Essay: Nanotherapeutics

1. Introduction
Nanotherapeutics is a rapidly progressing area in the field of Nanomedicine, which is being utilized to overcome several limitations of conventional drug, including poor aqueous solubility, lack of site specific targeting, rapid systemic clearance, intestinal metabolism and systemic toxicities. Nanotherapeutics includes, but not limited to, solid-lipid nanoparticles, gold nanoparticles, silver nanoparticles, mesoporous silica nanoparticles, nanocrystals, magnetic nanoparticles, carbon nanotubes, nanosponges, albumin nanoparticles, fullerene nanoparticles and polymeric nanoparticles[1-4].
Nanotechnology offers many advantages to drug delivery systems and the molecular imaging field as well as having the potential to literally revolutionize both of these fields. In terms of drug delivery systems, liposomes, micelles, dendrimers, and metal colloidals (diameters less than 100 nm) have been extensively studied to enhance the efficacy of therapeutic agents [5-9].
Owing to their small size and excellent biocompatibility, nanosized drug carriers can travel in the bloodstream for a long time, enabling them to reach a target site and effectively deliver therapeutic agents, all the while minimizing the inefficiency and side effects of free drugs.
In spite of the extensive research and success stories with other routes for drug delivery, the oral route is still the most favored route as a result of its convenience, low cost, and high patient compliance compared with numerous further routes. About 90 percent of drug products are administered via the oral route [10]. But, the oral route isn’t the most efficient route for a particular therapy. Novel drug delivery technologies are essential for new biological drugs such as nucleic acids and proteins in order to diminish the possible side effects and attain better patient compliance [11, 12].
The latest advances in nanotechnologies, especially in nanoparticles, make them very promising in the delivery of therapeutics, drug discovery and diagnostics [13].
The delivery of therapeutic compound to the target site is a major trouble in the treatment of various diseases. A conventional application of drugs is characterized by limited effectiveness, poor biodistribution, and lack of selectivity [14]. The nanoparticles (NPs) as drug delivery systems may offer a number of advantages such as protection of drugs against degradation, targeting the drugs to specific sites of action, organ or tissues, and delivery of biological molecules such as proteins, peptides, and oligonucleotides.
Applications of drug nanoparticles include: both biodegradable nanoparticles for systemic drug delivery and nonbiodegradable nanoparticles for drug dissolution modification have been studied [15-18]. Proposed applications for drug nanoparticles vary from drug targeting and delivery [15, 17, 19-23] to even gene [24-26] and protein [27, 28] therapies. Administration of nanoparticles by, for example, parenteral [16] ocular [29-31] , transdermal [32], and oral routes have been studied. However, the oral route is still the most convenient, preferred, and in a lot of cases, also the most cost-effective route of drug administration [28, 33-37].
There is considerable interest in recent years in developing biodegradable nanoparticles as a drug/gene delivery system [25, 38-41]. An ideal drug-delivery system possesses two elements: the ability to target and to control the drug release. Targeting will ensure high efficiency of the drug and minimize the side effects, especially when dealing with drugs that are supposed to kill cancer cells but can also kill healthy cells when delivered to them. Controlled drug release can decrease or even prevent its side effects.
The advantages of using nanoparticles for drug delivery applications rise from their three main basic properties. First, nanoparticles, because of their small size, can penetrate through smaller capillaries, which could allow efficient drug accumulation at the target sites [42, 43]. Second, the use of biodegradable materials for nanoparticle preparation can allow sustained drug release within the target site over a period of days or even weeks [44-46]. Third, the nanoparticle surface can be adapted to modify biodistribution of drugs or can be conjugated to a ligand to attain target-specific drug delivery [47, 48].
