Table Of ContentJournal of Microencapsulation, 2013;30(5): 490–497
(cid:2)2013Informa UK Ltd.
ISSN 0265-2048print/ISSN 1464-5246 online
DOI:10.3109/02652048.2012.752537
Controlled release behaviour of protein-loaded microparticles
prepared via coaxial or emulsion electrospray
Ying Wang1,2, Xiaoping Yang3, Wentao Liu4, Feng Zhang5, Qing Cai3 and Xuliang Deng1,2
1Department of Geriatric Dentistry, Peking University Schooland Hospital of Stomatology, Beijing 100081,China,
2Department of Prosthodontics, Peking University School andHospital of Stomatology, Beijing 100081,China,
3StateKey Laboratory of Organic-Inorganic Composites, Collegeof Materials Science and Engineering, Beijing
University of Chemical Technology, Beijing 100029,China, 4College of Animal Science andVeterinary Medicine,
Jilin University, Changchun, Jilin 130062,China, and5TheOral Clinic of the 2ndHospital of Beijing Armed Police
Force,Beijing 100037,China
Abstract
Biodegradablepoly(lactic-co-glycolicacid)(PLGA)microparticlesareaneffectivewaytoachievesustained
drugrelease.Inthisstudy,weinvestigatedasustainedreleasemodelofPLGAmicroparticleswithincor-
poratedproteinviaeitheremulsionorcoaxialelectrospraytechniques.PLGA(75:25)wasusedasthecarrier,
andbovineserumalbuminasamodelprotein.Coaxialelectrosprayresultedinatypeofcore–shellstructure
with mean diameters of 2.41(cid:2)0.60mm and a centralised protein distribution within the core. Emulsion
electrosprayformedbiggermicroparticleswithmeandiametersof22.75(cid:2)8.05mmandaheterogeneous
protein distribution throughout the microparticles. The coaxial electrospray microparticles presented a
muchslighterburstreleasethantheemulsionelectrospraymicroparticles.Loadingefficiencywassignifi-
cantlyhigher(p50.05)inthecoaxialgroupthanemulsiongroup.Thisindicatedthatbothemulsionand
coaxialelectrospraycouldproduceprotein-loadedmicroparticleswithsustainedreleasebehaviour,butthe
formerrevealedasuperiorapproachfordrugdelivery.
Keywords: microparticles,electrospray,controlledrelease,drugdelivery
Introduction including modest encapsulation efficiency, batch-nature
of the process, difficulty to scale-up, poor control of the
The concept of using polymer-based sustained-release particle size distribution, difficulty to generate sufficiently
delivery systems to maintain therapeutic drug concentra- small particles (5100nm), poor repeatability and limita-
tionsforextendedperiodshasbeenacceptedfordecades. tions with respect to encapsulation of hydrophilic agents
Drug carriers like microspheres can deliver molecules of (Jain, 2000; Almeria et al., 2011; Enlow et al., 2011).
interestoverlongertimesthanbystandardbolusinjection, Recently,electrosprayhasattractedmuchattentioningen-
while maintain therapeutic concentrations at target sites erating drug-loaded polymeric particle (Ding et al., 2005;
and reducing potential toxicity (Whittlesey and Shea, Ciach,2006;Xie etal.,2006).Itutilises electrostatic forces
2004). Consequently, the attempts to produce sustained- toejectpolymersolutionsormeltsintodroplets,producing
release microparticles were highlighted. Different ways, particles with diameters ranging from nanometres to
e.g. W /O/W double emulsion, coacervation and spray, micrometres after solvent evaporation. Electrosprayed
1 2
have been studied intensively (Gupta et al., 1998; Singh microparticles have been regarded as effective drug car-
and O’Hagan, 1998; Sinha and Trehan, 2003; Dai et al., riers(Loscertalesetal.,2002;Almeriaetal.,2010).
