Dissolution enhancement of gliclazide using pH change approach in presence of twelve stabilizers with various physico-chemical properties

Purpose. The micronization using milling process to enhance dissolution rate is extremely inefficient due to a high energy input, and disruptions in the crystal lattice which can cause physical or chemical instability. Therefore, the aim of the present study is to use in situ micronization process through pH change method to produce micron-size gliclazide particles for fast dissolution hence better bioavailability. Methods. Gliclazide was recrystallized in presence of 12 different stabilizers and the effects of each stabilizer on micromeritic behaviors, morphology of microcrystals, dissolution rate and solid state of recrystallized drug particles were investigated. Results. The results showed that recrystallized samples showed faster dissolution rate than untreated gliclazide particles and the fastest dissolution rate was observed for the samples recrystallized in presence of PEG 1500. Some of the recrystallized drug samples in presence of stabilizers dissolved 100% within the first 5 min showing at least 10 times greater dissolution rate than the dissolution rate of untreated gliclazide powders. Micromeritic studies showed that in situ micronization technique via pH change method is able to produce smaller particle size with a high surface area. The results also showed that the type of stabilizer had significant impact on morphology of recrystallized drug particles. The untreated gliclazide is rod or rectangular shape, whereas the crystals produced in presence of stabilizers, depending on the type of stabilizer, were very fine particles with irregular, cubic, rectangular, granular and spherical/modular shape. The results showed that crystallization of gliclazide in presence of stabilizers reduced the crystallinity of the samples as confirmed by XRPD and DSC results. Conclusion. In situ micronization of gliclazide through pH change method can successfully be used to produce micron-sized drug particles to enhance dissolution rate

Enhanced Rateless Coding and Compressive Sensing for Efficient Data/multimedia Transmission and Storage in Ad-hoc and Sensor Networks

In this dissertation, we investigate the theory and applications of the novel class of FEC codes called rateless or fountain codes in video transmission and wireless sensor networks (WSN). First, we investigate the rateless codes in intermediate region where the number of received encoded symbols is less that minimum required for full datablock decoding. We devise techniques to improve the input symbol recovery rate when the erasure rate is unknown, and also for the case where an estimate of the channel erasure rate is available. Further, we design unequal error protection (UEP) rateless codes for distributed data collection of data blocks of unequal lengths, where two encoders send their rateless coded output symbols to a destination through a common relay. We design such distributed rateless codes, and jointly optimize rateless coding parameters at each nodes and relaying parameters. Moreover, we investigate the performance of rateless codes with finite block length in the presence of feedback channel. We propose a smart feedback generation technique that greatly improves the performance of rateless codes when data block is finite. Moreover, we investigate the applications of UEP-rateless codes in video transmission systems. Next, we study the optimal cross-layer design of a video transmission system with rateless coding at application layer and fixed-rate coding (RCPC coding) at physical layer. Finally, we review the emerging compressive sensing (CS) techniques that have close connections to FEC coding theory, and designed an efficient data storage algorithm for WSNs employing CS referred to by CStorage. First, we propose to employ probabilistic broadcasting (PB) to form one CS measurement at each node and design CStorage- P. Later, we can query any arbitrary small subset of nodes and recover all sensors reading. Next, we design a novel parameterless and more efficient data dissemination algorithm that uses two-hop neighbor information referred to alternating branches (AB).We replace PB with AB and design CStorage-B, which results in a lower number of transmissions compared to CStorage-P.Electrical Engineerin

Rateless Codes with Optimum Intermediate Performance

Abstract—In this paper, we design several degree distributions for rateless codes with optimum intermediate packet recovery rates. In rateless coding, the employed degree distribution signif-icantly affects the packet recovery rate. Each degree distribution is designed based on the number of message packets, k, and desired coding overhead, γ, which is the ratio of the number of received packets, n, to k, i.e., γ = n k Previously designed degree distributions are tuned for full recovery of the entire source packets for γ’s slightly larger than 1, and as a consequence, they show very small packet recovery rates for γ < 1. Hence, finding degree distributions with maximal packet recovery rates in intermediate range, 0 < γ < 1, is of interest. We define packet recovery rates at three values of γ as our conflicting objective functions and employ NSGA-II multi-objective genetic algorithms optimization method to find several degree distributions with optimum packet recovery rates. We propose degree distributions for both cases of finite and infinite (asymptotic) k. I

Optimized cross-layer forward error correction coding for H.264 AVC video transmission over wireless channels

