Your browser doesn't support javascript.
loading
Show: 20 | 50 | 100
Results 1 - 20 de 21
Filter
Add more filters










Publication year range
1.
Interv Neuroradiol ; : 15910199241254558, 2024 May 15.
Article in English | MEDLINE | ID: mdl-38751106
2.
Vet Med Sci ; 10(3): e1445, 2024 05.
Article in English | MEDLINE | ID: mdl-38652025

ABSTRACT

BACKGROUND: This study aimed to evaluate the antimicrobial effects of zahter extract, zahter essential oil, laurel extract, and laurel essential oil on Salmonella Typhimurium inoculated on chicken wings. METHODS: A total of 10 groups, including eight study groups and two control groups were formed, consisting of zahter extract and zahter essential oil and laurel extract and laurel essential oil in different proportions. In the study, laurel extract at 6.4% and 12.8% concentrations, laurel essential oil at 0.2% and 0.4% concentrations, zahter extract at 0.2% and 0.4% concentrations, and zahter essential oil at 0.2% and 0.4% concentrations were used. RESULTS: The broth microdilution method was used to evaluate the antimicrobial activity of the extract and essential oils on the S. Typhimurium. Minimum inhibitory concentrations of the extracts and essential oils used in the study against S. Typhimurium were determined. The highest inhibitory effect on S. Typhimurium was observed in the 0.4% laurel essential oil group. It was determined that the inhibitory effect increased as the concentration of laurel essential oil increased. In addition, the antimicrobial activity of zahter essential oil is less inhibitory than the laurel extract, laurel essential oil, and zahter extract. CONCLUSION: According to the results of this study, it has been revealed that extracts and essential oils obtained from zahter and laurel plants, which have been shown to be natural antimicrobial, can be used in foods as an alternative to chemical additives. To develop research results, the applicability of these extracts and essential oils in different foodstuffs should be examined using different ingredients and concentrations.


Subject(s)
Chickens , Oils, Volatile , Plant Extracts , Salmonella typhimurium , Wings, Animal , Animals , Salmonella typhimurium/drug effects , Oils, Volatile/pharmacology , Oils, Volatile/chemistry , Plant Extracts/pharmacology , Plant Extracts/chemistry , Wings, Animal/drug effects , Poultry Diseases/microbiology , Microbial Sensitivity Tests , Anti-Bacterial Agents/pharmacology , Laurus/chemistry , Plant Oils/pharmacology , Plant Oils/chemistry , Anti-Infective Agents/pharmacology
3.
Angiology ; 75(5): 472-479, 2024 May.
Article in English | MEDLINE | ID: mdl-37163448

ABSTRACT

The importance of Carotid Artery Perivascular Adipose Tissue Density (CAPATd), a parameter that can be readily evaluated on emergency computed tomographic angiography (CTA), in acute stroke has not been adequately clarified. We created exploratory logistic regression models to detect the interaction between the effect of CAPATd and intravenous (IV) tissue plasminogen activator (tPA) in 174 patients (mean age 71 ± 14 years, 94 women) with acute ischemic stroke treated with IV-tPA alone. The CAPATd-average mean (-60.6 ± 18.7 vs -89.8 ± 25.3 Hounsfield units (HU), P = .002) and CAPATd-maximum (14.8 ± 68.9 vs -20.5 ± 39.8 HU, P = .020) values were higher on the ipsilateral side of carotid artery stenosis >60%. CAPATd-maximum ipsilateral emerged as an independent predictor for both modified Rankin's Score 0-2 (52%) [exp(ß) = .984] and mRS 0-1 outcome (32%) [exp(ß) = .828] in addition to admission National Institutes of Health Stroke Scale, age and carotid plaque burden. CAPATd-maximum ipsilateral was acceptably accurate (Area under the Receiver operating characteristic Curve was .607, P = .0109 for mRS 0-2 and .613, P = .0102 for mRS 0-1). Ipsilateral CAPATd ≥ -25 HU predicted both mRS >3 and mRS >2 with usable sensitivity (59.8% and 66.07%) and specificity (63.6% and 59.68%). In conclusion, higher maximum CAPATd measured on emergency CTA indicates poorer functional prognosis in acute stroke patients treated with IV-tPA.


