Atomic force microscopy visualization of poly(urethane urea) microphase rearrangements under aqueous environment

Area of Science:

• Materials Science
• Biomedical Engineering
• Polymer Chemistry

Background:

• Polyurethane biomaterials are crucial for medical devices.
• Surface properties, specifically nanoscale heterogeneities, are linked to polyurethane blood compatibility.
• Microphase separated morphology is hypothesized to cause these heterogeneities.

Purpose of the Study:

• To visualize surface microphase distribution in poly(urethane urea) block copolymers.
• To investigate the effect of aqueous conditions on polyurethane surface morphology.
• To correlate surface structure with varying hard segment content.

Main Methods:

• Tapping mode atomic force microscopy with phase imaging was employed.
• Experiments were conducted under aqueous conditions after prehydration.
• Poly(urethane urea) block copolymers with varied hard segment content were analyzed.

Main Results:

• Nanometer-sized raised features (50-70 nm wide, 10-15 nm high) were observed on the surface.
• Surface phase images under aqueous conditions differed significantly from ambient conditions, indicating water-induced reorientation.
• The polymer surface showed reduced soft phase material in water, with hard domains dominating even after dehydration.

Conclusions:

• Water induces significant structural reorientation at the surface of poly(urethane urea) biomaterials.
• The surface layer of these biomaterials becomes enriched in hard domains when exposed to aqueous environments.
• This water-induced surface restructuring may influence the blood compatibility of polyurethane-based medical devices.