Influence of PCL and PHBV on PLLA Thermal and Mechanical Properties in Binary and Ternary Polymer Blends.

PLLA, PCL and PHBV are aliphatic polyesters which have been researched and used in a wide range of medical devices, and all three have advantages and disadvantages for specific applications. Blending of these materials is an attractive way to make a material which overcomes the limitations of the individual polymers. Both PCL and PHBV have been evaluated in polymer blends with PLLA in order to provide enhanced properties for specific applications. This paper explores the use of PCL and PHBV together with PLLA in ternary blends with assessment of the thermal, mechanical and processing properties of the resultant polymer blends, with the aim of producing new biomaterials for orthopaedic applications. DSC characterisation is used to demonstrate that the materials can be effectively blended. Blending PCL and PHBV in concentrations of 5-10% with PLLA produces materials with average modulus improved by up to 25%, average strength improved by up to 50% and average elongation at break improved by 4000%, depending on the concentrations of each polymer used. PHBV impacts most on the modulus and strength of the blends, whilst PCL has a greater impact on creep behaviour and viscosity. Blending PCL and PHBV with PLLA offers an effective approach to the development of new polyester-based biomaterials with combinations of mechanical properties which cannot be provided by any of the materials individually.

Strategies for Enhancing Polyester-Based Materials for Bone Fixation Applications.

Polyester-based materials are established options, regarding the manufacturing of bone fixation devices and devices in routine clinical use. This paper reviews the approaches researchers have taken to develop these materials to improve their mechanical and biological performances. Polymer blending, copolymerisation, and the use of particulates and fibre bioceramic materials to make composite materials and surface modifications have all been studied. Polymer blending, copolymerisation, and particulate composite approaches have been adopted commercially, with the primary focus on influencing the in vivo degradation rate. There are emerging opportunities in novel polymer blends and nanoscale particulate systems, to tune bulk properties, and, in terms of surface functionalisation, to optimise the initial interaction of devices with the implanted environment, offering the potential to improve the clinical performances of fracture fixation devices.

International travel between global urban centres vulnerable to yellow fever transmission.

OBJECTIVE: To examine the potential for international travel to spread yellow fever virus to cities around the world. METHODS: We obtained data on the international flight itineraries of travellers who departed yellow fever-endemic areas of the world in 2016 for cities either where yellow fever was endemic or which were suitable for viral transmission. Using a global ecological model of dengue virus transmission, we predicted the suitability of cities in non-endemic areas for yellow fever transmission. We obtained information on national entry requirements for yellow fever vaccination at travellers' destination cities. FINDINGS: In 2016, 45.2 million international air travellers departed from yellow fever-endemic areas of the world. Of 11.7 million travellers with destinations in 472 cities where yellow fever was not endemic but which were suitable for virus transmission, 7.7 million (65.7%) were not required to provide proof of vaccination upon arrival. Brazil, China, India, Mexico, Peru and the United States of America had the highest volumes of travellers arriving from yellow fever-endemic areas and the largest populations living in cities suitable for yellow fever transmission. CONCLUSION: Each year millions of travellers depart from yellow fever-endemic areas of the world for cities in non-endemic areas that appear suitable for viral transmission without having to provide proof of vaccination. Rapid global changes in human mobility and urbanization make it vital for countries to re-examine their vaccination policies and practices to prevent urban yellow fever epidemics.

The Early Erosive and Abrasive Challenge: A Profilometric, Electron Microscopic and Microhardness Study Using Human, Bovine and Ovine Enamel.

