Real-time particle size and particle size distribution analyses
For a quantitative study of microparticle particle size, FBRM was used. The findings of the FBRM measurement relative to those obtained using an optical microscope and laser diffraction revealed that there were no variations in particle size of microcapsules as compared to those obtained using an optical microscope or laser diffraction (Table 1).
Table 1
Effect of polymer type on particle size mean of microparticles
Polymer
|
Particle size mean (µm) (± SD)
|
FBRM
|
Optical microscope
|
Laser diffraction
|
Ethyl cellulose 4 cp
|
83.24 (± 5.28)
|
88.78 (± 7.64)
|
84.65 (± 6.11)
|
Eudragit RL 100
|
73.42 (± 6.44)
|
79.62 (± 9.17)
|
75.37 (± 5.75)
|
Eudragit RS 100
|
59.36 (± 5.21)
|
63.96 (± 8.92)
|
60.14 (± 6.44)
|
Polycaprolactone (Mw. 10000)
|
51.29 (± 4.09)
|
57.86 (± 8.12)
|
53.46 (± 5.32)
|
PLGA (RG503H)
|
64.08 (± 3.18)
|
68.15 (± 6.95)
|
65.75 (± 4.37)
|
Furthermore, FBRM can be applied to track the change in chord length distributions (CLD) at different levels of microparticle ripening in real time. It can track the shape of microparticles, particle size changes, hardening rate, particle properties, and chord length distribution.
In microparticulate systems, the solidification rate of polymeric microparticles is a significant parameter that influences particle size, encapsulation strength, and the initial burst.12 Diffusion of the drug material out of the droplets and precipitation in the exterior phase will result from a very slow hardening of the emulsion droplets. The affinity between the solvent and the exterior phase, as well as the phase ratio, can influence the precipitation kinetics of the polymer solution droplets.
The solubility of the polymer in organic solvents influences the hardening speed of microparticles during the solvent evaporation process, which impacts on microparticle properties including particle size, amount of encapsulated drugs, matrix porosity, solvent residues, and initial drug release.3 Microparticles have been created using a variety of polymers with various physical properties (such as solubility, molecular weight, reactivity, viscosity, biodegradability, permeability, and so on). Poly(-caprolactone), poly(lactic-co-glycolic acid), Eudragit RS 100, Eudragit RL 100, and ethyl cellulose microparticles are only a few of the materials accessible.4–10
Biocompatible and biodegradable polyesters include poly(-caprolactone) (PCL) and poly(lactic-co-glycolic acid) (PLGA).4,5,9 Eudragit RS 100 and Eudragit RL 100 are methacrylic acid ester-free quaternary ammonium copolymers of ethyl acrylate and methyl methacrylate.10 Eudragit RL 100 is more permeable than Eudragit RS 100 since it incorporates more co-trimethylammonioethyl methacrylate chloride. Ethyl cellulose is a non-biodegradable hydrophobic polymer.11–15 The microparticle hardening rate of these polymers is unknown. As a result, it's important to understand how polymer properties affect the hardening time of polymeric microparticles.
As a function of time, the square weighted mean chord length of polymeric microparticles is plotted (Fig. 1a). All of the polymers formed small particles (less than 300 m).During solvent evaporation, various types of polymers applied in the formulation of polymeric microparticles result in a different square weighted mean (particle size). FBRM initially observed significant droplet sizes of all types of polymers when the organic polymer solution was emulsified. On both types of polymers, increasing the process time culminated in a decrease in particle size followed by a plateau size where the particle size remained unchanged. The particle size mean of microparticles when ethyl cellulose was utilized was greater than the others. The viscosity of the polymer solution has an effect on it. The high viscosity of Ethyl cellulose emulsion droplets reduced the organic phase's dispersibility in the aqueous media, resulting in larger particles. The viscosity data for polymer solutions can be found in.
The solubility of the polymer in the solvent affected the solidification rate of polymeric microparticles. The solubilities of polymers in dichloromethane were contrasted in this study (Table 2). In dichloromethane, ethyl cellulose (EC) had the lowest solubility, while polycaprolactone had the highest. As a result, polycaprolactone-based microparticles hardened at a slower rate than the others. Due to its poor solubility, ethyl cellulose has the highest hardening rate. In dichloromethane, Eudragit RL 100, Eudragit RS 100, and PLGA (RG503H) is more soluble than ethyl cellulose. 7,25,40−42 These properties cause microparticles to solidify at a slower rate than ethyl cellulose. The solidification of polymers with high solubilities took longer. They remained in the semi-solid state for longer, and it scattered more densely before fully solidifying, resulting in denser microparticles. In dichloromethane, Eudragit RL 100, Eudragit RS 100, and PLGA (RG503H) is more soluble than ethyl cellulose. These properties cause microparticles to solidify at a slower rate than ethyl cellulose. The solidification of polymers with high solubilities took longer.3 They remained in the semi-solid state for longer, and it scattered more densely before fully solidifying, resulting in denser microparticles.3,6
Table 2
Effect of polymer type on solubility in dichloromethane, viscosity of polymeric solution and particle size mean of microparticles
Polymer
|
Solubility (g/ml)
(± SD)
|
Viscosity (cSt)
(± SD)
|
Hardening time (min)
|
Ethyl cellulose 4 cp
|
0.86 (± 0.03)
|
10.31 (± 1.14)
|
10.5
|
Eudragit RL 100
|
1.04 (± 0.04)
|
4.72 (± 0.83)
|
25
|
Eudragit RS 100
|
1.42 (± 0.02)
|
3.84 (± 0.39)
|
19
|
Polycaprolactone (Mw. 10000)
|
1.89 (± 0.05)
|
3.15 (± 0.45)
|
55
|
PLGA (RG503H)
|
1.25 (± 0.06)
|
4.36 (± 0.52)
|
30
|
For both polymers, the droplet shrinkage may be divided into two phases. Within 9 minutes (EC), 15 minutes (Eudragit RS 100), 20 minutes (Eudragit RL 100), and 25 minutes (PLGA), the original droplet size shrank dramatically (RG503H). This was accompanied by a period with no further pronounced shrinkage, known as a discontinued or sluggish shrinkage phase (Fig. 1a). It shows that in the first (rapid) step, the solvent was rapidly removed, and that in the second (slow) phase, the embryonic microparticle droplets were transformed into stable microparticles. Polycaprolactone caused the droplet size decrease to occur for another 55 minutes, meaning that the embryonic microparticle droplets solidified between 50 and 55 minutes (Fig. 1a). The start of the plateau process for all polymers was 10.5 minutes (ethyl cellulose 4 cp), 25 minutes (Eudragit RL 100), 19 minutes (Eudragit RS 100), 55 minutes (polycaprolactone), and 30 minutes (PLGA (RG503H) based on FBRM results (Fig. 1b and Table 2).
