A review of particulate design for pharmaceutical powders and their production by spouted bed coating

Comprehensive Optimization of the Dispersion of Mixing Particles in an Inert-Particle Spouted-Bed Reactor (IPSBR) System

Effective gas dispersion and liquid mixing are significant parameters in the design of an inert-particle spouted-bed reactor (IPSBR) system. Solid particles can be used to ensure good mixing and an efficient rate of mass and heat transfer between the gas and liquid. In this study, computational fluid dynamics (CFD) coupled with the discrete phase model (DPM) were developed to investigate the effect of the feed gas velocity (0.5–1.5 m/s), orifice diameter (0.001–0.005 m), gas head (0.15–0.35 m), particle diameter (0.009–0.0225 m), and mixing-particle-to-reactor-volume fraction (2.0–10.0 vol.%) on the solid mass concentration, average solid velocity, and average solid volume fraction in the upper, middle, and conical regions of the reactor. Statistical analysis was performed using a second-order response surface methodology (RSM) with central composite design (CCD) to obtain the optimal operating conditions. Selected parameters were optimized to maximize the responses in the middle and upper regions, and minimize them in the conical region. Such conditions produced a high interfacial area and fewer dead zones owing to good particle dispersion. The optimal process variables were feed gas velocity of 1.5 m/s, orifice diameter of 0.001 m, gas head of 0.2025 m, a particle diameter of 0.01 m, and a particle load of 0.02 kg. The minimum average air velocity and maximum air volume fraction were observed under the same operating conditions. This confirmed the novelty of the reactor, which could work at a high feed gas velocity while maintaining a high residence time and gas volume fraction.

Design of taste-masked swellable drug particles using dry-coating technology with mechanical curing

A novel dry coating technique for fine particles that does not require any liquids has been developed. Swellable ordered-mixed drug particles (Swell-OM-spheres, SOS), using a modified starch as the core particle and a drug coating layer have been previously developed. In the present work, SOS particles were further processed to generate 100-μm taste-masking particles using an all dry coating processes. SOS particles were coated with a gastric-soluble powder using a mechanical powder processor. The coated particles (CPs) were subsequently heated while rotating in the same powder processor, completing film formation by a process termed dynamic curing. As a control, conventional film formation (static curing) was performed using a drying oven. The CPs obtained by these two curing processes had distinct appearances, but exhibited equivalent dissolution suppression effects in a medium at pH 6.8 (the pH of the oral cavity). The suppression effect was further improved by adding a plasticizer to the coating powder, even though a lower heating temperature was required. Orally disintegrating tablets incorporating these CPs exhibited excellent taste-masking performance, i.e., suppressing taste in saliva while accelerating dissolution in gastric juice. The dissolution behavior indicated that the CPs can provide an ON/OFF switching function in drug release.

Fabrication of Highly Filled Composites with an Innovative Miniaturized Spouted Bed

In nature bio-composites such as nacre show remarkable mechanical properties due to their complex hierarchical structure and high-volume fraction of its hard component. These composites are highly interesting for structural applications in different branches of industries for mechanical engineering and process technology. The aim of this work was to provide a scalable method for the production of highly filled composites by mimicking the structure of bio-composites. Therefore, composites from iron oxide (Fe2O3) and SBC-polymer (styrene-butadiene block copolymer) were fabricated by using a miniaturized spouted bed with an innovative fluidization gap design. Small iron oxide particles (25–45 μm) were fluidized in the spouted bed and coated with a polymer solution via a bottom spray nozzle. Afterwards the coated granules were hot-pressed and the mechanical properties of the obtained composites were tested. By this method composites with a bending strength of up to 6 MPa were fabricated. Although the mechanical properties of these artificial composites are still lower than those of the natural role models, it was shown that the spouted bed is a suitable technique for the fabrication of highly filled composites. For further optimization of the mechanical properties more complex and tailor-made starting materials will be used in following studies.