2005; Freitas et al., 2005; Tamber et al., 2005). But, some Protein-loadedmicroparticlescangenerallybeachieved
of those techniques had numerous shortcomings, by two different electrospray approaches: emulsion or
Addressforcorrespondence:XuliangDeng,DepartmentofGeriatricDentistry,22ZhongguancunNandajie,HaidianDistrict,Beijing100081,China.Tel:þ86
1082195637.Fax:þ861082195581.E-mail:[email protected]
((RReecceeiivveedd1122OOcctt22001122;;aacccceepptteedd2200NNoovv22001122))
hhttttpp::////wwwwww..iinnffoorrmmaahheeaalltthhccaarree..ccoomm//mmnncc
449900
Controlled release behaviour ofprotein-loaded microparticles 491
coaxial electrospray. Emulsion electrospray involves Materials and methods
mixing of aqueous solution containing proteins with
immiscible polymeric solution by ultrasonication (Xu and Materials
Hanna, 2006; Xie and Wang, 2007). Compared to other
conventionalproducing methods,thesecondemulsionor PLGA with a lactide–glycolide molar ratio of 75:25 (MW,
high temperature is omitted in emulsion electrospray. It 10kDa) was obtained from Birmingham Polymers
increases the drug-loading efficiency and is suited for (Birmingham, AL). BSA (purity 98%), fluorescein isothio-
encapsulation of thermosensitive bioactive compounds. cyanate-conjugated BSA (FITC–BSA) (MW 67kDa) was
However,itstillinvolvesthestepofatomisationofprotein purchased from Beijing Biosynthesis Biotechnology Co.
aqueous solution in organic polymer solution, which Ltd (Beijing, China). Rhodamine B (purity 80%) was pur-
causes bioactivity loss during ultrasonication (van de chased from Sigma–Aldrich (St. Louis, MO). Organic sol-
Weertetal.,2000).Besides,emulsionstabilityisalsoacru- vents 2,2,2-trifluoroethanol (TFE) (purity 99.9%) and
cialparameterfortheprocess,togetherwithotherparam- trichloromethane (THM) (purity 99.0%) were supplied by
etersasconcentration,voltageandflowrate. Sinapharm Chemical Reagent Beijing Co. Ltd (Beijing,
Coaxial electrospray was first reported by Loscertales China) and used directly. PBS (PH7.4) was purchased
et al. (2002). Two immiscible solutions are coaxially and from Beijing Zoman Biotechnology Co. Ltd (Beijing,
simultaneously electrosprayed through twoseparate feed- China).
ingchannelsintoonenozzle.Theeventualjet,bywhichthe
outer polymeric solution encapsulates the inner proteina-
ceous liquid, breaks into droplets to generate microparti- Coaxialelectrospray
cles with core–shell structure. This technique is preferred
for preparing protein-loaded microcapsules, because it BSA was dissolved in deionised water at a specified con-
totallyeliminatestheemulsionstepthatisbasicallyunsui- centration and the aqueous solution was mixed into
tableforsensitivebiomacromolecules(Xieetal.,2008;Wu PLGA/TFE solution to obtain the core solution. The
et al., 2009). Xie et al. (2008) have used poly (lactide-co- shell solution was set at 3% w/v PLGA/TFE and the con-
glycolide) (PLGA) dichloroform solution coating protein centrationofinnersolutionwastriedseveraltimesbefore
aqueous solution via coaxial electrospray and encapsulat- the most appropriate concentration was determined. The
ingbovineserumalbumin(BSA)orlysozymeinsidemicro- two solution was electrosprayed from a 20mL syringe
particles. Poly (ethyl glycol) was included in the core to with a steel needle (inner diameter of 0.5 and 0.8mm,
modify the electrospray process and drug release behav- respectively) both at a rate of 0.8mL/h continuously with
iour. Coaxial electrospray is envisioned a promising a programmable syringe pump (Top 5300, Japan). A volt-
approachtopreparebiomacromolecule-loadedmicrocap- age (15kV) was applied to the tip of the needle by the
sules forcontrolled drugdelivery applications. Becauseof use of a high-voltage supply (DW-P303-1AC, China) with
itscomplexity,however,coaxialelectrosprayisnotpopular a collection distance of 20cm. All the formulas used in
assingleneedleelectrospray. thisstudyarepresentedinTable1.Electrosprayedmicro-
In this study, we fabricated BSA-loaded core–shell particles were collected on a plate covered with alumin-
microcapsules by coaxial electrospray. To modify the ium foil. They were freeze dried for 1day before further
release of hydrophilic protein, the inner liquid was pre- characterisation.
pared by mixing BSA/H O solution into PLGA/trifluor-
2
oethanolsolution,toobtainakindofmatrix-typedelivery
system in the core and a wholly reservoir-type with the Emulsionelectrospray
PLGA shell. Emulsion electrospray was also performed.
