Flow and bulk density enhancements of pharmaceutical powders using a conical screen mill: A continuous dry coating device

Enhancing drug processibility through dry coating: Comparison at lab and pilot scales

Dry coating fine pharmaceutical powders with nano-silica has been shown to enhance their bulk properties and their blend processability at lab-scale, potentially facilitating tablet manufacturing. This study critically investigates key aspects of dry coating from industrial applicability perspective: (1) evaluating the selection of silica amount based on the host particle surface area coverage (SAC) against the industry standard 1 wt% addition, (2) assessing the feasibility of continuous dry coating using a pilot-scale conical screen mill (comil-U10) compared to the lab-scale batch high-intensity vibratory mixer (HIVM), and (3) investigating downstream processing improvements from dry coating via feedability and tabletability studies. Results from six different pharmaceutical powders (d50 ∼ 3-35 μm) demonstrated that SAC-based silica wt.% selection outperformed 1 wt% silica for bulk properties enhancements. Multi-faceted characterization revealed that FFC was the most reliable amongst Hausner's ratio, compressibility, and permeability tests. Three selected materials (d50 ∼ 16-26 μm) for comil processing showed remarkable one-flow category improvement, though two finer materials fell short of the HIVM performance. The dry coated materials demonstrated superior feed rate stability, demonstrating reduced flow variability, attributed to enhanced flowability and lower compressibility. Tablets of formulations containing dry-coated API using either comil or HIVM outperformed formulations with blended silica at three drug loads, 10 %, 30 %, and 60 %, likely due to better silica dispersion. These outcomes demonstrate the benefits of potentially scalable comil-based dry coating to continuous manufacturing of tableting, potentially eliminating the need for granulation.

Predicting Powder Blend Flowability from Individual Constituent Properties Using Machine Learning

PURPOSE

Predicting powder blend flowability is necessary for pharmaceutical manufacturing but challenging and resource-intensive. The purpose was to develop machine learning (ML) models to help predict flowability across multiple flow categories, identify key predictive features, and arrive at formulations with improved flow properties.

METHODS

A dataset of 410 blends, composed of 9 active pharmaceutical ingredients (APIs) and 18 excipients with varying silica dry-coating parameters, was analyzed. Supervised ML models were trained to predict various flowability categories (very cohesive, cohesive, semi-cohesive, well-flowing, and free-flowing). Particle size, morphology, surface properties, and coating parameters were used as features. Classification algorithms, including Random Forest (RF) and Extreme Gradient Boosting (XGBoost), were evaluated. Unsupervised clustering identified natural groupings within flowability data.

RESULTS

The best-performing models achieved up to 85% accuracy for predicting flowability regimes of individual components and 87% for blends. Individual components generally showed higher accuracy than blends, except in the uncoated scenario with 2 flow regimes, where blends outperformed with 94.67%. SHapley Additive exPlanations (SHAP) and Feature Importance analysis indicated dry coating parameters as the most influential factors, followed by particle size and morphology. ML models effectively identified category transitions between flow regimes, offering insights into blend optimization.

CONCLUSION

Integrating ML with mechanistic approaches effectively predicted powder blend flowability across diverse categories and elucidated feature-property relationships. These outcomes can facilitate the rational design of blends having enhanced flow properties at reduced experimental effort through judiciously selected dry coating of a blend constituent; making this approach promising for advancing pharmaceutical process and product development.

Facilitating direct compaction tableting of fine cohesive APIs using dry coated fine excipients: Effect of the excipient size and amount of coated silica

