Havazelet Bianco-Peled

Polymorphism of resistant starch type III

Starch fraction, which is resistant to enzymatic digestion, is produced during retrogradation. This fraction, termed resistant starch type III (RSIII), has health benefits such as pre-biotic effects, improving lipid and cholesterol metabolism, and reducing the risk of colon cancer. Since RSIII preserves its nutritional functionality during cooking processes, it may be used as a food ingredient. This research is part of a project that explores the relation between the structural properties and prebiotic behavior of RSIII. A procedure was developed for the production of different RSIII polymorphs from the same plant source, and applied to three different native starches. For all three types (high amylose corn starch, wheat starch, cornflour), the polymorph structure was determined by the crystallization temperature. Retrogradation at 40 8C lead to the formation of B-type polymorph, whereas incubation at 95 8C, produced a mixture of A- and V-type polymorphs. Differential scanning calorimetry measurements showed no measurable differences in the melting temperatures between the polymorphs, and exhibit an endothermic transition over the range of Tm ¼ 140 – 170 8C. q 2003 Elsevier Ltd. All rights reserved.

Defining the Role of Matrix Compliance and Proteolysis in Three-Dimensional Cell Spreading and Remodeling

Recent studies have identified extracellular matrix (ECM) compliance as an influential factor in determining the fate of anchorage-dependent cells. We explore a method of examining the influence of ECM compliance on cell morphology and remodeling in three-dimensional culture. For this purpose, a biological ECM analog material was developed to pseudo-independently alter its biochemical and physical properties. A set of 18 material variants were prepared with shear modulus ranging from 10 to 700 Pa. Smooth muscle cells were encapsulated in these materials and time-lapse video microscopy was used to show a relationship between matrix modulus, proteolytic biodegradation, cell spreading, and cell compaction of the matrix. The proteolytic susceptibility of the matrix, the degree of matrix compaction, and the cell morphology were quantified for each of the material variants to correlate with the modulus data. The initial cell spreading into the hydrogel matrix was dependent on the proteolytic susceptibility of the materials, whereas the extent of cell compaction proved to be more correlated to the modulus of the material. Inhibition of matrix metalloproteinases profoundly affected initial cell spreading and remodeling even in the most compliant materials. We concluded that smooth muscle cells use proteolysis to form lamellipodia and tractional forces to contract and remodel their surrounding microenvironment. Matrix modulus can therefore be used to control the extent of cellular remodeling and compaction. This study further shows that the interconnection between matrix modulus and proteolytic resistance in the ECM may be partly uncoupled to provide insight into how cells interpret their physical three-dimensional microenvironment.

Evaluating the mucoadhesive properties of drug delivery systems based on hydrated thiolated alginate.

Mucoadhesive polymers have been proposed as drug delivery carriers due to their ability to adhere to the mucus layer. A relatively new class of mucoadhesive polymers, termed thiomers, was suggested as an improved carrier capable of creating disulfide covalent bond with the mucus. Since the wet physiological environment is likely to cause any delivery system to adsorb water and arrive hydrated to its target, studying the performance of mucoadhesive systems in their hydrated form is of major importance. Model thiomer, alginate-thiol, were synthesized and characterized the product using Nuclear Magnetic Resonance (NMR), Fourier Transform Infra Red spectroscopy (FTIR). The swelling behavior was determined gravimetrically and found to be affected from the thiolation. Interactions between the alginate-thiol and mucin glycoproteins, which are believed to be an outcome of disulfide bonds, were verified using rheology experiments. Adhesion of hydrated tablets with different cross linking densities to porcines fresh small intestine tissue were characterized using a Lloyd Tensile Machine. It was shown that the thiolation did not improve the adhesion properties of hydrated tablets. It appears that the benefit achieved by adding thiol group to the polymer in dry tablet form was flawed in hydrated form due to formation of inter-molecular disulfide junctions.

Composite alginate hydrogels: An innovative approach for the controlled release of hydrophobic drugs.

We present an innovative methodology for the sustained delivery of hydrophobic drugs using composite hydrogels, prepared by embedding oil-in-water microemulsions in hydrophilic hydrogels. The hydrophobic nature of the microemulsion core enhances the solubilization of hydrophobic drugs, while the crosslinked matrix could be readily used as a solid controlled delivery vehicle. A microemulsion was formulated from pharmaceutical accepted components; the droplets diameter was shown to be about 10nm by dynamic light scattering, cryo-transmission electron microscopy and small-angle X-ray scattering (SAXS). Combining the microemulsion with alginate solution and crosslinking with calcium ions resulted in a clear hydrogel. A model hydrophobic drug, Ketoprofen, precipitated from the alginate hydrogel, but the drug-containing composite hydrogel was clear and macroscopically homogeneous. The nanostructure was investigated by SAXS; scattering plots indicate that oil droplets exist in the composite hydrogel. Release profiles of the drug from the composite hydrogel with various concentrations of polymer and crosslinker demonstrate the applicability of this system as a controlled delivery vehicle, and suggest that the release rate is governed not by the microemulsion structure but, rather, by the network properties. Furthermore, it was demonstrated that the release rate could be tailored for a specific application utilizing different alginate and calcium concentrations. The generalization of the methodology of including hydrophobic drugs in composite gels is discussed.

