Electric birefringence studies of biopolymer systems

Abstract

Important and novel electric birefringence measurements of immediate significance in the biomedical field are reported on a family of materials which form the major constituents of the cartilage connective tissue. Outstanding amongst the reported results is the confirmation of the Hardingham-Muir model for proteoglycan-hyaluronic acid aggregation, and the relative ease with which the technique was both able to substantiate the model, and, for the first time, to observe the gradual formation of the aggregate. The complex heteropolysaccharide, proteoglycan, has also been characterised by a wide ranging series of electric birefringence measurements. Other conformational changes studied by the technique on other cartilage materials and reported herein are the effects of pH changes on hyaluronic acid conformation, the enzymatic degradation of hyaluronic acid and the thermal denaturation of collagen. The work also considers aspects of the problems of application of theoretical models to flexible polymers and demonstrates what can be achieved on existing crude theories with the nitrocellulose in acetone system. Some exploratory measurements in the interfacial area between solute and solvent are reported for the bacterium E. coli and an aqueous suspension of PTFE particles. A diverse range of materials was studied with particular reference to the values of particle rotary diffusion constants derived from dispersion of birefringence with frequency and analysis of birefringence relaxation time decay rates following the application of a pulsed DC field. Comparisons are drawn between these values and explanations of the discrepancies observed are considered. Last, but not least, the design of an advanced and high sensitivity apparatus for the measurement of electric birefringence is reported. Unusually, the system adopts a vertical mode and the novel Kerr Cell design incorporated dispenses. with end windows. The use of this new compact design is suggested as the basis for commercial applications.