The possibility of attaining direct compression (DC) tableting using silica coated fine particle sized excipients was examined for high drug loaded (DL) binary blends of APIs. Three APIs, very-cohesive micronized acetaminophen (mAPAP, 7 μm), cohesive acetaminophen (cAPAP, 23 μm), and easy-flowing ibuprofen (IBU, 53 μm), were selected. High DL (60 wt%) binary blends were prepared with different fine-milled MCC-based excipients (ranging 20- 37 μm) with or without A200 silica coating during milling. The blend flowability (flow function coefficient -FFC) and bulk density (BD) of the blends for all three APIs were significantly improved by 1 wt% A200 dry coated MCCs; reaching FFC of 4.28 from 2.14, 7.82 from 2.96, and > 10 from 5.57, for mAPAP, cAPAP, and IBU blends, respectively, compared to the uncoated MCC blends. No negative impact was observed on the tablet tensile strength (TS) by using dry coated MCCs despite lower surface energy of silica. Instead, the desired tablet TS levels were reached or exceeded, even above that for the blends with uncoated milled MCCs. The novelty here is that milled and silica coated fine MCCs could promote DC tableting for cAPAP and IBU blends at 60 wt% DL through adequate flowability and tensile strength, without having to dry coat the APIs. The effect of the silica amount was investigated, indicating lesser had a positive impact on TS, whereas the higher amount had a positive impact on flowability. Thus, the finer excipient size and silica amounts may be adjusted to potentially attain blend DC processability for high DL blends of fine APIs.

Impact of dry coating lactose as a brittle excipient on multi-component blend processability

Previous work demonstrated the benefits of dry coating fine-grade microcrystalline cellulose (MCC) for enabling direct compression (DC), a favored tablet manufacturing method, due to enhanced flowability while retaining good compactability of placebo and binary blends of cohesive APIs. Here, fine brittle excipients, Pharmatose 450 (P450, 19 μm) and Pharmatose 350 (P350, 29 μm), having both poor flowability and compactability are dry coated with silica A200 or R972P to assess DC capability of multi-component cohesive API (coarse acetaminophen, 22 μm, and ibuprofen50, 47 μm) blends. Dry coated P450 and P350 not only attained excellent flowability and high bulk density but also heightened tensile strength hence processability, which contrasts with reported reduction for dry coated ductile MCC. Although hydrophobic R972P imparted better flowability, hydrophilic A200 better enhanced tensile strength, hence selected for dry coating P450 in multi-component blends that included fine Avicel PH-105. For coarse acetaminophen blends, substantial bulk density and flowability increase without any detrimental effect on tensile strength were observed; a lesser amount of dry coated P450 was better. Increased flowability, bulk density, and tensile strength, hence enhanced processability by reaching DC capability, were observed for 60 wt% ibuprofen50, using only 18 wt% of the dry coated P450, i.e. 0.18 wt% silica in the blend.

Selection of Silica Type and Amount for Flowability Enhancements via Dry Coating: Contact Mechanics Based Predictive Approach

PURPOSE

To investigate the effect of dry coating the amount and type of silica on powder flowability enhancement using a comprehensive set of 19 pharmaceutical powders having different sizes, surface roughness, morphology, and aspect ratios, as well as assess flow predictability via Bond number estimated using a mechanistic multi-asperity particle contact model.

METHOD

Particle size, shape, density, surface energy and area, SEM-based morphology, and FFC were assessed for all powders. Hydrophobic (R972P) or hydrophilic (A200) nano-silica were dry coated for each powder at 25%, 50%, and 100% surface area coverage (SAC). Flow predictability was assessed via particle size and Bond number.

RESULTS

Nearly maximal flow enhancement, one or more flow category, was observed for all powders at 50% SAC of either type of silica, equivalent to 1 wt% or less for both the hydrophobic R972P or hydrophilic A200, while R972P generally performed slightly better. Silica amount as SAC better helped understand the relative performance. The power-law relation between FFC and Bond number was observed.

CONCLUSION

Significant flow enhancements were achieved at 50% SAC, validating previous models. Most uncoated very cohesive powders improved by two flow categories, attaining easy flow. Flowability could not be predicted for both the uncoated and dry coated powders via particle size alone. Prediction was significantly better using Bond number computed via the mechanistic multi-asperity particle contact model accounting for the particle size, surface energy, roughness, and the amount and type of silica. The widely accepted 200 nm surface roughness was not valid for most pharmaceutical powders.

