not
shown) once the transmitter is secured into place. The connection face of connector
assembly 625 is on an angle so that the contacts and sealing features do not interfere
during mating and so that the total mating forces do not act to try to disengage the
transmitter and sensor base 600.
[00102] Figure 68 shows an exploded view of some components of sensor base
600. In this view, guidance structure 601 is omitted exposing probe 633 and riser 629
of trigger 631. In this embodiment, riser 629 is pressed upward which in turn pushes
the two rectangular beams 611 upward causing them to slide against the forward edges
of rectangular holes 613 (see Figure 6A) and be released. Once released, insertion
spring 603 no longer encounters resistance and causes slider 605 to quickly move
forward. In so doing, curved probe 633 will pass through the curved guidance structure
and partially pass through an opening (not shown) in the sensor base and may then be
inserted into the skin of a patient.
[00103] In this embodiment, trigger 631 is activated by placing the apparatus on
the skin of a patient and applying downward pressure causing trigger 631 and, thus,
riser 629, to rise upward in relation to the device.
[00104] Figure 6e depicts a cross-sectional view of sensor base 600. Here trigger
631 is more clearly shown. A curved feature on the top of trigger 631 holds probe 633
in place before insertion and helps guide curved probe 633 during insertion. Gap 635
between trigger 631 and base surface 615 close when trigger 631 is pushed up during
insertion.
[00105] Figure 7A depicts a probe guidance concept in accordance with an
embodiment of the present disclosure. Sensor 701 is shown with a permanently
attached top guide 703. In an embodiment, top guide 703 is insert-molded onto sensor
701. In another embodiment, top guide 703 is attached with adhesive bonding. In other
embodiments, top guide 703 is ultrasonically welded. Lower end guide 705 is part of
the housing body of the device (not shown). Upon insertion, sensor 701 slides within
lower end guide 705 which may be a molded feature of the housing body. In another
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Attorney Docket No. 112455-158826
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Date of Transmission: March 8, 2012
embodiment, lower end guide 705 is a separate piece bonded to the housing body
during manufacturing.
[00106] Lower end guide 705 is angled to allow sensor 701 to be inserted into the
skin at an angle other than 90-degrees relative to the skin. In other embodiments,
sensor 701 is inserted at other angles from 0-90 degrees, including 90 degrees.
[00107] Central sabot guide 707 is free-floating and remains roughly centrally
located on sensor 701 as sensor 701 is inserted into the skin. In other words, in an
embodiment, central sabot guide 707 is bonded to neither sensor 701 nor the insertion
device. Central sabot guide 707 prevents buckling of sensor 701 upon insertion. All
components of Figure 7 remain with the device after sensor 701 is inserted.
[00108] Although the guidance concept in Figure 7A is shown with three gUides, it
will be understood by one of ordinary skill in the art that more than three guides or less
than three guides can be employed to guide the sensor and prevent buckling. Although
the guidance concept depicted in Figure 7 is shown with cylindrical guides, it will be
understood by one of ordinary skill in the art that other geometries could be employed
including, but not nmited to, rectangular geometries. In various embodiments, the
guides are shaped and sized to accommodate the shape and size of the guidance
structure.
[00109] It will be understood by one of ordinary skill in the art that the guides
depicted in Figure 7A may be produced from a variety of materials including, but not
limited to, various plastics or metals.
[00110] In some embodiments, the central guide is composed of open cell foam
plastic easily collapses during insertion and have virtually no elasticity once
compressed.
[00111] In another embodiment, the central guide is a spiral of plastic with a center
hole that serves to guide the probe and prevent buckling during insertion. The spiral
may collapse during insertion and take up very little space when compressed. It may
remain within the body of the device upon insertion of the sensor. Manufacture of the
plastic spiral may be accomplished by molding or by employing a device similar to a
rotini pasta extruder.
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[00112] In another embodiment, the central guide is replaced by a series of thin
plastic disks each with a central hole. The disks may guide the probe and prevent
buckling during insertion. Upon insertion, the disks may close upon each other and take
up very little space when compressed. In various embodiments, the disks are molded
or stamped from a thin sheet of plastic.
[00113] In the embodiment depicted in Figure 7B, top guide 709 and central guide
711 facilitate the making of an electrical connection to sensor 701 as well as helping to
guide sensor 701 and prevent buckling during insertion. In these embodiments, the
guides are made of a suitable conductive material including any number of suitable
metals. In an embodiment, top guide 709 is soldered to an exposed core of the sensor
(not shown) and central guide 711 is soldered to silver cladding (not shown) via grooves
713. Soldering top guide 709 to sensor 701 creates a permanent attachment to sensor
701 and allows a mechanism for applying a high speed motive force (not shown) to act
directly against top guide 709 during insertion.
[00114] Referring now to Figure 7C which shows a cross-sectional view of an
embodiment of the sensor and guide design of Figure 7B placed into an insertion
device, electrical contact is made between the device and guides 709 and 711 by
employing a set of leaf spring contacts 713 built into the body of the device. Contact is
made near the end of the travel of sensor 701 upon insertion. In other embodiments,
electrical contact is made by soldered wires that are dressed away from sensor 701
between the top and central guides 709 and 711, respectively.
