Get 20M+ Full-Text Papers For Less Than $1.50/day. Start a 14-Day Trial for You and Your Team.

Learn More →

Synthesis, characterization, antibacterial activity in dark and in vitro cytocompatibility of Ag-incorporated TiO2 microspheres with high specific surface area

Synthesis, characterization, antibacterial activity in dark and in vitro cytocompatibility of... 1 Introduction implants, one of the most devastating complications of orthopedic surgery, is prominent. Implants are now a main component of medical practice, Unfortunately, when metal Ti exposed to air, an oxide promoting patient well-being and saving countless lives film on its surface would spontaneous format for the strong each year; however, along with these benefits comes some affinity between titanium (Ti) and oxygen (O). In addition, negative outcomes. Postoperative infection associated with under in vivo conditions, the oxide film will quickly * Yungang Luo Yungangl@hotmail.com Department of Orthopedics, Second Hospital, Jilin University, 130041 Changchun, China Department of Stomatology, Second Hospital, Jilin University, Department of Oral Medicine, West China Hospital of 130041 Changchun, China Stomatology, Sichuan University, Chengdu, China College of Chemistry, Jilin University, Qianjin Street, 130012 Changchun China 1234567890();,: 1234567890();,: 50 Page 2 of 10 Journal of Materials Science: Materials in Medicine (2018) 29:50 transform into a biofilm by combining with amylase and Nanosized TiO , owing to its remarkable NP size effect, protein, which exist throughout bodily fluid. This biofilm has always been the focus of biomaterial research; however, then acts as a protective shield against both host defenses the potential biological toxicity of NPs hinder its practical and antibacterial agents [1–3]. Antibiotic concentrations application in clinical settings. NP-constructed micro- might be as much as 1000-fold higher than needed to pre- spheres, which have both bulk size and the unique proper- vent the growth of inhibited bacteria in biofilms as to the ties of NPs, do provide an alternate route to making TiO planktonic bacteria [3, 4]. Given this, coating the surface of safer to use in biomaterials. implant device with antibacterial agents would be an In this study, NP-constructed microspheres Ag/TiO was effective solution [5]. prepared by a facile one-step process of homogeneous Various functional antimicrobial coatings have been precipitation. Ag at different concentrations doped into available, such as the FDA-approved INFUSE® bone graft TiO was fabricated and used to estimate its antibacterial (Medtronic) [6], CarriGen porous bone substitute material properties against gram-positive S. aureus and gram- (ETEX), [7] Cerasorb (Curasam) [8], and Spineplex P Bone negative E. coli. To investigate the cytocompatibility of Cement (Stryker) [9]. In general, antimicrobial coating Ag/TiO , MC3T3-E1 cells were used for the cytocompat- materials can be classified into two categories depending on ibility test. The results demonstrated that adding Ag parti- their method of intervention during infection and biofilm cles to TiO reduces bacterial growth while being nontoxic formation: coatings that physically prevent bacterial adhe- to mammalian cell growth. sion and those that release antimicrobial agents and kill adherent bacteria. The former always involve materials that could dissolve after a short period of time. Such as polymer 2 Material and methods brushes [10] and a layer-by-layer technique used in degradable multilayer coatings [11]. Though they have 2.1 Sample preparation shown great promise toward time-release coatings, the use of organics also brings some health risks in clinical The Ag-loaded TiO was prepared using the homogeneous applications. precipitation method. Silver nitrate (AgNO , 99.99%) was In contrast, materials that kill adherent bacteria are rela- used as the silver precursor with glycol as the solvent. To tively conventional. Antimicrobial peptides (AMPs) and 32.0 mL glycol were sequentially added 16.0 mL 1.25-mol/ quaternary ammonium salts (QASs) have exhibited positive L titanium sulfate (Ti[SO ] ), 0.05 mol/L AgNO , 24.0 g 4 2 3 effect in infection preventing [12, 13]. However, the potential urea (CO[NH ] ), and 2.0 mL 1.0-g/L polyvinylpyrrolidone 2 2 cytotoxicity limits their clinical usefulness [14, 15]. (PVP), followed by vigorous stirring to obtain a uniform Thus, antibacterial biomaterials for implant should solution. The volume of the mixture solution was fixed at simultaneously provide excellent antibacterial activity and 200 mL and the amount of AgNO was varied so that the cell compatibility. Among those are inorganic antibacterial molar ratio of Ag to TiO in the catalysts was within the agents, including silver (Ag), zinc oxide (ZnO), copper range of 0–2.5%. Subsequently, the reaction mixtures were oxide (Cu O, CuO), and Ti dioxide (TiO ), and so on. kept in an oscillating water bath at 90 °C for 4.0 h, with an 2 2 The antibacterial effect of TiO origin from its excellent oscillation frequency of 90–110 rpm. Finally, white pre- photo-catalytic activity [16]; however, the effect after light cipitates were collected, washed three times with deionized excitation will diminish in the dark [17, 18]. This is a cri- water, dried at 80 °C in an oven for ~4.0 h, and ground with tical flaw limiting its biomedical applications, since no light a mortar. The entire experiment process was done under exist around as soon as implants are placed in bone. For- darkened conditions. tunately, this situation can be improved by noble metal doping in TiO [19]. But researches on the antibacterial 2.2 Sample characterization ability in dark still not the masses. Ag has been known as disinfectant for its broad spectrum The elementary components and Ag concentrations in the of antimicrobial activities [20]. The extremely difficulty of samples were determined by energy-dispersive X-ray Ag resistance developed by bacteria is one of the greatest spectroscopy (EDS; EDAX-Falcon, Mahwah, NJ, USA) challenges in traditional antibiotics research, and does well with a resolution of 129 eV. in vivo applications [21, 22]. Giglio et al. [23] demonstrated The morphology was characterized by JSM-5500 LV the substantial antibacterial activity of hydrogel coatings of field-emission scanning electron microscope (SEM; JEOL, electro-synthesized Ag nanoparticle (AgNP-)modified poly Ltd., Tokyo, Japan) at an accelerating voltage of 30 kV. The (ethylene glycol diacrylate-)co-acrylic acid (PEGDA-AA) planar view was investigated using the TECNAI F20 high- on a Ti substrate against gram-positive (S. aureus) and resolution transmission electron microscopy (HR-TEM; FEI, gram-negative (Pseudomonas aeruginosa) bacteria. Hillsboro, OR, USA) at 200 kV. Distribution of Ag atoms in Journal of Materials Science: Materials in Medicine (2018) 29:50 Page 3 of 10 50 the TiO was monitored by EDS elemental mapping with an of the Ag/TiO powder. Cells were cultured with α-MEM 2 2 EDX-ray spectroscope attached to the HRTEM. (Gibco) supplemented with 10% fetal calf serum (Gibco) Crystal form of the powder was studied using the D/ and 100 mg/mL streptomycin coupled with 100 units/mL Max-2550 X-ray diffractometer (XRD; Rigaku Corporation, penicillin at 37 °C in a humidified atmosphere of .0% CO . Tokyo, Japan) fitted with a Cu Kα (λ = 1.5418 Å) source at The cells, which were ~70% confluent, were harvested by 50 kV and 200 mA, within the range of 2θ = 20 ~ 80° at a mild trypsinization, centrifuged, and resuspended in the scan speed of 10°/min. Nitrogen (N ) adsorption on the complete medium of α-MEM, and reseeded. The culture surface of samples was measured to calculate the specific media were refreshed every 2.0 d and all experiments were surface area using the Brunauer–Emmett–Teller (BET) repeated three times. equation [24]. A micrometrics ASAP 2420 surface area and porosity analyzer was used as described elsewhere [25]. The ESCALAB™ 250Xi X-ray Photoelectron Spectro- 2.4.2 Cell viability assay meter (XPS, ESCLAB 250, Thermo Scientific, Waltham, MA, USA) with an Al Kα radiation source (hν 1000 eV) was CCK-8 (Dojindo Laboratories, Kumamoto, Japan) was used used to identify the chemical constituents of the different to assess the cytotoxicity of the MC3T3-E1 cells in vitro. prepared samples and elemental states of the Ag particles. After counting, MC3T3-E1 cells were seeded at a density of 5000 cells/cm into 12-well plates. After incubation for 2.3 Antibacterial performance test 24.0 h, MC3T3-E1 cells were rinsed thoroughly with phosphate-buffered saline. The resuspended cells were then 2.3.1 Bacterial strains and growth conditions exposed to the Ag/TiO powders at 0.0885 g/cm having different amounts of Ag. Control groups involved the use of Strains of bacteria used for this evaluation were S. aureus α-MEM as the blank and the MC3T3-E1 cells not exposed (ATCC6538P) and E. coli (ATCC25922) purchased from to the samples as controls. The MC3T3-E1 cells used as a the www.bnbio.com. The bacteria were inoculated with positive control were cultured with all other conditions Luria-Bertani (LB) solid plate or liquid medium. being identical. After incubating