nanoparticle technology for drug delivery, 2006, p.427

Controlled Drug Delivery: Fundamentals and Applications, Second Edition, Revised and Expanded, edited by Joseph R.. Pharmaceutical Statistics: Practical and Clinical Applications, Secon

DRUGS AND THE PHARMACEUTICAL SCIENCES

A Series of Textbooks and Monographs

1 Pharmacokinetics, Milo Gibaldi and Donald Perrier

2 Good Manufacturing Practices for Pharmaceuticals: A Plan for Total Quality Control, Sidney H Willig, Murray M Tuckerman,

and William S Hitchings IV

3 Microencapsulation, edited by J R Nixon

4 Drug Metabolism: Chemical and Biochemical Aspects, Bernard Testa and Peter Jenner

5 New Drugs: Discovery and Development, edited by Alan A Rubin

6 Sustained and Controlled Release Drug Delivery Systems, edited by Joseph R Robinson

7 Modern Pharmaceutics, edited by Gilbert S Banker

and Christopher T Rhodes

8 Prescription Drugs in Short Supply: Case Histories, Michael A Schwartz

9 Activated Charcoal: Antidotal and Other Medical Uses, David O Cooney

10 Concepts in Drug Metabolism (in two parts), edited by Peter Jenner and Bernard Testa

11 Pharmaceutical Analysis: Modern Methods (in two parts), edited by James W Munson

12 Techniques of Solubilization of Drugs, edited by Samuel H Yalkowsky

13 Orphan Drugs, edited by Fred E Karch

14 Novel Drug Delivery Systems: Fundamentals, Developmental Concepts, Biomedical Assessments, Yie W Chien

15 Pharmacokinetics: Second Edition, Revised and Expanded, Milo Gibaldi and Donald Perrier

16 Good Manufacturing Practices for Pharmaceuticals: A Plan for Total Quality Control, Second Edition, Revised and Expanded, Sidney H Willig, Murray M Tuckerman, and William S Hitchings IV

17 Formulation of Veterinary Dosage Forms, edited by Jack Blodinger

18 Dermatological Formulations: Percutaneous Absorption, Brian W Barry

19 The Clinical Research Process in the Pharmaceutical Industry, edited by Gary M Matoren

20 Microencapsulation and Related Drug Processes, Patrick B Deasy

21 Drugs and Nutrients: The Interactive Effects, edited by Daphne A Roe and T Colin Campbell

22 Biotechnology of Industrial Antibiotics, Erick J Vandamme

23 Pharmaceutical Process Validation, edited by Bernard T Loftus

and Robert A Nash

24 Anticancer and Interferon Agents: Synthesis and Properties, edited by Raphael M Ottenbrite and George B Butler

25 Pharmaceutical Statistics: Practical and Clinical Applications,

Sanford Bolton

26 Drug Dynamics for Analytical, Clinical, and Biological Chemists,

Benjamin J Gudzinowicz, Burrows T Younkin, Jr., and Michael J Gudzinowicz

27 Modern Analysis of Antibiotics, edited by Adjoran Aszalos

28 Solubility and Related Properties, Kenneth C James

29 Controlled Drug Delivery: Fundamentals and Applications, Second Edition, Revised and Expanded, edited by Joseph R Robinson and Vincent H Lee

30 New Drug Approval Process: Clinical and Regulatory Management, edited by Richard A Guarino

31 Transdermal Controlled Systemic Medications, edited by Yie W Chien

32 Drug Delivery Devices: Fundamentals and Applications, edited by

Praveen Tyle

33 Pharmacokinetics: Regulatory • Industrial • Academic Perspectives, edited by Peter G Welling and Francis L S Tse

34 Clinical Drug Trials and Tribulations, edited by Allen E Cato

35 Transdermal Drug Delivery: Developmental Issues and Research

Initiatives, edited by Jonathan Hadgraft and Richard H Guy

36 Aqueous Polymeric Coatings for Pharmaceutical Dosage Forms,

edited by James W McGinity

37 Pharmaceutical Pelletization Technology, edited by Isaac Ghebre-Sellassie

38 Good Laboratory Practice Regulations, edited by Allen F Hirsch

39 Nasal Systemic Drug Delivery, Yie W Chien, Kenneth S E Su,

and Shyi-Feu Chang

40 Modern Pharmaceutics: Second Edition, Revised and Expanded,

edited by Gilbert S Banker and Christopher T Rhodes

41 Specialized Drug Delivery Systems: Manufacturing and Production

Technology, edited by Praveen Tyle

42 Topical Drug Delivery Formulations, edited by David W Osborne

and Anton H Amann

43 Drug Stability: Principles and Practices, Jens T Carstensen

44 Pharmaceutical Statistics: Practical and Clinical Applications,

Second Edition, Revised and Expanded, Sanford Bolton

45 Biodegradable Polymers as Drug Delivery Systems, edited by

Mark Chasin and Robert Langer

46 Preclinical Drug Disposition: A Laboratory Handbook, Francis L S Tse and James J Jaffe

47 HPLC in the Pharmaceutical Industry, edited by Godwin W Fong

and Stanley K Lam

48 Pharmaceutical Bioequivalence, edited by Peter G Welling,

Francis L S Tse, and Shrikant V Dinghe

49 Pharmaceutical Dissolution Testing, Umesh V Banakar

50 Novel Drug Delivery Systems: Second Edition, Revised and Expanded, Yie W Chien

51 Managing the Clinical Drug Development Process, David M Cocchetto and Ronald V Nardi

52 Good Manufacturing Practices for Pharmaceuticals: A Plan for Total Quality Control, Third Edition, edited by Sidney H Willig

