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Pharmaceutical sciences
Novel Drug Delivery Systems II
Characterization of Colloidal Carrier Systems
Paper Coordinator Principal Investigator
Dr. Vijaya Khader
Former Dean, Acharya N G Ranga Agricultural University
Content Writer
Prof. Farhan J Ahmad Jamia Hamdard, New Delhi Paper No. : 08 Novel Drug Delivery Systems II
Module No : 3 Characterization of colloidal carrier system
Development Team
Dr. Sushama Talegaonkar Jamia Hamdard, New Delhi
Content Reviewer Prof Asgar Ali Jamia Hamdard, New Delhi
Dr. Sushama Talegaonkar Jamia Hamdard, New Delhi
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Pharmaceutical sciences
Novel Drug Delivery Systems II
Characterization of Colloidal Carrier Systems
Description of Module
Subject Name Pharmaceutical Sciences
Paper Name Novel Drug Delivery Systems II
Module Name/Title Introduction to Colloidal and Supramolecular Drug Delivery System Module Id
Pre -requisites
Objectives Various techniques used for the characterization of colloidal drug delivery systems
Advantages and applications of characterization in colloidal drug delivery systems
Keywords X Ray Diffraction, SEM, TEM , DLS, AFM and Zeta Potential and Drug loading Content Reviewer
Dr. Vijaya Khader Dr. MC Varadaraj
Prof A K Tiwarey Punjabi University, Patiala
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Characterization of Colloidal Carrier Systems
CHARACTERIZATION OF COLLOIDAL AND SUPER MOLECULAR DELIVERY
1. INTRODUCTION
The vesicular dosage forms made of polymers/lipids in the size ranging from nanometers to micrometers are called as Colloidal Drug Carriers (CDCs). These CDCs can successfully transport the loaded drugs to the target site and can improve the therapeutic index of drugs by enhancing and/or reducing their toxicity. The representative examples of these colloidal drug carrier systems include liposomes, micelles, nanoparticles and nanoemulsions. Various natural and synthetic polymers (biodegradable or non-biodegradable) can be used to formulate CDCs such as proteins (albumin), carbohydrates (chitosan) and chemically modified carbohydrates (e.g. poly dextran/poly starch), poly (methyl methacrylate) and epoxy polymers. The characterization of CDCs includes particle size and size distribution, shape and surface morphology, zeta potential, infra red (IR) and raman spectroscopy (RS) studies, nuclear magnetic resonance (NMR) studies, differential scanning calorimetry (DSC) studies, x-ray diffraction (XRD), encapsulation efficiency, lamellarity and in vitro drug release study.
The CDCs have been found widespread applications in drug delivery, gene therapy, and medical imaging, drug targeting, bio responsive triggered systems and self-regulated drug delivery systems.
2. CHARACTERIZATION
The colloidal drug delivery system is characterized for different parameters like the mean diameter of particles and their size distribution, morphology and their surface charge, IR and NMR analysis, DSC and XRD studies, encapsulation efficiency, in vitro release studies and so on. This module emphasizes the various techniques being used for the characterization of CDCs.
2.1 Particle Size And Size Distribution
Particle Size, polydispersity index and surface charge of colloidal formulations are the essential parameters. As the particle size is decreased, the surface area-to volume ratio is increased; thus, most of the drug encapsulated in these particles would be present at or near the surface of particle and results in fast release of drugs. Thus, by regulating the size of a formulation, the rate of drug release can easily be controlled. The techniques of microscopy, dynamic light scattering (DLS), photon correlation spectroscopy (PCS) are used.