The advantages of using nanoparticles as drug delivery system include: (1) stable dosage forms of drugs which are either unstable [49, 50] or have unacceptably low bioavailability in non-nanoparticulate dosage forms[51, 52] ; (2) they control and sustain release of the drug during the transportation and at the site of localization [53], varying organ distribution of the drug and subsequent clearance of the drug so as to achieve increase in drug therapeutic efficacy and reduction in side effects [54]; (3) site-specific targeting can be achieved by attaching targeting ligands to surface of particles or use of magnetic guidance [55, 56]; (4) controlled release and particle degradation characteristics can be readily modulated by the choice of matrix constituents. Due to biodegradability, pH, ion and/or temperature sensibility of materials they allow sustained drug release within the target site over a period of days or weeks [40, 57]; (5) they can pass through smallest capillary vessels and be taken up by cells, which allow efficient drug accumulation at the target sites [58-60] because of their ultra-tiny volume and avoiding rapid clearance by phagocytes so their duration in blood stream is deeply prolonged. This is especially needed for tumors which are characterized by extensive angiogenesis, defective vascular architecture, impaired lymphatic drainage and increased production of permeability factors. This phenomenon is known as the enhanced permeability and retention effect [13, 57, 61]; (6) increased active agent surface area results in a faster dissolution of the active agent in an aqueous environment, such as the human body. Faster dissolution generally equates with greater bioavailability, smaller drug doses, less toxicity[62]. (7) Can be used for different routes of administration, including oral, nasal, intra-ocular and surface characteristics can be simply manipulated to achieve both passive and active drug targeting after parenteral administration and (8) reduction in fed/fasted variability (9) due to the impressive bioavailability, better encapsulation, control release and less toxic properties, various nanoparticle systems with biodegradable polymers such as PLGA, PLA, chitosan and gelatin are utilized for delivery of drugs of various types of diseases with better efficacy [63]. (10) In recent years oral bioavailability of many of poorly water soluble drugs can be modified by incorporating drugs into pH sensitive nanoparticles . (11) Nanoparticles are now used to study the expression of therapeutic genes, is a useful tool for gene therapy.
Pharmaceutical nanocarriers, that are designated as NPDDS, can be classified in different ways, which are according to the raw materials, physicochemical characteristics (size, charge, number of lamellae, permeability), preparation methods, in vivo behavior. In a classification according to the materials used in their preparation, NPDDS can be of lipidic nature as liposomes, micelles, Transfersomes, and solid lipid nanoparticles, or of polymeric nature as nanoparticles, micelles, and niosomes [65-67].
Various materials can be used to prepare nanoparticles such as proteins, polysaccharides and synthetic polymers. The choice of matrix materials is dependent on numerous factors, including : (a) size of nanoparticles required; (b) natural properties of the drug, e.g., aqueous solubility and stability; (c) surface characteristics such as charge and permeability; (d) degree of biodegradability, biocompatibility and toxicity; (e) Drug release profile wanted; and (f) Antigenicity of the final product.
In recent years, polymer–nanoparticle composite materials have attracted the attention of a number of researchers, due to their synergistic and hybrid properties derived from several components. Whether in solution or in bulk, these materials offer unique properties (mechanical, electrical, optical and thermal) [69].
The field of polymer nanoparticles (PNP) is rapidly growing and playing a pivotal role in a broad spectrum of areas ranging from electronics to the Photonics, conducting materials to sensors, medicine to biotechnology, pollution control of environmental technology, and so forth, during the last decades [70, 71] . New and newer polymers have been trying to develop nanoparticles for their application as drug carriers. Craparo et al., 2008 described the preparation and physicochemical and in vitro biological characterization of nanoparticles based on PEGylated, acryloylated polyaspartamide polymers.
Polymeric nanoparticles can be defined as colloidal particles ranging between 10 and 1000 nm in size and composed of either natural or artificial polymers [73]. Polymeric nanoparticles composed of the drug dispersed in an amorphous form within a polymer matrix. PNPs are promising vehicles for drug delivery by easy manipulation to prepare carriers with the objective of delivering the drugs to specific targets; such an advantage modifies the drug safety [74].
The compounds of interest are very beneficial for drug delivery applications because of their ability to control drug release and their protection properties [75]. Currently, stimuli-sensitive nanoparticles which affected by the changes in pH, temperature and magnetic fields gained great concern [76-79].
The term “polymeric nanoparticle” encompasses nanospheres and nanocapsules.
Nanospheres are defined as a polymeric matrix in which the drug is homogeneously dispersed (typically as a solid solution in polymer) and nanocapsules are described as a polymeric membrane that surrounds the drug in the matrix core[80] (either as a solid solution or a solution in oil).
Advantages of polymeric nanoparticles include: [81, 82]
(1) improve the stability of any volatile pharmaceutical agents, simply and economically fabricated in large quantities by a huge number of methods, (2) they present a significant improvement over conventional oral and intravenous routes of administration in terms of efficiency and effectiveness, (3) delivers a higher concentration of pharmaceutical agent to the required location, (4) the selection of polymer and the capability of modifying drug release from polymeric nanoparticles have made them typical choice for cancer therapy, delivery of vaccines, contraceptives and delivery of targeted antibiotics and (5) Polymeric nanoparticles can be easily included into other activities related to drug delivery, such as tissue engineering.
