ARTICLES nature PUBLISHED ONLINE: 26 AUGUST 2012 I DO1: 10. 1038/NMAT3404 materials Macroporous nanowire nanoelectronic scaffolds for synthetic tissues Bozhi tian, 2,3t, Jia Liut Tal Dvir2, 4f, Lihua jins Jonathan h. tsui2 Robert Langer, Daniel S Kohane 2* and Charles M. Lieber 5*,Quan Qing Zhigang Suo The development of three-dimensional (3D) synthetic biomaterials as structural and bioactive scaffolds is central to fields ranging from cellular biophysics to regenerative medicine. As of yet, these scaffolds cannot electrically probe the physicochemical ological microenvironments throughout their d macroporous interior, although this capability could have a marked impact in both electronics and biomaterials. here we address this challenge using macroporous, flexible and free-standing nanowire nanoelectronic scaffolds (nanoES), and their hybrids with synthetic or natural biomaterials. 3D macroporous nanoEs mimic the structure of natural tissue scaffolds, and they were formed by self-organization of coplanar reticular networks with built-in strain and by manipulation of 2D mesh matrices. NanoES exhibited robust electronic properties and have been used alone or combined with other biomaterials as biocompatible extracellular scaffolds for 3D culture of neurons, cardiomyocytes and smooth muscle cells. Furthermore, we show the integrated sensory capability of the nanoes by real-time monitoring of the local electrical activity within 3D nano ES/cardiomyocyte constructs, the response of 3D-nanoES-based neural and cardiac tissue models to drugs, and distinct ph changes inside and outside tubular vascular tooth muscle constructs ben lesign and functionalization of porous materials have network must have 3D interconnectivity and mechanical properties actively pursued to enable new material properties and similar to biomaterials applications-. In particular, the development of synthetic Here we introduce a conceptually new approach that meets this 3D macroporous biomaterials as extracellular matrices(ECMs) challenge by integrating nanoelectronics throughout biomaterials represents a key area because functionalized 3D biomaterials al- and synthetic tissues in three dimensions using macroporous low for studies of cell/tissue development in the presence of nanoelectronic scaffolds. We use silicon nanowire field-effect of the pharmacological response of cells within synthetic tissues capability for recording both extracellular and intracellular signals is expected to provide a more robust link to in vivo disease with subcellular resolution-. FET detectors respond to variations treatment than that from 2D cell cultures. Advancing fur- in potential at the surface of the transistor channel region, and ther such biomaterials requires capabilities for monitoring cells they are typically called active detectors. Metal-electrode222. throughout the 3D micro-environment. Although electrical sen- or carbon nanotube/nanofibre 2425-based passive detectors are not sors are attractive tools, it has not been possible to integrate considered in our work because impedance limitations(that is such elements with porous 3D scaffolds for localized real-time signal/noise and temporal resolution degrade as the onitoring of cellular activities and physicochemical change; metal or carbon electrodes is decreased)make it difficult to reduce such capability could lead to new lab-on-a-chip pharmacologi- the size of individual electrodes to the subcellular level -,a cal platforms.o and hybrid 3D electronics-tissue materials for size regime necessary to achieve a non-invasive 3D interface of synthetic biology electronics with cells in tissue Recently, there have been several reports describing the coupling Our approach(Fig. 1)involved stepwise incorporation of of electronics and tissues using flexible and/or stretchable planar biomimetic and biological elements into nanoelectronic networks devices-17 that conform to natural tissue surfaces. These planar across nanometre to centimetre size scales. First, chemically synthe- evices have been used to probe electrical activities near surfaces sized kinked or uniform silicon nanowires were de of the heart3-l5, brain 6 and skin".So far, seamless 3D integration randomly or in regular patterns for single-nanowire FETs-the of electronics with biomaterials and synthetic tissues has not nanoelectronic sensor elements of the hybrid biomaterials(step A, been achieved. Key points that must be addressed to achieve Fig. 1). Second, individual nanowire FEt devices were lithograph this goal include: the electronic structures must be macroporous, ically patterned and integrated into free-standing macroporous not planar, to enable 3D interpenetration with biomaterials; the scaffolds(step B, Fig. 1), the nanoES. The nanoES were designed electronic network should have nanometre to micrometre scale to mimic structures,and specifically, to be 3D, to have features comparable to biomaterial scaffolds; and the electronic nanometre to micrometre features with high(>99%)porosity 1 Department of Chemistry and Chemical Biology, Harvard University Cambridge Massachusetts 02138, USA, 2Department of Division of Critical Care Medicine, Children's Hospital Boston, Harvard Medical School, Boston, Massachusetts 02115, USA, David HKoc tegrative Cancer Research, Massachusetts Institute of Technology, Cambridge Massachusetts 02139, USA, Department of Chemical Eng sachusetts Institute of Technology Cambridge Massachusetts 02139, USA, 'School of Engineering and Applied Sciences, Harvard Universit Massachusetts 02138, USA. These authors contributed equally to this work. ' e-mail: Daniel. ohane @childrens. harvard.edu; cml@cmliris harvardedu NATURE MATERIALS I VOL 11 I NOVEMBER 2012 I G 2012 Macmillan Publishers Limited All rights reservedARTICLES PUBLISHED ONLINE: 26 AUGUST 2012 | DOI:10.1038/NMAT3404 Macroporous nanowire nanoelectronic scaffolds for synthetic tissues Bozhi Tian1,2,3† , Jia Liu1† , Tal Dvir2,4† , Lihua Jin5 , Jonathan H. Tsui2 , Quan Qing1 , Zhigang Suo5 , Robert Langer3,4, Daniel S. Kohane2 * and Charles M. Lieber1,5* The development of three-dimensional (3D) synthetic biomaterials as structural and bioactive scaffolds is central to fields ranging from cellular biophysics to regenerative medicine. As of yet, these scaffolds cannot electrically probe the physicochemical and biological microenvironments throughout their 3D and macroporous interior, although this capability could have a marked impact in both electronics and biomaterials. Here, we address this challenge using macroporous, flexible and free-standing nanowire nanoelectronic scaffolds (nanoES), and their hybrids with synthetic or natural biomaterials. 