Challenges encountered in the transfer of atorvastatin tablet manufacturing - commercial batch-based production as a basis for small-scale continuous tablet manufacturing tests

As is the case with batch-based tableting processes, continuous tablet manufacturing can be conducted by direct compression or with a granulation step such as dry or wet granulation included in the production procedure. In this work, continuous manufacturing tests were performed with a commercial tablet formulation, while maintaining its original material composition. Challenges were encountered with the feeding performance of the API during initial tests which required designing different powder pre-blend compositions. After the pre-blend optimization phase, granules were prepared with a roller compactor. Tableting was conducted with the granules and an additional brief continuous direct compression run was completed with some ungranulated mixture. The tablets were assessed with off-line tests, applying the quality requirements demanded for the batch-manufactured product. Chemical maps were obtained by Raman mapping and elemental maps by scanning electron microscopy with energy-dispersive X-ray spectroscopy. Large variations in both tablet weights and breaking forces were observed in all tested samples, resulting in significant quality complications. It was suspected that the API tended to adhere to the process equipment, accounting for the low API content in the powder mixture and tablets. These results suggest that this API or the tablet composition was unsuitable for manufacturing in a continuous line; further testing could be continued with different materials and changes in the process.

A concise summary of powder processing methodologies for flow enhancement

The knowledge of powder properties has been highlighted since the 19th century since most formulations focus on solid dosage forms, and powder flow is essential for various manufacturing operations. A poor powder flow may generate problems in the manufacturing processes and cause the plant's malfunction. Hence these problems should be studied and rectified beforehand by various powder flow techniques to improve and enhance powder flowability. The powder's physical properties can be determined using compendial and non-compendial methods. The non-compendial practices generally describe the powder response under the stress and shear experienced during their processing. The primary interest of the current report is to summarize the flow problems and enlist the techniques to eliminate the issues associated with the powder's flow properties, thereby increasing plant output and minimizing the production process inconvenience with excellent efficiency. In this review, we discuss powder flow and its measurement techniques and mainly focus on various approaches to improve the cohesive powder flow property.

Reviewing the Impact of Powder Cohesion on Continuous Direct Compression (CDC) Performance

The pharmaceutical industry is undergoing a paradigm shift towards continuous processing from batch, where continuous direct compression (CDC) is considered to offer the most straightforward implementation amongst powder processes due to the relatively low number of unit operations or handling steps. Due to the nature of continuous processing, the bulk properties of the formulation will require sufficient flowability and tabletability in order to be processed and transported effectively to and from each unit operation. Powder cohesion presents one of the greatest obstacles to the CDC process as it inhibits powder flow. As a result, there have been many studies investigating potential manners in which to overcome the effects of cohesion with, to date, little consideration of how these controls may affect downstream unit operations. The aim of this literature review is to explore and consolidate this literature, considering the impact of powder cohesion and cohesion control measures on the three-unit operations of the CDC process (feeding, mixing, and tabletting). This review will also cover the consequences of implementing such control measures whilst highlighting subject matter which could be of value for future research to better understand how to manage cohesive powders for CDC manufacture.

Enhanced blend uniformity and flowability of low drug loaded fine API blends via dry coating: The effect of mixing time and excipient size

Although previous research demonstrated improved flowability, packing, fluidization, etc. of individual powders via nanoparticle dry coating, none considered its impact on very low drug loaded blends. Here, fine ibuprofen at 1, 3, and 5 wt% drug loadings (DL) was used in multi-component blends to examine the impact of the excipients size, dry coating with hydrophilic or hydrophobic silica, and mixing times on the blend uniformity, flowability and drug release rates. For uncoated active pharmaceutical ingredients (API), the blend uniformity (BU) was poor for all blends regardless of the excipient size and mixing time. In contrast, for dry coated API having low agglomerate ratio (AR), BU was dramatically improved, more so for the fine excipient blends, at lesser mixing times. For dry coated API, the fine excipient blends mixed for 30 min had enhanced flowability and lower AR; better for the lowest DL having lesser silica, likely due to mixing induced synergy of silica redistribution. For the fine excipient tablets, dry coating led to fast API release rates even with hydrophobic silica coating. Remarkably, the low AR of the dry coated API even at very low DL and amounts of silica in the blend led to the enhanced blend uniformity, flow, and API release rate.

