sdarticle

Journal of Controlled Release 70 (2001) 1–20www.elsevier.com/ locate / jconrel

Review

Biodegradable polymeric nanoparticles as drug delivery devicesa a , a*Kumaresh S. Soppimath , Tejraj M. Aminabhavi , Anandrao R. Kulkarni ,

bWalter E. RudzinskiaDepartment of Chemistry, Polymer Research Group, Karnatak University, Dharwad 580 003, India

bDepartment of Chemistry, Southwest Texas State University, San Marcos, TX 78666, USA

Received 12 June 2000; accepted 28 September 2000

Abstract

This review presents the most outstanding contributions in the field of biodegradable polymeric nanoparticles used as drugdelivery systems. Methods of preparation, drug loading and drug release are covered. The most important findings on surfacemodification methods as well as surface characterization are covered from 1990 through mid-2000. 2001 ElsevierScience B.V. All rights reserved.

Keywords: Nanoparticle; Method of preparation; Surface modification; Drug delivery; Drug targeting

1. Introduction and reduce the toxicity or side effects [2]. However,developmental work on liposomes has been limited

Over the past few decades, there has been consid- due to inherent problems such as low encapsulationerable interest in developing biodegradable efficiency, rapid leakage of water-soluble drug in thenanoparticles (NPs) as effective drug delivery de- presence of blood components and poor storagevices. Various polymers have been used in drug stability. On the other hand, polymeric NPs offerdelivery research as they can effectively deliver the some specific advantages over liposomes. For in-drug to a target site and thus increase the therapeutic stance, NPs help to increase the stability of drugs /benefit, while minimizing side effects [1]. The proteins and possess useful CR properties.controlled release (CR) of pharmacologically active Nanoparticles generally vary in size from 10 toagents to the specific site of action at the therapeu- 1000 nm. The drug is dissolved, entrapped, encapsu-tically optimal rate and dose regimen has been a lated or attached to a NP matrix and depending uponmajor goal in designing such devices. Liposomes the method of preparation, nanoparticles, nanos-have been used as potential drug carriers instead of pheres or nanocapsules can be obtained. Nanocap-conventional dosage forms because of their unique sules are vesicular systems in which the drug isadvantages which include ability to protect drugs confined to a cavity surrounded by a unique polymerfrom degradation, target the drug to the site of action membrane, while nanospheres are matrix systems in

which the drug is physically and uniformly dis-persed. In recent years, biodegradable polymeric NPs*Corresponding author. Fax: 191-836-747-884.

E-mail address: [email protected] (T.M. Aminabhavi). have attracted considerable attention as potential

0168-3659/01/$ – see front matter 2001 Elsevier Science B.V. All rights reserved.PI I : S0168-3659( 00 )00339-4

2 K.S. Soppimath et al. / Journal of Controlled Release 70 (2001) 1 –20

drug delivery devices in view of their applications in 2.1.1. Solvent evaporation methodthe CR of drugs, their ability to target particular In this method, the polymer is dissolved in anorgans / tissues, as carriers of DNA in gene therapy, organic solvent like dichloromethane, chloroform orand in their ability to deliver proteins, peptides and ethyl acetate. The drug is dissolved or dispersed intogenes through a peroral route of administration [3,4]. the preformed polymer solution, and this mixture is

Some general aspects on micro- and nanoparticles then emulsified into an aqueous solution to make anhave been reviewed earlier [1,5–11]. A majority of oil (O) in water (W) i.e., O/W emulsion by using athese reviews have dealt with the NPs of poly(D,L- surfactant /emulsifying agent like gelatin, poly(vinyllactide), poly(lactic acid) PLA, poly(D,L-glycolide) alcohol), polysorbate-80, poloxamer-188, etc. AfterPLG, poly(lactide-co-glycolide), PLGA, and poly- the formation of a stable emulsion, the organic(cyanoacrylate) PCA. The present review details the solvent is evaporated either by increasing the tem-latest developments on the above mentioned poly- perature /under pressure or by continuous stirring.mers as well as NPs based on chitosan, gelatin, The effect of process variables on the properties ofsodium alginate and other hydrophilic /biodegradable NPs was discussed earlier [26]. The W/O/W methodpolymers. Surface modification aspects are also has also been used to prepare the water-solublecovered in more detail. The PLA, PLG and PLGA drug-loaded NPs [27]. Both the above methods use apolymers being tissue-compatible have been used high-speed homogenization or sonication. However,earlier as CR formulations in parentral and implanta- these procedures are good for a laboratory-scaletion drug delivery applications [12–14]. In addition, operation, but for a large-scale pilot production,poly(e-caprolactone), PCL, which was first reported alternative methods using low-energy emulsificationby Pitt et al. [15,16] for the CR of steroids and are required. In this pursuit, following approachesnarcotic antagonists as well as to deliver opthalmic have been attempted.drugs [17], and poly(alkylcyanoacrylate), PACA, arenow being developed as NPs. In addition, less 2.1.2. Spontaneous emulsification /solvent diffusionfrequently used polymers like poly(methylidene methodmalonate) [18], gelatin [19], chitosan [20] and so- In a modified version of the solvent evaporationdium alginate [21] will also be included in this method [28–30] the water-soluble solvent like ace-review. The important published literature within the tone or methanol along with the water insolubleperiod 1990–2000 is critically reviewed. The review organic solvent like dichloromethane or chloroformdoes not cover the entire literature within this period, were used as an oil phase. Due to the spontaneousbut the reader is advised to go to the original diffusion of water-soluble solvent (acetone or metha-literature in order to get more details. nol), an interfacial turbulence is created between two

phases leading to the formation of smaller particles.As the concentration of water-soluble solvent (ace-tone) increases, a considerable decrease in particle

2. Preparation of nanoparticles size can be achieved.

Conventionally, NPs have been prepared mainly 2.1.3. Salting out /emulsification–diffusion methodby two methods: (i) dispersion of the preformed The methods discussed above require the use ofpolymers; and (ii) polymerization of monomers. organic solvents, which are hazardous to the environ-

ment as well as to the physiological system [31]. TheUS FDA has specified the residual amount of organic

2.1. Dispersion of preformed polymers solvents in injectable colloidal systems [32,33]. Inorder to meet these requirements, Allemann and

Several methods have been suggested to prepare co-workers have developed two methods of prepar-biodegradable NPs from PLA, PLG, PLGA and ing NPs. The first one is a salting-out method [34,35]poly(e-caprolactone) by dispersing the preformed while the second one is the emulsification–solventpolymers [22–25]. diffusion technique [36,37].

K.S. Soppimath et al. / Journal of Controlled Release 70 (2001) 1 –20 3

2.1.4. Production of NPs using supercritical fluid [44], the solution is charged with the supercriticaltechnology fluid in the precipitation vessel containing solute of

Production of NPs with the desired physicochemi- interest in an organic solvent. At high pressures,cal properties to facilitate the targeted drug delivery enough anti-solvent will enter into the liquid phasehas been a topic of renewed interest in pharma- so that the solvent power will be lowered and theceutical industries. Conventional methods like sol- solute precipitates. After precipitation, when the finalvent evaporation, coacervation and in situ polymeri- operating pressure is reached, the anti-solvent flowszation often require the use of toxic solvents and/or through the vessel so as to strip the residual solvent.surfactants. Therefore, research efforts have been When the solvent content has been reduced to thedirected to develop the environmentally safer en- desired level, the vessel is depressurized and thecapsulation methods to produce the drug-loaded solid product is collected. A schematic of the SASmicron and submicron size particles. If solvent method is shown in Fig. 1. In a modified version ofimpurities remain in the drug-loaded NPs, then these the SAS technique [39], the solid of interest is firstbecome toxic and may degrade the pharmaceuticals dissolved in a suitable solvent and then this solutionwithin the polymer matrix. Supercritical fluids have is rapidly introduced into the supercritical fluidnow became the attractive alternatives because these through a narrow nozzle. The supercritical fluidare environmentally friendly solvents and the method completely extracts the solvent, causing the super-can be profitably used to process particles in high critical fluid insoluble solid to precipitate as finepurity and without any trace amount of the organic particles. This method, also called as gas anti-solventsolvent. Literature on the production of drug-loaded (GAS) technique, has been successfully used tomicroparticles using supercritical fluids is enormous produce microparticles as well as NPs.[38–44]. However, comparatively much less havebeen investigated to produce NPs [39,40]. It is 2.1.5. Polymerization methodsbeyond the scope of the present review to give an Nanoparticles can also be prepared by polymeri-entire coverage on supercritical fluid technology; we zation of monomers. Poly(alkylcyanoacrylate)s,will discuss only two of the most commonly used PACA, being biodegradable, have been used as tissuemethods of producing micro- or nanoparticles. adhesives in surgery since these are well tolerated in

In the rapid expansion of supercritical solution vivo [45,46]. This has prompted intense research(RESS) method the solute of interest is solubilized in activity to study polymerization reactions. Couvreura supercritical fluid and the solution is expanded et al. [47,48] reported the production of NPs (|200through a nozzle. Thus, the solvent power of super- nm diameter) by polymerizing mechanically thecritical fluid dramatically decreases and the soluteeventually precipitates. This technique is clean be-cause the precipitated solute is completely solvent-free. Unfortunately, most polymers exhibit little orno solubility in supercritical fluids, thus making thetechnique less of practical interest. RESS was verypopular in the late 80s and early 90s for particleproduction of bioerodible drug-loaded polymers likePLA. A uniform distribution of drug inside thepolymer matrix can be achieved by this method forlow molecular mass (,10 000) polymers. However,the RESS method cannot be used for high molecularmass polymers due to their limited solubility insupercritical fluids. For these reasons, much lessinformation is found in the literature over the past Fig. 1. Schematic diagram of the SAS method: PV1 and PV2 are6–7 years on this technique [41,43]. two volumetric pumps, N is nozzle, P is precipitation vessel, MV

In the supercritical anti-solvent (SAS) method is micrometric valve and EV is expansion vessel.


dispersed methyl or ethyl cyanoacrylate in aqueousacidic medium in the presence of polysorbate-20 as asurfactant without irradiation or an initiator. Here,the cyanoacrylic monomer is added to an aqueoussolution of a surface-active agent (polymerizationmedium) under vigorous mechanical stirring to poly-merize alkylcyanoacrylate at ambient temperature.Drug is dissolved in the polymerization mediumeither before the addition of the monomer or at theend of the polymerization reaction. The NP suspen-sion is then purified by ultracentrifugation or byresuspending the particles in an isotonic surfactant-free medium. The mechanism of polymerization ofPACA monomer is given below.

