(cid:40)(cid:91)(cid:75)(cid:76)(cid:69)(cid:76)(cid:87)(cid:3)2006(cid:3)
`
`

`

`Waters Techs. Corp. v. Biomedical Device Consultants & Labs
`IPR2018-00498
`Ex. 2006
`Page 1 of 21
`
`

`

`US 8,627,708 B2
` Page 2
`
`(56)
`
`References Cited
`
`US. pATENT DOCUMENTS
`
`7 348 175 B2
`a
`a
`7’363’821 B2
`7,472,604 B2
`7,587,949 B2
`7,621,192 32
`8,034,608 B2
`8,196,478 B2
`
`3/2008 Vilendrer et 31
`
`'
`
`4/2008 BlaCk et 31'
`1/2009 Moore et al.
`.
`9/2009 Dlngmann et al.
`.
`11/2009 Con“ et 31
`10/2011 Dancu
`6/2012 Lorenz et a1.
`
`8,318,414 B2
`2003/0066338 A1
`2003/0110830 A1
`2003/0125804 A1*
`
`11/2012 Dancu et a1.
`4/2003 Michalsky et al.
`6/2003 Dehdashtian et al.
`7/2003 Kruse et al.
`.................... 623/21
`
`2003/0199083 A1
`2004/0016301 A1
`2010/0225478 A1 *
`2011/0066237 A1
`2011/0146385 A1
`2011/0259439 A1
`
`10/2003 Vilendrer et £11.
`1/2004 Moreno et al.
`9/2010 McCloskey et al.
`3/2011 Matheny
`.
`6/2011 Welnberg et al.
`10/2011 Neerincx
`
`.......... 340/540
`
`* cited by examiner
`
`Page 2 of 21
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`Page 2 of 21
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`US. Patent
`
`Jan. 14, 2014
`
`Sheet 1 019
`
`US 8,627,708 B2
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`Page 3 of 21
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`Page 3 of 21
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`US. Patent
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`Jan. 14, 2014
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`Sheet 2 of9
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`US 8,627,708 B2
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`Page 4 of 21
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`Page 4 of 21
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`US. Patent
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`U.S. Patent
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`Page 9 of 21
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`

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`US. Patent
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`Jan. 14, 2014
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`US 8,627,708 B2
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`Page 10 of 21
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`U.S. Patent
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`Jan. 14, 2014
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`Sheet 9 of 9
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`US 8,627,708 B2
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`Page 11 of 21
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`

`

`1
`FATIGUE TESTING SYSTEM FOR
`PROSTHETIC DEVICES
`
`CROSS REFERENCE TO RELATED
`APPLICATIONS
`
`This application claims the benefit of priority pursuant to
`35 U.S.C. §l 19(e) of US. provisional application No.
`61/158,l85 filed 6 Mar. 2009 entitled “Apparatus and method
`for fatigue testing of prosthetic valves,” which is hereby
`incorporated herein by reference in its entirety.
`
`TECHNICAL FIELD
`
`The technology described herein relates to systems and
`methods for fatigue testing of prosthetic devices, in particu-
`lar, but not limited to, prosthetic vascular and heart valves,
`under simulated physiological loading conditions and high-
`cycle applications.
`
`BACKGROUND
`
`Prior prosthetic valve testing apparatus and methods typi-
`cally use a traditional rotary motor coupled with mechanisms
`to produce regular sinusoidal time varying pressure field con-
`ditions. To accurately simulate physiologic conditions and/or
`produce a more desirable test condition, especially at accel-
`erated testing speeds, a non-sinusoidal time dependent pres-
`sure field may be desired. This is not easily accomplished
`with a mechanistic approach. Furthermore, current systems
`employ a flexible metallic bellows or conventional piston and
`cylinder as drive members to provide the pressure actuation.
`Flexible metallic bellows are not ideal because they require
`high forces to operate and resonate at frequency, necessitating
`the use of larger driving systems and limiting the available
`test speeds. Piston and cylinder arrangements are not ideal
`because the seals employed in these systems are subjected to
`fiction and thus have severely limited life in high cycle appli-
`cations.
