Relaxation Profiles Research Articles

Slow dynamics of solid proteins – Nuclear magnetic resonance relaxometry versus dielectric spectroscopy

1H Nuclear Magnetic Resonance (NMR) relaxometry and Dielectric Spectroscopy (DS) have been exploited to investigate the dynamics of solid proteins. The experiments have been carried out in the frequency range of about 10 kHz-40 MHz for NMR relaxometry and 10−2Hz-20 MHz for DS. The data sets have been analyzed in terms of theoretical models allowing for a comparison of the correlation times revealed by NMR relaxometry and DS. The 1H spin–lattice relaxation profiles have been decomposed into relaxation contributions associated with 1H–1H and 1H-14N dipole – dipole interactions. The 1H–1H relaxation contribution has been interpreted in terms of three dynamical processes of time scales of 10−6s, 10−7s and 10−8s. It has turned out that the correlation times do not differ much among proteins and they are only weakly dependent on temperature. The analysis of DS relaxation spectra has also revealed three motional processes characterized by correlation times that considerably depend on temperature in contrast to those obtained from the 1H relaxation. This finding suggest that for solid proteins there is a contribution to the 1H spin–lattice relaxation associated with a kind of motion that is not probed in DS as it does not lead to a reorientation of the electric dipole moment.

Quantitative and qualitative analysis of segmental dielectric relaxations and space charge by TSDC in nanocomposites of natural rubber/clay

The effect of adding three different layered clays, a sodium montmorillonite and two commercial modified montmorillonites, on the morphology and molecular dynamics of natural rubber characterized by Transmission Electron Microscopy and Thermally Stimulated Depolarization Currents (TSDC) was studied. Carbon black was employed as reinforcing filler in a standard compound prepared and used for comparison purposes. The morphological results revealed that the sample with Cloisite\circledR 15A displays the highest degree of exfoliation, which suggests a stronger compatibility between the organic and inorganic phases. When the dispersion degree increases, a decrease of the activation energy was found from the quantitative analysis of the space charge dielectric relaxations. From the qualitative analysis of the dipolar dielectric relaxations around $T_{g}$, changes in the dielectric relaxation profile and in the peak localization were attributed to probable interactions between the nanofillers and the elastomer in the glass transition region of the NR.

Growth‐Factor Free Multicomponent Nanocomposite Hydrogels That Stimulate Bone Formation

AbstractSynthetic osteo‐promoting materials that are able to stimulate and accelerate bone formation without the addition of exogenous cells or growth factors represent a major opportunity for an aging world population. A co‐assembling system that integrates hyaluronic acid tyramine (HA‐Tyr), bioactive peptide amphiphiles (GHK‐Cu2+), and Laponite (Lap) to engineer hydrogels with physical, mechanical, and biomolecular signals that can be tuned to enhance bone regeneration is reported. The central design element of the multicomponent hydrogels is the integration of self‐assembly and enzyme‐mediated oxidative coupling to optimize structure and mechanical properties in combination with the incorporation of an osteo‐ and angio‐promoting segments to facilitate signaling. Spectroscopic techniques are used to confirm the interplay of orthogonal covalent and supramolecular interactions in multicomponent hydrogel formation. Furthermore, physico‐mechanical characterizations reveal that the multicomponent hydrogels exhibit improved compressive strength, stress relaxation profile, low swelling ratio, and retarded enzymatic degradation compared to the single component hydrogels. Applicability is validated in vitro using human mesenchymal stem cells and human umbilical vein endothelial cells, and in vivo using a rabbit maxillary sinus floor reconstruction model. Animals treated with the HA‐Tyr‐HA‐Tyr‐GHK‐Cu2+ hydrogels exhibit significantly enhanced bone formation relative to controls including the commercially available Bio‐Oss.

Electron Paramagnetic Resonance Spectroscopic Identification of the Fe-S Clusters in the SPASM Domain-Containing Radical SAM Enzyme PqqE.

