Silks play a crucial role in the survival and reproduction of many insects. Labial glands, Malpighian tubules, and a variety of dermal glands have evolved to produce these silks. The glands synthesize silk proteins, which become semicrystalline when formed into fibers. Although each silk contains one dominant crystalline structure, the range of molecular structures that can form silk fibers is greater than any other structural protein group. On the basis of silk gland type, silk protein molecular structure, and the phylogenetic relationship of silk-producing species, we grouped insect silks into 23 distinct categories, each likely to represent an independent evolutionary event. Despite having diverse functions and fundamentally different protein structures, these silks typically have high levels of protein crystallinity and similar amino acid compositions. The substantial crystalline content confers extraordinary mechanical properties and stability to silk and appears to be required for production of fine protein fibers.

Cationic lipid-mediated nucleic acid and protein delivery is becoming increasingly popular for in vitro and in vivo applications. While the chemistry of cationic lipid carriers is moving very rapidly, and more and more sophisticated molecules are being developed, it is worthwhile to look back to understand what has been achieved in the field of cationic lipids and why in some cases delivery based on cationic lipids works and in other cases it does not. For this purpose, DOTAP is one of the best candidates; it is the most widely used cationic lipid, it is relatively cheap, and it is efficient in both in vitro and in vivo applications. The vast amount of data that have accumulated on DOTAP and related molecules could provide invaluable clues to biophysical, structural, and biological mechanisms of transfection by cationic lipids. While many issues of cationic lipid transfection still remain unclear, this review will attempt to address mainly the following issues: (1) interplay of physicochemical parameters of DOTAP formulations; (2) impact of physicochemical parameters on transfection (lipofection) efficiency by cationic reagents, in vitro and in vivo; (3) structure-activity relationships of cationic lipid formulations in cell culture and in the living organism. In addition, in vivo applications of cationic lipids are reviewed, and the problems of local versus systemic administration of lipoplexes are discussed.

The ability of low-frequency ultrasound (LFUS) to release encapsulated drugs from sterically stabilized liposomes in a controlled manner was demonstrated. Three liposomal formulations having identical lipid bilayer compositions and a similar size ( approximately 100 nm) but differing in their encapsulated drugs and methods of drug loading have been tested. Two of the drugs, doxorubicin and methylpredinisolone hemisuccinate, were remote loaded by transmembrane gradients (ammonium sulfate and calcium acetate, respectively). The third drug, cisplatin, was loaded passively into the liposomes. For all three formulations, a short exposure to LFUS (<3 min) released nearly 80% of the drug. The magnitude of drug release was a function of LFUS amplitude and actual exposure time, irrespective of whether irradiation was pulsed or continuous. Furthermore, no change in liposome size distribution or in the chemical properties of the lipids or of the released drugs occurred due to exposure to LFUS. Based on our results, we propose that the mechanism of release is a transient introduction of porelike defects in the liposome membrane, which occurs only during exposure to LFUS, after which the membrane reseals. This explains the observed uptake of the membrane-impermeable fluorophore pyranine from the extraliposomal medium during exposure to LFUS. The implications of these findings for clinical applications of controlled drug release from liposomes are discussed.