Injectable nanocomposite hydrogels and electrosprayed nano (micro) particles for biomedical applications

Polymeric scaffolds have played important roles in biomedical applications due to their potentially practical performance such as delivery of bioactive components and/or regenerative cells. These materials were well designed to encapsulate bioactive molecules or/and nanoparticles for enhancing their performance in tissue regeneration and drug delivery systems.

© Springer Nature Singapore Pte Ltd 2018

H J Chun et al (eds.), Novel Biomaterials for Regenerative Medicine, Advances in Experimental

Medicine and Biology 1077, https://doi.org/10.1007/978-981-13-0947-2_13

Injectable Nanocomposite Hydrogels and Electrosprayed Nano(Micro)Particles

for Biomedical Applications

Nguyen Vu Viet Linh, Nguyen Tien Thinh, Pham Trung Kien, Tran Ngoc Quyen, and Huynh Dai Phu

Abstract

Polymeric scaffolds have played important

roles in biomedical applications due to their

potentially practical performance such as

delivery of bioactive components and/or

regenerative cells These materials were well-

designed to encapsulate bioactive molecules or/and nanoparticles for enhancing their per-formance in tissue regeneration and drug delivery systems In the study, several multi-functional nanocomposite hydrogel and poly-meric nano(micro)particles-electrosprayed platforms were described from their fabrica-tion methods and structural characterizations

to potential applications in the mentioned fields Regarding to their described perfor-mance, these multifunctional nanocomposite biomaterials could pay many ways for further studies that enables them apply in clinical applications

Keywords

Injectable hydrogel · Nanocomposite · Polysaccharide · Electrospray · Biomedical applications

13.1 Introduction

There has been a high demand of biomaterials in therapeutic treatment, replacement or regenera-tion of damaged tissues/organs, diagnostic proce-dure and etc leading to many studies on various advanced biocompatible and biodegradable mate-rials recently [1] Among of them, injectable and biocompatible polysaccharide-based hydrogels have paid much attention [2 3] The hydrogels

N V V Linh · H D Phu (*)

Faculty of Materials Technology, Ho Chi Minh City

University of Technology (HCMUT), Vietnam

National University, Ho Chi Minh City, Vietnam

National Key Lab for Polymer and Composite

Materials, HCMUT, Ho Chi Minh City, Vietnam

e-mail: nguyenvuvietlinh@hcmut.edu.vn ;

hdphu@hcmut.edu.vn

N T Thinh

Graduate School of Science and Technology, Vietnam

Academy of Science and Technology,

Ho Chi Minh City, Vietnam

Department of Pharmacy and Medicine, Tra Vinh

University, Tra Vinh City, Vietnam

P T Kien

Faculty of Materials Technology, Ho Chi Minh City

University of Technology (HCMUT), Vietnam

National University, Ho Chi Minh City, Vietnam

T N Quyen (*)

