Patent Description:
Stiction is the static friction that needs to be overcome to enable relative motion of stationary objects in contact. Stiction arises in syringes between the stopper and the inner wall of the syringe barrel. Syringe stiction reduction has typically been considered for ergonomic reasons, but also because it introduces a noise factor into the accuracy of conventional syringe pumps. Stiction control or reduction is typically approached in the context of lubricants or stopper design.

For syringe pumps designed to draw from the tip of a syringe, rather than depressing the plunger, the negative pressure required to draw from smaller syringe sizes can become prohibitive for any pump. Conventional syringe pumps are not as susceptible to stiction related problems as these "draw-from-the-tip" pumps. Syringe break-loose force or stiction data illustrating the pressures required to draw from a range of syringe sizes is shown in <FIG>.

Accordingly, there is a need in the art for improved solutions for reducing stiction and/or the negative pressure required to draw fluid from syringes.

A syringe assembly having the features defined within the preamble of claim <NUM> is for example known from <CIT>.

The present invention is directed to a syringe assembly having the features defined within claim <NUM>. Preferred embodiments defined within the dependent claims.

According to the invention the syringe assembly further comprises at least one pressure sensor configured to determine a vacuum pressure during fluid draw from the syringe by the infusion pump, wherein the vibrator is configured to vibrate based on the determined vacuum pressure.

In one preferred and non-limiting embodiment or aspect, the vibrator is connected to a housing of the infusion pump via a line.

These and other features and characteristics of the present invention, as well as the methods of operation and functions of the related elements of structures and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. As used in the specification and the claims, the singular form of "a", "an", and "the" include plural referents unless the context clearly dictates otherwise.

For purposes of the description hereinafter, the terms "upper", "lower", "right", "left", "vertical", "horizontal", "top", "bottom", "lateral", "longitudinal", and derivatives thereof, shall relate to the invention as it is oriented in the drawing figures.

The use of a vibration module attached to a syringe provides a solution to the high stiction (low pressure) problem. Vacuum pressure reductions, for example, of about <NUM>-<NUM>% have been demonstrated, and much better performance is expected. For example, if an objective is to induce small-scale cyclic axial motions (micro-dithering) in a syringe plunger, the plunger/rod system can be treated as a classical spring-mass-damper, with a cyclic driving force Fd. In this case, Newton's second law yields the 2nd order equation of motion as shown in Equation <NUM>: <MAT> where x is the axial coordinate of the syringe plunger, c is the damping coefficient, k is the spring constant, or stiffness of the plunger rod, m is the mass being oscillated, and again, Fd is the cyclic driving force.

This second order ordinary differential equation (ODE) is usually expressed in terms of the damping ratio ζ and un-damped natural frequency ωn, as shown in Equation <NUM>: <MAT> where ωn and ζ are respectively defined in Equation <NUM> and Equation <NUM>: <MAT> <MAT>.

The un-damped natural frequency ωn may be considered as a primary metric of interest. To maximize transfer of vibrational energy to the stopper, it is desirable to drive the plunger rod at or near the natural frequency of the system. <FIG> illustrates the first linear portion of the compression curve for four example plunger rods compressed between anvils in an Instron machine to measure their spring constant during the first small deflection. These curves, together with the mass of each rod/plunger pair can be used to calculate the natural frequency of each of the four test syringe sizes, as shown in the following Table <NUM>. Although not included in the example results shown in Table <NUM>, it is noted that the real mass of interest can include some or all of the fluid mass in the syringe, and may substantially decrease these natural frequencies.

<FIG> illustrate raw pressure traces over time for a <NUM> test syringe, a <NUM> test syringe, and a <NUM> test syringe, respectively, during an example test in which a syringe pump was plumbed to draw from the test syringes at flow rates selected to produce maximum stiction. A vibrator motor was affixed to the end of the plunger rod of each syringe with the motor axis perpendicular to the syringe axis. Each of the <NUM> test syringes were subjected to four test runs in an A-B-A-B-style (motor, no-motor, motor, no-motor) sequence. When used, the motor was tuned to vibrate at a frequency substantially equal to the vibration frequency of the syringe system including the syringe and the vibration motor. Each syringe was left undisturbed for about five minutes prior to each test run. Each test run continued, and the pressure-trace was recorded up until the first "break-loose" event.

<FIG> and <FIG> respectively summarize the minimum pressures achieved for each test run and the percent improvement for the vibration motor runs. Pressure reductions of <NUM>-<NUM>% during fluid draw were demonstrated with the vibration motor, as well as the ability of a vibrator to break the stiction of the occasional worst-case syringe.

