Early stage disc degeneration does not have an appreciable affect on stiffness and load transfer following vertebroplasty and kyphoplasty.

Vertebroplasty and kyphoplasty have been reported to alter the mechanical behavior of the treated and adjacent-level segments, and have been suggested to increase the risk for adjacent-level fractures. The intervertebral disc (IVD) plays an important role in the mechanical behavior of vertebral motion segments. Comparisons between normal and degenerative IVD motion segments following cement augmentation have yet to be reported. A microstructural finite element model of a degenerative IVD motion segment was constructed from micro-CT images. Microdamage within the vertebral body trabecular structure was used to simulate a slightly (I = 83.5% of intact stiffness), moderately (II = 57.8% of intact stiffness), and severely (III = 16.0% of intact stiffness) damaged motion segment. Six variable geometry single-segment cement repair strategies (models A-F) were studied at each damage level (I-III). IVD and bone stresses, and motion segment stiffness, were compared with the intact and baseline damage models (untreated), as well as, previous findings using normal IVD models with the same repair strategies. Overall, small differences were observed in motion segment stiffness and average stresses between the degenerative and normal disc repair models. We did however observe a reduction in endplate bulge and a redistribution in the microstructural tissue level stresses across both endplates and in the treated segment following early stage IVD degeneration. The cement augmentation strategy placing bone cement along the periphery of the vertebra (model E) proved to be the most advantageous in treating the degenerative IVD models by showing larger reductions in the average bone stresses (vertebral and endplate) as compared to the normal IVD models. Furthermore, only this repair strategy, and the complete cement fill strategy (model F), were able to restore the slightly damaged (I) motion segment stiffness above pre-damaged (intact) levels. Early stage IVD degeneration does not have an appreciable effect in motion segment stiffness and average stresses in the treated and adjacent-level segments following vertebroplasty and kyphoplasty. Placing bone cement in the periphery of the damaged vertebra in a degenerative IVD motion segment, minimizes load transfer, and may reduce the likelihood of adjacent-level fractures.

Non-resorbable glass fibre-reinforced composite with porous surface as bone substitute material: Experimental studies in vitro and in vivo focused on bone-implant interface

The development of load-bearing osseous implant with desired mechanical and surface properties in order to promote incorporation with bone and to eliminate risk of bone resorption and implant failure is a very challenging task. Bone formation and resoption processes depend on the mechanical environment. Certain stress/strain conditions are required to promote new bone growth and to prevent bone mass loss. Conventional metallic implants with high stiffness carry most of the load and the surrounding bone becomes virtually unloaded and inactive. Fibre-reinforced composites offer an interesting alternative to metallic implants, because their mechanical properties can be tailored to be equal to those of bone, by the careful selection of matrix polymer, type of fibres, fibre volume fraction, orientation and length. Successful load transfer at bone-implant interface requires proper fixation between the bone and implant. One promising method to promote fixation is to prepare implants with porous surface. Bone ingrowth into porous surface structure stabilises the system and improves clinical success of the implant. The experimental part of this work was focused on polymethyl methacrylate (PMMA) -based composites with dense load-bearing core and porous surface. Three-dimensionally randomly orientated chopped glass fibres were used to reinforce the composite. A method to fabricate those composites was developed by a solvent treatment technique and some characterisations concerning the functionality of the surface structure were made in vitro and in vivo. Scanning electron microscope observations revealed that the pore size and interconnective porous architecture of the surface layer of the fibre-reinforced composite (FRC) could be optimal for bone ingrowth. Microhardness measurements showed that the solvent treatment did not have an effect on the mechanical properties of the load-bearing core. A push-out test, using dental stone as a bone model material, revealed that short glass fibre-reinforced porous surface layer is strong enough to carry load. Unreacted monomers can cause the chemical necrosis of the tissue, but the levels of leachable resisidual monomers were considerably lower than those found in chemically cured fibre-reinforced dentures and in modified acrylic bone cements. Animal experiments proved that surface porous FRC implant can enhance fixation between bone and FRC. New bone ingrowth into the pores was detected and strong interlocking between bone and the implant was achieved.

