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Polyelectrolyte multilayer assembly as a function of pH and ionic strength using the polysaccharides chitosan and
Soheil Boddohi1, Christopher E Killingsworth, Matt J Kipper
1Department of Chemical and Biological Engineering, Colorado State University, Fort Collins, Colorado, USA.
Biomacromolecules
|June 21, 2008
Summary
Solution conditions significantly impact polyelectrolyte multilayer (PEM) assembly. Adjusting pH and ionic strength with heparin and chitosan allows control over PEM thickness, crucial for biomaterial development.
Area of Science:
- Materials Science
- Biochemistry
- Surface Chemistry
Background:
- Polyelectrolyte multilayers (PEMs) are versatile materials assembled via layer-by-layer (LBL) techniques.
- Biologically derived polysaccharides offer biocompatible building blocks for PEMs.
- Controlling PEM properties is essential for targeted applications.
Purpose of the Study:
- To investigate the influence of solution ionic strength and pH on the assembly of polysaccharide-based PEMs.
- To characterize the sensitivity of PEM thickness and composition to variations in processing parameters.
- To understand the underlying mechanisms governing PEM formation under different solution conditions.
Main Methods:
- Layer-by-layer (LBL) assembly of heparin and chitosan polyelectrolytes.
- In situ and ex situ thickness measurements using Fourier-transform surface plasmon resonance (FT-SPR) and spectroscopic ellipsometry.
- Chemical characterization via vibrational spectroscopy and X-ray photoelectron spectroscopy (XPS).
Main Results:
- PEM thickness per bilayer increased from <2 nm to >4 nm with pH changes when assembled in 0.2 M buffer.
- Higher and lower ionic strengths resulted in a narrower range of accessible PEM thicknesses.
- PEM molar composition showed limited sensitivity to pH and ionic strength, though pH affected inter-polyelectrolyte interactions.
Conclusions:
- Solution pH and ionic strength are critical parameters for tuning polysaccharide PEM thickness.
- The observed thickness variations can be explained by changes in polyelectrolyte chain charge density and conformation.
- This study provides insights into controlling PEM architecture for advanced material design.
