Spectroscopic and theoretical investigation of the [Fe2(bdt)(CO)6] hydrogenase mimic and some catalyst intermediates.

In [Fe-Fe] hydrogenase mimic systems the ene-1,2-dithiolene ligands play an important role in the stabilisation of the redox-active metal center. This is demonstrated by the benzenedithiolene (bdt) analogue, featuring six terminal carbonyl ligands connected to a di-iron metal center, i.e. [Fe2(bdt)(CO)6]. Here we present a combined experimental and theoretical study that elucidates key intermediates [Fe2(bdt)(CO)6]1- and [Fe2(bdt)(µ-CO)(CO)5]2- in the electrocatalytic production of dihydrogen. A DFT study shows that [Fe2(bdt)(CO)6]1- is the kinetic product after the first one electron reduction, while the previously proposed bridging intermediate species [Fe2(bdt)(µ-CO)(CO)5]1- is kinetically inaccessible. The doubly reduced species [Fe2(bdt)(µ-CO)(CO)5]2- was for the first time structurally characterized using EXAFS. XANES analysis confirms the existence of reduced iron zero species and confirms the distorted geometry that was suggested by the DFT calculations. Combining IR, UV-vis and XAS spectroscopic results with TD-DFT and FEFF calculations enabled us to assign the key-intermediate [Fe2(bdt)(CO)6]2-. This study emphasizes the strengths of combining computational chemistry with advanced spectroscopy techniques.

Carbon assimilation and transfer through kelp forests in the NE Atlantic is diminished under a warmer ocean climate.

Global climate change is affecting carbon cycling by driving changes in primary productivity and rates of carbon fixation, release and storage within Earth's vegetated systems. There is, however, limited understanding of how carbon flow between donor and recipient habitats will respond to climatic changes. Macroalgal-dominated habitats, such as kelp forests, are gaining recognition as important carbon donors within coastal carbon cycles, yet rates of carbon assimilation and transfer through these habitats are poorly resolved. Here, we investigated the likely impacts of ocean warming on coastal carbon cycling by quantifying rates of carbon assimilation and transfer in Laminaria hyperborea kelp forests-one of the most extensive coastal vegetated habitat types in the NE Atlantic-along a latitudinal temperature gradient. Kelp forests within warm climatic regimes assimilated, on average, more than three times less carbon and donated less than half the amount of particulate carbon compared to those from cold regimes. These patterns were not related to variability in other environmental parameters. Across their wider geographical distribution, plants exhibited reduced sizes toward their warm-water equatorward range edge, further suggesting that carbon flow is reduced under warmer climates. Overall, we estimated that Laminaria hyperborea forests stored ~11.49 Tg C in living biomass and released particulate carbon at a rate of ~5.71 Tg C year-1 . This estimated flow of carbon was markedly higher than reported values for most other marine and terrestrial vegetated habitat types in Europe. Together, our observations suggest that continued warming will diminish the amount of carbon that is assimilated and transported through temperate kelp forests in NE Atlantic, with potential consequences for the coastal carbon cycle. Our findings underline the need to consider climate-driven changes in the capacity of ecosystems to fix and donate carbon when assessing the impacts of climate change on carbon cycling.

Effect of pain neurophysiology education on physiotherapy students' understanding of chronic pain, clinical recommendations and attitudes towards people with chronic pain: a randomised controlled trial.

OBJECTIVE: To investigate the effect of pain neurophysiology education (PNE) on student physiotherapists': (1) knowledge of chronic pain; (2) attitudes towards patients with chronic pain; and (3) clinical recommendations for patients with chronic pain. DESIGN: Multicentre single-blind randomised controlled trial. SETTING: One UK and one Irish university. PARTICIPANTS: Seventy-two student physiotherapists. INTERVENTION: Participants received either PNE (intervention) or a control education. Both were delivered in a 70-minute group lecture. MAIN OUTCOME MEASURES: (1) The Revised Pain Neurophysiology Quiz to assess knowledge; (2) the Health Care Pain Attitudes and Impairment Relationship Scale (HC-PAIRS) to assess attitudes; and (3) a case vignette to assess the appropriateness of clinical recommendations. RESULTS: Post education, the PNE group had a greater increase in pain neurophysiology knowledge [mean difference 4.0 (95% confidence interval 3.2 to 4.7), P<0.01] and more improved attitudes [-17.5 (95% confidence interval -22.1 to -12.9), P<0.01] compared with the control group. Post education, students in the PNE group were more likely to make appropriate recommendations regarding work (94% vs 56%), exercise (92% vs 56%), activity (94% vs 67%) and bed rest (69% vs 33%) compared with those in the control group (P<0.05). CONCLUSION: The improvements in knowledge, attitudes and recommendations for pain management show that PNE is a potentially valuable part of the education of physiotherapy students, and could be used on a more widespread basis. There is a need to investigate whether these findings can be replicated in other healthcare professions, and how well these reported changes lead to changes in actual clinical behaviour and the clinical outcomes of patients.