Both systems were compared in terms of the processing PLGA/THMsolutionswerepreparedbydissolvingPLGAin
set-up and microparticles characterisation as well as the trichloroform as the continuous oil phase, with BSA dis-
releasekinetics. solved in deionised water as the inner aqueous phase.
Table 1. Preparationparametersofcoaxialelectrosprayusedinthisstudy.
Compositions
Coresolution(v/v¼1/5) Shellsolution
Theoreticaldrug Diameter Loading
Sample loading(w/w%) BSA/DIwater(w/v%) PLGA/TFE(w/v%) PLGA/TFE(w/v%) (mm) efficiency(%)
a-0%PLGAin 5 0.15 0 3 – 83.15(cid:2)2.78
b-6%PLGAin 4.65 6 3 2.25(cid:2)0.56 82.04(cid:2)3.46
c-5%PLGAin 4.15 5 3 2.37(cid:2)0.56 82.57(cid:2)3.02
d-4%PLGAin 3.65 4 3 2.41(cid:2)0.60 82.35(cid:2)3.08
e-4%PLGAin 3 2.19 4 3 2.39(cid:2)0.33 87.51(cid:2)3.53
f-4%PLGAin 1 0.73 4 3 2.39(cid:2)0.56 88.93(cid:2)3.77
g-4%PLGAin 0 0 4 3 2.37(cid:2)0.60 0
492 Y. Wang etal.
Table 2. Preparationparametersofemulsionelectrosprayusedinthisstudy.
Compositionsofemulsion(W/O¼1/10inv/v)
Theoreticaldrug Diameter Loading
Sample loading(w/w%) BSA/HO(w/v%) PLGA/THM(w/v%) (mm) efficiency(%)
2
h-2%PLGA 5 1 2 22.26(cid:2)5.40 74.65(cid:2)4.32
i-4%PLGA 2 4 22.12(cid:2)5.25 73.97(cid:2)3.98
j-6%PLGA 3 6 22.75(cid:2)8.05 74.34(cid:2)4.02
k-8%PLGA 4 8 23.12(cid:2)4.73 74.39(cid:2)3.24
l-6%PLGA 3 1.8 6 22.82(cid:2)4.95 75.83(cid:2)4.36
m-6%PLGA 1 0.6 6 22.34(cid:2)4.68 82.31(cid:2)4.34
n-6%PLGA 0 0 6 22.77(cid:2)4.79 0
The two immiscible solutions were mixed and emulsified multi-track images were captured with a 63(cid:3)/1.40NA
byultrasonicationfor30s,andthenelectrosprayedfroma objective.
20mL syringe with a steel needle (inner diameter of
0.6mm)atarateof1.8mL/hcontinuouslywithaprogram-
mablesyringepump(Top5300,Japan).Avoltageof10kV Determinationofproteinloadingefficiency
was applied to the tip of the needle by the use of a high-
voltage supply (DW-P303-1AC, China) with a collection The total protein content was determined according to a
distanceof20mm.Alltheformulasusedforemulsionelec- reported method (Sah, 1997) with some modification.
trosprayinthisstudyarepresentedinTable2. Briefly, microparticles (n¼8, 50mg for each) were incu-
batedin3mLDMSOfor1h,then4mL0.2MNaOHsolu-
tion containing 0.5% SDS was added for a further 1h
incubation at room temperature. The protein concentra-
Morphologicalcharacterisationofelectrospray
tion in the solution was measured by the Micro-BCATM
microparticles
assay(Pierce,Rockford,IL).Resultsarepresentedasload-
ing efficiency values, which indicated the percentage of
Scanningelectronmicroscopy
protein loaded in the microparticles with respect to the
Electrosprayed microparticles, mounted on metal stubs
total amount of protein used in the process. Blank micro-
using conductive double-sided tape, were sputter coated
sphereswereusedasreference.