for 1.0, 3.0, 5.0, 7.0 day, respectively, CCK-8 was added to every well and incubated 2.3.2 The disc diffusion test for 2.0 h; supernatant was transferred to new 12-well cell culture plates. The supernatant’s absorbance value of The antibacterial activity of Ag/TiO powder was evaluated optical density (OD) thereafter was measured using the using the disc diffusion test. The test is performed using the Varioskan Flash Multimode Reader (Thermo Scientific, guidelines of the Clinical and Laboratory Standards Institute Waltham, MA, USA) at a wavelength of 450 nm accom- [26]. Solutions of Ag/TiO samples with a concentration of panied by a reference wavelength of 630 nm. Finally, the 7.0 mg/mL were prepared using Ag/TiO powder in double- viability of MC3T3-E1 cells was expressed as a percentage distilled water. These solutions were then doped onto of relative growth rate (RGR) according to the following Whatman filters and sterilized with moist heat. Melted LB formula: medium (90 mL) was poured into petri dishes (Iwaki, RGRðÞ 100%¼ ðOD  OD Þ=ðOD  OD Þ test blank control blank Japan) and solidified. The agar surfaces were then inocu- 100% lated using a glass swab dipped in the bacterial cell sus- 5 6 pension. The suspension was adjusted to 10 –10 colony ð1Þ forming units (CFU) of the previous test organisms. After drying for approximately 5.0 min, the inoculated agar plates where, OD is the OD of the Ag/TiO sample and OD test 2 control were planted with the Ag/TiO dampened filter papers, and OD are the ODs of the MC3T3-E1 cells without 2 blank incubated for 16–18 h at 37.0 °C in dark, and examined for samples and the blank control sample (α-MEM medium). the diameter of the inhibitory zones where no visible bac- terial growth could be observed. Each sample was made in 2.5 Statistical analyses triplicate. The assays were performed in triplicate and data were 2.4 Cell viability expressed as the mean ± standard deviation. Each experi- ment was repeated three times with data of a typical 2.4.1 Cell culture experiment shown. A one-way analysis of variance com- bined with a Student-Newman-Keuls post hoc test was used Newborn mouse calvaria-derived preosteoblastic cells to determine the level of significance. p < 0.05 was regarded (MC3T3-E1 subclone 14) were used in the biological assays as significant. 50 Page 4 of 10 Journal of Materials Science: Materials in Medicine (2018) 29:50 3 Results The elemental constituents of the different prepared samples and chemical states of the samples were determined 3.1 Sample characterization by XPS. The XPS full survey spectra of TiO and Ag/TiO 2 2 samples and HR spectra of O 1 s, Ag 3d, and Ti 2p are EDS analysis showed that the samples were composed shown in Fig. 1m–p. The C signal is ascribed to adventi- mainly of the Ti, Ag, and O (Fig. 1a–g). Atomic con- tious contamination. Ag can be obviously confirmed in the centrations listed under the images in Fig. 1a–g revealed full spectrum of the 1.89 Ag/TiO sample shown in Fig. 1m that the atomic ratio percentage (at%) of Ag to Ti in the in addition to Ti and O. From the HR spectra in Fig. 1n, Ti Ag/TiO powder varied from 0 to 2.25%. The Ag/TiO 2p exhibits two peaks centered at 464.2 and 458.5 eV, 2 2 powder with different content of Ag is referred to in the assigned to the binding energies of Ti (2p ) and Ti (2p ), 1/2 3/2 following text as TiO , 0.12 Ag/TiO , 0.56 Ag/TiO , 0.82 respectively [27]. The split between Ti (2p ) and Ti (2p ) 2 2 2 1/2 3/2 4+ Ag/TiO , 1.1 Ag/TiO , 1.89 Ag/TiO , and 2.25 Ag/TiO is 5.7 eV, indicative of Ti in the anatase phase of TiO 2 2 2 2 2 where the numerals represent the atomic percentage of Ag [28, 29]. The binding energies of Ti2p were slightly lower to Ti. in the presence of Ag. The lower Fermi level, compared to Moreover, the anatase phase of TiO and tetragonal that of TiO , makes Ag responsible for the shift in binding 2 2 structure of Ag can be observed in the interior HR-TEM energy because of the transition of electrons from TiO to lattice pattern (Fig. 1h), in which the interplanar spacing of Ag and the subsequent outer cloud density changes in TiO ~0.352 and ~0.189 nm account for 101 and 200 planes of [30, 31]. The O 1 s peak (Fig. 1o) consists of three sub- anatase, respectively. In addition, the ~0.204 nm corre- peaks. The O 1s peak at binding energy of 529.7 and sponds to the interplanar spacing of 200 planes of Ag. 531.45 eV are assigned to the Ti-O bonds, which have the Surface morphology of the TiO and 1.89 Ag/TiO largest peak area [32]. The O 1s peak at 532.6 eV confirms 2 2 powder is shown in Fig. 1i. TiO powder was entirely the presence of the surface chemisorbed –OH of TiO 2 2 composed of spherical crystal units, whose diameter varied matrix [33]. The Ag 3d doublets at 367.71 eV (Ag 3d ) 5/2 from 2.0 to 5.0 μm. When loaded with Ag, the morphology and 373.80 eV (Ag 3d ) (Fig. 1p) with a spin energy 3/2 as well as diameter of the crystal units were similar to that separation of 6.09 eV correspond to the binding energy of of TiO alone. Ag [5], confirming the existence of the oxidized state of Ag Figure 1j exhibits the XRD patterns of the 1.89 Ag/TiO . in the Ag/TiO sample. 2 2 A typical XRD pattern of a TiO sample is shown in the image, and all characteristic diffraction peaks at 2θ = 25.3° 3.2 The disc diffusion test (101), 37.8° (004), 48.0° (200), and 55.1° (211) are readily indexed to the anatase phase of TiO according to JCPDS The results of the disc diffusion test were observed in Ag/ card No. 84-1285; however, the characteristic peaks of Ag TiO powder with different contents of Ag (Fig. 2). The were missing in the patterns. The absence of Ag peaks is samples show the inhibitory effect of Ag/TiO against both very likely a result of the small amount of added Ag, which E. coli (Fig. 2a1–a7) and S. aureus (Fig. 2b1–b7), which can be confirmed by the results of the HR-TEM lattice exhibit observable inhibition zones with a diameter pattern. >7.0 mm (Table 2), with the exception of TiO and 0.1 Ag/ The BET surface area is another important aspect that TiO against E. coli because of their smaller or no Ag can provide the basis for the antibacterial properties. The N content. Of the samples enhanced with increasing Ag con- adsorption-desorption isotherm of 1.89 Ag/TiO,as tent in the powder, 2.25 Ag/TiO showed the most promi- 2 2 observed in Fig. 1k, was used to study the pore structure of nent inhibiting effect (exhibits the largest inhibition zone) Ag/TiO samples, displaying a higher surface area of owing to the largest Ag content, which highlights the sig- 362.8 m /g. The Barrett-Joyner-Halenda pore size distribu- nificance of the amount of Ag incorporated into the powder tion curve corresponding to the isotherm is shown in the on preventing the colonization of bacteria. The antibacterial insert in Fig. 1k and indicates the presence of holes in the activity of the samples against S. aureus was significantly spherical crystal unit’s surface. The BET surface area of the stronger than that against E. coli. The diameter of the samples is as 355–365 m /g (Table 1). As the amount of Ag inhibition area of the S. aureus group was significantly particles on Ag/TiO increases, the specific surface area of different (P < 0.05) from that of the E. coli group, which the Ag/TiO powders decreases slightly. could be attributed to the disparity between the two bacteria The distributions of Ti, O, and Ag in the spherical crystal on the structure. For the E. coli group, there always exists units obtained by EDS elemental mapping are shown in an area in which there is a density reduction of bacterial Fig. 1l The elemental maps reveal that Ag is homo- colonies instead of a clear zone of inhibition as with the S. geneously dispersed throughout the spherical TiO crystal aureus group. This might be related to different antibacterial units. effects of Ag ions on the two bacteria. All of the above Journal of Materials Science: Materials in Medicine (2018) 29:50 Page 5 of 10 50 Fig. 1 Continued 50 Page 6 of 10 Journal of Materials Science: Materials in Medicine (2018) 29:50 Fig. 1 a–g EDS data obtained from Ag/TiO powder with different amount of Ag showing changes in Ag content with a range of 0–2.25% (at%). HR- TEM images of the 1.89 Ag/ TiO powder (h). Image I showing the structure of 1.89 Ag/TiO powder. j XRD of 1.89 Ag/TiO powder was shown. Nitrogen adsorption-desorption isotherm and the corresponding BJH pore size distribution curve (the insert in the bottom right- hand corners) acquired from 1.89 Ag/TiO (k). l The distributions of Ti, O, and Ag in the spherical crystal units of the 1.89 Ag/TiO . The XPS spectra of TiO and 1.89Ag/TiO 2 2 samples. The XPS full survey spectra (m) and the high- resolution spectra of Ti 2p (n), O 1s (o) of TiO and 1.89 Ag/TiO 2 2 samples and the high-resolution spectra of Ag 3d (p) of 1.89 Ag/ TiO Table 1 The BET surface area of the samples of 92–99%. According to the standard [34], when RGR is 90–100%, the cytotoxicity scale of a biomedical material is Sample name Specific surface area (m /g) noted as Grade 0, and when 75–90%, as Grade 1. A material TiO 359.98 that has a cytotoxicity of either Grade 0 or 1 means “no 0.56 Ag/TiO , 363.28 toxicity to the