Assessing the shock state of the lunar highlands: Implications for the petrogenesis and chronology of crustal anorthosites.

Our understanding of the formation and evolution of the primary lunar crust is based on geochemical systematics from the lunar ferroan anorthosite (FAN) suite. Recently, much effort has been made to understand this suite's petrologic history to constrain the timing of crystallisation and to interpret FAN chemical diversity. We investigate the shock histories of lunar anorthosites by combining Optical Microscope (OM) 'cold' cathodoluminescence (CL)-imaging and Fourier Transform Infrared (FTIR) spectroscopy analyses. In the first combined study of its kind, this study demonstrates that over ~4.5 Ga of impact processing, plagioclase is on average weakly shocked (<15 GPa) and examples of high shock states (>30 GPa; maskelynite) are uncommon. To investigate how plagioclase trace-element systematics are affected by moderate to weak shock (~5 to 30 GPa) we couple REE+Y abundances with FTIR analyses for FAN clasts from lunar meteorite Northwest Africa (NWA) 2995. We observe weak correlations between plagioclase shock state and some REE+Y systematics (e.g., La/Y and Sm/Nd ratios). This observation could prove significant to our understanding of how crystallisation ages are evaluated (e.g., plagioclase-whole rock Sm-Nd isochrons) and for what trace-elements can be used to differentiate between lunar lithologies and assess magma source compositional differences.

SCUBA divers as oceanographic samplers: The potential of dive computers to augment aquatic temperature monitoring.

Monitoring temperature of aquatic waters is of great importance, with modelled, satellite and in-situ data providing invaluable insights into long-term environmental change. However, there is often a lack of depth-resolved temperature measurements. Recreational dive computers routinely record temperature and depth, so could provide an alternate and highly novel source of oceanographic information to fill this data gap. In this study, a citizen science approach was used to obtain over 7,000 scuba diver temperature profiles. The accuracy, offset and lag of temperature records was assessed by comparing dive computers with scientific conductivity-temperature-depth instruments and existing surface temperature data. Our results show that, with processing, dive computers can provide a useful and novel tool with which to augment existing monitoring systems all over the globe, but especially in under-sampled or highly changeable coastal environments.

User settings on dive computers: reliability in aiding conservative diving.

INTRODUCTION: Divers can make adjustments to diving computers when they may need or want to dive more conservatively (e.g., diving with a persistent (patent) foramen ovale). Information describing the effects of these alterations or how they compare to other methods, such as using enriched air nitrox (EANx) with air dive planning tools, is lacking. METHODS: Seven models of dive computer from four manufacturers (Mares, Suunto, Oceanic and UWATEC) were subjected to single square-wave compression profiles (maximum depth: 20 or 40 metres' sea water, msw), single multi-level profiles (maximum depth: 30 msw; stops at 15 and 6 msw), and multi-dive series (two dives to 30 msw followed by one to 20 msw). Adjustable settings were employed for each dive profile; some modified profiles were compared against stand-alone use of EANx. RESULTS: Dives were shorter or indicated longer decompression obligations when conservative settings were applied. However, some computers in default settings produced more conservative dives than others that had been modified. Some computer-generated penalties were greater than when using EANx alone, particularly at partial pressures of oxygen (PO2) below 1.40 bar. Some computers 'locked out' during the multi-dive series; others would continue to support decompression with, in some cases, automatically-reduced levels of conservatism. Changing reduced gradient bubble model values on Suunto computers produced few differences. DISCUSSION: The range of possible adjustments and the non-standard computer response to them complicates the ability to provide accurate guidance to divers wanting to dive more conservatively. The use of EANx alone may not always generate satisfactory levels of conservatism.

The intra- and inter-observer reliability of a novel protocol for two-point discrimination in individuals with chronic low back pain.