AIM: This study aimed to test the null hypothesis that there are no significant differences in surface characteristics of eroded and abraded human, ovine and bovine enamel. DESIGN: Twenty enamel slabs were prepared from bovine, human and ovine incisor crowns, and randomly assigned to one of 4 treatments: 30 second/4 minute immersion at 1%/6% w/v citric acid. Post-erosion, an oscillatory brush was used for 20 seconds. Roughness parameters, height change and scanning electron microscopy were measured at each stage. RESULTS: Whilst the eroded surface became generally less rough after the abrasive challenge, there were significant tissue differences. Abraded microhardness was significantly increased compared to eroded values (P⟨0.001), Surface loss was also significantly different between tissue types (P⟨0.001). Bovine enamel showed similar trends to human enamel but was consistently harder and more resistant to surface change. Ovine enamel displayed little correlation with human enamel.Scanning electron microscopy images showed differences for each tissue that were consistent with the quantitative data. CONCLUSIONS: The null hypothesis was rejected; neither bovine nor ovine enamel can be reliably used interchangeably with human enamel for erosion/abrasion studies.

Assessment of the potential for international dissemination of Ebola virus via commercial air travel during the 2014 west African outbreak.

BACKGROUND: The WHO declared the 2014 west African Ebola epidemic a public health emergency of international concern in view of its potential for further international spread. Decision makers worldwide are in need of empirical data to inform and implement emergency response measures. Our aim was to assess the potential for Ebola virus to spread across international borders via commercial air travel and assess the relative efficiency of exit versus entry screening of travellers at commercial airports. METHODS: We analysed International Air Transport Association data for worldwide flight schedules between Sept 1, 2014, and Dec 31, 2014, and historic traveller flight itinerary data from 2013 to describe expected global population movements via commercial air travel out of Guinea, Liberia, and Sierra Leone. Coupled with Ebola virus surveillance data, we modelled the expected number of internationally exported Ebola virus infections, the potential effect of air travel restrictions, and the efficiency of airport-based traveller screening at international ports of entry and exit. We deemed individuals initiating travel from any domestic or international airport within these three countries to have possible exposure to Ebola virus. We deemed all other travellers to have no significant risk of exposure to Ebola virus. FINDINGS: Based on epidemic conditions and international flight restrictions to and from Guinea, Liberia, and Sierra Leone as of Sept 1, 2014 (reductions in passenger seats by 51% for Liberia, 66% for Guinea, and 85% for Sierra Leone), our model projects 2.8 travellers infected with Ebola virus departing the above three countries via commercial flights, on average, every month. 91,547 (64%) of all air travellers departing Guinea, Liberia, and Sierra Leone had expected destinations in low-income and lower-middle-income countries. Screening international travellers departing three airports would enable health assessments of all travellers at highest risk of exposure to Ebola virus infection. INTERPRETATION: Decision makers must carefully balance the potential harms from travel restrictions imposed on countries that have Ebola virus activity against any potential reductions in risk from Ebola virus importations. Exit screening of travellers at airports in Guinea, Liberia, and Sierra Leone would be the most efficient frontier at which to assess the health status of travellers at risk of Ebola virus exposure, however, this intervention might require international support to implement effectively. FUNDING: Canadian Institutes of Health Research.

Acute Respiratory Infections in Travelers Returning from MERS-CoV-Affected Areas.

We examined which respiratory pathogens were identified during screening for Middle East respiratory syndrome coronavirus in 177 symptomatic travelers returning to Ontario, Canada, from regions affected by the virus. Influenza A and B viruses (23.1%) and rhinovirus (19.8%) were the most common pathogens identified among these travelers.

Bond Strength and Adhesion Mechanisms of Novel Bone Adhesives.

Bone adhesives offer distinct advantages over the use of screws to attached internal fixation plates (IFPs). As the chemical composition of bone is similar to dentine, it is possible that the types of monomers used to make dentine adhesives could be utilised to affix IFPs to bone. The ability to attach a bio-resorbable IFP to porcine bone was assessed for the monomer 10-methacryloyloxydecyl dihydrogen phosphate (MDP), used either as a homopolymer or a copolymer with urethane dimethacrylate (MDP + U). Additionally, the addition of a priming step (MDP + U + P) was evaluated. The chemical interactions of the monomers with bone were assessed using XRD and imaged using TEM, revealing the formation of nano-layered structures with the MDP primer, something we believe has not been reported on bone. In a 6-week artificial aging study both MDP + U and MDP + U + P demonstrated adequate shear bond strength to affix bio-resorbable IFPs. The cytotoxicity profiles of the adhesive formulations were determined using indirect and direct contact with MC3T3 cells, with indirect conditions suggesting the MDP + U + P is as cytocompatible as the resorbable IFP. The findings of this study suggest our newly developed adhesive has the potential to be used as a bone adhesive to affix bioresorbable IFPs.

