Nanoparticlesfor the

encapsulations of drugs

Anil Khanal

Application of polymeric micelles-

1. They can be used in drug delivery systems

2. The core of the micelle is capable to accommodate/or solubilize

poorly water soluble drugs

3. They facilitate the sustain release of drugs

Micelles of double/ or triple hydrophilic block copolymers in aqueous

solutions

Micelles of ABC amphiphilic triblock copolymers in aqueous solutions

Methyl Glycol Chitosan (MGC)

A. Khanal, Y. Nakashima, Y. Li, K. Nakashima, N. Kawasaki and Y. Oishi, Fabrication of nanoaggregates of poly(ethylene oxide)-b-polymethacrylate by complex formation with chitosan or methylglycolchitosan, Colloids Surf.A: Physiochem. Eng. Asp., 2005, 260, 129-135

Chitosan

Double hydrophilic polymeric micelles

Binding of MGC in PEO-b-PMAA

• Bind by electrostatic

interaction

• Critical aggregation concentration

(0.002 gL-1)

MGC/PEO-b-PMAA nanoaggregates

Diameter : 81 nm

Binding of MGC in PEO-b-PMAA

Drawback of double hydrophilic micelles-

It does not have prolonged circulation time in the blood stream because it is unfrozen in nature. So, micelle collapses immediately when it is diluted more

than hundred times in the blood capillaries

Application of frozen micelles-

From the viewpoint of delivery systems for ionic drugs, another property is required in vivo: i.e. the micelle should not collapse after being highly diluted in the blood stream

For such a requirement, there seem to be two hopeful ways. One is to employ polymeric micelles with a cross-linked core, and the other is to use frozen micelles, in which the exchange of unimers between the micelle and the aqueous bulk phase takes a long time scale of hours or more

Poly(styrene)-b- Poly(2-Vinyl Pyridine)-b-Poly(ethylene oxide) (PS-PVP-PEO)

Frozen micelles based on ABC triblock copolymers

X= 11400, y= 12300, z= 3500

J. F. Gohy, N. Willet, S. Varshney, J. X. Zhang, R. Jérôme, 　 e-Polymers No 035 (2002).

Incorporation and release of cloxacillin sodium in micelles of Polystyrene-b-Poly(2-vinyl pyridine)-b-

Poly(ethylene oxide)

Incorporation and release of cloxacillin sodium in micelles of Polystyrene-b-Poly(2-vinyl pyridine)-b-

Poly(ethylene oxide)

Applications of CLX

a semi-synthetic antibiotic, endocarditis (An inflammation of the inner linings of the heart), Impetigo (skin infection)

Anionic drug cloxacillin sodium (CLX-) (PS-PVP-PEO)

A. Khanal, K. Nakashima, Incorporation and release of cloxacillin sodium in micelles of Polystyrene-b-Poly(2-vinyl pyridine)-b-Poly(ethylene oxide), J. Controlled Release, 2005, 108, 150-160.

0

2

4

6

8

10

12

0 50 100 150 200 250 300DN /%

z / m

V

65

70

75

80

85

90

95

0 50 100 150 200 250 300

DN / %

Dia

met

er /

nm

Ksv= 7.4103 M-1

F0 /F =1+Ksv [Q]

Ksv=7.4103 M-1

Release of CLX from the PS-PVP-PEO micelles Release of CLX from the PS-PVP-PEO micelles

0

0.5

0 20 40Time/ h

Ab

sorb

an

ce pH 7

pH 3

Release Kinetics of CLX from PS-PVP-PEO micelleRelease Kinetics of CLX from PS-PVP-PEO micelle

DM Dw2

k1 k2Dw1

Fig. Plots of the absorbance of CLX against time at pH 3 (a) and pH 7 (b). The solid lines indicate fitting curves based on proposed mathematical model.