Fundamental evaluation and optimization of porous spherical silica for developing functional fine particles via fluidized bed coating

Particle coating, a taste-masking technique for drugs, is limited by its long manufacturing time, which is caused by the decrease in the spray rate required to prevent particle agglomeration. Mesoporous silica particles, which have a high surface area and pore sizes in the range of 2-50 nm, possess high surface free energy; they have attracted significant interest for numerous applications in adsorption, separation, and catalysis and drug delivery. A form of mesoporous silica, microbead silicate, can prevent particle aggregation because of its good water absorbency and drying properties. Hence, it has been suggested to be applicable for particle coating. This study evaluated the physical properties and drug release capability of microbead silicate with different pore sizes. Although microbead silicate with small pores displayed a rapid drug release profile, drug release was incomplete. Contrastingly, microbead silicate with large pores achieved complete drug release even with high drug loading. Furthermore, in the case of 100% layering, the porosity of microbead silicate was maintained, thus sufficiently preventing aggregation due to the prevention of formation of liquid bridging of the coating solution. These results suggest that using microbead silicate with large pores for particle coating enables complete drug release while improving manufacturability.

Binder-free dry particulate coating process using a mild vibration field: Effects of glass-transition temperature and powdering method of polymeric coating agents on coating performance

We employed a new dry coating process with mild-intensity vibration to prepare a 100-µm-sized microparticle capable of prolonged release of a drug. To accomplish this without using a binder, a series of laboratory-made acrylic latexes with different glass transition temperatures (Tg) ranging from 30 °C to 80 °C were employed as coating agents, and the effects of Tg and powdering method of the coating agents on coating performance were investigated. The laboratory-made acrylic latexes were powdered by spray-drying (SD) or freeze-drying (FD). Diclofenac sodium (DS)-loaded ion-exchange-resin with particle size ∼100 µm was used as a core particle. The process utilized vibrations with amplitude of 0.5 mm and frequency of 90 Hz to form an ordered mixture composed of the core particles with the loosely-layered coating agents. Subsequently, the coating agents were fixed mechanically on the core particle by impaction of zirconia beads. The coating agents powdered by FD showed higher coating efficiencies than those powdered by SD, irrespective of the differences in Tg values. Among the coating agents powdered by FD, the particles coated at Tg = 60 °C exhibited the most prolonged drug-release, although the coating efficiency was not the highest. In our proposed process utilizing mild vibration, we demonstrated that adjusting the Tg of the coating agents is crucial to the formation of binder-free multiple coating layers for prolonged drug release.

Controlling Self-Assembly and Topology at Micro-Nano Length Scales Using a Contact-Free Mixed Nanocolloid Droplet Architecture

Spatially varying the ordering of colloids of multiple sizes at micro-nano scales finds application in different industrial processes including manufacturing of photonic crystals. In this work, we showcase a unique physics-based architecture through which we have been able to control the morphology of the precipitates evolving out of the drying of a contact-free droplet at micro to nano length scales. We show that by varying the relative concentration of the larger sized colloids, one can modulate evaporation, subsequent particle transport, and particle ordering at the droplet interface, thereby controlling the rates of certain instabilities like buckling. In this way, we have produced evaporation-induced self-assembly structures (devoid of any substrate effect) with striking topological and surface features. Furthermore, we proved that these instabilities can be further tuned using a measured amount of external heating through the alteration of the evaporation rates. Notwithstanding, we also quantified that the ordering of the mixed colloids varies, in a spatial sense, across the droplet surface, exhibiting unique patterns, porosity, and lattice arrangements, all at the nanoscale. The results assure that the fine-tuning of the macroscale parameters like heating rate and particle loading can be used to fine-tune the micro-nanoscale features in a droplet-based high-throughput bottom-up framework.

Preparation of Controlled-Release Particles Based on Spherical Porous Silica Used as the Drug Carrier by the Dry Coating Method