and James R Stoker

53 Prodrugs: Topical and Ocular Drug Delivery, edited by Kenneth B Sloan

54 Pharmaceutical Inhalation Aerosol Technology, edited by

57 Pharmaceutical Process Validation: Second Edition, Revised

and Expanded, edited by Ira R Berry and Robert A Nash

58 Ophthalmic Drug Delivery Systems, edited by Ashim K Mitra

59 Pharmaceutical Skin Penetration Enhancement, edited by

Kenneth A Walters and Jonathan Hadgraft

60 Colonic Drug Absorption and Metabolism, edited by Peter R Bieck

61 Pharmaceutical Particulate Carriers: Therapeutic Applications, edited by Alain Rolland

62 Drug Permeation Enhancement: Theory and Applications, edited by Dean S Hsieh

63 Glycopeptide Antibiotics, edited by Ramakrishnan Nagarajan

64 Achieving Sterility in Medical and Pharmaceutical Products, Nigel A Halls

65 Multiparticulate Oral Drug Delivery, edited by Isaac Ghebre-Sellassie

66 Colloidal Drug Delivery Systems, edited by Jörg Kreuter

67 Pharmacokinetics: Regulatory • Industrial • Academic Perspectives, Second Edition, edited by Peter G Welling and Francis L S Tse

68 Drug Stability: Principles and Practices, Second Edition, Revised and Expanded, Jens T Carstensen

69 Good Laboratory Practice Regulations: Second Edition, Revised

and Expanded, edited by Sandy Weinberg

70 Physical Characterization of Pharmaceutical Solids, edited by

Harry G Brittain

71 Pharmaceutical Powder Compaction Technology, edited by

Göran Alderborn and Christer Nyström

72 Modern Pharmaceutics: Third Edition, Revised and Expanded, edited by Gilbert S Banker and Christopher T Rhodes

73 Microencapsulation: Methods and Industrial Applications, edited by Simon Benita

74 Oral Mucosal Drug Delivery, edited by Michael J Rathbone

75 Clinical Research in Pharmaceutical Development, edited by Barry Bleidt and Michael Montagne

76 The Drug Development Process: Increasing Efficiency and Cost

Effectiveness, edited by Peter G Welling, Louis Lasagna, and Umesh V Banakar

77 Microparticulate Systems for the Delivery of Proteins and Vaccines, edited by Smadar Cohen and Howard Bernstein

78 Good Manufacturing Practices for Pharmaceuticals: A Plan for Total Quality Control, Fourth Edition, Revised and Expanded, Sidney H Willig and James R Stoker

79 Aqueous Polymeric Coatings for Pharmaceutical Dosage Forms:

Second Edition, Revised and Expanded, edited by James W McGinity

80 Pharmaceutical Statistics: Practical and Clinical Applications,

Third Edition, Sanford Bolton

81 Handbook of Pharmaceutical Granulation Technology, edited by

84 Pharmaceutical Enzymes, edited by Albert Lauwers and Simon Scharpé

85 Development of Biopharmaceutical Parenteral Dosage Forms, edited by John A Bontempo

86 Pharmaceutical Project Management, edited by Tony Kennedy

87 Drug Products for Clinical Trials: An International Guide to Formulation • Production • Quality Control, edited by Donald C Monkhouse

and Christopher T Rhodes

88 Development and Formulation of Veterinary Dosage Forms:

Second Edition, Revised and Expanded, edited by Gregory E Hardee and J Desmond Baggot

89 Receptor-Based Drug Design, edited by Paul Leff

90 Automation and Validation of Information in Pharmaceutical Processing, edited by Joseph F deSpautz

91 Dermal Absorption and Toxicity Assessment, edited by Michael S Roberts and Kenneth A Walters

92 Pharmaceutical Experimental Design, Gareth A Lewis, Didier Mathieu, and Roger Phan-Tan-Luu

93 Preparing for FDA Pre-Approval Inspections, edited by Martin D Hynes III

94 Pharmaceutical Excipients: Characterization by IR, Raman, and NMR Spectroscopy, David E Bugay and W Paul Findlay

95 Polymorphism in Pharmaceutical Solids, edited by Harry G Brittain

96 Freeze-Drying/Lyophilization of Pharmaceutical and Biological Products, edited by Louis Rey and Joan C May

97 Percutaneous Absorption: Drugs–Cosmetics–Mechanisms–Methodology, Third Edition, Revised and Expanded, edited by Robert L Bronaugh and Howard I Maibach

98 Bioadhesive Drug Delivery Systems: Fundamentals, Novel Approaches, and Development, edited by Edith Mathiowitz, Donald E Chickering III, and Claus-Michael Lehr

99 Protein Formulation and Delivery, edited by Eugene J McNally

100 New Drug Approval Process: Third Edition, The Global Challenge,

edited by Richard A Guarino

101 Peptide and Protein Drug Analysis, edited by Ronald E Reid

102 Transport Processes in Pharmaceutical Systems, edited by

Gordon L Amidon, Ping I Lee, and Elizabeth M Topp

103 Excipient Toxicity and Safety, edited by Myra L Weiner

and Lois A Kotkoskie

104 The Clinical Audit in Pharmaceutical Development, edited by

Michael R Hamrell

105 Pharmaceutical Emulsions and Suspensions, edited by Francoise Nielloud and Gilberte Marti-Mestres

106 Oral Drug Absorption: Prediction and Assessment, edited by

Jennifer B Dressman and Hans Lennernäs

107 Drug Stability: Principles and Practices, Third Edition, Revised

and Expanded, edited by Jens T Carstensen and C T Rhodes

108 Containment in the Pharmaceutical Industry, edited by James P Wood

109 Good Manufacturing Practices for Pharmaceuticals: A Plan for Total Quality Control from Manufacturer to Consumer, Fifth Edition, Revised and Expanded, Sidney H Willig

