Asymptotic limits on tablet coating variability based on cap-to-band thickness distributions: A discrete element model (DEM) study

Chen, Pei; Elliott, James A.

doi:10.1016/j.ces.2017.06.029

Cited by 22 publications

(9 citation statements)

References 28 publications

(52 reference statements)

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“…The numerical study is divided into two stages. In the first stage, the dynamics of tablets during mixing was modelled using Discrete Element Method (DEM) simulations, and in the second stage, as a post-processing step, a ray-tracing method (Toschkoff et al, 2015(Toschkoff et al, , 2013Pei and Elliott, 2017) was applied to the outputs of DEM simulations to trace the trajectory of the terahertz ray and detect its intersection with the tablet. DEM simulations were employed to model the mixing behaviour of tablets in a rotating pan as shown in Figure 2.…”

Section: Numerical Model Of In-line Measurementmentioning

confidence: 99%

“…Analytical and numerical modelling methods (Freireich and Wassgren, 2010;Toschkoff et al, 2013Toschkoff et al, , 2015Freireich et al, 2015;Boehling et al, 2016;Pei and Elliott, 2017), using the discrete element method (DEM), have recently been employed to investigate inter-and intra-tablet variability during the coating process. Freireich et al (2015) used glued spheres (multi-spheres) to model the shape of the tablet and calculated the dynamics of tablets in a rotating pan.…”

Section: Introductionmentioning

confidence: 99%

“…This method ensures that mass transfer is only applied to surface elements of the tablet that are not obstructed by other tablets in the tablet bed of the coater. The ray-tracing method can also be explicitly implemented to represent trajectories of discrete spray droplets (Toschkoff et al, 2015(Toschkoff et al, , 2013Pei and Elliott, 2017). In this method, the spray droplets are allowed to accumulate on the tablet surface where the locations of accumulations are the intersection points calculated from the direction of the ray and the position of the tablet.…”

Section: Introductionmentioning

confidence: 99%

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A quantitative comparison of in-line coating thickness distributions obtained from a pharmaceutical tablet mixing process using discrete element method and terahertz pulsed imaging

Chen

Lin

Markl

et al. 2018

Chemical Engineering Science

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The application of terahertz pulsed imaging (TPI) in the in-line configuration to monitor the coating thickness distribution of pharmaceutical tablets has the potential to improve the performance and quality of the spray coating process. In this study, an in-line TPI method is used to measure coating thickness distributions on pre-coated tablets during mixing in a rotating pan, and compared with results obtained numerically using the discrete element method (DEM) combined with a ray-tracing technique. The hit rates (i.e. the number of successful coating thickness measurements per minute) obtained from both terahertz in-line experiments and the DEM/ray-tracing simulations are in good agreement, and both increase with the number of baffles in the mixing pan. We demonstrate that the coating thickness variability as determined from the ray-traced data and the terahertz in-line measurements represents mainly the intra-tablet variability due to relatively uniform mean coating thickness across tablets. The mean coating thickness of the ray-traced data from the numerical simulations agrees well with the mean coating thickness as determined by the off-line TPI measurements. The mean coating thickness of in-line TPI measurements is slightly higher than that of off-line measurements. This discrepancy can be corrected based on the cap-to-band surface area ratio of the tablet and the cap-to-band sampling ratio obtained from ray-tracing simulations: the corrected mean coating thickness of the in-line TPI measurements shows a better agreement with that of off-line measurements.

