Accuracy of Micro Powder Dosing and Feeding Via a Vibratory Sieve-Chute

Accuracy of Micro Powder Dosing and Feeding via a Vibratory Sieve-Chute System

M.O. Besenhard^1,2, E. Faulhammer^1,2, S. Fathollahi^1,2, G. Reif², V. Calzolari³, S. Biserni³, A. Ferrari³, S.M. Lawrence⁴, M. Llusa¹, A. Paudel, J.G. Khinast^1,2*

1: Research Center Pharmaceutical Engineering (RCPE) GmbH, 8010 Graz, Austria
2: Graz University of Technology, Institute of Process and Particle Engineering, 8010 Graz, Austria
3: MG2, Via del Savena 18, I-40065, Pian di Macina di Pianoro, Bologna, Italy

4: GlaxoSmithKline, New Frontiers Science Park, Third Avenue, Harlow, Essex CM19 5AW, UK

* Corresponding author:

khinast@tugraz.at

Abstract:

This presentation describes our current studies on powder dosing [1] and feeding via a vibratory sieve-chute system, i.e., the MG2’s Microdose®. Figure 1 shows the operating principle and parts of the set-up. The chute is tilted at a fixed angle of 5° and sieves with 5-10 holes of e.g. 0.7mm in diameter are fixed on its top. The powder was discharged from the sieve into the chute and the capsule body using gravity. Vertical vibration occurred with a broad range of frequencies and amplitudes. The fill weight (fw ) during dosing events was recorded via a capacitance sensor, which had two parallel electrode plates encompassing the capsule body. The electrical field and the capacitance varied depending on of the powder quantity in the capsule. Due to this scale, fill weights could be recorded dynamically facilitating the analysis of filling characteristics, i.e., the fill rates and their robustness.

First, the range of frequencies and amplitudes was screened for settings that facilitated reasonable (no blocking of spilling in the sieve) fill rates for three lactose powders, serving as model substances. The filling characteristics were studied in detail within this operating space.

The filling rate was determined by averaging the slopes ( D fw(t) Dt  [mg s] ) of 30  filling profiles. The higher the probabilities of an unsteady filling behavior (as shown in Figure 5 b) or fluctuations in the filling rate are, the higher is the standard deviation ([mg/s]) of the evaluated slopes. Therefore, the latter can be used to characterize the robustness of the fill rate, which is of prime importance for selecting the settings for continuous (micro) feeding using such a system.

The results reveal similar operating spaces for all powders and the fill rate robustness varied distinctly in the operating space. Figure 2 depicts the results for one of the studied powders. Utilizing the gained knowledge on filling characteristics micro dosing studies have been performed, dosing capsules with 2.5 mg. These studies compared accuracy of dosing via a constant frequency and amplitude or a constant frequency but the amplitude manipulated by a PID controller. The results reveal that dosing was the most accurate when using constant settings, since the usage of PID control caused inhomogeneous powder beds on the chute, as shown in figure 3.

Figure  SEQ figure \* ARABIC 1: Principle of powder dosing via a vibratory sieve-chute system. The inlet shows a photo of the sieve used, and the red x depicts the position of an acceleration probe used to study the oscillation patterns.

Figure 2: Filling rate and its standard deviations (vertical bars) for InhaLac 230 in the amplitude and frequency settings of the operating space.

Figure 3: Powder bed in the chute during a PID controlled dosing (left) and dosing using a constant amplitude (right).

[1] Besenhard, M.O., Faulhammer, E., Fathollahi, S., Reif, G., Calzolari, V., Biserni, S., Ferrari, A., Lawrence, S.M., Llusa, M., Khinast, J.G. (2015). Accuracy of Micro Powder Dosing via a Vibratory Sieve-Chute System. European Journal of Pharmaceutics and Biopharmaceutics, accepted.