Forward error correction (FEC) codes that can provide unequal error protection (UEP) have been used recently for video transmission over wireless channels. These video transmission schemes may also benefit from the use of FEC codes both at the application layer (AL) and the physical layer (PL). However, the interaction and optimal setup of UEP FEC codes at the AL and the PL have not been previously investigated. In this paper, we study the cross-layer design of FEC codes at both layers for H.264 video transmission over wireless channels. In our scheme, UEP Luby transform codes are employed at the AL and rate-compatible punctured convolutional codes at the PL. In the proposed scheme, video slices are first prioritized based on their contribution to video quality. Next, we investigate the four combinations of cross-layer FEC schemes at both layers and concurrently optimize their parameters to minimize the video distortion and maximize the peak signal-to-noise ratio. We evaluate the performance of these schemes on four test H.264 video streams and show the superiority of optimized cross-layer FEC design.Peer reviewedElectrical and Computer Engineerin

Cstorage: Decentralized Compressive Data Storage In Wireless Sensor Networks

In this paper, we employ compressive sensing (CS) to design a distributed compressive data storage (CStorage) algorithm for wireless sensor networks (WSNs). First, we assume that no neighbor information or routing table is available at nodes and employ the well-known probabilistic broadcasting (PB) to disseminate sensors reading throughout the network to form compressed samples (measurements) of the network readings at each node. After the dissemination phase, a data collector may query any arbitrary set of M ≠N nodes for their measurement and reconstruct all N readings using CS. We refer to the first implementation of CStorage by CStorage-P. Next, we assume that nodes collect two-hop neighbor information and design a novel parameterless and scalable data dissemination algorithm referred to by alternating branches (ABs), and design CStorage-B. We discuss the advantages of CStorage-P and CStorage-B and show that they considerably decrease the total number of required transmissions for data storage in WSNs compared to existing work

Robust Lt Codes With Alternating Feedback

In this paper, we propose robust LT codes with alternating feedback (LT-AF codes), which lightly utilize the feedback channel and surpass the performance of existing LT codes with feedback. In LT-AF codes, we consider a loss prone feedback channel for the first time and propose the encoder to generate degree-one output symbols (encoded symbols) only in acknowledgement to the reception of feedbacks. Therefore, LT-AF codes become robust against feedback losses meaning that their performance does not deteriorate even at high feedback loss rates in contrast to previous work. To realize this, we design a new and parameterless coding degree distribution for LT-AF coding based on Ideal-Soliton (IS) distribution of LT codes. In addition, we design a new feedback scheme and use it in conjunction with an existing feedback method. Therefore, in LT-AF codes the decoder can alternate between either types of feedback based on its status. To generate our new type of feedback, we propose three novel algorithms to analyze the buffered output symbols at the decoder. We will show that LT-AF codes require a significantly lower coding overhead for a successful decoding. © 2014 Elsevier B.V. All rights reserved

Dissolution enhancement of gliclazide using in situ micronization by solvent change method

Gliclazide (GL) is a second-generation sulphonylurea. widely used for the treatment of non-insulin dependent diabetes mellitus. The low water-solubility of GL leads to a low dissolution rate and variable bioavailability. The aim of this study was to enhance the dissolution rate of GL by the preparation of micron-sized particles using a solvent change method. The in situ micronization process was carried out using solvent change method in the presence of HPMC or Brij 35 (0.05 or 0.1 g) as stabilizing agents. GL (0.5 or 1 g) was dissolved in acetone and the stabilizing agent in water (as non-solvent). The non-solvent was poured rapidly into the drug solution under stirring at 26,000 rpm by an ultra-homogenizer, and the resultant was freeze-dried. The crystalline shape of GL changed from rod-shape to diamond- or cube-shape. The FTIR and DSC results showed no interaction between the drug and the stabilizers. Presence of sharp peaks in the XRD diffractograms of microcrystals with 10 times smaller height than untreated crystals indicates that a crystalline habit modification has occurred in the microcrystals without any polymorphic changes. The particle size was reduced about 50 times and the dissolution efficiency of GL at 15 min (DE15%) was increased about 4 times

Gliclazide Microcrystals Prepared by Two Methods of In Situ Micronization: Pharmacokinetic Studies in Diabetic and Normal Rats

The low water-solubility of gliclazide (GL) leads to a low dissolution rate and variable bioavailability. The aim of this study was to investigate the effect of micronization on the absorption and pharmacokinetics of GL after oral administration in rats. GL microcrystals were prepared using solvent-change and pH-shift methods. Scanning electron microscopy showed considerable changes in the shape and size of crystals using both methods. In the optimized formulation of each method, the particle size of treated GL was reduced about 30 (from 290 to 9.9 μm) and 61 times (to 4.76 μm) by solvent-change and pH-shift methods, respectively. Recrystallized samples showed faster dissolution rate than untreated GL particles. Glucose-lowering effect, Cmax, and area under the drug concentration-time profile (area under the curve (AUC)) were compared in diabetic and normal rats. AUC and Cmax were increased by microcrystals in both groups of animals. Administration of 40 mg/kg of GL in the form of untreated drug and microcrystals obtained by solvent-change and pH-shift methods caused 12.49% and 21.04% enhancement in glucose-lowering effect of GL in diabetic rats, respectively