110 Advanced Pharmaceutical Solids, Jens T Carstensen

111 Endotoxins: Pyrogens, LAL Testing, and Depyrogenation, Second Edition, Revised and Expanded, Kevin L Williams

112 Pharmaceutical Process Engineering, Anthony J Hickey

and David Ganderton

113 Pharmacogenomics, edited by Werner Kalow, Urs A Meyer

and Rachel F Tyndale

114 Handbook of Drug Screening, edited by Ramakrishna Seethala

and Prabhavathi B Fernandes

115 Drug Targeting Technology: Physical • Chemical • Biological Methods, edited by Hans Schreier

116 Drug–Drug Interactions, edited by A David Rodrigues

117 Handbook of Pharmaceutical Analysis, edited by Lena Ohannesian and Anthony J Streeter

118 Pharmaceutical Process Scale-Up, edited by Michael Levin

119 Dermatological and Transdermal Formulations, edited by

Kenneth A Walters

120 Clinical Drug Trials and Tribulations: Second Edition, Revised

and Expanded, edited by Allen Cato, Lynda Sutton, and Allen Cato III

121 Modern Pharmaceutics: Fourth Edition, Revised and Expanded, edited by Gilbert S Banker and Christopher T Rhodes

122 Surfactants and Polymers in Drug Delivery, Martin Malmsten

123 Transdermal Drug Delivery: Second Edition, Revised and Expanded, edited by Richard H Guy and Jonathan Hadgraft

124 Good Laboratory Practice Regulations: Second Edition, Revised

and Expanded, edited by Sandy Weinberg

125 Parenteral Quality Control: Sterility, Pyrogen, Particulate, and Package Integrity Testing: Third Edition, Revised and Expanded, Michael J Akers, Daniel S Larrimore, and Dana Morton Guazzo

126 Modified-Release Drug Delivery Technology, edited by

Michael J Rathbone, Jonathan Hadgraft, and Michael S Roberts

127 Simulation for Designing Clinical Trials: A

Pharmacokinetic-Pharmacodynamic Modeling Perspective, edited by Hui C Kimko and Stephen B Duffull

128 Affinity Capillary Electrophoresis in Pharmaceutics and Biopharmaceutics, edited by Reinhard H H Neubert and Hans-Hermann Rüttinger

129 Pharmaceutical Process Validation: An International Third Edition,

Revised and Expanded, edited by Robert A Nash and Alfred H Wachter

130 Ophthalmic Drug Delivery Systems: Second Edition, Revised

and Expanded, edited by Ashim K Mitra

131 Pharmaceutical Gene Delivery Systems, edited by Alain Rolland

and Sean M Sullivan

132 Biomarkers in Clinical Drug Development, edited by John C Bloom and Robert A Dean

133 Pharmaceutical Extrusion Technology, edited by Isaac Ghebre-Sellassie and Charles Martin

134 Pharmaceutical Inhalation Aerosol Technology: Second Edition,

Revised and Expanded, edited by Anthony J Hickey

135 Pharmaceutical Statistics: Practical and Clinical Applications,

Fourth Edition, Sanford Bolton and Charles Bon

136 Compliance Handbook for Pharmaceuticals, Medical Devices,

and Biologics, edited by Carmen Medina

137 Freeze-Drying/Lyophilization of Pharmaceutical and Biological Products: Second Edition, Revised and Expanded, edited by Louis Rey

and Joan C May

138 Supercritical Fluid Technology for Drug Product Development, edited by Peter York, Uday B Kompella, and Boris Y Shekunov

139 New Drug Approval Process: Fourth Edition, Accelerating Global

Registrations, edited by Richard A Guarino

140 Microbial Contamination Control in Parenteral Manufacturing, edited by Kevin L Williams

141 New Drug Development: Regulatory Paradigms for Clinical Pharmacology and Biopharmaceutics, edited by Chandrahas G Sahajwalla

142 Microbial Contamination Control in the Pharmaceutical Industry, edited by Luis Jimenez

143 Generic Drug Product Development: Solid Oral Dosage Forms, edited by Leon Shargel and Izzy Kanfer

144 Introduction to the Pharmaceutical Regulatory Process, edited by

Ira R Berry

145 Drug Delivery to the Oral Cavity: Molecules to Market, edited by

Tapash K Ghosh and William R Pfister

146 Good Design Practices for GMP Pharmaceutical Facilities, edited by Andrew Signore and Terry Jacobs

147 Drug Products for Clinical Trials, Second Edition, edited by Donald

Monkhouse, Charles Carney, and Jim Clark

148 Polymeric Drug Delivery Systems, edited by Glen S Kwon

149 Injectable Dispersed Systems: Formulation, Processing, and Performance, edited by Diane J Burgess

150 Laboratory Auditing for Quality and Regulatory Compliance,

Donald Singer, Raluca-Ioana Stefan, and Jacobus van Staden

151 Active Pharmaceutical Ingredients: Development, Manufacturing,

and Regulation, edited by Stanley Nusim

152 Preclinical Drug Development, edited by Mark C Rogge and David R Taft

153 Pharmaceutical Stress Testing: Predicting Drug Degradation, edited by Steven W Baertschi

154 Handbook of Pharmaceutical Granulation Technology: Second Edition, edited by Dilip M Parikh

155 Percutaneous Absorption: Drugs–Cosmetics–Mechanisms–Methodology, Fourth Edition, edited by Robert L Bronaugh and Howard I Maibach