Subject(s)
Brain Ischemia , Ischemic Stroke , Stroke , Humans , Female , Middle Aged , Aged , Aged, 80 and over , Tissue Plasminogen Activator/therapeutic use , Fibrinolytic Agents/therapeutic use , Treatment Outcome , Stroke/diagnostic imaging , Stroke/drug therapy , Carotid Arteries , Retrospective Studies , Brain Ischemia/diagnostic imaging , Brain Ischemia/drug therapy
4.
J Oleo Sci ; 72(10): 901-910, 2023 Oct 03.
Article in English | MEDLINE | ID: mdl-37704448

ABSTRACT

The objective of the present study was to increase the frying stability of refined safflower oil (RSO) by blending it with refined olive pomace oil (ROPO) during deep fat frying. For this purpose; RSO, ROPO and their blends were utilized for frying of potato sticks at 180°C for 3 consecutive days. The frying stability of the oils was monitored by analyzing them for their free fatty acids, peroxide values, total polar contents, ultraviolet spectrophotometric indices at 232 and 270 nm, fatty acid profiles, p-anisidine values, α-tocopherol contents and photometric color indices. 3-monochloropropane-1,2-diol (3-MCPD) and glycidyl ester (GE) levels of oils before and after frying were measured as well. The results have shown that thermooxidative degradation products increased as the frying progressed for all oils, however the decomposition rate was found to slow down in blend oils by stabilizing with ROPO. Blending RSO with ROPO decreased linoleic and linolenic; but increased the oleic and palmitic acid percentages of the blends. C18:2/C16:0 ratio was found to decrease by frying for RSO and the blend oils, however ROPO was not affected significantly. 3-MCPD-E levels of the blends increased as the ratio of ROPO increased. Principal component analysis enabled a clear discrimination between oils with different composition throughout the frying process.

5.
J Stroke Cerebrovasc Dis ; 31(4): 106304, 2022 Apr.
Article in English | MEDLINE | ID: mdl-35065404

ABSTRACT

OBJECTIVES: Incidental acute ischemic lesions distinct from the primary neurological insult are identified on diffusion-weighted imaging (DWI) in a number of conditions where cerebral microvascular pathology plays a central role. Another major manifestation of cerebral small vessel disease (CSVD) is ischemic stroke named as recent small subcortical infarction (RSSI). In this study, we sought to identify the prevalence and predictors of incidental DWI lesions in patients with RSSI. MATERIALS AND METHODS: We retrospectively analyzed a consecutive series of acute ischemic stroke patients with DWI evidence of acute lesions solely localized to perforator artery territories. Images were evaluated for the presence of additional acute or subacute subcortical DWI lesions, apart from the symptomatic lesion. Clinical features including vascular risk factor burden, together with imaging markers of chronic CSVD, were compared among patients with and without incidental acute or subacute lesions. RESULTS: Among 396 patients with no alternate stroke etiology additional incidental subcortical DWI bright lesions were identified in 74 (19%) cases. These lesions were primarily localized in the corona radiata, or centrum semiovale. Patients with incidental DWI lesions were more likely to have a history of hypertension, a higher white matter hyperintensities burden in the periventricular and subcortical region, higher perivascular spaces burden in the basal ganglia, multiple cerebral microbleeds, and multiple chronic lacunes. Presence of multiple chronic lacunes (OR 5.98, 95% CI 3.18-11.24) and ≥2 vascular risk factors (OR 2.03, 95% CI 1.05-3.91) stood out as features significantly associated with incidental DWI lesions in multivariate analysis. CONCLUSIONS: Our study shows that acute or subacute ischemic lesions can be incidentally detected in approximately one-fifth of patients with RSSI. This observation suggests that the course of CSVD might be more active, temporally and spatially, in a distinct subgroup of RSSI patients, specifically those with a higher chronic lacune and vascular risk factor burden.