As EC microparticles are extracted quickly with solvent (Fig. 1), the polymer solidifies quickly on the droplet surface,16,28 resulting in diffuse scattering to some extent. The improvement in the FBRM signal must be interpreted as opacification shifts and particle solidification.
As a time function, the chord count or particle counts of polymeric microparticles reveal a curve (Fig. 2). FBRM initially observed lower chord counts as the organic polymer solution was emulsified; but, as the process time was increased, the chord counts increased, indicating an increase in particle counts, followed by a plateau period where the chord counts were stable. During the solvent evaporation process, Eudragit RL 100, PLGA (RG503H), Eudragit RS 100, and polycaprolactone showed identical chord counts profiles. The particle counts of ethyl cellulose microparticles is smaller than those of the other microparticles, owing to the processing of microparticles of the biggest size.
Eudragit RL 100, Eudragit RS 100, and PLGA (RG503H) had smaller particle sizes than ethyl cellulose, resulting in higher particle counts. The particle size of polycaprolactone was the lowest, but the particle count was not the largest. This is due to Polycaprolactone's particle properties, which create slightly transparent microparticles as opposed to other polymers (Fig. 5.d1). When a laser beam strikes a transparent microparticle, multiple reflections occur inside the microparticle, illuminating the whole sphere. As a more opaque microparticle is struck by a laser pulse, the light is dispersed to the detector, resulting in a higher scattering value.27,28,32,43 The backscattered signal is very strong due to the invisible microparticles' absorbance, resulting in a high degree of chord length (particle size) and low chord counts (particle counts).44–46 This is in conjunction with Greaves et al., as well as Sparks and Dobbs, who concluded that only opaque and highly reflective droplets or microparticles (with microstructure on the surface) provide repeatable and consistent effects.32,44,45
The formation of microparticles-based polymer materials was clearly supported by real-time particle size analysis and particle size distribution experiments of all polymeric microparticles with in situ polymerization. Surprisingly, these findings suggest that, based on the polymer structures, all of the polymer products used various microparticle forming mechanisms.
At the same concentration, the chord length distributions (particle size distribution) of various polymers determined by FBRM is different (Fig. 3). Since the number of microparticles was reduced, larger microparticles resulted in longer chord lengths and a lower peak particle number. In this case, increasing the viscosity of the polymer solution resulted in a larger square weighted mean chord length (particle size) and a wider chord length distribution. Polycaprolactone solution (organic phase) had a lower viscosity than other polymers, resulting in smaller microparticles. In comparison to other polymeric microparticles, this polymer provided narrower square weighted mean chord lengths and narrow chord length distributions.
Figure 4. Comparison of the square weighted chord length distribution for various polymer obtained by the FBRM method (O/W) [at 4 hours stirring time]
Because of the influence of the form and physical properties of the polymer, as well as its solubility in dichloromethane as a solvent, all microparticles possess varying levels of opacity (Fig. 5.a1-e1). Polymers with a high dichloromethane solubility took longer to solidify and remained in a semisolid state for longer. Before fully solidifying, the scattered process became more condensed. When the polymer matrix was shrunk for a longer period of time, the polymer matrix becomes thick, and the droplet gradually shrank into stable microparticles, leaving transparent droplets. Polymeric microparticles had a diameter ranging from 51 to 83 micrometers (FBRM) (Table 1). The mean particle size of microparticles made with a high viscosity polymer solution was greater than those made with a low viscosity solution. This is due to faster solidification on the surface of embryonic microparticle droplets, resulting in accelerated microparticle droplet shrinkage. Based on the data, the square weighted mean chord lengths (particle size mean) determined by FBRM were better estimated than those calculated by microscopic observation, as shown by the data's lower standard deviation (Table 1).
In the FBRM results, independent particle size analyses of microparticles and prepared polymeric microparticles are given (Fig. 1). The results showed that the final particle size measured did not vary as compared to the data collected by optical microscope and laser diffraction measurement (Table 1). It can be concluded that particle size measurement using the centered beam reflectance measurement (FBRM) method yields the same results as the method that has been evolved and proven with further advantages in terms of providing particle size data and population patterns of particles in suspension in real time and on-line. The FBRM technique allows for the measurement of parameter processes during particle forming without destroying the morphology or counts of the process's formed particles.