Graduate School of Science and Technology, Department

of Pharmacy and Medicine, Vietnam Academy of

Science and Technology, Ho Chi Minh City, Vietnam

e-mail: tnquyen@iams.vast.vn

13

fabricate from hydrophilic polymers, which can

retain significant amount of water or bio-fluid

allowing transportation of substances such as

nutrients and by-products from cell metabolism

Moreover, these materials were well-designed to

implant in a minimally invasive surgical

opera-tion, improve patient compliance, degrade along

with regeneration process of typical tissues and

deliver drug/bioactive compounds/cells on the

treated sites [4 6] Up to now, various injectable

hydrogel scaffolds have been fabricated via

physi-cal interactions of polymers or chemiphysi-cal reactions

of functional polymers such as hydrophobic

inter-action, stereocomplex affect, electrostatic

interac-tion, photochemical reacinterac-tion, Michael- type

reaction, Schiff-base reaction and enzyme-

mediated crosslinking reactions [7 9] Preparation

of the injectable horseradish peroxidase

enzyme-mediated hydrogels is emerging as an effective

method because it is a highly specific reaction,

which avoids side reactions or production of toxic

by-products leading to harm with cells and living

body [5 9] Every obtained scaffold has exhibited

some particular points on physical property,

speech of matrix dissolution, compatibility and

etc Recently, incorporation of nanoparticles and

the hydrogels produced multifunctional injectable

nanocomposite biomaterials for extending their

applications in tissue engineering, drug delivery,

antimicrobial materials, and bio-sensing systems

Besides performance of the mentioned

nano-composite hydrogels, polymeric

nano(micro)par-ticles (NMPs) recently have exhibited a great

potential in biomedical applications The

nanoparticles could be fabricated via two

physi-cal and chemiphysi-cal methods In the physiphysi-cal

meth-ods, polymeric NMPs are fabricated via various

techniques such as freeze drying, spray drying,

nano(micro) precipitation, self-assembly of

amphiphilic copolymers or phospholipids,

elec-trospinning, solvent evaporation and so on in

which polymers are dissolved in solutions For

the chemical methods, most of NMPs obtains

from polymerization of monomer solutions that

could be listed as micro emulsion, conventional

emulsion, controlled radical, surfactant-free

emulsion and etc [10] These polymeric NMPs

have received great interest due to their structural

versatility in fabricating process that could ciently load and release bioactive compounds, chemotherapeutics, contrast agents, proteins and nucleic acids to the desired sites Moreover, the drug release behavior of the particles is also adjustable by their structural materials and fabri-cating methods that satisfy with treatment and harmony with physiologically internal conditions such as pH, enzyme and biochemical reactions

effi-An incorporation of the particles with external stimuli such as temperature, near-IR irradiation, UV-Vis light, magnetic fields, ultrasound energy and etc., have also paved other ways for these materials in biomedical applications [11]

In this study, we introduce some injectable nanocomposite hydrogel systems and electro-sprayed NMPs that have been recently developed and performed a great potential for applying vari-ous biomedical fields In the chapter, besides some advanced biomaterials were published from devel-oped countries, many our studies are also included

to indicate an extensive development of these advanced biomedical materials in over the world

13.2 Injectable Nanocomposite

Hydrogel for Biomedical Applications

13.2.1 Nanoparticles

In recent years, several metallic nanoparticles

(NPs) have been emerging as the alternative didates in many conventional materials due to their novel well-known properties such as anti-bacterial, antiplasmodial, anti-inflammatory, anticancer, antiviral, and antifungal activities [12–22] Some kinds of inorganic and organic nanoparticles also exhibited osteoinductive and osteoconductive activities or high efficiency in drug delivery that have offered much potential in biomedical applications [23–28]

can-Approaches to produce nanoparticles are sified as “top down” and “bottom up” methods (Fig. 13.1) The top-down method used various physical and chemical processes to achieve the small-sized nanoparticles from its bulk form Of bottom up approach, the nanoparticles can be

clas-synthesized from ions, joining atoms, molecules

or small particles The bottom up approach

mostly relies on chemical and biological methods

of production [29, 30] Among different types of

nanoparticle production, chemical synthesis is

known as the most popular method using in

com-mercial scale due to the high efficiency compared

to other methods The obtained nanoparticles

tar-geted for various biomedical applications Until

now hundreds of nanoparticles-based products

approved in clinical applications or successes in

clinical trial phases [31–35]

13.2.2 Nanocomposites

and Biological

Nanocomposites

Nanocomposites is well-known as a biphasic

material in which has one nano-sized solid phase

dispersed in the bulk matrix The material has early applied in paint engineering and cosmetic from middle 1950s Thereafter, there had been widely studied and developed on the nanoparti-cles or nanofibers-based reinforcing materials for industrial applications The nanomaterial phase exhibiting large surface area contributes to signifi-cantly enhance interaction between the dispersing phase and the bulk matrix resulting in a mechani-cal improvement as compared to bulk materials According to their bulk matrices, they could be classified into three main categories: Ceramic matrix nanocomposites (CMNCs), metal matrix nanocomposites (MMNCs) and polymer matrix nanocomposites (PMNCs) [24, 25, 36] PMNCs have been frequently used in fabrication of scaf-folds for tissue engineering or drug delivery, anti-microbial materials, and biosensors systems

In tissue regeneration and drug delivery fields, many calcium phosphate-based PMNCs possess