In nanoparticles formulations wide variety of polymers can be used according to the nature of drug and usage. (i.e.) Biodegradable polymers for short term therapy (e.g. Chemotherapeutic agents) and non-biodegradable polymers for long term therapy (e.g. Vaccines) [83].
The PNPs are obtained from synthetic polymers, such as poly- Ɛ-caprolactone [84], poly-acrylamide [85] and polyacrylate [86], or natural polymers, e.g., Albumin [87], DNA[88], chitosan [88, 89] and gelatin [90].Based on in vivo behavior, PNPs may be classified as biodegradable, i.e., Poly (L-lactide) (PLA) [91], polyglycolide (PGA) [92], and non biodegradable, e.g. Polyurethane [93].
The drug release along the GIT can be controlled using pH-sensitive materials, in which the drug is released particularly in the small intestine near the absorption site. PH-dependent materials, which are insoluble in the acidic medium of the stomach, but dissolve in the intestinal fluid, are called enteric materials [94, 95].
These materials have been used to avoid the degradation of labile drugs caused by the acidic medium or gastric enzymes, to lessen irritation of the gastric mucosa, and to deliver drugs selectively to the site of absorption [94, 95]. Enteric coating materials are polymers, which have acid groups. In the acidic medium of the stomach the acid groups are nonionized, and the coating material is insoluble. Fast dissolution and drug release take place in the upper intestine as a function of pH change in the environment. The polymer acid groups are ionized at higher pH and the material dissolves [95].
Cellulose acetate phthalate (CAP) was the first synthetic polymer described in 1937, which gained soon high popularity as a gastric resistant polymer.
Later polyvinyl acetate phthalate (PVAP) and hydroxypropyl methylcellulose phthalate (HPMCP) were preferred, because of their lower permeability in the gastric fluid and improved stability against hydrolysis. Today the methacrylate copolymers Eudragit® L and S are two of the most widely used polymers for this purpose.
The drug release from the pH-sensitive nanoparticles follows certain mechanisms which include:
1- Drug burst releases when the nanoparticle carriers dissolve at specific pH conditions:
They usually exhibited burst release profiles because of the dissolution characters of the carriers; drug release from conventional nanoparticles was mainly by diffusion. For pH- sensitive nanoparticles, at low pH, the nanoparticles prepared from polycarboxylic acid were solid matrix encapsulating drug, little drug released. As they reach the small intestine, the pH changes from acidic to neutral (6–7.4), carboxylic acid groups deprotonated, the linear polymers dissolved and drugs released rapidly.
2- Drug releases when the polymers swell at specific pH conditions:
Another reason for drug release from nanoparticles was the swelling of the materials [96].
At low pH, the polymers, particularly cross-linked polymers, have a compact structure, which considerably decreased the porosity of the matrix. This caused a slower release of drug as a result of the greater resistance for diffusion of the drug out of the nanogel. However, at higher pH, the nanogel particles were in a swollen state with a higher porosity that favored the release of the drug because of the reduction in diffusion resistance.
3- The drug releases as a result of both polymer dissolution and swelling:
There was obscure boundary between drug dissolution and swelling for the carriers. Some nanoparticle systems might release drug through both the mechanisms. Li et al., 2006 [97] studied the release of insulin from chitosan–Eudragit L100-55 nanoparticles in vitro. The results proposed that at low pH, the nanoparticles were covered by Eudragit L100-55, little water permeated into the particles and when the pH value was elevated to 5.8, Eudragit L100-55 dissolved and water penetrated to the core of the particles. The particle size become larger as chitosan swelling and the higher porosity of chitosan caused rapid insulin release.
Depending on their characters, pH sensitive nanoparticles can be mainly divided into two types. One induces drug release at higher pH because of ionizable functional groups on the polymer backbone or side chain, for example, nanoparticles prepared using poly (methacrylic acid) [98], hydroxypropyl methylcellulose phthalate[99] and poly (acrylic acid) grafted poly(vinylidenefluoride)[100]. This kind of nanoparticles is typically used for oral drug delivery [97,101-109], where a physiological pH shifts along GIT facilitates the swelling or dissolution of the carriers. The other kinds of pH-sensitive nanoparticles have a reversed swelling or dissolution behavior of the former. It undergoes swelling in acidic environment and can be used to target tumors, lysosomes and endosomes, where pH is comparatively low [110].
Oral administration of poorly water-soluble drugs incorporated in pH-sensitive particles has been found to be very efficient through increasing drug bioavailability and achieving fast absorption [36,109, 111]. It has been considered that the good bioavailability of pH-controlled nanoparticulate drug systems depends on some properties, including the high specific surface area of the system, drug in an amorphous form or molecularly dispersed in the polymer matrix, and the release of drug close to the absorption site [36, 103, 111].
