Viscoelastic properties of aggrecan aggregate solutions: Dependence on aggrecan concentration and ionic strength

The Journal of Chemical Physics

Hecht

Rochas

et al. 2006

The distribution of counterions in solutions of high molecular mass hyaluronic acid, in near-physiological conditions where mono- and divalent ions are simultaneously present, is studied by small angle neutron scattering and anomalous small angle x-ray scattering. The solutions contain either sodium or rubidium chloride together with varying concentrations of calcium or strontium chloride. The effects of monovalent-divalent ion exchange dominate the amplitude and the form of the counterion cloud. In the absence of divalent ions, the shape of the anomalous scattering signal from the monovalent ions is consistent with the distribution calculated from the Poisson-Boltzmann equation, as found by other workers. In mixtures of monovalent and divalent ions, however, as the divalent ion concentration increases, both the diameter and the amplitude of the monovalent ion cloud decrease. The divalent counterions always occupy the immediate neighborhood of the charged polyanion. Above a given concentration their anomalous scattering signal saturates. Even in a large excess of divalent ions, ion exchange is incomplete.

“…7. This discrepancy is not due to neglect of the higher order terms in (8), as the difference between the two expressions is too small to be distinguishable in Fig. 3.…”

Section: Asaxs Measurements In Ha Solutions With Rb Ionsmentioning

confidence: 88%

Section: Introductionmentioning

confidence: 99%

Anomalous small angle x-ray scattering determination of ion distribution around a polyelectrolyte biopolymer in salt solution

The Journal of Chemical Physics

Hecht

Rochas

et al. 2006

“…Importantly, since the semi-rigidity of GAG chains is imparted by hydrogen bonding along the chain, the extended conformation of the bottlebrushes is not as sensitive to pH and Ca ++ ion fluctuation as other polyelectrolytes like DNA and polyacrylic acid [6]. Finally, the bottlebrush architecture and microgel properties limit the interpenetration of the GAG chains and aggrecan rheology does not exhibit entanglements up to large frequencies, which is important for its lubrication effects [77, 78]. …”

Section: Discussion Of Aggrecan Solution Behaviormentioning

confidence: 99%

Aggrecan, an unusual polyelectrolyte: Review of solution behavior and physiological implications

Chandran

2012

Acta Biomaterialia

Aggrecan is a high molecular weight, bottlebrush-shaped, negative-charged biopolymer that forms supermolecular complexes with hyaluronic acid. In the extracellular matrix of cartilage, aggrecan-hyaluronic acid complexes are interspersed in the collagen matrix and provide the osmotic properties required to resist deswelling under compressive load. In this review we compile aggrecan solution behavior from different experimental techniques, and discuss them in the context of concentration regimes that were identified in osmotic pressure experiments. At low concentration, aggrecan exhibits microgel-like behavior. With increasing concentration, the bottlebrushes self assemble into large complexes. In the physiological concentration range (2 < caggrecan < 8 % w/w), the physical properties of the solution are dominated by repulsive electrostatic interactions between aggrecan complexes. We discuss the consequences of the bottlebrush architecture on the polyelectrolyte characteristics of the aggrecan molecule, and its implications for cartilage properties and function.

“…Changes in the local environment, for example, due to hydration, salt concentration or ionic composition, influence the interactions with neighboring HA molecules and other surrounding species. [9][10][11][12] Fig. 1 illustrates schematically the organization of HA chains in the semidilute regime where the molecules strongly overlap.…”

Section: Introductionmentioning

confidence: 99%

Ions in hyaluronic acid solutions

The Journal of Chemical Physics

Basser

Londono

et al. 2009

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.