Evaluation of the adsorption affinity of proteins to calcium hydroxyapatites by desorption and pre-adsorption methods

Enhanced model protein adsorption of nanoparticulate hydroxyapatite thin films on silk sericin and fibroin surfaces

Hydroxyapatite coated metallic implants favorably combine the required biocompatibility with the mechanical properties. As an alternative to the industrial coating method of plasma spraying with inherently potential deleterious effects, sol-gel methods have attracted much attention. In this study, the effects of intermediate silk fibroin and silk sericin layers on the protein adsorption capacity of hydroxyapatite films formed by a particulate sol-gel method were determined experimentally. The preparation of the layered silk protein/hydroxyapatite structures on glass substrates, and the effects of the underlying silk proteins on the topography of the hydroxyapatite coatings were described. The topography of the hydroxyapatite layer fabricated on the silk sericin was such that the hydroxyapatite particles were oriented forming an oriented crystalline surface. The model protein (bovine serum albumin) adsorption increased to 2.62 µg/cm² on the latter surface as compared to 1.37 µg/cm² of hydroxyapatite on glass without an intermediate silk sericin layer. The BSA adsorption on glass (blank), glass/c-HAp, glass/m-HAp, glass/sericin/c-HAp, and glass/sericin/m-HAp substrates, reported as decrease in BSA concentration versus contact time.

Bioceramic Hydroxyapatite Granules for Purification of Biotechnological Products

Sorption experiments of bovine serum albumin (BSA) on hydroxyapatite (HAp) ceramic granules, prepared at three temperatures 900°C, 1000°C and 1150°C were performed at room temperature 18,6 °C and phosphate buffer, pH 5,83; 6.38 and 7,39. Thermal treatment contributed to the decrease of bovine serum albumin immobilization indicating that sorption process depended on HAp ceramics specific surface area and pH values of phosphate buffer solution. However, it was confirmed that granule size was also an important parameter for bovine serum albumin adsorption. As a result of these experiments, the most appropriate adsorption conditions and phosphate buffer pH values influence on to BSA sorption were analyzed.

Salt induced irreversible protein adsorption with extremely high loadings on electrospun nanofibers

LiCl is a kosmotrope that generally promotes protein salvation in aqueous solutions. Herein we report that LiCl embedded in electrospun polymeric nanofibers interestingly induced an abnormal protein adsorption and substantially augmented the adsorption capacity of the fibers. As a result, equilibrium protein loadings reached over 64% (w/w) of the dry mass of fibers, 9-fold higher than that observed in the absence of the salt. The adsorption appeared to be irreversible such that little protein loss was observed even after washing the fibers vigorously with fresh buffer solutions. We further examined the application of such intensified protein adsorption for enzyme immobilization. Proteins including bovine serum albumin (BSA) and protamine were first adsorbed, followed by covalent attachment of an outer layer of an enzyme, α-chymotrypsin. Such a multilayer-structured nanofibrous enzyme exhibited extremely high stability with no obvious activity loss even after being incubated for 8 months at 4 °C in aqueous buffer solution. The LiCl induced irreversible protein adsorption, which has been largely ignored in previous studies with electrospun materials, rendering an interesting scenario of interfacial protein-material interactions. It also reveals a new mechanism in controlling and fabricating molecular interactions at interfaces for development of a broad range of biomaterials.

An effective method for quantitative evaluation of proteins adsorbed on biomaterial surfaces

An effective method for the quantitative evaluation of proteins adsorbed on biomaterial surfaces has been developed. First, the kinetic behavior of a range of human fibrinogen (Fib) adsorbed onto polystyrene (PS) films was investigated by using a reflectometry interference spectroscopy setup. The specific molecular number of adsorbed proteins, N(p,) was then defined. According to the definition, the numbers of Fib molecules adsorbed on PS films were calculated. An atomic force microscope (AFM) was used to scan the lateral distribution of the Fib molecules adsorbed on the PS films. From the AFM images, the practical specific molecular numbers were obtained by direct counting of the molecules. In order that the adsorbed number of Fib molecules on a unit area of the PS films could be counted easily, the solution concentration of proteins was reduced to 5 ag/mL (10(-18)g/mL). There was good consistency between the numbers calculated with the formula defined by us and the numbers counted from AFM images. Therefore, the results of the present study prove the validity of our definition of the specific molecular number of adsorbed proteins and the effectiveness of the reflectometry interference spectroscopy-based method for quantitative evaluation of adsorptive proteins.

Fabrication and surface characterization of NH4PAA-stabilized HAZ suspensions

Fine composite powders of yttria (3 mol%) stabilized zirconia (Z, 10 wt%) and hydroxyapatite (HA), denoted as HAZ, were prepared by the co-precipitation method. The resulting powders were characterized by XRF, TEM, EDS, XRD, FTIR, TG-DTA, and BET surface area techniques. AES and FTIR were employed to determine the surface properties of the HAZ suspensions in the presence of NH4PAA as a dispersant, which confirmed that the surfaces of both HA and Z were affected by the adsorbed polymers. The mechanism of NH4PAA adsorption on the particles was discussed. Zeta potential measurements showed that the addition of NH4PAA resulted in a dramatic increase in the absolute value of zeta potential. NH4PAA considerably enhanced the stability of the HAZ suspension via electrosteric barrier mechanisms. TEM micrographs confirmed that particles were well dispersed in the suspension. The adsorption density of the dispersant was found to decrease with an increase in pH value.