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1. Self‐Folding Using Capillary Forces

   https://doi.org/10.1002/admi.201901677  

   Kwok, Kam Sang ; Huang, Qi ; Mastrangeli, Massimo ; Gracias, David H. ( December 2019 , Advanced Materials Interfaces)

   Self‐folding broadly refers to the assembly of 3D structures by bending, curving, and folding without the need for manual or mechanized intervention. Self‐folding is scientifically interesting because self‐folded structures, from plant leaves to gut villi to cerebral gyri, abound in nature. From an engineering perspective, self‐folding of sub‐millimeter‐sized structures addresses major hurdles in nano‐ and micro‐manufacturing. This review focuses on self‐folding using surface tension or capillary forces derived from the minimization of liquid interfacial area. Due to favorable downscaling with length, at small scales capillary forces become extremely large relative to forces that scale with volume, such as gravity or inertia, and to forces that scale with area, such as elasticity. The major demonstrated classes of capillary force assisted self‐folding are discussed. These classes include the use of rigid or soft and micro‐ or nano‐patterned precursors that are assembled using a variety of liquids such as water, molten polymers, and liquid metals. The authors outline the underlying physics and highlight important design considerations that maximize rigidity, strength, and yield of the assembled structures. They also discuss applications of capillary self‐folding structures in engineering and medicine. Finally, the authors conclude by summarizing standing challenges and describing future trends.

    

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2. Nonprehensile manipulation of a stick using impulsive forces

   https://doi.org/10.1007/s11071-022-07826-4  

   Khandelwal, Aakash ; Kant, Nilay ; Mukherjee, Ranjan ( January 2023 , Nonlinear Dynamics)
3. Self-assembly of shapes at constant scale using repulsive forces

   https://doi.org/https://doi.org/10.1007/s11047-018-9707-9  

   Luchsinger, Austin ; Schweller, Robert ; Wylie, Tim ( March 2019 , Natural computing)

   The algorithmic self-assembly of shapes has been considered in several models of self-assembly. For the problem of shape construction, we consider an extended version of the two-handed tile assembly model, which contains positive (attractive) and negative (repulsive) interactions. As a result, portions of an assembly can become unstable and detach. In this model, we utilize fuel-efficient computation to perform Turing machine simulations for the construction of the shape. In this paper, we show how an arbitrary shape can be constructed using an asymptotically optimal number of distinct tile types (based on the shape’s Kolmogorov complexity). We achieve this at O(1) scale factor in this straightforward model, whereas all previous results with sublinear scale factors utilize powerful self-assembly models containing features such as staging, tile deletion, chemical reaction networks, and tile activation/deactivation. Furthermore, the computation and construction in our result only creates constant-size garbage assemblies as a byproduct of assembling the shape. 

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4. Controlled microparticle separation using whispering gallery mode forces

   https://doi.org/10.1016/j.ifacol.2020.12.2519  

   Chang, Yuhe ; Svitelskiy, Oleksiy ; Ekinci, Kamil L. ; Andersson, Sean B. ( January 2020 , IFAC-PapersOnLine)

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5. Controlled microparticle separation using whispering gallery mode forces

   Chang, Yuhe ; Svitelskiy, Oleksiy ; Ekinci, Kamil L ; Andersson, Sean B ( July 2020 , IFAC World Congress)

   There is a wide variety of applications that require sorting and separation of micro- particles from a large cluster of similar objects. Existing methods can distinguish micro-particles by their bulk properties, such as their size, density, and electric polarizability. These methods, however, are not selective with respect to the individual geometry of the particles. In this work, we focus on the use of a resonance effect between a microparticle and an evanescent light field known as the Whispering Gallery Mode (WGM) force. The WGM force is highly sensitive to the radius of the particle and is both controllable and tunable. In this paper, we explore through simulation the design of a WGM-based device for micro-particle separation. In this device, particles flow in through an inlet and are carried over two actuation regions given by waveguides carrying laser light to generate the evanescent field. Particles are observed by a camera, allowing for feedback control on the power of the lasers. While the basic control structure is simple, there are several challenges, including unknown disturbances to the fluid flow, limited laser power, and uni-directional control over each actuation region. We combine Expectation Maximization with Kalman filtering to both estimate the unknown disturbance and filter the measurements into a position estimate. We then develop simple hybrid controllers and compare them to the ideal setting (without any constraints) based on a Linear–Quadratic–Gaussian (LQG) control approach. 

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