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PubMed2006

Characterisation of membrane mimetics on a dual polarisation interferometer.

Dual polarisation interferometry (DPI) has been used to characterise the formation of hybrid bilayer membranes (HBM) on a silicon-oxynitride surface. This technique allows the simultaneous determination of multiple physical properties of an HBM, as the HBM is being formed in a single experiment: mass, thickness in the z-direction (normal to the surface), tilt angle of the first layer and refractive index. Decanoic acid was covalently attached to an amine modified silicon-oxynitride sensor chip surface via 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride condensation reaction. The decanoic acid layer was 0.92+/-0.12 nm thick, indicating a tilt angle of 57 degrees from surface normal, and possessed a mass of 1.05+/-0.10 ng mm(-2) and a refractive index (RI) of 1.450+/-0.020. Phospholipid vesicles made from 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) or 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) were injected over the fatty acid surface to form an HBM. The DPPC HBM was 4.32+/-0.68 nm thick, with a total mass of 3.18+/-0.60 ng mm(-2) and a RI of 1.404+/-0.007. The DMPC HBM was 2.12+/-0.34 nm thick, with a total mass of 2.25+/-0.51 ng mm(-2), and a RI of 1.435+/-0.007. DPI thus provides an insight into HBM formation and differences between the structural organisation of HBMs of different composition.

Biomimetic Materials↗
PubMed2006

Homopolyvalent antibody-antigen interaction kinetic studies with use of a dual-polarization interferometric biosensor.

We used dual-polarization interferometry (DPI) to study the interaction kinetics between a 'homopolyvalent' antigen (Ag) and a monoclonal antibody (Ab). A model system, which uses a monoclonal Ab against a homopentameric Ag, C-reactive protein (CRP), is presented with principle and experiments for the study of the interactions between an Ab and an Ag that has multiple identical epitopes. This allows evaluation of the dissociation constant (K(D)) and of the binding stoichiometry by DPI based on measurements of phase changes of Ab-Ag complexes in the transverse magnetic (TM) and transverse electric (TE) polarization modes. The average experimental value of K(D) found by the DPI technique for anti-CRP Ab was shown to be in close agreement with the value obtained by an indirect competition-enzyme-linked immunosorbent assay (ELISA). Moreover, the total number of Ab combining sites on the DPI sensor chip was calculated, and the binding stoichiometry of the surface Ag-Ab complex was obtained. This study illustrates the advantages of the DPI method in biosensing in its capacity for simultaneous evaluation of the thickness and refractive index (density, mass) of adsorbed layers. This allowed a comprehensive analysis of affinity reactions between an Ab having two binding sites and a multi-sited Ag.

Antibodies, Monoclonal↗
PubMed2006

Malrotation in total knee arthroplasty: effect on tibial cortex strain captured by laser-based strain acquisition.

BACKGROUND: Malrotation of the tibial and femoral components has been recognized to be a clinical complication affecting the performance and durability of total knee arthroplasty. This study used a novel strain acquisition technique to determine the effect of tibio-femoral component malrotation on tibial torque and strain distribution of the proximal tibial cortex with a cemented fixed-bearing posterior-stabilized knee. METHODS: Using electronic speckle pattern interferometry, strain on the proximal tibia of human cadaveric knees was obtained in response to 1500N axial loading for neutrally aligned tibial and femoral components, and for 10 degrees internal and external malrotation between the tibial and femoral components. Local strain gage measurements were combined with full-field optical strain measurements to quantify effects on tibial cortex strain and strain distributions caused by the 10 degrees malrotations. In addition, tibial torque was measured for incremental degrees of tibio-femoral malrotation. FINDINGS: Tibio-femoral malrotations as small as 2 degrees caused tibial torque in excess of 4 Nm. At 10 degrees malrotation, tibial torque significantly increased to over 8 Nm (P<0.001) as compared to neutrally aligned components. Local strain gage results significantly increased from 500 muepsilon to 632 muepsilon compressive strain in response to 10 degrees external malrotation, and to 1000 muepsilon compressive strain in response to 10 degrees internal malrotation. Full-field optical strain reports yielded the highest strain of 2153 muepsilon for 10 degrees internal malrotation 30 mm below the joint line. INTERPRETATION: Laser-based strain measurement technology provides novel capabilities to capture cortex strain fields. The sensitivity of cortex strain and torsion to small amounts of tibio-femoral malrotation may explain factors contributing to aseptic implant loosening of the tibial component.