[00115] Figure 8 depicts a cross-sectional view of the bottom of an insertion
device in accordance with an embodiment. Sensor 801 is shown bowed and restrained
within the body of the device. The top curve of bowed sensor 801 extends slightly out
of exposed opening 807. As depicted in Figure 8, exposed opening 807 is situated on
the bottom surface of the device (the surface adapted to be placed onto the skin). The
device can be placed against the skin of a patient (not shown) and pressed down.
Force can be applied to the top of bowed sensor 801 to force sensor 801 to straighten
forcing proximal tip/end of sensor 801 into contact with the skin with enough pressure to
cause sensor 801 to penetrate the skin. Sensor 801 may contain core material with
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Attorney Docket No. 112455-158826
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sufficient elastic properties to store a sufficient amount of energy when bowed in order
to generate a high speed motive force when straightened.
[00116] In various embodiments, the direct drive linear solenoid actuator design of
Figure 9A is employed to provide a high speed motive force to a sensor. In these
embodiments, solenoid 901 is coupled to the main body of the device using support
structure 909. Support structure 909 includes cylindrical member 907 which contains a
hollow core_ Solenoid shaft 903 is extended so that it also becomes an insertion rod
directly impacting and providing a high speed motive force to the end of a sensor (not
shown). In an embodiment, solenoid shaft 903 is partially situated in cylindrical member
907. When power is applied to solenoid 901, shaft 903 travels through cylindrical
member 907 to provide a high speed motive force to a sensor for insertion. After
insertion, return spring 905, situated between the end of cylindrical member 907 and
shaft stop 911, causes the shaft to return to its pre-insertion position.
[00117] In various embodiments, the rotary solenoid actuator design of Figure 98
is employed to provide a high speed motive force to a sensor. In these embodiments, a
rotary solenoid 951 is coupled to the main body of the device using support structure
967. An arm 953 is attached to the solenoid's rotating plate 957 and the far end of the
arm is slotted and bent back on itself providing an opening for engaging pin 959
attached to the top end of rod 955. Whenever power is applied to solenoid 951, it turns
clockwise (as oriented in Figure 98) which causes rotating plate 957 to rotate and pin
959 to move along linear guide slot 961. The linear motion of pin 959 causes
associated rod 955 to move in a linear direction through hollow cylindrical member 965
which is part of the housing structure of the device. Rod 955 then impacts the end of a
sensor (not shown) and provides a high speed motive force for insertion of the sensor.
[00118] In various embodiments, the rod returns to its original position whenever
power is removed from the solenoid. In embodiments, a spring is incorporated into the
solenoid by the manufacturer to ensure that it returns to the rest position whenever
power is removed.
[00119] It will be appreciated by those of ordinary skill in the art that embodiments
of the disclosure which utilize solenoids are not limited by the configurations depicted in
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Figures 9A and 98. For example, the rotary solenoid embodiments depicted in Figure
98 incorporate a cam surface rather than a rotating arm connected to rotating plate.
Embodiments which use a linear solenoid actuator as in Figure 9A incorporate
intermediate components in various configurations to impact the end of the sensor
rather than utilizing an elongated solenoid shaft as depicted in Figure 9A.
[00120] Figure 10 depicts an embodiment employing a CO2 cartridge. As
depicted, the head of CO2 cartridge 1001 is placed into a hole in manifold 1003 and a
nut behind CO2cartridge 1001 tightened causing CO2 cartridge 1001 to move deeper
into the manifold where a hollow pin (not shown) pierces CO2cartridge 1001 and allows
the compressed CO2to enter the system. There are two internal manifold chambers
(not shown). One chamber connects to CO2cartridge 1001 and the other connects to
hollow pin 1009. A spring loaded valve (not shown) is located between them to initially
hold back pressure from cartridge 1001 and its associated manifold chamber.
Whenever spring loaded firing pin 1007 is allowed to strike valve head 1005, an internal
valve (not shown) temporarily opens and an amount of gas may flow from the manifold
chamber associated with CO2cartridge 1001 into the manifold chamber associated with
hollow tube 1009. Gas may then enter hollow tube 1009 and force rod 1011 to move
forward and strike a sensor (not shown) for insertion. As rod 1011 nears the end of
travel, exhaust port 1013 travels past the end of hollow tube 1009 allowing the C02 to
escape. Return spring 1015 is employed to move rod 1011 back to its original position
after insertion.
[00121] An embodiment employing an air pump is depicted in Figure 11 in a crosssectional
view. The embodiment shown in Figure 11 employs a similar manifold system
as in the CO2cartridge embodiment discussed previously. The manifold is encased in
housing structure 1104. When lever arm 1101 is pulled up, air may be sucked into a
manifold chamber associated with piston 1105 via a one-way valve (not shown).