Polymerization follows the anionic mechanism, Fig. 2. Schematic representation for the production of poly-(alkylcyanoacrylate) nanoparticles by anion polymerization.since it is initiated in the presence of nucleophilic

2 2 2initiators like OH , CH O and CH COO leading3 3

to the formation of NPs of low molecular mass due [49], but NP production is not possible above a pHto rapid polymerization. Such NPs are degraded very of 3.0, probably due to the aggregation and stepwisefast. In order to circumvent this problem and to molecular mass increase at lower pH. Other factorsproduce higher molecular mass as well as stable that influence the formation of NPs include theNPs, polymerization must be carried out in an acidic concentration of monomer and the speed of stirring.medium (pH 1.0–3.5). After dispersing the monomer The NPs of PACA have gained wide popularity inin an aqueous acidic medium containing surfactant recent years despite some major drawbacks such asand stabilizer, polymerization is continued for 3–4 h use of low pH (around 2) and cytotoxicity [50]. Thisby increasing the pH of the medium to obtain the has lead to the synthesis of new dialkyl-methylidenedesired products. malonic acid ester monomers [51] and the NPs of

During polymerization, various stabilizers like poly(methylidenemalonate), PDEMM were prepared,dextran-70, dextran-40, dextran-10, poloxamer-188, and these were found to be non-biodegradable both-184, -237, etc are added. In addition, some surfac- in vitro and in vivo [52,53]. To overcome thistants like polysorbate-20, -40 or -80 are also used. problem, new derivatives of PDEMM were preparedParticle size and molecular mass of NPs depend i.e., ethyl-2-ethoxycarbonylmethylenoxycarbonylupon the type and concentration of the stabilizer acrylate. NPs from these monomers were preparedand/or surfactant used. A schematic representation by the same methods as those adopted for thefor the production of poly(alkylcyanoacrylate) NPs is preparation of PACA NPs by anionic polymerizationshown in Fig. 2. The size and molecular mass of NPs [54]. The pH of the polymerization medium criticallydepend upon the pH of the polymerization medium influenced the physicochemical properties of NPs,


but the minimum sized NPs were produced in the pH preparation method involves ionic gelation, with arange of 5.5–6.0 when compared to pH 2.0 and pH mixture of two aqueous phases, of which one7.6 for the PBCA and PDEMM, respectively [55]. contains chitosan and a diblock copolymer of ethyl-The reaction scheme for the synthesis of PMM NPs ene oxide (EO), and the other contains a polyanionis given below. sodium tripolyphosphate (TPP). In this method, the

positively charged amino group of chitosan interactswith the negatively charged TPP. The size (200–1000 nm) and zeta potential (120 mv and 160 mv)of the NPs produced were modulated by varying thecomposition of chitosan with the PEO–PPO diblockpolymer. These NPs have shown good associationwith proteins, such as bovine serum albumin, tetanustoxoid and diptaheria toxoid [63,64], insulin [65] aswell as oligonucleotide [66].

Mao and co-workers [67,68] prepared the DNA–chitosan NPs by a complex coacervation techniqueand used for the oral gene delivery. The complexcoacervation technique was also used to prepare theAn attempt was also made to reduce the formationDNA–gelatin NPs [69]. The chitosan NPs are provedof oligomer and to increase the yield of PMM 2.1.2.to be better carriers than the gelatin-based NPs for[56]. The process variables like pH, concentration ofloading the immunological and antineoplastic pro-surfactant and monomer concentration have beenteins [70]. The chitosan NPs were also produced bymonitored to produce NPs with higher molecularthe emulsion coacervation method [71]. In thismass [57]. Recently, the preparation of ethyl-2method, chitosan and the drug to be loaded were(ethoxycarbonyl) ethyl methylene malonoate-co-dissolved in water and water-in-oil emulsion pre-ethylene oxide have been reported [58]; these poly-pared in liquid paraffin using an emulsifying agent.mers are associated with both the hydrophilic andTo this stable emulsion, another emulsion of NaOHhydrophobic functionalities and they may be betterin liquid paraffin was added. When in contact withpolymers to prepare the long-circulating NPs. TheNaOH, chitosan NPs were produced by the coacerva-hydrophilic NPs ,100 nm and narrow size dis-tion of the polymer. Alginate-based NPs were alsotribution were prepared by using the aqueous core ofdeveloped and used for the delivery of oligonucleo-the reverse micellar droplets as nanoreactors [59,60].tides [21,72].Other polymerization methods were also reported in

Novel biodegradable polyesters, consisting ofthe literature for the development of acrylic basedshort poly(lactone) chains grafted onto poly(vinylNPs but these are not discussed since they are notalcohol) (PVA) or charge-modified sulfobutyl-PVAbiodegradable.(SB-PVA) were prepared by bulk melt polymeri-zation of lactide and glycolide in the presence of

2.1.6. NPs prepared from hydrophilic polymers different core polyols. The modified backbones wereOther than the commonly-used synthetic hydro- obtained by reacting the activated PVA with the

phobic polymers, active research is now focused on sulfobutyl groups. By carefully adjusting the poly-the preparation of NPs using hydrophilic polymers mer composition, novel class of water-soluble comb-like chitosan, sodium alginate, gelatin, etc. Different like polyesters were prepared. These polymers un-methods have been adopted to prepare NPs from the dergo spontaneous self-assembling to produce NPs,hydrophilic polymers. Several hydrophobic–hydro- which form the stable complexes with a number ofphilic carriers having limited protein-loading capaci- proteins such as human serum albumin, titanousty have been prepared by using organic solvents toxoid and cytocrome C. However, the development[61,62]. Calvo and coworkers [63–66] have reported of NPs from such polymers does not require the usea method to prepare hydrophilic chitosan NPs. The of solvents or surfactants [73–75].


3. Drug loading when compared to chromatographic methods, whichrequire ultracentrifugation.

A successful NP system may be the one, which In addition to adsorption and incorporation, a newhas a high loading capacity to reduce the quantity of method of drug loading for the water-soluble drugsthe carrier required for administration. Drug loading was proposed by Yoo et al. [85]. In this method, druginto the NPs is achieved by two methods: one, by was chemically conjugated into NPs. The conjugatedincorporating the drug at the time of NP production doxorubicin–PLGA and doxorubicin-loaded PLGAor secondly, by adsorbing the drug after the forma- NPs were prepared by the spontaneous emulsion–tion of NPs by incubating them in the drug solution. solvent diffusion method. The encapsulation ef-It is thus evident that a large amount of drug can be ficiency of 96.6% and 3.5% loading of doxorubicin–entrapped by the incorporation method when com- PLGA conjugate have been achieved. For the un-pared to the adsorption [76,77]. Adsorption iso- conjugated doxorubicin, these values were, respec-therms for the NP/drug delivery system give vital tively 6.7% and 0.3% (w/w).information on the best possible formulation, thedrug binding capacity onto the surface of NPs andthe amount of drug adsorbed. For instance, Couvreur 4. Drug releaseet al. [78] reported the adsorption of two antineoplas-tic drugs viz, dactinimycin and methotrexate onto Drug release from NPs and subsequent biodegra-poly(methylcyanoacrylate) and poly- dation are important for developing the successful(ethylcyanoacrylate). It was observed that methotrex- formulations. The release rates of NPs depend upon:ate was bound to the NPs to a lesser extent than (i) desorption of the surface-bound/adsorbed drug;dactinimycin. Generally, in the case of PACA, it is (ii) diffusion through the NP matrix; (iii) diffusionobserved that longer the alkyl chain length higher the (in case of nanocapsules) through the polymer wall;affinity for the drugs. The capacity of adsorption is (iv) NP matrix erosion; and (v) a combined erosion /thus related to the hydrophobicity of the polymer and diffusion process. Thus, diffusion and biodegradationthe specific area of the NPs. In case of entrapment govern the process of drug release.method, an increase in concentration of the mono- Methods to study the in vitro release are: (i)mer, increases the association of drug, but a reverse side-by-side diffusion cells with artificial or bio-trend is observed with the drug concentration in the logical membranes; (ii) dialysis bag diffusion tech-dispersed solution. This observation was further nique; (iii) reverse dialysis sac technique; (iv) ultra-substantiated by Radwan [79] who studied the effect centrifugation; (v) ultrafiltration; or (vi) centrifugalof monomer concentration on % drug loading. These ultrafiltration technique. Despite the continuous ef-results indicate that there is a need to optimize the forts in this direction, there are still some technicalamount of monomer available for the drug entrap- difficulties to study in vitro drug release from NPsment. [86,87]. These are attributed to the separation of NPs

The type of surface-active materials and stabilizers from the release media. In order to separate NPs andhas an effect on drug loading [80]. Chukwu et al. to avoid the tedious and time-consuming separation[81] studied the adsorption of different psycho- techniques, dialysis has been used; here, the suspen-pharmacological agents onto NPs of poly- sion of NPs is added to the dialysis bags / tubes of(isobutylcyanoacrylate), PIBCA, in the pH range different molecular mass cut-off. These bags are thenbetween 2.0 and 7.4. Adsorption of drugs onto NPs incubated in the dissolution medium [88–90].followed the Langmuir mechanism [82,83]. In Another technique involves the use of a diffusionanother study [84], a dielectric method was used to cell consisting of donor and acceptor compartments;investigate the adsorption of b-blockers onto PIBCA this technique was used to separate through theNPs. In this method, the NP suspensions were taken artificial /biological membranes [91]. In this method,into a capacitance cell, exposed to a high-frequency kinetic study was not performed under the perfectfield (10 MHz) and the complex impedance was sink conditions, because the NPs were not directlymeasured. This technique is rapid and inexpensive diluted in the release media, but were separated from


the release media through the membrane. Thus, the drug from the core across the polymeric barrieramount of drug in the release media did not reflect layer. Hence, theoretically, the drug release shouldthe real amount released. In order to avoid the follow the zero-order kinetics. Calvo et al. [17]enclosure of NPs in the dialysis bag, Leavy and obtained almost the similar release profiles forBenita [92] used a reverse dialysis technique for the indomethacin from both NPs and nanocapsules. ThisO/W emulsion. In this method, NPs were added indicated that the polymer coating does not show anydirectly into the dissolution medium. The same barrier properties for the drug release. The drugtechnique was adopted by Calvo et al. [17] for the release from the nanocapsule takes place mainly byevaluation of NPs, nanocapsules and nanoemulsions. the partitioning of the drug; however, the main factorHowever, the method is not very sensitive for controlling the release is the volume of the aqueousstudying the rapid release formulations; but can only medium. For instance, with higher dilution of thebe used for the release of formulations having the dissolution media, a faster and complete release ofrelease time longer than 1 h [93]. the drug takes place. However, Lu et al. [97]

Release profiles of the drugs from NPs depend reported that the release of bovine serum albuminupon the nature of the delivery system. In the case of from PLA nanocapsule depends upon the moleculara matrix device, drug is uniformly distributed /dis- mass of the polymer, which indicates that the releasesolved in the matrix and the release occurs by may not occur by partitioning of the drug, but maydiffusion or erosion of the matrix. If the diffusion of be due to diffusion across the polymer coating.the drug is faster than matrix degradation, then the The method of drug incorporation into NPs hasmechanism of drug release occurs mainly by diffu- also shown an effect on drug release. Fresta et al.sion, otherwise it depends upon degradation [28]. [90] reported a higher burst up to 60–70% for theRapid initial release is attributed to the fraction of NPs loaded with drug by adsorption; here, the burstthe drug which is adsorbed or weakly bound to the effect is less and the remaining drug release is quitelarge surface area of the NPs, than to the drug slow. This study demonstrated that the incorporationincorporated in NPs. Following the dilution of the method has shown better sustained release charac-dissolution media under perfect sink conditions the teristics. When the drug is chemically conjugateddrug partition showed an increase due to the immedi- with PLGA NPs, the release took place over 25 days,ate release phase. Later, an exponential delayed whereas with those NPs containing unconjugatedrelease rate is observed probably due to the drug free drug, a rapid release in about 5 days occurreddiffusion from the matrix [94,95,35,17,28]. Release [85]. Here, the CR properties have been attributed toin the matrix type of NPs follows the first-order chemical degradation of the conjugated PLGA,kinetics [90,79]. which permitted water solubilization and subsequent