3D macroporous nanoES mimic the structure of natural tissue scaffolds, and they were formed by self-organization of coplanar reticular networks with built-in strain and by manipulation of 2D mesh matrices. NanoES exhibited robust electronic properties and have been used alone or combined with other biomaterials as biocompatible extracellular scaffolds for 3D culture of neurons, cardiomyocytes and smooth muscle cells. Furthermore, we show the integrated sensory capability of the nanoES by real-time monitoring of the local electrical activity within 3D nanoES/cardiomyocyte constructs, the response of 3D-nanoES-based neural and cardiac tissue models to drugs, and distinct pH changes inside and outside tubular vascular smooth muscle constructs. T he design and functionalization of porous materials have been actively pursued to enable new material properties and applications1–3 . In particular, the development of synthetic 3D macroporous biomaterials as extracellular matrices (ECMs) represents a key area because functionalized 3D biomaterials al￾low for studies of cell/tissue development in the presence of spatiotemporal biochemical stimulants3–6 , and the understanding of the pharmacological response of cells within synthetic tissues is expected to provide a more robust link to in vivo disease treatment than that from 2D cell cultures6–8 . Advancing fur￾ther such biomaterials requires capabilities for monitoring cells throughout the 3D micro-environment6 . Although electrical sen￾sors are attractive tools, it has not been possible to integrate such elements with porous 3D scaffolds for localized real-time monitoring of cellular activities and physicochemical change; such capability could lead to new lab-on-a-chip pharmacologi￾cal platforms9,10 and hybrid 3D electronics–tissue materials for synthetic biology11,12 . Recently, there have been several reports describing the coupling of electronics and tissues using flexible and/or stretchable planar devices13–17 that conform to natural tissue surfaces. These planar devices have been used to probe electrical activities near surfaces of the heart13–15, brain16 and skin17. So far, seamless 3D integration of electronics with biomaterials and synthetic tissues has not been achieved. Key points that must be addressed to achieve this goal include: the electronic structures must be macroporous, not planar, to enable 3D interpenetration with biomaterials; the electronic network should have nanometre to micrometre scale features comparable to biomaterial scaffolds; and the electronic 1Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA, 2Department of Anesthesiology, Division of Critical Care Medicine, Children’s Hospital Boston, Harvard Medical School, Boston, Massachusetts 02115, USA, 3David H. Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA, 4Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA, 5School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA. †These authors contributed equally to this work. *e-mail: Daniel.Kohane@childrens.harvard.edu; cml@cmliris.harvard.edu. network must have 3D interconnectivity and mechanical properties similar to biomaterials. Here we introduce a conceptually new approach that meets this challenge by integrating nanoelectronics throughout biomaterials and synthetic tissues in three dimensions using macroporous nanoelectronic scaffolds. We use silicon nanowire field-effect transistor (FET)-based nanoelectronic biomaterials, given their capability for recording both extracellular and intracellular signals with subcellular resolution18–21. FET detectors respond to variations in potential at the surface of the transistor channel region, and they are typically called active detectors21. Metal–electrode22,23 - or carbon nanotube/nanofibre24,25-based passive detectors are not considered in our work because impedance limitations (that is, signal/noise and temporal resolution degrade as the area of the metal or carbon electrodes is decreased) make it difficult to reduce the size of individual electrodes to the subcellular level21–23, a size regime necessary to achieve a non-invasive 3D interface of electronics with cells in tissue. Our approach (Fig. 1) involved stepwise incorporation of biomimetic and biological elements into nanoelectronic networks across nanometre to centimetre size scales. First, chemically synthe￾sized kinked18 or uniform silicon nanowires were deposited either randomly or in regular patterns for single-nanowire FETs—the nanoelectronic sensor elements of the hybrid biomaterials (step A, Fig. 1). Second, individual nanowire FET devices were lithograph￾ically patterned and integrated into free-standing macroporous scaffolds (step B, Fig. 1), the nanoES. The nanoES were designed to mimic ECM structures, and specifically, to be 3D, to have nanometre to micrometre features with high (>99%) porosity 986 NATURE MATERIALS | VOL 11 | NOVEMBER 2012 | www.nature.com/naturematerials © 2012 Macmillan Publishers Limited. All rights reserved