`
`The information included in this Background section ofthe
`specification, including any references cited herein and any
`description or discussion thereof, is included for technical
`reference purposes only and is not to be regarded subject
`matter by which the scope of the invention is to be bound.
`
`SUMMARY
`
`A design for a fatigue testing system for cyclic, long-term
`testing of various types of prosthetic devices (e.g., cardiac
`valves, vascular valves, stents, atrail septal defect technolo-
`gies, vascular linings, and others) is designed to impart a
`repeating loading condition for the test samples during a test
`run. However, the system is also designed to be variable in its
`abilities so it can accurately test multiple technologies. Thus,
`the system may be variably configured depending upon the
`device being tested to impart a particular loading profile to
`repeatedly expose the prosthetic device being tested to
`desired physiological loading conditions during a testing run.
`The purpose is to simulate typical or specific physiologic
`loading conditions on a vascular or heart prosthetic valve, or
`other prosthetic technology, at accelerated frequency over
`time to determine the eflicacy, resiliency, and wear of the
`devices.
`
`Fatigue testing is accomplished by first deploying the pros-
`thetic device in an appropriately sized sample holder, e.g., a
`rigid or flexible tube, canister, housing or other appropriate
`structure for holding the device being tested. The sample
`
`US 8,627,708 B2
`
`2
`
`holder is then placed between two halves of a test chamber
`that together form a reservoir for a working fluid. The test
`chamber is in turn mounted to a drive system. The sample
`holder and valve being tested are then subjected to physi-
`ological appropriate conditions which may include: pressure,
`temperature, flow rate, and cycle times.
`An implementation of a drive system for the fatigue testing
`system may include a linear actuator or magnetic-based drive
`motor coupled to a flexible rolling diaphragm. The drive
`system is coupled to a lower opening in the test chamber and
`is in fluid communication with the fluid reservoir in the test
`
`chamber. The flexible rolling diaphragm (or “rolling bellow”)
`is reciprocally moveable to pressurize and depressurize fluid
`and interacts with the lower section of the fluid reservoir to
`
`provide a motive force to drive the working fluid through its
`cycles within the test chamber, including the sample holders.
`Testing and test conditions are controlled by a control
`computer that permits both input oftest conditions and moni-
`tors feedback of the test conditions during a testing run.
`Computer system control may be either an open loop control
`that requires user intervention in the event a condition falls
`outside pre-set condition parameters or a closed loop control
`system in which the computer monitors and actively controls
`testing parameters to ensure that the test conditions remain
`within the pre-set condition parameters.
`The fatigue tester is capable of simulating physiologic
`conditions on prosthetic devices at an accelerated rate. The
`fatigue tester may also be configured to create either sinusoi-
`dal or non-sinusoidal pressure and/or flow waveforms across
`the prosthetic devices. Pressure waveforms may also be
`applied that produce a pre-defined pressure gradient over time
`to a prosthetic device being tested.
`In one exemplary implementation, a device for simulta-
`neous cyclic testing of a plurality of prosthetic devices is
`composed of a test chamber, a drive motor and a fluid dis-
`placement member. The test chamber is pres surizable and has
`a fluid distribution chamber with a first manifold defining a
`plurality of ports configured to receive and fluidicly couple
`with a first end of each of a respective plurality of sample
`holders. The fluid distribution chamber also defines an aper-
`ture in a lower face in fluid communication with a pressure
`source. The test chamber also has a fluid return chamber with
`
`a second manifold disposed opposite and spaced apart from
`the first manifold ofthe fluid distribution chamber. The mani-
`
`fold of the return chamber defines a plurality of ports config-
`ured to receive and fluidicly couple with a second end of each
`of the respective plurality of sample holders. A fluid return
`conduit both structurally and fluidily connects the fluid dis-
`tribution chamber to the fluid return chamber. The test cham-
`
`ber also has a compliance chamber which provides a volume
`for holding a gas or an elastic material that compresses under
`a pressure placed upon fluid in the test chamber and allows
`fluid in the test chamber to occupy a portion of the volume.