Recently, Polakovic et al. [96] theoretically release of the drug-conjugated PLGA oligomers intostudied the release of PLA NPs loaded with varying the medium. In case of drug release from hydrogelamounts (7–32% w/w) of lidocane. Two models NPs, release occurs mainly due to swelling, whichwere used to study the drug release: (i) by crystal can be controlled by either adding the hydrophilicdissolution and (ii) by diffusion through the polymer functional groups or by monitoring cross-linking ofmatrix. When the drug loading is ,10% (w/w) (the the matrix.drug is molecularly dispersed), the release kineticsshows a better fit to the diffusion model. Theexistence of lidocane crystals at higher concentration 5. Surface properties of NPs(.10%) is observed. Since the drug should dissolvefirst from the crystals and then diffuse from the 5.1. Protein adsorption and phagocytosis of NPsmatrix, the overall release mechanism could bedescribed by the dissolution model. Plasma protein adsorption and phagocytosis of

In the case of nanocapsules (reservoir-type drug- NPs is a subject that has been widely studied indelivery systems) the drug core is coated with the recent years. When the NPs are administered in-polymer and the release occurs by diffusion of the travenously they are easily recognized by the body


immune systems, which are then cleared from the of poly(oxyethylene) in the polymer has drasticallycirculation. Apart from the size of NPs, their surface decreased the protein adsorption when compared tohydrophobicity determines the amount of adsorbed the pure polyesters.blood components, mainly proteins (opsonins). These In another study by the same group of researcherswill determine the in-vivo fate of NPs [98,99]. [105], an attempt was made to correlate the ad-Binding of these opsonins onto the surface of NPs, sorption results with the in-vivo circulation of NPs.called opsonization, acts as a bridge between NPs The di-block and multi-block copolymers of PEGand phagocytes. Hence, for a qualitative and quan- were used as model polymers to show the decreasetitative understanding of the interaction of blood in adsorption of proteins; these NPs have shownproteins with NPs, it is necessary to design long- long-circulating properties. The reduced liver uptakecirculating NPs by surface modification. of NPs was dependent on the molecular mass and

In a study by Allemann et al. [100], it was surface density of PEG. The in-vitro protein rejectionreported that when the PLA NPs are incubated in properties of the PEG-coated poly-human plasma and serum, the IgG was found to be (alkylcyanoacrylate) NPs were investigated afterthe major protein along with albumin, apolipopro- when the freeze fracture of NPs were pre-incubatedtein-E, which were adsorbed on the surface. Compli- with fibrinogen as model blood protein [106]. Thement C components (part of immune system used decrease in protein adsorption onto PEG-coated NPs3

for the recognition of foreign surfaces) were also was evident by 2-DPAGE after incubating them inadsorbed onto the surface of NPs after incubation in human serum. The NPs were also long-circulating asthe serum reaching the level of antibody IgG. Blunk proved from in-vivo tests.et al. [101] studied the kinetics of protein adsorptiononto polystyrene NPs and confirmed that albumin 5.2. Surface characterization methodsand fibrinogen were adsorbed in a highly dilutedplasma (0.08 and 0.8%). However, in the plasma of Many techniques have been developed and used tohigh concentration (80%), proteins were displaced study the surface modification of NPs. The efficiencywithin seconds or even fractions of a second. The of surface modification can be measured either bystudy indicated that apolipoproteins A-I, C-III, E and estimating the surface charge, density of the func-J were the major proteins adsorbed onto NPs. tional groups or an increase in surface hydrophilicity.

A two-dimensional polyacrylamide gel electropho- One method used to measure the surface modi-resis (2-DPAGE) was used to estimate quantitatively fication is to determine zeta potential (j) of thethe interaction of plasma proteins with iron oxide aqueous suspension containing NPs. In this method,NPs in the presence of plasma proteins stabilized by the mobility of charged particles is monitored bypolysaccharide. Particles incubated in the plasma applying an electrical potential. The zeta potentialwere separated and were then washed with different values may be positive or negative depending uponwashing media. The protein adsorbed on NPs was the nature of the polymer or the material used forthen estimated by 2-DPAGE. By this, it was found surface modification. The extent of surface hydro-that fibrinogen, IgG and albumin were the major philicity can then be predicted from the values of j.plasma proteins adsorbed onto NP surface [102,103]. This is a widely used technique to understand theIn another study by Luck et al. [104], the interaction surface charges of NPs.of proteins with NPs was shown to depend upon the Another commonly used technique is electronmethod of NP preparation. For example, the amount spectroscopy for chemical analysis, ESCA, alsoof several apolipoproteins in plasma protein adsorp- called X-ray photoelectron spectroscopy (XPS). Thistion patterns of the spray-dried PLGA and PLA NPs technique is based on the emission of electrons fromwere distinctly higher than when compared to the materials, in response to irradiation by photons ofadsorption patterns of the particles produced by W/ sufficient energy, to cause ionization of the core-O/W emulsion technique. Some adsorbed proteins level electrons. These electrons are emitted at ener-were found to be specific for particles produced by gies characteristic of the atoms from which they arethe same method. The presence of hydrophilic chain emitted. Since photons have low penetration energy,


only those electrons pertaining to atoms at or near action with the surface even at lower concentrations˚the surface (up to 100 A) escape and these can be of the protecting polymeric layer. The biological

counted. For each atom type, the number of electrons consequences of steric protection of drug carriersemitted is related to the number of atoms of a with the surface-grafted polymers have been dis-particular type of atom. Using this technique, surface cussed and clinical applications of the long-circulat-elemental analysis was performed [107]. ing NPs have been studied [10]. A theoretical model

In another technique, the surface hydrophobicity of repulsion of proteins from the solid substrate wasof NPs can be directly measured by hydrophobic proposed by Joen et al. [110]. The steric repulsion,interaction chromatography. This technique involves van der Waals attractions and hydrophobic inter-the column chromatography, which is able to sepa- action free energy have been correlated. The modelrate materials based on the interaction with a hydro- provides a basis for the prevention of opsoninphobic gel matrix [108]. The nanoparticle and the gel deposition. High surface density and long chain-interaction is a function of surface hydrophobicity of lengths of PEG are necessary for low protein ad-NPs. Propyl agarose gel is used as a stationary phase sorption. However, surface density has a greaterand elution of NPs can be achieved by using the effect than the chain-length on steric repulsion andphosphate buffer. Eluent samples can be collected van der Waals attraction.and the optical density measured spectrophotomet- Bazile et al. [111] developed the NPs based onrically at 400 nm. The gel matrix can then be washed methoxy PEG–PLA i.e., Me-PEG–PLA and blendsto remove the NPs. of PLA with Me-PEG–PLA. These NPs, labeled by

14introducing C-labeled PLA in the formulation were5.3. Methods of surface modification more slowly captured by the cultured THP-1 mono-

cytes when compared to pluronic F68-coated PLASurface modification of biodegradable and long- NPs. The half-life of Me-PEG–PLA NPs was im-

circulating polymeric NPs has been achieved mainly proved by a factor of 180 (360 min) when comparedby two methods: (i) surface coating with hydrophilic to the uncoated and F68-coated NPs. Even though, apolymers / surfactants; and (ii) development of bio- high amount of radioactivity was located in the heartdegradable copolymers with hydrophilic segments. and blood vessels due to particle circulation, in otherSome of the widely used surface-coating materials phagocytic organs, radioactivity was found evenare: polyethylene glycol (PEG), polyethylene oxide after 6 h of i.v. administration indicating a delay in(PEO), poloxamer, poloxamine, polysorbate (Tween- phagocytosis. Tobio et al. [112] observed much80) and lauryl ethers (Brij-35). greater penetration of tetanus toxoid (TT) encapsu-

lated PEG–PLA NPs than PLA NPs after nasal5.3.1. PEG and PEO-coated NPs administration. A high persisting radioactivity was

PEG-coated NPs have received a lot of attention. found in body compartments up to 8 h after the125Gref et al. [109] described the one step method to introduction of I TT-loaded NPs.

prepare the PEG-coated NPs using amphiphilic Gref et al. [113] reported the preparation of blendPEG–polyester diblock copolymer as the starting NPs of PLA with monomethoxy polyoxyethylenematerial and showed that the protective coating (MPOE) by solvent evaporation method using so-affecting against the phagocytes depends upon den- dium cholate surfactant. The zeta potentials mea-sity and molecular mass of PEG. They also studied sured at various concentrations of NaCl varied fromthe biodistribution of covalently-attached PEG– 255 mV for PLA to 0 mV for blends dependingPLGA NPs. The protective effect of PEG on carriers upon the composition of MPOE in the NPs. The zetalike liposomes, NPs and micelles was studied by potential increased with an increasing amount ofTorchilin [11] in terms of the statistical behavior of MPOE suggesting that the MPOE chains that arepolymers. A mechanism was proposed which as- present on the surface of NPs mask the ionized

2sumes that the surface-grafted chains of flexible and COO end-group of PLA. These results are sup-hydrophilic polymers form dense conformational ported by a phagocytosis study on the monocytes.clouds thus preventing other polymers from inter- When MPOE content in the blend is greater than


2–3%, the MPOE chain adopts a brush-like configu- the PEG coated NPs. Peracchia et al. [121] alsoration forming a sterically-uncharged barrier, thereby prepared the methoxy PEG cyanoacrylate–hexadecylreducing the zeta potential and phagocytosis. cyanoacrylate amphiphilic NPs by polymer precipi-

Govender et al. [114] examined the drug-encapsu- tation or by solvent evaporation method; the PEGlation characteristics of PLA–PLA NPs using coating was confirmed by XPS. The particles ex-procaine hydrochloride, a water-soluble drug. The hibited a reduced cytotoxicity and enhanced degra-PLA–PEG NPs were produced by the nano-precipi- dation. NPs prepared in the presence of PEGs havetation technique. The drug-entrapment efficiencies of shown some advantages in preventing opsonizationthese NPs were compared with those of PLGA NPs. and thereby avoiding the MPS uptake [122]. ThisKim et al. [115] used the ESCA method to evaluate mechanism is explained in Fig. 3.the presence of PEG on the surface of indomethacin- PEO-surface modified systems have received anloaded Me-PEG–PLA NPs. The in-vitro cytotoxicity increased attention in recent years. Jaeghere et al.of these NPs did not show any remarkable cytotox- [123] studied the freeze-dried PEO-surface modifiedicity against the normal human fibroblast cells. NPs as a function of PEO chain length and surface

The optimum surface density of PEG on NPs density to avoid the MPS uptake. NPs were producedplays an important role in steric repulsion. These by salting-out method using the blends of PLA andNPs have shown a lower accumulation in the liver, PLA–PEO copolymers. In an effort to study thebut the observed high spleen uptake is due to the effect of surface density of PEO on the complimentremoval of PEG coating from the surface of NPs, an consumption, Vittaz et al. [124] used the diblockimportant property in spleen targeting [116]. In polymer of PLA and polyethylene oxide (PLA–addition, the distance between PEG chains on the PEO). It was found that as the PEO density on thesurface of NPs is critical to avoid the adsorption of surface of the NPs increases, a decrease in compli-plasma proteins. For instance, a decrease in the ment consumption is observed due to steric repulsiondistance between PEG chains on the surface from 6.2 of the surface to proteins. A preliminary study wasto 5.1 nm drastically decreases the adsorption of made on the synthesis of amphiphilic PEO–PPO–apolipoproteins up to 90%. This further confirms thatthe density of hydrophilic segment on the surface ofNPs is important in opsonization. However, anyfurther decrease in this distance did not showsignificant effects on the adsorption of plasma pro-teins [117].

