A Biogenic Photovoltaic Material.

A proof-of-concept for the fabrication of genetically customizable biogenic materials for photovoltaic applications is presented. E. coli is first genetically engineered to heterologously express the carotenoid biosynthetic pathway from plants. This modification yields a strain that overproduces the photoactive pigment lycopene. The pigment-producing cells are then coated with TiO2 nanoparticles via a tryptophan-mediated supramolecular interface, and subsequent incorporation of the resulting biogenic material (cells@TiO2 ) as an anode in an I- /I3- -based dye-sensitized solar cell yields an excellent photovoltaic (PV) response. This work lays strong foundations for the development of bio-PV materials and next-generation organic optoelectronics that are green, inexpensive, and easy to manufacture.

Wastewater Mediated Activation of Micromotors for Efficient Water Cleaning.

We present wastewater-mediated activation of catalytic micromotors for the degradation of nitroaromatic pollutants in water. These next-generation hybrid micromotors are fabricated by growing catalytically active Pd particles over thin-metal films (Ti/Fe/Cr), which are then rolled-up into self-propelled tubular microjets. Coupling of catalytically active Pd particles inside the micromotor surface in the presence of a 4-nitrophenol pollutant (with NaBH4 as reductant) results in autonomous motion via the bubble-recoil propulsion mechanism such that the target pollutant mixture (wastewater) is consumed as a fuel, thereby generating nontoxic byproducts. This study also offers several distinct advantages over its predecessors including no pH/temperature manipulation, limited stringent process control and complete destruction of the target pollutant mixture. The improved intermixing ability of the micromotors caused faster degradation ca. 10 times higher as compared to its nonmotile counterpart. The high catalytic efficiency obtained via a wet-lab approach has promising potential in creating hybrid micromotors comprising of multicatalytic systems assembled into one entity for sustainable environmental remediation and theranostics.

Colon or semicolon: gut sampling microdevices for omics insights.

Ingestible microdevices represent a breakthrough in non-invasive sampling of the human gastrointestinal (GI) tract. By capturing the native spatiotemporal microbiome and intricate biochemical gradients, these devices allow a non-invasive multi-omic access to the unperturbed host-microbiota crosstalk, immune/nutritional landscapes and gut-organ connections. We present the current progress of GI sampling microdevices towards personalized metabolism and fostering collaboration among clinicians, engineers, and data scientists.

An Ingestible Self-Polymerizing System for Targeted Sampling of Gut Microbiota and Biomarkers.

A proof-of-concept for the fabrication of a self-polymerizing system for sampling of gut microbiome in the upper gastrointestinal (GI) tract is presented. An orally ingestible microdevice is loaded with the self-polymerizing reaction mixture to entrap gut microbiota and biomarkers. This polymerization reaction is activated in the aqueous environment, like fluids in the intestinal lumen, and causes site-specific microsampling in the gastrointestinal tract. The sampled microbiota and protein biomarkers can be isolated and analyzed via high-throughput multiomic analyses. The study utilizes a hollow microdevice (Su-8, ca. 250 µm), loaded with an on-board reaction mixture (iron chloride, ascorbic acid, and poly(ethylene glycol) diacrylate monomers) for diacrylate polymerization in the gut of an animal model. An enteric-coated rat capsule was used to orally gavage these microdevices in a rat model, thereby, protecting the microdevices in the stomach (pH 2), but releasing them in the intestine (pH 6.6). Upon capsule disintegration, the microdevices were released in the presence of luminal fluids (in the small intestine region), where iron chloride reacts with ascorbic acid, to initiate poly(ethylene glycol) diacrylate polymerization via a free radical mechanism. Upon retrieval of the microdevices, gut microbiota was found to be entrapped in the polymerized hydrogel matrix, and genomic content was analyzed via 16s rRNA amplicon sequencing. Herein, the results show that the bacterial composition recovered from the microdevices closely resemble the bacterial composition of the gut microenvironment to which the microdevice is exposed. Further, histological assessment showed no signs of local tissue inflammation or toxicity. This study lays a strong foundation for the development of untethered, non-invasive microsampling technologies in the gut and advances our understanding of host-gut microbiome interactions, leading to a better understanding of their commensal behavior and associated GI disease progression in the near future.

Orally ingestible medical devices for gut engineering.

Orally ingestible medical devices provide significant advancement for diagnosis and treatment of gastrointestinal (GI) tract-related conditions. From micro- to macroscale devices, with designs ranging from very simple to complex, these medical devices can be used for site-directed drug delivery in the GI tract, real-time imaging and sensing of gut biomarkers. Equipped with uni-direction release, or self-propulsion, or origami design, these microdevices are breaking the barriers associated with drug delivery, including biologics, across the GI tract. Further, on-board microelectronics allow imaging and sensing of gut tissue and biomarkers, providing a more comprehensive understanding of underlying pathophysiological conditions. We provide an overview of recent advances in orally ingestible medical devices towards drug delivery, imaging and sensing. Challenges associated with gut microenvironment, together with various activation/actuation modalities of medical devices for micromanipulation of the gut are discussed. We have critically examined the relationship between materials-device design-pharmacological responses with respect to existing regulatory guidelines and provided a clear roadmap for the future.

