Quantitative Analysis of Protein Adsorption Kinetics written in collaboration with C.-H. Ho, P.Dryden and D. W. Britt , Department of Bioengineering, University of Utah, Salt Lake City, UT 84112, USA, http://afm1.pharm.utah.edu/PISMCourse/Kinetics/Kinetics.htmlProtein Adsorption: Kinetic and Thermodynamic viewIntroductionThe mechanism of protein adsorption and resistance can be explained byseveral factors such as adsorption isotherms, thermodynamic equilibrium andadsorption kinetics. Thermodynamic isotherms can be different from the experimentaladsorption isotherms because the adsorbing surface is rapidly saturated and shows thelimitation before reaching the true thermodynaimic isotherm.1 For example, the nonspherical protein can show the jump of adsorption isotherms. Protein adsorption kinetics (1) approach to interface(2) attachment to interface(3) structural rearrangement on the interface(4) detachment from the interface(5) transport from the interfaceProtein surface interactionProtein is normally hydrophobic and it is unfavorable in the water. And thepolymer surfaces are normally hydrophobic. Hydrophobic interaction between surfaceand polymer reduces the free energy and dehydration during this hydrophobicinteraction increase the entropy. If the protein is in the different ionic strength,electrostatic double layer will be related to the long range interaction however only thisionic charged surface can not explain whole forces. This electrostatic charge can beblocked or reduced by any interference between surface and protein.Quantification Technique1. Optical ellipsometry variable angle reflectometry, surface plasmon resonance (most commonly used). 2. spectroscopic techniques:1 Quantitative Analysis of Protein Adsorption Kinetics written in collaboration with C.-H. Ho, P.Drydenand D. W. Britt , Department of Bioengineering, University of Utah, Salt Lake City, UT 84112, USA,http://afm1.pharm.utah.edu/PISMCourse/Kinetics/Kinetics.htmlInfrared absorptionRaman scatteringFluorescence emission. 3. Other methodsRadioactive isotopesSolute depletion techniques Atomic force microscopy: Quantification of the kinetics and thermodynamics ofprotein adsorption using2, Isotherm analysis was performed under the basis ofAFM image. Kinetic and thermodynamic control of protein adsorption on thegrafted polymer layer on the hydrophobic surface3 According to the thermodynamic modeling and comparison with the experimentalresults by Satulysky et al., the prevention of the protein adsorption is quite more relatedto the equilibrium (thermodynamic control) than kinetic control. The thermodynamictheoretical model and comparison with experimental result shows the best polymergrafting on the surface, for the kinetic control, is to use non-attractive polymer onsurface but for the thermodynamic control, it is better to use the attractive polymer onthe surface as shown in figure. This is more realistic for the longer chain. There are several importance comments on this paper.(1) “The time scale for adsorption both for the initial adsorption and to reachequilibrium are orders of magnitude faster for surfaces with attractive interactions withpolymers”(2) “The kinetics of protein adsorption on surfaces with grafted polymers involves thecompetition between the strong bare attractive interactions between the surface and theproteins and the conformational entropy loss that the grafted polymers have to pay toaccommodate the proteins.”(3) In conclusion, on the protein control over finite time scales like drug delivery,kinetic control is more important so it needs relative higher density and long chain ofgrafting polymer. However for the long term use such as artificial heart or artery, thermodynamic control would be more important so it needs the attractive polymer on thesurface. 2 Robert T. T. et. al., Quantification of the kinetics and thermodynamics of protein adsorption using atomic force microscopy, Journal of Biomedical Research 2005 3 J. Satulovsky et. al., Kinetic and thermodynamic control of protein adsorption. Biophysics 2000.Figure (Left) Schematic representation of the ability of grafted polymers toprevent protein adsorption. For polymers attracted to the surface, there is no kineticbarrier but the protein competes with the polymer for adsorption sites. Polymersthat are not attracted to the surface present a large steric barrier but not very goodthermodynamic prevention because of the ability of the protein to deform thepolymer layer. (Right) The curves on the right show the calculated average shapesof two neighboring polymers as a function of time. The shape is defined here(20) by the lateral average radius of gyration of the chains as a function ofthe distance from the surface. Also, a protein is shown to scale,demonstrating that the deformation of the polymer layer is exactly what isneeded for the protein to reach the surface. The black curves correspond tot = 0, the green and blue curves are for the times marked by the same color arrowsin Fig. 2A, and the red curve is the final equilibrium state. Here are copied part to thermodynamic modeling in this paper. I need moreunderstanding for this part.Consider a protein solution of density b that is put into contact with a surface. The surface has polymers that are chemically attached to it at one of their ends. The presenceof the surface induces a gradient in the chemical potential of the protein. This gradient arises from the sudden inhomogeneous environment that appears in the direction perpendicular to the surface. The proteins in the close vicinity of the surface feel the bare attractive interaction of the surface as well as the repulsions induced by the polymermolecules. The balance between these interactions will result in a final equilibrium density profile and amount of protein adsorbed. The time evolution from the homogeneous system to the new equilibrium induced by the presence of the modified surface can be described (in the free-draining limit) with the help of a diffusion equation (15-18) of the form [ 1 ] where we have assumed that the diffusion in the xy plane is faster than the adsorption. This assumption is justified for the relatively low surface densities