Synthetic growth by self-lubricated photopolymerization and extrusion inspired by plants and fungi.

Many natural organisms, such as fungal hyphae and plant roots, grow at their tips, enabling the generation of complex bodies composed of natural materials as well as dexterous movement and exploration. Tip growth presents an exemplary process by which materials synthesis and actuation are coupled, providing a blueprint for how growth could be realized in a synthetic system. Herein, we identify three underlying principles essential to tip-based growth of biological organisms: a fluid pressure driving force, localized polymerization for generating structure, and fluid-mediated transport of constituent materials. In this work, these evolved features inspire a synthetic materials growth process called extrusion by self-lubricated interface photopolymerization (E-SLIP), which can continuously fabricate solid profiled polymer parts with tunable mechanical properties from liquid precursors. To demonstrate the utility of E-SLIP, we create a tip-growing soft robot, outline its fundamental governing principles, and highlight its capabilities for growth at speeds up to 12 cm/min and lengths up to 1.5 m. This growing soft robot is capable of executing a range of tasks, including exploration, burrowing, and traversing tortuous paths, which highlight the potential for synthetic growth as a platform for on-demand manufacturing of infrastructure, exploration, and sensing in a variety of environments.

Molecular simulation of hopping mechanisms of nanoparticles in regular cross-linked polymer networks.

We use coarse-grained simulations to explore the diffusion mechanism of nanoparticles with different sizes at various nanoparticle-polymer interactions in regular cross-linked polymer networks. The long time diffusivities of nanoparticles show a non-monotonic tendency at various nanoparticle-polymer interactions due to the intermittent hopping of nanoparticles through network cells. The preferred locations of small nanoparticles switch from the cell centers to the corners of cells as they interact with the network more strongly, which results in the hopping energy barrier between different cells switching from cell center localization to adsorption on networks. Steric hindrance seriously hampers large nanoparticles from hopping to neighboring network cells, and the interactions between the nanoparticle and network enhance the network deformability and also affect the hopping of nanoparticles. The multiple constraint mechanisms result in the non-monotonic diffusivities of nanoparticles with different interactions and non-Brownian motions at different time scales. Our work illustrates the hopping mechanisms of nanoparticles in polymer networks from thermodynamic and dynamic points of view.

Molecular simulation of the diffusion mechanism of nanorods in cross-linked networks.

We study the diffusion of rod-shaped nanocarriers with different rigidities and aspect ratios in cross-linked networks using coarse-grained molecular dynamics (CGMD) simulations. The diffusivity of the nanorods increases with a reduction in the rigidities of the nanorods and network, as well as with an increasing aspect ratio with respect to the same volume fraction of the nanorods. The nanorods show an anisotropic diffusion pathway through translocating along their major axes at short time scales, and the anisotropy of diffusion decreases at long time scales. Meanwhile, the diffusion of the nanorods shows a sub-diffusion regime that deviates from Brownian motion in most cases due to the trapping of the nanorods in a cage composed of the network. The nanorod could hop when it escapes from the cage and the hopping behavior depends on the rigidities of both the nanorod and network, as well as the local network density. The rotational motion of the trapped nanorod also enhances the probability of hopping. Our results may help in the understanding of the microscopic mechanism for the diffusion of rod-shaped and other relevant nanocarriers, in a cross-linked network environment.

Porous hollow fibers with controllable structures templated from high internal phase emulsions.

A technique to fabricate hollow fibers with porous walls via templating from high internal phase emulsions (HIPEs) has been demonstrated. This technique provides an environmentally friendly process alternative to conventional methods for hollow-fiber productions that typically use organic solvents. HIPEs containing acrylate monomers were extruded into an aqueous curing bath. Osmotic pressure effects, manipulated through differences in salt concentration between the curing bath and the aqueous phase within the HIPE were used to control the hollow structures of polyHIPE fibers. The technique was used to produce porous fibers (with millimeter-scale diameters and micronscale pores) having a hollow core (with a diameter of 50%-75% of the fiber diameter). Two potential applications of the hollow fibers were demonstrated. In vitro drug release studies using these hollow fibers show a controlled release profile that is consistent with the microstructure of the porous fiber wall. In addition, the presence of pores in the walls of polyHIPE fibers also enable size-selective loading and separation of functional materials from an external suspension.

Oxygen-Induced Bi5+-Self-Doped Bi4V2O11 with a p-n Homojunction Toward Promoting the Photocatalytic Performance.

Bi5+-self-doped Bi4V2O11 (Bi5+-BVO) nanotubes with p-n homojunctions are fabricated via an oxygen-induced strategy. Calcinating the as-spun fibers with abundant oxygen plays a pivotal role in achieving Bi5+ self-doping. Density functional theory calculations and experimental results indicate that Bi5+ self-doping can narrow the band gap of Bi4V2O11, which contributes to enhancing light harvesting. Moreover, Bi5+ self-doping endows Bi4V2O11 with n- and p-type semiconductor characteristics simultaneously, resulting in the construction of p-n homojunctions for retarding rapid electron-hole recombination. Benefiting from these favorable properties, Bi5+-BVO exhibits a superior photocatalytic performance in contrast to that of pristine Bi4V2O11. Furthermore, this is the first report describing the achievement of p-n homojunctions through self-doping, which gives full play to the advantages of self-doping.