Hank's Balanced Salt Research Articles

In-House Viral Transport Medium (VTM) Manufacture in the Time of Shortage, Supply and Crisis of COVID-19 at Veteran Affairs Medical Center (VAMC)

Introduction/ObjectiveWith the outbreak of COVID-19 caused by SARS-CoV-2, there have been challenges in the maintenance of adequate supplies both in terms of PPE and for testing. The shortage of commercial VTM for the transport of specimens for PCR testing has created a situation in which laboratories would need to manufacture their own in-house VTM as commonly used commercial VTM is unavailable. However, there is sparse literature on the emergency manufacture of VTM. Here, we describe the VAMC experience in manufacturing/quality control on its own VTM.ResultsVTM was manufactured by pathology and laboratory medicine using strict aseptic technique with Hanks Balanced Salt Solution (HBSS) 500 ml bottle with phenol red, sterile heat-inactivated fetal bovine serum (FBS) gentamicin sulfate (50 mg/mL) and amphotericin B (250 ug/ml). First, 50 ml of amphotericin B and 50 ml of gentamicin sulfate were mixed. Then 10 ml of FBS was mixed with the HBSS bottle and then 2 ml of the gentamicin/amphotericin B mixture was also mixed into the HBSS bottle. 3 ml aliquots were made from this mixture to constitute individual tubes of VTM for clinical use. Sterility for each batch (after 24-hour incubation at 37o C in the CO2 incubator) was assessed visually and by culture on a blood agar, chocolate agar, and thioglycolate mediums. An efficacy check was performed for each batch by spiking positive and negative controls into the VTM aliquots; RT-PCR for SARS-CoV-2 was executed to verify the medium did not degrade viral RNA and produced expected results for room temperature, refrigerated, and frozen samples. Previously manufactured VTM without phenol red also underwent sterility and efficacy checks.ResultsVTM was successfully manufactured in-house, allowing testing to continue despite the shortage. Sterility and efficacy checks on all lots and bottles from which the VTM aliquots were made passed with no growth detected and efficacy passing with all expected positives and negatives resulting as expected.ConclusionTo the author’s knowledge, this represents the first published abstract on VTM manufacture in this most unprecedented crisis involving COVID-19. In this national emergency with corresponding shortage of testing supplies including commercial VTM, the in-house manufacture of VTM is both feasible and prudent to ensure continuity of testing and quality patient/laboratory care.

Surface Characterization and Corrosion Resistance of Biomedical AZ31 Mg Alloy Treated by Microarc Fluorination.

The application prospect of biodegradable materials is being studied extensively. However, the high corrosion rate and its alloys in body fluids have been major limitations of the application of pure Mg (magnesium). To improve corrosion resistance of biodegradable AZ31 Mg alloy, we adopted microarc fluorination within a voltage range of 100-300 V in 46% hydrofluoric acid. To obtain morphologies, chemical compositions, and structural characteristics, field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) were performed, respectively. Results showed that the coating was mainly composed of MgF2. Electrochemical corrosion and immersion tests proved that the corrosion resistance of MAF-treated AZ31 Mg alloy was significantly improved compared with untreated AZ31 Mg alloy in HBSS (Hank's Balanced Salt Solution). Current densities of AZ31, MAF100, MAF150, MAF200, MAF250, and MAF300 were 342.4, 0.295, 0.228, 0.177, 0.199, and 0.212 μA/cm2, respectively. The roughness test indicated that samples under MAF treatment of 200 V, 250 V, and 300 V had large surface roughness. Meanwhile, the contact angle measurement and surface free energy test suggested that those samples had smaller contact angle and higher SFE than Ti. Thus, MAF-treated AZ31 Mg alloy might have promising application in various fields.

Adhesion improvement and in vitro characterisation of 45S5 bioactive glass coatings obtained by atmospheric plasma spraying

Plasma sprayed bioactive glass coatings were studied using crushed 45S5 bioactive glass powder. It is widely accepted that plasma sprayed coating microstructure is highly affected by the characteristics of the powder and the parameters set on the spraying process. Once the coating deposition was optimized, two strategies were carried out to analyse their effect on the coating adhesion: cooling with carbon dioxide while spraying and a post heat treatment to the as-sprayed coatings.Scanning electron microscopy and X-ray diffraction were used for analyse the obtained coatings. Additionally, coating adhesion to the substrate and degradation of the coatings in Tris buffer solution were evaluated for the different samples studied.Coatings have been tested in vitro to evaluate their response by immersion in simulated body fluid, Hank's Balanced Salt Solution.The results show an increase in the adhesion strength for the heat treated samples due to the stress relaxation achieved above glass transition temperature. Moreover, in the bioactivity test an apatite layer at the coatings surface was produced for all the strategies studied.

