Biomedical Engineering – From Theory to Applications

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364 Biomedical Engineering – From Theory to Applications can be used to predict the usefulness of a certain compound as photosensitizer. This is explained by the fact that the peripheral substitution does not significantly disturb the inner π electron ring of the porphyrinic macrocycle, which is responsible for the active electronic transitions in the above mentioned spectral range. 3.1.2 Emission properties Photodetection for tissue characterization in cancer is not new, the first study being reported by Policard in 1924, who noticed the fluorescence of a tumor under illumination with UV light. This fluorescence was considered to originates from tumor’s endogenous porphyrins (Masilamani et al., 2004). Some of the most important aspects of metaloporphyrins are connected to the photophysical characteristics of porphyrins in different media: fluorescence quantum yields (Φf) and fluorescence lifetimes (τf ). Fluorescence emission characteristics of porphyrinic compounds are also important features for the biomedical use of porphyrins. In case of their use in photodiagnosis, emission characteristics as fluorescence quantum yields and/or fluorescence lifetimes are of importance to differentiate the signal of the fluorescent marker from the fluorescence of the environmental matter. In case of PDT, all deactivation processes (fluorescence, phosphorescence, internal conversion, collisional quenching) play an important role in the very process of ROS generation (Fig. 3). Despite significant advantages, the porphyrinic compounds as photosensitizers have limitations. Due to the large conjugate systems, they easily form aggregates, which have a significantly lower ability to form reactive oxygen species and consequently decrease the photodynamic activity. In recent years, nanostructured materials such as liposomes, nanoparticles and micelles have been considered as potential carriers for porphyrinic compounds that may resolve the aforementioned problems. The presence of polar headgroups and hydrophobic chains in micellar structures allows the study of the potential affinity of a porphyrinic structure to cell-membrane type structures. 3.2 Main features for an efficient photosensitizer There is a great deal of interest in design and synthesis of new photosenzitizers with porphyrinoid structures, with improved characteristics that make worth their investigation as possible new PDT drugs. The general characteristics of a good sensitizer, displayed as basic requirements, are presented in Table 1. For photosensitizers designed to kill cancer or other mammalian cells, it has been found that their intracellular localization is another important parameter. For example, the photosensitizers which localize in mitochondria seem to be more powerful in killing cells than those locating in lysosomes (Mroz et al., 2009). Porphyrins are essential constituents of important biological systems. The porphyrin-type nucleus, along with metal ions, is found in cytochromes, peroxidases and catalases. Other biologically important porphyrins that occur in nature and in the human body are hemin (an iron porphyrin - the prosthetic group of hemoglobin and myoglobin), chlorophyll (magnesium porphyrin-like compound involved in plant photosynthesis), and vitamin B12 (cobalt porphyrin-like compound, commonly known as cobalamine). As a result of their vital role in biologic processes, metallo-porphyrins have always attracted chemist’s attention. Porphyrins proved to be valuable photosensitizers since they are non-toxic, are selectively retained in tumors, are cleared in a reasonable time from the body and skin, and thus photosensitive reactions are minimized. Moreover, porphyrins have got convenient
Trends in Interdisciplinary Studies Revealing Porphyrinic Compounds Multivalency Towards Biomedical Application amphiphilicity which renders them more photodynamically active than symmetrically hydrophobic or hydrophilic molecules. Required features Details Purity Substance of known composition, stable at room temperature Toxicity, overdosage, and side effects - Minimal toxicity in the absence of light - Cytotoxic in the presence of light of defined wavelength - Non- toxic metabolites; - Minimal side effects Absorption, distribution, Optimum ADME properties metabolism and excretion (ADME) Activation in the phototherapeutical window (600 to Activation and wavelength 850 nm) Singlet oxygen High singlet oxygen generation quantum yield () quantum yield Inexpensive Cost and availability Commercially available to allow extensive utilization - Good tumour/healthy tissue localization ratio Selectivity - Favourable subcellular localization to induce an apoptotic rather than a necrotic mode of cell death Mutagenicity/ Carcinogenicity Painless Combined treatment Multisession 365 Non-mutagenic Non-carcinogenic No pain during the procedure or in the following treatment stages No adverse interactions with other drugs or medical procedures Possibility for application in repeated sessions, without immunosuppressive effects Carriers Possibile formulation with different carriers Multivalency Marker and molecular beacon Upgradable chemical structures Table 1. Required features for an efficient photosensitizer Multiple effects desired (antitumoral and antimicrobial, antitumor and diagnosis) Marker or beacon The structure can be easily improved by simple chemical reactions 3.3 Timeline in the development of porphyrinoid photosensitizers Porphyrins were identified in the mid-nineteenth century, but it was not until the early twentieth century that they were used in medicine.
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BIOMEDICAL ENGINEERING - FROM THEOR
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free online editions of InTech Book
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VI Contents Chapter 9 Targeted Magn
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X Preface stand-alone and readers c
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2 Biomedical Engineering - From The
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4 Fig. 2. Process for retrieval inf
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6 Biomedical search engine Scientif
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12 Bireme http://regional.bv salud.
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14 Semantic Networks analysis Biome
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100 Biomedical Engineering - From T
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108 Method (Detection) CIEF-tITP-CZ
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110 Method (Detection) Analyte Matr
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120 6. Conclusion Biomedical Engine
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150 5. Conclusions Biomedical Engin
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162 1 st phase : half year 4 2 nd p
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166 7. Innovative active training B
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172 12. Maturing projects’ story
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180 16. Acknowledgments Biomedical
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190 R* M M M M MR*M O O O O M O R*
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196 Fig. 9. Chemical structure of 5
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198 Relative Intensity (AU) Biomedi
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204 2. Preparation of IO nanopartic
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256 3. Deposition techniques Biomed
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300 2. Nanoparticles in biomedical
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454 In this case, the eigenvalues a
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456 where Biomedical Engineering -
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472 Nb b b l l1 Biomedical Engineer
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478 Load F (μN) Parallel-oriented
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