Dual-Conductive and Stiffness-Morphing Microneedle Patch Enables Continuous In Planta Monitoring of Electrophysiological Signal and Ion Fluctuation.

The use of conductive microneedles presents a promising solution for achieving high-fidelity electrophysiological recordings with minimal impact on the interfaced tissue. However, a conventional metal-based microneedle suffers from high electrochemical impedance and mechanical mismatch. In this paper, we report a dual-conductive (i.e., both ionic and electronic conductive) and stiffness-morphing microneedle patch (DSMNP) for high-fidelity electrophysiological recordings with reduced tissue damage. The polymeric network of the DSMNP facilitates electrolyte absorption and therefore allows the transition of stiffness from 6.82 to 0.5139 N m-1. Furthermore, the nanoporous conductive polymer increases the specific electrochemical surface area after tissue penetration, resulting in an ultralow specific impedance of 893.13 Ω mm2 at 100 Hz. DSMNPs detect variation potential and action potential in real time and cation fluctuations in plants in response to environmental stimuli. After swelling, DSMNPs mechanically "lock" into biological tissues and prevent motion artifact by providing a stable interface. These results demonstrate the potential of DSMNPs for various applications in the field of plant physiology research and smart agriculture.

Contribution of Surface Energy to pH-Dependent Underwater Adhesion of an Acrylic Pressure-Sensitive Adhesive.

Maintaining the underwater adhesive performance over a broad range of solution pH is challenging but necessary for many biomedical applications. Therefore, understanding how environmental conditions influence the mechanisms of bonding and debonding of pressure-sensitive adhesives (PSAs) can provide guidelines for materials design. We investigate how the presence of acrylic acid as a co-monomer impacts the adhesion of a model PSA in aqueous environments of varying pH. The adhesives under investigation are poly(2-ethylhexyl acrylate), or poly(2-EHA), and poly(2-EHA) co-polymerized with 5 wt % acrylic acid, or poly(2-EHA- co-AA). We characterize bonding and debonding (adhesion) of the adhesives using probe tack measurements with a spherical hydrophobic glass probe. We analyze the performance of the two PSAs in air and in low-ionic-strength buffered aqueous solutions of pH 3- 11. We find that the presence of the acrylic acid co-monomer increases the cohesiveness of the PSA and leads to stronger adhesion under all conditions investigated. We also observe that the presence of the acrylic acid co-monomer imparts the PSA with a strong dependence of adhesion on the solution pH. Dynamic contact angle and ζ potential measurements support the hypothesis that deprotonation of the acrylic acid groups at higher pH causes the decrease in adhesion at higher pH. Rheological measurements do not show changes in the dynamic mechanical properties of the PSAs after exposure to solutions of pH 3- 11. Our measurements allow us to isolate the effect of the solution pH on the surface and bulk properties of the PSA. In the absence of the acrylic acid co-monomer, the bulk dissipation and the surface properties of the PSA are independent of the solution's pH.