Improving the Effectiveness of the Conical Screen Mill as a Dry-Coating Process at Lab and Manufacturing Scale

The conical screen mill (comill) is investigated as a dry-coating process for flowability and bulk density enhancement of pharmaceutical powders. In this study, the effectiveness of the comill is improved by using modified screens with reduced open area. In comparison to the screens provided by the comill manufacturer, the modified screens increase mean residence time of the process and improve the extent of flowability and bulk density enhancement. The effectiveness of the comill as a dry-coating process is demonstrated using Avicel PH 105, a fine grade of microcrystalline cellulose, as a model cohesive powder. The process is evaluated thoroughly using a lab scale comill and scalability is demonstrated using a manufacturing scale model. The use of the modified screens is also compared against the so-called "multi-pass" approach in which material is passed through the comill, collected, and passed through once or several times. While the "multi-pass" approach is offered as a simple method to increase mean residence time and to improve process effectiveness, the use of the modified screens is shown to be the superior approach. Due to the ubiquitous use of the comill and the improvement in effectiveness attained in this study, dry-coating is shown to be a practical and readily implemented process for the pharmaceutical industry.

Reduced Fine API Agglomeration After Dry Coating for Enhanced Blend Uniformity and Processability of Low Drug Loaded Blends

PURPOSE

The impact of dry coating on reduced API agglomeration remains underexplored. Therefore, this work quantified fine cohesive API agglomeration reduction through dry coating and its impact on enhanced blend uniformity and processability, i.e., flowability and bulk density of multi-component blends API loading as low as 1 wt%.

METHODS

The impact of dry coating with two different types and amounts of silica was assessed on cohesion, agglomeration, flowability, bulk density, wettability, and surface energy of fine milled ibuprofen (~ 10 µm). API agglomeration, measured using Gradis/QicPic employing gentler gravity-based dispersion, resulted in excellent size resolution. Multi-component blends with fine-sized excipients, selected for reduced segregation potential, were tested for bulk density, cohesion, flowability, and blend content uniformity. Tablets formed using these blends were tested for tensile strength and dissolution.

RESULT

All dry coated ibuprofen powders exhibited dramatic agglomeration reduction, corroborated by corresponding decreased cohesion, unconfined yield strength, and improved flowability, regardless of the type and amount of silica coating. Their blends exhibited profound enhancement in flowability and bulk density even at low API loadings, as well as the content uniformity for the lowest drug loading. Moreover, hydrophobic silica coating improved drug dissolution rate without appreciably reducing tablet tensile strength.

CONCLUSION

The dry coating based reduced agglomeration of fine APIs for all three low drug loadings improved overall blend properties (uniformity, flowability, API release rate) due to the synergistic impact of a minute amount of silica (0.007 wt %), potentially enabling direct compression tableting and aiding manufacturing of other forms of solid dosing.

Decoding Fine API Agglomeration as a Key Indicator of Powder Flowability and Dissolution: Impact of Particle Engineering

PURPOSE

Fine API agglomeration and its mitigation via particle engineering, i.e., dry coating, remains underexplored. The purpose was to investigate agglomeration before and after dry coating of fine cohesive APIs and impact on powder processability, i.e., flowability (FFC), bulk density (BD), and dissolution of BCS Class II drugs.

METHOD

Ibuprofen (three sizes), fenofibrate, and griseofulvin (5-20 µm), before and after dry coating with varying amounts of hydrophobic (R972P) or hydrophilic (A200) nano- silica, were assessed for agglomeration, FFC, BD, surface energy, wettability, and dissolution. The granular Bond number (Bo_g), a dimensionless parameter, evaluated through material-sparing particle-scale measures and particle-contact models, was used to express relative powder cohesion.

