Protein adsorption characteristics of nanoparticle-assembled hollow microspheres of hydroxyapatite and their composites with PLLA microporous membranes

Preparation of composite monoliths of quaternized chitosan and diatom earth for protein separation

In this study, composite monoliths with porous structures were prepared using quaternized chitosan and diatom earth for protein separation. Quaternized chitosan (N-[(2-hydroxy-3-trimethylammonium)propyl] chitosan chloride) dissolved in water was mixed with diatom earth and crosslinked with glutaraldehyde under low-temperature conditions to form a cryogel. Interconnected porous monoliths were obtained after removing ice crystals from the cryogel. The monoliths adsorbed bovine serum albumin selectively from the solution mixture of bovine serum albumin and bovine ɤ-globulin, and bovine ɤ-globulin was recovered in the flow-through fraction. The adsorption selectivity was enhanced by changing the solution pH from 6.8 to 5.5. The adsorption of bovine serum albumin by the monolith was replicated at least five times following its washing with a buffer containing 400 mM NaCl and subsequent regeneration with a 10 mM acetate buffer. The composited monolith is a promising adsorbent for the removal of acidic proteins, such as serum albumin contamination in neutral proteins, for example, ɤ-globulins, in bioproduction processes.

Protein-biomolecule interactions play a major role in shaping corona proteome: studies on milk interacted dietary particles

Despite the significance of surface absorbed proteins in determining the biological identity of nanoparticles (NPs) entering the human body, little is known about the surface corona and factors that shape their formation on dietary particles used as food additives. In this study, food grade NPs of silica and titania and their food additive counterparts (E551 and E171) were interacted with milk proteins or with skimmed milk and the levels of protein adsorption were quantified. Characteristics of proteins correlating with their level of adsorption to NPs were determined using partial least squares regression analysis. Results from individual protein-particle interactions revealed the significance of factors such as zeta potential, hydrophobicity and hydrodynamic size of particles, and protein characteristics such as the number of beta strands, isoelectric points, the number of amino acid units (Ile, Tyr, Ala, Gly, Pro, Asp, and Arg), and phosphorylation sites on their adsorption to particles. Similar regression analysis was performed to identify the characteristics of twenty abundant and enriched proteins (identified using LC-MS/MS analysis) for their association with the surface corona of milk-interacted particles. Contrary to individual protein-particle interactions, protein characteristics such as helices, turns, protein structures, disulfide bonds, the number of amino acid units (Cys, Met, Leu, and Trp), and Fe binding sites were significant for their association with the surface corona of milk interacted particles. This difference in factors identified from individual proteins and milk interacted particles suggested possible interactions of proteins with surface adsorbed biomolecules as revealed by scanning transmission X-ray microscopy and other biochemical assays.

Preparation and mechanism of hydroxyapatite hollow microspheres with different surface charge by biomimetic method

To meet the different application requirements in various fields, hydroxyapatite (HA) hollow microspheres with different surface charge were synthesized successfully by biomimetic method using Ca(NO₃)₂·4H₂O and (NH₄)₂HPO₄ in the presence of polyethylene glycol (PEG). Scanning electron microscopy (SEM), High-resolution TEM (HRTEM), X-ray powder diffraction (XRD), and Zeta PALS were used to characterize the obtained samples. The results indicated that the concentration of PEG and temperature significantly affect the morphology of the obtained samples. After incubation for 5 d, the HA hollow microspheres with positive surface charge, HA spherical nanoparticles with surface charge close to zero and calcium deficiency HA (d-HA) hollow microspheres with negative surface charge were obtained respectively in the presence of 5% PEG, 6% PEG and 7% PEG at 15 °C. Brunauer-Emmett-Teller (BET) revealed that the specific surface area of HA hollow microspheres reached 98.50 m²/g, while that of HA spherical nanoparticles were only 4.12 m²/g, hollow microspheres show a better application prospect. The possible formation mechanism was also discussed. Ca/P molar ratio >1.67, the surface charge of HA hollow microspheres inclines to be positive. Ca/P molar ratio <1.67, the surface charge of d-HA hollow microspheres tends to be negative.