156 Pharmacogenomics: Second Edition, edited by Werner Kalow,

Urs A Meyer and Rachel F Tyndale

157 Pharmaceutical Process Scale-Up, Second Edition, edited by

Uday B Kompella

University of Nebraska Medical Center

Omaha, Nebraska

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Products of nanotechnology are expected to revolutionizemodern medicine, as evidenced by recent scientific advancesand global initiatives to support nanotechnology and nano-medicine research The field of drug delivery is a direct bene-ficiary of these advancements Due to their versatility intargeting tissues, accessing deep molecular targets, and con-trolling drug release, nanoparticles are helping address chal-lenges to face the delivery of modern, as well as conventionaldrugs Since the majority of drug products employ solids,nanoparticles are expected to have a broad impact on drugproduct development The purpose of this book is to presentpractical issues in the manufacturing and biological applica-tion of nanoparticles Drug delivery scientists in industry,academia, and regulatory agencies, as well as students in bio-medical engineering, chemical engineering, pharmaceuticalsciences, and other sciences with an interest in drug delivery,

iii

will find this book useful It can also be used as a textbook fordrug delivery courses focusing on nanoparticles.

This book is organized into four sections The first sectiondescribes the distinguishing fundamental properties of nano-particles (Chap 1) as well as technologies for nanoparticlemanufacturing (Chaps 2–4) Nanoparticles can be manufac-tured by either breaking macro-particles using technologiessuch as milling and homogenization (Chap 2) or by buildingparticles from molecules dissolved in a solution using super-critical fluid technology (Chap 3) Nanoparticle manufacturingand properties can be further optimized by employing poly-mers or proteins as stabilizers (Chap 4)

The second section describes the characterization of particles at the material or physicochemical level (Chap 5) andrelates these properties to the delivery and effectiveness ofnanoparticles (Chap 6) as well as toxicological characteristics(Chap 7)

nano-The third section presents the various applications ofnanoparticles in drug delivery Depending on the route andpurpose of drug delivery, the requirements for nanoparticulatesystems can vary These aspects are discussed in Chapter 8 forinjectable delivery, Chapter 9 for oral delivery, Chapter 10 forbrain delivery, Chapter 11 for ocular delivery, and Chapter 12for gene delivery

Finally, the fourth section provides an overview of theclinical, ethical, and regulatory issues of nanoparticle-baseddrug delivery These are evolving areas and the drug productdevelopment experience with nanoparticles is limited Asmore data is gathered on the safety and efficacy of nanoparti-culate systems, a clearer view will emerge

Preparation of this book would not have been possiblewithout the valuable contributions from various experts inthe field We deeply appreciate their timely contributions.Also, we are thankful to our colleagues at Auburn Universityand the University of Nebraska Medical Center for theirsupport in preparing this book

Ram B GuptaUday B Kompella

Nanoparticle Suspension and Settling 4

Magnetic and Optical Properties 6

2 Manufacturing of Nanoparticles by Milling

and Homogenization Techniques 21Rainer H Mu€ller, Jan Mo€schwitzer, and

Faris Nadiem Bushrab

Production in Nonaqueous Liquids 35

Production in Hot-Melted Matrices 37

SAS with Enhanced Mass (EM) Transfer

(SAS-EM) Process for Nanoparticle

4 Polymer or Protein Stabilized Nanoparticles

from Emulsions 85Ram B Gupta

Introduction 85

Emulsification Solvent Evaporation Process 86Emulsification 87

Nanoparticle Hardening 93

Residual Solvent and Emulsifier 97

Protein Stabilized Nanoparticles 98

7 Toxicological Characterization of EngineeredNanoparticles 161Paul J A Borm and Roel P F Schins

Introduction: Medical Needs Addressable by

Nanoparticulate Drug Delivery 199

In Vitro and In Vivo Models 243

Gene Delivery Vectors 361

Polymers Used to Prepare DNA

PART IV: CLINICAL, ETHICAL, AND

REGULATORY ISSUES

13 Nanotechnology and Nanoparticles: Clinical,Ethical, and Regulatory Issues 381Makena Hammond and Uday B Kompella

Aniruddha C Amrite Department of Pharmaceutical

Sciences, University of Nebraska Medical Center, Omaha,

Nebraska, U.S.A.

Vivekanand Bhardwaj Department of Pharmaceutics, National Institute of Pharmaceutical Education and Research, Punjab, India

Paul J A Borm Centre of Expertise in Life Sciences,

Zuyd University, Heerlen, The Netherlands

Faris Nadiem Bushrab Department of Pharmaceutical

Technology, Biotechnology and Quality Management, Freie

Universita¨t, Berlin, Germany

Mahesh V Chaubal BioPharma Solutions, Baxter Healthcare, Round Lake, Illinois, U.S.A.

xi

Svetlana Gelperina Institute of Molecular Medicine, Moscow Sechenov Medical Academy, Moscow, Russia

Ram B Gupta Department of Chemical Engineering, Auburn University, Auburn, Alabama, U.S.A.

Makena Hammond College of Pharmacy, University of

Nebraska Medical Center, Omaha, Nebraska, and Virginia State University, Petersburg, Virginia, U.S.A.

