68 Recent Patents on Biomedical Engineering 2008, 1, 68-78 1874-7647/08 $100.00+.00 © 2008 Bentham Science Publishers Ltd. Recent Patents on Electrospun Biomedical Nanostructures: An Overview Sangamesh G. Kumbar a , Syam P. Nukavarapu a , Roshan James b , MaCalus V. Hogan a and Cato T. Laurencin a,b,c* a Department of Orthopaedic Surgery, University of Virginia, Virginia 22903, USA, b Department of Biomedical Engineering, University of Virginia, Virginia 22908, USA, c Department of Chemical Engineering, University of Virginia, Virginia 22904, USA Received: November 1, 2007; Accepted: November 20, 2007; Revised: November 23, 2007 Abstract: Nanostructures in the form of tubes, wires, crystals, rods, spheres, and fibers have been fabricated and assembled into various macrostructures for a variety of high technology applications. Nanofeatures impart several amazing properties to these macrostructures including high surface area, surface functionality, and superior mechanical, optical, electrical, and magnetic properties over the parent bulk material. Polymeric nanofibers in the form of nonwoven cloth, membrane, braids and tubes are extensively used for daily needs, and in addition used as filters, protective clothing, and for a variety of industrial and biomedical applications. Electrospinning or electrostatic spinning has emerged as a very popular technique to fabricate polymeric nanofiber matrices. More than 100 different polymers of natural, synthetic origin, their blends and composites have been electrospun into different three dimensional (3-D) macrostructures. Electrospinning provides opportunities to manipulate and control surface area, fiber diameter, porosity and pore size of nanofiber matrices. These nanofiber matrices closely mimic the structure of extracellular matrix (ECM) and influence cellular activities both in vitro and in vivo. Nanofiber macrostructures have been used as a vehicle to deliver therapeutic agents, as scaffolds for engineering various tissues and also serve as an integrated part of biomedical implants. Present review will cover some of the recent important patents that use electrospun nanofiber matrices for various biomedical applications. Keywords: Electrospinning, nanofibers, nanofiber coatings, biocompatible scaffolds, tubular conduits, tissue engineering, biomedical implants, core-shell nanofibers, bio-active agent delivery, nitric oxide delivery. INTRODUCTION Recent technological developments in microscopy and fabrication have revolutionized many areas of nanomaterial research. Technological improvements provide opportunities to visualize and manipulate materials into various nano- structures. Nanounits in the form of tubes, wires, crystals, rods, spheres, fibers and their composites have been fabri- cated and assembled into various macrostructures to serve the needs of high technology applications [1-6]. Surface modifications containing various nanotopographic features such as pores, ridges, grooves, fibers, nodes, and their com- binations are fabricated using various lithographic tech- niques to suit a variety of applications. These nanostructures due to their extremely small sizes offer properties such as high surface area to volume ratio, superior mechanical, sur- face, optical, electrical and magnetic properties over the pa- rent bulk material. Nanomaterials have wide ranging poten- tial in industrial, electronic and biomedical applications. Among these nanostructures; polymeric nanofibers are being explored for diverse applications in numerous forms such as nonwoven cloth, membrane, braids, and tubes. A literature survey for electrospun nanofibers and their applications based on a SciFinder Scholar search in the past 9 years presented in Fig. (1) clearly demonstrates the surging interest in nanofibers. Patents on electrospun nonwoven *Address correspondence to this author at the University Professor, Lillian T. Pratt Distinguished Professor, Chair of Orthopaedic Surgery, Professor of Biomedical and Chemical Engineering, The University of Virginia, 400 Ray C. Hunt Drive, Suite 330, Charlottesville, VA 22903, USA; Tel: 434 243 0250; Fax: 434 243 0252; Email: laurencin@virginia.edu nanofiber based device applications include filtration, mili- tary protective clothing, artificial leathers, sanitary pads, diapers, packaging materials sensors, photovoltaic devices, liquid-crystal display (LCD), ultra-light weight space craft materials, super efficient and functional catalysts and variety of biomedical and cosmetic applications [2,7-12]. Fibers with a diameter less than 1 micron are termed as nanofibers in broad sense. Nanofibers due to their extremely small size are shown to have very large surface area; fibers of diameter 100 nm are approximated to have a geometrical surface to mass of 100 m 2 /g [13]. Nanofiber matrices with different fiber diameters show a wide range of surface properties (e.g. hydrophilicity, hydrophobicity), superior mechanical properties (e.g. stiffness, tensile strength), and porosity compared with the other forms of the material. Fiber properties such as surface functionality, electrical conduc- tivity, weight and tensile strength are greatly determined by the specific polymers used to fabricate nanofibers. Polymeric nanofiber matrices can be fabricated using a variety of techniques such as drawing [14], template synthesis [15], temperature induced phase separation [16], molecular self assembly [17], and electrospinning [18-22]. Most of these techniques are inadequate because they are a discontinuous process, not scalable, specific to certain poly- mers and has no control on fiber diameter and orientation. However, electrospinning or electrostatic spinning has emerged as one of the most efficient techniques to fabricate polymeric nanofibers from polymer solutions and melts. Thus it is possible to fabricate polymeric fibers in the diameter range of ~ 3 nm to ~10 m using the same experi- mental set up while increasing the solution concentration.