Two-point discrimination is measured as an indicator of cortical reorganisation in musculoskeletal medicine. Nevertheless, data are lacking for the reliability of this measure in patients with non-specific chronic low back pain (NSCLBP). We aimed to quantify the intra- and inter-observer reliability of a novel protocol for measuring two-point discrimination in these patients. 35 participants (12 males, 23 females, mean age 52, SD 15 years) with NSCLBP were recruited. Three clinicians made 14 consecutive measurements of two-point discrimination with callipers. One of these clinicians repeated the assessment protocol within 7 d. During each measurement, the calliper width was widened in 5 mm increments until participants could consistently identify two points. Intra- and inter-observer agreement was quantified using mean difference, within-subject SD and limits of agreement (LOA). After using the first measurement for familiarisation, the mean of measurements 2-5 within an assessment resulted in the optimum compromise between clinic time constraints and acceptable intra-observer reliability; the within-subjects SD being 7.5 mm (LOA: 20.8 mm). Inter-observer reliability was generally poorer; requiring the mean of measurements 2-9 within an assessment for a similar within-subjects SD of 8.6 mm (LOA: 23.7 mm). It was estimated that these within-subjects SDs were small enough for a clinically-important change to be detected with a feasible sample size in future studies. The intra-observer reliability of our assessment protocol is acceptable for detecting a clinically relevant difference in two-point discrimination for future research purposes. Nevertheless, individual patient measurement variability is relatively high, especially between different clinicians.

Arctic marine phytobenthos of northern Baffin Island.

Global climate change is expected to alter the polar bioregions faster than any other marine environment. This study assesses the biodiversity of seaweeds and associated eukaryotic pathogens of an established study site in northern Baffin Island (72° N), providing a baseline inventory for future work assessing impacts of the currently ongoing changes in the Arctic marine environment. A total of 33 Phaeophyceae, 24 Rhodophyceae, 2 Chlorophyceae, 12 Ulvophyceae, 1 Trebouxiophyceae, and 1 Dinophyceae are reported, based on collections of an expedition to the area in 2009, complemented by unpublished records of Robert T. Wilce and the first-ever photographic documentation of the phytobenthos of the American Arctic. Molecular barcoding of isolates raised from incubated substratum samples revealed the presence of 20 species of brown seaweeds, including gametophytes of kelp and of a previously unsequenced Desmarestia closely related to D. viridis, two species of Pylaiella, the kelp endophyte Laminariocolax aecidioides and 11 previously unsequenced species of the Ectocarpales, highlighting the necessity to include molecular techniques for fully unraveling cryptic algal diversity. This study also includes the first records of Eurychasma dicksonii, a eukaryotic pathogen affecting seaweeds, from the American Arctic. Overall, this study provides both the most accurate inventory of seaweed diversity of the northern Baffin Island region to date and can be used as an important basis to understand diversity changes with climate change.

Bacillus subtilis vegetative isolate surviving chlorine dioxide exposure: an elusive mechanism of resistance.

AIMS: Oxidizing agents such as chlorine dioxide are widely used microbicides, including for disinfection of medical equipment. We isolated a Bacillus subtilis isolate from a washer-disinfector whose vegetative form demonstrated unique resistance to chlorine dioxide (0·03%) and hydrogen peroxide (7·5%). The aim of this study was to understand the mechanisms of resistance expressed by this isolate. METHODS AND RESULTS: A range of resistance mechanisms were investigated in the B. subtilis isolate and a reference B. subtilis strain (ATCC 6051) to include bacterial cell aggregation, the presence of profuse exopolysaccharide (EPS), and the expression of detoxification enzymes. The basis of resistance of the isolate to high concentrations of oxidizing agents was not linked to the presence of endospores. Although, the presence of EPS, aggregation and expression of detoxification enzymes may play a role in bacterial survival to low concentrations of chlorine dioxide, it is unlikely that the mechanisms helped tested to survive the bactericidal effect of higher oxidizer concentrations. CONCLUSIONS: Overall, the mechanisms conferring resistance to chlorine dioxide and hydrogen peroxide remains elusive. Based on recent advances in the mode of action of oxidizing agents and notably hydrogen peroxide, we postulate that additional efficient intracellular mechanisms may be involved to explain significant resistance to in-use concentrations of commonly used high-level disinfectants. SIGNIFICANCE AND IMPACT OF STUDY: The isolation of a highly resistant vegetative Gram-positive bacterium to a highly reactive oxidizing agent is worrying. Understanding the mechanisms conferring such resistance is essential to effectively control such bacterial isolates. Here, we postulate that there are still mechanisms of bacterial resistance that have not been fully characterized.