Pyrroloquinoline quinone (PQQ) is an important redox active quinocofactor produced by a wide variety of bacteria. A key step in PQQ biosynthesis is a carbon-carbon cross-link reaction between glutamate and tyrosine side chains within the ribosomally synthesized peptide substrate PqqA. This reaction is catalyzed by the radical SAM enzyme PqqE. Previous X-ray crystallographic and spectroscopic studies suggested that PqqE, like the other members of the SPASM domain family, contains two auxiliary Fe-S clusters (AuxI and AuxII) in addition to the radical SAM [4Fe-4S] cluster. However, a clear assignment of the electron paramagnetic resonance (EPR) signal of each Fe-S cluster was hindered by the isolation of a His6-tagged PqqE variant with an altered AuxI cluster. In this work, we are able to isolate soluble PqqE variants by using a less disruptive strep-tactin chromatographic approach. We have unambiguously identified the EPR signatures for four forms of Fe-S clusters present in PqqE through the use of multifrequency EPR spectroscopy: the RS [4Fe-4S] cluster, the AuxII [4Fe-4S] cluster, and two different clusters ([4Fe-4S] and [2Fe-2S]) bound in the AuxI site. The RS [4Fe-4S] cluster, the AuxII [4Fe-4S] cluster, and the [2Fe-2S] cluster form in the AuxI site can all be reduced by sodium dithionite, with g tensors of their reduced form determined as [2.040, 1.927, 1.897], [2.059, 1.940, 1.903], and [2.004, 1.958, 1.904], respectively. The AuxI [4Fe-4S] cluster that is determined on the basis of its relaxation profile can be reduced only by using low-potential reductants such as Ti(III) citrate or Eu(II)-DTPA to give rise to a g1 = 2.104 signal. Identification of the EPR signature for each cluster paves the way for further investigations of SPASM domain radical SAM enzymes.

An interpretation for the breakpoint of the relaxation profiles of the advancing and receding contact angles

The breakpoints of the profiles of the advancing (θa) and receding (θr) contact angles can be used to determine the critical micelle concentration of surfactant solution. Although the breakpoints of θa and θr matched with that of surface tension for some surfactant solutions (i.e. SDS), the physical meaning behind these breakpoints is yet to be ascertained. This study attempts to interpret these breakpoints by examining the evaporation process of the sessile drops of SDS, Triton X-100 and C12E6 solutions on parafilm. The surface area perturbance, during the period θa and θr were detected, resulted in a noticeable deviation of the L-G and L-S interfacial tensions (γlg and γls) from their respective equilibrium states. As θa and θr were detected during the L-G and L-S area perturbations, these deviations of γlg and γls played a crucial role in the relaxation profiles of θa and θr. Furthermore, the relaxations of θa and θr were affected by the extent up to which the γlg and γsl re-equilibrated with the drop concentration. This extent of re-equilibration, in turn, was dependent on the dynamic surface tension of a perturbed interface. Subsequently, it was found out that the breakpoints of θa and θr indicated the lowest bulk concentrations at which the γlg and γsl re-equilibrated when either θa or θr was detected using the evaporation method.

Conservation process of archaeological waterlogged wood studied by spectroscopy and gradient NMR methods

The properties of methyltrimethoxysilane-treated, waterlogged archeological elm wood were studied by magnetic resonance imaging and nuclear magnetic resonance (NMR) methods. The spatially resolved proton density images, spin–spin relaxation profiles, proton NMR spectra, and self-diffusion coefficients of the preservative agents were measured during drying. The resolution of the data allowed for the differentiation between the early and late wood areas of the elm wood and determination of the shrinkage of the sample in the tangential and radial directions, and it showed the different dynamics of methyltrimethoxysilane (MTMS) in the lumen cells of both early and late woods. The NMR spectra indicated that the MTMS, after rapid evaporation of ethanol, is bound to the wood. Identical measurements were also taken for the archeological elm wood treated with polyethylene glycol (PEG) and for an untreated wood sample. From the results, it can be concluded that MTMS showed significantly higher stability against shrinkage when compared to PEG. Therefore, it may be considered as an alternative preservative for archeological wood.

Simultaneous Optical Transmission Relaxation and Electrical Conductivity Relaxation Measurements of Oxygen Surface Exchange Kinetics during Crystallization

