Polymers remain the most versatile class of biomaterials, being extensively applied in medicine and biotechnology, as well as in the food and cosmetics industries. Polymers used as biomaterials should have chemical and physical characteristics appropriate for specific application. This can be achieved either during synthesis or by performing modifications.
In this work selected polymers were modified by ultrasound treatment in aqueous solutions. This technique allows carrying out the processes and obtaining products different than these in classical thermally initiated chemical reactions. Macromolecules in solution can undergo chemical transformations under the influence of ultrasound by at least three mechanisms: reactions of macromolecules with radicals generated during periodic compression of cavitation bubbles (i.e. minor gas bubbles created as a result of violation of continuity in liquid phase under ultrasound influence), pyrolysis in or at the boundary of cavitation bubbles (the implosive collapse of a bubble is an adiabatic process that leads to a rapid, momentary temperature increase), as well as mechanochemical effects (resulting from the shear forces generated around collapsing cavitation bubbles).
Selected water-soluble polymers were: poly(ethylene oxide), poly(ethylene glycol), poly(acrylic acid) and chitosan. Changes of weight-average molecular weights and molecular dimensions were determined by low-angle laser light-scattering and viscometry.
It was observed that ultrasound can act as an efficient tool for controlled degradation of polymers, but is also capable of inducing cross-linking processes. Controlled degradation induced by ultrasound is useful e.g. in producing low-molecular-weight chitosan, which is much more efficient in selected biomedical applications than the original, high-molecular-weight material.
This work has been financed by the State Committee for Scientific Research (grant No. 4 T09A 128 22).