Enzymatically Powered Surface-Associated Self-Motile Protocells.

Cell motility is central to processes such as wound healing, immune cell surveillance, and embryonic development. Motility requires the conversion of chemical to mechanical energy. An active area of research is to create motile particles, such as microswimmers, using catalytic and enzymatic reactions. Here, autonomous motion is demonstrated in adhesive polymer-based protocells by incorporating and harnessing the energy production of an enzymatic reaction. Biotinylated polymer vesicles that encapsulate catalase, an enzyme which converts hydrogen peroxide to water and oxygen, are prepared and these vesicles are adhered weakly to avidin-coated surfaces. Upon addition of hydrogen peroxide, which diffuses across the membrane, catalase activity generates a differential impulsive force that enables the breakage and reformation of biotin-avidin bonds, leading to diffusive vesicle motion resembling random motility. The random motility requires catalase, increases with the concentration of hydrogen peroxide, and needs biotin-avidin adhesion. Thus, a protocellular mimetic of a motile cell.

Enzymatically triggered rupture of polymersomes.

Polymersomes are robust vesicles made from amphiphilic block co-polymers. Large populations of uniform giant polymersomes with defined, entrapped species can be made by templating of double-emulsions using microfluidics. In the present study, a series of two enzymatic reactions, one inside and the other outside of the polymersome, were designed to induce rupture of polymersomes. We measured how the kinetics of rupture were affected by altering enzyme concentration. These results suggest that protocells with entrapped enzymes can be engineered to secrete contents on cue.

The effect of stabilizer on the mechanical response of double-emulsion-templated polymersomes.

Recent studies have shown that polymersomes templated by microfluidic double-emulsion possess several advantages such as high monodispersity and encapsulation efficiency compared with those generated based on thin-film rehydration and electroformation. Stabilizers, including bovine serum albumin (BSA) and polyvinyl alcohol (PVA), have been used to enhance the formation and stability of double emulsions that are used as templates for the generation of polymersomes. In this work, the effect of stabilizers on the mechanical response of double-emulsion-templated polymersomes using micropipette aspiration is investigated. It is demonstrated that the existence of stabilizers results in the inelastic response in poly-mersomes in the early stage of solvent removal. However, aged polymersomes that have little residual solvent show elastic behavior. Polymersomes prepared from PVA-stabilized double emulsions have noticeably lower area expansion moduli than polymersomes prepared from stabilizer-free and BSA-stabilized double emulsions, suggesting that PVA is incorporated in the bilayer membrane of polymersomes.

Anisotropic ionic conductivity in block copolymer membranes by magnetic field alignment.

The self-assembly of diblock copolymers provides a convenient route to the formation of mechanically robust films with precise and tunable periodic arrangements of two physically demixed but chemically linked polymeric materials. Chemoselective transport membranes may be realized from such films by selective partitioning of an active species into one of the polymer domains. Here, lithium ions were selectively sequestered within the poly(ethylene oxide) block of a liquid crystalline diblock copolymer to form polymer electrolyte membranes. Optimization of the membrane conductivity mandates alignment of self-assembled structures such that conduction occurs via direct as opposed to tortuous transport between exterior surfaces. We show here that magnetic fields can be used in a very simple and scalable manner to produce highly aligned hexagonally packed cylindrical microdomains in such membranes over macroscopic areas. We systematically explore the dependence of the ionic conductivity of the membrane on both temperature and magnetic field strength. A surprising order of magnitude increase in conductivity relative to the nonaligned case is found in films aligned at the highest magnetic field strengths, 6 T. The conductivity of field aligned samples shows a nonmonotonic dependence on temperature, with a marked decrease on heating in the proximity of the order-disorder transition of the system before increasing again at elevated temperatures. The data suggest that domain-confined transport in hexagonally packed cylindrical systems differs markedly in anisotropy by comparison with lamellar systems.

Electrostatic Assembly of Poly(ethylene glycol) Nanotubes.

Poly(ethylene glycol) (PEG)-based films, nanotubes, and nanotube arrays were successfully made using layer-by-layer (LbL) assembly ion-containing PEO derivatives on porous templates and planar substrates. PEG nanotubes are challenging to produce because PEG dissolves into solutions and solvents used during nanotube processing, but our techniques circumvent the issue. Nanotube dimensions were verified using microscopy and the average observed diameter was 155 nm. The PEG-based structures showed remarkable stability in water, salt water, and sodium hydroxide solution.

Design of Multi-Stage Roll Die Forming Process for Drum Clutch with Artificial Neural Network.

The multi-stage roll die forming (RDF) process is a plastic forming process that can manufacture a transmission part with a complex shape, such as a drum clutch, by using a die set with rotational rolls. However, it is difficult to satisfy dimensional accuracy because of spring-back and unfilling. The purpose of this study is to design a multi-stage RDF process for the manufacturing of a drum clutch to improve dimensional accuracy using an artificial neural network (ANN). Finite element (FE) simulation of the multi-stage RDF process is performed to predict the dimensional accuracy according to various clearances for each stage. Moreover, the ANN is used to determine the relationship between the clearance and dimensional accuracy of the drum clutch to reduce the number of FE simulation. The results of the FE simulation and ANN are used to determine the optimal clearance for each stage of the RDF process. Finally, the drum clutch is fabricated using the determined conditions. The experimental results are in good agreement with the results of FE simulation from the aspect of outer diameter, inner diameter, thickness of outer tooth, thickness of inner tooth, and face thickness of tooth.

Tuning the Mechanical Properties of Recombinant Protein-Stabilized Gas Bubbles Using Triblock Copolymers.

Gas bubbles enhance contrast in ultrasound sonography and can also carry and deliver therapeutic agents. The mechanical properties of the bubble shell play a critical role in determining the physical response of gas bubbles under ultrasound insonation. Currently, few methods allow for tailoring of the mechanical properties of the stabilizing layers of gas bubbles. Here, we demonstrate that blending of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) amphiphilic triblock copolymer with a recombinant protein, oleosin, enables the tuning of the mechanical properties of the bubble stabilizing layer. The areal expansion modulus of gas bubbles, as determined by micropipette aspiration, depends on the structure as well as the concentration of PEO-PPO-PEO triblock copolymers. We believe our method of using a mixture of PEO-PPO-PEO and oleosin can potentially lead to the formation of microbubbles with stabilizing shells that can be functionalized and tailored for specific applications in ultrasound imaging and therapy.

Layer-by-layer assembly of UV-resistant poly(3,4-ethylenedioxythiophene) thin films.

The layer-by-layer assembly technique was used to create electrically conductive films with poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT-PSS) and branched polyethylenimine (BPEI). Titanium dioxide (TiO(2)) and carbon black were used to prevent UV-degradation of these PEDOT-PSS thin film assemblies. Film growth and conductivity were studied, while varying composition and examining the effect of UV absorbing particles on the electrical conductivity. All films showed similar initial sheet resistances, but after exposure to 365 nm UV light for 9 days (correlating to approximately 4 years of sunlight), the films containing TiO(2) were up to 250 times more conductive. Additionally, the TiO(2) containing films were 27% more optically transparent than films made with PEDOT in the absence of TiO(2). The addition of colloidal titania allows the useful life of the PEDOT films to be extended without the detrimental effects of decreased transparency. Doping the PEDOT with dimethylsulfoxide produced eight bilayer films that were almost 6 times more conductive. However, the degradation rate for the doped PEDOT films without TiO(2) was 10 times greater than the doped films with TiO(2).