cell”. All data indicate that nearly all of the 1.10 Ag/TiO 359.17 TiO and Ag/TiO samples had no adverse impact on cell 2 2 1.89 Ag/TiO 354.06 viability. No significant difference in cell viability was 2.25 Ag/TiO 362.80 observed among the 0.12 Ag/ TiO , 0.56 Ag/ TiO , or 0.82 2 2 Ag/ TiO throughout the culturing period. highlights the distinct advantage that Ag has over other antibacterial agents, ones that might be effective on only 4 Discussion one of the two kinds of germ (gram-positive bacteria or gram-negative bacteria). The battle between surgeons and bacteria is a protracted war. Considering the susceptibility of artificial implant 3.3 Cell viability and proliferation surfaces to adhesion and colonization by microorganisms, implant-coating material having proper antibacterial prop- Figure 2c shows the viability of MC3T3-E1 cells cultured erties as well as cytocompatibility is being actively pur- in vitro with the TiO and Ag/TiO samples in α-MEM for sued. In this study, Ag/TiO antibacterial microspheres 2 2 2 1.0, 3.0, 5.0, and 7.0 d assessed by CCK-8 assay. When were produced using the conventional impregnation MC3T3-E1 cells were co-cultured with the sample, cell method. In this process, Ag particles attach to the TiO viability increased with time, especially on the seventh day, microsphere. The amount of Ag was adjusted by varying which exhibited a sharp increase. The initial relatively lower the amount of AgNO in the reaction solution. The TiO 3 2 viability at 1.0 and 3.0 d might be a result of the short microsphere powder with the proper amount of Ag exhibits adaptation period. The RGR of cells on the TiO and Ag/ relatively high antibacterial properties and no cytotoxic TiO samples at 5.0 and 7.0 days were >100% with the effects on MC3T3 cells. This study describes a simple exception of the 1.89 Ag/TiO and 2.25 Ag/TiO groups, approach by which to fabricate such Ag/TiO antibacterial 2 2 2 which showed relatively lower RGR values within the range coatings. Journal of Materials Science: Materials in Medicine (2018) 29:50 Page 7 of 10 50 The facile one-step homogeneous precipitation method was used in this work for preparing Ag/TiO antibacterial material. The crystal nucleation and growth of TiO involves the following reactions: COðÞ NH þ3H O ! CO "þ2NH H O ð2Þ 2 2 2 3 2 TiðÞ SO þ4NH H O ! TiO #þ2NðÞ H SO 4 3 2 2 4 4 2 2 ð3Þ þ2H O When heated up to 60 C, urea began to hydrolyze into CO and NH � H O. With the accumulation of NH � H O, 2 3 2 3 2 pH value of reaction solution increased which provides a favorable environment for the hydrolysis of Ti (SO ) . 4 2 TiO formed in the reaction precipitate and growth as a center of the nuclei. The formation of Ag can be given in sequence as fol- lows: 2AgNO ! 2Ag #þ2NO "þO"ð4Þ 2 2 The NH � H O formed in (1) also works as morphology 3 2 of catalyst in reaction system. Namely, the existence of NH � H O always lead to spherical morphology [35]. With the help of NH � H O, TiO and Ag nanoparticles self- 3 2 2 assemble into Ag/TiO microspheres, shown in Fig. 3a. And, at the same time, the gap between nanoparticles makes a hole net-like structure in the Ag/TiO microspheres, which lead to an excellent microstructure with a surface area of >355 m /g (Table 1). The high surface area makes it an ideal carrier for many drug-delivery applications. PVP in this reaction system acts as a stabilizer, inhibiting TiO and Ag nanoparticles from agglomerating and limiting nuclei size Fig. 2 The results of the disc diffusion test of Ag/TiO powder with [36]. With the help of dispersing agent ethylene glycol in different content of Ag against E. coli (a1–a7) and S. aureus (b1–b7) in dark. 1–7 correspond to samples of TiO , 0.12 Ag/TiO , 0.56 Ag/ 2 2 this study, a regular spherical TiO with a desirable range of TiO , 0.82 Ag/TiO , 1.1 Ag/TiO , 1.89 Ag/TiO , and 2.25 Ag/TiO , 2 2 2 2 2 Ag content can be produced in the medium. respectly. c RGR values of Ag/ TiO samples (*p < 0.05) and the Samples were highly effective against both gram-positive proliferation growth curve of the MC3T3 cells with incubation dura- bacteria (S. aureus) and gram-negative bacteria (E. coli), tion for 1, 3, 5 and 7 days which are the dominant bacteria of infections related to medical devices. The inhibition zone displayed in the disc diffusion test provides us clear evidence that the sur- Table 2 Averaged inhibition zones for TiO , 0.12 Ag/TiO , 0.56 Ag/ 2 2 rounding area of the material can also be protected. Cao TiO , 0.82 Ag/TiO , 1.1 Ag/TiO , 1.89 Ag/TiO , and 2.25 Ag/TiO 2 2 2 2 2 et al. [37] has confirmed that the physical Schotty contact Sample name Inhibition zone (mm) structure related to those boundaries at Ag/TiO is the main S. aureus E. coli reason for the antibacterial activity of Ag/TiO in dark. That is, in this structure, TiO is a semiconductor, and Ag is TiO 7.03 6.00 metal particle possessing electron storage behavior. The 0.12 Ag/TiO 7.48 6.00 electrons exist on bacterial membrane are electron donors. 0.56 Ag/TiO 9.48 8.34 Therefore, as suggested in Fig. 3b, in the dark, electrons 0.82 Ag/TiO 10.16 9.54 generated in bacteria metabolism are readily transferred 1.10 Ag/TiO 11.99 11.10 along the route of “bacterial membrane -TiO surface—Ag 1.89 Ag/TiO 12.63 11.41 /TiO interface—Ag metal particles” owing to the Schottky 2.25 Ag/TiO 13.48 12.00 barrier effect. This electron transfer mode blocks electron- 50 Page 8 of 10 Journal of Materials Science: Materials in Medicine (2018) 29:50 statement. As evidenced by the test, the Ag/TiO powder with the designated amount of Ag, 0.12 Ag/TiO , 0.56 Ag/ TiO , 0.82 Ag/TiO , or 1.1 Ag/TiO , demonstrated nearly 2 2 2 no opposing forces and even had a positive impact on the enhanced cell activities of MC3T3 cells. In addition, other samples with a higher content, such as 1.89 Ag/TiO and 2.25 Ag/TiO , although not similar to those of lower Ag content in promoting cell growth, exhibit no evident dele- terious effects on the basic ability of multiplication and survival of MC3T3-E1 cells. Furthermore, experimental evidence shows that biomaterials that contain a proper amount of Ag are compatible with mammalian cells, including osteoblasts [1, 41]. Generally, the Ag/TiO powder does have both good cytocompatibility and excel- lent antibacterial ability. 5 Conclusion By using Ti(SO ) as the Ti source, anatase microspheres 4 2 modified with Ag NPs were successfully produced using a Fig. 3 a The preparation reaction mechanism of Ag/TiO microsphere. urea-based homogeneous precipitation method. In the dark, b Illustration for electron transfer stimulated antibacterial action of Ag/ TiO microsphere in the dark. Namely, electrons are transferred along 2 the transferring route of “bacterial membrane -TiO surface the route of “bacterial membrane -TiO surface—Ag /TiO interface— 2 2 —Ag /TiO interface—Ag metal particles” for electrons Ag metal particles”, and lead to accumulation of valence-band hole (h + along owing to the Schottky barrier effect is the main reason ) at the TiO side that explains cytosolic and content leakage for the antibacterial effect. With a high specific surface area (oxidation) the NP-constructed Ag/TiO microspheres improves anti- hole recombination in TiO . As a result, redundant valence- bacterial performance against both S. aureus and E. coli. band holes (h ) at the TiO side adjacent the boundaries After incubation for 1.0 week, the Ag/TiO microspheres VB 2 2 can lead to biocide action through directly electrostatic showed an excellent cytocompatibility to MC3T3-E1 cells, effects-based reaction with the membrane lipids or stimu- as observed through the CCK8 test. NP-constructed Ag/ lating catalytic oxidation process. Consequently, pores TiO microspheres with high specific surface area prepared present on the outer membrane and eventually cytoplasm in this work provide us with a new choice for the applica- leak out and cell crack. tion of Ag/TiO biomaterial in medicine. Furthermore, the larger surface area provides Ag/TiO Funding This work was jointly supported by Science and Technology structure with more opportunities for contact with micro- Agency of Jilin Province (NO.20130206056GX) and Finance depart- organisms, which makes the sample a suitable vehicle in ment of Jilin Province (Research on dental implant coating materials with bacteriostatic activity). favor of the antibacterial properties of Ag. In addition, it is worth noting that, within our assay, samples were designed to be subjected to intense attack from bacteria with a con- Compliance with ethical standards 5 6 centration of 10 –10 CFU/mL. Such critical conditions are Conflict of interest The authors declare that they have no conflict of much harsher than those under normal circumstances interest. in vivo. It is also necessary to determine whether the Ag/TiO material possesses good cytocompatibility. But, whether the References electron transfering mode above still exists in mammalian cells has not known. In addition, although being larger and 1. Hardes J, Ahrens H, Gebert C, Streitbuerger A, Buerger H, Erren structurally more complex than prokaryotic cells, eukaryotic M, et al. Lack of toxicological side-effects in silver-coated megaprostheses in humans. Biomaterials. 