Poster R4 - Depth-Dependent Mechanical Characterization of Embedded TiO2 Nanoparticles Using Atomic Force Microscopy: Implications for Biomechanical Analysis

Introduction: Atomic force microscopy (AFM) is instrumental in probing the biomechanical properties of cells and tissues. Its precision in detecting nanoscale objects at various depths, however, may impact the accuracy of such measurements. Titanium dioxide (TiO2) nanoparticles are particularly relevant due to their adjustable mechanical properties and biocompatibility, which makes them suitable for biomedical applications. This study assesses AFM's ability to detect and characterize TiO2 nanoparticles under a polymer layer, quantifies the impact of particle depth on mechanical property measurements, and explores the implications for biological AFM applications, which typically involve three-dimensional, heterogeneous, and anisotropic samples.

Materials and

Methods: TiO2 nanoparticles, with diameters of approximately 300 nm and 900 nm, were embedded at various depths within a poly(methyl methacrylate) (PMMA) matrix on a glass substrate. The PMMA was spin-coated into multiple layers, each approximately 500 nm thick. Four layers were applied atop a thick PMMA substrate on the glass, exceeding 2 microns in thickness, with the particles interspersed between each layer for different samples. Thus, the depth of the embedded particles at each layer was known, ranging from 500 nm to 2000 nm, estimated by the thickness of each layer. We conducted AFM analysis at varied scan rates (0.1, to 2 Hz) and trigger voltages (0.1, to 1 V). Mechanical properties, including Young’s modulus and adhesion force, were assessed for both nanoparticle sizes at each depth and under each AFM setting.

Results, Conclusions, and Discussions:

Results: AFM successfully detected and distinguished between the two sizes of TiO2 nanoparticles within the PMMA matrix. The Young's modulus for the nanoparticles decreased as the embedment depth increased, irrespective of the nanoparticle size. This trend was more pronounced at lower scan rates and trigger voltages. Although adhesion forces also varied with depth, these changes were less consistent than those observed for Young's modulus.

Discussion and

Conclusions: Our findings confirm the feasibility of using AFM to characterize nanoscale objects within a polymer matrix and emphasize the need to account for embedment depth when assessing mechanical properties. Understanding this depth sensitivity is crucial to enhancing the utility of bio-AFM in complex biological systems. The depth-dependent variations in Young's modulus may be attributed to several factors, including alterations in the local mechanical environment around the nanoparticles and the interaction between nanoparticle and polymer properties at the AFM tip-sample interface. This study offers crucial insights for refining AFM parameters to enhance the biomechanical analysis of cells and tissues incorporating nanoscale components. Future research should focus on clarifying the mechanisms driving these depth effects and developing methods to adjust for these influences in AFM measurements.

Acknowledgements (Optional):