Peracchia et al. [118] used the emulsification andsolvent evaporation method to prepare the diblockMe-PEG–PLA copolymeric NPs containing 20 and33% of lidocaine. They confirmed high-density ofthe surface PEG by ESCA. However, the size of NPsproduced by the block copolymer was twice as highas those of PLGA NPs. This was attributed to anincrease in the chain length of PEG. Peracchia et al.[119,120] reported the chemical coupling of PEGwith PBCA NPs prepared by emulsion polymeri-zation in the presence of PEG, Me-PEG and (Me) -2

PEG. Polymerization was possible only in the pres-ence of PEG and Me-PEG as hydroxyl group was

Fig. 3. Effect of surface PEG density and its conformation on thenecessary for polymerization and association of PEGopsonization process: (A) opsonization takes place when the

on the surface of NPs. Higher PEG density was density is low, (B) opsonization is not possible at higher surfaceobserved on the surface of NPs when Me-PEG was density and (C) when both the end groups of PEG participate inused. A decrease in hydrophobicity was observed for surface modification.


PEO block copolymers (Plunoric) and poly(e-cap- uptake pathways are observed for NPs dependingrolactone) by bulk polymerization [125]. The size of upon their surface characteristics and the rodentthe NPs prepared varied from 116 to 196 nm, species. Coating was effective in stimulating thedepending upon the type of copolymer used. spleen uptake in rats and mice. Spleen uptake of

Fluoresbrite NPs was higher than Estapor NPs,5.3.2. Poloxamine and poloxamer coated NPs probably due to differences in the surface charac-

Poloxamer and poloxamine have been widely used teristics of NPs.in surface coating studies. Storm et al. [126] pre- Polystyrene-latex nanospheres (PSL-NS, meansented an overview of the advances made up to 1995 diameter, 85 nm) were coated with lactosyl-poly-on the surface modification of NPs to oppose the styrene (LPS, high affinity to hepatocytes) to evalu-MPS uptake. In a study by Illum and Davis ate their targeting characteristics to hepatocytes and[127,128], poloxamer and poloxamine were used as PSL-NS surfaces [133]. Hepatocytes were adheredthe coating materials to prepare the long-circulating specifically with the LPS-coated dishes made of theNPs of polystyrene and poly(methyl methacrylate). A same materials as PSL-NS. Flow cytometry inves-prolonged circulation time and reduction in liver tigations showed that the LPS-coated fluorescein-uptake in rabbits was found for the poloxamine- isothiocyanate (FITC)–PSL-NS were taken up bycoated polystyrene NPs (60 nm size) when compared hepatocytes when compared to the noncoated FITC–to the uncoated NPs of the same size. A decrease in PSL-NS as a control. These findings indicated thathepatic uptake of about 20% for the NPs prepared LPS–PSL-NS could target to hepatocytes. The sur-with poloxamer-188 and about 40% for the NPs face of LPS on PSL-NS showed higher hydrophil-coated with poloxamer-338 was observed. Rabbit icity than PEG-6000, Tween-80, poloxamer-407 and

131experiments with I-labelled polystyrene poloxamer-908, which indicated that LPS–PSL-NSpoloxamer-407 coated NPs showed the superior may avoid the reticuloendothelial system capture andperformance over that of poloxamer-338 to avoid the have a long plasma duration after the in-vivo i.v.hepatospleenic uptake. adminstration. Plasma coagulation can be prevented

Rudt and Muller [129] studied the uptake of by the addition of 0.1% of PVA in LPS–PSL-NSsurface modified poloxamine-coated polystyrene NPs solution when LPS–PSL-NS were injected. Theand found extremely low levels of uptake for 100 nm LPS–PSL-NS were the potential hepatocyte targetingsize NPs. Compared to poloxamer, poloxamine was carriers for the injectable formulations.more effective as a coating material to avoid the livercapture of rabbits [130]. Moghimi and Gray [131]developed the long-circulating poloxamine-908 5.3.3. Cyclodextrin /carbohydrate coated NPscoated polystyrene NPs (60 nm) that are resistant to Carbohydrates were also found to avoid the MPSMPS uptake. The time interval of administration was uptake when coated on the surface of NPs. To avoidimportant in maintaining the long circulation time. the MPS uptake the coated NPs with carbohydrate

Spleen-capture study of the fluorescent-labeled was reported by Cho et al. [134]. The NPs of PLApolystyrene NPs coated with poloxamer 407 or and poly(L-lysine)-grafted-polysaccharide were alsopoloxamine 908 was made [132] on two rodent developed for the delivery of DNA [135] and thesespecies viz., mouse and rat in order to assess the were found to be resistant against self-aggregationeffect of coating on their intraspleenic distribution. and nonspecific adsorption of the serum proteins.Two fluorescent polystyrene NPs used were: Recently, Duchene et al. [136] used amphiphilic

Estapor (FX-010, 185 nm, Prolabo, France) and cyclodextrin NPs to increase the loading of water-Fluoresbrite (Plain YG, 260 nm, Polysciences, soluble drugs and bioavailability of the poorly water-

UK). A fluorimetric investigation indicated that the soluble drugs intended for targeted delivery by theFluoresbrite NPs were more efficiently trapped by oral or parenteral route. In order to further increase

the spleen than the Estapor -based NPs in mice and the loading capacity, PIBCA NPs were loaded withrats. Results indicate an increase in the size of NPs the natural or hydroxypropyl cyclodextrins. The

after coating the Estapor NPs. Different spleen loading capacity increased with an increase in stabili-


ty constant of the inclusion drug/parent g-cyclo- biological membrane was studied and an increase indextrin and with a decrease in water solubility. the permeation of polysorbate-80 coated NPs

The PIBCA NPs were prepared by the anionic occurred [91]. A schematic representation of thepolymerization of isobutylcyanoacrylate in 0.01 M increased drug permeation from the polysorbate-80HCl containing 1% poloxamer-188 and in the pres- coated NPs through the biological membrane isence of cyclodextrins. The size, zeta potential and shown in Fig. 4.cyclodextrin content were influenced by the nature of Borchardt et al. [142] studied the uptake ofcyclodextrin. The smallest size particles were ob- polysorbate-80 coated poly(methyl methacrylate)tained from hydroxypropyl b-cyclodextrin, but the (PMMA) NPs by bovine brain microvessel endo-highest cyclodextrin content was obtained for b- thelial cell monolayers. These NPs showed an in-cyclodextrin. The cyclodextrin NPs or the polymeric creased uptake by the endothelial cells of the BBB.NPs containing cyclodextrin were useful in targeting Troster et al. [143] demonstrated a nine-fold increasethe water-insoluble drugs through oral or parentral in the accumulation of radioactivity in the brain arearoute. The presence of cyclodexrins in these NPs has after i.v. administration of polysorbate-80 coated

14drastically reduced the surface negativity probably C-PMMA NPs. A recent study by Steiniger et al.due to their hydrophilicity; hence, the cyclodextrin [144] suggested that polysorbate-80 coated poly-coated NPs may help in avoiding the MPS.

5.3.4. Polysorbate-coated NPs to penetrate theblood–brain barrier

Targeting drugs to the brain by crossing theblood–brain barrier (BBB) has been a challenge. Inthis pursuit, many attempts have been made todevelop novel drug delivery systems. BBB is formedby the tight endothelial cell junctions of the capil-laries within the brain, which limits the ability ofmany drugs to penetrate through the brain tissue inorder to enter the central nervous system (CNS). It isknown that many regulators of the brain functionssuch as cytokines, transferrin, enkephalins, endor-phins or delta sleep inducing peptides pass throughBBB from the vessels into brain [137,138] as well assome excitatory and depressant amino acids, pene-trate poorly through BBB. The poor BBB penetrationof such substances makes the problem of drugtargeting to the brain highly pertinent. However, thesurface modified NPs have been used to deliver theanti-inflammatory drugs acting on the CNS becausethese can pass through BBB [139,140].

The mechanism of enhancement of drug transportfrom the coated NPs through BBB is due to thenumber of mechanisms: (i) by binding the NPs to theinner endothelial lining of the brain capillaries andsubsequently, particles deliver drugs to the brain byproviding a large concentration gradient, thus en-hancing the passive diffusion; (ii) brain endothelial Fig. 4. The schematic representation of the drug uptake throughuptake by phagocytosis [141]. The effect of surfac- biological membrane from (A) free drug and (B) polysorbate-80tant coated NPs on drug permeation across the coated nanoparticle bound drug [91,141].


(alkylcyanoacrylate) NPs are superior over the un- also reported an increased analgesic activity ofcoated NPs to transport drugs across BBB. dalargin-loaded PBCA NPs coated with polysorbate-

Recently, investigations have been carried out 80 when administered in mice. In a further study,[145] with PBCA NPs as well as with the non- Alyautdin et al. [148] found that BBB crossing wasbiodegradable polystyrene (PS) NPs (200 nm in observed for low molecular mass and polar hydro-diameter) to study the transport of analgesic peptide, philic drug like tuborcurarin after loading it intodalargin to the brain. Its entry into the CNS of the polysorbate-80 coated PBCA NPs. An in-vivo per-mice was evaluated using the tail-flick procedure. fused rat brain was used along with the simultaneousLocomotor activity measurements were performed to recording of an electroencephalogram (EEG) sincecompare the toxicity of NPs. BBB permeability of the drug induces epileptic form seizures. An i.v.PBCA NPs was studied in-vitro using a co-culture of injection of the NPs demonstrated the appearance ofbovine brain capillary endothelial cells and rat EEG seizures 5 min after the administration.astrocytes. Dalargin associated with PBCA NPs and Schroeder et al. [149] studied the transport ofpolysorbate-80 induced a potent and prolonged anal- dalargin, kytorphin (centrally-acting analgesics) andgesia, which was not observed by using polystyrene amitriptyline (antidipressant)-loaded PBCA NPsNPs, but not using the PBCA NPs. Locomotor coated with polysorbate-80 across the BBB. In-vivoactivity dramatically decreased in the mice dosed analgesic activity carried out in mice showed awith PBCA NPs, but not with the polystyrene NPs. drastic enhancement of analgesia for the drug-loadedThe in-vitro and in-vivo results suggested that the NPs coated with polysorbate-80. The amitriptylinPBCA NPs induce a nonspecific opening of the BBB concentration in the brain increased, but the con-in the presence of polysorbate-80 allowing the centration in serum decreased for dextran-stabilizedtransport of dalargin into the CNS. Although polysorbate-80 coated NPs. These results indicatepolysorbate-80 coated PBCA NPs are useful in that the surface modification of NPs by coating withincreasing the penetration of drugs into the CNS, polysorbate-80 is effective in drug delivery throughpotential therapeutic applications are limited because BBB.of the high systemic NP concentration needed todeliver drugs to the CNS.

