Figure 1.
Volume-weighted size distributions of microfluidic-enabled (a) PEGylated and (b) anionic liposomes, revealing narrow size distributions over the full size range from 31 nm to 308 nm.
Figure 2.
Brightfield/fluorescence image overlays (top) and single-channel fluorescence images (bottom) for microtomed tissue sections following 15 min application of PEGylated or anionic liposome samples of varying diameters containing DiI lipophilic dye.
Significant dye penetration past the SC is observed with the smallest liposomes (31 nm diameter PEGylated and 41 nm anionic liposomes), while dye from the larger vesicles does not appear to cross the SC, indicating size-based passive transport independent of surface charge.
Figure 3.
DiI fluorescence intensity plot profiles for (a) PEGylated liposomes and (b) anionic liposomes as a function of porcine skin tissue penetration depth.
Measurements were performed 15 minute following liposome application. Each curve is representative of an average of 5 ROIs per image.
Figure 4.
Percentage of total DiI fluorescence signal seen below the SC for the different sizes of PEGylated and anionic liposomes.
Each plot reflects the average profile extracted from 5 ROIs per tissue section, with error bars reflecting standard deviation. SC thickness, estimated from averaged manual measurements using brightfield images of each tissue, ranged from 15 μm to 40 μm, in general agreement with previously reported values for porcine skin [32]. The small 31 nm PEGylated liposomes pass the SC in large numbers (91%), which is up to 590% greater than the larger 105 nm to 308 nm diameter liposomes. The small 41 nm anionic liposomes also reveal 65% of their total DiI signal under the SC, which is 200% greater than observed with 256 nm diameter liposomes of the same composition.
Figure 5.
Brightfield images of 3 representative tissue regions following application of 31(top), together with matched single channel fluorescence images for lipophilic DiI (middle) and hydrophilic SF (bottom).
Similar fluorescence distributions for both dyes are seen across multiple tissue sections, indicating successful penetration of intact liposomes through the epithelium.
Figure 6.
Penetration depth profiles of lipophilic and hydrophilic liposomal dyes within a tissue section following 15 min application of 31 nm PEGyated liposomes simultaneously loaded with both dyes.
Each curve is representative of an average of 5 ROIs per image. A Pearson's correlation coefficient of ρ = 0.92 reveals a high degree of colocalization between the dyes.