Characterization of hyaluronic acid with online multi-angle light scattering and differential viscometry

Importance of the Topic

Hyaluronic acid (HA) is a ubiquitous biopolymer in mammalian tissues with critical roles in ophthalmic, medical, pharmacological, and cosmetic applications. Accurate characterization of its molecular weight distribution, intrinsic viscosity, and conformation is essential for quality control and product development. Combining size-exclusion chromatography (SEC) with multi-angle light scattering (MALS), differential refractometry, and differential viscometry provides absolute, calibration-free measurements, overcoming limitations of traditional SEC methods.

Objectives and Study Overview

This study aimed to apply an integrated SEC-MALS-differential viscometry approach to seven HA samples from various sources (bacterial fermentation, umbilical cord, chicken comb) to:

• Determine absolute weight-average molecular weight (Mw) and polydispersity index (PDI).
• Measure root-mean-square radius (Rg) and hydrodynamic radius (Rh).
• Calculate intrinsic viscosity [η] and explore molecular conformation via Mark–Houwink–Sakurada (MHS) analysis.

Methodology and Instrumentation

Seven distinct HA samples (0.1 mg/mL in PBS) were injected (900 µL) onto an Aquagel-OH SEC column using an Agilent 1100 HPLC system. Detectors in series included:

• DAWN MALS for absolute molar mass and Rg without calibration standards.
• Optilab differential refractometer for concentration (dn/dc = 0.167 mL/g).
• ViscoStar differential viscometer employing a four-arm capillary bridge to measure specific viscosity (ηsp) with high S/N (~2200:1).

Band-broadening among detectors was corrected by proprietary software (ASTRA) to ensure accurate peak shape integration.

Key Results and Discussion

Absolute Mw values ranged from 2.6×10^5 to 1.8×10^6 g/mol with narrow to moderate PDI (1.02–1.45). Rg and Rh increased with Mw, and intrinsic viscosities spanned 632–2671 mL/g. MHS plots displayed marked curvature rather than ideal linear behavior, indicating HA’s transition from stiff, rod-like chains (high a ≈1.0 at low Mw) to Gaussian behavior (a ≈0.5 at high Mw). Instantaneous a values (ai) derived from second-order polynomial fits varied from ~1.1 down to ~0.5, highlighting HA’s unique polyelectrolyte conformation across its molar mass distribution.

Benefits and Practical Applications

SEC-MALS combined with differential viscometry offers:

• Calibration-free, absolute determination of molecular weight and conformation.
• High sensitivity and precision for quality assurance in HA production.
• Insights into polymer stiffness and chain behavior critical for formulation and performance optimization in biomedical and cosmetic products.

Future Trends and Potential Applications

Advances may include integration with online rheological measurements, accelerated algorithms for real-time MHS curvature analysis, and expansion to complex HA derivatives or blends. These developments could streamline process control in biomanufacturing and foster new HA-based therapeutics and biomaterials.

Conclusion

The integrated SEC-MALS-differential refractometry-viscometry platform enables robust, absolute characterization of HA’s molecular properties and conformation without reliance on calibration standards. This capability enhances understanding of HA behavior across its molecular weight range, supporting improved quality control and product innovation.

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