Determination of Stiffness and the Elastic Modulus of 3D-Printed Micropillars with Atomic Force Microscopy–Force Spectroscopy

Abstract

Nowadays, many applications in diverse fields are taking advantage of micropillars such as optics, tribology, biology, and biomedical engineering. Among them, one of the most attractive is three-dimensional microelectrode arrays for in vivo and in vitro studies, such as cellular recording, biosensors, and drug delivery. Depending on the application, the micropillar's optimal mechanical response ranges from soft to stiff. For long-term implantable devices, a mechanical mismatch between the micropillars and the biological tissue must be avoided. For drug delivery patches, micropillars must penetrate the skin without breaking or bending. The accurate mechanical characterization of the micropillar is pivotal in the fabrication and optimization of such devices, as it determines whether the device will fail or not. In this work, we demonstrate an experimental method based only on atomic force microscopy−force spectroscopy that allows us to measure the stiffness of a micropillar and the elastic modulus of its constituent material. We test our method with four different types of 3D inkjet-printed micropillars: silver micropillars sintered at 100 and 150 °C and polyacrylate microstructures with and without a metallic coating. The estimated elastic moduli are found to be comparable with the corresponding bulk values. Furthermore, our findings show that neither the sintering temperature nor the presence of a thin metal coating plays a major role in defining the mechanical properties of the micropillar.

Ultrasoft and High-Adhesion Block Copolymers for Neuromorphic Computing

“…In the pursuit of stable device performance, the importance of strong adhesion and low-modulus materials cannot be overstated. , To precisely quantify alterations in the elastic modulus and adhesion of the TBCs thin films, we employed atomic force microscopy (AFM) for characterization, − which works by analyzing the deflection of the cantilever tip when interacting with a sample surface (Figure A). This method provides intricate details about nanoscale interactions and material properties. − Here, we evaluated the interfacial adhesion by retracting the AFM cantilever from the TBCs films.…”

In Situ Nanomechanical Characterization Techniques for Soft Bioelectronic Interfaces and Their Building Blocks

“…Reproduced under the terms of the CC‐BY 4.0 license. [ 73 ] Copyright 2023, The Authors, published by American Chemical Society. e) SEM image of the nanopillars under investigation.…”

“…However, delamination or damage of the encapsulation layer dramatically decreases the performance of the device. Cortelli et al [ 73 ] showcased an experimental approach solely relying on AFM force spectroscopy, which furnished measurements for both the stiffness of a micropillar and the elastic modulus of its constituent material. This methodology was validated using four distinct varieties of 3D inkjet‐printed micropillars: silver micropillars sintered at temperatures of 100 °C and 150 °C and polyacrylate microstructures with and without a metallic coating.…”

“…Ultimate strength Nanowires Kim et al [70] Elastic modulus Nanofibers Morel et al [71] Elastic modulus Nanowires Antsov et al [72] Bending stiffness Micropillars Cortelli et al [73] Bending stiffness and failure stress Nanopillars Angeloni et al [74] Bending stiffness Thin films Abrahamians et al [75] Elastic modulus Thin films Cortelli et al [76] Fatigue Thin films Kim et al [78] lars, or thin films. Table 2 reports a summary of the in situ bending tests and the characterized micromechanical properties described below.…”

“…d) SEM image of PA 3D inkjet printed with a thin metallic coating and a schematic of the AFM experimental setup to investigate their bending. Reproduced under the terms of the CC-BY 4.0 license [73]. Copyright 2023, The Authors, published by American Chemical Society.…”