CELLETS® are pellets or spheres made of microcrystalline cellulose. The size ranges from 100 µm to 1400 µm. Being neutral starter cores, they can be used as carrier system for low-dosed APIs and allow diverse functional coating. See pellet technologies for a detailed description.


Electron microscopy yield perfect imaging data of the MCC pellets’ surfaces. Magnification: 250x, working distance 8.0 mm, voltage: 10 keV.

Available size classes are (click for more information):

  • CELLETS® 100
  • CELLETS® 200
  • CELLETS® 350
  • CELLETS® 500
  • CELLETS® 700
  • CELLETS® 1000

Any size class of CELLETS® have same striking advantages:

  • low friability and extreme hardness
  • insolubility in water
  • high spherictity
  • smooth surface
  • good monodispersity

See case studies to see these starter pellets in action!

Comparison of Mini-Tablets and Pellets as Multiparticulate Drug Delivery Systems for Controlled Drug Release


Mini-tablets made into hard capsules or administered using special dosing units, as well as pellets in hard capsules or compressed into tablets, offer the advantages of multiparticulate drug delivery systems and are suitable for controlled drug release using polymer coatings. Four different kinds of solid drug preparations were manufactured and investigated concerning drug release. Inert pellets were coated with the model drug sodium benzoate and, in a second step, with the insoluble polymer ethylcellulose. The coated pellets were compressed into mini-tablets and into normal tablets. Another kind of mini-tablet was compressed from a sodium benzoate compression mixture and finally coated with ethylcellulose. The coating of the tablets was performed using fluidized bed technology. The sodium benzoate release plots of the coated pellets show a lag time and retarded release according first-order kinetics. The mini-tablets and normal tablets compressed from pellets release sodium benzoate according to first-order kinetics as well, but without the lag time due to distinct ethylcellulose layer destruction during tableting. The release is retarded with increasing ethylcellulose layer thickness on directly compressed mini-tablets. The different formulations of coated pellets, mini-tablets, and normal tablets offer a broad choice for variable drug release kinetics depending on the biopharmaceutical and pharmacological requirements.


Drug- and polymer-coated pellets may be compressed into mini-tablets as well as into normal tablets. Pellets and mini-tablets compressed into tablets as a multiparticulate drug delivery system offer the advantage of being widely spread in the small intestine for improved drug absorption and increased bioavailability compared to normal tablets. With both tablet types (normal and mini), the sodium benzoate release is delayed depending on the thickness and properties of the ethylcellulose film on the pellets.
Ethylcellulose-coated mini-tablets obtained through the direct compression of sodium benzoate and excipients are an alternative method for multiparticulate drug delivery system preparation. The product is characterized by a slow release rate depending on the ethylcellulose film thickness that may be suitable when prolonged release is required. The variation in release is increased compared to pellets and normal multiple-unit tablets with pellets. Sodium benzoate layering on pellets in the fluidized bed and the subsequent tableting process are feasible for both mini-tablets and normal tablets, representing an interesting option when a variation in the final pharmaceutical form is required for marketing/patenting reasons.


F. Priese, D. Wiegel, C. Funaro, G. Mondelli, and B. Wolf
Coatings 202313(11), 1891; https://doi.org/10.3390/coatings13111891

Read more

Read more about how CELLETS 200 are employed in mini-tablets and pellets as multiparticulate drug delivery systems by F. Priese et al. here.

The primary objective of this research is to investigate the design and size on particle coating thickness. Furthermore,  illustrate how the design, size, and configurations of fluid-bed coating machinery influence variations in pellet coating thickness. This parameter plays a crucial role in governing the release of medication in prolonged-release pellets. Initially, the scientists conducted a series of coating experiments where the pellet cores were coated with Tartrazine dye. The aim was to evaluate the performance of the coating equipment in terms of the distribution of coating thickness, which was assessed based on color hue.

In the subsequent set of experiments, drug-layered pellets underwent film-coating with prolonged-release material. Brezovar et al. conducted dissolution profile tests to gauge the uniformity and thickness of the coating among pellets of different sizes. Pellets of kind CELLETS® 700 (IPC Dresden, Germany) had been employed. This investigation encompassed both laboratory and pilot scale applications. Laboratory-sized fluid-bed coaters GPCG1 (Glatt GmbH, Germany and BX FBD10, Brinox d.o.o., Slovenia) and a pilot-sized (BX FBD30, Brinox d.o.o., Slovenia) fluid-bed coater are used for these tests. The group made comparisons between two types of distribution plates and various adjustments in the height of the draft tube.

The dye coating study yielded highly valuable insights. The results provided the basis for refining the process and optimizing the utilization of process equipment, especially in conjunction with the appropriate process parameters. On the laboratory scale, we observed a preference for film coating larger drug-containing pellets. However, on the pilot scale, we achieved a preferential coating of smaller pellets through judicious adjustments, a development that holds significance in achieving a drug release profile independent of particle size for prolonged-release dosage forms.