Fig 13.1 Methods for fabrication of nano(micro)particles

a similar structure with biological

nanocompos-ites such as exoskeleton of arthropods and animal

bone as well as biocompatibility and

biodegrada-tion Several kinds of mineral nanoparticles like

hydroxyapatite, biphasic calcium phosphate,

bio-glass etc have been dispersed in the polymers

producing bioactive nanocomposite materials for

tissue regeneration Hydroxyapatite (HA), a

cal-cium phosphate, possesses chemical composition

and structure similar to mineral phase in human

bones with osteoinductive and osteoconductive

properties that has been utilized to fabricate

arti-ficial bionanocomposites for bone implantation

[23–27] Abundance of nano-sized HA and

poly-mers exhibit a high biocompatibility and good

mechanical properties that match with

require-ments for bone implant engineering [23–27]

Biphasic calcium phosphate and bio-glass are

also some similar properties of HA.  However,

these materials exhibit a high bio-mineralization

rate via an enhanced formation of crystalline

hydroxyapatite that contributes to new bone

for-mation Some studies also indicated that calcium

phosphate nanoparticles dispersed in polymer

matrices can partially protect some loaded

bio-molecules and polymer from biodegradation [32,

37] The calcium phosphate nanoparticles-based

materials have recently used as a platform for

delivery of bioactive molecules, drugs and genes

Calcium phosphate-alginate nanocomposite

per-forms a high drug loading efficiency (caffeic,

chlorogenic and cisplatin), control release of the

drugs and improvement in anticancer activity on

human osteosarcoma [38, 39] Several kinds of

calcium phosphate nanoparticles and

biopolymers- based nanocomposites delivered

effectively growth factors and/or osteogenic

drugs (BMP-2, FGF-2, bisphosphonate,

dexa-methasone etc.) that are considering as a novel

generation of the osteogenic stimulating

scaf-folds for bone regeneration [38–43]

Regarding outstanding properties of metal

nanoparticles on antimicrobial activity, there has

an emerging approach in which utilized them in

fabrication of antimicrobial nanocomposite for

practical applications such as agriculture, care, and the industry As prepared at nanoscale, the nanoparticles exhibit a highly active facet that

health-is more biologically reactive as compared to the bulk counterpart [40, 43] It is well-known that various biological polymers are elastic and flexi-ble to fabricate equipments, biomedical devices and household items The incorporation of the antimicrobial nanoparticles and polymers pro-duced several kinds of active nanocomposites as well as improvement in nanoparticles’ stability [40, 43] In some cases, the formulation could increase a higher antimicrobial activity as com-pared to their own nanoparticles due to synergic effects of the constituents such as antimicrobial or/and structural properties of polymeric phase and the active nanoparticles as sampled in Fig. 13.2 [24, 25, 44, 45]

An emerging approach of the biological nanocomposites in fabrication of biosensors and flexible electronics should be herein discussed Regarding to the elastic property of polymers and the specific interactions of nanoparticles, various biological nanocomposites have devel-oped for several biomedical applications such as pathogen detection, cancer tracking, detection of small biomolecules etc [46] In fact, S.K. Shukla

et  al developed an indium-tin oxide glass substrate- based bio-electrode that coated glu-cose oxidase- immobilized ZnO/chitosan-graft-poly(vinyl alcohol) The bio-electrode potentially responded to the glucose down to1.2 mM. In the electrode, ZnO play an important role in the enzyme immobilization and its excellent stabil-ity Wang also reported a gold nanoparticles–bacterial cellulose nanocomposite that effectively immobilized glucose oxidase and horseradish peroxidase for coating the glassy carbon elec-trode Gold nanorod particles-doped polyaniline and gold- graphene/chitosan nanocomposites performed a high efficiency in immobilizing glu-cose oxidase and cholesterol oxidase, respec-tively, and others that have exhibited a great potential of nanocomposite- based biosensors [47–52]

13.2.3 Hydrogels

and Nanocomposite

Hydrogels in Biomedical

Applications

It is well-known that hydrogel scaffolds are

play-ing an important role in biomedical applications

due to their practical performances such as

deliv-ery of bioactive components, platforms for tissue

engineering [53–55] The hydrogels consist of

hydrophilic polymers network are prepared via

various physical, chemical and enzyme-mediated

methods in which can encapsulate or immobilize

bioactive molecules, drugs, enzyme and

nanopar-ticles for tissue engineering or controlled drug

delivery, antimicrobial materials, biosensors

sys-tems etc [53–57] With swellable and porous

properties in aqueous solution, the hydrogel

sys-tems facilitate the transportation of substances

from cell metabolism, control delivery of drugs,

provision of signals from various biologically

specific interactions [58]

