Ions in hyaluronic acid solutions

Abstract

Hyaluronic acid ͑HA͒ is an anionic biopolymer that is almost ubiquitous in biological tissues. An attempt is made to determine the dominant features that account for both its abundance and its multifunctional role, and which set it apart from other types of biopolymers. A combination of osmotic and scattering techniques is employed to quantify its dynamic and static properties in near-physiological solution conditions, where it is exposed both to mono-and divalent counterions. An equation of state is derived for the osmotic pressure ⌸ in the semidilute concentration region, in terms of two variables, the polymer concentration c and the ionic strength J of the added salt, according to which ⌸ = 1.4ϫ 10 3 c 9/4 / J 3/4 kPa, where c and J are expressed in mole. Over the physiological ion concentration range, the effect of the sodium chloride and calcium chloride on the osmotic properties of HA solutions is fully accounted for by their contributions to the ionic strength. The absence of precipitation, even at high CaCl 2 concentrations, distinguishes this molecule from other biopolymers such as DNA. Dynamic light scattering measurements reveal that the collective diffusion coefficient in HA solutions exceeds that in aqueous solutions of typical neutral polymers by a factor of approximately 5. This property ensures rapid adjustment to, and recovery from, stress applied to HA-containing tissue. Small angle x-ray scattering measurements confirm the absence of appreciable structural reorganization over the observed length scale range 10-1000 Å, as a result of calcium-sodium ion exchange. The scattered intensity in the transfer momentum range q Ͼ 0.03 Å −1 varies as 1 / q, indicating that the HA chain segments in semidilute solutions are linear over an extended concentration range. The osmotic compression modulus c ‫ץ‬ ⌸ / ‫ץ‬c, a high value of which is a prerequisite in structural biopolymers, is several times greater than in typical neutral polymer solutions.

Length Scale Dependence of the Dynamic Properties of Hyaluronic Acid Solutions in the Presence of Salt

“…SAXS measurements were made at the insertion device of Sector 5 at the Advanced Photon Source (DND-CAT), with λ = 1.55 Å, in the range 0.0016 ≤ q ≤ 0.35 Å −1 . Complementary estimates of the osmotic modulus were made from measurements of the osmotic pressure π [13]. …”

Search for the Origin of Discrepancies in Osmotic Measurements of the PNIPAM - Water System

“…This difference, attributed to a decrease in the effective polymer concentration due to immobilisation of network chains in the vicinity of the cross-links, amounts to a reduction of 30%-50% in the value of A. Conversely, if incompletely screened ionic groups are present, the excluded volume interaction increases. In such cases, uncross-linked polymer solutions do exhibit a substantial increase in their osmotic prefactor A 2 , with no change in the value of n [40,41].…”

“…It is also remarkable that in the swollen state, neither response resembles that of a polyelectrolyte solution, where the osmotic pressure varies with ionic strength as I −0.75 (broken lines in Fig. 4b) [39,40]. A striking contrast to this behaviour is provided by polyelectrolyte gels in equilibrium with an infinite bath: the critical ion concentration in the surrounding solution at which the present gels collapse is about three orders of magnitude greater than for polyelectrolyte gels, and the ion exchange capacity is negligible [58].…”

A special instrument for the defined modification of polymer properties in solutions and polymer layers

“…These changes can include the organisation of macromolecular segments and coils, their mean size [9][10][11], rigidity, ability to occupy a phase boundary [12][13][14], viscosity [3,[15][16][17][18], temperature of phase transitions, etc. The effects of the preceding thermal exposure (thermal history) [6] or pH and ionic strength fluctuations in a solution [12,[19][20][21][22][23] are also appreciable. The changes in polymer conformation have a direct impact on the behaviour of a macromolecular system at the phase boundaries [12,14,24,25], which plays an important role, e.g., in the response of a hosting biological system [26,27].…”