Membrane formation at interfaces examined by analytical ultracentrifugation techniques

Analytical ultracentrifugation to support the development of biomaterials and biomedical devices

Analytical ultracentrifugation (AUC) primarily serves to investigate hydrodynamic and thermodynamic properties of natural and synthetic macromolecules and colloids in solution, dispersion or suspension. Beside such more conventional use, AUC can support materials development particularly by combining different optical systems, if the AUC is equipped with such, or using complementary data evaluation approaches. In this context, an Optima XL-I equipped with absorbance (AO) and interference optics (IO) was used alone or complementary to study the success of conjugation of biopolymers, to evaluate the completeness of the incorporation of macromolecules into micelles and vesicles, and to analyze the composition and homogeneity of macromolecular assemblies. The combination of AO and IO proved covalent binding of concanavalin A to dextran without macromolecular degradation as well as the formation of mixed micelles composed of two types of block copolymers. Further, AUC contributed to analyze the homogeneity, purity, size and size distribution of carbon monoxide-releasing macromolecular assemblies. These case studies revealed that the application possibilities of AUC are by far not completely discovered but can still be extended.

Progress in the characterization of synthetic (supramolecular) polymers by analytical ultracentrifugation

Analytical ultracentrifugation (AUC) is the leading technique for determining the molar mass, state of association in solution, and association constants of biological macromolecules. Even though it is little used for supramolecular polymers, this technique has already been shown to represent one of the best options in the characterization of these systems. The use of supramolecular assemblies in the field of nanotechnology requires the arrangement of such systems on surfaces, from solution. Therefore, the control and investigation of solution properties is of major importance. In this contribution we highlight the applicability and advantages of using AUC by presenting a summary of the results of the past few years on the characterization of various types of synthetic polymers and supramolecular polymer systems.

Optimal conditions of transplantable binary polyelectrolyte microcapsules

Binary polyanion/oligocation microcapsules, prepared in a one-step process, are proposed as an alternative to the common alginate/poly-L-lysine system used in bioencapsulation technology. The model system is based on natural polysaccharides and involves the anionic sodium alginate, or iota-carrageenan, complexed with cationic oligochitosan. This system has been characterized with respect to capsule formation, mechanical strength, and permeability. This paper provides a general description of the influence of the most pronounced parameters that can be used as a tool to modulate the properties of binary microcapsules. These parameters have been separated into two categories. The first, which includes molar mass of polyanion, pH, ionic strength, and concentration of both polyelectrolytes, can be used to simultaneously control capsule mechanical and structural properties. The second set, molar mass of polyanion and reaction time, influences only mechanical resistance without altering membrane permeability. Additional issues related to mechanical stability and the possible change of capsule properties following transplantation are discussed.