The present invention relates to electromechanical actuators, and more particularly, to devices for providing precisely controlled actuation of spray pump mechanisms.
The US Food and Drug Administration (FDA) strongly recommends automated actuation of nasal spray devices subject to in-vitro bioequivalence testing to decrease variability in drug delivery due to operator factors (including removal of potential analyst bias in actuation) and increase the sensitivity for detecting potential differences between drug products. The FDA further recommends that an automated actuation system have settings or controls for actuation force, length of stroke, actuation velocity, hold time, return time, delay time between successive actuations, and actuation number. Selection of appropriate settings should be relevant to proper usage of the nasal aerosol or nasal spray by the trained patient, and should be documented based on exploratory studies in which actuation force, actuation time, and other relevant parameters are varied. One such study includes “Guidance for Industry: Bioavailability and Bioequivalence Studies for Nasal Aerosols and Nasal Sprays for Local Action,” by Wallace P. Adams, U.S. Department of Health and Human Services, Food and Drug Administration, Center for Drug Evaluation and Research (CDER), June 1999.
Thorough characterization of the spray pump's performance in terms of its emitted spray pattern, plume geometry and/or droplet size distribution are known to be affected by the means in which the spray pump is actuated. For example, slow actuation will likely cause poor atomization, producing a stream-like flow. Fast actuation will likely cause too fine a spray to be produced, leading to poor absorption in the nasal mucosa and unwanted inhalation and deposition of the droplets in the throat and lungs.
From a mechanical perspective, over-actuation (forcing the spray pump assembly beyond its intended stopping point) of the spray pump device must be avoided. If the spray pump mechanism is over-actuated, permanent deformations can occur to the delicate pump orifice, swirl chambers and/or closure mechanisms, all of which can manifest themselves in higher than expected variability in the pump's spray performance and flow characteristics. Further, rigidly holding the nozzle of the spray pump in place during actuation is vital to ensure that the spray develops properly and exits the nozzle normally so that measurements of spray pattern, plume geometry and droplet size distribution are not artificially biased due to unwanted movement of the nozzle.
The Innova Systems (Pennsauken, N.J.) Nasal Spray Pump Actuators (NSP and eNSP) are prior art automated nasal spray actuators. Both models use the same operating principle: a pneumatic cylinder connected to a solid plate (contact plate) is used to compress the spray pump against a spring loaded holding plate and clip mechanism. Typically, these actuators are connected to a compressed air source and a computer interface to allow a user to set the actuation force, contact force, holding time, and dose time for the actuation event. In operation, these actuators adjust an air pressure regulator so that the pneumatic cylinder will first apply the prescribed contact force to the bottom side of the spray pump. Presumably, this application of the contact force is done to minimize the time delay in producing the spray and/or to prevent the compression plate from striking the spray pump with a dynamic load, which could damage the pump due to the high dynamic forces achievable in the system. Next, the pressure regulator is adjusted again so that the pneumatic cylinder applies the prescribed actuation force (typically higher than the contact force). This action compresses the spray pump at a rate determined by the pneumatic efficiency of the system and the mechanical spring resistance of the spray pump and fluid combination. The compression rate cannot be controlled. As a result, once the pressure regulator is set, the contact plate will move at a rate determined by the system, not the user.
Experience with using these actuators has shown the following difficulties and shortcomings:
1. Lack of position and velocity controls leads to uncontrolled, “air hammer”—like performance with substantial spray pump over-actuation. This phenomenon has led to measurable degradation in spray pump performance over time and larger than expected variations in delivered dosage content. These problems are likely due to progressive deterioration in the moving pump components due to over-actuation.
2. Lack of a nozzle holding mechanism leads to unwanted movements of the nozzle during actuation. This causes artificial distortions and substantial variability to appear in the associated spray pattern and plume geometry test data.
3. Difficulties associated with pneumatic control lead to oscillating contact force application and this leads to pre-spray droplets forming on the nozzle tip and measurable variability in spray pattern, plume geometry, and droplet size distribution data.
4. Reliance on variable quality, laboratory compressed air sources leads to inconsistent actuation performance and potential safety issues.
5. Uncertain actuation event-time triggering causes difficulty in acquiring time critical spray data such as spray pattern and plume geometry.
6. Uncertain applied force measurements do not give a user confidence that the actuator is applying the desired force to the spray pump.
7. Absence of recordable applied force and/or position/velocity data make it difficult to chronicle the actuation event history.