Roy J Haskell Pfizer Corporation, Michigan Pharmaceutical Sciences, Kalamazoo, Michigan, U.S.A.

Uday B Kompella Department of Pharmaceutical Sciences, College of Pharmacy, University of Nebraska Medical Center, Omaha, Nebraska, U.S.A.

Majeti Naga Venkata Ravi Kumar Department of

Pharmaceutics, National Institute of Pharmaceutical Education and Research, Punjab, India

Vinod Labhasetwar Department of Pharmaceutical Sciences, University of Nebraska Medical Center, Omaha, Nebraska, U.S.A Jan Mo¨schwitzer Department of Pharmaceutical Technology, Biotechnology and Quality Management, Freie Universita¨t, Berlin, Germany

Rainer H Mu ¨ ller Department of Pharmaceutical Technology, Biotechnology and Quality Management, Freie Universita¨t, Berlin, Germany

Moses O Oyewumi Division of Medicinal and Natural Products Chemistry, College of Pharmacy, University of Iowa, Iowa City, Iowa, U.S.A.

Barrett Rabinow BioPharma Solutions, Baxter Healthcare, Round Lake, Illinois, U.S.A.

Kevin G Rice Division of Medicinal and Natural Products Chemistry, College of Pharmacy, University of Iowa, Iowa City, Iowa, U.S.A.

Sanjeeb K Sahoo Department of Pharmaceutical Sciences, University of Nebraska Medical Center, Omaha, Nebraska, U.S.A Roel P F Schins Institut fur Umweltmedizinische Forschung (IUF), University of Du¨sseldorf, Du¨sseldorf, Germany

Fundamentals of Drug Nanoparticles

RAM B GUPTA Department of Chemical Engineering, Auburn University, Auburn, Alabama, U.S.A.

INTRODUCTION

In pharmaceutics,
90% of all medicines, the active ent is in the form of solid particles With the development innanotechnology, it is now possible to produce drug nanoparti-cles that can be utilized in a variety of innovative ways Newdrug delivery pathways can now be used that can increasedrug efficacy and reduce side effects For example, in 2005,the U.S Food and Drug Administration approved intra-venously administered 130-nm albumin nanoparticles loadedwith paclitaxel (AbraxaneTM) for cancer therapy, which epito-mizes the new products anticipated based on nanoparticulatesystems The new albumin/paclitaxel–nanoparticle formula-tion offers several advantages including elimination of

ingredi-PART I: TECHNOLOGIES FOR

NANOPARTICLE MANUFACTURING

1

toxicity because of cremophor, a solvent used in the previousformulation, and improved efficacy due to the greater dose ofthe drug that can be administered and delivered For betterdevelopment of the nanoparticulate systems, it is essential tounderstand the pharmaceutically relevant properties of nano-particles, which is the purpose of this chapter and this book

in general In the following narrative, some fundamental erties of nanoparticles including their size, surface area, set-tling velocity, magnetic and optical properties, and biologicaltransport are brought into the perspective of drug delivery.NANOPARTICLE SIZE

prop-To put the size of nanoparticles in perspective, Table 1 pares sizes of various objects Because of the comparable size

com-of the components in the human cells, nanoparticles are com-ofgreat interest in drug delivery It appears that nature, inmaking the biological systems, has extensively used nan-ometer scale If one has to go hand in hand with nature intreating the diseases one needs to use the same scale, whether

it is correcting a faulty gene, killing leprosy bacteria sittinginside the body cells, blocking the multiplication of viral gen-ome, killing a cancer cell, repairing the cellular metabolism,

or preventing wrinkles or other signs of aging One cannotuse a human arm to massage the hurt leg of an ant Sizematching is important in carrying out any activity Drugdelivery is aimed at influencing the biochemistry of the body

Table 1 Typical Size of Various Objects

Resolution of unaided human eyes 100,000

The basic unit of the biological processes is the cell and thebiochemical reactions inside it With the advent of nanoparti-cles it is now possible to selectively influence the cellular pro-cesses at their natural scales.

NANOPARTICLE SURFACE

We can generally see and discern objects as small as100,000 nm (100 mm) It is only in the past 300 years, with theinvention of microscopes, that we can see smaller objects.Today, one can see objects as small as individual atoms (about0.1 nm) using the scanning probe microscope Owing to theirsmall size, nanoparticles exhibit interesting properties, mak-ing them suitable for a variety of drug delivery applications.The number of molecules present on a particle surfaceincreases as the particle size decreases For a spherical solidparticle of diameter d, surface area per unit mass, Sg, is given as

%Surface molecules¼ð4=3Þp½d

3 ðd  sÞ3ð4=3Þp½d3 100

¼ 100 s

d

 3

3 sd

 2

þ3 sd

 

ð2ÞFor a typical low–molecular weight drug molecule

of 1-nm diameter, %surface molecules are calculated inTable 2 It is interesting to see that for a 10,000-nm (or10-mm) particle, a very small percentage of the molecules arepresent on the surface Hence, the dissolution rate is muchlower for the microparticles when compared to nanoparticles.When the particles are of nanometer length scale, surfaceirregularities can play an important role in adhesion, as theirregularities may be of the same order as the particles (1)

Nanoparticles can show a strong adhesion because of theincreased contact area for van der Waals attraction Forexample, Lamprecht et al (2) observed differential uptake/adhesion of polystyrene particle to inflamed colonic mucosa,with the deposition 5.2%, 9.1%, and 14.5% for 10-mm, 1000-nm,and 100-nm particles, respectively.

