Scale-up of the production of cassava starch based films using tape-casting

Most research on biodegradable and edible films uses the well-known casting technique, which allows the preparation of films of small dimensions. Besides, cassava starch films prepared by extrusion processes do not have good properties, because of the high shear rates applied. The tape-casting technique allows the spreading of a suspension on large supports, with the control of the thickness by an adjustable blade at the bottom of the spreading device. The drying of the film can be carried-out on the support itself, under controlled conditions. Film-forming suspensions with different formulations were prepared, varying the concentrations of starch (3 and 5 g/100 g of suspension), glycerol (0.20 and 0.25 g/g of starch) and cellulose fibers (0 and 0.30 g/g of starch) and used to produce films by tape-casting. The results showed that tape-casting is a suitable technology to scale-up the production of starch based films.     

The surrogate scaffold method for quantifying molecular release kinetics from drug delivery systems

The accurate determination of kinetics of therapeutic release from drug delivery vehicles is an essential step in the optimized design of such systems for biomedical and pharmaceutical applications. Most methods in current use for quantifying therapeutic release rates are developed to provide consistency, reproducibility, and ease of usage in a laboratory setting. These methods, however, do not necessarily mirror the release conditions when the drug delivery system comes into contact with the target tissue environment during application. As a result, the findings from these studies provide only comparative guidelines about the drug delivery rates and duration. Successful optimization of a drug delivery system requires complete, and accurate, knowledge about the release profile over an extended period of time to determine the initial release rate—including burst release if present, the rate of change of the release kinetics, and the maximum duration of delivery at a minimum therapeutic concentration level. We have developed an indirect method for the quantification of release kinetics suitable for nanoparticle-based drug delivery systems that utilizes a hydrogel scaffold as a tissue surrogate to better emulate therapeutic delivery into a target tissue environment. Details of the method and its application to the release of an angiogenic peptide from a nanoparticle emulsion are provided in this communication.     

Facile de Novo Sequencing of Tetrazine-Cyclized Peptides through UV-Induced Ring-Opening and Cleavage from the Solid Phase

While most FDA-approved peptide drugs are cyclic, the robust cyclization chemistry of peptides and the deconvolution of cyclic peptide sequences by using tandem mass spectrometry render cyclic peptide drug discovery difficult. Here we present the successful design of cyclic peptides on solid phase that addresses both of these problems. We demonstrate that this peptide cyclization method using dichloro-s-tetrazine on solid phase allows successful cyclization of a panel of random peptide sequences with various charges and hydrophobicities. The cyclic peptides can be linearized and cleaved from the solid phase by simple UV light irradiation, and we demonstrate that accurate sequence information can be obtained for the UV-cleaved linearized peptides by using tandem mass spectrometry. The tetrazine linker used in the cyclic peptides can further be explored for inverse electron-demand Diels-Alder (IEDDA) reactions for screening or bioconjugation applications in the future.     

A methodology for the design of photovoltaic water supply systems

Photovoltaic pumping systems are used nowadays as a valuable alternative to supply water to communities living in remote rural areas. Owing to the seasonal variation and the stochastic behavior of solar radiation, at certain times the supply of water may not be able to meet demand. A study has been made of the relationship between water pumping capacity, reservoir size and water demand, for a given water deficit. As a result, curves of equal water deficit (iso‐deficit lines) can be obtained for various combinations of PV pumping capacity and reservoir size. A methodology to generate those curves is described, using as its main tool the characteristic curve of the system, that is, the relationship between water flow and collected solar radiation. The characteristic curve represents the combined behavior of the water pumping system and the well. The influence of the minimum collected solar radiation level, necessary to start the system's operation (the critical radiation level I_C), is also analyzed. Results show that PV pumping systems with different characteristic curves, but with the same critical levels, yield the same set of iso‐deficit lines. This drastically reduces the number of necessary solutions to those corresponding to a few values of I_C. Iso‐deficit lines, calculated for the locality of Recife (PE), Brazil, are used to illustrate the sizing procedure PV water supply systems. Copyright © 2001 John Wiley & Sons, Ltd.