withgoldunderanargonatmosphere.Microparticlemor-
phology was examined by scanning electron microscope
(SEM,S-450;HitachiGlobal,Japan)atanacceleratingvolt-
Invitroreleasestudy
age of 10kV. Microparticle diameters were analysed with
Image J software (National Institutes of Health, Bethesda,
Thein vitrorelease study wasperformed in PBS(pH7.4),
MD).Approximately150countsforeachtypeofmicropar-
and samples were incubated with shaking at 65rpm at
ticleswereusedtocalculatethediameter.
37(cid:4)C. Initially, 3mL 0.01M PBS water was added to a
sealed vial containing 50mg BSA-loaded microparticles,
Transmissionelectronmicroscopy
and the system was maintained at the pre-set conditions
The microstructure of BSA-loaded microparticles was
for different times. At each time point, all the liquid was
examinedusinganH-7650B(HitachiGlobal)transmission
taken out by centrifugation and the vial was refilled with
electronmicroscope(TEM)equippedwithaCCDcamera,
3mL fresh PBS. The BSA concentration in the collection
and operated at 80kV. The samples for TEM observation supernatant was analysed by the Micro-BCATM assay
were prepared by direct deposition of electrosprayed
(Pierce). The results for the release test are presented as
microparticlesontocoppergrids.
cumulative release as a function of time: cumulative
release (%)¼Mt/Ml, where Mt is the amount of BSA
Laserscanningconfocalmicroscopy released at time t and Ml is the total amount of BSA
Tovisualisethepresenceanddistributionoftheproteinsin loadedinthemicroparticlesdeterminedbyproteinloading
the electrosprayed microparticles, FITC–BSA was used efficiency.Foreachgroup,theassaysamplesweretakenin
instead and fluorescent rhodamine B (50mg/mL) was triplicate(n¼3)ateachtimeinterval.
added into PLGA/THM or PLGA/TFE shell solutions.
Fluorescent-stained microparticles were emulsion and
coaxial electrosprayed as described above, collected on Statisticalanalysis
glassslides,andthenobservedbylaserscanningconfocal
microscopy(LSCM;ZEISSLSMExciter5System,CarlZeiss, Statistical analysis was conducted using one-way ANOVA
Germany). The excitation wavelengths for rhodamine B by SPSS software. Data were displayed as mean(cid:2)SD and
and FITC–BSA were 559 and 488nm, respectively, and statisticalsignificancewassetatp50.05.
Controlled release behaviour ofprotein-loaded microparticles 493
Figure1. TEMimagesofmicroparticlespreparedbycoaxialelectrospraytechnique.(A)Formulaa-0%PLGAin;(B)formulab-6%PLGAin;(C)formulac-5%
PLGAinand(D)formulad-4%PLGAin.
Figure2. SEMimage(A)andLCSMimage(B)andthediameterdistributions(C)ofmicroparticlespreparedbycoaxialelectrospraytechniqueofformula
d-4%PLGAin.
Results distinct core–shell structured microparticles formed in all
thethreecases.However,fibrilscouldnotbeavoidedcom-
Characterisationofcoaxialelectrosprayedmicroparticles pletely,iftheconcentrationoftheinnerPLGA/TFEsolution
wasabove5wt%(formulab-6%PLGAinandc-5%PLGAin).
Different formulas were attempted using coaxial electro- Satisfactory core–shell structured microparticles (formula
spray to obtain core–shell structure microparticles. The d-4% PLGAin) resulted when the concentration of inner
outer flow was set 3wt% PLGA/TFE solution. When the PLGA/TFEsolutionwas4wt%.