L-Cysteine-mediated modulation of copper trafficking in prostate cancer cells: an in vitro and in vivo investigation with 64Cu and 64Cu-PET.

Copper imbalance is implicated in many diseases, including cancer. Copper in blood is mainly transported by carrier proteins but a small fraction is bound to low molecular weight species, possibly amino acids. Their roles in cellular copper delivery are unknown. Our aim was to test whether accumulation of 64Cu into cancer-derived cells can be influenced by copper-binding serum amino acids. In vitro cellular accumulation of 64Cu was measured in Hank's Balanced Salt Solution in the presence of 100 μM l-histidine, l-methionine, l-cysteine and l-threonine. l-Cysteine markedly increased 64Cu accumulation and retention in DU145, PC3 and SK-OV-3 cells, while some other cell lines did not show an effect. This effect was not due to 64Cu delivery in the form of a 64Cu-cysteine complex, nor to reduction of 64Cu(ii) to 64Cu(i) by l-cysteine. Pre-incubation of cells with l-cysteine increased 64Cu accumulation, even if l-cysteine was removed from HBSS before 64Cu was added. The effect of l-cysteine on 64Cu accumulation was not mediated by increased glutathione synthesis. Despite the demonstrable in vitro effect, pre-injection of l-cysteine precursor N-acetyl-cysteine (NAC) in vivo did not enhance 64Cu delivery to DU145 xenografts in mice. Instead, it decreased 64Cu accumulation in the DU145 tumour and in brain, as assessed by PET imaging. We conclude that 64Cu is not delivered to DU145 cancer cells in vitro as a complex with amino acids but its cellular accumulation is enhanced by l-cysteine or NAC influx to cells. The latter effect was not demonstrable in vivo in the DU145 xenograft.

Characterization of a Bioresorbable Magnesium-Reinforced PLA-Integrated GTR/GBR Membrane as Dental Applications.

Inferior mechanical properties have always been a limitation of the bioresorbable membranes in GBR/GTR. This study is aimed at fabricating a bioresorbable magnesium-reinforced polylactic acid- (PLA-) integrated membrane and investigating its mechanical properties, degradation rate, and biocompatibility. The uncoated and fluoride-coated magnesium alloys, AZ91, were made into strips. Then, magnesium-reinforced PLA-integrated membrane was made through integration. PLA strips were used in the control group instead of magnesium strips. Specimens were cut into rectangular shape and immersed in Hank's Balanced Salt Solution (HBSS) at 37°C for 4, 8, and 12 d. The weight loss of the AZ91 strips was measured. Three-point bending tests were conducted before and after the immersion to determine the maximum load on specimens. Potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS) were conducted on coated and uncoated AZ91 plates to examine corrosion resistance. Murine fibroblast and osteoblast cells were cultured on circular specimens and titanium disks for 1, 3, and 5 d. Thereafter, WST test was performed to examine cell proliferation. As a result, the coated and uncoated groups showed higher maximum loads than the control group at all time points. The weight loss of AZ91 strips used in the coated group was lower than that in the uncoated group. PDP, EIS, SEM, and EDS showed that the coated AZ91 had a better corrosion resistance than the uncoated AZ91. The cell proliferation test showed that the addition of AZ91 did not have an adverse effect on osteoblast cells. Conclusively, the magnesium-reinforced PLA-integrated membrane has excellent load capacity, corrosion resistance, cell affinity, and proper degradation rate. Moreover, it has great potential as a bioresorbable membrane in the GBR/GTR application.