Pushing lever arm 1101 down moves link 1103 which is coupled to the shaft of piston
1105 which is forced into its associated manifold. The motion of piston 1105 into the
manifold compresses the air that has been sucked into the associated manifold
chamber on the upward stroke of lever arm 1101. When spring loaded firing pin 1109 is
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Attorney Docket No. 112455-158826
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Date of Transmission: March 8, 2012
allowed to strike valve head 1111, an internal valve (not shown) temporarily opens and
compressed air moves from the manifold chamber associated with piston 1105 into a
manifold chamber associated with hollow tube 1113. Gas then enters hollow tube 1113
and force rod 1115 to move forward and strike a sensor (not shown) for insertion. As
rod 1115 nears the end of travel, an exhaust port on the rod (not shown) travels past the
end of hollow tube 1113 allowing the compressed gas to escape. Return spring 1117 is
employed to move rod 1115 back to its original position after insertion.
[00122] Figure 12 depicts an embodiment employing a mechanical spring. In this
embodiment, bowed spring 1205 is initially bowed upward toward button 1201 and
placed into actuator frame 1207 part way along the length of rod 1209. If button 1201 is
pressed, it compresses power spring 1203 against bowed spring 1205 while a cut-out in
bowed spring 1205 engages a slot cut into rod 1209 to prevent the head of rod 1209
from moving forward. In an alternative embodiment, an outside ridge is employed
instead of a slot on rod 1209.
[00123] At a predetermined force, bowed spring 1205 exhibits an "oil can" effect
and its bow immediately reverses orientation. This action releases rod 1209 from the
ridge cut into bowed spring 1205 and rod 1209 is then driven forward by the force built
up in power spring 1203 which then strikes a sensor (not shown) with a high speed
motive force for insertion.
[00124] Figure 13A depicts a mechanical spring in accordance with embodiments
herein. Slider 1301 is pulled back to the far end of support structure 1303 creating
tension in springs 1305 which are supported by pins 1313. Referring now to Figure 138
which shows a cross-sectional view of the mechanical spring actuator, it can be seen
that slider 1301 has an angled feature 1317 which rests against an angled surface at
the top of rod 1315. Slider 1301 is held in place by a triggering mechanism (not shown).
Rod 1315 is attached to pin 1307 each end of which sits inside two angled slots 1309
(shown in Figure 13A) of support structure 1303. When the trigger releases slider 1301,
the slider moves forward forcing rod 1315 to move in a path parallel to slots 1309 due to
pin 1307. Rod 1315 then impacts a sensor (not shown) supplying a high speed motive
force for insertion. Toward the end of the travel of rod 1315 its angled top feature slips
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off of the corresponding angled feature of slider 1301 allowing the rod to return to its
rest position using the force provided by return spring 1311. When slider 1301 is pulled
back again, it rides along a cam surface (not shown) that directs it up out of the way of
the upper end of the rod and then back down behind it again, ready for the next firing.
[00125] Figure 14 depicts a cross-sectional view of a mechanical spring impact
device employed to provide a high speed motive force to a sensor for insertion
according to an embodiment. When button 1401 is pressed, trigger arm 1403 is driven
forward. A small shear member 1405 at the opposite end of trigger arm 1403 is initially
engaged with the top end of firing pin 1407 pulling firing pin 1407 away from rod 1411
and causing firing spring 1409 to compress and build up stored energy. As the shear
moves toward the end of its travel, firing pin 1407 slips off of the shear due to the
difference in the angle of their respective travel directions. At this point, firing pin 1407
travels forward with force supplied by compressed firing spring 1409 impacting rod 1411
and allowing the rod to impact a sensor (not shown) and supply a high speed motive
force for insertion.
[00126] Subsequently, trigger arm 1403 proceeds back toward its rest position
with force supplied by return spring 1413. Also, rod 1411 proceeds back to its rest
position with force supplied by return spring 1417. As the shear member passes over
the top end of firing pin 1407, the shear rotates to clear the upper end of firing pin 1407
and spring 1415 rotates the shear back into place to ready it for the next insertion.
[00127] Figure 15A depicts a wiring scheme in accordance with an embodiment of
the present disclosure. Sensor 1501 is shown with plastic bottom guide 1509 and
plastic center guide 1507. Lead wires 1503 are, in an embodiment, soldered to sensor
1501 and then insert-molded into top guide 1505. Referring now to Figure 158, the
opposite ends of lead wires 1503 are soldered to contacts 1511 on the body of the
device. An open groove 1513 in the guidance structure permits unobstructed
movement of lead wires 1503 during sensor insertion.
[00128] Prior to insertion, pad 1515 is partially attached to the device by partially
placing pins 1521 into receptacles 1523. Upon insertion of the sensor, pins 1521 are
fully depressed into receptacles 1523 which cause shorting bar 1517 to contact battery
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Date of Transmission: March 8, 2012
pads 1525 (only one shown) as pad 1515 is pushed into its final position. In this
manner, shorting bar 1517 serves to complete the power circuit of the device and turn it
on.