`The drive motor is configured to operate cyclically, acycli-
`cally, or a combination of both. The fluid displacement mem-
`ber is connected with and driven by the drive motor to provide
`the pressure source that increases and decreases a pressure on
`fluid in the test chamber. In this manner, cyclic and acyclic
`fluid pressures may be maintained throughout the test cham-
`ber.
`
`This Summary is provided to introduce a selection of con-
`cepts in a simplified form that are further described below in
`the Detailed Description. This Summary is not intended to
`identify key features or essential features of the claimed sub-
`ject matter, nor is it intended to be used to limit the scope of
`the claimed subject matter. A more extensive presentation of
`features, details, utilities, and advantages of the present
`
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`Page 12 of21
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`Page 12 of 21
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`

`

`US 8,627,708 B2
`
`3
`invention is provided in the following written description of
`various embodiments of the invention,
`illustrated in the
`accompanying drawings, and defined in the appended claims.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a combined isometric view and schematic dia-
`
`gram of an exemplary implementation of a fatigue testing
`system and a corresponding control system.
`FIG. 2A is a front elevation view of the fatigue testing
`system of FIG. 1.
`FIG. 2B is an enlarged view ofthe motor support in the area
`surrounded by the circle labeled 2B in FIG. 2A.
`FIG. 3 is a partial cross sectional view of a test chamber of
`the fatigue testing system taken along line 3-3 of FIG. 1.
`FIG. 4A is an isometric view in cross section of a portion of
`the fatigue testing system if FIG. 1 detailing a flexible rolling
`diaphragm pump connected to a linear piston drive system in
`a down stroke position.
`FIG. 4B is an isometric view in cross section of a portion of
`the fatigue testing system if FIG. 1 detailing a flexible rolling
`diaphragm pump connected to a linear piston drive system in
`an upstroke position.
`FIG. 5A is an isometric view in cross section of a portion of
`the test chamber of the fatigue testing system detailing an
`isolation valve in an open position.
`FIG. 5B is an isometric view in cross section of a portion of
`the test chamber of the fatigue testing system detailing the
`isolation valve in a closed position.
`FIG. 6 is a schematic diagram in cross section of an alter-
`native implementation of a test chamber for use in a fatigue
`testing system.
`FIG. 7 is a graph depicting three exemplary pressure con-
`trol waves for generation by test control software to provide
`pressure across a sample device being tested.
`FIG. 8 is a schematic diagram of a software and hardware
`implementation for controlling a fatigue testing system.
`FIG. 9 is a schematic diagram of an exemplary computer
`system for controlling a fatigue testing system.
`
`DETAILED DESCRIPTION
`
`The system of the present invention generally includes a
`linear actuator or magnetic based drive coupled to a flexible
`rolling bellows diaphragm to provide variable pressure gra-
`dients across test samples mounted in a test chamber housing
`a fluid reservoir. These components operate together to act as
`a fluid pump and, when combined with a fluid control system,
`provide the absolute pres sure and/or differential pres sure and
`flow conditions necessary to cycle test prosthetic devices
`mounted in the test chamber. The flexible rolling diaphragm
`thrusts toward the lower section ofthe test chamber to provide
`a motive force to drive the working fluid through cycles
`within the test chamber. The flexible diaphragm is coupled to
`a lower opening in the test chamber and is reciprocally move-
`able to pressurize and depressurize fluid within the lower
`section of the main housing. The flexible rolling bellows
`diaphragm drive system has a very low inertia as compared to
`other drive systems, e.g., a metal bellows or a standardpiston-
`in-cylinder drive. The flexible diaphragm is highly compliant
`with low resistance to axial deformation across its entire axial
`
`range of motion.