Subject(s)
Cerebral Small Vessel Diseases , Ischemic Stroke , Cerebral Infarction/diagnostic imaging , Cerebral Infarction/epidemiology , Cerebral Infarction/etiology , Cerebral Small Vessel Diseases/complications , Cerebral Small Vessel Diseases/diagnostic imaging , Cerebral Small Vessel Diseases/epidemiology , Humans , Magnetic Resonance Imaging/methods , Retrospective Studies
6.
Neuromuscul Disord ; 32(1): 50-56, 2022 01.
Article in English | MEDLINE | ID: mdl-34980537

ABSTRACT

Therapeutic advances in hereditary amyloid transthyretin (ATTRv) amyloidosis with polyneuropathy extended life expectancy and delayed symptom progression especially in patients with early disease. Thus, detection and monitoring of asymptomatic carriers gained importance. However, there is still limited consensus on genetic screening of ATTRv-polyneuropathy patients' family members and diagnostic tests that must be done in the follow-up. In this study, we followed prospectively five asymptomatic carriers of a family with ATTRV30M (p.Val50Met) mutation by different diagnostic tests for three years. The carriers were followed by neurological examination, nerve conduction studies, sympathetic skin response test, heart rate variability, SFN-SIQ and DN4 questionnaires, quantitative sensory testing (QST), skin biopsy and in vivo corneal confocal microscopy. Nerve conduction studies, sympathetic skin response test and heart rate variability were normal in all for three years. Baseline QST and SFN-SIQ were normal but became abnormal during follow-up of two individuals who developed small fiber neuropathy symptoms. Baseline intraepidermal nerve fiber density was low in three carriers and decreased to below normative values in all during follow-up, while corneal sub-basal nerve density was low in all carriers compared to controls during the entire follow-up. Thus, our study showed that SFN-SIQ and QST are useful diagnostic tools to detect the transition to symptomatic ATTRv-polyneuropathy.


Subject(s)
Amyloid Neuropathies, Familial/pathology , Skin/pathology , Adolescent , Adult , Amyloid , Biopsy , Female , Heterozygote , Humans , Male , Middle Aged , Mutation , Neural Conduction , Neurologic Examination , Prealbumin , Prospective Studies
7.
Neurol Sci ; 42(6): 2363-2369, 2021 Jun.
Article in English | MEDLINE | ID: mdl-33047201

ABSTRACT

OBJECTIVE: Sneddon's syndrome is a cerebrocutaneous non-inflammatory progressive distal arteriopathy, characterized by livedo racemosa, stroke, and neuropsychiatric symptoms. Our aim was to highlight the characteristic neuroimaging features of Sneddon's syndrome that might be helpful to clinicians in timely diagnosis of this entity. METHODS: Twelve patients (median age 49 years, 11 female) with primary Sneddon's syndrome, diagnosed in last 10 years, were analyzed from the perspective of magnetic resonance imaging (MRI) features. In addition, a novel pseudoangiomatosis score was defined for grading angiographic abnormalities (range: 0 to 6). RESULTS: Median interval from the onset of neurological symptoms to diagnosis was 6 years. Presentation was with acute stroke in 5, seizures in 3, dementia/speech problems in 2, seizures plus cognitive dysfunction in 1, and chronic progressive hemiparesis in 1. All patients had a typical lesion pattern on MRI. This included multiple (median 3) cortical-subcortical supratentorial and cerebellar non-territorial infarcts, accompanied by multifocal cerebral atrophy. Of note, large territorial infarcts due to cerebral parent artery occlusion, an embolic pattern with multi-territorial involvement on diffusion-weighted imaging, small vessel disease features like severe white matter involvement or lacunar infarcts, and cerebral hemorrhage in the absence of anticoagulation were not observed. MRI lesion severity was not correlated with angiographic arteriopathy severity, clinical stage, or presentation symptoms. CONCLUSION: Sneddon's syndrome is characterized by highly typical clinico-radiological features. Brain MRI has diagnostic value. By knowing the characteristics of the syndrome, misdiagnosis and potentially harmful treatment can be prevented in this entity that might pose a diagnostic challenge.