In an effort to deliver anticancer drugs to the brain 6. Delivery of proteins and peptides using NPsusing NPs, Gulyaev et al. [146] demonstrated thatthe brain concentration of systemically administered Peptide drugs are attracting, as their role indoxorubicin was enhanced by more than 60-fold by physiopathology is better understood and because ofbinding it to polysorbate-80 coated PBCA NPs. the progress made in biotechnology and bioengineer-Doxorubicin was selected as a model drug due to its ing. Particularly, the development of DNA-recombi-potent antitumor activity and because the drug is not nant technology has made these compounds availableable to cross the BBB by i.v. injection. Polysorbate- on large scale than in the past. However, the use of80 coated NPs reached the brain intact and released peptide in medicine is partly limited by their rapidthe drug after endocytosis by the brain blood vessel degradation by proteolytic enzymes in the gastroin-endothelial cells. High brain concentrations achieved testinal tract; thus, they need to be administeredin this study suggested a significant improvement in through the parentral route. The biological half-lifethe treatment of brain tumors. of peptides is short and needs frequent administra-

Alyautdin et al. [147] studied the efficiency of tions. On the other hand, their transport acrosspolysorbate-80 coated PBCA NPs in crossing BBB biological barriers is poor due to poor diffusivity andto deliver the water-insoluble analgesic drug, loper- lower partition coefficients. In this pursuit, themide, in mice. Intravenous injection of the particulate biodegradable delivery systems have beenpolysorbate-80 coated NPs resulted in a long and proposed for the safe and controlled parentral ad-significant analgesic effect, which was measured by ministration of peptides [150].the tail flick method, while the uncoated NPs were Proteins and peptides are unstable in PLGAunable to produce analgesia. Alyautdin et al. [141] because of the hydrophobicity and acidity of PLGA


[151]. Another problem is the fast burst release of release insulin from the nanospheres over a span of 6protein drugs from the PLGA matrices. In order to h. The 1.6% zinc insulin in PLGA with fumariccircumvent these problems, different approaches anhydride oligomer and iron oxide additives washave been explored to modify the properties of shown to be active orally and was able to control thePLGA matrices by using the hydrogel NPs plasma glucose levels. A number of properties of this[152,153]. This has prompted the development of formulation, including size, release kinetics, bioadhe-novel protein delivery systems. In these studies, siveness and ability to traverse the gastrointestinalbovine serum albumin (BSA) was encapsulated first epithelium have contributed to its oral efficacy.in PVA NPs, which were then loaded into PLGA In recent years, greater advances have been mademicrospheres using the phase separation method. The particularly by the research group of Professorprotein loaded PLGA–PVA composite NPs were Robert Langer at MIT (USA) on the development ofthen characterized and were having the nonporous gene delivery systems. However, a discussion onsurface to release BSA for over 2 months. In a recent these systems is beyond the scope of this review.study by Gasper et al. [154], it was shown that thepresence of end carboxyl group in PLGA resulted ina high protein loading of up to 4.86 mass% and the 7. Conclusionsrelease continued for about 20 days. On the otherhand, the presence of esterified carboxyl end groups The use of biodegradable polymers for the CR ofin PLGA led to a lower loading (2.65 mass%) of therapeutic agents is now well established. Althoughproteins and a release of up to 14 days. currently there are only a small number of commer-

The release kinetics and in-vivo effects of NPs cially available products that utilize this technologycontaining PGDF-Receptor b (PDGFRb) tyrphostin (e.g., Lupron Depot ), these polymers have great

inhibitor, AG-1295, AG-1295-loaded PLA NPs were utility for the CR of several drugs like vaccines,prepared by the spontaneous emulsification /solvent human growth hormone, insulin, anti-tumor agents,displacement technique [155]. The in-vitro release contraceptives and also vaccines. Long circulation ofrate and the impact of drug/polymer ratio on the size drugs in the body is the key in successful drugof NPs were determined. It was shown that by delivery and drug targeting to the site of action.modulating the formulation variables, release kinet- Many polymeric NPs have been developed for thisics and particle size were tailor-made to address the purpose. Certainly, surface modification is useful inclinical needs. A novel pulmonary delivery system of achieving these goals. From the polymer chemistryPLGA nanosphere (400 nm size) encapsulating the viewpoint, it is important to synthesize newer poly-physiologically active peptide was developed by mers and copolymers to match the hydrophilic andKawashima et al. [156]. These were prepared by hydrophobic properties. Production of NPs using theusing the modified emulsion solvent diffusion meth- environmentally friendly processes like supercriticalod in water. The aqueous dispersions of PLGA fluids is quite a promising area of research tonanospheres administered pulmonarily to guinea pig develop the products that are free from the unwantedvia nebulization reduced significantly the blood toxic residual solvents. Although many importantglucose level for over 48 h when compared to the goals have been reached in achieving stabilization ofnebulized aqueous solution of insulin as a reference. drugs in circulation, yet more investigations areAbout 85% of the drug was released from the needed to develop the newer materials in this area.nanospheres during the initial burst, followed by aprolonged release of the remaining drug for fewhours in saline solution at 378C. Acknowledgements

Zinc insulin was successfully encapsulated invarious polyester and polyanhydride nanosphere We immensely thank the Council of Scientific andformulations using the phase inversion nanoencapsu- Industrial Research, New Delhi, India [Grant [lation technique [157]. The encapsulated insulin 80(0025)97/EMR-II] for a major financial supportmaintained its biological activity and was able to of this study. Dr. Walter E. Rudzinski thanks the


[17] P. Calvo, J.L. Vila-Jato, M.J. Alonso, Comparative in vitroSouthwest Texas State University, San Marcos for aevaluation of several colloidal systems, nanoparticles,research enhancement grant. We also thank Dr. M.I.nanocapsules and nanoemulsions as ocular drug carriers, J.

Aralaguppi for his assistance. Pharm. Sci. 85 (1996) 530–536.[18] F. Lescure, C. Seguin, P. Breon, P. Bourrinet, D. Roy, P.

Couvreur, Preparation and characterization of novel poly-(methylidene malonate 2.1.2.)-made nanoparticles, Pharm.ReferencesRes. 9 (1994) 1270–1277.

[19] C.A. Farrugia, M.J. Grover, Gelatin behavior in dilute[1] J. Kreuter, Nanoparticles, in: J. Kreuter (Ed.), Colloidal Drug aqueous solutions: Designing a nanoparticulate formulations,

Delivery Systems, Marcel Dekker, New York, 1994, pp. J. Pharm. Pharmacol. 51 (1999) 643–649.219–342. [20] R. Fernandez-Urrusuno, P. Calvo, C. Remunan-Lopez, J.L.

[2] C.G. Knight (Ed.), Liposomes From Physical Structure To Villa-Jato, M.J. Alonso, Enhancement of nasal absorption ofTherapeutic Applications, Elsevier, Amsterdam, 1981. insulin using chitosan nanopartilces, Pharm. Res. 16 (1999)

[3] R. Langer, Biomaterials in drug delivery and tissue engineer- 1576–1581.ing: One laboratory’s experience, Acc. Chem. Res. 33 (2000) [21] I.C. Aynie, C. Vauthier, E. Fattal, M. Foulquier, P. Couvreur,94–101. Alginate nanoparticles as a novel carrier for antisense

[4] R.P. Lanza, R. Langer, W.L. Chick, Principles of Tissue oligonucleotide, in: J.E. Diederichs, R. Muler (Eds.), FutureEngineering, in: Academic Press, Austin, TX, 1997, pp. Strategies of Drug Delivery With Particulate Systems, Med-405–427. pharm Scientific Publisher, Stuttgart, 1998, pp. 5–10.

[5] L.B, Peppas, Recent advances on the use of biodegradable [22] C. Vauthier, S. Beanabbou, G. Spenlehauer, M. Veillard, P.microparticles and nanoparticles in the controlled drug Couvreur, Methodology of ultradispersed polymer system,delivery, Int. J. Pharm. 116 (1995) 1–9. S.T.P. Pharm. Sci. 1 (1991) 109–116.

[6] A. Zimmer, J. Kreuter, Microspheres and nanoparticles used [23] E. Allemann, R. Gurnay, E. Doelker, Drug-loaded nanopar-in ocular drug delivery systems, Adv. Drug. Deliv. Rev. 16 ticles-Preparation methods and drug targeting issues, Eur. J.(1995) 61–73. Pharm. 39 (1993) 173–191.

[7] P. Couvreur, L. Grislain, V. Lenaerts, F. Brasseur, P. Guiot, [24] P. Couvreur, C. Dubernet, F. Puisieux, Controlled drugin: P. Guiot, P. Couvreur (Eds.), Polymeric Nanoparticles and delivery with nanoparticles: Current possibilities and futureMicrospheres, CRC Press, Boca Raton, Florida, 1986. trends, Eur. J. Pharm. 41 (1995) 2–13.

[8] D.F. Raney, Biomimetic transport, rational drug delivery, [25] M.J. Alonso, Nanoparticulate drug carrier technology, in: C.Biochem. Pharmacol. 59 (2000) 105–114. Cohen, H. Bernstein (Eds.), Microparticulte Systems For the

[9] K.E. Uhrich, S.M. Cannizzaro, R.S. Langer, K.M. Shakes- Delivery of Proteins and Vaccines, Marcel Dekker, Newsheff, Polymeric systems for controlled drug release, Chem. York, 1996, pp. 203–242.Rev. 99 (1999) 3181–3198. [26] P.D. Scholes, A.G.A. Coombes, L. Illum, S.S. Davis, M.Vert,

[10] C. Monfardini, F.M. Veronese, Stabilization of substances in M.C. Davies, The preparation of sub-500 nm poly(lactide-circulation, Bioconjug. Chem. 9 (1998) 418–450. co-glycolide) microspheres for site-specific drug delivery, J.

[11] V.P. Torchilin, Polymer-coated long-circulating microparticu- Control. Rel. 25 (1993) 145–153.late pharmaceuticals, J. Microencapsul. 15 (1998) 1–19. [27] M.F. Zambaux, F. Bonneaux, R. Gref, P. Maincent, E.

[12] D.L. Wise, T.D. Fellman, J.E. Sanderson, R.L. Wentworth, Dellacherie, M.J. Alonso, P. Labrude, C. Vigneron, InfluenceLactide /glycolide acid polymers, in: G. Geregoriadis (Ed.), of experimental parameters on the characteristics of poly(lac-Drug Carriers in Biology and Medicine, Academic, London, tic acid) nanoparticles prepared by double emulsion method,1979, pp. 237–270. J. Control. Rel. 50 (1998) 31–40.

[13] T.M. Jackanicz, H.A. Nash, D.L. Wise, J.B. Gregory, Poly [28] T. Niwa, H. Takeuchi, T. Hino, N. Kunou, Y. Kawashima,lactic acid as a biodegradable carrier for contraceptive Preparations of biodegradable nanospheres of water-solublesteroids, Contraception 8 (1973) 227–234. and insoluble drugs with D,L-lactide /glycolide copolymer by

[14] L.C. Andersson, D.L. Wise, J.F. Howes, An injectable a novel spontaneous emulsification solvent diffusion methodsustained release fertility control system, Contraception 13 and the drug release behavior, J. Control. Rel. 25 (1993)(1976) 375–384. 89–98.

