Journal of the European Ceramic Society 27 (2007) 4181–4186 Hydroxyapatite nanoceramics: Basic physical properties and biointerface modification Daniel Aronov a , Anatoly Karlov b , Gil Rosenman a,∗ a School of Electrical Engineering, Department of Physical Electronics, Tel-Aviv University, 69978 Ramat-Aviv, Israel b Center for Orthopedic and Medical Material Sciences of the Siberian Branch of the Russian Academy of Medical Sciences, 634029 Tomsk, Russia Available online 9 April 2007 Abstract A new method of surface energy modification and engineering of the hydroxyapatite (HAp) nanoceramics coatings is presented. It is performed by electron-induced surface energy modification resulting in deep and tunable variation of its wettability state. It is found from electronic traps state spectroscopy studies of the HAp ceramics implemented by various methods such as photoluminescence and surface photovoltage spectroscopy, that the HAp nanoceramics is a wide band gap p-type semiconductor with complex structure of electron/hole bulk and surface localized states. It is shown that a low-energy electron irradiation leads to surface potential modulation and provides tailoring any wettability state in a wide range of contact angles by variation of injected and trapped electron charge. The diverse wettability states engineered on the HAp surface enable selective adhesion of basic biological cells such as proteins, DNA and various bacteria. © 2007 Elsevier Ltd. All rights reserved. Keywords: Apatite; Nanocomposite; Surfaces; Interfaces; Biomedical application 1. Introduction The promising trends in biotechnology and tissue engi- neering are based on development of advanced materials with biomimetic features created by designing and tailoring of spe- cific surface properties. 1 The modification of surface properties is directed to enhance the surface affinity to selective adhesion and proliferation of biological cells, improvement of biological response, and tissue compatibility. 2 Among various biocompatible materials, hydroxyapatite (HAp) is widely used in many biomedical applications. HAp is natural mineral ingredient of bones, tooth and calcified tis- sues in vertebrate. Man-made HAp is served for human implant coatings possessing beneficial biocompatibility and osteocon- ductivity resulting in bonding to a human hard tissue. It is known as a substrate for effective adhesion of proteins, peptides, lipids, bacteria, and strains. 3,4 In this work, we present a new approach to interface engineer- ing of the HAp nanoceramics coatings performed by electron- induced surface energy modification resulting in deep and tunable variation of its wettability (hydrophobic/hydrophilic) ∗ Corresponding author. E-mail address: gilr@eng.tau.ac.il (G. Rosenman). state. 5 It is found from studies of electronic traps state spec- troscopy of the HAp that the HAp nanoceramics is a wide band gap p-type semiconductor with complex structure of elec- tron/hole bulk and surface localized states. It is shown that a low-energy electron irradiation leads to surface potential modu- lation and provides tailoring any wettability state in a wide range of contact angles by variation of injected and trapped electron charge. The diverse wettability states engineered on the HAp surface enable selective adhesion of basic biological cells such as proteins, DNA and various bacteria. 2. Material surface modification and biocompatibility The key problem in biomedical and surface science is based on development of smart substrates with modified interface for amplifying affinity to biomolecules adhesion and biocells immobilization. 1–4 Several diverse techniques have been devel- oped for adapting biological substrates with interacted cells including deposition of self-assembled monolayers, electrical, light-induced and electrochemical methods, etc. 1,2 The common feature of the applied techniques is modification of the original surface energy and related properties (wettability, adsorption, adhesion, etc.) of the substrates. However, these methods are accompanied by surface chemical reactions, phase transitions, 0955-2219/$ – see front matter © 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jeurceramsoc.2007.02.121