Subject(s)
Cerebrovascular Disorders , Sneddon Syndrome , Brain/diagnostic imaging , Cerebral Hemorrhage , Cerebrovascular Disorders/complications , Cerebrovascular Disorders/diagnostic imaging , Female , Humans , Magnetic Resonance Imaging , Middle Aged , Sneddon Syndrome/complications , Sneddon Syndrome/diagnostic imaging
8.
Angiology ; 72(3): 279-284, 2021 03.
Article in English | MEDLINE | ID: mdl-33153275

ABSTRACT

Inflammation indices derived from complete blood counts (CBCs) have been proposed to estimate benefit and risk of intravenous (IV) tissue plasminogen activator (tPA) in acute ischemic stroke. In 165 acute ischemic patients, the neutrophil-to-lymphocyte ratio (NLR), platelet-lymphocyte ratio (PLR), lymphocyte-to-monocyte ratio, and systemic immune-inflammation index (SII) were calculated before and 24 hours after IV tPA. The area under receiver operating characteristic (AUC-ROC) curves, and positive and negative likelihood ratios (+LR,-LR) were produced to measure their diagnostic accuracy and clinical utility for tPA effectiveness, hemorrhage risk and third-month prognosis. None of the indices obtained "before" IV-tPA was found to be useful in determining acute and long-term functional efficacy and bleeding risk. Lymphocyte decrease, neutrophil increase, and parallel NLR and SII increase at the 24th-hour were associated with poor functional outcome. However, their clinical utility was not sufficient due to absence of effective thresholds. NLR threshold >5.65 provided ROC-AUC 0.86, sensitivity 71.3%, specificity 65.7%, -LR 0, +LR 3.76, and SII threshold >1781 had ROC-AUC 0.802, sensitivity 58.7%, specificity 72.7%, -LR 0.11, +LR 4.52, corresponding to an acceptable clinical yield. Systemic immune-inflammation index and NLR, but not other CBC-derived inflammatory parameters, have moderate utility as marker of tPA-related symptomatic hemorrhage occurrence.


Subject(s)
Fibrinolytic Agents/administration & dosage , Inflammation Mediators/blood , Ischemic Stroke/drug therapy , Thrombolytic Therapy , Tissue Plasminogen Activator/administration & dosage , Aged , Aged, 80 and over , Biomarkers/blood , Databases, Factual , Female , Fibrinolytic Agents/adverse effects , Hemorrhage/chemically induced , Humans , Infusions, Intravenous , Ischemic Stroke/blood , Ischemic Stroke/diagnosis , Lymphocyte Count , Male , Middle Aged , Neutrophils , Platelet Count , Predictive Value of Tests , Retrospective Studies , Risk Assessment , Risk Factors , Thrombolytic Therapy/adverse effects , Time Factors , Tissue Plasminogen Activator/adverse effects , Treatment Outcome
10.
Pain Pract ; 20(2): 204-210, 2020 02.
Article in English | MEDLINE | ID: mdl-31498522

ABSTRACT

BACKGROUND: Activation of peripheral and/or central trigeminovascular pain pathways are implicated in the pathogenesis of migraine. Small fibers mediate pain, thermal sensation, and autonomic functions. Axon flare response is correlated with local C-fiber activation and calcitonin gene-related peptide release. Laser speckle contrast analysis (LASCA) detects very subtle microcirculatory changes that are not visible to the naked eye. CASE: Axon flare response was elicited by 0.01 mL intradermal (i.d.) histamine introduced to the left forehead, trigeminal nerve ophthalmic branch (V1) skin area. Skin microvascular blood flow data were recorded using a LASCA real-time microcirculation imaging system. In the healthy control, prick stimulus slightly elevated focal skin microcirculation only at the stimulated focal area. However, in our patient with chronic migraine, the unilateral prick stimulation transiently (over 10 to 12 seconds) increased ipsilateral skin microcirculation at all 3 branches of the trigeminal nerve, with a slight expansion across the midline. Left V1 stimulation by i.d. histamine induced not only prominent but also long-lasting (10 to 15 minutes of recording time) axon flare response at the ipsilateral V1, V2, and V3 areas, with an expansion to the contralateral V1 area and without any report of allodynia or hyperalgesia. The treatment decreased axon flare characteristics probably by inhibiting neurogenic inflammation. DISCUSSION: The clinical characteristics and individual response to treatment vary widely across patients with pain. Here, we demonstrated the presence of transient spread of increased microcirculation at the ipsilateral trigeminal nerve, and also across the midline after prick stimulus, whereas a more prominent, widespread, and long-lasting histamine-induced axon flare response occurred in a rare subclass of patient who had chronic migraine with autonomic symptoms. The modulatory effect of the pharmacological intervention has also been objectively quantified by LASCA.