Oxygen exchange at the surface of mixed ionic and electronic conductors (MIECs) plays an integral role in the efficiency and lifetime of many electrochemical devices and is often the efficiency-limiting process at intermediate temperatures (300-600 °C). Despite development of many MIEC perovskite compositions for this purpose, there is still a need to deeply understand processing-structure-property relationships in relation to optimizing the surface exchange coefficient. In recent work, we observed by a new optical transmission relaxation (OTR) approach that perovskite SrTi0.65Fe0.35O3-d (STF35) films deposited by pulsed laser deposition at room temperature in the amorphous state, and subsequently annealed at the crystallization temperature, show immeasurably fast oxygen surface exchange kinetics in the intermediate temperature range [1,2]. In order to better understand this effect, our ongoing work has three aims: 1) to characterize the structural changes occurring in STF35 thin films upon crystallization using X-ray absorption spectroscopy 2) to relate the structural evolution to emergent functional properties, and 3) to evaluate the accuracy of the OTR technique for the measurement of oxygen surface exchange kinetics during crystallization. Towards this last goal, surface exchange coefficients (kchem) were analyzed using simultaneous electrical conductivity relaxation (ECR) and optical transmission relaxation (OTR) techniques on amorphous and crystalline films at various temperature points from 300-600 °C and as a function of oxygen activity in the films by varying the oxygen partial pressure (pO2). Our prior work has shown that the change in optical absorption of the films is directly proportional to the change in their oxygen concentration and change in hole concentration (via Fe valence changes). Therefore, we hypothesized that as the films oxidize or reduce, the amount of light absorbed increases or decreases in direct correspondence to the increase or decrease in p-type electronic conductivity in the film, assuming minimal changes in the electronic mobility with pO2 [3]. Across the different measurement conditions, our results showed excellent agreement in relaxation profiles and fitted kchem values between these two techniques (OTR and ECR) for crystalline films (within a factor of 2), demonstrating the applicability of the optical technique to the STF35 system. Further, both ECR and OTR showed the emergence of rapid oxygen exchange upon in situ crystallization, validating the earlier optically-based observation of this effect. This novel OTR technique provides a continuous, contact-free, and in situ measurement of the native surface kinetics in realistic operating conditions that has the potential to be applied to many other systems. [1] T. Chen, G.F. Harrington, K. Sasaki, and N.H. Perry, “Impact of microstructure and crystallinity on surface exchange kinetics of strontium titanium iron oxide perovskite by in situ optical transmission relaxation approach” Journal of Materials Chemistry A, 5, 23006-23019 (2017). [2] T. Chen, G.F. Harrington, J. Masood, K. Sasaki, and N.H. Perry, “Emergence of Rapid Oxygen Surface Exchange Kinetics During In Situ Crystallization of Mixed Conducting Thin Film Oxides” ACS Applied Materials and Interfaces (2019). [3] N.H. Perry, N. Kim, E. Ertekin, H.L. Tuller, “Origins and control of optical absorption in a non-dilute oxide solid solution: Sr(Ti,Fe)O3-x perovskite case study” Chemistry of Materials (2019).

A study on the determination of the critical micelle concentration of surfactant solutions using contact angle data

The critical micelle concentration (cmc) is an important parameter in colloidal and surface chemistry and a wide range of techniques have been devised for cmc determination. In this study, the determination of the cmc of surfactant solutions from the unique advancing and receding contact angle (CA) data was investigated. The sessile drop was formed from a pendant drop which had reached its equilibrium surface tension (ST) in a saturated atmosphere (~100% humidity). The CA was determined from the best-fit between the edge locations of drop and the Young-Laplace theoretical profile. The advancing and receding CAs were determined from the CA relaxation profiles of the sessile drops. It was observed that the breakpoints of the advancing and receding CAs of SDS solution drop coincided with the cmc determined from the ST data. However, the comparatively slower adsorption and bulk diffusion rates of TX-100 and C12E6 made the CA breakpoints deviate from that of ST. Thus, it was concluded that the approach of using the unique CA data for the determination of cmc could be applied only to those surfactants with a relatively high mass transport rate, such as SDS.

Neryl butyrate induces contractile effects on isolated preparations of rat aorta.

Neryl butyrate is a constituent of volatile oils obtained from aromatic plants. Aliphatic organic compound analogues chemically close to neryl butyrate possess vasodilator properties in rat aorta. To evaluate whether neryl butyrate has relaxing properties, this study tested its effects on isolated rat aorta. Unlike the analogues, neryl butyrate did not show relaxant profile in aortic rings precontracted with phenylephrine, but induced a contraction when it stimulated aortic rings under resting tonus. The contractile effect augmented in endothelium-denuded aortic rings. Treatment of endothelium-intact preparations with the nitric oxide synthase inhibitor L-NAME or the guanylyl cyclase inhibitor ODQ also augmented the contractile effect of neryl butyrate. Such phenomenon was absent in the presence of the cyclooxygenase inhibitor indomethacin. Contractile responses decreased in the presence of verapamil, a L-type Ca2+ channel blocker, or when Ca2+ was removed from the extracellular solution. Antagonists of α-adrenergic receptors (prazosin and yohimbine), but not the thromboxane-prostanoid receptor seratrodast, reversed the contraction induced by neryl butyrate. The α1A selective antagonist RS-17053 antagonized the neryl butyrate-induced contraction. The contraction caused by neryl butyrate was decreased by inhibiting the phospholipase C or the rho-associated kinase with U-73122 or Y-27632, respectively. Injected intravenously to awake rats, neryl butyrate induced arterial hypotension and bradycardia. Decreased frequency was also present in isolated right atrium preparations. In conclusion, the contractile effects of neryl butyrate were inhibited by α-adrenergic antagonists, indicating the involvement of α-adrenoceptors in the mechanism of action. In vivo, neryl butyrate caused hypotension, suggesting that other systemic influence than vasoconstriction may occur.