innerflowwascompletelyBSAaqueoussolution,noappar- SEM showed that microparticles made from formula
entcore–shellstructuredmicroparticlescouldbedetected d-4%PLGAinhad arelatively uniform spherical morphol-
(formula a-0% PLGA in, Figure 1A). Only nanopores were ogy, with an average diameter of 2.41(cid:2)0.60mm analysed
scattered inside the electrosprayed microspheres. To byImageJ(Figure2A).Tovisualisetheproteindistribution
increasetheviscosityoftheinnerflow,PLGA/TFEsolutions within the coaxially electrosprayed microparticles,
with different concentrations were applied. By dropping 50mg/mL fluorescent rhodamine B was introduced into
BSA aqueous solution into PLGA/TFE solutions, BSA the outer solution and FITC–BSA was used instead. The
nano-powderssuspendedinPLGAsolutionswereprepared microparticleswerepreparedunderexactlythesamecon-
andsuppliedasinnerflowwithPLGA/TFEoutersolution, ditionsasaboveandobservedonLSCM.Theredstainwas
andcoaxialelectrosprayed.Theviscosityoftheinnersolu- attributed to rhodamine B, representing the shell region,
tion had a significant effect on the morphology of coaxial whereas the green stain relating to FITC–BSA confirmed
electrosprayedmicroparticles.AsshowninFigure1(B)–(D), the encapsulation of protein inside the core area of the
494 Y. Wang etal.
Figure3. SEMimagesofmicroparticlespreparedbyemulsionelectrospraytechnique.(A)formulah-2%PLGA;(B)formulai-4%PLGA;(C)formulaj-6%
PLGAand(D)formulak-8%PLGA.
Figure4. TEMimage(A)andLCSMimage(B)ofmicroparticlespreparedbyemulsionelectrospraytechniqueandthediameterdistributionsofformula
j-6%PLGA(C).
microparticles (Figure2B). Thegreen fluorescence turned concentrated for emulsion electrospray, because particle
outtobeyellowishbecauseitblendedwiththeredstainof sized deviated to a certain extent and fibrils began to
rhodamineBintheshell. showup(formulak-8%PLGA,Figure3D).
Emulsionelectrosprayedmicroparticlesdemonstrateda
completely different interior structure from those coaxi-
ally electrosprayed. BSA aqueous solution was dispersed
Characterisationofemulsionelectrospraymicroparticles
throughout the microparticles, as confirmed by
Figure 4(A) and (B). TEM observation showed the porous
In addition to coaxial electrospray, microparticles can be
structureandyellowishstain(acombinationofredstainof
obtainedfromawiderangeofpolymericsolutionconcen-
rhodamineBandgreenstainofFITC–BSA)distributedover
trations using emulsion electrospray. As illustrated in
the microparticles. Some BSA was close to the surface of
Figure 3, as the concentration of PLGA/TFE solution
themicroparticleswithstronggreenstainingattheperiph-
increases from 2 to 8wt%, almost no fibre structures were
eral region. There was some strong green (FITC–BSA)
formed. However, the morphology of emulsion electro-
stainingnearthesurfaceofthemicroparticles(Figure2B).
sprayed microparticles changed significantly depending
onpolymericsolutionconcentration.Atlowsolutioncon-
centration (formula h-2% PLGA and i-4% PLGA), the
microparticles were shrunk and collapsed (Figure 3A Proteinloadingefficiencyandinvitrorelease
and B). By increasing the concentration to 6wt%, fine-
structured microspheres resulted with relatively uniform Protein loading efficiencies under different formulas were
size (formula j-6% PLGA, Figure 3C), which was analysed measured,andthosedataarelistedinTables1and2.On
as 22.75(cid:2)8.05mm (Figure 4C). 8wt% seemed a little average, the loading efficiencies of emulsion electrospray
Controlled release behaviour ofprotein-loaded microparticles 495
Figure5. Proteinreleaseprofilesfortheelectrospraymicroparticles.(A)Proteinreleaseprofilesfortheemulsionelectrospraymicroparticlestheoretically
loadedwith1wt%,3wt%and5wt%BSA.(B)Proteinreleaseprofilesforthecoaxialelectrospraymicroparticlestheoreticallyloadedwith1wt%,3wt%and
5wt%BSA.(*p50.05).