Subject(s)
Histamine/administration & dosage , Hyperalgesia/diagnosis , Migraine Disorders/diagnosis , Perfusion Imaging/methods , Thermography/methods , Trigeminal Nerve , Adult , Chronic Disease , Female , Flunarizine/administration & dosage , Histamine/adverse effects , Histamine H1 Antagonists/administration & dosage , Humans , Hyperalgesia/drug therapy , Hyperalgesia/physiopathology , Microcirculation/drug effects , Microcirculation/physiology , Migraine Disorders/drug therapy , Migraine Disorders/physiopathology , Trigeminal Nerve/drug effects , Trigeminal Nerve/physiopathology
11.
J Stroke Cerebrovasc Dis ; 28(7): 1853-1859, 2019 Jul.
Article in English | MEDLINE | ID: mdl-31072698

ABSTRACT

BACKGROUND AND AIMS: The Neutrophil-to-Lymphocyte Ratio (NLR) is suggested as a readily available and inexpensive biomarker to predict prognosis of acute stroke. Experience with intravenous (IV) tissue plasminogen activator (tPA) treatment is limited. METHODS: Total 142 (80 female, age: 69 ± 13 yearr) consecutive acute stroke patients treated with IV tPA were evaluated. Admission and 24th hour lymphocyte, neutrophil, and monocyte counts were measured and the NLR was calculated. RESULTS: Average NLR elevated (by 3.47 ± 6.75) significantly from admission to 24th hour (P< .001). Total 52% of patients exerted good response to IV tPA (NIHSS ≤1 or decrease in NIHSS ≥4 at end of 24 hour), while 27% showed dramatic response (decrease in NIHSS ≥8 at end of 24 hour). The patients with "thrombolysis resistance" had significantly higher 24 hour Neutrophil-to-Lymphocyte Ratio (24h NLR) (P= .001). At the end of 3rd month, 46.5% of patients had favorable (modified Rankin's score, mRS 0-2) and 32.4% had excellent (mRS 0-1) outcome. Patients without favorable/excellent outcome had significantly higher 24h NLRs. Regression analysis indicated that post-tPA, but not admission NLR, was an independent negative predictor of excellent (ß =-.216, P= .006) and favorable (ß = -.179, P= .034) outcome after adjustment for age, hypertension, and admission NIHSS. Nine patients who developed symptomatic intracerebral hemorrhage had elevated pre-tPA (7.6 ± 7.39 versus 3.33 ± 3.07, P< .001) and 24h NLR (26.2 ± 18.6 versus 5.78 ± 4.47, P< .001). Of note, receiver operating characteristics analysis failed to detect any reliable NLR threshold for absence of tPA effectiveness/dramatic response, 3rd month good/excellent outcome or any type tPA-induced hemorrhage. CONCLUSIONS: As a marker of stroke-associated acute stress response, the NLR, which increases during the first 24 hours, is an epiphenomenon of poor prognosis. However, pretreatment NLR values have no importance in predicting IV tPA response.