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Section: Numerical Model Of In-line Measurementmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A quantitative comparison of in-line coating thickness distributions obtained from a pharmaceutical tablet mixing process using discrete element method and terahertz pulsed imaging

Chen

Lin

Markl

et al. 2018

Chemical Engineering Science

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“…We trust that the results from this work will be useful in progressing toward automated control of the coating process of pharmaceutical cores. It should be desirable that current experimental results on color evolution by a random spray coating technique can be confirmed by future theoretical models, as recently investigated for thickness . In general, additional colorimetric research is necessary to achieve a satisfactory automatic control of coating processes in different pharmaceutical industries: Fixation of appropriate coating times, establishment of perceptible/acceptable color tolerances for industrial operators and final users, proposal of standard target colors to be reproduced in the coloration processes, and so on.…”

Section: Discussionmentioning

confidence: 99%

Color evolution during a coating process of pharmaceutical tablet cores by random spraying

Murillo

Rodríguez-Pulido

Heredia

et al. 2018

Color Research & Application

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Placebo white tablet cores (lactose anhydrous [47.6%], corn starch [23.8%], microcrystalline cellulose [19.1%], polyvinylpyrrolidone [7.9%], magnesium stearate [0.8%], and talcum powder [0.8%]) were coated with a colorant (hydroxypropyl methylcellulose [8% w/v], titanium dioxide [0.2% w/v], FD&C yellow No. 6 with aluminum lacquer [0.8% w/v], polyethylene glycol 4000 [0.4% w/v], and purified water [q.s.p. 100 mL]) using a random spraying method during 130 minutes. During the coating process, batches of 21 samples were extracted every 10 minutes and measured with a DigiEye imaging system. The initial cores showed very similar and uniform colors (Mean Color Difference from the Mean [MCDM] of 0.8 CIELAB units), but partially coated tablets showed lower uniformity (MCDM below 2.0 CIELAB units). There was a high color variability (MCDM about 4.0 CIELAB units) among tablets of the same batch in the period between 10 and 30 minutes, which decreased as the coating process progressed, until achieving a final acceptable value (MCDM below 2.0 CIELAB units). During the coating process, L* decreased, C*ab strongly increased, and h ab remained nearly constant (disregarding results at 0 and 10 minutes). CIELAB and CIEDE2000 color differences (mainly chroma differences) with respect to the initial color of the tablets were modeled as a function of time by exponential functions with three coefficients. The color change in the interval from 90 to 130 minutes (4.3 CIELAB units, or 2.6 CIEDE2000 units), may be considered negligible bearing in mind the color variability in the batches of 21 samples and typical values of visual color thresholds.

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“…There is a growing interest towards mechanistic modelling based on solid and gas phase motions such as DEM and computational fluid dynamics in order to comprehensively explain the process in terms of inter-and intra-tablet uniformity of the coating process [10][11][12][13][14][15]. Inputs to the DEM model typically include material properties, process parameters, and coater geometry, with the predicted outputs being inter-tablet and intra-tablet coating uniformity.…”

Section: Discrete Element Modelling and Ray-tracingmentioning

confidence: 99%

Steps towards numerical verification of the terahertz in‐line measurement of tablet mixing by means of discrete element modelling

Lin

Chen

Markl

et al. 2018

IET Microwaves, Antennas & Propagation

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In recent years terahertz in-line sensing has been used to monitor the film coating thickness of individual pharmaceutical tablets during the coating process. In the previous work, the in-line measurements were verified against off-line measurements of samples from the same population. Here we report on our recent progress to further verify the validity of the terahertz in-line measurement modality using discrete element modelling for an artificial lab-scale tablet mixing process inside a tablet pan coater. By coupling discrete modelling with a ray-tracing method it is then possible to estimate the cumulative measurements taken, which in turn can guide towards the fine-tuning of the selection criteria as part of measurement analysis.

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Asymptotic limits on tablet coating variability based on cap-to-band thickness distributions: A discrete element model (DEM) study

Cited by 22 publications

References 28 publications

A quantitative comparison of in-line coating thickness distributions obtained from a pharmaceutical tablet mixing process using discrete element method and terahertz pulsed imaging

A quantitative comparison of in-line coating thickness distributions obtained from a pharmaceutical tablet mixing process using discrete element method and terahertz pulsed imaging

Color evolution during a coating process of pharmaceutical tablet cores by random spraying

Steps towards numerical verification of the terahertz in‐line measurement of tablet mixing by means of discrete element modelling

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