NANOPARTICLE SUSPENSION AND SETTLING

Because of the small size of the nanoparticles, it is easy tokeep them suspended in a liquid Large microparticles preci-pitate out more easily because of gravitational force, whereasthe gravitational force is much smaller on a nanoparticle.Particle settling velocity, v, is given by Stokes’ law as

v¼d

2gðrs rlÞ

where g is gravitation acceleration (9.8 m/sec at sea level), rl

is liquid density (997 kg/m3 for water at 25C), ml is viscosity(0.00089 Pa/sec for water at 25C) For various particles sizes,settling velocities are calculated in Table 3 for a solid density(rs) of 1700 kg/m3

Thermal (Brownian) fluctuations resist the particlesettlement According to Einstein’s fluctuation–dissipationtheory, average Brownian displacement x in time t is given as

Table 2 % Surface Molecules in Particles

Particle size (nm) Surface molecules (%)

where kBis the Boltzman constant (1.38 1023J/K), and T istemperature in Kelvin Table 4 shows displacements forparticles of varying sizes in water at 25C The Brownianmotion of a 1000-nm particle due to thermal fluctuation inwater is 1716 nm/sec, which is greater than the settling velocity

of 430 nm/sec Hence, particles below 1000 nm in size will notsettle merely because of Brownian motion This imparts animportant property to nanoparticles, that they can be easilykept suspended despite high solid density Large microparti-cles easily settle out from suspension because of gravity, hencesuch suspensions need to carry a ‘‘shake well before use’’ label.Also, a microparticle suspension cannot be used for injection.For the nanoparticles, the gravitational pull is not strongerthan the random thermal motion of the particles Hence, nano-paticle suspensions do not settle, which provides a long self-life.However, settling can be induced using centrifugation ifneeded for particle separation Particle velocity under centri-fugation is given as:

 2

ð5Þ

Table 4 Brownian Motion of the Particles

Particle size (nm) Brownian displacement (nm in 1 sec)

Table 3 Particle Settling Velocities

Particle size (nm) Settling velocity (nm/sec)

where the centrifugal rotation is rotations per minute (rpm).For various particle sizes, centrifugal velocities calculatedfor a solid density (rs) of 1700 kg/m3 in water at 0.1 m fromthe axis of rotation are presented in Table 5.

MAGNETIC AND OPTICAL PROPERTIES

Small nanoparticles also exhibit unique magnetic and opticalproperties For example, ferromagnetic materials becomesuperparamagnetic below about 20 nm, i.e., the particles donot retain the magnetization because of the lack of magneticdomains; however, they do experience force in the magneticfield Such materials are useful for targeted delivery of drugsand heat For example, interaction of electromagnetic pulseswith nanoparticles can be utilized for enhancement of drugdelivery in solid tumors (3) The particles can be attached toantibodies directed against antigens in tumor vasculatureand selectively delivered to tumor blood vessel walls Thelocal heating of the particles by pulsed electromagnetic radia-tion results in perforation of tumor blood vessels, microcon-vection in the interstitium, and perforation of cancer cellmembrane, and therefore provides enhanced delivery of drugsfrom the blood into cancer cells with minimal thermal andmechanical damage to the normal tissues

Gold and silver nanoparticles show size-dependent cal properties (4) The intrinsic color of nanoparticles changeswith size because of surface plasmon resonance Such nano-particles are useful for molecular sensing, diagnostic, andimaging applications For example, gold nanoparticles canexhibit different colors based on size (Table 6)

opti-PRODUCTION OF NANOPARTICLES

Although any particle of a size <1-mm diameter is a ticle, several national initiatives are encouraging the develop-ment of particles <100 nm as they might exhibit some uniquephysical properties, and hence potentially different and use-ful biological properties However, achieving sizes <100 nm

is more readily feasible with hard materials compared to drugand polymer molecules, which are soft materials For hardmaterials, such as silica, metal oxides, and diamonds withmelting points above 1000C, nanoparticles in the 1–100 nmsize range have been prepared However, for drugs that areusually soft materials with melting point below 300C parti-cles in the 1–100 nm size range are more difficult to prepare.For this reason, it is a reasonable goal to aim at <300 nm par-ticles for drug and polymer materials There are several suc-cess stories for pharmaceutical materials in this size range.

Table 6 Size-Dependent Color Variation of Gold Nanoparticles

Wavelength for maximum absorption (nm) Nanoparticle size (nm) In water In AOT/water/isooctane (w 0 ¼ 10)

Abbreviation: AOT, sodium bis(2-ethyl hexyl)sulfosuccinate.

Source: From Ref 5.

Table 7 Number of Molecules in a Spherical Particle

Particle diameter Particle volume (mL) Number of molecules

Production of nanoparticles of soft materials is much morechallenging than that of hard materials because of the highstickiness of the former The bulk pharmaceuticals are avail-able in solids of large sizes (e.g., 1-mm-diameter powder), whichcan be often easily solubilized in solvent to obtain molecularsize Hence, there are two extremes of sizes: molecular size(each particle containing one molecule) and large size (e.g., eachparticle containing of the order of 1018molecules) For a drug of

500 molecular weight and 1 g/mL solid density, the numbers ofmolecules in different size particles are given in Table 7.Hence, to obtain nanoparticles in the 50–300 nm rangefor drug delivery, one requires of the order of 104–108 mole-cules in each particle This size has to be achieved from eithersolution phase (single molecule) or millimeter-size particle(1018 molecules) The first approach is where the particle isbroken down to nano size, whereas in the second approach,the particle will be built up from molecules The two generalapproaches for the production of drug nanoparticles aresketched in Figure 1

