Phospholipid molecules self-assemble to form bilayers that are poorly soluble in an aqueous solvent. Phospholipids may, however, be readily dissolved by mixing with a bile salt or amphiphilic drug surfactant that forms mixed surfactant/phospholipid micelles. Mixed bile salt/phospholipid micelles play an important role in the digestion of fats in the gastrointestinal tract as well as solubilizers of water-insoluble drugs and other drug delivery applications. The ability of surfactants to dissolve phospholipids largely depends on the chemical structure of both surfactant and phospholipid. While bile salt and amphiphilic drug surfactants, with a rigid chemical structure, are good solubilizers of phospholipids, conventional surfactants, with a flexible aliphatic hydrocarbon tail, are poor solubilizers. In addition, the chemical structure of phospholipids, such as tail lengths and charge number, or the fraction of a cosurfactant, for instance cholesterol, is expected to influence the ability to form mixed micelles. In this paper, the aggregation behaviour and mixed micelle formation of the phospholipid dimyristoyl phosphatidylglycerol (DMPC) and two different surfactants: the anionic surfactant sodium dodecyl sulfate (SDS) and the amphiphilic drug surfactant Sodium fusidate (SF, similar structure to that of bile salt), have been studied, and the transition from micelles to bilayers has  been determined for the different surfactants, as well as the size and structure of micelles and bilayers close to the points of transition. The self-assembly of the mixed micelles of surfactants/phospholipids have been investigated using surface tension measurements, refractive index increment and static and dynamic light scattering (SLS and DLS). The results suggest that the transition from micelles to bilayers are found to exist in the following range of bile salt/phospholipid compositions: For SF, 70-75 mol % phospholipid in the micelle was determined to be the point of transition, whilst 20-30 mol % for SDS. As the mole fractions of DMPC increased for both mixtures, the samples became turbid, which indicates the transition of micelles to bilayers. An exact value for molar ratio of transition might not be possible to determine from this study, but instead a, somewhat wider, range of values. In spite of this, a clear trend and difference between the two surfactants was observed.

The purpose of this study was to determine if size exclusion chromatography could be used to separate casein micelles from whey proteins for a rapid, direct test to measure percent casein in milk. A size exclusion chromatography column was developed for the separation having dimensions 100 by .4 cm. Packing material selected was glycophase coated porous glass supports. A Beckman DU-8B spectrophotometer monitored the casein and whey protein peaks as they eluted and a Tektronix 4052 computer accepted data points every 4 sec, storing these on tape. Absorbances and areas of each peak were used in the evaluation of samples. Treatments of temperature, pH and calcium addition were performed on a commingled milk sample from Utah State University Dairy Laboratory. It was determined that addition of calcium and pre-warming to 40 C before injection is important for good separation. Several samples of milk from individual cows were run through the column and parameters obtained. For each sample, percent casein was measured using the standard method of acid precipitation and Kjeldahl nitrogen determination. Percent casein was then estimated using area and absorbance of each casein peak from the elution plots of milk from individual cows. A regression line of predicted vs actual percent casein resulted in a correlation coefficient (r) of .92.

The effects of micelle forming surfactants hexadecyltrimethylammonium bromide, sodium dodecyl sulfate and igepal CA~6JO on the visible spectra of merocyanine dyes of the form 1-alkyl-4-[(3', 5'-alkyl oxocyclohexadienylidene)ethylidene]- 1,4-dihydropyridine were studied. In all cases the visible spectrum shifted to the red when the dye was incorporated into the micelles. The magnitude of the shifts was found to be dependent on the substituted groups and the positioning of the chromophore of the dye in the micelle aggregates. The shifts indicate a highly hydrated environment about the surfactant head groups and an environment equivalent to that of pure ethanol solvent at some undetermined penetration distance.

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Although great progress has been made, cancer still remains one of the most prevalent maladies plaguing mankind. New treatment methodologies using nanoparticles have come to the forefront by allowing for enhanced delivery of therapeutics to the tumor site. The design of the nanoparticle should allow for long circulation times, tumor-specific targeting and efficient release at the site of action. This requires that both the external shell and internal core of the nanoparticle be carefully selected to meet the maximal criteria of each of these steps. Poly(sialic acid) (PSA), a naturally occurring polysaccharide, meets all of the benchmarks of an effective exterior coating yet remains relatively unexplored in the field of drug delivery. Due to stealth properties, natural tumor targeting ability, and inherent pH-responsive elements, PSA has frequently been viewed as a “next-generation” surface coating. Just as important, the internal composition of the carrier should aid in effective drug loading but also rapid release. The selection of the core containing groups as well as therapeutic should be maximized in order to customize the carrier to drug. Here, we have developed PSA micelles composed of various internal groups selected to maximize drug loading and facilitate release. Loading of the chemotherapeutic doxorubicin was optimized through variations in non-covalent bonding forces between drug and carrier. Furthermore, PSA micelles composed of internal pH-responsive groups of varying hydrophobicity were also developed to tailor micelle swelling points at conditions analogous towards those found upon cellular uptake. Both of these were effective delivery platforms towards MCF-7 human breast adenocarcinoma cells. / Bioengineering