Aged↗
PubMed2026

A plasmid-associated immunoglobulin-binding protein in Acinetobacter baumannii.

BACKGROUND: Acinetobacter baumannii is a critical global health threat due to multidrug resistance and high mortality. Although antimicrobial resistance mechanisms are well characterised, the virulence determinants that drive severe infections remain poorly understood. METHODS: We screened 89 carbapenem-resistant clinical isolates of A. baumannii for virulence in animal infection models and combined comparative genomics with functional assays to identify virulence factors. An immunoglobulin-binding protein from A. baumannii (ImbA) encoded on the type D plasmid was selected and characterised. Protein-immunoglobulin interactions were analysed by pull-down and biolayer interferometry. Additional ImbA inhibition of IgG-Fc&#x3b3; receptor binding by flow cytometry were tested. Protective efficacy was evaluated in mice using vaccination or anti-ImbA antibodies. FINDINGS: A type D plasmid was consistently linked to high virulence in clinical isolates. The deletion of plasmid-encoded ImbA attenuated virulence. ImbA bound murine IgA and IgG with high affinity. The binding to the Fc region of IgG disrupted IgG-Fc&#x3b3; receptor interactions. Vaccination with recombinant ImbA improved survival and reduced bacterial dissemination in female mice with anti-ImbA antibodies partially protecting against lethal infection. Bacterial burdens in the blood were reduced in treated groups. INTERPRETATION: Our study demonstrates ImbA as an unrecognised plasmid-encoded virulence factor in A. baumannii. By intercepting host immunoglobulins, ImbA drives immune evasion and hypervirulence. Blocking ImbA by vaccination and antibody therapy restored host defence and improved outcomes in female mice, highlighting ImbA as a non-antibiotic therapeutic target with potential against multidrug-resistant A. baumannii. FUNDING: Bio&Medical Technology Development Program of the National Research Foundation (NRF), funded by the Korean government (MSIT) (No. RS-2023-00219213); Korea Research Institute of Bioscience and Biotechnology (KRIBB) Research Initiative Program.

Animals↗
PubMed2004

Emmetropisation under continuous but non-constant light in chicks.

It has been suggested that ambient lighting at night influences eye growth and might play a causal role in human myopia. To test this hypothesis, we reared newly hatched chicks under 12 hr light-dark or light-dim cycles with a light phase intensity of 1500 microW/cm(2) and variable dim phase intensities between 0.01 and 500 microW/cm(2). Other chicks were reared under constant light conditions with intensities between 1 and 1500 microW/cm(2). After three weeks, the chicks were examined by refractometry, ultrasound and caliper measurements of enucleated eyes. To relate ocular parameters with a retinal neurotransmitter likely involved in eye growth control, retinal and vitreal levels of dopamine and its principal metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), were measured by high performance liquid chromatography with electrochemical detection in the light, dark and dim phases. Diurnal fluctuations in axial length and choroidal thickness also were measured twice daily by partial coherence interferometry (PCI) in chicks under light-dark and the two brightest light-dim conditions. The eyes of chicks reared under most light-dim conditions had refractions and ocular dimensions comparable to those reared under light-dark conditions. At dim phase light intensities of 10 microW/cm(2) and above, the day-night changes in retinal dopamine metabolism were not observed. The daily fluctuations of axial length and choroidal thickness were altered with rearing under the two brightest dim light intensities, compared to the light-dark condition. Rearing under constant light with intensities ranging between 1 and 1500 microW/cm(2) produced a shallow anterior chamber and other eye alterations previously described for constant light rearing even though rearing under continuous light that fluctuated between these same intensities generally permitted normal eye growth. Thus, continuous but fluctuating light exerts different developmental effects on the eye than constant non-fluctuating light. Light-dim rearing may be more relevant to daily human light exposures than other laboratory lighting conditions and may provide an opportunity to study developmental interactions of visual quality (e.g. blur, defocus, etc.) and features of the light-dark cycle under conditions that perturb daily rhythms in dopamine metabolism and ocular dimensions. Such studies also could provide mechanistic insights into whether and how daily rhythms in retinal dopamine metabolism, axial length or choroidal thickness modulate refractive development.

