3.2.2. Surface Morphology and Lipid Distribution

images of SLH prepared with PG8 are shown.

3.2.2. Surface Morphology and Lipid Distribution Surface morphology, internal structure, and lipid distribution within fabricated SLH formulations were examined using SEM and confocal laser scanning micriscopy (Figures 3 and 4). Blank FS particles formed semi-spherical shapes of varying particle sizes with distinct concave-like structures (Figure 3A). No difference in appearance was observed between blank FS and 80% FS PG8 (Figure 3B). However, at 200% saturation level, regardless of the lipid used, FS particles appeared to form clusters and large aggregates (Figure 3C). In contrast, MPS appeared as angular structures and formed aggregates irrespective of the lipid used or FEN saturation level (Figure 3E,F). No difference in appearance was observed between SLH prepared with either lipid types; therefore, only SEM Surface morphology, internal structure, and lipid distribution within fabricated SLH formulations were examined using SEM and confocal laser scanning micriscopy (Figures 3 and 4). Blank FS particles formed semi-spherical shapes of varying particle sizes with distinct concave-like structures (Figure 3A). No difference in appearance was observed between blank FS and 80% FS PG8 (Figure 3B). However, at 200% saturation level, regardless of the lipid used, FS particles appeared to form clusters and large aggregates (Figure 3C). In contrast, MPS appeared as angular structures and formed aggregates irrespective of the lipid used or FEN saturation level (Figure 3E,F). No difference in appearance was observed between SLH prepared with either lipid types; therefore, only SEM images of SLH prepared with PG8 are shown.

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**Figure 3.** SEM images of (**A**) blank FS, (**B**) 80% FS PG8, (**C**) 200% FS PG8, (**D**) blank MPS, (**E**) 80% MPS PG8, and (**F**) 200% MPS PG8. **Figure 3.** SEM images of (**A**) blank FS, (**B**) 80% FS PG8, (**C**) 200% FS PG8, (**D**) blank MPS, (**E**) 80% MPS PG8, and (**F**) 200% MPS PG8.

Confocal imaging revealed that the lipid distribution within the silica microparticles was dependent on the type of silica and lipid used. More lipid was observed within the internal structure of FS particles than MPS, evidenced by the intensity of the fluorescently labeled lipid within the pores of the silica microparticles (Figure 4). However, it was evident that PG8 was less prone to imbibe into the porous matrix compared to C300, with lipid droplets tending to reside between inter-particle cavities, irrespective of the silica type. In contrast, C300 homogeneously distributed throughout the internal structure, with the presence of additional lipid droplets between the particles. Confocal imaging revealed that the lipid distribution within the silica microparticles was dependent on the type of silica and lipid used. More lipid was observed within the internal structure of FS particles than MPS, evidenced by the intensity of the fluorescently labeled lipid within the pores of the silica microparticles (Figure 4). However, it was evident that PG8 was less prone to imbibe into the porous matrix compared to C300, with lipid droplets tending to reside between inter-particle cavities, irrespective of the silica type. In contrast, C300 homogeneously distributed throughout the internal structure, with the presence of additional lipid droplets between the particles.

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**Figure 4.** Confocal images of: (**A**) SLH prepared with FS and (**B**) SLH prepared with MPS. Rhodamine B (red) was used to label silica, and coumarin 6 (green) was used to label lipid. **Figure 4.** Confocal images of: (**A**) SLH prepared with FS and (**B**) SLH prepared with MPS. Rhodamine B (red) was used to label silica, and coumarin 6 (green) was used to label lipid.

### *3.3. In Vitro Dissolution 3.3. In Vitro Dissolution*

The dissolution performance of various SLH prepared with FS and MPS, APO-fenofibrate, and crystalline FEN is reported in Figure 5. The equilibrium solubility of FEN in 0.0125 M SLS (0.36%) was 128 ± 0.01 µg/mL; thus, the study was performed under sink conditions. Crystalline FEN and APO-fenofibrate displayed 7.8% and 25.1% solubilization after 90 min, respectively. At 80% saturation level, all SLH formulations, irrespective of type of silica or lipid, exhibited significantly enhanced FEN dissolution, with FS formulations achieving 70.9–98.1% after 90 min and displaying slightly improved performance compared to MPS formulations (*p* > 0.05). FEN dissolution from FS formulations at 80% Seq corresponded to 8- to 10-fold and 2.6- to 3.2-fold increase in dissolution compared to crystalline FEN and APO-fenofibrate, respectively (*p* < 0.05). However, FEN dissolution from supersaturated SLH formulations was dependent on type of lipid and silica utilized. FS PG8 formulations at all saturation levels (80%, 200%, 400%, 600% Seq) achieved a comparable extent of The dissolution performance of various SLH prepared with FS and MPS, APO-fenofibrate, and crystalline FEN is reported in Figure 5. The equilibrium solubility of FEN in 0.0125 M SLS (0.36%) was 128 ± 0.01 µg/mL; thus, the study was performed under sink conditions. Crystalline FEN and APO-fenofibrate displayed 7.8% and 25.1% solubilization after 90 min, respectively. At 80% saturation level, all SLH formulations, irrespective of type of silica or lipid, exhibited significantly enhanced FEN dissolution, with FS formulations achieving 70.9–98.1% after 90 min and displaying slightly improved performance compared to MPS formulations (*p* > 0.05). FEN dissolution from FS formulations at 80% Seq corresponded to 8- to 10-fold and 2.6- to 3.2-fold increase in dissolution compared to crystalline FEN and APO-fenofibrate, respectively (*p* < 0.05). However, FEN dissolution from supersaturated SLH formulations was dependent on type of lipid and silica utilized. FS PG8 formulations at all saturation levels (80%, 200%, 400%, 600% Seq) achieved a comparable extent of FEN dissolution of ~80% after