Thread-Like Radical-Polymerization via Autonomously Propelled (TRAP) Bots.

Micromotor-mediated synthesis of thread-like hydrogel microstructures in an aqueous environment is presented. The study utilizes a catalytic micromotor assembly (owing to the presence of a Pt layer), with an on-board chemical reservoir (i.e., polymerization mixture), toward thread-like radical-polymerization via autonomously propelled bots (i.e., TRAP bots). Synergistic coupling of catalytically active Pt layer, together with radical initiators (H2 O2 and FeCl3 (III)), and PEGDA monomers preloaded into the TRAP bot, results in the polymerization of monomeric units into elongated thread-like hydrogel polymers coupled with self-propulsion. Interestingly, polymer generation via TRAP bots can also be triggered in the absence of hydrogen peroxide for cellular/biomedical application. The resulting polymeric hydrogel microstructures are able to entrap living cells (NIH 3T3 fibroblast cells), and are easily separable via a centrifugation or magnetic separation (owing to the presence of a Ni layer). The cellular biocompatibility of TRAP bots is established via a LIVE/DEAD assay and MTS cell proliferation assay (7 days observation). This is the first study demonstrating real-time in situ hydrogel polymerization via an artificial microswimmer, capable of enmeshing biotic/abiotic microobjects in its reaction environment, and lays a strong foundation for advanced applications in cell/tissue engineering, drug delivery, and cleaner technologies.

Micromotors for drug delivery in vivo: The road ahead.

Autonomously propelled/externally guided micromotors overcome current drug delivery challenges by providing (a) higher drug loading capacity, (b) localized delivery (less toxicity), (c) enhanced tissue penetration and (d) active maneuvering in vivo. These microscale drug delivery systems can exploit biological fluids, as well as exogenous stimuli, like light-NIR, ultrasound and magnetic fields (or a combination of these), towards propulsion/drug release. Ability of these wireless drug carriers towards localized targeting and controlled drug release, makes them a lucrative candidate for drug administration in complex microenvironments (like solid tumors or gastrointestinal tract). In this report, we discuss these microscale drug delivery systems for their therapeutic benefits under in vivo setting and provide a design-application rationale towards greater clinical significance. Also, a proof-of-concept depicting 'microbots-in-a-capsule' towards oral drug delivery has been discussed.

Bionic Manufacturing: Towards Cyborg Cells and Sentient Microbots.

Bio-inspired engineering applies biological design principles towards developing engineering solutions but is not practical as a manufacturing paradigm. We advocate 'bionic manufacturing', a synergistic fusion of biotic and abiotic components, to transition away from bio-inspiration toward bio-augmentation to address current limitations in bio-inspired manufacturing.

Autonomously propelled microscavengers for precious metal recovery.

We report biogenic micromotor design consisting of porous chalky elongated tubes (∼60 µm length) coated with Fe-Pt for dual functionality i.e. metallic gold formation and rapid isolation. These autonomously propelled scavengers once introduced in the reaction environment, showed rapid bubble-propulsion followed by high-purity separation of the visually-distinguishable gold metal particles (yellow in colour) from the reaction mixture. The concept presented here has excellent potential towards environmentally sustainable metal recovery, micron-level metal/mineral particulate extraction, electronic waste treatment and similar redox product separation among others.

Medibots: Dual-Action Biogenic Microdaggers for Single-Cell Surgery and Drug Release.

An innovative concept for the fabrication of dual-action microrobots capable of performing single-cell microsurgery along with a site-directed drug-delivery feature is presented. These multi-action plant-derived biocompatible "medibots" can play a pivotal role in understanding micromotor interactions at the cellular level, aiming toward the destruction of harmful cells (like cancer) among others in living systems.

Biogenic synthesis and characterization of gold nanoparticles by Escherichia coli K12 and its heterogeneous catalysis in degradation of 4-nitrophenol.

Room-temperature extracellular biosynthesis of gold nanoparticles (Au NPs) was achieved using Escherichia coli K12 cells without the addition of growth media, pH adjustments or inclusion of electron donors/stabilizing agents. The resulting nanoparticles were analysed by ultraviolet-visible (UV-vis) spectrophotometry, atomic force microscopy, transmission electron microscopy and X-ray diffraction. Highly dispersed gold nanoplates were achieved in the order of around 50 nm. Further, the underlying mechanism was found to be controlled by certain extracellular membrane-bound proteins, which was confirmed by Fourier transformation-infrared spectroscopy and sodium dodecyl sulfate polyacrylamide gel electrophoresis. We observed that certain membrane-bound peptides are responsible for reduction and subsequent stabilization of Au NPs (confirmed by zeta potential analysis). Upon de-activation of these proteins, no nanoparticle formation was observed. Also, we prepared a novel biocatalyst with Au NPs attached to the membrane-bound fraction of E. coli K12 cells serving as an efficient heterogeneous catalyst in complete reduction of 4-nitrophenol in the presence of NaBH4 which was studied with UV-vis spectroscopy. This is the first report on bacterial membrane-Au NP nanobiocomposite serving as an efficient heterogeneous catalyst in complete reduction of nitroaromatic pollutant in water.