Ling Chen

Bio: Ling Chen is an academic researcher from South China University of Technology. The author has contributed to research in topics: Starch & Amylose. The author has an hindex of 53, co-authored 226 publications receiving 7945 citations. Previous affiliations of Ling Chen include Chinese Ministry of Education.

Thermal degradation and stability of starch under different processing conditions

Abstract: The objectives of this paper are to review the thermal degradation and stability of starch and starch-based materials, including both fundamental sciences such as detecting techniques, the effect of amylose/amylopectin content in starches and starches modifications, as well as the effect of different processing environments, such as an open or sealed system, and shearless or shear stress conditions. The decomposition temperature of starches was increased with increasing amylopectin content in an open system. In the open system, the initial water content did not affect the decomposition temperature because all water had evaporated from samples prior to reaching the decomposition temperature. Two decomposition temperatures were observed in the sealed system: the first at lower temperature represents long chain scission; and the second at higher temperature involves decomposition of glucose ring. In the sealed system, the first degradation was increased with increasing amylopectin content. There is no observable difference of the second degradation for the samples containing different amylose/amylopectin ratios. The higher the moisture content is, the lower the second decomposition temperature is detected in the sealed system. Significant shear degradation was observed in amylopectin component of starch, while high amylose starch proved less sensitive to shear stress. The achievements in this area have increased the knowledge of polymer science, in particular to understand the degradation of natural polymers.

Progress in Green Polymer Composites from Lignin for Multifunctional Applications: A Review

Abstract: Rising environmental concerns and depletion of petro-chemical resources has resulted in an increased interest in biorenewable polymer-based environmentally friendly materials. Among biorenewable polymers, lignin is the second most abundant and fascinating natural polymer next to cellulose. Lignin is one of the three major components found in the cell walls of natural lignocellulosic materials. Lignin is widely available as a major byproduct of a number of industries involved in retrieving the polysaccharide components of plants for industrial applications, such as in paper making, ethanol production from biomass, etc. The impressive properties of lignin, such as its high abundance, low weight, environmentally friendliness and its antioxidant, antimicrobial, and biodegradable nature, along with its CO2 neutrality and reinforcing capability, make it an ideal candidate for the development of novel polymer composite materials. Considerable efforts are now being made to effectively utilize waste lignin as one ...

Simulated Biological Fluids with Possible Application in Dissolution Testing

Abstract: This literature review is a compilation of the composition and, in most cases, the preparation instructions for simulated biological fluids that may be used as dissolution media in the evaluation of dissolution profiles and amount of drug released from pharmaceutical dosage forms. The use of simulated biological fluids can give a better understanding of the release mechanisms and possible in vivo behavior of a product and enhance the predictive capability of the dissolution testing. A summary of the major characteristics of the most used routes of administration that may affect dissolution and absorption of drug substances is presented. The routes and simulated biological fluids covered by this review are: • Parenteral: simulated body fluid and simulated synovial fluid. • Oral: fasted-state simulated gastric fluid, fed-state simulated gastric fluid, fasted-state simulated intestinal fluid, fed-state simulated intestinal fluid, simulated colonic fluid, fasted-state simulated colonic fluid, and fed-state simulated colonic fluid. • Buccal and sublingual: simulated saliva. • Pulmonary: simulated lung fluid. • Vaginal: simulated vaginal fluid and simulated semen. • Ophthalmic: simulated tears. Simulated sweat is also included. Some examples of how these simulated biological fluids are used to evaluate dosage forms are included in each route of administration. INTRODUCTION Until some decades ago, most of the conventional pharmaceutical dosage forms were essentially injections, oral formulations (solutions, suspensions, tablets, and capsules), topical creams, and ointments. With the progress of drug delivery technology, novel dosage forms have been developed to overcome the problems associated with conventional drug delivery. Research has been directed toward the use of alternatives to the parenteral route for drugs that cannot be delivered orally. Potential alternative portals of drug entry to the systemic circulation include buccal, sublingual, nasal, pulmonary, and vaginal routes, among others. These routes of administration are also used for the local delivery of drugs directly to the site of action, with consequent reduction in the dose needed to produce a pharmacological effect, eliminating problems related to first-pass metabolism and possibly minimizing systemic side effects (1). An important application of dissolution testing is the prediction of in vivo performance of pharmaceutical dosage forms. The media typically used for quality control dissolution testing do not represent all aspects of the physiological conditions of the most used routes of administration and do not allow correlation with in vivo data. Prediction of dosage form performance in the site where most of the absorption occurs requires adequate simulation of the in vivo conditions. This paper describes some characteristics of the parenteral, oral, buccal and sublingual, pulmonary, ophthalmic, and vaginal routes that are important to consider when developing simulated media. A compilation of the composition and preparation of several simulated biological fluids, including simulated sweat, with potential use as dissolution media is presented. PARENTERAL ROUTE The most used routes of injection are intramuscular, intravenous, and subcutaneous and are normally associated with short-term effects. Novel implant devices that can adequately control drug release and provide a prolonged duration of effect have been developed (1). To evaluate the in vitro drug release from these dosage forms, the dissolution medium should have ion concentrations almost equal to those of the human plasma. Table 1 describes the ionic composition of simulated body fluid (SBF) and human blood plasma. Simulated body fluid was developed initially to evaluate the surface structural changes of glass-ceramics used to manufacture artificial vertebrae, ileum, tooth roots (2), and bioactive material used to repair hard tissues such as artificial middle-ear bone and maxillofacial implants (3). This simulated body fluid was prepared using the reagents listed in Table 2. These reagents were added to 700 mL of water in the order given in Table 2, one by one, after each reagent was completely dissolved. The pH was adjusted to 7.4 with 1 M *Corresponding author. diss-18-03-03.indd 15 8/31/2011 3:22:15 PM dx.doi.org/10.14227/DT180311P15

Role of clathrin- and caveolae-mediated endocytosis in gene transfer mediated by lipo- and polyplexes

Abstract: We investigated the effects of inhibitors of clathrin-mediated endocytosis (chlorpromazine and K(+) depletion) and of caveolae-mediated uptake (filipin and genistein) on internalization of FITC-poly-l-lysine-labeled DOTAP/DNA lipoplexes and PEI/DNA polyplexes by A549 pneumocytes and HeLa cells and on the transfection efficiencies of these complexes with the luciferase gene. Uptake of the complexes was assayed by fluorescence-activated cell sorting. Lipoplex internalization was inhibited by chlorpromazine and K(+) depletion but unaffected by filipin and genistein. In contrast, polyplex internalization was inhibited by all four inhibitors. We conclude that lipoplex uptake proceeds only by clathrin-mediated endocytosis, while polyplexes are taken up by two mechanisms, one involving caveolae and the other clathrin-coated pits. Transfection by lipoplexes was entirely abolished by blocking clathrin-mediated endocytosis, whereas inhibition of the caveolae pathway had no effect. By contrast, transfection mediated by polyplexes was completely blocked by genistein and filipin but was unaffected by inhibitors of clathrin-mediated endocytosis. Fluorescence colocalization studies with a lysosomal marker, AlexaFluor-dextran, revealed that polyplexes taken up by clathrin-mediated endocytosis are targeted to the lysosomal compartment for degradation, while the polyplexes internalized via caveolae escape this compartment, permitting efficient transfection.