Synthesis and Characterization of 50S8P Bioglass through Sol Gel Method

Bioactive glasses (BG) were applied in bone and dental applications as well as in tissue engineering. In this studies, a new bioglass 50S8P (50% SiO2, 22% CaO, 20% Na2O and 8% P2O5) with different aging time (3, 7, 10 and 15 days) was prepared by sol-gel method. These synthesized glasses were analyzed using X- ray powder diffraction (XRD), Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The bioactivity of all BG is evaluated by incubating the BG powder in Hank's Balanced Salt Solution (HBSS) for 7, 14 and 21 days. Thermal analyses indicated the compositions can be stabilized at 700°C. XRD confirmed the primary crystalline phase was Na4Ca4Si6O18. Formation of silica network is established with the existence of functional group Si-O-Si (tetrahedral), confirmed with FTIR analyses. In vitro test confirm the apatite formation on the BG surface with characteristic of carbonate group (C-O) and P-O band noticed from FTIR and morphology of apatite formation on BG surface was observe using SEM

Effect of Sr on the Bioactivity of Sol-Gel Derived New Silicate Bioglass S55P4

Strontium (Sr) stimulates osteoblast and inhibits osteoclast activities in-vitro and is used clinically as a treatment for osteoporosis. In this research, the effect of Sr substitution on the apatite formation of sol-gel derived bioactive glass (BG) (55.90SiO2-1.72P2O5 -21.67Na2O - (20.69-x) CaO -x SrO) (x=0, 5 and 8 mol. %) were investigated. The synthesized Sr doped BG samples were treated in Hank's Balanced Salt Solution (HBSS) for 14 days to study the bioactivity. The achieved samples were evaluated by X-ray powder diffraction (XRD) and Scanning electron microscope (SEM). In XRD, the hydroxyapatite (HA) crystalline peak for 8% Sr-BG is less compared with others. When Sr amount is increased to 8%, the low crystalline peaks of HA were detected although the same soaking duration. FTIR spectra supported the delay precipitation of calcium phosphate (CaP), especially for the specimen containing 8% Sr. After 14 days soaking, SEM images confirmed the bioactivity of the synthesized samples by the formation of apatite on the glass surface.

Antimicrobial Effectiveness of Calcium Silicate Sealers against a Nutrient-Stressed Multispecies Biofilm.

Purpose: This study compared the antimicrobial efficacy of calcium silicate sealers (BioRoot RCS and Total Fill BC) and conventional sealers (AH Plus and Tubli-seal) against planktonic bacteria and a nutrient-stressed multispecies biofilm. Methods: Antimicrobial properties of freshly mixed sealers were investigated using the direct contact test (DCT) and a nutrient-stressed multispecies biofilm comprised of five endodontic strains. Antimicrobial activity was determined using quantitative viable counts and confocal laser scanning microscopy (CLSM) analysis with live/dead staining. The pH of the sealers was analysed over a period of 28 days in Hanks Balanced Salt Solution (HBSS). Analysis of variance (ANOVA) with Tukey tests and the Kruskal–Wallis test were used for data analysis with a significance of 5%. Results: All endodontic sealers exhibited significant antimicrobial activity against planktonic bacteria (p < 0.05). BioRoot RCS caused a significant reduction in viable counts of the biofilms compared to AH Plus and the control (p < 0.05), while no significant difference could be observed compared to TotalFill BC and Tubli-seal (p > 0.05). CLSM analysis showed that BioRoot RCS and TotalFill BC exhibited significant biofilm inhibition compared to Tubli-seal, AH Plus and the control (p < 0.05). BioRoot RCS presented with the highest microbial killing, followed by TotalFill BC and Tubli-seal. Alkalizing activity was seen from the onset by BioRoot RCS, TotalFill BC and AH Plus. After 28 days, BioRoot RCS demonstrated the highest pH in HBSS (pH > 12). Conclusions: Calcium silicate sealers exhibited effective antimicrobial properties. This was demonstrated by superior biofilm inhibition capacity and microbial killing, with strong alkalizing activity compared to epoxy-based and zinc oxide-eugenol-based sealers.

Resveratrol Stimulates the Na+-Ca2+ Exchanger on the Plasma Membrane to Reduce Cytosolic Ca2+ in Rat Aortic Smooth Muscle Cells.

