CALIBRATION METHOD AND ABSOLUTE MEASUREMENTS OF AIR KERMA OF DIAGNOSTIC X-RAY REFERENCE QUALITIES USING A FREE-AIR IONISATION CHAMBER.

Accurate dose measurement is very important for diagnosing X-ray equipment. These equipment should be traced directly or indirectly to primary standard with as little uncertainty as possible. A parallel-plate free-air chamber was designed to measure air kerma of diagnostic X-ray absolutely. Different thickness of aluminium filters were used to obtain different radiation qualities according with IEC 61267. Correction factors were obtained by experiments and simulation, especially the air attenuation factor measured with vacuum method. The relative standard uncertainty of air kerma rate measurement was 0.46% and calibration factor was 0.53%. A transfer ionisation chamber was calibrated with Radiation Qualities in Radiation beams (RQR) qualities in National Research Council of Canada and National Institute of Metrology (NIM), the differences of calibration factors are less than 0.68%.

Cross-linked thermosensitive nanohydrogels for ocular drug delivery with a prolonged residence time and enhanced bioavailability.

AIM: A temperature-triggered, cross-linked nano hydrogel formulation (NPs-gel) was prepared to prolong the residence time of dexamethasone (DXM) in the eye and increase its bioavailability. RESEARCH DESIGN AND METHODS: The NPs-gel was prepared by combining a high pressure homogenization method with a cold solution method. Soy lecithin E200, lecithin oil, glycerol, kolliphor P188, kolliphor P407, and polycarbophil were the excipients used for the formation of NPs-gel containing DXM. The nanoparticle size, temperature-sensitive phase transition characteristics, in vitro and in vivo release behavior, corneal permeability, and eye irritation level of the NPs-gel were evaluated. RESULTS: The NPs-gel had slightly larger particle size than the DXM-loaded nanoparticles, yet it retained the properties of nanoparticles such as surface effect and size effect. The phase transition temperature was 33.2 °C, which is within the trigger conditions of intraocular temperature. Under physiological conditions, the adhesion and adhesion work of the NPs-gel were 1.1 and 2.1 times that of an in situ-formed gel, and the gel strength of NPs-gel was 1.8 times that of an in situ-formed gel. These results indicate that NPs-gel has greater adhesion and mechanical strength. The area under the curve of NPs-gel was 3.08 and 1.51 times that of DXM-loaded nanoparticles and in situ-formed gel, showing higher bioavailability. CONCLUSION: The NPs-gel is a suitable formulation to further enhance ocular drug delivery.

PLGA Nanoparticle Platform for Trans-Ocular Barrier to Enhance Drug Delivery: A Comparative Study Based on the Application of Oligosaccharides in the Outer Membrane of Carriers.

PURPOSE: The trans-ocular barrier is a key factor limiting the therapeutic efficacy of triamcinolone acetonide. We developed a poly(lactic-co-glycolic acid) nanoparticles (PLGA NPs) surface modified respectively with 2-hydroxypropyl-ß-cyclodextrin (2-HP-ß-CD), chitosan oligosaccharide and trehalose. Determination of the drug/nanoparticles interactions, characterization of the nanoparticles, in vivo ocular compatibility tests, comparisons of their corneal permeability and their pharmacokinetics in aqueous humor were carried out. METHODS: All PLGA NPs were prepared by the single emulsion and evaporation method and the drug-nanoparticle interaction was studied. The physiochemical features and in vitro corneal permeability of NPs were characterized while the aqueous humor pharmacokinetics was performed to evaluate in vivo corneal permeability of NPs. Ocular compatibility of NPs was investigated through Draize and histopathological test. RESULTS: The PLGA NPs with lactide/glycolide ratio of 50:50 and small particle size (molecular weight 10 kDa) achieved optimal drug release and corneal permeability. Surface modification with different oligosaccharides resulted in uniform particle sizes and similar drug-nanoparticle interactions, although 2-HP-ß-CD/PLGA NPs showed the highest entrapment efficiency. In vitro evaluation and aqueous humor pharmacokinetics further revealed that 2-HP-ß-CD/PLGA NPs had greater trans-ocular permeation and retention compared to chitosan oligosaccharide/PLGA and trehalose/PLGA NPs. No ocular irritation in vivo was detected after applying modified/unmodified PLGA NPs to rabbit's eyes. CONCLUSION: 2-HP-ß-CD/PLGA NPs are a promising nanoplatform for localized ocular drug delivery through topical administration.

