No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
In vitro antibacterial activity of oxide and non-oxide bioceramics for arthroplastic devices: II. In situ time-lapse Fourier transform infrared spectroscopy
Abstract
The metabolic response of gram-positive Staphylococcus epidermidis (S. epidermidis.) bacteria to bioceramic substrates was probed by means of Fourier transform infrared spectroscopy (FTIR). Oxide zirconia-toughened alumina (ZTA) and non-oxide silicon nitride (Si3N4) substrates were tested. Bacteria exposed to silica glass substrates were used as a control. S. epidermidis., a major cause of periprosthetic infections, was screened to obtain a precise time-lapse knowledge of its molecular composition and to mechanistically understand its interaction with different substrates. At the molecular level, the structure of proteins, lipids, nucleic acid, and aromatic amino acids evolved with time in response to different substrates. In combination with statistical validation and local pH measurements, a chemical lysis mechanism was spectroscopically observed in situ on the Si3N4 substrates. Utilization of FTIR in this study avoided fluorescence noise which occurred while probing the ZTA samples with Raman spectroscopy in a companion paper. The substrate-driven dynamics of polysaccharide and peptide variations in the bacterial cell wall, peculiar to Si3N4 bioceramics, are elucidated.
... The bioactivity of silicon nitride is associated with the cleavage of the Si-N bond followed by slow dissolution of the outermost atomic layers. This process produces silicic acid (SiOH 4 ) and surface silanols (Si-OH) while releasing nitrogen in the form of ammonia (NH 3 ) [20,21]. Moreover, the surface chemistry of Si 3 N 4 was successfully optimized using various thermochemical treatments to further promote its bioactivity [22,23]. ...
... In fact, the antibacterial behavior of Si 3 N 4 has been extensively characterized. It has been shown to be effective against several nosocomial strains including Staphylococcus epidermidis [17,21,26,27], Escherichia coli [26,27], methicillin-resistant Staphylococcus aureus [28], and Porphyromonas gingivalis [29]. ...
... Since the refractive index depends on the wavelength, the spectra obtained using ATR have a slightly different intensity ratio over the entire spectrum, and an adjustment may be required to compare with the transmission spectra [7]. When measuring the refractive index of thin films, various methods can be used, we used the following modified expression of Sellmeyer by Edwards and others, which is the most suitable dispersion equation for ambient temperature [8]. ...
FT-IR spectrometers are used to solve various problems of modern analytics. Designed for qualitative analysis, checking the refractive index of thin films, the thickness of thin films. We studied the mid-infrared transmission and absorption spectra, refractive index, layer thickness, standard deviation, incident angle, average interference fringes, and the coupling between silicon and oxygen of thin films obtained by the ion-plasma method.
... The samples were then stained with 2-(4-Amidinophenyl)-6-indolecarbamidine dihydrochloride (DAPI, Beyotime Biotech, Shanghai, China) and Actin-Tracker Red-Rhodamine (Beyotime Biotech, Shanghai, China) to observe the cell morphology using confocal laser scanning microscope (CLSM, Zessi, LSM800, Oberkochen, Germany). The morphology of the adhered cells on the discs was also observed by SEM (TESCAN Bmo, s.r.o., TESCAN MIRA, Brno, Czech Republic) after dehydrating the samples in gradient ethanol solutions (30,50,70,85,90, and 100%, respectively) for 10 min and drying at the critical point. ...
Silicon nitride is a bioceramic with great potential, and multiple studies have demonstrated its biocompatibility and antibacterial properties. In this study, silicon nitride was prepared by a microwave sintering technique that was different from common production methods. SEM and pore distribution analysis revealed the microstructure of microwave-sintered silicon nitride with obvious pores. Mechanical performance analysis shows that microwave sintering can improve the mechanical properties of silicon nitride. The CCK-8 method was used to demonstrate that microwave-sintered silicon nitride has no cytotoxicity and good cytocompatibility. From SEM and CLSM observations, it was observed that there was good adhesion and cross-linking of cells during microwave-sintered silicon nitride, and the morphology of the cytoskeleton was good. Microwave-sintered silicon nitride has been proven to be non-cytotoxic. In addition, the antibacterial ability of microwave-sintered silicon nitride against Staphylococcus aureus and Escherichia coli was tested, proving that it has a good antibacterial ability similar to the silicon nitride prepared by commonly used processes. Compared with silicon nitride prepared by gas pressure sintering technology, microwave-sintered silicon nitride has excellent performance in mechanical properties, cell compatibility, and antibacterial properties. This indicates its enormous potential as a substitute material for manufacturing bone implants.
... [11][12][13][14] SiN has been proposed as an alternative coating material due to its capacity to reduce wear and ion release from metallic substrates, while also possessing bacteriostatic properties. [15][16][17][18] SiN undergoes hydrolysis when exposed to aqueous environments, leading to its slow dissolution, which releases biocompatible ions. [19][20][21][22][23][24][25][26] The solubi-lity of any wear particles into biocompatible ions may indeed reduce the risk of adverse immune responses. ...
Silicon nitride (SiN) coatings may reduce unwanted release of metal ions from metallic implants. However, as SiN slowly dissolves in aqueous solutions, additives that reduce this dissolution rate would likely increase the lifetime and functionality of implants. Adding iron (Fe) and carbon (C) permits tuning of the SiN coatings' mechanical properties, but their effect on SiN dissolution rates, and their capacity to reduce metal ion release from metallic implant substrates, have yet to be investigated. Such coatings have recently been proposed for use in spinal implants; therefore, it is relevant to assess their impact on the viability of cells expected at the implant site, such as microglia, the resident macrophages of the central nervous system (CNS). To study the effects of Fe and C on the dissolution rate of SiN coatings, compositional gradients of Si, Fe and C in combination with N were generated by physical vapor deposition onto CoCrMo discs. Differences in composition did not affect the surface roughness or the release of Si, Fe or Co ions (the latter from the CoCrMo substrate). Adding Fe and C reduced ion release compared to a SiN reference coating, which was attributed to altered reactivity due to an increase in the fraction of stabilizing Si-C or Fe-C bonds. Extracts from the SiN coatings containing Fe and C were compatible with microglial viability in 2D cultures and 3D collagen hydrogels, to a similar degree as CoCrMo and SiN coated CoCrMo reference extracts. As Fe and C reduced the dissolution rate of SiN-coatings and did not compromise microglial viability, the capacity of these additives to extend the lifetime and functionality of SiN-coated metallic implants warrants further investigation.
... The antibacterial properties of ceramic materials have been gradually discovered recently. For example, the nanosized Si 3 N 4 was coated or incorporated in polymer films as an antibacterial material, which showed good antibacterial activity [34,35], and its antibacterial mechanism is being gradually explored [36,37]. ...
Meltblown (MB) nonwovens as air filter materials have played an important role in protecting people from microbe infection in the COVID-19 pandemic. As the pandemic enters the third year in this current global event, it becomes more and more beneficial to develop more functional MB nonwovens with special surface selectivity as well as antibacterial activities. In this article, an antibacterial polypropylene MB nonwoven doped with nano silicon nitride (Si3N4), one of ceramic materials, was developed. With the introduction of Si3N4, both the average diameter of the fibers and the pore diameter and porosity of the nonwovens can be tailored. Moreover, the nonwovens having a single-side moisture transportation, which would be more comfortable in use for respirators or masks, was designed by imparting a hydrophobicity gradient through the single-side superhydrophobic finishing of reactive organic/inorganic silicon coprecipitation in situ. After a nano/micro structural SiO2 precipitation on one side of the fabric surfaces, the contact angles were up to 161.7° from 141.0° originally. The nonwovens were evaluated on antibacterial activity, the result of which indicated that they had a high antibacterial activity when the dosage of Si3N4 was 0.6 wt%. The bacteriostatic rate against E. coli and S. aureus was up to over 96%. Due to the nontoxicity and excellent antibacterial activity of Si3N4, this MB nonwovens are promising as a high-efficiency air filter material, particularly during the pandemic.
... 107 The N-vacant sites quickly attract oxygen to form surface silanols, which are deprotonated due to the above-mentioned pH buffering effect and thus possess a negative charge (as experimentally proven by Fourier transform infrared spectroscopy). 108 This study, in line with previous findings, 13 suggests that the final products of Si 3 N 4 surface hydrolysis, namely, nitrogen radicals and deprotonated silanols, are key in SARS-CoV-2 viral inactivation. The silanol moieties induce deimination of positively charged arginine to form uncharged citrulline, as proven by studies of protein citrullination on silica particles in an aqueous environment. ...
Raman spectroscopy uncovered molecular scale markers of the viral structure of the SARS-CoV-2 Delta variant and related viral inactivation mechanisms at the biological interface with silicon nitride (Si3N4) bioceramics. A comparison of Raman spectra collected on the TY11-927 variant (lineage B.1.617.2; simply referred to as the Delta variant henceforth) with those of the JPN/TY/WK-521 variant (lineage B.1.617.1; referred to as the Kappa variant or simply as the Japanese isolate henceforth) revealed the occurrence of key mutations of the spike receptor together with profound structural differences in the molecular structure/symmetry of sulfur-containing amino acid and altered hydrophobic interactions of the tyrosine residue. Additionally, different vibrational fractions of RNA purines and pyrimidines and dissimilar protein secondary structures were also recorded. Despite mutations, hydrolytic reactions at the surface of silicon nitride (Si3N4) bioceramics induced instantaneous inactivation of the Delta variant at the same rate as that of the Kappa variant. Contact between virions and micrometric Si3N4 particles yielded post-translational deimination of arginine spike residues, methionine sulfoxidation, tyrosine nitration, and oxidation of RNA purines to form formamidopyrimidines. Si3N4 bioceramics proved to be a safe and effective inorganic compound for instantaneous environmental sanitation.