The dissolution of the particles should not be too fast, however, as this might cause drug precipitation [109] or crystallization [112], but should not be too slow which lead to the rapid elimination of the particles before absorption, either[109].
The advantages of pH-sensitive nanoparticles over other nanoparticles include: (a) the majority of carriers have been used as enteric-coating materials for a long time, and their safety has been approved. (b) The carriers show rapid drug release and then high drug concentration gradient as they undergo quick dissolving at definite pH and definite sites. The phenomenon is beneficial for the drug absorption. (c) They improve drug absorption comparing to the other conventional nanoparticles as they turn from the solid state to the hydrogel state at certain dissolution pH and so, the bioadhesion of the carrier to the mucosa becomes greater at specific fragment. (d) The drug stability can be enhanced more effectively using pH sensitive nanoparticles.
Different materials can be used for preparation of pH-sensitive nanoparticles:
a- pH-sensitive nanoparticles prepared from polyanions:
Such as Eudragits and HPMC phthalate.
b- pH-sensitive nanoparticles prepared from publications:
Chitosan is the main cationic polymer used to prepare pH-sensitive nanoparticles. It is the second most plentiful polymer in nature after cellulose.
c- pH-sensitive nanoparticles prepared from the mixture of polyanions and polycations:
Some techniques have been improved using the advantages of both polyanions and polycations [97,108, 113-116]. Most of the nanoparticle systems related consist of the positive-charged chitosan and a negative-charged polymer, such as Eudragit [97, 115, 117], poly (g-glutamic acid) [113, 114, 116], alginate [118], methacrylic acid [119] and polyaspartic acid [120].
d- Cross-linked polymers pH-sensitive nanoparticles (nanogels)
e- pH-sensitive nanomatrix prepared from Eudragit and nano porous silica:
A novel nanomatrix system for oral administration was developed in order to overcome the main problems of the nanoparticle colloid system which are its stability and scaling up. The system was composed of the pH-sensitive Eudragit and nano-porous silica previously used in pharmaceutical processes.
Historically, gelatin and cross-linked albumin were used to prepare the first nanoparticles proposed as carriers for therapeutic applications [121, 122]. Synthetic polymers were used to prepare the nanoparticles to avoid the usage of the proteins as they may stimulate the immune system and also, to minimize the toxicity of the cross-linking agents. At first, the nanoparticles were prepared using emulsion polymerization of acryl amide and by dispersion polymerization of methylmethacrylate [123, 124]. These nanoparticles were proposed as adjuvants for vaccines. Polymethacrylate (PMA) and polymethyl methacrylate (PMMA) have been broadly used in a variety of pharmaceutical and medical applications. Specifically, PMMA Eudragit® nanoparticles can be prepared by nanoprecipitation method [125]. PMMA can be used to prepare pH-sensitive nanoparticles in order to increase the drug oral bioavailability where, the side chain of these polymers can be modified to possess pH-dependent solubility.
Poly (methyl methacrylate) nanoparticles were first investigated as adjuvants for injectable vaccines [126, 127] when the achievement of a very prolonged immune response is desired due to that they are very slowly biodegradable. They are also of a great value for basic body distribution studies where the determination of the fate of intact particles has to be followed over an extended time period.
Several copolymers of methyl methacrylate and ethyl acrylate were developed as ester components with methacrylic acid for use as enteric polymers. These polymers are manufactured by an emulsion-polymerization process and are obtainable in numerous forms. The polymer content of carboxyl groups is the major factor affecting the dissolution properties of the polymer. They are synthetic cationic and anionic polymers of dimethyl aminoethyl methacrylates, methacrylic acid and methacrylic acid esters in varying ratios.
Polymethacrylates are used as tablet binders, tablet diluents and film forming agents e.g. Cationic methacrylate, methacrylic acid copolymer Type A, Type B and Type C [128].
Eudragit®S 100 is an anionic copolymer based on methacrylic acid and methyl methacrylate which is soluble at pH of 7 or higher [128, 129] , the ratio of the free carboxyl groups to the ester groups is approximately 1:2 and mean relative molecular mass of about 135,000. Its pH-dependent polymer so, it’s usually used as an enteric polymer for controlling drug release in GIT. It is practically insoluble in water, petroleum ether, ethyl acetate and dichloromethane while, it is freely soluble in acetone, alcohols (including ethanol 95%, methanol and propane-2-ole) and 1N NaOH solution [128].
