To investigate the mechanism of inhibition of silver ions on microorganisms, two strains of bacteria, namely Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus), were treated with AgNO(3) and studied using combined electron microscopy and X-ray microanalysis. Similar morphological changes occurred in both E. coli and S. aureus cells after Ag(+) treatment. The cytoplasm membrane detached from the cell wall. A remarkable electron-light region appeared in the center of the cells, which contained condensed deoxyribonucleic acid (DNA) molecules. There are many small electron-dense granules either surrounding the cell wall or depositing inside the cells. The existence of elements of silver and sulfur in the electron-dense granules and cytoplasm detected by X-ray microanalysis suggested the antibacterial mechanism of silver: DNA lost its replication ability and the protein became inactivated after Ag(+) treatment. The slighter morphological changes of S. aureus compared with E. coli recommended a defense system of S. aureus against the inhibitory effects of Ag(+) ions.

A mechanistic study of the antibacterial effect of silver ions on Escherichia coli and Staphylococcus aureus.

http://users.encs.concordia.ca/~mojtaba/elec6271/silver%20nanoparticles.pdf

Silver nanoparticles: green synthesis and their antimicrobial activities.

Synthesis and effect of silver nanoparticles on the antibacterial activity of different antibiotics against Staphylococcus aureus and Escherichia coli.

The biological approach to forming crystals is proving to be most surprising. Mollusks build their shells by using a hydrophobic silk gel, very acidic aspartic acid rich proteins, and apparently also an amorphous precursor phase from which the crystals form. All this takes place in a highly structured chitinous framework. Here we present ideas on how these disparate components work together to produce the highly structured pearly nacreous layer of the mollusk shell.

/pdf/mollusk-shell-formation-a-source-of-new-concepts-for-4d1anmsagc.pdf

Mollusk shell formation: a source of new concepts for understanding biomineralization processes.

The study of antimicrobial activity and preservative effects of nanosilver ingredient

The antimicrobial ceramics (AC) based on hydroxyapatite (HA) were made in a wet chemical process with additions of AgNO3, Cu(NO3)2. 3H2O and Zn(NO3)2. 6H2O. The ACs were composed of metal-ion substituted hydroxyapatite and nitrate-apatite, which was identified by X-ray diffraction. The viable count and turbidity measurement was adopted to observe the antimicrobial effects of the various ACs. The aerobic Escherichia coli was used in the study. An obvious antimicrobial effect against E. coli was observed in Ag+ AC. In contrast to Ag+ AC, it was difficult to ascertain any bactericidal effect in the case of Cu2+ and Zn2+ AC. The bactericidal effect of Ag+ was observed using a dialysis tube experiment. This suggests that Ag+ dissolved out and reacted with E. coli, thus inhibiting its growth.

Antimicrobial effects of metal ions (Ag+, Cu2+, Zn2+) in hydroxyapatite.

Implant-caused infections are considered to be serious and are common complications in orthopedic surgery, and various methods have been developed for delivering antibiotics at the bone±implant interface [1±4]. In previous studies, ion beam±assisted deposition (IBAD) was successfully used to produce a dense and ultra-adherent hydroxyapatite (HAp) coating on titanium alloy and alumina [5, 6]. It was also recently proven that HAp coatings on alumina substrate treated with 20 ppm AgNO3 had the structure of (Ag,Ca)10(PO4)6(OH)2, which exhibited excellent antimicrobial effects against E. coli, Ps. Aeruginosa, S. aureus and S. epidermidis, as shown in Table I. It is natural to investigate further whether this material still has good biocompatibility for future applications as antimicrobial implant materials. In this letter, the behavior of macrophages and osteoblasts on the newly developed Ag±HAp coated alumina and Ti6A14V substrates was evaluated in vitro. Ten kinds of samples were prepared for the scanning electron microscopy (SEM) study, as shown in Table II. Murine macrophages, cell line RAW264.7 and osteoblasts, MG63 were cultured in Dulbecco's modi®ed eagle medium (DMEM) supplemented with 10% fetal bovine serum (FBS) using a 37 8C, 5% CO2 incubator. 1 ml of full-grown bone cells with 2 ml DMEM was treated with 0.5 ml trypsinethylene diamine tetraacetic acid (trypsin-EDTA). 1 ml of the solution with about 10 cells=ml of activated bone cells was dropped onto the samples in six well dishes. Samples were incubated in a 37 8C humidi®ed atmosphere of 5% CO2 for 48 h. After that, the samples were treated with 3 ml of 3.7% formalin solution for 10 min and washed three times with phosphate buffer saline (PBS) solution. Bone

Ag-Substituted Hydroxyapatite Coatings with Both Antimicrobial Effects and Biocompatibility

Ion-beam assisted deposition (IBAD) was carried out to deposit hydroxyapatite (HAp) on alumina substrate. The amorphous coating layer on alumina substrate is crystallized to the dense HAp after a post-treatment process of annealing at 500 °C for 2 h and immersion in deionized water for 72 h at room temperature. The homogeneous and dense HAp coating is observed by scanning electron microscopy and the thickness of the coating is measured to be about 638 nm. The hardness of the coating layer in the as-deposited and post-treated samples is 475 and 508, respectively. The adhesive strength between HAp and α-alumina substrate was measured by a scratch test. The ion-beam sputtered coatings were used as control samples. The adhesion was found to be worse for ion-beam sputtering deposition (IBSD) than for IBAD.