A controlled-release formulation is a dosage form that could improve a patient's quality of life by reducing the frequency of administration, while ensuring the continued effect of the medicine and reducing the side effects. To prepare these controlled-release particles, a wet coating method in which a drug is coated with a controlled-release material using water or an organic solvent is used, but with this method, the coating process is very time-consuming and requires large amounts of energy for the drying phase. In addition, contact with water or an organic solvent may cause problems such as alteration of the drug. Therefore, the use of a dry coating method has attracted attention as a means of overcoming these issues. However, since the drug is fixed to the surface of a core particle, it is necessary to further coat it with a water-soluble material. We used spherical porous silica (SPS) particles, considering that the drug fixation via a water-soluble material would not be necessary if the drug were to be placed in the pores of these particles. We used SPS filled with theophylline (TP), a model drug, as the core particles. To prepare controlled-release particles (CRP), a controlled-release layer consisting of hydrogenated castor oil (HCO) was applied to the core particle surface by a dry coating method. The paddle method using 1% w/v polysorbate 80 solution as the test medium was employed to estimate the TP dissolution rate of the resulting CRPs. The 50% dissolution time of TP extended from 14 to 405 min with increasing the amount of the coated HCO. The Korsmeyer-Peppas model applied to the TP dissolution behavior yielded an n value of around 1. Moreover, the K value was comparable with the case in which a zero-order model was applied. It is thought that the dissolution of TP from CRPs will conform to the zero-order model.

Preparation of Controlled-Release Fine Particles Using a Dry Coating Method

Wet coating methods use organic solvents to prepare layered particles that provide controlled-release medications. However, this approach has disadvantages in that it can cause particle agglomeration, reduce pharmaceutical stability, and leave residual organic solvents. We used a dry coating method to overcome these issues. Fine particles (less than 50 μm in diameter) of controlled-release theophylline were created using theophylline (TP; model drug), polyethylene glycol 20,000 (PEG; drug fixative), hydrogenated castor oil (HCO; controlled-release material), hydrogenated rapeseed oil (HRSO; controlled-release material), and cornstarch (CS; core particle). An ultrahigh-speed mixer was employed to mix TP and CS for 5 min at 28,000 rpm. Subsequent addition of PEG produced single-core particles with a drug reservoir coating. Addition of HCO and HRSO to these particles produced a controlled-release layer on their surface, resulting in less than 10% TP dissolution after 8 h. We successfully demonstrated that this dry coating method could be used to coat 16-μm CS particles with a drug reservoir layer and a controlled-release layer, producing multi-layer coated single-core particles that were less than 50 μm in diameter. These can be used to prepare controlled-release tablets, capsules, and orally disintegrating tablets.

Evaluation of coat uniformity and taste-masking efficiency of irregular-shaped drug particles coated in a modified tangential spray fluidized bed processor

OBJECTIVE

To explore the feasibility of coating irregular-shaped drug particles in a modified tangential spray fluidized bed processor (FS processor) and evaluate the coated particles for their coat uniformity and taste-masking efficiency.

METHODS

Paracetamol particles were coated to 20%, w/w weight gain using a taste-masking polymer insoluble in neutral and basic pH but soluble in acidic pH. In-process samples (5, 10 and 15%, w/w coat) and the resultant coated particles (20%, w/w coat) were collected to monitor the changes in their physicochemical attributes.

RESULTS

After coating to 20%, w/w coat weight gain, the usable yield was 81% with minimal agglomeration (< 5%). Some aerodynamic modifications to particle shape and surface morphology were observed for the in-process samples with 5 and 10% coat compared with the uncoated particles. A 15%, w/w coat was optimal for inhibiting drug release in salivary pH with subsequent fast dissolution in simulated gastric pH.

CONCLUSION

The FS processor shows promise for direct coating of irregular-shaped drug particles with wide size distribution. The coated particles with 15% coat were sufficiently taste masked and could be useful for further application in orally disintegrating tablet platforms.

Preparation and properties of stretchable and tough alginate/polyacrylamide hollow capsules

Stretchable and tough hollow capsules were synthesized using alginate and polyacrylamide and their volume could be expanded at least 27 times their original size.

Comparison of film-coated retarded release pellets manufactured by layering technique or by bed rotor pelletization

In order to investigate the influence of coatings for controlled active pharmaceutical ingredient (API) release, two types of pellets were used. Microcrystalline pellets were coated with a model API using the Wurster fluidized bed technique in laboratory scale (layered Cellets). Another type of pellets consisting of microcrystalline cellulose and model API was manufactured by fluidized bed rotor pelletization (matrix pellets (MP)). Both kinds of pellets were coated in a Wurster fluidized bed process with a polymer mixture of ethylcellulose to achieve retarded API release. With layered Cellets and an increased thickness of the ethylcellulose layer, the lag-time was increased and the release rate was decreased. In the case of MP, retardation was less pronounced probable due to inhomogeneous polymer film formation as a result of the porous particle surface. To reduce the surface roughness, the MP were coated with polyvinylpyrrolidone (PVP) as an intermediate smoothing layer, in a first trial step by step. In a second trial, pelletization and the coating steps were performed in an uninterrupted process. Intermediate PVP coating improved the ethylcellulose film formation and led to a more pronounced retardation of API release. The uninterrupted process of matrix pellet manufacturing and coating results in a product with only low retarded release.