Nanocomposite hydrogels (NC gels) have

recently emerged as approaches to extend

appli-cable fields of these mentioned platforms that based on an incorporation of the hydrogels with nanoparticles By incorporating the interactions between nanoparticles and hydrogel network as well as physical, chemical, electrical, biological

as well as swelling/de-swelling properties of either material alone, NC gels could lead to an innovative means for producing multi- compartment and multifunctional materials For example, Meisam Omidi reported a thermo- and/

or pH sensitive, electro-responsive, magnetically responsive or light-responsive NC gel based on chitosan and carbon dots (CDs) exhibiting poten-tially dual applications as antibacterial and pH- sensitive nano-agents for enhancing wound healing and monitoring the pH at the same time The NC gel had a strong antibacterial activity [59] Moreover, under daylight at various pH val-ues, the color of the CDs changes from bright yellow towards dark yellow when increasing the

pH values indicating the pH sensitivity of the CDs even under daylight, whereas under UV light, the fluorescence intensity of the CDs is obviously affected from acidic milieu towards

Dopamine-mediatedadhesive bonding

basic This NC gels can be utilized as an

out-standing pH-sensitive probe for biomedical

applications, especially for monitoring the pH

values during the wound healing process [59]

Various carbon, polymeric, ceramic and/or

metal-lic nanomaterials-incorporated hydrogels

exhib-ited biological, optical and ambient stimulus

properties, which can be potential to apply in

clinical fields like tissue engineering, drug

deliv-ery system and biosensors as demonstrated in

Fig. 13.3 [58, 60, 61]

13.2.4 Injectable Nanocomposite

Hydrogels in Biomedical

Applications

For some implanted biomaterials and bio-

microfluid devices, in situ fabrication of various

hydrogel platforms has paid much attention

because it allows monomers (macromolecules) to

form a 3-D network that enables the hydrogels

conform to the shape of the defect sites or

sub-strate of the devices resulting in its better bio-

interaction, increment in interconnectivity,

site-specific drugs delivery, enhancing

bioavail-ability and minimizing side effects and/or match

with the structural device [62–66] Moreover,

these in situ implanted materials could improve

patient compliance due to its minimally invasive surgical operation Up to now, various injectable nanocomposite hydrogels have been reported at which were prepared via physical or chemical methods These materials could be formed by hydrophobic interaction, stereocomplex effect, electrostatic interaction, photochemical reaction, Michael-type reaction, Schiff-base reaction and enzyme-mediated crosslinking reactions [66–

68] Every obtained scaffold has exhibited some different behaviors on physical property, speech

of matrix dissolution, drug delivery rate, ibility and etc

compat-In tissue regeneration, various NC gels have been in situ fabricated from the combination of biodegradable polymers and bioactive inorganic materials, which proved an improvement in mechanical properties and mineralization of the nanocomposite materials for bone tissue engi-neering [8 69] Fu reported an injectable biode-gradable thermo-sensitive nano-hydroxyapatite and poly(ethylene glycol)-poly(ε-caprolactone)-poly(ethylene glycol)-based nanocomposite hydrogel exhibiting a potential for orthopedic tis-sue engineering The group also found that the injectable nano-hydroxyapatite dispersed PEG- PCL- PEG copolymer/collagen hydrogel per-formed a high cytocompatibility and better calvarial bone regeneration as compared the self-

Fig 13.3 Approaches in fabrication of nanocomposite hydrogel for biomedical applications

healing defects [70] Dang also introduced the

injectable NC gel using biphasic calcium

phos-phate (BCP), gelatin, and oxidized alginate [71]