Direct Observation of Surface Polarons in Capped CuInS2 Quantum Dots by Ultrafast Pump-Probe Spectroscopies.

Semiconductor nanocrystals are mostly prepared by colloid chemistry with organic surfactant molecules, and their surface polarization effect on the carrier relaxations arecritical to their optoelectronic applications. Until now, the surface polarization effect and detailed photophysical processes of these capped quantum dots (QDs) are still unclear. Here, we studied the dynamics of the photoinduced carriers and capping moleculevibrations of capped CuInS2 quantum dots by using the femtosecond pump-probe system in both visible and IR zones. It is identified that the capping molecular vibrations exhibit significant Fermion bleaching nature, whose relaxation profile is in good agreement with the radiative recombination dynamics of QDs in the visible region. These results demonstrate that the extrinsic surface polarons form by the coupling of photoinduced carriers and surface ligand vibrations, and take part in the photophysical processes of these QDs. This finding is helpful for the QD design and applications in photoelectronic devices.

Relaxivity of Gd‐Based MRI Contrast Agents in Crosslinked Hyaluronic Acid as a Model for Tissues

The efficiency of MRI contrast agents depends on the relaxation rate enhancement that they can induce at imaging fields. It is well known that, at these fields, large relaxation rates are obtained by binding of gadolinium(III) ions to large molecules. By the same token, the interaction of the gadolinium(III) complexes with macromolecules that are found in biological tissues can be responsible for an increase of the relaxation rate with respect to the value observed in liquids. We investigate here the relaxation enhancement of gadoteridol (Gd-HP-DO3A) in crosslinked hyaluronic acid, taken as model tissue, using fast field-cycling relaxometry. The analysis of the relaxation profiles as a function of the magnetic fields indicates that a sizable increase in the relaxation rates is due to a modest interaction of the contrast agent with the hydrogel and to the slower mobility of the water molecules outside the first-coordination sphere of the gadolinium(III) ion.

Stress relaxation and humidity dependence in sodium alginate-glycerol films

The control of viscoelastic properties of alginate biopolymer that mimics the matrix properties of biological substrates plays an important role for the success of its biomedical applications. For this purpose stress relaxation behavior of glycerol plasticized sodium alginate films is characterized at room temperature as a function of the glycerol concentration ranging up to 40%. A series of experiments are thus conducted at relative humidity levels of 38 ± 1% and 51 ± 1%. The glycerol content is demonstrated to amplify the effect of humidity on relaxation profiles. In the case of 30% glycerol, normalized stress at the level of 65% is recorded at the end of the first 30 min at the low humidity level, whereas the corresponding value drops to 8% with increased humidity. Alginate films with no glycerol content exhibit much higher normalized stresses of 89% and 73% at low and high humidity levels, respectively. In addition, stress relaxation is observed to continue well beyond the first 30 min, especially for glycerol concentrations lower than 30%, where 9-hour parameters for a stretched exponential Kohlrausch – Williams – Watts function are reported demonstrating the importance of relaxation time for successful modeling.

The development of optimal charging strategies for lithium-ion batteries to prevent the onset of lithium plating at low ambient temperatures

Abstract This study develops two novel charging strategies for lithium-ion batteries, designed to prevent the onset of lithium plating when the cells are charged at low ambient temperatures. Commercially available 3.1 Ah 18650-type cells with NCA and graphite electrodes have been selected for this study. Experimental results highlight that for these cells, lithium plating can be detected when the cells are charged with a traditional constant-current constant-voltage (CC-CV) profile at an ambient temperature of 5 °C and a charge rate of 1C. The occurrence of lithium plating is known to lead to a considerable capacity reduction. To avoid the onset of lithium plating with minimum impact on the charge time, two optimal charging strategies are proposed. The first is based on detecting the onset of lithium plating through the online analysis of the voltage relaxation profile (VRP). The second is to manage the cell charging process to achieve a pre-defined rate of battery degradation per charge cycle. Experimental results highlight that the capacity fade of cells using the proposed charging strategies can be significantly reduced compared to when charged using the conventional CC-CV approach by 45% and 70% respectively while minimizing their impact on the charging speed.