Link to publication:

The Effect of Design and Size of the Fluid‑Bed Equipment on the Particle Size‑Dependent Trend of Particle Coating Thickness and Drug Prolonged‑Release Profile
AAPS PharmSciTech (2023) 24, 93. doi:10.1208/s12249-023-02540-9
T. Brezovar, G. Hudovornik, M. Perpar, M. Luštrik, R. Dreu


Pellets are one of multiparticulate pharmaceutical forms and can offer numerous technical and biopharmaceutical advantages compared with single dose unit formulations, e.g. tablets and capsules. This study aimed at formulation of controlled-release pellets of doxazosin mesylate (DM), a widely used treatment for antihypertensive and benign prostatic hyperplasia. DM was loaded onto microcrystalline cellulose CELLETS® pellets using hydroalcoholic solution and alcoholic suspension layering techniques to achieve a minimum drug load of 4 mg DM/g pellets. DM-layered CELLETS were coated by Aquacoat dispersion (ready-made ethylcellulose dispersion) using a coating pan technique as a simple and widely utilized technique in pharmaceutical industry. Controlled-release DM-layered pellets showed a release profile comparable to the controlled-release commercial product Cardura® XL Tablet. Also, the mechanism of DM release from Aquacoat CELLETS® was mathematically modeled and imaged by scanning electron microscopy to elucidate drug release mechanisms from the prepared pellet formulations. Accelerated stability studies of the prepared pellets were performed under stress conditions of 40 °C, and 75 % RH for 3 months. In conclusion, preparation of controlled-release DM-layered CELLETS® is feasible using a simple and conventional coating pan technology. Read more about controlled-release doxazosin mesylate pellets.


H. A. Hazzah, M. A. EL-Massik, O. Y. Abdallah & H. Abdelkader, Journal of Pharmaceutical Investigation (2013), 43:333–342. doi:10.1007/s40005-013-0077-0

Additional information

CELLETS® are perfect starter beads for coating and layering of API, such as doxazosin mesylate. Multilayer formulation attempts enable defined release profiles and improved bioavailability. Check different pellet sizes from 100 µm to 1400 µm which fit to your formulation.

Need formulation services?

Contact our partner Glatt Pharmaceutical Services!

Pore Former basic drugs


Bioavailability of weakly basic drugs may be disrupted by dramatic pH changes or unexpected pH alterations in the gastrointestinal tract. Conventional organic acids or enteric coating polymers cannot address this problem adequately because they leach out or dissolve prematurely, especially during controlled release applications. Thus, a non-leachable, multifunctional terpolymer nanoparticle (TPN) made of cross-linked poly(methacrylic acid) (PMAA)-polysorbate 80-grafted-starch (PMAA-PS 80-g-St) was proposed to provide pH transition-independent release of a weakly basic drug, verapamil HCl (VER), by a rationally designed bilayer-coated controlled release bead formulation. The pH-responsive PMAA and cross-linker content in the TPN was first optimized to achieve the largest possible increase in medium uptake alongside the smallest decrease in drug release rate at pH 6.8, relative to pH 1.2. Such TPNs maintained an acidic microenvironmental pH (pHm) when loaded in ethylcellulose (EC) films, as measured using pH-indicating dyes. Further studies of formulations revealed that with the 1:2 VER:TPN ratio and 19% coating weight gain, bilayer-coated beads maintained a constant release rate over the pH transition and exhibited extended release up to 18 h. These results demonstrated that the multifunctional TPN as a pHm modifier and pH-dependent pore former could overcome the severe pH-dependent solubility of weakly basic drugs.


