Polymethyl Methylacrylate Research Articles

Technical note: TIGRE-DE for the creation of virtual monoenergetic images from dual-energy cone-beam CT.

Dual-energy (DE)-CBCT represents a promising imaging modality that can produce virtual monoenergetic (VM) CBCT images. VM images, which provide enhanced contrast and reduced imaging artifacts, can be used to assist in soft-tissue visualization during image-guided radiotherapy. This work reports the development of TIGRE-DE, a module in the open-source TIGRE toolkit for the performance of DE-CBCT and the production of VM CBCT images. This module is created to make DE-CBCT tools accessible in a wider range of clinical and research settings. We developed an add-on (TIGRE-DE) to the TIGRE toolkit that performs DE material decomposition. To verify its performance, sequential CBCT scans at 80 and 140kV of a Catphan 604 phantom were decomposed into equivalent thicknesses of aluminum (Al) and polymethyl-methylacrylate (PMMA) basis materials. These basis material projections were used to synthesize VM projections for a range of x-ray energies, which were then reconstructed using the Feldkamp-Davis-Kress (FDK) algorithm. Image quality was assessed by computing Hounsfield units (HU) and contrast-to-noise ratios (CNR) for the material inserts of the phantom and comparing with the constituent 80 and 140kV images. All VM images generated using TIGRE-DE showed good general agreement with the theoretical HU values of the material inserts of the phantom. Apart from the highest-density inserts imaged at the extremes of the energy range, the measured HU values agree with theoretical HUs within the clinical tolerance of±50 HU. CNR measurements for the various inserts showed that, of the energies selected, 60keV provided the highest CNR values. Moreover, 60keV VM images showed average CNR enhancements of 63% and 66% compared to the 80 and 140kV full-fan protocols. TIGRE-DE successfully implements DE-CBCT material decomposition and VM image creation in an accessible, open-source platform.

Exploration of photophysical behavior of lanthanide complex and its hybrids

The present work envisioned to synthesize europium complexes [Eu-(L)3-phen] (where, L is 4,4,4-Trifluoro-1-(2-furyl)-1,3-butanedione (TFB), phen-1,10 -phenanthroline) and its hybrids via embedding pure complex into silica and PMMA. The sol–gel method was adopted for incorporating europium complex into silica matrix as [Eu-(L)3-phen]-silica and this method was proved to be highly effective and excellent approach for obtaining such lanthanide hybrid material. Another hybrid was prepared by incorporating complex into PMMA (polymethyl methyl acrylate), an organic polymer, transformed into flexible thin film. The structure of the [Eu-(L)3-phen] was elucidated using various spectroscopic techniques, moreover Sparkle model calculation were utilized for prediction of ground state geometry. The photophysical properties of pure complex [Eu-(L)3-phen] and its hybrids were studied in detail and compared. The incorporation of pure complex into PMMA is highly supportive to enhance the stability of complex as evident from enhanced luminescent intensity, intensity ratio value 6.52, longer lifetime value 842μs and higher quantum efficiency 77% over pure complex. The organic polymer PMMA is expected to interact well with europium complex via antenna effect. The use of such inorganic and organic entities for hybrid preparation purposefully overcomes the flaws of lanthanide complexes in terms of thermal stability and mechanical strength. The promising and fascinating properties of synthesized lanthanide hybrids are fruitful in material research.

Cranioplasty Following Firearm Injury in Patients from War in Yemen: Retrospective Review of 23 Patients

