Atomic Force Microscopy Methods for Characterizing Protein Interactions with Microphase-Separated Polyurethane Biomaterials

  • Li-Chong Xu
  • Pranav Soman
  • Aashiish Agnihotri
  • Christopher A. Siedlecki


Understanding the molecular scale interactions between proteins and microphase-structured polyurethane (PU) biomaterials can provide mechanistic insights into the blood/biomaterial problem. This knowledge is critically important to provide design parameters for developing new blood-contacting materials with improved hemocompatibility. This chapter introduces a series of novel atomic force microscopy (AFM) techniques for characterization of PU biomaterials under ambient and physiologically relevant conditions. Techniques for measuring the interaction forces between proteins and surfaces or proteins and proteins, for measuring the bioactivity of proteins, and for correlating biological activity with material surface properties are discussed. The measurements reveal a complex interfacial environment where the material surface is undergoing dynamic changes at the same time as proteins are undergoing time-dependent conformational and bioactivity changes. Combining the ­traditional in vitro techniques for biocompatibility with these new AFM techniques offers new insights into the fundamental relationships between PU microphase structures and the biological response to these materials.


Atomic Force Microscopy Adhesion Force Platelet Adhesion Hard Segment Soft Segment 

Abbreviations and Symbols




Atomic force microscopy




Bovine serum albumin






Highly ordered pyrolytic graphite


Low-density polyethylene


Monoclonal antibody




phosphate-buffered saline










Poly(urethane urea)


Self-assembled monolayer


the set point amplitude of the oscillation of the cantilever


the free amplitude of the oscillation of the cantilever


the prefactor


the deflection of the cantilever (nm)


the initial deflection of the cantilever (nm)


the modulus (GPa)


the activation energy for protein unfolding (kT)


the adhesion force (nN)


the adhesion force at equilibrium (nN)


an empirical coefficient related to the initial interaction force (nN)


the domain height of fibrinogen (nm)


the equilibrium height of the domains at very long adsorption times (nm)


the initial height of molecule at the time of contact (nm)


the Planck constant


the Boltzmann constant


the spring constant of the cantilever (N/m)


the rate constant (s−1)


the thermal off-rate at zero force (s−1)


the ratio of set point amplitude and free amplitude of oscillation


the indentation depth (nm)


the radius of the tip (nm)


the Poisson ratio


the absolute temperature (K)


the contact time (s)


the water contact angle (degree)


the water adhesion tension (dyn/cm),


the loading rate (nN/s)


the effective distance between the bound and transition states (Å)


the movement of the piezo during compression of the surface (nm)


the cantilever deflection (nm)



The authors would like to thank Dr. James Runt, Dr. Jadwiga Weksler, and Dr. Ajay Padsalgikar for providing the PU biomaterials used in these studies. The authors would also like to thank Zachary Rice and Dr. James Garrett for technical contributions to the work.


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Copyright information

© Springer Science+Business Media, LLC 2009

Authors and Affiliations

  • Li-Chong Xu
    • 1
  • Pranav Soman
    • 1
  • Aashiish Agnihotri
    • 1
  • Christopher A. Siedlecki
    • 1
  1. 1.Departments of Surgery and Bioengineering, Biomedical Engineering Institute, College of MedicineThe Pennsylvania State UniversityHersheyUSA

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