Particle Size Analysis In Pharmaceutics And Oth...
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Relative sizes of particles and nanocarriers favourable for cellular uptake and ingestion through different endocytotic pathways. Vesicle size is one of the main parameters that determines clearance by the reticuloendothelial system (RES). The rate of uptake by the immune system cells increases by the increase in the size of the lipidic carriers.
(A,B) schematic representation of typical particle size graphs indicating a polydisperse sample (composed of heterogeneous population of particles) (A); and a monodisperse sample (containing homogenous population of particles) (B); (C,D) representation of the particle size distribution of a sample containing a polydisperse population of particles (with a high PDI value) (C); and a sample containing a monodisperse population of particles (with a low PDI value) (D).
An established method for the assessment of a single nanocarrier diameter and size distribution is flow cytometry (FCM). This technology is widely employed in analysing and sorting cells, bacteria, and other cell-sized particles. FCM has been applied in the analysis of multilamellar and large unilamellar vesicles (MLV and LUV) [102]. It employs light scattering to measure particles and vesicles in a continuous flow system. Samples have to be fluorescently labelled in order to be distinguished from the impurities and noise signal. Consequently, the scattered light at a 10 angle, or side scattered light at a 90 angle, or the fluorescence of the sample is measured. FCM is a very quick, reliable, robust and reproducible method. However, when employing light scattering detection, its operation can be disturbed by noisy signals from buffers, optics or electronics [98,101,102].
The most common techniques to determine particle size distribution are dynamic image analysis (DIA), static laser light scattering (SLS, also called laser diffraction), dynamic light scattering (DLS) and sieve analysis. This article presents the advantages and drawbacks of each technique, and their comparability among each other. Each method covers a characteristic size range within which measurement is possible. These ranges partly overlap. DIA, SLA and sieving, for example, all can measure particles in a range from 1 µm to 3 mm. However, the results for measuring the same sample can vary considerably. The table below provides an overview of the measuring ranges of the various technologies and the associated analyzers from Microtrac MRB.
With Dynamic Image Analysis (DIA), a large number of particles is moved past a camera system and analyzed in real time. Modern DIA systems acquire several hundred frames per second in and evaluate millions of individual particles within a few minutes. Fast cameras, bright light sources, short exposure times and powerful software are the prerequisites for this. The image below shows the measuring principle of Microtrac's CAMSIZER series as an example for a DIA analyzer.In contrast to sieve analysis DIA measures the particles in a completely random orientation. A variety of size as well as shape parameters are determined based on the particle images. Typical size parameters are, for example, breadth, length and diameter of equivalent circle (see Figure below).
With static laser light scattering (SLS) analysis, also called laser diffraction, particle size is measured indirectly by detecting intensity distributions of laser light scattered by particles at different angles. The figure below shows the setup of the Microtrac SYNC, a state-of-the-art laser granulometer with its unique Tri-Laser-Geometry and an additional camera module.
This technique is based on the phenomenon that light is scattered by particles and the correlation between intensity distribution and particle size is well-known. Simply put, large particles scatter the light to small angles while small particles produce large angle scattering patterns. Large particles produce rather sharp intensity distributions with distinctive maxima and minima at defined angles, the light scattering pattern of small particles becomes more and more diffuse and the overall intensity decreases. It is particularly difficult to measure differently sized particles in a polydisperse sample as the individual light scattering signals of the particles superimpose each other. Static laser light scattering (SLS) is an indirect method which calculates particle size distributions based on super-imposed scattered light patterns caused by a whole collective of particles. Additionally, the optical properties of the material (refractive index) must be known for small particles for the calculation to produces reliable results. Since the theory of SLS is based on the assumption of spherical particles, shape evaluation is not possible. A disadvantage of the SLS is the relatively low resolution and sensitivity. Oversized grain can also only be detected by modern analyzers from approx. 2 vol%. In order to resolve multi-modal distributions, the size of the two components must differ by at least a factor of 3. The big advantage of laser diffraction is that it is a fast, established technique offering great flexibility. With a measuring range from a few nanometers to millimeters, the method can be used for most requirements in particle technology. Image analysis cannot be used for particles
The figure above on the left shows the comparison between SLS, DIA and sieving using the example of a sample of ground coffee. The sieve analysis provides the finest result, the width measurement of the CAMSIZER X2 (DIA) giving a comparable result when particle width is considered. Laser analysis makes it impossible to compare the sieving, the result corresponds approximately to the xarea (diameter of the circle with the same area) od DIA. However, all particle dimensions are included in the result, which are then related to spherical particles. That is why SLS always delivers broader distributions than image analysis. This becomes even clearer in the right image. Here, a sample of cellulose fibers was measured with the CAMSIZER X2 and comparably with a laser granulometer. While image analysis differentiates between fiber thickness and length, this is not possible with laser diffraction. The measurement curve of the SLS initially runs parallel to the width measurement and then approaches the \"fiber length\".