3,4-Dihydroxyphenylacetic Acid↗
PubMed2005

Comparison of pilocarpine-induced and stimulus-driven accommodation in phakic eyes.

With the recent introduction of potentially accommodative intraocular lenses (IOL), there is a need for methods to evaluate their accommodative potential. In most studies assessing IOL movement, pilocarpine is used to stimulate contraction of the ciliary muscle. The aim of this study is to determine if pilocarpine-induced ciliary muscle contraction is comparable to physiological stimulus-driven accommodation in young and presbyopic subjects. Ten emmetropic young subjects (23-25 years) and 11 emmetropic presbyopic subjects (51-62 years) were included in this study. Anterior chamber depth (ACD) and lens thickness (LT) were assessed with partial coherence interferometry (PCI). A moveable stimulus was coupled to the PCI equipment for measurement of biometric lens changes. ACD was measured with the stimulus at infinity and then at the subjects individual nearpoint, and after application of two drops of 2% pilocarpine. In young subjects, there was no significant difference in lens change between nearpoint and pilocarpine stimulation. Presbyopic subjects showed no relevant lens change when accommodating at the nearpoint, however, under pharmacologically induced ciliary muscle contraction with pilocarpine, there was a significant forward shift of the anterior and posterior lens pole, leading to a translational forward lens shift of about 150 microm. This study demonstrates that pilocarpine acts "physiologically" in young phakic subjects, but is a "superstimulus" in presbyopic phakic subjects. Therefore, IOL movement may be overestimated when using pilocarpine to stimulate accommodation.

Accommodation, Ocular↗
PubMed2006

Predictability and limitations of non-invasive murine tonometry: comparison of two devices.

Our purpose was to evaluate the accuracy, reproducibility and predictive ability of two non-invasive tonometers developed for intraocular pressure (IOP) measurements in the mouse. The prototype impact-rebound tonometer (I-R) and a prototype optical interferometry tonometer (OIT) utilizing a fiberoptic pressure sensor, were compared. Enucleated eyes from C57/BL6 mice were used for the calibration. The anterior chamber was cannulated and the IOP was adjusted in increments of 5 cm of H2O (open stopcock method). A calibration curve was generated for each individual eye along with a master calibration curve for all eyes. Two operators measured the IOP. The instruments were then used in alternating order to measure the IOP in C57/BL6 and in DBA2/J animals. The same eyes were subsequently cannulated and the error of the non-invasive tonometers was determined. Both tonometers yielded almost equivalent ex vivo calibration curves with individual R2 of 0.9878 and 0.9902 respectively. Both instruments were highly reproducible. In vivo the I-R tonometer underestimated while the OIT overestimated the IOP. This error was systematic and therefore predictable. The confidence intervals of this error were determined by comparing the IOP estimates provided by each tonometer with the measurements obtained invasively by cannulation in vivo. The 95% CI of the error were 2.36 mmHg for the I-R and 2.62 mmHg for the OIT respectively. Non-invasive tonometry in the mouse is feasible. Both non-invasive instruments provide accurate and reproducible measurements with the OIT requiring calibration curves for each individual investigator.

Animals↗
PubMed2006

Optical coherence tomography for the characterization of basal cell carcinoma in vivo: a pilot study.