The silent witness: using dive computer records in diving fatality investigations.

Downloaded data from diving computers can offer invaluable insights into diving incidents resulting in fatalities. Such data form an essential part of subsequent investigations or in legal actions related to the diving incident. It is often tempting to accept the information being displayed from a computer download without question. However, there is a large variability between the makes and models of dive computer in how the data are recorded, stored and re-displayed and caution must be employed in the interpretation of the evidence. In reporting on downloaded data, investigators should be fully aware of the limitations in the data retrieved. They should also know exactly how to interpret parameters such as: the accuracy of the dive profile; the effects of different mode settings; the precision of displayed water temperatures; the potential for misrepresenting breathing rates where there are data from integrated monitoring systems, and be able to challenge some forms of displayed information either through re-modelling based on the pressure/time profiles or by testing the computers in standardised conditions.

Effect of textured insoles on balance and gait in people with multiple sclerosis: an exploratory trial.

OBJECTIVES: To investigate the immediate effects of textured insoles on balance and gait in people with multiple sclerosis (MS), and to explore any effects after 2 weeks of wear. STUDY DESIGN: Within-session repeated-measures design with an exploratory follow-up period. SETTING: Hospital gait laboratory. PARTICIPANTS: Forty-six individuals with MS (34 females, 12 males), with a mean (SD) age of 49 (7) years, who could walk 100m unassisted or using one stick/crutch. INTERVENTION: Participants were tested wearing three types of insoles in a random order: control (smooth), Texture 1 (Algeos) or Texture 2 (Crocs™). Participants were allocated at random to wear one type of textured insoles for 2 weeks, after which they were retested. MAIN OUTCOME MEASURES: Standing balance (centre of pressure excursions and velocity) was measured with eyes open and eyes closed on a Kistler force platform. Spatio-temporal parameters of gait were measured using a GAITRite system. RESULTS: The textured insoles had no significant immediate effects on balance or gait, apart from an increase in anteroposterior sway range with eyes open for Texture 2 insoles [mean difference 4.5 (95% confidence interval 0.6 to 8.4)mm]. After 2 weeks, balance was not significantly different, but both types of textured insoles showed significant effects on spatio-temporal parameters of gait, with mean stride length increases of 3.5cm (Texture 1) and 5.3cm (Texture 2) when wearing the insoles. CONCLUSIONS: After 2 weeks of wear, there were improvements in spatio-temporal parameters of gait. However, it is unclear whether this was a placebo effect or a learning effect.

An investigation of association between chronic musculoskeletal pain and cardiovascular disease in the Health Survey for England (2008).

BACKGROUND: Chronic musculoskeletal pain (CMP) may be associated with cardiovascular disease (CVD). This study aimed to investigate the association between CMP and CVD, and the contribution of physical activity and sedentary behaviour to any association. METHODS: We performed a secondary analysis of 3332 middle-aged (45-64 years) and 2022 older (65+ years) adults included in the Health Survey for England (2008). The survey contained self-reported physical activity/sedentary behaviour data. Objectively measured physical activity/sedentary behaviour using accelerometry (Actigraph™) was also available for a subset of the middle-aged (n = 715) and older (n = 492) participants. Logistic regression examined the association between CMP and CVD adjusted for self-reported and objectively measured physical activity, sedentary behaviour and a range of other CVD risk factors. RESULTS: There was a higher prevalence of CVD in those with CMP for both the middle-aged (22.5% vs. 13.5%) and the older (46.8% vs. 28.2%) adults (p < 0.001). After adjusting for CVD risk factors, older adults with CMP were significantly more likely to have CVD {odds ratio [95% confidence interval (CI)] 1.828 (1.452, 2.300); p < 0.001}. A similar non-significant trend was shown for the middle-aged adults [odds ratio (95% CI) 1.271 (0.975, 1.656); p = 0.076]. Neither self-reported nor objectively measured physical activity (or sedentary behaviour) had any meaningful effect on the association between CMP and CVD. CONCLUSIONS: CMP is associated with an increased risk of CVD and the association is stronger in older adults. Neither physical activity nor sedentary behaviour contributed to this relationship. Longitudinal studies are warranted to better understand the relationship between CVD and CMP.

Decompression management by 43 models of dive computer: single square-wave exposures to between 15 and 50 metres' depth.