[00129] Figures 16A and 168 depict a sensor electrical termination assembly in
accordance with an embodiment of the present disclosure. Figure 16A depicts an
exploded view of the embodiment. Sensor 1601 is fitted with a set of canted coil
springs 1603 positioned over the upper conductive regions of sensor 1601. Two small
rectangular housings 1605 are positioned over the springs and two rectangular sections
of sheet metal 1607 are placed into the corresponding grooves on rectangular housings
1605. Referring now to Figure 168, two leads 1609 extending from canted coil springs
1603 are fed through slots 1611 in rectangular housings 1605 and spot welded onto the
two sections of sheet metal 1607. Upon insertion of the sensor, this termination
assembly may be moved down the insertion channel (not shown). At the bottom of the
insertion channel, rectangular sheet metal 1607 makes contact with two formed spring
members protruding from the channel (not shown).
[00130] An alternative approach might be to reverse the orientation of the lower of
the two canted coil springs so that their leads come out of the lower end of the spring.
That way, the assembly is insert-molded into the rectangular housings to form a sealed
connection.
[00131] Another embodiment includes pre-positioning the termination assembly at
the bottom of the insertion channel. In that embodiment, a sensor travels through the
assembly and make electrical contact with the springs upon insertion.
[00132] Figures 17A and 178 show a paper guidance structure in accordance with
an embodiment of the present disclosure. As shown in Figure 17A, paper 1703 is
placed inside rectangular slot 1705 and above sensor 1701. Paper 1703 is used to
secure paper 1703 prior to insertion and to guide sensor 1701 during insertion. Prior to
insertion, sensor 1701 sits inside groove 1711 (visible in Figure 178) at a depth of, for
example, half the diameter of sensor 1701.
[00133] Referring now to Figure 178, an injection activation device (not shown)
pushes against the upper end of sensor 1701 and moves inside rectangular slot 1705
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during insertion. As it moves, the injection activation device separates paper 1703
along slot 1711 creating paper tear 1709 as sensor 1701 is inserted. Upon insertion,
the conductive regions of sensor 1701 come into contact with leaf springs 1707
electrically coupling sensor 1701 to the device.
[00134] In alternative embodiments, other similar materials can be substituted for
paper such as, for example, a thin plastic covering.
[00135] In an embodiment, additional components can be housed in one or more
separate modules that can be coupled to (for example, snapped to, wired to, or in
wireless communication with) the insertion device. For example, the separate module
may contain a memory component, a battery component, a transmitter, a receiver, a
transceiver, a processor, and/or a display component, etc.
[00136] In an embodiment, a sensor with SUbstantially uniform cross-section can
be utilized. Alternatively, in an embodiment, a sensor with a varied cross section can be
used. In embodiments, a sensor can be cylindrical, squared, rectangular, etc. In an
embodiment, a sensor is a wire-type sensor. In an embodiment, a sensor is flexible.
[00137] For purposes of describing embodiments herein, "stiffness" is defined as
the resistance of an elastic body to deflection or deformation by an external applied
force. The stiffness, k, of an object may be given by Equation (1):
k=P/l> (1 )
where P is the applied force and l> is the deflected distance.
[00138] For the purpose of this disclosure, flexibility is defined as the reciprocal of
stiffness. Thus, "flexibility" is defined as the amount of deflection of an elastic body for a
given applied force. Stiffness and flexibility are extensive material properties, meaning
that they depend on properties of the material as well as shape and boundary
conditions for the body being tested.
[00139] For a sensor implanted in a body, a reduction in stiffness of the sensor
reduces its resistance to deflection when SUbjected to external forces resulting from
motion of the body during various physical activities. Sensor stiffness, or resistance to
external forces caused by body motion, results in pain and discomfort to the sensor user
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during physical activities. Accordingly, to facilitate comfort to the sensor user, the
implanted sensor is designed to reduce stiffness (Le., increase flexibility).
The stiffness of an elongate cylindrical column, such as a wire, is related to the
deflection of its unsupported end with applied force.
[00140] The following standard formula (Equation (2)) applies to cantilevered
beams (beams supported at one end and unsupported at the other end):
y = W*L3 I (3E*I) (2)
where y is the deflection, W is the applied force, L is the unsupported length, E is the
modulus of elasticity (Young's modulus) of the wire material, and I is the minimum
second moment of inertia. The minimum second moment of inertia (I) is related to the
cross-sectional size and shape of the beam. The force (W) required for a given
deflection of the wire is given by Equation (3):
W = 3E*I*y I L3 (3)
[00141] Rearranging Equation (3) and setting L =1 to normalize for a unit length of
wire gives Equation (4):
W/y=3EI
[00142] Using the definition of stiffness in Equation (1), and noting that W is
equivalent to P and y is equivalent to ~ yields Equation (5):
k = 3E*1
[00143] For the cylindrical wire (circular cross-section), I, the minimum second
moment of inertia, is given by Equation (6):
29
(4)
(5)
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(6)
where r is the radius of the wire. Substituting the value of I of Equation (6) into Equation
(5) yields Equation (7):
k =3/4 * TT * E * r4 (7)
Equation (7) may be used to compare the stiffness of unit length of cylindrical wires of
varying radius and material properties. Note that stiffness increases as the 4th power of
the radius of the wire. Stiffness also increases as the modulus of elasticity for the wire
material increases.
