Electrospun biomimetic nanocomposite nanofibers of hydroxyapatite/chitosan for bone tissue engineering Yanzhong Zhang a, b , Jayarama Reddy Venugopal b , Adel El-Turki c , Seeram Ramakrishna b, d, e , Bo Su a, * , Chwee Teck Lim b, d, e, f, ** a Department of Oral and Dental Science, University of Bristol, Lower Maudlin Street, Bristol BS1 2LY, UK b Division of Bioengineering, National University of Singapore, 9 Engineering Drive 1, Singapore 117576, Singapore c Interface Analysis Centre, University of Bristol, 121 St. Michael’s Hill, Bristol BS2 8BS, UK d Department of Mechanical Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore 117576, Singapore e NUS Nanoscience & Nanotechnology Initiative, National University of Singapore, 2 Engineering Drive 3, Singapore 117576, Singapore f NUS Life Sciences Institute, National University of Singapore, 28 Medical Drive, Singapore 117456, Singapore article info Article history: Received 28 May 2008 Accepted 26 July 2008 Available online 20 August 2008 Keywords: Nanofibers Nanocomposite Electrospinning Hydroxyapatite Chitosan Bone tissue engineering abstract The development of bioinspired or biomimetic materials is essential and has formed one of the most important paradigms in today’s tissue engineering research. This paper reports a novel biomimetic nanocomposite nanofibers of hydroxyapatite/chitosan (HAp/CTS) prepared by combining an in situ co-precipitation synthesis approach with an electrospinning process. A model HAp/CTS nanocomposite with the HAp mass ratio of 30 wt% was synthesized through the co-precipitation method so as to attain homogenous dispersion of the spindle-shaped HAp nanoparticles (ca. 100  30 nm) within the chitosan matrix. By using a small amount (10 wt%) of ultrahigh molecular weight poly(ethylene oxide) (UHMWPEO) as a fiber-forming facilitating additive, continuous HAp/CTS nanofibers with a diameters of 214  25 nm had been produced successfully and the HAp nanoparticles with some aggregations were incorporated into the electrospun nanofibers. Further SAED and XRD analysis confirmed that the crys- talline nature of HAp remains and had survived the acetic acid-dominant solvent system. Biological in vitro cell culture with human fetal osteoblast (hFOB) cells for up to 15 days demonstrated that the incorporation of HAp nanoparticles into chitosan nanofibrous scaffolds led to significant bone formation oriented outcomes compared to that of the pure electrospun CTS scaffolds. The electrospun nano- composite nanofibers of HAp/CTS, with compositional and structural features close to the natural mineralized nanofibril counterparts, are of potential interest for bone tissue engineering applications. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Electrospinning has been broadly recognized as a unique and facile technique for producing ultrafine and continuous sub-micron fibers and/or nanofibers. While electrospinning of purely polymer material systems had been routinely and intensively researched in the past decade, recent demonstrations on the feasibility of incor- porating those non-electrospinnable inorganic nanoparticles into nanofibers to form composite nanofibers have made electro- spinning very attractive in fulfilling some specific functional applications [1–6], in particular, for bone tissue engineering. Natural bone, being an innate example of inorganic–organic bio- composites, consists in composition of approximately 70 wt% inorganic crystals (mainly hydroxyapatite with a chemical formula of Ca 10 (PO 4 ) 6 (OH) 2 ) and 30 wt% of organic matrix (mainly Type I collagen). Structurally, it is hierarchically organized from macro-, micro-, to nano-scale, where the basic building blocks are the plate- like HAp nanocrystals incorporated collagen nanofibers [7–10]. Thus, electrospun composite nanofibers, capable of composition- ally and structurally emulating the basic building blocks of those natural mineralized collagen nanofibers, would possess great potential in enabling researchers to use ‘‘bottom-up’’ strategy to engineer functional native bone-like substitutes by means of the contemporary tissue engineering approach. In the past few years, several different electrospun nano- composite fibers, such as PCL/CaCO 3 [11], HAp/gelatin [5], silk/HAp [6], PLA/HAp [12,13], and triphasic HAp/collagen/PCL [14,15] had been devised and explored for potential bone regeneration * Corresponding author. Department of Oral and Dental Science, University of Bristol, Lower Maudlin Street, Bristol BS1 2LY, UK. Tel.: þ44 117 9284361; fax: þ44 117 9284780. ** Corresponding author. Division of Bioengineering, National University of Sin- gapore, 9 Engineering Drive 1, Singapore 117576, Singapore. Tel.: þ65 6516 7801; fax: þ65 6779 1459. E-mail addresses: b.su@bristol.ac.uk (B. Su), ctlim@nus.edu.sg (C.T. Lim). Contents lists available at ScienceDirect Biomaterials journal homepage: www.elsevier.com/locate/biomaterials 0142-9612/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.biomaterials.2008.07.038 Biomaterials 29 (2008) 4314–4322