INTRODUCTION: Dive computers are used in some occupational diving sectors to manage decompression but there is little independent assessment of their performance. A significant proportion of occupational diving operations employ single square-wave pressure exposures in support of their work. METHODS: Single examples of 43 models of dive computer were compressed to five simulated depths between 15 and 50 metres' sea water (msw) and maintained at those depths until they had registered over 30 minutes of decompression. At each depth, and for each model, downloaded data were used to collate the times at which the unit was still registering "no decompression" and the times at which various levels of decompression were indicated or exceeded. Each depth profile was replicated three times for most models. RESULTS: Decompression isopleths for no-stop dives indicated that computers tended to be more conservative than standard decompression tables at depths shallower than 30 msw but less conservative between 30-50 msw. For dives requiring decompression, computers were predominantly more conservative than tables across the whole depth range tested. There was considerable variation between models in the times permitted at all of the depth/decompression combinations. CONCLUSIONS: The present study would support the use of some dive computers for controlling single, square-wave diving by some occupational sectors. The choice of which makes and models to use would have to consider their specific dive management characteristics which may additionally be affected by the intended operational depth and whether staged decompression was permitted.

Managing scientific diving operations in a remote location: the Canadian high Arctic.

Global climate change is expected to alter the Arctic bioregion markedly in coming decades. As a result, monitoring of the expected and actual changes has assumed high scientific significance. Many marine science objectives are best supported with the use of scientific diving techniques. Some important keystone environments are located in extremely remote locations where land-based expeditions offer high flexibility and cost-effectiveness over ship-based operations. However, the extreme remoteness of some of these locations, coupled with complex and unreliable land, sea and air communications, means that there is rarely quick access (< 48 h) to any specialized diving medical intervention or recompression. In 2009, a land based expedition to the north end of Baffin Island was undertaken with the specific aim of establishing an inventory of the diversity of seaweeds and their pathogens that was broadly representative of a high Arctic marine environment. This account highlights some of the logistical considerations taken on that expedition; specifically it outlines the non-recompression treatment pathway that would have been adopted in the event of a diver suffering decompression illness.

Transportation of divers with decompression illness on the west coast of Scotland.

INTRODUCTION: There is a time line for divers who develop decompression illnesses (DCI) from the completion of their dive to the initiation of recompression. The time to treatment is influenced by many factors; two being the time before acknowledgement that the diver has a pressure-related illness and the time taken for transfer from that point to commencment of recompression. METHOD: Time to onset of symptoms, and time from onset of symptoms to treatment were analysed for 233 divers, 202 recreational and 31 professional, presenting within 24 h of onset of symptoms to the Dunstaffnage Hyperbaric Unit between 1990 and 2009, who were transported by air, sea or road. RESULTS: Divers with severe DCI had significantly shorter times for onset of symptoms (95% confidence intervals 0.9 to 2.3 h longer for mild/moderate compared to severe DCI) and were transferred for treatment approximately twice as fast as those with mild/moderate symptoms (inter-quartile ranges: recreational divers, 2.25-5.63 h for mild/moderate DCI versus 1.54-3.25 h for severe DCI; professional divers, 2.63-11.13 h for mild/moderate DCI versus 2.25-2.92 h for severe DCI). Although choice of transport was most likely influenced both by location and disease severity, transfer modality did not significantly affect time to treatment for divers with severe DCI. In addition, no differences in time to treatment were observed between professional and recreational divers irrespective of disease severity. CONCLUSIONS: The data suggest that transport was optimised to fit the particular circumstances of the patient and that divers treated for DCI in Scotland may benefit from there being a single, integrated, co-ordinated clinical service.

Outcome of late-onset Perthes' disease using four different treatment modalities.

PURPOSE: The outcome of Perthes' disease in children over 8 years tends to be poor. It is unclear whether any treatment modality alters the natural history. This study compares the results of four treatment modalities for this group of patients. METHODS: A retrospective review was performed of prospectively collected data for 44 children (48 hips) with Catterall grade 2, 3 or 4 Perthes' disease with onset age 8 years or older followed to maturity. Patients were divided into four groups (a no-treatment group and three interventional groups). The interventional groups were demographically similar but the untreated patients were older and had poorer indices for most modalities. RESULTS: Overall for all treatment modalities only 19% had a satisfactory Stulberg grade II outcome. Poorer outcomes (as assessed by center-edge angle and percentage femoral head coverage) were associated with increasing age, greater initial head deformity, and more head involvement. Initial head deformity did not remodel for any group and progressed despite plaster treatment or varus osteotomy but not after acetabular augmentation. Acetabular augmentation gave better outcomes for C/B ratio and center-edge angle. CONCLUSIONS: Whatever the treatment, the outcome is poorer with increasing age. No treatment guarantees a good result for significant head involvement or initial deformity but acetabular augmentation improves C/B ratio and center-edge angle and prevents progressive femoral head deformity compared with no treatment, varus osteotomy, and plaster treatment.

