Vitor Baranauskas

Low-power laser irradiation improves histomorphometrical parameters and bone matrix organization during tibia wound healing in rats

The influence of daily energy doses of 0.03, 0.3 and 0.9 J of He-Ne laser irradiation on the repair of surgically produced tibia damage was investigated in Wistar rats. Laser treatment was initiated 24 h after the trauma and continued daily for 7 or 14 days in two groups of nine rats (n=3 per laser dose and period). Two control groups (n=9 each) with injured tibiae were used. The course of healing was monitored using morphometrical analysis of the trabecular area. The organization of collagen fibers in the bone matrix and the histology of the tissue were evaluated using Picrosirius-polarization method and Massons trichrome. After 7 days, there was a significant increase in the area of neoformed trabeculae in tibiae irradiated with 0.3 and 0.9 J compared to the controls. At a daily dose of 0.9 J (15 min of irradiation per day) the 7-day group showed a significant increase in trabecular bone growth compared to the 14-day group. However, the laser irradiation at the daily dose of 0.3 J produced no significant decrease in the trabecular area of the 14-day group compared to the 7-day group, but there was significant increase in the trabecular area of the 15-day controls compared to the 8-day controls. Irradiation increased the number of hypertrophic osteoclasts compared to non-irradiated injured tibiae (controls) on days 8 and 15. The Picrosirius-polarization method revealed bands of parallel collagen fibers (parallel-fibered bone) at the repair site of 14-day-irradiated tibiae, regardless of the dose. This organization improved when compared to 7-day-irradiated tibiae and control tibiae. These results show that low-level laser therapy stimulated the growth of the trabecular area and the concomitant invasion of osteoclasts during the first week, and hastened the organization of matrix collagen (parallel alignment of the fibers) in a second phase not seen in control, non-irradiated tibiae at the same period. The active osteoclasts that invaded the regenerating site were probably responsible for the decrease in trabecular area by the fourteenth day of irradiation.

Enhancement of diamond nucleation using the solid-liquid-gas interface energy

We demonstrate the enhancement of diamond nucleation through the use of the equilibrium forces at the solid-liquid-gas interface on a substrate wetted with droplets of an oil of low vapor pressure. Such a process is shown to produce well-faceted grains with densities of roughly 107 nuclei cm−2 (boundary), 105 nuclei cm−2 (oil-coated area), and 104 nuclei cm−2 (uncoated area) without the need for scratching or seeding the substrate. Diamond deposition was undertaken on silicon using ethanol and hydrogen in the feed of a hot-filament chemical vapor deposition reactor. The oil-covered regions, in addition to showing higher nucleation densities, have the merit that the intergrain spaces are covered with diamond structures, while the parts uncovered with oil exhibit intergrain spaces covered with diamond-like carbon.

Laser effects on osteogenesis

The traumatic or surgical cutting of a long bone is immediately followed by a sequence of repair processes in which the osteogenic cells of the periosteum start to proliferate and differentiate in osteoblast cells. In this work, we explored the influence of a He–Ne laser on osteogenesis after a controlled surgical fracture. We used young male adult Wistar rats (of mass between 250 and 300 g). The fracture was provoked by piercing a 2-mm-diameter hole in just one cortical tibia surface. Laser treatment was started 24 h after the surgery. The animals were separated into three groups, for different radiation doses, and after daily applications, they were sacrificed at 8 or 15 days. Light and electron microscopies revealed that the laser treatment of the lesion with doses of 31.5 and 94.7 J cm−2 resulted in the formation of thicker bony trabeculae, which indicates a greater synthesis of collagen fibers and therefore that the osteoblastic activity was increased by the low-energy laser radiation.

Laser‐induced chemical vapor deposition of polycrystalline Si from SiCl4

Polycrystalline Si films with average grain sizes of ∼8 μm have been grown by laser‐induced chemical vapor deposition from SiCl4. A cw CO2 laser operated at 10.6 μm was used to provide local heating of quartz substrates in an otherwise cool reactor to initiate the endothermic decomposition reaction. Deposition rates of 5.1 μm/min were obtained for films grown at an incident laser power of 18.9 W, resulting in sharply defined mesa structures due to the occurrence of the reverse reaction, etching of free Si, at cooler regions of the substrate surface closer to the edge of the 6‐mm irradiated zone. The diameter of the mesas was 1.4 mm with thicknesses up to 26 μm. Three modes of film growth, depending on the incident laser power, were observed.

Nitrogen-doped diamond films

We found that very high concentrations (up to 20% vol) of nitrogen in the ethanol/hydrogen gas mixture do not prejudice the diamond quality as determined by Raman spectroscopy. Nitrogen addition also increases the diamond growth rate, as was previously reported at low nitrogen concentrations. We observed that after a second heating cycle in air at temperatures between 300 and 673 K the electrical resistance versus temperature curves of the as-grown films presented a bulk semiconductor behavior. This stabilization was due to the oxidation of the as-grown hydrogenated surface. The electrical ionization energy Ed was found to be in the range of 1.62–1.90 eV corresponding to films produced with 0 to 20% vol nitrogen in the feed. The room temperature photoluminescence spectra of films produced at low nitrogen concentration suggest that Ed results from pure electronic transitions in the nitrogen-vacancy neutral defects; for samples produced with nitrogen concentrations in the range 15–20% vol the Ed values may ...

