Mechanosensitive Polymer Matrices of Biologically-Relevant Compliance Based on Upconverting Nanoparticles

Area of Science:

• Biomaterials Science
• Nanotechnology
• Biophysics

Background:

• Upconverting nanoparticles (UCNPs) are effective optical force sensors with desirable properties like low toxicity and photostability.
• Previous UCNP force sensors used polystyrene, limiting their application to tissues with specific mechanical properties.
• A need exists for UCNP-based sensors applicable to a wider range of biological tissues with varying stiffness.

Purpose of the Study:

• To develop versatile polymer-UCNP composite materials for optical biomechanical force sensing.
• To investigate the impact of different polymer matrices and UCNP core-shell architectures on force sensitivity.
• To demonstrate the in situ application of these composites for measuring forces in biological systems.

Main Methods:

• Embedded UCNPs into three polymer matrices: epoxy resin, polydimethylsiloxane, and alginate hydrogels.
• Investigated two core-shell architectures of SrLuF-based UCNPs with varying dopant concentrations.
• Calibrated force sensitivity using atomic force microscopy and confocal microscopy, employing the red to green emission ratio as the readout.
• Demonstrated macroscale force mapping in situ on a chicken bone joint.

Main Results:

• The SrLuF:YbErMn @ SrYF UCNP composite in epoxy resin showed the highest sensitivity (12 Δ%I_Red:I_Green per microNewton).
• Different polymer matrices and UCNP architectures significantly influenced the mechanosensitivity of the composites.
• The epoxy-UCNP composite successfully mapped forces on a macroscale in situ.

Conclusions:

• UCNP-polymer composites offer a modular and adaptable platform for optical force sensing.
• This technology can be applied to geometrically and mechanically diverse biological systems.
• The developed composites enable non-invasive, real-time measurement of biomechanical forces.