0

0.2

0.4

0.6

0.8

1

1.2

0 10 20 30 40 50 60 70

Time/h

At/

A ∞

At/ A

0

0.2

0.4

0.6

0.8

1

1.2

0 10 20 30 40 50 60 70

Time/h

At/A ∞

pH 7

At/ A

pH 3

k1= 0.046 h-1, k2= 1.1 h-1

k1= 0.074 h-1, k2= 1.1 h-1

(a)

(b)

1. Addition of CLX into the micellar solution at pH 3 decreases both the hydrodynamic diameter as well as the zeta-potential of the neat micelle. This fact clearly indicates that the electrostatic interaction between the anionic drug and the protonated PVP block of the micelle plays an important role during the incorporation of CLX into the micelle

2. In the releases experiments of CLX, the value of k1 is found to be 0.046 h-1 at pH 3 and 0.074 h-1 at pH 7. Due to the protonated nature of the PVP block at pH 3, the incorporated CLX is released more slowly from the micelle of PS-PVP-PEO than at pH 7 because at pH 3, the anionic drug CLX is bound to the protonated PVP block by electrostatic interaction while at pH 7, there is no such a strong interaction between CLX and the micelle

3. The obtained release time indicates that the retention of drugs in the micelles is long enough for the micelle to be employed for a controlled release of drugs

Conclusions-

Binding of counter ions into PS-PVP-PEO micelleBinding of counter ions into PS-PVP-PEO micelle

1. A. Khanal, K. Nakashima, N. Kawasaki, Y. Oishi, M. Uehara, H. Nakamura, Y. Tajima, Fabrication of organic-inorganic nano-complexes using ABC type triblock copolymer and polyoxotungstates, Colloid. Polym. Sci., 2005, 283, 1226-1232.

2. Y. Li, A. Khanal, N. Kawasaki, Y. Oishi, K. Nakashima, Physicochemical properties of micelles of poly(styrene-b-2-vinylpyridine-b-ethylene oxide) in aqueous solutions, Bull. Chem. Soc. Jpn., 2005, 78, 529-533.

3. A. Khanal, Y. Li, N. Takisawa, N. Kawasaki, Y. Oishi, K. Nakashima, Morphological change of the micelle of poly(styrene)-poly(2-vinylpyridine)-poly(ethylene oxide) induced by binding of sodium dodecylsulfate , Langmuir, 2004, 20, 4809-4812.

Sodium tungstate , polyoxotungtates ( Photocatalyst, anti-viral agent and anticoagulant activities)

Dextran sulfate (Anticoagulant activity)

sodium dodecylsulfate

Fine-tuning Cavity Size and Wall Thickness of Silica Hollow

Nanoparticlesby Templating Polymeric Micelles with

Core–Shell–Corona Structure

D. Liu, A. Khanal, K. Nakashima, Y. Inoue, and M. Yada, Fine-tuning cavity size and wall thickness of silica hollow nanoparticles by templating polymeric micelles with Core-Shell-Corona structure, Chem. Letter, 2009, 38, 130-131

A. Khanal, Y. Inoue, M. Yada, K. Nakashima, “Synthesis of silica hollow nano-particles templated by polymeric micelle with core-shell-corona structure,” J. Am. Chem. Soc. 2007, 129, 1534-1535.

Application of inorganic hollow nano-sphere:　

Catalysis, coatings, composite materials, dyes, ink, artificial cells, and fillers

Their hollow structure can be used as a micro- encapsulate for drugs

Hollow Silica nanoparticles

Methods for the preparation of inorganic hollow nano-particles

Template method

- Latex particles ( sub micrometer to micrometer)

- AB-type Polymeric micelles (less than 100 nanometer)

Drawbacks of AB-type polymeric micelles- We can not get uniform sized hollow inorganic nanoparticles

We can not control the cavity size and wall thickness of hollow inorganic nanoparticles

PS PVP PEO

PEO

PVP+

PS

PEO

PVP

PSpH >5

94 nm 74 nm

pH < 5

Scheme for synthesis of hollow silica nanoparticles by template

PS block forms the core of the micelle to be a template of the void space in the hollow silica

PVP block forms the shell to be a reaction field of the sol–gel reaction of silica precursors

PEO forms the corona to stabilize the polymer/silica intermediate composites

TEM picture of hollow silica nano-sphere prepared by templating the PS-PVP-PEO micelle. The concentration of the PS-PVP-PEO is 0.9 g/L and the molar ratio of PVP: TMOS is 1:23.