Mucoadhesion: a review of characterization techniques

Importance of the field: Mucoadhesive drug delivery vehicles attract much attention owing to benefits such as extended residence time of the drug at the site of application, a relatively rapid uptake of a drug into the systemic circulation, and enhanced bioavailability of therapeutic agents. Mucoadhesion, defined as the ability to adhere to the mucus gel layer covering organs that are exposed to the outer surface of the body yet are not covered with skin, such as the mouth and the respiratory tract, is a key element in the design of these drug delivery systems. Areas covered in this review: This review focuses on the numerous experimental methods that have been proposed over the years for mucoadhesion characterization. These techniques are categorized into directs methods, which measure the force or time required to detach the mocoadhesive from a mucus, and indirect methods, which asses the interactions between the mucoadhesive and mucin type glycoproteins. What the reader will gain: The comprehensive description of the available techniques could facilitate the selection of a characterization method that meets the requirements of a specific study. Moreover, a comparison between the results obtained in different laboratories is given whenever possible. Take home message: The challenge of adopting a universal test method that could be used to compare data from different research groups and rank new mucoadhesion candidates has not yet been met.

Alginate-PEGAc: a new mucoadhesive polymer.

We have synthesized a novel mucoadhesive polymer, alginate-polyethylenglycol acrylate (alginate-PEGAc), in which an alginate backbone carries acrylated polyethylenglycol. This polymer combines the strength, simplicity and gelation ability of alginate with the mucoadhesion properties arising from the characteristics and acrylate functionality of PEG. The strong bonding to the mucus results from a combination of PEGs ability to interpenetrate the mucus surface and a Michael-type addition reaction between an acrylate end group on a polymer and the sulfide end group of the mucin-type glycoprotein. We have synthesized alginate-PEGAc, verified the formation of the desired product by nuclear magnetic resonance, demonstrated the lack of cytotoxicity, and evaluated the ability of this polymer to function as a novel mucoadhesive material for controlled drug release. Based on our findings we believe that modifying other polymers with PEG-acrylate can open the way for the development of many other multifunctional biomaterials for a variety of biotechnological and biomedical applications.

Composite chitosan hydrogels for extended release of hydrophobic drugs

A composite chitosan hydrogel durable in physiological conditions intended for sustained release of hydrophobic drugs was investigated. The design is based on chitosan crosslinked with genipin with embedded biocompatible non-ionic microemulsion (ME). A prolonged release period of 48 h in water, and of 24h in phosphate buffer saline (PBS) of pH 7.4 was demonstrated for Nile red and curcumin. The differences in release patterns in water and PBS were attributed to distinct dissimilarities in the swelling behaviors; in water, the hydrogels swell enormously, while in PBS they expel water and shrink. The release mechanism dominating this system is complex due to intermolecular bonding between the oil droplets and the polymeric network, as confirmed by Fourier transform infrared spectroscopy (FTIR) experiments. This is the first time that oil in water microemulsions were introduced into a chitosan hydrogels for the creation of a hydrophobic drug delivery system.

Novel Biomimetic Adhesives Based on Algae Glue

Inspired by the remarkable adhesive capabilities to wet surfaces of the secretes of the brown alga Fucus serratus, novel glues have been designed and characterized. Formulations composed of phloroglucinol, alginate, and calcium ions are capable of adhering to a variety of surfaces. Rheological data show that the presence of phloroglucinol lowers the amount of Ca(2+) ions required for sol-gel transition, which indicates interactions between the alginate and the phloroglucinol. SAXS data support this claim. The phloroglucinol adhesive binds porcine tissues together with an adhesive strength of 17-25 kPa, which indicates appropriate mechanical properties for application as a soft tissue adhesive.

Mechanisms Controlling the Temperature-Dependent Binding of Proteins to Poly(N-isopropylacrylamide) Microgels

Poly(N‐isopropylacrylamide) (PNIPA) microgels may offer several advantages over PNIPA‐modified surfaces when used as sorbents in temperature‐sensitive chromatography. Yet, a full exploitation of these advantages requires a better understanding of the mechanisms controlling the separation process. As a model system, we have studied the binding of three proteins (bovine serum albumin (BSA), ovalbumin, and lysozyme) to PNIPA microgels. Binding experiments were conducted both below (25 °C) and above (37 °C) the volume phase transition temperature of the gel, Tc. The analysis of the binding isotherms has shown that although an average gel particle contained a larger amount of protein below the phase transition temperature, the concentration of the protein within the particle was higher above this temperature. These findings were attributed to changes in the binding loci due to temperature swings around Tc: whereas a sorption mechanism is dominant below this temperature, surface‐adsorption was more important above it. A comparison between the three studied proteins has shown that below Tc the binding increases with a decrease in the molecular weight. On the other hand, no significant difference in the bound protein amounts was observed above the phase transition temperature. Our results imply that, despite the increase in the gelapos;s hydrophobicity above the phase transition temperature, the resolution in bioseparations based on PNIPA gels is not necessarily better above Tc.

Nanostructuring of PEG–fibrinogen polymeric scaffolds☆

Recent studies have shown that nanostructuring of scaffolds for tissue engineering has a major impact on their interactions with cells. The current investigation focuses on nanostructuring of a biocompatible, biosynthetic polymeric hydrogel scaffold made from crosslinked poly(ethylene glycol)-fibrinogen conjugates. Nanostructuring was achieved by the addition of the block copolymer Pluronic F127, which self-assembles into nanometric micelles at certain concentrations and temperatures. Cryo-transmission electron microscopy experiments detected F127 micelles, both embedded within PEGylated fibrinogen hydrogels and in solution. The density of the F127 micelles, as well as their ordering, increased with increasing block copolymer concentration. The mechanical properties of the nanostructured hydrogels were investigated using stress-sweep rheological testing. These tests revealed a correlation between the block copolymer concentration and the storage modulus of the composite hydrogels. In vitro cellular assays confirmed that the increased modulus of the hydrogels did not limit the ability of the cells to form extensions and become spindled within the three-dimensional (3-D) hydrogel culture environment. Thus, altering the nanostructure of the hydrogel may be used as a strategy to control cellular behavior in 3-D through changes in mechanical properties of the environment.