... It should be noted however that ammonia is formed during the dissolution of SiN x , which may result in an elevated pH. However, this has been found to be beneficial in terms of antibacterial properties [155,156]. Further, there needs to be a compromise between the dissolution of the wear particles and the requirement of a coating that provides sufficient performance for the intended period of use i.e. significantly greater than 20-25 years. SiN x coatings have been manufactured both through PVD and CVD methods with a wide range of hardness (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24) [47,49,50,53] and Young's moduli [47,49,50]. ...
Hip and knee joint replacements are common and largely successful procedures that utilise implants to restore mobility and relieve pain for patients suffering from e.g. osteoarthritis. However, metallic ions and particles released from both the bearing surfaces and non-articulating interfaces, as in modular components, can cause hypersensitivity and local tissue necrosis, while particles originating from a polymer component have been associated with aseptic loosening and osteolysis. Implant coatings have the potential to improve properties compared to both bulk metal and ceramic alternatives. Ceramic coatings have the potential to increase scratch resistance, enhance wettability and reduce wear of the articulating surfaces compared to the metallic substrate, whilst maintaining overall toughness of the implant ensuring a lower risk of catastrophic failure of the device compared to use of a bulk ceramic. Coatings can also act as barriers to inhibit ion release from the underlying material caused by corrosion. This review aims to provide a comprehensive overview of wear-resistant coatings for joint replacements – both those that are in current clinical use as well as those under investigation for future use. While the majority of coatings belong predominantly in the latter group, a few coated implants have been successfully marketed and are available for clinical use in specific applications. Commercially available coatings for implants include titanium nitride (TiN), titanium niobium nitride (TiNbN), oxidized zirconium (OxZr) and zirconium nitride (ZrN) based coatings, whereas current research is focused not only on these, but also on diamond-like-carbon (DLC), silicon nitride (SiN), chromium nitride (CrN) and tantalum-based coatings (TaN and TaO). The coating materials referred to above that are still at the research stage have been shown to be non-cytotoxic and to reduce wear in a laboratory setting. However, the adhesion of implant coatings remains a main area of concern, as poor adhesion can cause delamination and excessive wear. In clinical applications zirconium implant surfaces treated to achieve a zirconium oxide film and TiNbN coated implants have however been proven comparable to traditional cobalt chromium implants with regards to revision numbers. In addition, the chromium ion levels measured in the plasma of patients were lower and allergy symptoms were relieved. Therefore, coated implants could be considered an alternative to uncoated metal implants, in particular for patients with metal hypersensitivity. There have also been unsuccessful introductions to the market, such as DLC coated implants, and therefore this review also attempts to summarize the lessons learnt.
... Now, we are making a toothbrush by applying a new bristle material: i.e., a bristle that contains ceramics. Some kinds of ceramics are known to have antibacterial activity [12], and our preliminary experiments showed that the ceramic-containing bristle material has an antibacterial property (data not shown). This is advantageous as a toothbrush, because a toothbrush is always exposed to bacteria in the oral cavity. ...
Toothbrushes after use are contaminated by many microorganisms including bacteria, fungi and viruses. We are thinking of making an anti-bacterial toothbrush by including ceramics in the bristle. But if the ceramic-containing bristles are too hard for the tooth and gingiva, it cannot be used as a toothbrush. So, before examining the antibacterial properties, we evaluated the feeling by asking students of dental hygiene. In our preliminary experiment, we determined the most appropriate width and length of ceramic-containing bristles. The students used this toothbrush and answered the questions. Almost all the students were satisfied with the new toothbrush with ceramic-containing bristles. Moreover, the new toothbrush was found to be comparable with the world-wide sold toothbrush. We obtained data that the ceramic-containing bristles were acceptable. Further study to investigate the anti-bacterial properties and effective cleanliness are in progress.
... Silicon has long been reported to play an important role in human physiology [13], which includes an increase in both osteoblastic activity and formation of bony hydroxyapatite [14,15]. The effect of nitrogen has been investigated to a lesser extent and mainly in the context of its antibacterial effect associated with Si 3 N 4 [12,16,17]. It is yet unknown if the concurrent presence of N and Si potentially provide an additional advantage over Si alone in osteogenesis. ...
The surface chemistry of silicon nitride plays an important role in stimulating osteoblasts to proliferate and produce bone tissue with improved efficiency. This property, which is advantageous in spinal fusion surgery has a chemical origin and is a direct consequence of the cleavage of covalent SN bonds in an aqueous environment. Building upon a wealth of published research on the stimulation of osteoblastic activity by silicon, the aim of this paper is to explore the role of nitrogen and, more specifically, the N/Si atomic ratio on the osteogenic response of Si3N4. The surface stoichiometry of Si3N4 was gradually altered toward a silicon-rich composition by systematically treating the Si3N4 surface with a high-power pulsed laser in an Ar gas atmosphere (i.e., operated at different pulse times, spot sizes, and voltages). Different analytical probes were used to characterize the surface including X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and energy dispersive X-ray spectroscopy (EDS). Osteoconductivity was tested in vitro using SaOS-2 osteosarcoma cells, and samples with different surface stoichiometry were compared for their osteogenic response. These experiments clearly indicated a fundamental role for nitrogen off-stoichiometry in osteogenesis, and showed that both cell proliferation and growth of bone tissue diminished with decreasing nitrogen content.
... This study included in situ time-lapse spectroscopic monitoring of gram-negative E. coli exposed to Si 3 N 4 in comparison with cultured bacteria and bacteria exposed to other biomaterials' substrates. The protocol was conceived to pair our recently published spectroscopic analyses of gram-positive Staphylococcus epidermidis (S. epidermidis, henceforth) tested under exactly the same conditions [10,15,16]. Raman and Fourier transform infrared (FTIR) spectroscopies were applied to monitor in situ the metabolic activity of the living bacterium exposed to different substrates with the specific objective to understand the chemical interactions taking place at the interface between bacteria and substrate. ...
... Time-lapse experiments clearly demonstrated that the antibacterial effect of Si 3 N 4 is time-dependent and correlates well with the pH profiles measured in proximity of the interface with acidic environments, proving that ceramic Si 3 N 4 has an active pH-buffering effect [14]. Fig. 1(b), shows the results of an in-vitro testing with osteosarcoma (SAOS-2) cell lines. ...
Due to the favourable combination of mechanical strength and fracture toughness, silicon nitride has been applied as a load-bearing bioceramic, in particular for implants used in spinal fusion surgery. Only recently it has been observed that the supposedly inert surface of silicon nitride is actually bioactive: a slow, but not negligible, pH controlled, ionic exchange between nitrogen and oxygen leads to the formation and elution of silicic acid and ammonia groups, also resulting in an effective protection against bacteria colonization. These properties could be further modulated by chemical and mechanical treatments.
... Now, we are making a toothbrush by applying a new bristle material: i.e., a bristle that contains ceramics. Some kinds of ceramics are known to have antibacterial activity [12], and our preliminary experiments showed that the ceramic-containing bristle material has an antibacterial property (data not shown). This is advantageous as a toothbrush, because a toothbrush is always exposed to bacteria in the oral cavity. ...
Three decades of research in the last century developed silicon nitride (Si3N4) as one of the strongest and toughest ceramic material for structural applications; but in this century, we newly discovered its gifted surface biochemistry. In an aqueous environment, Si3N4 undergoes surface hydrolysis with the slow but continuous elution of both silicon and nitrogen. A unique environment is created, which greatly enhances healing of soft and osseous tissues, inhibits bacterial biofilm formation, and eradicates viruses. The discovery of Si3N4’s biochemistry opens new paths in a wide array of different disciplines inside and outside of the physical body, including orthopedics, dentistry, virology, agronomy, and environmental remediation. In the biomedical field, it paves the way for a new generation of monolithic, composite, or coated implants for bone healing, including spinal arthrodesis, joint arthroplasty, craniomaxillofacial and dental devices. This review describes Si3N4’s surface chemistry in an aqueous environment in comparison with oxide ceramics. It discusses the pH-dependent elution kinetics of ammonia and ammonium as the main phenomenon behind its unparalleled behavior and demonstrates its friendly nature to mammalian cells while concurrently lysing invasive pathogens. Finally, a wider perspective is offered for future applications of Si3N4 in disease diagnosis and therapies, personal healthcare, agriculture, food and water safety, and environmental protection.
ABSTRACT
There are two major problems in the world, fuel deficiency and environmental pollution by fossil
fuels. Microalgae are regarded as one of the most feasible feedstocks for the manufacturing of
biofuels and are used in the degradation of fossil fuel spills. The present study was possessed to
investigate the ability of green alga Chlorella vulgaris, blue-green alga Synechococcus sp, and its
consortium to grow and degrade hydrocarbon such as kerosene (k) with different concentrations
(0, 0.5, 1, and 1,5%), and also using algal biomasses to produce biofuel. The algal growth was
estimated by optical density (O.D) at 600 nm, pigment contents such as Chlorophyll a,b carot�enoid, and dry weight. The kerosene degradation was estimated by FT-IR analysis after and before
the cultivation of algae and its consortium. The components of the methanol extract were
determined by GC-MS spectroscopy. The results denote the best growth was determined by O.D,
algae consortium with 1.5% Kerosene after ten days, meanwhile, the highest dry weight was with
C. vulgaris after ten days of cultivation. The FT-IR demonstrated the algae and consortium
possessed high efficacy to degrade kerosene. After 15 days of algae cultivation with 1% K, C.
vulgaris produced the maximum amount of lipids (32%). The GC-MS profile of methanol extract
of two algae and consortium demonstrated that Undecane was presented in high amounts, C.
vulgaris (19.9%), Synechococcus sp (82.16%), algae consortium (79.51%), and also were presented
moderate amounts of fatty acid methyl ester in Synechococcus sp. Overall, our results indicate that
a consortium of algae can absorb and remove kerosene from water, and at the same time produce
biofuels like biodiesel and petroleum-based fuels
Ceramic coatings have been widely investigated as a means to reduce wear and metallic ion release from joint implants. Silicon nitride-based coatings have been a topic of interest specifically due to their solubility in aqueous solutions. This could imply a reduced adverse immune response since the generated debris would dissolve. However, there are concerns regarding the dissolution rate and adhesion of these silicon nitride-based coatings. This study attempts to address the concern of dissolution rate as well as coating adhesion of silicon nitride coatings. We hypothesized that alloying with chromium and niobium would affect the adhesion, dissolution rate, and the resulting ion release and cell response to the coatings. A combinatorial approach was used to deposit sputtered coatings with compositional gradients both with and without a CrN interlayer. Compositional gradients were achieved for all the investigated elements: Si (38.6-46.9 at%), Nb (2.2-4.6 at%) and Cr (1.9-6.0 at%). However, while the presence of an interlayer reduced the delamination during adhesion testing, the differences in composition in the top coating did not affect the adhesion. Nor did the top coating's composition affect the surface roughness or the coatings' inherent mechanical properties (elastic modulus and hardness). All coating compositions were associated with a low Co release from the underlying metal and points with a higher Cr content (4.3-6.0 at%) gave an overall lower release of Si, Cr and Nb ions, possibly due to the formation of a stable oxide, which reduced the dissolution rate of the coating. Optimum chromium contents were furthermore found to give an enhanced in vitro fibroblast cell viability. In conclusion, the results indicate a possibility to tailor the ion release rate, which lends promise to further investigations such as tribocorrosive tests towards a future biomedical application.