`Plural sample holder tubes are coupled in parallel across
`the test chamber which has plural fluid distribution channels
`in communication with each ofthe sample holders. The lower
`distribution chamber of the test chamber has a single fluid
`reservoir in fluid flow communication with each of the plu-
`
`4
`
`rality of sample holders. The distribution chamber includes a
`manifold with a plurality of fluid outlet ports, and each fluid
`outlet port communicates with an inflow opening of a test
`holder. The upper return chamber ofthe test chamber includes
`a similar manifold with a plurality of fluid inflow ports and
`compliance chambers. Each fluid inflow port communicates
`with an outflow opening of a respective sample holder. A
`central return flow channel is provided between the return
`chamber and the distribution chamber of the test chamber
`
`reservoir to provide a return flow ofthe working fluid from the
`outflow section of the sample holders. A throttle control and
`a check valve are disposed at the inflow and outflow ends of
`the central return flow channel, respectively, to regulate fluid
`flow during testing. The throttle control serves to partially
`regulate the pressure across the prosthetic devices being
`tested as well as the return flow of the working fluid in the
`fluid test chamber.
`
`These components operate together to provide a differen-
`tial pressure and flow conditions necessary to cycle the pros-
`thetic device. The internal conditions, which may include,
`among other things, temperature, differential pressure, and
`system pressure, are electrically communicated to monitor-
`ing and controlling software on a test system computer. The
`motion of the fluid pump and therefore the system dynamics
`are controlled via test system control software. The pressure
`field resulting from the pump motion is easily controlled and
`can be set as a simple sine wave or as any complex user
`created waveform.
`
`One exemplary implementation of a fatigue testing system
`100 for any of a variety of prosthetic devices is depicted in
`FIGS. 1 through 5B. The fatigue testing system 100 may be
`understood as having two primary components, a test cham-
`ber 106 and a drive motor 105. The fatigue testing system 100
`may be both partially mounted upon and housed within a base
`housing 157 formed and supported by a number of frame
`members 102. In the implementation shown, the drive motor
`105 is housed within the base housing 157 while the test
`chamber 106 is supported on a base plate 111 forming a top
`surface ofthe base housing 157. The base housing 157 may be
`open on its sides or enclosed with removable panels as
`desired. A number of leveling feet 101 may be attached to the
`bottom of the base housing 157 to provide for leveling of the
`fatigue testing system 100 and thereby assist in creating con-
`sistent operating conditions across each of the multiple
`sample chambers of the fatigue testing system 100 as further
`described below.
`
`In the embodiment shown in FIGS. 1 and 2A with greater
`detail shown in FIG. 2B, the drive motor 105 may be a linear
`motor. The linear drive motor 105 is mounted vertically on a
`motor stabilizer 1 04 and is centered underneath the test cham-
`
`ber 106. The lower end ofthe drive motor 105 is supported by
`a spring 103 that interfaces with a horizontal foot 10411 of the
`motor stabilizer 104 that extends underneath the linear drive
`motor 105. A lower shaft extension 156 is attached to and
`
`extends downwardly from a thrust rod 108 of the linear drive
`motor 105, through the spring 103, and through a bearing-
`lined aperture in the foot 10411 of the motor stabilizer 104
`where it is secured on the underside ofthe foot 10411 as shown
`
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`in FIG. 2B. The spring 103 is mounted concentrically about
`the lower shaft extension 156 and abuts the lower end of the
`
`thrust rod 108 ofthe linear motor 105 to support the weight of
`the thrust rod 108 of the linear drive motor 105 when the
`
`65
`
`linear drive motor 1 05 is in an unpowered state. Further, in the
`event of a power failure during operation, the spring 103
`prevents the thrust rod 108 from dropping quickly and caus-
`ing an extremely large pressure gradient across test samples
`in the test chamber 1 06, which could damage the test samples.
`
`Page 13 of21
`
`Page 13 of 21
`
`

`

`US 8,627,708 B2
`
`5
`The upper end of the linear drive motor 105 is fixed to a
`motor support plate 109 that is in turn supported by several
`frame members 102 of the base housing 157. An aperture in
`the motor support plate 109 provides for passage ofthe upper
`end of the thrust rod 108 for alignment and mechanical con-
`nection with components interfacing with the test chamber
`106. It should be noted that while a linear drive motor 105 is
`
`depicted in the figures, other types of motors, for example, a
`regular DC motor or a voice coil, may be used to offer alter-
`nate functionality than the linear drive motor 105 of desired
`for a particular prosthetic device. The number of cycles com-
`pleted during a test session may be monitored by a cycle
`counter (not shown) that monitors the motion ofthe thrust rod
`1 08 ofthe linear motor 1 05, which may be aflixed to the motor
`support plate 109.