Highly adhesive hydroxyapatite coatings on alumina substrates prepared by ion-beam assisted deposition

Of all the biominerals, nacre—the lustrous “mother of pearl” layer of many mollusc shells, has been best investigated for its marvelous “brick and mortar” structure [1, 2] and is regarded as the “pearl in the crown” for its significance in the field of biomineralization [3]. It is believed that the “bricks” are of flat polygonal crystals of aragonite in all mollusc nacreous layers with their c-axes perpendicular to the layer plane [4]. A domain structure has been found to consist of 3–10 continuous flat platelets along the direction perpendicular to the nacre plane. The a-axes of these crystals are parallel to each other, but the a-axes in the neighboring domains are oriented differently [5]. It was reported recently that matrix sheets have pores that both allow the crystals to grow and keep them aligned crystallographically via mineral bridges [6] and a model was proposed to illustrate the configuration of crystal growth from one layer to the next without interruption [3]. However, so far the crystal orientation relationships between the neighboring aragonite platelets in the same lamina of the nacreous layer have not been systematically investigated. Such information should be especially valuable for the complete understanding of the microstructure of nacre. Our present work is undertaken to study the crystal orientation relationships in the single lamina in the nacreous layer of the Mytilus edulisshell and a new model is proposed to depict the growth configuration of nacre on the basis of this research and those of others. Mature bivalvia mollusc shell, Mytilus edulis, grown in the Bohai Sea at Qinhuangdao in North China, was selected for the experiments. They were washed with distilled water and air-dried at room temperature. The ultra-thin segments of the nacreous layer were obtained through mechanical grinding along the direction parallel to the surface of the shell and then by double-side ion milling. They were coated with carbon films of less than 10 nm. During ion milling and TEM investigation the samples were cooled with liquid nitrogen. TEM observation together with SAED was performed using a Hitachi-800 electron microscope operating at 200 kV. To investigate the crystal orientation relationships between neighboring platelets of the same lamina in the nacreous layer of Mytilus edulisshell, TEM with SAED was performed on individual crystal by using a selective area aperture. Fig. 1a is the TEM micrograph of an exemplary specimen of the nacreous layer and Fig. 1b–d are the SAED patterns of the neighboring platelets B, C and D noted in Fig. 1a. The Laue spots and the [0 0 1] crystal symmetry in these patterns demonstrate that the nacreous layer of Mytilus edulisstudied in this experiment is also composed of aragonite platelets with [0 0 1] direction perpendicular to the platelet plane. It is important to notice that the specimen was not rotated in the platelet plane and the diffraction patterns in Fig. 1b–d are completely uniform. This demonstrates that the crystal orientations of the three neighboring crystals are the same in three-dimension. The same results can also be obtained from other parts of this sample and other samples. The domains consist of 1–5 crystals and the angles in the platelet plane between two adjacent differently oriented domains vary from several degrees to tens of degrees. The schematic illustration of these domains is shown in Fig. 2. In one of our previous works we have studied the orientation relationships between neighboring crystals of the same lamina n the nacreous layer in the shells of Cristaria plicata andHyriopsis cumingli , and found this phenomenon is very rare in those two shells [5]. Akai and Kobayashi reported that in the nacreous layer of Mytilus edulis, the crystallographic orientations of the aragonite tablets are not random but fall in small range of rotation [7]. In the present study of Mytilus edulisshell, the domains with uniformly oriented adjacent crystals in the nacreous layer were found to be widespread. This result may be due to the enormous diversity of the organisms. Recently Schafferet al. [6] found that the matrix sheets between the successive laminae have pores that both allow the crystals to grow and keep them aligned crystallographically via mineral bridges along the growth direction. It is conceivable that mineral bridges could also exist between the neighboring crystals in the same lamina since the matrix sheets between the successive laminae and those between the adjacent crystals in the same lamina have the same structure. Also two or more crystals could be grown on a single crystal through the mineral bridges and hence have the same orientation. It is also possible that the crystal orientation will turn around a small angle in the platelet plane after grown via mineral bridge, which may be an appropriate explanation to the finds in reference [7]. Thus the growth configuration of the nacreous layer can be modeled in

T. N. Kim

Papers

Antimicrobial effects of metal ions (Ag+, Cu2+, Zn2+) in hydroxyapatite.

Ag-Substituted Hydroxyapatite Coatings with Both Antimicrobial Effects and Biocompatibility

Highly adhesive hydroxyapatite coatings on alumina substrates prepared by ion-beam assisted deposition

Crystal orientation domains found in the single lamina in nacre of the Mytilus edulis shell