Engineering

  • Letter |

    Liquid-crystalline elastomers combine rubber-like elasticity with the optical properties of liquid crystals, yet some of their properties depend on the particular liquid-crystal phase. Now, stretchable gels of the liquid-crystalline blue-phase I are reported. The blue-phase gels are electro-optically switchable under a moderate applied voltage, and their optical properties can be manipulated by an applied strain.

    • F. Castles
    • , S. M. Morris
    •  & H. J. Coles
  • Letter |

    Although human pluripotent stem cells (hPSCs) can be used to regenerate neural tissues, inefficient protocols and poorly defined culture conditions have hindered their use. It is now shown that soft, micropatterned culture substrates can induce hPSCs to differentiate into motor neurons with significantly improved yields and purity in comparison to rigid substrates, and that such mechanotransductive process involves the Hippo/YAP pathway and phosphorylation of the intracellular protein Smad.

    • Yubing Sun
    • , Koh Meng Aw Yong
    •  & Jianping Fu
  • Article |

    The use of encoded microparticles in industrial settings is hampered by issues of scalability, decoding robustness and encoding density. Now, easily decodable microparticles with spatially patterned rare-earth upconversion nanocrystals, exponentially scalable encoding capacities and ultralow decoding false-alarm rates that are insensitive to harsh processing environments and can be used in practical applications such as durable anti-counterfeiting labels and multiplexed bioassays are reported.

    • Jiseok Lee
    • , Paul W. Bisso
    •  & Patrick S. Doyle
  • Article |

    Excessive activity of matrix metalloproteinases (MMPs) occurs in many diseases; however, the systemic administration of MMP inhibitors can cause undesirable, off-target effects and hence, clinical translation has been hampered. Now, injectable polysaccharide-based hydrogels are shown to enable the localized delivery of an inhibitor of MMP following the hydrogels’ degradation in response to MMP activity. This targeted approach shows efficacy in a myocardial infarction model in large animals.

    • Brendan P. Purcell
    • , David Lobb
    •  & Jason A. Burdick
  • Progress Article |

    Microimaging techniques, such as interference and infrared microscopy, can be used as a tool to directly monitor guest profiles within nanoporous materials. Observation of the variation in these profiles leads to unprecedented insight into transport phenomena, including intracrystalline diffusion and surface permeation.

    • Jörg Kärger
    • , Tomas Binder
    •  & Jens Weitkamp
  • Article |

    Mechanical cues from the local cellular microenvironment can direct cell fate. Now, experiments with human mesenchymal stem cells cultured on phototunable soft poly(ethylene glycol) hydrogels show that the cells remember past physical environments—with the transcriptional co-activators YAP and TAZ acting as a mechanical rheostat—and therefore that appropriate doses of mechanical cues can be used to manipulate the cells’ fate.

    • Chun Yang
    • , Mark W. Tibbitt
    •  & Kristi S. Anseth
  • Article |

    The collective migration of epithelial cells arises from the interplay between intercellular forces and cellular signalling networks. It is now shown that the migration of an epithelium can be controlled by applying electric fields that bias the signalling networks, and that such galvanotactic control can prompt cell populations to make coordinated U-turns, undergo divergent or convergent migration, or move against an obstacle.

    • Daniel J. Cohen
    • , W. James Nelson
    •  & Michel M. Maharbiz
  • Progress Article |

    Solar cells based on colloidal quantum dots require specific charge-extraction strategies that take full advantage of the size-tunable absorption properties of the nanoparticles. This Progress Article reviews the recent engineering efforts aimed at maximizing the power-conversion efficiency of these devices by developing novel architectures as well as by optimizing the morphological and electronic properties of both the electrodes and quantum dot layers.

    • Xinzheng Lan
    • , Silvia Masala
    •  & Edward H. Sargent
  • Progress Article |

    Memory devices based on the spin-transfer-torque effect offer a range of attractive properties, such as speed of operation and low energy cost. This Progress Article outlines a strategy for assembling different nanodevices based on the spin-torque effect to achieve qualitatively different computing architectures.

    • N. Locatelli
    • , V. Cros
    •  & J. Grollier
  • Article |

    In wound healing, skin cells collectively migrate to maintain tissue cohesion despite the existence of inhomogeneities in the extracellular environment within the wound bed. Yet how the cell collective responds to heterogeneities in the extracellular matrix is not well understood. Now, it is shown that migrating human keratinocyte cell sheets form suspended multicellular bridges over non-adhesive regions on micropatterned substrates comprising alternating strips of fibronectin and non-adherent polymer.

    • Sri Ram Krishna Vedula
    • , Hiroaki Hirata
    •  & Benoit Ladoux
  • Review Article |

    The clinical application of vaccines has expanded from infectious diseases to cancer, enhancing our vision of how the immune system can be used to prevent and treat disease. This Review highlights recent developments, clinical successes and future challenges in the design of prophylactic, therapeutic and tolerance-inducing synthetic vaccines with inspiration from the natural immune system.

    • Darrell J. Irvine
    • , Melody A. Swartz
    •  & Gregory L. Szeto
  • Review Article |

    The use of macroscopic depots to deliver drugs — including small molecules, protein and cells — at the desired treatment site by using a carrier whose physical and chemical properties control the presentation of the drug increases drug effectiveness and reduces side effects. This Review discusses the advantages of macroscopic drug-delivery systems, the associated mechanisms of spatiotemporal control of drug presentation, and the design and use of multifunctional macroscopic drug-delivery devices.

    • Cathal J. Kearney
    •  & David J. Mooney
  • Article |

    Somatic cells can be reprogrammed into induced pluripotent stem cells biochemically through the expression of a few transcription factors. It is now shown that aligned microgrooves or nanofibres on cell-adhesive substrates can promote the reprogramming of somatic cells more efficiently through epigenetic regulation of genes related to pluripotency and the mesenchymal-to-epithelial transition. The findings suggest that the epigenetic state can be regulated by variations in cell morphology.

    • Timothy L. Downing
    • , Jennifer Soto
    •  & Song Li
  • Article |

    Although the collective cellular motion involved in, for example, wound healing and tumour invasion is suspected to be driven by mechanical stresses within the advancing cell monolayer, how motion and stress relate has remained elusive. Now, stress-microscopy observations of an epithelial cell sheet advancing towards a region where cells cannot adhere reveal that the cells located nearby such a region exert forces that pull them towards the unfilled space, regardless of whether the cells approach or recede from it.

    • Jae Hun Kim
    • , Xavier Serra-Picamal
    •  & Jeffrey J. Fredberg
  • Letter |

    The fabrication of composite microfibres with tunable topography and chemical composition is now possible with a microfluidic method that mimics the fibre-spinning process of spiders. The method allows for the synthesis of a variety of structurally and spatially coded fibres for multiple applications, such as directional water harvesting and the co-culture of encapsulated cells.

    • Edward Kang
    • , Gi Seok Jeong
    •  & Sang-Hoon Lee
  • Letter |

    Three-dimensional photonic devices are of interest as light emitters, detectors or waveguides. However, so far their fabrication has remained a challenge. The template-directed epitaxy of three-dimensional semiconductor structures now offers a new strategy for the realization of photonic devices, demonstrated by the realization of a three-dimensional photonic crystal light-emitting diode.

    • Erik C. Nelson
    • , Neville L. Dias
    •  & Paul V. Braun