single-step drug crystallization and formulation - … · 2013. 9. 13. · single-step drug...
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SINGLE-STEP DRUG CRYSTALLIZATION AND FORMULATION –
‘DESIGNER’ PHARMACEUTICALS ENABLED BY MICROFLUIDICS Reno A.L. Leon
1, Wai Yew Wan
1, Abu Zayed Md. Badruddoza
1, T. Alan Hatton
2, 3 and
Saif A. Khan1, 2*
1National University of Singapore, SINGAPORE
2Singapore MIT-Alliance, SINGAPORE and
3Massachusetts Institute of Technology, USA
ABSTRACT
We present a single step formulation platform for the fabrication of ‘designer’ pharmaceuticals where we specifically
co-formulate drugs and excipient as monodisperse spherical microparticles of ~200 µm size containing crystals of a hy-
drophobic model drug (ROY) embedded within a hydrophilic matrix of an excipient (sucrose) and a hydrophilic model
drug (glycine). For this we use capillary-based microfluidic double emulsions to perform formulation followed by
spherical crystallization via solvent evaporation. The method completely circumvents several energy intensive ‘top-
down’ processes in traditional manufacturing, thereby offering the potential for continuous, sustainable pharmaceutical
crystallization coupled with advanced formulations.
KEYWORDS: Co-formulation, Crystallization, Microfluidic double emulsion, Pharmaceuticals
INTRODUCTION
Pharmaceutical formulation processes, in which active pharmaceutical ingredients (APIs) are blended with additives
and excipients, are crucial downstream operations that account for a significant fraction of the energy consumption in the
entire manufacturing process. The processes include comminution, milling, sieving, blending and granulation through which
the crystalline APIs are processed into the final product; tablets. These processes have several drawbacks such as low process
efficiency, contamination, amorphisation, demixing, polymorphic transformation and are time consuming [1-6]. Direct
compression of spherical crystalline agglomerates and the use of bridging liquids for API-excipient formulations were
attempts to overcome these drawbacks despite which outstanding issues such as drug-excipient compatibility and wide
particle size distributions have remained as challenges [7].
Figure 1: (a) Schematic illustration of ‘bottom-up’ approach (center) for co-formulation using double emulsions
presented in comparison with contemporary pharmaceutical manufacturing steps (outer circle). Drug 1 (Red) represents
a hydrophobic API while Drug 2 (Yellow) represents a hydrophilic API, dispersed in a matrix comprising of an excipient
(Pink), (b) Schematic of experimental setup depicting generation of O1/W/O2 (Red/Blue/Yellow) double emulsion drops
with multiple (n-in-1) inner O1 droplets using capillary microfluidics, followed by evaporative crystallization to form
SAs. Temporal progress of crystallization is represented as an increase in opacity of the W phase due to the presence of
excipient.
In this study, we present single-step pharmaceutical formulation process enabled by microfluidics which yields
exquisite “designer” formulations in a bottom-up fashion that completely circumvents the energy intensive top-down
processes which are the mainstay of conventional manufacturing practice (Fig. 1a). Specifically, we co-formulate
hydrophobic drug molecules with a hydrophilic matrix using oil-in-water-in-oil (O1/W/O2) double emulsions. The double
978-0-9798064-6-9/µTAS 2013/$20©13CBMS-0001 1824 17th International Conference on MiniaturizedSystems for Chemistry and Life Sciences27-31 October 2013, Freiburg, Germany
emulsions through evaporative crystallization, yield spherical agglomerates (SAs). The SAs comprise of crystals of a
hydrophobic model drug (ROY) embedded within a hydrophilic matrix (sucrose) which in turn contains a hydrophilic
model drug (glycine) (drug-drug-excipient: ‘D2E’ formulation) – the first demonstration of its kind. We provide detailed
morphological and polymorphic characterization of the particles obtained.