Use of fiber-reinforced composite framework and thermochromic pigment in maxillofacial prostheses

The purpose of this investigation was to evaluate the possibility to enhance certain qualities of facial prostheses. Polymethyl methacrylate is still being used as base mate¬rial or clip carrier material, but it is hard and heavy, and debonding of the silicone from the acrylic base material is a frequent problem. This thesis aims to evaluate the use of fiber-reinforced composite (FRC) as framework material for maxillofacial silicone prostheses. FRC has been used as reinforcement in removable and fixed partial dentures since the 1990s. This material is lightweight and can be fabricated to compress the margins of the prosthesis slightly, to keep it tightly against the skin during jaw movements and facial expressions. Additionally, the use of a thermochromic pigment, colorless in room temperature and red in a cold environment, was studied in order to evaluate the possibility of using this color changing pigment in facial prostheses to mimic the color change of facial skin in cold weather. The tensile bond strength between pre-impregnated, unidirectional FRC and maxillofacial silicone elastomer was studied. Three different bonding agents or primers were compared. Bond strength was improved by one of the primers and by roughening the surface. The effect of a skin compressing glass fiber-reinforced composite framework on facial skin blood flow was studied by using a face mask, constructed with a compression pad corresponding to the outer margin of a glass fiber-reinforced framework beam of a facial prosthesis. The skin blood flow of ten healthy volunteers, aged 23-25 years, was measured during touch, light, and moderate compression of the skin, by using laser Doppler imaging technique. None of the compressions showed any marked effects on local skin blood flow. There were no significant differences between blood flow during compression and at baseline. Maxillofacial silicone elastomer was colored intrinsically with conventional color pigments: a control group containing only conventional pigments was compared to two test groups with 0.2 wt% and 0.6 wt% thermochromic pigment added. The color of the material was measured with a spectrophotometer in room temperature and after storage in a freezer. The color stability of the maxillofacial silicone elastomer colored with thermo¬chromic pigment was evaluated by artificial aging. The color dif¬ference of the L* (lightness) and a* values (redness), comparing color after the samples were stored at room temperature and in a freezer (-19°C), was statistically significant for both 0.2 wt% and 0.6 wt% thermo¬chromic pigment groups. The differences in the b* values (yellowness) were statistically significant for the 0.6 wt% group. Exposure to ultraviolet (UV) radiation led to visually noticeable and statistically signifi¬cant color changes (ΔE) in all color values in both test groups. The specimens containing thermochromic pigment were very sensitive to UV radiation. In conclusion, a framework of fiber-reinforced composite can successfully be bonded to maxillofacial silicone elastomer, and a framework beam, compressing the facial skin, did not remarkably alter the skin blood flow on healthy, young adults. The thermochromic pigment showed color change in maxillofacial silicone elastomer. However, artificial aging showed that it was too sensitive to UV radiation to be used, as such, in maxillofacial prostheses.

Photosensitivity of Laser Dye Mixtures in Polymer Matrix – A Photoacoustic Study

Laser induced photoacoustic (PA) technique is used in the study of photostability of polymethyl methacrylate (PMMA) films doped with Rhodamine 6G -Rhodamine B dye system. Energy transfer from a donor molecule to an acceptor molecule in a dye mixture affects the output of the dye system. Details of investigations on the role of laser power, modulation frequency and the irradiation wavelength on the photosensitivity of the dye mixture doped PMMA films are presented.

Propagation characteristics and wavelength tuning of amplified spontaneous emission from dye-doped polymer.

The propagation characteristics of amplified spontaneous emission (ASE) through a rhodamine 6 G-doped polymethyl methacrylate freestanding film waveguide were studied. This was done by shifting the excitation stripe horizontally along a transversely pumped waveguide. By this method, we could tune the ASE wavelength. The maximum tunability thus obtained was ~18 nm with a pump stripe length of 6 mm.