2.1.1 DYNAMIC LIGHT SCATTERING (DLS)
A small part of the parallel ray of light on passing through a transparent system get sprinkled elastically due to optical discontinuities in the medium, known as Rayleigh scattering. The solutions containing polymer molecules has been shown some supplementary scattering due to the presence of
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the solute molecules, and this form the basis to determine the concentration, their size as well as shape of the polymer molecules. The average size and molecular weights of polymer solutes can be determined by measuring the differences between scattered light intensity of the polymer solutions and the solvent. The quasielastic laser light scattering with a Zetasizer is used to determine the average particle size and size distribution of colloidal carrier’s suspension. The distilled water is added to dilute the colloidal carriers’ suspension and particle size is measured at room temperature by placing it into a polystyrene latex cell. The polydispersity index can also be determined as a measure of the particle size distribution of the dispersion. This index can range from 0 to 1.0, where 0 (zero) is used in an exclusively monodisperse system, and 1.0 for a polydisperse particle dispersion (Figure 1).
Figure 1: Schematic representation of particle size distributions
2.1.2 PHOTON CORRELATION SPECTROSCOPY (PCS)
Photon correlation spectroscopy is applied to measure size and size distribution of the submicron particles of range 5 nm to 5 μm. In Photon Correlation Spectroscopy, the movement of sub-micron particles in random direction is measured as a function of time. The principle of this technique is that smaller particles travelled with higher velocity in comparison to larger particles. The sub-micron particles causes diffraction of laser beam present in suspension. The rapid fluctuations cause diffusion
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of particles of the laser around a mean value at a definite angle (varying from 10 to 90°) and depends on particle size. The measured photoelectron time‐correlation function yields a histogram of the line width distribution which can be related uniquely to the particle size. The analysis is tested using simulated data with both unimodal and as well as bimodal size distributions. The technique determines the average particle size ranging from 3 nm and 3000 nm. The measurements result in polydispersity index, the average and mode effective hydrodynamic diameter as a measure of the width of the distribution.
2.1.3 MICROSCOPY
Microscopy is used as a most important instrument for the characterization of colloidal carrier system.
This technique can also be used to scrutinize morphology, size, and distribution of colloidal carriers, as well as the interactions of colloidal carriers with biological environments. Va rious microscopic techniques available for characterization of colloidal carrier includes traditional optical microscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), scanning tunneling microscopy, scanning probe microscopy (SPM), and super resolution microscopy.
2.1.3.1 OPTICAL MICROSCOPY
Optical microscopy has resolution in the micro-range to provide information about the structure. By means of transmitting light, slight film of sample is shed on the slide of microscope to e xamine under the microscope. When a fine grid of light passes through the sample in which the absorption coefficient is varied regionally, then the resultant image will occur with contrast regions. Polarized- light microscopy and phase-contrast microscopy are used commonly to attain the contrast. Polarized- light microscopy utilized the crossed polarizers by rotating the plane polarized light to get the structural data. The polarizing microscopy to examine the construction of liquid crystals of polymers can also be applied. Reflected-light microscopy is employed to look into the structural types of solid polymers. Confocal laser scanning microscopy, Raman microscopy, infrared microscopy and fluorescence microscopy are some other techniques being used to examine the structure of polymeric biomaterials.
2.1.3.2 SCANNING ELECTRON MICROSCOPY (SEM)
Scanning electron microscopy (SEM) (Figure 2) is a type of electron microscopy having the resolution of up to nano-range. It is also used to characterize the surface morphology of the colloidal vesicles. In SEM, a thin grid of electrons crosses an opaque specimen, and detectors from every point collected the emitted electrons to produce a remarkable three-dimensional image with an enormous depth of field. A drop of colloidal system is mounted on clear glass stub, dried in air and coated with a
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sputter coater and then examined under SEM. To produce the stable images, the sample before an examination is coated with a conducting film of gold or gold–palladium alloy of thickness of about 20 nm by means of evaporation or by sputtering.
Figure 2: Scanning electron micrograph of the particle 2.1.2.3 TRANSMISSION ELECTRON MICROSCOPY (TEM)
In transmission electron microscopy, an incident electron beam is passed through a thin foil specimen.