EXPERIMENTAL
O1\W\O2 double emulsions were generated using a glass capillary microfluidic setup (See schematic in Fig. 1b). The
inner-most oil phase (O1) constitutes ROY in dodecane-ethyl acetate mixture with surfactants. The middle aqueous phase
(W) was prepared by dissolving varying amounts of sucrose and glycine in ultra pure water. Light mineral oil with sur-
factants was used as the continuous phase (O2). All three fluids are infused using syringe pumps (Harvard PHD 2000)
and hydrodynamically flow focused through the nozzle of the collection capillary resulting in the formation of the double
emulsion drops. The double emulsion drops were collected and heated at 80-100oC on a hot plate to form spherical ag-
glomerates (SAs). High-speed real time imaging was performed with high speed digital cameras (Basler pI640 or Miro
Phantom EX2) mounted onto a stereomicroscope (Leica MZ16). The characterization of the SAs for size distribution,
morphology and polymorphism were performed using microscopic image analysis, field emission scanning electron mi-
croscopy (FE-SEM) and powder X-ray diffraction (PXRD).
RESULTS AND DISCUSSION
Real-time observation of droplet generation in the microfluidic device using high speed imaging allows for detailed
study of droplet morphology and flow regime. A uniform stream of double emulsions with multiple inner droplets (‘n’-
in-1) was produced while operating in the jetting regime resulting from the high viscosity of the outer O2 phase as com-
pared to that of the middle W phase [8]. The double emulsions (Fig. 2a) have a mean diameter of 382µm with a standard
deviation of 2%. A count of the number of inner O1 droplets within these double emulsions gives ‘n’ = 85±8 droplets.
The diameter of the inner O1 droplets is ~25µm. A typical SA of the ‘D2E’ formulation contains a loading ratio of 40:4:1
(sucrose/glycine/ROY). The loading can also be adjusted by altering (a) the number of O1 droplets, (b) the API concen-
tration in the O1 or W phase, (c) the overall diameter of the double emulsion droplet. The mean particle size of the SAs
obtained from crystallization of the double emulsions was ~200 µm with a standard deviation of <5% (Fig. 2b & Fig. 2c).
The SAs appear brown due to Maillard reaction, which occurs when reducing sugars are formulated in the presence of
amino-group containing compounds such as glycine [9, 10].
Figure 2: (a) Collected double emulsions of the ‘n’-in-1 droplet morphology, (b) Stereomicroscopic images of
monodisperse ‘D2E’ spherical agglomerates (SAs), (c) Size distribution histogram of SAs, (d) FESEM image of an SA of
glycine, sucrose and ROY exhibiting a rough surface with crystals packed together with sucrose, (e) Close-up of faceted
crystals located on the surface of the SAs, (f) XRD pattern of the ‘D2E’ SAs showing peaks corresponding to the yellow
prism and red plate polymorph of ROY and γ-glycine.
Electron microscopy reveals that the surface of the SAs is coarse (Fig. 2d). On closer observation (Fig. 2e), crystal
facets of ~2 µm were observed to populate the surface of the SAs; these facets can be attributed to the presence of gly-
cine. Following the imaging of the SAs, we proceeded to corroborate the presence of glycine and ROY using XRD anal-
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ysis. The XRD profile reveals the presence of γ-glycine and the red and yellow polymorphs of ROY respectively, as in-
dicated in Fig. 2f.
CONCLUSION
In conclusion, we demonstrate a microfluidic method for co-formulation of hydrophobic and hydrophilic APIs in the
form of monodisperse SAs with a narrow size distribution. This method potentially circumvents several drawbacks in
conventional processing, such as a broad size distribution in batch crystallization, de-mixing in blending and challenges
in the formulation of hydrophobic and hydrophilic APIs and excipients. Through further optimization of parameter space
especially through detailed engineering and feasibility studies of scale-up, the method can be made viable for accelerated,
energy and cost-efficient production of ‘designer’ pharmaceuticals. Our ongoing work beyond this initial proof-of-
concept demonstration involves detailed studies of the dynamics of crystallization in this chemically ‘complex’ emulsion
system.
ACKNOWLEDGEMENTS
The authors gratefully acknowledge research funding from the GSK-EDB Fund for Sustainable Manufacturing and
the Chemical and Biomolecular Engineering program of the National University of Singapore.
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[9] Ellis, G. P., The Maillard Reaction. In Advances in Carbohydrate Chemistry, Melville, L. W., Ed. Academic Press:
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CONTACT
* S.A. Khan, tel: +65-6516-5133; [email protected]
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