Developments in resin-based composites.

With the phasing down of dental amalgam use in response to the Minamata Convention, it is likely that resin-based composite restoratives will be the dental material of choice for the direct restoration of compromised dentition in the UK, at least for the foreseeable future. The current materials have a finite lifespan, with failures predominately due to either secondary caries or fracture. Consequently, there is considerable in vitro research reported each year with the intention of producing improved materials. This review describes the recent research in materials designed to have low polymerisation shrinkage and increased mechanical properties. Also described is research into materials that are either antimicrobial or are designed to release ions into the surrounding oral environment, with the aim of stimulating remineralisation of the surrounding dental tissues. It is hoped that by describing this recent research, clinicians will be able to gain some understanding of the current research that will potentially lead to new products that they can use to improve patient treatment in the future.

The effect of magnetic resonance imaging on mercury release from dental amalgam at 3T and 7T.

OBJECTIVES: To measure mercury release from standardised hydroxyapatite/amalgam constructs during MRI scanning and investigate the impact of static field strength and radiofrequency (RF) power on mercury release. METHODS: Amalgam was placed into 140 hydroxyapatite disks and matured for 14-days in artificial saliva. The solution was replaced, and samples split into five groups of 28 immediately prior to MRI. One group had no exposure, and the remainder were exposed to either a 3T or 7T MRI scanner, each at high and low RF power. Mercury concentration was measured by inductively coupled plasma mass spectrometry. Groups were compared using one-way ANOVA, and two-way ANOVA for main effects/ interaction of field strength/ RF power. RESULTS: Mercury concentration was increased in the 7T groups (high/ low: 15.43/ 11.33 ng mL-1) and 3T high group (3.59) compared to control (2.44). MRI field strength significantly increased mercury release (p < .001) as did RF power (p = .030). At 3T, mercury release was 20.3 times lower than during maturation of dental amalgam, and for the average person an estimated 1.50 ng kg-1 of mercury might be released during one 3T investigation; this is substantially lower than the tolerable weekly intake of 4,000 ng kg-1. CONCLUSION: Mercury release from amalgam shows a measurable increase following MRI, and the magnitude changes with magnetic field strength and RF power. The amount of mercury released is small compared to release during amalgam maturation. Amalgam mercury release during MRI is unlikely to be clinically meaningful and highly likely to remain below safe levels.

The effect on cast post dimensions of casting investment and airborne particle abrasion.

Cast posts can sometimes prove difficult to seat fully during fitting. This study compared two different liquid/water dilutions for phosphate bonded investment and the effect of controlled airborne particle abrasion on resulting post diameter. After measuring polymeric post patterns (n = 18), 3 groups were invested using concentrated solution and 3 groups using dilute solution. After casting they were weighed and remeasured then exposed to airborne particle abrasion. Both solutions produced oversized cast posts. Mean diameter reduction during airborne particle abrasion was 8 microm/10s taking an average of 41s to reach precast size. Where a post pattern fits tightly, airborne particle abrasion for 70s should reduce the casting sufficiently to accommodate the cement lute.

Baseline Specimens of Erosion and Abrasion Studies.