[15] C.G. Pitt, M.M. Gratzi, A.R. Jeffcot, R. Zweidinger, A. [29] P. Wehrle, B. Magenheim, S. Benita, The Influence ofSchindler, Sustained release drug delivery systems II: factors process parameters on the PLA nanoparticle size distributionaffecting release rate for poly(e-caprolactone) and related evaluated by means of factorial design, J. Pharm. Biopharm.biodegradable polyesters, J. Pharm. Sci. 68 (1979) 1534– 41 (1995) 19–26.1538. [30] H. Murakami, H. Yoshino, M. Mizobe, M. Kobayashi, H.

[16] C.G. Pitt, T.A. Marks, A. Schindler, Biodegradable drug Takeuchi, Y. Kawashima, Preparation of poly(D,L-lactide-co-delivery systems based on aliphatic polyesters: application to glycolide) latex for surface modifying material by a doublecontraceptives and narcotic antagonists, in: R. Baker (Ed.), coacervation method, Proced. Intern. Symp. Control. Rel.Controlled Release of Bioactive Materials, Academic, New Bioact. Mater. 23 (1996) 361–362.York, 1980, pp. 19–43. [31] D.T. Birnbaum, J.D. Kosmala, D.B. Henthorn, L.B. Peppas,


Controlled release of b-estradiol from PLAGA microparti- in: R.S. Manly (Ed.), Adhesion in Biological Systems,cles: The effect of organic phase solvent on encapsulation Academic, New York, 1970, pp. 185–199.and release, J. Control. Rel. 65 (2000) 375–387. [47] P. Couvreur, B. Kante, M. Roland, Les perspectives d’utilisa-

[32] R. Bodmeier, J.W. McGinity, Solvent selection in the prepa- ´tion des formes microdisperses comme vecteurs intracel-ration of poly(D,L-lactide) microspheres prepared by the lulaires, Pharm. Acta Helv. 53 (1978) 341–347.solvent evaporation method, Int. J. Pharm. 43 (1988) 179– [48] P. Couvreur, B. Kante, M. Roland, P. Goit, P. Bauduin, P.186. Speiser, Polycyanoacrylate nanocapsules as potential

[33] R. Arshaday, Preparation of porous and nonporous bio- lysosomotropic carriers: preparation, morphology and sorp-degradable polymeric hollow microspheres, J. Control. Rel. tive properties, J. Pharm. Pharmacol. 31 (1979) 331–332.17 (1991) 1–22.

[49] N. Behan, C. Birkinshaw, N. Clarke, A study of the factors[34] E. Allemann, R. Gurnay, E. Doelker, Preparation of aqueous

affecting the formation of poly(n-butylcyanoacrylate)polymeric nanodispersions by a reversible salting-out pro-

nanoparticles, Proced. Intern. Symp. Control. Rel. Bioact.cess: influence of process parameters on particle size, Int. J.Mater. 26 (1999) 1134–1135.Pharm. 87 (1992) 247–253.

[50] C. Lherm, R.H. Muller, F. Puiseux, P. Couvreur,[35] E. Allemann, J.C. Leroux, R. Gurnay, E. Doelker, InvitroAlkylcynoacrylate drug carriers: II. Cytotoxicity ofextended-release properties of drug-loaded poly(D,L-lactic)cyanoacrylate nanoparticles with different alkyl chain length,acid nanoparticles produced by a salting-out procedure,Int. J. Pharm. 84 (1992) 13–22.Pharm. Res. 10 (1993) 1732–1737.

[51] J.-L. De Keyser, C.J.C. De Cock, J.H. Poupaert, P. Dumont,[36] J.C. Leroux, E. Allemann, E. Doelker, R. Gurnay, New14 14Synthesis of C labeled acrylic derivatives: diethyl [3- C]approach for the preparation of nanoparticles by an emulsifi-

14methylidenemalonate and isobutyl [3- C] cyanoacrylate, J.cation–diffusion method, Eur. J. Pharm. Biopharm. 41Lable. Comp. Radiopharm. 27 (1989) 909–916.(1995) 14–18.

[52] J.-L. De Keyser, J.H. Poupaert, P. Dumont, Poly(diethyl[37] G.D. Quintanar, Q.A. Ganem, E. Allemann, H. Fessi, E.methylidenemalonate) nanoparticles as a potential drug car-Doelker, Influence of the stabilizer coating layer on therier: preparation, distribution and elimination after intraven-purification and freeze drying of poly (DL-lactic acid)

nanoparticles prepared by emulsification-diffusion technique, ous and peroral administration to mice, J. Pharm. Sci. 80J. Microencapsulation 15 (1998) 107–119. (1991) 67–70.

[38] J.W. Tom, P.G. Debenedetti, Particle formation with super- [53] T.K.M. Mabela, J.H. Poupaert, P. Dumont, A. Haemers,critical fluids — a review, J. Aerosol Sci. 22 (1991) 555– Development of poly(dialkyl methylidenemalonate)584. nanoparticles as drug carriers, Int. J. Pharm. 92 (1993)

[39] T.W. Randolph, A.D. Randolph, M. Mebes, S. Yeung, Sub- 71–79.micron-sized biodegradable particles of poly(L-lactic acid) [54] P. Breton, D. Roy, L. Marchal-Heussler, C. Seguin, P.via the gas antisolvent spray precipitation process, Biotech- Couvreur, F. Lescure, New poly(methylidene malonatenol. Prog. 9 (1993) 429–435. 2.1.2) nanoparticles: Recent developments, in: G. Gre-

[40] L. Benedetti, A. Bertucco, M. Lora, P. Pallado, in: Atti del 38 goriadis, B. McCormack, G. Poste (Eds.), Targeting ofCongresso I fluidi Supercriticai e le Loro Applicazioni, I. Drugs, Advances in System Constructs,Vol. 4, Plenum Press,Kikic and P. Alessi (Eds.), Trieste, 1995, p. 221. New York, 1994, pp. 161–172.

[41] K. Mishima, K. Matsuyama, D. Tanabe, S. Yamauchi, [55] F. Lescure, C. Seguin, P. Breton, P. Bourrinet, D. Roy, P.Microencapsulation of proteins by rapid expansion of super- Couvreur, Preparation and charecterization of novel poly-critical solution with a nonsolvent, AIChE J. 46 (2000) (methylidene malonoate 2.1.2.)-made nanoparticles, Pharm.857–865. Res. 11 (1994) 1270–1277.

[42] J.W. Tom, P.G. Debenedetti, Formation of bioerodiable [56] P. Breton, X. Guillon, D. Roy, F. Lescure, G. Riess, N. Bru,polymeric microspheres and microparticles by rapid expan- C. Roques-Carmes, Physico-chemical characterization, prep-sion of supercritical solution, Biotechnol. Prog. 7 (1991) aration and performance of poly(methylidene malonate 2.1.2)403–411. nanoparticles, Biomaterials 19 (1998) 271–281.

[43] J.W. Tom, P.G. Debenedetti, R. Jerome, Preparation of [57] N. Bru-Magniez, X. Guillon, P. Breton, P. Couvreur, F.poly(L-lactic acid) and composite poly(L-lactic acid)-pyrene Lescure, C. Roques-Carmes, G. Riess, Method for preparingby rapid expansion of supercritical solution, J. Supercrit. malonate methylidene nanoparticles, nanoparticles optionallyFluids 7 (1994) 9–29. containing one or several biologically active molecules,

[44] S. Mawson, K.P. Johnston, J.R. Combes, J.M. DeSimone, International Patent PCT WO 98/18455, 1998.Formation of poly(1,1,2,2-tetrahydroperfluorodecyl acrylate) [58] N. Bru-Magniez, V. Larras, G. Riess, P. Breton, P. Couvreur,submicron fibers and particles from supercritical carbon C. Roques-Carmes, Novel surfactant copolymers based ondioxide solutions, Macromolecules 28 (1994) 3182–3191. methylidene malonate, International Patent PCT WO 99/

[45] K.C. Pani, G. Gladieux, G. Brandes, R.K. Kulkarni, F. 38898, 1999.Leonarda, The degradation of n-butyl alpha-cyanoacrylate [59] A.N. Mitra, P.K. Ghosh, S. Sahoo, pH and thermoresponsivetissue adhesive, II, Surgery 63 (1968) 481–489. hydrogel nanoparticles, Proc. Intern. Symp. Control. Rel.

[46] F. Leonarda, Hemostatic application of alpha cyanoacrylates: Bioact. Mater. 25 (1998) 234–235.bonding mechanism and physiological degradation of bonds, [60] A.N. Mitra, P.K. Ghosh, S. Sahoo, Long circulating RES


evading hydrophilic nanoparticles, Proc. Intern. Symp. Con- dable comb polyesters, Proc. Intern. Symp. Control. Release.Bioact. Mater. 26 (1999) 159–160.trol. Rel. Bioact Mater. 25 (1998) 168–169.

[75] M.A. Breitenbach, W. Kamm, K.-D. Hungere, E. Hund, T.[61] R. Gref, Y. Minamitake, M.T. Peracchia, V. Trubetskoy, V.P.Kissel, Oral and nasal administration of tetanus toxoidTorchilin, R. Langer, Biodegradable long circulating poly-loaded nanoparticles consisting of novel charged biodegra-meric nanospheres, Science 18 (1994) 1600–1603.dable polyesters for mucosal vaccination, Proc. Intern. Symp.[62] M. Amiji, K. Park, in: S.W. Shalaby, Y. Ikada, R. Langer, J.Control. Release. Bioact. Mater. 26 (1999) 348–349.Williams, (Eds.), Polymers of Biological Significance, ACS

[76] M.J. Alenso, C. Losa, P. Calvo, J.L. Vila-Jato, Approaches toSymp. Ser. 540, Washington, DC, 1994.improve the association of amikacin sulphate to poly-[63] P. Calvo, C. Remunan-Lopez, J.L. Vila-Jato, M.J. Alonso,(cyanoacrylate) nanoparticles, Int. J. Pharm. 68 (1991) 69–

Novel hydrophilic chitosan and chitosan/polyethylene oxide76.

nanoparticles as protein carriers, J. Appl. Polym. Sci. 63[77] M. Ueda, A. Iwara, J. Kreuter, Influence of the preparation

(1997) 125–132. methods on the drying release behavior of loperamide-loaded[64] P. Calvo, C. Remunan-Lopez, J.L. Vila-Jato, M.J. Alonso, nanoparticles, J. Microencapsulation 15 (1998) 361–372.