A novel approach to a fine particle coating using porous spherical silica as core particles

Abstract The applicability of porous spherical silica (PSS) was evaluated as core particles for pharmaceutical products by comparing it with commercial core particles such as mannitol (NP-108), sucrose and microcrystalline cellulose spheres. We investigated the physical properties of core particles, such as particle size distribution, flow properties, crushing strength, plastic limit, drying rate, hygroscopic property and aggregation degree. It was found that PSS was a core particle of small particle size, low friability, high water adsorption capacity, rapid drying rate and lower occurrence of particle aggregation, although wettability is a factor to be carefully considered. The aggregation and taste-masking ability using PSS and NP-108 as core particles were evaluated at a fluidized-bed coating process. The functional coating under the excess spray rate shows different aggregation trends and dissolution profiles between PSS and NP-108; thereby, exhibiting the formation of uniform coating under the excess spray rate in the case of PSS. This expands the range of the acceptable spray feed rates to coat fine particles, and indicates the possibility of decreasing the coating time. The results obtained in this study suggested that the core particle, which has a property like that of PSS, was useful in overcoming such disadvantages as large particle size, which feels gritty in oral cavity; particle aggregation; and the long coating time of the particle coating process. These results will enable the practical fine particle coating method by increasing the range of optimum coating conditions and decreasing the coating time in fluidized bed technology.

Adhesion mechanisms of the contact interface of TiO2 nanoparticles in films and aggregates

Fundamental knowledge about the mechanisms of adhesion between oxide particles with diameters of few nanometers is impeded by the difficulties associated with direct measurements of contact forces at such a small size scale. Here we develop a strategy based on AFM force spectroscopy combined with all-atom molecular dynamics simulations to quantify and explain the nature of the contact forces between 10 nm small TiO(2) nanoparticles. The method is based on the statistical analysis of the force peaks measured in repeated approaching/retracting loops of an AFM cantilever into a film of nanoparticle agglomerates and relies on the in-situ imaging of the film stretching behavior in an AFM/TEM setup. Sliding and rolling events first lead to local rearrangements in the film structure when subjected to tensile load, prior to its final rupture caused by the reversible detaching of individual nanoparticles. The associated contact force of about 2.5 nN is in quantitative agreement with the results of molecular dynamics simulations of the particle-particle detachment. We reveal that the contact forces are dominated by the structure of water layers adsorbed on the particles' surfaces at ambient conditions. This leads to nonmonotonous force-displacement curves that can be explained only in part by classical capillary effects and highlights the importance of considering explicitly the molecular nature of the adsorbates.

Microencapsulation of probiotics for gastrointestinal delivery

The administration of probiotic bacteria as nutraceuticals is an area that has rapidly expanded in recent years, with a global market worth $32.6 billion predicted by 2014. Many of the health promoting claims attributed to these bacteria are dependent on the cells being both viable and sufficiently numerous in the intestinal tract. The oral administration of most bacteria results in a large loss of viability associated with passage through the stomach, which is attributed to the high acid and bile salt concentrations present. This loss of viability effectively lowers the efficacy of the administered supplement. The formulation of these probiotics into microcapsules is an emerging method to reduce cell death during GI passage, as well as an opportunity to control release of these cells across the intestinal tract. The majority of this technology is based on the immobilization of bacteria into a polymer matrix, which retains its structure in the stomach before degrading and dissolving in the intestine, unlike the diffusion based unloading of most controlled release devices for small molecules. This review shall provide an overview of progress in this field as well as draw attention to areas where studies have fallen short. This will be followed by a discussion of emerging trends in the field, highlighting key areas in which further research is necessary.