Recent studies have shown that bacteria can also undergo apoptosis, which has gradually attracted researchers’ attention. Cisplatin is a first-line drug to treat several cancers, but it can damage beneficial bacteria. Hence it is very important to explore the damage mechanism of cisplatin on beneficial bacteria. In this study, Lactobacillus paracasei, one kind of beneficial bacteria, was used as the model to investigate cisplatin damage. Conventional detection showed that cisplatin induced the apoptosis of Lactobacillus paracasei. Then Fourier transform infrared (FTIR) microspectroscopy was used to detect biomacromolecular changes in Lactobacillus paracasei apoptosis, and the following results were obtained: ① Second derivative IR spectra showed the changes of DNA, proteins, polysaccharides and lipids; ② Peak-area ratios suggested the changes of the protein and lipid structure and the decrease of DNA content; ③ Principal component analysis (PCA) further revealed significant changes in the DNA and protein content/structure. This study may have a new insight into the adverse reaction mechanism of cisplatin on Lactobacillus, moreover, it suggests that FTIR microspectroscopy may be a useful supplementary tool for investigating bacterial apoptosis.
This paper presents the use of soft template method to synthesize core and core–shell up-converting nanoparticles usefull for temperature sensing applications. Based on the stock solutions of core β-NaYF4:Er3+,Yb3+ nanoparticles and involving soft template method without any additional process of surface functionalization, it is possible to directly design the core–shell β-NaYF4:Er3+,Yb3+@NaYF4 nanoparticles, which can be perfectly dispersed in cyclohexane and surfactants like oleic acid (OA), triethanolamine (TEA) or Cetyltrimethylammonium bromide (CTAB). The morphological, crystalline and elemental characteristics of samples were investigated by Field Emission Scanning Electron Microscopy, X-Ray Diffraction, High Resolution Transmission Electron Microscopy, Selected Area Electron Diffraction patterns and Energy-Dispersive X-Ray Spectroscopy (EDX) measurements. The results showed that the synthesized NaYF4:Er3+,Yb3+@NaYF4 core–shell nanoparticles have roughly spherical shape, pure hexagonal β phase with core size of about 35 ± 5 nm and shell thickness of about 40 ± 5 nm. It has been shown that the coating of the β-NaYF4:Er3+,Yb3+ core with NaYF4 shell layer enables to enhance the green upconversion (UC) emission intensities in respect to red one. Under 976 nm excitation, the synthesized β-NaYF4:2%Er3+,19%Yb3+@NaYF4 core–shell nanoparticles revealed three strong emission bands at 520 nm, 545 nm and 650 nm corresponding to 2H11/2, 4S3/2 and 4F9/2 to 4I15/2 transitions of Er3+ ions with the lifetimes of 215, 193 and 474 µs, respectively. The calculated CIE chromaticity coordinates proved that the emission colour of core–shell nanoparticles was changed from red into yellowish green upon increasing the power density of the 976 nm laser from 0.73 to 9.95 W/cm2. The calculated slopes indicated that in the β-NaYF4:2%Er3+,19%Yb3+@NaYF4 core–shell nanoparticles, two-photon and three-photon UC processes took place simultaneously. Although the former one is similar as in the case of β-NaYF4:Er3+,Yb3+ bare core nanoparticles, the latter one, three-photon UC process for green emission occurs, due to cross relaxation processes of two Er3+ ions only within nanoparticles with core–shell architecture. Moreover, the energy difference between the 2H11/2 and 4S3/2 levels and associated constant of NaYF4@NaYF4 host lattice were determined and they reached ~ 813 cm−1 and 14.27 (r2 = 0.998), respectively. In order to investigate the suitability of nanoparticles for optical temperature sensing, the emission spectra were measured in a wide temperature range from 158 to 298 K. An exceptionally high value of relative sensitivity was obtained at 158 K and it amounted to 4.25% K−1. Further temperature increase resulted in gradual decrease of relative sensitivity, however, it maintained a high value > 1% K−1 in the entire analyzed temperature range.
This topic is based on the research and development of inorganic silver-loaded antibacterial materials with good antibacterial activity, and the preparation of silver-loaded calcium carbonate inorganic nano-antibacterial agents by redox reaction. At the same time, the mixed rare earth oxide was added to the ceramic glaze containing silver nano antibacterial agent, and the nano antibacterial building sanitary ceramics were prepared by firing at 1180 °C in an oxidizing atmosphere. This experiment investigated the effect of adding mixed rare earth oxides on the quality and properties of glaze. Experiments show that the new glaze has stronger antibacterial effect than the nano antibacterial glaze without mixed rare earth oxide, and the glaze quality is good. After adding 0.5 wt% of mixed rare earth oxide, the whiteness, abrasion resistance, hardness and thermal shock resistance of the glaze were significantly improved.This topic is based on the research and development of inorganic silver-loaded antibacterial materials with good antibacterial activity, and the preparation of silver-loaded calcium carbonate inorganic nano-antibacterial agents by redox reaction. At the same time, the mixed rare earth oxide was added to the ceramic glaze containing silver nano antibacterial agent, and the nano antibacterial building sanitary ceramics were prepared by firing at 1180 °C in an oxidizing atmosphere. This experiment investigated the effect of adding mixed rare earth oxides on the quality and properties of glaze. Experiments show that the new glaze has stronger antibacterial effect than the nano antibacterial glaze without mixed rare earth oxide, and the glaze quality is good. After adding 0.5 wt% of mixed rare earth oxide, the whiteness, abrasion resistance, hardness and thermal shock resistance of the glaze were significantly improved.
Background:
In lumbar fusion surgery, intervertebral spacer cages made of silicon nitride (Si3N4) ceramic are an available option among other biomaterials. While the surface chemistry of Si3N4 is known to favor bone fusion, large-scale clinical studies attesting to its efficacy are lacking. This multicenter retrospective study compared lumbar fusion outcomes for Si3N4 cages to previously reported data for other cage materials.
Methods:
Pre-operative patient demographics, comorbidities, changes in visual analog scale (ΔVAS) pain scores, complications, adverse events, and secondary surgical interventions (SSI) were compiled from the records of 450 patients who underwent Si3N4 lumbar spinal fusion at four separate U.S. surgical centers. For comparison, MEDLINE/PubMed and Google Scholar searches identified studies reporting similar outcomes for other biomaterials. A total of 1,025 patients from 26 cohorts reported in 14 publications met inclusion criteria for this control group.
Results:
Overall, the mean last-follow-up for all patients was 341±293 days (11.4±9.8 months), with the longest follow-up being 6.4 years. Patients with Si3N4 implants were similar in gender and age distribution to the control group but had higher BMI values (30.9±6.1 vs. 25.8±4.1, P<0.01) and lower tobacco use (15.8% vs. 30.0%, P<0.01). Both the Si3N4 and control groups showed significant improvements in VAS pain scores from preoperative to last follow-up. For the Si3N4 group, ΔVAS was 36.8±35.4 points compared to 37.6±22.5 points (P=0.63) for the metadata group. Complications and reoperations for the Si3N4 and the control groups were similar (i.e., 9.8% and 3.1% versus 12.4% and 2.9%, P=0.16 and P=0.84, respectively).
Conclusions:
Lumbar fusion with Si3N4 spacers compared favorably with the improvements reported with other commonly used biomaterial cages.
Background:
Intervertebral spacers made of silicon nitride (Si3N4) are currently used in cervical and thoracolumbar fusion. While basic science data demonstrate several advantages of Si3N4 over other biomaterials, large-scale clinical results on its safety and efficacy are lacking. This multicenter retrospective study examined outcomes for anterior cervical discectomy and fusion (ACDF) using Si3N4 cages. Results were compared to compiled metadata for other ACDF materials.
Methods:
Pre-operative patient demographics, comorbidities, changes in visual analog scale (VAS) pain scores, complications, adverse events, and secondary surgical interventions were collected from the medical records of 860 patients who underwent Si3N4 ACDF at four surgical centers. For comparison, MEDLINE/PubMed and Google Scholar searches were performed for ACDF using other cage or spacer materials. Nine studies with 13 cohorts and 736 patients met the inclusion criteria for this control group.
Results:
Overall, the mean last-follow-up for all patients was 319±325 days (10.6±10.8 months), with the longest follow-up being 6.5 years. In comparison to the metadata, patients from the Si3N4 groups were older (57.9±12.2 vs. 56.8±11.1 y, P=0.06) and had higher BMI values (30.0±6.3 vs. 28.1±6.5, P<0.01), but gender and smoking were not different. The Si3N4 patients reported significant improvements in VAS pain scores at last follow-up (i.e., pre-op of 71.0±22.1 vs. follow-up of 36.4±31.5, P<0.01). Although both preoperative and last-follow-up pain scores were higher for Si3N4 patients than the control, the overall change in scores (ΔVAS) was similar. From pre-op to last-follow up, ΔVAS values were 35.4±34.3 for patients receiving the Si3N4 implants versus 34.4±27.3 for patients from the meta-analysis (P=0.56). The complication and reoperation rate for the Si3N4 and the metadata were also comparable (i.e., 7.39% and 0.31% versus 9.79% and 0%, P=0.17 and 0.25, respectively).