RESULTS

Significant powder processability improvements after dry coating were observed: FFC increased by multiple flow regimes, BD increased by 25-100%, agglomerate ratio (AR) reduction by over an order of magnitude, and greatly enhanced API dissolution rate even with hydrophobic (R972P) silica coating. Scrutiny of particle-contact models revealed non-triviality in estimating API surface roughness, which was managed through the assessment of measured bulk properties. A power-law correlation was identified between AR and Bo_g and subsequently, between AR and FFC & bulk density; AR below 5 ensured improved processability and dissolution.

CONCLUSION

Agglomeration, an overlooked material-sparing measure for powder cohesiveness, was a key indicator of powder processability and dissolution. The significant agglomerate reduction was possible via dry coating with either silica type at adequate surface area coverage. Reduced agglomeration after dry coating also countered the adverse impact of increased surface hydrophobicity on dissolution.

Surface Modifiers on Composite Particles for Direct Compaction

Direct compaction (DC) is considered to be the most effective method of tablet production. However, only a small number of the active pharmaceutical ingredients (APIs) can be successfully manufactured into tablets using DC since most APIs lack adequate functional properties to meet DC requirements. The use of suitable modifiers and appropriate co-processing technologies can provide a promising approach for the preparation of composite particles with high functional properties. The purpose of this review is to provide an overview and classification of different modifiers and their multiple combinations that may improve API tableting properties or prepare composite excipients with appropriate co-processed technology, as well as discuss the corresponding modification mechanism. Moreover, it provides solutions for selecting appropriate modifiers and co-processing technologies to prepare composite particles with improved properties.

Improvements on multiple direct compaction properties of three powders prepared from Puerariae Lobatae Radix using surface and texture modification: comparison of microcrystalline cellulose and two nano-silicas

It has been reported that hydrophilic nano-silica (N) markedly improved direct compaction (DC) properties of Zingiberis Rhizoma alcoholic extract. This study aims to examine the broader scope and generality of the previous work by investigating (i) three powders, i.e., the directly pulverized product, ethanol extract, and water extract prepared from the same medicinal herb-Puerariae Lobatae Radix (named DP, EE, and WE) and (ii) the effects on their DC properties of co-processing with N, hydrophobic nano-silica (BN), or microcrystalline cellulose (C). Unexpectedly, C provided the best improvement on tabletability for WE, while N for both DP and EE. More importantly, only N could move all parent powders to a regime suitable for DC, and BN rather than C enabled parent WE to be directly compressed. Typically, 6/9 N-modified powders simultaneously met the requirements of DC on bulk density, flowability, and tablet tensile strength (σ_t). Principal component analysis indicated that DC properties were mainly governed by flowability and texture properties. The partial least-squares regression model revealed that flowability, texture parameters, and deformation behavior of powders were dominating factors impacting tablet σ_t and solid fraction. Overall, the findings are promising for the manufacture of high drug loading tablets of herbs by DC.

A Continuous Conical-Mill Operation for Dry Coating of Pharmaceutical Powders: The Role of Processing Time

Over the last decade, the conical mill has emerged as a potential piece of equipment to use for continuous dry coating pharmaceutical powders. In this work, silicon dioxide was used as a guest particle on two excipients, fast flow lactose (FFL) and grade PH200 microcrystalline cellulose (MCC), for dry coating by a conical mill with a modified screen that permitted batch and continuous mode operation. Samples were pre-processed in a V-blender. SEM images, particle size distribution, and EDS mapping were used to characterise the treated powders. Pre-processed samples showed some discrete coating of the host particle. After batch processing, the samples were covered with a complete coating. When processed at high impeller speed, coating of FFL was a mix of A200P and FFL fines generated by attrition. Continuous mode processed samples, which had a lower processing time, were coated discretely and showed a better coating than the pre-processed samples. Increasing guest/host mass ratio with FFL host particle had a positive impact on the quality of the coating. These results help to build the case that the processing time of the conical mill is a key parameter to the success of the conical mill as dry coating equipment in the pharmaceutical industry.