Milling of Large Particles or

Breaking-Down Process

Comminuting or grinding or milling is the oldest mechanicalunit operation for size reduction of solids and for producinglarge quantities of particulate materials Here, the material

is subjected to stress, which results in the breakage of the ticle Usually, the applied stress is more concentrated on the

par-Figure 1 Schematic of the two general nanoparticle production techniques.

already present cracks in the material, which causes crackpropagation leading to fracture With the decreasing particlesize, materials exhibit increasing plastic behavior making itmore difficult to break small particles than large particles.For many materials, a limit in the grindability can be reachedwhere subject to further grinding, no decrease in the particlesize is observed (6) An empirical index, known as Bond workindex (Wi) has been developed, which represents energyrequired for grinding (7).

Wi¼ 10 d 1=2product d1=2feed 

ð6Þ

To reduce the size of a 1-mm particle, the energyrequired in terms of Bond index is given in Table 8 for variousproduct sizes

Hence, it is very energy intensive to go down to ticles-size range Other than size, parameters of importanceare: (i) toughness/brittleness (in tough materials, stresscauses plastic deformation, whereas in brittle materialscracks are propagated; hence, size reduction of brittle materi-als is easier than for tough materials; sometimes, a materialcan be cooled to embrittle), and (ii) hardness, abrasiveness,particle shape and structure, heat sensitivity (only about 2%

nanopar-of the applied energy goes to size reduction, the rest is verted to heat; hence, heat-sensitive drugs require cooling),and explodability (most pharmaceuticals are organic materi-als; as the size is reduced air combustibility of the materialincreases, hence proper inerting is needed)

con-Table 8 Energy Need (Bond Work Index) for Reducing Size of 1-mm-Diameter Particles

Product diameter (mm) Energy required (Bond work index)

Most of the pharmaceutical size reduction operations lize high-shear wet milling for the production of nanoparticles.Milling is explained in detail in chapter 2 Typical operationtime for the wet milling may be hours to days, hence the drughas to show stability in that time period, otherwise millingcannot be used for unstable drugs In addition, one has to

uti-be aware of contamination due to milling media

Precipitation from Solution or

Building-Up Process

In this process, a drug is dissolved in a solvent to achievemolecular solution Then, the nanoparticle precipitate isobtained either by removing the solvent rapidly or by mixing

an antisolvent (nonsolvent) to the solution, reducing its bilizing strength Initially, nuclei are formed, which growbecause of condensation and coagulation giving the final par-ticles If the rate of desolubilization is slow, then sticky nuclei/particles are formed that have a higher tendency of agglo-meration, giving large-size final particles For example, if adrug is dissolved in a solvent (e.g., toluene) and then an

solu-Figure 2 Variation of the particle size as the antisolvent and its mixing are varied in the solvent–antisolvent precipitation process.

antisolvent (e.g., methanol) is added with mild mixing, onewill obtain drug precipitate of typically 1 mm particle size(Fig 2) To obtain nanoparticles, a high desolubilization rate

is needed, or use of a surfactant is required, which canisolate the particles until they are completely dry Based onthese requirements, two general methods for nanoparticleproduction are available: (i) supercritical fluid process, and(ii) emulsification–diffusion process In the precipitation pro-cess, one can add compounds (e.g., polymers for controlledrelease) that will coprecipitate with the drug for smart drugdelivery applications

The key aspect of getting nanoparticles of the desiredsize and size distribution is to control both the rate of antisol-vent action and the particle coagulation Precipitation-basedprocesses are described in chapters 3 and 4

BIOLOGICAL TRANSPORT OF NANOPARTICLES

For drug delivery, most of the sites are accessible througheither microcirculation by blood capillaries or pores present

at various surfaces and membranes Most of the apertures,openings, and gates at cellular or subcellular levels are ofnanometer size (Table 9); hence, nanoparticles are the mostsuited to reach the subcellular level One of the prime require-ments of any delivery system is its ability to move aroundfreely in available avenues and by crossing various barriersthat may come in the way Regarding the human body, themajor passages are the blood vessels through which materialsare transported in the body The blood vessels are not left inany organ as an open outlet of the pipe, rather they becomethinner and thinner and are finally converted to capillariesthrough branching and narrowing These capillaries go tothe close vicinity of the individual cells After reaching theirthinnest sizes, the capillaries start merging with each other

to form the veins These veins then take the contents back

to the heart for recirculation Hence, the supply chain in thebody is not in the form of a pipe having an open inlet to theorgan and outlet away from the organ Consequently, for

any moiety to remain in the vasculature, it needs to have itsone dimension narrower than the cross-sectional diameter ofthe narrowest capillaries, which is about 2000 nm Actually,for efficient transport the nanoparticle should be smallerthan 300 nm.