Abstract Background: Cranioplasty, the repair of a skull vault defect by insertion of an object (bone or nonbiological materials such as metal or plastic plates), is a well-known procedure in modern neurosurgery. Brain protection and cosmetic aspects are the major indications of cranioplasty. Aim of Study: This study is to compare the cosmetic outcome and complications rate after cranioplasty in patients with firearm injuries, coming from war in Yemen to our neurosurgery center in Egypt, with cranial bony defects. Patients and Methods: Patients were selected with the following inclusion criteria: 1-Size of defect: Patients with bony defects more than 3cm. 2-Location of the defect: Frontal, parietal and occipital defects, (temporal defects are covered with muscle and usually doesn't need repair). We reviewed 23 patients retrospectively, underwent crani-oplasty between March 2017 and November 2018. Titanium mesh (TM; 17 patients) and poly methyl methylacrylate (bone cement) reconstructed grafts (BC; 6 patients) were used as implants. Results: More than 95% of cases (22 patients) presented to us with history of primary wound debridement, bullet extraction (in some cases) and wound closure in Yemen before coming to our center in Egypt. Before surgery, 18.8% (4 patients) presented with pseu-domeningiocele formation, 2 patients presented with CSF leaking skin fistula. Intra-operatively, 82.6% (19 patients) of them didn't undergo any kind of duroplasty. Regardless of implanted materials, more than 82.6% (19 patients) of the CP patients were satisfied with the cosmetic outcome. No statistically significant difference was observed among the two groups. The TM group showed lower complication rates compared with BC group, while the BC group demonstrated a higher post-CP subgaleal collection rate (33.3%, 2 patients) than the TM group (5.8%, 1 patient). However, no significant difference in the incidence of post-CP infection was observed among the two groups. Conclusion: In comparison with TM and BC, cranioplasty with TM shows benefits in terms of lower post-CP complica-tion, less intraoperative bleeding loss, shorter operation time and in-hospital stay.

Improvement of Bamboo Properties via In Situ Construction of Polyhydroxyethyl Methylacrylate and Polymethyl Methylacrylate Networks

The chemical modification of bamboo culm was explored based on in situ construction of polyhydroxyethyl methylacrylate (PHEMA) and polymethyl methylacrylate (PMMA) networks into the cell walls. Scanning electron microscopy revealed that the synthesized polymers distributed in both the cell walls and the lumen with the pits blocked. The dimensional stability was tested under three water soaking-drying and moistening-drying cycles. The swelling efficiency of the treated bamboo was under 8% in three cycles of water soaking and drying cycles and was 4% in moistening-drying cycles. The anti-swelling efficiency was 60.5%, 52.7%, and 46.3%, respectively, in the moistening-drying cycles. Laboratory tests on mold resistance showed that no mycelium formed on the treated bamboo, while the untreated control was 100% covered by mold fungi.

Polymethyl-Methylacrylate (PMMA) Pulmonary Embolism After Vertebroplasty: A Report of a Delayed Presentation With Involvement of Hemiazygos Vein

Polymethyl-Methylacrylate (PMMA) Pulmonary Embolism After Vertebroplasty: A Report of a Delayed Presentation With Involvement of Hemiazygos Vein

Two-Color Surface Plasmon Polariton Enhanced Upconversion in NaYF4:Yb:Tm Nanoparticles on Au Nanopillar Arrays

Spectroscopic imaging and time-resolved spectroscopy are used to study the surface plasmon polariton (SPP) enhanced infrared to visible upconversion luminescence from NaYF4:Tm:Yb nanoparticles embedded in polymethyl methylacrylate (PMMA) supported on Au nanopillar arrays. The arrays have a lattice resonance associated with the SPP near 980 nm, near-resonant with the peak absorption of the Yb3+ ion, while a local surface plasmon resonance (LSPR) associated with the individual pillars is seen to enhance the near-infrared emission of Tm3+ ions near 780 nm. The two combined channels of enhancement result in a significantly higher enhancement of the near-infrared emission when compared to the visible upconversion lines of the Tm3+ ion, consistent with the interpretation of sequential surface plasmon assisted absorption and emission at two separate and disparate energies. The presence of SPP and LSPR was confirmed by spectrally resolved reflectivity, and the mechanisms for luminescence enhancement were further ...

Protection of corneal epithelial stem cells prevents ultraviolet A damage during corneal collagen cross-linking treatment for keratoconus

Background/aimsCross-linking of the cornea is usually carried out at a young age as a treatment to manage ectasia. The corneal limbal region contains delicate long-lived stem cells, which could potentially...