Direct observation of chemical vapor deposited diamond films by atomic force microscopy

Diamond polycrystals deposited by the hot‐filament chemical vapor deposition method on silicon (100) substrates have been examined by atomic force microscopy (AFM) in air. Measurements of the diamond unit cell show periodic spacings between 0.34 to 0.37 nm in a very good agreement with the theoretical value of the bulk constant of natural diamond (0.356 nm). Hybridized sp3 bonds can also be observed at the (111) surface.

Characterization of Langmuir-Blodgett films of parent polyaniline

Conducting Langmuir-Blodgett (LB) films have been fabricated from parent polyaniline (PAni) which was doped with functionalized acids. In order to optimize experimental conditions for the formation of stable Langmuir monolayers and their subsequent transfer onto solid substrates, PAni was dissolved in ten different combinations of chloroform solutions. Use was made of camphor sulfonic acid, dodecyl benzene sulfonic acid, and toluenesulfonic acid, and of the solvents N-methyl pyrrolidine and m-cresol as processing agents. Because acidic subphases have been employed, as-deposited LB films were already doped, which was confirmed by the appearance of a polaronic band in the UV-Vis absorption spectra. The absorbance peak increases with the number of deposited layers indicating that a suitable multilayer buildup is accomplished. When analysed by atomic force microscopy, PAni LB films show a fibrillar structure with the fibril width ranging from ≈60 to 160 nm.

The Ability of Low Level Laser Therapy to Prevent Muscle Tissue Damage Induced by Snake Venom

Antivenom therapy has been ineffective in neutralizing the severe local fast developing tissue damage following snakebite envenoming. Herein, some effects of in situ helium neon (HeNe) laser irradiation on rat nerve‐muscle preparation injected with Bothrops jararacussu venom are described. The tibialis anterior muscle was injected with venom diluted in 0.9% saline solution (60 μg/0.02 mL) or saline solution alone. Sixty minutes after venom injection, laser (HeNe) treatment was administered at three incident energy densities: dose 1, a single exposure of 3.5 J cm−2; dose 2, three exposures of 3.5 J cm−2; dose 3, a single exposure of 10.5 J cm−2. Muscle function was assessed through twitch tension recordings whereas muscle damage was evaluated through histopathologic analysis, morphometry of area of tissue affected and creatine kinase (CK) serum levels, and compared to unirradiated muscles. Laser application at the dose of 3.5 J cm−2 reduced the area of injury by 64% (15.9 ± 1.5%vs 44.2 ± 5.7%), decreased the neuromuscular blockade (NMB) by 62% (11.5 ± 2.5%vs 30.4 ± 5.2%) and reduced CK levels by 58% (from 455 ± 4.5% to 190.3 ± 23.4%) when compared with unirradiated controls. Dose 2 showed a poorer benefit than dose 1, and dose 3 was ineffective in preventing the venom effects. Measurements of the absorbance of unirradiated and irradiated venom solution showed no difference in absorption spectra. In addition, no difference in the intensity of partial NMB in nerve‐muscle preparation was shown by unirradiated and irradiated venom. The results indicate that the laser light did not alter venom toxicity. We conclude that HeNe laser irradiation at a dosage of 3.5 J cm−2 effectively reduces myonecrosis and the neuromuscular transmission blocking effect caused by B. jararacussu snake venom. Thus, low level laser therapy may be a promising tool to minimize the severity of some of the local effects of snake envenoming.

Columnar CVD diamond growth structure on irregular surface substrates

Abstract Columnar grain structure is always observed in CVD-diamond growth and is an important parameter to identify the morphology of thin and thick films. Structure defects, aspects of onset nucleation and film growth mechanisms can also be related to columnar growth. In this work we focused our attention on the columnar structure of CVD-diamond grown on irregular surfaces. We observed that there is a relationship among curvature radius of the substrate surface, the spread of the column volume and the growth rate of the diamond film. Growth rates on spherical surfaces of around 0.5 mm curvature radius have been observed to be up to three times bigger than the growth rates on planar surfaces. Also, the grain size distribution on planar and on the corner surfaces as a function of the growth rate has been studied. Characterization with scanning electron microscopy (SEM) and Raman scattering spectroscopy (RSS) has been performed.

Si ‐ SiO2 Electronic Interface Roughness as a Consequence of Si ‐ SiO2 Topographic Interface Roughness

Numerical calculations were used to assess the probable microscopic distribution of the electric field along or close to the actual Si-SiO 3 interface of a metal oxide semiconductor (MOS) capacitor biased into accumulation. Silicon wafers were oxidized to 20 nm at 1150°C by rapid thermal oxidation, according to two different thermal recipes in order to yield different Si-SiO 2 interface roughnesses. After oxide removal, typical atomic force microscopy (AFM) line scans of the silicon surface were exported into the MEDICI program as a description of the Si-SiO 2 , interface in order to calculate the electric field distribution within the oxide layer of a bidimensional MOS capacitor biased into accumulation. This distribution was found to be highly inhomogeneous even for relatively smooth Si-SiO 2 interfaces, displaying strong local electric field enhancements, the spatial distribution of which will be called electronic roughness in this work. Simple local oxide thinning at the position of the protrusions cannot account for these field enhancements, thus indicating that the shape of the protrusion is dictating the electronic roughness. The electronic roughness could be correlated with electric breakdown characteristics of actual MOS capacitors prepared on these wafers.