Influence of Pluronic F127 microenvironments on the photochemical nitric oxide release from S-nitrosoglutathione

Poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) (F127) hydrogels have been used to deliver nitric oxide (NO) topically in biomedical applications. Here, the effect of F127 microenvironments on the photochemical NO release from S-nitrosoglutathione (GSNO) was investigated in F127 solutions 7.6 wt% 15 wt% and 22.5 wt% at 15 °C and 37 °C. Small-angle X-ray Scattering (SAXS) and Differential Scanning Calorimetry (DSC) measurements, along with proton Nuclear Magnetic Resonance (1H NMR) spectral shifts and T2 relaxation data at six different concentration-temperature conditions, allowed identifying F127 microphases characterized by: a sol phase of unimers; micelles in non-defined periodic order, and a gel phase of cubic packed micelles. Kinetic measurements showed that GSNO photodecompositon proceeds faster in micellized F127 where GSNO is segregated to the intermicellar microenvironment. Real time kinetic monitoring of NO release and T2 relaxation profiles showed that NO is preferentially partitioned into the hydrophobic PPO cores of the F127 micelles, with the consequent decrease in its rate of release to the gas phase. These results show that F127 microphases affect both the kinetics of GSNO photodecomposition and the rate of NO escape and can be used to modulate the photochemical NO delivery from F127/GSNO solutions.

Erythromycin relaxes BALB/c mouse airway smooth muscle

AimsBitter taste receptor (TAS2R) agonists have bronchodilatory potentials. Erythromycin is a ligand of TAS2R10, but its relaxant profile is unknown. This study was performed to understand the relaxant effects of erythromycin and its potential mechanism. Main methodsAirway resistance was tested by the whole body plethysmography in the ovalbumin-aluminum hydroxide induced asthma model mice. Tracheal ring segment myography was used to investigate the isometric tension of the smooth muscle. The cyclic adenosine monophosphate (cAMP) concentration was measured by enzyme immunoassay kit. Changes in the calcium influx in airway smooth muscle cells (ASMCs) were surveyed using a real-time confocal microscopy. Key findingsErythromycin significantly relieved airway hyperreactivity in asthma model mice. Erythromycin relaxed mouse tracheal segments precontracted with carbachol, KCl, 5-hydroxytryptamine and U46619, and further dilated the tracheal rings relaxed by isoprenaline or atropine. Epithelium removal, indomethacin or NS-398 partially reduced the relaxation. U73122, 2-APB, iberiotoxin or ouabain did not change the concentration-relaxation curves of erythromycin on tracheal segments. Erythromycin didn't elevate cAMP level. CaCl2-induced contraction in the K+-rich solution was impaired by erythromycin in the Ca2+-free solution. The intercellular Ca2+ level in the ASMCs was decreased by erythromycin, which was partly inhibited by Bay K8644 but not gallein. SignificanceErythromycin had marked bronchodilatory effect. The relaxation might be related to the L-type voltage-dependent calcium channel, but not the gustducin-associated βγ/phospholipase-Cβ/inositol 1,4,5-tri-phosphate receptor/large conductance Ca2+-activated K+ channel pathway or a cAMP-dependent way.

Phonon relaxation time reconstruction from transient thermal grating experiments and comparison with density functional theory predictions

Phonon relaxation time and free path distributions are reconstructed from experimental measurements on a two-dimensional transient thermal grating and compared with density functional theory (DFT) results for silicon. The reconstruction is performed using the inverse problem formulation of Forghani et al. [Phys. Rev. B 94, 155439 (2016)]. The discrepancies observed between reconstructed and DFT results are analyzed in terms of the ability of each set of data to reproduce the experimental temperature relaxation profiles; the reconstructed data are found to predict temperature profiles in closer agreement with the experimental data than the DFT results, possibly due to discrepancies between the actual material and the idealized model studied in the DFT calculations. The reconstructed phonon properties accurately predict temperature relaxation profiles at grating length scales smaller than those spanned by the experimental data. This is a very important feature since in a variety of experimental setups, including the one providing the data in the present study, measurements are not available at all scales spanned by the material free paths.

