In vivo investigation of temporal effects and drug delivery induced by transdermal microneedles with optical coherence tomography

Evaluation of 3D Printability and Biocompatibility of Microfluidic Resin for Fabrication of Solid Microneedles

In this study, we have employed Digital Light Processing (DLP) printing technology for the fabrication of solid microneedle (MN) arrays. Several arrays with various geometries, such as cones, three-sided pyramids and four-sided pyramids, with different height to aspect ratios of 1:1, 2:1 and 3:1, were printed. Post-processing curing optimizations showed that optimal mechanical properties of the photocurable resin were obtained at 40 °C and 60 min. Ex vivo skin studies showed that piercing forces, penetration depth and penetration width were affected by the MN geometry and height to aspect ratio. Cone-shaped MNs required lower applied forces to penetrate skin and showed higher penetration depth with increasing height to aspect ratio, followed by three-sided and four-sided printed arrays. Cytotoxicity studies presented 84% cell viability of human fibroblasts after 2.5 h, suggesting the very good biocompatibility of the photocurable resin. Overall, DLP demonstrated excellent printing capacity and high resolution for a variety of MN designs.

Short-Term Follow-Up of a Randomized Controlled Trial of 0.5% and 5% 5-Fluorouracil After Microneedling for Treatment of Facial Actinic Keratoses

INTRODUCTION

Topical 5-fluorouracil (5-FU) is used to treat actinic keratosis, although side effects limit treatment. Microneedling might be a tool for reducing treatment duration.

OBJECTIVE

To evaluate microneedling to promote 5-FU delivery at different concentrations (0.5% and 5%) for actinic keratoses (AKs) treatment.

METHODS

Forty-four patients with facial AKs subjected to 1.0 mm microneedling on 1 side of the face were randomized into 5% 5-FU or 0.5% 5-FU groups. Evaluations of efficacy and safety were conducted on days 21 and 111.

RESULTS

Forty-four patients aged 47 to 85 years were enrolled. Complete clearance of AKs was similar within groups for the side of the face treated with microneedling and 5-FU and the side treated with 5-FU alone in both the 5% and 0.5% 5-FU groups. Microneedling and 5% 5-FU was superior to microneedling and 0.5% 5-FU to reduce AKs (p = .025). Microneedling and 5% 5-FU resulted in fewer adverse effects than 5% 5-FU alone (p = .011).

CONCLUSION

Topical 5% and 0.5% 5-FU delivery for 3 days after microneedling was effective for treating facial AKs and equivalent to 5% and 0.5% 5-FU alone for 15 days after 3 months of follow-up. Microneedling may potentiate 5-FU treatment, reducing treatment time without losing efficacy.

Bioimaging of Dissolvable Microneedle Arrays: Challenges and Opportunities

The emergence of microneedle arrays (MNAs) as a novel, simple, and minimally invasive administration approach largely addresses the challenges of traditional drug delivery. In particular, the dissolvable MNAs act as a promising, multifarious, and well-controlled platform for micro-nanotransport in medical research and cosmetic formulation applications. The effective delivery mostly depends on the behavior of the MNAs penetrated into the body, and accurate assessment is urgently needed. Advanced imaging technologies offer high sensitivity and resolution visualization of cross-scale, multidimensional, and multiparameter information, which can be used as an important aid for the evaluation and development of new MNAs. The combination of MNA technology and imaging can generate considerable new knowledge in a cost-effective manner with regards to the pharmacokinetics and bioavailability of active substances for the treatment of various diseases. In addition, noninvasive imaging techniques allow rapid, receptive assessment of transdermal penetration and drug deposition in various tissues, which could greatly facilitate the translation of experimental MNAs into clinical application. Relying on the recent promising development of bioimaging, this review is aimed at summarizing the current status, challenges, and future perspective on in vivo assessment of MNA drug delivery by various imaging technologies.

Engineering Microneedle Patches for Improved Penetration: Analysis, Skin Models and Factors Affecting Needle Insertion

Transdermal microneedle (MN) patches are a promising tool used to transport a wide variety of active compounds into the skin. To serve as a substitute for common hypodermic needles, MNs must pierce the human stratum corneum (~ 10 to 20 µm), without rupturing or bending during penetration. This ensures that the cargo is released at the predetermined place and time. Therefore, the ability of MN patches to sufficiently pierce the skin is a crucial requirement. In the current review, the pain signal and its management during application of MNs and typical hypodermic needles are presented and compared. This is followed by a discussion on mechanical analysis and skin models used for insertion tests before application to clinical practice. Factors that affect insertion (e.g., geometry, material composition and cross-linking of MNs), along with recent advancements in developed strategies (e.g., insertion responsive patches and 3D printed biomimetic MNs using two-photon lithography) to improve the skin penetration are highlighted to provide a backdrop for future research.