Conclusions:
ACDF outcomes using Si3N4 implants matched the clinical efficacy of other cage biomaterials.
Over the next two decades, strong demographic demand for arthroplastic devices coupled with decreased efficacy of antibiotics are predicted to result in an exponential increase in the number of periprosthetic joint infections (PJI). Advanced strategies are therefore required to improve the local peri-implant immune response and curb the pathogenic events of bacterial adhesion and biofilm formation. The use of biomaterials that autonomously counter infections is one approach to improve orthopedic outcomes. Using conventional molecular biology characterization methods and advanced Raman spectroscopy, this study examined the bacteriostatic response of two bioc-eramic materials commonly employed as prosthetic implants: zirconia-toughened alumina (ZTA) and silicon nitride (Si3N4). Unlike the ZTA, it was found that non-oxide Si3N4 possessed an inherently anti-infective surface chemistry which acted in a responsive way against bacterial loading. The mechanistic details of its behavior are elucidated. Non-oxide bioceramics appear promising, but their full development requires a transitional approach that integrates fundamental biochemical concepts with clinical outcomes.
Disinfectants and biocidal products have been widely used to combat Methicillin-resistant Staphylococcus aureus (MRSA) infections in homes and healthcare environments. Although disruption of cytoplasmic membrane integrity has been documented as the main bactericidal effect of biocides, little is known about the biochemical alterations induced by these chemical agents. In this study, we used Fourier transform infrared (FT-IR) spectroscopy and chemometric tools as an alternative non-destructive technique to determine the bactericidal effects of commonly used disinfectants against MRSA USA-300. FTIR spectroscopy permits a detailed characterization of bacterial reactivity, allowing an understanding of the fundamental mechanism of action involved in the interaction between bacteria and disinfectants. The disinfectants studied were ethanol 70% (N = 5), isopropanol (N = 5), sodium hypochlorite (N = 5), triclosan (N = 5) and triclocarban (N = 5). Results showed less than 5% colony forming units growth of MRSA treated with triclocarban and no growth in the other groups. Nearly 70,000 mid-infrared spectra from the five treatments and the two control (untreated; N = 4) groups of MRSA (bacteria grown in TSB and incubated at 37°C (Control I) / at ambient temperature (Control II), for 24h) were pre-processed and analyzed using principal component analysis followed by linear discriminant analysis (PCA-LDA). Clustering of strains of MRSA belonging to five treatments and the discrimination between each treatment and two control groups in MRSA (untreated) were investigated. PCA-LDA discriminatory frequencies suggested that ethanol-treated spectra are the most similar to isopropanol-treated spectra biochemically. Also reported here are the biochemical alterations in the structure of proteins, lipid membranes, and phosphate groups of MRSA produced by sodium hypochlorite, triclosan, and triclocarban treatments. These findings provide mechanistic information involved in the interaction between MRSA strains and hygiene products; thereby demonstrating the potential of spectroscopic analysis as an objective, robust, and label-free tool for evaluating the macromolecular changes involved in disinfectant-treated MRSA.
Statement of significance:
This research studies osseointegration processes comparing results from explanted PEEK and Si3N4 spinal spacers. Data show that the formation of hydroxyapatite on silicon nitride bio-ceramic surfaces happens with a peculiar mechanism inside the human body. Silicon and nitrogen were incorporated inside the bony tissue structure allowing the developing of off-stoichiometric bony apatite and stimulating progenitor cell differentiation/osteoblastic activity. Silicon and nitrogen ions released from the Si3N4 surface were detected through combined histologic analyses, Raman microspectroscopy, Fourier-transform-infrared, and X-ray photoelectron spectroscopies.
Surface
colonization by microorganisms leads to the formation of biofilms, i.e. aggregates of bacteria embedded within a matrix of extracellular polymeric substance. This promotes adhesion to the surface and protects bacterial community, providing an antimicrobial-resistant environment. The inhibition of biofilm growth is a crucial issue for preventing bacterial infections. Inorganic nanoparticle/Teflon-like (CFx) composites deposited via ion beam sputtering demonstrated very efficient antimicrobial activity. In this study, we developed Ag-CFx thin films with tuneable metal loadings and exceptional in-plane morphological and chemical homogeneity. Ag-CFx antimicrobial activity was studied via mid-infraredattenuated total reflection spectroscopy utilizing
specifically adapted multi-reflection waveguides. Biofilm was sampled by carefully depositing the Ag-CFx film on IR inactive regions of the waveguide. Real-time IR- spectroscopy was used to monitor Pseudomonas fluorescens biofilm growth inhibition induced by the bioactive silver ions released from the nanoantimicrobial coating. Few hours of Ag- CFx action were sufficient to affect significantly biofilm growth. These findings were corroborated by atomic force microscopy (AFM) studies on living bacteria exposed to the same nanoantimicrobial. Morphological analyses showed a severe bacterial stress, leading to membrane leakage/collapse or to extended cell lysis as a function of incubation time.
While the reciprocity between bioceramics and living cells is complex, it is principally governed by the implant’s surface chemistry. Consequently, a deeper understanding of the chemical interactions of bioceramics with living tissue could ultimately lead to new therapeutic strategies. However, the physical and chemical principles that govern these interactions remain unclear. The intricacies of this biological synergy are explored within this paper by examining the peculiar surface chemistry of a relatively new bioceramic, silicon nitride (Si3N4). Building upon prior research, this paper aims at obtaining new insights into the biological interactions between Si3N4 and living cells, as a consequence of the off-stoichiometric chemical nature of its surface at the nanometer scale. We show here yet unveiled details of surface chemistry and, based on these new data, formulate a model on how, ultimately, Si3N4 influences cellular signal transduction functions and differentiation mechanisms. In other words, we interpret its reciprocity with living cells in chemical terms. These new findings suggest that Si3N4 might provide unique new medicinal therapies and effective remedies for various bone or joint maladies and diseases.
The remarkable stoichiometric flexibility of hydroxyapatite (HAp) enables the formation of a variety of charged structural sites at the material’s surface which facilitates bone remodeling due to binding of biomolecule moieties in zwitterionic fashion. In this paper, we report for the first time that an optimized biomedical grade silicon nitride (Si3N4) demonstrated cell adhesion and improved osteoconductivity comparable to highly defective, non-stoichiometric natural hydroxyapatite. Si3N4’s zwitterionic-like behavior is a function of the dualism between positive and negative charged off-stoichiometric sites (i.e., N-vacancies versus silanols groups, respectively). Lattice defects at the biomaterial’s surface greatly promote interaction with positively- and negatively-charged functional groups in biomolecules, and result in the biologically effective characteristics of silicon nitride. These findings are anticipated to be a starting point for further discoveries of therapeutic bone-graft substitute materials.
Fourier transform infrared (FTIR) is a spectroscopy method that can identify variations in the total composition of microorganisms through the determination of changes in functional groups in biomolecules. FTIR measures the vibration and rotation of molecules influenced by infrared radiation at a specific wavelength. This technique allows the identification of structural changes in the molecular binding between microorganisms and metal atoms, which can provide information about the nature of their interactions. In this review article, we will describe the state of the art in current uses of FTIR for the elucidation of bacteria–nanoparticle interactions. We will describe advantages for the application of FTIR in the field of nanotoxicology, including higher signal-to-noise ratio, high energy throughput, as well as high accuracy and stability which are applicable to solid phase samples but not recommended for assays in the liquid phase. Limitations such as multiple background scans and post-processing analysis are not deniable. Comparison of FTIR with other commonly used tools such as Raman spectroscopy, mass spectrometry, nuclear magnetic resonance spectroscopy, and X-ray photoelectron spectroscopy is also discussed. Finally, we present an application of FTIR for the assessment of bacterial changes in response to the exposure to silver nanoparticles (AgNPs). The results showed that the AgNPs-induced structural changes in the peptide and amino acids region may lead to alterations of conformation and/or composition of Amid B and Amid III. These results showed that bacteria developed resistance toward AgNPs and resulted in changes in the genotype and expression in the phenotype. Here, ATR–FTIR provided the evidence of the AgNPs cytotoxicity-induced intracellular level alterations in bacteria.
Organisms of gram-negative phylum bacteroidetes, Porphyromonas gingivalis, underwent lysis on polished surfaces of silicon nitride (Si3N4) bioceramics. The antibacterial activity of Si3N4 was mainly the result of chemically driven principles. The lytic activity, although not osmotic in nature, was related to the peculiar pH-dependent surface chemistry of Si3N4. A buffering effect via the formation of ammonium ions (NH4+) (and their modifications) was experimentally observed by pH microscopy. Lysis was confirmed by conventional fluorescence spectroscopy; and the bacteria's metabolism was traced with the aid of in situ Raman microprobe spectroscopy. This latter technique revealed the formation of peroxynitrite within the bacterium itself. Degradation of the bacteria's nucleic acid, drastic reduction in phenilalanine, and reduction of lipid concentration were observed due to short-term exposure (6 days) to Si3N4. Altering the surface chemistry of Si3N4 by either chemical etching or thermal oxidation influenced peroxynitrite formation and affected bacteria metabolism in different ways. Exploiting the peculiar surface chemistry of Si3N4 bioceramics could be helpful in counteracting Porphyromonas gingivalis in an alkaline pH environment.
