Roadmap for Optical Tweezers 2023

Optical tweezers are tools made of light that enable contactless pushing, trapping, and manipulation of objects ranging from atoms to space light sails. Since the pioneering work by Arthur Ashkin in the 1970s, optical tweezers have evolved into sophisticated instruments and have been employed in a broad range of applications in life sciences, physics, and engineering. These include accurate force and torque measurement at the femtonewton level, microrheology of complex fluids, single micro- and nanoparticle spectroscopy, single-cell analysis, and statistical-physics experiments. This roadmap provides insights into current investigations involving optical forces and optical tweezers from their theoretical foundations to designs and setups. It also offers perspectives for applications to a wide range of research fields, from biophysics to space exploration

Developing a Multimodal System to Study Cellular Injuries, with the Focus on Traumatic Brain Injury

Traumatic Brain Injury (TBI) is a significant public health concern. The Centers for DiseaseControl and Prevention reported a notable increase in TBI-related incidents from 2006 to 2014. TBI occurs when an external force disrupts the normal function of the brain, leading to a range of outcomes, from mild to severe, with consequences ranging from full neurological recovery to mortality. Despite advances, TBI remains a leading cause of physical impairment and death, particularly among young people. This work focuses on developing a multimodal microscopy system that includes a custom- made, cost-effective Quantitative Phase Microscope (QPM) that is a pivotal tool in label-free imaging of transparent specimens, especially in cell biology. This microscopy system supports fluorescence imaging, enhancing flexibility for studying cellular structures and dynamics. The microscopy system is a promising tool for simulating traumatic brain injury in vitro, as it is integrated with a Laser-Induced Shockwave (LIS) system. The LIS system generates con- trolled shockwaves for brief shear stress applications to replicate conditions similar to those experienced in TBI. Optical Trapping (OT), using continuous laser light manipulation, is also combined with the LIS system, creating a versatile platform to investigate the interplay between shockwaves and optical trapping effects on biological specimens, particularly for xi single-cell manipulation. This integrated approach significantly improves the understand- ing of dynamic cellular responses, morphological changes, and intracellular dynamics under controlled conditions. A section of the thesis is dedicated to quantitative phase image processing, providing method- ologies to convert raw camera images into precise heightmaps, and addressing challenges in cell segmentation and feature extraction. The chapter aims to equip researchers with scien- tifically accurate tools for analyzing cellular structures. In the final chapter, we investigate the response of astrocyte cells to laser-induced shock- waves, focusing on morphological characteristics such as surface area, volume, and circular- ity. We chose astrocytes as the focal point of this investigation because astrocytes undergo a defense mechanism called astrogliosis when triggered. The experimental setup involves control and shockwave-exposed groups in a custom-made heating chamber with tightly con- trolled environmental conditions. Statistical analysis reveals significant differences in cellular parameters, providing insights into the impact of shockwaves on astrocyte cell morphology. This chapter contributes to understanding cellular responses to mechanical stimuli and opens avenues for further investigations into underlying mechanisms. Overall, the thesis offers a scientific exploration of advanced microscopy techniques and their applications in studying cellular dynamics and responses

Simulating Traumatic Brain Injury (TBI) using laser-induced shockwave under quantitative phase microscopy

Traumatic brain injury (TBI) occurs when an external shock causes injury to the brain. The mechanism of the disease is not completely understood yet. Studies have shown that astrocytes play various roles following brain injury. However, the exact functional role of them after TBI is still a matter of debate. Laser-induced shock waves (LIS) can create a precise controllable mechanical force that is capable of injuring or lysing cells to simulate the brain injury at the cellular level. Here, we propose a system that enables us to induce injuries in CNS cells with LIS and observe the whole process under a Quantitative phase microscope (QPM). Our system is also capable of adding another laser for optically trapping the cells to keep them at a certain distance from the center of the shockwave, as this distance is one of the important factors which determines the level of injury

Fluid Shear Stress Enhances the Phagocytic Response of Astrocytes.

Astrocytes respond to brain injury at a cellular level by the process of reactive astrogliosis, and are able to adjust their response according to the severity of the insult. Included in the reactive response is the process of phagocytosis, where astrocytes clean up surrounding cellular debris from damaged cells. In this study, we observe the process of phagocytosis by primary cortical astrocytes in the presence of media flow across the apical surface of the cells. Both static and cells under flow conditions respond consistently via phagocytosis of laser-induced cellular debris. We found that astrocytes exposed to shear flow initiate phagocytosis at a consistently faster rate than cells observed under static conditions. Shear forces created by laminar flow were analyzed as well as the flow fields created around astrocyte cells. Results suggest astrocyte phagocytosis is a mechanosensitive response, thus revealing the potential to enhance astrocyte phagocytic cleanup of damaged nervous tissue

Fluid Shear Stress Enhances the Phagocytic Response of Astrocytes.

Astrocytes respond to brain injury at a cellular level by the process of reactive astrogliosis, and are able to adjust their response according to the severity of the insult. Included in the reactive response is the process of phagocytosis, where astrocytes clean up surrounding cellular debris from damaged cells. In this study, we observe the process of phagocytosis by primary cortical astrocytes in the presence of media flow across the apical surface of the cells. Both static and cells under flow conditions respond consistently via phagocytosis of laser-induced cellular debris. We found that astrocytes exposed to shear flow initiate phagocytosis at a consistently faster rate than cells observed under static conditions. Shear forces created by laminar flow were analyzed as well as the flow fields created around astrocyte cells. Results suggest astrocyte phagocytosis is a mechanosensitive response, thus revealing the potential to enhance astrocyte phagocytic cleanup of damaged nervous tissue

A method to study cellular injuries using optical trapping combined with laser-induced shockwaves under quantitative phase microscope

There is a need for new methodologies to investigate cell apoptosis and recovery, cell adhesion, and cell-cell interactions in cellular biology and neurobiology. Such systems should be able to induce localized cell injuries and measure damage responses from single cells. In this regard, pulsed lasers can be used to produce Laser- Induced Shockwaves (LIS), which can cause cell detachments and induce cellular membrane injuries, by applying shear force in order of μN. Furthermore, since the resulting shear force can increase membrane permeability, chemicals and markers can then be transferred into cells non-invasively. Continuous-wave lasers can be used as Optical Tweezers (OT), to apply non-contact delicate forces, as low as 0.1f N, and deliver materials into cells, and also move the cells to different locations. In this paper, we introduce a combination of modalities to apply variable forces, from femto to micro newtons, to cells. Our system consists of a 1060nm continuous laser light source for OT and a 1030nm femtosecond pulsed laser for generating LIS. To have a direct measurement of changes in the cellular thickness and membrane dynamics, the cells are imaged under a Quantitative Phase Microscope (QPM). Our microscope is capable of Differential-Interference Microscopy (DIC) and Phase-Contrast microscopy (PhC) and fluorescent microscopy, making it a unique system for studying cell injuries