SELECTIVE ADSORPTION OF ACIDIC AND BASIC WHEY PROTEINS ON SINTERED HYDROXYAPATITES

ABSTRACT: Introduction: The protein–hydroxyapatite (HA) interface is pivotal in biomolecule purification, yet the influence of sintering on adsorption selectivity remains poorly understood. Objective: To determine how HA sintering temperature modulates the adsorption of an acidic (bovine serum albumin, BSA) and a basic (lactoferrin, Lf) whey protein. Methodology: HAs were prepared by precipitation (HAE0) and sintered at 500 °C (HAS5), 700 °C (HAS7) and 1000 °C (HAS10). Samples (50 mg) were incubated for 24 h with 1 mg mL⁻¹ protein solutions at pH 5.0–10.5 (25 °C, 200 rpm). Residual protein (A₂₈₀) yielded adsorption capacities (qₑ, mg g⁻¹; qₐ, mg m⁻²). Kinetics (10–480 min) were fitted to pseudo-first-, pseudo-second-order and intraparticle-diffusion models; ζ-potentials assessed surface charge. Results: All HAs were negatively charged (–17.3 to –39.7 mV), becoming less negative after adsorption. Lf reached a maximum qₑ of 95 mg g⁻¹ (HAS5, pH 5.0) and qₐ of 25 mg m⁻² (HAS10, pH 5.0); BSA attained 82 mg g⁻¹ (HAE0, pH 5.0) and 6 mg m⁻² (HAS10, pH 5.0). Increasing sintering temperature reduced specific surface area but increased crystallinity; this impaired BSA adsorption while enhancing Lf on an area basis. Kinetics followed the pseudo-second-order model best (R² > 0.99), indicating chemisorption control. Discussion: Greater exposure of the c-plane rich in phosphate sites and crystal densification in HAS10 strengthened electrostatic attraction with Lf under acidic pH, whereas carbonate removal and decreased porosity limited anchoring sites for BSA, whose adsorption depends more on surface area. Sintering therefore enables selective tuning of protein capture by HA. Conclusion: Highly crystalline HAs (1000 °C) favour lactoferrin adsorption, whereas unsintered samples maximise albumin capture. Controlling sintering temperature and pH provides an efficient route for designing separation matrices and controlled-release scaffolds.