Raman spectroscopy is a powerful analytical method that allows deposited and/or immobilized cells to be evaluated without complex sample preparation or labeling. However, a main limitation of Raman spectroscopy in cell analysis is the extremely weak Raman intensity that results in low signal to noise ratios. Therefore, it is important to seize any opportunity that increases the intensity of the Raman signal and to understand whether and how the signal enhancement changes with respect to the substrate used. Our experimental results show clear differences in the spectroscopic response from cells on different surfaces. This result is partly due to the difference in spatial distribution of electric field at the substrate/cell interface as shown by numerical simulations. We found that the substrate also changes the spatial location of maximum field enhancement around the cells. Moreover, beyond conventional flat surfaces, we introduce an efficient nanostructured silver substrate that largely enhances the Raman signal intensity from a single yeast cell. This work contributes to the field of vibrational spectroscopy analysis by providing a fresh look at the significance of the substrate for Raman investigations in cell research.
Rapid and reproducible discrimination between bacterial pathogens is a clear goal in microbiological laboratories when processing infected clinical samples. In this study Raman spectra were taken from at least 30 colonies of four strains of bacteria including Staphylococcus epidermidis (1457 and 9142) and Escherichia coli (K12 and Top 10) using the Renishaw in Via Raman microscope system. Analysis based on principal components suggests that even strain differentiation (e.g., 1457 versus 9142 or K12 versus Top10) is possible.
The anthropogenic production of greenhouse gases and their consequent effects on global climate have garnered international attention for years. A remaining challenge facing scientists is to unambiguously quantify both sources and sinks of targeted gases. Microbiological metabolism accounts for the largest source of nitrous oxide (N2O), mostly due to global conversion of land for agriculture and massive usage of nitrogen-based fertilizers. A most powerful method for characterizing the sources of N2O lies in its multi-isotope signature. This review summarizes mechanisms that lead to biological N2O production and how discriminate placement of 15N into molecules of N2O occurs. Through direct measurements and atmospheric modeling, we can now place a constraint on the isotopic composition of biological sources of N2O and trace its fate in the atmosphere. This powerful interdisciplinary combination of biology and atmospheric chemistry is rapidly advancing the closure of the global N2O budget.
Yeast cell wall matrix particles are composed entirely of beta-glucan and mannoprotein. Alkali-insoluble (1-->3)-beta-D-glucan was extracted from the yeast cell wall by an alkaline-acid method. IR spectra analysis showed that the product was chemically pure glucan, that is to say, it contained no other carbohydrates and proteins. So, the alkaline-acid method was ideal for extracting (1-->3)-beta-D-glucan from the yeast cell wall. We also purified and analyzed mannan oligosaccharides by the dilute alkali-Sevage method from the yeast cell wall.
This article reviews the mechanisms of bacterial adhesion to biomaterial surfaces and the factors affecting the adhesion. The process of bacterial adhesion includes an initial physicochemical interaction phase (phase one) and a late molecular and cellular interaction phase (phase two), which is a complicated process affected by many factors, including the characteristics of the bacteria themselves, the target material surface, and the environmental factors, such as the presence of serum proteins or bactericidal substances. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 43: 338–348, 1998
Over the next two decades, strong demographic demand for arthroplastic devices coupled with decreased efficacy of antibiotics are predicted to result in an exponential increase in the number of periprosthetic joint infections (PJI). Advanced strategies are therefore required to improve the local peri-implant immune response and curb the pathogenic events of bacterial adhesion and biofilm formation. The use of biomaterials that autonomously counter infections is one approach to improve orthopedic outcomes. Using conventional molecular biology characterization methods and advanced Raman spectroscopy, this study examined the bacteriostatic response of two bioc-eramic materials commonly employed as prosthetic implants: zirconia-toughened alumina (ZTA) and silicon nitride (Si3N4). Unlike the ZTA, it was found that non-oxide Si3N4 possessed an inherently anti-infective surface chemistry which acted in a responsive way against bacterial loading. The mechanistic details of its behavior are elucidated. Non-oxide bioceramics appear promising, but their full development requires a transitional approach that integrates fundamental biochemical concepts with clinical outcomes.
Polycrystalline silicon nitride (Si3N4), sintered with the addition of minor fractions of yttrium and aluminum oxides (i.e., Y2O3 and Al2O3), possesses uniquely adjustable surface chemistry that results in improved cell metabolism and enhanced bone formation. Building upon previous in vitro mineralization studies using osteosarcoma cells, this study examined interactions between various chemically modulated Si3N4 surfaces and murine mesenchymal progenitor cells (KUSA-A1). It was discovered that various pressurized thermal-treatments coupled with adiabatic and non-adiabatic cooling of sintered Si3N4 samples resulted in partial or full coverage of their surfaces with different Si–Y–O–N compounds. Full coverage by mostly yttrium silicate (β-Y2Si2O7) was obtained by non-adiabatic cooling, whereas partial coverage with N-apatite (Y10(SiO4)6N2) occurred under adiabatic conditions. These peculiar phases were found to be particularly efficient in stimulating the in vitro differentiation of KUSA-A1 cells into osteoblasts, although according to different microscopic mechanisms. The final amount of bone formation was nearly identical for both phases. Cell differentiation was monitored by assessing the concentration of the osteogenic marker γ-carboxyglutamate (i.e., Gla-osteocalcin). It was found to be ∼45% higher for Si3N4 samples possessing the N-apatite phase than for biomedical titanium alloy controls tested under exactly the same conditions. Concurrent measurements of the bone resorption marker Glu-osteocalcin (i.e., an undercarboxylated form of γ-carboxyglutamate) showed significant inhibition of osteoclastogenesis on these surface-treated Si3N4 samples as compared to the controls. Bone formation was assessed using in situ Raman microprobe spectroscopy and ex situ laser microscopy. These two independent analytical techniques consistently found an increase of ∼80% in expressed hydroxyapatite when compared to a biomedical titanium alloy. This study suggests that surface-treated Si3N4 may have a powerful anabolic, differentiating, and antiapoptotic effect on osteoblasts in vitro, and a concurrent inhibitive action on osteoclastogenesis. Given additional research, Si3N4 may represent a new therapeutic solution for bone disorders and for engineered implants that physiologically regulate bone growth processes.
The osseoconductivity of a silicon nitride bioceramic was examined as a function of chemical modifications of its as-fired surface. Biological and spectroscopic analyses showed that: (i) post-sintering annealing in N2-gas significantly improved apatite formation from human osteosarcoma (SaOS-2) cells; (ii) in situ Raman spectroscopic monitoring revealed new metabolic details of the SaOS-2 cells, including fine differences in intracellular RNA and membrane phospholipids; and, (iii) the enhanced apatite formation originated from a high density of positively charged surface groups, including both nitrogen vacancies (VN3+) and nitrogen N-N bonds (N4+) formed during N2-gas annealing. At homeostatic pH, these positive surface charges promoted binding of proteins onto an otherwise negatively charged surface of deprotonated silanols (SiO-). A dipole-like electric-charge which includes VN3+/N4+ and SiO- defective sites is proposed as a mechanism to explain the attractive forces between transmembrane proteins and the COO- and NH2+ terminus, respectively. This is analogous to the mechanism occurring in mineral hydroxyapatite where protein groups are specifically displaced by the presence of positively charged calcium loci (Ca+) and off-stoichiometry phosphorus sites (PO42-).
Against the increase of bacterial resistance to traditional antibiotics, antimicrobial peptides (AMP) are considered as promising alternatives. Bacterial biofilms are more resistant to antibiotics that their planktonic counterpart. The purpose of this study was to investigate the action of an AMP against a nascent bacterial biofilm. The activity of dermaseptin S4 derivative S4(1-16)M4Ka against 6h-old Pseudomonas fluorescens biofilms was assessed by using a combination of Attenuated Total Reflectance-Fourier Transform InfraRed (ATR-FTIR) spectroscopy in situ and in real time, fluorescence microscopy using the Baclight™ kit, and Atomic Force Microscopy (AFM, imaging and force spectroscopy). After exposure to the peptide at three concentrations, different dramatic and fast changes over time were observed in the ATR-FTIR fingerprints reflecting a concentration-dependent action of the AMP. The ATR-FTIR spectra revealed major biochemical and physiological changes, adsorption/accumulation of the AMP on the bacteria, loss of membrane lipids, bacterial detachment, bacterial regrowth, or inhibition of biofilm growth. AFM allowed estimating at the nanoscale the effect of the AMP on the nanomechanical properties of the sessile bacteria. The bacterial membrane elasticity data measured by force spectroscopy were consistent with ATR-FTIR spectra, and they allowed suggesting a mechanism of action of this AMP on sessile P. fluorescens. The combination of these three techniques is a powerful tool for in situ and in real time monitoring the activity of AMPs against bacteria in a biofilm.
Silicon nitride (Si3N4) has a distinctive combination of material properties such as high strength and fracture toughness, inherent phase stability, scratch resistance, low wear, biocompatibility, hydrophilic behavior, excellent radiographic imaging and resistance to bacterial adhesion, all of which make it an attractive choice for orthopaedic implants. Unlike oxide ceramics, the surface chemistry and topography of Si3N4 can be engineered to address potential in vivo needs. Morphologically, it can be manufactured to have an ultra-smooth or highly fibrous surface structure. Its chemistry can be varied from that of a silica-like surface to one which is predominately comprised of silicon-amines. In the present study, a Si3N4 bioceramic was subjected to thermal, chemical, and mechanical treatments in order to induce changes in surface composition and features. The treatments included grinding and polishing, etching in aqueous hydrofluoric acid, and heating in nitrogen or air. The treated surfaces were characterized using a variety of microscopy techniques to assess morphology. Surface chemistry and phase composition were determined using X-ray photoelectron and Raman spectroscopy, respectively. Streaming potential measurements evaluated surface charging, and sessile water drop techniques assessed wetting behavior. These treatments yielded significant differences in surface properties with isoelectric points ranging from 2 to 5.6, and moderate to extremely hydrophilic water contact angles from ∼65° to ∼8°. This work provides a basis for future in vitro and in vivo studies which will examine the effects of these treatments on important orthopaedic properties such as friction, wear, protein adsorption, bacteriostasis and osseointegration.