Impact of altered hydrophobicity and reduced agglomeration on dissolution of micronized poorly water-soluble drug powders after dry coating

The impact of dry coating with hydrophobic or hydrophilic nano-silica at 25-100% surface area coverage on dissolution of micronized poorly water-soluble drugs was investigated by examining their agglomeration and surface hydrophobicity. Ibuprofen (20 µm and 10 µm) and griseofulvin (10 µm) were selected having differing solubility, hydrophobicity, and surface morphology. Characterization involved particle agglomeration via two dry dispersion methods, drug dissolution using the USP IV method, cohesion reduction through shear testing, and powder wettability via the modified Washburn method. Dry coating dramatically reduced the cohesion hence agglomerate size of both the coated ibuprofen particles, but less for griseofulvin, attributed to its surface morphology. For hydrophobic silica, agglomerate size reduction outweighed the adverse impact of increased surface hydrophobicity for ibuprofen. For griseofulvin, the agglomerate reduction was much lower, not able to overcome the effect of increased drug particle hydrophobicity with hydrophobic silica coating. Hydrophilic silica coating reduced hydrophobicity for all three drug powders, leading to the synergistic improvement in the dissolution along with agglomerate size reduction. Overall, the combined effect of the drug particle surface hydrophobicity and agglomerate size, represented by specific surface area, could explain the dissolution behavior of these poorly water-soluble drugs.

Texture and surface feature-mediated striking improvements on multiple direct compaction properties of Zingiberis Rhizoma extracted powder by coprocessing with nano-silica

The study aims to markedly improve direct compaction (DC) properties of Zingiberis Rhizoma extracted powder (ZR) by modifying its texture and surface properties with nano-silica (NS). A wet coprocessing method was applied to evenly distribute up to 33.3% NS to ZR. To clarify uniqueness of NS, microcrystalline cellulose (MCC), a superior filler-binder in DC, was used as control. Coprocessed particles and physical mixtures (PMs) were comprehensively evaluated for surface features, micromeritic properties, and texture and compacting parameters. Compared to MCC, NS could more significantly modify the texture and surface features of ZR (e.g., hardness, cohesiveness, yield pressure, and nanoscaled surface roughness) via coprocessing, resulting in more striking improvements on multiple DC properties of ZR, including tabletability, flowability, lubricant sensitivity, hygroscopicity, etc. Especially, tensile strength (σ_t) of coprocessed ZR-NS (1:0.5) tablets was 4.62 and 3.22 times that of ZR and ZR-MCC counterparts pressed at 210 MPa, respectively. Moreover, percolation thresholds of σ_t enhancement were observed for ZR-NSs, but not for ZR-MCCs. Evaluation by the SeDeM expert system indicated that some ZR-NSs (but no ZR-MCCs) were qualified for DC. Collectively, coprocessing with NS by liquid dispersion appears to be a novel, effective, and pragmatic option for DC of drugs like ZR.

Systematic development of a high dosage formulation to enable direct compression of a poorly flowing API: A case study

In this work, the transfer of oral solid dosage forms, currently manufactured via wet granulation, to a continuous direct compression process was considered. Two main challenges were addressed: (1) a poorly flowing API (Canagliflozin) and (2) high drug loading (51 wt%). A scientific approach was utilised for formulation development, targeting flow and compaction behaviour suitable for manufacturing scale. This was achieved through systematic screening of excipients to identify feasible formulations. Targeted design of experiments based on factors such as formulation mixture and processing parameters were utilised to investigate key responses for tablet properties, flow and compaction behaviour. Flow behaviour was primarily evaluated from percentage compressibility and shear cell testing on a powder flow rheometer (FT4). The compaction behaviour was studied using a compaction simulator (Gamlen). The relationships between tablet porosity, tensile strength and compaction pressure were used to evaluate tabletability, compactibility and compressibility to assess scale-up. The success of this design procedure is illustrated by scaling up from the compaction simulator to a Riva Piccola rotary tablet press, while maintaining critical quality attributes (CQAs). Compactibility was identified as a suitable scale-up relationship. The developed procedure should allow accelerated development of formulations for continuous direct compression.