2007;28(18):2869–75. cells can also be affected as microbes thorough other ways https://doi.org/10.1016/j.biomaterials.2007.02.033. if the concentration of Ag around is too high [5, 38, 39]. 2. Schmalzried TP, Amstutz HC, Au MK, Dorey FJ. Etiology of Therefore, the effect of Ag on cells exhibits a dose- deep sepsis in total hip arthroplasty. The significance of hemato- dependent tend [40]. In this experiment, the CCK8 test on genous and recurrent infections. Clin Orthop Relat Res. 1992;280:200–7. the sample was well in accordance with the above Journal of Materials Science: Materials in Medicine (2018) 29:50 Page 9 of 10 50 3. Balcazar JL, Subirats J, Borrego CM. The role of biofilms as 18. Takai A, Kamat PV. Capture, store, and discharge. Shuttling environmental reservoirs of antibiotic resistance. Front Microbiol. photogenerated electrons across TiO2-silver interface. ACS Nano. 2015;6:1216. https://doi.org/10.3389/fmicb.2015.01216. 2011;5(9):7369–76. https://doi.org/10.1021/nn202294b. 4. Jones SM, Morgan M, Humphrey TJ, Lappin-Scott H. Effect of 19. Maa J, Xiong Z, David Waite T, Jern NgcW, Zhao X. Enhanced vancomycin and rifampicin on meticillin-resistant Staphylococcus inactivation of bacteria with silver-modified mesoporous TiO aureus biofilms. Lancet. 2001;357(9249):40–1. https://doi.org/10. under weak ultraviolet irradiation. Microporous Mesoporous 1016/s0140-6736(00)03572-8. Mater. 2011;144:97–104. 5. Zhao L, Wang H, Huo K, Cui L, Zhang W, Ni H, et al. Anti- 20. Zhao G, Stevens SE Jr. Multiple parameters for the comprehen- bacterial nano-structured titania coating incorporated with silver sive evaluation of the susceptibility of Escherichia coli to the nanoparticles. Biomaterials. 2011;32(24):5706–16. https://doi.org/ silver ion. Biometals. 1998;11(1):27–32. 10.1016/j.biomaterials.2011.04.040. 21. Wang J, Wang C, Kang YQ. The effects of annealing treatment on 6. Palmero P, Fornabaio M, Montanaro L, Reveron H, Esnouf C, microstructure and contact resistance properties of cold sprayed Chevalier J. Towards long lasting zirconia-based composites for Ag-SnO2 coating. J Alloy Compd. 2017;714:698–703. dental implants. Part I: innovative synthesis, microstructural 22. Rathbun RC, Liedtke MD. Continuing professional development characterization and in vitro stability. Biomaterials. and the Journal of Hospital Infection. J Hosp Infect. 2002;51 2015;50:38–46. https://doi.org/10.1016/j.biomaterials.2015.01. (1):73. https://doi.org/10.1053/jhin.2002.1112. 018. 23. De Giglio E, Cafagna D, Cometa S, Allegretta A, Pedico A, 7. Cohen HC, Frost DC, Lieberthal TJ, Li L, Kao WJ. Biomaterials Giannossa LC, et al. An innovative, easily fabricated, silver differentially regulate Src kinases and phosphoinositide 3-kinase- nanoparticle-based titanium implant coating: development and gamma in polymorphonuclear leukocyte primary and tertiary analytical characterization. Anal Bioanal Chem. 2013;405(2- granule release. Biomaterials. 2015;50:47–55. https://doi.org/10. 3):805–16. https://doi.org/10.1007/s00216-012-6293-z. 1016/j.biomaterials.2015.01.050. 24. Brunauer S, Emmett PH, Teller E. Adsorption of gases in multi- 8. Maldonado M, Wong LY, Echeverria C, Ico G, Low K, Fujimoto molecular layers. J Am Chem Soc. 1938;60:309–19. T, et al. The effects of electrospun substrate-mediated cell colony 25. Ding B, Kim J, Kimura E, Shiratori S. Layer-by-layer structured morphology on the self-renewal of human induced pluripotent films of TiO nanoparticles and poly(acrylic acid) on electrospun stem cells. Biomaterials. 2015;50:10–9. https://doi.org/10.1016/j. nanofibres. Nanotechnology. 2004;15:913–7. biomaterials.2015.01.037. 26. Wikler MA, Cockerill FR. Performance standards for anti- 9. Toh YC, Xing J, Yu H. Modulation of integrin and E-cadherin- microbial susceptibility testing: Eighteenth Informational Sup- mediated adhesions to spatially control heterogeneity in human plement Wayne: Clinical and Laboratory Standards Institute; pluripotent stem cell differentiation. Biomaterials. 2015;50:87–97. 2008. https://doi.org/10.1016/j.biomaterials.2015.01.019. 27. Hu H, Zhang W, Qiao Y, Jiang X, Liu X, Ding C. Antibacterial 10. Guo Q, Cai X, Wang X, Yang J. “Paintable” 3D printed structures activity and increased bone marrow stem cell functions of Zn- via a post-ATRP process with antimicrobial function for biome- incorporated TiO2 coatings on titanium. Acta Biomater. 2012;8 dical applications. J Mater Chem B Mater Biol Med. 2013;1:6644. (2):904–15. https://doi.org/10.1016/j.actbio.2011.09.031. 11. Manabe K, Kyung KH, Shiratori S. Biocompatible slippery fluid- 28. Blake DM, Maness PC, Huang Z, Wolfrum EJ, Huang J, Jacoby infused films composed of chitosan and alginate via layer-by-layer WA. Application of the photocatalytic chemistry of titanium self-assembly and their antithrombogenicity. ACS Appl Mater dioxide to disinfection and the killing of cancer cells. Sep Purif Interfaces. 2015;7(8):4763–71. https://doi.org/10.1021/a Methods. 1999;28:1–50. m508393n. 29. Roguska A, Kudelski A, Pisarek M, Lewandowska M, Dolata M, 12. Zhu X, Zhang L, Wang J, Ma Z, Xu W, Li J, et al. Character- Janik-Czachor M. Raman investigations of TiO2 nanotube sub- ization of antimicrobial activity and mechanisms of low amphi- strates covered with thin Ag or Cu deposits. J Raman Spectrosc. pathic peptides with different alpha-helical propensity. Acta 2009;40:1652–6. Biomater. 2015;18:155–67. https://doi.org/10.1016/j.actbio.2015. 30. You M, Kim TG, Sung TG. Synthesis of Cu-doped TiO nanorods 02.023. with various aspect ratios and dopant concentrations. Cryst 13. Liu G, Wu G, Jin C, Kong Z. Preparation and antimicrobial Growth Des. 2010;10:983–7. activity of terpene-based polyurethane coatings with carbamate 31. Gao Y, Fang P, Chen F, Liu Y, Liu Z, Wang D. Enhancement of group-containing quaternary ammonium salts. Prog Org Coat. stability of N-doped TiO2 photocatalysts with Ag loading. Appl 2015;80:150–5. Surf Sci. 2013;265:796–801. 14. Kazemzadeh-Narbat M, Noordin S, Masri BA, Garbuz DS, 32. Xin B, Wang P, Ding D, Liu J, Ren Z, Fu H. Effect of surface Duncan CP, Hancock RE, et al. Drug release and bone growth species on Cu-TiO2 photocatalytic activity. Appl Surf Sci. studies of antimicrobial peptide-loaded calcium phosphate coating 2008;254:2569–74. on titanium. J Biomed Mater Res Part B Appl Biomater. 2012;100 33. Khalid NR, Ahmed E, Hong ZL, Ahmad M, Zhang Y, Khalid S. (5):1344–52. https://doi.org/10.1002/jbm.b.32701. Cu-doped TiO2 nanoparticles/graphene composites for efficient 15. Kargupta R, Bok S, Darr CM, Crist BD, Gangopadhyay K, visible-light photocatalysis. Ceram Int. 2013;39:7107–13. Gangopadhyay S, et al. Coatings and surface modifications 34. Haishima Y, Isama K, Hasegawa C, et al. A development and imparting antimicrobial activity to orthopedic implants. Wiley biological safety evaluation of novel PVC medical devices with Interdiscip Rev Nanomed Nanobiotechnol. 2014;6(5):475–95. surface structures modified by UV irradiation to suppress plasti- https://doi.org/10.1002/wnan.1273. cizer migration[J]. J Biomed Mater Res A. 2013;101A 16. Visai L, De Nardo L, Punta C, Melone L, Cigada A, Imbriani M, (9):2630–2643. et al. Titanium oxide antibacterial surfaces in biomedical devices. 35. Stöber W, Fink A, Bohn E. Controlled growth of monodisperse Int J Artif Organs. 2011;34(9):929–46. https://doi.org/10.5301/ija silica spheres in the micron size range. J Colloid Interface Sci. o.5000050. 1968;26:62–9. 17. Henderson MA. A surface science perspective on photocatalysis. Surf Sci Rep. 2011;66:185–297. 50 Page 10 of 10 Journal of Materials Science: Materials in Medicine (2018) 29:50 36. Archana D, Singh BK, Dutta J, Dutta PK. Chitosan-PVP-nano 39. Park EJ, Yi J, Kim Y, Choi K, Park K. Silver nanoparticles induce silver oxide wound dressing: in vitro and in vivo evaluation. Int J cytotoxicity by a Trojan-horse type mechanism. Toxicol in Vitro. Biol Macromol. 2015;73:49–57. https://doi.org/10.1016/j.ijbioma 2010;24(3):872–8. https://doi.org/10.1016/j.tiv.2009.12.001. c.2014.10.055. 40. Kawata K, Osawa M, Okabe S. In vitro toxicity of silver nano- 37. Cao H, Qiao Y, Liu X, Lu T, Cui T, Meng F, et al. Electron particles at noncytotoxic doses to HepG2 human hepatoma cells. storage mediated dark antibacterial action of bound silver nano- Environ Sci Technol. 2009;43(15):6046–51. particles: smaller is not always better. Acta Biomater. 2013;9 41. Agarwal A, Weis TL, Schurr MJ, Faith NG, Czuprynski CJ, (2):5100–10. https://doi.org/10.1016/j.actbio.2012.10.017. McAnulty JF, et al. Surfaces modified with nanometer-thick sil- 38. Chernousova S, Epple M. Silver as antibacterial agent: ion, ver-impregnated polymeric films that kill bacteria but support nanoparticle, and metal. Angew Chem. 2013;52(6):1636–53. growth of mammalian cells. Biomaterials. 2010;31(4):680–90. https://doi.org/10.1002/anie.201205923. https://doi.org/10.1016/j.biomaterials.2009.09.092. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Materials Science: Materials in Medicine Springer Journals

Synthesis, characterization, antibacterial activity in dark and in vitro cytocompatibility of Ag-incorporated TiO2 microspheres with high specific surface area

Loading next page...