Many existing active pharmaceutical ingredients (APIs) (drug compounds) are either weak acids or weak bases; their water solubility can change significantly with the lumen pH changes along the gastrointestinal tract (GIT) as a result of variation in the ionization degree. Severe pH-dependent solubility could pose a great challenge to achieving consistent and predictable performance of oral dosage forms, as abrupt changes in release rate may result in unexpected dissolution, absorption, and bioavailability of the drug, leading to increased risks of adverse side effects or decreased therapeutic efficacy. This problem may be pronounced for weakly basic drugs with low solubility at high pH, especially those with a narrow therapeutic index, or requiring prolonged release, because in the lower GIT the pH is >6.8 [1]. Furthermore, food intake, disease state (e.g., inflammatory bowel disease, gastritis, colitis), concomitant medication (e.g., proton pump inhibitors), and inter- and intra-individual variations, among other factors, can alter the pH in the GIT, which deviates from the pH of simulated gastric and intestinal fluid for in vitro testing and prediction [2,3,4]. Hence, novel strategies to formulate weakly basic drugs with extreme pH-dependent solubility in controlled release forms could enhance the repertoire of advanced medications available to patients.
To compensate for the varying pH values in the GIT, several approaches have been employed. One approach is the addition of small-molecule pH modifiers to the immediate vicinity of the drug to change the microenvironmental pH (pHm), thus enhancing the drug solubility. For example, organic acids (e.g., adipic, fumaric, and succinic acids) have been introduced into formulations of weakly basic drugs, reducing the pHm sufficiently, thereby facilitating drug dissolution, irrespective of the pH of the bulk solvent [5,6,7,8,9,10,11]. Drug release will depend on the compatibility of the organic acid with the drug in terms of the buffering capacity of organic acids and the pKa of the drug. Nevertheless, the incorporation of organic acids remains challenging as they are prone to leach out from the formulation, leading to inefficient pH modulation over time [12]. Therefore, large amounts of organic acids are required in order to achieve prolonged pH-independent drug release [5,13], which often makes this approach inadequate for controlled release formulations.
Another approach to compensate for the reduction in drug solubility is the use of enteric coating polymers on tablets, pellets, or beads as permeability modifiers, which can increase drug permeability at higher pH. In such coatings, polymers with pH-dependent solubility or swellability are employed, either alone or incorporated in a hydrophobic polymer (e.g., ethylcellulose (EC)) that acts as a membrane barrier to drug diffusion, resulting in slowed drug release. For example, methacrylic acid–ethyl acrylate copolymer (Eudragit® L) and hydroxypropyl methylcellulose acetate succinate are frequently incorporated into these membranes as pore forming materials for pH-dependent release [13,14,15,16,17,18,19,20,21,22,23]. At a pH above their pKa’s, the pore formers dissolve and leach out of the membrane film to form channels that facilitate drug diffusion. However, as pore formers leach out, the film becomes more porous and weaker, increasing the risk of dose dumping due to weakened structure or ruptures of the coating [24].
Recent advances using biopolymer-based nanomaterials, molecular imprinted polymers, and mathematical and computational models have been used to address the various challenges of drug delivery systems [25,26,27,28,29]. Biopolymers such as starch, collagen, chitosan, etc., are useful for their biocompatibility, biodegradability, and ease of synthesis and modifications [25]. Controlled release dosage forms capable of being flexible, releasing drugs in a timely manner, with desired duration and dosage, are more important than ever, and mathematical and computational models also function as influential tools in addressing the potential mechanisms or impediments of drug delivery systems [26,27,28,29].
Previously, a crosslinked terpolymer nanoparticle (TPN), consisting of poly(methacrylic acid)-polysorbate 80-grafted-starch (PMAA-PS 80-g-St) [30,31,32,33], was incorporated into ethylcellulose films (TPN-EC) to respectively reduce or enhance the permeability of the film coating by a pH-dependent shrinking (at low pH) and swelling (at high pH) mechanism [34]. Unlike other soluble polymeric pore-formers, the TPN did not increase the viscosity of EC dispersions for coating, attributable to its crosslinking structure [31,32,33]. For the same reason, TPN did not leach out from cast TPN-EC films, maintaining good mechanical properties compared to conventional Eudragit® L-EC films. When used as a membrane coating over beads loaded with a water-soluble drug, diltiazem HCl, TPN-EC provided faster drug release at pH 6.8 than at pH 1.2 [34]. The biocompatibility of TPN was demonstrated previously in vitro using isolated rat hepatocytes [32].
Inspired by previous findings regarding the pH-dependent properties of TPN, in this work, we explore the application of TPN for the first time to develop an advanced, controlled release bilayer-coated bead formulation for weakly basic drugs that exhibits severe pH-dependent water solubility. Verapamil HCl (VER) was selected as a model drug because it undergoes extreme decrease in solubility by several orders of magnitude when the media pH is increased from acidic to neutral and weakly basic conditions [9,35]. By exploiting the pH-dependence of TPN, we proposed that an increase in permeability at high pH could help compensate for the low solubility of the drug in its unionized form, thereby permitting a constant release rate when transitioning from gastric to intestinal pH. Additionally, we explored the ability of TPN to serve as a pHm modifier, owing to the presence of its acidic functional groups in MAA. Because TPN is retained within EC, unlike traditional leachable pHm modifiers when formulated together with the drug in a matrix, the source of the acidifying agent could be sustained throughout dissolution, while preserving dosage form integrity.
To investigate the effectiveness of combining both the permeability and the pHm modulation strategies of TPN, experiments were performed using EC matrix free-films incorporated with VER and TPN (VER-TPN-EC) and a bilayer-coated bead design consisting of an inner VER-TPN-EC matrix, surrounded by an outer membrane composed of TPN-EC. As illustrated in Figure 1, the TPN composition was first adjusted by varying the amounts of the pH-responsive monomer, MAA, and cross-linker, N,N′-methylenebis(acrylamide) (MBA) for pH-dependent swelling (medium uptake) and drug release via experiments using composite free-films. The best-performing TPN-containing films were then tested for their ability to lower pHm. Subsequently, the TPN was incorporated into a bilayer-coated bead design, where it was expected to lower the pHm in the matrix layer and regulate permeability in the membrane layer by its pH-dependent swelling. The effects of formulation parameters such as VER:TPN ratio within the matrix layer and membrane coating level on the pH-independence of dissolution rate in various pH conditions were evaluated.
Figure 1. A flow chart of the optimization strategy to achieve pH transition-independent controlled release of VER from a TPN-containing bilayer-coated beads. Formulation strategy for TPN bilayer-coated beads containing weakly basic VER Optimization of TPN composition to achieve pHm modification and pH-dependent swelling, followed by strategic placement of TPN in the bilayer bead matrix and membrane layers are proposed to overcome pH-dependent solubility of VER. Figure created with BioRender.com (accessed on 15 December 2022).
Our cumulative research investigating the various applications of TPN (e.g., nanoparticle drug carrier in injectables, enteric coating agent and pore former in film coatings, recrystallization inhibitor in amorphous solid dispersions) is helping us widen the breadth of its capabilities. Namely, in the present research, the ability of TPN for pHm modification, pH-responsive swelling, nanoscale pore formation, interaction with drugs, and non-leachability comprise a set of multi-faceted features that set it apart from traditional excipients, which could improve the efficacy and quality of controlled release dosage forms for weakly basic drugs. As the landscape of new drug molecules continues to shift towards greater challenges (e.g., poor solubility, pH-dependent solubility, narrow therapeutic index, etc.) the need for more advanced, multifunctional excipients can be expected to increase.

