A. Ulatowska-Jarża

Investigations on photolon-and porphyrin-doped sol-gel fiberoptic coatings for laser-assisted applications in medicine

In view of laser-assisted medical applications, the construction of silica-based sol-gel fiberoptic sensors based on photolon (Ph) and protoporphyrin IX (PP IX) is discussed. Electron microscopy and AFM were used to characterize the silica sol-gel coatings. AFM measurements indicate a change in the surface porosity. The PP IX-based sensors were constructed as a one-layer optode as well as a multilayered structure. An additional hybrid sensor made up of alternate layers of PP IX-and Ph-doped sol-gel was also constructed and examined. Sol-gel matrices were prepared from silicate precursor tetraethylorthosilicate (TEOS) mixed with ethanol in acid-catalyzed hydrolysis. The carrier matrices of photosensitive dyes were produced with factor R = 20, where R denotes the ratio of solvent moles (ethanol) to the number of TEOS moles. A multilayered coating was built up using the reverse-dipping technique. The overall coating thickness was determined by electron microscopy. Doped sol-gels with different PP IX concentrations were used to produce fiberoptic coatings. The film optodes with a different number of layers were examined by fluorescence spectroscopy. It was found that photolon and protoporphyrin IX entrapped in sol-gel preserve their chemical reactivity and have contact with the external environment. The hybrid sensor demonstrated clear fluorescence and a reversible behavior in gaseous environments.

SOL-GELS FOR OPTICAL SENSORS

Sol-gel process allows for formation of glassy and ceramics materials in temperatures much lower than offered by conventional melting techniques. The first paper on sol-gels was published over 150 years ago by Ebelmen 1 , however, the rapid development of this technology and applications occurred in the last few years. There is a broad range of possible applications of solgel derived materials, what marked this technology as one of the most promising fields of contemporary material sciences 2-5 . Various materials can be produced by sol-gel methods: monoliths, thin films, fibers, powders can. Controlling of the physical and chemical parameters of production process yields materials with precisely tailored parameters such as mechanical strength, transparency, size and distribution of the pores network 7 . The sol-gel derived materials may provide excellent matrices for a variety of organic and inorganic compounds.

Optical properties of sol-gel fiber optic applicators for laser interstitial therapy

A new type of applicator for interstitial laser coagulation is proposed in this paper. The new fiber optic applicator is made by removing the original fiber cladding and replacing it with a sol-gel coating. The sol-gel coating was prepared from the silicate precursor TEOS (tetraethylorthosilicate), mixed with ethanol in acid, which catalyzes hydrolysis. The material is produced with the factor R = 20, where R denotes the number of solvent moles to the number of TEOS moles. In these studies, optical fibers were used from Laser Components (core diameter 400 µm, HCS, low OH). The external jacket was mechanically removed, leaving a remaining 2-cm length of bare fiber. The modified dip-coating method was used to cover the bare fibers with sol-gel material. Two types of applicators were produced: pure sol-gel coated devices and applicators with sol-gel coating doped with photosensitive dyes. The photodynamic activity of chlorophyll-based Photolon and Protoporphyrin IX (PPIX) incorporated within the sol-gels was studied spectrophotometrically. It was demonstrated that sol-gel applicators are capable of performing laser interstitial coagulation using a semiconductor cw laser at 980 nm. It was also demonstrated that the incorporated photosensibilizers retain their photochemical activity.

Advantages of sol-gel technologies for biomedical applications

Sol-get techniques have become very popular recently due to their high chemical homogeneity, low processing temperatures, and the possibility of controlling the size and morphology of particles. The sol-gel-derived materials provide excellent matrices for a variety of organic and inorganic compounds. One of the most important features of doped sol-gel materials is their ability for preservation of chemical and physical properties of the dopants. This feature marks those materials as almost unique hosts for a number of biologically important molecules which can be utilized in a number of biomedical applications. The advantages of sol-gel technology used for construction of biomedical sensors, laser materials or for delayed drug delivery, will be discussed.