 
/lp/springer_journal/synthesis-characterization-antibacterial-activity-in-dark-and-in-vitro-WV00BkpcIf
Publisher
Springer Journals
Copyright
Copyright © 2018 by Springer Science+Business Media, LLC, part of Springer Nature
Subject
Materials Science; Biomaterials; Biomedical Engineering; Regenerative Medicine/Tissue Engineering; Polymer Sciences; Ceramics, Glass, Composites, Natural Materials; Surfaces and Interfaces, Thin Films
ISSN
0957-4530
eISSN
1573-4838
DOI
10.1007/s10856-018-6042-8
pmid
29687280
Publisher site
See Article on Publisher Site

Abstract

1 Introduction implants, one of the most devastating complications of orthopedic surgery, is prominent. Implants are now a main component of medical practice, Unfortunately, when metal Ti exposed to air, an oxide promoting patient well-being and saving countless lives film on its surface would spontaneous format for the strong each year; however, along with these benefits comes some affinity between titanium (Ti) and oxygen (O). In addition, negative outcomes. Postoperative infection associated with under in vivo conditions, the oxide film will quickly * Yungang Luo Yungangl@hotmail.com Department of Orthopedics, Second Hospital, Jilin University, 130041 Changchun, China Department of Stomatology, Second Hospital, Jilin University, Department of Oral Medicine, West China Hospital of 130041 Changchun, China Stomatology, Sichuan University, Chengdu, China College of Chemistry, Jilin University, Qianjin Street, 130012 Changchun China 1234567890();,: 1234567890();,: 50 Page 2 of 10 Journal of Materials Science: Materials in Medicine (2018) 29:50 transform into a biofilm by combining with amylase and Nanosized TiO , owing to its remarkable NP size effect, protein, which exist throughout bodily fluid. This biofilm has always been the focus of biomaterial research; however, then acts as a protective shield against both host defenses the potential biological toxicity of NPs hinder its practical and antibacterial agents [1–3]. Antibiotic concentrations application in clinical settings. NP-constructed micro- might be as much as 1000-fold higher than needed to pre- spheres, which have both bulk size and the unique proper- vent the growth of inhibited bacteria in biofilms as to the ties of NPs, do provide an alternate route to making TiO planktonic bacteria [3, 4]. Given this, coating the surface of safer to use in biomaterials. implant device with antibacterial agents would be an In this study, NP-constructed microspheres Ag/TiO was effective solution [5]. prepared by a facile one-step process of homogeneous Various functional antimicrobial coatings have been precipitation. Ag at different concentrations doped into available, such as the FDA-approved INFUSE® bone graft TiO was fabricated and used to estimate its antibacterial (Medtronic) [6], CarriGen porous bone substitute material properties against gram-positive S. aureus and gram- (ETEX), [7] Cerasorb (Curasam) [8], and Spineplex P Bone negative E. coli. To investigate the cytocompatibility of Cement (Stryker) [9]. In general, antimicrobial coating Ag/TiO , MC3T3-E1 cells were used for the cytocompat- materials can be classified into two categories depending on ibility test. The results demonstrated that adding Ag parti- their method of intervention during infection and biofilm cles to TiO reduces bacterial growth while being nontoxic formation: coatings that physically prevent bacterial adhe- to mammalian cell growth. sion and those that release antimicrobial agents and kill adherent bacteria. The former always involve materials that could dissolve after a short period of time. Such as polymer 2 Material and methods brushes [10] and a layer-by-layer technique used in degradable multilayer coatings [11]. Though they have 2.1 Sample preparation shown great promise toward time-release coatings, the use of organics also brings some health risks in clinical The Ag-loaded TiO was prepared using the homogeneous applications. precipitation method. Silver nitrate (AgNO , 99.99%) was In contrast, materials that kill adherent bacteria are rela- used as the silver precursor with glycol as the solvent. To tively conventional. Antimicrobial peptides (AMPs) and 32.0 mL glycol were sequentially added 16.0 mL 1.25-mol/ quaternary ammonium salts (QASs) have exhibited positive L titanium sulfate (Ti[SO ] ), 0.05 mol/L AgNO , 24.0 g 4 2 3 effect in infection preventing [12, 13]. However, the potential urea (CO[NH ] ), and 2.0 mL 1.0-g/L polyvinylpyrrolidone 2 2 cytotoxicity limits their clinical usefulness [14, 15]. (PVP), followed by vigorous stirring to obtain a uniform Thus, antibacterial biomaterials for implant should solution. The volume of the mixture solution was fixed at simultaneously provide excellent antibacterial activity and 200 mL and the amount of AgNO was varied so that the cell compatibility. Among those are inorganic antibacterial molar ratio of Ag to TiO in the catalysts was within the agents, including silver (Ag), zinc oxide (ZnO), copper range of 0–2.5%. Subsequently, the reaction mixtures were oxide (Cu O, CuO), and Ti dioxide (TiO ), and so on. kept in an oscillating water bath at 90 °C for 4.0 h, with an 2 2 The antibacterial effect of TiO origin from its excellent oscillation frequency of 90–110 rpm. Finally, white pre- photo-catalytic activity [16]; however, the effect after light cipitates were collected, washed three times with deionized excitation will diminish in the dark [17, 18]. This is a cri- water, dried at 80 °C in an oven for ~4.0 h, and ground with tical flaw limiting its biomedical applications, since no light a mortar. The entire experiment process was done under exist around as soon as implants are placed in bone. For- darkened conditions. tunately, this situation can be improved by noble metal doping in TiO [19]. But researches on the antibacterial 2.2 Sample characterization ability in dark still not the masses. Ag has been known as disinfectant for its broad spectrum The elementary components and Ag concentrations in the of antimicrobial activities [20]. The extremely difficulty of samples were determined by energy-dispersive X-ray Ag resistance developed by bacteria is one of the greatest spectroscopy (EDS; EDAX-Falcon, Mahwah, NJ, USA) challenges in traditional antibiotics research, and does well with a resolution of 129 eV. in vivo applications [21, 22]. Giglio et al. [23] demonstrated The morphology was characterized by JSM-5500 LV the substantial antibacterial activity of hydrogel coatings of field-emission scanning electron microscope (SEM; JEOL, electro-synthesized Ag nanoparticle (AgNP-)modified poly Ltd., Tokyo, Japan) at an accelerating voltage of 30 kV. The (ethylene glycol diacrylate-)co-acrylic acid (PEGDA-AA) planar view was investigated using the TECNAI F20 high- on a Ti substrate against gram-positive (S. aureus) and resolution transmission electron microscopy (HR-TEM; FEI, gram-negative (Pseudomonas aeruginosa) bacteria. Hillsboro, OR, USA) at 200 kV. Distribution of Ag atoms in Journal of Materials Science: Materials in Medicine (2018) 29:50 Page 3 of 10 50 the TiO was monitored by EDS elemental mapping with an of the Ag/TiO powder. Cells were cultured with α-MEM 2 2 EDX-ray spectroscope attached to the HRTEM. (Gibco) supplemented with 10% fetal calf serum (Gibco) Crystal form of the powder was studied using the D/ and 100 mg/mL streptomycin coupled with 100 units/mL Max-2550 X-ray diffractometer (XRD; Rigaku Corporation, penicillin at 37 °C in a humidified atmosphere of .0% CO . Tokyo, Japan) fitted with a Cu Kα (λ = 1.5418 Å) source at The cells, which were ~70% confluent, were harvested by 50 kV and 200 mA, within the range of 2θ = 20 ~ 80° at a mild trypsinization, centrifuged, and resuspended in the scan speed of 10°/min. Nitrogen (N ) adsorption on the complete medium of α-MEM, and reseeded. The culture surface of samples was measured to calculate the specific media were refreshed every 2.0 d and all experiments were surface area using the Brunauer–Emmett–Teller (BET) repeated three times. equation [24]. A micrometrics ASAP 2420 surface area and porosity analyzer was used as described elsewhere [25]. The ESCALAB™ 250Xi X-ray Photoelectron Spectro- 2.4.2 Cell viability assay meter (XPS, ESCLAB 250, Thermo Scientific, Waltham, MA, USA) with an Al Kα radiation source (hν 1000 eV) was CCK-8 (Dojindo Laboratories, Kumamoto, Japan) was used used to identify the chemical constituents of the different to assess the cytotoxicity of the MC3T3-E1 cells in vitro. prepared samples and elemental states of the Ag particles. After counting, MC3T3-E1 cells were seeded at a density of 5000 cells/cm into 12-well plates. After incubation for 2.3 Antibacterial performance test 24.0 h, MC3T3-E1 cells were rinsed thoroughly with phosphate-buffered saline. The resuspended cells were then 2.3.1 Bacterial strains and growth conditions exposed to the Ag/TiO powders at 0.0885 g/cm having different amounts of Ag. Control groups involved the use of Strains of bacteria used for this evaluation were S. aureus α-MEM as the blank and the MC3T3-E1 cells not exposed (ATCC6538P) and E. coli (ATCC25922) purchased from to the samples as controls. The MC3T3-E1 cells used as a