Physicochemical and Antimicrobial Properties of Silver-Doped Hydroxyapatite Collagen Biocomposite Daniela Predoi , 1 Simona Liliana Iconaru, 1 Madalina Albu, 2 Cristian Catalin Petre, 3 Gabriel Jiga 3 1 National Institute of Materials Physics, P.O. Box MG 07, Magurele, Romania 2 Collagen Department, National Research & Development Institute for Textiles and Leather (INCDTP)—Division, Leather and Footwear Research Institute, Ion Minulescu Str.93, Bucharest 031215, Romania 3 Department of Strength of Materials, University Politehnica of Bucharest, Faculty of Engineering and Management of Technological Systems, 313 Splaiul Independentei, Bucharest, Romania Silver-doped hydroxyapatite (AgHAp) was prepared by co- precipitation method at room temperature. The obtained AgHAp was added in different amounts of collagen gel (AgHApC1 and AgHApC2). Afterward, the gel was lyophi- lized and the final AgHApC1 and AgHApC2 composite was achieved. The purity, crystallinity, and the phase composition of the AgHAp, AgHApC1, and AgHApC2 sam- ples were evaluated by X-ray diffraction (XRD). The planes corresponding to the 2h values for hydroxyapatite were found in the three samples analyzed in agreement with the crystalline hydroxyapatite. In the Fourier transform infrared (FT-IR) spectra of AgHApC1 and AgHApC2 sam- ples the peak characteristic to the presence of m 2 phos- phate mode at 472/cm was found. The peaks resulting from the m 4 vibration of the P–O mode, m 1 symmetric P–O stretching vibration and m 3 P–O stretching vibration of PO 32 4 were also evidenced in all the samples. The forma- tion of agglomerated particles with uniform particle size was evidenced by scanning electron microscope (SEM). The uniform distribution of the constituent elements was evidenced by mapping analysis. Furthermore, the strong antibacterial activity of AgHAp, AgHApC1, and AgHApC2 samples against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacterial strains was shown. The inhibition zone increased drastically with the increase of silver concentration. POLYM. ENG. SCI., 00:000–000, 2017. V C 2017 Society of Plastics Engineers INTRODUCTION One of the major risks associated with orthopedic and dental surgeries is the occurrence of postoperative infections [1, 2]. Lately, it was observed that the incidence of infections associat- ed with prosthetic joints are increasing [1, 2]. In this context, the development of a new biomaterial with improved antimicro- bial activity is an important issue. One of the most used materi- als in biomedical applications, member of the calcium phosphate family, is hydroxyapatite (HAp, Ca 10 (PO 4 ) 6 (OH) 2 ) [3]. HAp has attracted the attention of the researchers around the world due to the fact that it is the main inorganic component of bone tissue and it is used in various applications including implants, bone reconstruction, and drug delivery [4]. Moreover, studies reported in the literature demonstrated that HAp possesses special biological properties such as biocompati- bility, bioactivity, nontoxicity, and osteoinductivity [3]. In con- trast, hydroxyapatite poses a unique structure that allows various substitution with metallic ions, such as Ag, Zn, Cu, and Eu, which are of interest for medical applications [5]. This kind of substitutions is also useful for improving the biological (antimi- crobial) and the physicochemical properties of HAp [6]. Due to the lack of antimicrobial activity, the use of HAp in implantol- ogy is reduced [5]. Silver is known from ancient times for its antimicrobial activity against of various bacterial strains [2, 7]. Recent studies have shown that the microbiostatic and microbi- cidal properties of silver-doped hydroxyapatite depend on the silver content [5, 8–10]. Moreover, it is known that in most postoperative infections bacterial strain such as Staphylococcus aureus and Escherichia coli are involved, which generally become resistant to the treatment with antibiotics [2]. In this context, the use of silver as an antimicrobial agent was prefera- ble due to the fact that generally, the bacterial strains do not develop resistance in this case, compared to the case of treat- ments based on antibiotics [2]. In addition, the organic component of bone tissue is collagen (type I), a natural polymer with good biological properties [11]. Due to its properties, collagen has been used in cosmetic, phar- maceutics and medical applications [12, 13]. Collagen- hydroxyapatite composites could be obtained through various methods including freeze-drying, particulate leaching, solvent casting, thermally induced phase separating, and fiber bonding [14–21]. But the most used method is the freeze-drying of colla- gen fibers and HAp powder [22, 23]. The presence of collagen matrix improves the porosity of silver-doped hydroxyapatite, which is essential in tissue engi- neering [24, 25]. This kind of material acts as support for cell promoting, contributing to bone tissue regeneration [24, 26]. Therefore, this new type of biocomposite obtained from silver- doped hydroxyapatite and collagen may be of interest for bio- medical applications due to its similarity (from biological and physicochemical point of view) to the natural bone tissue [27–29]. The study presented in this article was focused on the synthe- sis and characterization of novel silver-doped hydroxyapatite in collagen matrix. The silver-doped hydroxyapatite in collagen biocomposites with ratio collagen gel/AgHAp of 1 (AgHApC1) and 4 (AgHApC2) were obtained. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to investi- gate the structural and morphological properties of AgHAp pow- ders and AgHApC1 and AgHApC2 biocomposite. In order to Correspondence to: D. Predoi; email: dpredoi@gmail.com Contract grant sponsor: Executive Agency for Higher Education, Research, Development and Innovation Funding (UEFISCDI); contract grant number: National PN II 259/2014; contract grant sponsor: Core Program; contract grant number: PN 10N/2016. DOI 10.1002/pen.24553 Published online in Wiley Online Library (wileyonlinelibrary.com). V C 2017 Society of Plastics Engineers POLYMER ENGINEERING AND SCIENCE—2017