The incident electrons interacting with the specimen are transformed to elastically scattered electrons, unscattered electrons or inelastically scattered electrons. The proportion of the space between the objective lens and the specimen; the space between the objective lens and its image plane determine the magnification. The unscattered or scattered electrons are concentrated by a number of electromagnetic lenses and cast on a screen to generate amplitude-contrast picture, electron diffraction, a phase-contrast image or a phantom picture of different darkness depending on the density of unscattered electrons. The power system is mounted onto a cold-stage kept at liquid nitrogen temperature and directly examined in the transmission electron microscope (Figure 3). The advantage of TEM is that it can facilitate the investigation of particular morphological features like
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crystal structure and its orientation by providing an electron diffraction pattern from a selected region.
The scale bar of the electron micrographs is used to determine the diameters of the colloidal formulations, aggregation/agglomeration, dispersion and dynamic displacement of colloidal carriers in an aqueous environment. The most significant application of TEM is the atomic-resolution real-space imaging of nanoparticles. TEM has advantages over SEM in providing better spatial resolution and capacity for additional analytical measurements.
Figure 3: Tranmission electron microscopic image of the particle 2.1.3.4 SCANNING PROBE MICROSCOPY (SPM)
The scanning probe microscopy (SPM) (Figure 4) techniques also include two other techniques that are atomic force microscopy (AFM) and scanning tunneling microscopy (STM) for studying surface structure of colloidal carrier. In all these techniques, a probe is scanned just above the surface at the time of scrutinizing the interactions between the surface and the probe. The essential components of STM include a sharp scanning tip, a scanner controlling the drift of the tip, a control unit to determine the position of the peak, a vibration isolation stage and feedback regulation electronics. In STM (Figure 4), an excavating current is running between the metallic tip and a conducting substrate and produce electron density images of conductive or semi-conductive surfaces and biomolecules attached on conductive substrates at the atomic scale. A low potential difference is applied between the scanning tip and the surface to produce tunneling of electrons then, the refraction of the countering
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current can be read when the point moves through the sample in the x–y plane to generate a map of charge density.
Figure 4: SPM images
In case of AFM, van der Waals force exists between the tip and the surface. The repulsive force act for short assortment in contact mode and attractive force for long range in non-contact mode. The atomic force microscope is type of scanning probe microscope having a very high resolution. It can demonstrate resolution of even fractions of nanometer and approximately 1000 times superior than the visual diffraction limit. The electrical current flowing between sample and tip can be broken, to generate a three-dimensional morphological image of the colloidal carrier with a resolution to nanometer level. AFM (Figure 5) can be used for scrutinizing the shape, size, structure, dispersion, sorption and aggregation of colloidal carriers by employing different scanning modes like noncontact mode or static mode, intermittent sample contact mode or tapping mode and contact mode or dynamic mode. It is also able to characterize the interaction of colloidal carriers with supported lipid bilayers.
It can also image the biomaterials without damaging its native surfaces.
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Figure 5: Atomic Force Microscopy Scan.
2.1.3.5 SUPER-RESOLUTION LIGHT MICROSCOPY (SRLM)
Super-resolution light microscopy (Figure 6) is light microscopy technology, which allocates the performance by imposing the diffraction properties of light according to Abbe’s equation and also exceeding the resolution to the nano range. It can also be performed by combining structured illumination microscopy with inverted microscope, which gave a high resolution up to nanometer by analyzing the sample data. A laser is used to produce the fluorescence excitation and images are take n through a digital camera charged by multiplying electrons. Epoxy sections prepared for routine transmission electron microscopy, are cut from the block of tissue for examination under super- resolution fluorescence light microscopy. Super-resolution techniques allow the capture of images with a higher resolving power than the diffraction limit. They descend into two broad categories,
"functional" super-resolution techniques, which use clever experimental techniques and known limitations on the subject being imaged to reconstruct a super-resolution picture, "true" super- resolution techniques, which capture information contained in evanescent waves.