Dynamic Light Scattering (DLS) is based on the Brownian motion of particles in suspensions. Smaller particles move faster, larger particles move more slowly. The light scattered by these particles contains information about the diffusion speed and thus about the size distribution. The particle size determined is a hydrodynamic diameter. The Stokes-Einstein equation describes the relationship between particle size, diffusion rate, temperature and viscosity:
The hydrodynamic diameter of the DLS is usually somewhat larger than the average particle size determined by static light scattering. DLS is particularly suitable for the analysis of nanoparticles where static light scattering reaches its limits. On the other hand, DLS only works for particle sizes up to 10 µm and is increasingly imprecise above 1 µm. In addition, many DLS analyzers offer the possibility of determining the zeta potential and the molecular weight.
Particle Replication in Non-Wetting Templates (PRINT) is a platform particle drug delivery technology that coopts the precision and nanoscale spatial resolution inherently afforded by lithographic techniques derived from the microelectronics industry to produce precisely engineered particles. We describe the utility of PRINT technology as a strategy for formulation and delivery of small molecule and biologic therapeutics, highlighting previous studies where particle size, shape, and chemistry have been used to enhance systemic particle distribution properties. In addition, we introduce the application of PRINT technology towards respiratory drug delivery, a particular interest due to the pharmaceutical need for increased control over dry powder characteristics to improve drug delivery and therapeutic indices. To this end, we have produced dry powder particles with micro- and nanoscale geometric features and composed of small molecule and protein therapeutics. Aerosols generated from these particles show attractive properties for efficient pulmonary delivery and differential respiratory deposition characteristics based on particle geometry. This work highlights the advantages of adopting proven microfabrication techniques in achieving unprecedented control over particle geometric design for drug delivery.
PRINT is an adaptation of micro- and nanomolding technologies, rooted in the microelectronics industry, that is used to fabricate monodisperse particles of controlled sizes and shapes using roll-to-roll manufacturing processes. It allows for the fabrication of monodisperse particles with precise control over size, shape, composition, and surface functionalization. Unlike many other particle fabrication techniques, the PRINT method is versatile and gentle enough to be compatible with the multitude of next-generation therapeutic and diagnostic agents, including small molecules, protein biologics, siRNA, and bioabsorbable and hydrophilic polymer matrix materials with embedded pharmaceutical cargo.
Aerodynamic particle sizing of all PRINT aerosols was performed using the aerodynamic particle sizer (APS) spectrometer (Model no. 3321, TSI Inc. Shoreview, MN, USA). Dry powder aerosols were dispensed into an aerosol generator using an insufflator device and a volume-calibrated hand pump (Penn Century Inc., PA, USA).
The PRINT fabrication approach predictably controls particle geometric and aerodynamic features, a differentiating attribute as compared to traditional particle generation approaches. In particular, micromolding strategies such as PRINT represent one of the only methods to precisely control particle shape and size. For PRINT, the particle geometry is directly derived from the semiconductor wafer, bringing inherent nanoscale precision to the particle geometry and offering the capability to generate unique, nonspherical shapes. It is possible to control geometric features such as length, aspect ratio, and edge curvature, as well as adding unique features such as fenestrations and biomimetic designs, as shown in Figure 2. The capability of PRINT to prepare micro- and nanoparticles of a diverse set of materials is due to the ability to mold materials in a variety of physical forms. In addition to the detailed studies presented here, particles have been prepared by polymerization [11] or solvent evaporation [23]. This flexibility lends itself to the preparation of pharmaceutically relevant particles such as hydrogels [15], PLGA controlled-release systems [13], stimuli-responsive particles [17], suspension formulations [14], or dry powder aerosols as presented here (Figures 2 and 3). This ability to control particle size, shape, and uniformity should also find advantageous use in many dosage forms, including oral, topical, and parenteral products. 59ce067264
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