Subject(s)
Brain Ischemia/drug therapy , Fibrinolytic Agents/administration & dosage , Lymphocytes , Neutrophils , Stroke/drug therapy , Thrombolytic Therapy , Aged , Aged, 80 and over , Brain Ischemia/blood , Brain Ischemia/diagnosis , Cerebral Hemorrhage/blood , Cerebral Hemorrhage/chemically induced , Disability Evaluation , Female , Fibrinolytic Agents/adverse effects , Humans , Infusions, Intravenous , Leukocyte Count , Male , Middle Aged , Predictive Value of Tests , Recovery of Function , Retrospective Studies , Risk Factors , Stroke/blood , Stroke/diagnosis , Thrombolytic Therapy/adverse effects , Time Factors , Treatment Outcome
12.
Agri ; 30(4): 153-164, 2018 Oct.
Article in English | MEDLINE | ID: mdl-30403278

ABSTRACT

Headache has special importance during pregnancy and postpartum period. The health-care professionals and patients report headache management as challenging during pregnancy and lactation period. Cautions are recommended in preganancy and lactation due to maternal and fetal/newborn risks. Most headaches in the first trimester are due primary headaches. Nevertheless, the incidence of secondary headaches increase in the last trimester and post-partum period. Red flags prompt early evaluation in a patient with headache. Assessment of headache patient requires a detailed history of the headache characteristics and performing appropriate examinations. Approach to headache and strategies to promote best practice in preganancy and lactation will be reviewed.


Subject(s)
Headache/drug therapy , Lactation , Pregnancy Complications/drug therapy , Prenatal Diagnosis , Puerperal Disorders/drug therapy , Analgesics/adverse effects , Analgesics/therapeutic use , Female , Humans , Pregnancy
13.
Dent Mater ; 34(10): 1518-1530, 2018 10.
Article in English | MEDLINE | ID: mdl-29958680

ABSTRACT

The common structural description of bovine enamel used in materials science studies - nano-sized hydroxyapatite crystallites form micron-sized prisms surrounded by protein sheaths, which in turn build a complex decussation pattern - overlook many important morphological information. This hampers the correct interpretation of the data determined by mechanical analysis. For a profound structural description of enamel morphology, the visualization of its building blocks by high-resolution electron microscopy and focused-ion beam tomography technique, which reveals their form, orientation and configuration at different regions of a tooth (cut in different directions), is undertaken in this work. We adapted here the paleontological classification system and terminology developed for the description of enamel microstructures seen in different species, and accordingly documented the morphological singularities of bovine incisor enamel. The appearance of the boundary regions between crystallites and prisms contradicts to the well-known protein sheath concept. Neighboring crystallites and prisms are not separated by prominent gap zones but they are largely in contact with each other. Proteins might exist within the pores of 20-30nm in size, which are distributed inhomogeneously through the boundary regions, rather than as protein sheaths covering each crystallite and prism.


Subject(s)
Dental Enamel/chemistry , Dental Enamel/ultrastructure , Tooth/chemistry , Tooth/ultrastructure , Animals , Cattle , Crystallization , In Vitro Techniques , Microscopy, Electron, Scanning , Surface Properties
14.
Sci Rep ; 7(1): 7314, 2017 08 04.
Article in English | MEDLINE | ID: mdl-28779139

ABSTRACT

In this work the fabrication of hard, stiff and strong nanocomposites based on polybutadiene and iron oxide nanoparticles is presented. The nanocomposites are fabricated via a general concept for mechanically superior nanocomposites not based on the brick and mortar structure, thus on globular nanoparticles with nanosized organic shells. For the fabrication of the composites oleic acid functionalized iron oxide nanoparticles are decorated via ligand exchange with an α,ω-polybutadiene dicarboxylic acid. The functionalized particles were processed at 145 °C. Since polybutadiene contains double bonds the nanocomposites obtained a crosslinked structure which was enhanced by the presence of oxygen or sulfur. It was found that the crosslinking and filler percolation yields high elastic moduli of approximately 12-20 GPa and hardness of 15-18 GPa, although the polymer volume fraction is up to 40%. We attribute our results to a catalytically enhanced crosslinking reaction of the polymer chains induced by oxygen or sulfur and to the microstructure of the nanocomposite.