The difficulty in obtaining human teeth that are caries-free that have similar environmental exposure, e.g., diet intake and water fluoridation has lead researchers to opt for bovine teeth as a substitute for erosion studies. Bovine mandibular incisors are readily available at abattoirs and often originate from the same region and are likely to consume similar dietary intake. The bovine teeth for erosion or abrasion studies usually undergo specimen preparation to produce a "flat surface" baseline specimen. Among other terms used to define baseline specimens for erosion and abrasion studies include phrases like "optically flat" and "flat and smooth surface." However, these terms might have no quantitative value as it does not justify the actual surface characteristics of the prepared flattened surface. In dentistry, roughness average (Ra) is the most commonly used parameter when reporting the roughness of specimens Reporting Ra alone might not be sufficient as it does not provide information regarding the surface texture as there is no distinction between valleys and peaks, nor does it provide information about the core structure of a material unlike the bearing area curve. The incorporation of Ra and BAP values in baseline specimens has the potential in predicting the wear or lubricating potential of these specimens. Furthermore, standardization of baseline specimens by acknowledging its surface roughness values ensures comparability of erosion and abrasion studies as different specimen preparation technique might influence the outcome or results of research.

STEMI associated with SARS-CoV-2 infection and the use of ECMO as a potential therapeutic approach in addition to the PCI.

A 55-year-old male presented to the emergency department with the complaints of chest pain that started 4 h before presentation. Pain was located over the anterior chest, 5 out of 10 intensity, with radiation to the left arm. Chest x-ray on admission showed severe diffuse bilateral pulmonary infiltrates concerning for COVID-19 pneumonia. Electrocardiogram showed inferior and lateral ST-segment elevation compatible with acute inferolateral myocardial infarction. Successful percutaneous coronary intervention (PCI) of the proximal and mid-right coronary artery using the balloon angioplasty and drug-eluting stent was performed. Post-PCI stenosis was 0% with a thrombolysis in myocardial infarction (TIMI) flow of 3. Five-day course of azithromycin and hydroxychloroquine was completed with no improvement overall. Patient received two doses of 400 mg of tocilizumab intravenously on hospital days 5 (HD#5) and #6. The patient was proned, on FiO2 100%, PEEP 15 cm H2O, on epoprostenol sodium and paralytics and eventually received venovenous ECMO, which improved outcome.

Evaluation of two novel aluminum-free, zinc-based glass polyalkenoate cements as alternatives to PMMA bone cement for use in vertebroplasty and balloon kyphoplasty.

Vertebroplasty (VP) and balloon kyphoplasty (BKP) are now widely used for treating patients in whom the pain due to vertebral compression fractures is severe and has proved to be refractory to conservative treatment. These procedures involve percutaneous delivery of a bolus of an injectable bone cement either directly to the fractured vertebral body, VB (VP) or to a void created in it by an inflatable bone tamp (BKP). Thus, the cement is a vital component of both procedures. In the vast majority of VPs and BKPs, a poly(methyl methacrylate) (PMMA) bone cement is used. This material has many shortcomings, notably lack of bioactivity and very limited resorbability. Thus, there is room for alternative cements. We report here on two variants of a novel, bioactive, Al-free, Zn-based glass polyalkenoate cement (Zn-GPC), and how their properties compare to those of an injectable PMMA bone cement (SIMPL) that is widely used in VP and BKP. The properties determined were injectability, radiopacity, uniaxial compressive strength, and biaxial flexural modulus. In addition, we compared the compression fatigue lives of a validated synthetic osteoporotic VB model (a polyurethane foam cube with an 8 mm-diameter through-thickness cylindrical hole), at 0-2300 N and 3 Hz, when the hole was filled with each of the three cements. A critical review of the results suggests that the performance of each of the Zn-GPCs is comparable to that of SIMPL; thus, the former cements merit further study with a view to being alternatives to an injectable PMMA cement for use in VP and BKP.

A review on dental whitening.