Nanosecond optical limiting response of sandwich-type neodymium dyphthalocyanine in a co-polymer host

The nanosecond optical limiting characteristics of sandwich-type neodymium diphthalocyanine in a co-polymer matrix of polymethyl methacrylate (PMMA) and methyl-2-cyanoacrylate have been studied for the first time. The measurements were performed using 9 ns laser pulses generated from a frequency-doubled Nd:YAG laser at 532 nm wavelength. The optical limiting performance of neodymium diphthalocyanine in co-polymer host was studied at different linear transmission. Laser damage threshold was also measured for the doped and undoped co-polymer samples. The optical limiting response is attributed to reverse saturable absorption which is due to excited-state absorption.

Capillary electrophoresis characterisation of a rapid prototyped PMMA chip for particle analysis

Màster en Nanociència i Nanotecnologia

Factores asociados a infección de fracturas abiertas de extremidades por accidentes de tránsito. Bogotá, 2012-2013

Los traumatismos por accidentes de tránsito, constituyen un problema de salud pública, a nivel mundial. Las lesiones más frecuentes son las fracturas de extremidades (84.3%). Las fracturas tienen un elevado riesgo de presentar infecciones, secuelas e incapacidades permanentes. Objetivo : Determinar si los factores asociados con la patología (lugar de fractura, clasificación de fractura, comorbilidades del paciente) y/o los factores relacionados con la atención médica (uso de profilaxis antibiótica diferente al protocolo institucional, tiempo prolongado para remisión, demoras en manejo quirúrgico) se asocian a mayor probabilidad de presentar infección de fracturas abiertas, en población mayor a 15 años, atendidos por accidente de tránsito, en una clínica de Bogotá de tercer nivel especializada en atención de SOAT, durante el período Octubre de 2012 a Octubre de 2013. Metodología: Estudio de casos y controles no apareado, relación 1:3, conformado por 43 casos (fracturas abiertas infectadas) y 129 controles (fracturas abiertas no infectadas). Resultados: La edad media de los casos fue de 39.42 +/- 16.82 años (med=36 años) y la edad media de los controles fue de 33.15 +/- 11.78 años (med=30 años). El 83.7% de los casos y el 78.3% de los controles corresponden al sexo masculino. Predominaron los accidentes en motocicleta en el 81.4% de los casos y el 86% de los controles. En el análisis bivariado se encuentra que la edad mayor a 50 años (p=0.042), una clasificación de la fractura grado IIIB o IIIC (p=0.02), cumplimiento del protocolo antibiótico institucional según el grado de fractura (p=0.014) y un tiempo mayor a 24 horas desde el momento del accidente al centro especializado en trauma (p=0.035) se asociaron significativamente con infección de la fractura abierta. En el análisis multivariado se encuentra únicamente que la clasificación de la fractura grado IIIB o IIIC se asocia con infección de la fractura OR 2.6 IC95% (1.187 – 5.781) (p=0.017). La duración de hospitalización fue mayor en los casos (32.37+/- 22.92 días, med=26 días) que en los controles (8.81 +/- 7.52 días, med=6 días) (p<0.001). El promedio de lavados quirúrgicos fue mayor en los casos (4.85±4.1, med=4.0) que en el grupo control (1.94±1.26, med=2) (p<0.001). Conclusiones: La infección posterior a una fractura abierta, implica costos elevados de atención con hospitalizaciones prolongadas y mayor frecuencia de intervenciones quirúrgicas como se evidencia en el presente estudio. Se debe fortalecer el sistema de remisión y contra remisión para acortar los tiempos de inicio de manejo especializado de los pacientes con fracturas abiertas. Se debe incentivar dentro de las instituciones, el cumplimiento de protocolos de profilaxis antibiótica según el grado de la fractura para disminuir el riesgo de complicación infecciosa.

Feedback dew-point sensor utilising optimally cut plastic optical fibres

A plastic optical fibre reflectance sensor that makes full use of the critical angle of the fibres is implemented to monitor dew formation on a Peltier-cooled reflector surface. The optical configuration permits isolation of optoelectronic components from the sensing head and better light coupling between the reflector and the detecting fibre, giving a better signal of the onset of dew formation on the reflector. Continuous monitoring of the rate of change in reflectance as well as the absolute reflectance signals, the use of a novel polymethyl-methacrylate-coated hydrophobic film reflector on the Peltier element and the application of feedback around the point of dew formation, further reduces the possibility of contamination of the sensor head. Under closed-loop operation, the sensor is capable of cycling around the point of dew formation at a frequency of 2.5 Hz.

