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Device Technologies and Biomedical Robotics

Device Technologies and Biomedical Robotics - Poster Session D

Poster I14 - Optimization of Solid Polymeric Microneedle Design for Enhanced Puncture Performance in Non-Invasive Monitoring of Interstitial Macromolecules with Simplified Fabrication Methods

Friday, October 25, 2024
3:30 PM - 4:30 PM EST
Location: Exhibit Hall E, F & G

Introduction:  As diabetes becomes increasingly widespread, rapid advancements in biotechnology and biosensors are addressing this growing challenge. According to the World Health Organization (2023), Globally, about 422 million people have diabetes, predominantly in low- and middle-income countries, and it causes 1.5 million deaths annually [1]. Focusing on human-centered design and the latest advancements in interstitial-glucose sensing technologies, this project aims to develop a wearable multi-marker sensor for diabetes. The goal is to enhance continuous diabetes care by providing non-invasive, real-time monitoring of key biomarkers.

A critical aspect of this research is effective puncture testing, focusing on microneedle arrays (MNAs) for continuous glucose monitoring. The design of these MNAs aims to optimize the surface area of gold-sputtered electrodes in contact with interstitial fluid (ISF). The MNAs, ranging from 700 to 1200 μm in length, are engineered to penetrate the stratum corneum and epidermis to reach the dermis, where ISF containing glucose and hormonal markers can be reliably accessed. Due to variations in skin thickness across different demographics (age, location, gender, and race), multiple skin models are used to represent these differences, ensuring the sensor’s effectiveness across diverse conditions.

Moreover, this research emphasizes combining facile fabrication techniques with improved understanding of the variables in a microneedle array and what truly allows them to effectively puncture skin to the desired extent [2]. These advancements not only enhance usability but also hold promise for broader adoption across various applications in health monitoring.

Materials and

Methods:  Microneedle arrays (MNAs) were created using laser-engraved Plexiglass acrylic sheets to form conical molds, optimized with Design of Experiments (DOE) for precise aspect ratios. Conical holes in the plexiglass were filled with PDMS, allowed to harden, and treated in a 1 M hydrochloric acid bath to oxidize the surface. Additional PDMS was then poured over the oxidized MNAs to produce a durable master mold for biocompatible needle casting. The MNAs were gold-sputtered and patterned into three-pronged electrodes (reference, working, and counter) connected to enameled 0.1 mm copper wire leads which ran through the body of the MNAs for electrochemical (e-chem) measurements [2].

A Design of Experiments (DOE) approach was employed to assess MNA performance in puncturing. Variables such as needle spacing, insertion speed, tip spacing, needle width, aspect ratio, and polymer type were analyzed. Response variables included average puncture depth and the number of successful punctures. Puncture tests were performed using the Mach-1 Micromechanical System with neonatal pig skin and layered Parafilm to simulate human skin [3]. The Mach-1 was programmed to lower the top plate, attached to a load cell, at various speeds to model different insertion velocities. Force measurements were recorded as the distance from the initial position varied. Graphs generated from these tests recorded the insertion force required for each MNA. Post-insertion, samples were treated with indicator dye to visualize punctures and analyzed with light microscopy to measure puncture depth.

Results, Conclusions, and Discussions: Data from the Design of Experiments (DOE) enabled the optimization of polymeric, conical, solid microneedles for effective dermal interaction and simulated interstitial fluid (ISF) monitoring. By fine-tuning the design based on polymer type and needle length, we achieved the desired puncture depth, ensuring patient comfort while accurately capturing ISF signals. Reliable ISF measurements are essential for monitoring glucose levels, reflecting both glucose diffusion from the blood and local metabolism [4]. Microneedles must range from 700 μm to 1200 μm in length to accurately detect electrochemical signals for glucose and other macromolecules [5-6]. This parameter optimization ensures reproducibility and cost-effectiveness in microneedle production, enhancing testing efficiency compared to outsourced molds.

While this research primarily focused on microneedle arrays, its implications extend to other non-invasive biosensors. The advancements in microneedle technology open new opportunities for developing sensors tailored to various health conditions, including hyperkalemia and other metabolic disorders. Given that approximately 129 million people in the U.S. suffer from at least one major chronic disease [7], there is a pressing need for effective, accessible monitoring solutions. This research lays a foundation for universities and lower-budget labs to innovate and create cost-effective, non-invasive diagnostic tools. Such advancements could significantly improve chronic disease management, patient outcomes, and overall health management strategies, expanding the reach and impact of advanced biosensing technologies.

Acknowledgements (Optional):  This work was funded by the Helmsley Charitable Trust. We would also like to recognize Brayden Nungesser for his contributions to much of the preliminary research for this study.