Device and programming abstractions for spatiotemporal control of active micro-particle swarms.

We present a hardware setup and a set of executable commands for spatiotemporal programming and interactive control of a swarm of self-propelled microscopic agents inside a microfluidic chip. In particular, local and global spatiotemporal light stimuli are used to direct the motion of ensembles of Euglena gracilis, a unicellular phototactic organism. We develop three levels of programming abstractions (stimulus space, swarm space, and system space) to create a scripting language for directing swarms. We then implement a multi-level proof-of-concept biotic game using these commands to demonstrate their utility. These device and programming concepts will enhance our capabilities for manipulating natural and synthetic swarms, with future applications for on-chip processing, diagnostics, education, and research on collective behaviors.

Liquid-handling Lego robots and experiments for STEM education and research.

Liquid-handling robots have many applications for biotechnology and the life sciences, with increasing impact on everyday life. While playful robotics such as Lego Mindstorms significantly support education initiatives in mechatronics and programming, equivalent connections to the life sciences do not currently exist. To close this gap, we developed Lego-based pipetting robots that reliably handle liquid volumes from 1 ml down to the sub-µl range and that operate on standard laboratory plasticware, such as cuvettes and multiwell plates. These robots can support a range of science and chemistry experiments for education and even research. Using standard, low-cost household consumables, programming pipetting routines, and modifying robot designs, we enabled a rich activity space. We successfully tested these activities in afterschool settings with elementary, middle, and high school students. The simplest robot can be directly built from the widely used Lego Education EV3 core set alone, and this publication includes building and experiment instructions to set the stage for dissemination and further development in education and research.

Microfluidic assembly kit based on laser-cut building blocks for education and fast prototyping.

Here, we present an inexpensive rapid-prototyping method that allows researchers and children to quickly assemble multi-layered microfluidic devices from easily pre-fabricated building blocks. We developed low-cost (<$2) kits based on laser-cut acrylic building block pieces and double-sided tape that allow users to generate water droplets in oil, capture living cells, and conduct basic phototaxis experiments. We developed and tested a 90-min lesson plan with children aged 12-14 yr and provide here the instructions for teachers to replicate these experiments and lessons. All parts of the kit are easy to make or order. We propose to use such easy to fabricate kits in labs with no access to current microfluidic tools as well as in classroom environments to get exposure to the powerful techniques of microfluidics.

Time capsule: an autonomous sensor and recorder based on diffusion-reaction.

We describe the use of chemical diffusion and reaction to record temporally varying chemical information as spatial patterns without the need for external power. Diffusion of chemicals acts as a clock, while reactions forming immobile products possessing defined optical properties perform sensing and recording functions simultaneously. The spatial location of the products reflects the history of exposure to the detected substances of interest. We refer to our device as a time capsule and show an initial proof of principle in the autonomous detection of lead ions in water.

Ferromagnetic inks facilitate large scale paper recycling and reduce bleach chemical consumption.

Deinking is a fundamental part of paper recycling. As the global paper consumption rises and exceeds even the annual paper production, recycling of this raw material is of high importance. Magnetic ink based on carbon coated magnetic nanoparticles enables an alternative approach to state of the art paper deinking. Magnetic deinking comprises three steps (preselection, washing, and magnetic separation of fibers). Preseparation of printed from nonprinted scraps of paper is feasible and reduces the paper mass which has to be fed into a deinking process. A consecutive washing process removes surficial magnetic ink that can be collected by application of a permanent magnet. Still, printed parts are subjected to a further continuous magnetic deinking step, where magnetic and nonmagnetic paper fibers can be separated. Magnetic deinking of a model print allows recovery of more than 80% of bright fibers without any harsh chemical treatment and the re-collection of more than 82% of magnetic ink.

Incorporation of penicillin-producing fungi into living materials to provide chemically active and antibiotic-releasing surfaces.

Living materials: artificial biological niches are loaded with the penicillin-producing mold Penicillium chrysogenum. This living material consumes food through a nanoporous top layer and releases the antibiotic on-site. No reloading of the active compound is needed. Gram-positive bacteria were efficiently killed if nearby, whereas Gram-negative bacteria (control experiment, not sensitive to penicillin) were not affected.

Phosphate starvation as an antimicrobial strategy: the controllable toxicity of lanthanum oxide nanoparticles.

Lanthanum oxide nanoparticles were utilized to scavenge phosphate from microbial growth media for the use of targeted nutrient starvation as an antimicrobial strategy. Only in phosphate poor environments a toxic effect was observed. The effect was shown on Escherichia coli, Staphylococcus carnosus, Penicillium roqueforti, and Chlorella vulgaris.

Incorporating microorganisms into polymer layers provides bioinspired functional living materials.

Artificial two-dimensional biological habitats were prepared from porous polymer layers and inoculated with the fungus Penicillium roqueforti to provide a living material. Such composites of classical industrial ingredients and living microorganisms can provide a novel form of functional or smart materials with capability for evolutionary adaptation. This allows realization of most complex responses to environmental stimuli. As a conceptual design, we prepared a material surface with self-cleaning capability when subjected to standardized food spill. Fungal growth and reproduction were observed in between two specifically adapted polymer layers. Gas exchange for breathing and transport of nutrient through a nano-porous top layer allowed selective intake of food whilst limiting the microorganism to dwell exclusively in between a confined, well-enclosed area of the material. We demonstrated a design of such living materials and showed both active (eating) and waiting (dormant, hibernation) states with additional recovery for reinitiation of a new active state by observing the metabolic activity over two full nutrition cycles of the living material (active, hibernation, reactivation). This novel class of living materials can be expected to provide nonclassical solutions in consumer goods such as packaging, indoor surfaces, and in biotechnology.

Nanoparticle cytotoxicity depends on intracellular solubility: comparison of stabilized copper metal and degradable copper oxide nanoparticles.

Metal nanoparticles have distinctly different chemical and physical properties than currently investigated oxides. Since pure metallic nanoparticles are igniting at air, carbon stabilized copper nanoparticles were used as representative material for this class. Using copper as a representative example, we compare the cytotoxicity of copper metal nanoparticles stabilized by a carbon layer to copper oxide nanoparticles using two different cell lines. Keeping the copper exposure dose constant, the two forms of copper showed a distinctly different response. Whilst copper oxide had already been reported to be highly cytotoxic, carbon-coated copper nanoparticles were much less cytotoxic and more tolerated. Measuring the two material's intra- and extracellular solubility in model buffers explained this difference on the basis of altered copper release when supplying copper metal or the corresponding oxide particles to the cells. Control experiments using pure carbon nanoparticles were used to exclude significant surface effects. Reference experiments with ionic copper solutions confirmed a similar response of cultures if exposed to copper oxide nanoparticles or ionic copper. These observations are in line with a Trojan horse-type mechanism and illustrate the dominating influence of physico-chemical parameters on the cytotoxicity of a given metal.