Protein adsorption test

When a medical device is in contact with body fluid such as blood, the first thing that occurs on the surface is protein adsorption [96-98]. Proteins in solution trying to minimize the total surface energy is the thermodynamic driving force of protein adsorption on solid surfaces. In blood contact protein adsorption is believed to be the initial event in thrombus formation [99-101], calcification [102-104], and biofilm attachment [105-107], which leads to the failure of implanted devices. Therefore, protein-reducing surface modifications of polyurethane biomaterials have been applied to improve the service life of implants. Previous studies of protein adsorption have focused on adsorption of albumin, IgG, and Fg, which are the predominant three proteins in blood plasma. Surface protein adsorption can be quantitated by several methods such as quartz crystal microbalance (QCM) [108-112], surface plasmon resonance (SPR) [113-118], and iodonization radiolabeling [78,119-125]. 

The QCM method utilizes the piezoelectric property of quartz crystals to measure extremely low mass changes per unit area. When an alternating electric current is applied to the quartz crystal, the quartz crystal produces an acoustic oscillation. Such oscillation frequency is partially dependent on the thickness of the crystal. If biomolecules such as proteins adsorb on the aystal and thus increase the crystal thickness, the instrument will pick up the frequency change and the mass of adsorption can be calculated by Sauerbrey s equation (Eqn (2.5), where A/is frequency change /o, resonate frequency Am, mass change A, area between electrode p, density of quartz p, shear modulus of quartz). 

The mechanism of iodination radiolabeling involves reactive iodine, generated by enzymatic or chemical oxidation of isotopic sodium iodide, reacting as an 

Brash studied Fg and antithrombin radiolabeled using and respectively, so that adsorption of both proteins could be measured in the mixture. After functionalization with ATH, the polyurethane surface (PEO-OH-ATH and PEO-COOH-ATH) preferentially binds with antithrombin rather than Eg, suggesting the strong heparin surface binding activity (Eigure 2.25). By labeling both Eg and antithrombin with different iodine isotopes, the authors obtained competitive adsorption information on the same heparin-modified surface. 

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FIG. 10 SEM photographs for sol-gel-derived (a) and plasticized-PVC (b) membranes encapsulating bis(12-crown-4) after protein adsorption test. (From Ref 27.)... 

PLL(375)-g[5.6]-PEG(5) Adsorption and Protein-Resistance Study. 3.2.1. PLL(375)-g[5.6]-PEG(5) Adsorption Characteristics. All of the following measurements were carried out in a flow-through cell, and both the PLL-g-PEG pretreatment and the protein-adsorption tests were carried out in situ and consecutively without an intermittent drying stage unless otherwise noted. 

Xu et al. coated Stober silica particles with polyethylene glycol (PEG) in order to improve the biocompatibUity of those particles and verified this improvement using a protein adsorption test. The article then further describes possible applications of encapsulation reagents for diagnosis, analysis or other measurements inside active biological systems. 

A good example of a surface-modified lens is the Sola/Bames-Hind Hydrocurve Flite lens, introduced in 1986. The material for the commercial Hydrocurve lens, bufilcon A [56030-52-5] contains methacrylic acid and has a high affinity for protein and subsequent deposition. The surface of the Flite lens was chemically modified with the addition of diazomethane (190) to reduce the surface charge. In vitro testing demonstrated a decrease in protein adsorption (191). 

Since protein adsorption to an anion exchange resin is reversible and does not constitute a classical immobilization, the ability of the resins to retain activity under various conditions must be determined. Macrosorb KAX DEAE bound -D-glucosidase was tested with solutions of primary interest for their final application. Several batch washes of a 1% w/v slurry were required to ensure complete equilibrium elution for a given concentration, as determined from the absence of pNPG units in subsequent washes. Several salt solutions of typical fermentation media components were tested. These included 3 mM to 50 mM solutions of MgSO, KHgPO, NaQ, and sodium acetate. Also, incubations with cellulase solutions were tested to determine if the proteins present in a cellulose hydrolysis would displace the -D-glucosidase. Both of these displacement studies were carried out at 22°C and 40 C. 

We have focused our attention on minimizing adsorption, but readers will note that the above data are still useful even if adsorption is the preferred technique. Braatz tested a polypropylene oxide polymer as part of his study and found that the protein adsorption was 6.4 mg/gram. Compare this with the data in Table 6.5. 

Complementary to the simple adsorption test, the mass balance of the separation could be investigated. This method is more accurate to determine the loss of free drug, which may occur due to variations in sample preparations methods, non-specific protein binding and to metabolism. The latter may also be tested in separate stability tests in plasma or applied matrix. 

Increasing levels of emulsification significantly depleted protein from the fat globule in the mix. The adsorbed protein content in the mix (mg m of fat surface area) correlated with major characteristic analyses describing the fat structure in ice cream (fat agglomerate size, fat agglomeration index, solvent extractable fat Fig. 6). Thus, the measurement of protein load in the mix can be used to predict ice-cream-fat stability and related structure. Structural analyses indicated enhanced interaction between fat and air as protein adsorption decreased. It was also observed that the fat content in the dripped portion collected from a meltdown test correlated well with other indices of fat destabilization. 

The adsorption of proteins at interfaces is a key step in the stabilization of numerous food and non-food foams and emulsions. Our goal is to improve our understanding of the relationships between the sequence of proteins and their surface properties. A theoretical approach has been developed to model the structure and properties of protein adsorption layers using the analogy between proteins and multiblock copolymers. This model seems to be particularly well suited to /5-casein. However, the exponent relating surface pressure to surface concentration is indicative of a polymer structure intermediate between that of a two-dimensional excluded volume chain and a partially collapsed chain. For the protein structure, this would correspond to attractive interactions between some amino acids (hydrogen bonds, for instance). To test this possibility, guanidine hydrochloride was added to the buffer. A transition in the structure and properties of the layer is noticed for a 1.5 molar concentration of the denaturant. Beyond the transition, the properties of the layer are those of a two-dimensional excluded volume chain, a situation expected when there are no attractive interac-... 

This chapter deals with a specific test of blood-surface interaction in vitro platelet retention in a column of beads (due to platelet adhesion and aggregation). Protein adsorption precedes platelet adsorption, and thus the in vitro platelet retention test involves competitive and sequential adsorption of proteins, the outcome of which produces surfaces having widely varying degrees of platelet retention. Except in the case of thrombin (3), plasma protein absorption on these surfaces has not been studied. 

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