The alginate-gelatin-BCP hydrogels provided a

favorable environment for bone in growth and

possibly biodegradation as compared with pure

hydrogel (alginate-gelatin hydrogel) The NC gel

implanted to femoral bone defects exhibited a

regenerated bone surface/volume ratio and bone

surface density higher than that of the hydrogel-

filled incisions Other injectable NC gel were

fabricated from fibrin nanoparticles and bioglass-

loaded chitin/poly(butylene succinate) enhanced

the osteoinductive properties [72] We have also

developed an enzyme-mediated and

biodegradation- controllable BCP -loaded

chito-san/gelatin hydrogel as demonstrated in Fig 13.4

that stimulated bio-mineralization as well as

pro-liferation of bone marrow mesenchymal stem

cells (MSCs) [73] Our obtained results indicated

that these injectable nanocomposite hydrogels

could be promising in bone regeneration

Various nanocomposite hydrogels have also

been well-performed in burn or wound healing

Our group in situ prepared curcumin nanoparticle

in an amphiphilic pluronic F127-g-chitosan

copolymer solution resulting fabrication of a

temperature responsive NC gel The synergic

incorporation has also produced a

multifunc-tional nanocomposite hydrogels by the

combina-tion of dual bioactive chitosan and nanocurcumin

components that has also led to NP-gels against

growth of both gram bacteria Moreover, the injectable NC gel enhanced 3rd burn healing rate

as compared to Silvirin (a commercial drugs for burn treatment) Preparation and application of the hydrogels are demonstrated in Fig. 13.5 [74]

Li also reported an injectable curcumin nanoparticles-loaded N,O-carboxymethyl chito-san/oxidized alginate hydrogel exhibiting a high wound healing efficiency [75] The system may also be applied for internal wounds due to its ability in minimally invasive implantation Moreover, some injectable NC-gels have also developed from incorporation of antibacterial metallic nanoparticles in biocompatible and bio-active hydrogels for inhibiting microbe growth at wound sites [76, 77]

Utilization of some inorganic and carbon- based nanomaterials for enhancing efficiency of various injectable delivery systems has recently become an approach Renae developed an inject-able silicate nanoplatelets and gelatin-based hydrogel to effectively deliver the hMSC growth factor and enhance proliferation of human endo-thelial cells resulting in produced significantly myocardial angiogenesis at the injected site [78]

An injectable NC gel for effective vasculogenesis and cardiac repair was developed based DNA- VEGF- complexed polyethylenimine  – graphene oxide nano-sheets and methacrylated gelatin (GelMA) hydrogels [79] Gold nano-rods doped into a thermally responsive hydrogels were able

to induce the contraction of the thermo- responsive

Fig 13.4 Horseradish peroxidase-mediated fabrication of chitosan/gelatin and BCP nanoparticles-based

nanocompos-ite hydrogel for born tissue regeneration

hydrogels and trigger the release of loaded

doxo-rubicin to inhibit breast cancer under NIR

irradi-ation [80] Other NIR-responsive nanoparticles

such as carbon nanotubes and graphene oxide

nanoparticles were also incorporated into thermo-

responsive polymers to harness NIR for remotely

controlled drug delivery [81, 82] The stimuli

responsive NC gel has also developed from

dopa-mine nanoparticle-loaded pNIPAAm-co-pAAm

hydrogel, in which was loaded bortezomib and

doxorubicin to apply in photo/thermal therapy

and multidrug chemotherapy NIR laser and

dopamine nanoparticles controlled release

behav-iors of doxorubicin and bortezomib, respectively

[83] Gold nanorods were dispersed into the

injectable N-isopropylacrylamide and

methacry-lated poly-β-cyclodextrin copolymers-based

hydrogels loaded doxorubicin that showed as an

effectively long-term drug delivery platform in

chemophotothermal synergistic cancer therapy

In addition, abundance of amphiphilic nature-

driven copolymers performed a great biological

properties could be ultilized for fabricating

sev-eral kinds of injectable materials [84, 85] Such

injectable multifunctional nanocomposite

hydro-gels would be well performed clinically in near

future

13.3 Electrosprayed

Microparticles for Biomedical Applications

In recent years, several nano (micro)particles

(NMPs) have been emerging as the potential didates in various drugs delivery systems due to their structural versatility in fabricating process that could efficiently load and deliver bioactive compounds, chemotherapeutics, proteins and nucleic acids to the desired site Drug release behavior of the particles is moreover adjustable

can-by their structural materials We therefore focus

on efficiency of electrospraying method in trolling drug delivery

con-13.3.1 Introduction

of Electrospraying Method for Drug Delivery

Electrospraying is a significant technique for ricating polymeric solid microparticles in drug carrier application There are a lot of prospective advantages of this method such as simple one- step process, no or limited denaturation of bio- macromolecules (drugs and proteins), high

