RESEARCH In vitro performance of silver-doped hydroxyapatite nanopowders—a micro study Ravinder Pal Singh 1 & Maninder Singh Mehta 1 & Parwinder Singh 2 & Rajan Verma 3 Received: 4 June 2017 /Accepted: 7 August 2017 # Australian Ceramic Society 2017 Abstract Silver-doped hydroxyapatite (AgHAP) nanopowders (NPs) have been receiving immense attention in orthopedic and dental implant applications owing to high bioactivity and antimi- crobial properties. This study comprehensively investigated the influence of in vitro immersion durations of 7 and 30 days on structural and physico-chemical properties of AgHAP NPs. XRD revealed that different immersion durations formed differ- ent secondary phases. Rietveld refinement suggested that with the increase in duration of immersion, inter-atomic distance be- tween atoms and crystallinity of NPs decreased, whereas distor- tion of lattice parameters, crystal size, and micro-strain of NPs increased. FTIR supported XRD phase analysis and confirmed the formation of apatite in all NPs. NPs that were agglomerated consisted of particles of irregular shapes and sizes as revealed by SEM. EDX corroborated with XRD phase analysis and detected all desirable elements constituting HAP phase. Disparity between hydrodynamic diameter (DLS testing) and crystal sizes deter- mined using Scherrer formula and Rietveld refinement was ob- served. In vitro pH measurement of SBF suggested the bioactive nature of NPs and also revealed the higher rate of solubility of AgHAP NPs. AgHAP NPs gained weight after 30 days of im- mersion in SBF. Keywords Silver . Hydroxyapatite . SBF . Immersion duration . Rietveld refinement Introduction Because of the smart biological properties, hydroxyapatite (HAP) nanopowder (NP) is a widely accepted biomaterial in the field of bone tissue engineering [1], having numerous ap- plications as artificial bone graft material [2] as well as bioac- tive coatings for orthopedic implants [3]. Bioactive materials must possess controlled degradation behavior that should syn- chronies with the sequence of cellular changes occurring dur- ing new tissue formation [4]. In the field of bone engineering, bioactivity is defined as the ability of the material to bond to bone tissue via formation of bone-like HAP layer on its sur- face [4, 5]. Kokubo [6] proposed that one of the essential requirements for an artificial material to bond to living bone is the formation of secondary bone-like apatite on its surface, when it is implanted in the living body. This in vivo formation of secondary apatite can also be reproduced in imitated simu- lated body fluid (SBF) mimicking ion concentrations nearly similar to that of human blood plasma [4, 7]. This is a univer- sally recognized method to evaluate the in vitro performance of synthetic biomaterials [8, 9]. Among the various factors, rate of in vitro secondary HAP formation depends on the structural and chemical composition of the material [4]. Therefore, reinforcement or doping with different metallic ion(s) may tailor the bioactivity and solubility properties of HAP matrix NPs. It has been well established that doping of element(s) such as silicon [10, 11], zinc [12, 13], strontium [14, 15], and silver (Ag) [16–20] etc. in HAP crystal structure extremely influence the structural, mechanical, antimicrobial, and biological properties of resultant NPs [10–20]. To date, however, array of studies have discussed the influence of Ag doping and its different doping concentrations on the physico- chemical, structural, antimicrobial, and biocompatibility prop- erties of resultant Ag-doped HAP (AgHAP) NPs, but perhaps, none/few [20] (if tested, but not comprehensively) reports systematically and comprehensively evaluated the in vitro per- formance of AgHAP NPs. * Ravinder Pal Singh er.ravinderpalsingh@gmail.com 1 Department of Mechanical Engineering, Sri Guru Granth Sahib World University, Fatehgarh Sahib, Punjab 140406, India 2 Department of Mechanical Engineering, Baba Banda Singh Bahadur Polytechnic College, Fatehgarh Sahib, Punjab 140406, India 3 Department of Mechanical Engineering, Thapar Polytechnic College, Patiala, Punjab 147001, India J Aust Ceram Soc DOI 10.1007/s41779-017-0118-7