Molecular interaction studies of the hyaluronan derivative, hylan A using atomic force microscopy

Intermolecular self-association of hylan chains can be observed in hylan of molecular weight ca. 1×107, with an indication of specific cross-linking protein points and inter-chain cross-links of molecular weight of between 10,000 and 80,000. When this high molecular weight hylan is autoclaved to Mw 1.8×106, to yield a molecular size of the same order as a conventional hyaluronan, the structural features of hylan are retained, with regions of network disintegration having single chains to which one or two chains are joined. After degradation by OH radicals, extended linear chains are found with some of the straight chains having branch points. These can be attributed to the unwinding of the hylan coils by the movement of a droplet of water across the mica surface. The effect of filtration by 1 μm filter does not reduce the measured Mw (corresponding to an intrinsic viscosity of 8188 at low shear rate). However, when stressed through a 0.45 μm filter the Mw falls to a quarter of its previous value. The cross-linked structure of the original hylan is shown to be equivalent to a hyaluronan of ca. 10×106, based on rheological measurements. The cross-linked structure confers stability to degradation by OH radicals not observed for hyaluronan. This distinctive behaviour of hylan is maintained for the entire range of molecular weights studied. The results confirm the tendency of hylan chains to readily undergo chain–chain association.