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Figure 6: Schematic representation by Super-resolution light microscopy 2.2 Shape And Surface Morphology
The characteristics of colloidal formulations depends upon physical surface structures, which counter the interactions of the colloids with adjacent species and the atomic or molecular compositions of the surfaces. The shape of colloidal carriers affects cellular uptake, biocompatibility and retention in tissues and organs. Silver NPs of plate-shaped are found to be more harmful than spherical, rod- shaped or wire shaped silver nanoparticles when tested against zebrafish embryos and E. coli. The flow properties and adhesion ability of colloidal carriers for delivery of drugs throughout the circulatory system and the in vivo circulation time of the formulations can be prescribed by amending the shapes of carriers. Surface charges, surface composition, surface energy and wettability, are the vital parameters that are considered among the various surface properties. Shape and surface morphology are determined by using freeze fracture electron microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Both SEM and TEM can determine the size and shape heterogeneity of colloidal carriers, as well as the dispersion and degrees of aggregation.
2.2.1 Freeze-fracture electron microscopy
The freeze-fracture machine was introduced by Hans Moor in 1961. The process of freeze-fracture technique consists of actually rupturing congealed biological sample to obtain the structural detail by envisaging the splinter plane by vacuum-deposition of platinum-carbon to make a model to examine under the transmission electron microscope. Acid is used to clean the replica by removing the adhering organic material and to prepare a thin platinum shell of fractured membrane surface which is then analyzed by electron microscopy. Freeze-fracture replication technique (Figure 7) is mainly used
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for the direct investigation of the three-dimensional structure of the particles or units that form up the dispersion, while simultaneously revealing their orientation and distribution with molecular resolution.
Figure 7: Freeze -fracture electron microscopy.
2.3 Zeta Potential
In an ionic solution, the charged particle surface is firmly bound to opposite charged ions which leads to forming a thin liquid layer known as the stern layer. This layer is attached by an outer diffuse layer consisting of loosely associated ions. These two layers ultimately compose the so-called electrical double layer. The electric potential on the shear surface is known as zeta potential. It is determined by measuring the velocity of the charged species towards the electrode in the existence of an external electric field across the sample solution. The samples are suitably diluted with solvent prior to measurements. An additional electrode is employed to assess the surface charge on colloidal formulations or zeta potential by utilizing the same instruments. The mean hydrodynamic diameter and polydispersity index (PI) of the particles are calculated with cumulant analysis by getting the hold of the three measurements. In zeta potential measurements, the repulsive forces between particles are measured to characterize the colloidal carriers. It imitates the electrical potential of particles and is
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disposed by the composition of the medium of the dispersion and the particle. It helps in determining the stability of colloidal system, as larger the repulsive forces between particles, more stable is the preparation as the particles do not come close to each other to form an aggregate. The zeta potential measurements are used to predict stability by quantifying these electrostatic interactions. The colloidal carrier systems with a surface charge above (+/-) 30 mV are found to be stable in the form of suspension due to absence of aggregation between the particles. It can also be used to find out possibility of encapsulation of charged active material in the colloidal carrier or adsorbtion onto the surface of the carriers. Zeta potential is affected by the concentration of surfactants and polymer.
Many polymers like poly (e-caprolactone), poly (D,Llactide), and lecithins convey a negative charge to the surface, whereas nonionic surfactants reduce the zeta potential. A nanocolloidal carrier with surface charge values above ±30 mV is stable because the repulsion between the particles prohibited their aggregation.
Laser doppler electrophoresis is used to measure the electrophoretic mobility. The sample is placed into a regular capillary electrophoresis cell outfitted with electrodes of gold. The electrophoretic mobility of the colloidal carrier system is recognized to estimate the surface net charge around lipid droplets. Prior to analysis, the colloidal carrier formulations are diluted and positioned directly into the module, to avoid any error due to multiple scattering effects.
2.4 Infrared and Raman Spectroscopy
A molecule undergoes various forms of vibration, each comprising of an intricate combination of bond stretches and deformations. The molecules exist in its ground state at low temperature and excited to higher energy states on absorbing radiant energy. This energy corresponds to the energy difference ∆E between the excited and ground states of the molecule and forms the basis of infrared (IR) spectroscopy. In a sample, the spectral transitions are observed by scanning through the entire IR frequency regions (400–4000 cm−1) and continuously supervising the intensity of transmitted light.