Resveratrol is well known to exhibit vascular relaxant and antihypertensive effects. In this study, we determined the effects of resveratrol on the modulation of cytosolic [Ca] level and adenosine 5'-triphosphate-induced Ca release from the sarcoplasmic reticulum (SR) in rat aortic smooth muscle cells (ASMCs) and explored its underlying mechanisms. In this article, cytosolic [Ca] and SR [Ca] in ASMCs were determined by Fluo-4/acetoxymethyl and Mag-Fluo-4/acetoxymethyl respectively. Resveratrol (20, 50, and 100 µM) caused a rapid and substantial reduction in cytosolic [Ca] in ASMCs bathed in normal Hank's Balanced Salt Solution or Ca-free Hank's Balanced Salt Solution. Pretreatment with resveratrol reduced adenosine 5'-triphosphate-induced SR Ca release and SR Ca content. In the cells bathed in Na-free physiological saline, which favors the reverse mode of the Na-Ca exchanger (NCX), resveratrol induced an increase in cytosolic [Ca] and SR [Ca]. However, its effect on cytosolic [Ca] was inhibited by the selective NCX inhibitor, SEA0400. Our findings suggest that resveratrol reduces cytosolic [Ca] and SR [Ca] in ASMCs in normal physiological saline, which might be, at least in part, mediated by the NCX.

Clarifying the influence of albumin on the initial stages of magnesium corrosion in Hank's balanced salt solution

Abstract The corrosion behavior of Mg, a promising biodegradable metallic material, in protein-containing pseudophysiological environment is still not fully understood. In this work, the influence of albumin on the corrosion behavior of commercially pure magnesium (CP Mg) is investigated during short-term tests in Hank's Balanced Salt Solution (HBSS). This work focuses on the reactions at the Mg/medium interface from the perspective of the interactions among albumin, media components and substrate. Hydrogen evolution tests demonstrate that the physiological amount of albumin (40 g L−1) accelerates Mg corrosion in HBSS during the first few hours but slows down the degradation afterwards. The presence of albumin decreases the concentration of free Ca2+ in HBSS and delays formation of protective co-precipitation products on Mg surface. The evolution of local pH (differs from typically monitored bulk pH) near Mg/medium interface in albumin-containing HBSS is reported for the first time. Comparison of local and bulk pH values elucidates the pH buffering effect of albumin during the immersion period. Based on these results, adsorption, chelating and pH buffering effects are summarized as three important aspects of albumin influence on Mg corrosion. Additionally, constant replenishment of medium components is shown to be an influential factor during the Mg corrosion tests.

Advancing the fathead minnow (Pimephales promelas) as a model for immunotoxicity testing: Characterization of the renal transcriptome following Yersinia ruckeri infection

Recent studies have utilized the fathead minnow (Pimephales promelas) to explore the immunotoxic effects associated with a variety of environmental contaminants in the absence of immunological stimuli. Though this approach allows for alterations in the resting immune system to be detected, previous evidence suggests that many immunotoxic effects may only manifest in the activated immune system. However, basic immune responses to pathogens have not been well described in this species. To expand the utility of the fathead minnow as a model for immunotoxicity testing, a more comprehensive understanding of the activated immune system is required. As such, the main goal of this study was to characterize the transcriptomic response to pathogen infection in the fathead minnow using RNA sequencing. To achieve this goal, female fathead minnows were intraperitoneally injected with either Hank's Balanced Salt Solution (sham-injected) or Yersinia ruckeri (pathogen-injected). Eight hours following injection, fish were sacrificed for the assessment of general morphological (i.e., mass, length, condition factor, hepatic index) and immunological (i.e., leukocyte counts, spleen index) endpoints. To assess the molecular immune response to Y. ruckeri, kidney tissue was collected for transcriptomic analysis. A comparison of sham- and pathogen-injected fish revealed that >1800 genes and >500 gene networks were differentially expressed.Gene networks associated with inflammation, innate immunity, complement, hemorrhaging and iron absorption are highlighted and their utility within the context of immunotoxicity is discussed. These data reveal pathogen-related molecular endpoints to improve data interpretation of future studies utilizing the fathead minnow as a model for immunotoxicity.

Polymorphonuclear leukocyte isolation from venous blood of the dog

The current study aimed to isolate neutrophils from venous blood samples of healthy dogs. Venous blood samples were obtained from Venae cephalica of clinically healthy dogs (n:5) into heparinized tubes. The blood samples (2 mL) and Percoll dilutions (45%, 54%, 63%, and 72%) prepared with Hanks Balanced Salt Solution were layered into sterile tubes. After centrifuge, the polymorphonuclear leukocytes (PMN) were aspirated between 63% and 72% interfaces of the Percoll dilutions into tubes. The samples of PMN observed under a light microscope. Viability was detected microscopically after stained with trypan blue dye. Diff-Quick staining was used to detect neutrophil purity of the isolated PMN. In the present study, the neutrophils ratio was calculated as 92% of the isolated polymorphonuclear cells. The neutrophil viability was calculated as 98% of PMNs isolated from the venous blood samples of healthy dogs. In the present study, the Percoll gradient centrifugation (72%, 63%, 54%, and 45%) is a fast technic for isolation of the neutrophils from venous blood samples of dogs.

