A light-driven artificial flytrap

The sophistication, complexity and intelligence of biological systems is a continuous source of inspiration for mankind. Mimicking the natural intelligence to devise tiny systems that are capable of self-regulated, autonomous action to, for example, distinguish different targets, remains among the grand challenges in biomimetic micro-robotics. Herein, we demonstrate an autonomous soft device, a light-driven flytrap, that uses optical feedback to trigger photomechanical actuation. The design is based on light-responsive liquid-crystal elastomer, fabricated onto the tip of an optical fibre, which acts as a power source and serves as a contactless probe that senses the environment. Mimicking natural flytraps, this artificial flytrap is capable of autonomous closure and object recognition. It enables self-regulated actuation within the fibre-sized architecture, thus opening up avenues towards soft, autonomous small-scale devices.


Supplementary Note 1: Order parameter.
In order to measure the order parameter of the polymeric network, a uniaxially aligned liquid crystalline elastomer (LCE) thin film was prepared using the same polymerization conditions as for the splay-aligned film used for preparing flytrap, and its absorption spectra parallel and perpendicular to the molecular director were measured. The LC cell was formed by using PVA-coated glass slides (rubbed in the same direction) with a separation distance of 5 µm, followed by infiltration of the same LC monomer mixture, polymerized in an identical manner as explained in the Methods Section. The The order parameter, S p , can be calculated as where ⫽ and ' are the measured absorbance values with light polarized parallel and perpendicular to the LC alignment, respectively. S p is determined to be 0.59 for the homogeneously aligned sample, by averaging the data in wavelength range 525 -575 nm. . (1) The change of central angle dγ at an equilibrium stage depends on the absorbed light power E of the LCE stripe: where k is the light-induced bending coefficient (k = 0.8 rad·mW -1 for a 6 mm long LCE stripe). The key of the calculation is to find out the specific form of E(P, d, γ), which depends on light power P, distance d and the deformed geometry (γ). For constant P and d, the LCE deforms into a well-defined, stable state. The central angle γ can be obtained by solving the equation where γ 0 is the original central angle of a 6 mm long LCE, γ 0 = -112°, α 0 = 236° (a negative value of γ 0 , or say, α 0 > 180° is due to the inner stress in the photo-polymerized LCE film).
For a general case, E can be obtained using a surface integral We apply this calculation method to one of the simplest cases -bending in front of a flat mirror, as schematically illustrated in Supplementary Figure 6b. Due to the mirror symmetry, the whole light illumination can be considered as a light cone with its apex at the fiber tip mirror-symmetric position (LCE'). The distance between the fiber tip and the light source is 2d, and the entire absorption occurs inside the LCE stripe whose area depends on the bending arc geometry (γ). As can be seen ) where a is the horizontal distance between LCE edge and the fiber center, b is the vertical distance between LCE edge and the light source and an approximated average distance between the LCE and the light source.

Supplementary
k / is the Gaussian beam radius.
For R s > a, For R s ≤ a, where l = 0.5 mm is the half length of the non-actuated region on the LCE stripe (gluing part).
Combining Supplementary equations (9) and (10)  Note that upon approaching to the closure stage the device reaches a small gripping angle, α < 50°, and the deformed geometry deviates significantly from the arc geometry approximation; at small distances, d < 5 mm, the size of the LCE becomes comparable with the distance, enhancing the inaccuracy in the approximation treatment by using an average distance . Thus, there exists a relatively large divergence between the calculated and experimental results at large │dα│ and small d regimes.
All numerical calculations are performed with Matlab R2013a.