Eudragit S100 is insoluble in acidic medium and dissolves above neutral pH. Dissolution occurs as a result of structural change of the polymer associated with ionization of the carboxylic functional group.
At acidic pH, Eudragit S100 particles posses low permeability because of hydrogen bonding between the hydroxyl group of carboxylic moiety and the carbonyl oxygen of the ester group in the polymer molecules. This bonding increase degree of compactness of the polymer and decrease its porosity and permeability [130], minimizing release of an encapsulating agent.
When the pH of aqueous medium is increased, Eudragit S100 start to dissolve as carboxylic functional groups ionizes. The reported theoretical dissolution threshold is pH 7.0 and pKa of polymer molecules is believed to be approximately 6 [131]. Moreover, swelling of Eudragit S100 matrix may accompany the dissolution process contributing to release. It is believed that Eudragit S swells at pH above 6.5 [132]. Therefore, release of active substance may be due to the combination of swelling and dissolution.
Hydroxyl propyl methyl cellulose phthalate (HPMCP):
These are natural cellulose synthetically modified to produce partly methyl ethers, 2-hydroxy propyl ethers and phthalyl esters. HPMCP is manufactured by esterification of hypromellose with phthalic anhydride. The level of alkyloxy and carboxybenzoyl substitutions determines the properties of polymer and in particular the pH at which it dissolves in aqueous medium.
HPMCP (also known as Hypromellose phthalate) [133] is commonly used in oral pharmaceutical formulations as an enteric coating material for tablets or granules [134-138]. Hypromellose phthalate is insoluble in gastric fluid, but will swell and dissolve speedily in the upper intestine. These polymers can be used as coating agents because they do not necessitate the addition of plasticizer or other film formers to fabricate coatings for oral formulations [128].
Hydroxypropyl methylcellulose phthalate (HPMCP), available in the market since 1971, it is a monophthalic acid ester of hypromellose, containing methoxy (-OCH3), 2-hydroxypropoxy (- OCH 2CHOHCH3) and phthaloyl (o-carboxybenzoyl C8H5O3) groups so, HPMCP is a cellulose in which some of the hydroxyl groups are replaced with methyl ethers, 2-hydroxy propyl ethers, or phthalyl esters.
Numerous different types of hypromellose phthalate are commercially presented with molecular weights in the range 20 000–200 000. Typical average values are 80000–130000 [133]. These types are (HP50, HP55 and HP55S) where HP55 grade is usually used for enteric coating, HP55S grade, because of its higher degree of polymerization compared with HP-55, it have greater solution viscosity, greater mechanical strength of the film and HP-50 dissolves at a lower pH value and is therefore appropriate for preparations which are designed to disintegrate in the upper part of the small intestine.
Trade name Eudragit S100 HPMCP HP-55
Chemical name Poly (methacrylic acid, methyl methacrylate) 1 : 2 [128]
Cellulose, 2-hydroxypropyl methyl ether, phthalic acid ester [133]
CAS number (25086-15-1 ) [128]
( 9050-31-1 ) [133]
pH solubility ≥ 7 [128, 129]
≥ 5.5 [139]
The most common three methods used to prepare the nanoparticles are: (1) dispersion of preformed polymers; (2) direct polymerization of monomers using classical polymerization reactions; and (3) ionic gelation or coacervation of hydrophilic polymers. However, other methods like supercritical fluid technology [140] and particle replication in non-wetting templates (PRINT) [141] can be also used to prepare nanoparticles.
Polymeric nanoparticles (PNPs) can be prepared from preformed polymers through several methods such as solvent evaporation, salting-out, dialysis and supercritical fluid technology which involving the rapid expansion of a supercritical solution or rapid expansion of a supercritical solution into a liquid solvent. In contrast, PNPs can be directly synthesized through the polymerization of monomers using a variety of polymerization techniques like mini-emulsion, micro-emulsion, surfactant-free emulsion and interfacial polymerization.
The choice of preparation method is made on the basis of a number of factors such as the type of polymeric systems, the area of application, size requirement, and the drug to be loaded. Since, method of preparation mainly affect the properties of produced nanoparticles, it is highly advantageous to have preparation techniques at hand to get PNPs with the required properties for a particular application.