Performance repeatability of fiberoptics applicators for laser therapy

The distribution of light emitted from the sol-gel coated fiberoptic applicator for interstitial laser therapy was examined. The silica sol-gel coatings were prepared from silicate precursor TEOS (tetraethylorthosilicate) mixed with ethyl alcohol in acid catalyzed hydrolysis. The applicator was produced with ratio R = 20, whereas R denotes the number of solvent moles (ethanol) to the number of TEOS moles. Then, the light pattern was captured by means of CCD camera and statistical pattern recognition method was applied to study the repeatability of light distribution. Two methods were applied: Fisher Linear Discriminant Analysis (FLDA) and Principal Component Analysis (PCA). The top match characteristic TM as calculated by statistical pattern recognition methods was taken as a factor corresponding to the performance repeatability. It was demonstrated that is possible to produce the sol-gel applicators with more than 92% repeatability.

Examination of light distribution from sol-gel based applicators for interstitial laser therapy

We describe here the construction of sol-gel based applicators for interstitial thermotheraphy. The silica sol-gel coatings were prepared from silicate precursor TEOS (tetraethylorthosilicate) mixed with ethyl alcohol in acid catalyzed hydrolysis. The matrices were produced with various ratios R=5, 10, 20, 32, 50, whereas R denotes the number of solvent molds (here ethanol) to the number of TEOS moles. The spatial light intensity distribution was examined in order to find out the influence of R factor on the light distribution shape. It was shows that the most homogeneous patterns are observed for sol-gel coatings with R factors equal 10 and 20.

Examination of light distribution from fibers coated with sol-gel films doped with porphyrine

The modification of optical fibers by exploiting various coatings may be important for construction of fiberoptics, sensors or applicators for interstitial laser therapy. We report here on sol-gel films placed on fiber cores, replacing the original fiber coatings. The silica sol-gel coatings where prepared form silicate precursor TEOS (tetraethylorthosilicate) mixed with ethyl alcohol in acid catalyzed hydrolysis. The matrices were produced with various ratios R=5, 15, 20, 32, 40, 50, whereas R denotes the number of solvent moles (here ethanol) to the number of TEOS moles. Two types of coatings were produced: pure sol-gel matrices and sol-gel doped with Protophyrin IX in two various concentrations. The angular light intensity distribution was examined in order to find out the influence of R factor on the light intensity distribution near the fiber tip. Then, the light pattern was captured by means of CCD camera and the three dimensional luminances were calculated. The same experiments were repeated for silica sol-gel coatings doped with natural porphyrine Protoporphyrine IX and different patterns were observed.

Photoactive sol-gel biocoatings

In this work we investigated the photoactive properties sol-gel biocoatings doped with Protoporphyrin IX (PP IX). It was demonstrated that PP IX entrapped in sol-gel preserves its chemical activity and may have contact with the external environment. The chemical reactions with zinc cations and pyridine, as well as protonation, occurred quite fast. This indicates, that the interconnected porous network could be easily penetrated by relatively large molecules (e.g. mentioned by pyridine molecule). Further, we observed that PP IX molecules do not leave the pores. Structural changes caused by the addition of PP IX to the sol-gel matrix influence not only on the optical properties, but also on durability of the coatings. The altering of PP IX doped silica sol-gel coatings is quite slow.

Sol-gel optics for biomeasurements

Sol-gel technique is a method for producing of glass-like materials without involving a melting process. Organic compounds such as alcoholates of silicon, sodium or calcium can be used. The irregular non-crystalline network forms a gel structure where the metallic atoms are bonded to oxygen atoms. Low-temperature treatment turns this gel into an inorganic glass-like structure. There are numbers of applications of these materials that can be produced in various forms and shapes. Here, silica based sol-gel bulks and thin films optodes for biomedical applications will be presented.

Examination of the haemolytic activity of sol-gel materials

Recently, the sol-gel based biomaterials are extendedly investigated with emphasis on theirs various applications, including medical ones. In this respect it is important to investigate the influence of sol-gel matrices on biological systems. The results of laboratory and biological testing of aqueous extracts of sol-gels are presented in this work. It was proved that it is possible to produce the sol-gel derived materials that will be non-haemolytic. This can be achieved by heating the materials in elevated temperatures. This effect can also be reached by suitably long aging (minimum 6 months).