`Several
`linkage components are provided between the
`drive motor 105 and the test chamber 106 as shown to best
`
`advantage in FIGS. 2A and 3. These components together
`form the drive member for creating a driving pressure on fluid
`in the system. An upper shaft extension 112 is fixed to and
`extends from an upper end of the thrust rod 108 and further
`extends axially within a cylinder 113. The cylinder 113 is
`supported about the upper shaft extension 112 within an
`alignment collar 107. The alignment collar 107 is further
`supported by a pair of alignment mounts 155 that are fixed to
`and extend upward from the motor support plate 109. The
`alignment collar 107 ensures that the cylinder 113 and the
`drive motor 105 maintain axial alignment.
`A central aperture in the bottom of the cylinder 113
`receives the upper shaft extension 112. This aperture in the
`bottom wall of cylinder 113 is lined with a bearing 162 to
`provide a low friction interface between the cylinder 113 and
`the upper shaft extension 112 as the upper shaft extension 112
`moves within the cylinder 113 as further described below. A
`piston 114 in the shape of an inverted cylindrical cup may be
`mounted to the top of the upper shaft extension 112 for axial
`displacement within the cylinder 1 13 as the linear drive motor
`105 drives the upper shaft extension 112 up and down.
`The fluid drive member can be sized based on the volumet-
`
`ric requirements of the test chamber 106 or test samples.
`Depending on the volume displacement required for a par-
`ticular application, the cylinder 113 and corresponding piston
`114 may be swapped out for sizes of larger or smaller diam-
`eter. The cylinder 113 and corresponding piston 114 may thus
`be provided in a variety of diameters in order to provide
`different volume displacements for a given stroke, and
`thereby pressure differentials, within the test chamber 106
`depending upon the type of sample being tested or the par-
`ticular testing protocol being implemented.
`The top edge of the cylinder 113 extends radially to form a
`flange 11311 that interfaces with a bottom surface of a drive
`adapter 117. The drive adapter 117 may also be provided in a
`variety of alternative different sizes to interface with different
`types of cylinders 113 of various diameters. Thus, corre-
`sponding drive adapters 117 and alignment collars 107 are
`similarly swapped for adjustment to the size of the cylinder
`113. For example, as shown in FIG. 3, the aperture in the drive
`adapter 117 is shaped as a frustum with a wider upper mouth
`toward the test chamber 106 and walls that then taper to a
`smaller opening at the interface with the top of the cylinder
`113. In another embodiment with a larger diameter cylinder
`113, the drive adapter 117 may have a larger diameter lower
`opening defining more sharply angled sidewalls of the frus-
`tum-shaped aperture and, in some embodiments, might even
`be cylindrical to accommodate a larger cylinder 113 of a
`common diameter.
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`In one implementation, the fluid drive member has a flex-
`ible diaphragm drive system as illustrated in FIGS. 3, 4A, and
`4B. The diaphragm 115 may be a cap-like or cup-like member
`constructed of a non-reactive and flexible thin rubber, poly-
`meric or synthetic based material. The flexible diaphragm
`115 is highly compliant with low resistance to axial deforma-
`tion across its entire axial range of motion within the cylinder
`113 and the aperture in the drive adapter 117. However,
`alternative configurations of the diaphragm 115 may be
`employed so long as the configuration is capable of low
`friction and low resistance to deformation under the influence
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`ofthe piston 114. The outer diameter ofthe sidewalls 11411 of
`the piston 114 is slightly smaller than the inner diameter ofthe
`cylinder 113 to provide a uniform gap therebetween. The gap
`is designed to be large enough to allow the sidewall of the
`diaphragm 115 to fold in half against itself, i.e., evert, within
`this gap when the sidewalls 11411 of the piston 114 are posi-
`tioned within the sidewalls ofthe cylinder 113. It may thus be
`noted that in operation flexible diaphragm 115 will operate as
`a rolling bellows when the linear drive motor 105 is actuated.