The frequency and intensity of vibrations are acted as the qualitative and quantitative mode to determine the structural configuration and composition of the molecules. Thus, IR spectroscopy is used as an important tool to recognize the functional groups with their modes of attachment, and in some cases the absorption spectrum is also used as molecular fingerprint to identify a molecule.
For colloidal carrier system, Fourier transform infrared (FTIR) spectroscopy (Figure 8) is used to study the characteristic spectral bands to determine the colloidal carrier and protein conjugation, and to demonstrate the conformational states of the bounded proteins. Moreover, FTIR has also been used for nanocolloidal carriers to study the confirmation of their functional molecules which are covalently
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spliced onto carbon nanotubes. Table 1 lists the functional groups with their absorption bands in IR spectroscopy.
Figure 8: FTIR spectra
Raman spectroscopy (RS) is the other vibrational spectroscopy, which provides structural information regarding the molecules by sensing the inelastic dispersion of photons (Figure 9). The vibrational energy of the molecule in its ground state is the scattered energy of the photon experiments. RS is normally considered to be corresponding to IR spectroscopy. It is appropriate for studying biological samples in aqueous solution because water molecules tend to be weak Raman scatterers. Moreover, the molecular information offered by RS can be employed to investigate the conformations of tissue factors and concentrations, which shows the potency of the RS for detecting tissue abnormalities.
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Figure 9: Raman spectra
The execution of surface enhanced Raman scattering (SERS) can strongly improve RS signals and increase spatial resolution, while the measured biomolecules are adhered to the surface of metallic constructions, such as commonly used gold or silver NP colloid substrates. SERS can be applied to analyze the surface functionalization, to monitor the conformational change in proteins conjugated with colloidal carriers, to record the release of drugs intracellular from the nanocarriers. A recently emerging technique of Raman spectroscopy is the Tip Enhanced Raman spectroscopy (TERS). It used the metallic tip without an orifice to gain the surface improvement of the Raman signals. SERS and TERS provide topological information of the nanocolloid along with their structural, chemical and electronic properties. Vibrational spectroscopy techniques are relatively uncomplicated, noncritical and can be used to scrutinize powders, films, and resolutions. Along with structural information, IR and Raman spectra may be applied to study macromolecular orientation, the crystalline character of polymers, and mean molecular weight.
Table 1: List of all chemical groups present in vibrational spectroscopy with their wavelength and wavenumber
Groups Wavelength(µm) Wavenumber(cm-1)
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OH 2.84–3.22 3520–3100
NH 2.86–3.23 3500–3100
CH 3.02–3.12 3310–3200
CH2 3.25 3080
=CH 3.31 3020
Ar H 3.24–3.33 3090–3000
CH3 3.36–3.39 3960
CH2 3.41–3.43 3920
C C 4.4–4.7 2250–2150
C=C 6.06–6.25 1650–1600
C N 4.17–4.76 2400–2100
C=O 5.4–6.3 1850–1582
C O C 7.9–8.3 1260–1200
C F 7.4–8.3 1350–1200
C Cl 13.7–15.9 730–630
Si O 8.1–9.8 1220–1020
Si C 11.63–13.28 860–700
Si CH3 7–9.4 1260
Si H 4.46 2240
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2.5 Nuclear Magnetic Resonance (NMR) Spectroscopy Studies
NMR is non-destructive/non-invasive technique which is established on the fact of nuclear magnetic resonance and give information about the structure, dynamics, reaction state of molecules and chemical environment. The intramolecular magnetic field close to an atom in a particle changes the resonance frequency, thus granting access to the details of the electronic structure of a particle. When located in a magnetic field, NMR active nuclei such as 1H, 13C, 15N, 17O, and 19F nuclei absorb electromagnetic radiation at a frequency characteristic of the isotope. When a strong external magnetic field is utilized along the material containing any of these nuclei, then they work as bar magnets and orient themselves in any of two energy states, i.e. either in a low-energy state with a corresponding configuration to the battlefield, or in a high-energy state having an opposite alignment in the area. In NMR spectra, (Figure 10) slight differences in the frequencies of NMR are observed due to different molecular environments of the nuclei. Therefore, the surrounding electrons shield the nuclei to different extents depending on their chemical nature. The changes or displacements in the resonance are known as chemical shifts. The measurement of chemical shift is done in parts pe r million (ppm). Tetramethylsilane (TMS) is chemically inert and used as a reference for chemical- shift. NMR is used both in the solid state and in solution to study the microstructural configuration of polymers. It is used to identify certain atoms or groups along with their positions in a polymer molecule by one-, two- and three-dimensional spectra.