Referring now to <FIG>, a syringe assembly <NUM> according to preferred and non-limiting embodiments or aspects comprises a syringe <NUM> and a vibrator <NUM> configured to vibrate at at least one frequency. The vibrator <NUM> is attached to the syringe <NUM>. The syringe assembly <NUM> may further comprise an infusion pump <NUM> configured to draw fluid from the syringe <NUM> with a negative pressure via a fluid line <NUM>. The syringe <NUM> comprises a plunger rod <NUM> and a syringe barrel <NUM> that extends between a proximal end 104a and a distal end 104b. The proximal end 104a of the syringe barrel <NUM> includes an opening <NUM> configured to receive a distal end 102b of the plunger rod <NUM> including a stopper <NUM>. The distal end 104a of the syringe barrel <NUM> can be connected to the infusion pump <NUM> via the fluid line <NUM> for fluid draw from the syringe <NUM> by the infusion pump <NUM>. In another example, the distal end 104a of the syringe barrel <NUM> may comprise a needle cannula for fluid transfer from the syringe <NUM> in response to compression of the plunger rod <NUM>.

The vibrator <NUM> may include one of an eccentric weight on a motor shaft, a piezoelectric drive, and an inductive drive. The vibrator <NUM> may receive a supply of power from the infusion pump <NUM>, another external power supply, or an internal battery (not shown). The vibrator can be configured to vibrate at any frequency including ultrasonic frequencies and lower frequencies. In some examples the vibrator <NUM> can include a controller including a processor and memory configured to control operation of the vibrator <NUM>. In another example, the vibrator <NUM> can be connected to an external controller via a wired or wireless connection to control operation of the vibrator <NUM>. In one implementation, the infusion pump <NUM> may include the external controller to control operation of the vibrator <NUM>. For example, the controller can control the vibrator to start or stop vibration, a frequency at which the vibrator vibrates, and/or a period or whether the vibrator <NUM> vibrates continuously, periodically, or based on sensor feedback as described in more detail herein. It is contemplated herein that the vibrator <NUM> could be rotational, linear uniaxial, or multiaxial. It is further contemplated herein that the vibrator <NUM> can include piezoelectric, inductive or other actuation technology.

In one example, the vibrator <NUM> can be attached to the plunger rod <NUM>. For example, the vibrator <NUM> can be attached to the proximal end 102a of the plunger rod <NUM> as shown in <FIG>, e.g., on top of a finger flange or disc at the proximal end 102a of the plunger rod <NUM>. The vibrator can be configured to impute motion to the plunger rod <NUM> in an axial direction of the syringe barrel <NUM> and/or the plunger rod <NUM>. For example, the vibrator <NUM> may be configured to vibrate back-and-forth in the proximal and distal directions of the syringe to impute motion in the axial direction thereof.

In another example, the vibrator <NUM> can be attached between the proximal end 102a and the distal end 102b of the plunger rod <NUM> as shown in <FIG>, e.g., along or within the shaft of the plunger rod <NUM> and/or between cross-shaped cross sections thereof. In still another implementation, the vibrator <NUM> can be attached to the syringe barrel <NUM> as shown in <FIG>, e.g., to an outer surface of the syringe barrel <NUM> between the proximal end 104a and the distal end 104b of the syringe barrel <NUM>. The vibrator <NUM> can be configured to impute motion to the plunger rod <NUM> and/or the syringe barrel <NUM> in a direction transverse to the axial direction of the syringe barrel <NUM> and/or the plunger rod <NUM>. For example, when attached to the syringe barrel, the vibrator <NUM> may be configured to vibrate back-and-forth in a direction transverse to the axial direction of the syringe <NUM>. It is noted herein that the vibrator <NUM> can be secured to any portion of the plunger rod <NUM>, or a portion of the syringe barrel <NUM>, as long as the vibrator is configured to impute axial motion to the syringe assembly.

The vibrator <NUM> may be removably attached to the syringe <NUM>. For example, the vibrator <NUM> can be attached to the syringe by at least one of an adhesive connection, a mechanical connection, and a magnetic connection. An adhesive connection may comprise a permanent or removable and reusable adhesive pad on the vibrator <NUM> that forms an adhesive connection between the vibrator <NUM> and the syringe <NUM>. A mechanical connection may comprise a band or clip configured to secure the vibrator <NUM> to the syringe barrel <NUM> or the plunger rod <NUM>. A magnetic connection may comprise a magnet on each of the vibrator <NUM> and the syringe barrel <NUM> or plunger rod <NUM> to secure the vibrator <NUM> to the syringe <NUM>.

