Protein adsorption and desorption

In contrast, on the surface of the amino-containing polymeric materials, protonated amino groups introduced in a small proportion under physiological conditions, destroy their surrounding hydrogen bonds to produce, here and there, gaps in the network [127, 128]. Thus, the network structures are considered to become more or less unstable. As a consequence, the residence time of protein molecules trapped by these defective networks will be shorter than in the case of polyHEMA or cellulose. On the surface of these amino-containing materials, reversible protein adsorption and desorption, and also replacement (Vroman effect) - or even protein rejection - will become possible. 

FIGURE 12.25 Schematic representation of protein adsorption and desorption as a function of temperature. 

Protein Adsorption and Desorption Rates and Kinetics. The TIRF flow cell was designed to investigate protein adsorption under well-defined hydrodynamic conditions. Therefore, the adsorption process in this apparatus can be described by a mathematical convection-diffusion model (17). The rate of protein adsorption is determined by both transport of protein to the surface and intrinsic kinetics of adsorption at the surface. In general, where transport and kinetics are comparable, the model must be solved numerically to yield protein adsorption kinetics. The solution can be simplified in two limiting cases 1) In the kinetic limit, the initial rate of protein adsorption is equal to the intrinsic kinetic adsorption rate. 2) In the transport limit, the initial protein adsorption rate, as predicted by Ldveque s analysis (23), is proportional to the wall shear rate raised to the 1/3 power. In the transport-limited adsorption case, intrinsic protein adsorption kinetics are unobservable. 

At present, the protein/surface interactions that determine adsorption kinetics are unclear. To clarify these interactions, the effects of polymer surface properties on protein adsorption and desorption rates have been investigated. BSA adsorption from a 1 mg% solution (1 mg% = 1 mg/100 mL) was studied using several polymers chosen for their wide range of surface properties and functionalities (22, Cheng, Y.L. et al.. J. Coll. Int. Sci., in press). The polymers and their surface properties (under the conditions of the BSA adsorption experiments) are listed in Table I. 

Brash and ten Hove (27) have shown that the early plasma protein adsorption and desorption events occur more slowly and can be more readily examined if the plasma is diluted. Using this approach, we found that exposure of each of the methacrylate polymers to 1% plasma (Fig. 4C) resulted in fibrinogen binding which showed maxima after 1 to 3 minutes of exposure followed by decreases in bound fibrinogen to an apparent plateau at less than 0.1 ug/cm. These kinetics are similar to those reported by Brash and ten Hove i2J) for glass, siliconized glass and polyethylene. 

Although ATR has been used to quantify the variation in composition at the surface in TPEs (Sung and Hu, 1980), a related utility is its ability to monitor in situ processes such as reaction injection molding (RIM) (Ishida and Scott, 1986) and protein adsorption onto a polyurethane substrate (Pitt and Cooper, 1986). In the latter, the effect of shear rate on the kinetics of protein adsorption and desorption from phosphate-buffered saline (PBS) was studied in a specially designed flow cell. A very thin film of the commercial MDI-ED-PTMO polyurethane Biomer was cast from solution onto a Ge ATR prism. The thickness of the film was less than the penetration depth so the protein concentration could be monitored after the infrared absorption of the polymer... 

Modulation of protein adsorption and desorption using photoinduced supermolecular interaction... 

FIGURE 7.11 Protein adsorption and desorption from the matrix. The adsorption of proteins in IMAC is based on the coordination between an immobilized metal ion and electron donor groups from the protein surface. Most commonly used are the transition-metal ions (Cu, Zn, Co, Fe ) as electron-pair acceptors (or electrophiles). 

A schematic diagram showing protein adsorption and desorption from the matrix is shown in Figure 7.11. 

---