Figure 10: Nuclear magnetic resonance (NMR) spectrum
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NMR spectroscopic analysis has also been gone through to determine several physiochemical characteristics of nanomaterials, including structure, purity and functionality in colloidal carriers like dendrimers, polymers and fullerene derivatives, as well as conformational changes occurring in the interactions between ligands and nanomaterials.
2.6 Differential Scanning Calorimetry (DSC) Studies
DSC apparatus is used for thermal analysis basically to measure the change in physical properties of a specimen due to variations in temperature against time. On the basis of temperature difference between sample and reference material, DSC examined the magnitude of heat absorbed or radiated by the sample on the basis of difference in temperature between the sample and the reference material.
DSCs may be heat-flux type and power-compensated type, on the basis of their mechanism of process. It measured the different amounts of thermal power required to maintain the same temperature both in sample and reference and plotted it as a function of temperature or time. DSC is useful in the investigation of thermal properties, providing both qualitative and quantitative information about the physicochemical state of the drug. The instrument is calibrated using Indium as standard. Samples will be placed in sealed aluminium pans and heated from at a rate of 10ºC/min under nitrogen atmosphere, with an empty pan as reference. The DSC analysis is shown in Figure 11.
Figure 11: DSC analysis 2.7 X-Ray Diffraction (XRD) Methods
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X-ray diffraction (Figure 12) is used as an important technique to investigate the mode of attachments of atoms or molecules in a material. If there is a systematic array of substructures like repeated distances of a same magnitude (in the range of 0.05–0.25 nm), the material produced an intrusion patterns and give information about the shape and size of the colloidal carrier structures. The two chief diffraction methods commonly used to study the structural arrangement of polymers in the colloidal carrier system are namely wide-angle x-ray scattering (WAXS) and small-angle x-ray scattering (SAXS). WAXS (5° to 120°) is used for studying the semi-crystalline structure of polymers having distances in nano range (0.1 to 5 nm) within the atoms. The crystalline substance of the polymer is obtained by measuring the diffusion from the amorphous part and the comparative intensities of the diffraction crest from the crystalline part. WAXS can also provide information about the helical structure of polymers that is the span of the frequent unit beside the fiber axis along with the number of repetitive units present in each turn in helical structures of linear polymers.
In SAXS, a part of an incident X-ray beam elastically scattered from the sample to form a scattering pattern on a two-dimensional flat X-ray detector which is perpendicular to the focal point of the incident X-ray beam. By examining the intensity of the scattered X-ray collected within the scattering angle (0.1 to 3°), it can estimate the shape, size/ size distribution, structure, and orientation of a variety of polymers and colloid bioconjugate systems in solution. SAXS (1° to 5°) is applied to detect voids or the dispersion of molecules in a lamellae structure of the materials with a scope of inter- atomic distances 5 to 70 nm.
Figure 12: X-ray powder diffraction pattern 2.8 Encapsulation Efficiency
The techniques like fluorescence spectroscopy, spectrophotometry, and enzyme based methods, and electrochemical techniques are used depending on the nature of the encapsulated material. Any
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purification technique can also be used to check the storage stability of colloidal formulation like leakage of content or the effect of various disruptive conditions on encapsulants.