`Many advantages of a low friction flexible diaphragm 115
`as opposed to a rigid metallic bellows or traditional piston and
`cylinder drive may be appreciated. The lateral surfaces of the
`diaphragm 115 evert between the sidewalls 11511 ofthe piston
`115 and the sidewalls of the cylinder 113 as the piston 114
`reciprocates within the cylinder 113 and drive adapter 117.
`However, this eversion occurs with very low friction and low
`heat generation, and exerts very little resistance to piston 114
`movement. As such, the drive motor can operate with a low
`driving force for either small or large displacements requiring
`low current draw and thus low energy expenditure. The flex-
`ible diaphragm 115 is highly compliant with low resistance to
`axial deformation across its entire axial range of motion.
`Alternative configurations of the diaphragm 115 may also be
`employed so long as the configuration is capable of very low
`fiction and very low resistance to deformation under the influ-
`ence ofthe piston 114.
`The cup-shaped flexible diaphragm 115 is mounted on top
`of the piston 114. The end wall of the diaphragm 115 is held
`against the top of the piston 114 by a rigid, disk-shaped cap
`116, which is fastened to the upper shaft extension 112 via
`fastener 158 (e. g., a set screw threaded within the upper
`extension shaft 112). A flange surface 115a extends radially
`outward and circumferentially around the opening to the cav-
`ity of the cup-shaped diaphragm 115. This flange surface
`11511 is sandwiched between the flange surface 11311 of the
`cylinder 113 and the bottom surface of the drive adapter 117
`to maintain a pressure seal between the test chamber 106 and
`the drive components. In view of FIG. 3, the tapering of the
`frustum- shaped wall defining the aperture in the drive adapter
`117 to an opening of comparable diameter to the diameter of
`the sidewalls forming the cylinder 113 becomes apparent, i.e.,
`the need for corresponding surfaces between the flange ofthe
`cylinder 113 and the bottom surface of the drive adapter 117
`to retain the flange surface 11511 of the diaphragm 115.
`A top surface of the drive adapter 117 is fastened to a
`plenum 118 that defines a center cylindrical aperture aligned
`coaxially with the aperture of the drive adapter 117 and the
`cavity defined by the cylinder 113. As shown in FIGS. 4A and
`4B, a plurality of ports may be defined within the sidewall of
`the plenum 118 to provide fluid fill, drainage, or other func-
`tionality within the linkage components below the test cham-
`ber 106. For the sake of clarity, the plenum 118 shown in FIG.
`3 depicts only a single sidewall port 143 that, in this embodi-
`ment, is used as a fluid inflow port. However, additional ports
`may be defined within the plenum 118 if desirable (see, e. g.,
`FIGS. 4A and 4B). If not in use for a particular test configu-
`
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`US 8,627,708 B2
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`7
`ration, the sidewall ports 143 in the plenum 118 may be
`plugged. The plenum 118 may be of constant diameter to
`interface with an aperture in the base plate 111 of the base
`housing 157. For this reason it can now be understood why in
`some embodiments the opening in the top surface ofthe drive
`adapter 117 may be of a larger diameter than the opening in
`the bottom surface of the drive adapter 117 as the drive
`adapter 117 mates with a constant diameter plenum 118 in
`contrast to a variable diameter cylinder 113.
`As previously indicated, the test chamber 106 sits atop of
`the base plate 111 on the base housing 157. The foundation of
`the test chamber 106 may in some embodiments include a
`gate guide plate 120 that also defines a central aperture that is
`coextensive in diameter with and concentrically aligned with
`the aperture in the base plate 111. A distribution chamber 126
`is supported by the gate guide plate 120. The gate guide plate
`120, the distribution chamber 126, and the base plate 111 may
`all be fastened together via bolts (not shown) extending
`upward from the underside of the base plate 111. A pair of
`gate seals 160 may be positioned between the gate guide plate
`120 and the distribution chamber 126. The gate seals 160 may
`be a set of stacked O-rings surrounding the central apertures
`in the gate guide plate 120 and the distribution chamber 126.
`The gate seals 160 may be slightly recessed within corre-
`sponding annular grooves formed in a bottom surface of the
`distribution chamber 126 and a top surface of the gate guide
`plate 120.
