Controlled Origami Folding of Hydrogel Bilayers with Sustained Reversibility for Robust Microcarriers

Abstract

Microencapsulation and controlled release have long been studied because of the high demand for practical delivery systems in the pharmaceutics and cosmetics fields. Multiphase emulsion drops have provided efficient templates for microcapsules, and various feasible methods have been developed for controlled release.[1] However, the emulsion-based approach has limitations for the in situ control of membrane permeability. Micro-origami has emerged as one of the most promising alternative approaches for producing tunable microcapsules with the potential to be applied, for example as drug carriers, [2] actuators, [3] microcontainers, [4] and microrobots.[5] Inspired by living organisms in nature such as the ice plant [6] and Venus flytrap, [7] two different micro-origami approaches have been employed to make various microstructures.[8] One approach uses solid patches connected by active hinge materials. Typical examples use various metalmetal, [9] metal-polymer, [10] and polymer-polymer [4] combinations. The patch and hinge system has enabled the capture, release, and gripping [11] of target materials, showing the feasibility of micro-origami structures. However, the microcapsule is limited to polyhedral shapes in this approach, and complete sealing of the gaps between patches requires exquisite control of the folding angles. Moreover, the delicate and complex fabrication processes make practical applications difficult. The second approach uses a bilayer structure composed of two different materials. For example, a metalpolymer bilayer can show bending/unbending when the polymeric active layer suffers significant volume change, but the metal layer remains unchanged. [12,13] Polymer materials have been employed in both layers to make biocompatible microcapsules. [14,15] However, complete sealing of the gaps in the bilayer contact regions remains an important, yet unmet, need. In addition, a simple and effective method for the fabrication of practical microcapsules has not yet been developed, and remains highly desirable. This is the main thrust of the present study.Herein, we report the use of biocompatible bilayer structures for the fabrication of tunable microcapsules based on micro-origami. Monodisperse bilayer microstructures were prepared using a facile photolithographic procedure, without employing photomask alignment. In addition, highly flexible hydrogels were selected as both active and passive layers, facilitating tight contact between patches. The bilayer structure therefore enabled in situ encapsulation, through a reversible transformation to microcapsules with a closed compartment. The resultant microcapsules showed negligible leakage of encapsulants and triggered release of the encapsulants could be achieved simply by inducing the unfolding of the hydrogel bilayer.The essential strategy of our approach relies on the anisotropic volume change of a hydrogel bilayer. As shown in Scheme 1 a, the active hydrogel layer shows significant volume expansion under external stimuli by swelling, whereas the passive h...

Capillary micromechanics for core–shell particles

“…Such microparticles with core-shell structures are especially important for applications such as encapsulation and controlled release, 20 contrast enhancement in ultrasonic imaging and photonics [8][9][10][11][12][13][14]4,2,3 . In these applications, the mechanical properties of core-shell microcapsules are of key importance.…”

“…In these applications, the mechanical properties of core-shell microcapsules are of key importance. Mechanical properties control the conditions under which the core-shell microcapsules are deformed elastically, plastically or even ruptured [15][16][17][18][19][20][21][22][23][24] . They 25 directly determine the volumetric and shape changes of the microcapsules under an applied external stress 25,26 , which for soft and biological materials can be surprisingly large.…”

“…The overall properties of such particles will 15 depend on the bulk properties of both the shell and the core material, as well as the internal structure of the particles. To control and understand the mechanics of these systems, it is thus essential to investigate and understand the relationship between the respective properties of core and shell, their microstructures 20 and their effects on the overall mechanical properties of the microparticles. Based on such understanding, design principles can be established allowing us to precisely tailor the mechanical behavior of composite microparticles to a desired application.…”

Biomimicry, Biofabrication, and Biohybrid Systems: The Emergence and Evolution of Biological Design

“…microscopic spheres, with potential applications as drug delivery devices or microrobots. [9] These spheres are composed of an active hydrogel layer, poly(2-hydroxyethyl methacrylate-coacrylic acid), and a passive hydrogel layer, poly(2-hydroxyethyl methacrylate). At basic pH levels, the active layer swelled, forming a closed hollow microsphere.…”

Pine cone scale-inspired motile origami

“…The shape transformation of soft materials also has potential applications in tissue engineering 23 : differential swelling or shrinkage creates internal stresses in the composite hydrogel sheet and transforms its shape in a specific manner. Biocompatible bilayer structures are used to fabricate tunable micro-capsules applied as robust micro-carriers 24 . Controlled motion of functional materials has various technical applications.…”