In one example, the vibrator <NUM> can be configured to vibrate at a natural frequency of a particular syringe <NUM>, the syringe assembly <NUM>, or a syringe system including the syringe <NUM> and the vibrator <NUM> itself. In another example, the vibrator <NUM> can be configured to vibrate at a plurality of different frequencies. The syringe assembly <NUM> may comprise at least one sensor <NUM>, e.g., an accelerometer, configured to determine a natural frequency of the syringe <NUM>, the syringe assembly <NUM>, or a syringe system including the syringe <NUM> and the vibrator <NUM>. The at least one sensor <NUM> can be connected to the vibrator <NUM> and/or the controller for the vibrator <NUM>. In one configuration, the sensor <NUM> can include an accelerometer. For example, the at least one sensor <NUM> can be configured to determine a dynamic response of the syringe assembly <NUM> to the plurality of different frequencies and determine the natural frequency of the syringe assembly <NUM> based on the dynamic response of the syringe assembly <NUM> to the plurality of different frequencies. For example, when the frequency at which the vibrator <NUM> is vibrating is equal to the natural frequency of the syringe assembly <NUM>, the amplitude of vibration increases exponentially, which is known as resonance. The at least one sensor <NUM> and/or the controller for the vibrator <NUM> can determine the frequency at which the syringe assembly <NUM> achieves maximum amplitude of vibration, i.e., resonance, and control the vibrator <NUM> to vibrate at the determined natural frequency during fluid draw from the syringe <NUM>. The vibrator <NUM> can be configured to vibrate at the natural frequency of the syringe assembly <NUM> determined by the at least one sensor <NUM>.

In some implementations, the vibrator <NUM> has a predetermined mass configured to tune the natural frequency of the syringe assembly <NUM> to a preselected natural frequency. For example, the mass of the vibrator <NUM> ca be designed to tune the natural frequency of the system including the syringe <NUM> and the vibrator <NUM> itself to a more desirable value, such as a preprogrammed vibration frequency of the vibrator <NUM>.

The vibrator <NUM> can be configured and/or controlled to vibrate one of continuously and periodically. For example, during fluid draw from the syringe <NUM> by the infusion pump <NUM>, the vibrator <NUM> may vibrate one of continuously and periodically at the natural frequency of the syringe assembly <NUM>. In another implementation, the syringe assembly <NUM> may further comprise at least one pressure sensor <NUM> configured to determine a vacuum pressure during fluid draw from the syringe <NUM> by the infusion pump <NUM>. The at least one pressure sensor <NUM> may be located along and/or within the fluid line <NUM> connecting the infusion pump <NUM> to the syringe <NUM> to draw the fluid from the syringe <NUM>. The at least one pressure sensor <NUM> can be connected to the vibrator <NUM> and/or the controller of the vibrator <NUM>, and the vibrator <NUM> can be configured or controlled to vibrate based on the level of negative pressure determined by the at least one pressure sensor <NUM>. For example, if the determined negative pressure violates a threshold pressure level, e.g., indicating a high stiction, the controller can control the vibrator <NUM> to vibrate based on the violated threshold to help reduce the stiction and the negative pressure required to continue fluid draw by the infusion pump <NUM>. In operation, when pressure in the pump reaches a threshold pressure, the vibrator <NUM> may turn on thereby breaking the stiction and reducing the negative pressure in the syringe, and allow the pump to continue. In one example, the vibrator <NUM> may only need to be turned on periodically to keep the negative pressure above the set threshold.

In one example, as shown in <FIG>, the vibrator <NUM> is connected to a housing of the infusion pump <NUM> via a line <NUM>, such as a string or dongle, which can reduce occurrences of lost vibrators <NUM> in the case of a reusable vibrator <NUM> to be used with multiple different syringes <NUM> at the same infusion pump <NUM>.

Claim 1:
A syringe assembly (<NUM>), comprising:
a syringe (<NUM>);
a vibrator (<NUM>) configured to vibrate at least one frequency, wherein the vibrator is attached to the syringe;
characterized in that
the syringe assembly includes at least one pressure sensor (<NUM>) configured to determine a vacuum pressure during fluid draw from the syringe by an infusion pump (<NUM>), wherein the vibrator is configured to vibrate based on the determined vacuum pressure.