15.
J Mech Behav Biomed Mater ; 63: 183-194, 2016 10.
Article in English | MEDLINE | ID: mdl-27415405

ABSTRACT

Exploring the structural strategies behind the optimized mechanical performance of hierarchical materials has been a focal point of extensive research over the past decades. Dental enamel is one such natural material, comprising a complicated hierarchical structure with a high level of mineral content. Bundles of hydroxyapatite nanofibers (level-1) Ø: 50nm form enamel rods (level-2) Ø: 5µm, which constitute bands (level-3) Ø: 50µm. While a number of studies in the last decade using advanced fracture mechanical methods have revealed an increasing trend in the fracture toughness of enamel with each additional level of hierarchy, there is still no general agreement on how hierarchical structuring affects the stiffness and strength of enamel. In this study, we identified the stiffness and strength values of the isolated rods (level-2) via micro-compression. The rods were tested in three different orientations with respect to the loading direction: parallel, perpendicular and oblique. The highest stress level withstood before catastrophic fracture was observed to be ~1500MPa in perpendicular orientation. In the oblique loading, the specimens failed by shearing and exhibited a damage-tolerant deformation behavior, which was attributed to the conjugation spots identified between the rods and interrod sheets. The elastic modulus was ~60GPa on average and similar in all orientations. The isotropy in stiffness was attributed to the mineral contacts residing between rods. This was verified by an analytical model derived for level-1 and extended over higher hierarchical levels. The experimental results obtained at level-2 were comparable to the compressive strength and stiffness values reported for level-1 and bulk enamel in the literature. In general, our results suggest that hierarchy has only a minor influence on the compressive properties of enamel.


Subject(s)
Compressive Strength , Dental Enamel , Dental Stress Analysis , Durapatite , Elastic Modulus , Pressure , Stress, Mechanical
16.
Nat Mater ; 15(5): 522-8, 2016 05.
Article in English | MEDLINE | ID: mdl-26828316

ABSTRACT

It is commonly accepted that the combination of the anisotropic shape and nanoscale dimensions of the mineral constituents of natural biological composites underlies their superior mechanical properties when compared to those of their rather weak mineral and organic constituents. Here, we show that the self-assembly of nearly spherical iron oxide nanoparticles in supercrystals linked together by a thermally induced crosslinking reaction of oleic acid molecules leads to a nanocomposite with exceptional bending modulus of 114 GPa, hardness of up to 4 GPa and strength of up to 630 MPa. By using a nanomechanical model, we determined that these exceptional mechanical properties are dominated by the covalent backbone of the linked organic molecules. Because oleic acid has been broadly used as nanoparticle ligand, our crosslinking approach should be applicable to a large variety of nanoparticle systems.

17.
Philos Trans A Math Phys Eng Sci ; 373(2038)2015 Mar 28.
Article in English | MEDLINE | ID: mdl-25713449

ABSTRACT

Tooth enamel has the critical role of enabling the mastication of food and also of protecting the underlying vital dentin and pulp structure. Unlike most vital tissue, enamel has no ability to repair or remodel and as such has had to develop robust damage tolerance to withstand contact fatigue events throughout the lifetime of a species. To achieve such behaviour, enamel has evolved a complex hierarchical structure that varies slightly between different species. The major component of enamel is apatite in the form of crystallite fibres with a nanometre-sized diameter that extend from the dentin-enamel junction to the oral surface. These crystallites are bound together by proteins and peptides into a range of hierarchical structures from micrometre diameter prisms to 50-100 µm diameter bundles of prisms known as Hunter-Schreger bands. As a consequence of such complex structural organization, the damage tolerance of enamel increases through various toughening mechanisms in the hierarchy but at the expense of fracture strength. This review critically evaluates the role of hierarchy on the development of the R-curve and the stress-strain behaviour. It attempts to identify and quantify the multiple mechanisms responsible for this behaviour as well as their impact on damage tolerance.