Statement of Significance
Silicon nitride (Si3N4) exhibits a unique combination of bulk mechanical and surface chemical properties that make it an ideal biomaterial for orthopaedic implants. It is already being used for interbody spinal fusion cages and is being developed for total joint arthroplasty. Its surface texture and chemistry are both highly tunable, yielding physicochemical combinations that may lead to enhanced osseointegration and bacterial resistance without compromising bulk mechanical properties. This study demonstrates the ease with which significant changes to Si3N4’s surface phase composition, charging, and wetting behavior can be induced, and represents an initial step towards a mechanistic understanding of the interaction between implant surfaces and the biologic environment.
The anthropogenic production of greenhouse gases and their consequent effects on global climate have garnered international attention for years. A remaining challenge facing scientists is to unambiguously quantify both sources and sinks of targeted gases. Microbiological metabolism accounts for the largest source of nitrous oxide (N2O), mostly due to global conversion of land for agriculture and massive usage of nitrogen-based fertilizers. A most powerful method for characterizing the sources of N2O lies in its multi-isotope signature. This review summarizes mechanisms that lead to biological N2O production and how discriminate placement of 15N into molecules of N2O occurs. Through direct measurements and atmospheric modeling, we can now place a constraint on the isotopic composition of biological sources of N2O and trace its fate in the atmosphere. This powerful interdisciplinary combination of biology and atmospheric chemistry is rapidly advancing the closure of the global N2O budget.
Methicillin-resistant Staphylococcus aureus (MRSA) is a major problem in clinical settings, and because it is resistant to most antimicrobial agents, MRSA infections are difficult to treat. We previously reported that synthetic macrocyclic bis(bibenzyl) derivatives, which were originally discovered in liverworts, had anti-MRSA activity. However, the action mechanism responsible was unclear. In the present study, we elucidated the action mechanism of macrocyclic bis(bibenzyl) RC-112 and its partial structure, IDPO-9 (2-hydroxyl phenyl ether). Survival experiments demonstrated that RC-112 had bactericidal effects on MRSA, whereas IDPO-9 had bacteriostatic effects. IDPO-9-resistant mutants exhibited cross-resistance to triclosan, but not to RC-112. The mutation was identified in the fabI, enoyl-acyl carrier protein reductase gene, a target of triclosan. We have not yet isolated the RC-112-resistant mutant. On the other hand, the addition of RC-112, unlike IDPO-9, caused the inflow of ethidium and propidium into S. aureus cells. RC-112-dependent ethidium outflow was observed in ethidium-loaded S. aureus cells. Transmission electron microscopy also revealed that S. aureus cells treated with RC-112 had intracellular lamellar mesosomal-like structures. Intracellular Na(+) and K(+) concentrations were significantly changed by the RC-112 treatment. These results indicated that RC-112 increased membrane permeability to ethidium, propidium, Na(+), and K(+), and also that the action mechanisms of IDPO-9 and the other compounds differed from each other.
Copyright © 2015. Published by Elsevier B.V.
The chemical composition, molecular structure and physicochemical properties of five Gram-positive bacterial
strain: Bacillus cereus, Bacillus subtilis, Sarcina lutea, Staphylococcus aureus, Micococcus luteus were investigated by Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), NMR spectroscopy and intact cell matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (IC MALDI TOF MS). An analysis of FTIR spectra as a function of pH revealed the three major types of cell wall functional groups – carboxyl group, amino group and phosphate group. An analysis of XPS spectra was determinate the major surface components of bacterial cell. 13C NMR and IC MALDI TOF MS spectra of six bacterial species were registered. Our findings indicate that chemical and structural differences in the cell composition of Gram-positive bacteria can be detected. The obtained results also demonstrate that the combination of FTIR, XPS and NMR spectroscopy with IC MALDI TOF MS technique yields useful information and complements other biochemical and physical methods of microbial cells characteristics.
Rapid and effective methods of pathogen identifications are of major interest in clinical microbiological analysis to administer timely tailored antibiotic therapy. Raman spectroscopy as a label-free, culture-independent optical method is suitable to identify even single bacteria. However, the low bacteria concentration in body fluids makes it difficult to detect their characteristic molecular fingerprint directly in suspension. Therefore, in this study Raman spectroscopy is combined with dielectrophoresis, which enables the direct translational manipulation of bacteria in suspensions with spatial non-uniform electrical fields so as to perform specific Raman spectroscopic characterization. A quadrupole electrode design is used to capture bacteria directly from fluids in well-defined micro sized regions. With live/dead fluorescence viability staining it is verified, that the bacteria survive this procedure for a certain range of field strengths. The dielectrophoretic enrichment of bacteria allows for obtaining high quality Raman spectra in dilute suspensions with an integration time of only one second. As proof-of-principle study the setup was tested with Escherichia coli and Enterococcus faecalis, two bacterial strains that are commonly encountered in urinary tract infections. Furthermore to verify the potential for dealing with real world samples, pathogens from patient's urine have been analyzed. With the additional help of multivariate statistical analysis a robust classification model could be built and allowed the classification of those two strains within a few minutes. In contrast the standard microbiological diagnostics base on very time-consuming cultivation tests. This setup holds the potential to reduce the crucial parameter diagnosis time by orders of magnitude.
The types of complexes that salicylate (2-hydroxy-benzoate) forms with the surface of goethite (α-FeOOH) in aqueous medium were studied in situ by using cylindrical internal reflection (CIR) Fourier transform infrared (FTIR) spectroscopy. Results obtained from CIR-FTIR studies were compared with adsorption isotherm experiments in order to relate the level of salicylate coverage to the nature of the surface complex. At lower surface coverages all the interfacial salicylate has a chelate structure in which one carboxylic oxygen and the ortho phenolic oxygen bind one Fe atom of the goethite surface. At higher surface coverages this chelate complex coexists with salicylate ions, which are weakly bound in the double layer.
Introduction to Corrosion Science is suitable for a one-semester course in corrosion science at the graduate or advanced undergraduate level for students that do not have backgrounds in electrochemistry but have taken introductory courses in materials science or physical chemistry. The text follows the approach of a physical chemist or materials scientist and is geared toward students of physical chemistry, materials science, and engineering. In addition, practicing corrosion engineers and materials engineers will find useful information that will broaden their understanding of the fundamental principles of corrosion science. This textbook grew out of classroom lectures, which the author presented as a Professorial Lecturer at George Washington University, Washington, D.C. Chapters on: • Charged interfaces • Electrochemical cells • Thermodynamics of corrosion • Corrosion kinetics and mixed potential theory • Concentration polarization and diffusion • Passivity • Crevice corrosion and pitting • Stress-corrosion cracking and corrosion fatigue • Corrosion inhibitors • Corrosion under organic coatings • AC impedance • High temperature oxidation Key features: • Detailed illustrations • Worked example problems • Problem sets after each chapter • Extensive references • Appendices to show the origin of important equations. © Springer Science+Business Media, LLC 2010. All rights reserved.
High purity alumina ceramics have been used for more than 25 years in biomedical applications due to their excellent wear behaviour and high strength. Nevertheless great effort have been undertaken to develop a material with increased strength combined with excellent wear properties. One candidate material family is ZTA-ceramics. Out of this family a new generation of that material is available now in which high strength, high toughness, high hardness and wear properties are combined. This material is a zirconia and platelet reinforced alumina ceramic (ZPTA). In more details ZPTA-ceramics are based on an alumina matrix containing homogeneously distributed metastable zirconia particles and 'in situ' formed hexagonal ternary aluminate platelets of a length of about 3 μm and a thickness of 0, 3 μm. The chemical composition and the microstructure were optimized to achieve a ceramic material combining all required properties: strength of more than 1200 MPa, fracture toughness of 6, 5 MPa√m and Vickers hardness HV1 of 1975 are typical. Extremely low wear rates have been detected in ring-on-disc and HIP simulator tests.
Aqueous solutions containing Ni(II) and a series of structurally related carboxylic acids were analyzed using attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and Ni K-edge X-ray absorption fine structure spectroscopy (XAFS). XAFS spectra were also collected for solutions containing Ni2+ and chelating ligands (ethylenediaminetetraacetic acid, nitrilotriacetic acid (NTA)) as well as soil fulvic acid. Limited spectral changes are observed for aqueous Ni(II) complexes with monocarboxylates (formate, acetate) and long-chain polycarboxylates (succinate, tricarballylate), where individual donor groups are separated by multiple bridging methylene groups. These spectral changes indicate weak interactions between Ni(II) and carboxylates, and the trends are similar to some earlier reports for crystalline Ni(II)-acetate solids, for which X-ray crystallography studies have indicated monodentate Ni(II)-carboxylate coordination. Nonetheless, electrostatic or outer-sphere coordination cannot be ruled out for these complexes. However, spectral changes observed for short-chain dicarboxylates (oxalate, malonate) and carboxylates that contain an alcohol donor group adjacent to one of the carboxylate groups (lactate, malate, citrate) demonstrate inner-sphere metal coordination by multiple donor groups. XAFS spectral fits of Ni(II) solutions containing soil fulvic acid are consistent with inner-sphere Ni(II) coordination by one or more carboxylate groups, but spectra are noisy and outer-sphere modes of coordination cannot be ruled out. These molecular studies refine our understanding of the interactions between carboxylates and weakly complexing divalent transition metals, such as Ni(II).
