Pharmaceutical nanotechnology
Microfluidic conceived Trojan microcarriers for oral delivery of nanoparticles

https://doi.org/10.1016/j.ijpharm.2015.06.028Get rights and content

Abstract

In this study, we report on a novel method for the synthesis of poly(acrylamide) Trojan microparticles containing ketoprofen loaded poly(ethyl acrylate) or poly(methyl acrylate) nanoparticles. To develop these composite particles, a polymerizable nanoemulsion was used as a template. This nanoemulsion was obtained in an elongational-flow micromixer (μRMX) which was linked to a capillary-based microfluidic device for its emulsification into micron range droplets. Downstream, the microdroplets were hardened into Trojan particles in the size range of 213–308 μm by UV initiated free radical polymerization. The nanoemulsion size varied from 98 –132 nm upon changes in surfactant concentration and number of operating cycles in μRMX. SEM and confocal microscopy confirmed the Trojan morphology. Under SEM it was observed that the polymerization reduced the size of the nanoemulsion down to 20–32 nm for poly(ethyl acrylate) and 10–15 nm for poly(methyl acrylate) nanoparticles. This shrinkage was confirmed by cryo-TEM studies. We further showed that Trojan microparticles released embedded nanoparticles on contact with suitable media as confirmed by transmission electron microscopy. In a USP phosphate buffer solution of pH 6.8, Trojan microparticles containing poly(ethyl acrylate) nanoparticles released 35% of encapsulated ketoprofen over 24 h. The low release of the drug was attributed to the overall low concentration of nanoparticles and attachment of some of nanoparticles to the poly(acrylamide) matrix. Thus, this novel method has shown possibility to develop Trojan particles convieniently with potential to deliver nanoparticles in the gastrointestinal tract.

Introduction

The oral route of administration is the most widely accepted route for delivering active pharmaceutical ingredients. But poor drug solubility, stability and absorption could lead to low bioavailability in the blood stream (Ensign et al., 2012). Moreover, in conventional dosage form, some drugs can also cause irritation of gastrointestinal tract (GIT). One way to remove these hurdles is by encapsulating the drug into micro- or nanoparticles. It has been reported by many authors that these particles have the ability to accumulate in inflamed areas and also reduce the toxic effect of irritant drugs (Ranjha et al., 2009).

In nanotechnology, scientists manipulate drugs and polymers at nanoscales (1–100 nm) that give unique chemical, physical and biological properties, quite different from micro- and macro systems (Anton et al., 2012, Anton et al., 2012). So far, nanotechnology provided significant improvement in drug solubility, drug delivery, cancer diagnosis and treatment (Bisht et al., 2008, Khan et al., 2013b, Khan et al., 2015a, Shahzad et al., 2014). Nanoparticles can be administered via parental, ocular, dermal, oral and inhalation routes. However, their administration involves numerous hurdles, for instance, when administered by oral route multiple factors affect the fate of these nanoparticles like pH, ionic concentration, enzymes, mucus, motility etc. In GIT, rapid secretion and shedding of mucus membrane along with motility primarily affect their accumulation and penetration through absorption site (Ensign et al., 2012). Secondly, handling of nanoparticles is more difficult than microparticles because sometimes former form aggregates while in suspension and can undergo hydrolysis or sedimentation (Gómez-Gaete et al., 2008).

Under such circumstances a composite system combining the advantages of nanoparticles and microparticles would be a promising option. In such system nanoparticles are dispersed in microparticles that make their handling convenient while providing protection till their delivery near the site of absorption thus improving their effectiveness. These nano-in-micro system are called Trojan particles (Anton et al., 2012).

Nanoemulsions, sometimes also referred as miniemulsions, ultrafine emulsions, submicron emulsions are transparent or translucent systems in the size range 50–200 nm and requires oil, water, surfactant and energy to break large oil drops (in case of O/W) into smaller ones (Antonietti and Landfester, 2002, Solans et al., 2005, Tadros et al., 2004). This results in an increase in the Laplace pressure (Δp) defined as the difference between inside and outside drop’s pressures and is inversely proportional to the drop’s radius (R) as shown in Eq. (1), where γ represents the interfacial tension. So for smaller droplets, high forces are required that are usually achieved by a more vigorous agitation (Anton et al., 2008, Tadros et al., 2004). Routine nano-emulsification processes include conventional devices such as ultrasonicator, high pressure homogenizer or microfluidizer® (Charles and Attama, 2011).Δp=2γR