[00144] Therefore, to reduce stiffness of the wire-based sensor and improve
comfort, the radius of the sensor wire can be reduced and/or a material with a lower
elastic modulus can be employed for the sensor wire.
[00145] The elastic modulus (E) for several common metals is shown in the
following Table 1 (in Newtons/m2 * 109
, commonly abbreviated as GPa):
Material E in units of GPa
(N/m2*109
)
Steel 186
Silver 72
Tantalum 186
Copper 117
Aluminum 69
Platinum 145
Table 1
In an exemplary embodiment, the wire is made of platinum-clad tantalum. Accordingly,
the wire may have an elastic modulus of about 186 GPa. Tantalum is desirable
because it resists fracture and/or fatigue failure when subjected to frequent bends. Also
note that tantalum has an elastic modulus substantially equivalent to that of steel. Other
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base materials, with a lower E value, are not preferred because of the risk of fatigue
and/or poor biocompatibility. Accordingly, for a given sensor material, the sensor
stiffness is determined primarily by the diameter of the sensor wire base material.
[00146] In some embodiments, the radius of the wire is about 0.075 mm to about
0.125 mm (e.g., a diameter of about 0.15 mm to about 0.25 mm), such as about 0.1
mm. This yields a flexibility of about 0.707 for the 0.075 wire and 0.091 for the 0.125
mm wire in units of mm/gram-force, measured on a wire with 10 mm unsupported
length. The calculations assume a bare steel or tantalum wire. The effect of any
membrane coating on a wire sensor is not included in the calculations as the membrane
can be very thin and its effect on flexibility is therefore negligible.
[00147] The following table, Table 2, shows the flexibility of tantalum or steel wires
of various radii, for an unsupported length of 10mm:
Wire Radius (mm) Flexibility (mm Stiffness (gdisplacement/
g- force/mm
force) displacement)
0.075 0.707 1.414
0.1 0.224 4.469
0.125 0.092 10.91
0.15 0.044 22.63
0.2 0.014 71.51
Table 2
Note that the flexibility decreases and stiffness increases with the fourth power of the
wire radius. The difference in flexibility for a small difference in wire radius can be
substantial.
[00148] In various embodiments, the sensor has a blunt tip (e.g., as shown in
Figures 1-4). By "blunt," it is meant that the diameter of the sensor at an end of the
sensor is substantially uniform (e.g., not having a sharp point). In embodiments, the
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sensor wire is coated with an outer membrane to facilitate biocompatibility and/or
optimize sensor performance. The coating process covers, fills, and/or softens any
sharp edges of the sensor wire. Additionally, an exposed metal tip could compromise
the electrochemical performance of the sensor. Furthermore, sharpening the sensor tip
requires additional steps and/or complexity in the sensor manufacturing process.
Accordingly, the tip of the sensor is blunt. Using methods and apparatuses described
herein, the blunt-tipped sensor can be inserted into skin without the use of a trocar or
other insertion device, while limiting/avoiding damage to the sensor and/or significant
damage to the skin.
[00149] Inserting the blunt-tipped sensor into skin requires more pressure to be
applied to the sensor than would be needed with a sharpened, rigid insertion device.
For example, a motive force of about 11 to about 53 Newtons is applied to the sensor to
insert the sensor into skin, or more specifically about 20 to about 22 Newtons.
[00150] In some embodiments, the relatively low stiffness and relatively high
insertion pressure for the sensor increases the risk of the sensor buckling during
insertion compared, for example, to a stiff, sharp needle. The behavior of the biosensor
during insertion through the skin is approximated by the buckling behavior of a column
subjected to a load as predicted by Euler's formula (Equation (8»:
Pcr=if E*I/ L2 (8)
where E is the modulus of elasticity of the sensor material, I is the minimum second
moment of inertia as defined in Equation (6) above, L is the unsupported length of the
column, and Per is the critical buckling load.
[00151] In terms of sensor wire stiffness as defined in Equation (5), the critical
buckling load is written as (Equation (9»:
Per=if*k / (3*L2) (9)
Therefore, the critical buckling load that is applied to the sensor wire is proportional to
the sensor stiffness and inversely proportional to the square of the unsupported length
32
Attorney Docket No. 112455-158826
IPN: P018X
Date of Transmission: March 8, 2012
of the sensor. This relationship emphasizes that a reduction in sensor wire stiffness to
improve comfort during use will reduce the force that can be applied for a given
unsupported sensor length during sensor insertion into the skin if buckling is to be
avoided.
[00152] For a sensor having an elastic modulus of 186 GPa (e.g., a platinum clad
tantalum sensor) and a radius of 0.1 mm subjected to a motive force of 22 Newtons, the
buckling length calculated using Equation (9) is about 2.5 mm. The phrase "buckling
length" is defined as the maximum unsupported length for a wire sensor of a given
stiffness, subject to a given load (force applied axially), which will not be subject to
buckling or collapse. Since the length of the sensor may be at least 12 mm inches (e.g.,
about 25 mm), the sensor requires a guidance structure to ensure that a maximum
unsupported length of the sensor during insertion is less than the buckling length (e.g.,
2.5 mm). Suitable guidance structures include the guidance structure 106 of Figure 1,
the guidance structure 303 of Figures 3A and 38, the guidance structure 409 of Figure 4
(including curved section 403), the guidance structure 601 of Figure 6A, guides 703
and/or 705 of Figures 7A-7e, support structure 909 of Figure 9A, and/or guidance
structures depicted in Figures 10-17B.