But, just moving in the vessels does not serve the drugdelivery purpose The delivery system must reach the site

at the destination level This requires crossing of the bloodcapillary wall to reach the extracellular fluid of the tissueand then again crossing of other cells, if they are in theway, and entering the target cell These are the major bar-riers in the transit A nanoparticle has to do a lot during thissojourn of the carrier through the vessels (capillaries) andacross the barriers

There are two routes for crossing the blood capillariesand other cell layers, i.e., transcellular and paracellular In

Table 9 Approximate Sizes of Components in a

Typical 20-mm Human Tissue Cell

Source: From Refs 8, 9.

the transcellular route, the particulate system has to enterthe cell from one side and exit the cell from the other side

to reach the tissue The particulate system has to survivethe intracellular environment to reach the target tissue.The other route is paracellular In this, the particlulatesystem is not required to enter the cell; instead, it movesbetween the cells These intercellular areas are known asthe junctions Passing through the junctions would obviatedestruction of the carrier by the cell system Paracellularmovement of moieties including ions, larger molecules, andleukocytes is controlled by the cytoskeletal association of tightjunctions and the adherence junctions called apical junctioncomplex While tight junctions act as a regulated barrier,the adherence junctions are responsible for the developmentand stabilization of the tight junctions Different epithelialand endothelial barriers have different permeabilities mainlybecause of the differences in the structure and the presence oftight junctions While epithelia and brain capillary endothe-lium exhibit a high degree of barrier function, the vascularendothelium in other tissues has greater permeability Thetight junctions control the paracellular transport For exam-ple, diffusion of large molecules may not be feasible, butmigration of white cells is allowed Understanding of this reg-ulation mechanism is important as this might enable us topave the way for the movement of nanoparticles in the bodywithout actually entering into the unintended cells

As the nanoparticle-based drug delivery is achieved byparticle transport, it is important to understand the bloodflow rates and volumes of various organs and tissues Consid-ering the body’s distribution network, the blood vascular sys-tem, the body could be divided into several compartmentsbased on the distributional sequencing and differentiation

by the blood vascular system (Table 10)

Nanoparticles can have deep access to the human bodybecause of the particle size and control of surface properties.Experiments by Jani et al (13,14) have elegantly demon-strated the size effect Polystyrene particles in the size range50–3000 nm were fed to rats daily for 10 days at a dose of1.25 mg/kg The extent of absorption of the 50-nm particles

was 34% and that of the 100-nm particles was 26% Of thetotal absorption, about 7% (50 nm) and 4% (100 nm) wereaccounted for in the liver, spleen, blood, and bone marrow.Particles >100 nm did not reach the bone marrow, and those

>300 nm were absent from the blood Particles were absent inthe heart or the lung tissue The rapid clearance of circulatingparticles from the bloodstream coupled with their high uptake

by liver and spleen can be overcome by reducing the particlesize, and by making the particle surface hydrophilic withcoatings, such as poloxamers or poloxamines (15)

Gaur et al (16) observed that 100-nm nanoparticles ofpolyvinylpyrrolidone had a negligible uptake by the macro-phages in liver and spleen, and 5–10% of these nanoparticlesremain in circulation even eight hours after intravenousinjection Because of longer residence in the blood, nanoparti-cles have potential therapeutic applications, particularly incancer; the cytotoxic agents encapsulated in these particlescan be targeted to tumors while minimizing the toxicity tothe reticuloendothelial system

Desai et al (17) studied the effect of glycolide) (PLGA) particle size (100 nm, 500 nm, 1 mm, and

poly(d,l-lactide-co-10 mm) on uptake in rat gastrointestinal tissue The uptake

of 100-nm-size particles by the intestinal tissue was fold higher compared to the larger-size microparticles Theuptake also depends on the type of tissue (i.e., Peyer’s patchand nonpatch) and the location (i.e., duodenum or ileum).Depending on the particle size, Peyer’s patch tissue had a2–200-fold higher uptake of particles than the nonpatch tis-sue The 100-nm particles were diffused throughout thesubmucosal layers, while the larger-size particles were predo-minantly localized in the epithelial lining of the tissue,because of the microparticle exclusion phenomena in thegastrointestinal mucosal tissue

15–250-Hillyer and Albrecht (18) studied the gastrointestinaluptake and subsequent tissue/organ distribution of 4-, 10-,28-, and 58-nm-diameter metallic colloidal gold particles fol-lowing oral administration to mice It was found that colloidalgold uptake is dependent on the particle size: smaller particlescross the gastrointestinal tract more readily Interestingly,

they observed that the particle uptake occurs in the smallintestine by persorption through single, degrading enterocytes

in the process of being extruded from a villus

Cellular uptake is greater for nanoparticles compared tomicroparticles In cultured human retinal pigment epithelialcells, an increase in the mass uptake of particles was observedwith decreasing particle size in the range of 20–2000 nm poly-styrene particles (19) Further, no saturable uptake wasobserved for these particles up to a concentration of 500 mg/

mL With 20-nm nanoparticles, the uptake by the 1-cm2 cellmonolayer was as high as 20%

Because of possible differences in particle uptake, geneexpression efficiencies can also be improved with smaller par-ticles Prabha et al (20) studied relative transfectivity of 70-and 202-nm-PLGA nanoparticles in cell culture The smallerparticles showed a 27-fold higher transfection than the largernanoparticles in COS-7 cell line and a fourfold higher trans-fection in HEK-293 cell line

CONCLUSIONS

Nanoparticles offer unique properties as compared to

micro-or macroparticles Salient features include the following:

 Small size

 High surface area

 Easy to suspend in liquids

 Deep access to cells and organelles

 Variable optical and magnetic properties

 Particles smaller than 200 nm can be easily sterilized

by filtration with a 0.22-mm filter

Drugs, being mostly organic compounds, are more sticky

in nature as compared to inorganic materials, such as silica ormetal oxides Hence, it is harder to make smaller nanoparti-cles of drugs compared with hard materials Drug nanoparti-cles can be produced either by milling of macroparticles or byfast precipitation from solutions, as described in the followingchapters