Browsing by Author "Khan, M."
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Item Open Access Combination of Paclitaxel and R-flurbiprofen loaded PLGA nanoparticles suppresses glioblastoma growth on systemic administration(Elsevier, 2020) Caban-Toktas, S.; Şahin, A.; Lule, S.; Esendagli, G.; Vural, İ.; Karlı-Oğuz, Kader K.; Söylemezoğlu, F.; Mut, M.; Dalkara, T.; Khan, M.; Capan, Y.Malignant gliomas are highly lethal. Delivering chemotherapeutic drugs to the brain in sufficient concentration is the major limitation in their treatment due to the blood-brain barrier (BBB). Drug delivery systems may overcome this limitation and can improve the transportation through the BBB. Paclitaxel is an antimicrotubule agent with effective anticancer activity but limited BBB permeability. R-Flurbiprofen is a nonsteroidal antienflammatory drug and has potential anticancer activity. Accordingly, we designed an approach combining R-flurbiprofen and paclitaxel and positively-charged chitosan-modified poly-lactide-co-glycolic acid (PLGA) nanoparticles (NPs) and to transport them to glioma tissue. NPs were characterized and, cytotoxicity and cellular uptake studies were carried out in vitro. The in vivo efficacy of the combination and formulations were evaluated using a rat RG2 glioma tumor model. Polyethylene glycol (PEG) modified and chitosan-coated PLGA NPs demonstrated efficient cytotoxic activity and were internalized by the tumor cells in RG2 cell culture. In vivo studies showed that the chitosan-coated and PEGylated NPs loaded with paclitaxel and R-flurbiprofen exhibited significantly higher therapeutic activity against glioma. In conclusion, PLGA NPs can efficiently carry their payloads to glioma tissue and the combined use of anticancer and anti-inflammatory drugs may exert additional anti-tumor activity.Item Open Access Optimization of a collapsed mode CMUT receiver for maximum off-resonance sensitivity(Institute of Electrical and Electronics Engineers, 2018-07-28) Khan, M.; Khan, T. M.; Taşdelen, A. S.; Yılmaz, Mehmet; Atalar, Abdullah; Köymen, HayrettinWe propose an airborne collapse capacitive micromachined ultrasonic transducer (CMUT) as a practical viable ultrasound transducer capable of providing a stable performance at the off-resonance frequencies. Traditional practice is to bias the CMUT plate close to collapse voltage to achieve high coupling coefficient and sense the incoming ultrasound as an open-circuit receive voltage signal of the transducer or short-circuit receive current (SCRC). Maintaining CMUT plate in the vicinity of collapse threshold is rather difficult. In this paper, an analytic approach to design an airborne collapsed-mode CMUT for maximum off-resonance sensitivity is presented. We use small-signal circuit model to evaluate the performance of a collapsed CMUT for varying operating conditions. CMUT operational parameters that yield the highest off-resonance SCRC are directly obtained from performance design curves. Collapsed CMUT plate is then biased in a critical biasing region that produces a stable and maximum off-resonance sensitivity. We experimentally verify and measure a stable sensitivity of a fabricated collapsed CMUT cell of -60 dB V/Pa at 100 kHz when biased between 50 to 65 V. We characterize our linear circuit model performance against the measured performance of collapsed CMUT in air within 4-dB tolerance. [2018-0058]Item Open Access Tunable Q matching networks for capacitive ultrasound transmitters(Springer New York LLC, 2021-05-06) Khan, M.; Khan, Talha MasoodAirborne capacitive micromachined ultrasonic transducers (CMUTs) have predominantly large input capacitive reactance with small series radiation resistance. To maximize the acoustic power radiation at resonance we employ low cost LC matching networks between the low output impedance driving source and CMUT transducer. Conventional LC networks, including pi and T-network topologies are employed to provide a high-Q match. An important free parameter that controls the bandwidth of match in pi and T-networks is the center impedance. Since a simple pi-network can be formed from two basic L-sections, the center impedance of two L-sections provides control over the bandwidth of match. Hence these are tunable-Q matching networks. We use the lumped circuit model of CMUT to derive the input impedance of CMUT at resonance. At resonance the lumped equivalent circuit of transducer can be reduced to a series RC circuit consisting of radiation resistance and transducer’s equivalent capacitance only. From the input impedance of CMUT we determine the lumped inductance and capacitances of various LC matching networks. The aim of these matching networks is to cancel the large input capacitive reactance of CMUT cell and to match the cell’s radiation resistance to source resistance at resonance. We report significant improvement in the radiated power when CMUT is driven at resonance using the proposed matching schemes.