hydrophobic/hydrophilic drug encapsulation

efficiency (EE) and loading capacity (LC),

con-trolling the morphology and size of solid

parti-cles and high permeability to small molecules

[86–88] Similar to some well-known drug

deliv-ery systems, electrospraying technique fabricated

particles have been studying to reduce or

over-come these drawbacks of conventional

therapeu-tic treatment by their prolong drug release and

release onsite with a safe dose Therefore, the

particles have been one of the most efficient

plat-forms for drug delivery system and tissue

engi-neering The mechanism release of drug from the

particulate microparticles consists of 2 steps: The

initial step is burst release since the drugs in and

on their surface diffuse to the environment The

second step is release at slow and more constant

by releasing the drug inside the particles due to

the erosion of microparticles, consequences of

degradation polymer matrix [89, 90] The release

profile was influenced by the morphology, size

and size distribution of the microparticles [91–

93] In more details, the wrinkle and hollow

par-ticles have pores and larger surface area than that

of the dense spheres, in consequence, the fluids

penetrate inner the particles faster and the drugs

are able to diffuse easily and rapidly Whereas,

the dense particles can reduce the fluid

penetra-tion and diffusion of drug in the polymer matrix

because the drugs can move out of the particles

through the pores so that it can maintain the

con-stant release kinetics In addition, the polymer

concentration as well as the molecular weight of

polymers (Mw), can tailor the morphology of

particles and their release profile [94–97] The

low molecule weight of polymers causes

inter-molecular interaction weaken, thus it cannot

encapsulate drug effectively and allow the

diffu-sion of drug from the polymer more easily [93]

Besides, burst release can happen from smaller

particles size Microparticles with smaller size

make the drug release faster due to the

penetra-tion of fluid and diffusion of drugs to the

environ-ment They have a larger surface area to volume

ratio than bigger particles so that they are eroded

quickly as a consequence of degradation polymer

matrix [98, 99] Furthermore, the size

distribu-tion of polymeric particles causes uncontrollable

release rate of drug since the different size have different the drug release rate

According to the of the essential literature of drug release and some factors which influence on release rate, the release of drug can be tailored by controlling the morphology and size of the mic-roparticles For electrospraying technique, how the morphology and size can be controlled? The fundamental principle of electrospraying method

is that the high voltage was applied between the tip of the needle and the collector Thanks to the electrical field force, the charged droplet issued from the tip will fly to the collector and form solid particles During electrospraying, there was the competition between the coulomb fission and the polymer diffusion in the droplets When the solvent evaporated, the charge density was increased inner the droplet and so that the cou-lomb fission divided a primary droplet into smaller droplets [98–100] Finally, the solid par-ticles were collected on the collector, as a conse-quence of the absolute evaporation of solvent as demonstrated in Fig. 13.6

According to a basic theory of this method, adjusting the solvent, polymer concentration and flow rate seriously influenced the morphol-ogy of the electrosprayed particles Each sol-vent has specific properties such as electrical conductivity, evaporation rate, and viscosity so that it causes the changing morphologies For faster- evaporating solvent as dichloromethane (DCM) has a low boiling point (40 °C) or chlo-roform (boiling point is 56  °C), the solvent in the droplet is evaporated quickly while the poly-mer chains don’t have enough time to diffuse to inside the droplet In addition, the surface of particles change solid although the solvent still

is inner the particles, and during the time vent diffuse and emit to the environment Therefore, the final particles on the collector are wrinkles or even hollows and porous From the opposite side, the low evaporating solvent as dimethyl formamide (DMF) and tetrahydrofu-ran (THF) have boiling points at 152  °C and

sol-65  °C, respectively The polymer chains have more time to diffuse from the surfaces of mic-roparticles to inner when the solvent move out and evaporate completely These result reported

ON OFF Micro-pump

technique for fabrication of

particles was fabricated in

our group

that electrosprayed particles are smaller and

smooth surface as well as dense [94, 96, 98,

101] Beside different evaporation rate, each

solvent has different conductivity (or dielectric

constant), it causes dissimilar to Coulomb

fis-sion in the droplet and leads to different

parti-cles size Xie et al reported that the size of PCL

particles reduced when the conductivity of

polymer solution increase, as a consequence of

using different solvent as DCM (0.000275 μS/

cm) and Acetonitrile (0.071 μS/cm) [94]