Quantitation of Cyclosporin A in Cell Culture Media by Differential Mobility Mass Spectrometry (DMS-MS/MS).

Cell permeability is an important factor in determining the bioavailability of therapeutics that is usually measured by cell culture testing. The concentration of pharmaceutical in a medium such as Hank's Balanced Salt Solution with HEPES organic buffer (HBSS-HEPES) is measured at a series of time points, making simplicity and high throughput of the analytical method important characteristics. We report an electrospray differential mobility spectrometry mass spectrometry method (nanoESI-DMS-MS) for the rapid determination of cyclosporin A (CsA, cyclosporine) concentration in such a buffer. DMS technology provides gas phase atmospheric pressure ion filtration for small-molecule bioanalytical methods that suppresses interfering ions and reduces chemical noise, without the use of chromatography. This allows simplified sample preparation, fast calibration curve development, and shortened analysis times. It has also been noted that the DMS prefilter can reduce contamination of the mass spectrometer by salts, thereby extending mass spectrometer system uptime.In the application described here, DMS-MS/MS is applied to cyclosporine A (CsA) in cell medium. Sample preparation is limited to dilution with an ammonium acetate-methanol-water mobile phase and the addition of CsA-d4 internal standard. The isotope ratio data are obtained in DMS-MS MRM mode observing NH3 loss from the ammonium adduct of the two species. A calibration curve with high linearity (R2=0.998) is rapidly obtained with nearly zero intercept, while it was found that a liquid chromatography LC-MS method required a preliminary SPE step to obtain a linear calibration curve. The time for data acquisition in the DMS-MS MRM method with flow injection (FIA) or infusion introduction at ESI flow of 400nL/min is typically 30s leading to a cycle time of less than 1min.

Mechanical and corrosion properties of Mg-Zn/HAP/Al2O3 hybrid composite

The effect of HAP and Al2O3 composition with constant of ceramic content of 15 wt. % on mechanical properties, microstructure, and corrosion behavior of degradable Mg-Zn/HAP/Al2O3 hybrid composite developed by powder metallurgy method were investigated. The microstructure was analyzed using an optical microscope and scanning electronic microscope while mechanical properties were evaluated for density and compression strength. Meanwhile, corrosion behavior in Hank Balanced salt solution (HBSS) was studied for 4 h. The addition of HAP and Al2O3 particles has improved the mechanical properties and corrosion properties of Mg-Zn alloy. The results show that 15 wt. % Al2O3 (without HAP) shows the higher density, hardness, and compression. However, the composite consisted of 10 wt. % HAP with 5 wt. % Al2O3 shows the lower corrosion rate.

New Ti-6Al-2Nb-2Ta-1Mo alloy as implant biomaterial: In vitro corrosion and in vivo osseointegration evaluations

Over the last decade, new titanium alloys are developed in different areas of implantology. The aim of this study was to characterize a new Ti-Al-Nb-Ta-Mo based alloy, with high potential for being used as a biomedical implant. The evaluation of Ti-6Al-2Nb-2Ta-1Mo was performed both in vitro (by monitoring its corrosion resistance in Hank's Balanced Salt Solution, HBSS) and in vivo (by evaluating the osseointegration following rabbit tibia implantation), by comparison with titanium and Ti-6Al-7Nb alloy. Electrochemical impedance spectroscopy (EIS) data showed high impedance values for all titanium samples after 1 week immersion times in HBSS at 37 °C. According to EIS analysis, the corrosion resistance of the Ti-6Al-2Nb-2Ta-1Mo alloy immersed in HBSS was higher compared to the standard cp-Ti or with the Ti-6Al-7Nb alloy. In addition, a higher degree of osseointegration was achieved by the Ti-6Al-2Nb-2Ta-1Mo alloy, thus probing that a higher resistance to electrochemical corrosion provided enhanced protection to the implant surface against biodegradation, thus positively affecting the qualitative and quantitative evolution of bone tissue repair.