Materials and Methods

2.1. Materials

Soluble corn starch, methacrylic acid (MAA), N,N′-methylenebisacrylamide (MBA), sodium thiosulfate (STS), potassium persulfate (KPS), sodium dodecyl sulfate (SDS), and sodium phosphate tribasic were purchased from Sigma Aldrich (Oakville, ON, Canada). Verapamil HCl (VER) was purchased from Spectrum Chemicals, (New Brunswick, NJ, USA). Hydrochloric acid (HCl) was purchased from Caledon (Georgetown, ON, Canada). SNARF-4F (#S23920) was purchased from Fisher Scientific (Ottawa, ON, Canada). Bromocresol green was purchased from Sigma Aldrich (Oakville, ON, Canada). Ethylcellulose (Surelease® E-7-19040) was kindly donated by Colorcon (West Point, PA, USA). Polyvinylpyrrolidone (PVP) (Kollidon®/PVPK30) was kindly donated by BASF (Ludwigshaven, Germany). Polysorbate 80 (Tween 80-LQ-(CQ)) was kindly donated by Croda (Edison, NJ, USA). Microcrystalline cellulose (MCC) beads ([…] annotation from the publisher: for example: CELLETS® 700) were used as the coating substrate […].


In this work, the multifunctionality of a nanogel TPN was investigated as a non-leachable pHm modifier and pH-responsive pore former in a bilayer-coated bead formulation for the pH transition-independent controlled release of weakly basic drugs. The results demonstrated that incorporation of TPN, comprised of pH-sensitive MAA and cross-linker MBA, enables the inner matrix layer of VER-TPN-EC to maintain a pHm approximately 1.5 unit lower than the external buffer pH, which may be further enhanced by coating with a TPN-EC membrane. In a simulated gastric and intestinal pH transition condition (i.e., from pH 1.2 to 6.8), the bilayer-coated beads with 16% to 19% WG resulted in a constant release rate during the pH transition, followed by a sustained release of VER up to 18 h, beyond the extent achieved when tested in single pH media. This ability to overcome the poor solubility of VER at high pH can be ascribed to the combinatory effects of the pH-dependent swelling of TPN that increased permeability, preferred retention of protons in the TPN due to Donnan equilibrium, pH-dependent complexation between MAA and VER, and the barrier to diffusion of buffer ions by the outer coating. This work suggests that the multifunctionality and tunability of TPN-EC formulations and the formulation design strategy may be expanded to tackle the challenges faced by other drugs with severe pH-dependence of water solubility.


Excerpt from: Pharmaceutics 2023, 15(2), 547; https://doi.org/10.3390/pharmaceutics15020547. by Hao Han R. Chang, Kuan Chen, Jamie Anne Lugtu-Pe, Nour AL-Mousawi, Xuning Zhang, Daniel Bar-Shalom, Anil Kane, and Xiao Yu Wu.


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Amorphous Solid Dispersions Layered onto Pellets - An Alternative to Spray Drying

This article “Amorphous Solid Dispersions Layered onto Pellets – An Alternative to Spray Drying?” is an excerpt from the publication of Neuwirth et al., Pharmaceutics 2023, 15(3), 764; https://doi.org/10.3390/pharmaceutics15030764.


Spray drying is one of the most frequently used solvent-based processes for manufacturing amorphous solid dispersions (ASDs). However, the resulting fine powders usually require further downstream processing when intended for solid oral dosage forms. In this study, we compare properties and performance of spray-dried ASDs with ASDs coated onto neutral starter pellets in mini-scale. We successfully prepared binary ASDs with a drug load of 20% Ketoconazole (KCZ) or Loratadine (LRD) as weakly basic model drugs and hydroxypropyl-methyl-cellulose acetate succinate or methacrylic acid ethacrylate copolymer as pH-dependent soluble polymers. All KCZ/ and LRD/polymer mixtures formed single-phased ASDs, as indicated by differential scanning calorimetry, X-ray powder diffraction and infrared spectroscopy. All ASDs showed physical stability for 6 months at 25 °C/65% rH and 40 °C/0% rH. Normalized to their initial surface area available to the dissolution medium, all ASDs showed a linear relationship of surface area and solubility enhancement, both in terms of supersaturation of solubility and initial dissolution rate, regardless of the manufacturing process. With similar performance and stability, processing of ASD pellets showed the advantages of a superior yield (>98%), ready to use for subsequent processing into multiple unit pellet systems. Therefore, ASD-layered pellets are an attractive alternative in ASD-formulation, especially in early formulation development at limited availability of drug substance.