microparticleswerealittlelowerthanthoseofcoaxialelec- which has made them attractive to researchers
trospray microparticles. The loading efficiencies in both (Scholten et al., 2011). Many kinds of materials can be
cases decreased as the drug loading increased. The usedtoproducemicroparticleswithdrugorproteinincor-
invitroreleasebehaviouroftheseBSA-loadedmicroparti- porated in by electrospray technique. Biodegradable algi-
cles was compared. For the emulsion electrospray micro- natehadbeenelectrosprayedintomicrosizeandwithBSA
particles(Figure 5A),asignificantinitialburst releasewas encapsulated(Suksamranetal.,2009).
detected.Within1day,430%oftheloadedBSAhadbeen Emulsion electrospray was investigated in the present
released.Afterwards,thereleaseratesloweddownbutwas study.Inthiscase,proteincouldbeentrappedintheelec-
sustainable,andthecumulativeBSAreleasewas50–60%at trosprayed microparticles by dissolving in water and dis-
theendof6weeks.Thecoaxialelectrospraymicroparticles persinginpolymericinorganicsolutionbyultrasonication.
showed better release behaviour than the emulsion elec- Theoretically, the proteins should be distributed evenly
trospray microparticles (Figure 5B). The initial burst throughout the electrosprayed microparticles, however,
release was minor. The BSA release remained at a steady they were scatteredthroughout the microparticles invari-
rate within the experimental period. About 40–50% BSA oussizesinmostcases.AsshowninFigure4,BSAinemul-
was released up to day 42. For all three emulsion groups, sion electrosprayed PLGA microparticles was unevenly
a burst release was observed within 24h, which was loaded.Especiallyattheedgeofthemicroparticles,stron-
24.02%(cid:2)0.27%, 26.15%(cid:2)0.35% and 28.80%(cid:2)1.14% for ger BSA signals were detected, as confirmed by the green
the 1%-BSA, 3%-BSA and 5%-BSA microparticles, respec- stain. This distribution pattern is closely related to the
tively. These values were significantly different (p40.05) structure and stability of water-in-oil emulsions (Yang
fromthecoaxialgroupswhencomparedbetweenthesame et al., 2011). The aqueous phase composed of BSA dis-
theoretical loading efficiency (d-4% PLGAin and j-6% solved in deionised water was dispersed into the organic
PLGA, e-4% PLGAin and l-6% PLGA, f-4% PLGAin and phase composed of PLGA/THM by ultrasonication. The
m-6% PLGA) groups at 24h time point. In both cases, scatteredaqueousdropletsmightmergeintodropsofvar-
onethingincommonwasthattheBSAreleaserateswere ious sizes during emulsion electrospray. Therefore, emul-
acceleratedasdrugloadingincreased. sion electrospray microparticles had a clear initial burst
releaseowingtotherapiddiffusionofwaterintothemicro-
particlessurfaceandtherapiddissolutionofBSAnearthe
Discussion surface into the release medium (Figure 5A). The burst
release would be more significant if the drug loading
Most clinical diseases require long-term treatment with wereincreased.
bioactive factors. Sustained release from polymeric Incontrast,thedevelopmentofcoaxialelectrosprayhas
matrixes has been proven as the simplest and most effec- providedanefficientwaytoamelioratetheproteinrelease
tive strategy to achieve that goal (Malathi and behaviour.Throughcoaxialjets,atypeofcore–shellnano-
Balasubramanian,2011).Tablets,films,gels,microparticles particles are generated by electrohydrodynamic forces, in
and nanoparticles are all possible pharmaceutical prepa- which proteins are usually embedded in the core region
rations. Microparticles and nanoparticles are preferred (Loscertales et al., 2002; Hwang et al., 2008; Xie et al.,
overothermethodsasaresultoftheirflexibilityinprepa- 2008). As illustrated in Figure 2, BSA could be only found
ration and use (Xu et al., 2009). Electrosprayed micropar- in the centre of coaxially electrosprayed microparticles
ticles have attractive features in narrow particle size with no hint of existence in the PLGA shell. These core–
distribution and minor loss of protein bioactivity in com- shell structured coaxial microparticles provide a barrier
parison with the conventional double-emulsion method, membrane that controls the protein diffusion rate