BACKGROUND: Optical coherence tomography combines principles of ultrasonography and optical interferometry to provide real-time cross-sectional images of subsurface microstructure of tissue in vivo. OBJECTIVE: The purpose of this pilot study was to define and characterize basal cell carcinoma by using optical coherence tomography. METHODS: Twenty-three patients with 49 lesions clinically suggestive of superficial basal cell carcinoma were recruited. Optical coherence tomography was used to characterize the features of the pearly papules in real time and in vivo. Shave biopsy and light microscopic images were compared with images from optical coherence tomography. RESULTS: Basal cell carcinoma was identified in 27 patients; all 27 had optical coherence tomographic images for comparison. Seven images were uninterpretable, probably because of technical problems. Of the remainder, 20 sites matched the histologic features seen on light microscopy, with excellent correlation between optical coherence tomographic images and histopathologic features of superficial, nodular, micronodular and infiltrative basal cell carcinomas. LIMITATIONS: This study was limited by the small number of patients examined. Also, as this study was not designed as an intent-to-diagnose study, the actual predictive value of optical coherence tomography technology remains unproven. CONCLUSIONS: Optical coherence tomography technology has potential for the diagnosis and histopathologic characterization of basal cell cancer. Additional studies to determine any practical role for optical coherence tomography are indicated.

Aged↗
PubMed2005

Depth-dependent strain of patellofemoral articular cartilage in unconfined compression.

This biomechanical study reports strain gradients in patellofemoral joint cross-sections of seven porcine specimens in response to 1% unconfined axial compression subsequent to specific amounts of off-set strain. Strain distributions were quantified with a customized laser-based electronic speckle pattern interferometry (ESPI) system in a non-contact manner, delivering high-resolution, high-sensitivity strain maps over entire patellofemoral cartilage cross-sections. Strain reports were evaluated to determine differences in strain magnitudes between the superficial, middle, and deep cartilage layers in femoral and patellar cartilage. In addition, the effect of 5%, 10%, 15%, and 20% off-set strain on depth-dependent strain gradients was quantified. Regardless of the amount of off-set strain, the superficial layer of femoral cartilage absorbed the most strain, and the deep layer absorbed the least strain. These depth-dependent strain gradients were most pronounced for 5% off-set strain, at which the superficial layer absorbed on average 5.7 and 23.7 times more strain as compared to the middle and deep layers, respectively. For increased off-set strain levels, strain gradients became less pronounced. At 20% off-set strain, differences in layer-specific strain were not statistically significant, with the superficial layer showing a 1.4 fold higher strain as the deep layer. Patellar cartilage exhibited similar strain gradients and effects of off-set strain, although the patellar strain was on average 19% larger as compared to corresponding femoral strain reports. This study quantified for the first time continuous strain gradients over patellofemoral cartilage cross-sections. Next to provision of a detailed functional characterization of normal diarthrodial joints, this novel experimental approach holds considerable attraction to investigate joint degenerative processes.

Animals↗
PubMed2005

Experimental investigation on thermocapillary drop migration at large Marangoni number in reduced gravity.

Results from a space experiment on thermocapillary drop migration conducted on board the Chinese spacecraft ShenZhou-4 are presented in this paper. In the experiment, isolated drops of Fluorinert liquid moved in a matrix liquid of 5cst silicone oil at values of the Marangoni numbers (Ma) ranging up to 5500 and the interferometry images showed the temperature distribution inside the test cell. The drop migration velocity was measured. The experimental results show that the scaled drop migration velocity V/V(YGB) obviously decreases with Ma increasing the values up to 5500. The space experimental results are also compared with those from our early experiments, other space experiments, and some theoretical predictions.

Journal Article↗
PubMed2005

Bubble vortex at surfaces of evaporating liquids.

Air bubble in volatile liquid on exiting to the surface spins a vortex maintaining integrity of the film over an indefinite period of time. The shear stress associated with the surface tension increase in the adiabatic evaporation cooling drags the warmer liquid inwards into the film counteracting its capillary drainage out under gravity. The chaotic patterns, visualized with the aid of light interferometry, depend on liquid volatility, degree of vapor saturation, and air convection. The circulation intensifies and the frequency of hydrodynamic instabilities in the multiphase flow increases on the transition to strong turbulent regimes with increasing evaporation rate. Self-consistency of the physical mechanisms of solute and evaporation inhibition of bubble coalescence is verified through dimensional parametric analysis.

Phase Transition↗
PubMed2005

Measurement of thickness and composition of a solvent film on a bubble.

