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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CONTACT

* S.A. Khan, tel: +65-6516-5133; saifkhan@nus.edu.sg

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