Conventional fabrication methods of Trojan particles usually follow a tedious and multistep procedure, i.e., nanoparticles are first synthesized, usually in a batch reactor (by nanoprecipitation, miniemulsion polymerization, solvent extraction etc.) and then dispersed in a suitable polymer solution and finally converted into Trojan microparticles by a spray drying process. However, these particles suffer from a large particle size distribution (Anton et al., 2012). Recently, some authors have prepared composite microcarriers by means of a capillary-based microfluidic system. They started with the preparation of porous silicon (PSi) micro or nanoparticles by a non microfluidic method and then drug molecules were incorporated in the particles by immersion method. Afterwards, these drug loaded micro or nanoparticles were dispersed in a polymer microparticles matrix using a microfluidic system to get composite microparticles. Thus Liu et al. (2014) prepared multi drug loaded composite microcarriers. Initially, atorvastatin was loaded in porous silicon (PSi) microparticles (ca. 5 μm) which were encapsulated into a pH-responsive polymer microparticles containing celecoxib to obtain multi-drug loaded polymer/PSi microcomposites. In a similar study, Zhang and coworkers (Zhang et al., 2014) initially conjugated PSi nanoparticles to mucoadhesive poly(methyl vinyl ether-co-maleic acid) (PMVEMA) using polyethyleneimine (PEI) as a linker to get PSi-PEI-PMVEMA nanoparticles. Then 5-florouracil was loaded in PSi-PEI-PMVEMA by immersion method and later targeted drug delivery microcarriers were fabricated in a microfluidic system by encapsulating PSi-PEI-PMVEMA nanoparticles inside a pH-responsive hydroxypropylmethylcellulose acetate succinate based polymer (ASHF) containing celecoxib to get hybrid carrier called PSi-PEI-PMVEMA@ASHF for colon cancer treatment. Despite the success of both approaches, these strategies involve, like for non microfluidic methods, multistep procedures and quite time consuming. Therefore continuous-flow methods for the production of Trojan microparticles with a minimum of operating steps are higly welcome.

In our previous work, we successfully used a capillary-based microfluidic system (Serra et al., 2007) to produce microbeads for controlled release (Khan et al., 2013a). We also modified the orignal device to produce successsively Janus particles for co-delivery of two active molecules with different solubilities (Khan et al., 2014) and core–shell particles for targeted dual drug delivery (Khan et al., 2015b). In this paper, we report on a new two-step semi-continuous process for the synthesis of Trojan microparticles from nanoemulsion templates using two differents microfluidic devices. At first, an elongational-flow micromixer was used to produce a polymerizable nanoemulsion that was later emulsified into microdroplets in a co-axial capillary-based microfluidic droplet generator. Trojan morphology was realized once nanoemulsion droplets and microdroplets were both polymerized at the same time by UV irriadtion at a suitable wavelength to maintain integrity of model drug ketoprofen. Resulting microparticles have the potential to improve delivery of drug loaded nanoparticles in GIT. To the best of our knowledge this is a first step toward the continuous synthesis of Trojan particles using microfluidic tools.

Section snippets

Material

Ethyl acrylate (EA), Methyl acrylate (MA), 1-hydroxycyclohexyl phenyl ketone (HCPK), Genocure DMHA, Acrylamide (Ac), methylene bis acrylamide (MBA), potassium dihydrogen phosphate, tween 80, ethanol, hexdecane and silicon oil of 500 cSt were purchased from Aldrich (Germany); sodium dodecyl sulphate (SDS) from Alfa Aesar (Germany). Ketoprofen was kindly gifted by Amoli Organics Ltd. (India). Syringe filters (0.45 and 0.2 μm) and dialysis tubings (Spectra/Por® Dialysis membrane MWCO 3500) were

Result and discussion

A new, facile and two-step semi-continuous microfluidic method is reported to synthesize Trojan microparticles. This method uses two different microfluidic devices, namely (a) an elongational-flow micromixer (μRMX) for the production of nanoemlusions and (b) a co-axial capillary-based microfluidic device to generate microdroplets of the former polymerizable nanoemulsion. The latter device also integrates a polymerizing zone where UV irradiation allows to convert nanodroplets and microdroplets

Conclusions

A new two-step semi-continuous process based on nanoemulsion templating was developed for the synthesis of ketoprofen loaded Trojan microparticles. Polymerizable nanoemulsions were produced in an elongational-flow micromixer (μRMX) which was later linked to a co-axial capillary-based microfluidic setup for the production of uniform microdroplets. These droplets were then polymerized downstream by means of a UV source having a wavelength far away from the maximum absorbance wavelength of

Acknowledgements

Sébastien Gallet, Christophe Mélart and Chheng Ngov are acknowledged for their help in experiments and setup design. IUK would like to acknowledge funding support by the Government College University, Faisalabad, Pakistan for this research work.

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