[00153] In some embodiments, the guidance structure includes a hollow tube that
surrounds the sensor, preventing the sensor from buckling. This may be referred to as
a coaxial guidance structure. The guidance structure provides support to the sensor on
all sides of the sensor. Figure 18 shows a simplified example of a sensor 1802
disposed in a coaxial guidance structure 1804 and placed on skin 1806. Another
example of a coaxial guidance structure 303 is shown in Figures 3A and 38.
[00154] Alternatively, the guidance structure includes an open guide channel,
which includes an open, curved groove in at least a portion of the guidance structure.
This type of guidance structure provides support to the sensor on only one side of the
sensor over at least a portion of the length of the sensor.
33
Attorney Docket No. 112455-158826
IPN: P018X
Date of Transmission: March 8, 2012
[00155] The sensor is pre-stressed (compressed) by the initial insertion force and
forced against the surface of the curved groove. The sensor is supported by the groove
and thus unable to buckle.
[00156] Figure 19 shows a simplified example of a sensor 1902 disposed in a
guidance structure 1904 placed on skin 1906. The guidance structure 1904 includes an
open guide channel 1908. Another example of an open guide channel is the curved
section 403 of guidance structure 409 shown in Figure 4.
[00157] In various embodiments, tensioning or tightening the skin before and/or
during insertion facilitates the sensor puncturing the skin and/or prevents sensor
buckling. Figures 20A and 20B illustrate a sensor 2002 disposed in guidance structure
2004 and being inserted into skin 2006. In Figure 20A, the skin 2006 is untensioned,
while in Figure 20B, the skin is tensioned. As shown by comparing Figure 20A with
Figure 20B, tensioning the skin reduces the indentation of the skin from the applied
force from the sensor tip (e.g., indentation of the skin until the sensor punctures the
skin). In some embodiments, it is desirable to have a maximum skin indentation of less
than the buckling length of the sensor (e.g., 2.5 mm as discussed above) to avoid
sensor buckling. Tensioning the skin facilitates keeping the maximum skin indentation
less than the buckling length.
[00158] In some embodiments, a sensor base (e.g., the sensor base 504 depicted
in Figure 5A) is disposed on the skin when the sensor is inserted into the skin. In some
embodiments, the sensor base includes an adhesive patch that is coupled to the skin.
The adhesive patch is less elastic than the skin and can be adhered to the skin except
for a relatively small area around the insertion site. The adhesion of the adhesive patch
prevents the skin from stretching, thereby limiting the indentation of the skin.
[00159] In some embodiments, the sensor insertion device includes a rounded
protrusion (also referred to as a nub) around the opening in the guidance structure. The
nub tensions the skin, thereby facilitating the sensor puncturing the skin and reducing
the unsupported length of the sensor. Additionally, the nub deforms the skin in a way
that positions the skin surface to be substantially perpendicular to the sensor insertion
path when the sensor is inserted at an angle. For example, Figure 21 illustrates a
34
Attorney Docket No. 112455-158826
IPN: P018X
Date of Transmission: March 8, 2012
sensor 2102 being inserted by a sensor insertion device 2104 into skin 2106. A nub
2108 indents the skin 2106, thereby tensioning the skin 2106 and causing the sensor
2102 to be sUbstantially perpendicular to the skin 2106 at the insertion site.
[00160] In various embodiments, the velocity of the sensor as it punctures the skin
can be selected to facilitate puncturing the skin with the blunt tip of the sensor. The
velocity of the sensor tip when it impacts the skin is important in assuring that the
sensor penetrates the skin without buckling.
[00161] The momentum of the sensor facilitates skin penetration. Momentum is a
function of velocity and mass. The mass of the moving parts of the sensor insertion
device (e.g., the mechanism that applies the motive force to the sensor) adds to the
mass of the sensor alone, thereby increasing the total moving mass and therefore the
momentum.
[00162] Additionally, inertia, which is closely related to momentum, is important in
determining how the skin reacts when the force of the sensor tip is applied. The skin
and connected subcutaneous tissue form an elastic body which is free to move or
deform when the pressure of the sensor tip is applied. However, this tissue also
possesses mass. This mass causes the tissue to respond to applied forces with inertia,
which limits the speed of movement and/or deformation of the skin in response to the
applied force of the sensor tip. The higher the sensor velocity, the less time the skin
has to move and/or deform in response to the sensor impact. Accordingly, a higher
sensor velocity facilitates the sensor penetrating the skin in a substantially straight line
(e.g., with minimal bending which may otherwise occur). In some embodiments, the
insertion velocity contributes along with skin tensioning to preventing sensor buckling
during insertion.