The second factor influences the morphology

of microparticles is the chain entanglements in

electrosprayed solution The number of chain

entanglements depends on the polymer

concen-tration and molecular weight (Mw) [98‚102–

104] There are a few entanglements when the

polymer concentration or Mw of polymer is low,

thus electrosprayed particles is a film, disk, or

semi-sphere in shape Whereas, high polymer

concentration or high molecular weight, the

polymer solution occurs with higher density of

chain entanglements, in consequence, tapered

particles, beaded fibers, and event fibers will be

created The electrosprayed microspheres were

achieved when the chain entanglements were

generated effectively And the electrosprayed

droplet cannot be separated and deformed by

Coulomb fission [105, 106] The low Mw

poly-mer can create the microspheres at high polypoly-mer

concentration instead of hollow and porous

par-ticles, whereas high Mw polymer can generate the microspheres at low concentration Because the polymer chains of high Mw polymer are lon-ger, they overlap together easier and enhances the formation of the entanglements in the droplets [93, 102, 107]

Flow rate factor also effects on the ogy of the electrosprayed particles A high flow rate causes particles deformed, aggregated and inconsistent morphology as a result of incom-pletely solvent evaporation At the same polymer solution, the high flow rate produces a lower amount of chain entanglements and higher amount of solvent in the droplet, so that the poly-mer matrix cannot conserve the droplet integrity under the Coulomb fission and solvent evapora-tion As a result, when the particles impact on the collector, they are collapsed and deformed For example, the PLGA particles were deformed and stick together at the flow rate of 2 mL/h while at

morphol-1 mL/h, they formed the separated microparticles [93, 108] Moreover, the size of particles created

by a high flow rate is bigger than that of low flow rate [94, 95]

Apart from solvent, polymer concentration and flow rate, applied voltage is one of factors influences on morphology of the particles When the applied voltage increased,the droplets were highly charged Therefore, the microspheres were stretched and changed to elongated parti-cles, tapered particles or beaded fibers [106,

109] In addition, the high voltage strengthens

the electric field force so that it makes the

elec-trospraying mode change and it impacts on the

size and size distribution or even the morphology

For instances, the multi-jet mode causes the

irregular shape of particles and broaden the size

distribution while the Taylor cone-jet mode

gen-erates the homogeneous particles and

monodis-persity The morphology of particles is stable and

homogeneous with the mono cone-jet mode

how-ever, the size of particles is increased slightly if

the applied voltage increased, as a consequence

of increasing Coulomb fission [93, 101]

In case of collecting distance, it should be

enough far to avoid deformed and aggregated

particles because the solvent cannot evaporate

completely and stay inside particles In Arya’s

reported, chitosan particles were deformed and

stick together at collecting distance of 6 cm, in

consequence, it created a film while microspheres

were formed separately at 7 cm [103] Increasing

the distances not only help polymer chain have

time to diffuse and rearrange within the particles

but also solvent was evaporated completely, so

that more microspheres were obtained [93]

When the collecting distance is expanded enough

far to create separate particles, the size of the

par-ticles is decreased when the collecting distance

increase, as a result of the droplet had been still

divided to smaller particles thanks to coulomb

fission However, at the constant voltage, if the

collecting distance is too far and it overcomes the

limitation, which maximizes of electric field

force, the particles size will reduce [93, 108]

Besides all factors were regarded above, a

diameter of the needle (Gauge) also influenced on

particles size and size distribution The

micropar-ticles which were produced by a bigger gauge

have smaller size because the size of the droplet

(or the volume of the droplet) at the tip of the

nee-dle reduces, in consequences, the final particles on

the collector have smaller sizes [93] However, the

big gauge (small size of inner diameter‘s needle)

can create the multi-jet mode, it leads to

polydis-persity and unrepeatable particles

13.3.2 Fabricating Mono-

Distribution and Homogeneous Morphology of PCL NMPs

by Studying Electrospraying Modes and Tailoring

the Parameters Processing

In this research, some kinds of solvent and vent mixture were used to investigate the influ-ence of solvent on microparticles morphology With the main purpose of fabrication the homo-geneous particles with smooth surfaces, the DMF solvent was chosen [94, 96, 97, 101] Therefore,