The term nanoprecipitation refers to a quite simple processing method for the fabrication of polymeric nanoparticles. The level of interest in nanoprecipitation waned for some decades, and the method regained recognition in the 50’s as a means of preparing colloids for stabilizing pigments [142], as well as industrially important components in paints, lacquers, and other coatings [142], While it had already been reported at least as early as the 1940’s as a way for isolation of purified analytical samples of synthetic polymers , nanoprecipitation regained a heightened level of patent interest in the 1950’s and 60’s this time as a cost effective method for purifying synthetic polyolefins [142].
In the late 80’s and early 90’s, Fessi et al.,1989 [143] patented the nanoprecipitation method as a procedure for the preparation of eligible colloidal systems of a polymeric substance in the form of nanoparticles [143].
Nanoprecipitation is also called solvent displacement method or interfacial precipitation method [143-148] .It depends on the precipitation of a preformed polymer from an organic solution and the diffusion of the organic solvent in the aqueous phase either in the presence or absence of a surfactant [143, 149-151].
The main principle of this technique is based on the interfacial deposition of a polymer after displacement of a semi polar solvent, miscible with water, from a lipophilic solution. Rapid diffusion of the solvent into non-solvent phase results in the decrease of interfacial tension between the two phases, which increases the surface area and causes the formation of small droplets of organic solvent [143, 152].
Nanoprecipitation system composed of three basic components: the polymer (synthetic, semi synthetic or natural), the polymer solvent and the non-solvent of the polymer. Organic solvent (i.e., Ethanol, acetone, hexane, methylene chloride or dioxane) which is miscible in water and can be easily removed by evaporation is chosen as polymer solvent. Because of this reason, acetone is considered to be the most commonly used polymer solvent in this method [143,153, 154].
Sometimes, it consists of binary solvent blends, acetone with small volume of water [155], blends of acetone with ethanol [156-158] and methanol [159].
The polymers commonly used are biodegradable polyesters, especially poly (Ɛ-caprolactone) (PCL) [160-164], polylactide (PLA) [165, 166] and poly (lactide-co-glycolide) (PLGA) [167, 168]. Eudragit [156] can also be used as many other polymers such as polyalkylcyanoacrylate (PACA) [169-171].
Natural polymers such as allylic starch [172], dextran ester [173], were also used ,though synthetic polymers have higher purity and better reproducibility than natural polymers [174]. On the other hand, some polymers are PEG copolymerized in order to decrease nanoparticle recognition by the reticular endothelial system [159].
PNP characteristics are influenced by the nature and concentration of their components [162, 164]. The key variables determining the success of the method and affecting the physicochemical properties of the PNP are those associated with the conditions of adding the organic phase to the aqueous phase, such as organic phase injection rate, aqueous phase agitation rate, the method of organic phase addition and the organic phase to aqueous phase ratio.
Lince et al.,2008 [175] indicated that the process of particle formation in the nanoprecipitation method includes three stages: nucleation, growth and aggregation. The separation between the nucleation and the growth stages is the key factor for formation of uniform particles. Ideally, operating conditions should allow a high nucleation rate strongly dependent on super saturation and low growth rate.
Nanoprecipitation method has some advantages over other method used for preparation of nanoparticles, which include that: (1) Major advantage of this method is the use of the solvents (Acetone/Ethanol) which are considered to be less toxic than water- immiscible solvents like dichloromethane and chloroform, (2) in this method, nanoparticles are formed spontaneously with high shear , (3) Further purification is not required because of the surfactant and solvent and (4) it is a simple, fast and reproducible method which is commonly used for the preparation of both nanocapsules and nanospheres.
The solvent displacement technique can be used to formulate nanocapsules by incorporating a small amount of nontoxic oil in the organic phase. Considering the oil-based central cavities of the nanocapsules, high loading efficiencies are usually obtained for lipophilic drugs when nanocapsules are prepared.
The major drawbacks of this preparation method include that: (1) the use of this simple method [176] is restricted to water-miscible solvents, in which the diffusion rate is sufficient to produce spontaneous emulsification. In some cases, spontaneous emulsification is not observed when the coalescence rate of the formed droplets is sufficiently high and this usually occurs with some water-miscible solvents that produce a certain instability when mixed with water [177] and (2) the nanoprecipitation technique possesses poor encapsulation efficacy in the case of hydrophilic drugs, because the drug can diffuse to the aqueous outer phase during polymer precipitation [151]. The encapsulation efficiency has been increased through modifying the drug solubility by changes in pH [178-180].So that, this technique is mostly appropriate for lipophilic drugs due to the miscibility of the organic solvent with the aqueous phase.
