Rapid prototyping of fiber-optic based micro-force sensors by two-photon polymerization

Ruiz-Cadalso, Daniel A.

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Rapid prototyping of fiber-optic based micro-force sensors by two-photon polymerization

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We have developed a 3D printed fiber-optic based micro-sensors for measurement of dynamically induced micro- to nano-Newton forces. The force-sensing transduction mechanism is based on a series of mechanical micro-springs and an optically reflective micro-plate with axial movement that are embedded at the distal end of single-mode optical fibers. These micro-sensors have low-stiffness, making them suitable for characterization of biomedical samples and soft materials, and are rapid prototyped by two-photon polymerization methods. By physical vapor deposition, a thin gold coating is added to the micro-plate to reflect the fiber’s output laser beam back into its core for subsequent quantification of force-induced phase changes, which are measured by interferometric methods. After conducting investigations to characterize the elastic properties of solidified photoresists for the selected fabrication parameters, which include laser power and exposure time, we designed and tuned the springs to perform over specific ranges of forces and displacements. The mechanical springs are characterized and calibrated by MEMS micro-force sensing probes attached to motorized nano-positioners to detect forces from 100 nano-Newtons to 500 micro-Newtons. We report the performance of the newly developed micro-force sensors as applied to several applications, including measurements of acoustically induced forces on the Tympanic Membrane surface to better understand hearing and middle-ear mechanics.

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