The model drugs ketoconazole (KCZ) and loratadine (LRD) were purchased from Sris Pharmaceuticals (Hyderabad, India). HPMCAS LG (hydroxypropyl-methylcellulose acetate succinate, wt%: methoxyl 20–24%, hydroxypropyl 5–9%, succinyl 14–18%; Mw = 18,000, HPMC-AS) was donated from Shin-Etsu Chemical (Tokyo, Japan). Eudragit L100-55 (methacrylic acid ethylacrylate copolymer, ratio 1:1, Mw = 320,000, EL100-55) was donated by Evonik (Darmstadt, Germany). Cellets 1000 (microcrystalline cellulose starter pellets, 1000–1400 µm) were provided by Glatt Pharmaceutical Services (Binzen, Germany). A detailed list of the pellets’ characteristics is shown in Table 1. Ethanol 96% (v/v) (technical grade) used in the sample preparation, and methanol (analytical grade) used for the HPLC analytics as well as the buffer salts disodium mono-hydrogen phosphate dodecahydrate (Na2HPO4·12H2O) and monosodium dihydrogen phosphate dodecahydrate (NaH2PO4·12H2O) were obtained from VWR Chemicals GmbH (Darmstadt, Germany).
Pellet Properties
d50 (xc min) [µm] 1123.44
SPAN 0.166
b/l 0.893
SPHT 0.956
Particle density [g/cm3] 1.452
Sm [cm2/g] 36.41

Table 1. Pellet properties of Cellets 1000. d50: mean particle diameter determined by the particle width; SPAN: width of the particle distribution; b/l: aspect ratio; SPHT: sphericity; Sm: specific surface area.

Pellet Coating (PC)
For pellet coating (PC) a laboratory scale fluid bed system Mini Glatt equipped with a Micro-Kit (Glatt GmbH, Binzen, Germany) was used. The coating was applied with a 0.5 mm two-fluid nozzle in bottom spray using the special bottom plate of the Micro-Kit to emulate a three-fluid nozzle with micro-climate. In the beginning, the machine was filled with 25.0 g of Cellets® 1000. The following process parameters were maintained throughout the process: Process gas flow 30 m3/h, product temperature 30.0 ± 1.0 °C (resulting inlet temperature 32–35 °C), spray pressure 1.5 bar and spray rate 1.0 ± 0.2 g/min. The final pellets had a theoretical drug-load of 10% (w/w) due to the fact that ASD and core pellets were used in a 1:1-ratio. […] To prepare the spraying solutions, the API and polymer were dissolved in ethanol 96% (v/v) under continuous stirring (solid content of 10% (w/w)). Prior to spraying, each solution was sonicated for 15 min to ensure complete dissolution of the components.
Subsequently, the coated pellets were manually sieved with a 2 mm mesh to eliminate multicore pellets. The pellets were dried under vacuum for 24 h at the same conditions as the SD powder.


In this study, we successfully prepared binary single phase ASDs of KCZ and LRD as weakly basic, slow crystallizing model APIs (drug load 20% (w/w)) using HPMC-AS or EL100-55 as pH-dependent soluble polymers via fluid bed pellet coating and spray drying. While the received ASD-pellets would not require further downstream processing other than capsule filling or tableting, the fine SD powder had to be transformed into dry granules. In combination with the slow crystallizers, KTZ and LOR, both manufacturing processes resulted in single-phased ASDs of high physical stability (up to 6 months) and similar dissolution performance when normalized to the total outer surface. The dissolution rate depends mainly on this total outer particle surface of the respective sample, independent of the manufacturing process, while the porosity of the sample had a minor impact on its dissolution behavior.
Especially for early formulation development, the high yield and ease of handling due to the pellet properties are strong advantages over the standard spray drying process. Nevertheless, the long process time in larger scale requires further process optimization in fluidized bed processing.
Amorphous solid dispersions Cellets 20230302

Figure: Amorphous solid dispersions.

[1] Neuwirth et al., Pharmaceutics 2023, 15(3), 764; https://doi.org/10.3390/pharmaceutics15030764

Benefits of multilayer high drug-loaded amorphous solid dispersions

Introduction on amorphous solid dispersions

What is the benefit of multilayer amorphous solid dispersions? Recently, several studies had been performed on amorphous solid dispersions working spheres or starter beads. Starter beads, such as MCC (Microcrystalline Cellulose) spheres are employed due to their high friability and chemical inertness. Some studies are even working on solventless pelletization and amorphization using high shear granulator techniques [1].

Amorphization of poorly water-soluble drugs is a promising approach to improve the solubility and dissolution rate as amorphous solids lack a crystal lattice with long-range order [2]. Unfortunately, a high chemical potential compared to crystalline forms makes amorphous forms thermodynamically unstable. Thus, amorphous drugs exhibit low physical stability and finally lack of recrystallization [3,4]. In turn, surface crystallization is to be minimized.

Multilayer amorphous solid dispersions

This is the key focus of a publication by Eline Boel and Guy Van den Mooter: They had been investigating a promising solution of multilayer high-drug load amorphous solid dispersions, as follows [5]:

Inhibiting surface crystallization is an interesting strategy to enhance the physical stability of amorphous solid dispersions (ASDs), still preserving high drug loads. The aim of this study was to investigate the potential surface crystallization inhibitory effect of an additional polymer coating onto ASDs, comprising high drug loads of a fast crystallizing drug, layered onto pellets. For this purpose, bilayer coated pellets were generated with fluid-bed coating, of which the first layer constitutes a solid dispersion of naproxen (NAP) in poly(vinylpyrrolidone-co-vinyl acetate) (PVP-VA) in a 40:60 or 35:65 (w/w) ratio, and ethyl cellulose (EC) composes the second layer. The physical stability of these double-layered pellets, in comparison to pellets with an ASD layer only, was assessed under accelerated conditions by monitoring with X-ray powder diffraction (XRPD) at regular time intervals. Bilayer coated pellets were however found to be physically less stable than pellets with an ASD layer only. Applying the supplementary EC coating layer induced crystallization and heterogeneity in the 40:60 and 35:65 (w/w) NAP-PVP-VA ASDs, respectively, attributed to the initial contact with the solvent. Caution is thus required when applying an additional coating layer on top of an ASD layer with fluid-bed coating, for instance for controlled release purposes, especially if the ASD consists of high loads of a fast crystallizing drug.