[00163] In a series of experiments, a sensor was inserted into a polymer gel
"artificial skin" target using a sensor insertion device having a pusher to apply a motive
force to the sensor for insertion. The velocity of the pusher was measured during
insertion of the sensor into the polymer gel. The velocity of the pusher approximates
the velocity of the sensor during insertion. A graph 2202 of the velocity of the pusher
versus displacement (distance from initial position) is shown in Figure 22A. A graph
35
Attorney Docket No. 112455-158826
IPN: P018X
Date of Transmission: March 8, 2012
2204 of the velocity of the pusher versus time is shown in Figure 228. Note that the
velocity shown in the graphs of Figures 22A-B is an absolute value. Accordingly, a
negative velocity, as occurs during a rebound or "bounce" of the pusher, is shown as a
positive value.
[00164] The graphs 2202 and 2204 include several repeatable features. For
example, note a bump 2206 near the start of the sensor travel, at about 2.5 mm of
displacement and about 0.001 seconds of time. This bump 2206 corresponds to a
reduction in velocity as the sensor housing travels over a retaining ridge in the guidance
structure. The retaining ridge prevents the sensor probe assembly from sliding out of its
starting position during shipping and handling of the device. A second small bump 2208
at about 5 mm of displacement and about 0.0015 seconds corresponds to the puncture
of the artificial skin.
[00165] A third bump 2210 at about 12.5 mm and about 0.0035 seconds is caused
by a rebound or "bounce" of the pusher once the sensor is seated in the sensor base.
As mentioned previously, the rebound is a negative velocity relative to the forward
insertion motion, but the graphs 2202 and 2204 show only the absolute value of the
velocity.
[00166] Accordingly, as shown in Figures 22A and 22B, the velocity of the sensor
during sensor insertion is about 6.4 meters per second (m/sec). In other embodiments,
the velocity of the sensor during sensor insertion is about 5 m/sec to about 15 m/sec.
The momentum driving the sensor insertion, as well as the velocity of the sensor,
determines the minimum successful insertion velocity. Among other factors, the
momentum, determined by the mass of all the moving parts coupled to the sensor,
affects the ability to the sensor to maintain its velocity when the sensor encounters the
resistance of the skin.
36
Attorney Docket No. 112455-158826
IPN: P018X
Date of Transmission: March 8, 2012
[00167] The insertion system is designed to place the sensor at any suitable angle
or range of angles relative to the surface of the skin. An insertion of the sensor
perpendicular to the skin surface is preferred because an insertion force perpendicular
to the skin surface minimizes any shifting of the skin beneath the sensor, flexing of the
sensor, and/or risk of buckling. Additionally, a perpendicular insertion prevents the
sensor from "skidding" or sliding across the skin surface instead of penetrating the skin.
[00168] However, a typical wire glucose sensor functions best with a penetration
of 12 millimeters (mm) or more. In relatively lean individuals, the subcutaneous tissue
may be as thin as 9 mm and a vertically placed sensor penetrates beyond the
subcutaneous tissue and possibly into muscle tissue. Penetration of muscle tissue can
cause additional pain and discomfort for the user.
[00169] Figure 23A shows a cross-sectional diagram of a sensor 2302 inserted
vertically into a skin surface 2304. The sensor has a penetration length of 12 mm below
the skin surface 2304. A subcutaneous tissue 2306 is disposed from approximately the
skin surface 2302 to a depth of 9mm. A muscle tissue 2308 is disposed below the
subcutaneous tissue 2306. Accordingly, the sensor 2302 extends through the
subcutaneous tissue 2306 and into muscle tissue 2308.
[00170] In some embodiments, the sensor is inserted at an angle of less than 90
degrees to the skin surface. This allows the desired length (e.g., 12 mm) of the sensor
to be placed in subcutaneous tissue while reducing the vertical depth of the placement
to assure that the entire length of the sensor remains in subcutaneous tissue. For
example, Figure 238 shows sensor 2302 inserted into the subcutaneous tissue 2306 at
an angle of about 30 degrees from the plane of the skin surface 2304. This allows a
length of 12 mm of the sensor to extend to a depth of approximately 6 mm in the
subcutaneous tissue 2304, thereby avoiding the muscle tissue 2308.
[00171] An angle of 30 degrees may still be sufficient for penetrating the skin
surface 2304 rather than sliding across the surface 2304 of the skin. Additionally, as
discussed above, in some embodiments the sensor insertion device includes a nub
surrounding the exit port of the guidance structure designed to deform the skin
37
Attorney Docket No. 112455-158826
IPN: P018X
Date of Transmission: March 8,2012
surrounding the insertion site to locally provide a skin surface 2304 that is substantially
perpendicular to the sensor 2302 during insertion.
[00172] Although certain embodiments have been illustrated and described herein
for purposes of description of the preferred embodiment, it will be appreciated by those
of ordinary skill in the art that a wide variety of alternate and/or equivalent embodiments
or implementations calculated to achieve the same purposes may be substituted for the
embodiments shown and described without departing from the scope of the present
disclosure. Those with skill in the art will readily appreciate that embodiments in
accordance with the present disclosure may be implemented in a very wide variety of
ways. This application is intended to cover any adaptations or variations of the
embodiments discussed herein. Therefore, it is manifestly intended that embodiments
in accordance with the present disclosure be limited only by the claims and the
equivalents thereof.
