Dynamic behavior of a comb-driven torsional microscanner is governed by a nonlinear parametric differential equation. Theoretically, such systems have multiple resonances located near the integer fractions of twice the mechanical resonance frequency. The number of observable parametric resonances strongly depends on the damping of the system, whereas the stable and unstable operating regions are determined by drive-voltage and drive-frequency. In atmospheric pressure, only first few of these parametric resonances are observable within the operation voltage range of the devices. This paper explores the effect of damping on the various characteristics of parametric resonances and some unusual scanner behavior rarely seen in mechanical structures. A numerical and an analytical model for comb-driven microscanners are presented. Frequency responses of various devices are experimentally measured inside a vacuum chamber at different ambient pressures ranging from atmospheric pressure to 30 mTorr. Experimental results are compared with analytical and simulation results.

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Achieving repeatable and successful results without causing excessive collateral damage is of paramount importance for photothermal laser applications. Predetermined laser parameters cannot ensure patient safety and treatment success due to variance between optical and thermal characteristics among subjects. Controlling laser irradiation with tissue temperature feedback is the current gold standard for various photothermal treatments (PTT) which are rate processes described by the Arrhenius temperature integral. This study establishes the validity of our low-cost design that makes tissue surface temperature control during photothermal laser applications more accessible in resource limited clinical environments. We demonstrated the practical performance and potential of our system with ex-vivo bovine liver irradiation using an ytterbium fiber laser (λ=1071nm) with two independent variables: laser power (3.4, 6.8 and 10.2W) and target surface temperature (55, 65 and 75∘C). Our system efficiently maintained tissue surface temperatures at target values in all laser power groups. In contrast, fixed-dose application groups displayed a high final temperature range and variation in the control experiment. Temperature–time responses of samples varied significantly, in agreement with a wide range of optical and thermal coefficients. Long exposure duration groups (lower power, higher target temperature) displayed more radical differences suggesting a dominance of optical and thermal characteristics over the response. The low-cost surface-temperature-controlled medical laser system we have developed is capable of ensuring the success and reproducibility of PTT modalities and patient safety.

ÖzetçeFotodinamik terapi (FDT) kanser tedavisinde belirli bir dalga boyundaki ışığa hassasiyeti olan bir kimyasal ajan ve laser ışıması kullanılarak uygulanan ve girişimsel olmayan bir tekniktir. Çalışmamızda, düşük konsantrasyonda (5 µg/ml) indosiyanin yeşil (İSY) ile uygulanan FDT'nin nöroblastoma hücre dizileri (SH-SY5Y) üzerindeki etkisi araştırılmıştır. İSY'nin hücre dizilerine (n = 7) uygulanmasının ardından, hücreler 24 saat inkübe edilmiş ve 60 J/cm 2 dozunda, sürekli dalga modunda laser ışıması (λ = 809 nm, 100 mW/cm 2 ) ile FDT gerçekleştirilmiştir. Uygulama esnasında bir kuyucuk içine odaklanmış kızılaltı ısıl-çift sensör kullanılarak sıcaklık monitörizasyonu yapılmış ve sıcaklıkta bir artış tespit edilmemiştir. Hücre canlılığı XTT testi ile belirlenmiştir. Laser, İSY ve İSY-FDT gruplarının hücre canlılığında istatistiksel olarak anlamlı bir azalma tespit edilmiştir. İSY-FDT grubunda kontrol grubuna göre hücre canlılığındaki bu azalmanın yaklaşık %83 oranında olduğu belirlenmiştir (p<0.01). İSY-FDT uygulaması nöroblastoma hücre dizilerinde sitotoksik etki göstermiştir. İdeal İSY konsantrasyonlarının ve laser parametrelerinin belirlenmesi amacıyla daha fazla bilimsel çalışma yapılmalıdır. AbstractPhotodynamic therapy (PDT) is a noninterventional technique used for cancer treatment. It makes use of a chemical agent sensitive to a specific wavelength of light and corresponding laser exposure. In our study, the effect of PDT with low concentration (5 µg/ml) indocyanine green (ICG) on the neuroblastoma cell lines (SH-SY5Y) was investigated. The cell lines (n = 7) were incubated for 24 hours after the administration of ther ICG. PDT was achieved with continuous wave laser irradiation (λ = 809 nm, 100 mW/cm 2 ) for a dose of 60 J/cm 2 . An infrared thermocouple sensor was focused in one of the wells for thermal monitoring. Temperature increase was not observed in any group during the treatment. Cell viability was measured by XTT assay. Laser, ICG and ICG-PDT groups showed a statistically significant decrease in cell viability. The cell viability decrease in ICG-PDT group was determined as approximately 83% in comparison to the control group (p<0.01). ICG-PDT treatment has cytotoxic effects on neuroblastoma cell lines. Further research on this subject should focus on determining the ideal ICG concentrations and laser parameters.

Photodynamic therapy (PDT) is a minimally invasive treatment for cancer therapy. It can be administered in combination with other treatments such as chemotherapy, radiotherapy, and surgical excision. PDT involves a photosensitizing agent that is activated by exposure to a specific wavelength of light. PDT is a cold photochemical process, there is no tissue heating. In our study, we investigated whether different laser parameters with different concentrations of indocyanine green (ICG) have cytotoxic and anti-proliferative effects on neuroblastoma. Plates were divided groups as control, only ICG concentrations (25 and 50 µg/ml), only laser treatment I (50 J/cm 2 ), only laser treatment II (100 J/cm 2 ), 25 µg/ml ICG + laser treatment I and 25 µg/ml ICG + laser treatment II, 50 µg/ml ICG + laser treatment I and 50 µg/ml ICG + laser treatment II. Neuroblastoma cell lines were irradiated with an in-house developed diode laser system (λ = 809 nm, 70 mW/cm 2 , 50 & 100 J/cm 2 ) in continuous wave operation mode after ICG application. Cell proliferation was measured by XTT assay after light irradiation. Cell proliferation was decreased in a dose-dependent manner in 25 and 50 µg/ml ICG concentrations when compared with control. The applied ICG concentrations (especially 50 µg/ml) had cytotoxic effects for neuroblastoma cell lines, SH-SY5Y. There was no difference between laser treatment groups (L 50 & 100 J/cm 2 ). However, PDT groups (laser exposure with ICG) showed significant inhibition of cell viability (p < 0.05). Additionally, laser exposure did not increase the well temperature above the incubation parameter. In conclusion, PDT has cytotoxic effects in neuroblastoma cell lines. Appropriate ICG dose -laser parameter combinations must be determined for each cell type. Different energy densities may cause different effects of PDT on inhibition of cell viability.