Unentrapped drug is separated from encapsulated drug with a refrigerated centrifuge by centrifugation. To determine the percentage of encapsulated drug lysis of colloidal formulation is done with absolute alcohol and sonication. The concentration of drug in absolute alcohol is determined spectrophotometrically either by using a UV-visible spectrophotometer or HPLC. The encapsulation efficiency expressed as entrapment percentage is calculated through the following relationship:
2.9 Lamellarity Determination
Lamellarity determination of colloidal formulation is done by using 31P NMR, Cryo-electron microscopy and small angle X-ray scattering (SAXS) techniques, TEM. The liposomal lamellarity widely varies based on the choice of lipids and preparation methods. In 31P NMR technique, the addition of Mn2+ reduces the 31P NMR signal from phospholipids of the colloidal formulation due to interactions with the phosphate groups of phospholipids and causing alteration in signals. The enormity of signals before and after addition of Mn2+ determines the degree of lamellarity. This technique is responsive to the Mn2+ and buffer concentrations, and the types of colloidal carriers under analysis. Freeze fracture electron microscopy and small angle X-ray scattering are the other techniques used for lamellarity determination.
2.10 In Vitro Drug Release
Drug release from colloidal formulations is estimated by using the dialysis method. A suitable volume of preparation is put in a dialysis bag. Dialysis tubing is made up of regenerated cellulose by tieding it’s both ends. The dialysis bag is hanging suitable solution retained at 37 ± 0.5 °C. The dispersion is shaken by using a magnetic bead at desired rpm for uniform distribution of contents. A definite quantity of dispersion is sampled and replaced with same amount of fresh buffer, after a suitable interval to maintain the uniform volume of PBS. The temperatures of samples are als o maintained.
The amount of drugs is enumerated with HPLC analysis and UV spectroscopy.
The drug release profile from an optimized formulation can also be studied with multi compartment rotating cell by using dialysis membrane. The drug encapsulated in nanocarriers is placed in donor
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phase with distilled water. The donar and receptor phase contains the same medium but the receptor phase is completely withdrawn after predetermined time to investigate the amount of drug release with UV spectrophotometer or HPLC at a desired wavelength.
2.11 Cell Line Studies
A cell line is a cell culture with cells that have the same genetic makeup. Every cell line is used for a precise study due to its unique and idiosyncratic features. It is therefore important to identify the characteristics of each cell lines. In cancer research, cell lines are used for the production of neoplasias in animal mock-up to closely imitate the initiation of original neoplasias in vivo. There are some common human cell lines used for cytotoxic studies. These includes HeLa, National Cancer Institute's 60 cancer cell lines (NCI60), prostate cancer cell lines like DU145, Lncap, PC3, breast cancer cell lines like MCF-7, MDA-MB-438, T47D, THP-1 (acute myeloid leukemia), bone cancer cell lines Saos-2 cells, MCF-7 (breast adenocarcinoma), NCI-H460 (non-small cell lung cancer) and A375-C5 (melanoma).
In cell transplant therapy, cell lines are used as a practical substitute but they have both stability and/or viability problems. Stem cells are used in vitro to generate a variety of cells. Rous in 1910 first of all suggested the idea of cell transformation and induced successfully a tumor through the filtered extract of tumor cells of chicken.
The cell line studies are done to assist in the selection of most efficacious compounds from a collection of different candidates with erratic stages of the preferred properties. In vitro cell-culture tumor models are used more widely but they are deficient of complexity of the natural microenvironment of the host organism.
The following formula is used to calculate the efficiency of cellular uptake:
In addition to the above mentioned analysis, the physical stability study, photodegradation s tudy, sterility testing, in vivo studies can be used to further characterize the colloidal drug delivery system.
3. CONCLUSION
It may be painstaking challenge to develop nanocolloidal systems with preferred drug release profiles, which can be easily regulated by changing the nature or morphology of the contiguous membrane.
The characterization of nanocolloid carriers is used to determine their suitability for different drugs
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and their stability in different environments. It also helps in determining the efficacy of a drug in a particular site. The nanocolloidal carrier system with desired characteristics can improve the stability, efficacy, tolerance and bioavailability of a drug.