Read more on doi:10.1016/j.ijpharm.2022.122455.

How about following up studies on ASD formulation with starter beads? Simply, contact us für MCC spheres, such as CELLETS® 700 (700-1000 µm, US mesh 18/25).

Your technology and formulation partner for amorphous solid dispersions:

Glatt in amorphous solid dispersions


[1] K. Kondo, T. Rades, European Journal of Pharmaceutics and Biopharmaceutics 181 (2022) 183–194 doi:10.1016/j.ejpb.2022.11.011

[2] B.C. Hancock, M. Parks, Pharm. Res. 17 (2000) 397-404.

[3] L.I. Blaabjerg, E. Lindenberg, T. Rades, H. Grohganz, K. Lobmann, Int. J. Pharm. 521 (2017) 232-238.

[4] A. Singh, G. Van den Mooter, Adv. Drug Deliv. Rev. 100 (2016) 27-50.

[5] E. Boel, G. Van den Mooter, International Journal of Pharmaceutics (2022) 122455. doi:10.1016/j.ijpharm.2022.122455


We identified, that amorphous solid dispersions gain in importance as they increase the solubility and dissolution rate of poorly water-soluble drugs. There are severall attempts, in which each of them positive aspects and certain issues occur. It’s time, drawing amorphous solids dispersions in a more general context and sheding some more light on elementary aspects. We like to point on an excellent summary given by Thomas Rades and Keita Kondo [Rades_2022]. Before switching over, we like to emphasis and anticipate one message: The lastest attempts for amorphous solid dispersions is using CELLETS® 175 (MCC spheres) which do not only act as drug carrier, but – due to best friability – as milling balls. You might like follow this attempt with MCC starter beads, so please contact us for getting some materials. Let’s now read more from Rades et al.:

Draw-back on Amorphous solid dispersions

Amorphization is a promising approach to improve the solubility and dissolution rate of poorly water-soluble drugs as amorphous solids lack a crystal lattice with long-range order [1]. However, since amorphous forms are thermodynamically unstable due to a high chemical potential compared to crystalline forms, amorphous drugs exhibit low physical stability and finally recrystallizes [2], [3]. Thus, strategies to stabilize amorphous forms are essential in the development of amorphous products and include the design of amorphous solid dispersions (ASDs) [4], [5] and co-amorphous formulations [6], [7], [8]. ASDs are the most common approach for preparing amorphous products and involve glass formation by molecularly dispersing drug compounds into an amorphous polymer [4], [5]. However, ASD preparations may require a large quantity of polymer to stabilize amorphized drug due to their low miscibility with drug molecules [9], leading to a high bulk volume of the amorphous products. Co-amorphous systems have recently attracted attention as an alternative approach to amorphous formulations and include the formation of a single amorphous phase in which multiple low molecular weight initially crystalline materials (including drug compounds) are uniformly mixed at the molecular levels [6], [7], [8]. Co-amorphous mixtures typically exhibit high physical stability and dissolution characteristics [6], [7], [10].

Co-amorphous systems are typically classified as drug-drug combinations and drug-excipient mixtures. In the former combinations, amorphous phases comprise two drug compounds, which act as a stabilizer for each other by forming intermolecular interactions [11], [12], [13]. These formulations are expected to offer a combination of drugs to enhance the therapeutic effects but their applicability is limited as drug-drug combinations forming co-amorphous solids are not necessarily suitable for combination therapy, or require fixed doses, not necessarily suitable for co-amorphization. In the co-amorphous drug-excipient systems, low molecular-weight substances (including organic acids [14], sugars [15] and amino acids [16]) act as a co-former and their properties and mixing ratio with the drug affect dissolution characteristics and physical stability of the resulting co-amorphous mixtures [8], [10]. Recently, various combinations of drug compounds and amino acids were systematically investigated [17], [18], indicating that co-amorphous mixtures with high dissolution characteristics and physical stability can be produced by selecting amino acids that can form interactions with the target drug compounds (e.g. pairs of acidic drugs and basic amino acids). Therefore, amino acids are a promising co-former class for co-amorphous formulations.

