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Micropore Closure Rates following Microneedle Application at Various Anatomical Sites in Healthy Human Subjects
Abayomi Tolulope Ogunjimi1, Christine Lawson1, Jamie Carr1
1Department of Pharmaceutical Sciences and Experimental Therapeutics, University of Iowa College of Pharmacy, Iowa City, Iowa, USA.
Introduction:
The continuous availability of open micropores is crucial for a successful microneedle (MN) drug delivery strategy. However, micropore lifetime depends on intrinsic skin functional and anatomical characteristics, which vary significantly at different anatomical sites.
Objective:
This pilot study explored if differences exist in micropore closure timeframes at 3 anatomical sites - upper arm, volar forearm, and abdomen.
Methods:
Healthy subjects (n = 35) self-identifying as Asian (n = 9), Bi-/multiracial (n = 2), Black (n = 9), Latino (n = 6), and White (n = 9) completed the study. The upper arm, volar forearm, and abdomen were treated with MNs; skin impedance and transepidermal water loss (TEWL) were measured at baseline and post-MN to confirm micropore formation. Impedance was measured for 3 days to evaluate micropore lifetime. Measurements of L*, which quantifies the skin lightness/darkness, were made using a tristimulus colorimeter. Micropore lifetime was determined by comparing baseline and post-MN impedance measurements, and micropore closure half-life was predicted using mathematical modeling.
Results:
Post-MN increase in TEWL and decrease in impedance were significant (p < 0.05), confirming successful micropore formation at all anatomical sites. When data were analyzed according to subject self-identified racial/ethnic groups, the mean micropore closure time at the abdomen (63.09 ± 13.13 h) was longer than the upper arm (60.34 ± 14.69 h) and volar forearm (58.29 ± 16.76 h). The predicted micropore closure half-life at anatomical sites was the abdomen (25.86 ± 14.96 h) ≈ upper arm (23.69 ± 13.67 h) > volar forearm (20.2 ± 11.99 h). Differences were not statistically significant between groups. Objective categorization by L* showed that the darker skin may be associated with longer micropore closure time at the abdomen site.
Conclusions:
Our results suggest that anatomical site of application may not be a source of significant variability in micropore closure time. These findings may help reduce the number of physiological parameters that need to be explicitly considered when developing drug products to support MN-assisted drug delivery strategies.
Insights
Micropore closure time after microneedle (MN) application varied slightly across anatomical sites, with the abdomen showing the longest duration. These findings suggest anatomical site may not significantly impact MN drug delivery strategies.
Area of Science:
- Dermatology
- Biomedical Engineering
- Pharmacology
Background:
- Continuous availability of open micropores is essential for microneedle (MN) drug delivery.
- Micropore lifetime is influenced by intrinsic skin characteristics, which differ across anatomical sites.
Purpose of the Study:
- To investigate potential differences in micropore closure timeframes at the upper arm, volar forearm, and abdomen.
- To assess the impact of anatomical location on microneedle-mediated drug delivery efficacy.
Main Methods:
- Healthy subjects (n=35) underwent microneedle treatment on the upper arm, volar forearm, and abdomen.
- Skin impedance and transepidermal water loss (TEWL) were measured to confirm micropore formation.
- Impedance measurements over 3 days, along with mathematical modeling, were used to determine micropore closure half-life.
Main Results:
- Micropore formation was confirmed by significant increases in TEWL and decreases in impedance across all sites.
- The abdomen exhibited the longest mean micropore closure time (63.09 ± 13.13 h), followed by the upper arm and volar forearm.
- Predicted micropore closure half-lives were longest for the abdomen (25.86 ± 14.96 h) and upper arm (23.69 ± 13.67 h) compared to the volar forearm (20.2 ± 11.99 h).
- Darker skin tones (L* values) showed a potential association with longer micropore closure times at the abdomen.
Conclusions:
- Anatomical site of application does not appear to be a major source of variability in micropore closure time.
- These findings can simplify the development of drug products for microneedle-assisted drug delivery by reducing the number of physiological parameters to consider.
