Determination of the pH Gradient in Hair Follicles of Human Volunteers Using pH-Sensitive Melamine Formaldehyde-Pyranine Nile Blue Microparticles

Abstract

Nanoparticles can be applied to the hair follicles, which can serve as reservoirs for triggered drug release. A valid measurement method for the determination of the pH within the hair follicle in vivo has not been shown yet. Here, melamine formaldehyde particles up to 9 µm in size were applied on 40 freshly plucked scalp hairs of eight individuals to determine the pH along the hair shaft down to the root area of the hair. For fluorescent pH indicators, pyranine and Nile blue were incorporated into the particles. Measurements were conducted using confocal laser scanning microscopy. A pH decay gradient could be found from the hair sheath towards the external hair shaft (p = 0.012) with pH values at the hair sheath of 6.63 ± 0.09, at the hair sheath end at 6.33 ± 0.11, and at the external hair shaft at 6.17 ± 0.09 (mean ± SE). The pH difference between the hair sheath end and the external hair shaft was found to be significant (p = 0.036). The results might be comparable with the pH within the hair follicle in vivo indicating a pH increase towards the hair root.

Advanced Skin Antisepsis: Application of UVA-Cleavable Hydroxyethyl Starch Nanocapsules for Improved Eradication of Hair Follicle-Associated Microorganisms

“…Numerous previous studies show the possibility of penetration of spherical nanoparticles into hair follicles inducing an enhanced follicular transport of therapeutics [ 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 ] and subsequent triggering of release by various external as well as internal trigger mechanisms. Several physical trigger mechanisms, based on diffusion [ 71 ] or infrared light [ 46 ] as well as chemical trigger mechanisms based on pH [ 72 , 73 ] or proteolysis [ 74 , 75 ] were demonstrated in previous studies. In a recent work, we have already demonstrated an intrafollicular release of the model drug SR101 from UVA-responsive NCs [ 26 ].…”

Selective Delivery of Tofacitinib Citrate to Hair Follicles Using Lipid-Coated Calcium Carbonate Nanocarrier Controls Chemotherapy-Induced Alopecia Areata

“…In addition, PL/ACC NPs with a particle size of ~280 nm had a higher dermal and follicular permeability In a release medium with pH 5.5, about 80.6% of TFC was released from PL/ACC-TFC NPs, but only 40% of TFC was released in a release medium with pH 7.4, indicating that TFC could be successfully released from PL/ACC-TFC NPs in a simulated acidic environment (Figure 2e). The pH of the follicular pore decreased from 6.5 to 4.5 with the deepening of the follicles [17]. PL/ACC-TFC NPs triggered more intense drug release in an acidic condition (pH 5.5) than that in a neutral condition (pH 7.4).…”

Tofacitinib Loaded Squalenyl Nanoparticles for Targeted Follicular Delivery in Inflammatory Skin Diseases

“…It is also important to highlight that a simple correlation between in vitro and in vivo release of TFB SqD NPs cannot be drawn, since the lipid derived SqD NPs would interact differently with the sebum milieu inside the HFs. In addition, the changing pH profile inside HFs was not taken into account [63,64]. Therefore, further in vivo experiments would be necessary to evaluate the release profile of TFB SqD NPs in HFs.…”