Effect of A-scan rate and interscan interval on optical coherence angiography

Optical coherence tomography angiography (OCTA) can provide rapid, volumetric, and noninvasive imaging of tissue microvasculature without the requirement of exogenous contrast agents. To investigate how A-scan rate and interscan time affected the contrast and dynamic range of OCTA, we developed a 1.06-µm swept-source OCT system enabling 100-kHz or 200-kHz OCT using two light sources. After system settings were carefully adjusted, almost the same detection sensitivity was achieved between the 100-kHz and 200-kHz modalities. OCTA of ear skin was performed on five mice. We used the variable interscan time analysis algorithm (VISTA) and the designated scanning protocol with OCTA images reconstructed through the correlation mapping method. With a relatively long interscan time (e.g., 12.5 ms vs. 6.25 ms for 200-kHz OCT), OCTA can identify more intricate microvascular networks. OCTA image sets with the same interscan time (e.g., 12.5 ms) were compared. OCTA images acquired with a 100-kHz A-scan rate showed finer microvasculature than did other imaging modalities. We performed quantitative analysis on the contrast from OCTA images reconstructed with different A-scan rates and interscan time intervals in terms of vessel area, total vessel length, and junction density.

Ultrahigh-resolution optical coherence tomography/angiography with an economic and compact supercontinuum laser

In this study, a Q-switch pumped supercontinuum laser (QS-SCL) is used as a light source for in vivo imaging via ultrahigh-resolution optical coherence tomography and angiography (UHR-OCT/OCTA). For this purpose, an OCT system based on a spectral-domain detection scheme is constructed, and a spectrometer with a spectral range of 635 - 875 nm is designed. The effective full-width at half maximum of spectrum covers 150 nm, and the corresponding axial and transverse resolutions are 2 and 10 µm in air, respectively. The relative intensity noise of the QS-SCL and mode-locked SCL is quantitatively compared. Furthermore, a special processing algorithm is developed to eliminate the intrinsic noise of QS-SCL. This work demonstrates that QS-SCLs can effectively reduce the cost and size of UHR-OCT/OCTA instruments, making clinical applications feasible.

Quantitative two-photon microscopy imaging analysis of human skin to evaluate enhanced transdermal delivery by hybrid-type multi-lamellar nanostructure

Transdermal skin delivery is a method to transport various topical formulations to a deeper skin layer non-invasively. Permeability analysis of many delivering agents has been mostly conducted by a simple tape stripping method. However, it cannot reveal a detailed depth-dependent distribution profile of transdermally delivered agents in the skin. In this work, we achieved a cellular-level depth-defined visualization of fluorophore-labelled human epidermal growth factor (EGF) transdermally delivered to human skin by using encapsulation with common liposomes and newly fabricated multi-lamellar nanostructures using a custom-design two-photon microscopy system. It was able to generate 3D reconstructed images displaying the distribution of human EGF inside the human skin sample with high-resolution. Based on a depthwise fluorescence intensity profile showing the permeation of human EGF, a quantitative analysis was performed to assess the transdermal delivery efficacy achieved by each formulation, showing a significant improvement of the efficacy with the utilization of multi-lamellar nanostructure.

In vivo studies of transdermal nanoparticle delivery with microneedles using photoacoustic microscopy

Microneedle technology allows micron-sized conduits to be formed within the outermost skin layers for both localized and systemic delivery of therapeutics including nanoparticles. Histological methods are often employed for characterization, and unfortunately do not allow for the in vivo visualization of the delivery process. This study presents the utilization of optical resolution-photoacoustic microscopy to characterize the transdermal delivery of nanoparticles using microneedles. Specifically, we observe the in vivo transdermal delivery of gold nanoparticles using microneedles in mice ear and study the penetration, diffusion, and spatial distribution of the nanoparticles in the tissue. The promising results reveal that photoacoustic microscopy can be used as a potential imaging modality for the in vivo characterization of microneedles based drug delivery.

Iron Oxide Nanoparticle-Powered Micro-Optical Coherence Tomography for in Situ Imaging the Penetration and Swelling of Polymeric Microneedles in the Skin

In recent years, polymeric microneedles (MNs) have attracted keen interests among researchers because of their applicability in transdermal drug delivery and interstitial skin fluid (ISF) extraction. When designing and characterizing such devices, it is critical to monitor their real-time in vitro and in vivo performances to optimize the desired effects, yet most of the existing methods are incapable of such functions. To address this unmet need, we develop a real-time noninvasive imaging methodology by integrating iron oxide (Fe₃O₄) nanoparticles into polymeric MNs to enhance image contrast for micro-optical coherence tomography (μOCT) imaging. Using the Fe₃O₄-integrated polystyrene-block-poly(acrylic acid) (PS-b-PAA) MNs as an example, we evaluate the influences of Fe₃O₄ concentrations on contrast enhancement in μOCT imaging and visualize the real-time swelling process of polymeric MNs in biological samples for the first time. Our results show that a concentration of ∼4-5 wt % Fe₃O₄ nanoparticles not only helps achieve the best contrast-to-noise ratio in μOCT imaging, which is 10 times higher than that without Fe₃O₄ nanoparticles in air and hydrogel, but also enables the real-time changes in the profile of MNs to be observed clearly in their swelling process in skin tissues. On the basis of such findings, we utilize the optimized concentration of Fe₃O₄ nanoparticles to further quantitatively study the swelling kinetics of PS-b-PAA MNs in agarose hydrogel and fresh skin tissues, which lasts ∼20 and ∼30-35 s, respectively. The suitability of such a methodology for enhancing μOCT imaging would greatly facilitate the development and clinical translation of MN-based medical technologies.