Influence of Material Properties on the Effectiveness of Glidants Used to Improve the Flowability of Cohesive Pharmaceutical Powders

This study investigated the effect of material properties, primarily particle size and surface energy, on the effectiveness of glidants used for the purpose of flowability enhancement. Three pharmaceutical grade glidants (Aerosil 200, Aerosil R972, and Cab-O-Sil M5P) were evaluated and blended with various pharmaceutical actives as well as cohesive excipients common to capsule and tablet formulation. Flowability enhancement was characterized by the flow function coefficient (ff _c ). An industry-relevant mixer (Turbula mixer) and a highly efficient and effective mixer (LabRAM vibratory mixer) were used to further understand the effect of material properties on glidant effectiveness. While concepts of inter-particle cohesion and interaction strength were applied to evaluate their usefulness in understanding and predicting flowability enhancement, theoretical expectations did not fully explain the behavior of all three glidants. However, the study suggests that the low surface energy and optimal particle size of Aerosil R972 relative to the other glidants results in lower inter-particle force and consequently better flowability. Aerosil R972 was also shown to be more effectively utilized in the Turbula mixing process particularly for larger (d₅₀ > 40 μm) and less cohesive (ff _c  > 3) materials. This may be due to its lower surface energy and hydrophobic surface which allows it to disperse easily. Overall, this study provides useful insight into the material properties which influence the effectiveness of glidants used in formulation development.

Crystal and Particle Engineering Strategies for Improving Powder Compression and Flow Properties to Enable Continuous Tablet Manufacturing by Direct Compression

Continuous manufacturing of tablets has many advantages, including batch size flexibility, demand-adaptive scale up or scale down, consistent product quality, small operational foot print, and increased manufacturing efficiency. Simplicity makes direct compression the most suitable process for continuous tablet manufacturing. However, deficiencies in powder flow and compression of active pharmaceutical ingredients (APIs) limit the range of drug loading that can routinely be considered for direct compression. For the widespread adoption of continuous direct compression, effective API engineering strategies to address power flow and compression problems are needed. Appropriate implementation of these strategies would facilitate the design of high-quality robust drug products, as stipulated by the Quality-by-Design framework. Here, several crystal and particle engineering strategies for improving powder flow and compression properties are summarized. The focus is on the underlying materials science, which is the foundation for effective API engineering to enable successful continuous manufacturing by the direct compression process.

Effects of Coating Materials and Processing Conditions on Flow Enhancement of Cohesive Acetaminophen Powders by High-Shear Processing With Pharmaceutical Lubricants

This study has investigated the surface coating efficiency and powder flow improvement of a model cohesive acetaminophen powder by high-shear processing with pharmaceutical lubricants through 2 common equipment, conical comil and high-shear mixer. Effects of coating materials and processing parameters on powder flow and surface coating coverage were evaluated. Both Carr's index and shear cell data indicated that processing with the lubricants using comil or high-shear mixer substantially improved the flow of the cohesive acetaminophen powder. Flow improvement was most pronounced for those processed with 1% wt/wt magnesium stearate, from "cohesive" for the V-blended sample to "easy flowing" for the optimally coated sample. Qualitative and quantitative characterizations demonstrated a greater degree of surface coverage for high-shear mixing compared with comilling; nevertheless, flow properties of the samples at the corresponding optimized conditions were comparable between 2 techniques. Scanning electron microscopy images demonstrated different coating mechanisms with magnesium stearate or l-leucine (magnesium stearate forms a coating layer and leucine coating increases surface roughness). Furthermore, surface coating with hydrophobic magnesium stearate did not retard the dissolution kinetics of acetaminophen. Future studies are warranted to evaluate tableting behavior of such dry-coated pharmaceutical powders.