Amorphous carbon nitride (a–CNx) coatings were deposited on Si3N4 disks by an ion beam assisted deposition system. The composition, structure and hardness of the a–CNx coatings were characterized by Auger electronic spectroscopy, Raman spectroscopy and nano-indentation tester, respectively. The influences of normal load and sliding speed on the friction coefficients and the specific wear rates for the a–CNx/Si3N4 tribo-pairs were investigated and analyzed synthetically by ball-on-disk tribometer. The worn surfaces were observed by optical microscope. The results showed that the a–CNx coatings contained 12 at.% nitrogen, and their structure was a mixture of sp2and sp3 bonds. The a–CNx coatings’ nanohardness was 29 GPa. The influence of sliding speed on the friction coefficients and the specific wear rate of the CNx coatings was more obvious than that of normal load. The friction coefficients and the specific wear rate of the CNx coatings decreased as the sliding speed increased. At a sliding speed higher than 0.1 m/s, the friction coefficients were less than 0.04. The specific wear rates of the a–CNx coatings were higher than those of Si3N4 balls at a sliding speed below 0.1 m/s, while the specific wear rates of the a–CNx coatings and the Si3N4 balls all fluctuated around a lower level of 10−8 mm3/Nm as the sliding speed increased beyond 0.2 m/s. To describe the wear behavior of a–CNx coatings sliding against Si3N4 balls in water with normal loads of 3–15 N and sliding speeds of 0.05–0.5 m/s, the wear-mechanism map for the a–CNx/Si3N4 tribo-pairs in water was developed.
Infrared absorption spectra of DNA and RNA as dry, lyophilized powders in KBr pellets, as hydrated KBr pellets, and in solution phase are reported. We find the symmetric and antisymmetric stretching vibrations of the phosphate linkage, νs(PO2-) and νas(PO2-), to be very sensitive to hydration, as intensity changes as well as frequency shifts are observed. An increase in water content causes DNA to undergo a structural transition form A-form to B-form. This observation leads us to believe that the frequency shifts are associated mostly with the conformational change, whereas the increase in intensities may be due to an increase in the local dielectric in the vicinity of the polar and solvent exposed phosphate groups. A similar effect was reported recently for the amide groups of proteins. The structure of RNA is less sensitive to hydration, and only the phophodiester stretching vibrations are affected by hydration. The solution transmission and ATR spectra of DNA and RNA solution are also compared and found to be identical to one another in the 950-1300 cm-1 frequency region. Furthermore, solution spectra resemble the fully hydrated solid-phase spectra.
The aim of this study was to investigate the surface analysis of human teeth using a pH-imaging microscope based on a semiconductor silicon sensor. Disks were cut from freshly extracted non-carious and carious human teeth. Samples were placed on an agar film to evaluate the surface pH distribution. Non-carious samples were treated with 37% phosphoric acid and then thoroughly rinsed. A reduction of the pH value was clearly detected after a phosphoric acid treatment. The pH distribution of carious lesions was lower than that of non-carious lesions. From these results, this pH-imaging technology has the potential to aid in carious assessments and carious treatments.
Aqueous attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectra of 24 aliphatic monocarboxylates have asymmetric COO− stretch frequencies (νas) of 1541 cm−1 to 1678 cm−1, while the symmetric stretch frequencies range from 1202 cm−1 to 1417 cm−1. The pKa values of these acids are linearly correlated with νas according to the equation (pKa = 66.70-0.04018νas, σ = 0.266 pKa units, r2 = 0.968). This correlation should be useful in determining the pKa values of acids in complex mixtures and the site pKa values of carboxyl groups in polyacids. Semi-empirical molecular orbital calculations using the AM1 parameter set give νas values which correlate well with experimental νas (σ = 11.3 cm−1), although model νas values are ≈ 500 cm−1 too high; the PM3 parameter set predicts νas values that are only ≈ 300 cm−1 too high, but which do not correlate as well with experiment (σ = 17.6 cm−1).
Potentiometric titration and zeta potential measurements are crucial techniques for the characterization of the surface properties of bacterial cells. In this study, we investigated the effects of two commonly used electrolytes, NaNO(3) and NaClO(4), on the viability and acid-base properties of Gram-positive bacteria Bacillus subtilis. B. subtilis are non-pathogenic bacteria which are often used to model the surface properties of pathogenic microorganisms of the same genus, including Bacillus anthracis and Bacillus cereus. The survival rates of bacterial cells treated with NaNO(3) were significantly higher in comparison with microorganisms treated with NaClO(4) (5.2-6.8 and 4.1-4.7log(10)cfu - colony-forming units, respectively). A decrease in the ionic strength (0.1M, 0.01M and 0.005M) of both electrolytes increased viable bacterial cell counts in NaNO(3) treatments and decreased viable bacterial counts in NaClO(4) treatments. Potentiometric titration revealed three dominant types of cell wall functional groups: the carboxyl group (pK(a) values of 4.58-4.89), the amino group (pK(a) values of 9.62-9.89) and the phosphate group (pK(a) values of 7.12-7.49). An increase in the ionic strength of electrolytes led to a decrease in total site concentrations and a drop in buffering capacity at the examined pH values. Based on zeta potential values, measured as a function of pH and ionic strength, the isoelectric point of B. subtilis was determined at pH 2.2 for 0.005M and 0.01M NaNO(3). Zeta potential increased with a rise in pH, and it decreased with an increase in ionic strength.
Attachment of live cells of Shewanella putrefaciens strain CN-32 to the surface of hematite (α-Fe2O3) was studied with in situ ATR-FTIR spectroscopy at variable pH (4.5 to 7.7) and contact times up to 24 hours. The IR-spectra indicate that phosphate based functional groups on the cell wall play an important role in mediating adhesion through formation of inner-sphere coordinative bonds to hematite surface sites. The inner-sphere attachment mode of microbial P groups varies with pH, involving either a change in protonation or in coordination to hematite surface sites as pH is modified. At all pH values, spectra collected during the early stages of adhesion show intense IR bands associated with reactive P-groups, suggestive of preferential coordination of P-moieties at the hematite surface. Spectra collected after longer sorption times show distinct frequencies from cell wall protein and carboxyl groups, indicating that bacterial adhesion occurring over longer time scales is to a lesser degree associated with preferential attachment of P-based bacterial functional groups to the hematite surface. The results of this study demonstrate that pH and reaction time influence cell-mineral interactions, implying that these parameters play an important role in determining cell mobility and biofilm formation in aqueous geochemical environments.
Silicon nitride (Si(3)N(4)) is an industrial ceramic used in spinal fusion and maxillofacial reconstruction. Maximizing bone formation and minimizing bacterial infection are desirable attributes in orthopedic implants designed to adhere to living bone. This study has compared these attributes of Si(3)N(4) implants with implants made from two other orthopedic biomaterials, i.e. poly(ether ether ketone) (PEEK) and titanium (Ti). Dense implants made of Si(3)N(4), PEEK, or Ti were surgically implanted into matching rat calvarial defects. Bacterial infection was induced with an injection of 1×10(4)Staphylococcus epidermidis. Control animals received saline only. On 3, 7, and 14days, and 3months post-surgery four rats per time period and material were killed, and calvariae were examined to quantify new bone formation and the presence or absence of bacteria. Quantitative evaluation of osteointegration to adjacent bone was done by measuring the resistance to implant push-out (n=8 rats each for Ti and PEEK, and n=16 rats for Si(3)N(4)). Three months after surgery in the absence of bacterial injection new bone formation around Si(3)N(4) was ∼69%, compared with 24% and 36% for PEEK and Ti, respectively. In the presence of bacteria new bone formation for Si(3)N(4), Ti, and PEEK was 41%, 26%, and 21%, respectively. Live bacteria were identified around PEEK (88%) and Ti (21%) implants, whereas none were present adjacent to Si(3)N(4). Push-out strength testing demonstrated statistically superior bone growth onto Si(3)N(4) compared with Ti and PEEK. Si(3)N(4) bioceramic implants demonstrated superior new bone formation and resistance to bacterial infection compared with Ti and PEEK.
We report on an investigation into a common problem in microbiology laboratories, which is associated with the difficulty of distinguishing/recognising different strains of the genus Staphylococcus. We demonstrate the potential of Raman spectroscopy as a rapid techniques allowing for the identification of different isolates for the detection of biofilm-positive and biofilm-negative Staphylococcus epidermidis strains. For this, the recorded spectra were interpreted using the approach of principal component analysis (PCA). (© 2010 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA)
This article reviews the mechanisms of bacterial adhesion to biomaterial surfaces and the factors affecting the adhesion. The process of bacterial adhesion includes an initial physicochemical interaction phase (phase one) and a late molecular and cellular interaction phase (phase two), which is a complicated process affected by many factors, including the characteristics of the bacteria themselves, the target material surface, and the environmental factors, such as the presence of serum proteins or bactericidal substances. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 43: 338–348, 1998
Pulsed UV light and infrared heat-treated Staphylococcus aureus cells were analyzed using transmission electron microscopy to identify the cell damage due to the treatment process. A 5-s
treatment with pulsed UV light resulted in complete inactivation of S. aureus even after enrichment. The temperature increase during the pulsed UV light treatment was insignificant, which suggested a
nonthermal treatment. S. aureus was also infrared heat treated using an infrared heating system with six infrared lamps. Five milliliters of S. aureus cells in phosphate buffer was treated at 700°C lamp temperature for 20min. The microscopic observation clearly indicated
that there was cell wall damage, cytoplasmic membrane shrinkage, cellular content leakage, and mesosome disintegration after
both pulsed UV light and infrared treatments. Fourier transform infrared microspectrometry was successfully used to classify
the pulsed UV light and infrared heat-treated S. aureus by discriminant analysis.
Carboxyls play an important role in the chemistry of natural organic molecules (NOM) in the environment, and their behavior is dependent on local structural environment within the macromolecule. We studied the structural environments of carboxyl groups in dissolved NOM from the Pine Barrens (New Jersey, USA), and IHSS NOM isolates from soils and river waters using attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy. It is well established that the energies of the asymmetric stretching vibrations of the carboxylate anion (COO−) are sensitive to the structural environment of the carboxyl group. These energies were compiled from previous infrared studies on small organic acids for a wide variety of carboxyl structural environments and compared with the carboxyl spectral features of the NOM samples. We found that the asymmetric stretching peaks for all NOM samples occur within a narrow range centered at 1578 cm−1, suggesting that all NOM samples examined primarily contain very similar carboxyl structures, independent of sample source and isolation techniques employed. The small aliphatic acids containing hydroxyl (e.g., d-lactate, gluconate), ether/ester (methoxyacetate, acetoxyacetate), and carboxylate (malonate) substitutions on the α-carbon, and the aromatic acids salicylate (ortho-OH) and furancarboxylate (O-heterocycle), exhibit strong overlap with the NOM range, indicating that similar structures may be common in NOM. The width of the asymmetric peak suggests that the structural heterogeneity among the predominant carboxyl configurations in NOM is small. Changes in peak area with pH at energies distant from the peak at 1578 cm−1, however, may be indicative of a small fraction of other aromatic carboxyls and aliphatic structures lacking α-substitution. This information is important in understanding NOM–metal and mineral-surface complexation, and in building appropriate structural and mechanistic models of humic materials.