`A shallow flat channel 159 of a width at least slightly
`greater than the diameter ofthe gate seals 160 may be formed
`to extend radially from the center aperture within the top
`surface of the gate guide plate 120. A flat rectangular knife or
`gate valve 119, shown to best advantage in FIGS. 5A and 5B,
`may be positioned within the channel in the gate guide plate
`120. The gate valve 119 is shown in a radially withdrawn,
`open position in FIG. 5A, such that there is an open passage
`between the center apertures defined within the gate plate 120
`and the distribution chamber 126. In this position, the gate
`seals 160 press against each other to create a fluid tight seal
`about the central apertures.
`In a closed state as depicted in FIG. 5B, the gate valve 119
`is pushed radially inward such that the flat plate forming the
`gate valve 119 extends completely across the center apertures
`and is sealed between the gate seals 160 to fluidically separate
`the gate guide plate 120 and the linkage elements below it
`from the rest of the test chamber 106 above it. Closure of the
`
`gate valve 119 thus allows for easy maintenance of the drive
`motor 105 or the piston driver 114 (e.g., replacement of the
`flexible bellows diaphragm 115) without having to drain the
`test chamber 106.
`
`As previously noted, the distribution chamber 126 is posi-
`tioned on top of the gate guide plate 120. The distribution
`chamber 126 defines a much wider but shallow cavity with an
`interior bottom wall that slants radially inward until it reaches
`a common diameter with the aperture ofthe gate plate 120. In
`this embodiment, one or more resistive heaters 130 may be
`embedded within the bulk of the distribution chamber 126
`
`underneath the fluid cavity defined by distribution chamber
`126. In one embodiment a separate heater 138 may be located
`immediately beneath each sample holder 129 (as further
`described below) to aid in the uniformity of heat distribution
`within the fluid in the test chamber 106.
`
`A distribution chamber manifold 153 is mounted to a top
`surface of the distribution chamber 126, for example, by
`bolting the two surfaces together about the perimeter. The
`distribution chamber manifold 153 may form a conical
`diverter surface 122 that extends downward into the cavity of
`the distribution chamber 126. A center bore 164 extends
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`through the distribution chamber manifold 153, including
`through the diverter 122. This center bore forms part of a
`return flow path 128 as further described below. The distri-
`bution chamber manifold 153 may further define a plurality of
`bores 166 spaced about the perimeter of the distribution
`chamber manifold 153. In the embodiment shown in FIGS. 1
`
`through 3, eight perimeter bores 166 are defined at a uniform
`radial distance from the center and are equiangularly spaced
`apart. However, in alternative embodiments, there may be
`greater or fewer perimeter bores 166 and different or non-
`uniform spacing may be implemented if desired. A sample
`inlet tube 147 forming the bottom half of a sample holder 129
`is connected within and seals against each of the perimeter
`bores 166 of the distribution chamber manifold 153.
`
`Similarly, a lower conduit wall 124(2) of a telescoping
`center conduit 124 mounts within and seals against the center
`bore 164 in the distribution chamber manifold 153. A one-
`
`way valve 127 or similar check valve is positioned within the
`center bore 164 of the distribution chamber manifold 153
`
`below the lower conduit wall 124(2) of the center conduit
`124. The second half of the center conduit 124 is formed as a
`
`cylindrical upper conduit wall 124(1) with an inner diameter
`substantially the same as an outer diameter of the lower
`conduit wall 124(2) such that the center conduit 124 can be
`expanded or contracted in length. One or more center seals
`161, for example, in the form of O-rings mounted within
`annular recesses in the outer surface ofthe lower conduit wall
`
`121(2) provide a fluid tight seal interface with the interior
`surface of the upper conduit wall 124(1).
`Each of the sample holders 129 is also composed of a
`sample outlet tube 148 that sits atop a respective sample inlet
`tube 147. The actual test sample 130 (e.g., a prosthetic device)
`may be sandwiched between the sample inlet tube 147 and
`sample outlet tube 148 to hold it in place within the test
`chamber 106. In other embodiments (not shown) each of the
`sample holders 129 may be an integral unit with a test sample
`130 mounted within by any of a variety of means that may be
`specifi