the www.bnbio.com. The bacteria were inoculated with positive control were cultured with all other conditions Luria-Bertani (LB) solid plate or liquid medium. being identical. After incubating for 1.0, 3.0, 5.0, 7.0 day, respectively, CCK-8 was added to every well and incubated 2.3.2 The disc diffusion test for 2.0 h; supernatant was transferred to new 12-well cell culture plates. The supernatant’s absorbance value of The antibacterial activity of Ag/TiO powder was evaluated optical density (OD) thereafter was measured using the using the disc diffusion test. The test is performed using the Varioskan Flash Multimode Reader (Thermo Scientific, guidelines of the Clinical and Laboratory Standards Institute Waltham, MA, USA) at a wavelength of 450 nm accom- [26]. Solutions of Ag/TiO samples with a concentration of panied by a reference wavelength of 630 nm. Finally, the 7.0 mg/mL were prepared using Ag/TiO powder in double- viability of MC3T3-E1 cells was expressed as a percentage distilled water. These solutions were then doped onto of relative growth rate (RGR) according to the following Whatman filters and sterilized with moist heat. Melted LB formula: medium (90 mL) was poured into petri dishes (Iwaki, RGRðÞ 100%¼ ðOD  OD Þ=ðOD  OD Þ test blank control blank Japan) and solidified. The agar surfaces were then inocu- 100% lated using a glass swab dipped in the bacterial cell sus- 5 6 pension. The suspension was adjusted to 10 –10 colony ð1Þ forming units (CFU) of the previous test organisms. After drying for approximately 5.0 min, the inoculated agar plates where, OD is the OD of the Ag/TiO sample and OD test 2 control were planted with the Ag/TiO dampened filter papers, and OD are the ODs of the MC3T3-E1 cells without 2 blank incubated for 16–18 h at 37.0 °C in dark, and examined for samples and the blank control sample (α-MEM medium). the diameter of the inhibitory zones where no visible bac- terial growth could be observed. Each sample was made in 2.5 Statistical analyses triplicate. The assays were performed in triplicate and data were 2.4 Cell viability expressed as the mean ± standard deviation. Each experi- ment was repeated three times with data of a typical 2.4.1 Cell culture experiment shown. A one-way analysis of variance com- bined with a Student-Newman-Keuls post hoc test was used Newborn mouse calvaria-derived preosteoblastic cells to determine the level of significance. p < 0.05 was regarded (MC3T3-E1 subclone 14) were used in the biological assays as significant. 50 Page 4 of 10 Journal of Materials Science: Materials in Medicine (2018) 29:50 3 Results The elemental constituents of the different prepared samples and chemical states of the samples were determined 3.1 Sample characterization by XPS. The XPS full survey spectra of TiO and Ag/TiO 2 2 samples and HR spectra of O 1 s, Ag 3d, and Ti 2p are EDS analysis showed that the samples were composed shown in Fig. 1m–p. The C signal is ascribed to adventi- mainly of the Ti, Ag, and O (Fig. 1a–g). Atomic con- tious contamination. Ag can be obviously confirmed in the centrations listed under the images in Fig. 1a–g revealed full spectrum of the 1.89 Ag/TiO sample shown in Fig. 1m that the atomic ratio percentage (at%) of Ag to Ti in the in addition to Ti and O. From the HR spectra in Fig. 1n, Ti Ag/TiO powder varied from 0 to 2.25%. The Ag/TiO 2p exhibits two peaks centered at 464.2 and 458.5 eV, 2 2 powder with different content of Ag is referred to in the assigned to the binding energies of Ti (2p ) and Ti (2p ), 1/2 3/2 following text as TiO , 0.12 Ag/TiO , 0.56 Ag/TiO , 0.82 respectively [27]. The split between Ti (2p ) and Ti (2p ) 2 2 2 1/2 3/2 4+ Ag/TiO , 1.1 Ag/TiO , 1.89 Ag/TiO , and 2.25 Ag/TiO is 5.7 eV, indicative of Ti in the anatase phase of TiO 2 2 2 2 2 where the numerals represent the atomic percentage of Ag [28, 29]. The binding energies of Ti2p were slightly lower to Ti. in the presence of Ag. The lower Fermi level, compared to Moreover, the anatase phase of TiO and tetragonal that of TiO , makes Ag responsible for the shift in binding 2 2 structure of Ag can be observed in the interior HR-TEM energy because of the transition of electrons from TiO to lattice pattern (Fig. 1h), in which the interplanar spacing of Ag and the subsequent outer cloud density changes in TiO ~0.352 and ~0.189 nm account for 101 and 200 planes of [30, 31]. The O 1 s peak (Fig. 1o) consists of three sub- anatase, respectively. In addition, the ~0.204 nm corre- peaks. The O 1s peak at binding energy of 529.7 and sponds to the interplanar spacing of 200 planes of Ag. 531.45 eV are assigned to the Ti-O bonds, which have the Surface morphology of the TiO and 1.89 Ag/TiO largest peak area [32]. The O 1s peak at 532.6 eV confirms 2 2 powder is shown in Fig. 1i. TiO powder was entirely the presence of the surface chemisorbed –OH of TiO 2 2 composed of spherical crystal units, whose diameter varied matrix [33]. The Ag 3d doublets at 367.71 eV (Ag 3d ) 5/2 from 2.0 to 5.0 μm. When loaded with Ag, the morphology and 373.80 eV (Ag 3d ) (Fig. 1p) with a spin energy 3/2 as well as diameter of the crystal units were similar to that separation of 6.09 eV correspond to the binding energy of of TiO alone. Ag [5], confirming the existence of the oxidized state of Ag Figure 1j exhibits the XRD patterns of the 1.89 Ag/TiO . in the Ag/TiO sample. 2 2 A typical XRD pattern of a TiO sample is shown in the image, and all characteristic diffraction peaks at 2θ = 25.3° 3.2 The disc diffusion test (101), 37.8° (004), 48.0° (200), and 55.1° (211) are readily indexed to the anatase phase of TiO according to JCPDS The results of the disc diffusion test were observed in Ag/ card No. 84-1285; however, the characteristic peaks of Ag TiO powder with different contents of Ag (Fig. 2). The were missing in the patterns. The absence of Ag peaks is samples show the inhibitory effect of Ag/TiO against both very likely a result of the small amount of added Ag, which E. coli (Fig. 2a1–a7) and S. aureus (Fig. 2b1–b7), which can be confirmed by the results of the HR-TEM lattice exhibit observable inhibition zones with a diameter pattern. >7.0 mm (Table 2), with the exception of TiO and 0.1 Ag/ The BET surface area is another important aspect that TiO against E. coli because of their smaller or no Ag can provide the basis for the antibacterial properties. The N content. Of the samples enhanced with increasing Ag con- adsorption-desorption isotherm of 1.89 Ag/TiO,as tent in the powder, 2.25 Ag/TiO showed the most promi- 2 2 observed in Fig. 1k, was used to study the pore structure of nent inhibiting effect (exhibits the largest inhibition zone) Ag/TiO samples, displaying a higher surface area of owing to the largest Ag content, which highlights the sig- 362.8 m /g. The Barrett-Joyner-Halenda pore size distribu- nificance of the amount of Ag incorporated into the powder tion curve corresponding to the isotherm is shown in the on preventing the colonization of bacteria. The antibacterial insert in Fig. 1k and indicates the presence of holes in the activity of the samples against S. aureus was significantly spherical crystal unit’s surface. The BET surface area of the stronger than that against E. coli. The diameter of the samples is as 355–365 m /g (Table 1). As the amount of Ag inhibition area of the S. aureus group was significantly particles on Ag/TiO increases, the specific surface area of different (P < 0.05) from that of the E. coli group, which the Ag/TiO powders decreases slightly. could be attributed to the disparity between the two bacteria The distributions of Ti, O, and Ag in the spherical crystal on the structure. For the E. coli group, there always exists units obtained by EDS elemental mapping are shown in an area in which there is a density reduction of bacterial Fig. 1l The elemental maps reveal that Ag is homo- colonies instead of a clear zone of inhibition as with the S. geneously dispersed throughout the spherical TiO crystal aureus group. This might be related to different antibacterial units. effects of Ag ions on the two bacteria. All of the above Journal of Materials Science: Materials in Medicine (2018) 29:50 Page 5 of 10 50 Fig. 1 Continued 50 Page 6 of 10 Journal of Materials Science: Materials in Medicine (2018) 29:50 Fig. 1 a–g EDS data obtained from Ag/TiO powder with different amount of Ag showing changes in Ag content with a range of 0–2.25% (at%). HR- TEM images of the 1.89 Ag/ TiO powder (h). Image I showing the structure of 1.89 Ag/TiO powder. j XRD of 1.89 Ag/TiO powder was shown. Nitrogen adsorption-desorption isotherm and the corresponding BJH pore size distribution curve (the insert in the bottom right- hand corners) acquired from 1.89 Ag/TiO (k). l The distributions of Ti, O, and Ag in the spherical crystal units of the 1.89 Ag/TiO . The XPS spectra of TiO and 1.89Ag/TiO 2 2 samples. The XPS full survey spectra (m) and the high- resolution spectra of Ti 2p (n), O 1s (o) of TiO and 1.89 Ag/TiO 2 2 samples and the high-resolution spectra of Ag 3d (p) of 1.89 Ag/ TiO Table 1 The BET surface area of the samples of 92–99%. According to the standard [34], when RGR is 90–100%, the cytotoxicity scale of a biomedical material is Sample name Specific