Diameter of PS core of neat micelle 14 nm (J. F. Gohy et al 　 e-Polymers No 035

2002)

Diameter of pore of hollow nano-silica 11 nm

Void space diameters and shell thickness of hollow silica nanosphere

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26

24

28

25 36

Conclusions:

1. We have successfully prepared a hollow silica nano-sphere with a high uniformity in size using a template of the ABC triblock copolymer micelle with a core-shell-corona architecture.

2. The void space diameter of hollow silica nanoparticles can be fine-tuned on a several nanometer scale by changing the length of the PS block.

3. The wall thickness of the hollow silica nanoparticles can be easily controlled by varying the concentration of the silica precursor.

4. The most interesting feature of this approach is the possibility that it might be applied to the preparation of other inorganic hollow particles with a controlled cavity size and wall thickness.

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Cationic liposome colloidal stability in the presence of guar derivatives suggests

depletion interactions may be operative in

artificial tears

A. Khanal, Y. Cui, R. Pelton, Y. Ren, L. Zhang, H. Ketelson and D. James, Cationic liposome colloidal stability in the presence of guar derivatives suggests depletion interactions may be operative in artificial tears, Biomacromolecules 2010, 11, 2460–2464.

Objective of This Work• Background:

– Hydroxypropyl guar (HPG) and borate combinations are used in formulations for lubricant eye drops.

• Objective– To understand how HPG

borate interacts with lipids.

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n

O

OO

OHO HOOH

O

OH

O

OH

O

O

CH3

OH

OB

OH

OH

Galactose

Mannose

Hydroxypropyl Guar (HPG)

Bound Borate Groups are Labile

• Binding constant is very low– 100 l/mol Springsteen Wang

2002

• pH must be alkaline, borate not boric is the binding species

O

OH

OH

O

O

OB

OH

OH

O

OH

OHHO

O

OHB

OH

OHHO

OH

H2O2

When does HPG-borate Behave as a Polyelectrolyte – Difficult to Predict

• Cases showing typical anionic polyelectrolyte behavior– HPG-borate gives bridging flocculation of cationic

latex Pelton et al. Langmuir 2009

– Adsorbs on cationic surface and complexes with cationic polyelectrolytes Cui et al Macromolecules 2008

• Non-typical cases– HPG-borate does not bind the cationic surfactant

DTAB Cui et al Langmuir 2009

Our Model Lipid – DOTAP Liposomes

• Diameter 97nm

• Electrophoretic mobility 2.4 /10-8m2/Vs

30

O

O H

NO

O

Cl

HPG-borate Adsorption onto DOTAP

• Without added salt HPG-borate does adsorb onto cationic liposomes.

• In 0.1 M NaCl there is no adsorption.

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HPG-borate Induced Aggregation

• Without added salt, HPG-borate induces DOTAP aggregation.

• With salt no effect at low HPG-borate conc., aggregation at high conc.

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MW Sensitivity – Classic Depletion Flocculation

• Polymer concentration for depletion is inversely related to MW.

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Depletion Flocculation

• There is a zone near the particle surfaces with lower polymer segment concentration.

• Osmotic (depletion) forces favor the particles coming together so depletion zones overlaps

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Carboxymethyl Guar (CMG)• A typical “weak”

polyelectrolyte

• pH dependant charge density

• Complexes with DTAB Langmuir 2009, 25 (24), 13712

35

n

O

OO

OHO HOOH

O

OH

O

OH

OH

OH

O

O

CO O

O

O

CMG Interactions with DOTAP

• Electrophoretic mobility shows anionic CMG adsorbs onto cationic DOTAP liposome.

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CMG Aggregates DOTAP Liposomes

• Dynamic light scattering and turbidity (not shown) shows liposome flocculation

• Behavior is consistent with conventional bridging flocculation.

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Conclusions• DOTAP behavior in the presence of HPG-borate depends upon the

salt concentration. Without added salt, HPG-borate binds to and aggregates the cationic liposomes whereas in salt concentrations in the range of physiological solutions, HPG-borate does not bind to cationic DOTAP liposomes.

• High concentrations of all studied guar derivatives induced DOTAP aggregation, driven by depletion forces. As expected, the polymer concentrations required to induce aggregation varied inversely with polymer molecular weight.