Resistance and cross-resistance to oxidising agents of bacterial isolates from endoscope washer disinfectors.

Bacteria isolated from washer disinfectors using chlorine dioxide as a high-level disinfectant were exposed to peracetic acid, chlorine dioxide and hydrogen peroxide to investigate their susceptibility and possible bacterial cross-resistance to these highly reactive oxidising biocides. A standard suspension test was used to establish a rate of kill of these biocides against two stable isolates (Bacillus subtilis and Micrococcus luteus). Suspension tests demonstrated that 'in use' concentrations were not always effective to provide the required disinfection efficacy within recommended exposure times and in some instances a 60min exposure was necessary to achieve a reduction in number by a factor of 10(5). It appears that vegetative Gram-positive isolates can become resistant to oxidising agents in vitro, and that cross-resistance to related compounds can occur. Since these bacteria are deemed to be susceptible to highly reactive biocides, there should be further study of the resistance mechanisms in these isolates to explain their survival.

Does systematic 2-field lymphadenectomy for esophageal malignancy offer a survival advantage? Results from 178 consecutive patients.

More extensive resection for esophageal cancer has been reported to improve survival in several series. We compared results from an unselected consecutive cohort of patients undergoing radical esophagectomy, including removal of all periesophageal tissue with a 2-field abdominal and mediastinal lymphadenectomy for esophageal and gastroesophageal malignancy. A prospective electronic database was reviewed for patients with esophageal malignancy undergoing an open esophagectomy between 1991 and 2004. Data were analyzed on an SPSS file (version 12.0, Chicago, IL, USA) using chi(2) or Fisher's exact test; odds ratio and 95% confidence interval; and the Kaplan-Meier method, log-rank test and Cox's proportional hazards regression for survival analysis. There were 178 patients with a median age of 65 years and a 70/30 male to female ratio. Median follow-up was 20.4 months. Pathology comprised adenocarcinoma in 64% of patients, squamous cell carcinoma 30%, and other malignancies 6%. Seventeen patients had neoadjuvant therapy. Hospital mortality was 3.3%. Complete resection was achieved in 87%. Local recurrence occurred at a median of 13 months in 6.7% of patients. Overall 5-year survival was 42%. For patients with invasive squamous cell carcinoma and adenocarcinoma the 5-year survival was 47% and 40.3%, respectively, and for patients without nodal involvement it was 71.5%, with one to four nodes involved, 23.5% and with >4 nodes, 5% (P < 0.001). Survival decreased with increasing direct tumor spread (P < 0.001) and pathological stage (P < 0.001). Esophageal resection with systematic 2-field lymphadenectomy can be performed with acceptable operative mortality and favorable survival.

In vitro fibroblast response to polyurethane organosilicate nanocomposites.

The term nanocomposite refers to organic:inorganic composites where one phase, typically the inorganic phase, has dimensions on the nanoscale. Several authors have noted the potential benefit of biomedical application of nanocomposite technology, and have suggested using quaternary ammonium compounds (QAC) as an organic modification to enhance dispersion of nanoparticles within polymer matrices. This study aimed to examine fibroblast responses in vitro to a range of nanocomposites using different organic modifiers. Composite materials were prepared from a polyether urethane (PEU) and various unmodified and organically modified montmorillonite (MMT) nanoparticles. QAC and amino undecanoic acid (AUA) modified-MMT were added to PEU at loadings ranging from approximately 1 to 15 wt %. Composites with organically modified QAC and AUA particles displayed partially exfoliated and intercalated silicate morphology, respectively. Nanocomposites showed increases in ultimate tensile properties for materials with lower QACMMT loadings. However QAC was shown to significantly inhibit cell growth following release from PEU-QACMMT under extraction conditions mimicking those of the physiological environment. Materials containing silicate modified using AUA were cytocompatible. The results of this study suggest that QAC may be unsuitable as organic modifiers for nanoparticles destined for biomedical use. Alternative modifiers based on AUA confer equivalent dispersion and are of low toxicity.