Pattern formation in transparent media using ultrashort laser pulses

We report results of a systematic study of the morphology of laser-written structures within transparent media like fused silica, borosilicate glass (BK7), and polymethylmethylacrylate (PMMA) using a high-energy, 5.1MHz repetition rate, femtosecond laser oscillator. Depending on experimental conditions, both smooth channels as well as dot patterns can be laser-written. The periodicity of the written dots is readily controlled by the energy dose, a single parameter that encompasses laser energy, translation speed at fixed repetition rate, and focusing conditions. We discover the importance of the direction in which laser-writing is carried out: the periodicity of the dot patterns written at fixed energy dose but with opposite writing directions is significantly different. In PMMA, extremely large rod-like structures (∼200µm) are observed whose formation is also dependent on writing direction. We quantify guidance of 632nm and 830nm light in structures written in BK7.

Simulation of electron solid interactions in NbC and NbN using Monte Carlo method

A computer program has been developed using Rutherford’s Screened Scattering Model and Energy loss model due to Bethe and applied to simulate the electron interaction pattern in the sample of NbC and NbN with a resist layer of PMMA (Polymethyl Methylacrylate). Using the program we have studied the extent of penetration, lateral spread for different electron energies and the degree of electron back scattering. It has been found that backscattering and lateral spread is more in case of NbC than in NbN signifying hard, refractory and ceramic properties of NbC.

High resolution computed tomography of the vertebrae yields accurate information on trabecular distances if processed by 3D fuzzy segmentation approaches

Introduction The structure of trabecular bone represents an aspect of bone properties that affects vertebral bone strength independently of bone mineral density [M. Kleerekoper, A. Villanueva, J. Stanciu, D. Rao, and A. Parfitt. The role of three-dimensional trabecular microstructure in the pathogenesis of vertebral compression fractures. Calcif. Tissue Int., 37:594–597, Dec 1985; E. Seeman and P. Delmas. Bone quality—the material and structural basis of bone strength and fragility. N. Engl. J. Med., 354:2250–2261, May 2006.]. Using the mathematical concept of fuzzy distance transformation (FDT), we evaluated the accuracy of measurements of trabecular distance (Tb.Di f ) which can be determined for vertebrae in vivo using high resolution computed tomography (HRCT). Methods In a first step extrema voxels with a very high likelihood of representing bone or marrow are identified. A probability level of being a bone voxel is assigned to all other voxel. This probability is based on the FDT of the voxel's gray-level, preprint submitted to Elsevier June 10, 2008; revised July 15, 2008 i.e. the shortest gray-value weighted distance to the marrow background. Next, the resulting bone structure is skeletonized. The space between the ridges of the skeleton is filled with the largest possible spheres. The average over the radii of the spheres defines Tb.Di f , a measure of trabecular distance. 14 whole vertebrae embedded in polymethyl methylacrylate were scanned by HRCT (voxel size 156 × 156 × 400 μm 3) inside an anthropomorphic abdomen phantom. Scans obtained on Scanco Xtreme CT (XCT, voxel size 82 3 μm 3) without the phantom were used as reference. Results Tb.Di f calculated on XCT data were almost identical to trabecular distance values (1/Tb.N⁎) determined with the manufacturer's standard software ( r 2 = 0.98). Tb.Di f values obtained with HRCT correlated strongly with Tb.Di f values obtained by XCT ( r 2 = 0.89). Over the range from 400 to 1400 μm trabecular distance could be estimated with a residual error of 78 μm. Conclusions The FDT based variable Tb.Di f provides 3D estimates of trabecular distances with residual errors of less than 100 μm using a HRCT protocol which also can be employed in vivo for assessing vertebral microarchitecture.

Der Riesenzell-Tumor des Knochens - Eine Analyse von 69 Fällen

1. The tumor stage of the giant cell tumor is an indicator for the prognosis and the need for adjuvant therapy. 2. Intralesional excisions without an adjuvant result in high rates of recurrence. 3. Polymethyl methyl acrylate (PMMA) largely prevents recurrences, provides stability and makes early functional treatment possible. 4. Broad excisions should only be performed in bone which is dispensable. 5. Recurrences frequently manifest themselves by pain. They can be removed intralesionally, as in primary therapy.

Guiding in the visible with "colorful" solid-core Bragg fibers

We report on the fabrication and characterization of solid-core all-polymer Bragg fibers consisting of a large-diameter polymethyl methylacrylate (PMMA) core surrounded by 50 alternating PMMA/Polystyrene (PS) polymer layers. By modifying the reflector layer thickness we illustrate that bandgap position can be adjusted at will in the visible. Moreover, such fibers are intensely colored in both the transmission and the outside reflection modes. Potential applications of such fibers are discussed.