Although, a surfactant is not necessary to ensure the formation of PNP by nanoprecipitation method, the particle size is affected by the surfactant nature and concentration [160, 164]. Furthermore, the addition of surfactants helps to maintain the stability of nanoparticle suspensions and prevents agglomeration over long storage periods [143].
Tween 80 Poloxamer 407
Chemical name Polyoxyethylene 20 Sorbitan
Monooleate [181]
α-Hydro-ω- hydroxypoly (oxyethylene) poly (oxypropylene) poly (oxyethylene) block copolymers [182]
Physical form Yellow oily liquid [181]
Solid [182]
Av. M. wt 1310 [181]
9840 –14600 [182]
HLB value 15.0 [181]
18–23 [182]
CAS number (9005-65-6) [181]
(9003-11-6) [182]
Pantoprazole is widely used proton pump inhibitor (PPIs) and it is a significant drug in the treatment of acid-related disorders [183] and biliary also effective against Helicobacter biliary infections alone or combined with other drugs, like metronidazole, clarithromycin or amoxicillin [184]. This drug was the first water soluble benzimidazole, sodium 5-(difluoromethoxy)-2-[[(3,4 – dimethoxy- 2- pyridinyl) methyl] sulfinyl]- 1H- benzimidazole sesquihydrate [185].
A molecule with benzimidazole substitution exhibits potent and long-lasting inhibition of gastric acid secretion by selectively interacting with the gastric proton pump (H+/K+-ATPase) in the parietal cell secretory membrane [183, 186].
The molecular formula is C16H14F2N3NaO4S×1. 5 H2O and molecular weight is 432.4 g/Mol[185]. Because of gradual degradation of pantoprazole sodium during heating, the melting point cannot be accurately determined. It is a white to off-white crystalline powder. The structural formula is: [185]
Pantoprazole has numerous advantages compared to its analogues (e.g., Omeprazole and lansoprazole) such as greater stability in a neutral PH environment, specific site of binding, and longer duration of action [187]. In addition, it shows no potential to either induce or inhibit the CYP 450 [183,184, 188]. It is a more selective inhibitor of acid secretion than other proton pump inhibitors [189].
Pantoprazole is used for treatment of erosive esophagitis, or “heartburn” caused by gatroesophageal reflux disease (GERD), a condition where the acid in the stomach washes back up into the esophagus. Pantoprazole can also be used to treat Zollinger-Ellison syndrome, a condition where the stomach produces too much acid.
The most common side effects of pantoprazole include blurred vision, dry mouth, abdominal pain, fatigue, flushed, dry skin, increased hunger, increased thirst, and increased urination. The other side effects are excess air or gas in either stomach or intestine and trouble in sleeping.
Mechanism of action:
In low PH values, pantoprazole is transformed into cationic sulfenamide, which is its active form [184, 190] , this drug accumulates in the highly acidic environment of the parietal-cell canalicular lumen and it is activated. The active form, tetracyclic cationic sulfonamide, reacts with thiol groups of cysteines 813 and 822 of transmembranal H+ / K+ ATPase[183, 186]. This conversion must take place beside the gastric parietal cells, so pantoprazole must be absorped intact by GIT [184].
The pantoprazole is an acid labile drug, which undergoes degradation in the stomach [191-194]. Therefore, the drug should be targeted to the intestine; to bypass the stomach. The gastro resistant drug delivery system is designed for the acid labile drugs due to the necessity to pass intact through the stomach for reaching the duodenum for absorption. The dosage form is prepared to bypass the stomach by formulating a solution for intravenous administration (lyophilized powder for reconstitution) or as gastric‐resistant tablets (oral delayed‐release dosage form) [195]. In the case of oral administration, the enteric coating prevents the drug from degradation in the gastric juice (at pH 1–2, for a few minutes [195-197]. Therefore the enteric coating, on the acid labile drug, is essential, thus they are less affected by pH. Thus the concept of gastro resistant drugs was generated.
The wavelength of maximum absorbance for pantoprazole sodium sesquihydrate (λmax) was found to be 283.5 nm in 0.1N Hcl (pH 1.2) and 288.5 nm in phosphate buffer (pH 6.8).
Calibration curves for pantoprazole sodium sesquihydrate in each of 0.1N Hcl (pH 1.2) and phosphate buffer (pH 6.8) were assessed from absorbance values, at λmax of a series of pantoprazole sodium sesquihydrate solutions containing different concentration of pantoprazole as shown in figure (1) and figure (2).
