CHYAFFStructure and Properties

The HYAFF series of semi-synthetic HA derivatives consist of alcohol esters of HA which vary in respect to the pendant alcohol group (benzyl and ethyl) and the level of esterification achieved. X-ray diffraction studies of the partial and total benzyl esters of HA (HYAFF 11p75 and HYAFF 11) indicate that the HYAFF derivatives exhibit a diffraction pattern similar to the unsubstituted HA. Molecular modeling based on the X-ray data demonstrates that the benzyl esters of HA have the same conformity and flexibility as unmodified HA. The ethyl ester of HA is known as HYAFF 7. Extruding HYAFF into organic solvents has allowed the production of fibers and membranes. The fibers can be woven and the membranes perforated to produce a wide range of biomaterials. These HYAFF-based biomaterials are biodegradable. The principle factor that determines the length of time it takes for the materials to degrade is the polymer used. The three most common polymers with increasing resistance to biodegradation are HYAFF 11p75 < HYAFF7 < HYAFF11. The length of time implanted products may remain can range from several weeks to several months and is also influenced by the physical conformation of the product and the site of the implantation (133). Degradation of the HYAFF occurs through an initial hydrolysis of the ester bond, which releases free alcohol. Solubilization if the material then follows and the free alcohol and HA are broken down by their normal metabolic pathway. This means that a wide range of safe and biodegradable medical devices can be developed for specific clinical applications.

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