Solvent-coated air bubbles in the air-assisted solvent extraction (AASX) process achieve the dual role of high solvent specific surface area and ease of phase separation. The properties and thickness of the solvent film control the process. As an approach to the study, the layer interferometry (in the UV-vis region) and FT-IR spectroscopy were used to measure the time dependent thickness and chemical composition, respectively, of a film formed by blowing an air bubble in kerosene-based solvents. The film was stabilized by the presence of 1.5 ppm silicone oil, as employed in AASX. The film appears to comprise two layers; an outer layer of almost constant thickness and an inner layer which decreased in thickness with time. The latter is considered relevant to AASX. Generally, the initial thickness was approximately 3 microm which decreased over several minutes to a final rupture thickness of 500 nm. The initial thickness is of the order determined indirectly. The chemical composition of the layer did not change with time.

Air↗
PubMed2006

Effect of mass transfer on the film drainage between colliding drops.

The influence of mass transfer on the drainage behaviour of the thin liquid film between two drops immersed in another liquid colliding at constant approach velocity has been studied experimentally. The liquid-liquid system used is glycerol in silicone oil. The transferred solute is acetone and the volume concentration difference across the interface ranges from 1 to 5%. The film thickness evolution has been measured using a laser interferometry technique. The direction of mass transfer (from the drops towards the film phase and inversely) has been investigated and the results compared to the case with no mass transfer. When the solute transfers from the drops towards the continuous phase, the drainage rate is significantly higher than in the case with no mass transfer. This result is interpreted as a consequence of the mass transfer induced surface mobility in the film region (the so-called Marangoni effect) due to localized surface tension differences. This effect has been demonstrated by the visualization of the flow patterns in the drops and in the film phase (using a particle tracer technique). In this case, the slope of the film height as a function of time seems to be independent of the approach velocity condition imposed on the drop and appears to be controlled by the interfacial tension gradient. In the opposite case, when the solute transfers from the continuous phase towards the drops, the film drainage rate is lowered with respect to the case of no mass transfer, goes to zero or even changes its sign depending on the mass transfer intensity. The results also show that in the range of solute concentration studied, the effect of mass transfer on the film drainage process takes place at large distances compared to the scales at which lubrication theory is valid.

Journal Article↗
PubMed2006

Photopatterning in poly-L-lysine thin films using UV-enhanced hydrophilicity.

Deep UV lithography on poly-L-lysine thin films was used to generate microarrays with enhanced hydrophilicity. This was manifested as adsorption of ambient humidity from air by areas exposed to UV fluence around 5 J/cm2 and was made visible by phase-contrast microscopy. Kinetics of adsorption was investigated by a novel technique involving fabrication of submicrometer hydrophilicity grating by two-beam UV interferometry. In an aqueous colloidal medium, gold and polystyrene microspheres preferentially attach to areas that are relatively less hydrophilic, i.e., those areas not exposed to UV light. This observation provides a method for fabricating micro- and nanoporous arrays with controlled porosity. The technique is demonstrated with microspheres of sizes between 250 nm and 10 microm.

Adsorption↗
PubMed2004

Comparative estimation of anterior chamber depth by ultrasonography, Orbscan II, and IOLMaster.

PURPOSE: To assess the degree of agreement of anterior chamber depth (ACD) measurements by 2 optical devices (Orbscan II and IOLMaster) and compare them with contact ultrasound A-scan. SETTING: Department of Ophthalmology at Hull Royal Infirmary, England. methods: In this prospective study of 81 eyes of 41 consecutive patients, ACD estimation was done by 3 methods-scanning slit topography (Orbscan II), partial coherence interferometry (IOLMaster), and contact ultrasound A-scan in that order. The same observer performed all measurements. Repeated measures Analysis of Variance (ANOVA) was used to analyze difference between ACD measurements by the 3 methods. Difference in measurements between methods was assessed using the paired t test. RESULTS: The mean ACD (+/-SD) by the 3 methods was 3.32 mm (0.60), 3.33 mm (0.61), and 2.87 mm (0.55), respectively. There was a statistically significant difference between measurements recorded by the 3 methods (P<.01). Mean contact A-scan measurements were 0.40 mm and 0.43 mm lower than by Orbscan II and IOLMaster respectively (P<.01). CONCLUSION: Applanation ultrasound gives consistently lower measurements for ACD compared to Orbscan II and IOLMaster. Although a high degree of agreement between Orbscan II and IOLMaster was noted, further studies are needed to assess the interchangeability of measurements in clinical practice.