An Impedance Measurement Platform for Cryopreservation Applications

One of the beneficial methods being widely used to preserve genetic resources of imperiled animals or improved agricultural animals is cryopreservation of germplasm. During this process, the biological structure of the cells remains relatively intact by freezing and storing them at very low temperatures. Freezing condition plays an essential role in cryopreservation procedure since the exposure of the cells to low temperature can cause damage to the cells [1]. Therefore, accurate monitoring of the freezing process can improve the recovery rate of the cells after thawing. During the phase change phenomena, the dielectric and conduction properties of ice changes [2]. Herein we present, a portable platform for monitoring of the freezing and thawing processes based on the electrical impedance of the samples during cryopreservation. The system is composed of a portable temperature and impedance measurement system in conjunction with an impedance sensing probe fabricated with printed circuit board (PCB) technology. The impedance measurement circuit, temperature measurement circuit, control unit for data acquisition and wireless communication and touch screen LCD with a graphical user interface are the building blocks of the measurement system that enables users to perform impedance measurement at single or multiple frequencies with various excitation signals (Figure 1A). Utilizing impedance measurement instead of DC resistance measurement enable us to monitor both dielectric properties and resistance changes during phase change and avoids the polarization of the electrodes. In addition, an impedance sensing probe was developed by using PCB technology, which provides accurate electrodes fabrication at low cost. The probe has been designed to be used within 0.5 ml French straw which is a conventional container in cryopreservation application. Pair of parallel electrodes were fabricated on the probe at three detection zones (Figure 1B). The system was evaluated at different cryopreservation conditions including various sample solutions and cooling rates. Hank's Balanced Salt Solution (HBSS) is being widely used in cryopreservation to maintain cells in a viable state. The system was characterized by measuring the impedance in HBSS and DI water solutions solution. The 0.5 ml French straws were filled sample solution along with the probe and a T-type thermocouple. Next, the samples were placed on top of the liquid nitrogen with a 2 cm gap to freeze, and after the sample temperature reached lower than -40 oC, the samples were left at room temperature to thaw. During this process, the impedance and temperature were measured inside the samples. Figures 1C and 1D show the magnitude and phase of the measured impedance for HBSS and DI water sample respectively. When the HBSS sample starts to freeze, the impedance magnitude does not change before the latent heat removal stage. However, the impedance phase starts to increase after the sample cools down. It reaches a minimum value during nucleation and increases during latent heat removal. Therefore, the phase change phenomena can be detected with the imaginary part of the impedance. In the DI water case, the impedance starts to increase by cooling down the solution when the nucleation happens there it remains relatively constant, and it keeps increasing after that. This shows that the solution containing various ions has different impedance characteristics, which can be used as a parameter to monitor the cryopreservation phenomena. The system was also characterized by different solutions containing salts and cryoprotectants, frozen at various cooling rates, to further investigate the potential of impedimetric sensors in quality control for cell freezing protocols. Figure 1

Microstructure, mechanical and corrosion properties of novel Mg-Sn-Ce alloys produced by high pressure die casting.

The aim of this study was to investigate the effect of adding 1, 2 and 4% wt of cerium on the microstructure, mechanical and corrosion properties of high pressure die casting (HPDC) Mg-4Sn alloys. Microstructure analyses of the alloys were carried out using X-Ray Diffraction (XRD) and Scanning Electron microscopy (SEM). The corrosion behaviors were determined with the potentiodynamic polarization and immersion tests in Hanks Balanced Salt Solution (HBSS), which is used as the artificial body fluid. The microstructural results showed that the addition of Ce to the main alloy creates new intermetallic phases (Ce5Sn4 and MgSnCe). In addition, Ce addition provided effectively the grain refinement of the alloys. While the hardness and yield strength of the Mg-4Sn alloy enhanced continuously with increasing Ce content, the tensile strength and elongation reached up to 2% wt. The corrosion resistance of the main alloy was improved by the addition of 1% wt of Ce. However, the Ce content, which is more than 1% wt decreased corrosion resistance.

A feasibility study of biodegradable magnesium-aluminum-zinc-calcium-manganese (AZXM) alloys for tracheal stent application.