496 Y. Wang etal.
(Lee et al., 2010), thus ensuring that BSA is released at a electrospray group had an apparently higher BSA load-
constant rate with an insignificant initial burst release ing efficiency than the emulsion electrospray group
(Figure5B),whichwasmorewelcomedbypracticalappli- (Tables 1 and 2). One of the reasons for this was that
cationforthefinecontrolofreleasebehaviour.Aresearch some protein denatured during the ultrasonication used
showedthatPVAcoatedPLGAmicroparticlesnotonlypre- for emulsion preparation (Wang et al., 2004). Besides,
sentedadecreaseinthedrugreleaserateduringtheinitial BSAencapsulatedinemulsionmicroparticleshadadirect
burst, but alsothe percentage of thedrug released by dif- contact with the air, which may cause more protein loss
fusion is substantially reduced, from 77% (TFE) to 52% duringtheelectrospunprocess.Moreover,thedrugloading
(TFE–DMSO) compared to uncoated ones (Almeria et al., could be increased by increasing inner protein aqueous
2011).TheDMSOhelpedPLGAdissolveandswellinTFE, solution flow rate or increasing inner protein concentra-
which made the protein released from the microparticles tion. But the inner solution flow had a great impact on
moreeasilyandthoroughly.ThosecoatingPVAservedasa microparticlesformation(Xieetal.,2008).Coaxialelectro-
barrierthatslowdownthedrugreleaserate.Andtheshell spray had avoided the shortcomings of emulsion electro-
PLGAinourcoaxialelectrosprayedexperimentjustplayed spray,thesefeatureshadmadecoaxialelectrosprayfurther
the same role in drug release. The hydrophilic BSA disso- favourable for preparing protein-loaded microparticles in
lutioninto water wasthekeystep during thedrugrelease comparisontoemulsionpreparation.
process.Apartfromthesurfacelocation,theporousstruc-
ture (Figure 4A) allowed the water entered inside of the
emulsionmicroparticlesfaster.However,thehydrophobic
Conclusion
PLGA shell (Figure 1D) of coaxial microparticles slowed
downthewatercontactwithBSAinthecore,thussignifi-
In conclusion, both emulsion and coaxial electrospray
cantlyreducedburstrelease.
techniques can produce protein-loaded microparticles to
Microparticle morphology might be another factor to
achievesustaineddrugrelease.Thecore–shellstructureof
consider for practical application. Microparticles from
thecoaxiallyelectrosprayedmicroparticles providedthem
emulsion electrospray usually demonstrated a shrunken
withagreaterabilitytocontrolreleasebehaviourandguar-
and wrinkled appearance, owing to the evaporation of a
anteed higher drug loading efficiencies in comparison
large amount of solvent in electrosprayed drops
with emulsion electrosprayed microparticles. This
(Figure 3). In fact, this was a common phenomenon in
study indicated that the coaxial electrospray might be a
microparticleformationusingelectrospray,whichremark-
superior approach to achieve sustained drug release
ably depended on concentrations of polymeric solutions.
with a minor initial burst release, which is preferable for
Thisdamagetoparticlemorphologycouldbeweakenedby
clinicaluse.
increasing the concentration of the polymeric solution,
however, it could not be too high for allowing fibre struc-
turetooccur(Enayatietal.,2009).Nevertheless,thecoax-
Declaration of interest
iallyelectrosprayedmicroparticlesresultedinmuchbetter
morphology.AsshowninFigure2(A),thecore–shellstruc-
tured microparticles had a relatively smooth surface with The authors report no conflict of interest. The authors
small pinholes. The morphology difference in the two alone are responsible for the content and writing of this
groups of electrospray microparticles suggested an addi- article.
tional reason for the rapid initial release from emulsion The authors acknowledge the National Basic Research
electrospray microparticles. Water molecules penetrated Program of China (2012CB933900), International Science
intoandBSAmoleculesdiffusedoutofthemicroparticles and Technology Cooperation Program (2010DFA51500),
rapidlythroughthemicroporesandmicroductsonthesur- National Natural Science Foundation of China (51073016
faceoftheparticles. and81171000)andtheProgramforNewCenturyExcellent
Additionally, there were other two notable differences TalentsinUniversity(NCET-11-0556).
existing between the emulsion and coaxial electrosprayed
microparticles in this study. Firstly, the mean diameter of
the emulsion electrosprayed microparticles was much References
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