Materials, operational energy inputs, and net energy ratio for photobiological hydrogen production

We estimate the energy content, the operational energy inputs, and the net energy ratio (NER) of an industrial tubular photobioreactor used for the photosynthetic production of H 2 by microalgae. The NER is the dimensionless ratio of the H 2 chemical energy output (higher heating value) to the total primary energy input into the system. The calculated H 2 output of the photobioreactor is based on a range of algal photosynthetic H 2 generation efficiencies, and on the application of standard theory for tubular solar collectors. For small diameter reactors ( ⩽ 50 mm ) the mixing energy is large, and can reduce the NER by a third or more, compared to bigger diameters. For a tubular photobioreactor, low-density polyethylene (LDPE) film and glass have significantly higher NERs than rigid polymers such as polymethyl methylacrylate (acrylic). Using a hypothetical improved microalgal H 2 generation efficiency of 5%, an NER ∼ 6 can be obtained for LDPE film and for glass. For mechanical and assembly reasons LDPE film is the material of choice. These results show that photobiological hydrogen could be a viable H 2 generation technology, if tight constraints on energy inputs are met.

Development of a Monte Carlo Simulation Suite for Predicting the Electron Beam Interaction with Resist on Semiconductor Substrates

In this paper, an indigenously developed computer program suite, based on Monte Carlo simulation, is presented to simulate and understand the electron beam interaction with resist and substrates. Using this program, for different energies, one can determine the path of the electrons in the solid, which consists of either a single layer or multiple layers and also calculate the energy loss of the electrons in the resist and the substrate. We have used the Rutherford model for electron scattering and the Bethe's continuous slowing down approximation for estimating the electron energy loss. In this model, the mean free path length of the electron is the key parameter for calculating the scattering cross sections of single and multiple layers. Using our program, we have studied the electron interactions on Si and GaAs substrates with polymethyl Methylacrylate (PMMA) as resist and are able to calculate the extent of electron backscattering and also the depth of penetration for different incident electron energies.

A modified fractional model to describe the viscoelastic behavior of solid amorphous polymers: The effect of physical aging

Amorphous polymers are viscoelastic materials. When they are subjected to dynamical loads, their behavior can be modeled by transform functions of stress and strain in the complex plane. In our work, a model based on the fractional calculus concept is proposed in order to predict the viscoelastic behavior of polymethylmethylacrylate (PMMA) over a wide temperature range between (Tg -190°C) and (Tg +15°C). The extended fractional solid model is shown to be capable of describing experimentally observed dynamic viscoelastic behavior over a wide temperature range, including multiple relaxations, using a limited number of free parameters. Structural recovery of PMMA was studied by dynamic mechanical spectrometry, and its effect on the different parameters is also discussed. Furthermore, from the fractional differential and fractional integral formulations. most of the relevant viscoelastic functions that quantify the degree of molecular mobility of amorphous polymers, like E(t), E*(τ). and H(t), can be derived analytically.

In vivo effect of pressurization of polymethyl methacrylate bone-cement : Biomechanical and histologic analysis

Sixteen goats underwent total hip arthroplasty, half with pressurized and half with unpressurized bone-cement. The animals underwent hemiarthroplasty of the contralateral hip immediately prior to sacrifice 6 weeks later. Samples were tested for interface strength and evaluated histologically. Pressurization of polymethyl methylacrylate improves the strength of the bone-cement interface in vivo, as well as in vitro. There is a regional variation in the strength of the bone-cement interface both in vivo and in vitro. The regional variation in the in vivo model is at least in part due to a biologic effect. Membranes forming at the bone-cement interface are usually fibrous and incomplete, allowing direct cement-to-bone contact. Membranes appear to be involved in the remodeling of bone. Polymethyl methacrylate causes significant necrosis of the cortex, with ensuing resorption of the cortical bone. There is a small, statistically insignificant trend toward increased resorption and decreased bone formation with pressurized cement. The amount of necrosis appears to be similar with pressurized and nonpressurized cement. Bone remodels to fill defects in the cement mantle.