Tissue engineering aims at developing functional substitutes for damaged tissues and organs. Before transplantation, cells are generally seeded on biomaterial scaffolds that recapitulate the extracellular matrix and provide cells with information that is important for tissue development. Here we review the nanocomposite nature of the extracellular matrix, describe the design considerations for different tissues and discuss the impact of nanostructures on the properties of scaffolds and their uses in monitoring the behaviour of engineered tissues. We also examine the different nanodevices used to trigger certain processes for tissue development, and offer our view on the principal challenges and prospects of applying nanotechnology in tissue engineering.

We report electrical properties of hybrid structures consisting of arrays of nanowire field-effect transistors integrated with the individual axons and dendrites of live mammalian neurons, where each nanoscale junction can be used for spatially resolved, highly sensitive detection, stimulation, and/or inhibition of neuronal signal propagation. Arrays of nanowire-neuron junctions enable simultaneous measurement of the rate, amplitude, and shape of signals propagating along individual axons and dendrites. The configuration of nanowire-axon junctions in arrays, as both inputs and outputs, makes possible controlled studies of partial to complete inhibition of signal propagation by both local electrical and chemical stimuli. In addition, nanowire-axon junction arrays were integrated and tested at a level of at least 50 "artificial synapses" per neuron.

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Two-dimensional electron and hole gas systems, enabled through band structure design and epitaxial growth on planar substrates, have served as key platforms for fundamental condensed matter research and high-performance devices. The analogous development of one-dimensional (1D) electron or hole gas systems through controlled growth on 1D nanostructure substrates, which could open up opportunities beyond existing carbon nanotube and nanowire systems, has not been realized. Here, we report the synthesis and transport studies of a 1D hole gas system based on a free-standing germanium͞silicon (Ge͞Si) core͞shell nanowire heterostructure. Room temperature electrical transport measurements clearly show hole accumulation in undoped Ge͞Si nanowire heterostructures, in contrast to control experiments on singlecomponent nanowires. Low-temperature studies show wellcontrolled Coulomb blockade oscillations when the Si shell serves as a tunnel barrier to the hole gas in the Ge channel. Transparent contacts to the hole gas also have been reproducibly achieved by thermal annealing. In such devices, we observe conductance quantization at low temperatures, corresponding to ballistic transport through 1D subbands, where the measured subband energy spacings agree with calculations for a cylindrical confinement potential. In addition, we observe a ''0.7 structure,'' which has been attributed to spontaneous spin polarization, suggesting the universality of this phenomenon in interacting 1D systems. Lastly, the conductance exhibits little temperature dependence, consistent with our calculation of reduced backscattering in this 1D system, and suggests that transport is ballistic even at room temperature.ballistic transport ͉ bandstructure design ͉ conductance quantization ͉ nanoscience ͉ single-electron transistor C arbon nanotubes and semiconductor nanowires have attracted considerable attention as 1D structures for fundamental studies and also as potential building blocks for nanodevices (1-3). Current synthetic methods can reproducibly yield nanotubes and nanowires with diameters of a few nanometers (4, 5), comparable with the de Broglie wavelength of the carriers. In this regime, quantum confinement may affect significantly transport through these materials, thus making them model platforms to study and use potentially unique properties of 1D systems (6, 7). Indeed, ballistic transport and conductance quantization have been observed in metallic (8) and semiconducting carbon nanotubes (9, 10). Similar effects have not been observed in semiconductor nanowires, although the ability to vary size, material composition, and electronic properties of semiconductor nanowires in a controlled manner (2, 3) offers substantial potential for creating designed 1D systems.Band structure engineering has been widely used in the past to yield interesting planar systems, including 2D electron gases in GaAs͞AlGaAs heterostructures (11) and 2D hole gases in Ge͞SiGe heterostructures (12). 2D electron and 2D hole gases have been central to mesoscopic physi...

This review focuses on the application of nanomaterials for neural interfacing. The junction between nanotechnology and neural tissues can be particularly worthy of scientific attention for several reasons: (i) Neural cells are electroactive, and the electronic properties of nanostructures can be tailored to match the charge transport requirements of electrical cellular interfacing. (ii) The unique mechanical and chemical properties of nanomaterials are critical for integration with neural tissue as long‐term implants. (iii) Solutions to many critical problems in neural biology/medicine are limited by the availability of specialized materials. (iv) Neuronal stimulation is needed for a variety of common and severe health problems. This confluence of need, accumulated expertise, and potential impact on the well‐being of people suggests the potential of nanomaterials to revolutionize the field of neural interfacing. In this review, we begin with foundational topics, such as the current status of neural electrode (NE) technology, the key challenges facing the practical utilization of NEs, and the potential advantages of nanostructures as components of chronic implants. After that the detailed account of toxicology and biocompatibility of nanomaterials in respect to neural tissues is given. Next, we cover a variety of specific applications of nanoengineered devices, including drug delivery, imaging, topographic patterning, electrode design, nanoscale transistors for high‐resolution neural interfacing, and photoactivated interfaces. We also critically evaluate the specific properties of particular nanomaterials—including nanoparticles, nanowires, and carbon nanotubes—that can be taken advantage of in neuroprosthetic devices. The most promising future areas of research and practical device engineering are discussed as a conclusion to the review.

Triggerable drug delivery systems enable on-demand controlled release profiles that may enhance therapeutic effectiveness and reduce systemic toxicity. Recently, a number of new materials have been developed that exhibit sensitivity to visible light, near-infrared (NIR) light, ultrasound, or magnetic fields. This responsiveness can be triggered remotely to provide flexible control of dose magnitude and timing. Here we review triggerable materials that range in scale from nano to macro, and are activated by a range of stimuli.

The interface between nanosystems and biosystems is emerging as one of the broadest and most dynamic areas of science and technology, bringing together biology, chemistry, physics, biotechnology, medicine, and many areas of engineering. The combination of these diverse areas of research promises to yield revolutionary advances in healthcare, medicine, and the life sciences through the creation of new and powerful tools that enable direct, sensitive, and rapid analysis of biological and chemical species. Devices based on nanowires have emerged as one of the most powerful and general platforms for ultrasensitive, direct electrical detection of biological and chemical species and for building functional interfaces to biological systems, including neurons. Here, we discuss representative ex amples of nanowire nanosensors for ultrasensitive detection of proteins and individual virus particles as well as recording, stimulation, and inhibition of neuronal signals in nanowire-neuron hybrid structures.

cardiomyocyte ͉ multiplexed recording ͉ nanodevice ͉ PDMS ͉ silicon