FEN dissolution of ~ 80% after 90 min, despite 600% FS PG8 displaying slower release kinetics (*p* >

90 min, despite 600% FS PG8 displaying slower release kinetics (*p* > 0.05) (Figure 5B). In contrast, FEN dissolution was significantly hindered in supersaturated MPS PG8 formulations, with 200% MPS PG8 achieving 43.9% FEN dissolution after 90 min, and was further reduced for 400% and 600% Seq with no significant difference compared to crystalline FEN and APO-fenofibrate (*p* > 0.05). *Pharmaceutics* **2020**, *12*, x FOR PEER REVIEW 12 of 22 formulations, with 200% MPS PG8 achieving 43.9% FEN dissolution after 90 min, and was further reduced for 400% and 600% Seq with no significant difference compared to crystalline FEN and APOfenofibrate (*p* > 0.05).

**Figure 5.** The in vitro dissolution profiles of crystalline FEN, APO-fenofibrate and FEN-loaded SLH formulations (at different saturation levels) in 0.0125 M SLS, dosed at 10 mg of FEN over 90 min at sink conditions. (mean ± SD, *n* = 3). (**A**) SLH C300 formulations, (**B**) SLH PG8 formulations, and (**C**) FEN % dissolution at 90 min vs % Seq. **Figure 5.** The in vitro dissolution profiles of crystalline FEN, APO-fenofibrate and FEN-loaded SLH formulations (at different saturation levels) in 0.0125 M SLS, dosed at 10 mg of FEN over 90 min at sink conditions. (mean ± SD, *n* = 3). (**A**) SLH C300 formulations, (**B**) SLH PG8 formulations, and (**C**) FEN % dissolution at 90 min vs % Seq.

The 200% FS C300 formulation achieved the highest FEN dissolution of 98.1%, which corresponds to approximately 4- and 14-fold increased dissolution compared to APO-fenofibrate and crystalline FEN, respectively (*p* < 0.05). However, this was not statistically significant when compared to 200% FS PG8 (*p* > 0.05). Only 66.8% and 64.6% FEN dissolution was observed from 400% and 600% Seq for FS C300 formulations, respectively. When MPS was utilized to solidify supersaturated C300 LBFs, a similar pattern was observed to supersaturated MPS PG8 formulations (Figure 5C), where the dissolution was significantly reduced with increased supersaturation. 200% MPS C300 achieved 55.2% FEN dissolution, whereas FEN dissolution of only 35.4% and 23.5% was attained from 400% and 600% MPS C300 formulations, respectively, with no significant difference compared to crystalline FEN and APO-fenofibrate (*p* > 0.05). The influence of silica type and saturation level on The 200% FS C300 formulation achieved the highest FEN dissolution of 98.1%, which corresponds to approximately 4- and 14-fold increased dissolution compared to APO-fenofibrate and crystalline FEN, respectively (*p* < 0.05). However, this was not statistically significant when compared to 200% FS PG8 (*p* > 0.05). Only 66.8% and 64.6% FEN dissolution was observed from 400% and 600% Seq for FS C300 formulations, respectively. When MPS was utilized to solidify supersaturated C300 LBFs, a similar pattern was observed to supersaturated MPS PG8 formulations (Figure 5C), where the dissolution was significantly reduced with increased supersaturation. 200% MPS C300 achieved 55.2% FEN dissolution, whereas FEN dissolution of only 35.4% and 23.5% was attained from 400% and 600% MPS C300 formulations, respectively, with no significant difference compared to crystalline FEN and APO-fenofibrate (*p* > 0.05). The influence of silica type and saturation level on FEN dissolution

was evident when FEN dissolution at 90 min was plotted against saturation level (Seq). As displayed in Figure 5C, SLH prepared with FS, irrespective of type of lipid or % Seq, achieved similar extent of dissolution (*p* > 0.05). In contrast, MPS stabilized SLH formulations displayed significant linear reduction in FEN dissolution with an increase in % Seq. The decrease in performance was more profound for MPS PG8 formulations (R<sup>2</sup> = 0.86) than MPS C300 formulations (R<sup>2</sup> = 0.80); however, it was not statistically significant (*p* > 0.05).