surface area (m /g) noted as Grade 0, and when 75–90%, as Grade 1. A material TiO 359.98 that has a cytotoxicity of either Grade 0 or 1 means “no 0.56 Ag/TiO , 363.28 toxicity to the cell”. All data indicate that nearly all of the 1.10 Ag/TiO 359.17 TiO and Ag/TiO samples had no adverse impact on cell 2 2 1.89 Ag/TiO 354.06 viability. No significant difference in cell viability was 2.25 Ag/TiO 362.80 observed among the 0.12 Ag/ TiO , 0.56 Ag/ TiO , or 0.82 2 2 Ag/ TiO throughout the culturing period. highlights the distinct advantage that Ag has over other antibacterial agents, ones that might be effective on only 4 Discussion one of the two kinds of germ (gram-positive bacteria or gram-negative bacteria). The battle between surgeons and bacteria is a protracted war. Considering the susceptibility of artificial implant 3.3 Cell viability and proliferation surfaces to adhesion and colonization by microorganisms, implant-coating material having proper antibacterial prop- Figure 2c shows the viability of MC3T3-E1 cells cultured erties as well as cytocompatibility is being actively pur- in vitro with the TiO and Ag/TiO samples in α-MEM for sued. In this study, Ag/TiO antibacterial microspheres 2 2 2 1.0, 3.0, 5.0, and 7.0 d assessed by CCK-8 assay. When were produced using the conventional impregnation MC3T3-E1 cells were co-cultured with the sample, cell method. In this process, Ag particles attach to the TiO viability increased with time, especially on the seventh day, microsphere. The amount of Ag was adjusted by varying which exhibited a sharp increase. The initial relatively lower the amount of AgNO in the reaction solution. The TiO 3 2 viability at 1.0 and 3.0 d might be a result of the short microsphere powder with the proper amount of Ag exhibits adaptation period. The RGR of cells on the TiO and Ag/ relatively high antibacterial properties and no cytotoxic TiO samples at 5.0 and 7.0 days were >100% with the effects on MC3T3 cells. This study describes a simple exception of the 1.89 Ag/TiO and 2.25 Ag/TiO groups, approach by which to fabricate such Ag/TiO antibacterial 2 2 2 which showed relatively lower RGR values within the range coatings. Journal of Materials Science: Materials in Medicine (2018) 29:50 Page 7 of 10 50 The facile one-step homogeneous precipitation method was used in this work for preparing Ag/TiO antibacterial material. The crystal nucleation and growth of TiO involves the following reactions: COðÞ NH þ3H O ! CO "þ2NH H O ð2Þ 2 2 2 3 2 TiðÞ SO þ4NH H O ! TiO #þ2NðÞ H SO 4 3 2 2 4 4 2 2 ð3Þ þ2H O When heated up to 60 C, urea began to hydrolyze into CO and NH � H O. With the accumulation of NH � H O, 2 3 2 3 2 pH value of reaction solution increased which provides a favorable environment for the hydrolysis of Ti (SO ) . 4 2 TiO formed in the reaction precipitate and growth as a center of the nuclei. The formation of Ag can be given in sequence as fol- lows: 2AgNO ! 2Ag #þ2NO "þO"ð4Þ 2 2 The NH � H O formed in (1) also works as morphology 3 2 of catalyst in reaction system. Namely, the existence of NH � H O always lead to spherical morphology [35]. With the help of NH � H O, TiO and Ag nanoparticles self- 3 2 2 assemble into Ag/TiO microspheres, shown in Fig. 3a. And, at the same time, the gap between nanoparticles makes a hole net-like structure in the Ag/TiO microspheres, which lead to an excellent microstructure with a surface area of >355 m /g (Table 1). The high surface area makes it an ideal carrier for many drug-delivery applications. PVP in this reaction system acts as a stabilizer, inhibiting TiO and Ag nanoparticles from agglomerating and limiting nuclei size Fig. 2 The results of the disc diffusion test of Ag/TiO powder with [36]. With the help of dispersing agent ethylene glycol in different content of Ag against E. coli (a1–a7) and S. aureus (b1–b7) in dark. 1–7 correspond to samples of TiO , 0.12 Ag/TiO , 0.56 Ag/ 2 2 this study, a regular spherical TiO with a desirable range of TiO , 0.82 Ag/TiO , 1.1 Ag/TiO , 1.89 Ag/TiO , and 2.25 Ag/TiO , 2 2 2 2 2 Ag content can be produced in the medium. respectly. c RGR values of Ag/ TiO samples (*p < 0.05) and the Samples were highly effective against both gram-positive proliferation growth curve of the MC3T3 cells with incubation dura- bacteria (S. aureus) and gram-negative bacteria (E. coli), tion for 1, 3, 5 and 7 days which are the dominant bacteria of infections related to medical devices. The inhibition zone displayed in the disc diffusion test provides us clear evidence that the sur- Table 2 Averaged inhibition zones for TiO , 0.12 Ag/TiO , 0.56 Ag/ 2 2 rounding area of the material can also be protected. Cao TiO , 0.82 Ag/TiO , 1.1 Ag/TiO , 1.89 Ag/TiO , and 2.25 Ag/TiO 2 2 2 2 2 et al. [37] has confirmed that the physical Schotty contact Sample name Inhibition zone (mm) structure related to those boundaries at Ag/TiO is the main S. aureus E. coli reason for the antibacterial activity of Ag/TiO in dark. That is, in this structure, TiO is a semiconductor, and Ag is TiO 7.03 6.00 metal particle possessing electron storage behavior. The 0.12 Ag/TiO 7.48 6.00 electrons exist on bacterial membrane are electron donors. 0.56 Ag/TiO 9.48 8.34 Therefore, as suggested in Fig. 3b, in the dark, electrons 0.82 Ag/TiO 10.16 9.54 generated in bacteria metabolism are readily transferred 1.10 Ag/TiO 11.99 11.10 along the route of “bacterial membrane -TiO surface—Ag 1.89 Ag/TiO 12.63 11.41 /TiO interface—Ag metal particles” owing to the Schottky 2.25 Ag/TiO 13.48 12.00 barrier effect. This electron transfer mode blocks electron- 50 Page 8 of 10 Journal of Materials Science: Materials in Medicine (2018) 29:50 statement. As evidenced by the test, the Ag/TiO powder with the designated amount of Ag, 0.12 Ag/TiO , 0.56 Ag/ TiO , 0.82 Ag/TiO , or 1.1 Ag/TiO , demonstrated nearly 2 2 2 no opposing forces and even had a positive impact on the enhanced cell activities of MC3T3 cells. In addition, other samples with a higher content, such as 1.89 Ag/TiO and 2.25 Ag/TiO , although not similar to those of lower Ag content in promoting cell growth, exhibit no evident dele- terious effects on the basic ability of multiplication and survival of MC3T3-E1 cells. Furthermore, experimental evidence shows that biomaterials that contain a proper amount of Ag are compatible with mammalian cells, including osteoblasts [1, 41]. Generally, the Ag/TiO powder does have both good cytocompatibility and excel- lent antibacterial ability. 5 Conclusion By using Ti(SO ) as the Ti source, anatase microspheres 4 2 modified with Ag NPs were successfully produced using a Fig. 3 a The preparation reaction mechanism of Ag/TiO microsphere. urea-based homogeneous precipitation method. In the dark, b Illustration for electron transfer stimulated antibacterial action of Ag/ TiO microsphere in the dark. Namely, electrons are transferred along 2 the transferring route of “bacterial membrane -TiO surface the route of “bacterial membrane -TiO surface—Ag /TiO interface— 2 2 —Ag /TiO interface—Ag metal particles” for electrons Ag metal particles”, and lead to accumulation of valence-band hole (h + along owing to the Schottky barrier effect is the main reason ) at the TiO side that explains cytosolic and content leakage for the antibacterial effect. With a high specific surface area (oxidation) the NP-constructed Ag/TiO microspheres improves anti- hole recombination in TiO . As a result, redundant valence- bacterial performance against both S. aureus and E. coli. band holes (h ) at the TiO side adjacent the boundaries After incubation for 1.0 week, the Ag/TiO microspheres VB 2 2 can lead to biocide action through directly electrostatic showed an excellent cytocompatibility to MC3T3-E1 cells, effects-based reaction with the membrane lipids or stimu- as observed through the CCK8 test. NP-constructed Ag/ lating catalytic oxidation process. Consequently, pores TiO microspheres with high specific surface area prepared present on the outer membrane and eventually cytoplasm in this work provide us with a new choice for the applica- leak out and cell crack. tion of Ag/TiO biomaterial in medicine. Furthermore, the larger surface area provides Ag/TiO Funding This work was jointly supported by Science and Technology structure with more opportunities for contact with micro- Agency of Jilin Province (NO.20130206056GX) and Finance depart- organisms, which makes the sample a suitable vehicle in ment of Jilin Province (Research on dental implant coating materials with bacteriostatic activity). favor of the antibacterial properties of Ag. In addition, it is worth noting that, within our assay, samples were designed to be subjected to intense attack from bacteria with a con- Compliance with ethical standards 5 6 centration of 10 –10 CFU/mL. Such critical conditions are Conflict of interest The authors declare that they have no conflict of much harsher than those under normal circumstances interest. in vivo. It is also necessary to determine whether the Ag/TiO material possesses good cytocompatibility. But, whether the References electron transfering mode above still exists in mammalian cells has not known. In addition, although being larger and 1. Hardes J, Ahrens H, Gebert C, Streitbuerger A, Buerger H, Erren structurally more complex than prokaryotic cells, eukaryotic M, et al. Lack of toxicological side-effects in silver-coated megaprostheses in humans. Biomaterials. 