The present study aims to synthesized biomaterial that has antibacterial properties. Currently the surgical implants associated infections are a major cause of implant failure. Synthesis of silver doped hydroxyapatite as an antibacterial agent has potential importance to overcome post-surgical infections in a variety of clinical applications. Five silver doped hydroxyapatite Ca10−xAgx(PO4)6(OH)2 (x = 0, 0.1, 0.3, 0.5, 0.7 M) samples were synthesized by precipitation method and sintered at 900 °C to obtain well crystallized structure. No minor phase developed with silver addition, hexagonal hydroxyapatite (JCPDS# 09-432) was the single phase identified in all silver doped hydroxyapatite samples. The lattice parameter a and c changed with increase in silver concentration. The results of in vitro bioactivity revealed the bone bonding ability of silver doped hydroxyapatite samples. The antibacterial test showed that silver doped hydroxyapatite was sensitive to Staphylococcus aureus bacteria. Addition of silver significantly (P < 0.005) increased the antibacterial activity.

Introduction

Bioceramics is a new class of biomaterials that is used to replace damaged tissues and bones. These bioceramic materials have the ability of direct bonding with host bone tissues [1,2]. Synthetic hydroxyapatite (Ca10 (PO4)6(OH)2) (HA) among these ceramics has been widely used for bone tissue engineering. Bones consist of 22% protein, 70% hydroxyapatite and 8% water. Natural bones are composed of hydroxyapatite nanoparticles having needle-like or rod-like shapes [3,4]. Chemical structure of HA is similar to human bone and it is widely used as coating for metal prosthesis, bone graft, drug [5] and antibiotics [6,7] carrier in bone-implant interface to reduce the bacterial infections. HA crystal is composed of OH−, Ca2+ and PO4 −۲ groups, which are closely packed in hexagonal arrangement and had space group of P63/m with lattice parameter a = b = 9.423 Ao and c = 6.875 Ao [8]. Although, hydroxyapatite is the most osteoconductive and biocompatible material among other calcium phosphates, but it has limited antibacterial resistance [9]. Bacterial infections are the main cause of implant failure [10]. To overcome this problem Ag+ is introduced to HA, since past silver has been recognized as strong inhibitor to bacterial growth [5]. Silver exhibits good thermal stability, low volatility, is biocompatible and non-toxic to human cell at low concentration along with superior antibacterial characteristics [11]. Previously, Ag+ doped HA had been synthesized by several precipitation methods [12], microwave refluxing method [3], sol-gel method [13] ultrasonic precipitation method [14] electrostatic spray-pyrolysis process [6] and sintered at different temperatures from 800 to 1200 °C to obtain monophasic fully crystallized silver doped hydroxyapatite. When larger ionic radius (1.28 Å) Ag+ is substituted to smaller ionic radius Ca+2 (0.99 Å) in hydroxyapatite lattice it provokes stress and strain in crystal structure [15]. These strains cause a stability problem in crystal structure. The theoretical limit of the Ag+ substituting Ca+2 is 20% [16], but the practical limit is much lower than this. It is essential to optimize the concentration of dopant and sintering temperature to obtain monophasic hydroxyapatite, previous study show that < 3% concentration of silver [5,6] did not alter the crystalline structure of hydroxyapatite. The aim of the study is to use optimize temperature and dopant concentration to obtain monophasic hydroxyapatite structure. In the present study the inexpensive and conventional precipitation method has been selected to synthesize silver doped hydroxyapatite. To evaluate the antibacterial properties of HA by incorporating Ag+ while maintaining bioactivity, and to demonstrate effects of Ag+ concentration on crystallite size, crystallinity and lattice parameters.