Characterisation of 2-HP-ß-cyclodextrin-PLGA nanoparticle complexes for potential use as ocular drug delivery vehicles.

Aim: 2-HP-ß-cyclodextrin-PLGA nanoparticle complexes were prepared to enhance the aqueous humour delivery of Triamcinolone acetonide.Materials & methods: Drug-loaded 2-HP-ß-CD/PLGA nanoparticle complexes prepared by adapting a quasi-emulsion solvent evaporation technique. In vitro drug release, in vitro transcorneal permeation study, histopathological study and in vivo transcorneal penetration of PLGA nanoparticles and 2-HP-ß-CD/PLGA nanoparticle complexes were evaluated. Results: Particle size distributions of 2-HP-ß-CD/PLGA nanoparticle complexes were 149.4 ± 3.7 nm and presented stable system. Corneal penetration studies revealed steady sustained drug release (First-order); 2-HP-ß-CD/PLGA nanoparticle complexes increased ocular bioavailability by increasing dispersion in the tear film and improving drug release. Conclusion: 2-HP-ß-CD/PLGA nanoparticle complex formulation is a promising alternative to conventional eye drops.

Study on contact performance of ultrasonic-assisted grinding surface.

The contact performance of ultrasonic-assisted grinding surface is studied in this paper. An improved simplified model of rough surface profile is proposed to find the microscopic feature parameters, such as the curvature radius of the asperity, which are suitable for contact analysis and calculation. Then a more accurate rough surface contact analysis model is obtained by combining the classical ZMC contact model. Based on the contact analysis model, the contact mechanism of ultrasonic-assisted grinding surface is studied. The contact stiffness and local maximum contact pressure of the surfaces under different cutting depths and ultrasonic amplitudes are calculated, and the correlation rule between the parameters of ultrasonic-assisted grinding and the contact performance of the machined surface is obtained: (1) With the increase of the cutting depth, the surface roughness of the workpiece increases; under the same load, the contact stiffness decreases and the maximum local contact pressure increases. (2) With the increase of the ultrasonic amplitude, the surface roughness of the workpiece first decreases and then increases. Under the same load, the contact stiffness increases first and then decreases, while the maximum local contact pressure resents an opposite variation trend. Under the experimental conditions, the surface contact performance of the workpiece is the best when the ultrasonic amplitude is 4 µm. Additionally, the contact performance of the ultrasonic-assisted grinding surface and the conventional grinding surface is compared: (1) When the ultrasonic amplitude is 4 µm, the surface roughness of the workpiece is at least 24% lower than that of the conventional grinding surface. (2) Under the same load, the surface contact stiffness of the ultrasonic-assisted grinding surface is increased by at least 68%, and the maximum local contact pressure is reduced by at least 17%. It is found that the interference motion of abrasive particles in the ultrasonic-assisted grinding process makes the surface height distribution more concentrated and the density of asperity increased, which results in a better contact performance compared with the conventional grinding surface.

Patients' subjective visual experiences during vitreous surgery under local anesthesia.

OBJECTIVE: To investigate patient's visual experience during vitreous surgery under local anesthesia. METHODS: A prospective and randomized study of 76 patients that underwent vitreous surgeries in our hospital between July 2010 and December 2010 was designed. All patients were interviewed half an hour before and within 1 hour after the surgery using a standardized questionnaire. Basic characteristics of patients and their intraoperative visual experiences like light, color, moving object, pain, fear, and the desire for general anesthesia before and after the surgery were recorded. RESULTS: Sixty patients (78.9%) perceived at least light perception, and 16 patients (21.1%) got no light perception throughout the entire duration of the operation. Forty one patients (53.9%) perceived only light, while 19 patients (25%) experienced moving objects. Thirty nine patients (51.3%) were frightened during their intraoperative visual experiences. Patients with better preoperative best-corrected visual acuity (BCVA) were more likely to be frightened (p=0.002). The frightened experience was affected notably by the different perceptions during operation, moving object (p=0.024), light (p=0.071), and color (p=0.071). Patients below 50 years old, especially from 20 to 30, were more likely to choose general anesthesia after the vitreous surgery. CONCLUSIONS: Most patients (78.9%) experienced at least light perception during the vitreous surgery under local anesthesia. There were no significant differences between the various visual experiences and their basic characteristics. Patients with better preoperative BCVA, perceived moving objects in their visual sensations seemed more likely to be frightened.