2007;28(18):2869–75. cells can also be affected as microbes thorough other ways https://doi.org/10.1016/j.biomaterials.2007.02.033. if the concentration of Ag around is too high [5, 38, 39]. 2. Schmalzried TP, Amstutz HC, Au MK, Dorey FJ. Etiology of Therefore, the effect of Ag on cells exhibits a dose- deep sepsis in total hip arthroplasty. The significance of hemato- dependent tend [40]. In this experiment, the CCK8 test on genous and recurrent infections. Clin Orthop Relat Res. 1992;280:200–7. the sample was well in accordance with the above Journal of Materials Science: Materials in Medicine (2018) 29:50 Page 9 of 10 50 3. Balcazar JL, Subirats J, Borrego CM. The role of biofilms as 18. Takai A, Kamat PV. Capture, store, and discharge. Shuttling environmental reservoirs of antibiotic resistance. Front Microbiol. photogenerated electrons across TiO2-silver interface. ACS Nano. 2015;6:1216. https://doi.org/10.3389/fmicb.2015.01216. 2011;5(9):7369–76. https://doi.org/10.1021/nn202294b. 4. Jones SM, Morgan M, Humphrey TJ, Lappin-Scott H. Effect of 19. Maa J, Xiong Z, David Waite T, Jern NgcW, Zhao X. Enhanced vancomycin and rifampicin on meticillin-resistant Staphylococcus inactivation of bacteria with silver-modified mesoporous TiO aureus biofilms. Lancet. 2001;357(9249):40–1. https://doi.org/10. under weak ultraviolet irradiation. Microporous Mesoporous 1016/s0140-6736(00)03572-8. Mater. 2011;144:97–104. 5. Zhao L, Wang H, Huo K, Cui L, Zhang W, Ni H, et al. Anti- 20. Zhao G, Stevens SE Jr. Multiple parameters for the comprehen- bacterial nano-structured titania coating incorporated with silver sive evaluation of the susceptibility of Escherichia coli to the nanoparticles. Biomaterials. 2011;32(24):5706–16. https://doi.org/ silver ion. Biometals. 1998;11(1):27–32. 10.1016/j.biomaterials.2011.04.040. 21. Wang J, Wang C, Kang YQ. The effects of annealing treatment on 6. Palmero P, Fornabaio M, Montanaro L, Reveron H, Esnouf C, microstructure and contact resistance properties of cold sprayed Chevalier J. Towards long lasting zirconia-based composites for Ag-SnO2 coating. J Alloy Compd. 2017;714:698–703. dental implants. Part I: innovative synthesis, microstructural 22. Rathbun RC, Liedtke MD. Continuing professional development characterization and in vitro stability. Biomaterials. and the Journal of Hospital Infection. J Hosp Infect. 2002;51 2015;50:38–46. https://doi.org/10.1016/j.biomaterials.2015.01. (1):73. https://doi.org/10.1053/jhin.2002.1112. 018. 23. De Giglio E, Cafagna D, Cometa S, Allegretta A, Pedico A, 7. Cohen HC, Frost DC, Lieberthal TJ, Li L, Kao WJ. Biomaterials Giannossa LC, et al. An innovative, easily fabricated, silver differentially regulate Src kinases and phosphoinositide 3-kinase- nanoparticle-based titanium implant coating: development and gamma in polymorphonuclear leukocyte primary and tertiary analytical characterization. Anal Bioanal Chem. 2013;405(2- granule release. Biomaterials. 2015;50:47–55. https://doi.org/10. 3):805–16. https://doi.org/10.1007/s00216-012-6293-z. 1016/j.biomaterials.2015.01.050. 24. Brunauer S, Emmett PH, Teller E. Adsorption of gases in multi- 8. Maldonado M, Wong LY, Echeverria C, Ico G, Low K, Fujimoto molecular layers. J Am Chem Soc. 1938;60:309–19. T, et al. The effects of electrospun substrate-mediated cell colony 25. Ding B, Kim J, Kimura E, Shiratori S. Layer-by-layer structured morphology on the self-renewal of human induced pluripotent films of TiO nanoparticles and poly(acrylic acid) on electrospun stem cells. Biomaterials. 2015;50:10–9. https://doi.org/10.1016/j. nanofibres. Nanotechnology. 2004;15:913–7. biomaterials.2015.01.037. 26. Wikler MA, Cockerill FR. Performance standards for anti- 9. Toh YC, Xing J, Yu H. Modulation of integrin and E-cadherin- microbial susceptibility testing: Eighteenth Informational Sup- mediated adhesions to spatially control heterogeneity in human plement Wayne: Clinical and Laboratory Standards Institute; pluripotent stem cell differentiation. Biomaterials. 2015;50:87–97. 2008. https://doi.org/10.1016/j.biomaterials.2015.01.019. 27. Hu H, Zhang W, Qiao Y, Jiang X, Liu X, Ding C. Antibacterial 10. Guo Q, Cai X, Wang X, Yang J. “Paintable” 3D printed structures activity and increased bone marrow stem cell functions of Zn- via a post-ATRP process with antimicrobial function for biome- incorporated TiO2 coatings on titanium. Acta Biomater. 2012;8 dical applications. J Mater Chem B Mater Biol Med. 2013;1:6644. (2):904–15. https://doi.org/10.1016/j.actbio.2011.09.031. 11. Manabe K, Kyung KH, Shiratori S. Biocompatible slippery fluid- 28. Blake DM, Maness PC, Huang Z, Wolfrum EJ, Huang J, Jacoby infused films composed of chitosan and alginate via layer-by-layer WA. Application of the photocatalytic chemistry of titanium self-assembly and their antithrombogenicity. ACS Appl Mater dioxide to disinfection and the killing of cancer cells. Sep Purif Interfaces. 2015;7(8):4763–71. https://doi.org/10.1021/a Methods. 1999;28:1–50. m508393n. 29. Roguska A, Kudelski A, Pisarek M, Lewandowska M, Dolata M, 12. Zhu X, Zhang L, Wang J, Ma Z, Xu W, Li J, et al. Character- Janik-Czachor M. Raman investigations of TiO2 nanotube sub- ization of antimicrobial activity and mechanisms of low amphi- strates covered with thin Ag or Cu deposits. J Raman Spectrosc. pathic peptides with different alpha-helical propensity. Acta 2009;40:1652–6. Biomater. 2015;18:155–67. https://doi.org/10.1016/j.actbio.2015. 30. You M, Kim TG, Sung TG. Synthesis of Cu-doped TiO nanorods 02.023. with various aspect ratios and dopant concentrations. Cryst 13. Liu G, Wu G, Jin C, Kong Z. Preparation and antimicrobial Growth Des. 2010;10:983–7. activity of terpene-based polyurethane coatings with carbamate 31. Gao Y, Fang P, Chen F, Liu Y, Liu Z, Wang D. Enhancement of group-containing quaternary ammonium salts. Prog Org Coat. stability of N-doped TiO2 photocatalysts with Ag loading. Appl 2015;80:150–5. Surf Sci. 2013;265:796–801. 14. Kazemzadeh-Narbat M, Noordin S, Masri BA, Garbuz DS, 32. Xin B, Wang P, Ding D, Liu J, Ren Z, Fu H. Effect of surface Duncan CP, Hancock RE, et al. Drug release and bone growth species on Cu-TiO2 photocatalytic activity. Appl Surf Sci. studies of antimicrobial peptide-loaded calcium phosphate coating 2008;254:2569–74. on titanium. J Biomed Mater Res Part B Appl Biomater. 2012;100 33. Khalid NR, Ahmed E, Hong ZL, Ahmad M, Zhang Y, Khalid S. (5):1344–52. https://doi.org/10.1002/jbm.b.32701. Cu-doped TiO2 nanoparticles/graphene composites for efficient 15. Kargupta R, Bok S, Darr CM, Crist BD, Gangopadhyay K, visible-light photocatalysis. Ceram Int. 2013;39:7107–13. Gangopadhyay S, et al. Coatings and surface modifications 34. Haishima Y, Isama K, Hasegawa C, et al. A development and imparting antimicrobial activity to orthopedic implants. Wiley biological safety evaluation of novel PVC medical devices with Interdiscip Rev Nanomed Nanobiotechnol. 2014;6(5):475–95. surface structures modified by UV irradiation to suppress plasti- https://doi.org/10.1002/wnan.1273. cizer migration[J]. J Biomed Mater Res A. 2013;101A 16. Visai L, De Nardo L, Punta C, Melone L, Cigada A, Imbriani M, (9):2630–2643. et al. Titanium oxide antibacterial surfaces in biomedical devices. 35. Stöber W, Fink A, Bohn E. Controlled growth of monodisperse Int J Artif Organs. 2011;34(9):929–46. https://doi.org/10.5301/ija silica spheres in the micron size range. J Colloid Interface Sci. o.5000050. 1968;26:62–9. 17. Henderson MA. A surface science perspective on photocatalysis. Surf Sci Rep. 2011;66:185–297. 50 Page 10 of 10 Journal of Materials Science: Materials in Medicine (2018) 29:50 36. Archana D, Singh BK, Dutta J, Dutta PK. Chitosan-PVP-nano 39. Park EJ, Yi J, Kim Y, Choi K, Park K. Silver nanoparticles induce silver oxide wound dressing: in vitro and in vivo evaluation. Int J cytotoxicity by a Trojan-horse type mechanism. Toxicol in Vitro. Biol Macromol. 2015;73:49–57. https://doi.org/10.1016/j.ijbioma 2010;24(3):872–8. https://doi.org/10.1016/j.tiv.2009.12.001. c.2014.10.055. 40. Kawata K, Osawa M, Okabe S. In vitro toxicity of silver nano- 37. Cao H, Qiao Y, Liu X, Lu T, Cui T, Meng F, et al. Electron particles at noncytotoxic doses to HepG2 human hepatoma cells. storage mediated dark antibacterial action of bound silver nano- Environ Sci Technol. 2009;43(15):6046–51. particles: smaller is not always better. Acta Biomater. 2013;9 41. Agarwal A, Weis TL, Schurr MJ, Faith NG, Czuprynski CJ, (2):5100–10. https://doi.org/10.1016/j.actbio.2012.10.017. McAnulty JF, et al. Surfaces modified with nanometer-thick sil- 38. Chernousova S, Epple M. Silver as antibacterial agent: ion, ver-impregnated polymeric films that kill bacteria but support nanoparticle, and metal. Angew Chem. 2013;52(6):1636–53. growth of mammalian cells. Biomaterials. 2010;31(4):680–90. https://doi.org/10.1002/anie.201205923. https://doi.org/10.1016/j.biomaterials.2009.09.092.

Journal

Journal of Materials Science: Materials in MedicineSpringer Journals

Published: Apr 23, 2018

References