Phase imaging atomic force microscopy in the characterization of biomaterials

Area of Science:

• Materials Science
• Surface Science
• Biomaterials Engineering

Background:

• Phase imaging atomic force microscopy (AFM) is crucial for biomaterial surface characterization.
• Phase images offer detailed surface properties beyond morphological data.
• Distinguishing chemical from morphological information in phase images remains a challenge.

Purpose of the Study:

• To investigate the primary contributors to phase images in atomic force microscopy.
• To differentiate between morphological and chemical signals in phase imaging of various materials.
• To establish optimal conditions for detecting chemical-dependent phase contrast.

Main Methods:

• Utilized phase imaging atomic force microscopy (AFM) to analyze non-carious human maxillary incisors, microphase-separated polyurethane, and self-assembling peptide nanofibers.
• Examined the relationship between phase signals and surface morphology (peaks and valleys).
• Tested different tapping modes (hard and light) and amplitude set points to identify chemical contrast.

Main Results:

• Phase images predominantly reflect morphological changes, with phase peaks correlating to morphological valleys and vice versa.
• Inherent surface roughness often masks chemical-dependent phase contrast.
• Chemical contrast was detectable in very rough samples using hard tapping mode (amplitude set point ratio: -0.4 to -0.8).
• Chemical contrast was detectable in medium-roughness samples using light tapping mode (amplitude set point: -0.1 to -0.4).

Conclusions:

• Phase imaging AFM primarily visualizes surface topography rather than chemical composition.
• Surface roughness significantly influences the detectability of chemical information.
• Optimized tapping modes and amplitude set points are essential for resolving chemical variations in biomaterials and other surfaces.