A new concept to improve the lithium plating detection sensitivity in lithium-ion batteries

Lithium plating significantly reduces the lifetime of lithium-ion batteries and may even pose a safety risk in the form of an internal short circuit, leading to catastrophic cell failure. Low temperatures, high charge currents and battery age are known to be contributing factors to increased lithium plating. To reduce or avoid battery ageing induced by lithium plating, a method for lithium plating detection is essential to help understand the favourable conditions under which battery charging is optimised. In this study, we present a concept to design an experiment-based approach to improve lithium plating detection sensitivity using the non-destructive voltage relaxation analysis method. Commercial NCA/graphite cells are employed for this study. Here, the reversible part of the plated lithium providing a unique cell voltage relaxation profile is used as a pseudo-measure to detect the onset of plating. This profile is observed while the cell is at rest as well as under a low C-rate discharge regime immediately after charging. It is found that the CV (Constant Voltage) phase cut-off current value significantly influences plating detection. To address this issue, a procedure to determine the optimal cut-off current in the CV phase of charging is introduced to improve the detection sensitivity. With the proposed method, plating detection chances are improved which will help in understanding the favourable conditions and developing plating control strategies. Furthermore, a correlation between lithium plating and Electrochemical Impedance Spectroscopy (EIS) measurements are utilized to demonstrate the influence of previous ageing conditions on lithium plating.

Stress Relaxation Related to Spontaneous Thin Film Buckling: Correlation between Finite Element Calculations and Micro Diffraction Analysis

Compressive residual stresses generated during thin film deposition may lead to undesirable film damage, such as delamination, buckling, and flaking, ultimately leading to the failure of the device employing the film. Understanding the residual stress generation and role in these damage mechanisms is necessary to preserve thin film integrity and optimize its functional properties. Thin shell theory has been used for decades to predict buckling but the results have not yet been correlated with experimental data since the techniques used to measure stress in metallic films were not able to do so at the required micron scale until recently. Micro scanning X-ray diffraction now enables the direct mapping of the local stress of metallic films. In this paper, finite element method based on thin shell theory and synchrotron X-ray micro diffraction have been used to determine stress maps of thin film buckling patterns. Calculations of the stress distribution in the metallic films have been performed taking into account the buckling geometry determined from optical measurements. Stress distributions over gold blisters and tungsten wrinkles obtained with the two techniques are in fair agreement and allow for the accurate determination of the stress relaxation profile from the bottom to the top of the buckling, validating the thin shell theory model.

Insights on the Alumina–Water Interface Structure by Direct Comparison of Density Functional Simulations with X-ray Reflectivity

Density functional theory molecular dynamics (DFT-MD) simulations are frequently used to predict the interfacial structures and dynamical processes at solid–water interfaces in efforts to gain a deeper understanding of these systems. However, the accuracy of these predictions has not been rigorously quantified. Here, direct comparisons between large-scale DFT-MD simulations and high-resolution X-ray reflectivity (XR) measurements of the well-defined Al2O3(001)/water interface reveal the relative accuracy of these two methods to describe interfacial structure, a comparison that is enabled by XR’s high sensitivity to atomic-scale displacements. The DFT-MD simulated and XR model-fit structures are qualitatively similar, but XR signals calculated directly from the DFT-MD predictions deviate significantly from the experimental data, revealing discrepancies in these two approaches. Differences in the derived interfacial Al2O3 relaxation profiles of ∼0.02 A within the top five layers are significant to XR, but a...

Quantitative measurement of T2, T1ρ and T1 relaxation times in articular cartilage and cartilage-bone interface by SE and UTE imaging at microscopic resolution.

Both spin-echo (SE) and ultra-short echo (UTE) based MRI sequences were used on a 7 T µMRI system to quantify T2, T1ρ and T1 relaxation times from articular cartilage to the cartilage-bone interface on canine humeral specimens at 19.5 µm pixel resolution. A series of five relaxation-weighted images were acquired to calculate one relaxation map (T2, T1ρ or T1), from which the depth-dependent profiles were examined between the SE method and the UTE method, over the entire non-calcified cartilage and within the cartilage-bone interface. SE-based methods enabled the quantification of relaxation profiles over the noncalcified cartilage, from 0 µm (articular surface) to approximately 460 µm in depth (near the end of radial zone). Most of the cartilage-bone interface was imaged by the UTE-based methods, to a tissue depth of about 810 µm. Pixel-by-pixel calculation of the relaxation times between the independent SE and UTE methods correlated well with each other. A better understanding of the tissue properties reliably over the cartilage-bone interface region by a non-invasive MRI approach could contribute to the clinical diagnostics of trauma-induced osteoarthritis.