Preparation of co-amorphous mixtures has been reported using melt quenching [13], [19], spray drying [20], [21], and ball milling [16], [22]. Since the resulting solids are in cake or powder forms (regardless of the preparation method), downstream processes including milling and granulation are usually essential to produce final dosage forms such as capsules and tablets for oral administration [23]. These processes can lead to increased risk of phase separations and crystallization due to moisture, thermal, and mechanical stresses. In ASD systems, to avoid the problems due to the downstream processes, one-step preparations of ASD granules by amorphizing drug compounds during the granulation process using fluidized bed processors [24], [25], [26], [27], [28], [29], [30] and high shear granulators [31], [32], [33], [34] have been investigated. However, to our knowledge, there are no reports on one-step preparation methods for co-amorphous granules. In the first part of the current study, we investigated the feasibility of solventless amorphization and pelletization using a high shear granulator and could obtain fully amorphized indomethacin-layered pellets by simply mixing indomethacin crystals and microcrystalline cellulose spheres without using solvent and heating. Indomethacin crystals were pulverized and amorphized due to collisions with the spheres and subsequently are deposited on the surface of the spheres. Therefore, we hypothesized that co-amorphous mixture-layered pellets can be produced through a one-step amorphization and pelletization process using this technique, as the preparation of co-amorphous mixtures has previously been performed by mechanical activation [16], [22]. Furthermore, this technique holds promise as an economical as well as sustainable approach to manufacture co-amorphous formulations as the need for solvent and/or heat is eliminated.

In previous research, various combinations of indomethacin and amino acids for co-amorphous preparations were systematically investigated. The findings suggest that arginine is an excellent co-former for indomethacin to prepare co-amorphous mixtures with fast dissolution characteristics and high physical stability [18], as an amorphous salt is formed due to strong interactions between the acidic drug indomethacin and the basic amino acid arginine [35], [36]. In the current study, to investigate whether co-amorphous layer pellets can be produced through a one-step amorphization and pelletization process, indomethacin and arginine were selected as the model drug and the co-former, respectively. In the first part of this study, indomethacin crystals were mixed with microcrystalline cellulose spheres (with various mean diameters of 140 μm, 195 μm, 275 μm, 414 μm, and 649 μm) at a weight ratio of 1:10 using a high shear granulator [added: TMG1/6, Glatt GmbH, Binzen, Germany]. Fully amorphized indomethacin-layered pellets were obtained using carriers of 414 μm in diameter, whereas partially amorphized indomethacin-layered pellets were obtained using carriers of 195 μm in diameter. This difference was likely due to the higher impact forces of larger carriers promoting mechanical activation of indomethacin crystals. In this part of the study, to clarify the effects of using arginine on the amorphization and pelletization of indomethacin, the smaller cellulose spheres of 195 μm in diameter were employed as carrier particles. Indomethacin crystals and arginine crystals were initially mixed at various molar ratios (1:1, 2:1, and 3:1), and then the resulting mixtures were high shear granulated with microcrystalline cellulose spheres at a weight ratio of 1:10. The resulting composite particles were characterized using solid-state and particle analytical techniques. To identify effective co-amorphization approaches, we examined high shear mixing under various jacket temperatures. Furthermore, physical stability and dissolution characteristics of co-amorphous layer pellets were investigated.


[Rades_2022] K. Kondo, T. Rades, 181 (2022) 183-194. doi:10.1016/j.ejpb.2022.11.011

[1] B.C. Hancock, M. Parks, Pharm. Res. 17 (2000) 397-404.

[2] L. Yu, Adv. Drug Deliv. Rev. 48 (2001) 27-42.

[3] L.R. Hilden, K.R. Morris, J. Pharm. Sci. 93 (2004) 3-12.

[4] T. Vasconcelos, S. Marques, J. das Neves, B. Sarmento, Adv. Drug Deliv. Rev. 100 (2016) 85-101.

[5] S. Baghel, H. Cathcart, N.J. O’Reilly, J. Pharm. Sci. 105 (2016) 2527-2544.

[6] R. Laitinen, K. Lobmann, C.J. Strachan, H. Grohganz, T. Rades, Int. J. Pharm. 453 (2013) 65-79.

[7] R.B. Chavan, R. Thipparaboina, D. Kumar, N.R. Shastri, Int. J. Pharm. 515 (2016) 403-415.

[8] S.J. Dengale, H. Grohganz, T. Rades, K. Lobmann, Adv. Drug Deliv. Rev. 100 (2016) 116-125.

[9] S. Janssens, G. Van den Mooter, J. Pharm. Pharmacol. 61 (2009) 1571-1586.

[10] R. Laitinen, K. Lobmann, H. Grohganz, P. Priemel, C.J. Strachan, T. Rades, Int. J. Pharm. 532 (2017) 1-12.

[11] S. Yamamura, H. Gotoh, Y. Sakamoto, Y. Momose, Eur. J. Pharm. Biopharm. 49 (2000) 259-265.

[12] M. Allesø, N. Chieng, S. Rehder, J. Rantanen, T. Rades, J. Aaltonen, J. Control. Release 136 (2009) 45-53.

[13] K. Lobmann, R. Laitinen, H. Grohganz, K.C. Gordon, C. Strachan, T. Rades, Mol. Pharm. 8 (2011) 1919-1928.

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[17] G. Kasten, H. Grohganz, T. Rades, K. Lobmann, Eur. J. Pharm. Sci. 95 (2016) 28-35.

[18] G. Kasten, K. Lobmann, H. Grohganz, T. Rades, Int. J. Pharm. 557 (2019) 366-373.

[19] A. Teja, P.B. Musmade, A.B. Khade, S.J. Dengale, Eur. J. Pharm. Sci. 78 (2015) 234-244.