Airway obstruction conditions are relatively rarely observed in clinical settings but nevertheless, extremely challenging to handle, especially when observed in pediatric patients. Several surgical procedures, including tracheal resection, end-to-end tracheal anastomosis, and tracheoplasty, have been developed and practised of late, to treat airway obstruction. However, the clinical outcome is typically not satisfactory due to airway restenosis conditions that develop following surgery. Various types of stents are currently available for airway stenting ranging from non-degradable silicone tubes and bio-inert metallic stents (bare or coated with polymer matrix) to hybrid silicone tubes strengthened by metallic cores, but none of the stents provides the satisfactory long-term effectiveness. Therefore, there is a significant clinical need for a biodegradable airway stent that would maintain airway patency and totally degrade over time after meeting the desired objectives. The present study aims to investigate biodegradable magnesium-aluminum-zinc-calcium-manganese (AZXM) alloy as a potential tracheal stent. The new AZXM alloy was fabricated by partially replacing aliminum in commercial AZ31 alloy with calcium. The present study demonstrates that calcium preferentially segregates along the grain boundaries as intermetallic phases (Mg2Ca) and is homogeneously distributed in the magnesium matrix. The extruded AZXM alloy showed less pitting, higher corrosion resistance in Hank's Balanced Salt Solution (HBSS) compared to the as-cast and solution-treated AZXM alloys and exhibited optimized mechanical properties. In vitro cytotoxicity evaluation using human trachea epithelial cells demonstrated excellent cyto-compatibility of AZXM alloys compared to pure Mg and commercial AZ31 validated by a very preliminary rabbit in vivo tracheal model study. Preliminary results show that the approach to use biodegradable AZXM alloys as a tracheal stent is indeed promising, although further alloy processing is required to improve the ductility needed followed by a more exhaustive in vivo study to demonstrate full viability for stent applications.

An in vitro study on dentin demineralization and remineralization: Collagen rearrangements and influence on the enucleated phase

Dentin remineralization is of clinical relevance in the therapy of caries and dentin hypersensitivity. This study is aimed at gaining more insights on a molecular scale, through IR spectroscopy, into dentin demineralization and remineralization. The dentin demineralization by ethylenediaminetetraacetic acid, EDTA (17%, 2 h) significantly altered the secondary structure distribution of collagen, upon loss of interaction with calcium ions. To investigate dentin remineralization, previously demineralized human dentin slices were soaked in Dulbecco's Phosphate Buffered Saline (DPBS) or Hank's Balanced Salt Solution HBSS, in close contact with three commercial cements used as sustained releasing sources of Ca2+ and OH− ions (i.e. calcium hydroxide- and calcium silicate-based cements). IR spectroscopy showed the occurrence of remineralization under these conditions. Collagen did not lose its ability to chelate Ca2+, and these interactions allowed collagen to rearrange into a conformation similar to that of sound dentin. This process appeared slower in HBSS than DPBS, as also shown by the lower degree of maturation of the inorganic phase enucleated in the former medium (amorphous calcium phosphate versus B-type carbonated apatite). Collagen appeared to act as a spatial constraint to crystal deposition, affecting crystallinity and carbonate content of the enucleated phase. Remineralization was found to strongly depend on the calcium releasing ability of the cements. The fast formation of a rough apatite biocoating may represent a favorable clinical condition in the context of mineralized tissue regeneration.

Effect of Silver on the Apatite Formation of Bioactive Silicate Glass

Abstract Silver (Ag) has the antibacterial property and can be easily introduced in glasses and glass-ceramics. In this research, the effect of Ag addition on the apatite formation of sol-gel derived new composition bioactive glass (BG) (55%SiO2 - 4% P2O5 -22%Na2O - (19-x) %CaO -x% Ag2O) (x=0, 5 and 8%) were investigated. The synthesized Ag doped BG samples were treated in Hank's Balanced Salt Solution (HBSS) for 14 days to study the bioactivity. The achieved samples were evaluated by X-ray powder diffraction (XRD) and Scanning electron microscope (SEM). The XRD spectra clearly show diffraction peaks of bone-like hydroxyapatite (HAp) for all samples after immersion in HBSS. However, the more intense of HAp peak at 32° was detected in Ag(5%) and Ag(8%) BGs compared with undoped BG. All glass samples are bioactive but BG with 8 wt% of Ag2O exhibited more apatite than the samples containing 5 wt% of Ag2O, as seen in SEM images. After 14 days immersion, full coverage of apatite in cluster crystal form on the Ag(8) glass surface was observed.