Chitosan and chitosan/ethylene oxide–propylene oxide [78] P. Couvreur, B. Kante, M. Roland, P. Speiser, Adsorption ofblock copolymer nanoparticles as novel carriers for proteins antineoplastic drugs to polyalkylcyanoacrylate nanoparticlesand vaccines, Pharm. Res. 14 (1997) 1431–1436. and their release in calf serum, J. Pharm. Sci. 68 (1979)

[65] R. Fernandez-urrusuno, P. Calvo, C. Remunan-Lopez, J.L. 1521–1523.Vila-Jato, M.J. Alonso, Enhancement of nasal absorption of [79] M.A. Radwan, In vitro evaluation of poly-insulin using chitosan nanoparticles, Pharm. Res. 16 (1999) isobutylcyanoacrylate nanoparticles as a controlled drug1576–1591. carrier for theophylline, Drug Dev. Ind. Pharm. 21 (1995)

[66] P. Calvo A.S. Boughaba, M. Appel, E. Fattal, M.J. Alonso, P. 2371–2375.Couvreur, Oligonucleotide–chitosan nanoparticles as new [80] M.A. Egea, F. Gamisani, J. Valero, M.E. Garcia, M.L.gene therapy vector, Proc. 2nd World Meeting APGI/APV Garcia, Entrapment of cisplatin into biodegradable poly-Paris, 1998, pp. 1111–1112. alkylcyanoacrylate nanoparticles, Farmaco 49 (1994) 211–

[67] H.-Q. Mao, K. Ray, S.M. Walsh, J.T. August, K.W. Leong, 217.DNA–chitosan nanoparticles for the gene delivery, Proc. [81] K. Chukwu, U. Ishroder, P. Sommerfeld, B.A. Sabel, Load-Intern. Symp. Control. Release. Bioact. Mater. 23 (1996) ing some psychopharmacologic agents onto poly(butyl-401–402. cyanoacrylate) nanoparticles-a means of targeting to the

[68] K. Ray, H.-Q. Mao, K.Y. Lin, S.-K. Huang, K.W. Leong, brain and improving therapeutic efficiency, Proced. Intern.Oral immunization with DNA–chitosan nanoparticles, Proc. Symp. Control. Rel. Bioact. Mater. 26 (1999) 1148–1149.Intern. Symp. Control. Release. Bioact. Mater. 26 (1999) [82] J. Vora, N. Bapat, M. Boroujerdi, Investigation of the relative348–349. affinity of doxorubicin for neutral and negatively charged

[69] V.L. Truong-Le, H. Mao, S. Walsh, K.W. Leong, J.T. August, particulate carriers, Drug Dev. Ind. Pharm. 19 (1993) 759–Delivery of DNA vaccine using gelatin–DNA nanoparticles, 771.Proc. Intern. Symp. Control. Rel. Bioact. Mater. 24 (1997) [83] J. Martin, P. Macchi, M. Hoffman, P. Maincent, Study of the39–40. binding mechanisms of drugs onto polyalkylcyanoacrylate

[70] X.-X. Tian, M.J. Groves, Formulation and biological activity nanoparticles, J. Pharm. Belg. 49 (1994) 498–508.`of antineoplastic proteoglycans derived from Mycobacterium [84] E. Benoit, O. Prot, P. Maincent, J. Bessiere, Adsorption of

vaccae in chitosan nanoparticles, J. Pharm. Pharmacol. 51 beta-blocker onto polyisobutylcyanoacrylate nanoparticles(1999) 151–157. measured by depletion and dielectric method, Pharm. Res. 11

[71] H. Tokumitsu, H. Ichikawa, Y. Fuukumori, Chitosan– (1994) 585–588.gadopenteic acid complex nanoparticles for gadolinium [85] H.S. Yoo, J.E. Oh, K.H. Lee, T.G. Park, Biodegradableneutron-capture therapy of cancer: preparation by novel nanoparticles containing doxorubicin–PLGA conjugate foremulsion–droplet coalescence technique and characteriza- sustained release, Pharm. Res. 16 (1999) 1114–1118.tion, Pharm. Res. 16 (1999) 1830–1835. [86] C. Washington, Drug release from microdisperse systems. A

[72] C. Vautheir, I. Aynie, P. Couvreur, E. Fattal, Pharmacokinetic critical review, Int. J. Pharm. 58 (1990) 1–12.and tissue disposition of oligonucleotide associated with [87] B. Magenheim, S. Benita, Nanoparticle characterization: aalginate nanoparticles, Proc. Intern. Symp. Control. Rel. comprehensive physicochemical approach, S.T.P. Pharm. Sci.Bioact. Mater. 25 (1998) 228–229. 1 (1991) 221–224.

[73] T. Jung, A. Breitenbach, T. Kissel, Sulfobutylated poly(vinyl [88] M.S. El-Samaligly, P. Rohdewald, H.A. Mohmoud, Poly-alcohol)-graft-poly(lactide-co-glycolide) facilitate the prepa- alkylcyanoacrylate nanocapsules, J. Pharm. Pharmacol. 38ration of small negatively charged biodegradable nanos- (1986) 216–218.pheres for protein delivery, J. Control. Rel. 67 (2000) 157– [89] A.M. LeRay, M. Vert, J.C. Gautier, J.P. Benoit, End-chain169. radiolabeling and in vitro stability studies of radiolabeled

[74] A. Breitenbach, G. Nykamp, T. Kissel, Self-assembling poly(hydroxy) nanoparticles, J. Pharm. Sci. 83 (1994) 845–colloidal carriers for protein delivery: nanoparticulate poly- 851.mer protein conjugates with novel water soluble biodegra- [90] M. Fresta, G. Puglisi, G. Giammona, G. Cavallaro, N.


¨Micali, P.M. Furneri, Pefloxacin mesilate- and ofloxacin- [105] R. Gref, A. Domb, P. Quellec, T. Blunk, R.H. Muller, J.M.loaded polyethylcyanoacrylate nanoparticles; characterization Verbavatz, R. Langer, The controlled intravenous deliveryof the colloidal drug carrier formulation, J. Pharm. Sci. 84 of drugs using PEG-coated sterically stabilized nanos-(1995) 895–901. pheres, Adv. Drug Deliv. Rev. 16 (1995) 215–233.

[91] G. Cavallaro, M. Fresta, G. Giammona, G. Puglisi, A.Villari, [106] M.T. Peracchia, S. Harnisch, H. Pinto-Alphandary, A.¨ ¨Entrapment of b-lactams antibiotics in poly- Gulik, J.C. Dedieu, D. Desmaele, J. d’Angelo, R.H. Muller,

ethylcyanoacrylate nanoparticles: studies on the possible in P. Couvreur, Visualization of in vitro protein-rejectingvivo application of this colloidal delivery system, Int. J. properties of PEGylated stealth polycyanoacrylate

Pharm. 111 (1994) 31–41. nanoparticles, Biomaterials 20 (1999) 1269–1275.[92] M.Y. Leavy, S. Benita, Drug release from submicron O/W [107] B.D. Ratner, A.B. Johnston, T.J. Lenk, Biomaterial surface,

emulsion: A new in vitro kinetic evaluation model, Int. J. J. Biomed. Mat. Res. Appl. Biomat. 21 (1987) 59–90.Pharm. 66 (1990) 29–37. [108] H. Carstensen, B.W. Muller, R.H. Muller, Adsorption of

[93] R. Jalil, J.R. Nixon, Biodegradable poly(lactic acid) and ethoxylated surfactants on nanoparticles. I. Characterizationpoly(lactide-co-glycolide) microcapsules: problems associ- by hydrophilic interaction chromatography, Int. J. Pharm.ated with preparative techniques and release properties, J. 67 (1991) 29–37.Microencapsul. 7 (1990) 297–325. [109] R. Gref, Y. Minamitake, M.T. Peracchia, V. Trubetskoy, R.

[94] B. Magenheim, M.Y. Levy, S. Benita, A new in vitro Langer, Biodegradable long-circulating polymerictechnique for the evaluation of drug release profiles from nanoparticles, Science 263 (1994) 1600–1603.colloidal carriers-ultrafiltration technique at low pressure, Int. [110] S.I. Joen, J.H. Lee, J.D. Andrade, P.G. de Gennes, Protein-J. Pharm. 94 (1993) 115–123. surface interactions in the presence of polyethylene oxide. I.

[95] J.M. Rodrigues Jr, H. Fessa, C. Bories, F. Pusieux, J.-Ph. Simplified theory, J. Colloid. Interf. Sci. 142 (1991) 149–Devissaguet, Premaquine-loaded poly(lactide) nanoparticles: 158.physicochemical study and acute tolerance in mice, Int. J. [111] D. Bazile, C. Prud Homme, M. Bassoullet, M. Marlard, G.Pharm. 126 (1995) 253–260. Spenlehauer, M. Veillard, Stealth Me-PEG–PLA nanoparti-

[96] M. Polakovic, T. Gorner, R. Gref, E. Dellacherie, Lidocaine cles avoid uptake by the mononuclear phagocyte system, J.loaded biodegradable nanospheres. II. modeling of drug Pharm. Sci. 84 (1995) 493–498.release, J. Control. Rel. 60 (1999) 169–177. [112] M. Tobio, R. Gref, A. Sanchez, R. Langer, M.T. Alonso,

[97] Z. Lu, J. Bei, S. Wang, A method of the preparation of Stealth PLA–PEG nanoparticles as protein carriers for nasalpolymeric nanocapsules without stabilizer, J. Control. Rel. administration, Pharm. Res. 15 (1998) 270–275.61 (1999) 107–112. [113] R. Gref, G. Miralles, E. Dellacherie, Polyoxyethylene-

[98] H. Muller, K.M. Willis, Surface modification of i.v. inject- coated nanospheres: effect of coating on zeta potential andable biodegradable nanoparticles with poloxamer polymers phagocytosis, Polymer Int. 48 (1999) 251–256.and poloxamine 908, Int. J. Pharm. 89 (1993) 25–31. [114] T. Govender, T. Riley, S. Stolnik, M.C. Garnett, L. Illum,

[99] C.J. Van Oss, Phagocytosis as a surface phenomenon, Annu. S.S. Davis, PLA–PEG nanoparticles for site specific deliv-Rev. Microbiol. 32 (1978) 19–39. ery: drug incorporation studies, J. Control. Rel. 64 (2000)

[100] E. Allemann, G. Patricia, J.C. Leroux, B. Luc, R. Gurnay, 269–347.Kinetics of blood component-adsorption on poly(D,L-lac- [115] S.Y. Kim, I.G. Shin, Y.M. Lee, Preparation and characteriza-tide) nanoparticles: Evidence of compliment C component tion of biodegradable nanospheres composed of methoxy3

involvement, J. Biomed. Mater. Res. 37 (1997) 229–234. poly(ethylene glycol) and DL-lactide block copolymer as¨[101] T. Blunk, M. Luck, A. Calvoer, D.F. Hochstrasser, J.C. novel drug carriers, J. Control. Rel. 56 (1998) 197–208.