38

Attorney Docket No. 112455-158826
IPN: P018X
Claims
•
Date of Transmission: March 8, 2012
What is claimed is:
1. An insertion device comprising:
a gUidance structure adapted to provide axial support to a flexible analyte sensor,
the guidance structure having an exit port; and
an injection activation device associated with the guidance structure, said
injection activation device having:
a mechanism adapted to apply a high speed motive force to the flexible
analyte sensor such that, when the high speed motive force is applied, the
flexible analyte sensor moves at least partially through the guidance structure
and at least partially passes through the exit port to cause insertion of only the
flexible analyte sensor into skin;
wherein the high speed motive force is configured such that a velocity of
the flexible analyte sensor at a time of insertion is approximately 5 meters per
second to approximately 15 meters per second.
2. The insertion device of claim 1, wherein the velocity of the flexible analyte sensor
at the time of insertion is approximately 6.4 meters per second.
3. The insertion device of claim 1, further comprising a housing having a bottom
surface associated with the guidance structure, the guidance structure configured so
that the sensor passes through the exit port at an angle from 10 to 40 degrees with
respect to the bottom surface of the housing.
4. The insertion device of claim 3, further comprising a nub surrounding the exit port
of the guidance structure, the nub configured to indent the skin at an insertion site such
that the sensor is inserted into the skin at an angle that is sUbstantially perpendicular to
a plane of a local skin surface at the insertion site.
39
Attorney Docket No. 112455-158826
IPN: P018X
Date of Transmission: March 8, 2012
5. The insertion device of claim 3, wherein the sensor is inserted with an inserted
length of the sensor of at least 12 millimeters.
6. The insertion device of claim 1, wherein the guidance structure is configured so
that an unsupported length of the sensor is less than a buckling length of the sensor.
7. The insertion device of claim 1, wherein the high speed motive force has a value
of about 11 to 53 Newtons.
8. The insertion device of claim 1, wherein the high speed motive force has a value
of about 22 Newtons.
9. An insertion device comprising:
a guidance structure adapted to provide axial support to a flexible analyte sensor,
the guidance structure having an exit port; and
an injection activation device associated with the guidance structure, said
injection activation device having:
a mechanism adapted to apply a high speed motive force to the flexible
analyte sensor such that, when the high speed motive force is applied, the
flexible analyte sensor moves at least partially through the guidance structure
and at least partially passes through the exit port to cause insertion of only the
flexible analyte sensor into skin;
wherein the guidance structure is configured so that an unsupported length of the
flexible analyte sensor is less than a buckling length of the flexible analyte sensor above
which the flexible analyte sensor will buckle from application of the high speed motive
force.
40
Attorney Docket No. 112455-158826
IPN: P018X
Date of Transmission: March 8, 2012
10. The insertion device of claim 9, wherein the buckling length of the sensor is
determined by a formula Pcr =TT
2*k I (3*L2), wherein Pcr is a value of the high speed
motive force applied to the sensor, k is a stiffness of the sensor, and L is the
unsupported length of the sensor.
11. The insertion device of claim 10 wherein the stiffness of the sensor is about 1.4
to about 22.6 grams-force per millimeter of deflection for an unsupported length of 10
millimeters.
12. The insertion device of claim 9, further comprising a tensioning structure
configured to tension a surface of the skin so that a distance from the surface of the skin
at an insertion site on the surface of the skin to the exit port is less than the buckling
length of the sensor.
13. The insertion device of claim 12, wherein the tensioning structure includes a nub
surrounding the exit port of the guidance structure, the nub configured to indent the skin
at an insertion site.
14. The insertion device of claim 12, wherein the tensioning structure includes an
adhesive patch disposed on the surface of the skin, the adhesive patch inclUding a hole
surrounding an insertion site of the sensor.
15. The insertion device of claim 9, wherein the high speed motive force has a value
of about 11 to 53 Newtons.
16. The insertion device of claim 9, wherein the high speed motive force has a value
of about 22 Newtons.
17. The insertion device of claim 9, wherein an insertion angle of the sensor with
respect to a plane of the skin is from 10 to 40 degrees.
41
Attorney Docket No. 112455-158826
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Date of Transmission: March 8, 2012
18. An analyte sensor, comprising:
an elongate wire;
an outer membrane surrounding the elongate wire at a distal end of the analyte
sensor, the distal end configured to be inserted into skin by a motive force applied to the
analyte sensor and without the aid of a sharpened introducer;
wherein the elongate wire has a stiffness of about 1.4 to about 22.6 grams-force
per millimeter of deflection for an unsupported length of 10 millimeters.
19. The analyte sensor of claim 18 wherein the wire has a diameter of about 0.15 to
about 0.30 millimeters.
20. The analyte sensor of claim 18, wherein the distal end of the sensor is
substantially blunt.
21. The analyte sensor of claim 18, wherein the elongate wire includes platinum-clad
tantalum.
22. The analyte sensor of claim 18, wherein the high speed motive force has a value
of about 11 to 53 Newtons.