Phase separated structures in tethered dPS–PMMA copolymer films revealed using X-ray scattering with a novel contrast enhancement agent

Tethered deuterated polystyrene-block-polymethyl methacrylate films have been examined by X-ray scattering both in their native state and following treatment with ruthenium tetroxide. The use of the stain, while increasing the thickness of the films, does not significantly alter the lateral structure or periodicity of the films and provides contrast between the two blocks. Both the periodicity of the films and the structure normal to the surface have been identified following staining. Experiments were also performed on films treated by a solvent exchange process, and the effects of staining on these films are discussed.

Phase separation in thin films of end-grafted block copolymers

An atomic force microscopy investigation was carried out on various thick (30–120 nm) polymethyl methacrylate-bpolystyrene and poly(2-(dimethyl amino)ethyl methacrylate)-b-polystyrene films prepared via a grafting-from method. The structure of the films was examined with both topographic and phase imaging. Several different morphologies were observed including a perforated lamellar phase with irregular perforations. In addition, complementary small-angle X-ray scattering and reflectometry results measurements on a non-grafted polymer are presented.

Simple solution for a complex problem: Proanthocyanidins, galloyl glucoses and ellagitannins fit on a single calibration curve in high performance-gel permeation chromatography

This study was undertaken to explore gel permeation chromatography (GPC) for estimating molecular weights of proanthocyanidin fractions isolated from sainfoin (Onobrychis viciifolia). The results were compared with data obtained by thiolytic degradation of the same fractions. Polystyrene, polyethylene glycol and polymethyl methacrylate standards were not suitable for estimating the molecular weights of underivatized proanthocyanidins. Therefore, a novel HPLC-GPC method was developed based on two serially connected PolarGel-L columns using DMF that contained 5% water, 1% acetic acid and 0.15 M LiBr at 0.7 ml/min and 50 degrees C. This yielded a single calibration curve for galloyl glucoses (trigalloyl glucose, pentagalloyl glucose), ellagitannins (pedunculagin, vescalagin, punicalagin, oenothein B, gemin A), proanthocyanidins (procyanidin B2, cinnamtannin B1), and several other polyphenols (catechin, epicatechin gallate, epicallocatechin gallate, amentoflavone). These GPC predicted molecular weights represented a considerable advance over previously reported HPLC-GPC methods for underivatized proanthocyanidins. (C) 2011 Elsevier B.V. All rights reserved.

Bond strength between acrylic resin and maxillofacial silicone

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Measurement of Interfacial Porosity at the Acrylic Resin/Denture Tooth Interface

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effect of water storage and heat treatment on the cytotoxicity of soft liners

Objective: To evaluate the effect of water storage time on the cytotoxicity of soft liners.Methods: Sample discs of soft liners Dentusoft, Dentuflex, Trusoft, Ufi-Gel-P and denture base acrylic resin Lucitone-550 were prepared and divided into four groups: GN: No treatment, G24: Stored in water at 37 degrees C for 24 h; G48: Stored in water at 37 degrees C for 48 h, GHW: Immersed in water at 55 degrees C for 10 min. To analyse the cytotoxic effect, three samples of each group were placed in tubes with Dubelcco's Modified Eagle Mediums and incubated at 37 degrees C for 24 h. During this period, the toxic substances were leached to the culture medium. The cytotoxicity was analysed quantitatively by the incorporation of radioactivity H-3-thymidine checking the number of viable cells (synthesis of DNA). The data were statistically analysed using two-way ANOVA and Tukey's honestly significant difference tests (alpha = 0.05).Results: Treatments did not reduce the cytotoxicity effect of the soft liners (p > 0.05). It was found that Ufi-Gel-P had a non-cytotoxic effect, Trusoft had a slightly cytotoxic effect, Dentuflex had a moderated cytotoxic effect, Dentusoft alternated between slightly and non-cytotoxic effect, and Lucitone-550 had non-cytotoxic effect when stored in water for 48 h.Conclusion: The effect of water storage and the heat treatment did not reduce the cytotoxicity of the soft liners.