OBJECTIVES: To provide a narrative review on vital dental whitening chemistry, toxicity and safety, vital dental whitening techniques, whitening systems, potential side effects of whitening and cyclic whitening using products with a range of concentrations and pH values. In addition, new developments and recommendations in the field of vital dental whitening will be presented to help clinicians understand the whitening process, its advantages, limitations, and the impact of whitening concentration and pH on enamel providing guidance in tailoring whitening treatments. DATA: Data were gathered using the following keywords: dental whitening, roughness, hardness, sensitivity, hydrogen peroxide, whitening pH, whitening concentration, whitening chemistry, colour, and toxicity. SOURCES: An electronic search was performed using PubMed and Scopus databases. Bibliographic material from papers reviewed was then used to find other relevant publications. CONCLUSIONS: The effectiveness of vital dental whitening depends on many factors, such as the concentration/pH of the whitening agent, application duration, chemical additives, and re-mineralising agents used. Developing new whitening products and technologies such as nano-additives and alternative carrier systems is showing promising results, and might prove efficient in maximising whitening benefits by accelerating the whitening reaction and/or minimising expected reversible/irreversible enamel structural damage.

Development and characterisation of dental composites containing anisotropic fluorapatite bundles and rods.

OBJECTIVES: To develop dental composites incorporating fluorapatite (FA) crystals as a secondary filler and to characterise degree of conversion, key mechanical properties and fluoride release. METHODS: FA rod-like crystals and bundles were hydrothermally synthesised and characterised by scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS), X-ray diffraction (XRD) and 19F MAS-NMR. Composites were formulated containing BisGMA/TEGDMA/BisEMA and barium-aluminium-silicate glass (0FA). FA crystals were incorporated at 10 (10FA), 20 (20FA), 30 (30FA) and 40wt% (40FA) maintaining a filler content of 80wt% (63-67vol%). Degree of conversion (DC), flexural strength (FS), flexural modulus (FM), fracture toughness (K1C), Vickers hardness (HV) and 2-body wear were measured. Fluoride release was measured in neutral and acidic buffers. RESULTS: XRD and 19F MAS-NMR confirmed that only FA was formed, whilst SEM revealed the presence of single rods and bundles of nano-rods. DC ranged between 56-60% (p>0.05). FA composites showed lower FM and lower FS (p<0.05), but comparable wear resistance and HV (p>0.05) to 0FA. 30FA and 40FA showed similar K1C to 0FA (p>0.05), with SEM showing evidence of toughening mechanisms, whereas 10FA and 20FA showed lower K1C (p<0.05). FA containing composites released fluoride that was proportional to the amount of FA incorporated (p<0.05) but only under acidic conditions. SIGNIFICANCE: The addition of FA to the experimental composites reduced strength and stiffness but not the DC, hardness or wear rate. 30FA and 40FA had a higher K1C compared to other FA groups. Fluoride release occurred under an accelerated acidic regime, suggesting potential as a bioactive 'smart' composite.

An in vitro model to assess effects of a desensitising agent on bacterial biofilm formation.

Desensitising agents are added to dentifrices to occlude exposed dentine tubules and reduce pain associated with dentine hypersensitivity. In occluding the tubules these agents may alter the surface layer of the dentine and consequently affect bacterial biofilm formation. This research sought to examine the effects of desensitising agents on dentinal biofilms using an in vitro model. A constant depth film fermenter (CDFF) was selected to mimic the oral environment and human dentine with exposed tubules was analysed. Calcium sodium phosphosilicate (CSPS) was selected as a model desensitising agent. Dentine discs were treated with pumice or CSPS-containing dentifrices with or without fluoride, or left untreated (control). Dual-species biofilms of Streptococcus mutans and Streptococcus sobrinus were grown in artificial saliva and analysed by viable counts, polymerase chain reaction (PCR) and scanning electron microscopy (SEM). SEM images confirmed the presence of occluded tubules after CSPS application and demonstrated the formation of biofilms containing extracellular matrix material. Analysis of PCR and viable count data using a one-way ANOVA showed no significant differences for bacterial composition for any of the four treatments. There were, however, trends towards increased numbers of bacteria for the pumice and CSPS treated samples which was reversed by the addition of fluoride to CSPS. In conclusion, CSPS was not found to have a significant effect on biofilms and an in vitro model for testing desensitising agents has been developed, however, further work is required to improve the reproducibility of the biofilms formed and to explore the trends seen.