sol-it has been used a mixture of two solvent When the mixture solvent of DMF and chloroform (DMF/CHCl3  =  3/1) was created, the morphol-ogy of particles was heterogeneous such as beaded fibers, elongated particles, and fibers (Fig. 13.7a) Because the physical properties of the solvent mixture such as solubility, evapora-tion rate and dielectric constant depended on both chloroform (56 °C, 4.8) and DMF (154 °C, 36.7) [110–112], so that the mixture caused an unstable spraying mode and formed collapsed, unstable and unrepeatable microparticles Especially, the different conductivity (or dielec-tric constant) caused dissimilar to Coulomb fis-sion in the droplet and leads to different particles size [110] Therefore, the solvent mixture made undesirable morphology of PCL particles and should not be used for electrospraying According

to Fig. 13.7b and c, the electrosprayed particles were microspheres although they were wrinkled This phenomenon was explained that DCM and chloroform had high evaporation rate (their low boiling points, DCM (40  °C) and chloroform (56  °C) [113]), It made the external surface of particles are solidified quickly and became wrin-kled Furthermore, the dielectric constant of chloroform (4.8) was lower than DCM (9.1) so that the Coulomb fission formed from the elec-trostatic force is smaller in consequence; the size

of PCL/DCM particles was smaller than the size

of PCL/chloroform particles

According to some previous studies,the

elec-trospraying mode appreciably influenced both

morphology and the size of the microparticles

since the shape of the primary droplet issued

from the tip of the needle can be formed some

unstable spraying modes such as dripping, multi-

jet, spindle and oscillating [109, 114] These

spraying modes are the undesirable because of

their instability and unpredictability In more

details, multi–jet mode and oscillating–jet

gen-erate the satellite and secondary droplets,

result-ing in a broader size distribution and unrepeatable

particles shapes In case of dripping and spindle

mode, the particles are bigger and deformed

because the solvent still exists inside the

parti-cles Whereas, the cone–jet mode generated

almost uniform morphology and size of

parti-cles, especially the Taylor cone-jet was the most

stable mode can maintain the spraying mode

permanently as well as obtain homogeneous

morphology and the mono-dispersity [98, 100,

109, 114, 115]

Our results indicated that when the flow rate

was lower 2 mL/h and the collecting distance was

from 5 cm to 25 cm, the surface tension of PCL

solution was higher than the coulomb fission as a

consequence of weak electrostatic force

(Fig. 13.8a) It led to the polymer drop which

ejected on the tip of the needle had irregular

shapes as a spindle In spindle mode, the

drop-lets, as well as electrosprayed particles, contained

solvent so that the particles were deformed and

aggregated When the collecting distance was

shorter (2.5–5 cm), the cone-jet mode was formed

because the electric field force was strengthened

but this area was narrow Increasing voltage to

15 kV, the spindle mode area decreased (flow rate

18 kV, it spread from 0.5 mL/h to 2 mL/h of flow rate and from 15 cm to 25 cm of collecting dis-tance Besides, at 18 kV, the oscillating–jet mode (the vacant cone was formed at the tip of the nee-dle and it changed position irregularly appeared when the flow rate is low (0.5–0.8 mL/h) and the collecting distance increased from 10  cm to

17  cm whereas the spindle mode varnished (Fig. 13.8c) [114] It was a result of strengthening electrostatic force thanks to increasing applied voltage and the presence of a small solution vol-ume ejected from tip of needle as a result of low flow rate Especially, at the short collecting dis-tance from 2.5 to 10 cm, the electric field force was strengthened by a high potential and a short collecting distance so that it overcame the surface tension of polymer solution, as a result of the larger multi-jet area In addition, increasing flow rate generated a greater volume of solution so that the cone-jet mode was obtained more easily, however, it also depended on the electrical field force, if it is strong, the multi-jet mode was cre-ated Therefore, when the applied voltage was increased to 24  kV, the multi–jet mode was

Fig 13.7 MicroparticlesSEM micrographs of 4% PCL

solutions in different solvents (a) Mixture ofChloroform

with DMF = 1:3 (v/v), (b) Chloroform, (c) DCM (Applied

voltage: 18  kV, collecting distance: 18  cm, flow rate:

1 mL/h, gauge 20G)