The redox reactions of the cytochrome c oxidase from Paracoccus denitrificans were investigated in a thin-layer cell designed for the combination of electrochemistry under anaerobic conditions with UVIVIS and IR spectroscopy. Quantitative and reversible electrochemical reactions were obtained at a surface-modified electrode for all cofactors as indicated by the optical signals in the 400–700 nm range. Fourier transform infrared (FTIR) difference spectra of reduction and oxidation (reduced-minus-oxidized and oxidized-minus-reduced, respectively) obtained in the 1800-1000 cm−1 range reveal highly structured band features with major contributions in the amide I (1620–1680 cm−1) and amide II (1580-1520 cm−1) range which indicate structural rearrangements in the cofactor vicinity. However, the small amplitude of the IR difference signals indicates that these conformational changes are small and affect only individual peptide groups. In the spectral region above 1700 cm−1, a positive peak in the reduced state (1733 cm−1) and negative peak in the oxidized state (1745 cm−1) are characteristic for the formation and decay of a COOH mode upon reduction. The most obvious interpretation of this difference signal is proton uptake by one Asp or Gin side chain carboxyl group in the reduced state and deprotonation of another Asp or Glu residue. Moreover, both residues could well be coupled as a donor-acceptor pair in the proton transfer chain. An alternative interpretation is in terms of a protonated carboxyl group which shifts to a different environment in the reduced state. The relevance of this first direct observation of protein protonation changes in the cytochrome c oxidase for vectorial proton transfer and the catalytic reaction is discussed.
A quantitative attenuated total reflectance Fourier transform infrared (ATR-FT-IR) spectroscopic method is developed for the analysis of total carboxylate concentration, [COO−], in aqueous solution. The short (12–13 μm) and highly reproducible pathlength of the ATR cell permits quantitative subtraction of the water peak at 1640 cm−1. Carboxylate quantitation is based on the area of the asymmetric stretching peak, which is nearly independent of compound structure. The molar absorptivity of alkyl carboxylates in water is 438 ± 58 l mol−1 cm−1, and the integrated molar absorptivity is 2.95 ± 0.08 × 104 l mol−1 cm−2 (n = 15 compounds, 0.1 M ≤ [COO−] ≤ 1.5 M). The [COO−] in solutions of mixed carboxylates is measured with a root mean square error of 2.4% and a small (+1.5) positive bias. The accuracy of the method is limited by the assumption that integrated absorbance is constant for all COO− groups.
Aqueous attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectra of 18 aliphatic di-carboxylic acids are reported as a function of pH. The spectra show isosbestic points and intensity changes which indicate that Beer's law is obeyed, and peak frequencies lie within previously reported ranges for aqueous carboxylates and pure carboxylic acids. Intensity sharing from the symmetric carboxylate stretch is evident in many cases, so that bands which are nominally due to alkyl groups show increased intensity at higher pH. The asymmetric stretch of the HA− species is linearly related to the microscopic acidity constant of the H2A species, with σpK<0.25 log units; this relationship falls on the same line as previously observed for mono-carboxylic acids. The linear relationship applies to the acidity constant of the HA− species only when the two acid groups are well separated (>2 intervening atoms). The results suggest that aqueous ATR-FTIR may be able to estimate `intrinsic' pKa values of carboxylic acids, in addition to providing quantitative estimates of ionization.
Fourier transform infrared (FT-IR) spectroscopy and Raman spectroscopy were used to study the cell injury and inactivation of Campylobacter jejuni from exposure to antioxidants from garlic. C. jejuni was treated with various concentrations of garlic concentrate and garlic-derived organosulfur compounds in growth media and saline at 4, 22, and 35°C. The antimicrobial activities of the diallyl sulfides increased with the number of sulfur atoms (diallyl sulfide < diallyl disulfide < diallyl trisulfide). FT-IR spectroscopy confirmed that organosulfur compounds are responsible for the substantial antimicrobial activity of garlic, much greater than those of garlic phenolic compounds, as indicated by changes in the spectral features of proteins, lipids, and polysaccharides in the bacterial cell membranes. Confocal Raman microscopy (532-nm-gold-particle substrate) and Raman mapping of a single bacterium confirmed the intracellular uptake of sulfur and phenolic components. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to verify cell damage. Principal-component analysis (PCA), discriminant function analysis (DFA), and soft independent modeling of class analogs (SIMCA) were performed, and results were cross validated to differentiate bacteria based upon the degree of cell injury. Partial least-squares regression (PLSR) was employed to quantify and predict actual numbers of healthy and injured bacterial cells remaining following treatment. PLSR-based loading plots were investigated to further verify the changes in the cell membrane of C. jejuni treated with organosulfur compounds. We demonstrated that bacterial injury and inactivation could be accurately investigated by complementary infrared and Raman spectroscopies using a chemical-based, "whole-organism fingerprint" with the aid of chemometrics and electron microscopy.
Achieving solid skeletal attachment is a requirement for the clinical success of orthopedic implants. Porous or roughened surfaces and coatings have been developed and used with mixed success to achieve attachment due to bone ingrowth. Silicon nitride is a high performance ceramic whose strength, imaging properties, and biocompatibility make it a candidate material for orthopedic implants. A porous form of silicon nitride, cancellous-structured ceramic (CSC), has been developed. CSC is a nonresorbable, partially radiolucent porous structure that can be bonded to orthopedic implants made of silicon nitride to facilitate skeletal attachment. The purpose of this study was to quantify the extent and rate of bone ingrowth into CSC in a large animal model. Cylindrical implants were placed bilaterally using staged surgeries in the medial femoral condyle of six sheep. Condyles were retrieved after 3 and 6 months in situ and prepared for examination of bone growth under SEM. Bone grew into CSC to extents and at rates similar to those reported for other titanium porous surfaces in studies involving large animals and postmortem retrievals in humans. Bone ingrowth was observed at depths of penetration greater than 3 mm in some implants after only 12 weeks in situ. Bone ingrowth into CSC is a viable method for achieving skeletal attachment.
This study describes a computer-based technique for classifying and identifying bacterial samples using Fourier-transform infrared spectroscopy (FT-IR) patterns. Classification schemes were tested for selected series of bacterial strains and species from a variety of different genera. Dissimilarities between bacterial IR spectra were calculated using modified correlation coefficients. Dissimilarity matrices were used for cluster analysis, which yielded dendrograms broadly equated with conventional taxonomic classification schemes. Analyses were performed with selected strains of the taxa Staphylococcus, Streptococcus, Clostridium, Legionella and Escherichia coli in particular, and with a database containing 139 bacterial reference spectra. The latter covered a wide range of Gram-negative and Gram-positive bacteria. Unknown specimens could be identified when included in an established cluster analysis. Thirty-six clinical isolates of Staphylococcus aureus and 24 of Streptococcus faecalis were tested and all were assigned to the correct species cluster. It is concluded that: (1) FT-IR patterns can be used to type bacteria; (2) FT-IR provides data which can be treated such that classifications are similar and/or complementary to conventional classification schemes; and (3) FT-IR can be used as an easy and safe method for the rapid identification of clinical isolates.
This chapter describes the ultrastructure, chemistry and function of the bacterial wall. Cell walls are dynamic and change to fulfill functions dictated by the cell in response to the environment. Most bacteria respond unequivocally to the Gram reaction; that is, some retain the large crystal violet-iodine complex (Gram-positive), whereas others are decolorized by the alcohol treatment (Gram-negative) and can be counterstained. Cell age, autolysin levels, and growth conditions can affect the Gram reaction. Unlike Gram-positive bacteria, freeze-cleaved and -etched Gram-negative cells present a number of cleavage sites within the wall that is an indication of multilayering. This wall is chemically and structurally more complex than its Gram-positive counterpart. Each of the layers of capsule, slime layers, and surface arrays reside above the wall and may be singular or in combination with one another. Each presents unique problems for preservation and visualization by electron microscopy. The chapter also discusses the functional aspects of walls that include (1) interaction with metals; (2) β-lactam drugs and low-level antibiotic resistance; and (3) functional discontinuities in the wall fabric.
This article reviews the mechanisms of bacterial adhesion to biomaterial surfaces and the factors affecting the adhesion. The process of bacterial adhesion includes an initial physicochemical interaction phase (phase one) and a late molecular and cellular interaction phase (phase two), which is a complicated process affected by many factors, including the characteristics of the bacteria themselves, the target material surface, and the environmental factors, such as the presence of serum proteins or bactericidal substances.
The surface speciation of orthophosphate ions on goethite has been studied as a function of pH, time, total phosphate concentration, and ionic medium by means of diffuse reflectance FTIR spectroscopy. The samples were prepared in accordance with a distribution diagram of surface species as calculated from thermodynamic data. In agreement with the thermodynamic model three dominating surface complexes could be distinguished with IR spectroscopy, and the relative distribution of the species was shown to be primarily a function of pH. The IR characteristics of the individual surface complexes were indicative of molecular symmetries of the PO(4) unit of C(3v), C(2v), and C(3v), respectively. This was concluded to be incompatible with the bidentate, bridging structural model previously suggested. Instead, the IR data are in good agreement with a monodentate coordination of phosphate to the surfaces, where the three surface complexes only differ in the degree of protonation. A comparison between the adsorption behavior of phosphate on goethite and hematite was also made. Here the importance of the aqueous stability of the adsorbent on the adsorption mechanism was shown.