Short phosphate glass fiber - PLLA composite to promote bone mineralization.

The clinical application of composites seeks to exploit the mechanical and chemical properties of materials which make up the composite, and in researching polymer composites for biomedical applications the aim is usually to enhance the bioactivity of the polymer, while maintaining the mechanical properties. To that end, in this study medical grade Poly(L-lactic) acid (PLLA) has been reinforced with short phosphate-based glass fibers (PGF). The materials were initially mixed by melting PLLA granules with the short fibers, before being extruded to form a homogenous filament, which was pelletized and used as feedstock for compression moulding. As made the composite materials had a bending strength of 51 MPa ±â€¯5, and over the course of eight weeks in PBS the average strength of the composite material was in the range 20-50 MPa. Human mesenchymal stromal cells were cultured on the surfaces of scaffolds, and the metabolic activity, alkaline phosphatase production and mineralization monitored over a three week period. The short fiber filler made no significant difference to cell proliferation or differentiation, but had a clear and immediate osteoinductive effect, promoting mineralization by cells at the material surface. It is concluded that the PLLA/PGF composite material offers a material with both the mechanical and biological properties for potential application to bone implants and fixation, particularly where an osteoinductive effect would be valuable.

Surface detail reproduction of elastomeric impression materials related to rheological properties.

OBJECTIVES: The purpose of this work was to discern, for elastomeric impression materials, the important rheological properties and importance of hydrophilicity for detail reproduction. METHODS: Viscosity, modulus and tan delta were measured using a controlled-stress rheometer in cone/plate configuration. The flow of the materials, immediately after mixing and at the manufacturer's stated working time, was measured using a shark fin test and the interaction with moist surfaces was determined by taking impressions from two different sized grooves in moist gypsum casts. RESULTS: Tan delta was found to be the parameter most indicative of the accuracy of the impression and the flow of the material. Impregum samples, a polyether material, exhibited the highest initial tan delta (7.4), the largest shark fins at both time periods and the most accurate impressions from both grooves. Aquasil, a polyvinylsiloxane material, had similar initial tan delta values (6.9) and impressions taken on the deep groove with this material closely matched the groove. The other two polyvinylsiloxane materials (Affinis and Flexitime) had significantly lower initial tan delta values (3.1 and 2.9, respectively), exhibited much smaller shark fins and a worse ability to accurately reproduce the deep groove. SIGNIFICANCE: For large features, it is clear that the higher the initial tan delta of the impression material the better the ability to replicate larger features. However, with smaller features the relative hydrophobicity of the material becomes an important factor, with more hydrophilic materials better able to reproduce fine detail.

Rare but Not Infrequent: Infective Endocarditis Caused by Abiotrophia defectiva.

Endocarditis (IE) is defined by an infection of a native or prosthetic heart valve, the mural endocardium, or an indwelling cardiac device. Although viridan-group streptococci (VGS) and Staphylococci species have collectively been considered as the most common cause of endocarditis, uncommon pathogens may also lead to the disease with significant morbidity and mortality. Abiotrophia defectiva, a nutritionally variant streptococci (NVS), is a virulent bacterium that preferentially affects endovascular structure and is implicated in many culture-negative endocarditis with dreadful complications such as heart failure, septic embolization, and valve destruction. Here, we report a case of a 60-year-old male patient, with a past medical history significant for hypertrophic obstructive cardiomyopathy, who was incidentally found to have mitral valve vegetative mass with an uncommon agent, A. defectiva. The patient was successfully treated with antimicrobial therapy. The objective of this article is to describe the possibility of uncommon cause of common diseases and raises awareness of infective endocarditis caused by A. defectiva among clinicians and microbiologists. Early and proper identification of this pathogen is important to achieve a better outcome.