[20] A. Beyer, L. Radi, H. Grohganz, K. Lobmann, T. Rades, C.S. Leopold, Eur. J. Pharm. Biopharm. 104 (2016) 72-81.

[21] E. Lenz, K.T. Jensen, L.I. Blaabjerg, K. Knop, H. Grohganz, K. Lobmann, T. Rades,

  1. Kleinebudde, Eur. J. Pharm. Biopharm. 96 (2015) 44-52.

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More information on ASD

Read more about amorphous solid dispersions in our application notes.


This case study is a short abstract on spouted bed characteristics, following closely findings in the publication by J. Vanamu and A. Sahoo [1].

Spouted bed systems are of highest importance for all powder processing industries, and more specific in pharmaceutical industry for coating and drying in pellet technologies [2]. These systems offer manufacturing particularly fine and temperature-sensitive particles from small to large scale: laboratory systems are capable of processing product volumes of very few grams, while production systems can handle capacities of several tons [3].

But how to control conditions in spouted beds for efficient process applications, like mixing, coating, or drying?

There might be certain reasons, that the hydrodynamic behavior of the spouted bed in the pharmaceutical industries is less investigated. The referred publication shed some light on the hydrodynamic characteristics of a spouted bed where the MCC Spheres (CELLETS®) are adopted as the bed material. These starter cores are ideal model systems due to their perfect sphericity and zero-level friability. At the same time, smooth and defined surface structure initiate perfect modelling conditions in the spouted bed dynamics.


CELLETS®, made of 100% Microcrystalline Cellulose, have been used as bed material. The physical properties of the CELLETS® are shown in Table 1. The CELLETS® particle morphology is represented in Figure 1.

Parameter Value
CELLETS® 700 and CELLETS® 1000
Size distribution 700-1000 µm (CELLETS® 700)

1000-1400 µm (CELLETS® 1000)

Bulk density 800 kg/m3
Particle sphericity > 0.9
Void fraction 0.42
Geldart classification B

Table 1: Physical properties of the CELLETS®.

SEM micrographs of CELLETS® 700

Figure 1: SEM micrographs of CELLETS® 700, found in [1].

Spouted bed: experiment setup

There are some international players on the market of spouted bed technologies, such as Glatt which seems to be the major one (Figure 2). In this framework, a self-made setup is used for experiments. The experiments that have been carried out in a column, which is fabricated from a Perspex sheet. This column consists of a cylindrical section of height 0.53 m and a diameter of the cylinder of 0.135 m. The column further converged the diameter of the cylinder to 0.05 m as a conical bottom having a length of 0.47 m. The spouting air is supplied by a compressed air line is controlled by a gas regulator. The airflow is controlled by a gate valve and a mesh plate having a mesh size less than the size of the bed material is employed as a separator preventing the backflow of the bed material. Images are captured using a high-speed video camera to gain more details of the hydrodynamic characteristics of the flow pattern inside the spouted bed geometry.

Spouted bed

Figure 2: Scheme of a spouted bed (Glatt, Germany).

Experiments & spouted bed results

Experiments are carried out with three different static bed heights of shallow depth wherein the bed height is in the range of factor 2-3 of the Inlet diameter using two different particle distribution classes at 500-710 µm and 700-1000 µm, respectively. Analyzed parameters are the pressure drop across the bed, the bed expansion ratio, and the clusters concerning the superficial gas velocity are focused in the following.

J. Vanamu et al. found that the “bed expansion ratio increases with increasing superficial gas velocity until the onset of external spouting, further increase in the superficial gas velocity, the bed expansion ratio decreases. With increasing the volume of bed, the bed expansion ratio decreases. In a larger volume of bed, the particles tend to spout into the freeboard region rather than expanding with higher superficial gas velocity”. Initial spouting is symmetric, but with increasing superficial gas velocity spouting becomes asymmetric, and asymmetry is more pronounced or starts at lower superficial gas velocities for smaller particles. This agrees with existing theories of hydrodynamic behavior in a fluidized environment. Respecting the necessarity of a proper flow behavior for mixing, coating or drying applications in drug processing, symmetric spouting is essential. In turn, the superficial gas velocity may be kept low.

In case that high superficial gas velocity regimes are required for the operations a draft tube may be installed within the column to achieve the symmetric spout formation.


This case study highlights the Hydrodynamic behavior of MCC spheres in a spouted bed using image processing method. MCC spheres in the range between 500-710 µm and 700-1000 µm had been employed. All spheres showed a symmetric and asymmetric spouting in the spouted bed. With increasing superficial gas velocity, the fully suspended particles are limited to a certain height in the freeboard region due to the gas-solid crossflow. A change from symmetric to asymmetric spouting is observed with increasing superficial gas velocity.

Keeping the conditions efficient for the mixing, coating or drying applications requires finally to suppress high superficial gas velocities, or changing the setup in such way, that symmetric spouting conditions are kept upright even at higher superficial gas velocities.


[1] J. Vanamu and A. Sahoo, Particuology 76 (2023) 101

[2] L. A. P. de Freitas, Particuology 42 (2019) 126

[3] Glatt GmbH, Binzen, Germany. Online on Nov 8, 2022: Spouted bed systems – Glatt – Integrated Process Solutions

Great thanks to Arihant Innochem Pvt. Ltd. who supplied and donated CELLETS® for this study.