Aged↗
PubMed2005

Pilocarpine-induced shift of an accommodating intraocular lens: AT-45 Crystalens.

PURPOSE: To measure the shift of an accommodating plate-haptic intraocular lens (IOL) along the visual axis induced by ciliary muscle contraction after application of pilocarpine. SETTING: Department of Ophthalmology, Medical University of Vienna, Vienna, Austria. METHODS: Fifty-four eyes of 28 patients with age-related cataract comprised this prospective study. Each patient received an AT-45 silicone accommodating IOL (Crystalens, Eyeonics Corp.) after standardized cataract surgery. In a subgroup of 24 eyes, capsular bag fibrosis was reduced by extensive polishing of the anterior capsule with a slit cannula. Assessment included measurements of anterior chamber depth, assessed with partial coherence interferometry, before and after application of pilocarpine 2% and evaluation of near visual acuity 1 month and 3 months postoperatively. RESULTS: A slight backward shift of the IOL of 151 mum in the nonpolished group (P < .001) and 122 mum in the polished group (P < .005) could be detected after application of pilocarpine. Polishing the capsule did not influence IOL shift. The median near visual acuity with distance correction 1 month and 3 months postoperatively was J5 and J4, respectively, in the nonpolished group and J6 at both times in the polished group. CONCLUSIONS: Pilocarpine induced a counterproductive active backward shift of the AT-45 IOL. Polishing of the capsular bag had no impact on accommodative ability. The reading performance of patients with the AT-45 IOL patients at 1 and 3 months was not significantly different from that of with a standard IOL under similar testing methods.

Accommodation, Ocular↗
PubMed2006

Influence of infusion volume on the ocular hemodynamic effects of peribulbar anesthesia.

PURPOSE: To test the hypothesis that ocular blood-flow response to peribulbar anesthesia can be reduced by using a smaller volume of anesthetic mixture. SETTING: Departments of Ophthalmology and Clinical Pharmacology, Medical University of Vienna, Vienna, Austria. METHODS: Twenty patients scheduled for bilateral age-related cataract surgery were enrolled in a prospective randomized balanced observer-masked crossover study. Two study days with a 2 mL injection volume or 5 mL injection volume used for peribulbar anesthesia were scheduled. On 1 study day, patients received the 1-dose regimen and on the other study day, when the contralateral eye had surgery, patients received the other injection volume. On both study days, the anesthetic mixture consisted of an equal amount of lidocaine, bupivacaine, and hyaluronidase independently of the injection volume. Intraocular pressure (IOP), blood pressure, and pulse rate were measured noninvasively. Ocular fundus pulsation amplitude (FPA) and peak systolic and end diastolic flow velocities in the central retinal artery were measured with laser interferometry and color Doppler imaging, respectively. The results were recorded as means +/- SD. RESULTS: Peribulbar anesthesia increased IOP and reduced FPA and flow velocities in the central retinal artery. The effects on IOP (5 mL, 35.1% +/- 16.0%; 2 mL, 14.1% +/- 14.1%; P<.001) and ocular hemodynamic parameters (FPA: 5 mL, -17.5% +/- 7.8%/2 mL, -7.3% +/- 7.2%, P<.001; peak systolic velocity: 5 mL, -19.5% +/- 10.7%/2 mL, -10.6% +/- 9.8%, P = .013; end diastolic velocity: 5 mL, -16.7% +/- 6.2%/2 mL, -8.4% +/- 7.3%, P = .005) were more pronounced with the 5 mL injection volume than with the 2 mL injection volume. CONCLUSIONS: An injection volume of 2 mL instead of 5 mL reduced the ocular blood-flow response to peribulbar anesthesia. This procedure may be used in patients with ocular vascular disease to reduce the incidence of anesthesia-induced ischemia and loss of vision.

Aged↗