¨Sanchez, B.W. Muller, R.H. Muller, Kinetics of plasma [116] M.T. Peracchia, E. Fattal, D. Desmaele, M. Bensard, J.P.protein adsorption on model particles for controlled drug Noel, J.M. Gomis, M. Appel, J. d’Angelo, P. Couvreur,

delivery and drug targeting, Eur. J. Pharm. Biopharm. 42 Stealth PEGylated polycyanoacrylate nanoparticles for(1996) 262–268. intravenous administration and spleenic targeting, J. Con-

¨ ¨[102] K. Thode, M. Luck, W. Semmler, R.H. Muller, M. Kresse, trol. Rel. 60 (1999) 121–128.Determination of plasma protein adsorption on magnetic [117] A. Gessnerl, B.R. Paulke, R.H. Muller, Plasma proteiniron oxide: sample preparation, Pharm. Res. 14 (1997) adsorption on poly(ethylene-glycol) (PEG) modified poly-905–910. styrene nanoparticles: influence of PEG surface density,

¨ ¨[103] K. Thode, M. Luck, W. Semmler, R.H. Muller, M. Kresse, Proc. Intern. Symp. Control. Rel. Bioact. Mater. 26 (1999)Influence of sample preparation on plasma protein ad- 597–598.sorption patterns on polysaccharide-stabilized iron oxide [118] M.T. Peracchia, R. Gref, Y. Minamitake, A. Domb, R.particles and end-terminal microsequencing of unknown Langer, PEG-coated injectable nanospheres prepared fromproteins, J. Drug Target. 5 (1997) 35–43. amphiphilic diblock and multiblock copolymers: investiga-

¨ ¨[104] M. Luck, K.F. Pistel, Y. Li, T. Blunk, R.H. Muller, T. tion of drug encapsulation and release characteristics, J.Kissel, Plasma protein adsorption on biodegradable micro- Control. Rel. 46 (1997) 223–231.spheres consisting of poly(D,L-lactide-co-glycolide), poly(L- [119] M.T. Peracchia, C. Vauthier, F. Puisieux, P. Couvreur,lactide) or ABA triblock copolymers containing poly(oxy- PEG–PIBCA nanoparticles with different PEG-coatingethylene), J. Control. Rel. 55 (1998) 107–120. configurations formed by chemical coupling of PEG,


Proced. Intern. Symp. Control. Rel. Bioact. Mater. 23 [132] M. Demoy, J.P. Andreux, C. Weingarten, B. Gouritin, V.(1996) 395–396. Guilloux, P. Couvreur, Spleen capture of nanoparticles:

[120] M.T. Peracchia, C. Vauthier, F. Puisieux, P. Couvreur, Influence of animal species and surface characteristics,Development of sterically stabilized poly(isobutyl-2- Pharm. Res. 16 (1999) 37–41.cyanoacrylate) nanoparticles by chemical coupling of poly- [133] T. Shinoda, A. Maeda, S. Kojima, S. Kagatani, Y. Konno,(ethylene glycol), J. Biomed. Mater. Res. 34 (1997) 317– T. Sonobe, T. Akaike, Nanosphere coated with lactosyl-326. polystyrene polymer as a targeting carrier to hepatocytes,

[121] M.T. Peracchia, C. Vauthier, D. Desmaele, A. Gulik, J.C. Drug Deliv. 6 (1999) 147–151.Dedieu, M. Demoy, J. d’Angelo, P. Couvreur, PEGylated [134] C.S. Cho, Y.I. Jeong, T. Ishihara, R. Takei, J.U. Park, K.H.nanoparticles from a novel methoxypolyethylene glycol Park, A. Maruyama, T. Akaike, Simple preparation ofcyanoacrylate–hexadecyl cyanoacrylate amphiphilic co- nanoparticles coated with carbohydrate-carrying polymers,polymer, Pharm. Res. 15 (1998) 550–556. Biomaterials 18 (1997) 323–326.

[122] M.T. Peracchia, C. Vauthier, C. Passirani, P. Couvreur, D. [135] A. Maruyama, T. Ishihara, S.W. Kim, T. Akaike, Nanoparti-Labarre, Compliment consumption by poly(ethylene glycol) cle DNA carrier with poly(L-lysine) grafted polysaccharidein different conformations chemically coupled to copolymer and poly(D,L-lactic acid), Bioconjug. Chem. 8poly(isobutyl-2-cyanoacrylate) nanoparticles, Life Sci. 61 (1997) 735–742.(1997) 741–761. [136] D. Duchene, D. Wouessidjewe, G. Ponchel, Cyclodextrins

[123] F.D. Jaeghere, E. Allemann, J.C. Leroux, W. Stevels, J. and carrier systems, J. Control. Rel. 62 (1999) 263–268.Feijen, E. Doelker, R. Gurny, Formulation and lyoprotec- [137] S. Raeissi, K. Audus, In vitro characterization of blood–tion of poly(lactic acid-co-ethylene oxide) nanoparticles: brain barrier permeability to delta sleep-inducing peptide, J.Influence on the physical stability and in vitro cell uptake, Pharm. Pharmacol. 41 (1989) 848–852.Pharm. Res. 16 (1999) 859–866. [138] B. Zlokovich, The in vivo approaches for studying peptide

[124] M. Vittaz, D. Razile, G. Spenlehauer, T. Verrecchia, M. interaction at the blood–brain barrier, Peptides 10 (1989)Veillard, F. Puisieux, D. Labarre, Effect of PEO surface 249–254.density on long-circulating PLA–PEO nanoparticles which [139] U. Schroeder, B.A. Sabel, Nanoparticles, a drug carrierare very low complement activators, Biomaterials 17 system to pass the blood–brain barrier, permit central(1996) 1575–1581. analgesic effects of i.v. dalargin injections, Brain Res. 710

[125] J.C. Ha, S.Y. Kim, Y.M. Lee, Poly(ethylene oxide)–poly- (1996) 121–124.(propylene oxide)–poly(ethylene oxide) (Plunoric) /poly(e- [140] U. Schroeder, P. Sommerfeld, B.A. Sabel, A efficacy of oralcaprolactone) (PCL) amphiphilic block copolymeric nanos- dalargin-loaded nanoparticle delivery across the blood–pheres I. Preparation and characterization, J. Control. Rel. brain barrier, Peptide 19 (1998) 777–780.62 (1999) 381–392. [141] R. Alyautdin, D. Gothier, V. Petrov, D. Kharkevich, J.

[126] S. Storm, S.O. Belliot, T. Daemen, D.D. Lasic, Surface Kreuter, Analgesic activity of the hexapeptide dalarginmodification of nanoparticles to oppose uptake by the adsorbed on the surface of polysorbate 80-coated poly(butylmononuclear system, Adv. Drug Deliv. Rev. 17 (1995) cyanoacrylate) nanoparticles, Eur. J. Pharm. Biopharm. 4131–48. (1995) 44–48.

[127] L. Illum, S.S. Davis, Effect of the nonionic surfactant [142] G. Borchardt, L.A. Kenneth, S. Fenlin, J. Kreuter, Uptakepoloxamer 338 on the fate and deposition of polystyrene of surfactant-coated poly(methyl methacrylate)-nanoparti-microspheres following intravenous administration, J. cles by bovine brain microvessel endothelial cell mono-Pharm. Sci. 72 (1983) 1086–1089. layers, Int. J. Pharmacol. 110 (1994) 29–35.

[128] L. Illum, S.S. Davis, The organ uptake of intravenously [143] S.D. Troster, U. Muller, J. Kreuter, Modification of theadministered colloidal particles can be altered using a body distribution of poly(methyl methacrylate) nanoparti-non-ionic surfactant (poloxamer 338), FEBS Letts. 167 cles in rats by coating with surfactants, Int. J. Pharm. 61(1984) 79–82. (1990) 85–100.

[129] S. Rudt, R.H. Muller, In vitro phagocytosis assay of nano- [144] S. Steiniger, D. Zenker, H.V. Briesen, D. Begley, J. Kreuter,and microparticles by chemiluminescence. III. Uptake of The influence of polysorbate 80-coated nanoparticles ondifferently sized surface-modified particles, and its correla- bovine brain capillary endothelial cells in vitro, Proced.tion to particle properties and in vivo distribution, Eur. J. Intern. Symp. Control. Rel. Bioact. Mater. 26 (1999) 790–Pharm. Sci. 1 (1993) 31–39. 791.

[130] L. Illum, S.S. Davis, R.H. Muller, E. Mak, P. West, The [145] J.C. Olivier, L. Fenart, R. Chauvet, C. Pariat, R. Cecchelli,organ distribution and circulation time of intravenously W. Couet, Indirect evidence that drug brain targeting usinginjected colloidal carriers sterically stabilized with a block polysorbate 80-coated polybutylcyanoacrylate nanoparticlescopolymer poloxamine 908, Int. J. Pharm. 89 (1993) 25– is related to toxicity, Pharm. Res. 16 (1999) 1836–1841.31. [146] A.E. Gulyaev, S.E. Gelperina, I.N. Skidan, A.S. Antropov,

[131] S.M. Moghimi, T.A. Gray, Single dose of iv injected G.Y. Kivman, J. Kreuter, Significant transport of doxorubi-poloxamine coated long-circulating particle triggers macro- cin into the brain with polysorbate 80-coated nanoparticles,phage clearance of subsequent doses in rats, Clin. Sci. 93 Pharm. Res. 16 (1999) 1564–1569.(1997) 371–379. [147] R.N. Alyautdin, V.E. Petrov, K. Langer, A. Berthold, D.A.


Kharkevich, J. Kreuter, Delivery of lopermide across the [153] N. Wang, X.S. Wu, J.K. Li, A heterogeneously structuredblood–brain barrier with polysorbate 80-coated poly- composite based on poly(lactic-co-glycolic acid) micro-butylcyanoacrylate nanoparticles, Pharm. Res. 14 (1997) spheres and poly(vinyl alcohol) hydrogel nanoparticles for25–328. long-term protein drug delivery, Pharm. Res. 16 (1999)

[148] R.N. Alyautdin, E.B. Tezikov, P. Ramga, D.A. Kharkevich, 1430–1435.D.J. Begley, J. Kreuter, Significant entry of tubocurarin into [154] R.M.M. Gasper, D. Blanco, M.E. Cruz, M.J. Alonso,the brain of rats by adsorption to polysorbate 80-coated Formulation of L-aspargainase-loaded poly(lactide-co-gly-polybutylcyanoacrylate nanoparticles: in situ brain perfu- colide) nanoparticles: influence of polymer properties onsion study, J. Microencapsulation 15 (1998) 67–74. enzyme loading, activity and in vitro release, J. Control.

[149] U. Schroeder, P. Sommerfeld, S. Ulrich, B.A. Sabel, Rel. 52 (1998) 53–62.Nanoparticle technology for delivery of drugs across the [155] I. Fishbein, M. Chorny, L. Rabinovich, S. Banai, I. Gati, G.blood–brain-barrier, J. Pharm. Sci. 87 (1998) 1305–1307. Golomb, Nanoparticulate delivery system of a tyrphostin

[150] P. Couvreur, F. Puiseux, Nano- and microparticles for the for the treatment of restenosis, J. Control. Rel. 65 (2000)delivery of peptides and proteins, Adv. Drug Deliv. Rev. 5 221–229.(1993) 141–162. [156] Y. Kawashima, H. Yamamoto, H. Takeuchi, S. Fujioka, T.

[151] T. Uchida, A. Yagi, Y. Oda, Y. Dakada, S. Goto, Instability Hino, Pulmonary delivery of insulin with nebulized DL-of bovine insulin in poly(lactide-co-glycolide) (PLGA) lactide /glycolide copolymer (PLGA) nanospheres tomicrospheres, Chem. Pharm. Bull. 44 (1996) 235–236. prolong hypoglycemic effect, J. Control. Rel. 62 (1999)

[152] J.K. Lin, N. Wang, X.S. Wu, A novel biodegradable system 279–287.based on gelatin NPs and poly(lactic-co-glycolic acid) [157] G.P. Carino, J.S. Jacob, E. Mathiowitz, Nanosphere basedmicrospheres for protein and peptide drug delivery, J. oral insulin delivery, J. Control. Rel. 65 (2000) 261–269.Pharm. Sci. 86 (1997) 891–895.

Documents

sdarticle