On the Determination of Mechanical Properties of Aqueous Microgels—Towards High-Throughput Characterization

Abstract

Aqueous microgels are distinct entities of soft matter with mechanical signatures that can be different from their macroscopic counterparts due to confinement effects in the preparation, inherently made to consist of more than one domain (Janus particles) or further processing by coating and change in the extent of crosslinking of the core. Motivated by the importance of the mechanical properties of such microgels from a fundamental point, but also related to numerous applications, we provide a perspective on the experimental strategies currently available and emerging tools being explored. Albeit all techniques in principle exploit enforcing stress and observing strain, the realization differs from directly, as, e.g., by atomic force microscope, to less evident in a fluid field combined with imaging by a high-speed camera in high-throughput strategies. Moreover, the accompanying analysis strategies also reflect such differences, and the level of detail that would be preferred for a comprehensive understanding of the microgel mechanical properties are not always implemented. Overall, the perspective is that current technologies have the capacity to provide detailed, nanoscopic mechanical characterization of microgels over an extended size range, to the high-throughput approaches providing distributions over the mechanical signatures, a feature not readily accessible by atomic force microscopy and micropipette aspiration.

Interactions between infernan and calcium: From the molecular level to the mechanical properties of microgels

“…The mechanical properties of infernan-based microgels measured by AFM showed the elastic moduli between 0.8 kPa and 8 kPa, depending on calcium and EPS concentrations. They are similar to the values reported for other microgels based on synthetic and natural polymers (Oevreeide et al, 2021). G'(w) and G''(w) moduli of these microgels correspond to those usually measured for engineered matrices and soft tissues, such as skin, brain and lung (Chaundhuri, Cooper-White, Janmey, Mooney, & Shenoy, 2020).…”

Translating Material Science into Bone Regenerative Medicine Applications: State-of-The Art Methods and Protocols

“…Indeed, while some bone substitutes are designed for prolonged in vivo resistance, other materials such as hydrogels or fast resorbable composites are easily degraded and soft. For these types of samples, micropipette aspiration, atomic force microscopy (AFM)-based nanoindentation, and squeezing in microchannel confinement can be performed for characterization of mechanical properties [ 33 ].…”

Mechanical characterization of soft microparticles prepared by droplet microfluidics

“…As a result, estimation of elastic modulus on a finite‐sized microsphere using this model may lead to deviation from a realistic value. Alternatively, Zhou et al 37 extended this model to consider the finite size of the microsphere through the finite element approach (Figure 6B, right). Through non‐linear regression of their computed finite element method (FEM) results, Equation was derived where each coefficient in the equation is set as, β 1 = 2.0142, β 2 = 2.1186, β 3 = 2.1187, β 4 = −1.4409, and β 5 = 0.3154, respectively.…”

“…Traditional theories employed for the study of spherical microparticles are the Hertz and Reissner theories. Hertz theory is the most simple and common approach to study microsphere mechanics which yields the following Equation for a small deformation induced by a spherical indenter with a radius of R p 37 where F is the force, is the indentation depth, is the effective radius calculated from the radius of the microsphere ( R ) and the indenter ( R p ), E is the Young's modulus, and v is the Poisson's ratio.…”

“…As a result, estimation of elastic modulus on a finite-sized microsphere using this model may lead to deviation from a realistic value. Alternatively, Zhou et al 37 extended this model to consider the finite size of the microsphere through the finite element approach (Figure 6B, right). Through non-linear regression of their computed finite element method (FEM) results, Equation 3 was derived…”