The proposed nanoprecipitation (solvent displacement or interfacial precipitation) [143-148] method enabled the formulation of polymeric nanoparticles by using organic phase with different concentrations of Eudragit S100 (ES100) and HPMC phthalate HP55 with using Tween 80 and Poloxamer 407 as surfactant with different concentrations and different ratio of organic phase: aqueous phase. Although, all formulae produce nanoparticles, formulation factors significantly affect the size of prepared polymeric nanoparticles.
3.1. Effect of polymer concentration and polymer type on particle size of plain PNPs :
Particle size of Eudragit S100 and HPMC Phthalate HP55 nanoparticles was directly proportional to polymer concentration (Eudragit S100 and HPMC Phthalate HP55 concentration respectively) as the particles size increased with increasing polymer concentration [211, 212] and this may be due to increasing the concentration of dissolved polymer resulted in increasing organic phase viscosity and reducing the efficiency of stirring which caused formation of the bigger emulsion droplets [213] and this can be also attributed to that higher viscosity that is predictable to increase polymer – polymer and polymer-solvent interactions [147, 214].
When polymer concentration in the case of Eudragit S100 and HPMC Phthalate HP55 was increased from 0.2 gm% to 0.8 gm% with Tween 80 concentration of 0.5% w/v and phase ratio of (1:2), particle size was increased from 390±9.4634 to 714±2.0548 and from 434±3.0912 to 863±0.9428 nm respectively. The same effect of polymer concentration on particle size was the same either in the case of increasing Tween 80 concentration and /or increasing the phase ratio as shown in the tables (4, 6 and 8) and figures (3, 5 and 7).
When polymer concentration in the case of Eudragit S100 and HPMC Phthalate HP55 was increased from 0.2 gm% to 0.8 gm% with Poloxamer 407 concentration of 0.5% w/v and phase ratio of (1:2), particle size was increased from 404±8.6538 to 747±1.6997 and from 598±1.633 to 905±4.0277 nm respectively. The same effect of polymer concentration on particle size was the same either in the case of increasing Poloxamer 407 concentration and / or increasing the phase ratio as shown in the tables (5, 7 and 9) and figures (4, 6 and 8).
These results were found to agree with the results of both Galindo-Rodriguez et al., 2004 [149] who prepared nanoparticles of Eudragit L100-55 using nanoprecipitation method to determine effect of polymer concentration on nanoparticle size using different organic solvents and he found that in all cases, increasing polymer concentration in organic phase resulted in increasing mean size [149],and D. Quintanar-Guerrero et al., 1999 [215] who used emulsion-diffusion method to prepare Eudragit E nanoparticles using Eudragit E/ethyl acetate/PVAL system and cellulose acetate phthalate (CAP) nanoparticles using cellulose acetate phthalate/2-butanone/Poloxamer 407 system and in two systems it was found that there is a switch between micro and nanoparticles depending on polymer concentration in internal organic phase where, as polymer concentration increased, size of produced particles significantly increased [215]. On the other hand, these results are disagreeing with those reported in Ahmed, I.S., et al.,2014 [216] who prepared poly-Ɛ- caprolactone nanoparticles by solvent displacement method and investigated the effect of polymer concentration on particle size. It was found that increasing polymer concentration from (0.5 to 0.8% w/v) at surfactant concentration (0.5% w/v) resulted in increasing particle size while, at the same surfactant concentration and increasing polymer concentration to (1% w/v) particle size decreased. Also, increasing polymer concentration from (0.5 to 0.8% w/v) at surfactant concentration (1% w/v) resulted in decreasing particle size while, at the same surfactant concentration and polymer concentration was increased to (1% w/v) particle size increased. These results were attributed to that at low polymer concentration and high surfactant concentration, the solubility of polymer in acetone/water mixture might have increased due to the solubilizing effect of the surfactant leading to slower rate of polymer precipitation and formation of larger particles. While at higher polymer concentration the effect of surfactant on solubility was less marked leading to higher precipitation rate and the formation of smaller particles [216].
The higher polymer concentration might also results in increasing viscosity of the organic phase, which might decrease the diffusion rate and might lower the rate of Ostwald ripening for the more viscous solutions so smaller particles were produced [217].
Eudragit S100 nanoparticles were smaller than those of HPMC phthalate HP55 while maintaining the same formulation conditions; this may be due to that polymer molecular weight that influences nanoparticle size as the higher polymer molecular weight, the smaller the nanoparticles [218].According to this, molecular weight of Eudragit S100 (150000 g/mole) [128] is greater than molecular weight of HPMC phthalate HP55 (78000 g/mole) [133], Eudragit S100 nanoparticles of were smaller than HPMC Phthalate HP55 nanoparticles.