Subject(s)
Dental Enamel/physiology , Tooth/physiology , Biophysics , Crystallization , Dental Enamel/chemistry , Dental Materials , Dental Pulp , Durapatite/chemistry , Elasticity , Humans , Hydrogen-Ion Concentration , Materials Testing , Pressure , Stress, Mechanical
18.
Acta Biomater ; 16: 187-95, 2015 Apr.
Article in English | MEDLINE | ID: mdl-25620794

ABSTRACT

In this work, the compressive elastic modulus and failure strength values of bovine enamel at the first hierarchical level formed by hydroxyapatite (HA) nanofibers and organic matter are identified in longitudinal, transverse and oblique direction with the uniaxial micro-compression method. The elastic modulus values (∼70 GPa) measured here are within the range of results reported in the literature but these values were found surprisingly uniform in all orientations as opposed to the previous nanoindentation findings revealing anisotropic elastic properties in enamel. Failure strengths were recorded up to ∼1.7 GPa and different failure modes (such as shear, microbuckling, fiber fracture) governed by the orientation of the HA nanofibers were visualized. Structural irregularities leading to mineral contacts between the nanofibers are postulated as the main reason for the high compressive strength and direction-independent elastic behavior on enamels first hierarchical level.


Subject(s)
Compressive Strength , Dental Enamel/chemistry , Animals , Cattle , Stress, Mechanical , Tooth/anatomy & histology
19.
J Mech Behav Biomed Mater ; 39: 210-7, 2014 Nov.
Article in English | MEDLINE | ID: mdl-25146675

ABSTRACT

Dental enamel - a naturally occurring biocomposite of mineral and protein - has evolved from a simple prismless to an advanced prismatic structure over millions of years. Exploring the mechanical function of its structural features with differing characteristics is of great importance for evolutionary developmental studies as well as for material scientists seeking to model the mechanical performance of biological materials. In this study, mechanical properties of prismless tuatara Sphenodon punctatus enamel were characterized. Using micro-cantilever bending samples the fracture strength and elastic modulus were found to be 640 ± 87 MPa and 42 ± 6 GPa, respectively in the orientation parallel to the crystallite long axis, which decreased in the orthogonal direction. The intrinsic fracture toughness of tuatara enamel ranged from 0.21 MPa m(1/2) and 0.32 MPa m(1/2). These values correspond to the lower limit of the range of values observed in prismatic enamel at the hierarchical level 1.


Subject(s)
Dental Enamel/chemistry , Animals , Biological Evolution , Elastic Modulus , Hardness , Jaw/pathology , Lizards , Materials Testing , Microscopy, Electron, Scanning , Pressure , Stress, Mechanical
20.
Langmuir ; 30(23): 6938-45, 2014 Jun 17.
Article in English | MEDLINE | ID: mdl-24874818

ABSTRACT

Demand for ionically conducting materials, as membranes and electrodes, is one of the driving forces of current research in chemistry, physics, and engineering. The lithium ion is a key element of these materials, and its assembly into nanostructures and mesophases is important for the membrane and electrode technologies. In this investigation, we show that hydrated lithium salts (such as LiCl·xH2O and LiNO3·xH2O, x is as low as 1.5 and 3.0, respectively) and pluronics (triblock copolymer such as PX where X is 65, 85, 103, and 123) form lyotropic liquid crystalline mesophases (LLCM), denoted as LiY·xH2O-PX-n (Y is Cl(-) or NO3(-), and n is the salt/PX mole ratio). The structure of the mesophase is hexagonal over a broad salt concentration and transforms to a cubic mesophase and then to disordered gel phase with an increasing salt content of the mixtures. The mesophases are unstable at low salt contents and undergo a phase separation into pure pluronics and salt-rich LLCMs. The salt content of the ordered mesophase can be as high as 30 mole ratio for each pluronic, which is a record high for any known salted phases. The mesophases also display high ac ionic conductivities, reaching up to 21 mS/cm at room temperature (RT), and are sensitive to the water content. These mesophases can be useful as ion-conducting membranes and can be used as media for the synthesis of lithium-containing nanoporous materials.

SELECTION OF CITATIONS
SEARCH DETAIL
...